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Jan 2012

Volume 30, Issue 1, Articles (01xxxx)

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J. Vac. Sci. Technol. B 30, 010801 (2012); http://dx.doi.org/10.1116/1.3661355 (28 pages)

Jarrett J. Dumond and Hong Yee Low
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High temperature imaging using a thermally compensated cantilever resistive probe for scanning thermal microscopy

Y. Zhang, P. S. Dobson, and J. M. R. Weaver

J. Vac. Sci. Technol. B 30, 010601 (2012); http://dx.doi.org/10.1116/1.3664328 (5 pages)

Online Publication Date: 1 December 2011

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The authors have designed and fabricated AFM probes with an integrated resistive temperature sensor and a grooved cantilever structure. The grooved structure compensates for the bilayer thermal bending that normally occurs during scanning thermal microscopy of hot samples. These new probes show reduced bending at high temperatures when compared to commercial, conventional cantilever probes with a similar stiffness. This indicates that the mechanical balance introduced by the grooved structure plays a major role in reducing thermal bending. Successful temperature mapping is demonstrated on an active heater device reaching 108 °C, a sample that would be beyond the imaging capability of conventional probes.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Effect of annealing on interfacial and band alignment characteristics of HfO2/SiO2 gate stacks on Ge substrates

Xue-Fei Li, Xiao-Jie Liu, Ying-Ying Fu, Ai-Dong Li, Wen-Qi Zhang, Hui Li, and Di Wu

J. Vac. Sci. Technol. B 30, 010602 (2012); http://dx.doi.org/10.1116/1.3665416 (4 pages)

Online Publication Date: 5 December 2011

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The authors have investigated the effect of 500 °C annealing for 60 s in N2 on interfacial and band alignment characteristics of HfO2/SiO2 gate stacks on n-type Ge substrates. X-ray photoelectron spectroscopy analyses reveal that the SiO2 interlayer can effectively suppress Ge outdiffusion during HfO2 growth and subsequent postdeposition annealing process. The electrical measurement shows that capacitance equivalent thickness of 1.75 nm and a leakage current density of 3.9 × 10−3 A/cm2 at gate bias of flatband voltage (Vfb) + 1 V was obtained for the annealed sample. The conduction band offsets at the HfO2/SiO2/Ge with and without annealing are found to be 2.22 and 2.07 eV, respectively.
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79.60.Jv Interfaces; heterostructures; nanostructures
73.20.At Surface states, band structure, electron density of states
81.40.Gh Other heat and thermomechanical treatments

Extraction of a low-current discharge from a microplasma for nanoscale patterning applications at atmospheric pressure

Seung Whan Lee, Hamidreza Zamani, Philip X.-L. Feng, and R. Mohan Sankaran

J. Vac. Sci. Technol. B 30, 010603 (2012); http://dx.doi.org/10.1116/1.3669523 (5 pages) | Cited 2 times

Online Publication Date: 15 December 2011

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The authors present a scheme to extract a low-current discharge from a microplasma at atmospheric pressure for nanopatterning applications. The extracted discharge is generated by applying a high positive voltage to an independent electrode and accelerating electrons from the microplasma. Current-voltage (I–V) characteristics of the extracted discharge show high stability at low currents and tunability over a wide range of currents. Exposure of metal precursor loaded films to the extracted discharge results in electrochemical reduction of metal ions to solid metal, as confirmed by X-ray photoelectron spectroscopy. Combining this approach with masking techniques allows the transfer of nanoscale patterns of metal at ambient conditions.
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81.16.Rf Micro- and nanoscale pattern formation
73.61.At Metal and metallic alloys
79.60.Bm Clean metal, semiconductor, and insulator surfaces

Determination of crystal orientation of silicon via shape-controlled vapor-solid growth of copper nanoparticles

Jin-Woo Han and M. Meyyappan

J. Vac. Sci. Technol. B 30, 010604 (2012); http://dx.doi.org/10.1116/1.3672007 (4 pages)

Online Publication Date: 21 December 2011

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Crystal lattice orientations of substrates are inspected via morphology of copper particles generated by a vapor-solid growth process. The high thermal energy enables diffusion of copper ions into the crystal substrate, and then the copper ions on the substrate are preferentially gathered, forming single-crystalline metal particles. The shapes of the particles are bounded by the facets to minimize the surface energy. Thus, polyhedral particles are truncated and bounded by {100}, {110}, and {111} facets, which results in equilateral square and triangle shapes on (100) and (111) plane substrates, respectively. The directions of the sides of the square and triangle shapes indicate <100> and <110> directions, respectively.
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61.50.-f Structure of bulk crystals
68.35.Md Surface thermodynamics, surface energies
81.07.Bc Nanocrystalline materials
81.10.Bk Growth from vapor
81.10.Dn Growth from solutions
66.30.J- Diffusion of impurities

Directed assembly in epitaxial zinc oxide films on focused ion beam modified sapphire substrates

Benjamin D. Myers, Blake L. Stevens, Dorota I. Rożkiewicz, Scott A. Barnett, and Vinayak P. Dravid

J. Vac. Sci. Technol. B 30, 010605 (2012); http://dx.doi.org/10.1116/1.3672006 (5 pages)

Online Publication Date: 22 December 2011

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A new method for directed self-assembly using focused ion beam (FIB) and physical vapor deposition is presented. The high resolution and site-specific patterning capabilities of FIB are coupled with the self-assembly process in heteroepitaxial thin film growth. An efficient FIB-induced damage mechanism is exploited to pattern amorphous regions in sapphire substrates which direct the subsequent assembly of a sputter-deposited zinc oxide film. This novel approach allows for the fabrication of in-plane nano- to microscale heterostructures comprising epitaxial regions with high strain and defect density that are separated by regions of randomly oriented (in-plane) grains with much lower strain and defect density.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
61.72.-y Defects and impurities in crystals; microstructure
81.05.Dz II-VI semiconductors

Carbon monoxide detection sensitivity of ZnO nanorod-gated AlGaN/GaN high electron mobility transistors in different temperature environments

Chien-Fong Lo, Lu Liu, Byung-Hwan Chu, Fan Ren, Stephen J. Pearton, Sylvain Doré, Chien-Hsing Hsu, Jihyun Kim, Amir M. Dabiran, and Peter P. Chow

J. Vac. Sci. Technol. B 30, 010606 (2012); http://dx.doi.org/10.1116/1.3672010 (4 pages) | Cited 3 times

Online Publication Date: 22 December 2011

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The effect of ambient temperature on the detection sensitivity of carbon monoxide (CO) using ZnO nanorod-gated AlGaN/GaN high electron mobility transistor (HEMT) sensors was studied over a range of temperatures from 25 to 400 °C. An increase of the HEMT drain current was observed for exposure to the CO-containing ambients, due to chemisorbed oxygen on the ZnO surface reacting with CO to form CO2 and releasing electrons to the oxide surface, increasing the counter charges in the two-dimensional electron gas channel of the HEMT. By increasing the detection temperature from 25 °C to 150 °C, the CO detection sensitivity, ΔI/I, and detection limit were significantly improved from 0.23% to 7.5% and from 100 ppm to ∼30 ppm, respectively. However, the sensitivity of the CO detection was degraded by the decrease of mobility and saturation drain current of HEMT at temperatures higher than 200 °C.
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85.30.Tv Field effect devices
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing

Fabrication of stable and reproducible submicron tunnel junctions

I. M. Pop, T. Fournier, T. Crozes, F. Lecocq, I. Matei, B. Pannetier, O. Buisson, and W. Guichard

J. Vac. Sci. Technol. B 30, 010607 (2012); http://dx.doi.org/10.1116/1.3673790 (4 pages) | Cited 3 times

Online Publication Date: 6 January 2012

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The authors have performed a detailed study of the time stability and reproducibility of submicron Al/AlOx/Al tunnel junctions, fabricated using standard double angle shadow evaporations. The authors have found that by aggressively cleaning the substrate before the evaporations; thus preventing any contamination of the junction, they obtained perfectly stable oxide barriers. The authors also present measurements on large ensembles of junctions which prove the reproducibility of the fabrication process. The measured tunnel resistance variance in large ensembles of identically fabricated junctions is in the range of only a few percent. Finally, the authors have studied the effect of different thermal treatments on the junction barrier. This is especially important for multiple step fabrication processes which imply annealing the junction.
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73.40.Gk Tunneling
73.40.Ns Metal-nonmetal contacts
81.65.Cf Surface cleaning, etching, patterning
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