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26 Apr 2010

Volume 96, Issue 17, Articles (17xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 96, 173501 (2010); http://dx.doi.org/10.1063/1.3409475 (3 pages)

Seoung-Ki Lee, Houk Jang, Musarrat Hasan, Jae Bon Koo, and Jong-Hyun Ahn
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Delay of the excited state lasing of 1310 nm InAs/GaAs quantum dot lasers by facet coating

Yu-Lian Cao (曹玉莲), Tao Yang (杨涛), Peng-Fei Xu (徐鹏飞), Hai-Ming Ji (季海铭), Yong-Xian Gu (谷永先), Xiao-Dong Wang (王晓东), Qing Wang (王青), Wen-Quan Ma (马文全), and Liang-Hui Chen (陈良惠)

Appl. Phys. Lett. 96, 171101 (2010); http://dx.doi.org/10.1063/1.3418647 (3 pages) | Cited 1 time

Online Publication Date: 26 April 2010

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In this letter, we present a facet coating design to delay the excited state (ES) lasing for 1310 nm InAs/GaAs quantum dot lasers. The key point of our design is to ensure that the mirror loss of ES is larger than that of the ground state by decreasing the reflectivity of the ES. In the facet coating design, the central wavelength is at 1480 nm, and the high- and low-index materials are Ta2O5 and SiO2, respectively. Compared with the traditional Si/SiO2 facet coating with a central wavelength of 1310 nm, we have found that with the optimal design the turning temperature of the ES lasing has been delayed from 90 to 100 °C for the laser diodes with cavity length of 1.2 mm. Furthermore, the characteristic temperature (T0) of the laser diodes is also improved.
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42.55.Px Semiconductor lasers; laser diodes
42.60.By Design of specific laser systems
42.60.Fc Modulation, tuning, and mode locking

Large near-infrared lateral photovoltaic effect observed in Co/Si metal-semiconductor structures

Chong Qi Yu and Hui Wang

Appl. Phys. Lett. 96, 171102 (2010); http://dx.doi.org/10.1063/1.3419903 (3 pages) | Cited 2 times

Online Publication Date: 27 April 2010

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The operating frequencies of current position-sensitive detectors (PSDs) based on lateral photovoltaic effect (LPE) are mainly concentrated in the visible or ultraviolet region. Here we report a remarkable near-infrared-sensitive LPE in nanoscale metal-semiconductor structures of Co/Si. We show that by manipulating the Co thickness, the optimum light wavelength for obtaining the largest LPE in such Co/Si structures can be controlled in infrared region. Besides, the observed lateral photovoltage position sensitivity of 82 mV/mm at 832 nm light wavelength in Co(3.5 nm)/Si is considerably large, suggesting this simple structure a potential candidate for infrared-sensitive PSDs.
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72.40.+w Photoconduction and photovoltaic effects
78.30.-j Infrared and Raman spectra
78.40.-q Absorption and reflection spectra: visible and ultraviolet
61.46.-w Structure of nanoscale materials

Porous silicon structures for low-cost diffraction-based biosensing

Judson D. Ryckman, Marco Liscidini, J. E. Sipe, and S. M. Weiss

Appl. Phys. Lett. 96, 171103 (2010); http://dx.doi.org/10.1063/1.3421545 (3 pages) | Cited 9 times

Online Publication Date: 28 April 2010

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We present a strategy for label-free biosensing using porous silicon diffraction gratings. The gratings are fabricated using a cost-effective, high-throughput stamping technique. Unlike traditional diffraction-based biosensors that rely on microcontact printing or lithography to create gratings for the localization of analytes on the top surface of the grating, in our structure analytes are free to infiltrate the porous network and increase the effective refractive index of the grating. The large surface area of porous silicon available for molecular binding offers the potential for enhanced diffraction response compared to nonporous gratings with limited surface area. Small molecule detection of 3-aminopropyltriethoxysilane is demonstrated.
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87.80.-y Biophysical techniques (research methods)
07.07.Df Sensors (chemical, optical, electrical, movement, gas, etc.); remote sensing
42.79.Dj Gratings

Switching operation of lasing wavelength in mid-infrared ridge-waveguide quantum cascade lasers coupled with microcylindrical cavity

Y. Wakayama, S. Iwamoto, and Y. Arakawa

Appl. Phys. Lett. 96, 171104 (2010); http://dx.doi.org/10.1063/1.3413949 (3 pages) | Cited 3 times

Online Publication Date: 29 April 2010

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We demonstrated switching operation of lasing wavelength in GaAs-based mid-infrared coupled-cavity quantum cascade lasers. Our cavity structures consist of a ridge-waveguide Fabry–Perot cavity coupled with a microcylindrical cavity. Individual control of currents injected into both cavities enabled single-mode operation and facilitated intentional mode switching between coupled-cavity modes with spacing over 120 nm. The integrated microcylindrical cavity expanded the separation of coupled-cavity modes due to the small size of the cavity and enabled switching the lasing wavelength over a wide spectral range.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
42.55.Sa Microcavity and microdisk lasers
42.82.Bq Design and performance testing of integrated-optical systems
42.60.By Design of specific laser systems

A multilevel recording method of phase-change materials

Chaoyu Xiang and Lih-Hsin Chou

Appl. Phys. Lett. 96, 171105 (2010); http://dx.doi.org/10.1063/1.3409118 (3 pages)

Online Publication Date: 30 April 2010

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In this letter, a method of using ellipsometer parameters to analyze the phase-change material effects of polarized light is exhibited theoretically. The potential usage of polarized light on phase-change materials for information recording is demonstrated by calculating the polarized reflective light angle difference between amorphous and crystalline phases of Te doped GeSb9 films based on this exhibited theory from the ellipsometer data.
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42.79.Vb Optical storage systems, optical disks
42.79.Wc Optical coatings
42.70.Ln Holographic recording materials; optical storage media

Lensfree on-chip imaging using nanostructured surfaces

Bahar Khademhosseinieh, Ikbal Sencan, Gabriel Biener, Ting-Wei Su, Ahmet F. Coskun, Derek Tseng, and Aydogan Ozcan

Appl. Phys. Lett. 96, 171106 (2010); http://dx.doi.org/10.1063/1.3405719 (3 pages) | Cited 5 times

Online Publication Date: 30 April 2010

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We introduce the use of nanostructured surfaces for lensfree on-chip microscopy. In this incoherent on-chip imaging modality, the object of interest is directly positioned onto a nanostructured thin metallic film, where the emitted light from the object plane, after being modulated by the nanostructures, diffracts over a short distance to be sampled by a detector-array without the use of any lenses. The detected far-field diffraction pattern then permits rapid reconstruction of the object distribution on the chip at the subpixel level using a compressive sampling algorithm. This imaging modality based on nanostructured substrates could especially be useful to create lensfree fluorescent microscopes on a compact chip.
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87.85.Rs Nanotechnologies-applications
87.64.M- Optical microscopy
87.63.L- Visual imaging
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Supersonic regimes of plasma expansion during optical breakdown in air

Alexey A. Ilyin, Ivan G. Nagorny, and Oleg A. Bukin

Appl. Phys. Lett. 96, 171501 (2010); http://dx.doi.org/10.1063/1.3421537 (2 pages) | Cited 2 times

Online Publication Date: 27 April 2010

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Expansion regimes of plasma (fast ionization wave, laser supported radiation wave, and laser supported detonation wave) produced by laser–induced breakdown in air have been studied. To determine a pattern of plasma expansion a numerical investigation of propagation velocity dependence on laser radiation intensity was used. Calculation results agree with the experimental data and show that the most expected high-speed mechanism is fast ionization wave.
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52.40.Mj Particle beam interactions in plasmas

Temporary-resolved measurement of electron density in small atmospheric plasmas

A. Shashurin, M. N. Shneider, A. Dogariu, R. B. Miles, and M. Keidar

Appl. Phys. Lett. 96, 171502 (2010); http://dx.doi.org/10.1063/1.3389496 (3 pages) | Cited 4 times

Online Publication Date: 27 April 2010

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A new method for temporally resolved measurements of absolute values of plasma density applicable for wide spectrum of small-size atmospheric plasmas and utilizing Rayleigh microwave scattering on the tested plasma object is proposed. The absolute electron density measurements in an atmospheric plasma jet revealed presence of two consecutive breakdowns during the half-wave of the discharge-driven high voltage. The ionization mechanisms of both breakdowns are considered.
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52.70.Gw Radio-frequency and microwave measurements
52.50.Dg Plasma sources
52.20.-j Elementary processes in plasmas
52.80.-s Electric discharges
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Nitrogen vacancies at InN (1math00) surfaces: A theoretical study

A. Terentjevs, A. Catellani, and G. Cicero

Appl. Phys. Lett. 96, 171901 (2010); http://dx.doi.org/10.1063/1.3409224 (3 pages) | Cited 7 times

Online Publication Date: 28 April 2010

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We present an ab initio atomistic study of the effects of nitrogen vacancies both in InN bulk and at (1math00) nonpolar surface and confirm that these defects act as n-type impurities. Based on the dependence of the vacancy formation energy on the distance from the surface, we predict that at thermodynamic equilibrium these defects tend to segregate in the outermost surface layers reaching a concentration which is few orders of magnitude higher than in the bulk phase. Considering out-of-equilibrium growth and in view of the large calculated energy barrier that characterize vacancy diffusion, we also predict that the N enriched layer will extend hundreds of angstroms from the surface for typical growth processes. This vacancy accumulation at surface is consistent with the observed high electron accumulation layer.
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73.20.Hb Impurity and defect levels; energy states of adsorbed species
68.35.Dv Composition, segregation; defects and impurities
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
61.72.jd Vacancies

Optical and electronic properties of post-annealed ZnO:Al thin films

Yumin Kim, Woojin Lee, Dae-Ryong Jung, Jongmin Kim, Seunghoon Nam, Hoechang Kim, and Byungwoo Park

Appl. Phys. Lett. 96, 171902 (2010); http://dx.doi.org/10.1063/1.3419859 (3 pages) | Cited 25 times

Online Publication Date: 30 April 2010

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This study examined the optical and electronic properties of post-annealed Al-doped ZnO (ZnO:Al) thin films. The lowest resistivity was observed after annealing a sputter-deposited ZnO:Al film at 350 °C. X-ray photoelectron spectroscopy revealed a ∼ 0.4 eV shift in the Fermi level when the carrier concentration was increased to 1.6×1020 cm−3 by Al doping and annealing. The optical band gap increased from 3.2 eV for insulating ZnO to 3.4 eV for conducting ZnO:Al, and was associated with conduction-band filling up to ∼ 0.4 eV in a renormalized band gap. Schematic band diagrams are shown for the ZnO and ZnO:Al films.
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78.66.Hf II-VI semiconductors
81.15.Cd Deposition by sputtering
79.60.Bm Clean metal, semiconductor, and insulator surfaces
61.72.Cc Kinetics of defect formation and annealing
73.61.Ga II-VI semiconductors
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
71.20.Nr Semiconductor compounds

Structural transformation induced changes in the optical properties of nanocrystalline tungsten oxide thin films

S. K. Gullapalli, R. S. Vemuri, and C. V. Ramana

Appl. Phys. Lett. 96, 171903 (2010); http://dx.doi.org/10.1063/1.3421540 (3 pages) | Cited 21 times

Online Publication Date: 30 April 2010

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Nanocrystalline tungsten oxide (WO3) films were grown by reactive magnetron sputter-deposition. The structure and optical properties of WO3 films were evaluated using grazing incidence x-ray diffraction and optical spectroscopic measurements. The effect of ultramicrostructure was significant on the optical characteristics of WO3 films. The band gap decreases from 3.25 to 2.92 eV with increasing grain-size from ∼ 9 to 50 nm while the films exhibit a transition from monoclinic to tetragonal phase. A direct microstructure-property relationship found suggests that tuning properties of WO3 films for desired applications can be achieved by tuning the conditions and controlling the phase.
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68.55.A- Nucleation and growth
81.07.Bc Nanocrystalline materials
61.46.-w Structure of nanoscale materials
81.15.Cd Deposition by sputtering
78.66.Li Other semiconductors
78.20.-e Optical properties of bulk materials and thin films
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Quantum cascade detectors for very long wave infrared detection

A. Buffaz, M. Carras, L. Doyennette, A. Nedelcu, X. Marcadet, and V. Berger

Appl. Phys. Lett. 96, 172101 (2010); http://dx.doi.org/10.1063/1.3409139 (3 pages) | Cited 9 times

Online Publication Date: 26 April 2010

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A high responsivity GaAs/AlGaAs quantum cascade detector is demonstrated at a wavelength of 15 μm. The quantum design is optimized for negative bias operation, so that the capture of photoexcited electrons back to the fundamental level is minimized. The detectivity of the detector presented here reaches 1.1×1012 Jones at 25 K for an applied bias of −0.6 V.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors

Direct microscopic correlation of crystal orientation and luminescence in spontaneously formed nonpolar and semipolar GaN growth domains

B. Bastek, O. August, T. Hempel, J. Christen, M. Wieneke, J. Bläsing, A. Dadgar, A. Krost, and U. Wendt

Appl. Phys. Lett. 96, 172102 (2010); http://dx.doi.org/10.1063/1.3386539 (3 pages) | Cited 4 times

Online Publication Date: 26 April 2010

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We present a direct microscopic correlation between local optical properties, characterized by spectrally resolved cathodoluminescence microscopy and the microscopic crystallographic orientation determined by electron backscatter diffraction at identical sample positions of nonpolar and semipolar GaN growth domains simultaneously formed during metal-organic vapor phase epitaxy on the same r-plane sapphire substrate. The luminescence from all nonpolar, (11math0) grown crystallites is dominated by the basal plane stacking fault luminescence, while all crystallites having semipolar (11math6) orientation show a luminescence characterized by pure excitonic emission, i.e., without any contribution of stacking faults, and with an order of magnitude enhanced quantum efficiency.
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68.55.J- Morphology of films
78.66.Fd III-V semiconductors
78.60.Hk Cathodoluminescence, ionoluminescence
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
81.15.Kk Vapor phase epitaxy; growth from vapor phase
68.55.ag Semiconductors

Random pn-junctions for physical cryptography

C. Jaeger, M. Algasinger, U. Rührmair, G. Csaba, and M. Stutzmann

Appl. Phys. Lett. 96, 172103 (2010); http://dx.doi.org/10.1063/1.3396186 (3 pages) | Cited 2 times

Online Publication Date: 27 April 2010

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In this paper, we report on high-rectification pn-diodes (rectification ratios up to 2×107) prepared by aluminum-induced crystallization on crystalline Si-wafers, which exhibit highly random I(V) characteristics. We argue that arrays of such diodes can be employed as physical uncloneable functions for cryptography. To resolve the structure of the active diode area, focused-ion beam imaging was used. The I(V) curves of the diodes reveal that both a smaller polycrystalline silicon film thickness and a smaller diode size lead to increasing randomness due to the increasing inhomogeneity of thinner films and due to more pronounced grain boundary effects for smaller diodes.
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85.30.Kk Junction diodes
68.55.ag Semiconductors
81.05.Hd Other semiconductors
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.40.Ns Metal-nonmetal contacts
73.40.Ei Rectification

Synthesis of high-density PtSi nanocrystals for memory application

Bei Li, Jingjian Ren, and Jianlin Liu

Appl. Phys. Lett. 96, 172104 (2010); http://dx.doi.org/10.1063/1.3421546 (3 pages) | Cited 7 times

Online Publication Date: 27 April 2010

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Vapor-solid-solid growth mechanism was employed to synthesize PtSi nanocrystals with density of 1.5×1012 cm−2 by introducing SiH4 onto Pt-catalyzed SiO2/Si substrate. The nanocrystal density and average size were measured by scanning electron microscope and the nanocrystal chemical nature was determined by x-ray photoelectron spectroscope. Metal-oxide-semiconductor memory with PtSi nanocrystals was fabricated and characterized, showing very good memory performance.
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81.16.-c Methods of micro- and nanofabrication and processing

Electron energy band alignment at the NiO/SiO2 interface

V. V. Afanas’ev, M. Badylevich, M. Houssa, A. Stesmans, Gagan Aggrawal, and S. A. Campbell

Appl. Phys. Lett. 96, 172105 (2010); http://dx.doi.org/10.1063/1.3413960 (3 pages) | Cited 1 time

Online Publication Date: 27 April 2010

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Study of the NiO/SiO2 interface band diagram using optical absorption, photoconductivity, and internal photoemission measurements reveals that deposited Ni oxides have a band gap of 3.2±0.1 eV, with the top of the valence band at 5.3±0.1 eV below the conduction band of SiO2 and showing no measurable sensitivity to the oxygen surplus in the layer up to 20%. Annealing in a reducing ambient (forming gas) at 400 °C results in narrowing of the band gap and an up shift in the occupied electron state edge by ≈ 1 eV, which is tentatively associated with partial reduction in the NiO layer.
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73.20.-r Electron states at surfaces and interfaces
71.20.-b Electron density of states and band structure of crystalline solids
79.60.Jv Interfaces; heterostructures; nanostructures
78.56.-a Photoconduction and photovoltaic effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Cd Deposition by sputtering
68.55.A- Nucleation and growth
73.50.Pz Photoconduction and photovoltaic effects
81.40.Gh Other heat and thermomechanical treatments

Theoretical study of Fe-doped p-type ZnO

Bei Deng, Zhiyou Guo, and Huiqing Sun

Appl. Phys. Lett. 96, 172106 (2010); http://dx.doi.org/10.1063/1.3422486 (3 pages) | Cited 9 times

Online Publication Date: 28 April 2010

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Based on first-principles calculations, we present a study for p-type ZnO doping. We find that by doping Fe into the p-type ZnO, the resulting FeZn–2NO complex is a stable acceptor that has shallower ε(0/−) transition level and lower formation energy in comparison with the isolated NO. Moreover, the FeZn–VZn pair is another resulting defect that is a shallow acceptor, for which the minimum formation energy occurs at the O-rich limit. As parent defects, FeZn behave as deep donor that do not lead to overcompensation. Therefore, Fe-related acceptor complexes may be promising candidates for p-type ZnO doping.
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61.72.uj III-V and II-VI semiconductors
71.55.Eq III-V semiconductors

Space-charge-limited hole current in poly(9,9-dioctylfluorene) diodes

H. T. Nicolai, G. A. H. Wetzelaer, M. Kuik, A. J. Kronemeijer, B. de Boer, and P. W. M. Blom

Appl. Phys. Lett. 96, 172107 (2010); http://dx.doi.org/10.1063/1.3391668 (3 pages) | Cited 15 times

Online Publication Date: 28 April 2010

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Characterization of the hole transport in blue-emitting polymers as poly(9,9-dioctylfluorene) (PFO) is strongly hindered by their large ionization potential of ∼ 6 eV. Using common anodes as poly(3,4-ethylenedioxythiophene)/poly(styrenesulphonic acid) leads to a strongly injection limited current. We demonstrate that molybdenum trioxide forms an Ohmic hole contact on PFO, enabling the observation of a space-charge-limited current(SCLC). This allows a direct determination of the hole mobility PFO of 1.3×10−9 m2/V s at room temperature, in good agreement with previously reported mobility values determined by time-of-flight measurements.
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85.60.Jb Light-emitting devices
81.05.Lg Polymers and plastics; rubber; synthetic and natural fibers; organometallic and organic materials
72.20.Fr Low-field transport and mobility; piezoresistance
73.40.Ns Metal-nonmetal contacts

Electron and hole spin cooling efficiency in InAs quantum dots: The role of nuclear field

P. Desfonds, B. Eble, F. Fras, C. Testelin, F. Bernardot, M. Chamarro, B. Urbaszek, T. Amand, X. Marie, J. M. Gérard, V. Thierry-Mieg, A. Miard, and A. Lemaître

Appl. Phys. Lett. 96, 172108 (2010); http://dx.doi.org/10.1063/1.3394010 (3 pages) | Cited 4 times

Online Publication Date: 28 April 2010

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The spin dynamics of a resident carrier, hole or electron, in singly charged InAs/GaAs quantum dots has been measured by pump-probe experiments. The relative strength of the hole to the electron hyperfine couplings with nuclei is obtained by studying the magnetic-field dependence of the resident-carrier spin polarization. We find, in good agreement with recent theoretical studies, that the hole hyperfine coupling is ten times smaller than the electron one.
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75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Ds Spin waves
75.50.Pp Magnetic semiconductors

Tunneling magnetoresistance on the surface of a topological insulator with periodic magnetic modulations

Ya Zhang and Feng Zhai

Appl. Phys. Lett. 96, 172109 (2010); http://dx.doi.org/10.1063/1.3421536 (3 pages) | Cited 11 times

Online Publication Date: 30 April 2010

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We investigate the band and transport features of Dirac electrons on the surface of a three-dimensional topological insulator under the modulation of a periodic exchange field provided by an array of ferromagnetic insulating (FI) stripes. The Dirac point is shifted (unchanged) by the superlattice when the magnetizations of adjacent FI stripes are parallel (antiparallel). For a finite magnetic superlattice, there exists a full transmission gap for both the parallel and antiparallel configurations. When the two kinds of transmission gaps have no overlap, a large magnetoresistance ratio with a tunable sign can be achieved.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Stochastic resonance in a nanoscale Y-branch switch

F. Hartmann, D. Hartmann, P. Kowalzik, A. Forchel, L. Gammaitoni, and L. Worschech

Appl. Phys. Lett. 96, 172110 (2010); http://dx.doi.org/10.1063/1.3425669 (3 pages) | Cited 1 time

Online Publication Date: 30 April 2010

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The self-gating effect in a nanoscale Y-branch switch was exploited to tune the bistable switching so small that noise induced switching occurs. In this regime, the time-dependent response to a weak external periodic signal was studied. The noise-activated switching of the junction was synchronized with the weak external periodic signal due to the presence of the sole internal noise. A maximum synchronization is found and interpreted in terms of stochastic resonance.
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84.32.Dd Connectors, relays, and switches
02.50.Ey Stochastic processes
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Microstrip superconducting quantum interference device amplifier: Conditional stability

D. Kinion and John Clarke

Appl. Phys. Lett. 96, 172501 (2010); http://dx.doi.org/10.1063/1.3377898 (3 pages) | Cited 4 times

Online Publication Date: 26 April 2010

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The scattering parameters of an amplifier based on a dc superconducting quantum interference device are directly measured at 4.2 K as functions of the bias current and applied magnetic flux. These parameters are used to determine the stability of the amplifier with arbitrary source and output load impedances. It was found that the amplifier is conditionally stable, and that the stability is improved by decreasing the gain or adding negative feedback. With suitable bias selection, the amplifier is shown to be sufficiently stable to allow operation with a resonant source impedance.
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84.40.Az Waveguides, transmission lines, striplines
85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.30.Le Amplifiers

Anomalous magnetic field effects during pulsed injection metal-organic chemical vapor deposition of magnetite films

Anna Zukova, Arunas Teiserskis, Y. K. Gun’ko, Ana M. Sánchez, and Sebastiaan van Dijken

Appl. Phys. Lett. 96, 172502 (2010); http://dx.doi.org/10.1063/1.3418622 (3 pages) | Cited 2 times

Online Publication Date: 26 April 2010

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We report on large external magnetic field effects during pulsed injection metal-organic chemical vapor deposition of magnetite films on MgO(001). The application of a 1 T field during the growth process significantly increases the saturation magnetization of magnetite by 150%–220% at a deposition temperature of 550 and 600 °C, while the enhancement of the remanent magnetization is even larger. This anomalous magnetic field effect does not drastically alter the crystalline texture, surface morphology, and film thickness of magnetite, but is explained by a suppression of antiphase-boundary formation during film growth.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
75.70.Ak Magnetic properties of monolayers and thin films
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
68.35.B- Structure of clean surfaces (and surface reconstruction)
68.55.jm Texture

Magnetoresistance and magnetocaloric effect at a structural phase transition from a paramagnetic martensitic state to a paramagnetic austenitic state in Ni50Mn36.5In13.5 Heusler alloys

Arjun K. Pathak, Igor Dubenko, Christopher Pueblo, Shane Stadler, and Naushad Ali

Appl. Phys. Lett. 96, 172503 (2010); http://dx.doi.org/10.1063/1.3422483 (3 pages) | Cited 11 times

Online Publication Date: 27 April 2010

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It is established, using magnetization measurements, that Ni50Mn36.5In13.5 is in a paramagnetic state (PS) above and below the martensitic transition temperature (TM). Magnetoresistance (MR) and magnetic entropy changes (ΔSM) in the vicinity of TM were studied. MR and ΔSM at TM were found to be ≈−8% and ≈ +24 J Kg−1 K−1, respectively, at ΔH = 5 T. Although MR and ΔSM values were lower than compared to those found in other Heusler systems, the significantly smaller hysteresis observed in Ni50Mn36.5In13.5 makes this compound, and other such compounds that undergo a martensitic transition in a PS, promising for the study and applications of magnetocaloric magnetic materials.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
64.70.kd Metals and alloys
81.30.Kf Martensitic transformations
75.20.En Metals and alloys
75.30.Sg Magnetocaloric effect, magnetic cooling
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
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Giant magnetocaloric effects by tailoring the phase transitions

N. T. Trung, L. Zhang, L. Caron, K. H. J. Buschow, and E. Brück

Appl. Phys. Lett. 96, 172504 (2010); http://dx.doi.org/10.1063/1.3399773 (3 pages) | Cited 18 times

Online Publication Date: 27 April 2010

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The MnCoGe alloy can crystallize in either the hexagonal Ni2In- or the orthorhombic TiNiSi-type of structure. In both phases MnCoGe behaves like a typical ferromagnet with a second-order magnetic phase transition. For MnCoGeBx with B on interstitial positions, we discover a giant magnetocaloric effect associated with a single first-order magnetostructural phase transition, which can be achieved by tuning the magnetic and structural transitions to coincide. The results obtained on the MnCoGe-type alloys may be extensible to other types of magnetic materials undergoing a first-order structural transformation and can open up some possibilities for searching magnetic refrigerants for room-temperature applications.
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75.30.Sg Magnetocaloric effect, magnetic cooling
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
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