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27 Sep 2010

Volume 97, Issue 13, Articles (13xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 97, 133303 (2010); http://dx.doi.org/10.1063/1.3491815 (3 pages)

Yoshihide Fujisaki, Yoshiki Nakajima, Daisuke Kumaki, Toshihiro Yamamoto, Shizuo Tokito, Takahiro Kono, Jun-ichi Nishida, and Yoshiro Yamashita
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Structural origin of the intermediate phase in Ge–Se glasses

G. Chen, F. Inam, and D. A. Drabold

Appl. Phys. Lett. 97, 131901 (2010); http://dx.doi.org/10.1063/1.3495775 (3 pages) | Cited 4 times

Online Publication Date: 27 September 2010

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We have conducted x-ray absorption near-edge structure (XANES) experiments on germanium selenide glasses, in search of a structural signature of the intermediate phase (IP). Quantitative analyses of the XANES spectra reveal compositional plateaus that coincide with the IP reversibility window, providing structural evidence for the IP. Molecular dynamic simulations have been performed to understand the atomistic origin of the electronic structure of the glasses. The IP originates from a competition between amorphous GeSe2 and amorphous Se clusters and produces measurable signatures. Our study provides atomistic insight into the structural origin of the IP in Ge–Se glasses.
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64.70.dg Crystallization of specific substances
64.70.Q- Theory and modeling of the glass transition
78.70.Dm X-ray absorption spectra
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
71.23.Cq Amorphous semiconductors, metallic glasses, glasses

A numerical method for designing acoustic cloak with homogeneous metamaterials

Weiren Zhu (朱卫仁), Changlin Ding (丁昌林), and Xiaopeng Zhao (赵晓鹏)

Appl. Phys. Lett. 97, 131902 (2010); http://dx.doi.org/10.1063/1.3492851 (3 pages) | Cited 8 times

Online Publication Date: 27 September 2010

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Based on the form invariance of Helmholtz equation, we present a rhombic acoustic cloak constructed with homogeneous metamaterials. In free space, the proposed cloak can effectively conceal an object inside under a given incident direction. Another application, namely carpet cloak, was also demonstrated by full wave simulations. The proposed cloak provided great convenience in the fabrication process due to the spatially uniform of relative density and modulus tensors.
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43.20.El Reflection, refraction, diffraction of acoustic waves
43.20.Fn Scattering of acoustic waves

Origins of size-dependent lattice dilatation in tetragonal Sn nanowires: Surface stress and growth stress

Ho Sun Shin, Jin Yu, Jae Yong Song, Hyun Min Park, and Yong-Sung Kim

Appl. Phys. Lett. 97, 131903 (2010); http://dx.doi.org/10.1063/1.3493179 (3 pages) | Cited 1 time

Online Publication Date: 27 September 2010

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Through experiments and theoretical analyses, we demonstrate that Sn nanowires can shrink or expand when the radius decreases from 120 to 1.2 nm. Single crystalline nanowires manifest [100]-longitudinal lattice dilatations that originate from the strong anisotropy of the surface stress. Compressive growth stress, which is generated in the radial direction during the growth of nanowires within templates, leads to greater elongation due to the Poisson effect. The surface stress-induced lattice strains are intrinsic, whereas the growth stress-induced lattice strains can be released. For polycrystalline nanowires, lattice contractions occur because the anisotropy of surface stresses is effectively reduced.
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81.07.Gf Nanowires
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.dj Poisson's ratio
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties

Stability, geometry, and electronic structure of an alternative I-III-VI2 material, CuScS2: A hybrid density functional theory analysis

David O. Scanlon and Graeme W. Watson

Appl. Phys. Lett. 97, 131904 (2010); http://dx.doi.org/10.1063/1.3491179 (3 pages)

Online Publication Date: 27 September 2010

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Cu based I-III-VI2 materials have received much attention due to their utility in solar cell applications. The vast majority these studies have focused on materials with group IIIA cations as the trivalent metal. In this study we utilize the screened hybrid exchange functional, HSE06, to investigate the stability of CuScS2 in the crystal structures of all the other I-III-VI2 materials, and find that it preferentially forms in its own unique structure. We analyze the electronic structure and optical properties of CuScS2 and in light of this discuss its semiconducting ability.
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61.66.Fn Inorganic compounds
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.05.Hd Other semiconductors
71.20.Nr Semiconductor compounds

Fabrication of micropillars by laser-induced thermoplastic method

Leyan Wang, Dongxian Zhang, Haijun Zhang, and J. Z. Jiang

Appl. Phys. Lett. 97, 131905 (2010); http://dx.doi.org/10.1063/1.3493180 (3 pages) | Cited 4 times

Online Publication Date: 28 September 2010

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A laser-induced thermoplastic formation technology for three dimension microstructure has been investigated theoretically and experimentally. An experimental system is built up and formation experiments are carried out on different kinds of thermoplastic materials. The appearance dependence of microstructures (micropillars) on the fabricating parameters has been discussed. Critical parameters for microstructure formation are concluded to be laser power, liquid temperature and material absorptance. By analyzing different melting-solidifying conditions, the balance between melting and solidifying velocities has been considered to be necessary for continuous micropillar growth. Based on theoretical analyses, micropillars with better HW ratio and better resolution are demonstrated.
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81.16.-c Methods of micro- and nanofabrication and processing
61.72.-y Defects and impurities in crystals; microstructure
61.41.+e Polymers, elastomers, and plastics
64.70.dj Melting of specific substances
81.30.Fb Solidification
42.62.-b Laser applications

Dye-sensitized solar cells based on anatase TiO2 nanocrystals exposing a specific lattice plane on the surface

Puhong Wen, Zhuoqi Tao, Yoshie Ishikawa, Hiroshi Itoh, and Qi Feng

Appl. Phys. Lett. 97, 131906 (2010); http://dx.doi.org/10.1063/1.3494087 (3 pages) | Cited 2 times

Online Publication Date: 28 September 2010

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Dye-sensitized solar cells (DSCs) using anatase TiO2 nanocrystals exposing a specific lattice plane on the surface were studied. It was found that dye adsorption strongly depends on the lattice plane exposed on the TiO2 nanocrystal surface, which greatly affects DSC performance. TiO2 nanocrystals exposing mainly the (010) plane have a higher dye adsorption capacity and a higher Voc for DSC than normal spherical nanocrystals. TiO2 nanocrystals with a large adsorption constant Kad can yield a high Jsc. The highest Jsc (20.6 mA/cm2) was achieved by using TiO2 nanocrystals with the specific lattice plane on the surface.
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88.40.H- Solar cells (photovoltaics)

Time-resolved spectroscopy of InAsP/InP(001) quantum dots emitting near 2 μm

D. Elvira, A. Michon, B. Fain, G. Patriarche, G. Beaudoin, I. Robert-Philip, Y. Vachtomin, A. V. Divochiy, K. V. Smirnov, G. N. Gol’tsman, I. Sagnes, and A. Beveratos

Appl. Phys. Lett. 97, 131907 (2010); http://dx.doi.org/10.1063/1.3495985 (3 pages) | Cited 2 times

Online Publication Date: 29 September 2010

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By using superconducting single photon detectors, we perform time-resolved characterization of a small ensemble of InAsP/InP quantum dots grown by metal organic vapor phase epitaxy, emitting at wavelengths between 1.6 and 2.2 μm. We demonstrate that alloying phosphorus with InAs allows to shift the emission wavelength toward higher wavelengths, while keeping the high optical quality of these quantum dots at room temperature, with no decrease in their radiative lifetime.
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78.47.D- Time resolved spectroscopy (>1 psec)
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.A- Nucleation and growth
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Spectroscopic characterization of bismuth embedded Y zeolites

Hong-Tao Sun, Yoshio Sakka, Yuji Miwa, Naoto Shirahata, Minoru Fujii, and Hong Gao

Appl. Phys. Lett. 97, 131908 (2010); http://dx.doi.org/10.1063/1.3496460 (3 pages) | Cited 10 times

Online Publication Date: 29 September 2010

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Bismuth embedded Y zeolites were studied by using UV-vis- near infrared (NIR) diffuse reflectance, Raman, and steady-state NIR photoluminescence spectroscopy. The results suggest that Bi53+ and Bi+ active centers coexist in the dehydrated and hydrated zeolite framework, both of which contribute to NIR emission. Furthermore, it was revealed that the high-temperature annealing leads to the formation of Bi2O3 clusters, which act as blocks for selectively closing down the “in-out windows” of H2O and O2 molecules in the zeolites. It is believed that these materials can find a wide array of applications as active media of broadly tunable micro or nano-optical sources.
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78.55.Hx Other solid inorganic materials
81.40.Gh Other heat and thermomechanical treatments
78.30.Hv Other nonmetallic inorganics
78.40.Ha Other nonmetallic inorganics
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Size dependent carrier recombination in ZnO nanocrystals

G. Pozina, L. L. Yang, Q. X. Zhao, L. Hultman, and P. G. Lagoudakis

Appl. Phys. Lett. 97, 131909 (2010); http://dx.doi.org/10.1063/1.3494535 (3 pages) | Cited 6 times

Online Publication Date: 29 September 2010

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Experimental and theoretical studies of fluorescence decay were performed for colloidal ZnO nanocrystals. The fluorescence lifetime reduces from 22 ps to ∼ 6 ps with decreasing nanocrystal radius. We postulate that non-radiative surface states dominate the carrier dynamics in small ZnO nanocrystals and perform Monte Carlo simulations incorporating carrier diffusion and carrier recombination to model the experimental fluorescence decay dynamics. The percentage of excitons undergoing nonradiative decay due to surface trapping is as high as 84% for nanocrystals with 8 nm radius, which explains the ultrafast decay dynamics observed in small ZnO nanostructures even at low temperatures.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
78.55.Et II-VI semiconductors
73.22.-f Electronic structure of nanoscale materials and related systems
71.35.-y Excitons and related phenomena
81.05.Dz II-VI semiconductors

Straining of SiGe ultrathin films with mesoporous Si substrates

A. Boucherif, N. P. Blanchard, O. Marty, P. Regreny, G. Guillot, G. Grenet, and V. Lysenko

Appl. Phys. Lett. 97, 131910 (2010); http://dx.doi.org/10.1063/1.3494594 (3 pages) | Cited 1 time

Online Publication Date: 29 September 2010

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We report on the fabrication and characterization of ultrathin (down to 50 nm) tensile strained SiGe films on mesoporous Si substrates. Low temperature oxidation of the porous substrate relaxes the compressive strain in the as grown monocrystalline (mc) SiGe. Applying this method to a 50 nm thick mc-Si0.72Ge0.28 film, a tensile strain >0.78% can be achieved without compromising crystalline quality and up to 1.45 % without the appearance of cracks.
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68.60.Bs Mechanical and acoustical properties
62.20.F- Deformation and plasticity
81.40.Lm Deformation, plasticity, and creep
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors

Improved thermal stability of gas-phase Mg nanoparticles for hydrogen storage

Gopi Krishnan, G. Palasantzas, and B. J. Kooi

Appl. Phys. Lett. 97, 131911 (2010); http://dx.doi.org/10.1063/1.3495772 (3 pages) | Cited 1 time

Online Publication Date: 30 September 2010

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This work focuses on improving the thermal stability of Mg nanoparticles (NPs) for use in hydrogen storage. Three ways are investigated that can achieve this goal. (i) Addition of Cu prevents void formation during NP production and reduces the fast evaporation/voiding of Mg during annealing. (ii) Alloying can prevent Mg evaporation: e.g., Mg with Ni forms a thermally stable core/shell (MgNi2/Ni) preventing Mg evaporation during annealing. (iii) Covering Mg NPs with a Ti film leads to suppression of Mg evaporation during vacuum annealing. Indeed, hydrogenation of the Ti/Mg NPs shows formation of the γ-MgH2 phase as for pure Mg NPs.
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81.07.Bc Nanocrystalline materials
81.40.Gh Other heat and thermomechanical treatments
84.60.Ve Energy storage systems, including capacitor banks
88.30.R- Hydrogen storage
64.70.F- Liquid-vapor transitions
61.72.Qq Microscopic defects (voids, inclusions, etc.)

Negative permittivity and left-handed behavior of doped manganites in millimeter waveband

M. K. Khodzitsky, S. I. Tarapov, D. P. Belozorov, A. M. Pogorily, A. I. Tovstolytkin, A. G. Belous, and S. A. Solopan

Appl. Phys. Lett. 97, 131912 (2010); http://dx.doi.org/10.1063/1.3491155 (3 pages) | Cited 4 times

Online Publication Date: 30 September 2010

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The “effective plasma frequency” of strontium-doped lanthanum manganite was determined basing on its double negative properties. The zone of high transmission (double negative zone) for spatially partitioned layered manganite specimen, immersed into dielectric matrix, was studied experimentally in millimeter waveband. It turns out that frequency dependence of manganite permittivity is well described by Drude formula, which includes only one parameter—the “effective plasma frequency.” Additionally, the negativity of the refraction index has been directly proved in experiments studying electromagnetic waves refraction in manganite prism.
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77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
77.22.Ch Permittivity (dielectric function)
72.30.+q High-frequency effects; plasma effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Reduction of nonradiative recombination center for ZnO films grown under Zn-rich conditions by metal organic chemical vapor deposition

Eiji Fujimoto, Kenji Watanabe, Yuji. Matsumoto, Hideomi Koinuma, and Masatomo Sumiya

Appl. Phys. Lett. 97, 131913 (2010); http://dx.doi.org/10.1063/1.3492855 (3 pages) | Cited 2 times

Online Publication Date: 1 October 2010

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ZnO films were grown by metalorganic chemical vapor deposition using the repeated temperature modulation in an H2 ambient. The crystalline quality, as defined by the full-width at half-maximum of the ω (10math1) reflection, was found to be correlated with the photoluminescence (PL) lifetime at 300 K. The fine structure of the PL spectra for the samples grown under Zn-rich condition at 8 K indicated the higher order (n = 2) structure of free exciton A, two electron satellites and phonon-replicas. The internal quantum efficiency and the PL lifetime at 300 K were 5.5% and 2.6 ns, respectively, indicating a reduction in Zn vacancies in the ZnO films.
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68.55.ag Semiconductors
78.55.Et II-VI semiconductors
78.66.Hf II-VI semiconductors
81.05.Dz II-VI semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
61.72.jd Vacancies
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