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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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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) | Cited 1 time

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.
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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

Origin of the defects-induced ferromagnetism in un-doped ZnO single crystals

Peng Zhan, Zheng Xie, Zhengcao Li, Weipeng Wang, Zhengjun Zhang, Zhuoxin Li, Guodong Cheng, Peng Zhang, Baoyi Wang, and Xingzhong Cao

Appl. Phys. Lett. 102, 071914 (2013); http://dx.doi.org/10.1063/1.4793574 (5 pages)

Online Publication Date: 22 February 2013

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We clarified, in this Letter, that in un-doped ZnO single crystals after thermal annealing in flowing argon, the defects-induced room-temperature ferromagnetism was originated from the surface defects and specifically, from singly occupied oxygen vacancies denoted as F+, by the optical and electrical properties measurements as well as positron annihilation analysis. In addition, a positive linear relationship was observed between the ferromagnetism and the F+ concentration, which is in support with the above clarification.
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61.72.jd Vacancies
72.80.Ey III-V and II-VI semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors
78.40.Fy Semiconductors
81.05.Dz II-VI semiconductors
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