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Defect-mediated adsorption of methanol and carbon dioxide on BaTiO₃(001)

J. Garra, J. M. Vohs, and D. A. Bonnell

J. Vac. Sci. Technol. A 27, L13 (2009); http://dx.doi.org/10.1116/1.3168563 (5 pages) | Cited 1 time

Online Publication Date: 14 July 2009

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The surface chemistry of single crystal barium titanate (BaTiO₃) has been studied using temperature programmed desorption (TPD). TPD measurements were performed with several probe molecules, including methanol and carbon dioxide. The role of oxygen vacancies in the adsorption and reaction of these molecules was examined by annealing the crystal under oxidizing or reducing conditions prior to performing TPD. It is shown that the adsorption and reaction of methanol and carbon dioxide are enhanced on BaTiO₃(001) by annealing the crystal under reducing conditions.

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68.43.Mn	Adsorption kinetics
68.43.Nr	Desorption kinetics
61.72.jd	Vacancies
81.40.Gh	Other heat and thermomechanical treatments
82.65.+r	Surface and interface chemistry; heterogeneous catalysis at surfaces
61.72.Cc	Kinetics of defect formation and annealing

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Staircase and saw-tooth field emission steps from nanopatterned n-type GaSb surfaces

M. Kildemo, Y. Inntjore Levinsen, S. Le Roy, and E. Søndergård

J. Vac. Sci. Technol. A 27, L18 (2009); http://dx.doi.org/10.1116/1.3168562 (6 pages)

Online Publication Date: 13 August 2009

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High resolution field emission experiments from nanopatterned GaSb surfaces consisting of densely packed nanocones prepared by low ion-beam-energy sputtering are presented. Both uncovered and metal-covered nanopatterned surfaces were studied. Surprisingly, the field emission takes place by regular steps in the field emitted current. Depending on the field, the steps are either regular, flat, plateaus, or saw-tooth shaped. To the author’s knowledge, this is the first time that such results have been reported. Each discrete jump in the field emission may be understood in terms of resonant tunneling through an extended surface space charge region in an n-type, high aspect ratio, single GaSb nanocone. The staircase shape may be understood from the spatial distribution of the aspect ratio of the cones.

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79.70.+q	Field emission, ionization, evaporation, and desorption
68.47.Fg	Semiconductor surfaces
81.15.Cd	Deposition by sputtering
73.40.Gk	Tunneling
77.22.Jp	Dielectric breakdown and space-charge effects
81.05.Ea	III-V semiconductors

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Mechanics of stretchable inorganic electronic materials

J. Song, H. Jiang, Y. Huang, and J. A. Rogers

J. Vac. Sci. Technol. A 27, 1107 (2009); http://dx.doi.org/10.1116/1.3168555 (19 pages) | Cited 4 times

Online Publication Date: 31 July 2009

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Electronic systems that offer elastic mechanical responses to high strain deformation are of growing interest due to their ability to enable new applications whose requirements are impossible to satisfy with conventional wafer-based technologies. This article reviews the mechanics of stretchable inorganic materials on compliant substrates. Specifically, three forms of stretchable structures are reviewed. The first one is stretchable ribbon, which provides one-dimensional stretchability. The second is stretchable nanomembranes, which can be stretched in all directions. The last is a noncoplanar mesh design, which has the advantage of providing large stretchability up to and exceeding 100%. Mechanics models and their comparison to experiment are reviewed for these three cases. Such models provide design guidelines for stretchable electronics.

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81.40.Jj	Elasticity and anelasticity, stress-strain relations
81.40.Lm	Deformation, plasticity, and creep
62.20.D-	Elasticity
62.20.F-	Deformation and plasticity

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Interface-mediated ultrafast carrier conduction in oxide thin films and superlattices for energy

Shriram Ramanathan

J. Vac. Sci. Technol. A 27, 1126 (2009); http://dx.doi.org/10.1116/1.3186616 (9 pages) | Cited 1 time

Online Publication Date: 31 July 2009

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Some recent observations on carrier (electronic and ionic) transport in thin film and nanostructured metal oxides and superlattices, where interfaces play a dominant role in overall conductivity response, are reviewed. Conduction in nominally pure oxides is compared to heavily aliovalently doped oxides (that correspond to changes in the Debye length over few orders of magnitude). The role of dopant segregation and their spatial variation in affecting transport is pointed out. The ability to utilize interfaces in enabling ultrafast-ion conduction as well as the creation of novel interfacial materials and implications in energy technologies as well as some scientific questions that may warrant further attention are highlighted.

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73.61.-r	Electrical properties of specific thin films
73.63.Bd	Nanocrystalline materials
66.30.H-	Self-diffusion and ionic conduction in nonmetals
01.30.Rr	Surveys and tutorial papers; resource letters

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Transition between kinetic and mass transfer regimes in the initiated chemical vapor deposition from ethylene glycol diacrylate

Gozde Ozaydin-Ince and Karen K. Gleason

J. Vac. Sci. Technol. A 27, 1135 (2009); http://dx.doi.org/10.1116/1.3168553 (9 pages) | Cited 2 times

Online Publication Date: 31 July 2009

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In this work, initiated chemical vapor deposition (iCVD) of the poly(ethylene glycol diacrylate) is reported and the effects of process parameters on the deposition rates are investigated. The systematic studies of depositions performed at different filament temperatures showed that the deposition rates increased with the temperature due to the increase in the radical concentration which was monitored with a gas-phase Fourier transform infrared spectroscopy. For temperatures below 242±3 and 224±2 °C for 2 and 1 SCCM (SCCM denotes cubic centimeter per minute at STP) of monomer flowrates, respectively, a reaction-kinetics limited regime was observed, where the deposition kinetics was limited by the decomposition of the radicals. In this regime, the deposition rates were highly dependent on the filament temperature and the apparent activation energy was found to be 166±5 kJ/mol, consistent with the cleavage of the O–O bond in the tert-butyl peroxide initiator as the rate limiting reaction in the deposition mechanism. Above these temperatures, transition to a mass transfer limited regime was observed where the deposition rates were less dependent on the filament temperature. In the studies performed at different substrate temperatures, on the other hand, an inverse relation between the deposition rate and the substrate temperature was observed which indicated an adsorption limited regime. The studies presented in this work demonstrate the dependence of the deposition kinetics on the process temperatures, which can also be applied to other iCVD systems to achieve higher deposition rates and better conformality.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
78.66.Qn	Polymers; organic compounds
68.55.am	Polymers and organics
82.30.Lp	Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.43.-h	Chemisorption/physisorption: adsorbates on surfaces
78.30.Jw	Organic compounds, polymers

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Characterization of x-ray photocathode in transmission mode for imaging application

Hiromi Ikeura-Sekiguchi, Tetsuhiro Sekiguchi, Masaki Koike, and Kazutoshi Yagi-Watanabe

J. Vac. Sci. Technol. A 27, 1144 (2009); http://dx.doi.org/10.1116/1.3168559 (5 pages)

Online Publication Date: 31 July 2009

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The performance of an Al x-ray transmission photocathode was experimentally characterized by measuring the total electron yield from backsurface photocathodes of varying thickness. It was demonstrated that the backsurface electron yield is proportional to the x-ray photocurrent transmitted through the photocathode for thicknesses thicker than the optimum thickness. The optimum photocathode thickness with the highest conversion efficiency was found to be approximately 70 nm at 2.963 keV. An escape depth of the secondary electrons was determined to be approximately 13 nm from the yield-versus-thickness data fitted with a semiempirical equation. Using this parameter, the dependence of the optimum photocathode thickness on the x-ray energy was calculated for the 30–10000 eV range. As one example of imaging applications, different photoemission images in the transmission and reflection modes are also presented.

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85.60.Ha	Photomultipliers; phototubes and photocathodes
07.85.-m	X- and γ-ray instruments
72.40.+w	Photoconduction and photovoltaic effects

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Internal energy distribution change of sputtered Al atom under several hundreds of eV oxygen ion-beam bombardment by resonant laser ionization sputtered neutral mass spectroscopy

Shun-Ichi Hayashi and Naoyoshi Kubota

J. Vac. Sci. Technol. A 27, 1149 (2009); http://dx.doi.org/10.1116/1.3168560 (4 pages)

Online Publication Date: 31 July 2009

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It is important to evaluate the internal energy of the sputtered neutral particles to optimize their resonant ionization efficiency. In this study, the internal energy of the sputtered Al atom, especially the ground state math

and the lowest-lying excited state math

(112 cm⁻¹), was monitored by using resonant laser postionization sputtered neutral mass spectrometry. The results of the authors showed the density of the ground state of the sputtered Al atom drastically decreased due to surface oxidation, as well as the enhancement of the secondary Al⁺ yield.

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79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces
68.49.Sf	Ion scattering from surfaces (charge transfer, sputtering, SIMS)
81.65.Mq	Oxidation

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A new experimental setup for high-pressure catalytic activity measurements on surface deposited mass-selected Pt clusters

Yoshihide Watanabe and Noritake Isomura

J. Vac. Sci. Technol. A 27, 1153 (2009); http://dx.doi.org/10.1116/1.3179160 (6 pages) | Cited 2 times

Online Publication Date: 31 July 2009

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A new experimental setup to study catalytic and electronic properties of size-selected clusters on metal oxide substrates from the viewpoint of cluster-support interaction and to formulate a method for the development of heterogeneous catalysts such as automotive exhaust catalysts has been developed. The apparatus consists of a size-selected cluster source, a photoemission spectrometer, a scanning tunneling microscope (STM), and a high-pressure reaction cell. The high-pressure reaction cell measurements provided information on catalytic properties in conditions close to practical use. The authors investigated size-selected platinum clusters deposited on a TiO₂(110) surface using a reaction cell and STM. Catalytic activity measurements showed that the catalytic activities have a cluster-size dependency.

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82.65.+r	Surface and interface chemistry; heterogeneous catalysis at surfaces
62.50.-p	High-pressure effects in solids and liquids
68.37.Ef	Scanning tunneling microscopy (including chemistry induced with STM)
68.47.Jn	Clusters on oxide surfaces
81.15.Cd	Deposition by sputtering
71.20.Be	Transition metals and alloys
79.60.-i	Photoemission and photoelectron spectra

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Measurement of electron temperatures and electron energy distribution functions in dual frequency capacitively coupled CF₄/O₂ plasmas using trace rare gases optical emission spectroscopy

Zhiying Chen, Vincent M. Donnelly, Demetre J. Economou, Lee Chen, Merritt Funk, and Radha Sundararajan

J. Vac. Sci. Technol. A 27, 1159 (2009); http://dx.doi.org/10.1116/1.3179162 (7 pages) | Cited 2 times

Online Publication Date: 31 July 2009

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Measurements of electron temperatures (T_e) and electron energy distribution functions (EEDFs) in a dual frequency capacitively coupled etcher were performed by using trace rare gas optical emission spectroscopy (TRG-OES). The parallel plate etcher was powered by a high frequency (60 MHz) “source” top electrode and a low frequency (13.56 MHz) “substrate” bottom electrode. T_e first increased with pressure up to ∼ 20 mTorr and then decreased at higher pressures. Increasing the bottom rf power resulted in higher electron temperatures. Electron temperatures in 90% CF₄+10% O₂ plasmas were similar to those in 80% CF₄+20% O₂ plasmas. EEDF exhibited bi-Maxwellian characteristics with enhanced high energy tail, especially at pressures >20 mTorr.

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52.25.Os	Emission, absorption, and scattering of electromagnetic radiation
52.70.Kz	Optical (ultraviolet, visible, infrared) measurements

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Sputter deposition of Al-doped ZnO films with various incident angles

Yasushi Sato, Kei Yanagisawa, Nobuto Oka, Shin-ichi Nakamura, and Yuzo Shigesato

J. Vac. Sci. Technol. A 27, 1166 (2009); http://dx.doi.org/10.1116/1.3186618 (6 pages) | Cited 2 times

Online Publication Date: 31 July 2009

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Al-doped ZnO (AZO) films were sputter deposited on glass substrates heated at 200 °C under incident angles of sputtered particles at 0° (incidence normal to substrate), 20°, 40°, 60°, and 80°. In the case of normal incidence, x-ray diffraction pole figures show a strong [001] preferred orientation normal to the film surface. In contrast, in the case wherein the incident angles were higher than 60°, the [001] orientation inclined by 25°–35° toward the direction of sputtered particles. Transmission electron microscopy revealed that the tilt angle of the [001] orientation increased with increasing angle of the incident sputtered particles, whereas the columnar structure did not show any sign of inclination with respect to the substrate plane.

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81.15.Cd	Deposition by sputtering
68.55.ag	Semiconductors
68.55.jm	Texture
61.72.uj	III-V and II-VI semiconductors

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Structure, optical, and magnetic properties of facing-target reactive sputtered Ti_1−xFe_xO_2−δ films

Y. B. Jiang, W. B. Mi, E. Y. Jiang, and H. L. Bai

J. Vac. Sci. Technol. A 27, 1172 (2009); http://dx.doi.org/10.1116/1.3168557 (6 pages)

Online Publication Date: 10 August 2009

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Structure, optical, and magnetic properties of the anatase Ti_1−xFe_xO_2−δ films fabricated by facing-target reactive sputtering were investigated. Structural analyses indicate that there are no impurity phases in the films and the grain size reaches maximum when Fe content x is 0.017. The optical band gap of the Ti_1−xFe_xO_2−δ films decreases with the increasing x. Photoluminescence (PL) spectra show that direct and indirect band-to-band transitions coexist, and the indirect radiative recombination can be regarded as a one photon and two phonon coupling courses. The PL intensity due to oxygen vacancies enhances and the refractive index of the fims increases with the increasing x. The Ti_1−xFe_xO_2−δ films exhibit room-temperature ferromagnetism due to the oxygen vacancies.

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68.55.ag	Semiconductors
81.15.Cd	Deposition by sputtering
71.20.Nr	Semiconductor compounds
78.20.Ci	Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
75.50.Cc	Other ferromagnetic metals and alloys
63.20.D-	Phonon states and bands, normal modes, and phonon dispersion
78.66.Li	Other semiconductors
78.55.Hx	Other solid inorganic materials

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Critical evaluation of band bending determination in organic films from photoemission measurements

J. Ivanco and D. R. T. Zahn

J. Vac. Sci. Technol. A 27, 1178 (2009); http://dx.doi.org/10.1116/1.3196814 (5 pages)

Online Publication Date: 10 August 2009

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Electronic properties of conjugated films, namely, the band bending as derived from photoemission spectroscopy, are critically discussed. The study demonstrates that conclusions on the presence of the band bending deduced from the shift of electronic energy levels with the organic film thickness may be erroneous if the analysis does not consider the evolution of the film’s work function. The work function change—besides that being induced by the interfacial dipole—may occur due to the change in the molecular orientation from the lying down toward upright, as it often occurs with the increased thickness of molecular films.

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71.20.Rv	Polymers and organic compounds
73.20.At	Surface states, band structure, electron density of states
79.60.Fr	Polymers; organic compounds
73.30.+y	Surface double layers, Schottky barriers, and work functions

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Fabrication of microtemplates for the control of bacterial immobilization

Yasuhiro Miyahara, Koji Mitamura, Nagahiro Saito, and Osamu Takai

J. Vac. Sci. Technol. A 27, 1183 (2009); http://dx.doi.org/10.1116/1.3179158 (5 pages)

Online Publication Date: 13 August 2009

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The authors described a region-selective immobilization methods of bacteria by using superhydrophobic/superhydrophilic and superhydrophobic/poly(ethylene glycol) (PEG) micropatterns for culture scaffold templates. In the case of superhydrophobic/superhydrophilic micropatterns, the superhydrophobic surface was prepared first by microwave-plasma enhanced chemical vapor deposition (MPECVD) from trimethylmethoxysilane. Then the superhydrophilic regions were fabricated by irradiating the superhydrophobic surface with vuv light through a stencil mask. In the case of the superhydrophobic/PEG micropatterned surfaces, PEG surfaces were fabricated first by chemical reaction of ester groups of p-nitrophenyl PEG with NH₂ group of NH₂-terminated self assembled monolayer from n-6-hexyl-3-aminopropyltrimethoxysilane. The superhydrophobic regions were fabricated by MPECVD thorough a stencil mask. In this study four bacteria were selected from viewpoint of peptidoglycan cell wall (E. coli versus B. subtilis), extracellular polysaccharide (E.coli versus P. stutzeri, P. aeruginosa), and growth rate (P. stutzeri versus P. aeruginosa). The former micropattern brought discrete adhesions of E. coli and B. subtilis specifically on the hydrophobic regions, Furthermore, using the superhydrophobic/PEG micropattern, adhesion of bacteria expanded for E. coli, B. subtilis, P. stutzeri, and P. aeruginosa. They observed a high bacterial adhesion onto superhydrophobic surfaces and the inhibitive effect of bacterial adhesion on PEG surfaces.

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87.80.-y	Biophysical techniques (research methods)
81.65.Cf	Surface cleaning, etching, patterning
52.77.Dq	Plasma-based ion implantation and deposition
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.05.Lg	Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
87.17.Rt	Cell adhesion and cell mechanics

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Scattering of neutral hydrogen at energies less than 1 keV from tungsten and diamondlike carbon surfaces

Patrick P. Hughes, Michael A. Coplan, Jeffery N. DeFazio, Dennis J. Chornay, Michael R. Collier, Keith W. Ogilvie, and Mark D. Shappirio

J. Vac. Sci. Technol. A 27, 1188 (2009); http://dx.doi.org/10.1116/1.3196788 (8 pages)

Online Publication Date: 18 August 2009

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Neutral atom to negative ion conversion efficiencies were studied for polished tungsten and diamondlike carbon surfaces using a beam of incident hydrogen atoms. Neutral atoms at energies below 1 keV were scattered from the surfaces using incident angles between 6° and 20° measured from the surface plane. The angular and energy distributions of negative ions backscattering from the surfaces were measured and used to calculate the fraction of the incident beam that was converted to negative ions. The highest number and the lowest overall energy loss of backscattered ions were both observed near the specular reflection angle of the incident beam for the two surface materials studied. The total conversion efficiency was calculated to be near 2% for the tungsten and diamondlike carbon surfaces. Measurements taken while the surfaces were heated show a significant reduction in conversion efficiency, which is credited to the removal of adsorbates from the top layers of the surfaces.

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68.49.Bc	Atom scattering from surfaces (diffraction and energy transfer)
79.20.Rf	Atomic, molecular, and ion beam impact and interactions with surfaces

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Turbomolecular pump rotor-bearing system analysis and testing

Hsiao-Wei D. Chiang, Chih-Pin Kuan, and Hsin-Lung Li

J. Vac. Sci. Technol. A 27, 1196 (2009); http://dx.doi.org/10.1116/1.3179157 (8 pages)

Online Publication Date: 25 August 2009

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During turbomolecular pump design, it is very critical to know the dynamic behavior of the rotor-bearing system, which is also of great importance to the pump performance. In this study, a typical small size turbomolecular pump was used. Using an inertial coordinate system, the dynamic models of the pump rotor-bearing systems included gyroscopic moments, rotary inertias, and bending and shear deformations. The models were analyzed in order to predict the natural frequencies, to produce critical speed maps, and to estimate the bearing stiffness. These rotor-bearing system analyses were then applied to the turbomolecular pump rotor system applications. Both theoretical and experimental analyses were used to study the rotor-bearing system. Modal testing and dynamic test were used to verify the analytical results, including the critical speed map and the bearing stiffness. Very good agreement was demonstrated between the analysis and the test data. The analysis demonstrated that the rotor operation of 51 600 rpm is very close to the second critical speed, which may have caused the recent pump bearing failures near the pump bottom. The analysis can also provide guidelines to avoid the second order critical speed mode shape failures.

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89.20.Kk

Engineering

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Modular ultrahigh vacuum-compatible gas-injection system with an adjustable gas flow for focused particle beam-induced deposition

D. Klingenberger and M. Huth

J. Vac. Sci. Technol. A 27, 1204 (2009); http://dx.doi.org/10.1116/1.3196789 (7 pages)

Online Publication Date: 25 August 2009

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A gas-injection system (GIS) heats up a powdery substance and transports the resulting gas through a capillary into a vacuum chamber. Such a system can be used to guide a (metal)organic precursor gas very close to the focal area of an electron or ion beam, where a permanent deposit is created and adheres to the substrate. This process is known as focused particle beam-induced deposition. The authors present design principles and give construction details of a GIS suitable for ultrahigh vacuum usage. The GIS is composed of several self-contained components which can be customized rather independently. It allows for a continuously adjustable gas-flow rate. The GIS was attached to a standard scanning electron microscope (JEOL 6100) and tested with the tungsten precursor W(CO)₆. The analysis of the deposits by means of atomic force microscopy and energy dispersive x-ray spectroscopy provides clear evidence that excellent gas-flow-rate stability and ensuing growth rate and metal-content reproducibility are experienced.

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81.15.-z	Methods of deposition of films and coatings; film growth and epitaxy
68.55.A-	Nucleation and growth
81.15.Jj	Ion and electron beam-assisted deposition; ion plating
82.80.Ej	X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
68.37.Hk	Scanning electron microscopy (SEM) (including EBIC)
68.37.Ps	Atomic force microscopy (AFM)

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Techniques of cryogenic reactive ion etching in silicon for fabrication of sensors

M. David Henry, Colin Welch, and Axel Scherer

J. Vac. Sci. Technol. A 27, 1211 (2009); http://dx.doi.org/10.1116/1.3196790 (6 pages)

Online Publication Date: 25 August 2009

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Cryogenic etching of silicon, using an inductively coupled plasma reactive ion etcher (ICP-RIE), has extraordinary properties which can lead to unique structures difficult to achieve using other etching methods. In this work, the authors demonstrate the application of ICP-RIE techniques which capitalize on the cryogenic properties to create different sensors geometries: optical, electrical, magnetic, and mechanical. The three techniques demonstrated are (1) single step deep etches with controllable sidewall profiles. Demonstrating this, silicon pillars with over 70 μm depth and less than 250 nm sidewall roughness were etched using only 1.6 μm of photoresist for use as solar cells. (2) Using the cryogenic etch for thick metallization and liftoff with a thin photoresist mask. Demonstrating this second technique, a magnetic shim was created by deposition of 6.5 μm of iron into 20 μm deep etched trenches, using the remaining 1.5 μm photoresist etch mask as the liftoff mask. Using the same technique, 15 μm of copper was lifted off leaving a 20 μm deep plasma enhanced chemical vapor deposition silicon oxide coated, silicon channel with copper. (3) Use of a two step cryogenic etch for deep etching with reduced sidewall undercutting. This was demonstrated by fabrication of deep and anisotropic microelectromechanical systems structures; a mechanical resonator was etched 183 μm deep into silicon with less than 3 μm of undercutting. This work also describes the etch parameters and etch controls for each of these sensors.

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81.65.Cf

Surface cleaning, etching, patterning

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Formation and evolution of craters in carbon steels during low-energy high-current pulsed electron-beam treatment

Kemin Zhang, Jianxin Zou, Thierry Grosdidier, and Chuang Dong

J. Vac. Sci. Technol. A 27, 1217 (2009); http://dx.doi.org/10.1116/1.3207948 (10 pages) | Cited 2 times

Online Publication Date: 25 August 2009

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The authors investigated in detail the formation and evolution of microcraters induced by low-energy high-current pulsed electron-beam treatment on several quenched and tempered carbon steels. They have shown that the crater formation mechanism is the same for the three selected steels regardless of the carbon content and original microstructure state. Melting starts at the subsurface layer during treatment, resulting in the nucleation of small droplets preferentially at grain or phase boundaries. Under further heating, the boiling droplets erupt through the surface. The liquid around these craters shrinks to supply the lost part and, during the cooling process, leads to the formation of the funnel-like crater morphology. Microirregularities help retain locally the heat flux and, consequently, serve as nucleation sites for crater formations. By increasing the number of pulses, microirregularities were gradually removed and melted layer depth increased. As a result, crater formation became less effective. On the other hand, some of the already formed craters were deepened, while others were eliminated during the following pulses. The above processes together cause the crater density to first increase and then decrease, whereas the surface roughness first increases and then remains at the same level with increasing number of pulses.

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68.35.bd	Metals and alloys
68.35.Gy	Mechanical properties; surface strains
61.72.Mm	Grain and twin boundaries
64.60.Q-	Nucleation
81.65.-b	Surface treatments
81.40.Gh	Other heat and thermomechanical treatments

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Does hydrogen change the fullerenelike structure in CN_x thin films?

Debdulal Roy, Manish Chhowalla, Niklas Hellgren, and G. A. J. Amaratunga

J. Vac. Sci. Technol. A 27, 1227 (2009); http://dx.doi.org/10.1116/1.3207949 (4 pages)

Online Publication Date: 28 August 2009

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The authors have reported the structure of the nanoclusters in carbon nitride thin films before [ D. Roy et al., Phys. Rev. B 70, 035406 (2004) ]. In this work, effects of the addition of hydrogen in the deposition gas mixture on the structures of carbon nitride thin films prepared by magnetron sputtering were investigated using Raman spectroscopy. Raman measurements showed that the structures of carbon nanoclusters remained unaffected by the addition of hydrogen in the carbon nitride films. On the other hand, the structures of amorphous thin films were affected by the addition of hydrogen in the deposition gas mixture. These are explained in terms of changes in the ratios of the D-peak to the G-peak intensities and shifts in the G-peak centers.

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68.55.J-	Morphology of films
78.30.Hv	Other nonmetallic inorganics
78.35.+c	Brillouin and Rayleigh scattering; other light scattering
81.15.Cd	Deposition by sputtering

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Photoluminescence enhancement by rapid thermal annealing for ZnO epitaxial films grown on Si (100) by pulsed laser deposition

Q. He, X. N. Wang, H. B. Wang, J. H. Zhu, Hao Wang, and Y. Jiang

J. Vac. Sci. Technol. A 27, 1231 (2009); http://dx.doi.org/10.1116/1.3207952 (4 pages)

Online Publication Date: 31 August 2009

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ZnO single-crystalline films were prepared by predepositing a homobuffer layer on Si (100) substrate in a pulsed laser deposition system. The effect of short-time rapid thermal annealing under N₂ and O₂ ambient on the optical property was systematically studied by photoluminescence measurements from 77 K to room temperature. Different from the adverse effect of the O₂-assisted rapid thermal annealing on the optical quality, N₂-assisted rapid thermal annealing can greatly enhance the ultraviolet emission while eliminate the deep-level emission band including separate green, yellow, and orange luminescence peaks. Such ambient-dependent photoluminescence enhancement was attributed to the elimination of oxygen interstitial in the ZnO film.

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78.55.Et	II-VI semiconductors
78.66.Hf	II-VI semiconductors
68.55.ag	Semiconductors
71.55.Gs	II-VI semiconductors
61.72.Cc	Kinetics of defect formation and annealing
81.15.Fg	Pulsed laser ablation deposition
61.72.jj	Interstitials

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Highly conformal film growth by chemical vapor deposition. I. A conformal zone diagram based on kinetics

A. Yanguas-Gil, Y. Yang, N. Kumar, and J. R. Abelson

J. Vac. Sci. Technol. A 27, 1235 (2009); http://dx.doi.org/10.1116/1.3207745 (9 pages) | Cited 2 times

Online Publication Date: 1 September 2009

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The authors present a unified description of conformal film growth in recessed features by low pressure chemical vapor deposition. Experimental data on step coverage and growth rate are interpreted in terms of a kinetic model for the elementary surface processes. This model is combined with the continuity equation for gas transport and consumption to predict the values of the precursor pressure and substrate temperature (p,T) that are necessary for conformal coverage to occur for a given precursor. They introduce a conformal zone diagram that considers the gas phase limitations (maximum precursor pressure and onset of secondary reactions), the surface limitations (minimum reaction temperature, precursor adsorption and desorption rates, and film growth rate), and the aspect ratio of the feature to be coated; the allowed intersection between the resulting boundaries defines the (p,T) zone for conformal growth. Sufficient precursor pressure is identified as a major requirement for conformal film growth, one that is not met by many commercially available molecules. Finally, they derive an approximate analytical solution to the inverse problem: what are the experimental conditions necessary to afford a desired degree of step coverage on a given aspect ratio feature at a desired growth rate. The solution depends on a set of rate constants in the kinetic model that can be extracted from measurements of the film growth rate as a function of precursor pressure and substrate temperature on trench or planar substrates.

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68.55.at	Other materials
82.20.Db	Transition state theory and statistical theories of rate constants
81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.43.Mn	Adsorption kinetics
68.43.Nr	Desorption kinetics

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Highly conformal film growth by chemical vapor deposition. II. Conformality enhancement through growth inhibition

A. Yanguas-Gil, N. Kumar, Y. Yang, and J. R. Abelson

J. Vac. Sci. Technol. A 27, 1244 (2009); http://dx.doi.org/10.1116/1.3207746 (5 pages) | Cited 2 times

Online Publication Date: 1 September 2009

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The authors present a novel strategy for enhancing conformality in chemical vapor deposition (CVD) based on the concept of growth inhibition. In Part I, they showed how surface site blocking was responsible for the increase in conformality observed at higher pressures in high vapor pressure precursors. In this work, they apply this concept to enhance conformality by considering a secondary species that acts as an inhibitor of the precursor. The experimental results obtained for the growth of TiB₂ from Ti(BH₄)₃dme (dme = dimethoxyethane), with dme acting as the growth inhibitor, agree well with the models, based on a first order adsorption/desorption kinetics, and show how this strategy greatly enhances the conformality of nonconformal precursors. Finally, they show how multiple surface mechanisms including surface site blocking, associative desorption, long surface residence time of by-products, or coadsorption of two reactants can induce growth inhibition. Consequently, this strategy can be potentially applied to many existing CVD systems, provided suitable molecular inhibitors are identified.

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81.15.Gh	Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A-	Nucleation and growth
62.50.-p	High-pressure effects in solids and liquids
68.43.Nr	Desorption kinetics
68.43.Mn	Adsorption kinetics