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24 Jan 2011

Volume 98, Issue 4, Articles (04xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 98, 043101 (2011); http://dx.doi.org/10.1063/1.3536475 (3 pages)

Zhichao Ruan and Shanhui Fan
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Thermal oxidation of silicon carbide: A comparison of n-type and p-type doped epitaxial layers

Xiao-An Fu, Kenji Okino, and Mehran Mehregany

Appl. Phys. Lett. 98, 042109 (2011); http://dx.doi.org/10.1063/1.3549294 (3 pages)

Online Publication Date: 28 January 2011

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The kinetics of wet thermal oxidation of both n-type and p-type doped 6H-SiC epitaxial layers grown on p-type 6H-SiC wafers has been investigated. The oxidation rates are affected significantly by doping concentration. The kinetics of wet thermal oxidation abides by the Deal–Grove model B. E. Deal and A. S. Grove, [J. Appl. Phys. 36, 3770 (1965)] . The linear oxidation rate constant B/A and the parabolic oxidation rate constant B are obtained by fitting the measured data to the Deal–Grove model.
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81.05.Hd Other semiconductors
81.65.Mq Oxidation
61.72.up Other materials

Thermoelectric effect of multiferroic oxide interfaces

Chenglong Jia and Jamal Berakdar

Appl. Phys. Lett. 98, 042110 (2011); http://dx.doi.org/10.1063/1.3549863 (3 pages) | Cited 1 time

Online Publication Date: 28 January 2011

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We investigate the thermoelectric properties of electrons at the interface of an oxide heterostructure and in the presence of a multiferroic oxide with spiral spin order. We find that there is no (spin) Hall current generated by the temperature gradient. A Seebeck effect is, however, present. Due to the magnetoelectric coupling, the charge and thermal conductivities are electrically controllable via the spin spiral helicity. Moreover, the thermopower exhibits a sign change when tuning the carrier density electro-statically.
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72.20.Pa Thermoelectric and thermomagnetic effects
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.-e Ferroelectricity and antiferroelectricity
75.85.+t Magnetoelectric effects, multiferroics
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
73.40.-c Electronic transport in interface structures
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Magnetic microstructure and magnetotransport in Co2FeAl Heusler compound thin films

Mathias Weiler, Franz D. Czeschka, Andreas Brandlmaier, Inga-Mareen Imort, Günter Reiss, Andy Thomas, Georg Woltersdorf, Rudolf Gross, and Sebastian T. B. Goennenwein

Appl. Phys. Lett. 98, 042501 (2011); http://dx.doi.org/10.1063/1.3544559 (3 pages) | Cited 1 time

Online Publication Date: 24 January 2011

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We correlate simultaneously recorded magnetotransport and spatially resolved magneto-optical Kerr effect (MOKE) data in Co2FeAl Heusler compound thin films micropatterned into Hall bars. Room temperature MOKE images reveal the nucleation and propagation of domains in an externally applied magnetic field and are used to extract a macrospin corresponding to the mean magnetization direction in the Hall bar. The anisotropic magnetoresistance calculated using this macrospin is in excellent agreement with magnetoresistance measurements. This suggests that the magnetotransport in Heusler compounds can be adequately simulated using simple macrospin models, while the magnetoresistance contribution due to domain walls is of negligible importance.
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75.70.Ak Magnetic properties of monolayers and thin films
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
78.66.Bz Metals and metallic alloys
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
72.15.Gd Galvanomagnetic and other magnetotransport effects

Kinetic depinning of a magnetic domain wall above the Walker field

E. R. Lewis, D. Petit, L. O’Brien, A.-V. Jausovec, H. T. Zeng, D. E. Read, and R. P. Cowburn

Appl. Phys. Lett. 98, 042502 (2011); http://dx.doi.org/10.1063/1.3543844 (3 pages) | Cited 4 times

Online Publication Date: 24 January 2011

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The dynamical interaction between a transverse domain wall and a T-shaped trap is investigated, for domain wall motion in the oscillatory regime above the Walker field. We demonstrate experimentally the existence of distinct static and kinetic depinning fields in this regime, and show that the oscillatory motion of the domain wall leads to a distribution of kinetic depinning fields. Micromagnetic simulations are in good qualitative agreement with our experimental results.
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75.78.Fg Dynamics of domain structures
75.78.Cd Micromagnetic simulations
75.60.Ch Domain walls and domain structure

Effect of the number of layers on determination of spin asymmetries in current-perpendicular-to-plane giant magnetoresistance

Tomohiro Taniguchi, Hiroshi Imamura, Tomoya M. Nakatani, and Kazuhiro Hono

Appl. Phys. Lett. 98, 042503 (2011); http://dx.doi.org/10.1063/1.3531758 (3 pages)

Online Publication Date: 24 January 2011

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Current-perpendicular-to-plane giant-magnetoresistance effect in a ferromagnetic/nonmagnetic multilayer is studied theoretically by solving the diffusion equation of the spin accumulation without assuming the periodic boundary condition. We show that the Valet and Fert theory underestimates spin asymmetries with decreasing the number of layers.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)

Low spin current-driven dynamic excitations and metastability in spin-valve nanocontacts with unpinned artificial antiferromagnet

M. Eggeling, T. Dimopoulos, T. Uhrmann, O. Bethge, R. Heer, V. Höink, and H. Brückl

Appl. Phys. Lett. 98, 042504 (2011); http://dx.doi.org/10.1063/1.3537953 (3 pages) | Cited 1 time

Online Publication Date: 24 January 2011

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This work investigates the spin-torque-related dynamics of nonuniform magnetic vortexlike states in spin-valve nanocontacts, employing an unpinned artificial antiferromagnet as polarizer and amorphous CoFeB as free layer. Subgigahertz spectra are obtained for contacts of 150–200 nm in diameter. Low critical current density and reversibility of the dynamic spectra with respect to the current are obtained. The spectral power and linewidth depend on the in-plane magnetic field, assuming maximum, respectively minimum, values within the free layer’s magnetization switching. For certain field and current windows metastable dynamic states are clearly demonstrated.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Ee Antiferromagnetics
75.30.Ds Spin waves
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.07.Lk Nanocontacts
75.75.-c Magnetic properties of nanostructures

Nonlinear amplification and mixing of spin waves in a microstrip geometry with metallic ferromagnets

Yuri Khivintsev, J. Marsh, V. Zagorodnii, I. Harward, J. Lovejoy, P. Krivosik, R. E. Camley, and Z. Celinski

Appl. Phys. Lett. 98, 042505 (2011); http://dx.doi.org/10.1063/1.3541787 (3 pages) | Cited 3 times

Online Publication Date: 24 January 2011

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We explore the nonlinear mixing and amplification of magnetic polariton modes in ultrasmall waveguides. Ultrasmall waveguide geometries can produce large oscillating microwave fields—up to about 500 Oe. Using these large fields, we examine nonlinear ferromagnetic dynamics in ribbons of Permalloy and Fe. In particular if two microwave signals at different frequencies are sent into the waveguide, we can increase the transmission of one wave by adding energy to the other wave. We also demonstrate the creation of new frequencies and the development of a comb of equally spaced frequencies. These experimental results are explained with perturbation theory and micromagnetics calculations.
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85.70.-w Magnetic devices
84.40.Az Waveguides, transmission lines, striplines

Study and tailoring spin dynamic properties of CoFeB during rapid thermal annealing

Yaping Zhang, Xin Fan, Weigang Wang, Xiaoming Kou, Rong Cao, Xing Chen, Chaoying Ni, Liqing Pan, and John Q. Xiao

Appl. Phys. Lett. 98, 042506 (2011); http://dx.doi.org/10.1063/1.3549188 (3 pages) | Cited 4 times

Online Publication Date: 26 January 2011

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We studied the real-time evolution of magnetic dynamic and static properties of 20 nm CoFeB thin film during annealing at 380 °C. The ferromagnetic resonance linewidth quickly reduces by 30% within 300 s annealing, and monotonically increases upon longer annealing. The magnetic static coercivity shows similar trend. The underlying physical relation between linewidth and anisotropy can be connected by the two-magnon scattering theory. By doping of Nb into CoFeB films, the damping was maintained at a low value within 2000 s annealing. This method to tailor the dynamic properties of CoFeB may benefit the development of magnetics and spintronics based microwave devices.
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75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Gw Magnetic anisotropy
61.72.Cc Kinetics of defect formation and annealing

The effect of Co substitution on the magnetic properties of the Heusler alloy Ni50Mn33Sn17

R. Y. Umetsu, A. Sheikh, W. Ito, B. Ouladdiaf, K. R. A. Ziebeck, T. Kanomata, and R. Kainuma

Appl. Phys. Lett. 98, 042507 (2011); http://dx.doi.org/10.1063/1.3548558 (3 pages) | Cited 4 times

Online Publication Date: 26 January 2011

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Magnetic measurements and neutron powder diffraction experiments on Ni50Mn33Sn17 and Ni45Co5Mn33Sn17 alloys were performed in order to establish the magnetic structures and the effects of Co substitution on the magnetic properties. It was shown that the magnetic coupling between the Mn moments on the 4a and 4b sites changed from being antiferromagnetic to ferromagnetic by substitution of Co. As a result of the change in the magnetic structure due to the Co substitution, the ferromagnetic properties of Ni–Co–Mn–Sn are enhanced. These results have enabled the concentration dependence of the magnetic moment to be quantified.
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75.30.Cr Saturation moments and magnetic susceptibilities
75.50.Ee Antiferromagnetics
75.25.-j Spin arrangements in magnetically ordered materials (including neutron and spin-polarized electron studies, synchrotron-source x-ray scattering, etc.)
75.50.Cc Other ferromagnetic metals and alloys

Enhanced critical current properties in Ba0.6K0.4+xFe2As2 superconductor by overdoping of potassium

Chunlei Wang, Lei Wang, Zhaoshun Gao, Chao Yao, Dongliang Wang, Yanpeng Qi, Xianping Zhang, and Yanwei Ma

Appl. Phys. Lett. 98, 042508 (2011); http://dx.doi.org/10.1063/1.3549195 (3 pages) | Cited 3 times

Online Publication Date: 27 January 2011

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Phase-pure polycrystalline Ba0.6K0.4+xFe2As2 with 0 ≤ x ≤ 0.1 were prepared using a one-step solid-state reaction method. We found that overdoping of potassium can improve the critical current density (Jc). High-field Jc for samples with x = 0.1 is three times higher than that for samples with x = 0. Overdoping of K has minimal effect on the critical transition temperature (Tc). Less than 0.5 K degradations in Tc was measured for samples with x = 0.1. Transmission electron microscopy (TEM) revealed high concentration of dislocations in samples with x = 0.1, resulting in enhanced flux pining. Further analyses on magnetization loops for powder samples confirm that K overdoping can promote intragrain Jc. Our results indicate that slight excess of K in Ba0.6K0.4Fe2As2 superconductor is beneficial to high-field applications.
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74.25.Sv Critical currents
74.70.Xa Pnictides and chalcogenides
74.25.Wx Vortex pinning (includes mechanisms and flux creep)
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
74.25.Ha Magnetic properties including vortex structures and related phenomena

Self-assembled oxide nanopillars in epitaxial BaFe2As2 thin films for vortex pinning

Yi Zhang, Christopher T. Nelson, Sanghan Lee, Jianyi Jiang, Chung Wung Bark, Jeremy D. Weiss, Chiara Tarantini, Chad M. Folkman, Seung-Hyub Baek, Eric E. Hellstrom, David C. Larbalestier, Chang-Beom Eom, and Xiaoqing Pan

Appl. Phys. Lett. 98, 042509 (2011); http://dx.doi.org/10.1063/1.3532107 (3 pages) | Cited 9 times

Online Publication Date: 27 January 2011

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We report the structure and chemistry of the self-assembled oxide nanopillars that form in superconducting Co-doped BaFe2As2 thin film grown by pulsed laser deposition. The oxide nanopillars consist of a BaFeO2 phase, form epitaxially on the SrTiO3 template, and grow coherently with the BaFe2As2 film. The nanopillars are square with a uniform size of 4–5 nm, which is close to twice the superconducting coherence length. Despite a volume content of ∼ 5%, the nanopillars do not degrade the structural quality of the BaFe2As2 matrix. Indeed the nanopillars provide exceptionally strong vortex pinning and high critical current density due to the very close correlation of pillar and vortex core diameters.
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74.25.Wx Vortex pinning (includes mechanisms and flux creep)
81.16.Dn Self-assembly
74.78.Na Mesoscopic and nanoscale systems
81.15.Fg Pulsed laser ablation deposition

Magnetization reversal in exchange biased IrMn/Fe ring arrays

Yu-feng Hou, Qing-feng Zhan, and Kannan M. Krishnan

Appl. Phys. Lett. 98, 042510 (2011); http://dx.doi.org/10.1063/1.3549187 (3 pages) | Cited 2 times

Online Publication Date: 28 January 2011

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We investigated the effect of exchange bias on the magnetization reversal behavior in ring-shaped IrMn/Fe lithographic structures. The magnetic anisotropy geometry of the exchange biased ring is revealed by fitting for the angular dependence of the exchange bias, Heb, and coercivity, Hc. Magnetic force microscopy images obtained at different field values along the hysteresis loop show that along the bias direction, the ring exhibits a magnetic reversal via nonuniform domain nucleation while perpendicular to the bias direction, the magnetic reversal occurs via coherent rotation. The difference in magnetic switching modes for these two field orientations is confirmed by micromagnetic simulations and interpreted by the effective field model.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Gw Magnetic anisotropy
75.30.Et Exchange and superexchange interactions
75.60.Jk Magnetization reversal mechanisms
75.60.Ch Domain walls and domain structure
75.78.Cd Micromagnetic simulations
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Transport properties of the new Fe-based superconductor KxFe2Se2 (Tc = 33 K)

Yoshikazu Mizuguchi, Hiroyuki Takeya, Yasuna Kawasaki, Toshinori Ozaki, Shunsuke Tsuda, Takahide Yamaguchi, and Yoshihiko Takano

Appl. Phys. Lett. 98, 042511 (2011); http://dx.doi.org/10.1063/1.3549702 (3 pages) | Cited 23 times

Online Publication Date: 28 January 2011

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We synthesized the new Fe-based superconductor K0.8Fe2Se2 single crystals. The obtained single crystal exhibited a sharp superconducting transition and the onset and zero-resistivity tempera-ture were estimated to be 33 and 31.8 K, respectively. A high upper critical field of 192 T was obtained. The anisotropy of superconductivity of K0.8Fe2Se2 was ∼ 3.6. Both the high upper critical field and comparably low anisotropy are advantageous for applications under a high magnetic field.
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74.25.F- Transport properties
74.70.-b Superconducting materials other than cuprates
74.25.Dw Superconductivity phase diagrams
74.25.Ha Magnetic properties including vortex structures and related phenomena
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Understanding electroforming in bipolar resistive switching oxides

F. Gomez-Marlasca, N. Ghenzi, M. J. Rozenberg, and P. Levy

Appl. Phys. Lett. 98, 042901 (2011); http://dx.doi.org/10.1063/1.3537957 (3 pages) | Cited 5 times

Online Publication Date: 25 January 2011

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We study electroforming on the resistive switching (RS) behavior of silver-manganite interfaces. Using the technique of hysteresis switching loops we define an electroforming procedure that enables us to study its influence on the RS behavior in a systematic manner. We show that two similar electroforming procedures may lead to either RS or no RS at all. We explain the observed behavior by associating the forming procedure and the memory switching operation to major and minor hysteresis loops, respectively. With the obtained insight we propose a simple and nearly optimal electroforming procedure.
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85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
85.70.Ec Magnetostrictive, magnetoacoustic, and magnetostatic devices
82.45.-h Electrochemistry and electrophoresis
81.10.Fq Growth from melts; zone melting and refining
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Epitaxial growth of lanthanide oxides La2O3 and Sc2O3 on GaN

Jesse S. Jur, Virginia D. Wheeler, Daniel J. Lichtenwalner, Jon-Paul Maria, and Mark A. L. Johnson

Appl. Phys. Lett. 98, 042902 (2011); http://dx.doi.org/10.1063/1.3541883 (3 pages) | Cited 3 times

Online Publication Date: 26 January 2011

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Deposition of lanthanide oxides on GaN is investigated as a means to produce stable dielectric with good interface quality. Epitaxial growth of cubic 〈111〉-oriented Sc2O3 is observed on GaN [0001] with a lattice mismatch of 7.2%, whereas La2O3 growth, with a lattice mismatch of ∼ 21%, results in a mixed phase epitaxial film comprised of the bixbyite and hexagonal allotropes. Substantial roughening accompanies this mixed phase film. By inserting a thin Sc2O3 interfacial layer between La2O3 and GaN and a Sc2O3 capping layer, the crystal quality of the predominantly La2O3 layer is improved and the stack is stabilized against hydroxide formation under ambient conditions.
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68.55.A- Nucleation and growth
77.55.-g Dielectric thin films
61.66.Fn Inorganic compounds
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Design of subwavelength superscattering nanospheres

Zhichao Ruan and Shanhui Fan

Appl. Phys. Lett. 98, 043101 (2011); http://dx.doi.org/10.1063/1.3536475 (3 pages) | Cited 5 times

Online Publication Date: 24 January 2011

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We design a subwavelength superscattering nanosphere with plasmonic-dielectric-plasmonic layer structure. We show that the scattering cross section of such a particle can be significantly enhanced by employing multiple resonances with different total angular momenta, and by ensuring that all these resonances have almost the same frequency and operate in the overcoupling region.
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72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
81.16.-c Methods of micro- and nanofabrication and processing
73.22.Lp Collective excitations

Watching bismuth nanowires grow

Jinhee Ham, Wooyoung Shim, Do Hyun Kim, Kyu Hwan Oh, Peter W. Voorhees, and Wooyoung Lee

Appl. Phys. Lett. 98, 043102 (2011); http://dx.doi.org/10.1063/1.3535956 (3 pages) | Cited 3 times

Online Publication Date: 25 January 2011

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We report real-time high temperature scanning electron microscopy observations of the growth of bismuth nanowires via the on-film formation of nanowires (OFF-ON) method. These observations provide experimental evidence that thermally induced-stress on a Bi film is the driving force for the growth of Bi nanowires with high aspect ratios, uniform diameter, and high-quality crystallinity. Our results show that immobile grain boundaries in the Bi film are required for the growth of nanowires so that grain broadening resulting in hillock formation can be prevented. This study not only provides an understanding of the underlying mechanism, but also affords a strategy for facilitating nanowire growth by OFF-ON.
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81.07.Gf Nanowires
81.16.-c Methods of micro- and nanofabrication and processing
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)
61.72.Mm Grain and twin boundaries
81.05.Bx Metals, semimetals, and alloys

Air trapped nanocavity induced superhydrophobicity on GaN microbelt

Prasana Sahoo, S. Dhara, S. Dash, Baldev Raj, I. Manna, and A. K. Tyagi

Appl. Phys. Lett. 98, 043103 (2011); http://dx.doi.org/10.1063/1.3541877 (3 pages) | Cited 4 times

Online Publication Date: 26 January 2011

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In the present study, nanotextured surface protrusion induced superhydrophobicity in GaN microbelt is reported. The results show that along with nanometer-scale topographic features, the special air trapped nanocavities formed beneath the liquid droplet are solely responsible for the transition of superhydrophobicity having hydrophilic origin in GaN. The built-in nanocavities, ( ∼ 80 nm in diameter) provide an ideal model for producing stable air trapped region. A calculation of shape of the meniscus at the interface of air and water in an isolated cavity correlates well with the macroscopic surface wetting behavior.
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68.08.Bc Wetting
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)

Growth of multilayers of Bi2Se3/ZnSe: Heteroepitaxial interface formation and strain

H. D. Li, Z. Y. Wang, X. Guo, Tai Lun Wong, Ning Wang, and M. H. Xie

Appl. Phys. Lett. 98, 043104 (2011); http://dx.doi.org/10.1063/1.3548865 (3 pages) | Cited 6 times

Online Publication Date: 26 January 2011

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Multilayers of Bi2Se3/ZnSe with the periodicity of a few nanometers were grown by molecular-beam epitaxy on Si(111). While epitaxial growth of Bi2Se3 on ZnSe proceeded by two-dimensional nucleation, ZnSe growth on Bi2Se3 showed the three-dimensional growth front. Therefore, the two complementary interfaces of Bi2Se3/ZnSe were asymmetric in morphological properties. Strain-relaxation rates were found to differ between epitaxial ZnSe and Bi2Se3, which could be attributed to the specific growth modes and the properties of Bi2Se3 and ZnSe surfaces.
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68.65.Ac Multilayers
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Dz II-VI semiconductors
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.40.+i Anelasticity, internal friction, stress relaxation, and mechanical resonances

Raman spectroscopy of iodine molecules trapped in zeolite crystals

Wenhao Guo, Dingdi Wang, Juanmei Hu, Z. K. Tang, and Shengwang Du

Appl. Phys. Lett. 98, 043105 (2011); http://dx.doi.org/10.1063/1.3549194 (3 pages) | Cited 2 times

Online Publication Date: 26 January 2011

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We study the Raman spectroscopy of neutral iodine molecules confined in the channels of zeolite AlPO4-5 (AFI) and AlPO4-11 (AEL) crystals, which shows that the molecular vibration states are significantly modified by the confinements from the nanosize channels. An iodine molecule trapped in the AEL crystal has an effective internuclear potential close to an ideal harmonic oscillator, while that in the AFI crystal behaves similarly to that in free space. The results are further confirmed by measuring the temperature dependence of Raman spectral width.
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33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.70.Jg Line and band widths, shapes, and shifts

Photoabsorption and photoelectric process in Si nanocrystallites

Anchala, S. P. Purohit, and K. C. Mathur

Appl. Phys. Lett. 98, 043106 (2011); http://dx.doi.org/10.1063/1.3548861 (3 pages)

Online Publication Date: 27 January 2011

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Using the effective mass approximation, we investigate the photoabsorption and photoelectric process in the conduction band of a single electron charged spherical Si semiconductor quantum dot nanostructure embedded in the amorphous SiO2 matrix. We consider the potential barrier at the interface as of (i) infinite and (ii) finite heights. The effect of self-energy associated with surface polarization due to the charging of the quantum dot is also considered. Our results of photoabsorption coefficient for (1s-1p) transition are found to be in good agreement with the available experimental data.
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73.61.Cw Elemental semiconductors
78.67.Hc Quantum dots
72.40.+w Photoconduction and photovoltaic effects
61.46.-w Structure of nanoscale materials

Binding of deposited gold clusters to thiol self-assembled monolayers on Au(111) surfaces

Leila Costelle, Tommi T. Järvi, Minna T. Räisänen, Vladimir Tuboltsev, and Jyrki Räisänen

Appl. Phys. Lett. 98, 043107 (2011); http://dx.doi.org/10.1063/1.3548862 (3 pages) | Cited 3 times

Online Publication Date: 27 January 2011

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We study the mechanisms involved in Au nanocluster deposition on thiol self-assembled monolayer modified Au(111) surfaces. Molecular dynamics simulations reveal a wide range of cluster-surface binding configurations within a very narrow deposition energy range (0.2–0.6 eV/atom for ∼ 2.5 nm diameter clusters). These go from noncovalent to full contact and include surprising intermediate cases in which the clusters are bound to the underlying Au(111) surface via molecular links and nanowires. Experiments show that, subsequently, the clusters are covered by thiols and slightly flattened.
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81.16.Dn Self-assembly
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials

Silicon nanowires for high-specificity and high-selectivity sensors under low-frequency scanning

Xiaodie He, Chunsheng Guo, Yang Liu, Chi Him A. Tsang, Dorothy Duo Duo Ma, Ruiqin Zhang, Ning-Bew Wong, Zhenhui Kang, and Shuit-Tong Lee

Appl. Phys. Lett. 98, 043108 (2011); http://dx.doi.org/10.1063/1.3549067 (3 pages) | Cited 2 times

Online Publication Date: 28 January 2011

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The high specificity and selectivity of H–Si nanowire bundles, which are single crystalline and composed of pure Si without oxygen, for detecting water (peak at 12 Hz) and ethanol (peak at 70 Hz) in their mixture are measured by a frequency scanning test. The signal amplitude deduced between the work channel and the reference channel {[(VR-VS)/VR]×100%} is defined as the impedance recorded under different scanning frequencies.
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07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
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Bulk heterojunction solar cells with thick active layers and high fill factors enabled by a bithiophene-co-thiazolothiazole push-pull copolymer

J. Peet, L. Wen, P. Byrne, S. Rodman, K. Forberich, Y. Shao, N. Drolet, R. Gaudiana, G. Dennler, and D. Waller

Appl. Phys. Lett. 98, 043301 (2011); http://dx.doi.org/10.1063/1.3544940 (3 pages) | Cited 26 times

Online Publication Date: 24 January 2011

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A push-pull copolymer is presented which can be used in bulk heterojunction (BHJ) solar cells with active layers greater than 200 nm and fill factors above 60%. The efficiencies of most BHJ solar cells are limited by the fact that they have active layers which are between 60 and 110 nm. While this thickness regime enables peak quantum efficiencies (EQE) of 60%–70%, the ability to fabricate thicker devices would increase average EQE values and thus device efficiencies. Discovery of materials which can maintain high performance at large thicknesses will enable higher performance in BHJ hero cells and increase the commercial viability of this technology.
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88.40.jr Organic photovoltaics
88.40.hj Efficiency and performance of solar cells
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Semitransparent organic solar cells with organic wavelength dependent reflectors

Yulia Galagan, Michael G. Debije, and Paul W. M. Blom

Appl. Phys. Lett. 98, 043302 (2011); http://dx.doi.org/10.1063/1.3546171 (3 pages) | Cited 6 times

Online Publication Date: 24 January 2011

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Semitransparent organic solar cells employing solution-processable organic wavelength dependent reflectors of chiral nematic (cholesteric) liquid crystals are demonstrated. The cholesteric liquid crystal (CLC) reflects only in a narrow band of the solar spectrum and remains transparent for the remaining wavelengths. The reflective band is matched to the absorption spectrum of the organic solar cell such that only unabsorbed photons that can contribute to the photocurrent are reflected to pass through the active layer a second time. In this way, the efficiency of semitransparent organic solar cells can be enhanced without significant transparency losses. An efficiency increase of 6% was observed when a CLC reflector with a reflection band of 540–620 nm was used, whereas the transparency of the organic solar cells is only suppressed in the 80 nm narrow bandwidth.
Show PACS
88.40.jr Organic photovoltaics
88.40.H- Solar cells (photovoltaics)
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
42.70.Jk Polymers and organics
42.70.Df Liquid crystals
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