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27 Feb 2012

Volume 100, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 093101 (2012); http://dx.doi.org/10.1063/1.3687190 (4 pages)

Jinhai Mao, Li Huang, Yi Pan, Min Gao, Junfeng He, Haitao Zhou, Haiming Guo, Yuan Tian, Qiang Zou, Lizhi Zhang, Haigang Zhang, Yeliang Wang, Shixuan Du, Xingjiang Zhou, A. H. Castro Neto, et al.
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Non-equilibrium longitudinal and transverse optical phonons in terahertz quantum cascade lasers

Miriam S. Vitiello, Rita C. Iotti, Fausto Rossi, Lukas Mahler, Alessandro Tredicucci, Harvey E. Beere, David A. Ritchie, Qing Hu, and Gaetano Scamarcio

Appl. Phys. Lett. 100, 091101 (2012); http://dx.doi.org/10.1063/1.3687913 (4 pages) | Cited 1 time

Online Publication Date: 27 February 2012

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We report on the experimental observation of non-equilibrium longitudinal (LO) and interface transverse-like (IF-TO) optical phonons populations associated with electron transport in resonant-phonon THz quantum-cascade lasers. The measured LO-phonon occupation numbers are in excellent agreement with the result of Monte Carlo simulations at a phonon in-plane wave number q = 4.2 × 10+4 cm−1, and they remain about 40% larger than the IF-TO ones.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
43.35.Gk Phonons in crystal lattices, quantum acoustics
02.70.Ss Quantum Monte Carlo methods

Ultrasonic variable-focus optical lens using viscoelastic material

Daisuke Koyama, Ryoichi Isago, and Kentaro Nakamura

Appl. Phys. Lett. 100, 091102 (2012); http://dx.doi.org/10.1063/1.3688937 (3 pages) | Cited 2 times

Online Publication Date: 27 February 2012

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A variable-focus lens that employs acoustic radiation force and a viscoelastic material and that has no mechanical moving parts is investigated. The lens has a simple and thin structure that consists of an annular ultrasonic transducer and silicone gel. An axially symmetric acoustic standing wave can be generated in the gel by exciting a vibration mode in the radial direction on the transducer. The lens profile can be altered by varying the acoustic radiation force of the transducer. The focal length can be controlled by varying the transducer input voltage so that the lens functions as a variable-focus lens.
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42.79.Bh Lenses, prisms and mirrors
43.38.-p Transduction; acoustical devices for the generation and reproduction of sound

Influence of a depletion layer on localized surface waves in doped semiconductor nanostructures

S. Vassant, F. Pardo, P. Bouchon, R. Haïdar, F. Marquier, J. J. Greffet, and J. L. Pelouard

Appl. Phys. Lett. 100, 091103 (2012); http://dx.doi.org/10.1063/1.3689747 (3 pages) | Cited 1 time

Online Publication Date: 27 February 2012

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We report THz polarized reflectivity measurements on a doped GaAs grating made of thin walls with subwavelength dimensions and periodicity. A clear dip appears in the TM-polarized reflectivity spectrum, due to the excitation of a localized surface plasmon-phonon mode along the grating walls. The theoretical model used to describe the electromagnetic response of the grating shows the importance of the depletion layer at the GaAs surface and indicates a high sensitivity of the reflectivity dip frequency to the surface potential.
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73.22.Lp Collective excitations
78.30.Fs III-V and II-VI semiconductors
78.68.+m Optical properties of surfaces
81.05.Ea III-V semiconductors
42.79.Dj Gratings
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

The polarization field dependence of Ti/Al based Ohmic contacts on N-type semipolar GaN

Roy B. Chung, Hung-Tse Chen, Chih-Chien Pan, Jun-Seok Ha, Steven P. DenBaars, and Shuji Nakamura

Appl. Phys. Lett. 100, 091104 (2012); http://dx.doi.org/10.1063/1.3690878 (3 pages)

Online Publication Date: 28 February 2012

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We report on the polarization field dependence of the Ti/Al based n-type contacts on various polar and semipolar GaN planes. The contact resistance of the metal contacts on N-face GaN could be lowered by photoelectrochemical (PEC) etching, which formed a pyramidal feature on the surface with {10mathmath} facets. The contact resistance on the semipolar (10mathmath) surface was 6.3 × 10−5 Ω cm2, showing even lower contact resistance than the PEC etched N-face when annealed at 450 °C. Among few semipolar planes, (10mathmath), (11mathmath), and (11math2), the contact resistance was the lowest with (11mathmath) plane, which is the plane with the stronger polarization field than (10mathmath) and more Ga rich surface than (11math2) plane.
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73.40.Ns Metal-nonmetal contacts
81.40.Gh Other heat and thermomechanical treatments
81.65.Cf Surface cleaning, etching, patterning
73.40.Cg Contact resistance, contact potential

High-Q aluminum nitride photonic crystal nanobeam cavities

W. H. P. Pernice, C. Xiong, C. Schuck, and H. X. Tang

Appl. Phys. Lett. 100, 091105 (2012); http://dx.doi.org/10.1063/1.3690888 (4 pages) | Cited 8 times

Online Publication Date: 29 February 2012

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We demonstrate high optical quality factors in aluminum nitride (AlN) photonic crystal nanobeam cavities. Suspended AlN photonic crystal nanobeams are fabricated in sputter-deposited AlN-on-insulator substrates using a self-protecting release process. Employing one-dimensional photonic crystal cavities coupled to integrated optical circuits, we measure quality factors up to 146 000. By varying the waveguide-cavity coupling gap, extinction ratios in excess of 15 dB are obtained. Our results open the door for integrated photonic bandgap structures made from a low loss, wide-transparency, nonlinear optical material system.
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42.65.Wi Nonlinear waveguides
42.70.Qs Photonic bandgap materials
42.79.Gn Optical waveguides and couplers
42.82.Cr Fabrication techniques; lithography, pattern transfer

Experimental observation of leaky modes and plasmons in a hybrid resonance element

R. Magnusson, H. G. Svavarsson, J. Yoon, M. Shokooh-Saremi, and S. H. Song

Appl. Phys. Lett. 100, 091106 (2012); http://dx.doi.org/10.1063/1.3690951 (3 pages)

Online Publication Date: 29 February 2012

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We provide experimental evidence of a hybrid photonic device supporting simultaneously surface-plasmon polaritons and resonant leaky modes. A fabricated metallo-dielectric structure exhibits a pronounced plasmonic resonance at 799 nm wavelength and a modal resonance at 669 nm in transverse magnetic polarization. In transverse electric polarization, a weak modal resonance appears at 725 nm wavelength. We identify the corresponding modes by computing the attendant internal field distributions. Numerically computed spectra are in good agreement with our measurements. Since traditional modal and plasmonic devices find many uses, their hybrid versions may enable the extension of their applicability.
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73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Enhancement of light extraction efficiency by evanescent wave coupling effect in ridge-shaped AlGaInP/GaInP quantum wells

Guo-Dong Hao and Xue-Lun Wang

Appl. Phys. Lett. 100, 091107 (2012); http://dx.doi.org/10.1063/1.3689005 (3 pages)

Online Publication Date: 29 February 2012

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The optical properties of a sub-wavelength-sized ridge-shaped AlGaInP/GaInP quantum well structure fabricated by selective-area metal organic vapor phase epitaxy are investigated. The ridge structure exhibits an 8.5 times stronger photoluminescence intensity at room temperature than a planar structure, corresponding to an enhancement of at least 13.6 times in the light extraction efficiency of the ridge sample with respect to the planar sample. Both emission pattern measurements and theoretical simulation demonstrate that the high light extraction efficiency originates from the evanescent wave coupling effect in a narrow ridge structure, which can directly extract the light outside the escape cones to air.
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78.67.De Quantum wells
81.05.Ea III-V semiconductors
81.07.St Quantum wells
78.55.Cr III-V semiconductors

Microcavity enhanced single photon emission from an electrically driven site-controlled quantum dot

C. Schneider, T. Heindel, A. Huggenberger, T. A. Niederstrasser, S. Reitzenstein, A. Forchel, S. Höfling, and M. Kamp

Appl. Phys. Lett. 100, 091108 (2012); http://dx.doi.org/10.1063/1.3689782 (4 pages) | Cited 10 times

Online Publication Date: 29 February 2012

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In this work we report on the integration of single site-controlled quantum dots (SCQDs) into electrically driven micropillar cavities. The electroluminescence of these devices features emission of single SCQDs with inhomogeneous broadenings down to 170 µeV. The enhancement of electroluminescence by quantum dot-cavity coupling is demonstrated by temperature dependent investigations. Single photon emission from a spatially and spectrally coupled SCQD-resonator system is confirmed by photon autocorrelation measurements under electrical excitation yielding a g(2)(0) value of 0.42.
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78.67.Hc Quantum dots
07.10.Cm Micromechanical devices and systems
78.60.Fi Electroluminescence

Site-controlled InP/GaInP quantum dots emitting single photons in the red spectral range

Vasilij Baumann, Florian Stumpf, Christian Schneider, Stefan Kremling, Lukas Worschech, Alfred Forchel, Sven Höfling, and Martin Kamp

Appl. Phys. Lett. 100, 091109 (2012); http://dx.doi.org/10.1063/1.3690872 (3 pages) | Cited 5 times

Online Publication Date: 1 March 2012

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We report on site-controlled growth of InP/GaInP quantum dots (QDs) on GaAs substrates. The QD nucleation sites are defined by shallow nanoholes etched into a GaInP layer. Optimized growth conditions allow us to realize QD arrays with excellent long range ordering on nanohole periods as large as 1.25 µm. Single QD lines with an average linewidth of 553 µeV and best values below 200 µeV are observed. Photoluminescence spectroscopy reveals excitonic and biexcitonic emission in the wavelength range of about 670 nm (1.85 eV) with an exciton-biexciton splitting of 1.8 meV. Second-order photon-autocorrelation measurements show clear single photon emission with g(2)(0) = 0.13 ± 0.01.
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81.16.Rf Micro- and nanoscale pattern formation
81.65.Cf Surface cleaning, etching, patterning
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
81.07.Ta Quantum dots

Experimental observation of helical microbunching of a relativistic electron beam

E. Hemsing, A. Knyazik, F. O’Shea, A. Marinelli, P. Musumeci, O. Williams, S. Tochitsky, and J. B. Rosenzweig

Appl. Phys. Lett. 100, 091110 (2012); http://dx.doi.org/10.1063/1.3690900 (4 pages) | Cited 2 times

Online Publication Date: 1 March 2012

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Experimental observation of the microbunching of a relativistic electron beam at the second harmonic interaction frequency of a helical undulator is presented. The microbunching signal is observed from the coherent transition radiation of the electron beam and indicates experimental evidence of a dominantly helical electron beam density distribution. This result is in agreement with theoretical and numerical predictions and provides a proof-of-principle demonstration of proposed schemes designed to generate light with orbital angular momentum in high-gain free-electron lasers.
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41.60.Cr Free-electron lasers

Excitations of surface plasmon polaritons in double layer metal grating structures

N. Anttu, Z. Q. Guan, U. Håkanson, H. X. Xu, and H. Q. Xu

Appl. Phys. Lett. 100, 091111 (2012); http://dx.doi.org/10.1063/1.3690947 (3 pages) | Cited 1 time

Online Publication Date: 1 March 2012

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We study the light scattering properties of double layer gratings (DLGs) made from Au on SiO2 substrates. It is found that surface plasmon polaritons (SPPs) can be excited in the DLGs for a separation of up to 150 nm between the two Au grating layers and the collective reflectance spectra exhibit a strong resonant peak and a closely lying dip as a result of the surface plasmon polariton excitations. It is also found that the angle-resolved specular reflectance spectra show a dip-peak pair structure, while the angle-resolved reflectance spectra of higher diffracted orders show a complementary peak-dip pair structure. Finally, operation of the DLGs for efficient wavelength demultiplexing is proposed and discussed in light of these results.
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42.79.Dj Gratings
73.43.Lp Collective excitations
78.66.Bz Metals and metallic alloys

Robust generation of bright two-color entangled optical beams from a phase-insensitive optical parametric amplifier

Xiaomin Guo, Junjun Zhao, and Yongmin Li

Appl. Phys. Lett. 100, 091112 (2012); http://dx.doi.org/10.1063/1.3690876 (3 pages)

Online Publication Date: 2 March 2012

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Bright two-color continuous variable (CV) entangled optical beams at 0.8 and 1.5 μm are generated by utilizing a phase-insensitive optical parametric amplifier with only 1.5 μm signal field injected. Without locking the relative phase between the signal and pump fields, the amplitude quadrature difference squeezing of 3.30 dB and phase quadrature sum squeezing of 3.35 dB are observed, which satisfy the entanglement criterion. The demonstrated scheme here eliminates the necessity of precise phase control between the signal and pump fields and enables robust generation of two-color CV entangled states.
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42.65.Yj Optical parametric oscillators and amplifiers
03.67.Bg Entanglement production and manipulation
03.65.Ud Entanglement and quantum nonlocality (e.g. EPR paradox, Bell's inequalities, GHZ states, etc.)
42.50.Dv Quantum state engineering and measurements
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Terahertz emission from a two-color plasma filament in a slot waveguide

D. Dietze, K. Unterrainer, and J. Darmo

Appl. Phys. Lett. 100, 091113 (2012); http://dx.doi.org/10.1063/1.3691921 (3 pages)

Online Publication Date: 2 March 2012

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Terahertz emission in forward direction from a long two-color filament placed in the center of a slot waveguide is reported. The waveguide improves the collection and imaging of the generated THz radiation. By tuning the plate separation and position of the waveguide along the filament axis, the emitted mode can be matched to the collection optics. We achieved an increase of the detected electric field by 40% and of the THz pulse energy by four times compared to the case without waveguide.
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84.40.Az Waveguides, transmission lines, striplines
52.40.Fd Plasma interactions with antennas; plasma-filled waveguides
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Single-layer behavior and slow carrier density dynamic of twisted graphene bilayer

Lan Meng, Yanfeng Zhang, Wei Yan, Lei Feng, Lin He, Rui-Fen Dou, and Jia-Cai Nie

Appl. Phys. Lett. 100, 091601 (2012); http://dx.doi.org/10.1063/1.3691952 (4 pages) | Cited 5 times

Online Publication Date: 2 March 2012

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We report scanning tunneling microscopy and scanning tunneling spectroscopy (STS) of twisted graphene bilayer on SiC substrate. For twist angle ∼4.5°, the Dirac point ED is located about 0.40 eV below the Fermi level EF due to the electron doping at the graphene/SiC interface. We observed an unexpected result that the local Dirac point around a nanoscaled defect shifts towards the Fermi energy during the STS measurements (with a time scale about 100 s). This behavior was attributed to the decoupling between the twisted graphene and the substrate during the measurements, which lowers the carrier density of graphene simultaneously.
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73.63.-b Electronic transport in nanoscale materials and structures
61.48.Gh Structure of graphene
71.20.Tx Fullerenes and related materials; intercalation compounds
73.22.Pr Electronic structure of graphene
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Emissive properties of SiO2 thin films through photonic windows

D. Hernández, M. Garín, T. Trifonov, A. Rodríguez, and R. Alcubilla

Appl. Phys. Lett. 100, 091901 (2012); http://dx.doi.org/10.1063/1.3688031 (3 pages)

Online Publication Date: 27 February 2012

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In this work, we study the selective emission properties of silicon-based three-dimensional photonic crystals coated with thin films of silicon dioxide presenting temperature emission measurements at 600 K of oxidized macroporous silicon structures. The photonic band gap of the structure is centered at 9 μm with 2.5 μm bandwidth. Through this photonic window defined by the gap, a narrow emission peak arises from the oxide layer. We propose the given structure as a selective thermal source for infrared spectroscopy applications in the fingerprint spectral region (6–12 μm wavelength).
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78.67.Pt Multilayers; superlattices; photonic structures; metamaterials
78.30.Am Elemental semiconductors and insulators
78.66.Db Elemental semiconductors and insulators
61.43.Gt Powders, porous materials
42.70.Qs Photonic bandgap materials

Soft-phonon mode observation in Li2Ge4O9 phase above room temperature

Yoshihiro Takahashi, Jun Kunitomo, Kensaku Nakamura, Minoru Osada, and Takumi Fujiwara

Appl. Phys. Lett. 100, 091902 (2012); http://dx.doi.org/10.1063/1.3688603 (3 pages)

Online Publication Date: 27 February 2012

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Li2Ge4O9 is known to be a ferroelectric phase with Curie temperature at Tc ∼ −93 °C. In this study, we found both the lowest-frequency phonon and heat-capacity anomalies around 100 °C in the Li2Ge4O9 phase, demonstrating their presence in the structural phase-transition. The phase transition is probably triggered by regularization of distorted GeO6 octahedra in the paraelectric phase, resulting in another phase consisting of the regular octahedral GeO6 unit, which was supported by in situ measurement of emission of 2E → 4A2 transition in the Mn4+-doped phase. It is deduced that the phase transition is more dynamic than ferroelectric phase-transition originating in ordering of the Li ions.
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77.80.B- Phase transitions and Curie point
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
64.70.K- Solid-solid transitions
68.35.Ja Surface and interface dynamics and vibrations

Thermal transport in crystalline Si/Ge nano-composites: Atomistic simulations and microscopic models

Feng Hao, Daining Fang, and Zhiping Xu

Appl. Phys. Lett. 100, 091903 (2012); http://dx.doi.org/10.1063/1.3688943 (4 pages) | Cited 5 times

Online Publication Date: 27 February 2012

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Thermal transport in Si/Ge nano-composites, consisting of crystalline silicon as matrix and aligned germanium nanowires as inclusions, is investigated here through non-equilibrium and equilibrium molecular dynamics (MD) simulations. Our results show increasing of temperature gradient at the interface between silicon and germanium, which is limited in an interfacial phase of few lattices. A thermal boundary phase is included explicitly in our three-phase model, in companion with the modified effective medium theory, to be compared with MD simulation results with various nanowire concentrations. The results suggest that the presence of nanowires leads to a dramatic decrease of κ for heat transfer across nanowires arising from interfacial phase, while along the interfaces, the reduction of phonon mean free path due to interfacial scattering lowers κ of silicon matrix and germanium nanowires.
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73.63.Bd Nanocrystalline materials
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)
63.22.Gh Nanotubes and nanowires
66.70.Df Metals, alloys, and semiconductors
61.72.Qq Microscopic defects (voids, inclusions, etc.)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Extraordinary acoustic reflection enhancement by acoustically transparent thin plates

Zhaojian He, Shasha Peng, Rui Hao, Chunyin Qiu, Manzhu Ke, Jun Mei, and Zhengyou Liu

Appl. Phys. Lett. 100, 091904 (2012); http://dx.doi.org/10.1063/1.3691182 (4 pages) | Cited 1 time

Online Publication Date: 28 February 2012

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We report an observation of the extraordinary high reflection of acoustic waves in water by thin epoxy plates partitioned by subwavelength cuts, whereas such plates without structure are acoustically transparent as the acoustic properties of epoxy are close to water. It is demonstrated that this exotic phenomenon results from the resonant excitation of the local modes within the individual pieces derived by the cuts. The experiment agrees well with the theory. Potential applications of such simple structures can be anticipated, e.g., in blocking sound.
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43.40.-r Structural acoustics and vibration
62.65.+k Acoustical properties of solids

Organic salts as super-high rate capability materials for lithium-ion batteries

Y. Y. Zhang, Y. Y. Sun, S. X. Du, H.-J. Gao, and S. B. Zhang

Appl. Phys. Lett. 100, 091905 (2012); http://dx.doi.org/10.1063/1.3689764 (4 pages) | Cited 2 times

Online Publication Date: 28 February 2012

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First-principles calculation reveals that organic salts could be super-high rate capability electrode materials for Li-ion batteries. We show that di-lithium terephthalate, an anode material demonstrated recently by experiment, has low Li diffusion barrier (EA). A resonant bonding model for the low EA is developed, which leads to the prediction that di-potassium terephthalate (K2TPA) has even lower EA (150 meV), with diffusion rate orders of magnitude higher than that in Li-intercalated graphite. The calculated anode voltage (0.62 V), specific energy density (209 mA·h/g), and volume change upon lithiation (5%) make K2TPA a promising anode material for power-intensive applications such as electric-vehicles.
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82.47.Aa Lithium-ion batteries
66.30.Ny Chemical interdiffusion; diffusion barriers
68.35.Fx Diffusion; interface formation
71.15.-m Methods of electronic structure calculations
82.45.Fk Electrodes

Electrochromic switchable mirror glass with controllable reflectance

Kazuki Tajima, Hiromi Hotta, Yasusei Yamada, Masahisa Okada, and Kazuki Yoshimura

Appl. Phys. Lett. 100, 091906 (2012); http://dx.doi.org/10.1063/1.3691256 (3 pages) | Cited 1 time

Online Publication Date: 29 February 2012

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An electrochromic switchable mirror glass with controllable reflectance was developed. The conditions for fabricating InGaZnO4 (IGZO) thin film, which serves as a transparent conductor, were investigated. The mirror glass with IGZO thin film exhibited multiple colors arising from interference between multilayers. The mirror glass with IGZO thin film fabricated at a working pressure of 0.4 Pa showed high transmittance (63%) in the transparent state and low reflectance (16%) in the reflective state at a wavelength of 670 nm. Moreover, the developed mirror glass had low glare in the reflective state because the reflection of direct, bright light was reduced.
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42.79.Bh Lenses, prisms and mirrors
42.79.Wc Optical coatings
42.70.Ce Glasses, quartz

Defect evolution and interplay in n-type InN

Christian Rauch, Filip Tuomisto, Arantxa Vilalta-Clemente, Bertrand Lacroix, Pierre Ruterana, Simon Kraeusel, Ben Hourahine, and William J. Schaff

Appl. Phys. Lett. 100, 091907 (2012); http://dx.doi.org/10.1063/1.3688038 (3 pages) | Cited 2 times

Online Publication Date: 1 March 2012

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The nature and interplay of intrinsic point and extended defects in n-type Si-doped InN epilayers with free carrier concentrations up to 6.6×1020 cm−3 are studied using positron annihilation spectroscopy and transmission electron microscopy and compared to results from undoped irradiated films. In as-grown Si-doped samples, mixed In-N vacancy complexes (VIn-VN) are the dominant III-sublattice related vacancy defects. An increase in the number of VN in these complexes toward the interface suggests high concentrations of additional isolated VN and VN-clusters near the GaN buffer layer and coincides with elevated dislocation densities in that area.
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71.55.Eq III-V semiconductors
78.70.Bj Positron annihilation
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)

A 3-dimensional time-resolved photothermal deflection “Mirage” method

N. G. C. Astrath, L. C. Malacarne, G. V. B. Lukasievicz, H. S. Bernabe, J. H. Rohling, M. L. Baesso, J. Shen, and S. E. Bialkowski

Appl. Phys. Lett. 100, 091908 (2012); http://dx.doi.org/10.1063/1.3691253 (4 pages) | Cited 1 time

Online Publication Date: 2 March 2012

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A three-dimensional time-resolved theory and experiment for photothermal deflection spectroscopy is developed. The heat conduction equations for two semi-infinite media consisting of an opaque sample and a fluid are solved considering temperature and energy flux balance conditions for a Gaussian heat source. The time dependent perpendicular deflection signal is calculated and compared to experimental measurements on glassy carbon and copper samples. Excellent agreement with literature values for thermal diffusivity of the samples is found. The transient behavior is analyzed for different coupling fluids.
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66.25.+g Thermal conduction in nonmetallic liquids
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
78.47.D- Time resolved spectroscopy (>1 psec)
78.20.nb Photothermal effects
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Compositional instability in InAlN/GaN lattice-matched epitaxy

Q. Y. Wei, T. Li, Y. Huang, J. Y. Huang, Z. T. Chen, T. Egawa, and F. A. Ponce

Appl. Phys. Lett. 100, 092101 (2012); http://dx.doi.org/10.1063/1.3690890 (3 pages) | Cited 3 times

Online Publication Date: 27 February 2012

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The InxAl1−xN/GaN system is found to show compositional instability at the lattice-matched composition (x = 0.18) in epitaxial layers grown by metal organic chemical vapor deposition. The breakdown in compositional homogeneity is triggered by threading dislocations with a screw component propagating from the GaN underlayer, which tend to open up into V-grooves at a certain thickness of the InxAl1−xN layer. The V-grooves coalesce at ∼200 nm and are filled with material that exhibits a significant drop in indium content and a broad luminescence peak. Transmission electron microscopy suggests that the structural breakdown is due to heterogeneous nucleation and growth at the facets of the V-grooves.
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81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Characterization of germanium/silicon p–n junction fabricated by low temperature direct wafer bonding and layer exfoliation

Farzan Gity, Ki Yeol Byun, Ko-Hsin Lee, Karim Cherkaoui, John M. Hayes, Alan P. Morrison, Cindy Colinge, and Brian Corbett

Appl. Phys. Lett. 100, 092102 (2012); http://dx.doi.org/10.1063/1.3688174 (3 pages)

Online Publication Date: 27 February 2012

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The current transport across a p-Ge/n-Si diode structure obtained by direct wafer bonding and layer exfoliation is analysed. A low temperature anneal at 400 °C for 30 min was used to improve the forward characteristics of the diode with the on/off ratio at −1 V being >8000. Post anneal, the transport mechanism has a strong tunnelling component. This fabrication technique using a low thermal budget (T ≤ 400 °C) is an attractive option for heterogeneous integration.
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85.30.Kk Junction diodes

Strong dipole coupling in nonpolar nitride quantum dots due to Coulomb effects

K. Schuh, S. Barthel, O. Marquardt, T. Hickel, J. Neugebauer, G. Czycholl, and F. Jahnke

Appl. Phys. Lett. 100, 092103 (2012); http://dx.doi.org/10.1063/1.3688900 (4 pages) | Cited 1 time

Online Publication Date: 27 February 2012

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Optical properties of polar and nonpolar nitride quantum dots (QDs) are determined on the basis of a microscopic theory which combines a continuum elasticity approach to the polarization potential, a tight-binding model for the electronic energies and wavefunctions, and a many-body theory for the optical properties. For nonpolar nitride quantum dots, we find that optical absorption and emission spectra exhibit a weak ground-state oscillator strength in a single-particle calculation whereas the Coulomb configuration interaction strongly enhances the ground-state transitions. This finding sheds new light on existing discrepancies between previous theoretical and experimental results for these systems, as a weak ground state transition was predicted because of the spatial separation of the corresponding electron and hole state due to intrinsic fields whereas experimentally fast optical transitions have been observed.
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78.67.Hc Quantum dots
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.21.La Quantum dots
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
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