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15 Apr 2009

Volume 105, Issue 8, Articles (08xxxx)

Issue Cover Spotlight Figure

J. Appl. Phys. 105, 081101 (2009); http://dx.doi.org/10.1063/1.3091395 (20 pages)

N. G. Rudawski, K. S. Jones, S. Morarka, M. E. Law, and R. G. Elliman
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Surface structure of strontium titanate

Jianli Wang, Min Fu, X. S. Wu, and Dongmei Bai

J. Appl. Phys. 105, 083526 (2009); http://dx.doi.org/10.1063/1.3106615 (8 pages) | Cited 12 times

Online Publication Date: 22 April 2009

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Perfect and defective surface structures for (001) SrTiO3 are determined in considering a supercell with 11 atomic layers using the first-principles calculations. The amplitude of the surface rumpling for the SrO-terminated surface is much larger than that for the TiO2-terminated surface, although both SrO- and TiO2-terminated surfaces are stable for a comparable range of the TiO2 chemical potential. The distance between the first and second planes compresses while that of the second and third planes expands due to the relaxation of the slab. The top sites of the oxygen atoms of SrO-termined surface and the fourfold symmetry hollow sites of TiO2-termined surface are favorable for Ti or Sr adsorbate. The relative stability of the defect species or reactions varies with the equilibrium conditions. The dominant surface defect is Ti substitutional defect and a TiO–TiO2 double layers may form at the surface, which has been confirmed by experiments.
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68.47.Gh Oxide surfaces
68.35.bt Other materials

Effect of interfacial roughness correlation on diffuse scattering intensity in a neutron supermirror

R. Maruyama, D. Yamazaki, T. Ebisawa, and K. Soyama

J. Appl. Phys. 105, 083527 (2009); http://dx.doi.org/10.1063/1.3108542 (8 pages) | Cited 3 times

Online Publication Date: 22 April 2009

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Neutron supermirrors are increasingly important devices for transporting, bending, and focusing neutron beams. Reflected neutrons from a supermirror are divided into specular and off-specular (diffuse) components. Suppression of the diffuse component is important since it reduces the signal-to-noise ratio, a serious problem when a supermirror is used in a focusing system for purposes such as small angle scattering measurements. The diffuse intensity can be decreased by more than one order of magnitude by adopting NiC/Ti multilayers instead of conventional Ni/Ti multilayers. In order to obtain insight into the mechanism that controls the diffuse intensity from a supermirror, the crystal structure of Ni and NiC monolayers and the interface structure of Ni/Ti and NiC/Ti multilayers were investigated. The crystallite size in the NiC monolayer was found to be smaller than that in the Ni monolayer by a factor of 4.1 by x-ray diffraction measurement. The interface structure of the Ni/Ti and NiC/Ti multilayers was observed by neutron reflectivity and diffuse intensity measurements. For the NiC/Ti multilayer, the lateral correlation length was smaller by a factor of 3.6 than for the Ni/Ti multilayer, whereas the vertical correlation length was greater by a factor exceeding 25. Diffuse intensity calculations based on the distorted wave Born approximation revealed that these differences explain the difference between the diffuse intensity of the Ni/Ti and NiC/Ti supermirrors. This study demonstrated that a multilayer with a large vertical correlation length and a small lateral correlation length effectively suppresses the diffuse intensity from a supermirror.
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68.35.Ct Interface structure and roughness
68.65.Cd Superlattices
03.75.Be Atom and neutron optics

Shockless compression of z-cut quartz to 7 GPa

T. Jaglinski, B. M. LaLone, C. J. Bakeman, and Y. M. Gupta

J. Appl. Phys. 105, 083528 (2009); http://dx.doi.org/10.1063/1.3109211 (6 pages) | Cited 3 times

Online Publication Date: 22 April 2009

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Using a recently developed compact pulsed power generator (CPPG), z-cut quartz samples were subjected to shockless uniaxial strain compression to 7 GPa peak stress. Over this stress range, the behavior of z-cut quartz under shock compression [ J. Appl. Phys. 88, 5671 (2000) ] is nonlinear elastic and in good agreement with predictions based on the measured values of the second and third order elastic constants. In-material and free surface velocities were measured in the present work and analyzed, using a Lagrangian analysis, to provide a continuous loading curve for z-cut quartz. The wavelet speed-particle velocity (Cu-u, where Cu ≡ (Δh/Δt)u) results were somewhat sensitive to the CPPG panel design details, as well as the velocity data acquisition and reduction techniques. Improvements to provide optimal data were discussed and used to provide accurate longitudinal stress-density response to 7 GPa (6% density compression). The Cu-u curves, a more stringent measure of the material response to nonlinear compression, were within 0.6% of the values predicted using shock compression measurements. This excellent agreement demonstrates that the shockless compression response of quartz is indistinguishable from the shock response in the nonlinear elastic regime and provides a good foundation for comparing the inelastic response of solids under shockless and shock compression. The present work also demonstrated the use of the CPPG as a laboratory capability for examining the shockless compression of materials.
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81.05.-t Specific materials: fabrication, treatment, testing, and analysis
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Improving the acousto-optical interaction in a Mach–Zehnder interferometer

Maria B. Dühring and Ole Sigmund

J. Appl. Phys. 105, 083529 (2009); http://dx.doi.org/10.1063/1.3114552 (9 pages) | Cited 9 times

Online Publication Date: 22 April 2009

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A method for modeling the interaction of the mechanical field from a surface acoustic wave and the optical field in the waveguides of a Mach–Zehnder interferometer is presented. The surface acoustic wave is generated by an interdigital transducer using a linear elastic plane model of a piezoelectric, inhomogeneous material, and reflections from the boundaries are avoided by applying perfectly matched layers. The optical modes in the waveguides are modeled by time-harmonic wave equations for the magnetic field. The two models are coupled using stress-optical relations and the change in effective refractive index introduced in the Mach–Zehnder interferometer arms by the stresses from the surface acoustic wave is calculated. It is then shown that the effective refractive index of the fundamental optical mode increases at a surface acoustic wave crest and decreases at a trough. The height and the width of the waveguides are varied for a silicon on insulator sample, and it is shown that the difference in effective refractive index between the waveguides can be increased 12 times for the right choice of waveguide size such that the optical modulation is improved. The difference is four times bigger if the waveguides are kept single moded. It is furthermore shown that the difference increases more than ten times when the waveguides are buried below the surface, where the mechanical stresses have their maximum, and in the case where two interdigital transducers are used the difference is increased 1.5 times.
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78.20.hb Piezo-optical, elasto-optical, acousto-optical, and photoelastic effects
07.60.Ly Interferometers
43.38.Fx Piezoelectric and ferroelectric transducers
43.35.Sx Acoustooptical effects, optoacoustics, acoustical visualization, acoustical microscopy, and acoustical holography
43.20.Mv Waveguides, wave propagation in tubes and ducts

Improved atomistic damage generation model for binary collision simulations

Iván Santos, Luis A. Marqués, Lourdes Pelaz, and Pedro López

J. Appl. Phys. 105, 083530 (2009); http://dx.doi.org/10.1063/1.3110077 (8 pages) | Cited 7 times

Online Publication Date: 23 April 2009

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We have carried out a classical molecular dynamics study to quantify the conditions under which damage is generated by ion implantation in silicon at energies below the displacement threshold. The obtained results have been used to construct a general framework for damage generation which captures the transition from ballistic (high above the displacement threshold) to thermal (around and below the displacement threshold) regime. The model, implemented in a binary collision code, has been successfully used to simulate monatomic and especially molecular implantations, where nonlinear effects occur. It reproduces the amount and morphology of generated damage at atomic level in good agreement with classical molecular dynamics simulations but with a computational gain factor of ∼ 103 to ∼ 104. The incorporation of this damage model to process simulators will improve the prediction of amorphization conditions and provide a convenient tool for simulating molecular implants not available to date. Although this work has been focused on silicon, the model can be applied with appropriate calibration to other materials where the thermal regime of damage generation plays an important role.
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81.05.Cy Elemental semiconductors
61.72.uf Ge and Si

Electron microscopy study of CeOx–Pd/α-Al2O3 catalysts for methane dry reforming

M. S. Moreno, F. Wang, M. Malac, T. Kasama, C. E. Gigola, I. Costilla, and M. D. Sánchez

J. Appl. Phys. 105, 083531 (2009); http://dx.doi.org/10.1063/1.3115405 (6 pages) | Cited 2 times

Online Publication Date: 23 April 2009

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We have investigated the interaction between Pd and Ce in a (0.47 wt %) CeOx–Pd(1 wt %)/α-Al2O3 catalyst that is used in the reforming reaction of CH4 with CO2. The freshly reduced catalyst was characterized by various electron microscopy techniques, such as elemental mapping, Z-contrast imaging, and electron energy-loss spectroscopy to understand the role of Ce on a microscopic scale. The high spatial resolution elemental mapping indicates that CeOx is located in close proximity of the palladium nanoparticles. High-resolution lattice images and energy-loss spectra obtained in the vicinity of the Pd particles show an anisotropic distribution of CeOx crystallites limited to the interface region between Pd and the substrate but not covering the surface of the Pd nanoparticles. Energy-loss near edge fine structure of Pd M edges reveals that the Pd nanoparticles are not oxidized.
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89.20.Kk Engineering

In situ x-ray diffraction study of metal induced crystallization of amorphous germanium

W. Knaepen, S. Gaudet, C. Detavernier, R. L. Van Meirhaeghe, J. Jordan Sweet, and C. Lavoie

J. Appl. Phys. 105, 083532 (2009); http://dx.doi.org/10.1063/1.3110722 (7 pages) | Cited 15 times

Online Publication Date: 23 April 2009

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Metal induced crystallization (MIC) is a technique that lowers the crystallization temperature of amorphous semiconductors. The process has mainly been used to influence the crystallization of amorphous silicon (a-Si) and multiple studies on this subject have already been performed. The research of the MIC of amorphous Ge (a-Ge) has been mostly limited to the use of a Ni or Al film. This paper focuses on the characterization of the crystallization behavior of a-Ge films in the presence of 20 transition metals (Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Mn, Re, Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, and Al). The kinetics of the crystallization process are also systematically studied for the seven metals that lower the initial crystallization temperature the most. In addition, the influence of the thickness of the metal film was determined for the case of a Au and Al film. A comparison of the influence of the various metals on a-Ge and a-Si is made and the similarities and differences are discussed using existing models for the MIC process.
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64.70.kg Semiconductors
68.55.jd Thickness
61.43.Dq Amorphous semiconductors, metals, and alloys

Temperature dependence of excitonic transitions in a-plane AlN epitaxial layers

Hideaki Murotani, Takahiro Kuronaka, Yoichi Yamada, Tsunemasa Taguchi, Narihito Okada, and Hiroshi Amano

J. Appl. Phys. 105, 083533 (2009); http://dx.doi.org/10.1063/1.3116183 (6 pages) | Cited 4 times

Online Publication Date: 24 April 2009

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The excitonic optical properties of a-plane AlN epitaxial layers have been studied by means of temperature-dependent photoluminescence (PL) and optical reflectance (OR) spectroscopy. An exciton resonance and free-exciton luminescence were clearly observed up to room temperature in the OR and PL measurements, respectively. Analysis of the low temperature OR spectrum enabled us to obtain a splitting energy of 7.3 meV between longitudinal and transverse-exciton resonances for AlN, which was approximately one order of magnitude larger than that for GaN. An emission from the upper branch of the excitonic polariton was also observed at temperatures above 100 K, reflecting thermal repopulation of excitonic polaritons from the lower to the upper branch. In addition, the temperature dependence of the transverse-exciton resonance could be well described using an empirical equation based on Bose–Einstein statistics, in which the Einstein characteristic temperature was estimated to be 455 K.
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78.66.Fd III-V semiconductors
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)

Performance analysis and parametric optimum criteria of an irreversible Bose–Otto engine

Hao Wang, Sanqiu Liu, and Jizhou He

J. Appl. Phys. 105, 083534 (2009); http://dx.doi.org/10.1063/1.3103315 (8 pages) | Cited 5 times

Online Publication Date: 24 April 2009

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An irreversible cycle model of a Bose–Otto engine is established, in which finite time thermodynamic processes and the irreversibility result from the nonisentropic compression and expansion processes are taken into account. Based on the model, expressions for the power output and efficiency of the Bose–Otto engine are derived. On the basis of the thermodynamic properties of ideal Bose gas, the effects of the irreversibility and the compression ratio of the two isochoric processes on the performance of the Bose–Otto engine are revealed and some important performance parameters are optimized. Furthermore, some optimal operating regions including those for the power output, efficiency, and the temperatures of the cyclic working substance at two important state points are determined and evaluated. Finally, several special cases are discussed in detail.
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89.20.Kk Engineering

Correlated structural reordering and dopant redistribution in annealed polycrystalline CdTe

V. Consonni and G. Feuillet

J. Appl. Phys. 105, 083535 (2009); http://dx.doi.org/10.1063/1.3112019 (6 pages) | Cited 3 times

Online Publication Date: 27 April 2009

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Postdeposition heat treatments are found to strongly influence the structural and optical properties of chlorine doped polycrystalline CdTe films. From scanning electron microscopy images and diffraction measurements, annealing is shown to induce a major structural reordering. The strong texturation along the 〈100〉 orientation indicates that the overall crystalline quality has been considerably improved. Upon annealing, a bimodal distribution of grain sizes is also observed, which points out an abnormal grain growth mechanism. Additionally, deformation twins, which are detrimental for the transport properties, are replaced by thicker annealing twins. Through time-of-flight secondary ion mass spectroscopy and 4 K cathodoluminescence measurements, an overall decrease in the chlorine concentration and a spatial redistribution of chlorine atoms are evidenced and clearly correlated with the observed structural reordering: β acceptor complexes, which are commonly predominant in as-grown chlorine doped polycrystalline CdTe, are found to dissociate into chlorine donors and A centers upon annealing. This is attributed to the thermally activated diffusion of chlorine, which leads to its re-evaporation from the films. Furthermore, the low chlorine concentration in the annealed films allows one to infer a value of 135±3 meV for the ionization energy of the chlorine A centers, as deduced from the donor-acceptor pair position in the cathodoluminescence spectra.
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81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization
78.60.Hk Cathodoluminescence, ionoluminescence
78.66.Hf II-VI semiconductors
68.55.jm Texture
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.sh Impurity distribution

Void shape evolution and formation of silicon-on-nothing structures during hydrogen annealing of hole arrays on Si(001)

K. Sudoh, H. Iwasaki, R. Hiruta, H. Kuribayashi, and R. Shimizu

J. Appl. Phys. 105, 083536 (2009); http://dx.doi.org/10.1063/1.3116545 (5 pages) | Cited 8 times

Online Publication Date: 27 April 2009

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We have studied the structural evolution of voids in the Si substrate and the formation of silicon-on-nothing (SON) structures upon spontaneous reshaping of square arrays of cylindrical holes on Si(001) substrates by hydrogen annealing. Vertically elongated voids covered with {111}, {100}, {110}, and {113} facets are initially formed by the closure of the hole inlets. This step is followed by volume preserving shape changes of the faceted voids in the bulk Si. In situations where the hole-hole separation is sufficiently small, void coalescence occurs due to the shape changes of individual voids, leading to the formation of a SON structure. Until void coalescence, the shapes of individual voids change without being affected by the adjacent voids. Numerical simulations of the shape change of a completely faceted void via solely surface diffusion have been performed and have reproduced the observed shape change.
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61.72.Qq Microscopic defects (voids, inclusions, etc.)
68.35.Fx Diffusion; interface formation
68.35.bg Semiconductors
61.72.Cc Kinetics of defect formation and annealing

Comprehensive study of the Raman shifts of strained silicon and germanium

C.-Y. Peng, C.-F. Huang, Y.-C. Fu, Y.-H. Yang, C.-Y. Lai, S.-T. Chang, and C. W. Liu

J. Appl. Phys. 105, 083537 (2009); http://dx.doi.org/10.1063/1.3110184 (10 pages) | Cited 4 times

Online Publication Date: 27 April 2009

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Raman shifts are investigated on silicon and germanium substrates under the uniaxial tensile strain on various substrate orientations. The strain splits the triply degenerate optical (LO, TO) phonons at the zone center (math ≈ 0). The redshifts of Si Raman peaks induced by the tensile strain on all substrate orientations are observed. With the specific polarization of the incident light, however, the unusual blueshifts of Ge Raman peaks induced by the tensile strain are observed on (110) and (111) Ge substrates. By using the suitable phenomenological constants and taking the Raman selection rules into consideration, the experimental results are in reasonable agreement with the lattice dynamical theory.
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78.30.Am Elemental semiconductors and insulators
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
68.47.Fg Semiconductor surfaces
42.25.Ja Polarization

Addition effect of SnO in optical property of Bi2O3-containing aluminoborate glass

Hirokazu Masai, Yoshihiro Takahashi, and Takumi Fujiwara

J. Appl. Phys. 105, 083538 (2009); http://dx.doi.org/10.1063/1.3115472 (4 pages) | Cited 2 times

Online Publication Date: 27 April 2009

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We have found that an addition of SnO in a bismuth-containing aluminoborate glass, (CaO–B2O3–Bi2O3–Al2O3–TiO2) (CaBBAT), decreases both the optical absorption coefficient in the visible region and the relative intensity of x-ray photoelectron spectroscopy (XPS) signal at 157 eV. Since signal intensity of electron spin resonance (ESR) at g = 1.95 also decreased with increasing amount of SnO, it is suggested that bismuth radical-like species exist in the glass and that SnO reacts with the bismuth species. Concentration dependence of SnO in the XPS and in the ESR spectra shows that we can assign the observed signal to bismuth radical species in the glass. We, therefore, conclude that there is qualitative correlation between the optical absorption in the visible region and bismuth radical species in the CaBBAT glass.
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78.40.Pg Disordered solids
79.60.-i Photoemission and photoelectron spectra
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
76.30.-v Electron paramagnetic resonance and relaxation
78.20.-e Optical properties of bulk materials and thin films

Mechanical and electronic properties of 5d transition metal diborides MB2 (M = Re, W, Os, Ru)

Jie Wang and Yun-Jiang Wang

J. Appl. Phys. 105, 083539 (2009); http://dx.doi.org/10.1063/1.3116722 (6 pages) | Cited 8 times

Online Publication Date: 27 April 2009

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First-principles method is used to investigate the structural, mechanical, and electronic properties of 5d transition metal diborides MB2 (M = Re, W, Os, Ru). Our calculations show hexagonal ReB2 and WB2 have much larger elastic moduli and tensile shear strengths than orthorhombic OsB2 and RuB2. The elastic moduli and ideal strength are both calculated to be in a sequence of ReB2>WB2>OsB2>RuB2. Electronic structures show that strong directional covalent B–B and M–B bonds exist in the materials, which is the origin of their high modulus, large strength, and high hardness.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
81.40.Lm Deformation, plasticity, and creep
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds

Structure and elastic properties of boron suboxide at 240 GPa

Y. P. Lu and D. W. He

J. Appl. Phys. 105, 083540 (2009); http://dx.doi.org/10.1063/1.3110105 (7 pages)

Online Publication Date: 28 April 2009

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Structure and elastic properties of boron suboxide at high pressure have been investigated using generalized gradient approximation within the plane-wave pseudopotential density functional theory. The elastic constants are calculated using the finite strain method. The pressure dependences of lattice parameters, elastic constants, aggregate elastic moduli, and sound velocities of boron suboxide are predicted. It is found that the most stable structure of hcp boron suboxide at zero pressure corresponds to the ratio c/a of about 2.274 and the equilibrium lattice parameters a0 and c0 are about 5.331 and 12.124 Å, respectively. The high-pressure elastic constants indicate that boron suboxide is mechanically stable up to 368 GPa. The pressure dependence of the calculated normalized volume and the aggregate elastic moduli agree well with the recent experimental results. The sound velocities along different directions for the structure of boron suboxide are obtained. It shows that the velocities of the shear wave decrease as pressure increases but those of all the longitudinal waves increase with pressure. Moreover, the azimuthal anisotropy of the compression and shear aggregate wave velocities for different pressures are predicted. They change behavior with increasing pressure around 87 GPa because of an electronic topological transition. A refined analysis has been made to reveal the high pressure elastic anisotropy in boron suboxide.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.20.dq Other elastic constants
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Dx Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
62.50.-p High-pressure effects in solids and liquids
62.30.+d Mechanical and elastic waves; vibrations
61.66.Fn Inorganic compounds

Optical enhancement in nanoparticle-decorated ZnO nanorods

Tzung-Hsuan Lin, Chung-Liang Cheng, Han-Yu Shih, and Yang-Fang Chen

J. Appl. Phys. 105, 083541 (2009); http://dx.doi.org/10.1063/1.3116548 (3 pages) | Cited 2 times

Online Publication Date: 28 April 2009

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Based on the concept of optical enhancement in nanoparticle-mediated coupling, a novel composite consisting of ZnO nanorods and ZnO nanoparticles has been synthesized and characterized. The ZnO nanoparticles can be regarded as light-coupling media to increase the absorption cross section of excitation light as well as the emission extraction efficiency due to the relaxation of momentum selection rule. With our devised ZnO nanostructures, the band gap emission of ZnO nanorods can be enhanced by up to 8.5 times. The strategy of optical enhancement provided here should be very useful in designing many other nanostructures for high efficiency optoelectronic devices.
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78.66.Hf II-VI semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Thermal stability of semi-insulating property of Fe-doped GaN bulk films studied by photoluminescence and monoenergetic positron annihilation techniques

Masashi Kubota, Takeyoshi Onuma, Yujiro Ishihara, Akira Usui, Akira Uedono, and Shigefusa F. Chichibu

J. Appl. Phys. 105, 083542 (2009); http://dx.doi.org/10.1063/1.3110205 (9 pages) | Cited 3 times

Online Publication Date: 28 April 2009

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The thermal stability of electrical resistivity (ρ) is one of the crucial functions of semi-insulating (SI) substrates. In this paper, we describe the thermal stability of SI property in Fe-doped GaN (GaN:Fe) films grown by hydride vapor phase epitaxy, in view of point defect chemistry by means of monoenergetic positron annihilation and photoluminescence (PL) measurements. PL spectra of GaN:Fe at 8 K exhibited broad emission bands in UV, blue, and yellow spectral regions, as well as a series of characteristic infrared peaks with a sharp zero-phonon line at 1.300 eV. A ρ value higher than 108 Ω⋅cm was obtained when the doping concentration of Fe, [Fe], exceeded the major shallow donor (Si) concentration (5×1017 cm−3). For those SI samples, the relative intensity of the yellow luminescence band at 2.2 eV, of which the origin has been attributed to Ga vacancies (VGa) and/or defect complexes composed of VGa and O, over the UV/blue emission was remarkably decreased. Simultaneously, the Doppler broadening S parameter for the positron annihilation measurement, which represents the size or concentration of negatively charged vacancy type point defects such as VGa, was decreased. The results are consistent with the increase in formation energy of VGa due to the downward shift of the Fermi level by Fe doping. The values of ρ, S, and W parameters that represents the fraction of positrons annihilated with core electrons, in the bulk region did not change remarkably while the positron diffusion length was increased by the annealing in N2 between 600 and 1050 °C. Although the defect concentration in uncapped surface region was increased remarkably by annealing at 1050 °C due to the surface decomposition, the present results indicate that GaN:Fe can be used as a thermally stable SI substrate for electronic devices because the surface does not decompose during the epitaxial growths of overlayers.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
78.70.Bj Positron annihilation
68.60.Dv Thermal stability; thermal effects
61.72.sh Impurity distribution
61.72.jd Vacancies

Reverberation technique for yield strength experiments at ultrahigh pressure and strain rate

P. DeMange, J. D. Colvin, H. S. Park, and S. M. Pollaine

J. Appl. Phys. 105, 083543 (2009); http://dx.doi.org/10.1063/1.3093840 (9 pages)

Online Publication Date: 28 April 2009

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Ultrahigh pressure and strain-rate (pressure ⪢10 GPa and strain rate ⪢105 s−1) are now attainable using high-power laser systems. A laser pulse drives a shock through a reservoir material which then unloads onto the target specimen. Laser velocimetry measurements at the back surface of the specimen are used to infer the material response. Material strength experiments have been proposed in which the pressure wave reverberates within the specimen and the cumulative resistance to compression by material strength is measured from the recorded velocimetry signature. In this work, ultrahigh pressure and strain-rate reverberation experiments are performed in tantalum, aluminum, and copper to investigate the yield strength behavior in this extreme regime. The experimental results indicate that the measurement sensitivity to yield strength is dominated by the lateral wave effects or impeded by the occurrence of spall. However, computer hydrodynamic code simulations are used to develop an experimental design based on shaping of the laser drive pulse that circumvents these difficulties. Simulations using the Steinberg–Guinan yield strength model and applying the design indicate the capability of measuring a factor-of-2 strength deviation from that predicted by the model with accuracy equal to or greater than the velocimetry measurement error.
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07.10.-h Mechanical instruments and equipment
42.62.Eh Metrological applications; optical frequency synthesizers for precision spectroscopy
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

Pore collapse in powder metal mixtures during shock compression

D. J. Reding

J. Appl. Phys. 105, 083544 (2009); http://dx.doi.org/10.1063/1.3116729 (9 pages) | Cited 3 times

Online Publication Date: 29 April 2009

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A multiscale modeling approach is proposed to simulate the mechanical response in porous energetic mixtures during shock loading. A spherically symmetric single pore model is developed that incorporates viscoplastic and temperature dependent effects for a mixture. Our proposed model introduces parameters that capture microstructural effects due to changes in mixture morphology, particle size, and magnitude of the shock load applied to the mixture. These parameters are used to describe geometric, inertial, and constituent interaction effects. The proposed pore collapse model is incorporated into a gas-gun simulation and the parameters are studied with comparisons to experimental results for an intermetallic powder mixture containing Ni+Al.
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62.50.Ef Shock wave effects in solids and liquids
61.43.Gt Powders, porous materials
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity

Incorporation of phosphorus donors in (110)-textured polycrystalline diamond

A. Lazea, J. Barjon, J. D’Haen, V. Mortet, M. D’Olieslaeger, and K. Haenen

J. Appl. Phys. 105, 083545 (2009); http://dx.doi.org/10.1063/1.3116736 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2009

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The incorporation efficiency of phosphorus was studied as a function of the surface orientation of grains in (110)-textured polycrystalline chemical vapor deposited diamond. Cathodoluminescence mapping of such films exhibits large local differences in relative intensities stemming from P-bound and free excitons. Combined with electron backscattering diffraction mapping, these data allow assessing of the donor concentration as a function of the grain orientation. While [P] can vary between 1015 and >1018 cm−3 within one film, misorientation angles of more than 10° with respect to the exact [110] axis assure an enhanced incorporation of P with concentrations surpassing 5×1017 cm−3. The role of the surface morphology in the observation of these large incorporation differences is explained.
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61.72.up Other materials
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.jm Texture
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.47.Fg Semiconductor surfaces
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Amorphous to fcc-polycrystal transition in Ge2Sb2Te5 thin films studied by electrical measurements: Data analysis and comparison with direct microscopy observations

Pietro La Fata, Felice Torrisi, Salvatore Lombardo, Giuseppe Nicotra, Rosaria Puglisi, and Emanuele Rimini

J. Appl. Phys. 105, 083546 (2009); http://dx.doi.org/10.1063/1.3093915 (8 pages) | Cited 5 times

Online Publication Date: 29 April 2009

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We experimentally investigate the isothermal amorphous-to-fcc polycrystalline phase transition process in amorphous Ge2Sb2Te5 thin films prepared by sputtering. The amorphous layers were either as deposited or formed by Ar+ ion implantation after crystallization at 300 °C. The kinetics of the amorphous-to-polycrystal transition are analyzed through electrical measurements, in which the Johnson–Mehl–Avrami–Kolmogorov theory is employed. The procedure to extract the kinetics of the phase transition from conductivity versus time data is carefully discussed and compared to data of cross-sectional transmission electron microscopy images versus anneal time. By following this proposed procedure, the nucleation and growth parameters, and the activation energies have been determined. Results indicate that the process of isothermal crystallization in Ge2Sb2Te5 takes place in two stages, in which the Avrami exponent changes in the range from 3 to 1. These results are understood in terms of modifications in the kinetics of the phase transition.
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64.70.dg Crystallization of specific substances
64.70.kg Semiconductors
81.15.Cd Deposition by sputtering
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
73.61.Jc Amorphous semiconductors; glasses

Sputtered In2O3 and ITO thin films containing zirconium

T. A. Gessert, Y. Yoshida, C. C. Fesenmaier, and T. J. Coutts

J. Appl. Phys. 105, 083547 (2009); http://dx.doi.org/10.1063/1.3116542 (6 pages) | Cited 5 times

Online Publication Date: 29 April 2009

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Additions of Zr to In2O3 (IO) and In2O3:SnO2 (ITO) sputtered thin films are studied. We find that Zr allows IO-based films to maintain optical transparency as oxygen partial pressure in the sputter ambient decreases, and it also maintains high carrier concentration as the oxygen partial pressure increases. Applying this guidance could indicate pathways to improve film properties in large-area deposition systems. We also find that for films deposited at optimum oxygen partial pressure, the optical transparency of the IO-based films improves as Zr is added, especially in the near-infrared spectral region. Analysis of these films using Drude theory approximations indicate that optical improvement is due to an increase in dielectric permittivity caused by Zr addition. We propose that controlling dielectric permittivity may be an important strategy in improving other transparent conducting oxides (TCOs), as well as indicative of an important pathway to developing new TCOs.
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78.66.Li Other semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.30.Hv Other nonmetallic inorganics
77.22.Ch Permittivity (dielectric function)
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