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28 Nov 2011

Volume 99, Issue 22, Articles (22xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 221902 (2011); http://dx.doi.org/10.1063/1.3663578 (3 pages)

Aparna Deshpande, Kai Felix Braun, and Saw-Wai Hla
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X-ray interference effects on the determination of structural data in ultrathin La2/3Sr1/3MnO3 epitaxial thin films

D. Pesquera, X. Marti, V. Holy, R. Bachelet, G. Herranz, and J. Fontcuberta

Appl. Phys. Lett. 99, 221901 (2011); http://dx.doi.org/10.1063/1.3663574 (3 pages) | Cited 2 times

Online Publication Date: 28 November 2011

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We analyze x-ray diffraction data to extract cell parameters of ultrathin films on closely matching substrates. We focus on epitaxial La2/3Sr1/3MnO3 films grown on (001) SrTiO3 single crystalline substrates. It will be shown that, due to extremely high structural similarity of film and substrate, the data analysis must explicitly consider the distinct phase of the diffracted waves by substrate and films to extract reliable unit cell parameters. The implications of this finding for the understanding of strain effects in ultrathin films and interfaces will be underlined.
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68.55.-a Thin film structure and morphology
62.20.D- Elasticity
62.20.F- Deformation and plasticity
81.40.Jj Elasticity and anelasticity, stress-strain relations

Determination of chemical specific atomic interaction with scanning tunneling microscope

Aparna Deshpande, Kai Felix Braun, and Saw-Wai Hla

Appl. Phys. Lett. 99, 221902 (2011); http://dx.doi.org/10.1063/1.3663578 (3 pages) | Cited 1 time

Online Publication Date: 28 November 2011

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We present an experimental technique to comparatively determine the shape of tip-atom interaction potential and interaction strength of individual atoms on a surface using a scanning tunnelling microscope. From the atom manipulation signals, the tip-atom force vector angle is measured as a function of distance. Remarkably, the force angle is found to increase linearly with reducing tip-height for a small distance variation, which enables to deduce the shape of tip-atom interaction potential, and the lateral force required to move individual atoms on a surface. This technique will be useful to comparatively determine interaction strengths of molecules and biomolecular systems on surfaces.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Ultrafast decay of high frequency optical phonon mode in KTiOPO4

Shan Yang (杨山), Sanjay Adhikari, Manoj Dobbala, and Feruz Ganikhanov

Appl. Phys. Lett. 99, 221903 (2011); http://dx.doi.org/10.1063/1.3664218 (3 pages)

Online Publication Date: 28 November 2011

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Decay of the strongest optical phonon mode in KTiOPO4 was directly traced using femtosecond coherent anti-Stokes Raman scattering spectroscopy. Dephasing of the Raman active mode at ∼700 cm−1 proceeds with the nonlinear polarization dephasing time of 495 ± 10 fs. The dephasing is solely due to the phonon energy decay with corresponding homogeneous linewidth of 21.4 ± 0.5 cm−1. Low temperature linewidth of 14.7 cm−1 is estimated from our data assuming that down-conversion phonon relaxation process is dominant. Our results can help to understand stimulated Raman generation and oscillation of Stokes wave in laser systems where Raman gain is critically dependent on dephasing time.
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63.20.dd Measurements
78.30.Hv Other nonmetallic inorganics
78.47.jh Coherent nonlinear optical spectroscopy

Role of correlation effects in the superconducting material: InV6S8

M. Ramzan and R. Ahuja

Appl. Phys. Lett. 99, 221904 (2011); http://dx.doi.org/10.1063/1.3664219 (3 pages)

Online Publication Date: 28 November 2011

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In this letter, we present the high pressure studies to compute the structural parameters and electronic structure of InV6S8, using the first principles density functional theory (DFT) and DFT + U methods. While LDA and GGA fail to give the correct electronic and structural properties, the DFT + U method performs well to reproduce the experimental observed quantities of InV6S8. We analyze the electronic structures and nesting of InV6S8 at different pressure values and show that the nesting of energy bands reduces with compression. Finally, we conclude that the Hubbard like correction is necessary to take into account the correlation effects, which are very important in the correct description of InV6S8, by choosing the moderate value of U.
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74.20.Pq Electronic structure calculations
74.25.Jb Electronic structure (photoemission, etc.)
71.10.Fd Lattice fermion models (Hubbard model, etc.)
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Energy-filtered phase retrieval using the transport of intensity equation

V. J. Keast, M. J. Gladys, T. C. Petersen, C. Dwyer, C. T. Koch, T. Haber, and G. Kothleitner

Appl. Phys. Lett. 99, 221905 (2011); http://dx.doi.org/10.1063/1.3663572 (3 pages)

Online Publication Date: 29 November 2011

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Energy-filtered imaging was combined with phase retrieval to study plasmon scattering contributions to electron phase shifts surrounding gold nanoparticles. Spectral windows with sufficient energy resolution to exclude plasmon scattering were used to measure through-focal intensity derivatives and retrieve phase maps via the transport of intensity equation. Phase excursions in the phase maps that included plasmon scattering were found to disagree with theory by at least an order of magnitude. This discrepancy was attributed to subtle particle instabilities under the electron beam, which lead to systematic errors in the retrieved phase maps.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.22.Lp Collective excitations
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Enhanced and reduced transmission of acoustic waves with bubble meta-screens

Alice Bretagne, Arnaud Tourin, and Valentin Leroy

Appl. Phys. Lett. 99, 221906 (2011); http://dx.doi.org/10.1063/1.3663623 (3 pages) | Cited 2 times

Online Publication Date: 29 November 2011

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We present a class of sonic meta-screens for manipulating air-borne acoustic waves at ultrasonic or audible frequencies. Our screens consist of periodic arrangements of air bubbles in water or possibly embedded in a soft elastic matrix. They can be used for soundproofing but also for exalting transmission at an air/water interface or even to achieve enhanced absorption.
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62.60.+v Acoustical properties of liquids
47.55.D- Drops and bubbles
81.40.Jj Elasticity and anelasticity, stress-strain relations

Broadband polarization transformation via enhanced asymmetric transmission through arrays of twisted complementary split-ring resonators

Zeyong Wei, Yang Cao, Yuancheng Fan, Xing Yu, and Hongqiang Li

Appl. Phys. Lett. 99, 221907 (2011); http://dx.doi.org/10.1063/1.3664774 (3 pages) | Cited 9 times

Online Publication Date: 29 November 2011

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This study proposes an ultrathin chiral metamaterial slab stacked with twisted complementary split-ring resonators (CSRRs) for highly efficient broadband polarization transformation. The polarization of linearly polarized electromagnetic waves can be rotated in a specific direction by passing it through such a slab having a thickness of about one-tenth the operational wavelength. Microwave experiments verified the theoretically predicted conversion efficiency of up to 96% covering a bandwidth of 24% of the central wavelength. CSRRs with circular symmetry provide increased interlayer coupling strength, which produces a high-efficiency broadband response and strong isolation of the original polarization.
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41.20.Jb Electromagnetic wave propagation; radiowave propagation
81.05.Xj Metamaterials for chiral, bianisotropic and other complex media

Electronic structure and symmetry of valence states of epitaxial NiTiSn and NiZr0.5Hf0.5Sn thin films by hard x-ray photoelectron spectroscopy

Xeniya Kozina, Tino Jaeger, Siham Ouardi, Andrei Gloskowskij, Gregory Stryganyuk, Gerhard Jakob, Takeharu Sugiyama, Eiji Ikenaga, Gerhard H. Fecher, and Claudia Felser

Appl. Phys. Lett. 99, 221908 (2011); http://dx.doi.org/10.1063/1.3665621 (3 pages) | Cited 5 times

Online Publication Date: 30 November 2011

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The electronic band structure of thin films and superlattices made of Heusler compounds with NiTiSn and NiZr0.5Hf0.5Sn composition was studied by means of polarization dependent hard x-ray photoelectron spectroscopy. The linear dichroism allowed to distinguish the symmetry of the valence states of the different types of layered structures. The films exhibit a larger amount of "in-gap" states compared to bulk samples. It is shown that the films and superlattices grown with NiTiSn as starting layer exhibit an electronic structure close to bulk materials.
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71.20.Be Transition metals and alloys
73.21.Cd Superlattices
73.50.Lw Thermoelectric effects
73.61.At Metal and metallic alloys
79.60.Bm Clean metal, semiconductor, and insulator surfaces
79.60.Dp Adsorbed layers and thin films
79.60.Jv Interfaces; heterostructures; nanostructures

Energy-level and optical properties of nitrogen doped TiO2: An experimental and theoretical study

P. P. González-Borrero, H. S. Bernabé, N. G. C. Astrath, A. C. Bento, M. L. Baesso, M. V. Castro Meira, J. S. de Almeida, and A. Ferreira da Silva

Appl. Phys. Lett. 99, 221909 (2011); http://dx.doi.org/10.1063/1.3664104 (3 pages) | Cited 6 times

Online Publication Date: 30 November 2011

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Photoacoustic spectroscopy was used to study nitrogen-doped titanium dioxide film. The energy positions of defect and impurity centre levels are reported. The energy levels were obtained using the excitation method and the mechanisms of the photoacoustic signal generation are discussed. The visible light absorption of the yellow film was explained considering electronic transitions between localized states within the band gap and the transitions from these states into the conduction band. Moreover, first principles calculations revealed that nitrogen doping and oxygen vacancies in titanium dioxide induce defect levels within the gap which account for the absorption in the visible light.
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78.66.Nk Insulators
61.72.jd Vacancies
78.20.Pa Photoacoustic effects
62.65.+k Acoustical properties of solids
71.20.Ps Other inorganic compounds
71.55.Ht Other nonmetals

Measuring the ordering of closely packed particles

Nizan Meitav and Erez N. Ribak

Appl. Phys. Lett. 99, 221910 (2011); http://dx.doi.org/10.1063/1.3665187 (3 pages) | Cited 2 times

Online Publication Date: 1 December 2011

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We look at irregularity and phase transitions in two-dimensional patterns. Two independent methods are provided for identifying and measuring hexagonal close packing of particles. We implemented these methods on images of melting colloidal films at different melting processes. We could easily spot various defects in the hexagonal crystal film. The feasibility of the methods is also demonstrated on human retinal images, for measuring the unit cell size and fraction of close-packed cone photoreceptors.
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64.70.dj Melting of specific substances
82.70.Dd Colloids

Temperature stability of the pentacene thin-film phase

Armin Moser, Jiří Novák, Heinz-Georg Flesch, Tatjana Djuric, Oliver Werzer, Anja Haase, and Roland Resel

Appl. Phys. Lett. 99, 221911 (2011); http://dx.doi.org/10.1063/1.3665188 (3 pages) | Cited 1 time

Online Publication Date: 1 December 2011

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This work presents the influence of temperatures above 300 K on the crystal structure and morphology of pentacene thin films. The thermal expansion of the unit cell and the relative amount of different phases are investigated via grazing incidence x-ray diffraction. Geometrical considerations about the specific molecular packing of the thin-film phase explain the anisotropic non-linear expansion. Furthermore, around 480 K, a phase transformation of the thin-film phase to the bulk phase is observed. In contrast, only a weak influence of the temperature on the height distribution of the thin-film phase crystallites is found.
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68.55.ag Semiconductors
65.40.De Thermal expansion; thermomechanical effects

Interband optical properties of silicon [001] quantum wells using a two-conduction-band k · p model

Fabienne Michelini and Issam Ouerghi

Appl. Phys. Lett. 99, 221912 (2011); http://dx.doi.org/10.1063/1.3663974 (3 pages)

Online Publication Date: 1 December 2011

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Using analytical k · p calculations, we are able to describe the zone-center interband optical properties of Si [001] quantum wells in agreement with first principle calculations. Within the k · p band formalism, we understand how the sp*-like character of the conduction band minimum determines a total anisotropy of the polarization. Similarly, its indirect gap nature generates atomic-scale oscillations of the optical matrix elements, which suggests a giant variability of the absorption. Our results are also in agreement with photoluminescence experiments on ultrathin Si/SiO2 films.
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78.67.De Quantum wells
71.15.-m Methods of electronic structure calculations
73.20.At Surface states, band structure, electron density of states
73.21.Fg Quantum wells
78.55.Ap Elemental semiconductors
78.66.Db Elemental semiconductors and insulators

Rapid growth and formation mechanism of ultrafine structural oxide eutectic ceramics by laser direct forming

H. J. Su, J. Zhang, L. Liu, J. Eckert, and H. Z. Fu

Appl. Phys. Lett. 99, 221913 (2011); http://dx.doi.org/10.1063/1.3664108 (3 pages) | Cited 3 times

Online Publication Date: 1 December 2011

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Melt growth of oxide eutectic is an important and fast-growing research topic in the fields of both applied physics and materials science. Rapid one-step fabrication of melt-grown oxide ceramics with large size is developed using laser direct forming. The near 100% density of Al2O3/YAG eutectic ceramic in situ composite free of pore and cracks is rapidly melted/solidified directly from Al2O3-Y2O3 powder without any preforming or sintering. Uniform three-dimensional network of ultrafine nanostructured eutectic microstructure is obtained. The direct experimental evidence of faceted-nonfaceted eutectic transition at high growth rate is presented and the physical model of the microstructural formation based on atom cluster elementary process is proposed. This technology provides a rapid freeform fabrication of high-performance complex shaped ceramics for various applications.
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81.16.Mk Laser-assisted deposition
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
81.30.Fb Solidification
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)

Anisotropy of electron and hole g-factors in (In,Ga)As quantum dots

A. Schwan, B.-M. Meiners, A. Greilich, D. R. Yakovlev, M. Bayer, A. D. B. Maia, A. A. Quivy, and A. B. Henriques

Appl. Phys. Lett. 99, 221914 (2011); http://dx.doi.org/10.1063/1.3665634 (3 pages) | Cited 7 times

Online Publication Date: 1 December 2011

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The g-factor tensors of electron and hole in self-assembled (In,Ga)As/GaAs quantum dots are studied by time-resolved ellipticity measurements in a three dimensional vector magnet system. Both g-factor tensors show considerable deviations from isotropy. These deviations are much more pronounced for the hole than for the electron and are described by different anisotropy factors, which can even have opposite signs.
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71.20.Nr Semiconductor compounds
73.21.La Quantum dots
81.07.Ta Quantum dots
81.16.Dn Self-assembly
78.47.D- Time resolved spectroscopy (>1 psec)
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Evaluating the electrical properties of silicon wafer solar cells using hyperspectral imaging of luminescence

Matthew P. Peloso, Jen Sern Lew, Thorsten Trupke, Marius Peters, Roland Utama, and Armin G. Aberle

Appl. Phys. Lett. 99, 221915 (2011); http://dx.doi.org/10.1063/1.3664134 (3 pages) | Cited 2 times

Online Publication Date: 1 December 2011

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A line-imaging spectrometer is used to collect the spectrum of electroluminescence at each point of a multicrystalline silicon wafer solar cell. Characterization of the diffusion lengths of minority charge carriers is developed using a specific feature of the luminescence spectral signature. It is shown that various material and device parameters affecting the luminescence spectral signature may be determined independently. Diffusion length images derived from the proposed hyperspectral method are assessed against diffusion lengths obtained by light beam induced current measurements. Using hyperspectral imaging, diffusion lengths of minority charge carriers in a silicon wafer solar cell can be determined.
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88.40.jj Silicon solar cells
88.40.hj Efficiency and performance of solar cells

Slow light in one dimensional metallic-dielectric photonic crystals due to sign change of the effective dielectric constant

Yun Shen, Guo Ping Yu, and Guo Ping Wang

Appl. Phys. Lett. 99, 221916 (2011); http://dx.doi.org/10.1063/1.3666028 (3 pages) | Cited 3 times

Online Publication Date: 1 December 2011

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We numerically show slow light can be achieved in one dimensional metallic-dielectric photonic crystals as a result of sign change of the effective dielectric constant. Due to the occurrence of slow light, rainbow trapping effect is realizable in chirped one dimensional metallic-dielectric photonic crystals where thicknesses of metal slabs linearly increase. The results imply the potential applications in constructing nanoscale optical buffer, memories, filter, sorter, etc. for high density integration of optical circuits.
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42.70.Qs Photonic bandgap materials
77.22.Ch Permittivity (dielectric function)

A strain relief mode at interface of GaSb/GaAs grown by metalorganic chemical vapor deposition

W. Zhou, W. Tang, and K. M. Lau

Appl. Phys. Lett. 99, 221917 (2011); http://dx.doi.org/10.1063/1.3663571 (3 pages) | Cited 1 time

Online Publication Date: 2 December 2011

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An “atomic chain-like” array distinct from interfacial misfit dislocation arrays was characterized at the interface of GaSb/GaAs grown by metalorganic chemical vapor deposition. Using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and x-ray energy-dispersive spectroscopy, we obtained the chemical composition of this structure and confirmed significant anion intermixing within the GaAsSb alloy layer at the interface. Atomic-scale HAADF-STEM imaging and geometric phase analysis revealed variations in the local strain field, indicating that the GaAsSb layer can partially relax the lattice misfit strain. Our results indicate that self-organized alloy intermixing during GaSb epilayer growth on GaAs provides strain relief.
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81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
68.47.Fg Semiconductor surfaces
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
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