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28 Dec 2009

Volume 95, Issue 26, Articles (26xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 261901 (2009); http://dx.doi.org/10.1063/1.3268436 (3 pages)

Weiqiang Wang, Richard Clark, Aiichiro Nakano, Rajiv K. Kalia, and Priya Vashishta
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Design of one-dimensional optical pulse-shaping filters by time-domain topology optimization

Lirong Yang, Andrei V. Lavrinenko, Jørn M. Hvam, and Ole Sigmund

Appl. Phys. Lett. 95, 261101 (2009); http://dx.doi.org/10.1063/1.3278595 (3 pages) | Cited 6 times

Online Publication Date: 28 December 2009

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Time-domain topology optimization is used here to design optical pulse-shaping filters in Si/SiO2 thin-film systems. A novel envelope objective function as well as explicit penalization are used to adapt the optimization method to this unique class of design problems.
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42.79.Ci Filters, zone plates, and polarizers
42.15.Eq Optical system design
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
02.60.Pn Numerical optimization
42.70.-a Optical materials

Polychromatic beam splitting by fractional stimulated Raman adiabatic passage

F. Dreisow, M. Ornigotti, A. Szameit, M. Heinrich, R. Keil, S. Nolte, A. Tünnermann, and S. Longhi

Appl. Phys. Lett. 95, 261102 (2009); http://dx.doi.org/10.1063/1.3279134 (3 pages) | Cited 7 times

Online Publication Date: 28 December 2009

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We propose and demonstrate a femtosecond laser inscribed micro-optical device for broadband beam splitting based on the interruption of the stimulated Raman adiabatic passage. For the spectral characterization waveguide fluorescence microscopy is applied by exciting nonbridging oxygen holes and exciton defects at several wavelengths. Additionally, spectrally resolved nearfield imaging shows octave spanning 50:50 beam splitting.
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42.79.Fm Reflectors, beam splitters, and deflectors
42.82.Gw Other integrated-optical elements and systems
42.65.Dr Stimulated Raman scattering; CARS
42.65.Es Stimulated Brillouin and Rayleigh scattering
42.82.Cr Fabrication techniques; lithography, pattern transfer

Performance of hybrid entanglement photon pair source for quantum key distribution

M. Fujiwara, M. Toyoshima, M. Sasaki, K. Yoshino, Y. Nambu, and A. Tomita

Appl. Phys. Lett. 95, 261103 (2009); http://dx.doi.org/10.1063/1.3276559 (3 pages) | Cited 3 times

Online Publication Date: 29 December 2009

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We report on the experimental demonstration of a source of hybrid entanglement pairs between two different degrees of freedom, a 1550 nm time-bin qubit and an 810 nm polarization qubit. The polarization qubit at 810 nm is transformed by an asymmetric Mach–Zehnder interferometer consisted of a Glan laser prism and a polarization-maintaining fiber. We obtained visibilities of 95.8% and 88% with tolerance ±0.2% and ±1% along Z-Z and X-X axes on the Poincare sphere, respectively, with a coincidence count rate of more than 800 c/s after entanglement format transformation. These values are well above the threshold of 70.7% needed to violate a Bell inequality and allow distilling a secure key in the quantum key distribution.
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03.67.Dd Quantum cryptography and communication security
03.67.Bg Entanglement production and manipulation
42.50.Dv Quantum state engineering and measurements

NaSb3F10: A new second-order nonlinear optical crystal to be used in the IR region with very high laser damage threshod

Gang Zhang, Jingui Qin, Tao Liu, Yanjun Li, Yicheng Wu, and Chuangtian Chen

Appl. Phys. Lett. 95, 261104 (2009); http://dx.doi.org/10.1063/1.3257728 (3 pages) | Cited 6 times

Online Publication Date: 29 December 2009

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This paper reports the second-order nonlinear optical (NLO) property of NaSb3F10, a potential new NLO material in the infrared region. The compound exhibits a phase-matchable second harmonic generation (SHG) efficiency of about 3.2 times that of KH2PO4 based on the powder SHG measurement. A measurement indicates that its laser damage threshold is as high as about 1.3 GW/cm2, which is much higher than all those IR NLO crystals reported in the literature. It also shows excellent transparency in the range of 0.25–7.8 μm with relativity high thermal stability. Single crystal of the size 12×10×8 mm3 has been grown in aqueous solution by a slow evaporation technique.
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42.70.-a Optical materials
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.25.Bs Wave propagation, transmission and absorption
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High-speed Ge photodetector monolithically integrated with large cross-section silicon-on-insulator waveguide

Dazeng Feng, Shirong Liao, Po Dong, Ning-Ning Feng, Hong Liang, Dawei Zheng, Cheng-Chih Kung, Joan Fong, Roshanak Shafiiha, Jack Cunningham, Ashok V. Krishnamoorthy, and Mehdi Asghari

Appl. Phys. Lett. 95, 261105 (2009); http://dx.doi.org/10.1063/1.3279129 (3 pages) | Cited 22 times

Online Publication Date: 29 December 2009

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We demonstrate a compact, high speed Ge photodetector efficiently butt-coupled with a large cross-section silicon-on-insulate (SOI) waveguide in which the Ge p-i-n junction is placed in the horizontal direction to enable very high speed operation. The demonstrated photodetector has an active area of only 0.8×10 μm2, greater than 32 GHz optical bandwidth, and a responsivity of 1.1 A/W at a wavelength of 1550 nm. Very importantly the device can readily be integrated with high performance wavelength-division-multiplexing filters based on large cross-section SOI waveguide to form monolithic integrated silicon photonics receivers for multichannel terabit data transmission applications.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
42.82.Et Waveguides, couplers, and arrays
42.79.Gn Optical waveguides and couplers
42.65.Re Ultrafast processes; optical pulse generation and pulse compression
42.79.Ci Filters, zone plates, and polarizers
42.79.Sz Optical communication systems, multiplexers, and demultiplexers

Resistance to edge recombination in GaAs-based dots-in-a-well solar cells

Tingyi Gu, Mohamed A. El-Emawy, Kai Yang, Andreas Stintz, and Luke F. Lester

Appl. Phys. Lett. 95, 261106 (2009); http://dx.doi.org/10.1063/1.3277149 (3 pages) | Cited 6 times

Online Publication Date: 30 December 2009

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Insensitivity to edge recombination is observed in GaAs-based InAs/InGaAs quantum dots-in-a-well (DWELL) solar cells by comparing its current-voltage (IV) plot to GaAs control samples. The edge recombination current component is extracted by analyzing devices of different areas and then compared to DWELL cells of comparable dimensions. The results demonstrate that GaAs-based solar cells incorporating a DWELL design are relatively insensitive to edge recombination by suppressing lateral diffusion of carriers in the intrinsic layer, and thus promising for applications that require small area devices such as concentration or flexible surfaces.
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88.40.J- Types of solar cells
72.20.Fr Low-field transport and mobility; piezoresistance
73.63.Kv Quantum dots

Generation and recombination rates at ZnTe:O intermediate band states

Weiming Wang (王伟明), Albert S. Lin, Jamie D. Phillips, and Wyatt K. Metzger

Appl. Phys. Lett. 95, 261107 (2009); http://dx.doi.org/10.1063/1.3274131 (3 pages) | Cited 17 times

Online Publication Date: 30 December 2009

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Carrier generation and recombination processes of ZnTeO thin films are studied by time-resolved photoluminescence, where carrier lifetimes at oxygen states and the conduction band are inferred to be >1 μs and <100 ps, respectively. The radiative recombination coefficient for optical transitions from oxygen states to the valence band is extracted to be 1.2×10−10 cm3 sec−1 based on the excitation dependence of decay time constants. Rate equation analysis further suggests an increase in electron lifetime at the conduction band as oxygen states occupation is critical in achieving high conversion efficiency for solar cells based on multiphoton processes in these materials.
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81.05.Dz II-VI semiconductors
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.61.Ga II-VI semiconductors
88.40.H- Solar cells (photovoltaics)
71.20.Nr Semiconductor compounds
78.47.jd Time resolved luminescence
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Application of a composite plasmonic substrate for the suppression of an electromagnetic mode leakage in InGaN laser diodes

Piotr Perlin, Katarzyna Holc, Marcin Sarzyński, Wolfgang Scheibenzuber, Łucja Marona, Robert Czernecki, Mike Leszczyński, Michał Bockowski, Izabella Grzegory, Sylwester Porowski, Grzegorz Cywiński, Piotr Firek, Jan Szmidt, Ulrich Schwarz, and Tadek Suski

Appl. Phys. Lett. 95, 261108 (2009); http://dx.doi.org/10.1063/1.3280055 (3 pages) | Cited 5 times

Online Publication Date: 30 December 2009

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We demonstrate an InGaN laser diode, in which the waveguiding quality of the device is improved by the introduction of highly doped (plasmonic) layer constituting an upper part of the GaN substrate. Thanks to this, we were able to suppress the electromagnetic mode leakage into the substrate without generating additional strain in the structure, in contrast to the typical design relying on thick AlGaN claddings. The plasmonic substrate is built as a stack of gallium nitride layers of various electron concentrations deposited by a combination of hydride epitaxy and high-pressure solution method. The mentioned improvements led to the reduction of the threshold current density of our devices down to 2 kA/cm2 and to the optimization of the near and far field pattern.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.79.Gn Optical waveguides and couplers

Holographic assembly of semiconductor CdSe quantum dots in polymer for volume Bragg grating structures with diffraction efficiency near 100%

Xiangming Liu, Yasuo Tomita, Juro Oshima, Katsumi Chikama, Koutatsu Matsubara, Takuya Nakashima, and Tsuyoshi Kawai

Appl. Phys. Lett. 95, 261109 (2009); http://dx.doi.org/10.1063/1.3276914 (3 pages) | Cited 1 time

Online Publication Date: 31 December 2009

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We report on the fabrication of centimeter-size transmission Bragg gratings in semiconductor CdSe quantum dots dispersed 50 μm thick photopolymer films. This was done by holographic assembly of CdSe quantum dots in a photopolymerizable monomer blend. Periodic patterning of CdSe quantum dots in polymer was confirmed by a fluorescence microscope and confocal Raman imaging. The diffraction efficiency from the grating of 1 μm spacing was near 100% in the green with 0.34 vol % CdSe quantum dots, giving the refractive index modulation as large as 5.1×10−3.
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42.40.Eq Holographic optical elements; holographic gratings
42.86.+b Optical workshop techniques
78.67.Hc Quantum dots
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters
42.70.Jk Polymers and organics

Linearly polarized light emission from InGaN light emitting diode with subwavelength metallic nanograting

Liang Zhang, Jing Hua Teng, Soo Jin Chua, and Eugene A. Fitzgerald

Appl. Phys. Lett. 95, 261110 (2009); http://dx.doi.org/10.1063/1.3276074 (3 pages) | Cited 5 times

Online Publication Date: 31 December 2009

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Surface emitting linearly polarized InGaN/GaN light emitting diode (LED) is demonstrated using a subwavelength metallic nanograting. The aluminum based grating with a period of 150 nm is fabricated on top of the p-contact layer in a conventional InGaN LED structure grown on (0001) oriented sapphire substrate. Polarization ratio can reach 7:1, the highest ever reported polarization ratio directly from a light emitting diode. The polarization characteristics are studied in details both experimentally and theoretically, suggesting an effective way to make polarized light emission devices.
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85.60.Jb Light-emitting devices
81.16.-c Methods of micro- and nanofabrication and processing
42.82.-m Integrated optics
42.79.Dj Gratings

Strong enhancement of Raman-induced nonreciprocity in silicon waveguides by alignment with the crystallographic axes

Michael Krause, Hagen Renner, and Ernst Brinkmeyer

Appl. Phys. Lett. 95, 261111 (2009); http://dx.doi.org/10.1063/1.3279151 (3 pages) | Cited 2 times

Online Publication Date: 31 December 2009

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Raman gain in silicon photonic wires depends on the relative propagation directions of the pump and Stokes waves due to strong longitudinal mode-field components. Here we show that this Raman-induced nonreciprocity can be varied in a wide range by changing the orientation of the waveguide with respect to the crystallographic axes. In a 〈001〉 orientation, the nonreciprocity reaches its maximum which is larger by more than two orders of magnitude as compared to the traditional 〈011〉 orientation. The waveguide is then practically Raman-inactive for copropagation, while the contradirectional Stokes wave may experience significant Raman gain.
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84.40.Az Waveguides, transmission lines, striplines
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Fast reaction mechanism of a core(Al)-shell (Al2O3) nanoparticle in oxygen

Weiqiang Wang, Richard Clark, Aiichiro Nakano, Rajiv K. Kalia, and Priya Vashishta

Appl. Phys. Lett. 95, 261901 (2009); http://dx.doi.org/10.1063/1.3268436 (3 pages) | Cited 3 times

Online Publication Date: 28 December 2009

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Atomistic mechanisms of oxidation in a laser flash heated core (Aluminum)-shell (Alumina) nanoparticle are investigated using multimillion-atom molecular dynamics simulations. We find a thermal-to-mechanochemical transition of oxidation mechanism when the initial core temperature is above 6000 K. The transition from thermal diffusion to mechanically enhanced diffusion to ballistic transport is accompanied by a change in the intermediate reaction products from Al rich Al2O to oxygen rich AlO2 clusters. Higher initial temperature of the core causes catastrophic failure of the shell, which provides direct oxidation pathways for core Al, resulting in faster energy release.
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82.20.Hf Product distribution
66.30.Xj Thermal diffusivity
82.20.Wt Computational modeling; simulation
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
82.30.-b Specific chemical reactions; reaction mechanisms
73.23.Ad Ballistic transport

The effect of environment on the radial breathing mode of supergrowth single wall carbon nanotubes

P. T. Araujo, C. Fantini, M. M. Lucchese, M. S. Dresselhaus, and A. Jorio

Appl. Phys. Lett. 95, 261902 (2009); http://dx.doi.org/10.1063/1.3276909 (3 pages) | Cited 4 times

Online Publication Date: 28 December 2009

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It has been shown that “supergrowth” single wall carbon nanotubes (SWNTs) exhibit a radial breathing mode frequency ωRBM dependence on tube diameter dt given by ωRBM = 227/dt. This result gave rise to two distinct scenarios for SWNTs: one for the supergrowth radial breathing mode and another for all the other samples reported in the literature. Here we show that, by dispersing the supergrowth SWNTs in surfactant or bringing them into interacting bundles, it is possible to merge these two scenarios, where now the supergrowth SWNT properties are similar to all SWNT properties reported so far in the literature.
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61.46.Fg Nanotubes
78.67.Ch Nanotubes
81.07.De Nanotubes
78.30.Na Fullerenes and related materials

Spectroscopic evidence for limited carrier hopping interaction in amorphous ZnO thin film

Deok-Yong Cho, Jeong Hwan Kim, Kwang Duk Na, Jaewon Song, Cheol Seong Hwang, Byeong-Gyu Park, Jae-Young Kim, Chul-Hee Min, and Se-Jung Oh

Appl. Phys. Lett. 95, 261903 (2009); http://dx.doi.org/10.1063/1.3275738 (3 pages) | Cited 5 times

Online Publication Date: 28 December 2009

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The electronic structure of amorphous ZnO film (a-ZnO) was examined by O K- and Zn L3-edge x-ray absorption spectroscopy and valence band photoemission spectroscopy. Comparative studies of a-ZnO and a wurtzite ZnO (w-ZnO) revealed a decrease in Zn 4s-O 2p hybridization strength and the localization of Zn 4s band as a consequence of local structural disorder, indicating limited electron hopping interactions in a-ZnO. The 0.1 eV higher Fermi-level of a-ZnO compared to w-ZnO suggests that the electrical properties of a-ZnO are different from those in w-ZnO due to structural disorder, even in the absence of impurities or grain boundaries.
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78.66.Hf II-VI semiconductors
79.60.Bm Clean metal, semiconductor, and insulator surfaces
78.70.Dm X-ray absorption spectra
73.61.Ga II-VI semiconductors
72.20.Ee Mobility edges; hopping transport
68.55.ag Semiconductors

Electrical and optical properties of p-type InGaN

B. N. Pantha, A. Sedhain, J. Li, J. Y. Lin, and H. X. Jiang

Appl. Phys. Lett. 95, 261904 (2009); http://dx.doi.org/10.1063/1.3279149 (3 pages) | Cited 11 times

Online Publication Date: 29 December 2009

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Mg-doped InxGa1−xN alloys were grown by metal organic chemical vapor deposition on semi-insulating c-GaN/sapphire templates. Hall effect measurements showed that Mg-doped InxGa1−xN epilayers are p-type for x up to 0.35. Mg-acceptor levels (EA) as a function of x, (x up to 0.35), were experimentally evaluated from the temperature dependent hole concentration. The observed EA in Mg-doped In0.35Ga0.65N alloys was about 43 meV, which is roughly four times smaller than that in Mg doped GaN. A room temperature resistivity as low as 0.4 Ω cm (with a hole concentration ∼ 5×1018 cm−3 and hole mobility ∼ 3 cm2/V s) was obtained in Mg-doped In0.22Ga0.78N. It was observed that the photoluminescence (PL) intensity associated with the Mg related emission line decreases exponentially with x. The Mg energy levels in InGaN alloys obtained from PL measurements are consistent with those obtained from Hall-effect measurements.
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78.66.Fd III-V semiconductors
61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
73.61.Ey III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Photoluminescence properties of midinfrared dilute nitride InAsN epilayers with/without Sb flux during molecular beam epitaxial growth

Rui Chen, S. Phann, H. D. Sun, Q. Zhuang, A. M. R. Godenir, and A. Krier

Appl. Phys. Lett. 95, 261905 (2009); http://dx.doi.org/10.1063/1.3280861 (3 pages) | Cited 5 times

Online Publication Date: 30 December 2009

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We report on the comparative studies of photoluminescence (PL) properties of molecular beam epitaxy grown dilute InAsN epilayers with and without antimony (Sb) flux during the growth. Both samples exhibit strong midinfrared (MIR) emission at room temperature, while the sample with Sb flux has much higher intensity. At low temperatures, these samples exhibit totally different PL features in terms of line width, peak position, intensity, and their dependences on temperature and excitation density. Our results clearly indicate that part of Sb atoms serve as a surfactant that effectively improves the optical quality of MIR dilute nitrides.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
68.55.ag Semiconductors
71.20.Nr Semiconductor compounds
71.35.-y Excitons and related phenomena
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy

Rayleigh surface wave in a piezoelectric wafer with subsurface damage

Xiaoshan Cao, Feng Jin, and Insu Jeon

Appl. Phys. Lett. 95, 261906 (2009); http://dx.doi.org/10.1063/1.3276568 (3 pages) | Cited 1 time

Online Publication Date: 30 December 2009

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An analytical study is carried out on the propagation of Rayleigh surface waves in a piezoelectric wafer with subsurface damage. The region of subsurface damage is considered to be a functionally graded piezoelectric thin film. The findings show the influence of the gradient parameter, thickness of the region of subsurface damage, and three different types of damage on the properties of surface-wave propagation, including the phase velocity and electromechanical coupling factor. They can provide theoretical guidance in nondestructive evaluation for the analysis of the reliability and durability of electronic devices made of piezoelectric wafers.
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77.65.-j Piezoelectricity and electromechanical effects
81.70.-q Methods of materials testing and analysis
68.60.Bs Mechanical and acoustical properties

Temperature dependent structural properties of nanocrystalline SnS structures

M. Devika, N. Koteeswara Reddy, Fernando Patolsky, K. Ramesh, and K. R. Gunasekhar

Appl. Phys. Lett. 95, 261907 (2009); http://dx.doi.org/10.1063/1.3277148 (3 pages) | Cited 6 times

Online Publication Date: 30 December 2009

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This letter explores the structural behavior of nanocrystalline tin mono sulfide (SnS) structures with respect to temperature (100–600 K). These studies emphasize that the structural properties of SnS nanocrystalline structures depend on the surrounding temperature. The lattice parameters of SnS nanocrystals slightly varied like their microstructures with the increase of temperature. These changes strongly influence the optical properties of SnS nanostructures. On the other hand, the structures exhibited higher strain ( ∼ 0.44%) than that of microstructured (0.3%) and bulk (0.12%) counterparts. The observed results are discussed under the light of existing concepts and reported.
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61.46.Hk Nanocrystals
81.05.Hd Other semiconductors
65.80.-g Thermal properties of small particles, nanocrystals, nanotubes, and other related systems
78.67.Bf Nanocrystals, nanoparticles, and nanoclusters

Toward quantum interference of photons from independent quantum dots

M. Benyoucef, L. Wang, A. Rastelli, and O. G. Schmidt

Appl. Phys. Lett. 95, 261908 (2009); http://dx.doi.org/10.1063/1.3275702 (3 pages) | Cited 4 times

Online Publication Date: 31 December 2009

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The authors present steps toward the experimental realization of indistinguishable single photon sources based on independent unstrained GaAs quantum dots (QDs), which are embedded in planar cavities to improve the light collection efficiency. The emission lines of two QDs are brought into resonance and overlapped at a beam splitter. The coherence properties of the emitted photons are investigated by measuring the first-order field correlation function. Despite the fact that the short dephasing time of the selected QDs prevents us to observe quantum interference between the two photons, the approach could be applied to other QDs.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
73.21.La Quantum dots
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors
42.79.Fm Reflectors, beam splitters, and deflectors

The influence of As/III pressure ratio on nitrogen nearest-neighbor environments in as-grown GaInNAs quantum wells

R. Kudrawiec, V.-M. Korpijärvi, P. Poloczek, J. Misiewicz, P. Laukkanen, J. Pakarinen, M. Dumitrescu, M. Guina, and M. Pessa

Appl. Phys. Lett. 95, 261909 (2009); http://dx.doi.org/10.1063/1.3275712 (3 pages) | Cited 4 times

Online Publication Date: 31 December 2009

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The energy fine structure, corresponding to different nitrogen nearest-neighbor environments, was observed in contactless electroreflectance (CER) spectra of as-grown GaInNAs quantum wells (QWs) obtained at various As/III pressure ratios. In the spectral range of the fundamental transition, two CER resonances were detected for samples grown at low As pressures whereas only one CER resonance was observed for samples obtained at higher As pressures. This resonance corresponds to the most favorable nitrogen nearest-neighbor environment in terms of the total crystal energy. It means that the nitrogen nearest-neighbor environment in GaInNAs QWs can be controlled in molecular beam epitaxy process by As/III pressure ratio.
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62.50.-p High-pressure effects in solids and liquids
78.20.Jq Electro-optical effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.21.Fg Quantum wells
78.66.Fd III-V semiconductors

Second harmonic generation from graphene and graphitic films

Jesse J. Dean and Henry M. van Driel

Appl. Phys. Lett. 95, 261910 (2009); http://dx.doi.org/10.1063/1.3275740 (3 pages) | Cited 9 times

Online Publication Date: 31 December 2009

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Optical second harmonic generation (SHG) of 800 nm, 150 fs fundamental pulses is observed from exfoliated graphene and multilayer graphitic films mounted on an oxidized silicon (001) substrate. The SHG anisotropy is observed as a sample is rotated about the surface normal. For p-polarized fundamental and SHG light, the isotropic SHG from a graphene layer only slightly interferes with the fourfold symmetric response of the underlying substrate, while other samples show a threefold symmetry characteristic of significant SHG in the multilayer graphitic films. The dominance of the threefold anisotropy is maintained from bilayer graphene to bulk graphite.
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78.67.Wj Optical properties of graphene
68.65.Pq Graphene films
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.66.Nk Insulators

Recombination dynamics of photoluminescence in thiol-protected gold nanoclusters

G. W. Shu, C. C. Lin, H. P. Chung, J. L. Shen, C. A. J. Lin, C. H. Lee, W. H. Chang, W. H. Chan, H. H. Wang, H. I. Yeh, C. T. Yuan, and J. Tang

Appl. Phys. Lett. 95, 261911 (2009); http://dx.doi.org/10.1063/1.3277184 (3 pages) | Cited 4 times

Online Publication Date: 31 December 2009

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Recombination dynamics of photoluminescence (PL) in Au nanoclusters (NCs) with different capping molecules were studied with time-resolved PL. Based on the emission-energy of carrier lifetimes; we suggest that the fast and slow PL decay of Au NCs originates from recombination of the linear Au–S bond and the staple motif, respectively. The effect of carrier localization in Au NCs was found to depend on the capping molecules. The zero-dimensionality of carriers in Au NCs was demonstrated by the temperature dependence of the time-resolved PL.
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78.55.Kz Solid organic materials
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
78.47.jd Time resolved luminescence
61.46.Bc Structure of clusters (e.g., metcars; not fragments of crystals; free or loosely aggregated or loosely attached to a substrate)
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.63.Bd Nanocrystalline materials

Investigation of compositional inhomogeneities in complex polycrystalline Cu(In,Ga)Se2 layers for solar cells

X. Fontané, V. Izquierdo-Roca, L. Calvo-Barrio, A. Pérez-Rodríguez, J. R. Morante, Dominik Guettler, A. Eicke, and A. N. Tiwari

Appl. Phys. Lett. 95, 261912 (2009); http://dx.doi.org/10.1063/1.3280049 (3 pages)

Online Publication Date: 31 December 2009

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In-depth resolved composition inhomogeneities of polycrystalline Cu(In,Ga)Se2 (CIGS) complex layers for high efficiency solar cells were investigated with Raman scattering measurements. In-depth resolved analysis of the frequency of the main CIGS Raman mode in the spectra measured after sputtering of the layers at different depths lead to identification of different compositions across the layer thickness. These data are in good agreement at both qualitative and quantitative levels with the in-depth resolved composition analysis of the samples by sputtered neutral mass spectroscopy. In addition, Raman measurements also allow detection of additional phases as ordered vacancy compounds.
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78.30.Hv Other nonmetallic inorganics
68.55.ag Semiconductors
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Low-temperature ballistic transport in nanoscale epitaxial graphene cross junctions

S. Weingart, C. Bock, U. Kunze, F. Speck, Th. Seyller, and L. Ley

Appl. Phys. Lett. 95, 262101 (2009); http://dx.doi.org/10.1063/1.3276560 (3 pages) | Cited 5 times

Online Publication Date: 28 December 2009

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We report on the observation of inertial-ballistic transport in nanoscale cross junctions fabricated from epitaxial graphene grown on SiC(0001). Ballistic transport is indicated by a negative bend resistance of R12,43 ≈ −170 Ω, which is measured in a nonlocal, four-terminal configuration at 4.2 Κ and which vanishes as the temperature is increased above 80 K.
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73.23.Ad Ballistic transport
81.05.ue Graphene
73.63.Fg Nanotubes
68.55.ap Fullerenes
61.48.Gh Structure of graphene

High subthreshold field-emission current due to hydrogen adsorption in single-walled carbon nanotubes: A first-principles study

Parham Yaghoobi, Md. Kawsar Alam, Konrad Walus, and Alireza Nojeh

Appl. Phys. Lett. 95, 262102 (2009); http://dx.doi.org/10.1063/1.3275785 (3 pages) | Cited 2 times

Online Publication Date: 28 December 2009

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Show Abstract
We investigate the effect of hydrogen adsorption on field-emission current from a single-walled carbon nanotube using first-principles calculations. The results show a new emission regime at field values around the field-emission threshold of bare nanotubes, with emission currents comparable to those of the high-field regime. This current enhancement can be explained with the surface dipole created as a result of the difference in electronegativity between carbon and hydrogen that contributes to electron extraction from the nanotube.
Show PACS
79.70.+q Field emission, ionization, evaporation, and desorption
68.43.Mn Adsorption kinetics
73.63.Fg Nanotubes
72.20.Ht High-field and nonlinear effects
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