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19 Mar 2007

Volume 90, Issue 12, Articles (12xxxx)

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Appl. Phys. Lett. 90, 123101 (2007); http://dx.doi.org/10.1063/1.2716242 (3 pages)

G. Z. Shen, Y. Bando, J. Q. Hu, and D. Golberg
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Effects of carbon nanotubes on electro-optical characteristics of liquid crystal cell driven by in-plane field

Sang Youn Jeon, Seung Hwan Shin, Seok Jin Jeong, Seung Hee Lee, Seok Ho Jeong, Young Hee Lee, Hyun Chul Choi, and Kyeong Jin Kim

Appl. Phys. Lett. 90, 121901 (2007); http://dx.doi.org/10.1063/1.2714311 (3 pages) | Cited 25 times

Online Publication Date: 19 March 2007

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Homogeneously aligned nematic liquid crystal (LC) cells doped with carbon nanotubes (CNTs) driven by an in-plane field were fabricated and their electro-optic characteristics were investigated. The effective cell retardation values showed no difference between doped and undoped LC cells in the absence of electric field. However, in the presence of electric field, it was smaller in the CNT-doped cell than in the undoped cell, resulting in the decrease of transmittance. Furthermore, the CNT-doped cell exhibited a slight increase in the driving voltage due to the increase of the twist elastic constant (K22) and the decrease in the decay response time due to the decrease in the rotational viscosity (γ) and γ/K22 compared to the undoped cell.
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42.70.Df Liquid crystals
78.20.Jq Electro-optical effects
61.72.up Other materials
62.10.+s Mechanical properties of liquids
66.20.-d Viscosity of liquids; diffusive momentum transport

Assessment of accumulated fatigue damage in solid plates using nonlinear Lamb wave approach

Mingxi Deng and Junfeng Pei

Appl. Phys. Lett. 90, 121902 (2007); http://dx.doi.org/10.1063/1.2714333 (3 pages) | Cited 26 times

Online Publication Date: 19 March 2007

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The feasibility of using the nonlinear effect of primary Lamb wave propagation for assessing accumulated fatigue damage in solid plates is theoretically analyzed. After the aluminum sheets are subjected to tension-tension fatigue loading for different numbers of loading cycles, they are subjected to ultrasonic tests near the driving frequency where Lamb waves have a strong nonlinearity. This is followed by the measurement of the amplitude-frequency curves for second harmonics of the considered Lamb waves. The experimental results show that the effect of second-harmonic generation by Lamb wave propagation is very sensitive to the accumulation of fatigue damage of solid plates.
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46.50.+a Fracture mechanics, fatigue and cracks
43.35.Pt Surface waves in solids and liquids
43.25.-x Nonlinear acoustics
68.35.Iv Acoustical properties
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.M- Structural failure of materials

Symmetry properties and anisotropic excitonic response for GaN films grown on semipolar (11−22)-, (10−11)-, and (10−13)-oriented GaN substrates

Bernard Gil

Appl. Phys. Lett. 90, 121903 (2007); http://dx.doi.org/10.1063/1.2715003 (3 pages) | Cited 6 times

Online Publication Date: 19 March 2007

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The author analyzes the optical properties of GaN homoepitaxies grown on semipolar (11−2x)- and (10−1x)-oriented GaN substrates. He works here in the specific cases of (11−22)-, (10−11)-, and (10−13)-orientations which currently deserve intense experimental activity. The author finds the optical anisotropy of the GaN films to be strictly ruled by the angle between the growth plane and the ⟨001⟩ direction of the GaN material.
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78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena

Heteroepitaxial growth of sixfold symmetric osmium on Si (111) and Si (100)

Tai-Yen Peng, C. K. Lo, Y. D. Yao, and San-Yuan Chen

Appl. Phys. Lett. 90, 121904 (2007); http://dx.doi.org/10.1063/1.2711658 (3 pages) | Cited 3 times

Online Publication Date: 19 March 2007

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Growing sixfold symmetric osmium (Os) epitaxial films with suitable buffer layers was developed. Using a Cu buffer layer, the lattice mismatch between Os (0002) and Si (100) was significantly reduced from >30% to ∼ 7% to grow Os films with twin relationships and weak sixfold symmetries. On the other hand, the Cu/Au buffer layer was selected to form a fcc (111) surface mesh on H–Si (111)-1×1, and therefore sixfold symmetric Os films were grown due to the lower lattice mismatch. Such growth properties may be applied in the high density magnetic random access memory manufacturing processes to connect the magnetic tunnel junction growth and Cu metal line directly.
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68.55.A- Nucleation and growth
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
68.35.Gy Mechanical properties; surface strains
68.60.Bs Mechanical and acoustical properties
61.72.Mm Grain and twin boundaries

Anomalous thermal stability of cubic tin confined in a nanotube

B. Wang, G. Ouyang, Y. H. Yang, and G. W. Yang

Appl. Phys. Lett. 90, 121905 (2007); http://dx.doi.org/10.1063/1.2715136 (3 pages) | Cited 5 times

Online Publication Date: 19 March 2007

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In situ observations of transmission electron microscopy have indicated that the cubic Sn phase confined in a nanotube has extreme stability even when the temperature is more than 700 °C, significantly higher than the melting point (231.9 °C) of tin. A thermodynamic model was established to pursue the physical origins of the anomalous stability of the confined cubic Sn phase. It was found that the epitaxial interface confinement of SnO2/Sn and the difference of thermal expansion between the core and shell play crucial roles in the unusual stability of the cubic Sn at high temperature.
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65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
61.46.Fg Nanotubes

Schottky ultraviolet photodiode using a ZnO hydrothermally grown single crystal substrate

Haruyuki Endo, Mayo Sugibuchi, Kousuke Takahashi, Shunsuke Goto, Shigeaki Sugimura, Kazuhiro Hane, and Yasube Kashiwaba

Appl. Phys. Lett. 90, 121906 (2007); http://dx.doi.org/10.1063/1.2715100 (3 pages) | Cited 32 times

Online Publication Date: 20 March 2007

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A Schottky ultraviolet photodiode using a (0001) ZnO single crystal grown by the hydrothermal growth method is reported. The photodiode consisted of a semitransparent Pt film for the Schottky electrode and an Al thin film for the Ohmic electrode. The photodiode had polarity dependences on current-voltage characteristics and on responsivity. In the case of the Schottky electrode on the zinc surface, the responsivity was 0.185 A/W at a wavelength of 365 nm. On the other hand, the responsivity was 0.09 A/W for an oxygen surface. The results are attributed to the polarity dependences of surface chemical reactivity and the surface state density on ZnO surfaces.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes
85.60.Gz Photodetectors (including infrared and CCD detectors)

Microstructure analysis of c-axis oriented aluminum nitride thin films by high-resolution transmission electron microscopy

Z. Q. Yao, Q. Ye, Y. Q. Li, Y. S. Zou, W. J. Zhang, and S. T. Lee

Appl. Phys. Lett. 90, 121907 (2007); http://dx.doi.org/10.1063/1.2715173 (3 pages) | Cited 7 times

Online Publication Date: 20 March 2007

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The microstructure, in particular, the surface and interface regions, of the c-axis orientated AlN films deposited on Si (100) substrates was studied. The films showed an evolutionary columnar growth process. In contrast to the previous reports, high-resolution transmission electron microscopy revealed that the AlN films grew directly on substrates without an amorphous interlayer, despite the large lattice mismatch between AlN and Si. The occurrence of misoriented and/or amorphous top layer suggested a subsurface growth/relaxation process of the AlN films by reactive sputtering.
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81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology
68.55.A- Nucleation and growth
81.15.Cd Deposition by sputtering

Wafer-level microelectromechanical system structural material test by electrical signal before pull-in

Yuh-Chung Hu and Po-Yuan Huang

Appl. Phys. Lett. 90, 121908 (2007); http://dx.doi.org/10.1063/1.2714998 (3 pages) | Cited 1 time

Online Publication Date: 21 March 2007

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The letter develops a wafer-level testing method to examine Young’s modulus and residual stress of structural material of capacitive microdevice by measuring the pre-pull-in capacitance variation of the microtest beam made of the material to be tested. The required instrument is only a precision LCR meter. The extracted Young’s moduli and residual stresses of demonstrated samples agree very well with the experimental measurement. The present method is expected to be applicable to the wafer-level testing in microdevice manufacture and compatible with the wafer-level testing in integrated circuit industry, since the test and pickup signals are both electrical.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
81.70.Bt Mechanical testing, impact tests, static and dynamic loads

Phase transition of ultrathin AlN interlayer at AlGaN/GaN interface

Duanjun Cai and Junyong Kang

Appl. Phys. Lett. 90, 121909 (2007); http://dx.doi.org/10.1063/1.2711379 (3 pages)

Online Publication Date: 21 March 2007

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The authors report the wurtizite to zinc-blende phase transition of ultrathin AlN interlayer at the interface of AlGaN/GaN. The shape transformation of the pinhole from hexagon to dodecagon exhibits the structural transition of the interfacial layer, where exists an AlN segregation interlayer. By transmission electron diffraction, the structure of AlN interlayer is determined to be zinc blende. Ab initio simulations demonstrate that the epitaxial strain favors the formation of the high Al segregation and the phase transition.
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64.70.K- Solid-solid transitions
68.35.Ct Interface structure and roughness
68.55.-a Thin film structure and morphology
64.75.-g Phase equilibria

Effect of ionization rates on dynamic recovery processes during electron-beam irradiation of 6H-SiC

In-Tae Bae, William J. Weber, Manabu Ishimaru, and Yoshihiko Hirotsu

Appl. Phys. Lett. 90, 121910 (2007); http://dx.doi.org/10.1063/1.2715135 (3 pages) | Cited 6 times

Online Publication Date: 21 March 2007

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The authors have investigated the effects of 200 and 300 keV electron-beam irradiations on amorphization in 6H-SiC at 100 and 295 K. Amorphization is induced by the accumulation of defects produced by direct atomic displacements. Dynamic recovery of these defects during irradiation, due to temperature increases and ionization effects, results in increases in the amorphization dose. By comparing with previous data for 2 MeV electrons and 1.5 MeV Xe ions, the results demonstrate that ionization-enhanced recovery in 6H-SiC dramatically increases above an ionization rate threshold.
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61.82.Fk Semiconductors
61.80.Fe Electron and positron radiation effects
61.43.Dq Amorphous semiconductors, metals, and alloys

Role of gross well-width fluctuations in bright, green-emitting single InGaN/GaN quantum well structures

Nicole K. van der Laak, Rachel A. Oliver, Menno J. Kappers, and Colin J. Humphreys

Appl. Phys. Lett. 90, 121911 (2007); http://dx.doi.org/10.1063/1.2715166 (3 pages) | Cited 25 times

Online Publication Date: 21 March 2007

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Gross well-width fluctuations have been observed by transmission electron microscopy (TEM) in single InGaN/GaN quantum wells (QWs) grown by metal-organic vapor phase epitaxy. Similar thickness variations are observed in commercial, green InGaN/GaN multi-QW light emitting diodes. Atomic force microscopy studies of equivalent epilayers suggest that these fluctuations arise from a network of interlinking InGaN strips, which are found (using TEM) to be indium rich at their centers. Plan-view TEM indicates that 90±8% of all threading dislocations (TDs) intersect the QW plane between the InGaN strips. Excitons may be localized at the strips’ centers, preventing nonradiative recombination at TDs.
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68.65.Fg Quantum wells
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
71.35.-y Excitons and related phenomena

Modified efficient cluster packing model for calculating alloy compositions with high glass forming ability

A. P. Wang, J. Q. Wang, and E. Ma

Appl. Phys. Lett. 90, 121912 (2007); http://dx.doi.org/10.1063/1.2715172 (3 pages) | Cited 4 times

Online Publication Date: 21 March 2007

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The efficient cluster packing model for bulk metallic glasses (BMGs) has been modified and extended to allow quantitative predictions of alloy compositions with high glass forming ability. The compositions calculated using this simple method compare favorably with the vast majority of the BMGs discovered in recent years. In addition, a Hf-based BMG has been obtained at the predicted composition.
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61.43.Fs Glasses
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)

Improved conductivity of transparent single-wall carbon nanotube thin films via stable postdeposition functionalization

Bhavin B. Parekh, Giovanni Fanchini, Goki Eda, and Manish Chhowalla

Appl. Phys. Lett. 90, 121913 (2007); http://dx.doi.org/10.1063/1.2715027 (3 pages) | Cited 78 times

Online Publication Date: 22 March 2007

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A simple postdeposition method for improving the conductivity of transparent and conducting single-wall carbon nanotube (SWNT) thin films via exposure to nitric acid and thionyl chloride is reported. A systematic study on a range of films of variable density and from different commercial sources of SWNTs is performed. The functionalized films possess sheet resistances as low as that of indium tin oxide (ITO) ( ∼ 30 Ω/◻) albeit at lower transmittance ( ∼ 50%). At 80±5% transmittance, the functionalized films have resistance values ranging from 150 to 300 Ω/◻. The SWNT films, however, are more flexible than ITO. The stability of the functionalized films upon annealing and processing in solvents (water, methanol, and chloroform) is also reported.
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73.63.Fg Nanotubes
78.67.Ch Nanotubes
78.30.Hv Other nonmetallic inorganics

Creep in protective α-Al2O3 thermally grown on β-NiAl

B. W. Veal, A. P. Paulikas, and P. Y. Hou

Appl. Phys. Lett. 90, 121914 (2007); http://dx.doi.org/10.1063/1.2715105 (3 pages) | Cited 10 times

Online Publication Date: 22 March 2007

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The authors report systematic measurements of creep relaxation in α-Al2O3, thermally grown in air on (100) single crystals of stoichiometric β-NiAl, at temperatures between 950 and 1100 °C. Creep was monitored using time dependent in situ measurements of strain relaxation in the oxide following imposition of a stress resulting from a sudden temperature change. The in-plane elastic strain was obtained using a sin2 ψ x-ray diffraction technique exploiting synchrotron radiation. The authors found that strain relaxation rates were comparable to those observed in fine grained α-Al2O3 ceramics when the latter results were extrapolated to the lower temperatures examined here. Creep rates at stress levels of 100 MPa, or less, are proportional to σn, with n ⩽ 2, consistent with a diffusional creep mechanism.
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81.65.-b Surface treatments
81.40.Lm Deformation, plasticity, and creep
62.20.Hg Creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
68.60.Bs Mechanical and acoustical properties

Defect distribution in a-plane GaN on Al2O3

F. Tuomisto, T. Paskova, R. Kröger, S. Figge, D. Hommel, B. Monemar, and R. Kersting

Appl. Phys. Lett. 90, 121915 (2007); http://dx.doi.org/10.1063/1.2715128 (3 pages) | Cited 12 times

Online Publication Date: 22 March 2007

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The authors studied the structural and point defect distributions of hydride vapor phase epitaxial GaN film grown in the [11−20] a direction on (1−102) r-plane sapphire with metal-organic vapor phase deposited a-GaN template using transmission electron microscopy, secondary ion mass spectrometry, and positron annihilation spectroscopy. Grown-in extended and point defects show constant behavior as a function of thickness, contrary to the strong nonuniform defect distribution observed in GaN grown along the [0001] direction. The observed differences are explained by orientation-dependent and kinetics related defect incorporation.
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68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.S- Impurities in crystals
61.72.Nn Stacking faults and other planar or extended defects
61.72.Lk Linear defects: dislocations, disclinations
61.72.J- Point defects and defect clusters
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

Tension-compression asymmetry in homogeneous dislocation nucleation in single crystal copper

M. A. Tschopp and D. L. McDowell

Appl. Phys. Lett. 90, 121916 (2007); http://dx.doi.org/10.1063/1.2715137 (3 pages) | Cited 9 times

Online Publication Date: 22 March 2007

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This letter addresses the dependence of homogeneous dislocation nucleation on the crystallographic orientation of pure copper under uniaxial tension and compression. Molecular dynamics simulation results with an embedded-atom method potential show that the stress required for homogeneous dislocation nucleation is highly dependent on the crystallographic orientation and the uniaxial loading conditions; certain orientations require a higher stress in compression (e.g., [110] and [111]) and other orientations require a higher stress in tension ([100]). Furthermore, the resolved shear stress in the slip direction is unable to completely capture the dependence of homogeneous dislocation nucleation on crystal orientation and uniaxial loading conditions.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.50.-f Structure of bulk crystals

Ordering of ErAs nanoparticles embedded in epitaxial InGaAs layers

Dmitri O. Klenov, Joshua M. O. Zide, James M. LeBeau, Arthur C. Gossard, and Susanne Stemmer

Appl. Phys. Lett. 90, 121917 (2007); http://dx.doi.org/10.1063/1.2715174 (3 pages) | Cited 7 times

Online Publication Date: 22 March 2007

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The authors report on the microstructures of semimetallic ErAs nanoparticles embedded in epitaxial InGaAs layers by codeposition of Er. The size of the particles (1–3 nm) was approximately independent of the amount of deposited Er. At large ErAs concentrations (>3 at. %), the particles showed a strong tendency to order on the {114} planes of the semiconductor matrix. The ordering was only observed along one of the ⟨110⟩ directions, likely reflecting the strong anisotropy in surface diffusion.
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68.35.Fx Diffusion; interface formation
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation

Velcro® nonlinear mechanics

Nicola Maria Pugno

Appl. Phys. Lett. 90, 121918 (2007); http://dx.doi.org/10.1063/1.2715478 (2 pages) | Cited 5 times

Online Publication Date: 22 March 2007

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In this letter a Velcro® nonlinear mechanics is presented. In particular, a calculation of the “elastic strength” of hooks with friction is derived. The author quantifies, as the intuition and Velcro® material suggest, that hooks (and loops) allow reversible strong attachment, finding elastic plastic or hyperelastic nonlinear behaviors, as a function of the competition between friction and finite displacements. Thus, the author presents here a Velcro® nonlinear mechanics to design and optimize hooked systems.
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46.25.-y Static elasticity
46.55.+d Tribology and mechanical contacts
46.35.+z Viscoelasticity, plasticity, viscoplasticity

Growth of nonpolar AlN (11math0) and (1math00) films on SiC substrates by flow-rate modulation epitaxy

Tetsuya Akasaka, Yasuyuki Kobayashi, and Toshiki Makimoto

Appl. Phys. Lett. 90, 121919 (2007); http://dx.doi.org/10.1063/1.2716207 (3 pages) | Cited 12 times

Online Publication Date: 23 March 2007

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Nonpolar AlN (11math0) and (1math00) films were grown on SiC substrates by flow-rate modulation epitaxy (FME), wherein trimethylaluminum and NH3 were alternately supplied. FME provides both AlN (11math0) and (1math00) films with good crystallinity and smooth surfaces, whereas AlN (1math00) films obtained by conventional metal-organic chemical vapor deposition exhibit poor crystallinity and rough surfaces with deep trenches consisting of (000math) and (1math01) N-face microfacets. FME effectively eliminates these trenches, because the microfacets are unstable and have faster growth rates because of the enhanced migration of Al atoms in the absence of excess N surface coverage under the Al-rich condition.
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68.55.A- Nucleation and growth
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.05.Ea III-V semiconductors
68.55.-a Thin film structure and morphology

Characterization of the texture of silicide films using electron backscattered diffraction

K. De Keyser, C. Detavernier, and R. L. Van Meirhaeghe

Appl. Phys. Lett. 90, 121920 (2007); http://dx.doi.org/10.1063/1.2716362 (3 pages) | Cited 8 times

Online Publication Date: 23 March 2007

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Electron backscattered diffraction (EBSD) was used to characterize the texture of NiSi films. The various texture components (i.e., the types of preferred orientation, e.g., axiotaxy or epitaxy) could be identified, and their volume fraction could be quantified. Moreover, the spatial distribution of texture components could be studied in blanket films. Orientation imaging microscopy using EBSD is a promising technique to study the texture of silicide or germanide films both on blanket and patterned substrates.
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68.55.-a Thin film structure and morphology
79.20.Hx Electron impact: secondary emission
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