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28 Sep 2009

Volume 95, Issue 13, Articles (13xxxx)

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Appl. Phys. Lett. 95, 131107 (2009); http://dx.doi.org/10.1063/1.3236752 (3 pages)

Marcus Eichfelder, Wolfgang-Michael Schulz, Matthias Reischle, Michael Wiesner, Robert Roßbach, Michael Jetter, and Peter Michler
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Effect of Co, Ni, and Cu substitution on the electronic structure of hexagonal YMnO3 studied by x-ray absorption spectroscopy

K. Asokan, Y. S. Chen, C. W. Pao, H. M. Tsai, C. W. O. Lee, C. H. Lin, H. C. Hsueh, D. C. Ling, W. F. Pong, J. W. Chiou, M.-H. Tsai, O. Peña, and C. Moure

Appl. Phys. Lett. 95, 131901 (2009); http://dx.doi.org/10.1063/1.3224905 (3 pages) | Cited 5 times

Online Publication Date: 28 September 2009

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X-ray absorption spectroscopy measurements have been performed to elucidate local electronic and atomic structures of orthorhombic 3d-transition metal-doped yttrium manganites (YMnO3) with chemical formulae YMn2/3Me1/3O3 (Me = Co, Ni, and Cu). The Mn L3- and K-edges x-ray absorption near-edge structure (XANES) demonstrate the direct substitution of Me2+ for Mn3+, so that the positive effective charge of Mn ions are increased. Me-doping is also found to induce substantial broadening of the Mn L3-edge feature, which suggests enhancement of the delocalization of Mn 3d eg subbands and conductivity. Local spin density approximation (LSDA)+U (Hubbard U parameter) calculations were used to understand their electronic structures.
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71.20.Ps Other inorganic compounds
61.72.up Other materials
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.70.Dm X-ray absorption spectra

In situ studies of interfacial contact evolution via a two-axis deflecting cantilever microinstrument

Fang Liu, Ian Laboriante, Brian Bush, Christopher S. Roper, Carlo Carraro, and Roya Maboudian

Appl. Phys. Lett. 95, 131902 (2009); http://dx.doi.org/10.1063/1.3238282 (3 pages) | Cited 6 times

Online Publication Date: 29 September 2009

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The time-dependent assessment of two contacting polycrystalline silicon surfaces is realized using a microinstrument that allows for in situ surface analysis. The evolution in contact resistance, morphology, and chemistry is probed as a function of contact cycle. Initially, the contact resistance is found to decrease and then increase with impact cycle. Upon prolonged cycling, the fracture of Si grains is observed which grow to form a wear crater. The electrical, morphological, and chemical analyses suggest that the wear of rough polysilicon surfaces due to impact proceeds through three distinct phases, namely plastic deformation of asperities, adhesive wear, and grain fracture.
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68.35.bg Semiconductors
68.35.Gy Mechanical properties; surface strains
07.10.Cm Micromechanical devices and systems
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
73.40.Cg Contact resistance, contact potential
68.47.Fg Semiconductor surfaces
81.40.Pq Friction, lubrication, and wear
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Lm Deformation, plasticity, and creep

Suppression of nonradiative processes in long-lived polar GaN/AlN quantum dots

J. Renard, P. K. Kandaswamy, E. Monroy, and B. Gayral

Appl. Phys. Lett. 95, 131903 (2009); http://dx.doi.org/10.1063/1.3238311 (3 pages) | Cited 7 times

Online Publication Date: 30 September 2009

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We present a temperature-dependent time-resolved photoluminescence study of the nonradiative processes in polar GaN/AlN quantum dots and quantum wells. The photoluminescence decay times of quantum wells drop above 50 K due to the presence of nonradiative recombination centers. In contrast, the three-dimensional carrier confinement in quantum dots efficiently suppresses nonradiative processes up to room temperature, even for radiative decay times reaching the microsecond range.
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81.05.Ea III-V semiconductors
78.67.De Quantum wells
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
78.47.jd Time resolved luminescence
73.21.Fg Quantum wells
73.21.La Quantum dots
81.07.Ta Quantum dots
81.07.St Quantum wells

A body-centered-cubic polymorph of the Ge2Sb2Te5 phase change alloy

Y. Q. Cheng, M. Xu, H. W. Sheng, Y. Meng, X. D. Han, and E. Ma

Appl. Phys. Lett. 95, 131904 (2009); http://dx.doi.org/10.1063/1.3240885 (3 pages) | Cited 5 times

Online Publication Date: 1 October 2009

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In Ge2Sb2Te5 (GST), the prototype phase-change alloy for data storage, in situ x-ray diffraction experiments reveal a pressure-induced crystalline-amorphous-crystalline transition sequence, all at the same fixed composition and in one experimental cycle. A body-centered-cubic polymorph is discovered at high pressures; the formation of this phase is attributable to its high packing density rendered possible by the switch from covalent to metallic bonding as predicted by ab initio calculations.
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64.70.kg Semiconductors
62.50.-p High-pressure effects in solids and liquids
61.50.Lt Crystal binding; cohesive energy

Observations on the melting of Au nanoparticle deposits and alloying with Ni via in situ synchrotron radiation x-ray diffraction

Tzu-Hsuan Kao, Jenn-Ming Song, In-Gann Chen, Teng-Yuan Dong, Weng-Sing Hwang, and Hsin-Yi Lee

Appl. Phys. Lett. 95, 131905 (2009); http://dx.doi.org/10.1063/1.3242373 (3 pages) | Cited 3 times

Online Publication Date: 2 October 2009

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Through monitoring the evolution of the x-ray diffraction peaks, the transient low temperature melting of Au nanoparticles and following alloying with the substrate were demonstrated via in situ synchrotron radiation x-ray diffraction. Upon heating, the broad diffraction peak of nanosized Au particles with the average diameter of 2.5 nm was suppressed at about 200 °C and soon became sharp due to melting and subsequent solidification. If the test was conducted on a Ni film, an unstable intermetallic compound Au3Ni appeared with crystallized Au, which resulted from the reaction between the supercooled liquid of Au and Ni. However, it decomposed at 275 °C and above.
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64.70.dj Melting of specific substances
81.30.Fb Solidification
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
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