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24 Dec 2007

Volume 91, Issue 26, Articles (26xxxx)

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Appl. Phys. Lett. 91, 261106 (2007); http://dx.doi.org/10.1063/1.2825578 (3 pages)

W. M. Zhu, T. Zhong, A. Q. Liu, X. M. Zhang, and M. Yu
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Tuning the crystal structure and magnetic properties of Fe doped In2O3 nanocrystals

Dewei Chu, Yu-Ping Zeng, Dongliang Jiang, and Zhongming Ren

Appl. Phys. Lett. 91, 262503 (2007); http://dx.doi.org/10.1063/1.2815661 (3 pages) | Cited 13 times

Online Publication Date: 26 December 2007

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Fe doped In2O3 nanocrystals were synthesized by a coprecipitation method under external magnetic fields. X-ray diffraction data and high-resolution transmission electron microscopy analyses indicated the formation of single phase without any parasitic phases. The crystal structure of the nanocrystals is tuned by changing Fe concentrations and intensities of magnetic fields. Room temperature ferromagnetism in Fe doped In2O3 nanocrystals can be activated by suitable magnetic fields.
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61.46.Hk Nanocrystals
61.66.Fn Inorganic compounds
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Tt Fine-particle systems; nanocrystalline materials
81.16.-c Methods of micro- and nanofabrication and processing

Electrical spin injection into the InAs/GaAs wetting layer

C. H. Li, G. Kioseoglou, A. T. Hanbicki, R. Goswami, C. S. Hellberg, B. T. Jonker, M. Yasar, and A. Petrou

Appl. Phys. Lett. 91, 262504 (2007); http://dx.doi.org/10.1063/1.2827585 (3 pages) | Cited 4 times

Online Publication Date: 26 December 2007

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We have used transport measurements, transmission electron microscopy, and polarization dependent photo- and electroluminescence to characterize the InAs/GaAs(001) wetting layer (WL) system. Transport data confirm formation of a two-dimensional electron gas in modulation-doped structures. The optical pumping of the WL in an undoped structure provides a ratio of radiative to spin lifetime (τr/τs) ∼ 1, which is constant over the measurement range of 10–100 K. We demonstrate efficient spin injection from an Fe Schottky tunnel contact into the WL, and achieve an electron spin polarization of ∼ 55% from 5 to 50 K, which decreases monotonically with increasing temperature.
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73.40.Ns Metal-nonmetal contacts
72.25.Dc Spin polarized transport in semiconductors
72.25.Mk Spin transport through interfaces
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.60.Fi Electroluminescence
78.55.Cr III-V semiconductors

Exchange bias in self-organized Nd0.5Sr0.5MnO3 bilayer film

Y. H. Hyun, S. Y. Park, Y. P. Lee, V. G. Prokhorov, and V. L. Svetchnikov

Appl. Phys. Lett. 91, 262505 (2007); http://dx.doi.org/10.1063/1.2825418 (3 pages) | Cited 4 times

Online Publication Date: 26 December 2007

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The self-organized Nd0.5Sr0.5MnO3 bilayer film with a homogeneous chemical composition and different microstructures has been prepared by rf-magnetron sputtering. The top layer of the film has a columnlike nanostructure while the bottom one forms an epitaxial crystal structure. The magnetic properties of the film mimic the behavior of superparamagnetic particles grown onto the ferromagnetic layer. An exchange-bias effect was observed at a temperature below the blocking one, even in the present ferromagnetic hybrid system.
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75.30.Et Exchange and superexchange interactions
75.50.Dd Nonmetallic ferromagnetic materials
75.70.Ak Magnetic properties of monolayers and thin films

A universal relation between resistivity and magnetization in paramagnetic state of manganites

J. Z. Wang, J. R. Sun, G. J. Liu, F. X. Hu, T. Y. Zhao, and B. G. Shen

Appl. Phys. Lett. 91, 262506 (2007); http://dx.doi.org/10.1063/1.2825473 (3 pages) | Cited 2 times

Online Publication Date: 26 December 2007

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A systematic study on the resistivity-magnetization relation above the Curie temperature (TC) has been performed for the manganites with different properties, such as the epitaxial La0.67Ca0.33MnO3 film on a SrTiO3 substrate, which has the weakest magnetic correlation above TC, the La0.27Nd0.4Ca0.33MnO3 polycrystalline, which exhibits a charge ordering in the paramagnetic state, and the ceramics Eu0.55Sr0.45MnO3 and La0.474Bi0.193Ca0.33Mn0.994Cr0.006O3, which show strong short-range magnetic orders above TC. A quantitative, yet universal, relation of the form ρ = AT exp[(ε-αm2)/T] is observed in all of the manganites, with an essentially constant coefficient of α ≈ 800±60 K, where m is the normalized magnetization and ε is the activation energy for polarons. The underlying physics for this relation has been analyzed based on the double exchange model.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
73.61.Ng Insulators
75.20.Ck Nonmetals
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.70.Ak Magnetic properties of monolayers and thin films

A nuclear magnetic resonance spectrometer for operation around 1 MHz with a sub-10-mK noise temperature, based on a two-stage dc superconducting quantum interference device sensor

L. V. Levitin, R. G. Bennett, A. Casey, B. P. Cowan, C. P. Lusher, J. Saunders, D. Drung, and Th. Schurig

Appl. Phys. Lett. 91, 262507 (2007); http://dx.doi.org/10.1063/1.2828113 (3 pages) | Cited 3 times

Online Publication Date: 26 December 2007

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We have developed a nuclear magnetic resonance spectrometer with a series tuned input circuit for measurements on samples at millikelvin temperatures based on an integrated two-stage superconducting quantum interference device current sensor, with an energy sensitivity ε = 26±1h when operated at 1.4 K. To maximize the sensitivity, both the nuclear magnetic resonance spectrometer pickup coil and tuning capacitor need to be cooled, and the tank circuit parameters should be chosen to equalize the contributions from circulating current noise and voltage noise in the superconducting quantum interference device. A noise temperature TN = 7±2 mK was measured, at a frequency of 0.884 MHz, with the circuit parameters close to optimum.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.71.Ba Superconducting magnets; magnetic levitation devices
84.32.Tt Capacitors

Improving the IcRn product and the reproducibility of high Tc Josephson junctions made by ion irradiation

M. Sirena, X. Fabrèges, N. Bergeal, J. Lesueur, G. Faini, R. Bernard, and J. Briatico

Appl. Phys. Lett. 91, 262508 (2007); http://dx.doi.org/10.1063/1.2828133 (3 pages) | Cited 1 time

Online Publication Date: 26 December 2007

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A simple model has been proposed to explain the spread in the characteristics of high Tc Josephson junctions made by ion irradiation, assuming that the source of dispersion is the slit’s size variation. Accordingly, increasing ion energy should lead to a significant reduction of inhomogeneities. Test samples have been fabricated using two different beam energies. As predicted, the spread in critical current decreases upon increasing energy. Moreover, since the actual width of the barrier is reduced in this case, the IcRn product increases significantly. These results seem promising for future technological applications.
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74.81.Fa Josephson junction arrays and wire networks
85.25.-j Superconducting devices
74.72.-h Cuprate superconductors
61.80.Jh Ion radiation effects
74.25.Sv Critical currents

A cascade switching superconducting single photon detector

M. Ejrnaes, R. Cristiano, O. Quaranta, S. Pagano, A. Gaggero, F. Mattioli, R. Leoni, B. Voronov, and G. Gol’tsman

Appl. Phys. Lett. 91, 262509 (2007); http://dx.doi.org/10.1063/1.2828138 (3 pages) | Cited 39 times

Online Publication Date: 26 December 2007

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We have realized superconducting single photon detectors with reduced inductance and increased signal pulse amplitude. The detectors are based on a parallel connection of ultrathin NbN nanowires with a common bias inductance. When properly biased, an absorbed photon induces a cascade switch of all the parallel wires generating a signal pulse amplitude of 2 mV. The parallel wire configuration lowers the detector inductance and reduces the response time well below 1 ns.
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85.25.Pb Superconducting infrared, submillimeter and millimeter wave detectors
85.25.Oj Superconducting optical, X-ray, and γ-ray detectors (SIS, NIS, transition edge)
81.07.-b Nanoscale materials and structures: fabrication and characterization
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Magnetization dynamics in planar spin transfer devices and stabilization by repulsion in a spin-flip transistor

Ya. B. Bazaliy

Appl. Phys. Lett. 91, 262510 (2007); http://dx.doi.org/10.1063/1.2822407 (3 pages) | Cited 2 times

Online Publication Date: 27 December 2007

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In systems with dominating easy-plane anisotropy, magnetization dynamics is governed by effective one dimensional equation for the in-plane angle. Rederiving this equation in the presence of spin torques, we obtain a convenient and intuitive description of spin transfer devices. In the case of a spin-flip transistor, the method provides a surprising prediction: the device can be stabilized in the (normally unstable) energy saddle point by a spin torque repelling from that point. Stabilization by repulsion happens due to the presence of dissipative environment and requires a Gilbert damping constant that is large enough to ensure overdamped dynamics at zero current.
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75.30.Gw Magnetic anisotropy
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.25.-b Spin polarized transport
85.75.-d Magnetoelectronics; spintronics: devices exploiting spin polarized transport or integrated magnetic fields

Peculiarities of the extraordinary Hall effect of planar arrays Fe nanoparticles embedded in an ultrathin Pt film

V. T. Volkov, V. I. Levashov, V. N. Matveev, and V. A. Berezin

Appl. Phys. Lett. 91, 262511 (2007); http://dx.doi.org/10.1063/1.2827174 (3 pages) | Cited 2 times

Online Publication Date: 27 December 2007

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The extraordinary Hall effect was investigated for planar arrays Fe nanoparticles embedded in an ultrathin Pt matrix. It was found that the slope of Hall resistance (RH) reversed sign at ±0.15 T for Fe particles of mean thickness 0.3 nm. The dependence is presumably due to the effect of two spin-orbital induced mechanisms of carriers scattering, skew scattering, and side jump, with the skew component of positive sign and the side jump component of negative sign. For Fe samples, 0.6 nm thick RH increases monotonically with the magnetic field value. At low temperatures, the superparamagnetism of the samples disappeared.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
75.50.Tt Fine-particle systems; nanocrystalline materials
71.70.Ej Spin-orbit coupling, Zeeman and Stark splitting, Jahn-Teller effect

Tuning the perpendicular magnetic anisotropy in tetragonally distorted FexCo1−x alloy films on Rh (001) by varying the alloy composition

F. Luo, X. L. Fu, A. Winkelmann, and M. Przybylski

Appl. Phys. Lett. 91, 262512 (2007); http://dx.doi.org/10.1063/1.2821370 (3 pages) | Cited 8 times

Online Publication Date: 27 December 2007

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Tetragonally distorted FexCo1−x alloy films are grown on Rh (001) showing a strong perpendicular magnetic anisotropy in a wide thickness and composition range. This large perpendicular magnetic anisotropy is chemical composition dependent and reaches a maximum at x = 0.4. For this composition, we observed an out-of-plane easy axis of magnetization at room temperature with film thickness up to 15 ML. Our experiments show that the proper adjustment of the Fermi level (EF) by the variation of the FexCo1−x alloy composition and the corresponding tetragonal distortion results in a large perpendicular magnetic anisotropy.
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75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy
71.20.Gj Other metals and alloys

Electron holography study of the temperature variation of the magnetic order parameter within circularly chained nickel nanoparticle rings

Akira Sugawara, Kei-ichi Fukunaga, M. R. Scheinfein, H. Kobayashi, H. Kitagawa, and A. Tonomura

Appl. Phys. Lett. 91, 262513 (2007); http://dx.doi.org/10.1063/1.2827586 (3 pages) | Cited 4 times

Online Publication Date: 27 December 2007

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The magnetic structure within circular chains composed of 30-nm-diameter, polymer-coated nickel particles was studied by electron holography. The magnetic flux closure due to dipolar coupling was confirmed at zero external magnetic field. Its long-range order parameter was determined from the magnitude of the electron phase shift, and it was found to decrease more rapidly than that of bulk nickel as a function of temperature. The results of Monte Carlo simulations indicated that the temperature variation of the order-parameter was explained in terms of weakened dipolar coupling field ascribed to the decay of the bulk magnetization and enhanced thermal fluctuations.
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75.75.-c Magnetic properties of nanostructures
75.50.Tt Fine-particle systems; nanocrystalline materials
75.40.Mg Numerical simulation studies
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.05.Bx Metals, semimetals, and alloys

Electronic structure of Fe-doped In2O3 magnetic semiconductor with oxygen vacancies: Evidence for F-center mediated exchange interaction

Shu-jun Hu, Shi-shen Yan, Xue-ling Lin, Xin-xin Yao, Yan-xue Chen, Guo-lei Liu, and Liang-mo Mei

Appl. Phys. Lett. 91, 262514 (2007); http://dx.doi.org/10.1063/1.2828041 (3 pages) | Cited 20 times

Online Publication Date: 27 December 2007

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Based on the first-principles calculations, the electronic structure and magnetic properties of Fe-doped In2O3 were theoretically investigated. The presence of the predominating defects in oxide, i.e., oxygen vacancies, can lead to strong ferromagnetic coupling between the nearest neighboring Fe cations. Spin density and band-projected charge distribution in the vicinity of the oxygen vacancies reveal that the ferromagnetic exchange is mediated by the donor impurity state, which mainly consists of Fe:3d and Fe:4s electrons trapped in oxygen vacancies. Such results provide direct evidence for the F-center mediated exchange interaction in oxide-based magnetic semiconductors.
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75.50.Pp Magnetic semiconductors
71.20.Ps Other inorganic compounds
75.30.Et Exchange and superexchange interactions
71.15.-m Methods of electronic structure calculations
75.50.Dd Nonmetallic ferromagnetic materials

Electronic transport and magnetoresistance in ultrathin manganite-titanate junctions

Y. W. Xie, J. R. Sun, Y. N. Han, and B. G. Shen

Appl. Phys. Lett. 91, 262515 (2007); http://dx.doi.org/10.1063/1.2828135 (3 pages) | Cited 3 times

Online Publication Date: 28 December 2007

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We present a systematic study on the rectifying behaviors of the heterojunctions composed of a ultrathin La0.67Sr0.33MnO3 film ( ∼ 2 nm in thickness) and a SrTiO3 substrate doped by 0.05 or 1 wt % Nb. These junctions exhibit excellent rectifying behaviors and a remarkable bias-dependent magnetoresistance (up to 60% under a field of 5 T). The transport behaviors are dominated by thermal process and tunneling process for the junctions with low and high Nb contents, respectively.
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75.70.-i Magnetic properties of thin films, surfaces, and interfaces
72.20.My Galvanomagnetic and other magnetotransport effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
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Hydrogen in Si(100)–SiO2–HfO2 gate stacks: Relevant charge states and their location

Julien Godet, Peter Broqvist, and Alfredo Pasquarello

Appl. Phys. Lett. 91, 262901 (2007); http://dx.doi.org/10.1063/1.2828027 (3 pages) | Cited 11 times

Online Publication Date: 26 December 2007

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Using a density functional approach, we study the energetics of various charged hydrogen states in the Si(100)–SiO2–HfO2 gate stack. We describe the SiO2–HfO2 transition region through model structures of amorphous hafnium silicate HfxSi1−xO2 with different Hf contents x. Hydrogen is found to be amphoteric with a +/− charge transition level lying close to the Si conduction band minimum. This implies that protons are the most stable form of hydrogen for most electron chemical potentials in the Si band gap. Formation energies of the positively charged state across the Si(100)–SiO2–HfO2 stack indicate that protons mainly locate in the Si–SiO2 or SiO2–HfO2 transition regions.
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71.15.Mb Density functional theory, local density approximation, gradient and other corrections
71.20.Ps Other inorganic compounds
73.20.At Surface states, band structure, electron density of states

Analysis of crystallographic evolution in (Na,K)NbO3-based lead-free piezoceramics by x-ray diffraction

Ke Wang and Jing-Feng Li

Appl. Phys. Lett. 91, 262902 (2007); http://dx.doi.org/10.1063/1.2825280 (3 pages) | Cited 33 times

Online Publication Date: 28 December 2007

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The crystallographic structure of (Na,K)NbO3-based compounds and phase transitional behavior in (1−x)(K0.5Na0.5)NbO3–xLiNbO3 (x = 0, 3, 6, and 8 mol %) ceramics were accurately determined using high resolution x-ray diffraction (XRD). The phase transition between orthorhombic and tetragonal was distinctly characterized focusing on the XRD peak changes in {222} and {400} diffraction planes, by which lattice parameters of the perovskite type subcell, a, b, and c as well as angle β can be calculated. The discontinuous change in angle β at x = 6 mol % is located at the phase transitional region, where enhanced piezoelectric constant d33 = 215 pC/N was obtained. The present study provides a precise as well as simple method to investigate crystallographic structures in (Na,K)NbO3-based ceramics.
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61.66.Fn Inorganic compounds
81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.65.Bn Piezoelectric and electrostrictive constants

Investigation on switching kinetics in epitaxial Pb(Zr0.2Ti0.8)O3 ferroelectric thin films: Role of the 90° domain walls

Wei Li and Marin Alexe

Appl. Phys. Lett. 91, 262903 (2007); http://dx.doi.org/10.1063/1.2825414 (3 pages) | Cited 22 times

Online Publication Date: 28 December 2007

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Ferroelectric switching behavior of single-crystal-like epitaxial Pb(Zr0.2Ti0.8)O3 thin films with different densities of 90° domain walls was investigated under various applied fields. It was found that the saturated switchable polarization of about 170 μC/cm2 did not vary with applied field in the films with low density or no 90° domain walls and obeys Kolmogorov-Avrami-Ishibashi theory. The presence of the 90° domain walls inhibits the motion of 180° domain walls, contributing to the change of the switching kinetics to nucleation-limited-switching model.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Fm Switching phenomena
77.80.Dj Domain structure; hysteresis
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
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Low temperature grown carbon nanotube interconnects using inner shells by chemical mechanical polishing

Daisuke Yokoyama, Takayuki Iwasaki, Tsuyoshi Yoshida, Hiroshi Kawarada, Shintaro Sato, Takashi Hyakushima, Mizuhisa Nihei, and Yuji Awano

Appl. Phys. Lett. 91, 263101 (2007); http://dx.doi.org/10.1063/1.2824390 (3 pages) | Cited 35 times

Online Publication Date: 26 December 2007

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Vertically aligned multiwalled carbon nanotubes (MWCNTs) were synthesized by remote plasma chemical vapor deposition at a low temperature of 390 °C, which meets the requirement of the large scale integration (LSI) process. For wiring application, we measured the electrical properties of MWCNT-via structures with and without chemical mechanical polishing (CMP). The via resistances were reduced using inner shells of MWCNTs whose caps were opened due to CMP. The improved resistance after annealing at 400 °C was 0.6 Ω for 2 μm vias. Our process is suitable for LSI because the temperature never exceeds the allowable temperature of 400 °C in the Si LSI process.
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85.40.Ls Metallization, contacts, interconnects; device isolation
85.40.Sz Deposition technology
85.35.Kt Nanotube devices

Confocal microscope photoluminescence and electrical characteristics of single poly(3-hexylthiophene) nanowire strand

Seok Ho Lee, Dong Hyuk Park, Kihyun Kim, Jinsoo Joo, Dae-Chul Kim, Hyun-Jun Kim, and Jeongyong Kim

Appl. Phys. Lett. 91, 263102 (2007); http://dx.doi.org/10.1063/1.2824460 (3 pages) | Cited 8 times

Online Publication Date: 26 December 2007

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The photoluminescence (PL) spectra and images of a single strand of poly(3-hexylthiophene) (P3HT) nanowires with different doping states were compared by means of a laser confocal microscope with a high spatial resolution. The P3HT nanowires were electrochemically synthesized by using an ionic liquid as a dopant. From the ultraviolet and visible absorption spectra, the doping and dedoping effects of the P3HT nanowires through the treatment of organic solvent were investigated. The electrical conductivity of the single strand of the lightly doped P3HT nanowires was estimated to be ∼ 3.5×10−3 S/cm, which was higher than that ( ∼ 5.4×10−5 S/cm) of the dedoped one. From the laser confocal microscope PL experiments, we quantitatively observed more homogeneous and three to eight times brighter light emission from the single strand of the dedoped P3HT nanowires.
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78.55.Kz Solid organic materials
78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
73.63.-b Electronic transport in nanoscale materials and structures
78.40.Me Organic compounds and polymers

Optical investigation of type II GaSb/GaAs self-assembled quantum dots

Diego Alonso-Álvarez, Benito Alén, Jorge M. García, and José M. Ripalda

Appl. Phys. Lett. 91, 263103 (2007); http://dx.doi.org/10.1063/1.2827582 (3 pages) | Cited 24 times

Online Publication Date: 26 December 2007

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We have studied the emission and absorption properties of type II GaSb/GaAs quantum dots embedded in a p-i-n photodiode. The excitation power evolution provides clear signatures of the spatially separated confinement of electrons and holes in these nanostructures. We have estimated the confinement potential for the holes to be ∼ 500 meV, leading to an intense room temperature emission assisted by recapture processes from the wetting layer. Photocurrent measurements show strong absorption in the wetting layer and in the quantum dots at room temperature which are important for photodetection applications based in this system.
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78.55.Cr III-V semiconductors
78.67.Hc Quantum dots
81.16.Dn Self-assembly
73.63.Kv Quantum dots
73.50.Pz Photoconduction and photovoltaic effects

Polarization and temperature dependence of photoluminescence from zincblende and wurtzite InP nanowires

A. Mishra, L. V. Titova, T. B. Hoang, H. E. Jackson, L. M. Smith, J. M. Yarrison-Rice, Y. Kim, H. J. Joyce, Q. Gao, H. H. Tan, and C. Jagadish

Appl. Phys. Lett. 91, 263104 (2007); http://dx.doi.org/10.1063/1.2828034 (3 pages) | Cited 43 times

Online Publication Date: 26 December 2007

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We use polarization-resolved and temperature-dependent photoluminescence of single zincblende (ZB) (cubic) and wurtzite (WZ) (hexagonal) InP nanowires to probe differences in selection rules and bandgaps between these two semiconductor nanostructures. The WZ nanowires exhibit a bandgap 80 meV higher in energy than the ZB nanowires. The temperature dependence of the PL is similar but not identical for the WZ and ZB nanowires. We find that ZB nanowires exhibit strong polarization parallel to the nanowire axis, while the WZ nanowires exhibit polarized emission perpendicular to the nanowire axis. This behavior is interpreted in terms of the different selection rules for WZ and ZB crystal structures.
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81.07.Vb Quantum wires
81.05.Ea III-V semiconductors
78.67.Lt Quantum wires
78.55.Cr III-V semiconductors

Incorporation of Sb in InAs/GaAs quantum dots

S. I. Molina, A. M. Sánchez, A. M. Beltrán, D. L. Sales, T. Ben, M. F. Chisholm, M. Varela, S. J. Pennycook, P. L. Galindo, A. J. Papworth, P. J. Goodhew, and J. M. Ripalda

Appl. Phys. Lett. 91, 263105 (2007); http://dx.doi.org/10.1063/1.2826546 (3 pages) | Cited 12 times

Online Publication Date: 27 December 2007

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The formation of a quaternary InGaAsSb alloy is shown to occur in the core of epitaxial GaSb capped InAs/GaAs quantum dots emitting at 1.3 μm. The existence of the four constituent elements is demonstrated by using spatially resolved low-loss electron energy loss spectroscopy and aberration-corrected high angle annular dark field scanning transmission electron microscopy. The intermixing process giving rise to the formation of this quaternary alloy takes place despite the large miscibility gap between InAs and GaSb binary compounds, and is probably driven by the existence of strain in the quantum dots.
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79.20.Uv Electron energy loss spectroscopy
68.65.Hb Quantum dots (patterned in quantum wells)

Self-assembly of silicide quantum dot arrays on stepped silicon surfaces by reactive epitaxy

L. Fernández, M. Löffler, J. Cordón, and J. E. Ortega

Appl. Phys. Lett. 91, 263106 (2007); http://dx.doi.org/10.1063/1.2828036 (3 pages) | Cited 5 times

Online Publication Date: 27 December 2007

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Reactive epitaxy of Co on vicinal Si(111) surfaces is found to be a flexible and a convenient method for the preparation of dense arrays of Co silicide quantum dots. In the present work, submonolayer amounts of Co were deposited at 800 K on vicinal and flat Si surfaces, analyzing the resulting structures by scanning tunneling microscopy. On vicinal Si(111) surfaces with relatively narrow ( ∼ 40–100 Å) terrace width, such reactive epitaxy leads to self-assembled arrays of CoSi2 quantum dots with a sharp size distribution function. In contrast, the growth of Co on flat Si(111) results in an inhomogeneous array of dots mixed with a variety of silicide phases.
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68.65.Hb Quantum dots (patterned in quantum wells)
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Stress-induced band gap tuning in ⟨112⟩ silicon nanowires

A. J. Lu, R. Q. Zhang, and S. T. Lee

Appl. Phys. Lett. 91, 263107 (2007); http://dx.doi.org/10.1063/1.2826267 (3 pages) | Cited 14 times

Online Publication Date: 28 December 2007

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We show via density functional calculations that the electronic band structures of ⟨112⟩-oriented hydrogenated silicon nanowires (SiNWs) could be significantly altered by axial stresses. In particular, an axial compression could cause an indirect-to-direct band gap transition in ⟨112⟩ SiNWs. As direct energy band may induce strong light-emission properties of Si, the possibility of indirect-to-direct band transition via axial stress has fundamental implications in exploiting SiNWs for optoelectronic applications.
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73.21.Hb Quantum wires
71.20.Mq Elemental semiconductors
71.15.Mb Density functional theory, local density approximation, gradient and other corrections

Piezoresponse imaging of lead zirconate titanate microfibers and numerical analysis of its electric field distribution

Yu Wang and Jorge Santiago-Avilés

Appl. Phys. Lett. 91, 263108 (2007); http://dx.doi.org/10.1063/1.2827564 (3 pages) | Cited 1 time

Online Publication Date: 28 December 2007

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Piezoresponse imaging technique was transplanted from thin film to probe polarization domains and local properties in single electrospun lead zirconate titanate microfibers. The corresponding electric field distribution was numerically analyzed. The biased conic tip is found to produce a field that peaks on its apex and decreases rapidly toward the bottom metal electrode. A strong field exists only in a thin surface region and cannot pole the affected domain even with its magnitude of 108 V/m on the fiber surface.
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77.80.-e Ferroelectricity and antiferroelectricity
77.55.-g Dielectric thin films
77.22.Ej Polarization and depolarization
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Realization of n-Zn1−xMgxO/i-ZnO/SiOx/n+-Si heterostructured n-i-n light-emitting diodes by low-cost ultrasonic spray pyrolysis

J. L. Zhao, X. W. Sun, S. T. Tan, G. Q. Lo, D. L. Kwong, and Z. H. Cen

Appl. Phys. Lett. 91, 263501 (2007); http://dx.doi.org/10.1063/1.2824813 (3 pages) | Cited 12 times

Online Publication Date: 27 December 2007

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Show Abstract
n-Zn1−xMgxO/i-ZnO/SiOx/n+-Si heterostructured light-emitting diodes have been demonstrated by low-cost ultrasonic spray pyrolysis. The current-voltage measurement shows typical characteristics of a back-to-back diode due to the double Schottky barriers induced by the SiOx layer. Blue electroluminescence peaking at 460 nm was observed at room temperature when a positive bias of ∼ 4 V was applied on the Si substrate. The electroluminescence is suggested to be dominated by the donor-acceptor pair recombination in the i-ZnO layer, where the holes were injected from the valence band of Si into the acceptor level of i-ZnO.
Show PACS
85.60.Jb Light-emitting devices
85.30.De Semiconductor-device characterization, design, and modeling
85.30.Hi Surface barrier, boundary, and point contact devices
81.15.Rs Spray coating techniques
78.60.Fi Electroluminescence
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