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8 Oct 2012

Volume 101, Issue 15, Articles (15xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 153501 (2012); http://dx.doi.org/10.1063/1.4756693 (3 pages)

Brandon G. Cook, William R. French, and Kálmán Varga
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Determination of 16O and 18O sensitivity factors and charge-exchange processes in low-energy ion scattering

H. Téllez, R. J. Chater, S. Fearn, E. Symianakis, H. H. Brongersma, and J. A. Kilner

Appl. Phys. Lett. 101, 151602 (2012); http://dx.doi.org/10.1063/1.4758699 (4 pages)

Online Publication Date: 10 October 2012

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Quantitative analysis in low-energy ion scattering (LEIS) requires an understanding of the charge-exchange processes to estimate the elemental sensitivity factors. In this work, the neutralization of He+ scattered by 18O-exchanged silica at energies between 0.6 and 7 keV was studied. The process is dominated by Auger neutralization for Ei < 0.8 keV. An additional mechanism starts above the reionization threshold. This collision-induced neutralization becomes the dominant mechanism for Ei > 2 keV. The ion fractions P+ were determined for Si and O using the characteristic velocity method to quantify the surface density. The 18O/16O sensitivity ratio indicates an 18% higher sensitivity for the heavier O isotope.
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79.20.Fv Electron impact: Auger emission
82.30.Fi Ion-molecule, ion-ion, and charge-transfer reactions
82.20.Tr Kinetic isotope effects including muonium
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces

Molecular dynamics prediction of interfacial strength and validation through atomic force microscopy

Ulises Galan and Henry A. Sodano

Appl. Phys. Lett. 101, 151603 (2012); http://dx.doi.org/10.1063/1.4758988 (4 pages)

Online Publication Date: 11 October 2012

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Molecular dynamics (MD) simulations are performed to calculate the interfacial energy between zinc oxide (ZnO) and graphitic carbon. The MD model consists of a ZnO slab and a single layer of graphitic carbon. The calculation was validated experimentally by atomic force microscopy (AFM) liftoff. A polishing process was applied to create a tip with a flat surface that was subsequently coated with a ZnO film allowing force displacement measurement on highly oriented pyrolitic graphite to validate the simulations. The MD simulation and AFM lift-off show good agreement with adhesive energies of 0.303 J/m2 and 0.261 ± 0.054 J/m2, respectively.
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68.35.Np Adhesion
68.35.Gy Mechanical properties; surface strains
68.37.Ps Atomic force microscopy (AFM)
81.65.Ps Polishing, grinding, surface finishing

Quantum oscillations from a two-dimensional electron gas at a Mott/band insulator interface

Pouya Moetakef, Daniel G. Ouellette, James R. Williams, S. James Allen, Leon Balents, David Goldhaber-Gordon, and Susanne Stemmer

Appl. Phys. Lett. 101, 151604 (2012); http://dx.doi.org/10.1063/1.4758989 (4 pages) | Cited 1 time

Online Publication Date: 11 October 2012

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We report on the magnetotransport properties of a prototype Mott insulator/band insulator perovskite heterojunction in magnetic fields up to 31 T and at temperatures between 360 mK and 10 K. Shubnikov-de Haas oscillations in the magnetoresistance are observed. The oscillations are two-dimensional in nature and are interpreted as arising from either a single, spin-split subband or two subbands. In either case, the electron system that gives rise to the oscillations represents only a fraction of the electrons in the space charge layer at the interface. The temperature dependence of the oscillations is used to extract an effective mass of ∼1 me for the subband(s). The results are discussed in the context of the t2g-states that form the bottom of the conduction band of SrTiO3.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
72.20.My Galvanomagnetic and other magnetotransport effects

Absorptivity modulation on wavy molten steel surfaces: The influence of laser wavelength and angle of incidence

A. F. H. Kaplan

Appl. Phys. Lett. 101, 151605 (2012); http://dx.doi.org/10.1063/1.4759126 (4 pages)

Online Publication Date: 11 October 2012

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The modulation of the angle-dependent Fresnel absorptivity across wavy molten steel surfaces during laser materials processing, like drilling, cutting, or welding, has been calculated. The absorptivity is strongly altered by the grazing angle of incidence of the laser beam on the processing front. Owing to its specific Brewster-peak characteristics, the 10.64 μm wavelength CO2-laser shows an opposite trend with respect to roughness and angle-of-incidence compared to lasers in the wavelength range of 532-1070 nm. Plateaus or rings of Brewster-peak absorptivity can lead to hot spots on a wavy surface, often in close proximity to cold spots caused by shadow domains.
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81.05.Bx Metals, semimetals, and alloys
68.35.bd Metals and alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
79.20.Ds Laser-beam impact phenomena
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An innovative cloak enables arbitrary multi-objects hidden with visions and movements

Tsung-Yu Huang (黃宗鈺), Hsin-Cheng Lee (李信成), Ieng-Wai Un (阮英偉), and Ta-Jen Yen (嚴大任)

Appl. Phys. Lett. 101, 151901 (2012); http://dx.doi.org/10.1063/1.4757868 (4 pages)

Online Publication Date: 9 October 2012

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We propose an innovative cloak to enable arbitrary multi-objects hidden with visions and movements. We develop the cloak with spatially varying constitutive parameters by employing transformation optics with two-step coordinate transformations and testify the performance of the cloak by finite element based simulation software. In simulation, the electric field distributions (Ez) of the cloak for different circumstances agree with the analytical prediction well.
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42.70.-a Optical materials
41.20.-q Applied classical electromagnetism
42.25.Bs Wave propagation, transmission and absorption

Micromachined switchable metamaterial with dual resonance

W. Zhang, A. Q. Liu, W. M. Zhu, E. P. Li, H. Tanoto, Q. Y. Wu, J. H. Teng, X. H. Zhang, M. L. J. Tsai, G. Q. Lo, and D. L. Kwong

Appl. Phys. Lett. 101, 151902 (2012); http://dx.doi.org/10.1063/1.4759029 (4 pages) | Cited 2 times

Online Publication Date: 9 October 2012

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We experimentally demonstrate a micromachined switchable metamaterial with dual mode resonance which is induced at THz regime under oblique incidence. Here, we explore, both theoretically and experimentally, the dynamic dual mode switching by reshaping metamaterial elements using micromachined actuators. The mode switching allows robust control over the transmission and the reflection of the metamaterial at 0.76 THz and 1.16 THz. Such switchable dual mode metamaterial promises wide applications in optical switches, tunable filters, and THz detectors.
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81.05.Xj Metamaterials for chiral, bianisotropic and other complex media
84.40.-x Radiowave and microwave (including millimeter wave) technology
85.85.+j Micro- and nano-electromechanical systems (MEMS/NEMS) and devices

Vanadium bound exciton luminescence in 6H-SiC

S. C. Wang, G. Wang, Y. Liu, L. B. Jiang, W. J. Wang, and X. L. Chen

Appl. Phys. Lett. 101, 151903 (2012); http://dx.doi.org/10.1063/1.4757883 (4 pages)

Online Publication Date: 9 October 2012

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The source responsible for V2 (1.398 eV) luminescence in 6H-SiC is recognized as a favorable defect for quantum information processing. However, the origin of V2 luminescence is still controversial. With careful photoluminescence measurements, it is found that V2 line shows clear bound exciton luminescence features. Furthermore, a mechanism based on neutral vanadium donor bound exciton is put forward to explain the origin of V2 luminescence. The results may provide some insights to understanding the nature of the promising qubit candidates in SiC.
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78.55.Hx Other solid inorganic materials
71.35.-y Excitons and related phenomena

Characterization and simulation of the first extensional mode of rectangular micro-plates in liquid media

T. Manzaneque, V. Ruiz, J. Hernando-García, A. Ababneh, H. Seidel, and J. L. Sánchez-Rojas

Appl. Phys. Lett. 101, 151904 (2012); http://dx.doi.org/10.1063/1.4758470 (4 pages) | Cited 2 times

Online Publication Date: 9 October 2012

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This Letter reports on the characterization of the first extensional mode of AlN-actuated mid-point supported resonant microplates in liquid media. Devices of different dimensions were fabricated and both optical and electrical measurements were performed in order to identify the modal shape under study and determine its quality factor. The dependence of the quality factor on the plate dimensions is discussed based on analytical and finite element simulation results. A quality factor of 100 was achieved in water at 3.8 MHz, and the suitability of this kind of device to work under high viscous condition (up to 51 cP) was demonstrated.
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47.85.Np Fluidics
47.11.Fg Finite element methods
47.61.-k Micro- and nano- scale flow phenomena

Deformation behaviors of InP pillars under uniaxial compression

Sheng-Rui Jian, T.-H. Sung, J. C. Huang, and Jenh-Yih Juang

Appl. Phys. Lett. 101, 151905 (2012); http://dx.doi.org/10.1063/1.4758479 (4 pages) | Cited 1 time

Online Publication Date: 9 October 2012

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We report the deformation behavior of single-crystal InP(100) micropillars, measuring about 1 μm in diameter and 2 μm in height, subjected to uniaxial compression at room temperature. The engineering stress-strain results indicated that the yield strength of InP pillar is about 2.5 GPa, and the presence of a drastic strain burst right after yielding. Cross-sectional transmission electron microscopy microstructural observations reveal the formation of extremely dense twins. The results indicate that the plastic deformation in InP micropillars is dominated by explosive generation of deformation twins under the high stress state.
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81.40.Lm Deformation, plasticity, and creep
62.20.fq Plasticity and superplasticity
61.72.Mm Grain and twin boundaries
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.fg Shape-memory effect; yield stress; superelasticity

Observation of polyamorphism in the phase change alloy Ge1Sb2Te4

B. Kalkan, S. Sen, J.-Y. Cho, Y.-C. Joo, and S. M. Clark

Appl. Phys. Lett. 101, 151906 (2012); http://dx.doi.org/10.1063/1.4759106 (5 pages)

Online Publication Date: 10 October 2012

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A high-pressure synchrotron x-ray diffraction study of the phase change alloy Ge1Sb2Te4 demonstrates the existence of a polyamorphic phase transition between the “as deposited” low density amorphous (LDA) phase and a high density amorphous (HDA) phase at ∼10 GPa. The entropy of the HDA phase is expected to be higher than that of the LDA phase resulting in a negative Clapeyron slope for this transition. These phase relations may enable the polyamorphic transition to play a role in the memory and data storage applications.
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81.30.Hd Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder
64.70.K- Solid-solid transitions
65.60.+a Thermal properties of amorphous solids and glasses: heat capacity, thermal expansion, etc.
68.60.Wm Other nonelectronic physical properties

The cooling effect on structural, electrical, and optical properties of epitaxial a-plane ZnO:Al on r-plane sapphire grown by pulsed laser deposition

Chun-Yen Peng, Yuan-An Liu, Wei-Lin Wang, Jr-Sheng Tian, and Li Chang

Appl. Phys. Lett. 101, 151907 (2012); http://dx.doi.org/10.1063/1.4759032 (4 pages) | Cited 2 times

Online Publication Date: 11 October 2012

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Here, the unambiguous effect of cooling rate on structural, electrical, and optical properties of a-plane ZnO:Al on r-plane sapphire grown by pulsed laser deposition at 700 °C is reported. A high cooling rate (∼100 °C/min) can result in stripe morphology along m-direction and significant deformation on the epitaxial films of a-plane ZnO:Al with deteriorated crystallinity and significantly lowered resistivity. Also, photoluminescence spectra exhibit high intensities of excess violet and green emissions with low intensity of near band edge luminescence. Comparison with pure a-plane ZnO films is also presented.
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81.05.Dz II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
78.66.Hf II-VI semiconductors
78.55.Et II-VI semiconductors
73.61.Ga II-VI semiconductors
61.66.Fn Inorganic compounds

Structural-dependent thermal conductivity of aluminium nitride produced by reactive direct current magnetron sputtering

B. E. Belkerk, A. Soussou, M. Carette, M. A. Djouadi, and Y. Scudeller

Appl. Phys. Lett. 101, 151908 (2012); http://dx.doi.org/10.1063/1.4757298 (4 pages)

Online Publication Date: 11 October 2012

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This Letter reports the thermal conductivity of aluminium nitride (AlN) thin-films deposited by reactive DC magnetron sputtering on single-crystal silicon substrates (100) with varying plasma and magnetic conditions achieving different crystalline qualities. The thermal conductivity of the films was measured at room temperature with the transient hot-strip technique for film thicknesses ranging from 100 nm to 4000 nm. The thermal conductivity was found to increase with the thickness depending on the synthesis conditions and film microstructure. The conductivity in the bulk region of the films, so-called intrinsic conductivity, and the boundary resistance were in the range [120–210] W m−1 K−1 and [2-30 × 10−9] K m2 W−1, respectively, in good agreement with microstructures analysed by x-ray diffraction, high-resolution-scanning-electron-microscopy, and transmission-electron-microscopy.
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81.05.Ea III-V semiconductors
81.15.Cd Deposition by sputtering
66.70.Df Metals, alloys, and semiconductors
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Excellent p-n control in a high temperature thermoelectric boride

Satofumi Maruyama, Yuzuru Miyazaki, Kei Hayashi, Tsuyoshi Kajitani, and Takao Mori

Appl. Phys. Lett. 101, 152101 (2012); http://dx.doi.org/10.1063/1.4758297 (4 pages)

Online Publication Date: 8 October 2012

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Polycrystalline samples of YxAlyB14 (x ∼ 0.57) with different fractional occupancies y (0.41 ≤ y ≤ 0.63) were synthesized and their thermoelectric properties investigated. Electrical conductivities generally followed three-dimensional variable range hopping with a rapid delocalization indicated as electrons were increased. Positive Seebeck coefficients were obtained for the Al-poor sample, y = 0.41, which was shifted in the negative direction with increase of y. Maximum Seebeck coefficient values were approximately 400 μV K−1 at 850 K and −200 μV K−1 at 1000 K, for p-type and n-type, respectively. Excellent control of p-n characteristics was achieved in a system with the same crystal structure and consisting of the same elements.
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72.15.Jf Thermoelectric and thermomagnetic effects
73.50.Dn Low-field transport and mobility; piezoresistance
61.66.Dk Alloys

Large linear magnetoresistance and magnetothermopower in layered SrZnSb2

Kefeng Wang and C. Petrovic

Appl. Phys. Lett. 101, 152102 (2012); http://dx.doi.org/10.1063/1.4758298 (3 pages)

Online Publication Date: 9 October 2012

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We report the large linear magnetoresistance ( ∼ 300% in 9 T field at 2 K) and magnetothermopower in layered SrZnSb2 crystal with quasi-two-dimensional Sb layers. A crossover from the semiclassical parabolic field dependent magnetoresistance to linear field dependent magnetoresistance with increasing magnetic field is observed. The magnetoresistance behavior can be described very well by combining the semiclassical cyclotron contribution and the quantum limit magnetoresistance. Magnetic field also enhances the thermopower. Our results can be well understood by the magnetotransport of Dirac states in the bulk band structure.
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72.15.Gd Galvanomagnetic and other magnetotransport effects
72.15.Jf Thermoelectric and thermomagnetic effects
75.47.De Giant magnetoresistance

Simple tuning of carrier type in topological insulator Bi2Se3 by Mn doping

Y. H. Choi, N. H. Jo, K. J. Lee, H. W. Lee, Y. H. Jo, J. Kajino, T. Takabatake, K.-T. Ko, J.-H. Park, and M. H. Jung

Appl. Phys. Lett. 101, 152103 (2012); http://dx.doi.org/10.1063/1.4755767 (4 pages)

Online Publication Date: 9 October 2012

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Bi2Te3 is a well-known thermoelectric material for room-temperature operations because it has a high Seebeck coefficient, and the charge carrier type is easily tunable. However, the carrier type of Bi2Se3 is not tunable, which is one of the weaknesses for the thermoelectric applications, in spite of its high Seebeck coefficient. Here, we report the tuning of charge carriers in Bi2Te3 from n type to p type by doping Mn into the Bi sites. The carrier type is n type up to the Mn doping level of 5% and changes to p type above 5% Mn doping. The temperature-dependent resistivity of Bi2−xMnxSe3 shows a metallic behavior for x < 0.05, while for x ≥ 0.05, it shows an upturn at low temperatures. This provides evidence that by Mn doping, the Fermi level is continuously tuned from the bulk conduction band to the bulk valence band. The Seebeck coefficient increases monotonically with increasing temperature, and the absolute values are same for both n- and p-type samples. This implies that Bi2Se3 is another candidate of high-temperature thermoelectric materials, like Bi2Te3, simply by Mn doping.
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72.80.Sk Insulators
73.20.Hb Impurity and defect levels; energy states of adsorbed species
61.72.up Other materials
71.20.Ps Other inorganic compounds
72.20.Pa Thermoelectric and thermomagnetic effects

Influence of V/III growth flux ratio on trap states in m-plane GaN grown by ammonia-based molecular beam epitaxy

Z. Zhang, C. A. Hurni, A. R. Arehart, J. S. Speck, and S. A. Ringel

Appl. Phys. Lett. 101, 152104 (2012); http://dx.doi.org/10.1063/1.4759037 (4 pages)

Online Publication Date: 10 October 2012

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Deep level transient spectroscopy (DLTS) and deep level optical spectroscopy (DLOS) were utilized to investigate the behavior of deep states in m-plane, n-type GaN grown by ammonia-based molecular beam epitaxy (NH3-MBE) as a function of systematically varied V/III growth flux ratios. Levels were detected at EC − 0.14 eV, EC − 0.21 eV, EC − 0.26 eV, EC − 0.62 eV, EC − 0.67 eV, EC − 2.65 eV, and EC − 3.31 eV, with the concentrations of several traps exhibiting systematic dependencies on V/III ratio. The DLTS spectra are dominated by traps at EC − 0.14 eV and EC − 0.67 eV, whose concentrations decreased monotonically with increasing V/III ratio and decreasing oxygen impurity concentration, and by a trap at EC − 0.21 eV that revealed no dependence of its concentration on growth conditions, suggestive of different physical origins. Higher concentrations of deeper trap states detected by DLOS with activation energies of EC − 2.65 eV and EC − 3.31 eV in each sample did not display measureable sensitivity to the intentionally varied V/III ratio, necessitating further study on reducing these deep traps through growth optimization for maximizing material quality of NH3-MBE grown m-plane GaN.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.ag Semiconductors
71.55.Eq III-V semiconductors
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors

Strain effects and band parameters in MgO, ZnO, and CdO

Qimin Yan, Patrick Rinke, Momme Winkelnkemper, Abdallah Qteish, Dieter Bimberg, Matthias Scheffler, and Chris G. Van de Walle

Appl. Phys. Lett. 101, 152105 (2012); http://dx.doi.org/10.1063/1.4759107 (4 pages)

Online Publication Date: 10 October 2012

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We have derived consistent sets of band parameters (bandgaps, crystal-field splittings, effective masses, Luttinger, and EP parameters) and strain deformation potentials for MgO, ZnO, and CdO in the wurtzite phase. To overcome the limitations of density-functional theory in the local-density and generalized gradient approximations, we employ a hybrid functional as well as exact-exchange-based quasiparticle energy calculations in the G0W0 approach. We demonstrate that the band and strain parameters derived in this fashion are in very good agreement with the available experimental data and provide predictions for all parameters that have not been determined experimentally so far.
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81.40.Lm Deformation, plasticity, and creep
71.15.Mb Density functional theory, local density approximation, gradient and other corrections
73.22.-f Electronic structure of nanoscale materials and related systems
62.25.-g Mechanical properties of nanoscale systems
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
62.20.F- Deformation and plasticity

Hall effect measurements on InAs nanowires

Ch. Blömers, T. Grap, M. I. Lepsa, J. Moers, St. Trellenkamp, D. Grützmacher, H. Lüth, and Th. Schäpers

Appl. Phys. Lett. 101, 152106 (2012); http://dx.doi.org/10.1063/1.4759124 (4 pages) | Cited 4 times

Online Publication Date: 11 October 2012

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We have processed Hall contacts on InAs nanowires grown by molecular beam epitaxy using an electron beam lithography process with an extremely high alignment accuracy. The carrier concentrations determined from the Hall effect measurements on these nanowires are lower by a factor of about 4 in comparison with those measured by the common field-effect technique. The results are used to evaluate quantitatively the charging effect of the interface and surface states.
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72.20.My Galvanomagnetic and other magnetotransport effects
81.16.Nd Micro- and nanolithography
73.63.Nm Quantum wires
68.65.La Quantum wires (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.21.Hb Quantum wires

Angular-dependences of giant in-plane and interlayer magnetoresistances in Bi2Te3 bulk single crystals

Z. J. Yue, X. L. Wang, and S. X. Dou

Appl. Phys. Lett. 101, 152107 (2012); http://dx.doi.org/10.1063/1.4756941 (4 pages)

Online Publication Date: 11 October 2012

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Angular-dependences of in-plane and interlayer magnetotransport properties in n-type Bi2Te3 bulk single crystals have been investigated over a broad range of temperatures and magnetic fields. Giant in-plane magnetoresistances (MR) of up to 500% and interlayer MR of up to 200% were observed, respectively. The observed MR exhibits quadratic field dependences in low fields and linear field dependences in high fields. The angular dependences of the MR represent strong anisotropy and twofold oscillations. The observed angle-dependent, giant MR might result from the strong coulomb scattering of electrons as well as impurity scattering in the bulk conduction bands of n-type Bi2Te3. The strong anisotropy of the MR may be attributable to the anisotropy of electron mobility, effective mass, and relaxation time in the Fermi surface. The observed giant anisotropic MR in n-type Bi2Te3 bulk single crystals paves the way for Bi2Te3 single crystals to be useful for practical applications in magnetoelectronic devices such as disk reading heads, anisotropic magnetic sensors, and other multifunctional electromagnetic applications.
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72.20.My Galvanomagnetic and other magnetotransport effects
75.47.De Giant magnetoresistance
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor
71.20.Nr Semiconductor compounds
72.10.Fk Scattering by point defects, dislocations, surfaces, and other imperfections (including Kondo effect)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Degenerate crystalline silicon films by aluminum-induced crystallization of boron-doped amorphous silicon

J. D. Hwang, L. C. Luo, T. J. Hsueh, and S. B. Hwang

Appl. Phys. Lett. 101, 152108 (2012); http://dx.doi.org/10.1063/1.4759151 (4 pages)

Online Publication Date: 11 October 2012

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Degenerate p-type crystalline silicon film with a hole concentration of 4 × 1021 cm−3 was investigated using aluminum-induced crystallization (AIC) of boron-doped amorphous silicon (a-Si). The AIC mechanism is different from that in the undoped AIC-Si. Boron atoms accumulate at Al layer forming a boron bump and segregate the Al atoms into Si layer, resulting to the formation of AlSi alloy. The degeneracy is not attributed to boron doping but instead to the AlSi alloy. Observations show that Al and Si layer transfer occurs not at original interface of Al and Si, but at the boron bump.
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68.55.ag Semiconductors
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.
61.43.Dq Amorphous semiconductors, metals, and alloys
81.05.Gc Amorphous semiconductors
61.72.uf Ge and Si
81.05.Cy Elemental semiconductors
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High temperature magnetic properties of SmCo5/α-Fe(Co) bulk nanocomposite magnets

Chuanbing Rong, Narayan Poudyal, X. B. Liu, Ying Zhang, M. J. Kramer, and J. Ping Liu

Appl. Phys. Lett. 101, 152401 (2012); http://dx.doi.org/10.1063/1.4758480 (3 pages) | Cited 2 times

Online Publication Date: 8 October 2012

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To find alternative high temperature magnets containing no heavy rare earths for power applications, SmCo5/Fe bulk nanocomposite magnets with enhanced energy density and high thermal stability have been produced by using a ball-milling plus warm-compaction route. Up to 30% of the Fe soft magnetic phase has been added to the composites with grain size <20 nm distributed homogenously in the matrix of the SmCo5 hard magnetic phase. It was observed that the microstructure does not change with temperature up to 500 °C. It is also observed that the thermal stability of bulk nanocomposite samples is closely related to bulk density. Energy products above 11 MGOe have been obtained at 300 °C in fully dense bulk SmCo5/Fe nanocomposite magnets, which is 65% higher than that of a single-phase counterpart at the same temperature.
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81.05.Bx Metals, semimetals, and alloys
81.07.Bc Nanocrystalline materials
81.20.Wk Machining, milling
75.75.-c Magnetic properties of nanostructures
75.50.Ww Permanent magnets
75.50.Tt Fine-particle systems; nanocrystalline materials

Propagation and scattering of spin waves in curved magnonic waveguides

V. S. Tkachenko, A. N. Kuchko, M. Dvornik, and V. V. Kruglyak

Appl. Phys. Lett. 101, 152402 (2012); http://dx.doi.org/10.1063/1.4757994 (5 pages) | Cited 2 times

Online Publication Date: 9 October 2012

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We report a continuous medium theory of dispersion and scattering of spin waves propagating in thin nanowire magnonic waveguides with curved regions. Assuming that the static magnetization is aligned along the waveguide, the curvature leads to a “geometrical” effective magnetic field term that is proportional to the square of the ratio of the exchange length to the radius of curvature of the waveguide. The term is small enough to favor the use of bended nanowire waveguides in planar magnonic data architectures. However, a stronger (multiple) winding (e.g., within helical structures) could enable design of magnonic waveguides with desired properties.
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75.30.Ds Spin waves
75.75.-c Magnetic properties of nanostructures
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)

Effect of inter-bit material on the performance of directly deposited bit patterned media

Naganivetha Thiyagarajah, Huigao Duan, Debra L. Y. Song, Mohamed Asbahi, Siang Huei Leong, Joel K. W. Yang, and Vivian Ng

Appl. Phys. Lett. 101, 152403 (2012); http://dx.doi.org/10.1063/1.4758478 (5 pages)

Online Publication Date: 9 October 2012

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We evaluated the effects of inter-bit material on the switching performance of bit patterned media (BPM) fabricated by direct deposition of magnetic material onto pre-patterned substrates. We performed a controlled experiment to vary the sidewall thickness and symmetry in bits with nominally identical size and pitch. Thick, asymmetric sidewalls resulted in significant broadening of the switching field distribution to 14%–20% compared to 10%–11% for bits with thin, symmetric sidewalls. These differences were attributed to changes in the intrinsic properties and dipolar interactions as supported by micromagnetic simulations. Our results highlight the importance of controlling inter-bit material to achieve high-density BPM.
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75.30.-m Intrinsic properties of magnetically ordered materials
75.78.Cd Micromagnetic simulations
75.60.-d Domain effects, magnetization curves, and hysteresis
75.70.-i Magnetic properties of thin films, surfaces, and interfaces

Giant magnetoresistance effect in graphene with asymmetrical magnetic superlattices

Q. H. Huo, R. Z. Wang, and H. Yan

Appl. Phys. Lett. 101, 152404 (2012); http://dx.doi.org/10.1063/1.4757881 (5 pages) | Cited 1 time

Online Publication Date: 10 October 2012

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We investigate a giant magnetoresistance (MR) effect in periodic, asymmetric magnetic superlattices (MSLs) on graphene. The MR ratio shows a strong dependence on both the interval of magnetic barriers and the asymmetry degree of the structures. With the increase of the number of periods, there is only one MR peak and the drift of the position of the peak appears around a specific Fermi energy. The highest value of the maximal MR ratio can be up to 1017%. Our studies indicate that the graphene-based asymmetric MSLs structure is an ideal candidate of a giant MR device, e.g., the magnetic reading device.
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75.47.De Giant magnetoresistance
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
73.22.Pr Electronic structure of graphene
72.20.My Galvanomagnetic and other magnetotransport effects
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Growth and ferromagnetic resonance properties of nanometer-thick yttrium iron garnet films

Yiyan Sun, Young-Yeal Song, Houchen Chang, Michael Kabatek, Michael Jantz, William Schneider, Mingzhong Wu, Helmut Schultheiss, and Axel Hoffmann

Appl. Phys. Lett. 101, 152405 (2012); http://dx.doi.org/10.1063/1.4759039 (5 pages) | Cited 1 time

Online Publication Date: 11 October 2012

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Growth of nm-thick yttrium iron garnet films and ferromagnetic resonance (FMR) linewidth properties in the films are reported. The films were grown on gadolinium gallium garnet substrates by pulsed laser deposition (PLD). Films in the 5–35 nm thickness range showed a (111) orientation and a surface roughness between 0.1 and 0.3 nm. The 10 nm films showed a 10 GHz FMR linewidth of about 6 Oe and a damping constant of 3.2 × 10−4. The FMR linewidth increases with both the surface roughness and the surface Fe deficiency. Thicker films exhibit a smaller FMR linewidth and a lower damping constant.
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76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
81.15.Fg Pulsed laser ablation deposition
75.70.Ak Magnetic properties of monolayers and thin films
75.50.Cc Other ferromagnetic metals and alloys
68.55.A- Nucleation and growth
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