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Mar 2005

Volume 23, Issue 2, pp. L1-873

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Fabrication of 5 nm gap pillar electrodes by electron-beam Pt deposition

Gian Carlo Gazzadi and Stefano Frabboni

J. Vac. Sci. Technol. B 23, L1 (2005); http://dx.doi.org/10.1116/1.1872015 (3 pages) | Cited 17 times

Online Publication Date: 5 April 2005

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Using a focused ion beam (FIB)-scanning electron microscope (SEM) workstation, free-standing nanoelectrodes were grown by SEM-assisted Pt deposition between FIB-patterned Au pads. Two pillar electrodes were first grown with opposite-tilted geometries up to a spacing of 120 nm. By SEM scanning over the pillar tips, under a precursor gas flow, gap reduction down to 5 nm was monitored in live imaging mode. As shown by transmission electron microscopy (TEM) analysis, the deposit consisted of Pt crystallites embedded in amorphous C. Local annealing by high-current TEM irradiation increased the size of the Pt grains, which produced clear diffraction rings. The annealing procedure did not affect the overall shape of the tips, indicating good mechanical stability of the pillars. We show how this FIB-SEM approach is suitable to fabricate multielectrode nanostructures by depositing a third pillar electrode below the gap of the tilted electrodes.
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81.16.Nd Micro- and nanolithography
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
82.45.Fk Electrodes
81.40.Gh Other heat and thermomechanical treatments
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Fabrication of a nanosized current-driven spin valve device using proximity correction in electron-beam lithography

Hyunjung Yi, T. H. Y. Nguyen, Joonyeon Chang, and K. H. Shin

J. Vac. Sci. Technol. B 23, 339 (2005); http://dx.doi.org/10.1116/1.1861031 (5 pages) | Cited 1 time

Online Publication Date: 17 February 2005

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Nanosized junctions of 100×200 nm2 size were successfully fabricated on magnetic metallic multilayers in a current-driven spin-valve device by the suitable choice of the electron-beam resist, as well as careful control of back-scattering effects in electron-beam lithography. ZEP520A was chosen as an e-beam sensitive resist because its dry-etching resistance is high enough to act as an etching mask during the ion milling. The severe back-scattering effect from the underlying metallic multilayers was reasonably modified by employing the doughnut-pattern method. The doughnut-pattern method gave a set of proximity parameters (α, β, and η) with which we did the simulation to obtain the effective dose factors of each segment of the pattern. The magnetotransport signals from our devices were quite comparable to previous results from those made by different methods of other research groups. Consequently, the fabrication of nanosized current driven spin valves can be performed less complicatedly by using ZEP520A as an etching mask.
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85.40.Hp Lithography, masks and pattern transfer
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields
81.16.Nd Micro- and nanolithography

Fourier transform infrared spectroscopy studies of water-polymer interactions in chemically amplified photoresists

Laurie A. McDonough, Viktor Chikan, Zee Hwan Kim, Stephen R. Leone, and William D. Hinsberg

J. Vac. Sci. Technol. B 23, 344 (2005); http://dx.doi.org/10.1116/1.1861034 (5 pages) | Cited 2 times

Online Publication Date: 17 February 2005

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Fourier-transform infrared absorption spectroscopy is implemented to measure the infrared spectrum of water absorbed by the poly(t-butoxycarbonylstyrene) and the ketal-protected poly(hydroxystyrene) polymer photoresists. The shape and intensity of the OH stretching band of the water spectrum is monitored in a variety of humidity conditions in order to obtain information on the hydrogen-bonding interactions between the water and the polymer chains. The band is deconvoluted into four subbands, which represent four types of water molecules in different environments. Because of the hydrophilicity of the polymers studied, a large portion of the sorbed water molecules is believed to be strongly bound to the polar sites of the polymer. The ratios of each type of water are found to be dependent on the humidity conditions to which the sample was exposed. At higher humidities, there is an increase in the fraction of free and weakly bound water molecules. These findings are used to explain the humidity dependence of the deprotection reaction rates, since certain types of water may slow transport of reactive species within the polymer network.
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68.43.Mn Adsorption kinetics
82.30.Rs Hydrogen bonding, hydrophilic effects
78.30.C- Liquids
85.40.Hp Lithography, masks and pattern transfer

Diffusion of dopants in highly ( ∼ 1020 cm−3) n- and p-doped GaSb-based materials

Oliver Dier, Markus Grau, Christian Lauer, Chun Lin, and Markus-Christian Amann

J. Vac. Sci. Technol. B 23, 349 (2005); http://dx.doi.org/10.1116/1.1861035 (5 pages) | Cited 4 times

Online Publication Date: 17 February 2005

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Diffusion of dopants at high doping concentrations ( ∼ 1020 cm−3) of GaSb, GaInAsSb, and InAsSb grown in a molecular beam epitaxy system and doped with silicon, beryllium, and tellurium were investigated. The electrically active doping concentration for each material was determined by van der Pauw measurements, while the doping profiles were measured by secondary-ion-mass spectroscopy. The samples were annealed to analyze the diffusion behavior. Two different growth techniques to achieve high doping levels were compared: δ dopings and deposition with reduced growth rate. The diffusion of Be in InAsSb:Be could not be prevented, neither by a low growth rate nor by intermediate GaSb spacers. A strong diffusion of Be and Te was found for δ-doped samples in InAsSb, whereas in slowly grown material the diffusion can be limited for Te as dopant.
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66.30.J- Diffusion of impurities
61.72.uj III-V and II-VI semiconductors
61.72.S- Impurities in crystals

Micropatterning organosilane self-assembled monolayers with plasma etching and backfilling techniques

Adam W. Harant, Stephen G. Whipple, Kenneth Douglas, and Christopher N. Bowman

J. Vac. Sci. Technol. B 23, 354 (2005); http://dx.doi.org/10.1116/1.1861041 (5 pages) | Cited 2 times

Online Publication Date: 17 February 2005

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Organosilane self-assembled monolayers (SAMs) were micropatterned using standard photoresist-based lithographic and plasma etching techniques. Etched regions were backfilled with a second SAM containing a different organic substituent. By repeating the patterning process, a complex, multifunctional patterned surface composed of three different SAMs (amino-, methyl-, and thiol-terminated) was formed. Since two distinct etching steps are used, the backfilled SAMs can be deposited in trenches of different depths. Multifunctional, micropatterned SAMs were visualized by friction mode scanning probe microscopy (SPM). Gold-coated SPM tips yielded high contrast friction images from surfaces patterned with thiol-terminated SAMs.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly
68.47.Pe Langmuir-Blodgett films on solids; polymers on surfaces; biological molecules on surfaces
52.77.Bn Etching and cleaning

Fabrication and characterization of p-type silicon field-emitter arrays for lithography

T. F. Teepen, A. H. V. van Veen, H. van’t Spijker, S. W. H. K. Steenbrink, A. van Zuuk, C. Th. H. Heerkens, M. J. Wieland, N. J. van Druten, and P. Kruit

J. Vac. Sci. Technol. B 23, 359 (2005); http://dx.doi.org/10.1116/1.1861045 (11 pages) | Cited 2 times

Online Publication Date: 17 February 2005

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p-doped silicon field emitters were studied experimentally to assess their usefulness in multibeam electron lithography. Both individual emitters and emitter arrays were fabricated from single crystal Si wafers with several doping levels. Current-voltage curves were measured for different temperatures and illumination conditions. The typical plateaus in the I-V curves and the sensitivity to light known from the literature were reproduced. Stability measurements showed a very stable total emission current even while the angular emission distribution fluctuated strongly, giving unstable currents in apertured beams. Measured light response times varied between 34 ns and 20 μs, depending on experimental conditions. It was found that in the plateau of the I-V curve, the energy of the electrons shifts over up to 100 eV when changing the extraction voltage over a few kilovolts. In operation, when the current is stable, the energy shift is rather unstable. The experimental results are discussed within a model of the emission process involving an induced p-n junction inside the tip. The conclusion is that p-doped silicon field emitters are not particularly useful for applications in electron beam lithography.
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07.77.Ka Charged-particle beam sources and detectors
29.25.Bx Electron sources
42.82.Cr Fabrication techniques; lithography, pattern transfer

Performance improvement of diamondlike carbon membrane masks for electron projection lithography

Isao Amemiya, Hiroshi Yamashita, Kazutake Taniguchi, Sakae Nakatsuka, Ikuru Kimura, and Osamu Nagarekawa

J. Vac. Sci. Technol. B 23, 370 (2005); http://dx.doi.org/10.1116/1.1861928 (5 pages) | Cited 1 time

Online Publication Date: 17 February 2005

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This article describes the fabrication of eight-inch continuous membrane masks with a 15‐nm-thick support membrane for electron projection lithography (EPL). In order to develop an extremely thin support membrane with a tensional stress, two techniques were applied; one is a low pressure deposition process to improve the membrane bulk density, and the other is Si addition during the conventional carbon membrane deposition for improving the atomic distance mismatch between substrate and deposited film, and also to address the membrane volume strain cause by the rise in the tensional stress under the low pressure deposition condition. By using Si-additional techniques, an extremely thin membrane with a tensional stress was formed under the conditions of less than 0.5 Pa chamber pressure. Long-term membrane stress stability of Si-added extremely thin membranes were particularly improved. It was less than 3 MPa in elapsed times of 400 h. The zero-loss electron transmittance for the fabricated 15‐nm-thick membrane mask was measured to be 70.4%. Due to the development of an extremely thin membrane with high zero-loss electron transmittance of more than 50%, our high-performance membrane masks are superior to the complementary stencil masks in terms of exposure throughput.
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85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Three-dimensional multilayered microstructure fabricated by imprint lithography

H. Ooe, M. Morimatsu, T. Yoshikawa, H. Kawata, and Y. Hirai

J. Vac. Sci. Technol. B 23, 375 (2005); http://dx.doi.org/10.1116/1.1861929 (5 pages) | Cited 10 times

Online Publication Date: 17 February 2005

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The fabrication of a three-dimensional multilayered microstructure is demonstrated by the imprint and reversal imprint technique. We have studied polymer properties and pressing conditions as important parameters for selecting the reversal imprint modes. We investigated the conditions that are required to form the fluid channels and the through holes. Using these advanced processes, three-dimensional microfluid channels with through holes were successfully fabricated at low cost and high throughput. This technique is one of the most promising methods for making various advanced microstructures such as compact and multifunctional chemical devices.
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85.40.Hp Lithography, masks and pattern transfer
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.16.Nd Micro- and nanolithography

Shot noise power spectrum of planar field emitters

K. Rangaswamy, M. Cahay, and K. L. Jensen

J. Vac. Sci. Technol. B 23, 380 (2005); http://dx.doi.org/10.1116/1.1865092 (9 pages) | Cited 3 times

Online Publication Date: 17 February 2005

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A quantum-mechanical wave impedance approach is used to calculate the shot noise power spectrum of the emission current from planar metallic cathodes. The formalism takes into account the effects of the image force potential in front of the cathode. For metals with low work function, the Fano factor which characterizes the reduction of the shot noise power SI below the Schottky result 2 q IA (where q is the magnitude of the charge of the electron and IA is the time average of the anode current) is calculated as a function of the applied external electric field. Simple analytical expressions for the Fano factor are derived for the cathode operated in the thermionic (Richardson) and tunneling (Fowler–Nordheim) regimes. The value of the Fano factor is found to be reduced substantially below the value calculated when the effects of the image charge potential are neglected.
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72.70.+m Noise processes and phenomena
79.40.+z Thermionic emission
73.30.+y Surface double layers, Schottky barriers, and work functions
84.47.+w Vacuum tubes

Reduction of plasma-induced damage in SiO2 films during pulse-time-modulated plasma irradiation

Yasushi Ishikawa, Mitsuru Okigawa, Seiji Samukawa, and Satoshi Yamasaki

J. Vac. Sci. Technol. B 23, 389 (2005); http://dx.doi.org/10.1116/1.1861033 (6 pages) | Cited 7 times

Online Publication Date: 9 March 2005

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Use of a pulse-time-modulated (TM) plasma is an effective way to reduce vacuum ultra-violet (VUV) radiation damage in SiO2 films because such a plasma can reduce the quantity of high-energy electrons while maintaining the electron density during the off time of the TM plasma. To understand the effects of VUV radiation, we measured the VUV-induced current in SiO2 films using a simple on-wafer monitoring technique. We found that the plasma-induced-current in the SiO2 films strongly depended on the VUV photon energy. Under the same conditions, the density of E′ centers in SiO2 films also depended on the photon energy. That is, the plasma-induced currents in the SiO2 films detected by on-wafer monitoring corresponded to the density of E′ centers (dangling bonds) in the films. By using a TM plasma, the plasma-induced current and the E′ center density in SiO2 films can be reduced during the plasma-off time. Consequently, use of a TM plasma can eliminate VUV radiation damage. These results also confirm that our developed on-wafer monitor can predict plasma-induced damage.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
61.82.Ms Insulators
71.55.Ht Other nonmetals
77.55.-g Dielectric thin films
52.77.-j Plasma applications
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Effect of plasma interactions with low-κ films as a function of porosity, plasma chemistry, and temperature

Marcus A. Worsley, Stacey F. Bent, Stephen M. Gates, Nicholas C. M. Fuller, Willi Volksen, Michelle Steen, and Timothy Dalton

J. Vac. Sci. Technol. B 23, 395 (2005); http://dx.doi.org/10.1116/1.1861038 (11 pages) | Cited 20 times

Online Publication Date: 9 March 2005

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Integration of new low-κ interlayer dielectrics (ILD) with current damascene schemes is a continuing issue in the microelectronics industry. During integration of the ILD, processing steps such as plasma etching, resist strip, and chemical-mechanical planarization are known to chemically alter a layer of the dielectric. Here, porous organosilicate glass (OSG) ILD films, which—according to the 2004 edition of the International Technology Roadmap for Semiconductors—are projected for use in the 65 and 45 nm nodes, are investigated. spectroscopic ellipsometry, x-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy are used to characterize the modified layer of the ILD after exposure to O2 or H2 resist strip plasmas. The effects of the two types of plasma etch chemistries on the formation of the modified layer were found to differ significantly. These effects include both the degree of modification (i.e., chemical composition) and depth of the modified layer. A key difference between the O2 and H2 plasmas is that silicon hydride groups are present in the modified layer after exposure to H2 plasma but not after exposure to the O2 plasma. In addition, the influence of OSG porosity on the etch rate and modified layer thickness was investigated for porosities ranging from 0–45 %. As expected, the etch rate was found to increase rapidly with porosity. Finally, conditions including reactive gas concentrations and substrate temperature for the H2 plasma were varied. These parameters produced considerable changes in the chemistry of the modified layer, especially in the amount of hydrogen incorporated into the film. Details of these results will be discussed in the context of the mechanism by which modification and etching occurs as well as which process variables dominate those phenomena.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
85.40.Hp Lithography, masks and pattern transfer
77.22.Ch Permittivity (dielectric function)
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.55.-g Dielectric thin films
52.40.Hf Plasma-material interactions; boundary layer effects
61.43.Gt Powders, porous materials
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.Dp Adsorbed layers and thin films
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
61.43.Fs Glasses
78.35.+c Brillouin and Rayleigh scattering; other light scattering
81.65.-b Surface treatments

Anion variations at semiconductor interfaces: ZnSe(100)/GaAs(100) superlattices

H. H. Farrell and Randall A. LaViolette

J. Vac. Sci. Technol. B 23, 406 (2005); http://dx.doi.org/10.1116/1.1861044 (11 pages)

Online Publication Date: 9 March 2005

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We extended our study of heterovalent interfaces between ZnSe(100) and GaAs(100) in superlattices using first-principles, density-functional theory calculations. Here, we concentrate on the changes in interfacial binding energy that occur when the stoichiometry is varied in the anion layer adjacent to the interface. This follows earlier work where the cation stoichiometry was varied. We studied three general categories of simple heterojunctions: those with only As–Zn bonding, those with only Se–Ga bonding, and those with mixed As–Zn and Se–Ga bonding. We also considered more complex interface configurations. Several different variations in interfacial stoichiometry that are conceptually based on the heteroepitaxial growth of ZnSe(100) on the GaAs(100)(2×4)β2 surface structure were studied. In addition, the effects induced by the presence of vacancies in the vicinity of the surface were investigated. These more complex interfaces are discussed in terms of published experimental results. Finally, the possibility that the energy of the interface can be described in terms of the energy of the bonds that span that interface was also examined. We find that, for all of the 14 interfaces studied, the interface energy can be expressed as a simple sum of the per-bond-pair energies with an average error of less than 3%. Therefore, in these systems, the energies of the interfacial bonds are “additive” to a good approximation.
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68.35.−p
73.61.Eq
76.31.Ga
81.05.Dz II-VI semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Edge effects characterization of phase shift mask

Gek Soon Chua, Cho Jui Tay, Chenggen Quan, and Qunying Lin

J. Vac. Sci. Technol. B 23, 417 (2005); http://dx.doi.org/10.1116/1.1865112 (8 pages) | Cited 1 time

Online Publication Date: 9 March 2005

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The demand for steadily decreasing dimensions in semiconductor devices is driving the need for increased resolution in optical lithography. The use of phase shift masks (PSMs) is among such resolution enhancement techniques. PSM are well known to show prominent diffraction effects, which cannot be described by the assumption of an infinitely thin mask (Kirchhoff approach) that is used in many commercial photolithography simulators. A correct prediction of sidelobe printability, process window and linearity of an OPC mask requires a rigorous application of diffraction theory. Optical lithography simulation employing a time-domain finite-difference (TDFD) algorithm (TEMPEST) has been used effectively to study the problem of aerial image intensity imbalance through focus with alternating phase shift masks (altPSMs). Using Geometrical Theory of Diffraction (GTD), and the solutions to canonical problems, we obtained a relationship between mask edge and disturbance in an image space. The main objective to develop useful formulations that can be readily applied to diffraction in mask technology. Rigorous analysis of diffraction effect on altPSMs using the GTD approach is discussed and results show that the effect of shifter edge angle is equivalent to that of shifter width.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Effect of sidewall properties on the bottom microtrench during SiO2 etching in a CF4 plasma

Jae-Ho Min, Gye-Re Lee, Jin-Kwan Lee, Sang Heup Moon, and Chang-Koo Kim

J. Vac. Sci. Technol. B 23, 425 (2005); http://dx.doi.org/10.1116/1.1865113 (8 pages) | Cited 4 times

Online Publication Date: 9 March 2005

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Factors that affect microtrench formation during the etching of SiO2 in a CF4 plasma were investigated using an experimental set-up, which comprised a Faraday cage and step-shaped substrates consisting of a SiO2 bottom and slanted sidewalls of different materials. This set-up permitted the etched micropattern to be observed on a magnified scale under conditions that are similar to actual processes. SiO2 and fluorocarbon polymer were used as sidewall surface materials to investigate the effect of sidewall properties on the microtrench. The depth of the microtrench characteristically changed with the sidewall angle, reaching a maximum at 70° under the condition used in this study. This can be explained by the effect of two competitive factors: secondary etching of the bottom by ions reflected from the sidewall, which contributes to the bottom etch rate, and the shadowing effect of the sidewall, which decreases the etch rate. Secondary etching, as estimated from the difference in the bottom etch rates between two cases of an ordinary sidewall and a sidewall with an extremely rough surface, showed a maximum at a sidewall angle of 80°–82.5°, while the shadowing effect was increased monotonously with sidewall angle. The rates of secondary etching were higher for the polymer sidewall than for the SiO2 sidewall for sidewall angles lower than 70°, but opposite relative magnitudes were observed for angles higher than 70°. The result obtained at angles lower than 70° can be explained based on a model in which a fluorocarbon film formed on the sidewall, which was particularly thick for a polymer sidewall, acted as a source of etchant radicals, thus contributing to bottom etching. The opposite trend observed at angles higher than 70° can be attributed to the roughness of the sidewall surface, which was higher for the polymer sidewall, which affected the reflection of ions on the surface and, eventually, secondary etching.
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52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effect of electric field on chemical bonds of carbon-doped silicon oxide as evidenced by in situ Fourier transform infrared spectroscopy

K. Y. Yiang, W. J. Yoo, and Ahila Krishnamoorthy

J. Vac. Sci. Technol. B 23, 433 (2005); http://dx.doi.org/10.1116/1.1865114 (4 pages) | Cited 1 time

Online Publication Date: 9 March 2005

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In this study, we use in situ Fourier transform infrared (FTIR) spectroscopy on a carbon-doped silicon oxide (SiOCH) to determine the origins of its lower breakdown strength (compared to SiO2) and the precursors of dielectric breakdown. While subjecting the SiOCH film to externally applied electric fields, the FTIR spectra are recorded. Changes in peak area ratios and intensities are determined and correlated to field-induced perturbation of chemical bonds in SiOCH. This is a potentially powerful technique which provides new insights into the dielectric degradation and breakdown phenomena.
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77.22.Jp Dielectric breakdown and space-charge effects
77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
78.30.Hv Other nonmetallic inorganics

In situ fabrication of metal gate/high-κ dielectric gate stacks using a potential lower cost front-end process for the sub-90 nm CMOS technology node

Daniel Damjanovic, Rajendra Singh, and Kelvin F. Poole

J. Vac. Sci. Technol. B 23, 437 (2005); http://dx.doi.org/10.1116/1.1865115 (6 pages)

Online Publication Date: 9 March 2005

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In this article we discuss the advantages of in situ fabrication of metal gate/high-κ gate stacks using single wafer processing. The aim was to develop an in situ process for the sub-90 nm CMOS regime, which allows for a reduction in the number of processing steps and consequently the number of processing tools, while also providing for improved device performance, yield and reliability. In this work, we demonstrate improved electrical characteristics of ultrathin high dielectric constant films processed by rapid thermal processing (RTP) assisted metal-oxide chemical vapor deposition (MOCVD), where the silicon wafer underwent an in situ precleaning treatment followed by an in situ oxide deposition, in situ oxide anneal, and an in situ metallization step. Gate leakage currents on the order of 10−11 A/cm2 at a gate voltage of 1 V and an EOT of 1.5 nm were measured across the Al2O3 gate oxide of the gate stacks. These results present an improvement of two orders of magnitude over gate leakage currents measured across Al2O3 gate oxides with comparable EOT values reported in literature.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Sz Deposition technology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)

Surface morphology of epitaxial LiF(110) and CaF2(110) layers

Akira Sugawara and K. Mae

J. Vac. Sci. Technol. B 23, 443 (2005); http://dx.doi.org/10.1116/1.1865116 (6 pages) | Cited 2 times

Online Publication Date: 9 March 2005

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Regular ridge-and-valley surface structures were spontaneously formed by the homoepitaxial growth of LiF(110) and CaF2(110). The surface structure was examined by in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM). The LiF(110) homoepitaxial surfaces exhibited regular ridge-and-valley structures composed of {100} facets and [001] macrosteps, and the ridge spacings increased with growth temperature. The CaF2(110) surfaces also exhibited regular ridge-and-valley structures composed of {111} facets and [1math0] macrosteps when deposited above 400 °C. Annealing alone did not produce a well-developed ridge-and-valley structure. The highly mobile admolecules supplied during deposition played a central role on the morphological evolution of the surfaces. The heteroepitaxial growth of LiF and CaF2 on {100}-faceted NaCl(110) substrates was also examined. Although the LiF(110) exhibited a regular ridge-and-valley structure, CaF2(110) formed arrays of islands at the bottom of the grooves.
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68.55.-a Thin film structure and morphology
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.Gh Other heat and thermomechanical treatments
68.35.B- Structure of clean surfaces (and surface reconstruction)

Effects of B content on microstructure and mechanical properties of nanocomposite Ti–Bx–Ny thin films

Y. H. Lu, P. Sit, T. F. Hung, Haydn Chen, Z. F. Zhou, K. Y. Li, and Y. G. Shen

J. Vac. Sci. Technol. B 23, 449 (2005); http://dx.doi.org/10.1116/1.1865117 (9 pages) | Cited 9 times

Online Publication Date: 9 March 2005

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Thin films of Ti–Bx–Ny were deposited on Si(100) at room temperature by reactive unbalanced dc magnetron sputtering in an Ar–N2 gas mixture. The effects of B content on microstructure and mechanical properties of these films have been analyzed using x-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy, x-ray diffraction, transmission electron microscopy, atomic force microscopy, micro-indentation measurements, and an optical interference method. Microstructure studies revealed that depending upon the amount of B addition, the films showed two- or three-phase nanocomposite structure. At B contents below about 10 at. %, the films consisted of mainly TiN bondings with a small amount of TiB and BN bondings. As the B content increased, TiB gradually transformed to TiB2 and the films consisted of nanocrystalline (nc-) TiN embedded in an amorphous (a‐) TiB2 matrix. A maximum hardness of ∼ 44 GPa was observed in a film with B content of 19 at. %. The improved mechanical properties of Ti–Bx–Ny films with the addition of B into TiN were attributed to their densified microstructure with development of fine grain size and different phase combination. The reduction in grain size has also been supported by means of a Monte Carlo simulation. When B contents reached ∼ 42 at. % or above, an amorphous-like nanocomposite of nc‐TiN/a‐TiB2/a‐BN was formed. The effect of thin a‐TiB2 layer in stabilizing nc-TiN structure is also elucidated and explained on the basis of structural and thermodynamic stability.
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68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
78.30.Hv Other nonmetallic inorganics
81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.07.Bc Nanocrystalline materials
68.37.Xy Scanning Auger microscopy, photoelectron microscopy
79.60.-i Photoemission and photoelectron spectra
81.15.Cd Deposition by sputtering
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
68.37.Lp Transmission electron microscopy (TEM)
68.37.Ps Atomic force microscopy (AFM)
79.60.Dp Adsorbed layers and thin films
78.66.Sq Composite materials

Synthesis of multiwalled carbon nanotubes using C14H10O7W catalyst

Yoon Huh, Jeong Yong Lee, Sang Kyu Choi, and Cheol Jin Lee

J. Vac. Sci. Technol. B 23, 458 (2005); http://dx.doi.org/10.1116/1.1865118 (5 pages) | Cited 2 times

Online Publication Date: 9 March 2005

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High-purity carbon nanotubes were synthesized using a novel catalyst: tungsten-containing complex (C14H10O7W). The carbon nanotubes have a multiwalled structure that is hollow on the inside and a clean surface without carbonaceous particles. The carbon nanotubes have average diameters in the range of 20–60 nm and lengths of 30 μm. Transmission electron microscopy analysis reveals that the inner graphite sheets of these nanotubes are highly crystallized, but the outer graphite sheets are defective. The microstructures of the carbon nanotubes produced from C14H10O7W, tungsten hexacarbonyl [W(CO)6], and iron pentacarbonyl [Fe(CO)5] were analyzed using high-resolution transmission electron microscopy. We demonstrate that the tungsten-based catalyst can effectively be used to produce the carbon nanotubes.
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81.16.Hc Catalytic methods
61.46.-w Structure of nanoscale materials
81.07.De Nanotubes
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
81.05.U- Carbon/carbon-based materials

Copper diffusion barrier properties of CVD boron carbo-nitride

E. R. Engbrecht, Y.-M. Sun, K. H. Junker, J. M. White, and J. G. Ekerdt

J. Vac. Sci. Technol. B 23, 463 (2005); http://dx.doi.org/10.1116/1.1865072 (5 pages) | Cited 4 times

Online Publication Date: 11 March 2005

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The copper diffusion barrier properties of amorphous boron carbo-nitride (BCxNy) films were studied. The BCxNy films were deposited by chemical vapor deposition at 360 °C and 1 Torr using dimethylamine borane with no reaction gas (BC0.37N0.15), with NH3(BC0.19N0.44), or with C2H4(BC0.90N0.08); their dielectric constants were 4.1, 4.4, and 3.9, respectively. A SiC0.76N0.44 film was used to benchmark the study. Barrier films were deposited on 7 nm thermal oxide/n-type Si substrates. The leakage current for BC0.90N0.08, 1.1×10−8 A/cm2 at 0.5 MV/cm, is the lowest of the three but it is larger than that of the benchmark SiC0.76N0.44 film, 5.5×10−9 A/cm2. Time dependent dielectric breakdown is used to test barrier time-to-failure of Cu-gate capacitors at 150 °C and +2 to 5 MV/cm. BC0.90N0.80 displayed barrier performance comparable to SiC0.76N0.44 and was noticeably better than BC0.37N0.15 and BC0.19N0.44. Overall, BCxNy barriers are promising and are improved with lower boron content, fewer B–B bonds, and increased B–C bonds.
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66.30.Ny Chemical interdiffusion; diffusion barriers
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Jp Dielectric breakdown and space-charge effects
77.22.Ch Permittivity (dielectric function)

Approach to interface roughness of silicide thin films by micro-Raman imaging

F. F. Zhao, W. X. Sun, Y. P. Feng, J. Z. Zheng, Z. X. Shen, C. H. Pang, and L. H. Chan

J. Vac. Sci. Technol. B 23, 468 (2005); http://dx.doi.org/10.1116/1.1868646 (7 pages) | Cited 1 time

Online Publication Date: 11 March 2005

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The rough interface between a silicide film and a Si substrate induces large junction leakage currents in Si-based devices. In this work, we demonstrate that micro-Raman imaging can be used to characterize the interface roughness, without any special sample preparation. Pure metal (Ni and Ti) thin films and the subsequently formed silicide thin films after annealing (NiSi and TiSi2) were investigated using the intensity of the Si Raman band at 520 cm−1. Uniformity results of the pure metal films are in good agreement with those obtained using global four-point-probe measurement. In comparison, the signals obtained from the interfaces between Si and NiSi are nonuniform with large variations. The intensity of the major peak of NiSi at 214 cm−1 shows a point-to-point correlation with the intensity of the Si peak at 520 cm−1, which reveals that the local grain orientation affects the diffusion velocity of Ni atoms and the growth of NiSi. Images of Ti-silicides show that the interface of the C49 TiSi2 phase is much smoother than that of the C54 TiSi2 phase which is due to different formation mechanisms. Simulation was carried out based on two interfacial models, a two-step interface and a sinusoidal interface, to understand the correlation between the average attenuation of the Si Raman signal and the film thickness.
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68.35.Ct Interface structure and roughness
78.30.Hv Other nonmetallic inorganics
68.35.Fx Diffusion; interface formation
66.30.Ny Chemical interdiffusion; diffusion barriers

Effects of Pd activation on the self annealing of electroless copper deposition using Co(II)–ethylenediamine as a reducing agent

Chang Hwa Lee and Jae Jeong Kim

J. Vac. Sci. Technol. B 23, 475 (2005); http://dx.doi.org/10.1116/1.1868673 (5 pages) | Cited 6 times

Online Publication Date: 11 March 2005

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We investigated the effect of Pd activation on self-annealing in electroless Cu deposits using Co(II)–ethylenediamine as a reducing agent. The size and population of Pd particles were controlled by Pd ion concentration and activation time, which resulted in changes in the sheet resistances. While the low population of Pd particles (<109 cm−2) was unable to create completely continuous Cu film in subsequent electroless deposition and induced high film resistivity due to the voids, Pd particles that were over 20 nm in diameter increased the resistivity by raising the surface roughness of the Cu film. The optimal Pd activation condition was with Pd particle density of 1.73×109 cm−2 with 14 nm diameters. The resistivity of the Cu film in the optimal activation condition decreased to 2.46 μΩ cm. The deposited Cu film showed a low resistivity and a strong Cu (111) texture with the decrease in size and increase in the number of the Pd particles.
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82.45.Mp Thin layers, films, monolayers, membranes
82.45.Jn Surface structure, reactivity and catalysis
85.40.Ls Metallization, contacts, interconnects; device isolation
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Mechanism of simultaneous formation of refractory-metal free C40 and C49 TiSi2 induced by Q-switched Nd:Yttrium–aluminum–garnet laser irradiation

S. C. Tan, A. See, T. Yu, Z. X. Shen, and J. Lin

J. Vac. Sci. Technol. B 23, 480 (2005); http://dx.doi.org/10.1116/1.1868693 (6 pages)

Online Publication Date: 11 March 2005

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In this article, we demonstrate the usefulness of using a Q-switched Nd:Yttrium–aluminum–garnet laser to induce various phases of TiSi2 in 350 Å of Ti layer deposited onto (100) Si substrates by varying the pulse width, τ, and energy fluence of the laser. Two sets of experiments were carried out. In the first set of experiments, τ and energy fluence of the laser are set at 0.18 μs and approximately 1.5 J/cm2, respectively. The laser annealed Ti/Si sample was then characterized using micro-Raman spectroscopy and it was found that C49 TiSi2 is formed at two different temperatures. One is formed at a nonmelting temperature, 680 °C, and the other formation temperature is at a high temperature of around 1975 °C. A mechanism is proposed to explain the formation of C49 under these two different conditions. In addition, we also note that C40 is formed between these two temperatures. In the second set of experiments, increasing τ to 1.6 μs and reducing the energy fluence to approximately 1.0 J/cm2 resulted in the formation of pure refractory C40. This refractory metal free C40 phase is confirmed with glancing angle x-ray diffraction.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)
61.82.Fk Semiconductors
78.30.Hv Other nonmetallic inorganics

Effects of nickel and titanium thickness on nickel/titanium ohmic contacts to n-type silicon carbide

Jae Hyun Park and Paul H. Holloway

J. Vac. Sci. Technol. B 23, 486 (2005); http://dx.doi.org/10.1116/1.1868694 (9 pages) | Cited 6 times

Online Publication Date: 11 March 2005

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Titanium/nickel/titanium ohmic contacts to 4H n-SiC nitrogen doped to 3.55×1018 and 1.22×1019 cm−3 have been studied. As-deposited Ti/Ni/Ti/SiC structures were rectifying, but became ohmic upon annealing at 1000 °C for 2 min in a N2 ambient. A nickel silicide phase (Ni2Si) was formed during annealing, and smooth interfaces were observed when a Ti layer was present between the Ni and SiC. The dependence of ohmic contact resistance on Ni and Ti layer thickness was studied. Contacts with a 20 nm bottom Ti layer showed a contact resistance of 1×10−4 Ω cm2, while maintaining an interfacial rms roughness of 7.5 nm. Contacts with thicker bottom Ti layers (>20 nm) were rectifying with a nonlinear current–voltage behavior even after annealing, and there was still a distinct Ti layer between the Ni and SiC. The lack of an ohmic contact was attributed to the Ti layer acting as a diffusion barrier restricting the formation of Ni2Si. The Ni thickness was varied from 90 to 30 nm over a 20 nm Ti bottom layer, but the specific contact resistances (ρC) (3.3×10−4±2.5×10−4 Ω cm2) did not vary significantly with Ni thickness. Thicker Ni(>30 nm) contacts showed a nonuniform carbon distribution with graphite-rich zones at the silicide/SiC interface. Thin Ni contacts (30 nm) showed more uniform carbon distribution than in the contacts with thicker Ni, and no significant carbon-rich zone at the silicide/SiC interface.
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73.40.Cg Contact resistance, contact potential
68.35.Fx Diffusion; interface formation

Fermi level pinning on Si0.83Ge0.17 surface by inductively coupled plasma treatment

Iee-Gon Kim, Kyoung Jin Choi, and Jong-Lam Lee

J. Vac. Sci. Technol. B 23, 495 (2005); http://dx.doi.org/10.1116/1.1868652 (4 pages) | Cited 1 time

Online Publication Date: 17 March 2005

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Effects of inductively coupled plasma (ICP) treatment on Fermi level pinning on the surface of Si0.83Ge0.17 was studied by current–voltage and x-ray photoemission spectroscopy measurements. ICP treatment induced the growth of silicon oxide, suggesting that Si vacancies are generated under the oxide. From linear fitting of Schottky barrier heights with metal work functions, it was found that surface state density increased from 6.60×1012 to 1.13×1013/cm2 eV by the ICP treatment, leading to the pinning of surface Fermi level about EC ∼ 0.53 eV. From this, it is suggested that the Si vacancies are the main surface states in pinning Fermi level on the ICP-treated surface.
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73.61.Cw Elemental semiconductors
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
52.77.Dq Plasma-based ion implantation and deposition
73.30.+y Surface double layers, Schottky barriers, and work functions

Rutile films grown by molecular beam epitaxy on GaN and AlGaN/GaN

P. J. Hansen, V. Vaithyanathan, Y. Wu, T. Mates, S. Heikman, U. K. Mishra, R. A. York, D. G. Schlom, and J. S. Speck

J. Vac. Sci. Technol. B 23, 499 (2005); http://dx.doi.org/10.1116/1.1868672 (8 pages) | Cited 19 times

Online Publication Date: 17 March 2005

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Titanium dioxide (TiO2, with the rutile structure) was grown on (0001) oriented GaN and (0001) Al0.33Ga0.67N/GaN heterostructure field effect transistor (HFET) structures by molecular beam epitaxy. X-ray diffraction showed (100)TiO2‖(0001)GaN(AlGaN) and [001]TiO2‖〈11math0〉GaN(AlGaN) with three rotational variants of the TiO2. Transmission electron microscopy of 50 nm thick TiO2 films on GaN and AlGaN/GaN showed sharp interfaces with no intermixing or reaction between the oxide and semiconductor. The TiO2 exhibited a columnar film microstructure with a lateral domain size of a few nanometers parallel to (101)TiO2 and a few tens of nanometers parallel to (10math)TiO2. Metal–oxide HFETs with 50 nm thick TiO2 dielectric layers under the gate were processed and compared to HFETs without the TiO2 dielectric layer. The transconductance of the HFETs with TiO2 was 140 mS/mm, approximately 20% less than HFETs with no dielecric, and the pinchoff voltages of the two stuctures were comparable. The dielectric constant of the TiO2 was ∼ 70. The gate leakage current of the HFETs with TiO2, ∼ 4×10−6 mA/mm at 50 V, was approximately 4 orders of magnitude lower than that of the HFETs with no dielectric. Band offset measurements were performed using x-ray photoelectron spectroscopy, and the valence band of the rutile TiO2 and the GaN nearly line up.
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77.55.-g Dielectric thin films
68.55.-a Thin film structure and morphology
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Nanoimprint and nanocontact technologies using hydrogen silsesquioxane

Ken-ichiro Nakamatsu, Keiichiro Watanabe, Katsuhiko Tone, Hideo Namatsu, and Shinji Matsui

J. Vac. Sci. Technol. B 23, 507 (2005); http://dx.doi.org/10.1116/1.1868695 (6 pages) | Cited 8 times

Online Publication Date: 17 March 2005

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Room-temperature nanoimprint lithography (RT-NIL) and nanocontact printing (RT-NCP) processes using hydrogen silsesquioxane (HSQ) are promising techniques for fabricating various nanostructure devices. We have evaluated the linewidth dependence of the HSQ imprinted depth and the baking-temperature dependence of HSQ replicated patterns after RT-NIL. We have also demonstrated an advanced bilayer resist process with HSQ as a top layer and AZ photoresist as a bottom layer; this process can be used to fabricate high-aspect resist patterns on a Si substrate for RT-NIL and RT-NCP. The etching-rate ratio of the AZ photoresist to HSQ exceeds 100 for O2 reactive-ion etching, which means the etching tolerance of the HSQ top layer is sufficient to enable its use as a mask. We have fabricated high-aspect nanostructure patterns with 100 nm linewidth and 1 μm height using RT-NIL and 150 nm linewidth and 1 μm height by using RT-NCP. Furthermore, we have successfully transferred Au electrode patterns from a mold onto HSQ resin by using the adhesion properties of HSQ.
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81.16.Nd Micro- and nanolithography
85.40.Hp Lithography, masks and pattern transfer

Fabrication of polysilicon thin-film transistors using nickel/copper double-layer-induced lateral crystallization

Chi-Chieh Chen, Bo-Chuan Yang, and Si-Chen Lee

J. Vac. Sci. Technol. B 23, 513 (2005); http://dx.doi.org/10.1116/1.1875312 (6 pages) | Cited 1 time

Online Publication Date: 17 March 2005

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The material properties and thin-film transistors characteristics of nickel/copper-induced polysilicon are investigated. It was discovered that by combining Cu and Ni, the lateral growth rate of polysilicon is about an order of magnitude higher than that induced by Ni alone, and much better than the Cu-induced case. The grain size of Ni/Cu-induced polysilicon is 1.5 times larger than that of Ni alone, and also 30 times larger than that of the Cu induced case. The mechanism is attributed to the Cu-enhanced Ni silicide migration. The Ni/Cu-induced low-temperature polysilicon thin-film transistor shows a field-effect mobility of 10–25 cm2/V s, a threshold voltage of 8–22 V, and an on/off current ratio about 106–107.
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85.30.Tv Field effect devices

Investigation of a nanocrystalline silicon phase embedded in SiOx thin films grown by pulsed laser deposition

Enza Fazio, Enrico Barletta, Francesco Barreca, Fortunato Neri, and Sebastiano Trusso

J. Vac. Sci. Technol. B 23, 519 (2005); http://dx.doi.org/10.1116/1.1880252 (6 pages) | Cited 4 times

Online Publication Date: 17 March 2005

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The formation of nanocrystalline silicon clusters in SiOx thin films has been investigated by means of micro-Raman and Fourier transform infrared spectroscopic techniques. The samples were deposited, by means of pulsed laser ablation of a silicon target in a controlled oxygen gas environment, on substrates heated up to 883 K. Experimental results show that, by appropriately varying the deposition parameters, it is possible to achieve a fully coordinated silicon dioxide phase with the contemporary development of a nanometer-sized crystalline silicon phase and/or an amorphous one. Comparison between the effect of a relatively high substrate temperature and of a post-deposition annealing treatment have been exploited. From the line-shape analysis of the silicon TO vibrational mode Raman band, crystalline silicon volume fractions up to 90% have been estimated, while the nanocrystalline cluster sizes remained almost constant around 3.5 nm. A good agreement between our results and the predictions of silicon nanoclusters formation by a silicon atom diffusion-controlled mechanism has been found.
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81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
82.45.Mp Thin layers, films, monolayers, membranes

Influence of electric field intensity on the copper catalyst-mediated crystallization of amorphous silicon

Young-Bae Kim, Chul-Ho Kim, Hyun-Chul Kim, Young-Woong Kim, Hyun-Pyo Jeon, and Duck-Kyun Choi

J. Vac. Sci. Technol. B 23, 525 (2005); http://dx.doi.org/10.1116/1.1880272 (5 pages) | Cited 2 times

Online Publication Date: 17 March 2005

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The effects of electric field intensity on the crystallization of amorphous silicon (a-Si) using the field-aided lateral crystallization (FALC) process have been studied in the range of 0–180 V∕cm. The crystallization velocity increases as the electric field intensity increases. Moreover, the better quality of polycrystalline silicon resulted in the films that crystallized faster. The activation energy of the metal-induced lateral crystallization process calculated from the Arrhenius plot is 1.79 eV (±0.03 eV), whereas that of the FALC process is 1.65 eV (±0.04 eV) regardless of the electric field intensities. It is also shown that the electric field affects both the enhancement of the preexponential factor in the Arrhenius equation and the decrease in the energy barrier height for the crystallization. In particular, the effect is almost the same in the temperature range of 400–500 °C. The increase in the crystallization velocity is attributed to the field-enhanced diffusion of copper ions in the Cu3Si crystallization mediator and the amorphous Si.
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82.45.Wx Polymers and organic materials in electrochemistry
81.05.Gc Amorphous semiconductors
82.45.Jn Surface structure, reactivity and catalysis

Ferromagnetic properties of (Ga,Mn)N nanowires grown by a chemical vapor deposition method

Jeong Min Baik and Jong-Lam Lee

J. Vac. Sci. Technol. B 23, 530 (2005); http://dx.doi.org/10.1116/1.1880212 (4 pages)

Online Publication Date: 18 March 2005

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Ferromagnetic (Ga,Mn)N nanowires were grown on sapphire substrates at 900 °C by a chemical vapor deposition. Synchrotron radiation photoemission spectroscopy revealed that no secondary phases were found in the grown nanowire, meaning the dissolution of Mn atoms to form a solid solution in GaN nanowire. Fermi level was apart by 3.0 eV in the GaN nanowire (n-type), and it shifted toward the valance band maximum with ammonia flow rate. The Ga–to–N ratio decreased with the increase of ammonia flow rate, leading to the increase of Ga vacancies. From this, it is suggested that both increases in magnetic moment and Curie temperature with ammonia flow rate originated from the solid solution of Mn and Ga vacancies.
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75.50.Pp Magnetic semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.65.La Quantum wires (patterned in quantum wells)
81.05.Ea III-V semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
71.20.Nr Semiconductor compounds
79.60.Jv Interfaces; heterostructures; nanostructures

Study of neutral-beam etching conditions for the fabrication of 7-nm-diameter nanocolumn structures using ferritin iron-core masks

Tomohiro Kubota, Tomohiro Baba, Hiroyuki Kawashima, Yukiharu Uraoka, Takashi Fuyuki, Ichiro Yamashita, and Seiji Samukawa

J. Vac. Sci. Technol. B 23, 534 (2005); http://dx.doi.org/10.1116/1.1880232 (6 pages) | Cited 5 times

Online Publication Date: 18 March 2005

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We fabricated nanocolumn structure by using a low energy neutral beam and a ferritin iron-core mask. By using Cl2 gas plasma for generating neutral beam, we obtained a better etching profile than with SF6 gas plasma. Though Cl2:SF6 = 90:10 enabled faster etching than Cl2 gas without degrading the etching profile when the etching depth was 25 nm, a mixture with any quantity of SF6 gas resulted in a poor etching profile when the etching depth was 50 nm. The beam energy was optimized for the 50-nm depth using Cl2 gas by changing the rf bias power to the bottom electrode of the neutral-beam source. Using the optimum beam energy, extremely high etching selectivity of the Si to ferritin iron-core masks (about 80) as well as highly anisotropic etching profile could be realized. As a result, the diameter of the top of the Si nanocolumn structure was 7 nm, which was identical to that of the iron core in the ferritin. Additionally, the etching profile was almost vertical. We were also able to achieve a high aspect ratio of about 4.6. It is very difficult for conventional plasma etching processes to fabricate such fine structure, because the high-energy photons enhanced the etching of the iron-core mask in the conventional plasma processes.
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81.16.Nd Micro- and nanolithography
81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning

Process method to suppress the effect of phase errors in alternating phase shift masks

Navab Singh, Moitreyee M. Roy, Sohan S. Mehta, and A. O. Adeyeye

J. Vac. Sci. Technol. B 23, 540 (2005); http://dx.doi.org/10.1116/1.1885012 (7 pages)

Online Publication Date: 18 March 2005

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We have developed a process method to suppress the effect of phase errors in alternating phase shift masks. Our method uses double exposure at reversed focus offsets to nullify the intensity imbalance caused by the phase errors. We have evaluated our technique using 120 nm half-pitch line space patterns and found it very successful with remarkable improvement in usable depth of focus without loosing exposure latitude. We also observed that our technique could bring immunity against the lens aberrations such as defocus and astigmatism.
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85.40.Hp Lithography, masks and pattern transfer

Evaluation of the effectiveness of H2 plasmas in removing boron from Si after etching of HfO2 films in BCl3 plasmas

C. Wang and V. M. Donnelly

J. Vac. Sci. Technol. B 23, 547 (2005); http://dx.doi.org/10.1116/1.1875292 (7 pages) | Cited 8 times

Online Publication Date: 23 March 2005

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Etching of high dielectric constant (“high-k”) materials in BCl3-containing plasmas leaves behind a boron residue on underlying Si or SiO2 surfaces during the over-etching period. Boron is a p-type dopant and therefore it is best if it is removed prior to subsequent processing. We have investigated the effectiveness of H2 plasmas in removing this boron-containing layer. Following etching of HfO2 thin films in a high-density BCl3 plasma, including a 60 s overetch period, samples were transferred under vacuum to a UHV chamber equipped with x-ray photoelectron spectroscopy (XPS). After observing areal density B-coverages of ∼ 1×1015 cm−2 (equivalent of ∼ 1 monolayer), the samples were transferred back to the plasma reactor for exposure to the H2 cleaning plasma, and then reexamined by XPS. Optical emission spectroscopy was used to monitor B deposition on and removal from the plasma chamber walls. B deposition on the reactor walls during BCl3 plasma exposure reached saturated coverage in ∼ 2 min. Following this, the H2 plasma removed half of the B on the walls in 90 s and 90% in 320 s. B was rapidly removed (<5 s) from BCl3 plasma over-etched Si surfaces provided that the walls were first cleaned in the H2 plasma, with the Si sample held in the UHV chamber during the chamber cleaning process. Conversely, it took much longer ( ∼ 180 s) to remove all detectable B on the sample surface if the sample and the reactor chamber walls were cleaned in the H2 plasma at the same time. Apparently B is transported from the walls to the Si surface in this latter case. Etching rates of 22 and 1700 Å/min were measured for SiO2 and Si, respectively, in the H2 cleaning plasma. The fast etching of Si allows still shorter cleaning times, or preferably dilute H2 plasmas to be effective in removing B with less Si removal, provided the chamber walls are first cleaned in an H2 plasma.
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81.65.Cf Surface cleaning, etching, patterning
52.77.Bn Etching and cleaning
77.55.-g Dielectric thin films
79.60.Bm Clean metal, semiconductor, and insulator surfaces
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.

Combined in situ and ex situ analysis of hydrogen radical and thermal removal of native oxides from (001) GaAs

Kurt G. Eyink and Larry Grazulis

J. Vac. Sci. Technol. B 23, 554 (2005); http://dx.doi.org/10.1116/1.1884122 (5 pages) | Cited 5 times

Online Publication Date: 23 March 2005

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We are currently involved in the study of regrowth of InAs on nanopatterned GaAs surfaces. The nanopatterning is accomplished through the movement of the sample while in contact with a diamond tip maintained at a constant load. Native oxides present on these surfaces introduce an obstacle to the subsequent regrowth. Therefore, the removal of this oxide is a prerequisite step for the study of the subsequent regrowth on these patterned surfaces. In this study we used in situ spectroscopic ellipsometry (SE) and reflection high energy electron diffraction (RHEED) as well as ex situ atomic force microscopy to follow the hydrogen cleaning and thermal removal of the native oxides from the GaAs surface. SE and RHEED were used to follow the oxide desorption process in situ and were used to determine when the surface was clean. Post AFM analysis indicated that the thermally desorbed oxide surface contained pits which were approximately 100 Å deep and covered 15% of the surface. Hydrogen radical cleaning was studied at substrate temperatures between 400–535 °C using a pressure of approximately 1×10−6 Torr and a cracking thermocouple reading of 900 °C. The time to produce a clean surface was found to decrease as the temperature was increased. At the highest temperatures, cleaning took less than 10 min. AFM analysis indicated smooth surfaces were produced up to 500 °C. Above 500 °C, pitting was seen to occur similar to that observed for thermal oxide desorption. It was found that the onset of this pitting coincided with time at which spectroscopic ellipsometry indicated a change in the oxide layer.
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81.65.Cf Surface cleaning, etching, patterning
68.43.Mn Adsorption kinetics

Ideally ordered 10 nm channel arrays grown by anodization of focused-ion-beam patterned aluminum

C. Y. Peng, C. Y. Liu, N. W. Liu, H. H. Wang, A. Datta, and Y. L. Wang

J. Vac. Sci. Technol. B 23, 559 (2005); http://dx.doi.org/10.1116/1.1884123 (4 pages) | Cited 6 times

Online Publication Date: 23 March 2005

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Arrays of ideally ordered alumina nanochannels with unprecedented ∼ 10 nm pore size, 40–50 nm interpore spacing, and improved channel uniformity have been fabricated by anodizing an aluminum substrate with a guiding pattern on its surface. The pattern is an array of hexagonally close-packed concaves fabricated by focused ion beam direct sputtering; and its lattice constant is carefully matched to the conditions of the subsequent anodization process in order to achieve effective guiding in the growth of the nanochannels and therefore the ordering of an array.
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81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
81.05.Rm Porous materials; granular materials
81.07.-b Nanoscale materials and structures: fabrication and characterization
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Carbon nanotube field emitter manufactured by anodic-alumina template and Ni-CNT composite plating

Hyungdong Kang, Sangmoon Lee, and Haisung Lee

J. Vac. Sci. Technol. B 23, 563 (2005); http://dx.doi.org/10.1116/1.1885010 (3 pages)

Online Publication Date: 23 March 2005

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We present a method of manufacturing carbon nanotube (CNT) field emitters using anodic-alumina templates and Ni-CNT composite plating. Using the anodized aluminum sheet as a substrate affects a reduction of field deformation near the film surface during the electroplating. This improves the emission uniformity considerably and also enhances the emission-site density by nearly an order of magnitude compared to the emitter prepared on a plain Cu plate. The emission characteristics are discussed in terms of the surface morphology and the interlayer resistance.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
81.15.Pq Electrodeposition, electroplating

Dielectric properties enhancement of ZrO2 thin films induced by substrate biasing

A. P. Huang, Paul K. Chu, H. Yan, and M. K. Zhu

J. Vac. Sci. Technol. B 23, 566 (2005); http://dx.doi.org/10.1116/1.1885011 (4 pages) | Cited 5 times

Online Publication Date: 23 March 2005

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We have fabricated zirconia (ZrO2) thin films on Si (100) wafers that possess excellent dielectric properties such as high permittivity up to 53 and excellent frequency stability. The good performance is mainly attributed to the improvement in the crystallinity and orientation of the thin films and the interfacial structure using substrate biasing. The bias endues positive ions with high energy and diffusion of the incident particles and relaxation of the surface are enhanced by collisions between the impinging positive ions accelerated through the plasma sheath and substrate atoms. In addition, the higher nuclei density on the surface as a result of substrate biasing is beneficial to the fabrication of oriented thin films and the dielectric properties of the thin films are improved as the substrate bias goes up. The results increase our understanding of the factors leading to the deposition of high-quality ZrO2 dielectric thin films that are able to meet the requirements for capacitors in next-generation memory devices.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
68.35.Ct Interface structure and roughness
66.30.-h Diffusion in solids

Optical measurement and fabrication from a Morpho-butterfly-scale quasistructure by focused ion beam chemical vapor deposition

Keiichiro Watanabe, Takayuki Hoshino, Kazuhiro Kanda, Yuichi Haruyama, Takashi Kaito, and Shinji Matsui

J. Vac. Sci. Technol. B 23, 570 (2005); http://dx.doi.org/10.1116/1.1868697 (5 pages) | Cited 12 times

Online Publication Date: 4 April 2005

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The Morpho-butterfly wing reflects interfered brilliant blue, which originates from nanostructures on its scales, for any incidence angle of white light. We have fabricated a Morpho-butterfly-scale quasistructure using focused ion beam chemical vapor deposition and observed brilliant blue reflection from this quasistructure with an optical microscope. We measured the reflection from real Morpho-butterfly scales and from the quasistructure with a photonic multichannel spectral analyzer system. The reflection spectra of the quasistructure were very similar to those of Morpho-butterfly scales.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.16.-c Methods of micro- and nanofabrication and processing
78.40.Ha Other nonmetallic inorganics

Development and characterization of silane antisticking layers on nickel-based stamps designed for nanoimprint lithography

M. Keil, M. Beck, T. G. I. Ling, M. Graczyk, L. Montelius, and B. Heidari

J. Vac. Sci. Technol. B 23, 575 (2005); http://dx.doi.org/10.1116/1.1880292 (10 pages) | Cited 5 times

Online Publication Date: 4 April 2005

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In this study we will report on the development of a process to establish antisticking layers on nickel-based stamps, which are used in several industrial applications of nanoimprint lithography or related methods. The fluorinated alkyl silane films have been deposited onto different Ni-based stamp surfaces in order to minimize the adhesion tendency at the stamp/polymer interface. Film thickness, chemical composition, purity, and binding mechanisms of the silane groups to different stamp surface materials have been determined by photoelectron spectroscopy (XPS). In the case of electroplated nickel stamps—where low imprint qualities are observed—multilayer thick films cover the stamp surfaces, consisting of polymerized, cross-linked alkyl silanes, which are poorly bound to the surface. In order to overcome these restrictions a 100 Å thick polycrystalline titanium layer has been established in a sandwich position between the nickel substrate and the silane film. Here, silane film thicknesses in the monomolecular region together with evidences for strong covalent linkage between the silane groups and the oxidized Ti surface can be concluded from the XPS results, leading to film properties and imprint qualities, which are comparable to those formerly observed for silicon stamps.
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68.55.-a Thin film structure and morphology
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Gas-assisted focused ion beam etching characteristics of niobium

X. L. Fu, P. G. Li, A. Z. Jin, H. Y. Zhang, H. F. Yang, and W. H. Tang

J. Vac. Sci. Technol. B 23, 585 (2005); http://dx.doi.org/10.1116/1.1884121 (3 pages) | Cited 1 time

Online Publication Date: 4 April 2005

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The gas-assisted focused ion beam etching characteristics of niobium have been investigated systematically in I2 and XeF2 gas atmosphere, respectively. The effects of the etching parameters, such as: ion beam current, dwell time, overlap percentage and gas species, on the niobium etching rate and on the gas-assisted etching enhancement have been studied. It was found that the overlap percentage had little effect on the etching characteristics of niobium. It also showed that the I2 radicals are more reactant with niobium than XeF2 radicals, and to obtain maximum improvement from the gas-assisted etching process one needs to select a smaller ion beam current with a shorter beam dwell time.
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81.65.Cf Surface cleaning, etching, patterning
61.80.Jh Ion radiation effects
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Microstructure and mechanical properties of superhard Ti–B–C–N films deposited by dc unbalanced magnetron sputtering

In-Wook Park, Kwang Ho Kim, Augusto O. Kunrath, Dalong Zhong, John J. Moore, A. A. Voevodin, and E. A. Levashov

J. Vac. Sci. Technol. B 23, 588 (2005); http://dx.doi.org/10.1116/1.1884125 (6 pages) | Cited 10 times

Online Publication Date: 4 April 2005

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Superhard quarternary Ti–B–C–N films were successfully deposited on AISI 304 stainless steel substrates by a dc unbalanced magnetron sputtering technique from a Ti–B–C composite target. The relationship between microstructures and mechanical properties was investigated in terms of the nanosized crystallites∕amorphous system. The synthesized Ti–B–C–N films were characterized using x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). These analyses revealed that our Ti–B–C–N films are composites of solid-solution (Ti,C,N)B2 and Ti(C,N) crystallites distributed in an amorphous boron nitride (BN) phase including some of carbon, CNx, B2O3 components. The hardness of the Ti–B–C–N films increased with the increase of N content up to a maximum value of approximately 45 GPa at 10 at. % N, with a subsequent decrease in hardness at higher N content. This value is considerably higher than the hardness measured in our Ti–B–C films ( ∼ 35 GPa). The Ti–B–C–N(10 at .%) film also showed the highest H3/E*2 value ( ∼ 1.7 GPa) among the coatings produced. A systematic investigation of the microstructures and mechanical properties of Ti–B–C–N films prepared with various N contents is reported in this paper.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
68.35.Gy Mechanical properties; surface strains
62.20.Qp Friction, tribology, and hardness
68.60.Bs Mechanical and acoustical properties
79.60.Jv Interfaces; heterostructures; nanostructures
68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering

Electronic defect states at annealed metal/4H–SiC interfaces

S. Tumakha, S. H. Goss, L. J. Brillson, and R. S. Okojie

J. Vac. Sci. Technol. B 23, 594 (2005); http://dx.doi.org/10.1116/1.1884124 (5 pages) | Cited 3 times

Online Publication Date: 6 April 2005

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We have used low energy electron-excited nanoscale luminescence spectroscopy (LEEN) to study the formation of electronic surface states at metal/4H–SiC contacts. These junctions were formed using both low and high reactivity metals to study how the nature of interface chemical bonding affects the interface state formation. We observe evidence for the formation and removal of localized states at energies that have been associated with morphological SiC defects. Metals such as Au and Ag with no strong chemical reactivity exhibited the most pronounced changes. Conversely, chemically-reactive metals such as Ti and Ni exhibited only minor changes and only with high temperature annealing. These observations suggest that native defects rather then metal-specific chemical bonding dominate the interface electronic features.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.60.-b Other luminescence and radiative recombination
81.40.Gh Other heat and thermomechanical treatments

Influence of scaling effects on designing for power efficiency of a micropreconcentrator

K. A. Cook and A. M. Sastry

J. Vac. Sci. Technol. B 23, 599 (2005); http://dx.doi.org/10.1116/1.1886821 (13 pages)

Online Publication Date: 6 April 2005

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Rapid and reliable assessment of volatile and semivolatile organic compounds in the environment using gas chromatography (GC) is often limited by cost of analysis, and time delays between sampling and analysis. Many environmental monitors incorporating GC systems are too large for portability, and lack sufficient sensitivity and/or selectivity to serve as practical environmental monitors. Frequently, a complete system redesign, due to nonlinear power scaling relative to component size, is required to reduce the mass and volume of power supplies, especially for the micro-systems of present interest. Here, we examined four strategies in reducing power demand by the largest consumer of power in a model micro GC, the preconcentrator. Our simulations included alterations in heater pad placement/size, reduction of thermal mass in the device, vacuum sealing, and incorporation of a gas dwell time during preconcentrator heating. Our numerical results were in general agreement with experimental findings in simpler systems, in terms of the benefits of vacuum sealing. The greatest reductions in power demand were achieved with vacuum sealing (51%) and reductions in thermal mass (15%). Future work will address structural and materials issues involved in reduction of thermal mass, and also optimization of power supplies required to meet the multilevel power demands of these complex microelectromechanical systems.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
82.80.Bg Chromatography
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Three-dimensional time-resolved analysis for the discharge of plasma display panel using the scanned-point detecting system

Hoon-Young Choi, Seok-Hyun Lee, Seung-Gol Lee, and Jeong-Hyun Seo

J. Vac. Sci. Technol. B 23, 612 (2005); http://dx.doi.org/10.1116/1.1861043 (6 pages)

Online Publication Date: 6 April 2005

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52.75.-d Plasma devices
85.60.Pg Display systems
52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.80.-s Electric discharges
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back to top Theory, Modeling and Simulation of Field Emitters

Time dependent models of field-assisted photoemission

Kevin L. Jensen, Donald W. Feldman, and Patrick G. O’Shea

J. Vac. Sci. Technol. B 23, 621 (2005); http://dx.doi.org/10.1116/1.1861047 (11 pages) | Cited 8 times

Online Publication Date: 6 April 2005

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A time-dependent model of photoemission, developed to analyze current from and laser heating of metals and dispenser photocathodes, is here applied to examine the impact of geometrical field enhancement and the contribution of tunneling to the photocurrent from a tungsten needle in terms of temporal response, quantum efficiency, and cathode performance. First, a review is given of an updated Fowler–Dubridge model of quantum efficiency including quantum mechanical effects. Second, a prolate spheroidal model of a tungsten needle is given to determine applied fields and incident angles necessary to evaluate emitted current and laser heating effects. Third, a time-dependent model of laser heating of an electron distribution is given which affects the photoemitted current and (if conditions are right) gives field and thermal components as well. Finally, the methodology is related to the experimental findings of Garcia and Brau [Nucl. Instrum. Methods Phys. Res. A 483, 273 (2002) ], in which an intense laser illuminates a tungsten needle under sufficiently high fields that the photoemitted current contains field and thermal emission components and effects.
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79.60.Bm Clean metal, semiconductor, and insulator surfaces
85.60.Ha Photomultipliers; phototubes and photocathodes
79.40.+z Thermionic emission
73.40.Gk Tunneling

Effect of aspect ratio and anode location on the field emission properties of a single tip based emitter

R. C. Smith, J. D. Carey, R. D. Forrest, and S. R. P. Silva

J. Vac. Sci. Technol. B 23, 632 (2005); http://dx.doi.org/10.1116/1.1880072 (4 pages) | Cited 22 times

Online Publication Date: 6 April 2005

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The effect on the field emission characteristics of the aspect ratio of an isolated emitter, together with the position of the anode electrode are reported. We show by computational simulation that the field enhancement factor β is only dependant on the emitter height h, radius r, when the anode to cathode separation D is greater than three times the height of the emitter away from the tip. In this regime the enhancement factor is independent of the anode location and approaches a value depicted by h and r alone and is described by the expression β0 = (1+math)m where α = 2 and m = 1. As the anode is brought close to the tip of the emitter, the emitter tip and anode approximate a parallel plate configuration and the enhancement factor tends to unity. Extracted enhancement factor and threshold fields are described by a modified applied electric field taking D−h as the separation. Comparison with previously reported experimental results is also given.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Db Field emitters and arrays, cold electron emitters

Space-charge effects of electrons and ions on the steady states of field-emission-limited diodes

Ming-Chieh Lin

J. Vac. Sci. Technol. B 23, 636 (2005); http://dx.doi.org/10.1116/1.1875352 (4 pages) | Cited 7 times

Online Publication Date: 6 April 2005

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Space-charge effects of electrons and ions on the steady state of a field-emission-limited diode (FELD) are investigated via a self-consistent approach. The field-emission process is described quantum mechanically by the Fowler–Nordheim equation. The cathode plasma and surface properties are considered within the framework of the effective work function approximation. Ionization effects at the anode as well as electron space-charge effects are described by Poisson’s equation. The numerical calculations are carried out self-consistently to yield the steady states of the bipolar field-emission-limited flow of the FELD. We found that the stationary state of the diode exhibits a cut-off voltage. The electric field on the cathode surface is found to be saturated in the high voltage regime and is determined by the effective work function approximately. In addition, the ion current included in the Poisson’s equation has been treated as a tuning parameter. The analytical formula of the electron current density has been derived. The field-emission currents in the presence of saturated ion currents can be enhanced to be nearly 1.8 times of the case with no ion current.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.30.Fg Bulk semiconductor and conductivity oscillation devices (including Hall effect devices, space-charge-limited devices, and Gunn effect devices)
85.45.Bz Vacuum microelectronic device characterization, design, and modeling

Electron optics and electrical studies of a single Spindt-type field emitter

Y. Désières, P. Nicolas, F. Sermet, F. Geffraye, and S. Gidon

J. Vac. Sci. Technol. B 23, 640 (2005); http://dx.doi.org/10.1116/1.1880092 (5 pages)

Online Publication Date: 6 April 2005

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Experimental and numerical investigations of the field emission of a single molybdenum Spindt emitter are presented. Experimental results show that the emission is localized at nanometric areas on the top of the tip. An effective numerical model of the tip has been developed to describe the main characteristics of the experimental beam pattern. The Lagrange constant of this model has been estimated to 15 nm V1/2.
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85.45.Db Field emitters and arrays, cold electron emitters
41.85.-p Beam optics

Numerical study of the electrostatic field gradients present in various planar emitter field emission configurations relevant to experimental research

Adolfo González-Berríos, Fabrice Piazza, and Gerardo Morell

J. Vac. Sci. Technol. B 23, 645 (2005); http://dx.doi.org/10.1116/1.1849194 (4 pages) | Cited 11 times

Online Publication Date: 6 April 2005

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The generally assumed validity of the V/dCA approximation for the cathode surface electric field under commonly employed electron field emission configurations was studied. Using appropriate typical dimensions for each configuration, the magnitude of the electric field over the cathode area under the probe was obtained, and especially near critical (i.e., sharp) regions that could lead to residual gas ionization, dielectric breakdown and emission of electrons from unintended areas. The results indicate that the V/dCA approximation is far from being universally applicable to all the field emission measuring configurations. In particular, the cylindrical probe anode with flat tip gives the most uniform ES, which nearly equals V/dCA over most of the cathode area under the probe. Spherical and hemispherical probes, on the other hand, result in ES close to V/dCA only locally near the center, and much lower anywhere around the center. Moreover, the parallel-plate configurations lead to significantly detrimental field enhancement effects near the edges that discourage their use. These results have important implications in the correct evaluation of cold cathode materials for applications requiring large emitting areas or large current densities.
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79.70.+q Field emission, ionization, evaporation, and desorption
77.22.Jp Dielectric breakdown and space-charge effects

Ring-shaped images as a result of nonuniform field emission from capped carbon nanotubes

L. D. Filip, D. Nicolaescu, M. Tanemura, S. Kanemaru, and J. Itoh

J. Vac. Sci. Technol. B 23, 649 (2005); http://dx.doi.org/10.1116/1.1864059 (8 pages) | Cited 6 times

Online Publication Date: 6 April 2005

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A model for electron field emission from carbon nanotubes (CNTs) has been developed and modeling results are presented. The model assumes that for high emission currents, part of the electrons behave as quasifree. As a result, the spatial confinement quantization of their states appears, the tunneling field emission taking place from these states into the vacuum. The probability of finding an electron in a small axial interval is higher close to the CNT cylindrical body, while the extraction field is higher on the CNT hemispherical tip. These two opposite trends lead to enhancement of the CNT lateral field emission for higher extraction voltages. The model outlines the possibility of inhomogeneous electron field emission for very thin CNTs at high emission levels and the appearance of peculiar ring-shaped and/or spot-shaped field emission images, in accordance to available experimental observations.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.63.Fg Nanotubes
73.40.Gk Tunneling

Field electron emission from two-dimensional electron gas

V. Filip, D. Nicolaescu, H. Wong, M. Nagao, and P. L. Chu

J. Vac. Sci. Technol. B 23, 657 (2005); http://dx.doi.org/10.1116/1.1886820 (8 pages) | Cited 5 times

Online Publication Date: 6 April 2005

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The article presents a quantum mechanical model for the electron field emission from semiconductor surfaces covered by dielectric layers. By systematically connecting electronic wave functions at various interfaces, the model obtains in a unified manner the field emission current density from both clean and dielectric-covered semiconductor substrates. No energy quantization is imposed for the interface layer and thermodynamic nonequilibrium is allowed between the conduction electrons from the interface (accumulation) layer and those of the bulk. The model is applied to study the electron field emission from Si tips covered by ultrathin oxide layers and also to explain the resonance effects observed in field emission from Si covered by thicker dielectric layers.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
68.47.Fg Semiconductor surfaces
back to top Characterization of Field Emitters

Field emission under extreme conditions from carbon nanopearls in a foam-like arrangement

A. Levesque, P. Vincent, Vu Thien Binh, D. Guillot, and M. D. Brookes

J. Vac. Sci. Technol. B 23, 665 (2005); http://dx.doi.org/10.1116/1.1849193 (6 pages) | Cited 5 times

Online Publication Date: 6 April 2005

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We studied field emission properties of carbon nanopearls for application as cold cathodes in low vacuum conditions (up to 10−4 Torr). The nanopearls are spherical in shape, 150 nm in diameter, and composed of both amorphous and nanocrystalline regions. The nanopearls form two-dimensional “strings” which give rise to a macroscopic three-dimensional foam-like material. For this study, we have synthesized uniform layers of nanopearls by chemical vapor deposition directly on the apex of tungsten tips and performed comparative field emission measurements under different gas pressures. We present field emission current stabilities in the μA range under nitrogen and oxygen atmosphere up to 10−4 Torr, which corresponded to field emission current densities up to 1 A/cm2, and were obtained for hours with a simple “retroaction” voltage control. These results show that field emission with nanopearls is a promising way for applications requiring high current densities in high pressure environment. The long lifetime of nanopearls cathodes at high pressures is a consequence of the foam-like structure of the deposited layers of the nanopearls, leading to a self-healing process of the emission sites that were continuously destroyed by retro-ion sputtering during emission.
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79.70.+q Field emission, ionization, evaporation, and desorption
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Scanning anode field emission microscopy analysis for studies of planar cathodes

V. Semet, R. Mouton, and Vu Thien Binh

J. Vac. Sci. Technol. B 23, 671 (2005); http://dx.doi.org/10.1116/1.1857911 (5 pages) | Cited 11 times

Online Publication Date: 6 April 2005

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In a scanning anode field emission microscope the field emission current is extracted by a small spherical anode brought, at micrometric proximity, in front of a planar cathode surface. Therefore, the field over the emission area is not uniform and direct quantitative interpretation from the total field emission current versus applied voltage is misleading. The potential distribution of the system composed of a sphere in front of a plane have been calculated to determine the field distribution over the surface in order to define the active field emitting zone and to extract the current density versus the local applied field from the measured total field emission current versus applied voltage characteristics.
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82.45.Fk Electrodes
68.37.Vj Field emission and field-ion microscopy

Field emission from teepee-shaped carbon nanotube bundles

H. Busta, Z. Tolt, J. Montgomery, and A. Feinerman

J. Vac. Sci. Technol. B 23, 676 (2005); http://dx.doi.org/10.1116/1.1885009 (4 pages)

Online Publication Date: 6 April 2005

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Randomly, but perpendicular to the surface, oriented carbon nanotubes of about 5 μm in height and submicrometer spacing were coated with 3.5 μm plasma enhanced CVD silicon dioxide. Subsequent removal of the oxide in buffered HF, followed by de-ionized water rinse and nitrogen blow drying resulted in the formation of a peculiar pattern of nanotubes similar in shape to teepees or the hair cells of the inner ear. Since several nanotubes can supply current to the apexes of these bundles and since the spacing between the apexes is increased, thus reducing the electrostatic screening effect, these structures might have interesting field emission properties. Field emission measurements were performed at pressures of about 1×10−8 Torr. Room temperature emission was poor with turn-on fields of about 30 V/μm due to surface contamination effects. Turn-on fields of about 15 V/μm and macroscopic current densities of 50 mA/cm2 were obtained when the measurements were performed at 170 °C.
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81.07.De Nanotubes
79.70.+q Field emission, ionization, evaporation, and desorption
61.46.-w Structure of nanoscale materials
73.63.Fg Nanotubes
81.65.-b Surface treatments

Pulsed field emitted current from different commercial samples in the purpose of a free electron laser application

R. Ganter, K. Li, M. Dehler, J. Gobrecht, L. Rivkin, and A. Wrulich

J. Vac. Sci. Technol. B 23, 680 (2005); http://dx.doi.org/10.1116/1.1857892 (2 pages) | Cited 3 times

Online Publication Date: 6 April 2005

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The development of an electron gun with the lowest possible emittance would help reduce the total length and cost of a free electron laser. Recent progress in vacuum microelectronics makes field emitter tips an attractive technology to explore for high brightness electron sources. In order to be a good candidate for a low emittance gun, field emission cathodes must provide at least the peak current, stability, and homogeneity of current state of the art electron sources. In this article, we report on current voltage measurements of commercially available field emitter samples in both continuous and pulsed mode. Pulsed electron emission is of particular interest for a free electron laser application. As mentioned by other authors [ F. Charbonnier, Appl. Surf. Sci. 94/95, 26 (1996) ; P. R. Schwoebol et al., J. Vac. Sci. Technol B 19, 980 (2001) ], higher peak current and more stable emission can be achieved when using short square voltage pulses at low frequency. We present maximum peak currents achieved with 100 ns long voltage pulses at low frequency (50 Hz). In such a pulsed mode, the risk of excessive heating and cathode damaging is considerably reduced.
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85.45.Db Field emitters and arrays, cold electron emitters
84.47.+w Vacuum tubes
79.70.+q Field emission, ionization, evaporation, and desorption

Characterization of an advanced high-efficiency electron emission device

Nobuyasu Negishi, Tomonari Nakada, Kazuto Sakemura, Yoshiyuki Okuda, Hideo Satoh, Atsushi Watanabe, Takamasa Yoshikawa, Kiyohide Ogasawara, and Nobuyoshi Koshida

J. Vac. Sci. Technol. B 23, 682 (2005); http://dx.doi.org/10.1116/1.1884119 (5 pages) | Cited 5 times

Online Publication Date: 6 April 2005

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As previously reported, the emission characteristics of metal-insulator-semiconductor (MIS) electron emission devices could be significantly improved by introducing microdimple structures into the emission sites. In this paper, we describe the characteristics of efficient cold electron emitters from a viewpoint of application to flat panel display (FPD). First, the forming operation for the device to activate the dynamic emission is discussed on a basis of the experimental analyses of the electrical properties and output electron energy spectra. Next it is demonstrated that the device has some desirable features as an excitation source of FPD: a high emission current density, a low operation voltage, emission uniformity, and stable emission with small angle dispersion. It is also shown from the result of lifetime evaluation that the device shows a half-life of 3000 h, and that the deteriorated emission can be recovered by the dc reactivation treatment.
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85.45.Db Field emitters and arrays, cold electron emitters

Energy distributions of field emission electrons from silicon emitters

Hidetaka Shimawaki, Yousuke Suzuki, Katsumi Sagae, Yoichiro Neo, and Hidenori Mimura

J. Vac. Sci. Technol. B 23, 687 (2005); http://dx.doi.org/10.1116/1.1885007 (4 pages) | Cited 1 time

Online Publication Date: 6 April 2005

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The energy distributions of field-emitted electrons from single-tip n type and p type Si field emitters have been analyzed. The energy distributions of both n type and p type Si emitters show a single peak, and the peak position shifts slightly towards the low energy side in the n type emitter as the gate voltage is increased. In the case of the p type emitter a considerably larger shift towards lower energies is observed. The distributions from the n type emitter have the same threshold energies near the Fermi level energy and become broader with the increase in the gate voltage. On the other hand, the threshold energies of the p type emitter are more than 1.5 eV below the Fermi level and shift to the lower energy side as well as the peak position in the energy distribution with increasing the gate voltage. In addition, the energy distributions of the p type emitter are considerably broad in comparison with those of the n type emitter, but the full width half maximums (FWHMs) of the distributions do not significantly change with the increase in the gate voltage. These results suggest that for the n type Si field emitter electrons are basically supplied from the Si conduction band and are emitted from the neighborhood of the conduction band under the effect of the band bending and electron trapping in surface and oxide states at the interfaces of the emitter. On the other hand, for the p type Si field emitter, electrons are mainly emitted through the interface states supplied from the valence band of Si.
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85.45.Db Field emitters and arrays, cold electron emitters

High current, high current density field emitter array cathodes

P. R. Schwoebel, C. A. Spindt, and C. E. Holland

J. Vac. Sci. Technol. B 23, 691 (2005); http://dx.doi.org/10.1116/1.1849189 (3 pages) | Cited 15 times

Online Publication Date: 6 April 2005

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Microfabricated field emitters have shown the potential for very high current densities (>100 A/cm2) and total emission currents (>1 A). However, realizing this potential has been elusive, primarily because these cathodes exhibit insufficient emission uniformity over an emitter array. In this article we report the development of an in situ processing method based on emitter tip self-heating during operation that is shown to improve emission uniformity between emitter tips. Two tips differing in emission current by three orders of magnitude for a given voltage as fabricated are shown to be essentially identical in their emission characteristics after controlled pulsing to very high emission current. When the method was applied to a 50 000 tip array, it produced 300 mA of emission (40 A/cm2). The experimental arrangement prevented advancing to higher emission levels due to space charge limitations. It is expected that 1 A of emission at ∼ 100 A/cm2 is possible with appropriate modifications to the experimental apparatus.
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85.45.Db Field emitters and arrays, cold electron emitters
79.70.+q Field emission, ionization, evaporation, and desorption

Regeneration of gated carbon nanotube field emission

David S. Y. Hsu and Jonathan L. Shaw

J. Vac. Sci. Technol. B 23, 694 (2005); http://dx.doi.org/10.1116/1.1851534 (4 pages) | Cited 2 times

Online Publication Date: 6 April 2005

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We report large increases in field emission current when operating carbon nanotubes in substantial pressures of hydrogen, especially when the nanotubes were contaminated. We have previously demonstrated two different configurations of integrally gated carbon nanotube field emitter arrays (cNTFEAs), CNTs grown inside microfabricated gate apertures with and without silicon posts. Salient features of these in situ grown microgated cNTFEAs include the absence of electrical arcing, low operating voltage, and enhancing effect of some residual ambient gases. Operating both configurations of cNTFEAs without special precleaning in greater than 10−5 Torr hydrogen produced orders of magnitude enhancement in emission. For a cNTFEA intentionally degraded by oxygen, the operation in hydrogen resulted in a 340-fold increase in emission current at constant gate voltage. The results suggested a dependence on atomic hydrogen produced from the interaction between emission electrons and molecular hydrogen. The observed emission enhancement could be due to a surface dipole formation, hydrogen doping, or removal of oxygen-containing surface species.
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85.45.Db Field emitters and arrays, cold electron emitters
85.35.Kt Nanotube devices

Influence of mechanical stress on electron field emission of multiwalled carbon nanotube–polymer composites

C. H. P. Poa, R. C. Smith, S. R. P. Silva, and C. Q. Sun

J. Vac. Sci. Technol. B 23, 698 (2005); http://dx.doi.org/10.1116/1.1868692 (4 pages) | Cited 4 times

Online Publication Date: 6 April 2005

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Field emission properties of carbon nanotubes under mechanical stress have been investigated. The emission threshold fields initially decrease from 2.3 to 0.6 V/μm before rising back to 3.1 V/μm with increasing mechanical stress applied externally to the film. This behavior from nanotube composites has not been reported and is believed to be associated with modification to the work function of the nanotubes. This work suggests a possible application for these composite films as electromechanical high power switches.
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81.07.De Nanotubes
81.40.Jj Elasticity and anelasticity, stress-strain relations

Stable and high emission current from carbon nanotube paste with spin on glass

Jae-Hong Park, Jin-San Moon, Jae-Hee Han, Alexander S. Berdinsky, Ji-Beom Yoo, Chong-Yun Park, Joong-Woo Nam, Jonghwan Park, Chun Gyoo Lee, and Deok Hyeon Choe

J. Vac. Sci. Technol. B 23, 702 (2005); http://dx.doi.org/10.1116/1.1880192 (5 pages) | Cited 1 time

Online Publication Date: 6 April 2005

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A carbon nanotube (CNT) paste was synthesized by mixing multiwalled CNTs (MWNTs), organic vehicles, and inorganic binder. The paste with spin on glass (SOG) showed improved uniformity, dispersion, and adhesion characteristics of the CNT paste layer. The emission characteristics of CNT paste with SOG were improved, and compared to those of a CNT paste with a glass frit. When the organic vehicle was changed from ethyl cellulose to acryl solution, current density of CNT paste increased. The firing condition for CNT pastes was investigated and optimized. It was found that firing at 450 °C under N2 was the most suitable condition for pastes with MWNTs. We obtained stable and high emission current of 100 mA at an electric field of 8.35 V/μm from CNT paste with SOG printed on a Ni plate.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes

Emission statistics for Si and HfC emitter arrays after residual gas exposure

D. Nicolaescu, M. Nagao, T. Sato, V. Filip, S. Kanemaru, and J. Itoh

J. Vac. Sci. Technol. B 23, 707 (2005); http://dx.doi.org/10.1116/1.1864058 (11 pages) | Cited 6 times

Online Publication Date: 6 April 2005

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Field emission arrays (FEAs) comprising 100 Si or HfC coated Si emitters have been fabricated. The FEAs emission properties were measured in ultra high vacuum conditions and after being subject to Ar and O2 residual gases with partial pressures in the range 10−6 to 10−4 Pa. The influence of residual gases on the FEAs field emission properties has been comparatively assessed using the model parameter extraction method. The array field emission model uses equations that describe the electron emission current from individual emitters of given radius R and work function ϕ together with nonuniform distribution functions giving the dispersion of these parameters within the array. A simplified relationship for the array emission current depending on a single integral instead of a double one has been derived. A nonlinear extraction algorithm using partial derivatives of the objective function is used, which gives fast and accurate results. Both Si and HfC emitters exhibit (to a different degree) tightening of the radius distribution with time and more uniform emission, when exposed to O2 residual gas. The current degradation of Si and HfC arrays, when exposed to Ar residual gas, is mostly associated with the work function increase. HfC emitters have higher emission currents, lower noise level, and better stability of the emission than Si emitters. These properties are discussed in terms of the array parameter statistics.
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85.45.Db Field emitters and arrays, cold electron emitters
85.30.De Semiconductor-device characterization, design, and modeling
73.30.+y Surface double layers, Schottky barriers, and work functions

Uniformity measurement of electron emission from carbon nanotubes using electron-beam resist

J. H. Lee, S. H. Lee, W. S. Kim, H. J. Lee, J. N. Heo, T. W. Jeong, C. H. Choi, J. M. Kim, J. H. Park, J. S. Ha, H. J. Lee, J. W. Moon, M. A. Yoo, J. W. Nam, S. H. Cho, et al.

J. Vac. Sci. Technol. B 23, 718 (2005); http://dx.doi.org/10.1116/1.1861036 (5 pages) | Cited 7 times

Online Publication Date: 6 April 2005

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The field-emission sites’ distribution was measured to monitor the emission uniformity from randomly oriented carbon-nanotube (CNT) emitters using electron-beam resists (ER). The dot-patterned CNT emitters were fabricated by screen-printing a photoimageable CNT paste on an indium doped tin oxide (ITO) coated glass plate. An ER-coated Si substrate used as an anode provides the detection of the location and amount of the electron emission from the partial number of active emission sites among many existing CNTs. The measurements were carried out with the variation of electrical fields through continuous- or pulsed-voltage applications on a diode-type configuration. Developed ER images after a similar dosage of field-emission current flow indicate that emission uniformity is improved as the electrical field is increased. This method suggests that the emission uniformity could be estimated for various conditions of emitter preparation, such as CNT type, paste composition, and dispersion process, as well as the variation of the electrical field, the existence of a resistive layer, and so on.
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85.45.Db Field emitters and arrays, cold electron emitters
85.35.Kt Nanotube devices
85.40.Hp Lithography, masks and pattern transfer
81.16.Nd Micro- and nanolithography

Noise and emission characteristics of NbC/Nb field emitters

F. M. Charbonnier, L. A. Southall, and W. A. Mackie

J. Vac. Sci. Technol. B 23, 723 (2005); http://dx.doi.org/10.1116/1.1864064 (8 pages) | Cited 2 times

Online Publication Date: 6 April 2005

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Several applications require single field emitters with adequate long-term stability and life in a moderate vacuum. Our previous studies have shown that the refractory carbides of transition metals are capable of higher currents and are more environmentally tolerant than common field emitter materials such as W, Mo, or Si. We undertook a systematic study of the emission characteristics and stability of individual NbC/Nb microtips at low currents and at residual pressures ranging from 10−9 to 10−5 Torr. We reported preliminary results one year ago [ J. Vac. Sci. Technol. B 22, 1643 (2004) ]. We now present additional data and interpretations. These experimental data were obtained by two types of measurement: (a) continuous recording of the field emitted current at a fixed voltage and (b) recording of the emitted current with a saw-tooth applied voltage, which yields a large number of Fowler–Nordheim plots which are analyzed by the slop-intercept method. Our experimental results show greater instability than we expected. We conclude that for NbC/Nb emitters fabricated by physical vapor deposition, emission is dominated by a very small number of extremely sharp but unstable nanoprotrusions, with an effective emitting area (from the slope-intercept charts) of the order of a few nm2. Consequently, we lack the stability and control of the beam directional intensity which are required for most applications. Prior to stable operation, single emitters should be conditioned to eliminate sharp protrusions, enhance paraxial emission, and increase the effective emitter area. We are now studying effective conditioning techniques for microtips.
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85.45.Db Field emitters and arrays, cold electron emitters
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Ion-beam morphological conditioning of carbon field emission cathode surfaces

Charles E. Hunt, Andrei G. Chakhovskoi, and Yu Wang

J. Vac. Sci. Technol. B 23, 731 (2005); http://dx.doi.org/10.1116/1.1880052 (4 pages) | Cited 5 times

Online Publication Date: 6 April 2005

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Samples of reticulated vitreous carbon (RVC) and paste graphite film have been evaluated for field-emission properties both before and after surface modification. The RVC has been treated using an open-air laser method. The graphite has been treated using an Ar-ion flood bombardment method. Both methods result in a change in surface morphology of the emission cathode which physically resembles results obtained using current or voltage stress treatment methods. Emission properties become more uniform, exhibit less noise, and, in the best cases, match results seen from carbon nanotubes or ultra-nanocrystalline diamond cathodes. The results demonstrate a method for obtaining large total currents at optimal extraction voltages, from large-area, low-cost cathodes. This method is useful for applications, such as field-emission lamps and x-ray tubes, which do not require nanofabricated, lithographically-patterned cathode structures.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.U- Carbon/carbon-based materials
61.80.Jh Ion radiation effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
85.45.Bz Vacuum microelectronic device characterization, design, and modeling

Observation of electron emission pattern from nanosplit emitter fabricated using beam assisted process

K. Murakami, N. Yamasaki, S. Abo, F. Wakaya, and M. Takai

J. Vac. Sci. Technol. B 23, 735 (2005); http://dx.doi.org/10.1116/1.1875372 (6 pages) | Cited 3 times

Online Publication Date: 6 April 2005

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A fabrication process of nanosplit emission sites has been developed with a minimum gap size of 12 nm using beam assisted processing. The electron emission patterns on a phosphor screen from a conventional single emitter and nanosplit emitters with various gap sizes were observed at room temperature and 77 K. The emission patterns from the conventional single emitter had a single spot at all the gate voltages. On the other hand, the emission patterns with two spots and additional spots were observed from the nanosplit emitters at gate voltages close to the turn-on voltages and the two spots became overlapped at a higher gate voltage.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.16.-c Methods of micro- and nanofabrication and processing
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy

Scanning tunneling microscopy observations of hafnium carbide thin films as a field emission material

T. Sato, M. Saida, K. Horikawa, M. Sasaki, M. Nagao, S. Kanemaru, T. Matsukawa, J. Itoh, and S. Yamamoto

J. Vac. Sci. Technol. B 23, 741 (2005); http://dx.doi.org/10.1116/1.1849192 (4 pages) | Cited 1 time

Online Publication Date: 6 April 2005

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We have already reported superior characteristics of field emission from hafnium carbide (HfC)-coated Si field emission arrays. To clarify the microscopic feature of HfC films related to electron emission, the topograph and local work function (LWF) of the HfC film deposited on Si(100) substrates are examined in an atomic scale by using scanning tunneling microscopy (STM). From the STM/LWF images of the sputtering-cleaned film, it is revealed that the HfC film consists of grains with about 10 nm in size, and that the surface stoichiometry at the grain boundaries becomes carbon rich due to preferential sputtering after higher energy argon ion sputtering.
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79.70.+q Field emission, ionization, evaporation, and desorption
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
73.30.+y Surface double layers, Schottky barriers, and work functions
68.49.Sf Ion scattering from surfaces (charge transfer, sputtering, SIMS)
68.47.Fg Semiconductor surfaces
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
61.72.Mm Grain and twin boundaries
back to top Fabrication and Post-Fabrication Treatment of Field Emitters

Low temperature burnable carbon nanotube paste component for carbon nanotube field emitter backlight unit

Sora Lee, Won Bin Im, Jong Hyuk Kang, and Duk Young Jeon

J. Vac. Sci. Technol. B 23, 745 (2005); http://dx.doi.org/10.1116/1.1884120 (4 pages) | Cited 12 times

Online Publication Date: 7 April 2005

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A new component of carbon nanotube (CNT) paste is explored with an attempt to develop a carbon nanotube field emitter backlight unit (CNT-FE BLU) fabricated by the screen-printing method. To reduce the residual organic binder materials on the surface of single-wall carbon nanotube (SWCNT), the P(MMA-co-BMA) random copolymer is developed as a new binder material. The weight of the residue after burning process at 350 °C was measured by thermo gravimetric analysis (TGA). The percentage of residue was 0.015% of the initial weight, which is only a quarter of the residual percentage of commercial binder material. The measured field emission property demonstrated that the developed P(MMA-co-BMA) was effective in reducing the residue on the surface of the CNT, which is critically important for improving the field emission property of CNT-FE BLU fabricated by the screen-printing method.
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81.07.De Nanotubes
81.16.-c Methods of micro- and nanofabrication and processing
79.70.+q Field emission, ionization, evaporation, and desorption
81.65.-b Surface treatments

Screen printed carbon nanotube field emitter array for lighting source application

Jae-Hong Park, Gil-Hwan Son, Jin-San Moon, Jae-Hee Han, Alexander S. Berdinsky, D. G. Kuvshinov, Ji-Beom Yoo, Chong-Yun Park, Joong-Woo Nam, Jonghwan Park, Chun Gyoo Lee, and Deok Hyeon Choe

J. Vac. Sci. Technol. B 23, 749 (2005); http://dx.doi.org/10.1116/1.1851535 (5 pages) | Cited 16 times

Online Publication Date: 7 April 2005

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We have investigated carbon nanotube (CNT)-field emitter array (FEA) for the application of lighting system like back light unit (BLU) in liquid crystal display (LCD). The photosensitive CNT paste was synthesized by mixing of multiwalled carbon nanotubes (MWNTs), spin on glass (SOG), organic vehicle, photosensitive monomers, photosensitive oligomers and photo initiators. Uniform CNT paste films were obtained by using backside exposure technique and emission properties of CNT paste were evaluated depending on variation in SOG content and firing conditions. Then we prepared line patterned CNT-FEAs using photolithography and measured their I–V characteristics and brightness.
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85.45.Db Field emitters and arrays, cold electron emitters
85.35.Kt Nanotube devices

Selective growth of carbon nanotubes on silicon protrusions

Hideki Sato, Koichi Hata, Hideto Miyake, Kazumasa Hiramatsu, and Yahachi Saito

J. Vac. Sci. Technol. B 23, 754 (2005); http://dx.doi.org/10.1116/1.1885008 (5 pages) | Cited 5 times

Online Publication Date: 7 April 2005

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Selective growth of carbon nanotubes (CNTs) to required positions is a matter of importance for an application to electron sources for field emitter arrays. Although some techniques have been proposed concerning the selective growth of carbon nanotubes, they have complex processes and difficulties in reliability and controllability. We have developed the selective CNT growth technique, which consists of fabrication of pyramid-shaped protrusion arrays on silicon (Si) substrate by a liftoff process, selective deposition of metal catalyst film on the vertexes of the protrusions, and growth of the CNTs on the metal catalyst by chemical vapor deposition (CVD). Here we report the detailed growth characteristics of CNTs selectively grown by thermal CVD (TCVD) on vertexes of pyramid-shaped protrusions fabricated on Si substrate. The growth of CNTs by TCVD gave long, randomly oriented and dispersed CNT growth, which was completely different from growth regimes given by plasma enhanced CVD (PECVD), i.e., vertically aligned and bundled growth. The array of the CNTs grown by TCVD gave better field emission characteristics than that with the CNTs grown by PECVD. That was presumably because the CNTs grown by TCVD gave longer and more dispersive CNT growth than PECVD and consequently gave higher field enhancement on the CNTs. It is also shown that the single growth of the CNT is successfully performed using this process.
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81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
79.70.+q Field emission, ionization, evaporation, and desorption
81.16.-c Methods of micro- and nanofabrication and processing

Effect of thermal annealing on emission characteristics of nanoelectron source fabricated using beam-assisted process

K. Murakami, N. Yamasaki, S. Abo, F. Wakaya, and M. Takai

J. Vac. Sci. Technol. B 23, 759 (2005); http://dx.doi.org/10.1116/1.1884117 (3 pages) | Cited 3 times

Online Publication Date: 7 April 2005

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The thermal annealing effects on a single-field emitter fabricated by beam-assisted processing were investigated from the viewpoint of the leakage current between the gate and cathode. The cathode current of the field emitters before annealing did not show a linear dependence in Fowler–Nordheim (FN) plots due to the leakage current. However, the current showed a linear dependence in FN plots at and above 200 °C. Thermal annealing increased the emission efficiency. The maximum efficiency was almost 100% after annealing at 750 °C. The percentage of working nanoelectron sources was also increased by annealing T ≥ 500 °C. The postannealing is effective in reducing the leakage current of the field emitters because of the removal of contaminants arising from the beam-induced process.
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81.40.Gh Other heat and thermomechanical treatments
85.45.Db Field emitters and arrays, cold electron emitters
85.35.-p Nanoelectronic devices
79.70.+q Field emission, ionization, evaporation, and desorption
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning

Influence of gas atmosphere during laser surface treatment of CNT cathode

W. Rochanachirapar, K. Murakami, N. Yamasaki, S. Abo, F. Wakaya, M. Takai, A. Hosono, and S. Okuda

J. Vac. Sci. Technol. B 23, 762 (2005); http://dx.doi.org/10.1116/1.1868698 (3 pages) | Cited 4 times

Online Publication Date: 7 April 2005

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An ultraviolet laser was used to irradiate the screen-printed carbon nanotube (CNT) cathodes in air, N2, and O2 atmospheres in various pressures. The emission current density of CNT cathodes at a field of 6.6 V/μm was increased by a factor of 400 after laser irradiation in an O2 atmosphere, which was enhanced by the increase in O2 pressure. On the other hand, N2 has less influence on the laser irradiation effect. The enhancement in electron emission by laser irradiation in air was found to be 20% of that in an O2 atmosphere with the same pressure, because of the partial pressure of the oxygen in air.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
79.70.+q Field emission, ionization, evaporation, and desorption
81.65.-b Surface treatments
61.82.-d Radiation effects on specific materials
61.46.-w Structure of nanoscale materials

Laser surface treatment of carbon nanotube cathodes for field emission displays with large diagonal size

W. Rochanachirapar, K. Murakami, N. Yamasaki, S. Abo, F. Wakaya, M. Takai, A. Hosono, and S. Okuda

J. Vac. Sci. Technol. B 23, 765 (2005); http://dx.doi.org/10.1116/1.1884118 (4 pages) | Cited 11 times

Online Publication Date: 7 April 2005

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Excimer lasers with various wavelengths, power densities and beam profiles, have been used to irradiate to carbon nanotube-cathodes (CNT-cathodes) for field emission displays (FEDs) with large diagonal size. KrF (248 nm) and XeCl (308 nm) lasers were used with average power densities varied from 3 to 9 MW/cm2. The beam shapes of the laser beam were adjusted as a square spot of 8×8 mm2 for the KrF laser and a stripe of 180×0.4 mm2 for XeCl laser using a beam homogenizer. The emission characteristics of CNT-cathodes were improved after laser irradiation. The turn-on-field became as low as 0.7 V/μm and the emission current density became as high as 1.5 mA/cm2 at an applied field of 2.5 V/μm by KrF laser irradiation with a power density of 4 MW/cm2. Homogeneous emission-site distribution could be obtained by a square beam or a stripe beam processing with steps from 0.2 to 0.5 mm. The emission pattern became more homogeneous with increase in laser power density. The laser processing time for large diagonal sizes using a stripe beam of 365–200×0.4 mm2 have been estimated, giving a processing time of 92–138 s for a cathode of diagonal size 60 in. with an aspect ratio of 4:3.
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81.05.ub Fullerenes and related materials
81.65.-b Surface treatments
85.35.Kt Nanotube devices
61.82.Rx Nanocrystalline materials
85.45.Fd Field emission displays (FEDs)
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.62.-b Laser applications

Reduction of the work function on Mo(100) surface covered with ZrO2

Hideaki Nakane, Shinya Satoh, and Hiroshi Adachi

J. Vac. Sci. Technol. B 23, 769 (2005); http://dx.doi.org/10.1116/1.1851532 (3 pages) | Cited 4 times

Online Publication Date: 7 April 2005

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The work function of a metal for electron source is one of the measures for evaluating the ability of electron emission, but the values are different depending on the crystal surfaces. In case of molybdenum, the Mo(100) surface has a relatively high value of 4.3 eV, however it can be reduced to 2.1 eV by heating with a slight layer of zirconium oxide. It is observed that field emission electrons are dominantly extracted from a (100) surface of a molybdenum sharp needle emitter, when the surface is modified with a zirconium oxide. The work function of the surface is estimated from Fowler–Nordheim plots. The estimated average value is 2.1 eV, which is remarkably small compared with a commonly accepted value of work function for a ZrO/W(100) thermal field emitter, namely 2.7–2.9 eV, while the smallest reported value is 2.4 eV. It is expected that smaller values of work function are desirable for cathode materials to get fine focused electron beams, because less chromatic aberration can be realized. It should be noticed from practical view points that the reduced work function is reproduced easily by applying several times of flash heating after being exposed to air.
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73.30.+y Surface double layers, Schottky barriers, and work functions
79.70.+q Field emission, ionization, evaporation, and desorption

Fabrication and field emission characteristics of high density carbon nanotube microarrays

C. C. Chuang, J. H. Huang, C. C. Lee, and Y. Y. Chang

J. Vac. Sci. Technol. B 23, 772 (2005); http://dx.doi.org/10.1116/1.1880132 (4 pages) | Cited 4 times

Online Publication Date: 7 April 2005

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High density carbon nanotube field emitter arrays (CNT-FEAs) with various multilayer cathode structures have been fabricated on Si utilizing conventional integrated circuit technology and microwave-heated chemical vapor deposition process. The CNT-FEAs were configured as triode emitters with 1-μm thermal SiO2 as the insulator and 400-nm Cr as the gate, and compared per the resulting morphologies, Raman spectra, and field emission characteristics. It was found that the Ni/Cr/Si cathode structure is the best fit for selective growth of CNTs in gate holes. In particular, a CNT-FEA fabricated on Ni(60 nm)/Cr(80 nm)/Si cathode structure has yielded excellent emission characteristics, with low turn-on and threshold fields, being, respectively, at 0.45 and 3.7 V/μm. This triode CNT device also exhibited a uniform image of high brightness( ∼ 1800 cd/m2) on a green-phosphor coated idium-tin-oxide glass and a relatively stable emission current, being tested at a constant anode voltage of 1000 and 900 V, respectively.
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85.45.Db Field emitters and arrays, cold electron emitters
81.07.De Nanotubes
85.35.Kt Nanotube devices
78.30.Na Fullerenes and related materials
61.46.-w Structure of nanoscale materials

High current field emission from carbon nanofiber films grown using electroplated Ni catalyst

Kyung Ho Park, Jong Hyuk Yim, Soonil Lee, and Ken Ha Koh

J. Vac. Sci. Technol. B 23, 776 (2005); http://dx.doi.org/10.1116/1.1880153 (5 pages) | Cited 5 times

Online Publication Date: 7 April 2005

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Carbon nanofibers (CNFs) with various structures were synthesized using electroplated nickel catalysts on diverse metal buffer layers via hot-filament chemical-vapor-deposition method. High-density thick CNFs were grown on copper and gold buffer layers whereas low-density thin CNFs were grown on chromium and titanium buffer layers. All CNFs revealed solid structure without hollow cores, and graphitic platelets of CNFs consisted of a mixed structure of stacked and herringbone arrangement. CNF films grown on gold buffer layers showed high-emission-current density and temporal stability: 170 mA/cm2 at 7.3 V/μm, and 10.3% fluctuation over 10 h at the current density of 6 mA/cm2, respectively.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.05.U- Carbon/carbon-based materials

Investigation of a microtriode with a planar field emitter-extractor source fabricated by direct-write nanolithography using electron beam induced deposition

Josef Sellmair, Klaus Edinger, and Hans W. P. Koops

J. Vac. Sci. Technol. B 23, 781 (2005); http://dx.doi.org/10.1116/1.1875332 (5 pages) | Cited 7 times

Online Publication Date: 7 April 2005

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A simple microtriode with planar field emission cathode is investigated. Electron optical performance and field distribution are simulated using numerical electron optics. A field emitter tip is fabricated by direct write nanolithography with electron beam induced deposition. The emission properties are studied in UHV and high vacuum. Measurements of currents from deposited emitters are recorded with milli-second resolution to monitor short-term variations in long-term measurements. Emission currents of a few nanoamperes are observed over several days without and with the use of an ion mirror. Depending on vacuum conditions the currents show a characteristic variation of up to 50%. The work is aimed to develop a planar micro-triode with very high current-carrying capability and low transconductance.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Bz Vacuum microelectronic device characterization, design, and modeling
84.47.+w Vacuum tubes
81.16.Nd Micro- and nanolithography
85.45.Db Field emitters and arrays, cold electron emitters

Growth aspects of nanocrystalline diamond films and their effects on electron field emissions

K. Subramanian, W. P. Kang, J. L. Davidson, and W. H. Hofmeister

J. Vac. Sci. Technol. B 23, 786 (2005); http://dx.doi.org/10.1116/1.1880112 (7 pages) | Cited 2 times

Online Publication Date: 7 April 2005

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In this article, we report aspects of the growth of nanocrystalline diamond films using microwave-assisted plasma chemical vapor deposition and their relation to electron field emission. Nanodiamond films with grain size as small as 5–10 nm by CH4/H2/N2 microwave plasma enhanced chemical vapor deposition (MPECVD) and 10–20 nm by CH4/H2 MPECVD have been achieved. An effective means to grow nanodiamond films is to increase the nucleation rate and decrease the growth rate by adjusting the CVD process parameters. With its relation to field emission, we infer that the combination of high dopant concentration resulting in lower electrical resistance of the diamond film and increased sp2 bonded nondiamond carbon content contributes effectively to the enhancement of field emission characteristics, while the reduction in grain size of the nanodiamond film has no similar effect.
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81.05.U- Carbon/carbon-based materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
52.77.Dq Plasma-based ion implantation and deposition
79.70.+q Field emission, ionization, evaporation, and desorption
61.72.S- Impurities in crystals

Effects of deposition and synthesis parameters on size, density, structure, and field emission properties of Pd-catalyzed carbon nanotubes synthesized by thermal chemical vapor deposition

S. Wei, W. P. Kang, W. H. Hofmeister, J. L. Davidson, Y. M. Wong, and J. H. Huang

J. Vac. Sci. Technol. B 23, 793 (2005); http://dx.doi.org/10.1116/1.1880152 (7 pages) | Cited 5 times

Online Publication Date: 7 April 2005

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The effects of deposition parameters and NH3 pretreatment on the size and distribution of Pd catalytic particles and subsequently their effects on the characteristics of the synthesized carbon nanotubes (CNTs) were systematically investigated. It was found that the size of Pd particles decreases and the particle density (total number of Pd particles per unit area) increases as the Pd film thickness decreases. Moreover, pretreatment of Pd film in NH3 gas promotes smaller Pd particles and higher particle density which is beneficial for CNT growth. The CNTs were synthesized by thermal chemical vapor deposition at 750 °C using methane (CH4) as the carbon source, and a mixture of Ar/H2 (80 vol %: 20 vol %) as a carrier gas with NH3 serving as a processing reagent. The incorporation of NH3 in CNT synthesis, per the specific pretreatment of catalytic film, has a distinct effect on the size and morphology of CNTs produced. The interrelation between processing, structure and emission behavior of CNTs produced with different synthesis conditions was examined by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and field emission measurements.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
79.70.+q Field emission, ionization, evaporation, and desorption

Edge-shaped diamond field emission arrays

R. S. Takalkar, J. L. Davidson, W. P. Kang, A. Wisitsora-at, and D. V. Kerns

J. Vac. Sci. Technol. B 23, 800 (2005); http://dx.doi.org/10.1116/1.1864061 (5 pages) | Cited 4 times

Online Publication Date: 7 April 2005

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This article presents the fabrication, characterization, and field emission behavior of edge-shaped diamond field emission arrays. Edge-shaped field emitter geometry is advantageous in the pursuit of high emission current since each edge can have a continuous multiple emission site along the edge as determined by the microstructure of the edge surface. Thus in totality an edge emitter provides significantly larger emission area and hence has the potential for larger current or transconductance for field emission devices. The edge arrays were fabricated via a mold transfer technique on a silicon substrate utilizing silicon micropatterning and etching, followed by chemical-vapor deposited diamond deposition. Arrays of micropatterned edge-shaped diamond emitters were developed and tested for field emission. Moreover, field emission characteristics were improved by further sharpening the edge apex achieving a lower turn-on field and higher emission current. Edge sharpening was achieved by introducing a silicon oxidation step in the mold fabrication process before the diamond deposition step. This oxidation process not only sharpened the edge but also served as a gate dielectric for the development of a self-aligned gated triode device.
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85.45.Db Field emitters and arrays, cold electron emitters
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.65.Cf Surface cleaning, etching, patterning
81.16.Rf Micro- and nanoscale pattern formation
85.40.Hp Lithography, masks and pattern transfer
81.65.Mq Oxidation
81.10.Fq Growth from melts; zone melting and refining

Effect of Ti interlayer on the growth of carbon nanotubes on Si by microwave-heated chemical vapor deposition

J. H. Huang, Y. S. Chen, C. C. Chuang, Y. M. Wong, and W. P. Kang

J. Vac. Sci. Technol. B 23, 805 (2005); http://dx.doi.org/10.1116/1.1861032 (4 pages) | Cited 3 times

Online Publication Date: 7 April 2005

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The effect of Ti layer on the growth of aligned carbon nanotubes on Si using Pd, Ni, or Co as catalysts by microwave-heated chemical vapor deposition was systematically studied. For all growths, a thin Ti layer of 16 or 22 nm, a thin catalyst layer of 6–30 nm, a growth time of 15–45 min, and a growth temperature of 590 or 690 °C were varying deposition parameters. It was found that the growths with Ni or Co as the catalyst on Ti-coated Si could always produce well-aligned carbon nanotubes. However, a carbonaceouslike film was found to exist on the top of nanotubes in most Ni-catalyzed carbon nanotube films. In contrast, carbon nanotubes grown from Pd catalyst were generally not aligned. Furthermore, the nanotubes grown from Pd at 590 °C are crooked or twist, and very short.
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81.07.De Nanotubes
61.46.-w Structure of nanoscale materials
81.16.Hc Catalytic methods
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces

Electron field emission from carbon nanotubes on porous alumina

D. Lysenkov, H. Abbas, G. Müller, J. Engstler, K. P. Budna, and J. J. Schneider

J. Vac. Sci. Technol. B 23, 809 (2005); http://dx.doi.org/10.1116/1.1868696 (5 pages) | Cited 4 times

Online Publication Date: 7 April 2005

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We have synthesized carbon nanotubes by chemical vapor deposition using ferrocene as single source organometallic precursor both on commercial (Anodisc®) and electrochemically etched porous alumina templates. Carbon nanotubes of about 20 nm diameter and some μm in length appeared apart on the alumina membranes. Integral field emission measurements of these cathodes were performed in a diode configuration with luminescent screen. High emitter number densities of at least 10 000/cm2 and current densities up to 32 mA/cm2 were obtained at an electric field of 7.2 V/μm. Cathode processing at pressures in the range from 10−7 to 5×10−4 mbar resulted in improved current stability measured over 18 h. High resolution emitter distributions obtained with the field emission scanning microscope yielded up to 62 000 emitters/cm2 at 23 V/μm. Single emitter investigations showed Fowler–Nordheim behavior up to 1 μA and current limits up to 12 μA in dc operation. Reversible switching between different emission states was also observed. Possible explanations of these phenomena and their impact for applications will be discussed.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
back to top Field Emission Devices and Applications

X-ray generation from large area carbon-based field emitters

H. Busta, S. Lesiak, B. Zwicker, J. Montgomery, Z. Wan, and A. Feinerman

J. Vac. Sci. Technol. B 23, 814 (2005); http://dx.doi.org/10.1116/1.1880172 (5 pages) | Cited 2 times

Online Publication Date: 7 April 2005

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Cylindrical-shaped graphite field emitters with total emission areas of about 100 and 800 cm2 were used to construct an x-ray source in which the anode consists of a 107 cm long quartz tube, 7.7 cm outer diameter, and a wall thickness of 0.4 cm. Except for the end portions, the tube is coated with a 5 μm Cu film. The emitter surface is 0.35 cm separated from the quartz tube. Electrons originating from the emitter surface impinge upon the copper film and some of them are converted into x rays. The x rays penetrating the quartz tube can be utilized for irradiation experiments where ionizing radiation is desirable. X-ray spectra, photon count rate, and dose rate were measured, as well as current-voltage characteristics of the two field emitter configurations. Within the “hot” zone of the 5 and 30.5 cm long emitter regions, the dose is uniform within ±20% in the lateral direction and ±20% along the inner surface of the quartz tube. (The “hot” zone is defined as the region where the x rays are generated). It was established that the photon count and the dose scale proportional with the emission current and increase exponentially with target voltage. The x-ray source was operated to 42.5 kV at a pressure of 5×10−7 Torr.
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07.85.-m X- and γ-ray instruments

Desorption/ionization mass spectrometry on array of silicon microtips

Anna Gorecka-Drzazga, Jan Dziuban, Wlodzimierz Drzazga, Agnieszka Kraj, and Jerzy Silberring

J. Vac. Sci. Technol. B 23, 819 (2005); http://dx.doi.org/10.1116/1.1861046 (5 pages) | Cited 3 times

Online Publication Date: 7 April 2005

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The matrix-free laser desorption/ionization of the biosamples for time-of-flight mass spectrometry from an array of gated silicon tips has been presented. The gated silicon tips were fabricated similar to the well-known electron-field-emitters gated sources. In this method, called desorption/ionization on silicon tips array, an array of gated silicon sharp tips covered with a biosample and irradiated by a pulsed ultraviolet laser serves as the effective source of ions, replacing standard ionization platforms. Tests have confirmed that the effective laser desorption/ionization of the low-mass biosamples, such as dopamine and leucyl-glycyl-glycine tripeptide, may be obtained. It is possible that the method will play a very important role in post-genetic proteomic investigations.
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82.80.Rt Time of flight mass spectrometry
68.43.Mn Adsorption kinetics
81.05.Cy Elemental semiconductors
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)

Composite-layered solid-state field controlled emitter for a better control of the cathode surface barrier

V. Semet, Vu Thien Binh, J. P. Zhang, J. Yang, M. Asif Khan, and R. Tsu

J. Vac. Sci. Technol. B 23, 824 (2005); http://dx.doi.org/10.1116/1.1864065 (7 pages) | Cited 5 times

Online Publication Date: 7 April 2005

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Experimental measurements have shown that electron emission was obtained from metallic planar surfaces covered with ultrathin wide band gap semiconductor layers. To get a better control of the effective surface barrier, we proposed a composite-layer nanostructured solid-state field controlled emitter with two ultrathin layers of 4 nm GaN and 2 nm Al0.5Ga0.5N. This composite structure defined a quantum well at the cathode surface. The threshold of the applied field to obtain electron emission was in the range of 100 V/μm. To interpret these experimental results, we propose a dual-barrier model related to the nanostructured layers and a serial two-step mechanism for the electron emission. In a first step, under the polarization, the electrons are injected into the ultrathin surface layer from the cathode substrate, creating a concentration of electrons in the GaN quantum well. This electron concentration or space charge formation induced an energy shift leading to a relative lowering of the vacuum level compared to the Fermi level of the substrate. We have measured the electron emission dependence with field and temperature of these cathodes and have determined an effective surface tunnelling barrier ⩽ 0.5 eV consistent with an effective thermal activation energy of ∼ 0.85 eV. Estimation of the effective barrier due to space charge formation from to the occupation of the localized bands in the quantum well is in good agreement with the experimental data.
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79.70.+q Field emission, ionization, evaporation, and desorption
82.45.Fk Electrodes
73.20.At Surface states, band structure, electron density of states
73.30.+y Surface double layers, Schottky barriers, and work functions

High intensity pulse x-ray generation by using graphite-nanocrater cold cathode

Takahiro Matsumoto and Hidenori Mimura

J. Vac. Sci. Technol. B 23, 831 (2005); http://dx.doi.org/10.1116/1.1854692 (5 pages) | Cited 4 times

Online Publication Date: 7 April 2005

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Graphite nanostructures fabricated by a simple plasma etching onto a graphite substrate provide an intense emission source of electrons. This cathode does not have the adherence problem commonly seen in carbon deposited emission layera such as carbon nanotubes and graphite nanofibers, thus making it promising for applications in high power devices. The performance of this cold cathode was demonstrated by obtaining high-intensity pulse x-ray generation. High-speed x-ray radiography images of dynamical processes of the order of 10 μs were also shown by using the pulse x-ray source.
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81.16.-c Methods of micro- and nanofabrication and processing
52.77.Bn Etching and cleaning
81.65.Cf Surface cleaning, etching, patterning
81.05.U- Carbon/carbon-based materials
85.45.-w Vacuum microelectronics

Method and structure for local emission regulation and arc prevention in field emitter arrays

Jonathan L. Shaw and David S. Y. Hsu

J. Vac. Sci. Technol. B 23, 836 (2005); http://dx.doi.org/10.1116/1.1849191 (4 pages) | Cited 2 times

Online Publication Date: 7 April 2005

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Field emission from air-exposed silicon and other surfaces typically occurs at energies up to several volts below the Fermi level, and the energies can change substantially during emission. We conclude this behavior results from emission from initial states in a dielectric (oxide) surface coating, and that the energies of these states change relative to the emitter Fermi level due to changing oxide state density and charge density. When emission occurs below the bulk Fermi level, energy is deposited into the emitter. In some cases this energy can be coupled to chemical bonds, creating states in the oxide and improving electron transport. If the power density deposited this way becomes excessive, oxide breakdown and arc initiation can result. Thus preventing excessive emission current at potentials more than 1–2 V positive relative to the bulk Fermi level may prevent arc initiation. We propose that might be done by building a second (filter) aperture above each gate aperture in an array, and placing the aperture at a low positive voltage relative to the emitter contact. That structure creates a potential barrier for emitted electrons, which will cause those electrons emitted at excessively positive potentials to be returned to the gate electrode. A circuit element in series with the gate electrode will reduce the gate voltage, thereby limiting the current emitted at low energy. To limit or regulate the total emission current, a small resistor or other circuit element can be placed in series with the emitter, forcing the emission energy to be reduced in response to a given current.
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85.45.Db Field emitters and arrays, cold electron emitters

Smith–Purcell radiation using a single-tip field emitter

Yoichiro Neo, Yosuke Suzuki, Katsumi Sagae, Hidetaka Shimawaki, and Hidenori Mimura

J. Vac. Sci. Technol. B 23, 840 (2005); http://dx.doi.org/10.1116/1.1851536 (3 pages) | Cited 2 times

Online Publication Date: 7 April 2005

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We have successfully observed Smith–Purcell radiation (SPR) using a single-tip n-type Si field emitter in the visible wavelength from 400 to 700 nm at low input power level with beam currents of 20–200 nA and accelerating voltages of 25–30 kV. Several peaks corresponding to the third and fourth harmonics of SPR are obtained using a 550 nm period metal grating and redshifted with decrease of the acceleration voltage. The measured peaks are well explained by the SPR theory.
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79.70.+q Field emission, ionization, evaporation, and desorption
85.45.Db Field emitters and arrays, cold electron emitters
42.79.Dj Gratings

Characterization of nano-size YVO4:Eu and (Y,Gd)VO4:Eu phosphors by low voltage cathodo- and photoluminescence

Jong Hyuk Kang, Michael Nazarov, Won Bin Im, Jin Young Kim, and Duk Young Jeon

J. Vac. Sci. Technol. B 23, 843 (2005); http://dx.doi.org/10.1116/1.1861048 (6 pages) | Cited 5 times

Online Publication Date: 7 April 2005

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Low voltage cathodoluminescence (LVCL) and photoluminescence measurement were carried out to better understand the role of Gd in (Y,Gd)VO4:Eu phosphor and to compare two different synthesis methods (solid-state reaction, coprecipitation reaction) and their preparing conditions. From the analysis of LVCL measurement, it is understood that the luminescence of YVO4:Eu and (Y,Gd)VO4:Eu phosphors might be interpreted as originating from a two-level system and for reasons of enhanced luminescence intensity of (Y,Gd)VO4:Eu phosphor, the effect of Gd on the symmetry of Eu sites dominates over that of interaction between Gd and Eu. It is also found that nano-size phosphor of YVO4:Eu synthesized by coprecipitation reaction shows lower quantum yield in comparison with that synthesized by solid-state reaction due to the presence of secondary phase produced after heat treatment.
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78.55.Hx Other solid inorganic materials
78.60.Hk Cathodoluminescence, ionoluminescence
81.16.Be Chemical synthesis methods
82.60.-s Chemical thermodynamics
81.40.Gh Other heat and thermomechanical treatments

Field-emission based vacuum device for the generation of terahertz waves

Ming-Chieh Lin, Kuo-Hua Huang, Pu-Shih Lu, Pei-Yi Lin, and Ruei-Fu Jao

J. Vac. Sci. Technol. B 23, 849 (2005); http://dx.doi.org/10.1116/1.1864063 (4 pages) | Cited 8 times

Online Publication Date: 7 April 2005

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Terahertz (THz), waves i.e., electromagnetic radiation in the frequency extending from 0.1 to 10 THz (wavelengths of 3 mm down to 0.03 mm), have been used to characterize the electronic, vibrational, and compositional properties of solid, liquid, and gas phase materials during the past decade. More and more applications in imaging science and technology call for the well development of THz wave sources. Amplification and generation of a high frequency electromagnetic wave are a common interest of field emission based devices. In the present work, we propose a vacuum electronic device based on field emission mechanism for the generation of THz waves. To verify our thinking and designs, the cold tests and the hot tests have been studied via the simulation tools, SUPERFISH and MAGIC. In the hot tests, two types of electron emission mechanisms are considered. One is the field emission and the other is the explosive emission. The preliminary design of the device is carried out and tested by the numerical simulations. The simulation results show that an electronic efficiency up to 4% can be achieved without employing any magnetic circuits.
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84.47.+w Vacuum tubes
79.70.+q Field emission, ionization, evaporation, and desorption
52.40.Db Electromagnetic (nonlaser) radiation interactions with plasma

Polysilicon metal-insulator-semiconductor electron emitter

Alexander Govyadinov, Thomas Novet, David Pidwerbecki, Sriram Ramamoorthi, Jim Smith, John Chen, Chuck Otis, David Neiman, and Paul Benning

J. Vac. Sci. Technol. B 23, 853 (2005); http://dx.doi.org/10.1116/1.1864060 (11 pages) | Cited 3 times

Online Publication Date: 7 April 2005

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The flat metal-insulator-semiconductor (MIS) electron emitter is a simple design, allowing easy manufacture. The emitters are relatively insensitive to environment, allowing them to operate in poorer vacuum conditions than are necessary for oxide thermionic or microtip field emitters. In most literature reports, MIS and metal-insulator-metal devices are limited in emission current (<0.001 A/cm2) by their low efficiencies (⪡0.1%). We have observed emission currents as high as 2–10 A/cm2 at efficiencies from 3%–10%. Our best results are from emitters comprised of 5–7.5 nm gold/15 nm SiO2/100 nm polysilicon/n++ doped silicon substrate. The roles of each component of the flat emitter were investigated. The polysilicon serves a dual role: Bumps on its surface act as field-enhanced emission sites while the bulk of the film behaves as a self-adjusting ballast resistor preventing run away emission from any one emission site. The thin gold layer self-assembles into a nanomesh with >400 pores/μm2 through which electrons are emitted. Energy distribution and angular divergence of emitted electrons were measured. A coherent explanation of emission including the origination of the divergence is presented. Pros and cons of the MIS emitter and potential application are discussed.
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79.70.+q Field emission, ionization, evaporation, and desorption
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)

Fabrication of Si field emitter array in local vacuum package

Daiji Noda, Masanori Hatakeyama, Masanori Kyogoku, Kimiya Ikushima, Kazuaki Sawada, and Makoto Ishida

J. Vac. Sci. Technol. B 23, 864 (2005); http://dx.doi.org/10.1116/1.1851533 (4 pages) | Cited 2 times

Online Publication Date: 7 April 2005

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We have fabricated a local vacuum package enclosing a Si field emitter array on Si substrate. To maintain the low pressure required for electron emission, a titanium evaporation getter was made as a bridge structure with the Si field emitter array in local vacuum package. The local vacuum package technique was adapted to the IC process for on-chip device fabrication. This technique will be very useful for many applications with high performance.
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85.45.Db Field emitters and arrays, cold electron emitters
85.30.-z Semiconductor devices

Transistor characteristics of thermal chemical vapor deposition carbon nanotubes field emission triode

Y. M. Wong, W. P. Kang, J. L. Davidson, W. Hofmeister, S. Wei, and J. H. Huang

J. Vac. Sci. Technol. B 23, 868 (2005); http://dx.doi.org/10.1116/1.1864062 (6 pages) | Cited 7 times

Online Publication Date: 7 April 2005

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A study of thermal chemical vapor deposition (CVD) grown carbon nanotubes (CNTs) field emitters in a triode amplifier configuration is reported. The CNT transistor characteristics were examined by integrating gate and anode with CNT cathode in two structural forms, utilizing a TEM grid (transmission electron microscope specimen holder) as the gate electrode and a micropatterned CNT with self-aligned gate. The TEM-grid CNT triode displayed clearly gate-controlled current modulation behavior with distinct cutoff, linear, and saturation regions, and a reasonable gate turn-on field of ∼ 5.4 V/μm despite a large cathode-gate spacing of ∼ 120 μm. The field emission result established the basic transistor characteristics of CNTs in a triode configuration. A CNT triode construct with a self-aligned gated fabrication technique was also developed to realize a monolithic triode structure with shorter gate-cathode spacing, lowering gate voltage, and enhancing emission current. The triode exhibited a significantly lower gate turn-on voltage of ∼ 40 V, and gate-controlled modulation of the emission current. An anode current density of ∼ 30 mA/cm2 was achieved at a gate voltage of ∼ 80 V and an anode voltage of ∼ 200 V. The dc characteristics for both of the CNT triodes were investigated, including Ia versus Va for different Vg. Moreover, dc parameters such as transconductance, amplification factors, and anode resistance of the triode amplifier were determined. The CNT triodes exhibited useful amplification factor and high output impedance.
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79.70.+q Field emission, ionization, evaporation, and desorption
81.07.De Nanotubes
85.35.Kt Nanotube devices
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
73.63.Fg Nanotubes
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