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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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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

Anomalous optical switching and thermal hysteresis behaviors of VO2 films on glass substrate

Jian Li and Joonghoe Dho

Appl. Phys. Lett. 99, 231909 (2011); http://dx.doi.org/10.1063/1.3668089 (3 pages) | Cited 3 times

Online Publication Date: 9 December 2011

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In order to study the optical switching of vanadium dioxide (VO2) and its thermal hysteresis behavior, we fabricated VO2 films on glass substrates at various oxygen pressures. Only the VO2 films made at 5–10 mTorr displayed x-ray diffraction peaks and metal-insulator transition. Upon heating and cooling, remarkably, these samples exhibited significant optical switching behaviors with a clockwise thermal hysteresis in the infrared range of >850 nm or with a counterclockwise thermal hysteresis in the near visible range of 650–850 nm. The temperature dependence of optical absorption was explained by the O2p-V3d splitting depending on the structural transition of VO2.
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78.66.Nk Insulators
81.15.Fg Pulsed laser ablation deposition
68.55.at Other materials
64.70.K- Solid-solid transitions
71.30.+h Metal-insulator transitions and other electronic transitions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Intra-excitonic relaxation dynamics in ZnO

Alexej Chernikov, Martin Koch, Bernhard Laumer, Thomas A. Wassner, Martin Eickhoff, Stephan W. Koch, and Sangam Chatterjee

Appl. Phys. Lett. 99, 231910 (2011); http://dx.doi.org/10.1063/1.3668102 (3 pages)

Online Publication Date: 9 December 2011

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The temperature and carrier-density dependent excitonic relaxation in bulk ZnO is studied by means of time-resolved photoluminescence. A rate-equation model is used to analyze the population dynamics and the transitions between different exciton states. Intra-excitonic (n = 1) to (n = 2) relaxation is clearly identified at low excitation densities and lattice temperatures with a characteristic time constant of 6 ± 0.5 ps.
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78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
73.20.Mf Collective excitations (including excitons, polarons, plasmons and other charge-density excitations)

Vacancies, twins, and the thermal stability of ultrafine-grained copper

C. Saldana, A. H. King, E. A. Stach, W. D. Compton, and S. Chandrasekar

Appl. Phys. Lett. 99, 231911 (2011); http://dx.doi.org/10.1063/1.3669404 (3 pages) | Cited 5 times

Online Publication Date: 9 December 2011

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Ultrafine-grained metals have impressive strength but lack the thermal stability necessary for most applications. Nano-scale, deformation twinned copper microstructures exhibit a rare combination of strength and stability. While storing less energy in their interfaces than other nanostructured metals, they also exhibit lower vacancy supersaturations, reducing the driving force and mobility for microstructure evolution. From a thermal stability perspective, the nano-twinned microstructure may thus be preferred over the more commonly produced nano-scale equiaxed microstructures.
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61.72.jd Vacancies
61.72.Mm Grain and twin boundaries
81.40.Lm Deformation, plasticity, and creep
62.20.F- Deformation and plasticity
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