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25 Jun 2012

Volume 100, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 100, 261104 (2012); http://dx.doi.org/10.1063/1.4711253 (4 pages)

Marcelo Davanço, Jun Rong Ong, Andrea Bahgat Shehata, Alberto Tosi, Imad Agha, Solomon Assefa, Fengnian Xia, William M. J. Green, Shayan Mookherjea, and Kartik Srinivasan
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Intracavity and resonant Raman crystal fiber laser

Chien-Chih Lai, Chih-Peng Ke, Shih-Kun Liu, Chia-Yao Lo, Dong-Yo Jheng, Shih-Chang Wang, Si-Rong Lin, Pinghui S. Yeh, and Sheng-Lung Huang

Appl. Phys. Lett. 100, 261101 (2012); http://dx.doi.org/10.1063/1.4730949 (3 pages) | Cited 2 times

Online Publication Date: 25 June 2012

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We demonstrated an efficient, compact, and continuous-wave Raman crystal fiber laser (RCFL) using an intracavity and resonant χ(3) approach. The gain and nonlinear medium was Cr4+:Y3Al5O12 double-clad crystal fiber grown using the codrawing laser-heated pedestal growth technique. The RCFL threshold was only 50 mW, and the slope efficiency reached 14.3% above a pump power of 350 mW. The result is in good agreement with theory, which indicates a near-100% quantum efficiency of resonant stimulated Raman scattering.
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42.55.Wd Fiber lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.Jf Beam characteristics: profile, intensity, and power; spatial pattern formation
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.81.Bm Fabrication, cladding, and splicing

Nanophotonic detection of side-coupled nanomechanical cantilevers

V. T. K. Sauer, Z. Diao, M. R. Freeman, and W. K. Hiebert

Appl. Phys. Lett. 100, 261102 (2012); http://dx.doi.org/10.1063/1.4731210 (4 pages) | Cited 1 time

Online Publication Date: 25 June 2012

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A silicon nanophotonic Mach-Zehnder interferometer (MZI) is used to detect the mechanical resonance of a cantilever external to a nanophotonic waveguide. Small cantilever devices, below the cut-off for waveguide supported modes, are fabricated ∼140 nm away from one MZI arm. Cantilever resonant frequencies up to 60 MHz are measured with mechanical quality factors around 20 000 and signal to noise ratios up to 1000. Phase-locked loop frequency stability measurements indicate a mass sensitivity of 2 zg in an example cantilever of 0.5 pg mass. An interferometric transduction mechanism is confirmed, and the system is shown to work effectively in all-optical operation.
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42.79.-e Optical elements, devices, and systems
42.79.Gn Optical waveguides and couplers
42.82.Et Waveguides, couplers, and arrays
07.60.Ly Interferometers
06.30.Ft Time and frequency

Fabrication and luminescent properties of core-shell InGaN/GaN multiple quantum wells on GaN nanopillars

J.-R. Chang, S.-P. Chang, Y.-J. Li, Y.-J. Cheng, K.-P. Sou, J.-K. Huang, H.-C. Kuo, and C.-Y. Chang

Appl. Phys. Lett. 100, 261103 (2012); http://dx.doi.org/10.1063/1.4731629 (4 pages) | Cited 1 time

Online Publication Date: 25 June 2012

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Core-shell InGaN/GaN multiple quantum wells (MQWs) on GaN nanopillars were fabricated by top-down etching followed by epitaxial regrowth. The regrowth formed hexagonal sidewalls and pyramids on the nanopillars. The cathodoluminescence of MQWs blue shifts as the location moves from top to bottom on both the pillar sidewalls and pyramid facets, covering a spectral linewidth of about 100 nm. The MQWs on the pillar sidewalls have a higher InN fraction than those on the pyramid facets. The photoluminescent wavelength is stable over two orders of carrier density change due to the smaller quantum confined Stark effect on the nanopillar facets.
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81.05.Ea III-V semiconductors
78.20.Jq Electro-optical effects
78.55.Cr III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
78.67.De Quantum wells
81.07.St Quantum wells

Telecommunications-band heralded single photons from a silicon nanophotonic chip

Marcelo Davanço, Jun Rong Ong, Andrea Bahgat Shehata, Alberto Tosi, Imad Agha, Solomon Assefa, Fengnian Xia, William M. J. Green, Shayan Mookherjea, and Kartik Srinivasan

Appl. Phys. Lett. 100, 261104 (2012); http://dx.doi.org/10.1063/1.4711253 (4 pages) | Cited 7 times

Online Publication Date: 25 June 2012

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We demonstrate room temperature heralded single photon generation in a CMOS-compatible silicon nanophotonic device. The strong modal confinement and slow group velocity provided by a coupled resonator optical waveguide produced a large four-wave-mixing nonlinearity coefficient γeff ≈ 4100 W−1 m−1 at telecommunications wavelengths. Spontaneous four-wave-mixing using a degenerate pump beam at 1549.6 nm created photon pairs at 1529.5 nm and 1570.5 nm with a coincidence-to-accidental ratio exceeding 20. A photon correlation measurement of the signal (1529.5 nm) photons heralded by the detection of the idler (1570.5 nm) photons showed antibunching with g(2)(0) = 0.19±0.03. The demonstration of a single photon source within a silicon platform holds promise for future integrated quantum photonic circuits.
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85.30.Tv Field effect devices
85.35.Ds Quantum interference devices

Effect of proton bombardment on InAs dots and wetting layer in laser structures

I. O’Driscoll, P. Blood, P. M. Smowton, A. Sobiesierski, and R. Gwilliam

Appl. Phys. Lett. 100, 261105 (2012); http://dx.doi.org/10.1063/1.4730964 (4 pages)

Online Publication Date: 26 June 2012

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The effect of proton bombardment on carrier lifetime and photoluminescence of InAs quantum dots was measured. Optical absorption and transmission electron microscopy show the dots retain their integrity under bombardment. A decrease in ground state photoluminescence with increasing dose is not explained by the decrease in dot carrier lifetime alone, but also by bombardment-induced non-radiative recombination in the wetting layer, which reduces the dot electron population at fixed excitation. To exploit the relative radiation immunity of quantum dots, it is necessary to maximise the dot density and capture probability per dot to minimize the effect of wetting layer recombination.
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78.67.Hc Quantum dots
81.05.Ea III-V semiconductors
81.07.Ta Quantum dots
61.80.Jh Ion radiation effects
73.21.La Quantum dots
78.55.Cr III-V semiconductors

Optimal control of coherent anti-Stokes Raman scattering image contrast

Gero Bergner, Sebastian Schlücker, Bernd Kampe, Peter Dittrich, Benjamin Dietzek, and Jürgen Popp

Appl. Phys. Lett. 100, 261106 (2012); http://dx.doi.org/10.1063/1.4731205 (4 pages)

Online Publication Date: 26 June 2012

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Optimal control of coherent anti-Stokes Raman scattering (CARS) image contrast is reported. The setup combines an evolutionary strategy and a closed-loop feedback with a liquid-crystal spatial modulator to control the spectrum of the Stokes pulse within a CARS scheme to optimize the vibrational contrast of CARS images. The CARS excitation spectrum is optimized for image contrast at a pre-determined wavenumber position. The optimization feedback uses an image-contrast parameter generated from the image itself as the experimentally imposed fitness parameter. This strategy allows for enhancing the image contrast by a factor of up to 2.6.
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42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.79.Hp Optical processors, correlators, and modulators
42.30.Va Image forming and processing
02.60.Pn Numerical optimization
07.05.Dz Control systems

In situ optofluidic control of reconfigurable photonic crystal cavities

Noud W. L. Speijcken, Mehmet A. Dündar, Alvaro Casas Bedoya, Christelle Monat, Christian Grillet, Peter Domachuk, Richard Nötzel, Benjamin J. Eggleton, and Rob W. van der Heijden

Appl. Phys. Lett. 100, 261107 (2012); http://dx.doi.org/10.1063/1.4732093 (5 pages) | Cited 3 times

Online Publication Date: 27 June 2012

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The mobile nature of fluids is fully exploited in planar photonic crystals to not only tune and reconfigure in situ optical microcavities, in a continuous and reversible manner, but also to create “a posteriori” spatially programmable cavities. Both the amount of liquid and the location of the selectively infiltrated area can be accurately controlled either mechanically, using a microfiber manipulator, or optically, using a laser-controlled evaporation and recondensation scheme. The wide applicability is illustrated by tuning a cavity resonance over 50 nm, adjusting the frequency splitting of an originally degenerate cavity mode, and by freely moving a liquid-induced cavity through dragging a microdroplet.
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42.70.Qs Photonic bandgap materials
42.79.-e Optical elements, devices, and systems
42.81.-i Fiber optics

Photoluminescence of boron nitride nanosheets exfoliated by ball milling

Lu Hua Li, Ying Chen, Bing-Ming Cheng, Meng-Yeh Lin, Sheng-Long Chou, and Yu-Chain Peng

Appl. Phys. Lett. 100, 261108 (2012); http://dx.doi.org/10.1063/1.4731203 (4 pages) | Cited 4 times

Online Publication Date: 27 June 2012

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The photoluminescence of boron nitride (BN) nanosheets exfoliated by ball milling method has been investigated. At room temperature, the nanosheets have strong deep ultraviolet (DUV) light emission at 224 nm and weak defect-related UV (∼300 nm) emission. The DUV peak profile slightly changes with the increase of milling time due to the increase of stacking faults caused by the shear force during milling. The decreased ∼300 nm emission after milling treatments has been attributed to the preferential orientation of the BN nanosheets on substrate and the strong polarization anisotropy of BN materials in luminescence.
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81.05.Ea III-V semiconductors
81.20.Wk Machining, milling
78.40.Fy Semiconductors
61.72.Nn Stacking faults and other planar or extended defects
78.55.Cr III-V semiconductors
81.16.-c Methods of micro- and nanofabrication and processing

Optically gated tunable terahertz filters

Stefan F. Busch, Steffen Schumann, Christian Jansen, Maik Scheller, Martin Koch, and Bernd M. Fischer

Appl. Phys. Lett. 100, 261109 (2012); http://dx.doi.org/10.1063/1.4729480 (3 pages)

Online Publication Date: 27 June 2012

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We present a fast and flexible terahertz filter based on diffractive gratings combined with an optically gated modulator. The terahertz radiation is diffracted by blazed gratings, and the individual frequency components are focused onto an optically excited semiconductor. Different light patterns are used to create free carriers in the bulk semiconductor material, leading to a spatial modulation of its transmission. This approach enables us to damp arbitrary frequencies and allows us to design and implement filters with almost any frequency response. By using the digital light processing technique, the switching time between different filter settings is as short as 16 ms.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
42.79.Dj Gratings
42.79.Hp Optical processors, correlators, and modulators

Hot electron extraction from CdTe quantum dots via beta carotene molecular energy levels

T. Pazhanivel, D. Nataraj, V. P. Devarajan, K. Senthil, M. Seol, and K. Yong

Appl. Phys. Lett. 100, 261110 (2012); http://dx.doi.org/10.1063/1.4730623 (5 pages)

Online Publication Date: 28 June 2012

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We report our findings related to hot electron extraction from CdTe quantum dots, and we were able to do this by using beta carotene as an electron acceptor. Transient absorption spectra with two slow recovering negative bleaches at the absorption maximum of the molecule and quantum dot have indicated the slowing down of cooling process and the existence of hot carriers in this hybrid system.
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78.67.Hc Quantum dots
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
72.20.Ht High-field and nonlinear effects
78.30.Fs III-V and II-VI semiconductors
78.40.Fy Semiconductors
78.55.Et II-VI semiconductors

Gain measurements of scattering-assisted terahertz quantum cascade lasers

David Burghoff, Chun Wang Ivan Chan, Qing Hu, and John L. Reno

Appl. Phys. Lett. 100, 261111 (2012); http://dx.doi.org/10.1063/1.4732518 (4 pages) | Cited 4 times

Online Publication Date: 29 June 2012

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Using terahertz time-domain spectroscopy, the gain of scattering-assisted terahertz quantum cascade lasers is measured. By examining the intersubband gain and absorption over a wide range of bias voltages, we experimentally detect energy anticrossings—revealing information about the mechanism of laser action—and compare the resonant-tunneling injection scheme to the scattering-assisted injection scheme. The temperature performance of the gain medium is also measured and discussed, and an additional intersubband transition is identified that contributes to scattering-assisted lasing action at high temperatures.
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42.55.Px Semiconductor lasers; laser diodes
07.57.Pt Submillimeter wave, microwave and radiowave spectrometers; magnetic resonance spectrometers, auxiliary equipment, and techniques
42.25.Bs Wave propagation, transmission and absorption
42.25.Fx Diffraction and scattering

Sampled grating, distributed feedback quantum cascade lasers with broad tunability and continuous operation at room temperature

S. Slivken, N. Bandyopadhyay, S. Tsao, S. Nida, Y. Bai, Q. Y. Lu, and M. Razeghi

Appl. Phys. Lett. 100, 261112 (2012); http://dx.doi.org/10.1063/1.4732801 (4 pages) | Cited 3 times

Online Publication Date: 29 June 2012

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A dual-section, single-mode quantum cascade laser is demonstrated in continuous wave at room temperature with up to 114 nm (50 cm−1) of tuning near a wavelength of 4.8 μm. Power above 100 mW is demonstrated, with a mean side mode suppression ratio of 24 dB. By changing the grating period, 270 nm (120 cm−1) of gap-free electrical tuning for a single gain medium has been realized.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking
42.79.Dj Gratings
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The importance of scattering, surface potential, and vanguard counter-potential in terahertz emission from gallium arsenide

D. L. Cortie and R. A. Lewis

Appl. Phys. Lett. 100, 261601 (2012); http://dx.doi.org/10.1063/1.4730954 (3 pages) | Cited 2 times

Online Publication Date: 25 June 2012

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It is well established that under excitation by short (<1 ps), above-band-gap optical pulses, semiconductor surfaces may emit terahertz-frequency electromagnetic radiation via photocarrier diffusion (the dominant mechanism in InAs) or photocarrier drift (dominant in GaAs). Our three-dimensional ensemble Monte Carlo simulations allow multiple physical parameters to vary over wide ranges and provide unique direct insight into the factors controlling terahertz emission. We find for GaAs (in contrast to InAs), scattering and the surface potential are key factors. We further delineate in GaAs (as in InAs) the role of a vanguard counter-potential. The effects of varying dielectric constant, band-gap, and effective mass are similar in both emitter types.
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78.70.Gq Microwave and radio-frequency interactions
63.20.-e Phonons in crystal lattices
68.35.Fx Diffusion; interface formation
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Characterization of the local crystallinity via reflectance of very slow electrons

Z. Pokorná, Š. Mikmeková, I. Müllerová, and L. Frank

Appl. Phys. Lett. 100, 261602 (2012); http://dx.doi.org/10.1063/1.4729879 (4 pages)

Online Publication Date: 25 June 2012

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The reflectance of very slow electrons from solids and its electron energy dependence are shown as characteristic for the crystal system and its spatial orientation so they can serve, e.g., to fingerprinting the orientation of grains in polycrystals. Measurements on single crystals and polycrystals are validated via electron backscatter diffraction analyses. Sensitivity of the method to fine details of crystallinity is demonstrated.
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61.66.Bi Elemental solids
61.85.+p Channeling phenomena (blocking, energy loss, etc.)
79.20.Kz Other electron-impact emission phenomena

Electronic structure of delta-doped La:SrTiO3 layers by hard x-ray photoelectron spectroscopy

A. M. Kaiser, A. X. Gray, G. Conti, B. Jalan, A. P. Kajdos, A. Gloskovskii, S. Ueda, Y. Yamashita, K. Kobayashi, W. Drube, S. Stemmer, and C. S. Fadley

Appl. Phys. Lett. 100, 261603 (2012); http://dx.doi.org/10.1063/1.4731642 (4 pages) | Cited 1 time

Online Publication Date: 27 June 2012

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We have employed hard x-ray photoemission (HAXPES) to study a delta-doped SrTiO3 layer that consisted of a 3-nm thickness of La-doped SrTiO3 with 6% La embedded in a SrTiO3 film. Results are compared to a thick, uniformily doped La:SrTiO3 layer. We find no indication of a band offset for the delta-doped layer, but evidence of the presence of Ti3+ in both the thick sample and the delta-layer, and indications of a density of states increase near the Fermi energy in the delta-doped layer. These results further demonstrate that HAXPES is a powerful tool for the non-destructive investigation of deeply buried doped layers.
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71.20.Ps Other inorganic compounds
79.60.-i Photoemission and photoelectron spectra
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Micro-Raman spectroscopy of graphene grown on stepped 4H-SiC (0001) surface

K. Grodecki, R. Bozek, W. Strupinski, A. Wysmolek, R. Stepniewski, and J. M. Baranowski

Appl. Phys. Lett. 100, 261604 (2012); http://dx.doi.org/10.1063/1.4730372 (4 pages) | Cited 1 time

Online Publication Date: 28 June 2012

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Graphene grown by chemical vapor deposition on 4H-SiC (0001) was studied using micro-Raman spectroscopy and atomic force microscopy (AFM). AFM revealed that the graphene structure grown on on-axis substrates has a stepped morphology. This is due to step bunching, which results from etching in hydrogen as well as from the process of graphene formation itself. It was shown by micro-Raman spectroscopy that the properties of graphene present on step edges and on terraces are quite different. Graphene on terraces is uniform with a relatively small thickness and strain fluctuations. On the other hand, graphene on step edges has a large thickness and strain variations occur. A careful analysis of micro-Raman spatial maps led us to the conclusion that the carrier concentration on step edge regions is lowered when compared with terrace regions.
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78.30.Na Fullerenes and related materials
78.66.Tr Fullerenes and related materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology
68.37.Ps Atomic force microscopy (AFM)

Simultaneous flattening of Si(110), (111), and (001) surfaces for three-dimensional Si nanowires

Yukinori Morita and Hiroyuki Ota

Appl. Phys. Lett. 100, 261605 (2012); http://dx.doi.org/10.1063/1.4731789 (4 pages)

Online Publication Date: 28 June 2012

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We prepared atomically flat Si(110), (111), and (001) surfaces using identical preparation conditions for a low-pH (pH < 1) HF treatment and a subsequent low-temperature (∼800 °C) anneal in H2. Atomic-resolution scanning tunneling microscopy (STM) revealed that the treated Si(110) surfaces were atomically flat with a hydrogen-terminated 1 × 1 atomic arrangement. Similar features were also confirmed by STM analysis of 1 × 1:H on Si(111) and 2 × 1:H on Si(001) surfaces. Using this technique, well-ordered cross sections of three-dimensional Si nanowires surrounded by simultaneously flattened (110), (111), (001) facets were realized for nanowires with 〈100〉, 〈110〉, 〈111〉, and 〈112〉 long-axis orientations.
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81.05.Cy Elemental semiconductors
81.65.Cf Surface cleaning, etching, patterning
81.07.Gf Nanowires
82.45.Vp Semiconductor materials in electrochemistry
61.72.Cc Kinetics of defect formation and annealing
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)
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Ultraviolet emission efficiency enhancement of a-plane AlGaN/GaN multiple-quantum-wells with increasing quantum well thickness

Huei-Min Huang, Chiao-Yun Chang, Yu-Pin Lan, Tien-Chang Lu, Hao-Chung Kuo, and Shing-Chung Wang

Appl. Phys. Lett. 100, 261901 (2012); http://dx.doi.org/10.1063/1.4730438 (4 pages) | Cited 1 time

Online Publication Date: 25 June 2012

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The defect-induced carrier localization in nonpolar a-plane (Al,Ga)N/GaN multiple quantum wells (MQWs) structures with different well thickness have been investigated. A strong variation of temperature-dependent photoluminescence peak energy was observed and attributed to the existence of the localized states. The degree of carrier localization in these defect-induced states was more prominent in the case of MQWs with the wider well width. In addition, the ultraviolet light emission efficiency revealed a 3-fold enhancement with increasing the well width from 1.6 nm to 7.3 nm, due to the strong carrier localization generated from the quantum-wire-like features formed by the intersection between basal stacking faults and quantum wells.
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78.55.Cr III-V semiconductors
78.67.De Quantum wells
61.72.Nn Stacking faults and other planar or extended defects
71.55.Eq III-V semiconductors
73.21.Fg Quantum wells

Quantum Monte Carlo study of high-pressure cubic TiO2

M. Abbasnejad, E. Shojaee, M. R. Mohammadizadeh, M. Alaei, and Ryo Maezono

Appl. Phys. Lett. 100, 261902 (2012); http://dx.doi.org/10.1063/1.4730608 (4 pages) | Cited 2 times

Online Publication Date: 25 June 2012

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We have studied the high-pressure cubic fluorite polymorph of TiO2 (c-TiO2) using the diffusion Monte Carlo (DMC) method. The estimated bulk modulus is within the range reported previously in density functional studies, high, but does not rival that of diamond. The calculated excitation energies within DMC are consistent with the results of GW approximation. The infrared frequency of c-TiO2, obtained via the frozen phonon method within DMC, shows non-negligible anharmonicity. This suggests that c-TiO2 might be stabilized if this anharmonicity is considered. Our DMC results could help to establish more accurate results for c-TiO2 compared with the widely-scattered mean-field results.
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61.66.Fn Inorganic compounds
63.20.Ry Anharmonic lattice modes
78.30.Hv Other nonmetallic inorganics
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
62.50.-p High-pressure effects in solids and liquids

Strategy for designing broadband epsilon-near-zero metamaterial with loss compensation by gain media

L. Sun and K. W. Yu

Appl. Phys. Lett. 100, 261903 (2012); http://dx.doi.org/10.1063/1.4730380 (4 pages) | Cited 4 times

Online Publication Date: 26 June 2012

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A strategy is proposed to design the broadband gain-doped epsilon-near-zero (GENZ) metamaterial. Based on the Milton representation of effective permittivity, the strategy starts in a dimensionless spectral space, where the effective permittivity of GENZ metamaterial is simply determined by a pole-zero structure corresponding to the operating frequency range. The physical structure of GENZ metamaterial is retrieved from the pole-zero structure via a tractable inverse problem. The strategy is of great advantage in practical applications and also theoretically reveals the cancellation mechanism of the broadband near-zero permittivity phenomenon in the spectral space.
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42.70.-a Optical materials
77.22.Ch Permittivity (dielectric function)

Tunable coupled surface acoustic cavities

M. M. de Lima, Jr., P. V. Santos, Yu. A. Kosevich, and A. Cantarero

Appl. Phys. Lett. 100, 261904 (2012); http://dx.doi.org/10.1063/1.4730398 (4 pages) | Cited 1 time

Online Publication Date: 26 June 2012

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We demonstrate the electric tuning of the acoustic field in acoustic microcavities (MCs) defined by a periodic arrangement of metal stripes within a surface acoustic delay line on LiNbO3 substrate. Interferometric measurements show the enhancement of the acoustic field distribution within a single MC, the presence of a “bonding” and “anti-bonding” modes for two strongly coupled MCs, as well as the positive dispersion of the “mini-bands” formed by five coupled MCs. The frequency and amplitude of the resonances can be controlled by the potential applied to the metal stripes.
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43.58.Kr Spectrum and frequency analyzers and filters; acoustical and electrical oscillographs; photoacoustic spectrometers; acoustical delay lines and resonators
42.79.Jq Acousto-optical devices

High efficient external resonator Raman laser based on the monoclinic single crystal BaTeMo2O9

Zeliang Gao, Shande Liu, Shaojun Zhang, Weiguo Zhang, Jingliang He, and Xutang Tao

Appl. Phys. Lett. 100, 261905 (2012); http://dx.doi.org/10.1063/1.4730635 (4 pages) | Cited 2 times

Online Publication Date: 26 June 2012

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In this paper spontaneous Raman spectra of monoclinic single crystals of BaTeMo2O9 (BTM) along the Z axis has been characterized, and a highly efficient stimulated Raman scattering laser operating at 1178 nm has been realized based on the BTM crystal. The Raman resonator possesses a threshold of 28 MW/cm2 at 1064 nm and a maximum output pulse energy of 19.2 mJ for the first-order Stokes with an optical-to-optical conversion efficiency of 48% and a slope efficiency of 61.2%. The largest optical-to-optical conversion efficiency can reach 50.4% at a pump energy of 28.8 mJ. Our experimental results demonstrate that BTM can be used as an excellent near and mid-infrared Raman laser material.
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42.55.Ye Raman lasers
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering

Infrared absorbance of silicene and germanene

Friedhelm Bechstedt, Lars Matthes, Paola Gori, and Olivia Pulci

Appl. Phys. Lett. 100, 261906 (2012); http://dx.doi.org/10.1063/1.4731626 (3 pages) | Cited 6 times

Online Publication Date: 27 June 2012

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Calculating the complex dielectric function for optical interband transitions we show that the two-dimensional crystals silicene and germanene possess the same low-frequency absorbance as graphene. It is determined by the Sommerfeld finestructure constant. Deviations occur for higher frequencies when the first interband transitions outside K or K′ contribute. The low-frequency results are a consequence of the honeycomb geometry but do not depend on the group-IV atom, the sheet buckling, and the orbital hybridization. The two-dimensional crystals may be useful as absorption normals in silicon technology.
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78.30.Na Fullerenes and related materials
61.48.Gh Structure of graphene
73.22.Pr Electronic structure of graphene
77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
78.67.Wj Optical properties of graphene

Experimental realization of a broadband conformal mapping lens for directional emission

Chendong Gu, Kan Yao, Weixin Lu, Yun Lai, Huanyang Chen, Bo Hou, and Xunya Jiang

Appl. Phys. Lett. 100, 261907 (2012); http://dx.doi.org/10.1063/1.4731877 (3 pages) | Cited 2 times

Online Publication Date: 27 June 2012

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We experimentally realize a transformation lens for directional emission at microwave frequencies. The refractive index of the lens, based on the design of conformal mapping, has variation from 1 to 4 inside a semi-circular geometry. By drilling subwavelength holes in dielectric plates inhomogeneously, we design the lens sample. The scanning measurements of the electric field of the lens demonstrate the high directivity of emission, within a broadband working frequency region of 7-11 GHz.
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84.40.-x Radiowave and microwave (including millimeter wave) technology
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Inter-tube thermal conductance in carbon nanotubes arrays and bundles: Effects of contact area and pressure

William J. Evans, Meng Shen, and Pawel Keblinski

Appl. Phys. Lett. 100, 261908 (2012); http://dx.doi.org/10.1063/1.4732100 (4 pages) | Cited 4 times

Online Publication Date: 28 June 2012

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We use molecular dynamics simulations to compute junction thermal conductance of carbon nanotubes as a function of crossing angle and pressure, and conductivity of arrays and bundles consisting of multiple junctions as a function of pressure. Two types of arrays are investigated: crossbar structures consisting of alternating orthogonal layers of nanotubes and close-packed bundles of parallel oriented tubes. Conductance of 90° junction increases with pressure 4 fold before saturation; cross-plane thermal conductivity of crossbar structures increases by a factor of 2. For parallel junctions pressure doubles the conductance while thermal conductivity of nanotubes bundles is more or less pressure independent.
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66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
81.07.De Nanotubes
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
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