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15 Feb 2010

Volume 96, Issue 7, Articles (07xxxx)

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Appl. Phys. Lett. 96, 072501 (2010); http://dx.doi.org/10.1063/1.3314301 (3 pages)

T. Hesjedal and T. Phung
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The cubic to tetragonal phase transition in SrTiO3 single crystals near its surface under internal and external strains

R. Loetzsch, A. Lübcke, I. Uschmann, E. Förster, V. Große, M. Thuerk, T. Koettig, F. Schmidl, and P. Seidel

Appl. Phys. Lett. 96, 071901 (2010); http://dx.doi.org/10.1063/1.3324695 (3 pages) | Cited 7 times

Online Publication Date: 16 February 2010

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The displacive phase transition in SrTiO3 was investigated by means of x-ray diffraction. We used 4.5 keV photons thus probing only a very thin region near the surface. In the low temperature phase the lattice parameters evolve substantially different than in bulk material. We also investigated the phase transition under the influence of an epitaxial coating with YBaCu2O7 and found the nature of the phase transition changed. The near-surface region behaves like an epitaxial thin SrTiO3 film.
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64.70.K- Solid-solid transitions
61.50.Ks Crystallographic aspects of phase transformations; pressure effects
61.66.Fn Inorganic compounds

Three-dimensional photovoltaics

Bryan Myers, Marco Bernardi, and Jeffrey C. Grossman

Appl. Phys. Lett. 96, 071902 (2010); http://dx.doi.org/10.1063/1.3308490 (3 pages) | Cited 6 times

Online Publication Date: 16 February 2010

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The concept of three-dimensional (3D) photovoltaics is explored computationally using a genetic algorithm to optimize the energy production in a day for arbitrarily shaped 3D solar cells confined to a given area footprint and total volume. Our simulations demonstrate that the performance of 3D photovoltaic structures scales linearly with height, leading to volumetric energy conversion, and provides power fairly evenly throughout the day. Furthermore, we show that optimal 3D structures are not simple box-like shapes, and that design attributes such as reflectivity could be optimized using three-dimensionality.
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88.40.H- Solar cells (photovoltaics)
84.60.Jt Photoelectric conversion

Electronic structure of ZnTe:O and its usability for intermediate band solar cell

Byounghak Lee and Lin-Wang Wang

Appl. Phys. Lett. 96, 071903 (2010); http://dx.doi.org/10.1063/1.3298553 (3 pages) | Cited 7 times

Online Publication Date: 16 February 2010

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The electronic structures of lattice highly mismatched ZnTe1−xOx alloys are calculated with the linear scaling three-dimensional fragment method. We found that the intermediate band states should be described as a result of the coupling between O impurity states rather than the coupling of the impurity state with the conduction band states. We also found that this system can be used for intermediate band state solar cell with a theoretical efficiency of 63%.
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71.20.Nr Semiconductor compounds
71.55.Gs II-VI semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
88.40.J- Types of solar cells

Electrical failure in blends of chemically identical, soft thermoplastic elastomers with different elastic stiffness

Matthias Kollosche and Guggi Kofod

Appl. Phys. Lett. 96, 071904 (2010); http://dx.doi.org/10.1063/1.3319513 (3 pages) | Cited 16 times

Online Publication Date: 16 February 2010

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Investigations on the effect of stiffness on breakdown strength in polymer materials are typically performed indirectly by variation of temperature. Here, the stiffness is varied directly using blends of chemically identical, physically crosslinking elastomers, thus avoiding possible temperature-induced variations in electric and ionic conductivity. Avoiding a chemically crosslinking system rules out variations due to crosslinkers or initiators. Measurements were carried out with a hemispherical indenter resting on a slab of the material with constant load. A theory recently proposed by Zhao and Suo was adapted to the experimental conditions and found to apply well, with no free fitting parameters.
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77.22.Jp Dielectric breakdown and space-charge effects
77.84.Jd Polymers; organic compounds
62.20.dq Other elastic constants
81.40.Jj Elasticity and anelasticity, stress-strain relations

Reaction rate in reversible A↔B reaction-diffusion processes

M. Sinder, V. Sokolovsky, and J. Pelleg

Appl. Phys. Lett. 96, 071905 (2010); http://dx.doi.org/10.1063/1.3319840 (2 pages) | Cited 1 time

Online Publication Date: 16 February 2010

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The reversible A↔B reaction-diffusion process, where species A and B are initially mixed and diffuse with different diffusion coefficients, is usually simulated in the framework of the quasiequilibrium approximation. In this paper the reaction rate of such process is investigated. It is shown that despite the fact that a reaction-diffusion process is considered as the quasiequilibrium process the contribution of the reaction in changes of the species concentration is comparable with the diffusion contribution. Moreover, the ratio of the reaction to diffusion contributions is independent of time and coordinate. Using published experimental data the reaction rate and its profile are calculated.
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82.20.-w Chemical kinetics and dynamics
66.30.Dn Theory of diffusion and ionic conduction in solids

Surface plasmon enhanced energy transfer between type I CdSe/ZnS and type II CdSe/ZnTe quantum dots

C. H. Wang, C. W. Chen, Y. T. Chen, C. M. Wei, Y. F. Chen, C. W. Lai, M. L. Ho, P. T. Chou, and M. Hofmann

Appl. Phys. Lett. 96, 071906 (2010); http://dx.doi.org/10.1063/1.3315876 (3 pages) | Cited 7 times

Online Publication Date: 17 February 2010

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Fluorescence resonant energy transfer (FRET) has been investigated between donor-acceptor pairs of type I CdSe/ZnS and type II CdSe/ZnTe quantum dots (QDs). An Au nanoparticles assisted FRET enhancement was clearly demonstrated. It is found that the efficiency of the energy transfer depends on the excitation wavelength and is largest when in resonance with the Au surface plasmon mode. With the large tunability of the emission intensity in near infrared region, our finding paves an excellent route for creating highly efficient optoelectronic devices and bioimaging labels derived from type II QDs.
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78.67.Hc Quantum dots
78.55.Et II-VI semiconductors
73.21.La Quantum dots
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
71.20.Nr Semiconductor compounds

Gate voltage dependence of nuclear spin relaxation in an impurity-doped semiconductor quantum well

M. Ono, H. Kobayashi, S. Matsuzaka, Y. Ohno, and H. Ohno

Appl. Phys. Lett. 96, 071907 (2010); http://dx.doi.org/10.1063/1.3309687 (3 pages) | Cited 4 times

Online Publication Date: 17 February 2010

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We investigated the gate voltage dependence of the nuclear spin relaxation in a Schottky-gated n-GaAs/AlGaAs (110) quantum well by the time-resolved Kerr rotation measurement combined with the nuclear magnetic resonance technique. The Fermi contact hyperfine interaction is enhanced by decreasing the background electron density, as the electrons become localized at impurity site. The energy relaxation time T1 and the decay time of the Rabi oscillation T2Rabi can be controlled by more than a factor of 10 and a factor of ∼ 2, respectively.
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76.60.Es Relaxation effects
78.20.Jq Electro-optical effects
78.67.De Quantum wells
73.21.Fg Quantum wells
71.70.Jp Nuclear states and interactions
61.72.U- Doping and impurity implantation

Role of negatively charged defects in the lattice contraction of Al–Si–N

C. A. Pignedoli, D. Passerone, H. J. Hug, A. Pélisson-Schecker, and J. Patscheider

Appl. Phys. Lett. 96, 071908 (2010); http://dx.doi.org/10.1063/1.3323093 (3 pages) | Cited 1 time

Online Publication Date: 17 February 2010

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Experiments reveal that incorporation of substitutional Si in wurtzite AlN up to 6 at. % results in a lattice contraction in the [0001] direction. The contraction is linear and, for higher silicon contents, the lattice parameters remain constant. We investigate the geometric and electronic properties of Al–Si–N compounds with Si content varying from 0 to 9 at. % by means of ab initio simulations based on density functional theory. We demonstrate that charged defects are necessary to support the experimental evidence of a shrinking cell parameter: an ideal Al–Si–N wurtzite structure with delocalized charges would undergo lattice expansion due to Coulomb repulsion upon Si incorporation. Charged defects that act as acceptors and compensate the excess charge coming from Si overcompensate the lattice expansion and therefore promote a lattice contraction.
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61.66.Fn Inorganic compounds
61.72.jd Vacancies
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Misfit strain relaxation in m-plane epitaxy of InGaN on ZnO

Z. H. Wu, K. W. Sun, Q. Y. Wei, A. M. Fischer, F. A. Ponce, Y. Kawai, M. Iwaya, S. Kamiyama, H. Amano, and I. Akasaki

Appl. Phys. Lett. 96, 071909 (2010); http://dx.doi.org/10.1063/1.3315944 (3 pages) | Cited 1 time

Online Publication Date: 18 February 2010

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The microstructure of m-plane InGaN epilayers grown on m-plane ZnO has been found to depend significantly on indium composition for the range from 0.07 to 0.17, where anisotropic lattice mismatch between InGaN and ZnO results in decreasingly tensile and increasingly compressive stress along the a and c lattice axes, respectively. For indium compositions below ∼ 0.10, periodic arrays of misfit dislocations with a Burgers vector of 1/3[11math0] are observed parallel to the [0001] direction. For indium compositions above ∼ 0.12, generation of basal-plane stacking faults relieve the compressive stress along the [0001] direction. These characteristic mechanisms of strain relaxation should provide new approaches to engineer thick InGaN layers with reduced lattice misfit strain.
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68.55.ag Semiconductors
61.72.Nn Stacking faults and other planar or extended defects
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.72.Lk Linear defects: dislocations, disclinations
81.05.Ea III-V semiconductors

Tunable sound directional beaming assisted by acoustic surface wave

Y. Cheng, J. Y. Xu, and X. J. Liu

Appl. Phys. Lett. 96, 071910 (2010); http://dx.doi.org/10.1063/1.3315952 (3 pages)

Online Publication Date: 18 February 2010

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We investigate the tunable directional beaming of sound wave from a subwavelength slit surrounded by asymmetric surface gratings. The surface gratings are optimally designed to directionally couple the modulated acoustic surface wave modes into surrounding medium along specific direction. The underlying mechanism of direction tuning is explored by the means of wave-vector analysis. The theoretical results predicated by the wave-vector analysis are in good agreement with the numerical results obtained using full-wave simulation. We observe that the full width at half maximum of the sound beam is less than 5° within a wide beaming angle region, and the beaming angle can be tuned by the structural parameters of surface grating.
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43.35.Pt Surface waves in solids and liquids
43.20.Mv Waveguides, wave propagation in tubes and ducts
43.38.Rh Surface acoustic wave transducers

Bandgap structure of thermally excited surface phonon polaritons

Igal Balin, Nir Dahan, Vladimir Kleiner, and Erez Hasman

Appl. Phys. Lett. 96, 071911 (2010); http://dx.doi.org/10.1063/1.3319539 (3 pages) | Cited 3 times

Online Publication Date: 18 February 2010

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A wide bandgap of thermally excited surface phonon polaritons (SPhPs) is experimentally observed. Formation of the bandgap and coupling to radiative waves is done by a binary biharmonic structure formed on a SiC substrate. The bandgap width is controlled by the ratio of the two harmonic magnitudes of the structure’s profile. The characteristic one-dimensional Van Hove singularity is experimentally observed in the spectral density of states of the SPhPs. Moreover, an inverse relation is found between the gap width and the squared spatial coherence length of the emitted thermal radiation, as predicted by theoretical calculations.
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68.35.Ja Surface and interface dynamics and vibrations
81.05.Hd Other semiconductors
71.20.Nr Semiconductor compounds
73.22.Lp Collective excitations
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Stress- and magnetic field-induced entropy changes in Fe-doped Ni–Mn–Ga shape-memory alloys

D. E. Soto-Parra, Eduard Vives, David González-Alonso, Lluís Mañosa, Antoni Planes, Ricardo Romero, J. A. Matutes-Aquino, R. A. Ochoa-Gamboa, and H. Flores-Zúñiga

Appl. Phys. Lett. 96, 071912 (2010); http://dx.doi.org/10.1063/1.3309755 (3 pages) | Cited 5 times

Online Publication Date: 18 February 2010

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Isothermal stress- and magnetic field-induced entropy changes in a Fe-doped Ni–Mn–Ga alloy have been measured in the limits of low applied stress and magnetic field. We have obtained that in this limit while elastocaloric is conventional, giving rise to an increase of entropy when a stress is applied, magnetocaloric effect is inverse, which means that entropy decreases by application of an applied magnetic field. This inverse effect is a consequence of the magnetostructural coupling driven by the martensitic transition.
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75.30.Sg Magnetocaloric effect, magnetic cooling
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.30.Kf Martensitic transformations
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity
65.40.gd Entropy

Kinetic Monte Carlo simulations of nanocolumn formation in two-component epitaxial growth

Shu Zheng, Wenguang Zhu, Y. F. Gao, G. M. Stocks, and Zhenyu Zhang

Appl. Phys. Lett. 96, 071913 (2010); http://dx.doi.org/10.1063/1.3310066 (3 pages) | Cited 2 times

Online Publication Date: 18 February 2010

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Recent experiments have demonstrated that well-ordered one-dimensional column nanostructures can be formed via self-assembly in a variety of two-component epitaxial systems, including diluted magnetic semiconductors and high-TC superconductors. Here we use kinetic Monte Carlo simulations based on a (1+1)-dimensional lattice model to study the morphological evolution of strain-free two-component films during epitaxial growth in the nonequilibrium kinetic regime. Our simulations show that columnlike nanostructures are only formed in the system when the interatomic bond energies EAA, EBB, and EAB satisfy the inequality of EAB⪡(EAA+EBB)/2 at sufficiently high growth temperatures and low deposition rates.
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81.16.Dn Self-assembly
68.55.J- Morphology of films
68.55.A- Nucleation and growth

Tunable electrical and optical properties of hafnium nitride thin films

I. L. Farrell, R. J. Reeves, A. R. H. Preston, B. M. Ludbrook, J. E. Downes, B. J. Ruck, and S. M. Durbin

Appl. Phys. Lett. 96, 071914 (2010); http://dx.doi.org/10.1063/1.3327329 (3 pages) | Cited 1 time

Online Publication Date: 19 February 2010

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We report structural and electronic properties of epitaxial hafnium nitride films grown on MgO by plasma-assisted pulsed laser deposition. The electronic structure measured using soft x-ray absorption and emission spectroscopy is in excellent agreement with the results of a band structure calculation. We show that by varying the growth conditions we can extend the films’ reflectance further toward the UV, and we relate this observation to the electronic structure.
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71.20.Ps Other inorganic compounds
78.70.Dm X-ray absorption spectra
81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
78.66.-w Optical properties of specific thin films
52.77.Dq Plasma-based ion implantation and deposition

Morphological stability and specific resistivity of sub-10 nm silicide films of Ni1−xPtx on Si substrate

Zhen Zhang, Shi-Li Zhang, Bin Yang, Yu Zhu, Stephen M. Rossnagel, Simon Gaudet, Andrew J. Kellock, Jean Jordan-Sweet, and Christian Lavoie

Appl. Phys. Lett. 96, 071915 (2010); http://dx.doi.org/10.1063/1.3323097 (3 pages) | Cited 10 times

Online Publication Date: 19 February 2010

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This letter studies the morphological stability and specific resistivity of sub-10 nm silicide films of Ni, Ni0.95Pt0.05, and Ni0.9Pt0.1 formed on Si(100) substrate. When the deposited metal films are below 1 to 4 nm in thickness depending on the Pt content, the resultant silicide films tend to become epitaxially aligned to the Si substrate and hence exhibit an extraordinary morphological stability up to 800 °C. The presence of Pt in the silicides increases the film resistivity through alloy scattering, but alleviates, owing to a reduced electron mean free path, the frequently encountered sharp increase in resistivity in the sub-10 nm regime.
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68.55.J- Morphology of films
73.61.At Metal and metallic alloys
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