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3 Aug 2009

Volume 95, Issue 5, Articles (05xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 95, 052901 (2009); http://dx.doi.org/10.1063/1.3190518 (3 pages)

Didit Yudistira, Sarah Benchabane, Davide Janner, and Valerio Pruneri
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Evidence for preferential rearrangements of martensite variants by magnetic field in antiferromagnetic CoO crystal

Z. H. Nie, Y. Ren, T. Terai, Y. D. Wang, D. E. Brown, and T. Kakeshita

Appl. Phys. Lett. 95, 051914 (2009); http://dx.doi.org/10.1063/1.3195730 (3 pages) | Cited 1 time

Online Publication Date: 5 August 2009

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The synchrotron high-energy x-ray diffraction provides the direct crystallographic evidence for the magnetic-field-driven preferential rearrangements of martensite multivariants in antiferromagnetic CoO crystal. When a magnetic field was incrementally applied up to 6 T on the CoO single crystal cooled below the Néel temperature, the martensite variants with the magnetization easy-axis parallel to the magnetic field direction (math) were consumed, while the variants with magnetic moments perpendicular to math were enhanced. The microscopic origin for the observation is discussed, which provides important information for understanding the magnetic-field-driven strain observed in the antiferromagnetic alloys, with a selection principle on martensite variants different from that found in the ferromagnetic shape memory alloys.
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81.30.Kf Martensitic transformations
62.20.fg Shape-memory effect; yield stress; superelasticity
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Ee Antiferromagnetics

Correlation of crystalline defects with photoluminescence of InGaN layers

Nikolai Faleev, Balakrishnam Jampana, Omkar Jani, Hongbo Yu, Robert Opila, Ian Ferguson, and Christiana Honsberg

Appl. Phys. Lett. 95, 051915 (2009); http://dx.doi.org/10.1063/1.3202409 (3 pages) | Cited 11 times

Online Publication Date: 6 August 2009

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We report structural studies of InGaN epilayers of various thicknesses by x-ray diffraction, showing a strong dependence of the type and spatial distribution of extended crystalline defects on layer thickness. The photoluminescence intensity for the samples was observed to increase with thickness up to 200 nm and decrease for higher thicknesses, a result attributed to creation of dislocation loops within the epilayer. Correlation of physical properties with crystalline perfection open the way for optimized designs of InGaN solar cells, with controlled types and dislocation densities in the InGaN epilayers, a key requirement for realizing high photocurrent generation in InGaN.
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78.66.Fd III-V semiconductors
61.72.Ff Direct observation of dislocations and other defects (etch pits, decoration, electron microscopy, x-ray topography, etc.)
72.40.+w Photoconduction and photovoltaic effects
78.55.Cr III-V semiconductors

Enhancement in interface robustness regarding thermal oxidation in nanostructured Al2O3 deposited on 4H-SiC

S. A. Corrêa, G. G. Marmitt, N. M. Bom, A. T. da Rosa, F. C. Stedile, C. Radtke, G. V. Soares, I. J. R. Baumvol, C. Krug, and A. L. Gobbi

Appl. Phys. Lett. 95, 051916 (2009); http://dx.doi.org/10.1063/1.3195702 (3 pages) | Cited 1 time

Online Publication Date: 6 August 2009

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Experimental evidences of enhanced stability of Al2O3/SiC structures following thermal annealing are presented. 5- and 40-nm-thick Al2O3 films evaporated on the Si- and C-terminated faces of 4H-SiC were annealed up to 1000 °C in different atmospheres, leading to crystallization and densification of Al2O3, with an increase in the band gap. Exposure to O2 at high temperatures produced SiO2 and AlSixOy at the Al2O3/SiC interface, with less silicate on the Si-terminated face. Annealing in N2 before exposure to O2 hindered oxygen diffusion and exchange, leading to more stable thin film structures from the point of view of atomic transport.
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68.35.Ct Interface structure and roughness
61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
64.70.Nd Structural transitions in nanoscale materials
64.70.K- Solid-solid transitions

Enhanced photochromism in nanostructured molybdenum trioxide films

Gisia Beydaghyan, Serge Doiron, Alain Haché, and P. V. Ashrit

Appl. Phys. Lett. 95, 051917 (2009); http://dx.doi.org/10.1063/1.3196548 (3 pages) | Cited 4 times

Online Publication Date: 6 August 2009

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We present evidence of enhancement of photochromism in nanostructured thin films of molybdenum oxide fabricated by glancing angle deposition. The strong correlation of coloration response with the internal surface area of the films provides evidence of the importance of nanostructuring on the photochromic effect and the vital role played by the availability of water in the photochromic mechanism.
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78.66.Nk Insulators
78.20.-e Optical properties of bulk materials and thin films

Conduction band intersubband transitions in Ge/SiGe quantum wells

M. De Seta, G. Capellini, Y. Busby, F. Evangelisti, M. Ortolani, M. Virgilio, G. Grosso, G. Pizzi, A. Nucara, and S. Lupi

Appl. Phys. Lett. 95, 051918 (2009); http://dx.doi.org/10.1063/1.3198204 (3 pages) | Cited 6 times

Online Publication Date: 7 August 2009

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In this letter we present the experimental evidence of intersubband absorption in the conduction band of compressively strained germanium quantum wells bounded by Ge-rich SiGe barriers. The measured absorption energies are in the terahertz range and are interpreted by means of tight binding calculations which include self-consistent band-bending and depolarization effects. From the comparison of experimental and numerical results a conduction band offset along the L line of about 120 meV has been estimated for the studied heterostructures.
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73.21.Fg Quantum wells
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.15.Ap Basis sets (LCAO, plane-wave, APW, etc.) and related methodology (scattering methods, ASA, linearized methods, etc.)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions

X-ray initiation of nonthermal growth of single crystal pyramids in amorphous barium titanate

Y. Feldman, V. Lyahovitskaya, G. Leitus, I. Lubomirsky, E. Wachtel, V. A. Bushuev, G. Vaughan, Z. Barkay, and Yu. Rosenberg

Appl. Phys. Lett. 95, 051919 (2009); http://dx.doi.org/10.1063/1.3200231 (3 pages) | Cited 2 times

Online Publication Date: 7 August 2009

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Nonthermal crystallization of amorphous barium titanate (BTO) was initiated by a monochromatic x-ray microbeam from a synchrotron radiation source. Following x-ray exposure, micron-sized BTO single crystals with a true square pyramid shape appeared on the surface of an amorphous BTO substrate-free film. The location and size of the areas in which crystal growth appeared fit well the x-ray microbeam path and size, respectively. A plausible mechanism of x-ray induced initiation of nonthermal crystallization in BTO is proposed. The observed phenomenon holds promise for materials engineering at nanoscale and crystallization of amorphous materials in situations where heating must be avoided.
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81.10.-h Methods of crystal growth; physics and chemistry of crystal growth, crystal morphology, and orientation
61.43.-j Disordered solids

High-pressure Raman spectroscopy of carbon onions and nanocapsules

J. J. Guo, G. H. Liu, X. M. Wang, T. Fujita, B. S. Xu, and M. W. Chen

Appl. Phys. Lett. 95, 051920 (2009); http://dx.doi.org/10.1063/1.3200246 (3 pages) | Cited 2 times

Online Publication Date: 7 August 2009

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We report high-pressure Raman spectra of carbon onions and nanocapsules investigated by diamond anvil cell experiments. The pressure coefficient and elastic behavior of carbon onions and nanocapsules are found to be very similar to those of multiwall carbon nanotubes. Additionally, detectable structure changes, particularly the collapse of the concentric graphite structure, cannot been seen at pressures as high as ∼ 20 GPa, demonstrating that carbon onions and nanocapsules have significant hardness and can sustain very high pressures.
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78.30.Hv Other nonmetallic inorganics
62.20.Qp Friction, tribology, and hardness
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.D- Elasticity

Breakdown of anomalous channeling with ion energy for accurate strain determination in GaN-based heterostructures

A. Redondo-Cubero, K. Lorenz, R. Gago, N. Franco, S. Fernández-Garrido, P. J. M. Smulders, E. Muñoz, E. Calleja, I. M. Watson, and E. Alves

Appl. Phys. Lett. 95, 051921 (2009); http://dx.doi.org/10.1063/1.3202421 (3 pages) | Cited 3 times

Online Publication Date: 7 August 2009

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The influence of the beam energy on the determination of strain state with ion channeling in GaN-based heterostructures (HSs) is addressed. Experimental results show that anomalous channeling may hinder an accurate analysis due to the steering effects at the HS interface, which are more intense at lower ion energies. The experimental angular scans have been well reproduced by Monte Carlo simulations, correlating the steering effects with the close encounter probability at the interface. Consequently, limitations in the determination of the strain state by ion channeling can be overcome by selecting the adequate beam energy.
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61.80.Jh Ion radiation effects
68.65.Ac Multilayers
68.35.Gy Mechanical properties; surface strains
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Degradation of oxide-passivated boron-diffused silicon

Andrew F. Thomson and Keith R. McIntosh

Appl. Phys. Lett. 95, 052101 (2009); http://dx.doi.org/10.1063/1.3195656 (3 pages) | Cited 3 times

Online Publication Date: 3 August 2009

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Recombination in oxide-passivated boron-diffused silicon is found to increase severely at room temperature. The degradation reaction leads to a 45 fold increase in emitter recombination that saturates in ∼ 120 days, irrespective of whether the samples received a forming-gas anneal. The degradation was also examined for diffusions stored at 50, 75, and 100 °C. The results indicate that the degradation follows a second-order reaction where the time constant of one component of the reaction is 10–40 times shorter than the other, and where the activation energy of the fast reaction is 0.19±0.05 eV. Subsequent to degradation, annealing in air reduces the recombination with increasing anneal temperature saturating at ∼ 300 °C to a value that is about four times higher than the predegradation value. A likely cause of this degradation is a reaction of atomic hydrogen at the silicon-oxide-silicon interface.
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81.65.Rv Passivation
66.30.J- Diffusion of impurities
61.72.Cc Kinetics of defect formation and annealing

Quaternary semiconductors with positive crystal field splitting: Potential high-efficiency spin-polarized electron sources

Shiyou Chen, Wan-Jian Yin, Ji-Hui Yang, X. G. Gong, Aron Walsh, and Su-Huai Wei

Appl. Phys. Lett. 95, 052102 (2009); http://dx.doi.org/10.1063/1.3193662 (3 pages) | Cited 3 times

Online Publication Date: 4 August 2009

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Traditional high efficiency spin-polarized electron sources (SPES) consist mainly of binary or pseudobinary zinc-blende GaAs based materials, whereas their ternary analogs II-IV-V2 (II = Zn, Cd, IV = Si, Ge, Sn, and V = As) as well as II-VI ternary analogs I-III-VI2 (I = Cu, Ag, III = Al, Ga, In, and VI = Se) have not drawn wide attention because their crystal field splitting ΔCF near the valence band maximum is either negative or close to zero in their ground state chalcopyrite structure. Using first-principles calculations, we show that some derivative quaternary I-III-II2-VI4 and II-IV-III2-V4 compounds can have coherent ground state stannite or kesterite structures with large and positive ΔCF due to their increased chemical and structural flexibility. We propose that ZnSiAl2As4 and CdGeAl2As4 in the stannite structure, and ZnSnGa2As4 and CuAlCd2Se4 in the kesterite structure could be good candidate SPES materials with high polarization and quantum efficiency.
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72.25.Dc Spin polarized transport in semiconductors
73.20.At Surface states, band structure, electron density of states
71.15.-m Methods of electronic structure calculations
71.70.Ch Crystal and ligand fields
61.50.Ah Theory of crystal structure, crystal symmetry; calculations and modeling

Enhanced transmission through a subwavelength aperture using metamaterials

Atilla Ozgur Cakmak, Koray Aydin, Evrim Colak, Zhaofeng Li, Filiberto Bilotti, Lucio Vegni, and Ekmel Ozbay

Appl. Phys. Lett. 95, 052103 (2009); http://dx.doi.org/10.1063/1.3195074 (3 pages) | Cited 6 times

Online Publication Date: 4 August 2009

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We report an enhanced transmission through a single circular subwavelength aperture that is incorporated with a split ring resonator (SRR) at the microwave regime. Transmission enhancement factors as high as 530 were observed in the experiments when the SRR was located in front of the aperture in order to efficiently couple the electric field component of the incident electromagnetic wave at SRR’s electrical resonance frequency. The experimental results were supported by numerical analyses. The physical origin of the transmission enhancement phenomenon was discussed by examining the induced surface currents on the structures.
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84.40.Az Waveguides, transmission lines, striplines
41.20.Jb Electromagnetic wave propagation; radiowave propagation

Charge carrier concentration and temperature dependent recombination in polymer-fullerene solar cells

A. Foertig, A. Baumann, D. Rauh, V. Dyakonov, and C. Deibel

Appl. Phys. Lett. 95, 052104 (2009); http://dx.doi.org/10.1063/1.3202389 (3 pages) | Cited 24 times

Online Publication Date: 6 August 2009

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We performed temperature dependent transient photovoltage and photocurrent measurements on poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester bulk heterojuction solar cells. We found a strongly charge carrier concentration and temperature dependent Langevin recombination prefactor. The observed recombination mechanism is discussed in terms of bimolecular recombination. The experimental results were compared with charge carrier extraction by linearly increasing voltage measurements done on the same blend system. We explain the charge carrier dynamics, following an apparent order larger than two, by dynamic trapping of charges in the tail states of the Gaussian density of states.
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72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
72.40.+w Photoconduction and photovoltaic effects
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.50.Pz Photoconduction and photovoltaic effects
84.60.Jt Photoelectric conversion

Characteristics of an electroless plated-gate transistor

Li-Yang Chen, Huey-Ing Chen, Chien-Chang Huang, Yi-Wen Huang, Tsung-Han Tsai, Yi-Chun Liu, Tai-You Chen, Shiou-Ying Cheng, and Wen-Chau Liu

Appl. Phys. Lett. 95, 052105 (2009); http://dx.doi.org/10.1063/1.3202404 (3 pages) | Cited 3 times

Online Publication Date: 6 August 2009

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Temperature-dependent characteristics of an interesting pseudomorphic high electron mobility transistor with an electroless plated (EP) gate metal are studied and demonstrated. Under the low-temperature and low-energy electrochemical deposition conditions, the EP deposition technique provides an oxide-free metal-semiconductor interface with the reduction in surface damages. Experimentally, for a 1×100 μm2 gate-dimension EP-device, significant improvements of forward voltage, gate leakage current, Schottky barrier height, ideality factor, transconductance, drain saturation current, and IDS operating regime are found. In addition, good thermal stability of device properties are found as the temperature is increased from 300 to 500 K. Under an accelerated stress test, the studied EP-device also shows better performance over a wide temperature range. Therefore, the studied EP-gate device has a promise for high-performance electronic applications.
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85.30.Tv Field effect devices
81.15.Pq Electrodeposition, electroplating
73.40.Ns Metal-nonmetal contacts
73.30.+y Surface double layers, Schottky barriers, and work functions

Chemical and electronic surface structure of 20%-efficient Cu(In,Ga)Se2 thin film solar cell absorbers

M. Bär, I. Repins, M. A. Contreras, L. Weinhardt, R. Noufi, and C. Heske

Appl. Phys. Lett. 95, 052106 (2009); http://dx.doi.org/10.1063/1.3194153 (3 pages) | Cited 14 times

Online Publication Date: 6 August 2009

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The chemical and electronic surface structure of 20%-efficient Cu(In,Ga)Se2 thin film solar cell absorbers was investigated as a function of deposition process termination (i.e., ending the growth process in absence of either Ga or In). In addition to the expected In (Ga) enrichment, direct and inverse photoemission reveal a decreased Cu surface content and a larger surface band gap for the “In-terminated” absorber.
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71.20.Nr Semiconductor compounds
68.35.bg Semiconductors
84.60.Jt Photoelectric conversion
79.60.Dp Adsorbed layers and thin films

Measurement of the Peltier coefficient of semiconductors by lock-in thermography

Hilmar Straube, Jan-Martin Wagner, and Otwin Breitenstein

Appl. Phys. Lett. 95, 052107 (2009); http://dx.doi.org/10.1063/1.3194156 (3 pages) | Cited 6 times

Online Publication Date: 6 August 2009

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Lock-in thermography is applied to image Joule heating and Peltier-type heat transport separately. Images obtained for a multicrystalline silicon solar cell are quantitatively evaluated using an integration method. The results are interpreted in terms of diffusion and electron/hole drag contributions. The approach presented is especially interesting where the thermal contact resistance to the sample is a problem and where versatility with respect to sample geometry is needed. A further advantage of the method is that it does not need any separate power or temperature calibration.
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07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
72.15.Jf Thermoelectric and thermomagnetic effects
84.60.Jt Photoelectric conversion

Ultrafast dynamics of four-state magnetization reversal in (Ga,Mn)As

Yonggang Zhu, Xinhui Zhang, Tao Li, Xia Huang, Lifen Han, and Jianhua Zhao

Appl. Phys. Lett. 95, 052108 (2009); http://dx.doi.org/10.1063/1.3202395 (3 pages) | Cited 4 times

Online Publication Date: 7 August 2009

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The ultrafast dynamics of in-plane four-state magnetization reversal from compressively strained (Ga,Mn)As film was investigated by magneto-optical Kerr rotation measurement. The magnetization reversal signal was dramatically suppressed upon pumping, and recovered slowly with time evolution. The low switching field Hc1 increased abruptly from 30 to 108 G on the first several picoseconds and recovered back to the value before optical pumping within about 500 ps, whereas the high switching field Hc2 did not change obviously upon pumping, implying a domain-wall nucleation/propagation at low fields and coherent magnetization rotation at high fields in the magnetization reversal process.
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75.70.Ak Magnetic properties of monolayers and thin films
75.50.Pp Magnetic semiconductors
75.60.Jk Magnetization reversal mechanisms
78.20.Ls Magneto-optical effects
75.60.Ch Domain walls and domain structure
78.47.J- Ultrafast spectroscopy (<1 psec)
78.66.Fd III-V semiconductors

Charge trap memory characteristics of AlOx shell-Al core nanoparticles embedded in HfO2 gate oxide matrix

Jun Seok Lee, Jung Yup Yang, and Jin Pyo Hong

Appl. Phys. Lett. 95, 052109 (2009); http://dx.doi.org/10.1063/1.3202412 (3 pages) | Cited 5 times

Online Publication Date: 7 August 2009

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The memory behavior of natively oxidized AlOx shell-Al nanoparticles (NPs) in a metal oxide semiconductor (MOS) structure was investigated. Transmission electron microscopy images clearly demonstrate the formation of an AlOx shell (thicknesses of 1–1.5 nm), surrounding Al (sizes of 5–7 nm) core NPs in the MOS structure. Electrical measurements exhibited a memory window of 3.6 V, together with a promising charge retention time of about 10 years. A possible band model needed for enhanced retention characteristics was given by considering the electron/hole barrier width and the additional interface states through the AlOx shell as a method of tunneling barrier engineering.
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61.46.Df Structure of nanocrystals and nanoparticles ("colloidal" quantum dots but not gate-isolated embedded quantum dots)
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.40.Gk Tunneling
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping
73.63.Bd Nanocrystalline materials

Direct detection of grain boundary scattering in damascene Cu wires by nanoscale four-point probe resistance measurements

Yusuke Kitaoka, Takeshi Tono, Shinya Yoshimoto, Toru Hirahara, Shuji Hasegawa, and Takayuki Ohba

Appl. Phys. Lett. 95, 052110 (2009); http://dx.doi.org/10.1063/1.3202418 (3 pages) | Cited 14 times

Online Publication Date: 7 August 2009

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Four-terminal conductivity measurements of damascene copper (Cu) wires with various widths have been performed using platinum-coated carbon nanotube (CNT) tips in a four-tip scanning tunneling microscope. Using CNT tips enabled the probe spacing to be reduced to 70 nm, which is the shortest probe spacing in interconnect wire measurements achieved so far. The measured resistivity of Cu increased as the line width decreased and direct evidence of individual grain boundary scattering was observed when the probe spacing was varied on a scale comparable to the grain size of the Cu wires ( ∼ 200 nm).
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73.63.Nm Quantum wires
61.72.Mm Grain and twin boundaries

Origin and suppression of V-shaped defects in the capping of self-assembled InAs quantum dots on graded Si1−xGex/Si substrate

H. Tanoto, S. F. Yoon, T. K. Ng, C. Y. Ngo, C. Dohrman, E. A. Fitzgerald, L. H. Tan, and C. H. Tung

Appl. Phys. Lett. 95, 052111 (2009); http://dx.doi.org/10.1063/1.3189086 (3 pages) | Cited 3 times

Online Publication Date: 7 August 2009

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Self-assembled InAs quantum dots (QDs) on graded Si1−xGex/Si substrate were observed to adopt a truncated pyramidal shape when capped with GaAs. Our results suggest that atomic migration from the QD apex to the GaAs cap layer contributes to the formation of the symmetrical V-shaped defects near the top edges of the truncated pyramidal QDs. By employing an In0.1Ga0.9As cap, material migration and strain around the QDs were reduced, hence suppressing the occurrence of the V-shaped defects. Furthermore, photoluminescence thermal quenching rate of the QDs is significantly slower compared to the QDs with GaAs cap. Finally, 1.3 μm room-temperature photoluminescence was observed.
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81.07.Ta Quantum dots
81.05.Ea III-V semiconductors
81.16.Dn Self-assembly
68.65.Hb Quantum dots (patterned in quantum wells)
78.67.Hc Quantum dots
78.55.Cr III-V semiconductors

Enhancement of carrier transport properties of BixSb2−xTe3 compounds by electrical sintering process

Chien-Neng Liao and Li-Chieh Wu

Appl. Phys. Lett. 95, 052112 (2009); http://dx.doi.org/10.1063/1.3196315 (3 pages) | Cited 4 times

Online Publication Date: 7 August 2009

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BixSb2−xTe3 (x = 0.4 and 0.5) powders were pressed and sintered by passing a high-density electric current under nitrogen ambient. The electrically sintered BixSb2−xTe3 was found to have a marked increase in Hall mobility but a moderate reduction in carrier density. We propose that electric-current induced atomic diffusion plays an important role in modulating crystal defects in BixSb2−xTe3 compounds. The hot-pressed Bi0.4Sb1.6Te3 shows a threefold increase in ZT after electrical sintering process. With the electrical sintering approach we can preserve fine-grain microstructure, and hence low thermal conductivity of BixSb2−xTe3 with reasonable electrical resistivity and Seebeck coefficient.
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72.20.My Galvanomagnetic and other magnetotransport effects
72.80.Sk Insulators
72.20.Pa Thermoelectric and thermomagnetic effects
61.72.J- Point defects and defect clusters
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
61.43.Gt Powders, porous materials
66.70.Lm Other systems such as ionic crystals, molecular crystals, nanotubes, etc.
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Magnetoelectric effect at the SrRuO3/BaTiO3 (001) interface: An ab initio study

Manish K. Niranjan, J. D. Burton, J. P. Velev, S. S. Jaswal, and E. Y. Tsymbal

Appl. Phys. Lett. 95, 052501 (2009); http://dx.doi.org/10.1063/1.3193679 (3 pages) | Cited 25 times

Online Publication Date: 3 August 2009

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Ferromagnet/ferroelectric interface materials have emerged as structures with strong magnetoelectric coupling that may exist due to unconventional physical mechanisms. Here we present a first-principles study of the magnetoelectric effect at the ferromagnet/ferroelectric SrRuO3/BaTiO3 (001) interface. We find that the exchange splitting of the spin-polarized band structure, and therefore the magnetization, at the interface can be altered substantially by reversal of the ferroelectric polarization in the BaTiO3. These magnetoelectric effects originate from the screening of polarization charges at the SrRuO3/BaTiO3 interface and are consistent with the Stoner model for itinerant magnetism.
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75.80.+q Magnetomechanical effects, magnetostriction
75.50.Dd Nonmetallic ferromagnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
72.25.Mk Spin transport through interfaces
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.10.Lp Band and itinerant models
77.22.Ej Polarization and depolarization

Photovoltaic effect in the La0.67Ca0.33MnO3/LaMnO3/SrTiO3:Nb heterojunctions with variant LaMnO3 layers

A. D. Wei, J. R. Sun, W. M. Lü, and B. G. Shen

Appl. Phys. Lett. 95, 052502 (2009); http://dx.doi.org/10.1063/1.3194776 (3 pages) | Cited 4 times

Online Publication Date: 3 August 2009

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Influence of LaMnO3 layer, 0–12 nm in thickness, on photovoltaic effect (PVE) has been experimentally studied for the La0.67Ca0.33MnO3/LaMnO3/SrTiO3:Nb junction. Presence of LaMnO3 causes an obvious weakening of the PVE, demonstrated by the reduction in the carrier density excited by each photon. The interfacial barrier deduced from the PVE shows a rapid growth, from ∼ 1.22 to ∼ 1.45 eV, as the layer thickness increases from 0 to 2 nm, and saturates at ∼ 1.5 eV above 2 nm. On the contrary, current-voltage characteristics suggest a smooth reduction in interfacial barrier with layer thickness. These results can be quantitatively understood assuming the occurrence of a notch and a spike in the conduction band edges at the interface of the junction.
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73.50.Pz Photoconduction and photovoltaic effects
73.40.-c Electronic transport in interface structures
73.20.At Surface states, band structure, electron density of states
73.61.Ng Insulators

Periodicity in Al/Ti superconducting single electron transistors

Sarah J. MacLeod, Sergey Kafanov, and Jukka P. Pekola

Appl. Phys. Lett. 95, 052503 (2009); http://dx.doi.org/10.1063/1.3194777 (3 pages)

Online Publication Date: 3 August 2009

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We present experiments on single Cooper-pair transistors made of two different superconducting materials. We chose Ti and Al to create an energy gap profile such that the island has a higher gap than the leads, thereby acting as a barrier to quasiparticle tunneling. Our transport measurements demonstrate that quasiparticle poisoning is suppressed in all our TiAlTi structures (higher gap for the island) with clear 2e periodicity observed, whereas full quasiparticle poisoning is observed in all AlTiAl devices (higher gap for the leads) with e periodicity.
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85.35.Gv Single electron devices
74.70.-b Superconducting materials other than cuprates
71.20.-b Electron density of states and band structure of crystalline solids

Enhanced superconducting transition temperature in FeSe0.5Te0.5 thin films

Weidong Si, Zhi-Wei Lin, Qing Jie, Wei-Guo Yin, Juan Zhou, Genda Gu, P. D. Johnson, and Qiang Li

Appl. Phys. Lett. 95, 052504 (2009); http://dx.doi.org/10.1063/1.3195076 (3 pages) | Cited 34 times

Online Publication Date: 3 August 2009

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We report magnetoresistive and structural measurements of superconducting FeSe0.5Te0.5 epitaxial thin films grown by pulsed laser deposition. Enhanced onset superconducting transition temperature ( ∼ 17 K) is observed in some of these films. Structural analysis by x-ray diffraction and high resolution transmission electron microscopy reveal that these films generally have significantly shorter out-of-plane lattice constant c than the bulk value, suggesting that the out-of-plane changes have a dominating impact on the superconducting transition in iron-based superconductors. Our data also indicate that the upper critical field Hc2(0) of those films may reach as high as 50 T.
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74.62.Bf Effects of material synthesis, crystal structure, and chemical composition
74.78.-w Superconducting films and low-dimensional structures
74.25.Ha Magnetic properties including vortex structures and related phenomena
81.15.Fg Pulsed laser ablation deposition
61.66.Fn Inorganic compounds

A superconducting transistorlike device having good input-output isolation.

I. P. Nevirkovets

Appl. Phys. Lett. 95, 052505 (2009); http://dx.doi.org/10.1063/1.3189283 (3 pages) | Cited 2 times

Online Publication Date: 3 August 2009

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A multiterminal superconducting device with the S1IS2FIS3 structure (where S, I, and F denote a superconductor, an insulator, and a ferromagnetic material) is fabricated and characterized. Introducing a thin ferromagnetic layer into the middle electrode dramatically reduces parasitic back action of the acceptor junction (S1IS2) bias current on the injector junction (S2FIS3) current-voltage characteristic as compared with that for the formerly reported quiteron, a device exploiting similar operation principle.
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85.25.Cp Josephson devices
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