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Jul 2012

Volume 30, Issue 4, Articles (04xxxx)

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J. Vac. Sci. Technol. B 30, 041805 (2012); http://dx.doi.org/10.1116/1.4731255 (7 pages)

Meena S. Rajachidambaram, Tamas Varga, Libor Kovarik, Rahul Sanghavi, Vaithiyalingam Shutthanandan, Suntharampillai Thevuthasan, Seung-Yeol Han, Chih-Hung Chang, and Gregory S. Herman
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Field emission property of carbon-doped TiO2 nanotube arrays with controllable doping content of carbon

You-Min Kang, Cheng-Wei Wang, Jian-Biao Chen, Lin-Qing Wang, Dong-Sheng Li, Wei-Dong Zhu, and Feng Zhou

J. Vac. Sci. Technol. B 30, 041801 (2012); http://dx.doi.org/10.1116/1.4718708 (5 pages)

Online Publication Date: 18 May 2012

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To achieve an optimum cold cathode emitter, well-aligned TiO2/Ti nanotube arrays (TNAs) were synthesized by anodic oxidation and doped with carbon by pyrolysis of C2H2 at 550 °C. By controlling the carbon doping content, the field emission (FE) properties of carbon-doped TiO2/Ti nanotube arrays (C-TNAs) were optimized. Compared with the high turn-on field of 19.19 V/μm from pure TNAs, the turn-on field of C-TNAs was decreased to 11.60, 6.35, 4.10, and 5.77 V/μm when the doping content of carbon was increased to 0.62, 0.82, 1.81, and 3.31 at. %, respectively. Obviously, the FE properties of TNAs were dramatically improved and optimized by adjusting the carbon doping content, which can be attributed to the typical tubular morphology, an enhanced conductivity, and a reduced work function.
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81.07.De Nanotubes
81.16.Be Chemical synthesis methods
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
79.70.+q Field emission, ionization, evaporation, and desorption
73.63.Fg Nanotubes
73.30.+y Surface double layers, Schottky barriers, and work functions

2D ordered arrays of nanopatterns fabricated by using colloidal crystals as templates

Benzhong Wang, Mingyong Han, and Soo Jin Chua

J. Vac. Sci. Technol. B 30, 041802 (2012); http://dx.doi.org/10.1116/1.4720097 (7 pages)

Online Publication Date: 22 May 2012

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A facile approach to fabricate two-dimensional (2D) ordered arrays of nanostructures is described in this paper. The approach uses spin-coating liquid materials onto a monolayer or multilayer colloidal crystal template to form a uniform film containing the template. After solidifying, the film is partially etched to expose the template which is then removed by selective etching. The fabrication procedure can produce large-area, size-tunable, periodic nanostructures with excellent structural uniformity. Large-area silica nanostructures with P6 mm symmetry have been formed by employing a dry etching technique. Experimental and simulating results also show that unique 2D nanostructures, with the feature size being much smaller than the diameter of the spherical particles used, can be obtained through three-dimensional silica nanopatterns, acted as a mask, and formed by a bilayer or trilayer colloidal crystal template.
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81.07.Bc Nanocrystalline materials
81.16.Rf Micro- and nanoscale pattern formation
81.30.Fb Solidification
81.65.Cf Surface cleaning, etching, patterning
64.70.D- Solid-liquid transitions

Polymer nanocomposites with improved resistance to ionizing radiation

Vesna Borjanović, Lahorija Bistričić, Lara Mikac, Gary E. McGuire, Ivana Zamboni, Milko Jakšić, and Olga Shenderova

J. Vac. Sci. Technol. B 30, 041803 (2012); http://dx.doi.org/10.1116/1.4724310 (13 pages) | Cited 1 time

Online Publication Date: 5 June 2012

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In the present study, three different nanocomposites of poly(dimethylsiloxane) (PDMS) with 1 wt. % of nanoparticles of detonation nanodiamond (DND) (PDMS-DNDS), zinc oxide (ZnO) (PDMS-ZnO), and single-walled carbon nanotubes (SWNTs) (PDMS-SWNTs) were irradiated under vacuum at room temperature with a 2 MeV proton beam with fluences in the 1013–1015 cm−2 range. Modification of the structures and properties of the nanocomposite materials were monitored as a function of proton fluence. Specifically, the vibrational dynamics of PDMS nanocomposites for unirradiated and irradiated samples were investigated using Raman and Fourier transform infrared spectroscopy in the attenuated total reflection mode (FTIR-ATR) and compared. The results were also compared with the results obtained for the unirradiated/irradiated pure PDMS polymer. The Raman and FTIR-ATR spectra of the PDMS nanocomposites exhibit an overall reduction in intensity of the characteristic vibrational bands of the irradiated samples. However, an important difference between the irradiated pure PDMS versus PDMS nanocomposites’ Raman and FTIR spectra appeared; comparable structural degradation of polymer nanocomposites with ZnO, DND, and SWNT fillers takes place at least at 1 or even 2 orders of magnitude higher fluence than for pure PDMS, indicating the potential use of ZnO-based, DND-based, and SWNT-based polymer composites in high radiation environments. The highest resistance to radiation was demonstrated for PDMS-ZnO samples. Since the benefit is realized at a low loading, the cost of the nanocomposite can be kept low and the polymer retains the other beneficial properties that make them attractive.
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61.82.Rx Nanocrystalline materials
78.30.Na Fullerenes and related materials
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
78.67.Sc Nanoaggregates; nanocomposites
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.80.Jh Ion radiation effects

Very low angle annular dark field imaging in the scanning transmission electron microscope: A versatile tool for micro- and nano-characterization

Frieder H. Baumann

J. Vac. Sci. Technol. B 30, 041804 (2012); http://dx.doi.org/10.1116/1.4729287 (6 pages)

Online Publication Date: 14 June 2012

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The author shows how very low angle annular dark field (VLAADF) imaging in the scanning transmission electron microscope (STEM) is used to delineate regions of different orientation or structural phase in the same material. First, the author describes the settings used to obtain images in which only very low indexed beams contribute to the image formation. These settings can be implemented easily on any commercial STEM/TEM by choosing the appropriate camera length and objective aperture. The author then demonstrates how VLAADF was used to perform detailed grain size studies in Cu interconnects, and show how the technique can be used to outline the amorphous region within the crystalline matrix in a phase change memory device. The author finishes by addressing and discussing the dependence of the “orientation contrast” on the main imaging parameters.
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07.78.+s Electron, positron, and ion microscopes; electron diffractometers

Formation of zinc oxide films using submicron zinc particle dispersions

Meena S. Rajachidambaram, Tamas Varga, Libor Kovarik, Rahul Sanghavi, Vaithiyalingam Shutthanandan, Suntharampillai Thevuthasan, Seung-Yeol Han, Chih-Hung Chang, and Gregory S. Herman

J. Vac. Sci. Technol. B 30, 041805 (2012); http://dx.doi.org/10.1116/1.4731255 (7 pages)

Online Publication Date: 27 June 2012

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The thermal oxidation of submicron metallic Zn particles was studied as a method to form nanostructured ZnO films. The particles used for this work were characterized by electron microscopy, x ray diffraction, and thermal analysis to evaluate the Zn-ZnO core shell structure, surface morphology, and oxidation characteristics. Significant nanostructural changes were observed for films annealed to 400 °C or higher, where nanoflakes, nanoribbons, nanoneedles, and nanorods were formed as a result of stress induced fractures arising in the ZnO outer shell due to differential thermal expansion between the metallic Zn core and the ZnO shell. Mass transport occurs through these defects due to the high vapor pressure for metallic Zn at temperatures above 230 °C, whereupon the Zn vapor rapidly oxidizes in air to form the ZnO nanostructures. The Zn particles were also incorporated into zinc indium oxide precursor solutions to form thin film transistor test structures to evaluate the potential of forming nanostructured field effect sensors using simple solution processing.
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81.05.Dz II-VI semiconductors
81.07.-b Nanoscale materials and structures: fabrication and characterization
81.16.Pr Micro- and nano-oxidation
81.65.Mq Oxidation
85.30.Tv Field effect devices
61.46.-w Structure of nanoscale materials

Nanofabricated quantum dot array formation through annealing of nano-patterned planar InAs

Kurt G. Eyink, Lawrence Grazulis, Krishnamurthy Mahalingam, Jodie Shoaf, Veronica Hart, Daniel Esposito, John Hoelscher, Marlon Twyman, and David H. Tomich

J. Vac. Sci. Technol. B 30, 041806 (2012); http://dx.doi.org/10.1116/1.4731471 (7 pages)

Online Publication Date: 29 June 2012

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Quantum dots (QDs) are typically formed using a self-assembly process that results in random placement and size distributions, thus limiting their applicability for many devices. In this work, we report a process which uses nano-patterned planar InAs and subsequent annealing under As stabilized conditions to produce QDs with uniform placement and size distribution. The authors demonstrate the ability to form ordered QD arrays with a density of 3 × 1010 dots/cm2 and QD base widths of <30 nm. The authors achieved photoluminescence from the patterned area at a temperature below 100 K.
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81.16.Rf Micro- and nanoscale pattern formation
81.16.Dn Self-assembly
78.55.Cr III-V semiconductors
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Study of silica nano-pattern erosion in H2SO4-H2O2 mixture using spectroscopic ellipsometry

Zhaoning Yu, Nobuo Kurataka, Hieu Tran, and Gene Gauzner

J. Vac. Sci. Technol. B 30, 041807 (2012); http://dx.doi.org/10.1116/1.4732121 (4 pages)

Online Publication Date: 29 June 2012

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To overcome the difficulty in measuring the extremely slow erosion of transparent silica, we apply spectroscopic ellipsometry (SE) optical critical dimension measurements on a subwavelength surface relief grating instead of a blank silica substrate. By analyzing the nano-grating SE spectra, we find that the H2SO4-H2O2 Piranha cleaning widely used for organic contaminants removal also etches silica slowly—up to a molecular monolayer is partially removed from the silica surface by each cleaning cycle. Based on these findings, we conclude that silica dissolution is an important factor to be considered in applications such as template cleaning in nanoimprint lithography.
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81.65.Cf Surface cleaning, etching, patterning
64.75.Bc Solubility
62.20.Qp Friction, tribology, and hardness
81.16.Rf Micro- and nanoscale pattern formation
81.40.Pq Friction, lubrication, and wear

Si delta doping inside InAs/GaAs quantum dots with different doping densities

Ke-Fan Wang, Yongxian Gu, Xiaoguang Yang, Tao Yang, and Zhanguo Wang

J. Vac. Sci. Technol. B 30, 041808 (2012); http://dx.doi.org/10.1116/1.4732462 (6 pages) | Cited 1 time

Online Publication Date: 3 July 2012

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During the growth process of InAs/GaAs self-assembled quantum dots (QDs), Si delta doping with different doping densities was carried out during initial QD formation. Atomic force microscopy (AFM) reveals that this Si doping affects the QD morphology only slightly. Conductive AFM measurements show that the current on the surface QDs increases at low doping densities, but decreases unexpectedly at high doping densities. Temperature-dependent photoluminescence (PL) measurements show that an optimized Si doping density (5 × 1011 cm−2) improves the PL thermal stability for an intermediate temperature range from 125 to 225 K and enhances the PL intensity up to 35 times at room temperature. These results indicate that the Si doping density plays a key role in the electrical and optical properties of InAs QDs.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
81.16.Dn Self-assembly
61.72.U- Doping and impurity implantation
68.37.Ps Atomic force microscopy (AFM)

Effect of acetylene concentration and thermal ramping rate on the growth of spin-capable carbon nanotube forests

Kyung H. Lee, Dae Woong Jung, Dorothea Burk, Lawrence J. Overzet, and Gil S. Lee

J. Vac. Sci. Technol. B 30, 041809 (2012); http://dx.doi.org/10.1116/1.4736985 (6 pages)

Online Publication Date: 11 July 2012

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Spin-capable multiwalled carbon nanotube (MWCNT) forests that can form webs, sheets, and yarns provide a promising means for advancing various technologies. It is necessary to understand the critical factors to grow spin-capable carbon nanotubes (CNTs) in a repeatable fashion. Here we show how both the spinning capability and morphology of MWCNT forests are significantly changed by controlling the C2H2 concentration and ramp rate of temperature. The acetylene gas flow was varied in the range of 0.25–6.94% by volume. The MWCNTs grown at C2H2 concentrations between 1.47–3.37% are well-aligned and become spin-capable. The well-aligned forests have higher areal density and shorter distance between CNTs. The thermal ramp rate was also changed from 30 °C/min to 70 °C/min. A specific range of thermal ramp rate is also required to have the suitably sized nanoparticles with sufficient density resulting in higher CNT areal density for spinnable MWCNTs. A ramp rate of 50 °C/min forms suitable sized nanoparticles with sufficient density to produce CNT forests with a higher areal density and a shorter tube spacing.
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81.16.-c Methods of micro- and nanofabrication and processing
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Characterization of vertical Si nanowire p-n diodes fabricated by metal-assisted etching and AAO templates

Namyong Kwon, Namkyu Kim, Sihyun Sung, Byungyun Kang, and Ilsub Chung

J. Vac. Sci. Technol. B 30, 041810 (2012); http://dx.doi.org/10.1116/1.4737155 (8 pages)

Online Publication Date: 13 July 2012

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Vertical Si nanowire p-n diodes were fabricated utilizing both anodic aluminum oxide (AAO) templates and metal-assisted etching. AAO templates with different diameters were fabricated on a p(2.5 μm)-n junction substrate using a two-step anodization and pore widening process. The average diameters of the AAO templates were 36.3, 57.4, and 78.1 nm. Vertical Si nanowire p-n diodes were then fabricated by metal-assisted etching, with average diameters of 37.4, 53.3, and 62.8 nm. The lengths of the vertical Si nanowires were controlled by varying the etching times. For the fully etched (3 μm) Si nanowire, the p-n diodes with smaller diameters yielded higher current densities than those with larger diameters, due to mobility enhancement. However, such dependency was not observed for the partially etched (500 nm) Si nanowire p-n diodes. It was concluded that the recombination current is too dominant in the depletion region to improve mobility in one-dimensional transport.
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85.30.Kk Junction diodes

Differences in erosion mechanism and selectivity between Ti and TiN in fluorocarbon plasmas for dielectric etch

Florian Weilnboeck, Elliot Bartis, Sivan Shachar, Gottlieb S. Oehrlein, David Farber, Tom Lii, and Chet Lenox

J. Vac. Sci. Technol. B 30, 041811 (2012); http://dx.doi.org/10.1116/1.4736979 (10 pages)

Online Publication Date: 20 July 2012

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Metallic masking materials are promising candidates for plasma-based pattern transfer into low-k materials for fabricating integrated circuits. Improving etching selectivity (ES) between the low-k and hardmask material requires a fundamental understanding of material erosion in fluorocarbon (FC) plasmas. The authors have previously reported on the erosion mechanism and plasma parametric dependencies of Ti etch in FC discharges. The present work focuses on elucidating differences in the erosion behavior between Ti and TiN hardmasks. The authors studied erosion of Ti, TiN, and organosilicate glass (OSG), a reference low-k material, in CF4/Ar and C4F8/Ar plasmas. Changes in surface composition, FC surface reaction layer thicknesses, erosion rates, and corresponding ES were established by x-ray photoelectron spectroscopy and in situ ellipsometry. The authors found that the erosion stages and plasma parameter dependent surface compositions were similar for Ti and TiN. The previously established dependence of Ti erosion rates on FC layer thickness and energy deposition on the hardmask surface by ions generally holds for TiN as well. However, TiN etch rates (volumetric removal rates) and etch yields (atomic removal rates) were increased by a factor of 1–1.4 compared to Ti. This difference can be explained by the rapid removal of N from the TiN surface, increasing the Ti atom number density at the surface above values of the Ti hardmask. The resulting increase in surface reactivity is in good agreement with the enhanced erosion rates compared to Ti. Differences in erosion rates have a direct impact on the ES and the highest ES relative to OSG (up to 15) were achieved for Ti hardmasks in CF4/Ar plasmas with low ion energy.
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81.65.Cf Surface cleaning, etching, patterning
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
52.77.Bn Etching and cleaning
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Ht Disordered structures
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