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3 Sep 2012

Volume 101, Issue 10, Articles (10xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 103101 (2012); http://dx.doi.org/10.1063/1.4748099 (5 pages)

Massimo Cuscunà, Annalisa Convertino, Emiliano Zampetti, Antonella Macagnano, Alessandro Pecora, Guglielmo Fortunato, Laura Felisari, Giuseppe Nicotra, Corrado Spinella, and Faustino Martelli
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Controlling spatial distribution of thermal poling induced second-order optical nonlinearity with multilayered structures

Hong-Lin An and Simon Fleming

Appl. Phys. Lett. 101, 101101 (2012); http://dx.doi.org/10.1063/1.4749814 (4 pages)

Online Publication Date: 4 September 2012

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Fused silica plates with boron-doped silicate multilayered thin films are thermally poled to create second-order optical nonlinearity for nonlinear optical applications. Measurement results from second harmonic microscopy show that the spatial distribution of the induced nonlinearity peaks at the interfaces between different layers where there is an abrupt change in boron concentration. A simple model is suggested to simulate the nonlinearity-trapping effect at the interfaces. This nonlinearity-trapping effect is not restricted to interfaces with abrupt refractive index changes; results from silica plates with deposited multilayered pure silica thin films show that the interface between the silica substrate and the silica thin film also has the nonlinearity-trapping effect.
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78.66.Nk Insulators
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
68.55.-a Thin film structure and morphology

Impact of resonator geometry and its coupling with ground plane on ultrathin metamaterial perfect absorbers

Li Huang, Dibakar Roy Chowdhury, Suchitra Ramani, Matthew T. Reiten, Sheng-Nian Luo, Abul K. Azad, Antoinette J. Taylor, and Hou-Tong Chen

Appl. Phys. Lett. 101, 101102 (2012); http://dx.doi.org/10.1063/1.4749823 (4 pages) | Cited 2 times

Online Publication Date: 4 September 2012

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We investigate the impact of resonator geometry and its coupling with ground plane on the performance of metamaterial perfect absorbers. Using a cross-resonator as an example structure, we find that the absorber thickness can be further reduced through modifying the geometric dimensions of the resonators. Numerical simulations and theoretical calculations reveal that destructive interference of multiple reflections is responsible for the near-unity absorption. The near-field coupling between the resonator array and ground plane can be significant. When this coupling is taken into account, the theoretical results calculated using the interference model are in excellent agreement with experiments and numerical simulations.
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42.79.-e Optical elements, devices, and systems
42.70.-a Optical materials

Buried heterostructure vertical-cavity surface-emitting laser with semiconductor mirrors

G. Zhao, Y. Zhang, D. G. Deppe, K. Konthasinghe, and A. Muller

Appl. Phys. Lett. 101, 101103 (2012); http://dx.doi.org/10.1063/1.4750062 (3 pages)

Online Publication Date: 4 September 2012

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We report a buried heterostructure vertical-cavity surface-emitting laser fabricated by epitaxial regrowth over an InGaAs quantum well gain medium. The regrowth technique enables microscale lateral confinement that preserves a high cavity quality factor (loaded Q ≈ 4000) and eliminates parasitic charging effects found in existing approaches. Under optimal spectral overlap between gain medium and cavity mode (achieved here at T = 40 K), lasing was obtained with an incident optical power as low as Pth = 10 mW (λp = 808 nm). The laser linewidth was found to be ≈ 3 GHz at Pp ≈ 5 Pth.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
42.79.Bh Lenses, prisms and mirrors

Apodized focusing subwavelength grating couplers for suspended membrane waveguides

Zhenzhou Cheng, Xia Chen, Chi Yan Wong, Ke Xu, and Hon Ki Tsang

Appl. Phys. Lett. 101, 101104 (2012); http://dx.doi.org/10.1063/1.4750071 (4 pages)

Online Publication Date: 4 September 2012

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We demonstrate an apodized focusing subwavelength grating (SWG) for suspended membrane waveguides on silicon-on-insulator. Finite-difference time-domain simulation predicts −1.7 dB coupling efficiency and a 3 dB bandwidth of ∼50 nm for the transverse-magnetic mode apodized SWG, which has 98% field overlap with propagation mode in the single mode fiber. A modified phase matching formula is proposed to design the focusing apodized SWG. Better than −3.0 dB coupling efficiency and a 3 dB optical bandwidth of ∼50 nm is demonstrated experimentally.
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42.81.Qb Fiber waveguides, couplers, and arrays
42.82.Bq Design and performance testing of integrated-optical systems
42.15.Eq Optical system design
42.79.Dj Gratings

1550 nm ErAs:In(Al)GaAs large area photoconductive emitters

S. Preu, M. Mittendorff, H. Lu, H. B. Weber, S. Winnerl, and A. C. Gossard

Appl. Phys. Lett. 101, 101105 (2012); http://dx.doi.org/10.1063/1.4750244 (4 pages) | Cited 1 time

Online Publication Date: 4 September 2012

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We report on high power terahertz (THz) emission from ErAs-enhanced In0.52Al0.48As-In0.53Ga0.47As superlattices for operation at 1550 nm. ErAs clusters act as efficient recombination centers. The optical power is distributed among a large, microstructured area in order to reduce the local optical intensity. A THz field strength of 0.7 V/cm (1 V/cm peak-to-peak) at 100 mW average optical power has been obtained, with emission up to about 4 THz in air, limited by the detection crystal used in the system.
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81.05.Ea III-V semiconductors
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
73.63.-b Electronic transport in nanoscale materials and structures
78.70.Gq Microwave and radio-frequency interactions

High-Q AlN photonic crystal nanobeam cavities fabricated by layer transfer

S. Sergent, M. Arita, S. Kako, K. Tanabe, S. Iwamoto, and Y. Arakawa

Appl. Phys. Lett. 101, 101106 (2012); http://dx.doi.org/10.1063/1.4751336 (4 pages)

Online Publication Date: 5 September 2012

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High-quality-factor one-dimensional photonic crystal nanobeam cavities embedding GaN/AlN quantum dots are fabricated by an epilayer transfer method. The GaN/AlN quantum dots are first grown on SiC before being transferred to a Si substrate using a hydrogen silsesquioxane bonding layer and highly selective back-etching of the SiC. Nanobeam cavities are then fabricated by electron-beam lithography, dry etching, and HF underetching of the bonding layer. The resulting nanocavity exhibits quality factors larger than 6.3 × 103, the highest quality factor reported to date for an optically active group-III nitride photonic crystal nanocavity.
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42.82.Cr Fabrication techniques; lithography, pattern transfer
42.70.Qs Photonic bandgap materials

Study of semiconductor quantum dots influence on photorefractivity of liquid crystals

A. Anczykowska, S. Bartkiewicz, M. Nyk, and J. Mysliwiec

Appl. Phys. Lett. 101, 101107 (2012); http://dx.doi.org/10.1063/1.4750060 (4 pages)

Online Publication Date: 5 September 2012

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In this paper, we present the results of doping nematic liquid crystals (nLCs) with semiconductor quantum dots (QDs) where we discuss the CdS and CdSe QDs influence on the optical properties of investigated liquid crystal structures, i.e., diffraction efficiency enhancement. We also present the mathematical model describing the interaction between QDs and nLC molecules in the liquid crystal volume. The aim of this study is to improve the comprehension of the mechanisms of photorefractive effect observed in functionalized liquid crystal structures, which can lead to the development of more efficient holographic materials for dynamic data processing applications.
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78.20.Mg Photorefractive effects
78.15.+e Optical properties of fluid materials, supercritical fluids and liquid crystals
61.30.Cz Molecular and microscopic models and theories of liquid crystal structure
42.70.Df Liquid crystals

Gray-scale and color optical encryption based on computational ghost imaging

Mehrdad Tanha, Reza Kheradmand, and Sohrab Ahmadi-Kandjani

Appl. Phys. Lett. 101, 101108 (2012); http://dx.doi.org/10.1063/1.4748875 (3 pages) | Cited 1 time

Online Publication Date: 5 September 2012

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We propose two approaches for optical encryption based on computational ghost imaging. These methods have the capability of encoding ghost images reconstructed from gray-scale images and colored objects. We experimentally demonstrate our approaches under eavesdropping in two different setups, thereby proving the robustness and simplicity thereof for encryption compared with previous algorithms.
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42.30.Va Image forming and processing
42.30.Wb Image reconstruction; tomography
84.40.Ua Telecommunications: signal transmission and processing; communication satellites

Self-accelerating parabolic beams in quadratic nonlinear media

Ido Dolev, Ana Libster, and Ady Arie

Appl. Phys. Lett. 101, 101109 (2012); http://dx.doi.org/10.1063/1.4748979 (4 pages)

Online Publication Date: 5 September 2012

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We present experimental observation of self-accelerating parabolic beams in quadratic nonlinear media. We show that the intensity peaks of the first and second harmonics are asynchronous with respect to one another in the two transverse coordinates. In addition, the two coupled harmonics have the same acceleration within and after the nonlinear medium. We also study the evolution of second harmonic accelerating beams inside the quadratic media and their correlation with theoretical beams.
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42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Chalcogenide microwire based Raman laser

Raja Ahmad and Martin Rochette

Appl. Phys. Lett. 101, 101110 (2012); http://dx.doi.org/10.1063/1.4751850 (3 pages) | Cited 1 time

Online Publication Date: 6 September 2012

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We present a Raman fiber laser based on a chalcogenide glass microwire. The microwire is pumped in the C-band, and the resulting laser oscillates in the L-band. The power conversion efficiency of the device is ∼17%, and the laser threshold is 23.2 dBm (pulse energy = 4.65 pJ) in peak pump power. By extension, the device can be used for all-optical wavelength conversion of existing laser sources in the useful transmission window of chalcogenide, from the C-band up to a wavelength of ∼10 μm in the mid-infrared.
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42.55.Wd Fiber lasers
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.70.Ce Glasses, quartz
42.60.By Design of specific laser systems

Frequency and amplitude stabilized terahertz quantum cascade laser as local oscillator

Y. Ren, D. J. Hayton, J. N. Hovenier, M. Cui, J. R. Gao, T. M. Klapwijk, S. C. Shi, T.-Y. Kao, Q. Hu, and J. L. Reno

Appl. Phys. Lett. 101, 101111 (2012); http://dx.doi.org/10.1063/1.4751247 (4 pages) | Cited 1 time

Online Publication Date: 6 September 2012

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We demonstrate an experimental scheme to simultaneously stabilize the frequency and amplitude of a 3.5 THz third-order distributed feedback quantum cascade laser as a local oscillator. The frequency stabilization has been realized using a methanol absorption line, a power detector, and a proportional-integral-derivative (PID) loop. The amplitude stabilization of the incident power has been achieved using a swing-arm voice coil actuator as a fast optical attenuator, using the direct detection output of a superconducting mixer in combination with a 2nd PID loop. Improved Allan variance times of the entire receiver, as well as the heterodyne molecular spectra, are demonstrated.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.79.-e Optical elements, devices, and systems
33.20.Bx Radio-frequency and microwave spectra
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Size effect on the electron wind force for electromigration at the top metal-dielectric interface in nanoscale interconnects

Zhuo-Jie Wu and Paul S. Ho

Appl. Phys. Lett. 101, 101601 (2012); http://dx.doi.org/10.1063/1.4750067 (5 pages)

Online Publication Date: 4 September 2012

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We report a classical model on the size effect of the electron wind force on a metal atom at the metal-dielectric interface in nanoscale interconnects. The effect is expressed as a size factor S for the effective charge Z*e. It is found that the size factor decreases with scaling due to reduced electron drift momentum as a result of scattering at interfaces and grain boundaries. The electron wind force on the metal atoms at the top metal-dielectric interface is enhanced by the interface scattering. This force enhancement is partially mitigated by the grain boundary scattering.
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66.30.Qa Electromigration
72.30.+q High-frequency effects; plasma effects
61.72.Mm Grain and twin boundaries

Doubling of rocking resonance frequency of an adhesive microparticle vibrating on a surface

Armin Saeedi Vahdat, Saber Azizi, and Cetin Cetinkaya

Appl. Phys. Lett. 101, 101602 (2012); http://dx.doi.org/10.1063/1.4751109 (4 pages)

Online Publication Date: 7 September 2012

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For some spherical micro-particles on a vibrating flat substrate, in addition to their predicted rocking resonance frequencies, other resonance peaks at their doubles are observed. Here, a mathematical model and experimental results are presented for explaining this observation. It is determined that the frequency doubling is caused by nonlinear coupling between the out-of-plane and rocking modes of motion, and whirling-like motion that must be present for the presence of doubling effect. It is also found that the work-of-adhesion values extracted from the experimental resonance frequencies of a set of particles using the developed model are in good agreement with those reported in the literature.
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68.35.Np Adhesion
68.35.Gy Mechanical properties; surface strains
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Correlating surface segregation and microstructural evolution of electrochemically deposited copper

Michael Rizzolo, Steve Novak, Eric Lifshin, and Kathleen A. Dunn

Appl. Phys. Lett. 101, 101901 (2012); http://dx.doi.org/10.1063/1.4750252 (3 pages)

Online Publication Date: 4 September 2012

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Electroplating bath additives become problematic when incorporated into electrochemically deposited copper as impurities. The surface segregation of these impurities during spontaneous microstructural transformation was monitored by secondary ion mass spectrometry and found to be no different than the surface chemistry of the non-transforming plated samples or even sputtered copper. The results show that microstructural transformation of electroplated copper progresses despite the presence of impurities, suggesting foreign constituents are not in fact responsible for grain boundary pinning in these films.
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68.35.Dv Composition, segregation; defects and impurities
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Pq Electrodeposition, electroplating
82.80.Ms Mass spectrometry (including SIMS, multiphoton ionization and resonance ionization mass spectrometry, MALDI)
68.55.at Other materials
61.72.Mm Grain and twin boundaries

Praseodymium valence determination in Lu2SiO5, Y2SiO5, and Lu3Al5O12 scintillators by x-ray absorption spectroscopy

Mariya Zhuravleva, Stephan Friedrich, and Charles L. Melcher

Appl. Phys. Lett. 101, 101902 (2012); http://dx.doi.org/10.1063/1.4748168 (4 pages)

Online Publication Date: 5 September 2012

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Until now, determination of both Pr3+ and Pr4+ at the low concentration levels commonly used in single crystal scintillators has proven to be difficult. We have found that it is possible to use synchrotron radiation and superconducting tunnel junction detectors to measure the X-ray absorption on the M4 and M5 edges of Pr to directly determine Pr3+ and Pr4+ in Lu2SiO5, Y2SiO5, and Lu3Al5O12. The spectra were measured at room temperature and compared to model samples of trivalent and tetravalent praseodymium, which provided clear signatures of the two charge states. The results show predominant Pr(III) in most samples.
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71.55.Ht Other nonmetals
78.70.Ps Scintillation
78.55.Hx Other solid inorganic materials
78.70.Dm X-ray absorption spectra

Selectively probing vibrations in a plasmonic supracrystal

Pierre-Adrien Mante, Hung-Ying Chen, Meng-Hsien Lin, Yu-Chieh Wen, Shangjr Gwo, and Chi-Kuang Sun

Appl. Phys. Lett. 101, 101903 (2012); http://dx.doi.org/10.1063/1.4750140 (5 pages) | Cited 1 time

Online Publication Date: 5 September 2012

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The coupling of plasmonic resonances with the multiple phonon modes of a plasmonic supracrystal is studied. Ultrafast optical pump-probe spectroscopy with variable wavelength allows the selective detection of the breathing mode, the interparticle vibrations, and the vibration of the whole structure. Thanks to this selectivity, the characterization of the bonding strength between nanoparticles in different directions of the supracrystal is possible. The observation of these vibrations could be useful for the realization of future phonon modulated photonic and plasmonic devices.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
71.45.Gm Exchange, correlation, dielectric and magnetic response functions, plasmons
78.47.J- Ultrafast spectroscopy (<1 psec)

Prospects for achieving high dynamic compression with low energy

Michael R. Armstrong, Jonathan C. Crowhurst, Sorin Bastea, William M. Howard, Joseph M. Zaug, and Alexander F. Goncharov

Appl. Phys. Lett. 101, 101904 (2012); http://dx.doi.org/10.1063/1.4751107 (3 pages) | Cited 1 time

Online Publication Date: 5 September 2012

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Laser driven dynamic compression experiments may, in materials with picosecond equilibration times, be possible with orders of magnitude less drive energy than currently used. As we show, the compression energy for geometrically similar experiments varies as the third power of the time scale of compression. For materials which equilibrate and can be characterized on picosecond time scales, the compression energy can be orders of magnitude smaller than the 1–100 ns scale time scale of many current experiments. The use of substantially lower compression energy is a great practical advantage in such experiments, potentially enabling the observation of extreme states of matter with table top scale laser systems.
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42.62.-b Laser applications
78.47.J- Ultrafast spectroscopy (<1 psec)

Defect microstructural evolution in ion irradiated metallic nanofoils: Kinetic Monte Carlo simulation versus cluster dynamics modeling and in situ transmission electron microscopy experiments

Donghua Xu, Brian D. Wirth, Meimei Li, and Marquis A. Kirk

Appl. Phys. Lett. 101, 101905 (2012); http://dx.doi.org/10.1063/1.4748980 (5 pages) | Cited 1 time

Online Publication Date: 5 September 2012

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Understanding materials degradation under intense irradiation is important for the development of next generation nuclear power plants. Here we demonstrate that defect microstructural evolution in molybdenum nanofoils in situ irradiated and observed on a transmission electron microscope can be reproduced with high fidelity using an object kinetic Monte Carlo (OKMC) simulation technique. Main characteristics of defect evolution predicted by OKMC, namely, defect density and size distribution as functions of foil thickness, ion fluence and flux, are in excellent agreement with those obtained from the in situ experiments and from previous continuum-based cluster dynamics modeling. The combination of advanced in situ experiments and high performance computer simulation/modeling is a unique tool to validate physical assumptions/mechanisms regarding materials response to irradiation, and to achieve the predictive power for materials stability and safety in nuclear facilities.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
61.82.Rx Nanocrystalline materials
61.80.Jh Ion radiation effects

Raman spectroscopy of the interlayer shear mode in few-layer MoS2 flakes

G. Plechinger, S. Heydrich, J. Eroms, D. Weiss, C. Schüller, and T. Korn

Appl. Phys. Lett. 101, 101906 (2012); http://dx.doi.org/10.1063/1.4751266 (3 pages) | Cited 5 times

Online Publication Date: 5 September 2012

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Single- and few-layer MoS2 has recently gained attention as an interesting material system for opto-electronics. Here, we report on scanning Raman measurements on few-layer MoS2 flakes prepared by exfoliation. We observe a Raman mode corresponding to a rigid shearing oscillation of adjacent layers. This mode appears at very low Raman shifts between 20 and 30 cm−1. Its position strongly depends on the number of layers, which we independently determine using atomic force microscopy and investigation of the other characteristic Raman modes. Raman spectroscopy of the shear mode, therefore, is a useful tool to determine the number of layers for few-layer MoS2 flakes.
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
78.30.Hv Other nonmetallic inorganics

Cationic point defects in CuGaSe2 from a structural perspective

C. Stephan, T. Scherb, C. A. Kaufmann, S. Schorr, and H.-W. Schock

Appl. Phys. Lett. 101, 101907 (2012); http://dx.doi.org/10.1063/1.4751338 (4 pages)

Online Publication Date: 6 September 2012

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The chalcopyrite semiconductors show large tolerances to deviations from stoichiometry by keeping the crystal structure. Such deviations always cause structural inhomogeneities and charge mismatches which influence the material properties. We studied the type and concentration of cationic point defects on Cu-poor CuGaSe2 powders by the complementary use of neutrons and photons. It is demonstrated that the main existing defects in this Cu-poor wide gap semiconductor are copper-vacancies (VCu) and gallium on interstitial sites (Gai). The latter may explain why tailoring a highly efficient CuGaSe2 solar cell is an even more challenging task than previously expected.
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61.72.jj Interstitials
61.72.jd Vacancies
61.66.Bi Elemental solids
61.66.Dk Alloys
88.40.H- Solar cells (photovoltaics)
88.40.jn Thin film Cu-based I-III-VI2 solar cells
61.66.Fn Inorganic compounds

Influence of volume fraction on the yield behavior of giant electrorheological fluid

Zhenyang Song, Yuchuan Cheng, Jinghua Wu, Jianjun Guo, and Gaojie Xu

Appl. Phys. Lett. 101, 101908 (2012); http://dx.doi.org/10.1063/1.4751264 (3 pages)

Online Publication Date: 6 September 2012

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In this letter, we provide a phenomenological model to explain the recently discovered volume fraction effect in giant electrorheological (ER) fluids. We attribute the exponential dependence of yield stress on volume fraction to the repulsive interaction between particle chains. The increase of particle concentration increases the inter-chain repulsive interaction, which raises potential energy in electrorheological fluid and consequently the yield stress. The acquired normal force data validated our model.
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62.10.+s Mechanical properties of liquids
47.65.Gx Electrorheological fluids

Enhanced thermoelectric properties of CePd3−xPtx

S. R. Boona and D. T. Morelli

Appl. Phys. Lett. 101, 101909 (2012); http://dx.doi.org/10.1063/1.4751265 (4 pages) | Cited 1 time

Online Publication Date: 6 September 2012

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We have explored the structural, magnetic, and thermoelectric properties of the CePd3−xPtx (0 < x < 1) solid solution. The similar chemical properties of palladium and platinum appear to result in a minimal perturbation to the intermediate valent state that is responsible for high Seebeck coefficient, while the large mass difference between the two elements significantly reduces the lattice thermal conductivity. The result is a 40% increase of the thermoelectric figure of merit at 100 K and a 30% increase at 300 K; the latter value is the highest value ever reported for any CePd3-based material.
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72.15.Jf Thermoelectric and thermomagnetic effects
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
71.28.+d Narrow-band systems; intermediate-valence solids
75.20.Hr Local moment in compounds and alloys; Kondo effect, valence fluctuations, heavy fermions
61.66.Dk Alloys
75.30.Cr Saturation moments and magnetic susceptibilities

Mechanical properties of metal-organic frameworks: An indentation study on epitaxial thin films

S. Bundschuh, O. Kraft, H. K. Arslan, H. Gliemann, P. G. Weidler, and C. Wöll

Appl. Phys. Lett. 101, 101910 (2012); http://dx.doi.org/10.1063/1.4751286 (4 pages) | Cited 2 times

Online Publication Date: 6 September 2012

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We have determined the hardness and Young's modulus of a highly porous metal-organic framework (MOF) using a standard nanoindentation technique. Despite the very low density of these films, 1.22 g cm−3, Young's modulus reaches values of almost 10 GPa for HKUST-1, demonstrating that this porous coordination polymer is substantially stiffer than normal polymers. This progress in characterizing mechanical properties of MOFs has been made possible by the use of high quality, oriented thin films grown using liquid phase epitaxy on modified Au substrates.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
61.43.Gt Powders, porous materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.Qp Friction, tribology, and hardness
68.55.-a Thin film structure and morphology

Anisotropic optical transmission of femtosecond laser induced periodic surface nanostructures on indium-tin-oxide films

Chih Wang, Hsuan-I Wang, Chih-Wei Luo, and Jihperng Leu

Appl. Phys. Lett. 101, 101911 (2012); http://dx.doi.org/10.1063/1.4751983 (4 pages)

Online Publication Date: 7 September 2012

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Two types of periodic nanostructures, self-organized nanodots and nanolines, were fabricated on the surfaces of indium-tin-oxide (ITO) films using femtosecond laser pulse irradiation. Multiple periodicities (approximately 800 nm and 400 nm) were clearly observed on the ITO films with nanodot and nanoline structures and were identified using two-dimensional Fourier transformation patterns. Both nanostructures show the anisotropic transmission characteristics in the visible range, which are strongly correlated with the geometry and the metallic content of the laser-induced nanostructures.
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78.66.Li Other semiconductors
78.47.J- Ultrafast spectroscopy (<1 psec)
42.62.-b Laser applications
78.40.Fy Semiconductors
81.16.Mk Laser-assisted deposition
81.16.Dn Self-assembly

Strong atomic ordering in Gd-doped GaN

Manabu Ishimaru, Kotaro Higashi, Shigehiko Hasegawa, Hajime Asahi, Kazuhisa Sato, and Toyohiko J. Konno

Appl. Phys. Lett. 101, 101912 (2012); http://dx.doi.org/10.1063/1.4751245 (4 pages)

Online Publication Date: 7 September 2012

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Gd-doped GaN (Ga1−xGdxN) thin films were grown on a GaN(001) template by radio frequency plasma-assisted molecular beam epitaxy and characterized by means of x-ray diffraction (XRD) and transmission electron microscopy (TEM). Three samples with a different Gd composition were prepared in this study: x = 0.02, 0.05, and 0.08. XRD and TEM results revealed that the low Gd concentration GaN possesses the wurtzite structure. On the other hand, it was found that an ordered phase with a quadruple-periodicity along the [001] direction in the wurtzite structure is formed throughout the film with x = 0.08. We proposed the atomistic model for the superlattice structure observed here.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
61.72.uj III-V and II-VI semiconductors
68.55.ag Semiconductors
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