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7 Jun 2004

Volume 84, Issue 23, pp. 4599-4816

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 4650 (2004); http://dx.doi.org/10.1063/1.1759390 (3 pages)

David I. Woodward, Ian M. Reaney, Gaiying Y. Yang, Elizabeth C. Dickey, and Clive A. Randall
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Enhanced strain relaxation in a two-step process of GexSi1−x/Si(001) heterostructures grown by low-temperature molecular-beam epitaxy

Yu. B. Bolkhovityanov, A. S. Deryabin, A. K. Gutakovskii, M. A. Revenko, and L. V. Sokolov

Appl. Phys. Lett. 84, 4599 (2004); http://dx.doi.org/10.1063/1.1734683 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2004

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Two-layer GexSi1−x heterostructures, with a finite fraction of germanium up to x = 0.48 and a thickness of at most 0.65 μm, were grown by molecular-beam epitaxy. It is shown that plastic relaxation of the second step is significantly enhanced. It is assumed that threading dislocations with a density of 105–106 cm−2, which appear in the first step in the process of its plastic relaxation, are sources of misfit dislocations positioned between the first and second steps. Cross-sectional transmission electron microscopy showed the superior quality of the dislocation network in the stepped regions. Threading dislocation densities in the second step were determined with the help of etching pits and were found to be close to 105 cm−2. © 2004 American Institute of Physics.
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68.55.A- Nucleation and growth
81.05.Hd Other semiconductors
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
68.60.Bs Mechanical and acoustical properties
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.37.Lp Transmission electron microscopy (TEM)
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Optical nonlinearity of monodispersed, capped ZnS quantum particles

V. V. Nikesh, Aditya Dharmadhikari, Hiroshi Ono, Shinji Nozaki, G. Ravindra Kumar, and Shailaja Mahamuni

Appl. Phys. Lett. 84, 4602 (2004); http://dx.doi.org/10.1063/1.1748840 (3 pages) | Cited 13 times

Online Publication Date: 19 May 2004

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ZnS quantum dots are synthesized by a high-temperature chemical route with narrow size distribution at diameters of 1.4 and 1.8 nm. Significantly small size dispersion of 1.4-nm-sized ZnS quantum dots is vivid from the transmission electron microscopic measurements. The nonlinear absorption is measured at wavelengths 532 and 520 nm using a picosecond laser in an open aperture z-scan setup. The measured two-photon absorption coefficients are 0.08 and 0.2 cm/GW for smaller and larger nanoparticles. Two photon absorption cross sections for nanoparticles are about six orders of magnitude larger than bulk ZnS. © 2004 American Institute of Physics.
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81.05.Dz II-VI semiconductors
81.07.Bc Nanocrystalline materials
81.07.Ta Quantum dots
78.67.Hc Quantum dots
68.37.Lp Transmission electron microscopy (TEM)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
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Waveguide networks in three-dimensional layer-by-layer photonic crystals

Curtis Sell, Caleb Christensen, Jason Muehlmeier, Gary Tuttle, Zhi-Yuan Li, and Kai-Ming Ho

Appl. Phys. Lett. 84, 4605 (2004); http://dx.doi.org/10.1063/1.1751212 (3 pages) | Cited 20 times

Online Publication Date: 19 May 2004

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Different types of waveguides and connections between them were fabricated in a three-dimensional (3D) layer-by-layer photonic crystal. The waveguides were formed by removing either a single rod or a series of rod fragments running in three mutually orthogonal directions. This provides the potential of forming a 3D network of waveguide channels with cross sectional dimensions on the order of one lattice constant. The propagation behavior of guided modes in these waveguide networks was probed using a network analyzer. High transmission efficiency (with loss below 0.5 dB) through various waveguide bends and networks with carefully designed geometries has been achieved. © 2004 American Institute of Physics.
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42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
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Polymer field-effect transistors by a drawing method

Shuichi Nagamatsu, Wataru Takashima, Keiichi Kaneto, Yuji Yoshida, Nobutaka Tanigaki, and Kiyoshi Yase

Appl. Phys. Lett. 84, 4608 (2004); http://dx.doi.org/10.1063/1.1751222 (3 pages) | Cited 19 times

Online Publication Date: 19 May 2004

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We demonstrated the polymer field-effect transistors (FETs) utilizing regioregular poly(3-alkylthiophene)s (P3AT) films prepared by a drawing method. The P3AT film exhibited large optical dichroic ratio, which originated in the polymer backbones aligned to the drawing direction. In-plane anisotropy and enhancement of FET characteristics have been observed that are caused by molecular alignment. In the case of poly(3-dodecylthiophene), the hole mobility along the drawing direction was enhanced by a factor of 25 compared with that of spin-coated film. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
73.50.Dn Low-field transport and mobility; piezoresistance
73.61.Ph Polymers; organic compounds

Electromechanical coupling coefficient for surface acoustic waves in single-crystal bulk aluminum nitride

G. Bu, D. Ciplys, M. Shur, L. J. Schowalter, S. Schujman, and R. Gaska

Appl. Phys. Lett. 84, 4611 (2004); http://dx.doi.org/10.1063/1.1755843 (3 pages) | Cited 20 times

Online Publication Date: 19 May 2004

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The electromechanical coupling coefficient K2 for surface acoustic waves propagating on c and a surfaces of bulk AlN single crystals has been measured using the S11-parameter method in the frequency range of 160–360 MHz. The extracted values of K2 are 0.11% and 0.47% for the c and a surfaces, respectively. By fitting our experimental data to our numerical simulation results, we have estimated piezoelectric constants, which are in a reasonable agreement with literature data. Our results are consistent with the negative sign of the e15 constant. © 2004 American Institute of Physics.
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68.35.Iv Acoustical properties
77.65.Dq Acoustoelectric effects and surface acoustic waves (SAW) in piezoelectrics
68.47.Fg Semiconductor surfaces

Transparent conducting metal electrode for top emission organic light-emitting devices: Ca–Ag double layer

R. B. Pode, C. J. Lee, D. G. Moon, and J. I. Han

Appl. Phys. Lett. 84, 4614 (2004); http://dx.doi.org/10.1063/1.1756674 (3 pages) | Cited 59 times

Online Publication Date: 19 May 2004

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We have fabricated a transparent conducting double-layer metal electrode for top emission organic light-emitting devices which consists of thin layers of Ca and Ag metals of different thicknesses, deposited by the vacuum evaporation technique. The process is clean and does not damage the underlaying organic layers. High optical transparency over 70%, low reflectivity (14%) in the visible region, and low electrical sheet resistance (12 ohms/square) in Ca(10 nm)–Ag(10 nm) structures are reported. This transparent conducting Ca–Ag metal electrode opens a practical way to fabricate top-emitting organic displays without generating damage-induced states. © 2004 American Institute of Physics.
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81.05.Bx Metals, semimetals, and alloys
42.79.Kr Display devices, liquid-crystal devices
85.60.Pg Display systems
68.55.A- Nucleation and growth
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.40.Kc Metals, semimetals, and alloys
78.66.Bz Metals and metallic alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
73.61.At Metal and metallic alloys
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Excited-state spectroscopy on a nearly closed quantum dot via charge detection

J. M. Elzerman, R. Hanson, L. H. Willems van Beveren, L. M. K. Vandersypen, and L. P. Kouwenhoven

Appl. Phys. Lett. 84, 4617 (2004); http://dx.doi.org/10.1063/1.1757023 (3 pages) | Cited 10 times

Online Publication Date: 19 May 2004

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We demonstrate a method for measuring the discrete energy spectrum of a quantum dot connected very weakly to a single lead. A train of voltage pulses applied to a metal gate induces tunneling of electrons between the quantum dot and a reservoir. The effective tunnel rate depends on the number and nature of the energy levels in the dot made accessible by the pulse. Measurement of the charge dynamics thus reveals the energy spectrum of the dot, as demonstrated for a dot in the few-electron regime. © 2004 American Institute of Physics.
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73.21.La Quantum dots
73.40.Gk Tunneling
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Optically switched conductivity of epitaxial diamond on nitrogen doped diamond substrates

M. W. Geis, K. E. Krohn, J. M. Lawless, S. J. Deneault, M. F. Marchant, J. C. Twichell, T. M. Lyszczarz, J. E. Butler, D. D. Flechtner, and R. Wright

Appl. Phys. Lett. 84, 4620 (2004); http://dx.doi.org/10.1063/1.1757637 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2004

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Epitaxial diamond with remarkably low p-type doping (1×1014–1×1017 cm−3) and exceptionally low compensation ∼ 1×1013 cm−3, has enabled the demonstration of a optically-switched conduction modulation of the epitaxial layer. Charge exchange between the diamond substrate and the epitaxial layer makes it possible to modulate the conductivity of the epitaxial layer. Incandescent light will make the lightly p-doped epitaxial layer insulating and ultraviolet radiation will make the layer conductive again. Once the layer conductivity has been established it will remain in the same electrical state for days, if kept in the dark. © 2004 American Institute of Physics.
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78.66.Db Elemental semiconductors and insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
61.72.up Other materials
73.61.Cw Elemental semiconductors
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Propagation of an intense femtosecond laser pulse through a thin foil filter

Kenichi Kinoshita, Alexei Zhidkov, Tomonao Hosokai, Takeru Ohkubo, and Mitsuru Uesaka

Appl. Phys. Lett. 84, 4623 (2004); http://dx.doi.org/10.1063/1.1758296 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2004

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In order to improve the contrast of a nanosecond prepulse, the interaction of 12 TW, 50 femtosecond laser pulses with thin foil, as a filter, is investigated. Due to the collisional absorption, the prepulse produces rapidly expanding plasma and can lose 90% of its energy. At a properly chosen thickness of the filter, more than 60% of energy of the femtosecond main pulse is shown to be transmitted through the expanded underdense plasma with reduced prepulse contrast ratio. © 2004 American Institute of Physics.
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42.25.Bs Wave propagation, transmission and absorption
42.79.Ci Filters, zone plates, and polarizers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
52.50.Jm Plasma production and heating by laser beams (laser-foil, laser-cluster, etc.)
79.20.Ds Laser-beam impact phenomena
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Specific heat of single-walled boron nitride nanotubes

Y. Xiao, X. H. Yan, J. Xiang, Y. L. Mao, Y. Zhang, J. X. Cao, and J. W. Ding

Appl. Phys. Lett. 84, 4626 (2004); http://dx.doi.org/10.1063/1.1759061 (3 pages) | Cited 13 times

Online Publication Date: 19 May 2004

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Based on a force constant model, we have calculated the phonon spectrum and specific heat of single-walled boron nitride nanotubes. Compared with carbon nanotubes, boron nitride nanotubes have a larger specific heat. The fitting formulas for diameter and chirality dependence of specific heat at 300 K are given. © 2004 American Institute of Physics.
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81.07.De Nanotubes
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
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Suppression of subcutaneous oxidation during the deposition of amorphous lanthanum aluminate on silicon

L. F. Edge, D. G. Schlom, R. T. Brewer, Y. J. Chabal, J. R. Williams, S. A. Chambers, C. Hinkle, G. Lucovsky, Y. Yang, S. Stemmer, M. Copel, B. Holländer, and J. Schubert

Appl. Phys. Lett. 84, 4629 (2004); http://dx.doi.org/10.1063/1.1759065 (3 pages) | Cited 50 times

Online Publication Date: 19 May 2004

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Amorphous LaAlO3 thin films have been deposited by molecular beam deposition directly on silicon without detectable oxidation of the underlying substrate. We have studied these abrupt interfaces by Auger electron spectroscopy, high-resolution transmission electron microscopy, medium-energy ion scattering, transmission infrared absorption spectroscopy, and x-ray photoelectron spectroscopy. Together these techniques indicate that the films are fully oxidized and have less than 0.2 Å of SiO2 at the interface between the amorphous LaAlO3 and silicon. These heterostructures are being investigated for alternative gate dielectric applications and provide an opportunity to control the interface between the silicon and the gate dielectric. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.65.Mq Oxidation
79.20.Fv Electron impact: Auger emission
68.55.-a Thin film structure and morphology
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
68.37.Lp Transmission electron microscopy (TEM)
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Silicon nanopillars for mechanical single-electron transport

Dominik V. Scheible and Robert H. Blick

Appl. Phys. Lett. 84, 4632 (2004); http://dx.doi.org/10.1063/1.1759371 (3 pages) | Cited 48 times

Online Publication Date: 19 May 2004

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Nanomechanical systems have been shown to accurately regulate the flow of electric current. We present the concept and demonstrate experimental operation of a vertical electromechanical single-electron transistor. The device is fabricated from silicon forming a nanopillar situated between source and drain contacts. The advantage of this concept is its straightforward manufacturing, which only includes two processing steps: Electron-beam lithography and reactive ion etching. The device operates at room temperature and at frequencies in the range of 350–400 MHz. A theoretical model of the operation of this device is given, explaining qualitatively the obtained experimental data. © 2004 American Institute of Physics.
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85.35.Gv Single electron devices
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
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Hydrogen-induced reversible changes in drain current in Sc2O3/AlGaN/GaN high electron mobility transistors

B. S. Kang, R. Mehandru, S. Kim, F. Ren, R. C. Fitch, J. K. Gillespie, N. Moser, G. Jessen, T. Jenkins, R. Dettmer, D. Via, A. Crespo, B. P. Gila, C. R. Abernathy, and S. J. Pearton

Appl. Phys. Lett. 84, 4635 (2004); http://dx.doi.org/10.1063/1.1759372 (3 pages) | Cited 10 times

Online Publication Date: 19 May 2004

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Pt contacted AlGaN/GaN high electron mobility transistors with Sc2O3 gate dielectrics show reversible changes in drain–source current upon exposure to H2-containing ambients, even at room temperature. The changes in current (as high as 3 mA for relatively low gate voltage and drain–source voltage) are approximately an order of magnitude larger than for Pt/GaN Schottky diodes and a factor of 5 larger than Sc2O3/AlGaN/GaN metal–oxide–semiconductor (MOS) diodes exposed under the same conditions. This shows the advantage of using a transistor structure in which the gain produces larger current changes upon exposure to hydrogen-containing ambients. The increase in current is the result of a decrease in effective barrier height of the MOS gate of 30–50 mV at 25 °C for 10% H2/90% N2 ambients relative to pure N2 and is due to catalytic dissociation of the H2 on the Pt contact, followed by diffusion to the Sc2O3/AlGaN interface. © 2004 American Institute of Physics.
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85.30.Tv Field effect devices
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Enhanced mass sensing using torsional and lateral resonances in microcantilevers

L. B. Sharos, A. Raman, S. Crittenden, and R. Reifenberger

Appl. Phys. Lett. 84, 4638 (2004); http://dx.doi.org/10.1063/1.1759379 (3 pages) | Cited 33 times

Online Publication Date: 19 May 2004

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We present a method to detect, with enhanced sensitivity, a target mass particle attached eccentrically to a microcantilever by measuring multiple three-dimensional modes in the microcantilever vibration spectrum. Peaks in the spectrum reveal a complex coupling between the bending, torsional, and lateral motions and detailed finite element models assist in their interpretation. The mass sensitivities of the torsional and lateral mode frequencies are an order of magnitude greater, and their Q factors significantly higher, than that of the conventionally used fundamental bending mode. These modes offer significantly enhanced mass sensing capabilities within the realm of existing microcantilever technology. © 2004 American Institute of Physics.
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06.30.Dr Mass and density
07.10.Cm Micromechanical devices and systems
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Characterization of breakdown in ultrathin oxides by hot carrier emission

J. C. Tsang and B. P. Linder

Appl. Phys. Lett. 84, 4641 (2004); http://dx.doi.org/10.1063/1.1759383 (3 pages) | Cited 4 times

Online Publication Date: 19 May 2004

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Hot carrier luminescence excited at low voltages across ultrathin gate oxides is used to describe the localized transport during progressive oxide breakdown. The emission identifies the locations of initial breakdown spots in field effect transistors. The transitions from stress-induced leakage currents to reversible breakdown to final breakdown are accompanied by changes in the efficiency of the emission showing an evolution from inelastic to elastic transport. © 2004 American Institute of Physics.
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77.55.-g Dielectric thin films
77.22.Jp Dielectric breakdown and space-charge effects
85.30.Tv Field effect devices
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Measurement of polarization charge and conduction-band offset at InxGa1−xN/GaN heterojunction interfaces

H. Zhang, E. J. Miller, E. T. Yu, C. Poblenz, and J. S. Speck

Appl. Phys. Lett. 84, 4644 (2004); http://dx.doi.org/10.1063/1.1759388 (3 pages) | Cited 37 times

Online Publication Date: 19 May 2004

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The spontaneous and piezoelectric polarization fields in group-III nitride semiconductors lead to the presence of large electrostatic sheet charge densities at nitride semiconductor heterojunction interfaces. Precise quantitative knowledge of these polarization-induced charge densities and of the band-edge discontinuities at nitride heterojunction interfaces is therefore essential in nitride semiconductor device design and analysis. We have used capacitance–voltage profiling to measure the conduction-band offset and polarization charge density at InxGa1−xN/GaN heterojunction interfaces with x = 0.054 and x = 0.09. We obtain conduction-band offsets ΔEC = 0.09±0.07 eV for x = 0.054 and ΔEC = 0.22±0.05 eV for x = 0.09, corresponding to an averaged conduction-to-valence-band offset ratio ΔEC:ΔEV of 58:42. Our measurements yield polarization charge densities of (1.80±0.32)×1012 e/cm2 for x = 0.054 and (4.38±0.36)×1012 e/cm2 for x = 0.09. These values are smaller than those predicted by recent theoretical calculations, but in good agreement with values inferred from a number of optical experiments. © 2004 American Institute of Physics.
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73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
81.05.Ea III-V semiconductors
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Quantitative microwave evanescent microscopy of dielectric thin films using a recursive image charge approach

Chen Gao, Bo Hu, Pu Zhang, Mengming Huang, Wenhan Liu, and I. Takeuchi

Appl. Phys. Lett. 84, 4647 (2004); http://dx.doi.org/10.1063/1.1759389 (3 pages) | Cited 15 times

Online Publication Date: 19 May 2004

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A recursive image charge approach has been successfully developed for quantitative microwave microscopy of dielectric thin films using the scanning evanescent microwave microscope. With this approach and the recursion-to-circulation algorithm, frequency shift of the microscope as functions of the thickness of the film, dielectric constants of the film and the substrate can be efficiently computed in a circulation way. © 2004 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
77.55.-g Dielectric thin films
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Vacancy ordering in reduced barium titanate

David I. Woodward, Ian M. Reaney, Gaiying Y. Yang, Elizabeth C. Dickey, and Clive A. Randall

Appl. Phys. Lett. 84, 4650 (2004); http://dx.doi.org/10.1063/1.1759390 (3 pages) | Cited 30 times

Online Publication Date: 19 May 2004

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A crystal structure is proposed for reduced barium titanate, BaTiO3−δ, δ≈0.33, formed during the degradation of Ni–BaTiO3 X7R multilayer ceramic capacitors. High-resolution transmission electron microscopy and selected-area electron diffraction have been used in combination with computer simulations to show that oxygen vacancies accrete on every third pseudocubic {111} plane, resulting in a cell with space group P3m1. Additionally, from electron energy loss spectroscopy, it is proposed that Ti4+ is reduced to Ti3+ as a mechanism of charge compensation within oxygen-deficient octahedra. © 2004 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
61.72.J- Point defects and defect clusters
61.66.Fn Inorganic compounds
79.20.Uv Electron energy loss spectroscopy
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Thermal diffusivity and conductivity of supercooled liquid in Zr41Ti14Cu12Ni10Be23 metallic glass

Michiaki Yamasaki, Shinya Kagao, Yoshihito Kawamura, and Kenji Yoshimura

Appl. Phys. Lett. 84, 4653 (2004); http://dx.doi.org/10.1063/1.1759768 (3 pages) | Cited 21 times

Online Publication Date: 19 May 2004

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We measured the thermal diffusivity of amorphous solid and supercooled liquid in a Zr41Ti14Cu12Ni10Be23 bulk metallic glass (BMG) and its crystalline counterpart alloy at temperatures ranging from room temperature to 700 K, using a laser flash method. The thermal diffusivity and conductivity of the amorphous solid were weakly temperature dependent and increased with increasing temperature up to the glass transition temperature. The thermal diffusivity of the supercooled liquid was approximately 3.5×10−6 m2 s−1 and quite constant with temperature. The amorphous solid and supercooled liquid of Zr41Ti14Cu12Ni10Be23 BMG showed lower thermal diffusivity and conductivity than the crystalline counterpart in the range from room temperature to crystallization temperature. © 2004 American Institute of Physics.
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61.43.Dq Amorphous semiconductors, metals, and alloys
66.70.-f Nonelectronic thermal conduction and heat-pulse propagation in solids; thermal waves
64.70.P- Glass transitions of specific systems
64.70.Q- Theory and modeling of the glass transition
64.70.K- Solid-solid transitions
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Fast Fourier demodulation

Yuval Carmon and Erez N. Ribak

Appl. Phys. Lett. 84, 4656 (2004); http://dx.doi.org/10.1063/1.1759770 (2 pages) | Cited 3 times

Online Publication Date: 19 May 2004

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We present a fast Fourier demodulation method for calculating the distortion in a repetitive pattern. The technique is based on applying digital demodulation, then using only the anti-Hermitian part of the pattern in Fourier space. After demodulation, we are left with the Fourier transform of the sought phase information only. Using also the Hermitian part, we would have gotten the object itself. We investigate the boundaries of the technique, as related to aberration content, amplitude variations, and sensitivity to noise. © 2004 American Institute of Physics.
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02.30.Nw Fourier analysis
02.70.-c Computational techniques; simulations
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Magnetization dependence on strain in the Ni–Mn–Ga magnetic shape memory material

I. Suorsa, E. Pagounis, and K. Ullakko

Appl. Phys. Lett. 84, 4658 (2004); http://dx.doi.org/10.1063/1.1759771 (3 pages) | Cited 11 times

Online Publication Date: 19 May 2004

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Magnetic shape memory (MSM) materials can generate up to 10% strain when exposed to a magnetic field. The magnetization of the MSM material is closely related to its strain level. Modeling this relationship is of prime importance, especially in sensor and motion generation applications. In the present work, the magnetization curve of a Ni2MnGa MSM material was measured at different strain levels. The measurements were performed at magnetic fields of up to 130 kA/m, which includes the range used in most sensor applications. The measurement setup is described, and the results are compared with two models of magnetization dependence on strain, a linear and a nonlinear model. It is demonstrated that at high magnetic field strength values the relationship is linear, while at low fields (H<40 kA/m) the dependence between the strain and the magnetization is nonlinear. © 2004 American Institute of Physics.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Rs Electrical and magnetic properties related to treatment conditions
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Stress profile and thermal expansion of layered materials determined from surface stresses

Jürgen Malzbender

Appl. Phys. Lett. 84, 4661 (2004); http://dx.doi.org/10.1063/1.1759773 (2 pages) | Cited 4 times

Online Publication Date: 19 May 2004

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A simple method of inferring the stress profile and the effective difference in thermal expansion or strain in an unconstrained elastic multilayer system from a measurement of a limited number of surface stresses as obtained for example using x-ray diffraction or Raman spectroscopy is outlined. Explicit relationships are given for bilayered systems. The analysis procedure is exemplified for literature data of electronics materials, solid oxide fuel cells and thermal barrier systems. Following the outlined procedure, a determination of the stress profile and difference in thermal expansion for composites of alternating layers is also possible. © 2004 American Institute of Physics.
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65.40.De Thermal expansion; thermomechanical effects
78.30.Hv Other nonmetallic inorganics
82.47.Ed Solid-oxide fuel cells (SOFC)
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Low-resistance and transparent ohmic contacts to p-type GaN using Zn–Ni solid solution/Au scheme

June-O Song, Dong-Seok Leem, and Tae-Yeon Seong

Appl. Phys. Lett. 84, 4663 (2004); http://dx.doi.org/10.1063/1.1759774 (3 pages) | Cited 5 times

Online Publication Date: 19 May 2004

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High-quality Zn–Ni solid solution(8 nm)/Au(8 nm) ohmic contacts on p-GaN (5×1017 cm−3) have been investigated by means of current–voltage (I–V) measurements and x-ray photoemission spectroscopy. The as-deposited contact shows nonlinear I–V characteristics. However, oxidizing the contacts at 530 °C for 1 min in air ambient gives rise to considerable improvement in their I–V behaviors, yielding a specific contact resistance of 5.2×10−5 Ω cm2. The light transmittance of the annealed Zn–Ni solid solution/Au contacts is measured to be better than 74% at a wavelength of 470 nm. Green light-emitting diodes (LEDs) fabricated with the annealed Zn–Ni solid solution/Au contacts give a forward-bias voltage of 3.39 V at an injection current of 20 mA, which is better than that of the LEDs with the oxidized Ni/Au contacts. © 2004 American Institute of Physics.
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73.40.Cg Contact resistance, contact potential
73.40.Rw Metal-insulator-metal structures
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NbO as gate electrode for n-channel metal-oxide-semiconductor field-effect-transistors

W. Gao, J. F. Conley, and Y. Ono

Appl. Phys. Lett. 84, 4666 (2004); http://dx.doi.org/10.1063/1.1759780 (3 pages) | Cited 1 time

Online Publication Date: 19 May 2004

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Niobium mono-oxide (NbO) is investigated as a potential candidate for gate electrode to replace poly-silicon gate in metal-oxide-semiconductor field-effect transistors. NbO was found to have a work function of 4.18±0.05 eV on SiO2 and to be stable up to 1000 °C with SiO2 and HfO2 gate dielectrics. The low work function and high stability make NbO suitable for n-channel metal-oxide-semiconductor field-effect transistors devices. The method of deposition is critical during the fabrication to minimize the incorporation of Nb, NbO2, and Nb2O5 which are detrimental to the stability and conductivity of the gate electrode and extra care is needed to avoid further oxidation of NbO. © 2004 American Institute of Physics.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.61.Ng Insulators
81.15.Cd Deposition by sputtering
85.30.Tv Field effect devices
68.55.A- Nucleation and growth
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Guided self-assembly of metallic nanowires and channels

B. Erdem Alaca, Huseyin Sehitoglu, and Taher Saif

Appl. Phys. Lett. 84, 4669 (2004); http://dx.doi.org/10.1063/1.1759781 (3 pages) | Cited 25 times

Online Publication Date: 19 May 2004

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A method is presented to form metallic nanowires and nanochannels by guided self-assembly. The method relies on an initial plasma-enhanced chemical vapor deposition of a silicon oxide film with altered chemistry on a silicon wafer, and the cracking of the film due to tensile stresses upon annealing. The fabricated stress concentration features on the Si substrate control the number of cracks and their orientation. These cracks are then filled with electroless nickel, and the subsequent removal of SiO2 produces a controlled network of nanowires of about 100 nm in dimension. In addition to nanowires, nanobridges, and nanocantilevers have also been fabricated by releasing the wires, confirming that the resulting structures are rather robust. © 2004 American Institute of Physics.
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81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.40.Gh Other heat and thermomechanical treatments
68.60.Bs Mechanical and acoustical properties
81.15.Pq Electrodeposition, electroplating
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials
68.35.Gy Mechanical properties; surface strains
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