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18 Feb 2013

Volume 102, Issue 7, Articles (07xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 102, 073101 (2013); http://dx.doi.org/10.1063/1.4790646 (4 pages)

V. Reboud, J. Romero-Vivas, P. Lovera, N. Kehagias, T. Kehoe, G. Redmond, and C. M. Sotomayor Torres
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Molecular beam epitaxial growth and optical properties of red-emitting (λ = 650 nm) InGaN/GaN disks-in-nanowires on silicon

S. Jahangir, M. Mandl, M. Strassburg, and P. Bhattacharya

Appl. Phys. Lett. 102, 071101 (2013); http://dx.doi.org/10.1063/1.4793300 (5 pages)

Online Publication Date: 20 February 2013

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We have investigated the radiative properties of InGaN disks in GaN nanowires grown by plasma enhanced molecular beam epitaxy on (001) silicon substrates. The growth of the nanowire heterostructures has been optimized to maximize the radiative efficiency, or internal quantum efficiency (IQE), for photoluminescence emission at λ = 650 nm. It is found that the IQE increases significantly (by ∼10%) to 52%, when post-growth passivation of nanowire surface with silicon nitride or parylene is applied. The increase in efficiency is supported by radiative- and nonradiative lifetimes derived from data obtained from temperature dependent- and time-resolved photoluminescence measurements. Light emitting diodes with p-i-n disk-in-nanowire heterostructures passivated with parylene have been fabricated and characterized.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
85.60.Jb Light-emitting devices
78.67.Uh Nanowires
81.07.Gf Nanowires
78.55.Cr III-V semiconductors

Numerical simulations of time-domain interferometric soft X-ray microscope with broadband high-order harmonic light sources

Reika Kanya, Atsushi Iwasaki, Takahiro Teramoto, and Kaoru Yamanouchi

Appl. Phys. Lett. 102, 071102 (2013); http://dx.doi.org/10.1063/1.4793301 (3 pages)

Online Publication Date: 20 February 2013

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A scheme for achieving high spatial resolution in soft X-ray microscopy with coherent broadband light sources is proposed, in which the chromatic aberration at a Fresnel zone plate lens can be canceled out by introducing time-delayed double pulses as an input light and by the Fourier transformation of recorded images with respect to the time delay. Numerical simulations of microscope images show that the spatial resolution of the proposed method is determined only by specifications of zone plates even when a broadband soft X-ray is used as a light source.
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07.85.Tt X-ray microscopes
42.79.Bh Lenses, prisms and mirrors
42.79.Ci Filters, zone plates, and polarizers
02.60.-x Numerical approximation and analysis

Light-driven three-dimensional rotational motion of dandelion-shaped microparticles

Hagay Shpaisman, David B. Ruffner, and David G. Grier

Appl. Phys. Lett. 102, 071103 (2013); http://dx.doi.org/10.1063/1.4793401 (4 pages)

Online Publication Date: 20 February 2013

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Chemically synthesized colloidal particles featuring large-scale surface asperities can be trapped and manipulated in fluid media through holographic optical trapping. Light scattering by these particles' surface features provides a mechanism for holographic optical traps also to exert torques on them, thereby setting them in steady rotation about arbitrary axes in three dimensions. When pairs of rotating particles are brought close enough that their surface features mesh, they form microscopic gear trains. These micro-opto-mechanical systems can be arranged in any desired three-dimensional configuration.
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42.50.Wk Mechanical effects of light on material media, microstructures and particles
42.40.My Applications

Improved Kerr constant and response time of polymer-stabilized blue phase liquid crystal with a reactive diluent

Ji-Liang Zhu, Shui-Bin Ni, Yue Song, En-Wei Zhong, Yi-Jun Wang, Chao Ping Chen, Zhicheng Ye, Gufeng He, Dong-Qing Wu, Xiao-Long Song, Jian-Gang Lu, and Yikai Su

Appl. Phys. Lett. 102, 071104 (2013); http://dx.doi.org/10.1063/1.4793416 (4 pages)

Online Publication Date: 20 February 2013

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A polymer-stabilized (PS) blue phase liquid crystal (BPLC) with fast response time and large Kerr constant is investigated by doping a low molecular weight monomer (N-vinylpyrrollidone) into a conventional PS-BPLC consisting of BPLC, RM257, and 1,1,1-trimethylolpropane triacrylate. With this polymer network system, Kerr constant and the response can be improved simultaneously. Compared to the conventional PS-BPLC, Kerr constant of the proposed PS-BPLC can increase by 54% and the response time can decrease by 23% at the same time. The contrast ratio can be kept at a high level, over 1000:1 at λ = 633 nm.
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61.30.Vx Polymer liquid crystals
78.20.Jq Electro-optical effects
61.72.up Other materials

Active subnanometer spectral control of a random laser

Marco Leonetti and Cefe López

Appl. Phys. Lett. 102, 071105 (2013); http://dx.doi.org/10.1063/1.4792759 (4 pages) | Cited 1 time

Online Publication Date: 20 February 2013

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We demonstrate an experimental technique that allows to achieve a robust control on the emission spectrum of a micro random laser and to select individual modes with sub-nanometer resolution. The presented approach relies on an optimization protocol of the spatial profile of the pump beam. Here we demonstrate not only the possibility to increase the emission at a wavelength but also that we can “isolate” an individual peak suppressing unwanted contributions form other modes.
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42.55.Mv Dye lasers
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation

Wavelength selective p-GaN/ZnO colloidal nanoparticle heterojunction photodiode

Liqiao Qin, Dali Shao, Christopher Shing, and Shayla Sawyer

Appl. Phys. Lett. 102, 071106 (2013); http://dx.doi.org/10.1063/1.4793210 (4 pages)

Online Publication Date: 20 February 2013

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An ultraviolet heterojunction photodiode consisting of epitaxially grown p-GaN layers and polyvinyl alcohol coated ZnO colloidal nanoparticles exhibits a lowpass and bandpass alternative property depending on the illumination direction. At 0 V bias, a time response on the order of 10 s of milliseconds was demonstrated with a responsivity on the order of mA/W with about 100 nW of ultraviolet illumination. The rectification ratio at ±5 V was 1000 under dark environment. Deposition of colloidal ZnO nanoparticles on an independent p-GaN substrate introduces a technique to create a heterostructure pn junction photodiode with wavelength selection by back illumination.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.30.Kk Junction diodes

Photoresponses of manganese-doped gallium nitride grown by metalorganic vapor-phase epitaxy

Jinn-Kong Sheu, Feng-Wen Huang, Yu-Hsuan Liu, P. C. Chen, Yu-Hsiang Yeh, Ming-Lun Lee, and Wei-Chih Lai

Appl. Phys. Lett. 102, 071107 (2013); http://dx.doi.org/10.1063/1.4793432 (3 pages)

Online Publication Date: 21 February 2013

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The photoresponses of gallium nitride (GaN) doped with manganese (Mn) grown by metalorganic vapor-phase epitaxy were investigated. The transmission spectroscopy obtained from the Mn-doped GaN exhibited three distinct absorption thresholds at approximately 365, 650, and 830 nm, respectively. The below-band-gap absorption peaks were attributed to the fact that the deep Mn-related states mediate the electronic transition between the valence and conduction bands. A below-band-gap spectral response ranging from 400 nm to 1000 nm was also observed from a typical GaN p-i-n photodetector with Mn-doped absorption layer. The significant below-band-gap spectral responses showed that the Mn-doped GaN-based materials have promising applications in intermediate band solar cells.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
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Stoichiometry dependence and thermal stability of conducting NdGaO3/SrTiO3 heterointerfaces

F. Gunkel, K. Skaja, A. Shkabko, R. Dittmann, S. Hoffmann-Eifert, and R. Waser

Appl. Phys. Lett. 102, 071601 (2013); http://dx.doi.org/10.1063/1.4792509 (4 pages)

Online Publication Date: 19 February 2013

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The structural and electrical properties of conducting NdGaO3/SrTiO3 (NGO/STO) heterostructures grown at various deposition temperatures were investigated. X-ray diffraction and X-ray photoelectron spectroscopy reveal a strong impact of the growth temperature on both crystallinity and cation stoichiometry of the NGO thin films. This stoichiometry variation significantly affects the electrical properties of the NGO/STO interface. High temperature conductance measurements under oxygen equilibrium conditions show a distinct conductance contribution of the NGO/STO interface up to 1000 K and exclude a conduction effect caused by a mere reduction of the STO substrate. Above 1000 K, the interface conduction is degrading due to a thermal instability. Both stoichiometry variation in as-grown films and thermal instability are attributed to the preferential evaporation of gallium from the NGO thin films at elevated temperatures.
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73.40.-c Electronic transport in interface structures
79.60.Jv Interfaces; heterostructures; nanostructures
81.15.Fg Pulsed laser ablation deposition
61.66.Bi Elemental solids
61.66.Dk Alloys
68.35.Ct Interface structure and roughness

Hydrogen plasma microlithography of graphene supported on a Si/SiO2 substrate

Baran Eren, Thilo Glatzel, Marcin Kisiel, Wangyang Fu, Rémy Pawlak, Urs Gysin, Cornelia Nef, Laurent Marot, Michel Calame, Christian Schönenberger, and Ernst Meyer

Appl. Phys. Lett. 102, 071602 (2013); http://dx.doi.org/10.1063/1.4793197 (5 pages)

Online Publication Date: 19 February 2013

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In this work, a silicon stencil mask with a periodic pattern is used for hydrogen plasma microlithography of single layer graphene supported on a Si/SiO2 substrate. Obtained patterns are imaged with Raman microscopy and Kelvin probe force microscopy, thanks to the changes in the vibrational modes and the contact potential difference (CPD) of graphene after treatment. A decrease of 60 meV in CPD as well as a significant change of the D/G ratio in the Raman spectra can be associated with a local hydrogenation of graphene, while the topography remains invariant to the plasma exposure.
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78.67.Wj Optical properties of graphene
52.77.-j Plasma applications
78.30.Na Fullerenes and related materials
63.22.Rc Phonons in graphene

Unveiling the mechanisms of dressed-photon–phonon etching based on hierarchical surface roughness measure

Makoto Naruse, Takashi Yatsui, Wataru Nomura, Tadashi Kawazoe, Masaki Aida, and Motoichi Ohtsu

Appl. Phys. Lett. 102, 071603 (2013); http://dx.doi.org/10.1063/1.4793233 (5 pages)

Online Publication Date: 20 February 2013

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Dressed-photon–phonon (DPP) etching is a disruptive technology in planarizing material surfaces because it completely eliminates mechanical contact processes. However, adequate metrics for evaluating the surface roughness and the underlying physical mechanisms are still not well understood. Here, we propose a two-dimensional hierarchical surface roughness measure, inspired by the Allan variance, that represents the effectiveness of DPP etching while conserving the original two-dimensional surface topology. Also, we build a simple physical model of DPP etching that agrees well with the experimental observations, which clearly shows the involvement of the intrinsic hierarchical properties of dressed photons, or optical near-fields, in the surface processing.
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81.65.Cf Surface cleaning, etching, patterning
63.20.dd Measurements
71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Comparison of CsBr and KBr covered Cu photocathodes: Effects of laser irradiation and work function changes

Weidong He, Subramanian Vilayurganapathy, Alan G. Joly, Tim C. Droubay, Scott A. Chambers, Juan R. Maldonado, and Wayne P. Hess

Appl. Phys. Lett. 102, 071604 (2013); http://dx.doi.org/10.1063/1.4793214 (5 pages)

Online Publication Date: 20 February 2013

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Thin films of CsBr and KBr were deposited on Cu(100) to investigate photoemission properties of these potential photocathode materials. After prolonged laser ultraviolet irradiation photoemission, quantum efficiency increases by factors of 26 and 77 for KBr/Cu(100) and CsBr/Cu(100) photocathodes, respectively. Immediately following thin film deposition, a decrease in work function is observed, compared to bare Cu, in both cases. Quantum efficiency enhancements are attributed to the decrease in photocathode work function, and photo-induced processes that introduce defect states into the alkali halide bandgap. Our results suggest that KBr, a relatively stable alkali-halide, also has potential for photocathode applications.
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85.60.Ha Photomultipliers; phototubes and photocathodes

Tuning the carrier density of LaAlO3/SrTiO3 interfaces by capping La1−xSrxMnO3

Y. J. Shi, S. Wang, Y. Zhou, H. F. Ding, and D. Wu

Appl. Phys. Lett. 102, 071605 (2013); http://dx.doi.org/10.1063/1.4793576 (4 pages)

Online Publication Date: 22 February 2013

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We present a systematical study on the electronic transport properties of the insulating LaAlO3 (3 unit cells)/SrTiO3 interfaces capping with thin layers of La1−xSrxMnO3, whose formal polarization is continually tuned by Sr doping. When the Sr doping is lower than 2/3, the LaAlO3/SrTiO3 interfaces show metallic behaviors. The carrier mobility is almost independent on the Sr doping for metallic interface, indicating that the capping layer does not change the density of the oxygen vacancies and the interface intermixing. However, the sheet carrier densities monotonically decrease as increasing Sr doping, which is ascribed to the decrease of the La1−xSrxMnO3 formal polarization. These results strongly support the intrinsic mechanism of the polar catastrophe model and provide a new approach to tailor the interface states of complex oxide heterostructures.
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73.40.-c Electronic transport in interface structures
61.72.jd Vacancies
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Microcrystalline diamond micromechanical resonators with quality factor limited by thermoelastic damping

Hadi Najar, Amir Heidari, Mei-Lin Chan, Hseuh-An Yang, Liwei Lin, David G. Cahill, and David A. Horsley

Appl. Phys. Lett. 102, 071901 (2013); http://dx.doi.org/10.1063/1.4793234 (4 pages)

Online Publication Date: 19 February 2013

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Thin-film microcrystalline diamond micromechanical resonators with mechanical quality factor limited by thermoelastic dissipation in the diamond film are demonstrated. Surface micromachined double ended tuning fork resonators were fabricated from in-situ boron doped microcrystalline diamond films deposited using hot filament chemical vapor deposition. Time-domain thermoreflectance measurements show thermal conductivity of 110 W m−1 K−1 for heat transport through the thickness of the diamond film. Measurement of the quality factor of resonators spanning a frequency range 0.5–10 MHz shows a maximum Q = 81 646 and demonstrates good agreement with quality factor limited by thermoelastic dissipation using 100 W m−1 K−1 for the in-plane thermal conductivity of the diamond film.
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85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices
07.10.Cm Micromechanical devices and systems

Atomistic simulation study of brittle failure in nanocrystalline graphene under uniaxial tension

Ajing Cao and Jianmin Qu

Appl. Phys. Lett. 102, 071902 (2013); http://dx.doi.org/10.1063/1.4793088 (5 pages)

Online Publication Date: 19 February 2013

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We show that, using molecular dynamic simulations, nanocrystalline (NC) graphene fails by brittle fracture along grain boundaries under uniaxial tension at room temperature. Initiated from either a grain-boundary triple junction or an array of vacancies on a preferential grain boundary, fracture occurs by unzipping atomic bonds along a preferential grain boundary. In sharp contrast to NC metals, no mobile dislocations are generated throughout the entire loading process, and the deformation remains fully elastic (albeit nonlinear) until the breaking of the first atomic bond due to high local stress near the initiation defect sites. Breaking of the first atomic bond triggers a cascade of bond breaking events along a preferential grain boundary that leads to the final brittle fracture failure. For the NC graphene monolayer sheet with an average grain size of ∼25 nm considered here, the predicted uniaxial tensile strength is 96.2 ± 4.2 GPa, which is one of the highest among all polycrystalline materials.
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81.05.ue Graphene
61.72.Mm Grain and twin boundaries
81.07.Bc Nanocrystalline materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
61.72.jd Vacancies
62.20.mm Fracture

Impact of substrate temperature on the structural and optical properties of strain-balanced InAs/InAsSb type-II superlattices grown by molecular beam epitaxy

Shi Liu, Hua Li, Oray O. Cellek, Ding Ding, Xiao-Meng Shen, Zhi-Yuan Lin, Elizabeth H. Steenbergen, Jin Fan, Zhao-Yu He, Jing Lu, Shane R. Johnson, David J. Smith, and Yong-Hang Zhang

Appl. Phys. Lett. 102, 071903 (2013); http://dx.doi.org/10.1063/1.4793231 (4 pages)

Online Publication Date: 20 February 2013

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Molecular beam epitaxial growth of strain-balanced InAs/InAs1−xSbx type-II superlattices on GaSb substrates has been investigated for substrate temperatures from 400 °C to 450 °C. The Sb composition is found to vary linearly with substrate temperature at constant V/III ratios. For samples grown at the optimized substrate temperature (410 °C), superlattice zero-order peak full-width at half-maximums are routinely less than 25 arc sec using high-resolution X-ray diffraction. Cross-sectional transmission electron microscopy images show the absence of any visible defects. Strong photoluminescence covers a wavelength range from 5.5 to 13 μm at 12 K. Photoluminescence linewidth simulations show satisfactory agreement with experiments.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.55.Cr III-V semiconductors
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Magnetic influence on the martensitic transformation entropy in Ni-Mn-In metamagnetic alloy

J. M. Barandiaran, V. A. Chernenko, E. Cesari, D. Salas, P. Lazpita, J. Gutierrez, and I. Orue

Appl. Phys. Lett. 102, 071904 (2013); http://dx.doi.org/10.1063/1.4793412 (4 pages)

Online Publication Date: 20 February 2013

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We study the martensitic transformation (MT) of metamagnetic shape memory alloy Ni50Mn34.5In15.5 in the magnetic fields up to 12 T. The observed dependence of the MT temperature, Tm, on the field is highly nonlinear. As far as magnetization change, ΔM, remains field-independent, a depart from linearity of Tm(H) function is attributed to a decrease of the transformation entropy, ΔS. This decrease correlates with the parameter (TC-Tm), controlled by magnetic field, where TC is the Curie temperature of austenite, and with the dependence of ΔS on the width of the MT temperature interval deduced from a ferroelastic model of MT.
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81.30.Kf Martensitic transformations
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
64.70.kd Metals and alloys
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

All-optical tuning of the Stokes shift in PbS quantum dots

B. Ullrich and J. S. Wang

Appl. Phys. Lett. 102, 071905 (2013); http://dx.doi.org/10.1063/1.4793413 (3 pages)

Online Publication Date: 21 February 2013

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The Stokes shift of colloidal 4.7 nm PbS quantum dots was measured between 5 and 300 K at incrementally increasing continuous laser intensities. The results demonstrate Stokes shift tuning by optical means only at stable given temperatures due to optically enforced electronic state alteration in the quantum dots. The tuning phenomenon is perfectly fit by a semi-empirical model, which provides a design tool for the chromaticity of quantum dots at different optical pump intensities.
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78.67.Hc Quantum dots
82.70.Dd Colloids
73.21.La Quantum dots
78.55.Hx Other solid inorganic materials

Improved electromechanical behavior in castable dielectric elastomer actuators

Samin Akbari, Samuel Rosset, and Herbert R. Shea

Appl. Phys. Lett. 102, 071906 (2013); http://dx.doi.org/10.1063/1.4793420 (5 pages)

Online Publication Date: 21 February 2013

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Non-viscoelastic castable elastomers are replacing the polyacrylate VHB films in the new generations of dielectric elastomer actuators (DEAs) to achieve fast and reliable actuation. We introduce the optimum prestretch conditions to enhance the electromechanical behavior of the castable DEAs resulting in large actuation strain. For castable actuator in which the thickness is selected independent of the prestretch, uniaxial prestretch mode offers the highest actuation strain in the transverse direction compared to biaxial and pure shear. We experimentally demonstrate that miniaturization hinders the loss of tension and up to 85% linear actuation strain is generated with a 300 × 300 μm2 polydimethylsiloxanes-based DEA.
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07.07.Tw Servo and control equipment; robots
82.35.-x Polymers: properties; reactions; polymerization

Why does the second peak of pair correlation functions split in quasi-two-dimensional disordered films?

K. Zhang, H. Li, L. Li, and X. F. Bian

Appl. Phys. Lett. 102, 071907 (2013); http://dx.doi.org/10.1063/1.4793187 (4 pages)

Online Publication Date: 21 February 2013

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Molecular dynamics simulation has been performed to study the splitting of the second peak in pair correlation functions of quasi-two-dimensional disordered film. A quasi-two-dimensional inhomogeneous structural model, which contains both crystal-like and disordered regions, supports the hypothesis that the splitting of the second peak is result of a statistical average of crystal-like and disordered structural regions in the system, not just the amorphous structure. The second-peak splitting can be viewed as a prototype of the crystal-like peak exhibiting distorted and vestigial features.
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68.55.-a Thin film structure and morphology
02.50.-r Probability theory, stochastic processes, and statistics
61.43.Bn Structural modeling: serial-addition models, computer simulation

Nanoindentation models and Young's modulus of monolayer graphene: A molecular dynamics study

Xinjun Tan, Jian Wu, Kaiwang Zhang, Xiangyang Peng, Lizhong Sun, and Jianxin Zhong

Appl. Phys. Lett. 102, 071908 (2013); http://dx.doi.org/10.1063/1.4793191 (4 pages)

Online Publication Date: 21 February 2013

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We studied the nanoindentation of monolayer graphene by molecular dynamics simulations. It is found that the response of graphene to indentation is deflection dependent. In small deflection range, the response obeys point load model, while large-deflection indentation follows the sphere load model. Hence, we proposed to make sectional fittings and use different response models in different deflection ranges. In this way, a consistent Young's modulus is obtained that is almost independent of the size ratio of intender to graphene and the pretensions of graphene. The calculated Young's modulus is about 1.00 TPa, in good agreement with the experiments.
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62.20.de Elastic moduli
62.25.-g Mechanical properties of nanoscale systems
81.40.Jj Elasticity and anelasticity, stress-strain relations

Improved light extraction efficiency of cerium-doped lutetium-yttrium oxyorthosilicate scintillator by monolayers of periodic arrays of polystyrene spheres

Zhichao Zhu, Bo Liu, Chuanwei Cheng, Yasha Yi, Hong Chen, and Mu Gu

Appl. Phys. Lett. 102, 071909 (2013); http://dx.doi.org/10.1063/1.4793303 (3 pages)

Online Publication Date: 22 February 2013

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In this Letter, monolayers of arrays of periodic polystyrene (PS) spheres are designed to couple onto the surface of cerium-doped lutetium-yttrium oxyorthosilicate scintillator to improve the light extraction efficiency. The enhancement of extraction efficiency up to 38% relative to the reference case without polystyrene spheres is achieved. Combining with the simulation for the transmission as well as its dispersion relation, detailed analysis of the effect of whispering gallery modes and diffraction on the extraction mechanism are given. As a result, the optimal diameter of 414 nm is obtained based on a trade-off between the transmission loss and the diffraction enhancement.
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78.55.Hx Other solid inorganic materials
78.70.Ps Scintillation

Graphene hydrogenation by molecular hydrogen in the process of graphene oxide thermal reduction

V. M. Mikoushkin, S. Yu. Nikonov, A. T. Dideykin, A. Ya. Vul', D. A. Sakseev, M. V. Baidakova, O. Yu. Vilkov, and A. V. Nelyubov

Appl. Phys. Lett. 102, 071910 (2013); http://dx.doi.org/10.1063/1.4793484 (4 pages)

Online Publication Date: 22 February 2013

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Thermal reduction in molecular hydrogen of the graphene oxide films has been studied by X-ray photoelectron spectroscopy using synchrotron radiation. The restoration process was revealed to be accompanied by hydrogenation due to collisionally induced interaction of molecular hydrogen with carbon atoms. One side hydrogenated graphene films consisting of 20 μm one monolayer flakes were fabricated on SiO2/Si surface with hydrogen concentration as far as 40 at. %, at which the 0.3 eV bandgap opening was observed. It was shown that both H-coverage and bandgap width of the films can be controlled by varying the temperature of the heat treatment.
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81.05.ue Graphene
79.60.Bm Clean metal, semiconductor, and insulator surfaces
81.40.Gh Other heat and thermomechanical treatments
61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
65.80.Ck Thermal properties of graphene

High resolution transmission electron microscopy characterization of fcc → 9R transformation in nanocrystalline palladium films due to hydriding

Behnam Amin-Ahmadi, Hosni Idrissi, Renaud Delmelle, Thomas Pardoen, Joris Proost, and Dominique Schryvers

Appl. Phys. Lett. 102, 071911 (2013); http://dx.doi.org/10.1063/1.4793512 (4 pages)

Online Publication Date: 22 February 2013

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Sputtered nanocrystalline palladium thin films with nanoscale growth twins have been subjected to hydriding cycles. The evolution of the twin boundaries has been investigated using high resolution transmission electron microscopy. Surprisingly, the ∑3{112} incoherent twin boundaries dissociate after hydriding into two phase boundaries bounding a 9R phase. This phase which corresponds to single stacking faults located every three {111} planes in the fcc Pd structure was not expected because of the high stacking fault energy of Pd. This observation is connected to the influence of the Hydrogen on the stacking fault energy of palladium and the high compressive stresses building up during hydriding.
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68.35.Rh Phase transitions and critical phenomena
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
68.60.Bs Mechanical and acoustical properties
61.72.Mm Grain and twin boundaries
61.72.Nn Stacking faults and other planar or extended defects

Ambient condition laser writing of graphene structures on polycrystalline SiC thin film deposited on Si wafer

Naili Yue, Yong Zhang, and Raphael Tsu

Appl. Phys. Lett. 102, 071912 (2013); http://dx.doi.org/10.1063/1.4793520 (5 pages)

Online Publication Date: 22 February 2013

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We report laser induced local conversion of polycrystalline SiC thin-films grown on Si wafers into multi-layer graphene, a process compatible with the Si based microelectronic technologies. The conversion can be achieved using a 532 nm CW laser with as little as 10 mW power, yielding ∼1 μm graphene discs without any mask. The conversion conditions are found to vary with the crystallinity of the film. More interestingly, the internal structure of the graphene disc, probed by Raman imaging, can be tuned with varying the film and illumination parameters, resembling either the fundamental or doughnut mode of a laser beam.
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78.66.Li Other semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
61.48.Gh Structure of graphene
42.62.-b Laser applications
78.30.Hv Other nonmetallic inorganics

Modulation of persistent photoconductivity by electric-field-controlled strain in thin films of La0.39Pr0.24Ca0.37MnO3

J. F. Wang, Y. C. Jiang, Z. P. Wu, and J. Gao

Appl. Phys. Lett. 102, 071913 (2013); http://dx.doi.org/10.1063/1.4793534 (4 pages)

Online Publication Date: 22 February 2013

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Thin films of La0.39Pr0.24Ca0.37MnO3 (LPCMO) were epitaxially grown on 0.7PbMg1/3Nb2/3O3-0.3PbTiO3 (PMN-PT) substrates. These LPCMO films exhibited low-temperature persistent photoconductivity (PPC) when illuminated by a visible light of 532 nm. Not only the resistance but also PPC were modulated by electric fields across PMN-PT. Detailed analysis and in situ x-ray diffraction indicate that such modulations were mainly due to the change of lattice deformation by applied electric fields via converse piezoelectric effect. It was also found that light and strain influence the phase competition in different ways.
Show PACS
73.61.Ng Insulators
77.65.-j Piezoelectricity and electromechanical effects
77.84.Bw Elements, oxides, nitrides, borides, carbides, chalcogenides, etc.
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
77.55.hn Other piezoelectric or electrostrictive films
73.50.Pz Photoconduction and photovoltaic effects
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