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30 Jun 2008

Volume 92, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 92, 264101 (2008); http://dx.doi.org/10.1063/1.2951485 (3 pages)

Wei Xiang Jiang, Tie Jun Cui, Qiang Cheng, Jessie Yao Chin, Xin Mi Yang, Ruopeng Liu, and David R. Smith
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Shear-strain-induced low symmetry phase and domain ordering in epitaxial La0.7Sr0.3MnO3 thin films

S. W. Jin, G. Y. Gao, Z. Huang, Z. Z. Yin, X. Zheng, and Wenbin Wu

Appl. Phys. Lett. 92, 261901 (2008); http://dx.doi.org/10.1063/1.2952764 (3 pages) | Cited 3 times

Online Publication Date: 30 June 2008

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The domain structure in epitaxial La0.7Sr0.3MnO3 films grown on (LaAlO3)0.3(Sr2AlTaO6)0.7(001) substrates has been investigated by x-ray reciprocal space maps on (003), (103), (math03), (013), and (0math3) reflections in the high-resolution scattering zone containing the c* axis, and the transmission electron microscopy. We revealed that at above 20 nm, the films show clearly a low symmetry monoclinic phase, and the shear strain relaxation can induce a patterned domain structure and in-plane superlattice in the films. The domain width versus the film thickness and the shear strain effect on the Curie temperature of the films were also discussed.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.Lx Magnetic oxides
75.47.Gk Colossal magnetoresistance
75.60.Ch Domain walls and domain structure
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
68.55.-a Thin film structure and morphology

Poisson’s Ratio and Intrinsic Plasticity of Metallic Glasses

S. J. Poon, Aiwu Zhu, and G. J. Shiflet

Appl. Phys. Lett. 92, 261902 (2008); http://dx.doi.org/10.1063/1.2952827 (3 pages) | Cited 22 times

Online Publication Date: 30 June 2008

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Through a comparison of the activation barrier densities for plastic deformation and brittle fracture at the yield point, a condition for intrinsic plasticity versus brittleness of metallic glasses under shear loading is derived. The quantitative role of Poisson’s ratio ν on fracture is revealed and additional effects due to local shear modulus (G) fluctuations are pointed out. The findings account for the onset of plasticity near reported ν values, as well as the brittleness of some high-ν alloys. Structural relaxation increases G and reduces fluctuations, incurring dual adverse effects on ductility. Implications for designing ductile metallic glasses are discussed.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mj Brittleness
62.20.fk Ductility, malleability

Cylindrical-to-plane-wave conversion via embedded optical transformation

Wei Xiang Jiang, Tie Jun Cui, Hui Feng Ma, Xiao Yang Zhou, and Qiang Cheng

Appl. Phys. Lett. 92, 261903 (2008); http://dx.doi.org/10.1063/1.2953447 (3 pages) | Cited 31 times

Online Publication Date: 1 July 2008

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We investigate the conversion from cylindrical waves to plane waves in a short range through a metamaterial layer which has a circular shape in the inner outline and a square shape in the outer outline. Based on an embedded optical transformation, analytical formulas of the permittivity and permeability tensors are presented for the metamaterial layer which converts the cylindrical waves to plane waves. The designed conversion materials are validated by full-wave simulations using the finite-element method. The proposed structure can be used either as a four-beam antenna or a compact range for near-field measurement of plane waves.
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42.70.-a Optical materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Correlation between hardness and elastic moduli of the ultraincompressible transition metal diborides RuB2, OsB2, and ReB2

Hsiu-Ying Chung, Michelle B. Weinberger, Jenn-Ming Yang, Sarah H. Tolbert, and Richard B. Kaner

Appl. Phys. Lett. 92, 261904 (2008); http://dx.doi.org/10.1063/1.2946665 (3 pages) | Cited 45 times

Online Publication Date: 1 July 2008

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The ultraincompressible transition metal diborides RuB2, OsB2, and ReB2 were synthesized by arc melting the elemental metals and boron under an argon atmosphere at ambient pressure. The hardness and Young’s modulus were measured using nanoindentation with a Berkovich diamond indenter. The bulk modulus and shear modulus were derived based on an isotropic model and then plotted as a function of hardness. A strong correlation is observed between the hardness and shear modulus for these transition metal diborides.
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81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.Qp Friction, tribology, and hardness
62.20.de Elastic moduli
62.20.M- Structural failure of materials

Anisotropic medium with parabolic dispersion

Linfang Shen, Jin-Jei Wu, and Tzong-Jer Yang

Appl. Phys. Lett. 92, 261905 (2008); http://dx.doi.org/10.1063/1.2953546 (3 pages) | Cited 2 times

Online Publication Date: 1 July 2008

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A layered metamaterial which is predicted by the effective medium theory to be an anisotropic medium with partial zero permittivities is analyzed carefully. It is shown that such a material has a dispersion relation in parabolic form, which is quite different from the known ones. This material may be viewed as a homogeneous medium but is spatially dispersive strongly. The structured medium may support either forward wave or backward wave, depending on the magnitude of the wave vector. Moreover, it is demonstrated that this medium with parabolic dispersion is especially suitable for the transmission of Gaussian beam with subwavelength width.
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42.70.-a Optical materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Anisotropic crystallographic properties, strain, and their effects on band structure of m-plane GaN on LiAlO2(100)

B. Liu, R. Zhang, Z. L. Xie, J. Y. Kong, J. Yao, Q. J. Liu, Z. Zhang, D. Y. Fu, X. Q. Xiu, P. Chen, P. Han, Y. Shi, Y. D. Zheng, S. M. Zhou, and G. Edwards

Appl. Phys. Lett. 92, 261906 (2008); http://dx.doi.org/10.1063/1.2951618 (3 pages) | Cited 11 times

Online Publication Date: 1 July 2008

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The m-plane GaN films grown on LiAlO2(100) by metal-organic chemical vapor deposition exhibit anisotropic crystallographic properties. The Williamson–Hall plots point out they are due to the different tilts and lateral correlation lengths of mosaic blocks parallel and perpendicular to GaN[0001] in the growth plane. The symmetric and asymmetric reciprocal space maps reveal the strain of m-plane GaN to be biaxial in-plane compress εxx = −0.79% and εzz = −0.14% with an out-of-plane dilatation εyy = 0.38%. This anisotropic strain further separates the energy levels of top valence band at Γ point. The energy splitting as 37 meV as well as in-plane polarization anisotropy for transitions are found by the polarized photoluminescence spectra at room temperature.
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68.55.-a Thin film structure and morphology
71.20.Nr Semiconductor compounds
68.60.Bs Mechanical and acoustical properties
78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors

Quantitative determination of the dopant distribution in Si ultrashallow junctions by tilted sample annular dark field scanning transmission electron microscopy

A. Parisini, V. Morandi, S. Solmi, P. G. Merli, D. Giubertoni, M. Bersani, and J. A. van den Berg

Appl. Phys. Lett. 92, 261907 (2008); http://dx.doi.org/10.1063/1.2951896 (3 pages) | Cited 9 times

Online Publication Date: 1 July 2008

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In this letter, it is shown how the application of a Z-contrast scanning transmission electron microscopy technique to the study of the dopant signal in ultrashallow junctions in Si can lead, in the case of As in Si, to a quantitative determination of the dopant depth profile at subnanometer resolution. The quantitative results thus obtained demonstrate that As accumulates on the Si side of the SiO2/Si interface with a negligible loss of dopant into the oxide. Modeling of the effect indicates that segregation occurring during the recrystallization of the implanted layer is the dominant cause of this dopant pileup.
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61.72.sh Impurity distribution
61.72.uf Ge and Si
68.37.Hk Scanning electron microscopy (SEM) (including EBIC)
68.37.Lp Transmission electron microscopy (TEM)
68.35.Dv Composition, segregation; defects and impurities
81.40.Ef Cold working, work hardening; annealing, post-deformation annealing, quenching, tempering recovery, and crystallization

Size dependence of twin formation energy in cubic SiC at the nanoscale

Yongfeng Zhang, Hyun Woo Shim, and Hanchen Huang

Appl. Phys. Lett. 92, 261908 (2008); http://dx.doi.org/10.1063/1.2953976 (3 pages) | Cited 3 times

Online Publication Date: 1 July 2008

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This letter reports the size dependence of twin formation energy in cubic SiC at the nanoscale, while the bulk value is nearly zero. Atomic edges surround the twin boundary of SiC nanowires, and they are responsible for the finite twin formation energy and its size dependence. Based on classical molecular statics calculations, the average formation energy of convex and concave edges is 73 meV/nm. Effectively, the twin formation energy is inversely proportional to the length of edges surrounding the twin boundary. Results of this letter make it possible to understand large separations of twin boundaries in SiC nanowires.
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68.65.La Quantum wires (patterned in quantum wells)
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)
61.72.Mm Grain and twin boundaries

Cool white III-nitride light emitting diodes based on phosphor-free indium-rich InGaN nanostructures

C. B. Soh, W. Liu, J. H. Teng, S. Y. Chow, S. S. Ang, and S. J. Chua

Appl. Phys. Lett. 92, 261909 (2008); http://dx.doi.org/10.1063/1.2952459 (3 pages) | Cited 20 times

Online Publication Date: 1 July 2008

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Phosphor-free cool white emitting light emitting diodes (LEDs) have been fabricated using a dual stacked InGaN/GaN multiple quantum wells (MQWs) comprising of a lower set of MQWs emitting yellow and an upper set of MQWs emitting blue. The lower set of MQWs incorporates indium-rich InGaN connected-dot nanostructures with a height of ∼ 1.0 nm in the well. The well is first grown with an InGaN layer serving as the wetting layer, then treated with trimethylindium (TMIn) to initiate nanostructure growth of another InGaN layer to complete the well layer. This gives a broadened yellow emission peak. With the combination of emission from the upper blue emitting InGaN/GaN MQWs subsequently grown, cool white light emission is achieved. The In-rich nanostructures formed during TMIn treatment enhance indium incorporation in InGaN well and also act as effective radiative recombination sites for carriers at the lower set of MQWs.
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85.60.Jb Light-emitting devices
73.21.Fg Quantum wells
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.60.Fi Electroluminescence

Optical detection of deoxyribonucleic acid hybridization with InGaN/GaN multiple quantum wells

H. Y. Shih, T. T. Chen, C. H. Wang, K. Y. Chen, and Y. F. Chen

Appl. Phys. Lett. 92, 261910 (2008); http://dx.doi.org/10.1063/1.2948907 (3 pages) | Cited 1 time

Online Publication Date: 1 July 2008

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Based on the high surface sensitivity of piezoelectric polarization of strained nitride semiconductors, surface functionalized nitride light emitting devices (LEDs) provide an excellent opportunity for the development of biological sensors. To demonstrate our working principle, a probe chip based on In0.22Ga0.78N/GaN multiple quantum wells has been constructed and exposed to target DNA solutions, matched and/or mismatched, with different concentrations. The pronounced changes of photoluminescence spectra as well as Raman scattering A1(LO) spectra in matched target DNA clearly illustrate the feasibility of our proposed mechanism. The results shown here open up a new possibility for the application of nitride LEDs in biosensor engineering.
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85.60.Jb Light-emitting devices
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.67.Hc Quantum dots
87.14.gk DNA
87.85.Rs Nanotechnologies-applications

First principles molecular dynamics study of CdS nanostructure temperature-dependent phase stability

Bin Wen and Roderick V. N. Melnik

Appl. Phys. Lett. 92, 261911 (2008); http://dx.doi.org/10.1063/1.2952835 (3 pages) | Cited 11 times

Online Publication Date: 1 July 2008

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First principles molecular dynamics simulations are used to determine the relative stability of wurtzite, graphitic, and rocksalt phases of the CdS nanostructure at various temperatures. Our results indicate that in the temperature range from 300 to 450 K, the phase stability sequence for the CdS nanostructure is rocksalt, wurtzite, and graphitic phases. The same situation holds for bulk CdS crystals under high pressure and 0 K. Our work also demonstrates that although the temperature can affect the total energy of the CdS nanostructure, it cannot change its phase stability sequence in the temperature range studied in this letter.
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71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.15.Nc Total energy and cohesive energy calculations

Effects of hydrogen on the optical properties of ZnCdO/ZnO quantum wells grown by molecular beam epitaxy

I. A. Buyanova, X. J. Wang, G. Pozina, W. M. Chen, W. Lim, D. P. Norton, S. J. Pearton, A. Osinsky, J. W. Dong, and B. Hertog

Appl. Phys. Lett. 92, 261912 (2008); http://dx.doi.org/10.1063/1.2953178 (3 pages) | Cited 7 times

Online Publication Date: 1 July 2008

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Temperature-dependent cw- and time-resolved photoluminescence (PL), as well as optically detected magnetic resonance (ODMR) measurements are employed to evaluate effects of deuterium (2H) doping on optical properties of ZnCdO/ZnO quantum well structures grown by molecular beam epitaxy. It is shown that incorporation of 2H from a remote plasma causes a substantial improvement in radiative efficiency of the investigated structures. Based on transient PL measurements, the observed improvements are attributed to efficient passivation by hydrogen of competing nonradiative recombination centers via defects. This conclusion is confirmed from the ODMR studies.
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78.67.De Quantum wells
78.55.Et II-VI semiconductors
78.47.D- Time resolved spectroscopy (>1 psec)
61.72.uj III-V and II-VI semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Rv Passivation

Transverse vibrations driven negative thermal expansion in a metallic compound GdPd3B0.25C0.75

Abhishek Pandey, Chandan Mazumdar, R. Ranganathan, S. Tripathi, D. Pandey, and S. Dattagupta

Appl. Phys. Lett. 92, 261913 (2008); http://dx.doi.org/10.1063/1.2953175 (3 pages) | Cited 6 times

Online Publication Date: 2 July 2008

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We have observed negative thermal expansion (NTE) in a metallic, polycrystalline, and structurally ordered cubic compound GdPd3B0.25C0.75. Our analysis suggest that the NTE observed in this compound does not stems from valence or magnetic instability of lattice ions, which is in general the case of metallic compounds exhibiting such an anomaly. We propose a possible alternative mechanism, namely, the transverse vibrations at low temperatures arising from site anisotropy, that induce the lattice contraction thereby resulting in isotropic NTE. The observed NTE also reflects its effect on the electrical transport properties of this compounds.
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65.40.De Thermal expansion; thermomechanical effects

[0001] composition modulations in Al0.4Ga0.6N layers grown by molecular beam epitaxy

A. Wise, R. Nandivada, B. Strawbridge, R. Carpenter, N. Newman, and S. Mahajan

Appl. Phys. Lett. 92, 261914 (2008); http://dx.doi.org/10.1063/1.2953451 (3 pages) | Cited 3 times

Online Publication Date: 3 July 2008

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Al0.4Ga0.6N layers grown by molecular beam epitaxy on (0001) AlN/sapphire composite substrates were examined using transmission electron microscopy. The layers show modulated structures consisting of Al-rich and Ga-rich regions. 1:1 atomic ordering on the (0001) planes was not observed. To rationalize the formation of modulations, we invoke the presence of phase separation induced Al-rich and Ga-rich regions at the AlGaN/composite interface, the development of surface undulations due to the presence of two-dimensional stresses between these regions and asymmetry in the wetting characteristics of the Al-rich and Ga-rich regions. Arguments are also developed to explain the absence of 1:1 ordering in these layers.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.37.Lp Transmission electron microscopy (TEM)
64.75.Qr Phase separation and segregation in semiconductors
68.08.Bc Wetting

Optical property and electronic band structure of a piezoelectric compound Ga3PO7 studied by the first-principles calculation

Z. X. Cheng and X. L. Wang

Appl. Phys. Lett. 92, 261915 (2008); http://dx.doi.org/10.1063/1.2955827 (3 pages)

Online Publication Date: 3 July 2008

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The structure, electronic, and optical properties of a piezoelectric material, Ga3PO7, were studied by first-principles calculations in the framework of density functional theory. The calculated structure is in agreement with the experimental data. Band structure reveals that Ga3PO7 has a band gap of 3.69 eV. Analysis of partial density of states and Mulliken charge population indicates existence of GaO5 and PO4 anion groups in Ga3PO7. Furthermore, its optical properties, including dielectric constant, absorption, reflectivity, refractive index, and electron loss were calculated and analyzed, which show that Ga3PO7 has potential applications based on combination of its piezoelectric and optical properties.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.-j Piezoelectricity and electromechanical effects
71.20.Ps Other inorganic compounds
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
77.22.Ch Permittivity (dielectric function)

Surface electronic properties of ZnO nanoparticles

Cuong Ton-That, Matthew R. Phillips, Matthew Foley, Steve J. Moody, and Anton P. J. Stampfl

Appl. Phys. Lett. 92, 261916 (2008); http://dx.doi.org/10.1063/1.2952955 (3 pages) | Cited 9 times

Online Publication Date: 3 July 2008

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The surface electronic structure of ZnO nanoparticles has been studied with photoemission and x-ray absorption spectroscopies. Contrary to expectation, ZnO:Zn phosphor nanoparticles were found to contain a lower oxygen vacancy density on the surface than undoped ZnO counterparts, but oxygen vacancies are in different chemical environments. Cathodoluminescence shows intense green luminescence from the ZnO:Zn surface, while the undoped nanoparticles exhibit only the near-band-edge emission. The results indicate the roles of surface oxygen vacancies and their environment in the previously unexplained green luminescence from the ZnO:Zn material.
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78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
73.22.-f Electronic structure of nanoscale materials and related systems
73.20.At Surface states, band structure, electron density of states
78.70.Dm X-ray absorption spectra
78.60.Hk Cathodoluminescence, ionoluminescence
79.60.Bm Clean metal, semiconductor, and insulator surfaces
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