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22 Oct 2012

Volume 101, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 171101 (2012); http://dx.doi.org/10.1063/1.4758996 (4 pages)

Wolfram H. P. Pernice and Harish Bhaskaran
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Effect of length scale on mechanical properties of Al-Cu eutectic alloy

C. S. Tiwary, D. Roy Mahapatra, and K. Chattopadhyay

Appl. Phys. Lett. 101, 171901 (2012); http://dx.doi.org/10.1063/1.4761944 (4 pages)

Online Publication Date: 22 October 2012

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This paper attempts a quantitative understanding of the effect of length scale on two phase eutectic structure. We first develop a model that considers both the elastic and plastic properties of the interface. Using Al-Al2Cu lamellar eutectic as model system, the parameters of the model were experimentally determined using indentation technique. The model is further validated using the results of bulk compression testing of the eutectics having different length scales.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
68.35.Gy Mechanical properties; surface strains
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Elasticity of diamond at high pressures and temperatures

Maribel Núñez Valdez, Koichiro Umemoto, and Renata M. Wentzcovitch

Appl. Phys. Lett. 101, 171902 (2012); http://dx.doi.org/10.1063/1.4754548 (4 pages)

Online Publication Date: 23 October 2012

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We combine density functional theory within the local density approximation, the quasiharmonic approximation, and vibrational density of states to calculate single crystal elastic constants, and bulk and shear moduli of diamond at simultaneous high pressures and temperatures in the ranges of 0–500 GPa and 0–4800 K. Comparison with experimental values at ambient pressure and high temperature shows an excellent agreement with our first-principles results validating our method. We show that the anisotropy factor of diamond increases to 40% at high pressures and becomes temperature independent.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.20.dq Other elastic constants
62.50.-p High-pressure effects in solids and liquids
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Tunable phononic crystals based on cylindrical Hertzian contact

Feng Li, Duc Ngo, Jinkyu Yang, and Chiara Daraio

Appl. Phys. Lett. 101, 171903 (2012); http://dx.doi.org/10.1063/1.4762832 (4 pages)

Online Publication Date: 23 October 2012

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We investigate the tunability of phononic crystals consisting of arrays of cylindrical elements using theoretical, numerical, and experimental approaches. We show that when these systems are excited by a continuous dynamic signal under large static precompression, they support a characteristic band structure whose cutoff frequency can be controlled by changing the alignment angles or the static precompression. Furthermore, we report the formation of an additional pass band when there exists particles' eccentricity, which is caused by the coupling mechanism between longitudinal and shear modes.
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63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
71.20.-b Electron density of states and band structure of crystalline solids

Modulated structure in the martensite phase of Ni1.8Pt0.2MnGa: A neutron diffraction study

Sanjay Singh, K. R. A. Ziebeck, E. Suard, P. Rajput, S. Bhardwaj, A. M. Awasthi, and S. R. Barman

Appl. Phys. Lett. 101, 171904 (2012); http://dx.doi.org/10.1063/1.4760270 (4 pages) | Cited 1 time

Online Publication Date: 23 October 2012

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7M orthorhombic modulated structure in the martensite phase of Ni1.8Pt0.2MnGa is reported by powder neutron diffraction study, which indicates that it is likely to exhibit magnetic field induced strain. The change in the unit cell volume is less than 0.5% between the austenite and the martensite phases, as expected for a volume conserving martensite transformation. The magnetic structure analysis shows that the magnetic moment in the martensite phase is higher compared to Ni2MnGa, which is in good agreement with magnetization measurement.
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81.30.Kf Martensitic transformations
64.70.kd Metals and alloys
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Cc Other ferromagnetic metals and alloys

Fe-doped InN layers grown by molecular beam epitaxy

Xinqiang Wang, Shitao Liu, Dingyu Ma, Xiantong Zheng, Guang Chen, Fujun Xu, Ning Tang, Bo Shen, Peng Zhang, Xingzhong Cao, Baoyi Wang, Sen Huang, Kevin J. Chen, Shengqiang Zhou, and Akihiko Yoshikawa

Appl. Phys. Lett. 101, 171905 (2012); http://dx.doi.org/10.1063/1.4764013 (4 pages)

Online Publication Date: 24 October 2012

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Iron(Fe)-doped InN (InN:Fe) layers have been grown by molecular beam epitaxy. It is found that Fe-doping leads to drastic increase of residual electron concentration, which is different from the semi-insulating property of Fe-doped GaN. However, this heavy n-type doping cannot be fully explained by doped Fe-concentration ([Fe]). Further analysis shows that more unintentionally doped impurities such as hydrogen and oxygen are incorporated with increasing [Fe] and the surface is degraded with high density pits, which probably are the main reasons for electron generation and mobility reduction. Photoluminescence of InN is gradually quenched by Fe-doping. This work shows that Fe-doping is one of good choices to control electron density in InN.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.72.up Other materials
72.20.Fr Low-field transport and mobility; piezoresistance
78.55.Hx Other solid inorganic materials

Harnessing electromechanical membrane wrinkling for actuation

Andrew T. Conn and Jonathan Rossiter

Appl. Phys. Lett. 101, 171906 (2012); http://dx.doi.org/10.1063/1.4764101 (4 pages) | Cited 1 time

Online Publication Date: 24 October 2012

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Dielectric elastomers are soft electromechanical transducers that can exhibit unstable wrinkling behavior under large electric fields. This instability can be exploited by optimizing electrode boundaries to accentuate or attenuate localized wrinkling. An analytical model is presented, which demonstrates that the critical electric field to induce wrinkling can be lowered as the electrode geometry changes from convex to concave. This allows a single dielectric elastomer membrane to generate either biaxial or uniaxial extension in specific regions. A prototype 56 μm thick membrane actuator incorporates this principle to generate an in-plane rotational output, producing an actuation stroke of 15.7°.
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07.07.Mp Transducers

Patterned optical anisotropy in woven conjugated polymer systems

C. Müller, M. Garriga, and M. Campoy-Quiles

Appl. Phys. Lett. 101, 171907 (2012); http://dx.doi.org/10.1063/1.4764518 (5 pages)

Online Publication Date: 25 October 2012

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Weaving of highly oriented conjugated polymer/polyethylene tapes is demonstrated to permit the generation of concealed patterns that can be detected under appropriate polarized light illumination. This is achieved by exploiting the fact that the amount of transmitted light varies with the superposition sequence of semi-transparent objects that feature a high degree of linear birefringence as well as linear dichroism. An analysis based on Müller calculus provides a theoretical description of the observed optical behavior.
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78.66.Qn Polymers; organic compounds
42.70.Jk Polymers and organics
78.20.Fm Birefringence

Bulk silica-based luminescent materials by sol-gel processing of non-conventional precursors

J. A. Rodríguez, C. Fernández-Sánchez, C. Domínguez, S. Hernández, and Y. Berencén

Appl. Phys. Lett. 101, 171908 (2012); http://dx.doi.org/10.1063/1.4764561 (4 pages)

Online Publication Date: 25 October 2012

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The sol-gel synthesis of bulk silica-based luminescent materials using innocuous hexaethoxydisilane and hexamethoxydisilane monomers, followed by one hour thermal annealing in an inert atmosphere at 950 °C–1150 °C, is reported. As-synthesized hexamethoxydisilane-derived samples exhibit an intense blue photoluminescence band, whereas thermally treated ones emit stronger photoluminescence radiation peaking below 600 nm. For hexaethoxydisilane-based material, annealed at or above 1000 °C, a less intense photoluminescence band, peaking between 780 nm and 850 nm that is attributed to nanocrystalline silicon is observed. Mixtures of both precursors lead to composed spectra, thus envisaging the possibility of obtaining pre-designed spectral behaviors by varying the mixture composition.
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78.55.Hx Other solid inorganic materials
81.10.Dn Growth from solutions
81.10.Fq Growth from melts; zone melting and refining
81.15.Lm Liquid phase epitaxy; deposition from liquid phases (melts, solutions, and surface layers on liquids)
81.40.Gh Other heat and thermomechanical treatments
61.72.Cc Kinetics of defect formation and annealing
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