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28 Jan 2013

Volume 102, Issue 4, Articles (04xxxx)

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Appl. Phys. Lett. 102, 041101 (2013); http://dx.doi.org/10.1063/1.4777564 (5 pages)

K. Winkler, C. Schneider, J. Fischer, A. Rahimi-Iman, M. Amthor, A. Forchel, S. Reitzenstein, S. Höfling, and M. Kamp
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Lifetime of sub-THz coherent acoustic phonons in a GaAs-AlAs superlattice

A. A. Maznev, Felix Hofmann, Adam Jandl, Keivan Esfarjani, Mayank T. Bulsara, Eugene A. Fitzgerald, Gang Chen, and Keith A. Nelson

Appl. Phys. Lett. 102, 041901 (2013); http://dx.doi.org/10.1063/1.4789520 (4 pages) | Cited 1 time

Online Publication Date: 28 January 2013

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We measure the lifetime of the zone-center 340 GHz longitudinal phonon mode in a GaAs-AlAs superlattice excited and probed with femtosecond laser pulses. By comparing measurements conducted at room temperature and liquid nitrogen temperature, we separate the intrinsic (phonon-phonon scattering) and extrinsic contributions to phonon relaxation. The estimated room temperature intrinsic lifetime of 0.95 ns is compared to available calculations and experimental data for bulk GaAs. We conclude that ∼0.3 THz phonons are in the transition zone between Akhiezer and Landau-Rumer regimes of phonon-phonon relaxation at room temperature.
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63.20.kg Phonon-phonon interactions
78.47.J- Ultrafast spectroscopy (<1 psec)
78.67.Pt Multilayers; superlattices; photonic structures; metamaterials

Size-dependent transition of deformation mechanism, and nonlinear elasticity in Ni3Al nanowires

Yun-Jiang Wang, Guo-Jie J. Gao, and Shigenobu Ogata

Appl. Phys. Lett. 102, 041902 (2013); http://dx.doi.org/10.1063/1.4789528 (5 pages)

Online Publication Date: 28 January 2013

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A size-dependent transition of deformation mechanism is revealed in Ni3Al nanowire under atomistic uniaxial tension. Deformation twinning is replaced by phase transformation when the diameter of Ni3Al nanowire reduces to a critical value near 4 nm. Enhanced size-dependent nonlinear elasticity is observed in the nanowires, in comparison to their bulk counterpart which is benchmarked by combined density functional and atomistic study. This study provide fundamental understanding on the size-dependent deformation mechanisms of nanostructured alloys.
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81.05.Bx Metals, semimetals, and alloys
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
62.20.D- Elasticity
62.20.F- Deformation and plasticity
81.07.Gf Nanowires

Atomistic simulation based prediction of the solvent effect on the molecular mobility and glass transition of poly (methyl methacrylate)

Shawn Mishra and Sinan Keten

Appl. Phys. Lett. 102, 041903 (2013); http://dx.doi.org/10.1063/1.4788744 (5 pages)

Online Publication Date: 28 January 2013

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We present an investigation of the retained solvent effect on the glass transition temperature (Tg) of poly(methyl methacrylate) (PMMA) through all-atom molecular dynamics simulations. Addition of a weakly interactive solvent, tetrahydrofuran (THF), causes a depression of the PMMA Tg that can be identified through an analysis of the mean squared displacement of the polymer chains from atomistic trajectories. Our results are in very good agreement with an atomistically informed theoretical model based on free volume theory and demonstrate the applicability of molecular simulation to discern solvent effects on polymer thermomechanical behavior in silico.
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64.70.pj Polymers
64.70.Q- Theory and modeling of the glass transition
61.43.Bn Structural modeling: serial-addition models, computer simulation
81.40.Gh Other heat and thermomechanical treatments

Elastic and anelastic properties close to the Curie temperature of Fe-based bulk metallic glass

J. Torrens-Serra, M. Stoica, J. Bednarcik, J. Eckert, and S. Kustov

Appl. Phys. Lett. 102, 041904 (2013); http://dx.doi.org/10.1063/1.4789776 (4 pages)

Online Publication Date: 28 January 2013

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Linear and non-linear ultrasonic damping, Young's modulus, and non-linear modulus defect have been studied in a Fe-based bulk metallic glass close to its Curie temperature, TC. We found that the acoustic technique used offers four different parameters which can be used to evaluate the TC. We show that ultrasonic measurements at a frequency of around 105 Hz detect both critical phenomena close to TC and intrinsic magnetomechanical damping in the ferromagnetic state. However, the values of absorption and Young's modulus anomaly observed over the critical range are quite low and do not permit reliable analysis of the critical exponents.
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81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.80.+q Magnetomechanical effects, magnetostriction
62.20.de Elastic moduli

Thermally induced porous structures in printed gallium coating to make transparent conductive film

Shengfu Mei, Yunxia Gao, Haiyan Li, Zhongshan Deng, and Jing Liu

Appl. Phys. Lett. 102, 041905 (2013); http://dx.doi.org/10.1063/1.4789978 (4 pages)

Online Publication Date: 28 January 2013

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A directly printable gallium-based film with both optically transmissive and electrically conductive properties was proposed and demonstrated. The structures, electrical, and optical behaviors of the film printed on the substrate were experimentally investigated. It was disclosed that the porous structure induced inside the printed gallium film by thermal treatment is the main reason for the significant improvement of optical transmittance. A visible transmittance of 47% with a sheet resistance of 16.17 Ω/sq was obtained when the thermal treatment temperature and time are maintained at 400 °C and 40 min, respectively.
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73.61.At Metal and metallic alloys
78.66.Bz Metals and metallic alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
61.43.Gt Powders, porous materials
68.55.-a Thin film structure and morphology

Optical properties of SrTiO3 on silicon(100)

Yao Tian, Carolina Adamo, Darrell G. Schlom, and Kenneth S. Burch

Appl. Phys. Lett. 102, 041906 (2013); http://dx.doi.org/10.1063/1.4789752 (4 pages)

Online Publication Date: 29 January 2013

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Epitaxial buffer layers enable the many functionalities found in perovskites to be integrated with silicon. However, epitaxial growth of SrTiO3 on silicon is tricky and has so far only been achieved by molecular beam epitaxy. Nonetheless, previous investigations of these films were limited by the amorphous layer occurring at the interface. Through a combination of improved interface quality and an improved model, we report the optical properties of SrTiO3 films on Si(100) investigated by spectroscopic ellipsometry. We find that the data are best described by a model with two different SrTiO3 layers, potentially resulting from variations in the oxygen content.
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78.66.Nk Insulators
78.40.Ha Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.aj Insulators

Direct ab-initio molecular dynamic study of ultrafast phase change in Ag-alloyed Ge2Sb2Te5

B. Prasai, G. Chen, and D. A. Drabold

Appl. Phys. Lett. 102, 041907 (2013); http://dx.doi.org/10.1063/1.4789877 (4 pages)

Online Publication Date: 29 January 2013

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We employed ab-initio molecular dynamics to directly simulate the effects of Ag alloying (less than 5% Ag concentration) on the phase change properties of Ge2Sb2Te5. The short range order is preserved, whereas a slight improvement in the chemical order is observed. A slight decrease in the fraction of tetrahedral Ge (sp3 bonding) is reflected in the reduction of the optical band gap and in the increased dielectric constant. Simulations of the amorphous to crystalline phase change cycle revealed the fact that the crystallization speed in Ag0.5Ge2Sb2Te5 is not less than that in Ge2Sb2Te5. Moreover, the smaller density difference and the larger energy difference between the two phases of Ag0.5Ge2Sb2Te5 (compared to Ge2Sb2Te5) suggest a smaller residual stress in devices due to phase transition and improved thermal stability for Ag0.5Ge2Sb2Te5. The potential viability of this material suggests the need for a wide exploration of alternative phase change memory materials.
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64.70.dg Crystallization of specific substances
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity

Magnetic transition broadening and local lattice distortion in the negative thermal expansion antiperovskite Cu1−xSnxNMn3

P. Tong, Despina Louca, Graham King, Anna Llobet, J. C. Lin, and Y. P. Sun

Appl. Phys. Lett. 102, 041908 (2013); http://dx.doi.org/10.1063/1.4790151 (4 pages)

Online Publication Date: 30 January 2013

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The local distortion indicated by the split of the Cu/Sn-Mn bonds for the negative thermal expansion (NTE) materials Cu1−xSnxNMn3 (x = 0.1 and 0.5) was observed using neutron pair distribution function. The distribution of Cu/Sn-Mn bonds upon Sn doping is suggested to be attributable to the fluctuation in the hybridization of Mn d with Sn p orbitals. Accordingly, the antiferromagnetic (AFM) coupling mediated by the p-d hybridization fluctuates in strength. Consequently, the AFM transition closely coupled with the volume change is broadened, leading to the NTE.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.50.Ee Antiferromagnetics
65.40.De Thermal expansion; thermomechanical effects

Strain engineering enhancement of surface plasmon polariton propagation lengths for gold nanowires

Xue Ben and Harold S. Park

Appl. Phys. Lett. 102, 041909 (2013); http://dx.doi.org/10.1063/1.4790293 (4 pages)

Online Publication Date: 30 January 2013

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We present in this work the notion of using elastic strain engineering to reduce the intrinsic losses in a metal for subwavelength optical signal processing. By using a simple, analytical waveguide model, we demonstrate that application of uniaxial tensile strains below the yield strain of gold nanowires results in substantial increases of more than 70% in the surface plasmon polariton propagation lengths at optical frequencies. The enhancement is primarily due to a reduction in the core electron density, and is found to be size-independent for a wide range of nanowire diameters, while exhibiting a linear dependence on the applied tensile strain.
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71.36.+c Polaritons (including photon-phonon and photon-magnon interactions)
72.20.Fr Low-field transport and mobility; piezoresistance
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
81.40.Lm Deformation, plasticity, and creep
62.20.fg Shape-memory effect; yield stress; superelasticity

Critical-temperature/Peierls-stress dependent size effects in body centered cubic nanopillars

Seung Min Han, Gang Feng, Joo Young Jung, Hee Joon Jung, James R. Groves, William D. Nix, and Yi Cui

Appl. Phys. Lett. 102, 041910 (2013); http://dx.doi.org/10.1063/1.4776658 (5 pages)

Online Publication Date: 30 January 2013

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The size-dependent plasticity of body centered cubic (bcc) metals is different from face centered cubic (fcc) metals: the size-effect exponent n varies for different bcc metal nanopillars (n = 0.8–1.0 for V, Nb; n = 0.3–0.5 for Ta, Mo, W). This inconsistency is first explained through a simple model based on the temperature-dependent Peierls stress. The bcc V nanopillars with a low critical temperature and Peierls stress showed a fcc-like size effect with n = 0.79, and our in-situ TEM compression study revealed that fcc-like dislocation starvation occurred in bcc V nanopillars, indicating that a small Peierls stress in V contributes to the fcc-like behavior.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
62.23.-c Structural classes of nanoscale systems

Self-organized Archimedean spiral pattern: Regular bundling of fullerene through solvent evaporation

Yong-Jun Chen, Kosuke Suzuki, Hitoshi Mahara, Kenichi Yoshikawa, and Tomohiko Yamaguchi

Appl. Phys. Lett. 102, 041911 (2013); http://dx.doi.org/10.1063/1.4789906 (5 pages)

Online Publication Date: 30 January 2013

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We report the spontaneous generation of an Archimedean spiral pattern of fullerene via the evaporation of solvent. The self-organized spiral pattern exhibited equi-spacing on the order of μm between neighboring stripes. The characteristics of the spirals, such as the spacing between stripes, the number of stripes, and the band width of stripes, could be controlled by tuning the thickness of the liquid bridge and the concentration of solution. The mechanism of pattern formation is interpreted in terms of a specific traveling wave on the liquid-solid interface accompanied by a stick-slip process of the contact line.
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61.48.-c Structure of fullerenes and related hollow and planar molecular structures
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear

Novel pressure-induced phase transitions in Co3O4

Shigeto Hirai and Wendy L. Mao

Appl. Phys. Lett. 102, 041912 (2013); http://dx.doi.org/10.1063/1.4790387 (4 pages)

Online Publication Date: 31 January 2013

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Co3O4 represents an intriguing strongly correlated system since it is a spin liquid originating from A-site magnetic frustration. We conducted in-situ high pressure synchrotron x-ray diffraction experiments on Co3O4, and found two new monoclinic phases with the P121/c1 and C12/m1 structures. These high pressure phases are distinct from the high pressure structures that were previously reported for other 3d transition metal spinel oxides. The charge transfer does not drive the normal spinel to transform into a symmetry equivalent inverse spinel, and instead we observe transformations into the new monoclinic phases which have two distinct Co2+ and Co3+ octahedral sites.
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64.70.K- Solid-solid transitions
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
62.50.-p High-pressure effects in solids and liquids

Shape-anisotropic heterogeneous nucleation and magnetic Gibbs-Thomson effect in itinerant-electron metamagnetic transition of La(Fe0.88Si0.12)13 magnetocaloric compound

A. Fujita, T. Kondo, M. Kano, and H. Yako

Appl. Phys. Lett. 102, 041913 (2013); http://dx.doi.org/10.1063/1.4789902 (5 pages)

Online Publication Date: 31 January 2013

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Macroscopic anisotropy of spatial selectivity in magnetic nucleation and growth was clarified for itinerant-electron metamagnetic transition of La(Fe0.88Si0.12)13 by the time-dependent Ginzburg-Landau model combined with the Maxwell electromagnetic equation. Spontaneous generation of voltage supports symmetric growth in the longitudinal direction of the specimen as predicted by the simulation. The difference between nucleation-growth behaviors in thermally induced transition and those in field-induced transition is also elucidated. Electrical resistivity measurements also detect anisotropic growth of the induced phase. These results imply that the magnetic-dipole version of Gibbs-Thomson effect governs growth behavior.
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75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Sg Magnetocaloric effect, magnetic cooling
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys
72.15.Jf Thermoelectric and thermomagnetic effects
75.30.Gw Magnetic anisotropy

Molecular beam epitaxy of high structural quality Bi2Se3 on lattice matched InP(111) substrates

S. Schreyeck, N. V. Tarakina, G. Karczewski, C. Schumacher, T. Borzenko, C. Brüne, H. Buhmann, C. Gould, K. Brunner, and L. W. Molenkamp

Appl. Phys. Lett. 102, 041914 (2013); http://dx.doi.org/10.1063/1.4789775 (4 pages) | Cited 2 times

Online Publication Date: 1 February 2013

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Epitaxial layers of the topological insulator Bi2Se3 have been grown by molecular beam epitaxy on laterally lattice-matched InP(111)B substrates. High resolution X-ray diffraction shows a significant improvement of Bi2Se3 crystal quality compared to layers deposited on other substrates. The measured full width at half maximum of the rocking curve is Δω = 13 arc sec, and the (ω−2θ) scans exhibit clear layer thickness fringes. Atomic force microscope images show triangular twin domains with sizes increasing with layer thickness. The structural quality of the domains is confirmed on the microscopic level by transmission electron microscopy.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.aj Insulators

Random analysis on controlled buckling structure for energy harvesting

Yong Wang, Teng Ma, Hongyu Yu, and Hanqing Jiang

Appl. Phys. Lett. 102, 041915 (2013); http://dx.doi.org/10.1063/1.4789998 (5 pages)

Online Publication Date: 1 February 2013

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The controlled buckling piezoelectric structures can be used for stretchable energy harvesting due to the stretchability and piezoelectricity. In this paper, the ambient environmental excitation is modeled as a bound-limited white noise, and the random analysis is conducted to study the system response of controlled buckling structures. The spatial distribution of the harvestable energy is revealed, and the optimal locations of electrodes for maximal energy output are indicated. The optimal locations of electrodes are robust to the upper bound of environment excitation and the applied strain. This work provides a theoretical basis for stretchable energy harvesting using controlled buckling structures.
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84.60.-h Direct energy conversion and storage
88.05.-b Energy analysis
77.65.-j Piezoelectricity and electromechanical effects
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