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14 Dec 2009

Volume 95, Issue 24, Articles (24xxxx)

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Appl. Phys. Lett. 95, 242102 (2009); http://dx.doi.org/10.1063/1.3272858 (3 pages)

W. H. Lim, F. A. Zwanenburg, H. Huebl, M. Möttönen, K. W. Chan, A. Morello, and A. S. Dzurak
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The effect of hydrogen charging on Ln-based amorphous materials

C. P. Chuang, J. H. Huang, W. Dmowski, P. K. Liaw, R. Li, T. Zhang, and Y. Ren

Appl. Phys. Lett. 95, 241901 (2009); http://dx.doi.org/10.1063/1.3266521 (3 pages) | Cited 2 times

Online Publication Date: 14 December 2009

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In present work, the effects of hydrogen charging on Ln-based (Ln = La,Ce) bulk-metallic glasses (BMG) are studied. The (La0.5Ce0.5)65Al10Co25 were charged with hydrogen by an electrochemical method in an alkali solution. The hydrogen concentration in the sample after a 36 h charge can reach as high as 1286 w-ppm. With the presence of hydrogen atoms, the hardness of specimen increased by 80% compared to the as-cast samples. The structural evolution of the amorphous matrix due to the hydrogen-uptake process was investigated by the high-energy x-ray scattering technique. The sample surface was crystallized after hydrogen charging. X-ray diffraction measurements revealed broad crystalline peaks superimposed on an amorphous-scattering pattern. The crystalline phase grew from the surface to at least one hundred microns deep into the amorphous matrix. The atomic arrangements of both amorphous and crystalline phases were characterized by the atomic pair-distribution function.
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82.80.Fk Electrochemical methods
61.43.Fs Glasses
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.

Liquid Ge2Sb2Te5 studied by extended x-ray absorption

A. V. Kolobov, P. Fons, M. Krbal, R. E. Simpson, S. Hosokawa, T. Uruga, H. Tanida, and J. Tominaga

Appl. Phys. Lett. 95, 241902 (2009); http://dx.doi.org/10.1063/1.3272680 (3 pages) | Cited 3 times

Online Publication Date: 15 December 2009

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We report on x-ray absorption studies of the structure of the liquid phase of a prototypical phase-change material Ge2Sb2Te5. We demonstrate that the local structure of liquid Ge2Sb2Te5 is very similar to that of amorphous Ge2Sb2Te5. Ge atoms in the liquid phase are found to be covalently bonded suggesting a semiconducting nature of the melt.
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61.25.-f Studies of specific liquid structures
78.70.Dm X-ray absorption spectra

Comprehensive doping and temperature studies of spin relaxation in InSb

D. Guzun, E. A. DeCuir, Jr., Vas. P. Kunets, Yu. I. Mazur, G. J. Salamo, S. Q. Murphy, P. A. R. Dilhani Jayathilaka, T. D. Mishima, and M. B. Santos

Appl. Phys. Lett. 95, 241903 (2009); http://dx.doi.org/10.1063/1.3274040 (3 pages)

Online Publication Date: 15 December 2009

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Time resolved pump-probe measurements of the spin relaxation rate in thick epilayers and bulk InSb have been carried out for a wide range of doping concentrations (intrinsic—2×1018 cm−3) and temperatures (20 to 300 K). Our results are consistent with the dominance of the Elliott–Yafet mechanism across a wide range of carrier concentrations and temperatures for which the electron energy is less than 100 meV.
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73.61.Ey III-V semiconductors
61.72.uj III-V and II-VI semiconductors
78.47.D- Time resolved spectroscopy (>1 psec)
73.50.Dn Low-field transport and mobility; piezoresistance
78.66.Fd III-V semiconductors

Dominant recombination centers in Ga(In)NAs alloys: Ga interstitials

X. J. Wang, Y. Puttisong, C. W. Tu, Aaron J. Ptak, V. K. Kalevich, A. Yu. Egorov, L. Geelhaar, H. Riechert, W. M. Chen, and I. A. Buyanova

Appl. Phys. Lett. 95, 241904 (2009); http://dx.doi.org/10.1063/1.3275703 (3 pages) | Cited 11 times

Online Publication Date: 16 December 2009

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Optically detected magnetic resonance measurements are carried out to study formation of Ga interstitial-related defects in Ga(In)NAs alloys. The defects, which are among dominant nonradiative recombination centers that control carrier lifetime in Ga(In)NAs, are unambiguously proven to be common grown-in defects in these alloys independent of the employed growth methods. The defects formation is suggested to become thermodynamically favorable because of the presence of nitrogen, possibly due to local strain compensation.
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76.70.Hb Optically detected magnetic resonance (ODMR)
61.72.jj Interstitials
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.61.Ey III-V semiconductors

Effect of annealing on atomic ordering of amorphous ZrTaTiNbSi alloy

Tsung-Han Yang, Rong-Tang Huang, Cheng-An Wu, Fu-Rong Chen, Jon-Yiew Gan, Jien-Wei Yeh, and Jagdish Narayan

Appl. Phys. Lett. 95, 241905 (2009); http://dx.doi.org/10.1063/1.3273387 (3 pages) | Cited 5 times

Online Publication Date: 16 December 2009

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In this letter, we have reported on initial stages of atomic ordering in ZrTaTiNbSi amorphous films during annealing. The atomic ordering and structure evolution were studied in Zr17Ta16Ti19Nb22Si26 amorphous films as a function of annealing temperature in the temperature range from 473 to 1173 K. Up to annealing temperature of 1173 K, the films retained amorphous structure, but the degree of disorder is increased with the increase in temperature. The formation of Si–M covalent bonds, which contributed to the local atomic arrangement, occurred in the initial stages of ordering. The bonding reactions between Si and other metal species explain the anomalous structural changes which were observed in x-ray diffraction and transmission electron microscopy. We discuss the stages of phase transformation for amorphous films as a function of annealing temperature. From these results, we propose that annealing leads to formation of random Si–M4 tetrahedron, and two observed rings, a first and second in the electron diffraction patterns compared to M–M and Si–M bond length, respectively.
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81.40.Gh Other heat and thermomechanical treatments
68.55.-a Thin film structure and morphology
64.70.kd Metals and alloys
61.43.Fs Glasses
81.15.Cd Deposition by sputtering
81.05.Bx Metals, semimetals, and alloys

Photoluminescence induced by thermal annealing in SrTiO3 thin film

JaeHoon Rho, SeungHun Jang, Young Dong Ko, SeungJin Kang, Dong-Wook Kim, J.-S. Chung, Miyoung Kim, Moonsup Han, and Eunjip Choi

Appl. Phys. Lett. 95, 241906 (2009); http://dx.doi.org/10.1063/1.3275707 (3 pages) | Cited 5 times

Online Publication Date: 17 December 2009

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We have grown SrTiO3 thin films by rf-sputtering and studied its photoluminescence (PL) property after postannealing treatments. While the as-grown film does not show any PL signal, visible frequency PL emissions are induced by high temperature (T>550 °C) annealing. When subsequent low-T (50 °C) and long term (>8 months) annealing was made, the PL-spectra evolved into another pattern in which four distinct luminescence peaks appear simultaneously at λ = 1.8, 2.2, 2.7, and 3.1 eV. We propose that these remarkable room temperature PL effects are due to both metastable and energetically stabilized defect states formed inside the band gap.
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78.55.Hx Other solid inorganic materials
78.66.Nk Insulators
81.40.Gh Other heat and thermomechanical treatments
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
81.15.Cd Deposition by sputtering

MnSe phase segregation during heteroepitaxy of Mn doped Ga2Se3 on Si(001)

T. C. Lovejoy, E. N. Yitamben, S. M. Heald, F. S. Ohuchi, and M. A. Olmstead

Appl. Phys. Lett. 95, 241907 (2009); http://dx.doi.org/10.1063/1.3273858 (3 pages) | Cited 1 time

Online Publication Date: 17 December 2009

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Heteroepitaxial thin films of Mn-doped Ga2Se3 are grown by molecular beam epitaxy on Si(001):As. Mn-doped films are laminar for the first 1–2 nm, after which oriented islands with flat tops are observed by scanning tunneling microscopy. In contrast with the bulk phase diagram, which predicts MnGa2Se4 precipitates, the precipitates are identified by bond length measurements from extended x-ray absorption fine structure as rocksalt MnSe. This difference is attributed to superior lattice matching of MnSe to the substrate, and an epitaxial relationship between the MnSe and Si substrate is inferred.
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64.75.Qr Phase separation and segregation in semiconductors
64.75.St Phase separation and segregation in thin films
68.55.ag Semiconductors
78.70.Dm X-ray absorption spectra
81.05.Hd Other semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Hole-electron electrical coupling in photorefractive materials

Ivan de Oliveira, Renata Montenegro, and Jaime Frejlich

Appl. Phys. Lett. 95, 241908 (2009); http://dx.doi.org/10.1063/1.3272681 (2 pages) | Cited 2 times

Online Publication Date: 18 December 2009

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We describe an improved mathematical model for photorefractive materials exhibiting hole-electron competition where the constants accounting for electrical coupling between holes and electrons are independently adjusted for each one of them. Experimental results from photorefractive titanosillenite crystals with hole-electron competition, and particularly from a vanadium doped sample, are shown to be better described by this modified model than by the classical one already reported in the literature.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
42.70.Gi Light-sensitive materials
42.70.Ln Holographic recording materials; optical storage media
42.40.Ht Hologram recording and readout methods
42.79.Vb Optical storage systems, optical disks

Observation of hypersonic phononic crystal effects in porous silicon superlattices

L. C. Parsons and G. T. Andrews

Appl. Phys. Lett. 95, 241909 (2009); http://dx.doi.org/10.1063/1.3275742 (3 pages) | Cited 11 times

Online Publication Date: 18 December 2009

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Brillouin light scattering experiments were carried out on porous silicon superlattices with modulation wavelengths in the range 37–167 nm. Phonon frequencies deduced from the Brillouin spectra show good agreement with those obtained from an elastic continuum model for a system with one-dimensional periodicity. Evidence for the existence of a hypersonic phononic bandgap and zone-folded longitudinal acoustic phonons is reported.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
81.05.Cy Elemental semiconductors
73.21.Cd Superlattices
81.05.Rm Porous materials; granular materials
78.35.+c Brillouin and Rayleigh scattering; other light scattering

Effects of nanowire coalescence on their structural and optical properties on a local scale

V. Consonni, M. Knelangen, U. Jahn, A. Trampert, L. Geelhaar, and H. Riechert

Appl. Phys. Lett. 95, 241910 (2009); http://dx.doi.org/10.1063/1.3275793 (3 pages) | Cited 17 times

Online Publication Date: 18 December 2009

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The effects of GaN nanowire coalescence have been investigated on a local scale by combining high-resolution transmission electron microscopy imaging with spatially resolved cathodoluminescence measurements. Coalescence induces the formation of a network of boundary dislocations, above which I1-type basal-plane stacking faults are nucleated. The former contributes to the reduction in the crystalline quality at the bottom of coalesced nanowires while the latter leads to intense excitonic radiative transitions at 3.42 eV in their center. Despite coalescence, the top of coalesced nanowires presents a very high crystalline quality, resulting in strong radiative recombinations of donor bound excitons at 3.47 eV.
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78.67.Uh Nanowires
71.35.-y Excitons and related phenomena
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.)
78.60.Hk Cathodoluminescence, ionoluminescence
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)

High pressure phase transformation in iron under fast compression

Marina Bastea, Sorin Bastea, and Richard Becker

Appl. Phys. Lett. 95, 241911 (2009); http://dx.doi.org/10.1063/1.3275797 (3 pages) | Cited 1 time

Online Publication Date: 18 December 2009

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We observe kinetic features—velocity loops—at the α to ϵ phase transformation of iron, similar with the ones reported when water is frozen into its ice VII phase under comparable experimental conditions. By using a phase nucleation and growth kinetic model with pressure dependent phase interface velocity we find that the thermodynamic path followed by the sample is strongly dependent on the drive conditions and sample characteristics. The velocity loops become broader and shallower at slower compressions, while on faster time–scales, e.g., for laser drivers, the loops form at higher velocities and may eventually disappear.
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62.50.-p High-pressure effects in solids and liquids
64.70.kd Metals and alloys
65.40.G- Other thermodynamical quantities
64.60.qj Studies of nucleation in specific substances
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