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21 May 2012

Volume 100, Issue 21, Articles (21xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 213701 (2012); http://dx.doi.org/10.1063/1.3701135 (4 pages)

Wen Lo, Ara Ghazaryan, Chien-Hsin Tso, Po-Sheng Hu, Wei-Liang Chen, Tsung-Rong Kuo, Sung-Jan Lin, Shean-Jen Chen, Chia-Chun Chen, and Chen-Yuan Dong
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Demonstration of shortwavelength infrared photodiodes based on type-II InAs/GaSb/AlSb superlattices

A. M. Hoang, G. Chen, A. Haddadi, S. Abdollahi Pour, and M. Razeghi

Appl. Phys. Lett. 100, 211101 (2012); http://dx.doi.org/10.1063/1.4720094 (4 pages) | Cited 6 times

Online Publication Date: 22 May 2012

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We demonstrate the feasibility of the InAs/GaSb/AlSb type-II superlattice photodiodes operating at the short wavelength infrared regime below 3 μm. An n-i-p type-II InAs/GaSb/AlSb photodiode was grown with a designed cut-off wavelength of 2 μm on a GaSb substrate. At 150 K, the photodiode exhibited a dark current density of 5.6 × 10−8 A/cm2 and a front-side-illuminated quantum efficiency of 40.3%, providing an associated shot noise detectivity of 1.0 × 1013 Jones. The uncooled photodiode showed a dark current density of 2.2 × 10−3 A/cm2 and a quantum efficiency of 41.5%, resulting in a detectivity of 1.7 × 1010 Jones.
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85.60.Dw Photodiodes; phototransistors; photoresistors
72.40.+w Photoconduction and photovoltaic effects
72.70.+m Noise processes and phenomena
73.21.Cd Superlattices

Terahertz time-domain spectroscopy of anisotropic complex conductivity tensors in silicon nanowire films

Meehyun Lim, Sung-Jin Choi, Gyu-Seok Lee, Myeong-Lok Seol, Youngwoong Do, Yang-Kyu Choi, and Haewook Han

Appl. Phys. Lett. 100, 211102 (2012); http://dx.doi.org/10.1063/1.4721490 (4 pages)

Online Publication Date: 22 May 2012

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The effective complex conductivity tensor of a highly anisotropic, vertically aligned silicon nanowire film was measured by terahertz time-domain spectroscopy. The silicon nanowires were fabricated on a p-type silicon substrate by metal-assisted chemical etching, which resulted in a film with uniaxially anisotropic optical properties. The measured terahertz transverse and longitudinal conductivity values were in excellent agreement with the results of calculations based on the Drude-Smith and Lorentz models, respectively.
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78.47.J- Ultrafast spectroscopy (<1 psec)
78.67.Uh Nanowires
81.07.Gf Nanowires
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.66.Db Elemental semiconductors and insulators
81.65.Cf Surface cleaning, etching, patterning

Controlled-NOT gate operating with single photons

M. A. Pooley, D. J. P. Ellis, R. B. Patel, A. J. Bennett, K. H. A. Chan, I. Farrer, D. A. Ritchie, and A. J. Shields

Appl. Phys. Lett. 100, 211103 (2012); http://dx.doi.org/10.1063/1.4719077 (4 pages) | Cited 4 times

Online Publication Date: 22 May 2012

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The initial proposal for scalable optical quantum computing required single photon sources, linear optical elements such as beamsplitters and phaseshifters, and photon detection. Here, we demonstrate a two qubit gate using indistinguishable photons from a quantum dot in a pillar microcavity. As the emitter, the optical circuitry, and the detectors are all semiconductor, this is a promising approach towards creating a fully integrated device for scalable quantum computing.
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42.79.Sz Optical communication systems, multiplexers, and demultiplexers
42.50.-p Quantum optics
42.82.-m Integrated optics

Screen printed ZnO ultraviolet photoconductive sensor on pencil drawn circuitry over paper

Kamran ul Hasan, Omer Nur, and Magnus Willander

Appl. Phys. Lett. 100, 211104 (2012); http://dx.doi.org/10.1063/1.4720179 (3 pages) | Cited 2 times

Online Publication Date: 23 May 2012

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Many applications require a low-cost and large-scale mode of flexible electronics with reasonably high photoresponse that can be detected without high precision measurement systems. We demonstrate a very easy to fabricate ZnO UV sensor, made on common pencil drawn circuit over a paper. ZnO nanocrystals were extracted in a high throughput via a simple and green route. This sensor is well capable of detecting UV light and demonstrates features comparable to those of made with complex and expensive techniques.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
85.60.-q Optoelectronic devices
81.07.Bc Nanocrystalline materials

Partial rectification of the plasmon-induced electrical tunnel current in discontinuous thin gold film at optical frequency

M. M. A. Yajadda, K.-H. Müller, D. I. Farrant, and K. Ostrikov

Appl. Phys. Lett. 100, 211105 (2012); http://dx.doi.org/10.1063/1.4720513 (4 pages) | Cited 1 time

Online Publication Date: 23 May 2012

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The effect of plasmon oscillations, induced by pulsed laser irradiation, on the DC tunnel current between islands in a discontinuous thin gold film is studied. The tunnel current is found to be strongly enhanced by partial rectification of the plasmon-induced AC tunnel currents flowing between adjacent gold islands. The DC tunnel current enhancement is found to increase approximately linearly with the laser intensity and the applied DC bias voltage. The experimental data can be well described by an electron tunnelling model which takes the plasmon-induced AC voltage into account. Thermal heating seems not to contribute to the tunnel current enhancement.
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78.66.Bz Metals and metallic alloys
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
73.40.Gk Tunneling

Monolithically integrated, resonant-cavity-enhanced dual-band mid-infrared photodetector on silicon

Jianfei Wang, Timothy Zens, Juejun Hu, Piotr Becla, Lionel C. Kimerling, and Anuradha M. Agarwal

Appl. Phys. Lett. 100, 211106 (2012); http://dx.doi.org/10.1063/1.4722917 (3 pages)

Online Publication Date: 24 May 2012

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In this paper, we present experimental demonstration of a resonant-cavity-enhanced mid-infrared photodetector monolithically fabricated on a silicon substrate. Dual-band detection at 1.6 μm and 3.7 μm is achieved within a single detector pixel without cryogenic cooling, by using thermally evaporated nanocrystalline PbTe as the photoconductive absorbers. Excellent agreement between theory and experiment is confirmed. The pixel design can potentially be further extended to realizing multispectral detection.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
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Interfacial confinement in core-shell nanowires due to high dielectric mismatch

A. A. Sousa, T. A. S. Pereira, A. Chaves, J. S. de Sousa, and G. A. Farias

Appl. Phys. Lett. 100, 211601 (2012); http://dx.doi.org/10.1063/1.4720402 (4 pages) | Cited 1 time

Online Publication Date: 22 May 2012

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We theoretically investigate the role of the dielectric mismatch between materials on the energy levels and recombination energies of a core-shell nanowire. Our results demonstrate that when the dielectric constant of the core material is lower than that of the shell material, the self-image potential pushes the charge carriers towards the core-shell interface in such a way that the ideal confinement model is no longer suitable. The effects of this interfacial confinement on the electronic properties of such wires, as well as on its response to applied magnetic fields, are discussed.
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73.22.-f Electronic structure of nanoscale materials and related systems
73.20.At Surface states, band structure, electron density of states
77.22.Ch Permittivity (dielectric function)

Contributions of atomic diffusion and plastic deformation to the plasma surface activation assisted diffusion bonding of zirconium-based bulk metallic glass

H. Y. Chen, J. Cao, X. G. Song, and J. C. Feng

Appl. Phys. Lett. 100, 211602 (2012); http://dx.doi.org/10.1063/1.4721665 (4 pages) | Cited 2 times

Online Publication Date: 24 May 2012

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A mathematical model was established to estimate the contributions of atomic diffusion and plastic deformation to the diffusion bonding of zirconium-based bulk metallic glasses. Additionally, the surface state was introduced into the model since oxide film is the main barrier to atomic bonding across interface. The model calculation displayed that the contribution of plastic deformation to void closure was six orders of magnitude higher than atomic diffusion. The joints with ion etching before bonding were achieved to verify the model. The experimental strength of joints had a sound fit with the theoretical strength calculated by the model.
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81.40.Lm Deformation, plasticity, and creep
81.65.Cf Surface cleaning, etching, patterning
62.20.fg Shape-memory effect; yield stress; superelasticity
64.70.pe Metallic glasses
66.30.hh Glasses
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Large, uni-directional actuation in dielectric elastomers achieved by fiber stiffening

Jiangshui Huang, Tongqing Lu, Jian Zhu, David R. Clarke, and Zhigang Suo

Appl. Phys. Lett. 100, 211901 (2012); http://dx.doi.org/10.1063/1.4720181 (4 pages) | Cited 2 times

Online Publication Date: 21 May 2012

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Cylindrical actuators are made with dielectric elastomer sheets stiffened with fibers in the hoop direction. When a voltage is applied through the thickness of the sheets, large actuation strains are achievable in the axial direction, with or without pre-straining and mechanical loading. For example, actuation strains of 35.8% for a cylinder with a prestrain of 40%, and 28.6% for a cylinder without pre-strain have been achieved without any optimization. Furthermore, the actuation strain is independent of the aspect ratio of the cylinder, so that both large strains and large displacements are readily actuated by using long cylinders.
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85.50.-n Dielectric, ferroelectric, and piezoelectric devices

Ultrafast optical response originating from carrier-transport processes in undoped GaAs/n-type GaAs epitaxial structures

Takayuki Hasegawa, Yoshihiro Takagi, Hideo Takeuchi, Hisashi Yamada, Masahiko Hata, and Masaaki Nakayama

Appl. Phys. Lett. 100, 211902 (2012); http://dx.doi.org/10.1063/1.4720157 (4 pages) | Cited 1 time

Online Publication Date: 22 May 2012

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We have investigated ultrafast optical responses of undoped GaAs/n-type GaAs (i-GaAs/n-GaAs) epitaxial structures at room temperature using a reflection-type pump-probe technique. The built-in electric field in the i-GaAs layer is controlled by its thickness. It is found that the decay time of a photoexcitation-induced reflectivity change in a sub-picosecond range decreases with an increase in the built-in electric field strength. The observed optical response is related to the transport process of photogenerated carriers from the i-GaAs layer to the n-GaAs layer. The shortest response time about 60 fs demonstrates that the i-GaAs/n-GaAs structure is useful for ultrafast optical applications.
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78.47.je Time resolved light scattering spectroscopy
73.61.Ey III-V semiconductors
72.40.+w Photoconduction and photovoltaic effects

Yielding and plastic slip in ZnO

T. H. Sung, J. C. Huang, J. H. Hsu, S. R. Jian, and T. G. Nieh

Appl. Phys. Lett. 100, 211903 (2012); http://dx.doi.org/10.1063/1.4720169 (4 pages) | Cited 2 times

Online Publication Date: 22 May 2012

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The mechanical properties of ZnO were examined using nanoindentation and microcompression. The modulus, hardness, onset of yielding, and shear strength of the as-grown wafer measured by nanoindentation are 140, 7.1, 12, and 3.6 GPa. The onset of shearing (3.6 GPa) corresponds to the theoretical shear strength. Young’s modulus and yield strength measured from micropillar samples were 123 and 3 GPa. The primary slip plane forms an acute angle of 62° with respect to the basal planes, indicting it is pyramidal. Thermal annealing does not affect the residual stresses but can reduce the defect concentration, thus improves the ZnO luminescent properties.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
61.72.U- Doping and impurity implantation
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
81.05.Dz II-VI semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence

Electrostatically driven collapsible Au thin films assembled using transfer printing for thermal switching

Hohyun Keum, Myunghoon Seong, Sanjiv Sinha, and Seok Kim

Appl. Phys. Lett. 100, 211904 (2012); http://dx.doi.org/10.1063/1.4720397 (4 pages)

Online Publication Date: 22 May 2012

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We report deterministic assembly of 100 nm thick suspended gold films using transfer printing that are mechanically collapsible. We demonstrate the latter using electrostatic force to establish and break physical contact between the film and a silicon dioxide substrate in a reversible and repeatable manner. Modeling the thermal conductance at the interface between the suspended film and the substrate, we show that the fabricated structure behaves as a thermal switch. The on-state corresponds to the collapsed film and the off-state to the fully suspended film. The on- to off-state ratio for thermal conductance exceeds 106 in theory.
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81.07.Bc Nanocrystalline materials
82.70.Kj Emulsions and suspensions
68.55.at Other materials
72.15.Eb Electrical and thermal conduction in crystalline metals and alloys

Time resolved pump-probe scattering in MnAs/GaAs(001): A look into the dynamics of α-β stripe domains

Maurizio Sacchi, Carlo Spezzani, Enrico Allaria, Eugenio Ferrari, Marcello Coreno, Massimiliano Marangolo, Mahmoud Eddrief, Victor Etgens, and Giovanni De Ninno

Appl. Phys. Lett. 100, 211905 (2012); http://dx.doi.org/10.1063/1.4720398 (4 pages)

Online Publication Date: 22 May 2012

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Scattering of 130 nm radiation with 100 fs pulse length was used to monitor the α/β-striped microstructure in MnAs/GaAs(001), after a 390 nm 5 mJcm−2 pump pulse. A strong reduction of the Bragg peak intensity, corresponding to a widening of the β-stripes, takes place with a characteristic time of 15 ps. These results are relevant within the context of using MnAs/GaAs(001) as a template for the growth of ferromagnetic films, whose magnetization direction can be controlled by modifying the template temperature.
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75.70.Ak Magnetic properties of monolayers and thin films
78.47.J- Ultrafast spectroscopy (<1 psec)
61.72.-y Defects and impurities in crystals; microstructure
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Temperature dependence of the energy gap and spin-orbit splitting in a narrow-gap InGaAsSb solid solution

M. Motyka, F. Janiak, G. Sęk, J. Misiewicz, and K. D. Moiseev

Appl. Phys. Lett. 100, 211906 (2012); http://dx.doi.org/10.1063/1.4720515 (4 pages)

Online Publication Date: 22 May 2012

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Temperature dependence of the energy gap and the spin-orbit split off transition in a thick layer of narrow-gap InGaAsSb material with high In content has been determined by a combination of photoluminescence and photoreflectance. The respective temperature coefficients have been found to be equal for both the transitions and determined to be α = −0.41 meV/K. For the investigated In0.86Ga0.14As0.83Sb0.17 alloy, the separation energy of the split-off band has been obtained to be Δso = 0.460 eV and experimentally evidenced to be independent on temperature, which opens broad application prospects for these multinary (multicomponent) narrow gap compounds and their heterostructures.
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71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect
78.55.Cr III-V semiconductors
71.20.Nr Semiconductor compounds

Exciton confinement and trapping dynamics in double-graded-bandgap quantum nanowires

J. Szeszko, V. V. Belykh, P. Gallo, A. Rudra, K. F. Karlsson, N. N. Sibeldin, and E. Kapon

Appl. Phys. Lett. 100, 211907 (2012); http://dx.doi.org/10.1063/1.4721660 (4 pages)

Online Publication Date: 22 May 2012

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We fabricate and study quantum dot structures incorporating quasi-one-dimensional excited states. The structures are realized by graded bandgap GaAs/AlGaAs quantum wires self-formed inside inverted tetrahedral pyramids. The ground state transitions exhibit typical characteristics of fully confined excitons, including single photon emission. Efficient carrier thermalization and relaxation, as well as correlated photon emission is observed also among the excited states, indicating the formation of quasi-one-dimensional multi-exciton states. These structures offer interesting possibilities for collecting and directing charge carriers towards heterostructured potential traps.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.21.Hb Quantum wires
73.22.-f Electronic structure of nanoscale materials and related systems
81.15.Kk Vapor phase epitaxy; growth from vapor phase
61.46.Km Structure of nanowires and nanorods (long, free or loosely attached, quantum wires and quantum rods, but not gate-isolated embedded quantum wires)
81.07.Gf Nanowires

Parametric optomechanical oscillations in two-dimensional slot-type high-Q photonic crystal cavities

Jiangjun Zheng, Ying Li, Mehmet Sirin Aras, Aaron Stein, Ken L. Shepard, and Chee Wei Wong

Appl. Phys. Lett. 100, 211908 (2012); http://dx.doi.org/10.1063/1.4719107 (5 pages) | Cited 4 times

Online Publication Date: 22 May 2012

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We experimentally demonstrate an optomechanical cavity based on an air-slot photonic crystal cavity with optical quality factor Qo = 4.2 × 104 and a small modal volume of 0.05 cubic wavelengths. The optical mode is coupled with the in-plane mechanical modes with frequencies up to hundreds of MHz. The fundamental mechanical mode shows a frequency of 65 MHz and a mechanical quality factor of 376. The optical spring effect, optical damping, and amplification are observed with a large experimental optomechanical coupling rate gom/2π of 154 GHz/nm, corresponding to a vacuum optomechanical coupling rate g*/2π of 707 kHz. With sub-mW or less input power levels, the cavity exhibits strong parametric oscillations. The phase noise of the photonic crystal optomechanical oscillator is also measured.
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42.70.Qs Photonic bandgap materials
42.82.-m Integrated optics

Full-field deformation of magnetorheological elastomer under uniform magnetic field

Xinglong Gong, Guojiang Liao, and Shouhu Xuan

Appl. Phys. Lett. 100, 211909 (2012); http://dx.doi.org/10.1063/1.4722789 (3 pages)

Online Publication Date: 23 May 2012

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A digital holographic interferometry was applied to analyze the morphology transformation of the magnetorheological elastomer, and both the contraction and stretch deformation were observed under applying an external magnetic field on the sample. Both isolated particles and grouped particles were observed in the magnetorheological elastomer sample, and these two kinds of particles resulted in the concave-convex deformation of the sample. The deformation of magnetorheological elastomer was calculated by using a 2D finite element model, and the results agreed well with the experimental analysis.
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75.80.+q Magnetomechanical effects, magnetostriction
81.40.Jj Elasticity and anelasticity, stress-strain relations
83.60.Np Effects of electric and magnetic fields
83.80.Wx Filled elastomers
62.20.D- Elasticity
62.20.F- Deformation and plasticity

Band-gap tuning at the strong quantum confinement regime in magnetic semiconductor EuS thin films

Panagiotis Poulopoulos, Björn Lewitz, Andreas Straub, Spiridon D. Pappas, Sotirios A. Droulias, Sotirios Baskoutas, and Paul Fumagalli

Appl. Phys. Lett. 100, 211910 (2012); http://dx.doi.org/10.1063/1.4720167 (4 pages) | Cited 1 time

Online Publication Date: 23 May 2012

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Ultraviolet-visible absorption spectra of nanoscaled EuS thin films reveal a blue shift of the energy between the top-valence and bottom-conduction bands. This band-gap tuning changes smoothly with decreasing film thickness and becomes significant below the exciton Bohr diameter ∼3.5 nm indicating strong quantum confinement effects. The results are reproduced in the framework of the potential morphing method in Hartree Fock approximation. The large values of the effective mass of the holes, due to localization of the EuS f-states, limit the blue shift to about 0.35 eV. This controllable band-gap tuning of magnetic semiconductor EuS renders it useful for merging spintronics and optoelectronics.
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71.20.Nr Semiconductor compounds
75.50.Pp Magnetic semiconductors
78.66.Li Other semiconductors
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
78.40.Fy Semiconductors
71.35.Ji Excitons in magnetic fields; magnetoexcitons

L10 structure formation in slow-cooled Fe-Au nanoclusters

P. Mukherjee, Y. Zhang, M. J. Kramer, L. H. Lewis, and J. E. Shield

Appl. Phys. Lett. 100, 211911 (2012); http://dx.doi.org/10.1063/1.4720180 (3 pages) | Cited 4 times

Online Publication Date: 23 May 2012

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An ordered L10 structure has been formed in near-stoichiometric Fe-Au alloy nanoparticles. The L10 structure with a = 0.367 nm and c = 0.360 nm was observed in nanoclusters with diameters below 10 nm after slow cooling from 600 °C. The stable L10 structure formed from a parent fcc solid solution phase observed in the as-formed clusters. The fcc phase has a lattice parameter of 0.417 nm, significantly expanded compared to both Au and γ-Fe. The saturation magnetization and coercivity of both fcc and L10 structures were much lower than expected considering Fe dilution effects suggesting competing ferromagnetic and anti-ferromagnetic ordering.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Bb Fe and its alloys
81.16.-c Methods of micro- and nanofabrication and processing
75.50.Ee Antiferromagnetics

Atomistic study on the strength of symmetric tilt grain boundaries in graphene

Ajing Cao and Yutang Yuan

Appl. Phys. Lett. 100, 211912 (2012); http://dx.doi.org/10.1063/1.4722786 (3 pages) | Cited 3 times

Online Publication Date: 24 May 2012

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Molecular dynamics (MD) simulations were employed to study the mechanical response of various bicrystal graphene consisting of symmetric tilt boundary subject to uniaxial tensile loading at room temperature. We found that the strength of zigzag-oriented graphene increases slightly with mis-orientation angle, while the strength of armchair-oriented graphene deceases slightly with mis-orientation angle. Given that the difference in strength is small, one might conclude that the dependence of strength of graphene sheet containing grain boundaries upon tilt mis-orientation angle is rather weak. The origin for such weak dependence is believed to be that these grain boundaries all consisting of pentagon-heptagon pairs do not resemble nano-cracks, which result in rather heterogeneous stress field around the crack tip and therefore stress gradient plays an important role.
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61.72.Mm Grain and twin boundaries
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
62.20.mt Cracks

Nano γ′/γ″ composite precipitates in Alloy 718

P. J. Phillips, D. McAllister, Y. Gao, D. Lv, R. E. A. Williams, B. Peterson, Y. Wang, and M. J. Mills

Appl. Phys. Lett. 100, 211913 (2012); http://dx.doi.org/10.1063/1.4721456 (3 pages) | Cited 1 time

Online Publication Date: 24 May 2012

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Nanoscale composite precipitates of Alloy 718 have been investigated with both high-resolution scanning transmission electron microscopy and phase field modeling. Chemical analysis via energy-dispersive x-ray spectroscopy allowed for the differentiation of γ′ and γ″ particles, which is not otherwise possible through traditional Z-contrast methods. Phase field modeling was applied to determine the stress distribution and elastic interaction around and between the particles, respectively, and it was determined that a composite particle (of both γ′ and γ″) has an elastic energy that is significantly lower than, for example, single γ′ and γ″ precipitates which are non-interacting.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
81.40.Jj Elasticity and anelasticity, stress-strain relations
81.40.Lm Deformation, plasticity, and creep
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
62.20.de Elastic moduli
62.20.F- Deformation and plasticity

Plasmonic versus dielectric enhancement in thin-film solar cells

Maria B. Dühring, N. Asger Mortensen, and Ole Sigmund

Appl. Phys. Lett. 100, 211914 (2012); http://dx.doi.org/10.1063/1.4719203 (4 pages) | Cited 2 times

Online Publication Date: 24 May 2012

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Several studies have indicated that broadband absorption of thin-film solar cells can be enhanced by use of surface-plasmon induced resonances of metallic parts like strips or particles. The metallic parts may create localized modes or scatter incoming light to increase absorption in thin-film semiconducting material. For a particular case, we show that coupling to the same type of localized slab-waveguide modes can be obtained by a surface modulation consisting of purely dielectric strips. The purely dielectric device turns out to have a significantly higher broadband enhancement factor compared to its metallic counterpart. We show that the enhanced normalized short-circuit current for a cell with silicon strips can be increased 4 times compared to the best performance for strips of silver, gold, or aluminium. For this particular case, the simple dielectric grating may outperform its plasmonic counterpart due to the larger Ohmic losses associated with the latter.
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88.40.hj Efficiency and performance of solar cells
88.40.jj Silicon solar cells

Experimental determination of thermal profiles during laser spike annealing with quantitative comparison to 3-dimensional simulations

Krishna Iyengar, Byungki Jung, Michael Willemann, Paulette Clancy, and Michael O. Thompson

Appl. Phys. Lett. 100, 211915 (2012); http://dx.doi.org/10.1063/1.4717745 (3 pages)

Online Publication Date: 25 May 2012

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Thin film platinum resistors were used to directly measure temperature profiles during laser spike annealing (LSA) with high spatial and temporal resolution. Observed resistance changes were calibrated to absolute temperatures using the melting points of the substrate silicon and thin gold films. Both the time-dependent temperature experienced by the sample during passage of the focussed laser beam and profiles across the spatially dependent laser intensity were obtained with sub-millisecond time resolution and 50 µm spatial resolution. Full 3-dimensional simulations incorporating both optical and thermal variations of material parameters were compared with these results. Accounting properly for the specific material parameters, good agreement between experiments and simulations was achieved. Future temperature measurements in complex environments will permit critical evaluation of LSA simulations methodologies.
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84.32.Ff Conductors, resistors (including thermistors, varistors, and photoresistors)
64.70.dj Melting of specific substances
61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
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Luminescence from two-dimensional electron gases in InAlN/GaN heterostructures with different In content

M. F. Romero, M. Feneberg, P. Moser, C. Berger, J. Bläsing, A. Dadgar, A. Krost, E. Sakalauskas, and R. Goldhahn

Appl. Phys. Lett. 100, 212101 (2012); http://dx.doi.org/10.1063/1.4720087 (4 pages)

Online Publication Date: 21 May 2012

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The luminescence properties of InxAl1−xN/GaN heterostructures are investigated systematically as a function of the In content (x = 0.067 − 0.208). The recombination between electrons confined in the two-dimensional electron gas and free holes in the GaN template is identified and analyzed. We find a systematic shift of the recombination with increasing In content from about 80 meV to only few meV below the GaN exciton emission. These results are compared with model calculations and can be attributed to the changing band profile and originating from the polarization gradient between InAlN and GaN.
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78.55.Cr III-V semiconductors
71.35.-y Excitons and related phenomena
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

Analysis and modeling of the experimentally observed anomalous mobility properties of periodically Si-delta-doped GaN layers

Zhiyuan Zheng, Zimin Chen, Yingda Chen, Shanjin Huang, Bingfeng Fan, Yulun Xian, Weiqing Jia, Zhisheng Wu, Gang Wang, and Hao Jiang

Appl. Phys. Lett. 100, 212102 (2012); http://dx.doi.org/10.1063/1.4720395 (4 pages)

Online Publication Date: 21 May 2012

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We report the anomalous mobility properties of Si-delta-doped GaN with periodically doping profile. Samples with different delta-doping periods or with varied Si source flow were investigated. It is found that for the short delta-doping-period (<26.5 nm) samples, the Hall mobility increases with decreasing electron concentration; while for the longer-doping-period samples, the situation is just the opposite. To interpret this observation, a two-layer model has been built up for long-period samples based on secondary ion mass spectroscopy measurements. The fitting results using this model are well consistent with the experimental data.
Show PACS
72.20.My Galvanomagnetic and other magnetotransport effects
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
72.80.Ey III-V and II-VI semiconductors
72.80.Cw Elemental semiconductors
61.72.uj III-V and II-VI semiconductors
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