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5 Dec 2011

Volume 99, Issue 23, Articles (23xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 99, 233701 (2011); http://dx.doi.org/10.1063/1.3651756 (3 pages)

Melis Hazar, Robert L. Steward, Jr., Chia-Jung Chang, Cynthia J. Orndoff, Yukai Zeng, Mon-Shu Ho, Philip R. LeDuc, and Chao-Min Cheng
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Dynamically reconfigurable terahertz metamaterial through photo-doped semiconductor

Dibakar Roy Chowdhury, Ranjan Singh, John F. O’Hara, Hou-Tong Chen, Antoinette J. Taylor, and Abul K. Azad

Appl. Phys. Lett. 99, 231101 (2011); http://dx.doi.org/10.1063/1.3667197 (3 pages) | Cited 6 times

Online Publication Date: 5 December 2011

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We demonstrate reconfigurable terahertz metamaterial (MM) in which constituent resonators can be switched from split-ring resonators (SRRs) to closed-ring resonators via optical excitation of silicon islands strategically placed in the split gap. Both the fundamental and the third-order resonance modes experience monotonic damping due to increasing conductive losses in the photo-doped silicon region. More importantly, increasing the optical fluence (>200 μJ/cm2) results in the excitation of the second-order resonance mode, which is otherwise forbidden in a split-ring resonator for the incidence polarization in our experiments. Such dynamical control of metamaterial resonances could be implemented in active terahertz devices to achieve additional functionalities.
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81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
84.40.Az Waveguides, transmission lines, striplines
81.05.Cy Elemental semiconductors

Tunable true-time delay of a microwave photonic signal realized by cross gain modulation in a semiconductor waveguide

Weiqi Xue and Jesper Mørk

Appl. Phys. Lett. 99, 231102 (2011); http://dx.doi.org/10.1063/1.3665946 (3 pages)

Online Publication Date: 5 December 2011

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We experimentally demonstrate the realization of a tunable true-time delay for microwave signals by exploiting cross gain modulation among counter-propagating optical beams in a semiconductor optical amplifier. Broadband operation from ∼5 to ∼35 GHz is observed. The physical effect originates from the combination of carrier dynamics and propagation effects, and the experimental results are well accounted for by a numerical model. We find that, in contrast to the case of the co-propagating beams, the bandwidth is not limited by the lifetime of excited carriers. The trade-off between the magnitude of the true-time delay and the microwave bandwidth is discussed.
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42.60.Fc Modulation, tuning, and mode locking
84.40.-x Radiowave and microwave (including millimeter wave) technology
42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems

Highly unidirectional Y-junction-coupled S-section quantum-dot ring lasers

Nathan J. Withers, Hongjun Cao, Gennady A. Smolyakov, and Marek Osiński

Appl. Phys. Lett. 99, 231103 (2011); http://dx.doi.org/10.1063/1.3665955 (3 pages) | Cited 2 times

Online Publication Date: 6 December 2011

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Fabrication and characterization of Y-junction-coupled S-section InAs/InGaAs/GaAs quantum-dot ring lasers with high unidirectionality is reported. Stable unidirectional operation of the ring lasers is ensured by a new design that suppresses the unwanted counterpropagating modes more effectively than it was possible in the previous S-section-racetrack design.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.86.+b Optical workshop techniques

Electrically tuneable spectral responsivity in gated silicon photodiodes

Kamran Abid, Xingsheng Wang, Ali Z. Khokhar, Scott Watson, Sulaiman Al-Hasani, and Faiz Rahman

Appl. Phys. Lett. 99, 231104 (2011); http://dx.doi.org/10.1063/1.3665613 (3 pages)

Online Publication Date: 6 December 2011

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We report the observation of electrically tuneable spectral responsivity in silicon-based photodetectors. The current flowing through a lateral p-i-n junction photodiode can be changed by changing either the gate bias or the intensity of incident light, with the devices exhibiting typical optical responsivities of 65 A/W. The peak sensitivity of the device can be changed over the entire visible region by changing the gate voltage in a 5 V range. This happens because with increasing gate bias, an accumulation layer of holes is pulled closer to the Si-SiO2 interface, enhancing the blue response of the device.
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85.60.Dw Photodiodes; phototransistors; photoresistors
85.60.Gz Photodetectors (including infrared and CCD detectors)

Control of random lasing in ZnO/Al2O3 nanopowders

Toshihiro Nakamura, Bishnu P. Tiwari, and Sadao Adachi

Appl. Phys. Lett. 99, 231105 (2011); http://dx.doi.org/10.1063/1.3665913 (3 pages) | Cited 3 times

Online Publication Date: 6 December 2011

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We demonstrate that the random lasing wavelength of ZnO/Al2O3 nanopowders can be controlled by varying the weight fraction of Al2O3. This controllability is due to the fact that the extent of self-absorption by ZnO nanopowder can be modified by changing the photon-transport mean free path. The lasing threshold excitation power is also dependent on the weight fraction of Al2O3. The random lasing characteristic can be explained well by a theoretical model based on the photon-transport mean free path.
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42.55.Zz Random lasers
42.60.By Design of specific laser systems
42.55.Px Semiconductor lasers; laser diodes

Atomistic pseudopotential theory of optical properties of exciton complexes in InAs/InP quantum dots

Ming Gong, Weiwei Zhang, Guang Can Guo, and Lixin He

Appl. Phys. Lett. 99, 231106 (2011); http://dx.doi.org/10.1063/1.3669507 (3 pages) | Cited 5 times

Online Publication Date: 7 December 2011

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The photoluminescence (PL) spectra of exciton complexes in quantum dots (QDs) are of primary importance to understand their optical properties, which are well understood in InAs/GaAs QDs both theoretically and experimentally. However the knowledge can not be directly applied to InAs/InP QDs. In this work, we investigate the differences of the PL spectra of the two dots using an empirical pseudopotential method. The alignment of exciton complex transition lines of the two QDs are very different and the reasons are explained. We show that the “hidden” correlation energies in InAs/InP QDs are smaller than those in InAs/GaAs QDs and the lifetime of exciton complexes in InAs/InP QDs are about twice longer than those in InAs/GaAs QDs.
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78.67.Hc Quantum dots
71.35.-y Excitons and related phenomena
78.55.Cr III-V semiconductors

Temperature stability of Bloch surface wave biosensors

Francesco Michelotti and Emiliano Descrovi

Appl. Phys. Lett. 99, 231107 (2011); http://dx.doi.org/10.1063/1.3666031 (3 pages) | Cited 1 time

Online Publication Date: 7 December 2011

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We report on the experimental characterization of the thermal sensitivity of biosensors based on the coupling of Bloch surface waves (BSW) on amorphous silicon nitride/silicon one dimensional photonic crystals (1DPC). The results show that the silicon alloys compensate the thermo-optic effect taking place in the external medium and indicate that a class of temperature insensitive biosensors can be fabricated by properly designing the layout of the 1DPC. The experimental results are in very good agreement with numerical simulations based on a transfer matrix approach. Moreover, the BSW biosensors show a resolution of 0.03 °C for the measurement of temperature.
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87.85.jc Electrical, thermal, and mechanical properties of biological matter
78.20.nb Photothermal effects
42.70.Qs Photonic bandgap materials

Saturation effects in femtosecond laser ablation of silicon-on-insulator

Hao Zhang, D. van Oosten, D. M. Krol, and J. I. Dijkhuis

Appl. Phys. Lett. 99, 231108 (2011); http://dx.doi.org/10.1063/1.3666423 (3 pages)

Online Publication Date: 8 December 2011

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We report a surface morphology study on single-shot submicron features fabricated on silicon on insulator by tightly focused femtosecond laser pulses. In the regime just below single-shot ablation threshold nano-tips are formed, whereas in the regime just above single-shot ablation threshold, a saturation in the ablation depth is found. We attribute this saturation by secondary laser absorption in the laser-induced plasma. In this regime, we find excellent agreement between the measured depths and a simple numerical model. When the laser fluence is further increased, a sharp increase in ablation depth is observed accompanied by a roughening of the ablated hole.
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52.38.Mf Laser ablation
78.47.J- Ultrafast spectroscopy (<1 psec)
68.47.-b Solid-gas/vacuum interfaces: types of surfaces

Nonlinear-optical brain anatomy by harmonic-generation and coherent Raman microscopy on a compact femtosecond laser platform

Lyubov V. Doronina-Amitonova, Aleksandr A. Lanin, Olga I. Ivashkina, Marina A. Zots, Andrei B. Fedotov, Konstantin V. Anokhin, and Aleksei M. Zheltikov

Appl. Phys. Lett. 99, 231109 (2011); http://dx.doi.org/10.1063/1.3664345 (3 pages) | Cited 2 times

Online Publication Date: 8 December 2011

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An extended-cavity Cr:forsterite laser is integrated with a photonic-crystal fiber soliton frequency shifter and a periodically poled lithium niobate spectrum compressor for simultaneous harmonic-generation and coherent Raman brain imaging. Adapting the laser beam focusing geometry to the tissue morphology is shown to enable complementarity enhancement in tissue imaging by second- and third-harmonic generation, as well as coherent Raman scattering, facilitating quantitative image analysis.
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87.63.lt Laser imaging
42.62.Be Biological and medical applications
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
42.81.Wg Other fiber-optical devices

A dual-mode quantum dot laser operating in the excited state

F. Grillot, N. A. Naderi, J. B. Wright, R. Raghunathan, M. T. Crowley, and L. F. Lester

Appl. Phys. Lett. 99, 231110 (2011); http://dx.doi.org/10.1063/1.3667193 (3 pages) | Cited 6 times

Online Publication Date: 9 December 2011

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A dual-mode laser operating in the excited states (ESs) of a quantum dot is realized by combining asymmetric pumping and external optical feedback stabilization. In generating two single-mode emission peaks, a mode separation ranging from 1.3-THz to 3.6-THz is demonstrated over temperature. This effect is attributed to the unique carrier dynamics of the quantum-dot gain medium via the excited state inhomogeneous linewidth coupled with a proper external control. These results are particularly important towards the development of future THz optoelectronic sources with compact size, low fabrication cost, and high performance.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
42.60.By Design of specific laser systems

Model for nanosecond laser induced damage in potassium titanyl phosphate crystals

Frank R Wagner, Guillaume Duchateau, Anne Hildenbrand, Jean-Yves Natoli, and Mireille Commandré

Appl. Phys. Lett. 99, 231111 (2011); http://dx.doi.org/10.1063/1.3668097 (3 pages) | Cited 3 times

Online Publication Date: 9 December 2011

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A model for nanosecond laser induced damage in the bulk of potassium titanyl phosphate nonlinear optical crystals is presented. In a first step, laser-induced damage precursors are produced by multiphoton absorption. In a second step, the damage precursors are activated. Damage occurs if the precursor activation rate exceeds a critical value. Basic considerations allow evaluating the parameters of the model. The validity of the model is discussed by comparing it to several experimental observations, in particular, the decrease of the laser damage threshold during second harmonic generation of 1064 nm pulses.
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61.80.Ba Ultraviolet, visible, and infrared radiation effects (including laser radiation)
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Controlled spontaneous emission in plasmonic whispering gallery antennas

Ernst Jan R. Vesseur and Albert Polman

Appl. Phys. Lett. 99, 231112 (2011); http://dx.doi.org/10.1063/1.3665622 (3 pages)

Online Publication Date: 9 December 2011

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We present a plasmonic whispering gallery nanoantenna doped with an ATTO680 dye that shows cavity-modified spontaneous emission. The plasmonic ring antenna consists of a circular groove cavity in a single-crystal Au surface that sustains resonances with different azimuthal and radial mode order. We observe spectral reshaping of the dye emission that can be tuned over a broad band by varying the cavity resonance conditions.
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84.40.Ba Antennas: theory, components and accessories

Enhanced-heating effect during photoacoustic imaging-guided high-intensity focused ultrasound

Huizhong Cui and Xinmai Yang

Appl. Phys. Lett. 99, 231113 (2011); http://dx.doi.org/10.1063/1.3669441 (3 pages) | Cited 2 times

Online Publication Date: 9 December 2011

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Photoacoustic imaging (PAI) technique has been used to monitor thermal lesion formation during high-intensity focused ultrasound (HIFU) treatment. While previous studies focused on photoacoustic detection of changes in temperature during HIFU treatment, we report an enhanced-heating effect when PAI is used to monitor HIFU treatment. We found that the temperature induced by HIFU could be significantly enhanced when the diagnostic laser system for photoacoustic detection was operating during HIFU treatment. This finding demonstrates an advantage of using PAI to guide HIFU therapy.
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87.63.lt Laser imaging

Copropagating pump and probe experiments on Si-nc in SiO2 rib waveguides doped with Er: The optical role of non-emitting ions

D. Navarro-Urrios, F. Ferrarese Lupi, N. Prtljaga, A. Pitanti, O. Jambois, J. M. Ramírez, Y. Berencén, N. Daldosso, B. Garrido, and L. Pavesi

Appl. Phys. Lett. 99, 231114 (2011); http://dx.doi.org/10.1063/1.3665950 (3 pages) | Cited 1 time

Online Publication Date: 9 December 2011

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We present a study that demonstrates the limits for achieving net optical gain in an optimized waveguide where Si nanoclusters in SiO2 codoped with Er3+ are the active material. By cross correlating absorption losses measurements with copropagant pump (λpump = 1.48 µm) and probe (λprobe = 1.54 µm) experiments we reveal that the role of more than 80% of the total Er3+ population present on the material (intended for optical amplification purposes) is to absorb the propagating light, since it is unfeasible to invert it.
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42.79.Gn Optical waveguides and couplers
42.87.-d Optical testing techniques
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Forward and backward cavity pressure acceleration of macroparticles

S. Borodziuk, T. Chodukowski, Z. Kalinowska, A. Kasperczuk, T. Pisarczyk, J. Ullschmied, E. Krousky, M. Pfeifer, K. Rohlena, J. Skala, and P. Pisarczyk

Appl. Phys. Lett. 99, 231501 (2011); http://dx.doi.org/10.1063/1.3662972 (3 pages)

Online Publication Date: 5 December 2011

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In this paper we present our new results obtained during the experiment performed on Prague Asterix Laser System. We used cavity pressure acceleration method [Borodziuk et al., Appl. Phys. Lett. 95, 231501 (2009)] to obtain superfast macroparticles. Two different ways of macroparticle acceleration were investigated: “forward” and “backward” acceleration. The best results for the velocity (obtained for 20 μm polystyrene foil) approach 1.0 × 108 cm/s. Also, the hydrodynamic efficiency of the energy transfer to the accelerated macroparticle is much higher compared to conventional ablative experiments. Additionally, application of the “covered channel” targets gives an evident increase of density of accelerated plasma outbursting from the channel, which is a key problem from the point of view of possible applications in impact fast ignition area.
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52.38.Kd Laser-plasma acceleration of electrons and ions
52.25.Fi Transport properties

Gd plasma source modeling at 6.7 nm for future lithography

Bowen Li, Padraig Dunne, Takeshi Higashiguchi, Takamitsu Otsuka, Noboru Yugami, Weihua Jiang, Akira Endo, and Gerry O’Sullivan

Appl. Phys. Lett. 99, 231502 (2011); http://dx.doi.org/10.1063/1.3666042 (3 pages) | Cited 7 times

Online Publication Date: 8 December 2011

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Plasmas containing gadolinium have been proposed as sources for next generation lithography at 6.x nm. To determine the optimum plasma conditions, atomic structure calculations have been performed for Gd11+ to Gd27+ ions which showed that n = 4 − n = 4 resonance transitions overlap in the 6.5–7.0 nm region. Plasma modeling calculations, assuming collisional-radiative equilibrium, predict that the optimum temperature for an optically thin plasma is close to 110 eV and that maximum intensity occurs at 6.76 nm under these conditions. The close agreement between simulated and experimental spectra from laser and discharge produced plasmas indicates the validity of our approach.
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52.25.Os Emission, absorption, and scattering of electromagnetic radiation
52.38.Kd Laser-plasma acceleration of electrons and ions
52.50.Dg Plasma sources
52.65.-y Plasma simulation
52.80.-s Electric discharges
52.20.Hv Atomic, molecular, ion, and heavy-particle collisions

Multimode terahertz-wave generation using coherent Cherenkov radiation

K. Kan, J. Yang, A. Ogata, T. Kondoh, K. Norizawa, and Y. Yoshida

Appl. Phys. Lett. 99, 231503 (2011); http://dx.doi.org/10.1063/1.3666043 (3 pages) | Cited 3 times

Online Publication Date: 9 December 2011

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Multimode terahertz(THz)-wave generation using coherent Cherenkov radiation (CCR) was investigated. The frequency spectra of CCR, which utilized a metal-wrapped hollow dielectric tube of 7 mm outer radius and a picosecond electron bunch of 27 MeV beam energy, were measured by a Michelson interferometer with a 4.2 K silicon bolometer. In this study, discrete spectral components at frequencies of 0.09, 0.14, and 0.36 THz were observed experimentally and explained as transverse magnetic (TM) modes of TM03, TM04, and TM09, respectively, according to a theoretical calculation for the tube.
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41.60.Bq Cherenkov radiation
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
07.60.Ly Interferometers
41.75.-i Charged-particle beams
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Optical anisotropy of GaSb type-II nanorods on vicinal (111)B GaAs

Takuya Kawazu, Yoshihiro Akiyama, Takeshi Noda, Takaaki Mano, Yoshiki Sakuma, and Hiroyuki Sakaki

Appl. Phys. Lett. 99, 231901 (2011); http://dx.doi.org/10.1063/1.3665394 (3 pages) | Cited 1 time

Online Publication Date: 5 December 2011

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We form self-assembled GaSb type-II nanorods on a vicinal (111)B GaAs substrate by molecular beam epitaxy and study their optical anisotropy. The GaSb nanorods are elongated and aligned along the [−1 0 1] direction, where the average length, width, and height are about 84, 30, and 2.5 nm. In polarized photoluminescence (PL) measurements, the peak of the GaSb nanorods is observed at about 1.1 eV, where the PL intensity is largest for the [−1 0 1] polarization and smallest for the polarization perpendicular to it. The degree of polarization is more than 20% and depends on the recombination energy. By comparing with a theoretical model based on 4 × 4 Luttinger-Kohn Hamiltonian, we find that the experimental results are explained by considering the Sb/As inter-diffusion and the nanorod height distribution.
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78.67.Qa Nanorods
66.30.Ny Chemical interdiffusion; diffusion barriers
78.55.Cr III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.16.Dn Self-assembly

Edge surface modes in magnetically biased chemically doped graphene strips

Dimitrios L. Sounas and Christophe Caloz

Appl. Phys. Lett. 99, 231902 (2011); http://dx.doi.org/10.1063/1.3665944 (3 pages) | Cited 1 time

Online Publication Date: 5 December 2011

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The characteristics of surface modes along magnetically biased chemically doped graphene strips at terahertz frequencies are investigated. Both edge and bulk modes exist, with power densities concentrated near the edges and in the middle of the strip, respectively. It is shown that placing a perfect electric conductor plate near one of the strip edges shorts the modes propagating along this edge. This results in strong non-reciprocity, which may be used for the realization of non-reciprocal phase shifters.
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78.70.Gq Microwave and radio-frequency interactions

Effect of shell thickness on two-photon absorption and refraction of colloidal CdSe/CdS core/shell nanocrystals

Bao-Hua Zhu, Hui-Chao Zhang, Zong-Yan Zhang, Yi-Ping Cui, and Jia-Yu Zhang

Appl. Phys. Lett. 99, 231903 (2011); http://dx.doi.org/10.1063/1.3665400 (3 pages) | Cited 2 times

Online Publication Date: 6 December 2011

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Colloidal CdSe nanocrystals (NCs) are successively overcoated with CdS monolayers (MLs), and the effective two-photon absorption (TPA) coefficient and refractive index of this series of CdS/CdSe core/shell NCs are measured by a Z-scan technique at 800 nm wavelength. The TPA and nonlinear refraction are enhanced dramatically with the CdS shell growth towards 3 MLs, but decreased with the further shell growth. The effects of surface states, local field, and intrinsic piezoelectric polarization are discussed to explain the optical nonlinearity of the colloidal core/shell NCs.
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81.16.-c Methods of micro- and nanofabrication and processing
82.70.Dd Colloids
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.65.Bn Piezoelectric and electrostrictive constants
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Torsion-induced mechanical couplings of single-walled carbon nanotubes

Renjie Zhao and Chenglin Luo

Appl. Phys. Lett. 99, 231904 (2011); http://dx.doi.org/10.1063/1.3665938 (3 pages) | Cited 3 times

Online Publication Date: 7 December 2011

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Torsion-induced mechanical couplings of single-walled carbon nanotubes (SWCNTs) are studied by using molecular dynamics simulations. We show that these mechanical couplings are strongly dependent on the chirality of SWCNTs. In particular, the structural difference between armchair and zigzag nanotubes can remarkably influence the Poynting effect [J. H. Poynting, Proc. R. Soc. Lond. A 82, 546 (1909)], i.e., torsion-induced axial strain response. For SWCNTs with large aspect ratios and small chiral angles, an intriguing torsion-induced bending effect is observed. This effect results from the release of torsion-induced axial stress and may probably affect the torsional oscillation behavior of nanoelectromechanical systems based on SWCNTs.
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81.40.Lm Deformation, plasticity, and creep
61.48.De Structure of carbon nanotubes, boron nanotubes, and other related systems
62.20.F- Deformation and plasticity
62.25.-g Mechanical properties of nanoscale systems
81.07.De Nanotubes
81.40.Jj Elasticity and anelasticity, stress-strain relations

Quantum mechanically guided design of transition metal doped SrCo0.875M0.125O3−δ (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn)

Bernd M. Linke, Denis Music, Jens Emmerlich, and Jochen M. Schneider

Appl. Phys. Lett. 99, 231905 (2011); http://dx.doi.org/10.1063/1.3666032 (3 pages)

Online Publication Date: 7 December 2011

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Perovskites are employed during energy conversion as membranes in conventional power plants or as fuel cell electrodes. To enable future materials design a quantum-mechanical model was developed to describe vacancy formation and the resulting chemical expansion. Cubic strontium cobaltite (SrCo0.875M0.125O3−δ) was doped with all 3d transition elements. A strong correlation between calculated energies of formation for vacancies and experimental oxygen flux literature data was identified.
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61.72.jd Vacancies
61.72.up Other materials

Characterization of GaSb/GaAs interfacial misfit arrays using x-ray diffraction

Charles J. Reyner, Jin Wang, Kalyan Nunna, Andrew Lin, Baolai Liang, Mark S. Goorsky, and D. L. Huffaker

Appl. Phys. Lett. 99, 231906 (2011); http://dx.doi.org/10.1063/1.3666234 (3 pages) | Cited 1 time

Online Publication Date: 8 December 2011

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We report a nondestructive, large-area method to characterize dislocation formation at a highly lattice-mismatched interface. The analysis is based on x-ray diffraction and reciprocal space mapping using a standard, lab-based diffractometer. We use this technique to identify and analyze a two-dimensional array of 90° misfit dislocations at a GaSb/GaAs interface. The full width at half maximum of the GaSb 004 reciprocal lattice point is shown to decrease with increasing GaSb epilayer thickness, as expected from theoretical models. Based on these measurements, the variation in the spatial dislocation frequency is calculated to be 1%.
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61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
68.35.bg Semiconductors
68.47.Fg Semiconductor surfaces
81.05.Ea III-V semiconductors
68.35.Ct Interface structure and roughness

The order-disorder transition in GeTe: Views from different length-scales

T. Matsunaga, P. Fons, A. V. Kolobov, J. Tominaga, and N. Yamada

Appl. Phys. Lett. 99, 231907 (2011); http://dx.doi.org/10.1063/1.3665067 (3 pages) | Cited 4 times

Online Publication Date: 8 December 2011

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GeTe is a narrow band gap semiconductor that undergoes a ferroelectric-to-paraelectric phase transition at ∼705 K. While earlier studies of average structure using Bragg diffraction concluded that the transition was displacive, structural probing of short and intermediate order shows evidence for an order-disorder transition. Here, we report and contrast the structure on different length scales with temperature using a radial distribution function analysis obtained from x-ray based total scattering and show that the order-disorder model is consistent with experiment.
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64.60.Cn Order-disorder transformations
64.70.K- Solid-solid transitions
78.70.Ck X-ray scattering
61.66.Fn Inorganic compounds

Carrier dynamics and activation energy of CdTe quantum dots in a CdxZn1−xTe quantum well

W. I. Han, J. H. Lee, J. S. Yu, J. C. Choi, and H. S. Lee

Appl. Phys. Lett. 99, 231908 (2011); http://dx.doi.org/10.1063/1.3669412 (3 pages) | Cited 4 times

Online Publication Date: 8 December 2011

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We investigate the optical properties of CdTe quantum dots (QDs) in a Cd0.3Zn0.7Te quantum well (QW) grown on GaAs (100) substrates. Carrier dynamics of CdTe/ZnTe QDs and quantum dots-in-a-well (DWELL) structure is studied using time-resolved photoluminescence (PL) measurements, which show the longer exciton lifetime of the DWELL structure. The activation energy of the electrons confined in the DWELL structure, as obtained from the temperature-dependent PL spectra, was also higher than that of electrons confined in the CdTe/ZnTe QDs. This behavior is attributed to the better capture of carriers into QDs within the surrounding QW.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.67.Hc Quantum dots
81.07.Ta Quantum dots
78.66.Hf II-VI semiconductors
78.47.jd Time resolved luminescence
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