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27 Aug 2012

Volume 101, Issue 9, Articles (09xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 101, 091102 (2012); http://dx.doi.org/10.1063/1.4747168 (3 pages)

Hagay Shpaisman, Bhaskar Jyoti Krishnatreya, and David G. Grier
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Hard HfB2 tip-coatings for ultrahigh density probe-based storage

Noureddine Tayebi, Angel Yanguas-Gil, Navneet Kumar, Yuegang Zhang, John R. Abelson, Yoshio Nishi, Qing Ma, and Valluri R. Rao

Appl. Phys. Lett. 101, 091909 (2012); http://dx.doi.org/10.1063/1.4748983 (5 pages)

Online Publication Date: 29 August 2012

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Probe-tip mechanical wear is a fundamental issue facing probe-based storage, which can cause serious degradation of the write-read resolution over the device lifetime. HfB2 conductive coatings grown at low temperatures using chemical vapor deposition possess high mechanical properties that are ideal for this technology. Here, we show that HfB2 coated probe-tips can potentially enhance a previously demonstrated 5 km wear endurance mechanism developed using PtIr coated probe-tips to beyond 8 km, thereby increasing the lifetime of probe-based memory devices. We foresee the extension of this coating technology to other scanning probe based systems and nanoelectromechanical devices.
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85.70.Li Other magnetic recording and storage devices (including tapes, disks, and drums)
62.20.Qp Friction, tribology, and hardness
81.40.Pq Friction, lubrication, and wear
68.55.at Other materials
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Temperature dependent recombination dynamics in InP/ZnS colloidal nanocrystals

R. Shirazi, O. Kopylov, A. Kovacs, and B. E. Kardynał

Appl. Phys. Lett. 101, 091910 (2012); http://dx.doi.org/10.1063/1.4749276 (4 pages)

Online Publication Date: 30 August 2012

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In this letter, we investigate exciton recombination in InP/ZnS core-shell colloidal nanocrystals over a wide temperature range. Over the entire range between room temperature and liquid helium temperature, multi-exponential exciton decay curves are observed and well explained by the presence of bright and dark exciton states, as well as defect states. Two different types of defect are present: one located at the core-shell interface and the other on the surface of the nanocrystal. Based on the temperature dependent contributions of all four states to the total photoluminescence signal, we estimate that the four states are distributed within a 20 meV energy band in nanocrystals that emit at 1.82 eV.
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71.35.-y Excitons and related phenomena
71.55.Ht Other nonmetals
73.20.At Surface states, band structure, electron density of states
78.55.Hx Other solid inorganic materials
79.20.Fv Electron impact: Auger emission
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Direct writing of Au nanoneedles array on glass by confined laser spinning

Yingling Yang, Dong Lin, and Gary J. Cheng

Appl. Phys. Lett. 101, 091911 (2012); http://dx.doi.org/10.1063/1.4746427 (3 pages)

Online Publication Date: 30 August 2012

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Generation of gold nanoneedles on glass by confined laser spinning was explored by using a nanosecond pulsed laser. When the coated Au thin film was irradiated under the confinement of glass, gold nanoneedles were formed by spreading the molten liquid of gold under high pressure. The mechanism of the confined laser spinning process is studied. The maximum velocity and instability of molten liquid during confined laser spinning were estimated. The diameter of nanoneedles can be controlled by changing the thickness of coated gold thin film. Large scale of gold nanoneedles can be formed by this direct writing method and collected by confined glass.
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81.15.Fg Pulsed laser ablation deposition
81.16.Mk Laser-assisted deposition
62.50.-p High-pressure effects in solids and liquids
68.55.aj Insulators
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Characterization of Ni(Si,Ge) films on epitaxial SiGe(100) formed by microwave annealing

Cheng Hu, Peng Xu, Chaochao Fu, Zhiwei Zhu, Xindong Gao, Asghar Jamshidi, Mohammad Noroozi, Henry Radamson, Dongping Wu, and Shi-Li Zhang

Appl. Phys. Lett. 101, 092101 (2012); http://dx.doi.org/10.1063/1.4748111 (5 pages) | Cited 1 time

Online Publication Date: 27 August 2012

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Microwave annealing (MWA) is investigated as an alternative technique to rapid thermal processing with halogen lamp heating (RTP) for low-temperature silicide formation on epitaxially grown Si0.81Ge0.19 layers. Phase formation, resistivity mapping, morphology analysis, and composition evaluation indicate that the formation of low-resistivity NiSi1−xGex by means of MWA occurs at temperatures about 100 °C lower than by RTP. Under similar annealing conditions, more severe strain relaxation and defect generation are therefore found in the remaining Si0.81Ge0.19 layers treated by MWA. Although silicidation by microwave heating is in essence also due to thermal effects, details in heating mechanisms differ from RTP.
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81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
81.15.Kk Vapor phase epitaxy; growth from vapor phase
73.61.Le Other inorganic semiconductors
68.55.ag Semiconductors
68.35.bg Semiconductors
61.72.Cc Kinetics of defect formation and annealing

Dopants effect on the band structure of PbTe thermoelectric material

Y. Takagiwa, Y. Pei, G. Pomrehn, and G. J. Snyder

Appl. Phys. Lett. 101, 092102 (2012); http://dx.doi.org/10.1063/1.4748363 (3 pages) | Cited 2 times

Online Publication Date: 27 August 2012

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PbTe is a promising thermoelectric material and its dimensionless figure of merit, zT, can be enhanced by optimizing the band structure near the Fermi level via chemical doping. This letter describes the dopants effect on bandgap, Eg, and effective mass, m*, for disordered La- and I-doping, based on theoretical calculations. Eg increases with increasing La and decreases with increasing I concentration. While m* increases upon La-doping, I-doping does not change m* noticeably. The calculated results are qualitatively consistent with the experimental results and explain the higher zT, up to 1.4 at 800 K, observed in I-doping PbTe compared to La-doping.
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61.72.up Other materials
61.72.sd Impurity concentration
72.80.Jc Other crystalline inorganic semiconductors
71.20.Nr Semiconductor compounds
72.20.Pa Thermoelectric and thermomagnetic effects
71.18.+y Fermi surface: calculations and measurements; effective mass, g factor

Full swing logic inverter with amorphous SiInZnO and GaInZnO thin film transistors

Pulak Chandra Debnath and Sang Yeol Lee

Appl. Phys. Lett. 101, 092103 (2012); http://dx.doi.org/10.1063/1.4747800 (3 pages)

Online Publication Date: 27 August 2012

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A high-performance n-channel metal-oxide-semiconductor inverter implemented consisting of enhancement mode driving thin-film transistor with amorphous Ga-In-Zn-O (a-GIZO) and depletion mode load with amorphous Si-In-Zn-O (a-SIZO) is demonstrated. The threshold voltage of the post-annealed a-SIZO load thin film transistor (TFT) exhibits negative value while the threshold voltage of the GIZO driving TFT exhibits positive value. The proposed inverter composed of a-SIZO and a-GIZO TFT shows much improved switching characteristics with higher voltage gain.
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84.30.Sk Pulse and digital circuits
85.30.Tv Field effect devices

Hydrostatic pressure and strain effects in short period InN/GaN superlattices

I. Gorczyca, T. Suski, N. E. Christensen, and A. Svane

Appl. Phys. Lett. 101, 092104 (2012); http://dx.doi.org/10.1063/1.4748325 (5 pages) | Cited 2 times

Online Publication Date: 28 August 2012

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The electronic structures of short-period pseudomorphically grown superlattices (SLs) of the form mInN/nGaN are calculated and the band gap variation with the well and the barrier thicknesses is discussed including hydrostatic pressure effects. The calculated band gap shows a strong dependence on the superlattice geometry. The superlattice gap vanishes for n = m ≥ 4. These effects are related to the existence of the internal electric fields that strongly influence the valence- and conduction-band profiles and thus determine the effective band gap and emission energies. The electric field strength depends strongly on the strain conditions and SL geometry, but weakly on the applied external hydrostatic pressure.
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71.20.Nr Semiconductor compounds
73.21.Cd Superlattices
78.67.De Quantum wells
81.07.St Quantum wells
78.55.Cr III-V semiconductors

Low-temperature formation of epitaxial graphene on 6H-SiC induced by continuous electron beam irradiation

Heungseok Go, Jinsung Kwak, Youngeun Jeon, Sung-Dae Kim, Byung Cheol Lee, Hyun Suk Kang, Jae-Hyeon Ko, Nam Kim, Bum-Kyu Kim, Jung-Woo Yoo, Sung Youb Kim, Young-Woon Kim, Soon-Yong Kwon, and Kibog Park

Appl. Phys. Lett. 101, 092105 (2012); http://dx.doi.org/10.1063/1.4748592 (4 pages)

Online Publication Date: 28 August 2012

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It is observed that epitaxial graphene forms on the surface of a 6H-SiC substrate by irradiating electron beam directly on the sample surface in high vacuum at relatively low temperature (∼670 °C). The symmetric shape and full width at half maximum of 2D peak in the Raman spectra indicate that the formed epitaxial graphene is turbostratic. The gradual change of the Raman spectra with electron beam irradiation time increasing suggests that randomly distributed small grains of epitaxial graphene form first and grow laterally to cover the entire irradiated area. The sheet resistance of epitaxial graphene film is measured to be ∼6.7 kΩ/sq.
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68.55.ap Fullerenes
81.05.ue Graphene
78.66.Tr Fullerenes and related materials
78.30.Na Fullerenes and related materials
73.61.Wp Fullerenes and related materials
61.80.Fe Electron and positron radiation effects

Band alignment of a carbon nanotube/n-type 6H-SiC heterojunction formed by surface decomposition of SiC using photoelectron spectroscopy

Takahiro Maruyama, Satoshi Sakakibara, Shigeya Naritsuka, Wataru Norimatsu, Michiko Kusunoki, Hiroyuki Yamane, and Nobuhiro Kosugi

Appl. Phys. Lett. 101, 092106 (2012); http://dx.doi.org/10.1063/1.4748792 (4 pages)

Online Publication Date: 28 August 2012

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Energy band alignment at the interface between carbon nanotubes (CNTs) and n-type 6H-SiC formed by the surface decomposition of SiC was investigated using high-resolution photoelectron spectroscopy (PES). Valence band spectra of the CNT films showed a Fermi edge, indicating metallic character. PES results revealed that a Schottky barrier was formed at the interface and the barrier height was 1.38 eV. Current-voltage measurements of the interface showed rectifying behavior, which was consistent with the PES results.
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73.30.+y Surface double layers, Schottky barriers, and work functions
73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
79.60.Jv Interfaces; heterostructures; nanostructures
73.40.Ei Rectification

Anomalous behavior of negative bias illumination stress instability in an indium zinc oxide transistor: A cation combinatorial approach

Seungha Oh, Bong Seob Yang, Yoon Jang Kim, Myeong Sook Oh, Mi Jang, Hoichang Yang, Jae Kyeong Jeong, Cheol Seong Hwang, and Hyeong Joon Kim

Appl. Phys. Lett. 101, 092107 (2012); http://dx.doi.org/10.1063/1.4748884 (5 pages) | Cited 1 time

Online Publication Date: 29 August 2012

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This study examined the effects of the indium fraction in indium zinc oxide (IZO) on the performance and stability of IZO thin film transistors (TFTs). The field-effect mobility and sub-threshold swing were much improved with increasing In fraction; 41.0 cm2/Vs and 0.2 V/decade, respectively, at 85 at. % In, compared to 1.1 cm2/Vs and 2.4 V/decade of ZnO TFTs. In contrast, a local minimum negative bias illumination stress instability was observed near 73–77 at. % In. This behavior was explained by a poly-crystalline to amorphous phase transition in IZO thin films.
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85.30.Tv Field effect devices

High energy sideband on the magnetic polaron related luminescence in EuTe

E. Heredia, P. Motisuke, P. H. de Oliveira Rappl, M. J. S. P. Brasil, and F. Iikawa

Appl. Phys. Lett. 101, 092108 (2012); http://dx.doi.org/10.1063/1.4748981 (4 pages)

Online Publication Date: 29 August 2012

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We investigated the near band gap luminescence of EuTe thin films grown by molecular beam epitaxy, using excitation intensities up to 2 × 105 W/cm2. Besides the previously reported high energy emissions MX1 and MX2, we observed an additional emission band at higher energies. This higher-energy band is only detected when high excitation intensities, over 2 kW/cm2, are used. With increasing externally applied magnetic field, this additional emission band shifts to lower energies at a rate even higher than the MX1. The two bands, however, have different temperature dependences and decay times, suggesting that distinct electronic states are involved in their emission.
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78.55.Hx Other solid inorganic materials
71.38.-k Polarons and electron-phonon interactions
68.55.ag Semiconductors
75.50.Pp Magnetic semiconductors
71.20.Nr Semiconductor compounds
75.70.Ak Magnetic properties of monolayers and thin films

Time-resolved optical measurements of minority carrier recombination in a mid-wave infrared InAsSb alloy and InAs/InAsSb superlattice

B. V. Olson, E. A. Shaner, J. K. Kim, J. F. Klem, S. D. Hawkins, L. M. Murray, J. P. Prineas, M. E. Flatté, and T. F. Boggess

Appl. Phys. Lett. 101, 092109 (2012); http://dx.doi.org/10.1063/1.4749842 (4 pages) | Cited 3 times

Online Publication Date: 30 August 2012

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Measurements of carrier recombination rates using time-resolved differential transmission are reported for an unintentionally doped mid-wave infrared InAsSb alloy and InAs/InAsSb superlattice. Measurements at 77 K yield minority carrier lifetimes of 3 μs and 9 μs for the InAsSb alloy and InAs/InAsSb superlattice, respectively. The un-optimized InAsSb-based materials also exhibit long lifetimes (>850 ns) at temperatures up to 250 K, indicating the potential use for these materials as mid-wave infrared photodetectors with improved performance over current type-II superlattice photodetectors at both cryogenic and near-ambient operating temperatures.
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73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
73.61.Ey III-V semiconductors
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
85.60.Gz Photodetectors (including infrared and CCD detectors)
78.47.D- Time resolved spectroscopy (>1 psec)
72.20.Jv Charge carriers: generation, recombination, lifetime, and trapping

Low-temperature pseudo-metal-oxide-semiconductor field-effect transistor measurements on bare silicon-on-insulator wafers

A. Diab, L. Pirro, I. Ionica, X. Mescot, G. Ghibaudo, and S. Cristoloveanu

Appl. Phys. Lett. 101, 092110 (2012); http://dx.doi.org/10.1063/1.4748984 (4 pages)

Online Publication Date: 30 August 2012

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We extend the pseudo-metal-oxide-semiconductor field-effect transistor (Ψ-MOSFET) technique to the low-temperature range in order to investigate the transport properties of as-fabricated silicon-on-insulator (SOI) wafers. This paper shows experimental results on the temperature dependence of drain current and extracted parameters (hole and electron mobility, subthreshold slope, and threshold voltage). In ultrathin SOI films, the coupling between channel and free surface is strong, degrading the subthreshold swing and threshold voltage. The impact of interface trap density is significant at low temperature. The good correlation between experimental and theoretical curves proves the feasibility of Ψ-MOSFET measurements on bare silicon-on-insulator wafers at low-temperature.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
85.30.Tv Field effect devices
72.20.Fr Low-field transport and mobility; piezoresistance
73.20.At Surface states, band structure, electron density of states
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Strong exchange bias with the (110)-oriented BiFeO3 films

Feiming Bai, Guo Yu, Yicheng Wang, Lichuan Jin, Huizhong Zeng, Xiaoli Tang, Zhiyong Zhong, and Huaiwu Zhang

Appl. Phys. Lett. 101, 092401 (2012); http://dx.doi.org/10.1063/1.4748160 (5 pages) | Cited 1 time

Online Publication Date: 27 August 2012

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Epitaxial BiFeO3 films were grown on the (001)-, (110)-, and (111)-oriented SrTiO3 substrates. Using CoFe as ferromagnetic layer, we have shown that both large exchange bias and coercive field enhancement can be observed in the (001)- and (110)-oriented BiFeO3. But no exchange bias was found in the (111)-oriented BiFeO3 films, which can be understood by the lack of either 109° or 71° ferroelectric domain walls and the preservation of the spatial modulated cycloid spin structure. The observation of large exchange bias field with the (110)-oriented BiFeO3 film may lead to an alternative choice towards reversible control exchange bias by electrical field.
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75.85.+t Magnetoelectric effects, multiferroics
77.84.-s Dielectric, piezoelectric, ferroelectric, and antiferroelectric materials
77.80.-e Ferroelectricity and antiferroelectricity
77.80.Dj Domain structure; hysteresis
68.55.at Other materials
77.22.Ej Polarization and depolarization

Prevention of dewetting during annealing of FePt films for bit patterned media applications

A. T. McCallum, D. Kercher, J. Lille, D. Weller, and O. Hellwig

Appl. Phys. Lett. 101, 092402 (2012); http://dx.doi.org/10.1063/1.4748162 (4 pages) | Cited 3 times

Online Publication Date: 27 August 2012

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We investigated different fabrication methods for (002) textured high anisotropy L10-FePt thin continuous films. While depositing at elevated temperature or post-annealing yields discontinuous or very rough films unsuitable for bit patterned media (BPM) fabrication, post-annealing with an additional SiO2 cap layer results in smooth continuous L10-FePt thin films that can be used for patterning. The SiO2 layer can be removed after annealing without significantly damaging the FePt, thus allowing additional deposition of lower anisotropy layers for forming exchange coupled composite or other layered BPM structures.
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81.05.Bx Metals, semimetals, and alloys
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
81.40.Gh Other heat and thermomechanical treatments
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
75.70.Ak Magnetic properties of monolayers and thin films
75.30.Gw Magnetic anisotropy

Information-signal-transfer rate and energy loss in coupled vortex-state networks

Ji-Hye Kim, Ki-Suk Lee, Hyunsung Jung, Dong-Soo Han, and Sang-Koog Kim

Appl. Phys. Lett. 101, 092403 (2012); http://dx.doi.org/10.1063/1.4748885 (4 pages) | Cited 1 time

Online Publication Date: 28 August 2012

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We employed analytical and micromagnetic numerical calculations to elucidate coupled-vortex-gyration-enabled information-signal transfer and the related energy attenuation between vortex-state nanodisks. Specifically, we explored the vortex-gyration transfer rate and the energy attenuation coefficient in terms of the material parameters and dimensions of the coupled disks. Both the micromagnetic simulation and analytical results indicated that the transfer rate is determined by the relative polarization configuration, the saturation magnetization Ms, the radius (R)-to-thickness (L) ratio (R/L) of the given magnetic disks, and the interdistance, whereas the energy attenuation is governed by the intrinsic damping constant as well as the values of Ms, L, and R of the single disks. This work provides a foundation for manipulation of the technologically essential parameters in signal processing, namely speed and energy loss, based on coupled vortex-state networks.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
02.60.-x Numerical approximation and analysis

Crossover to striped magnetic domains in Fe1−xGax magnetostrictive thin films

M. Barturen, B. Rache Salles, P. Schio, J. Milano, A. Butera, S. Bustingorry, C. Ramos, A. J. A. de Oliveira, M. Eddrief, E. Lacaze, F. Gendron, V. H. Etgens, and M. Marangolo

Appl. Phys. Lett. 101, 092404 (2012); http://dx.doi.org/10.1063/1.4748122 (4 pages) | Cited 1 time

Online Publication Date: 28 August 2012

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We have studied the magnetic properties at room temperature of Fe1−xGax (FeGa) epitaxial thin films grown on ZnSe/GaAs(100) for 0.14 ≤ x ≤ 0.29 range concentration, and film thicknesses, d = 36 and 72 nm. The study was performed by means of magnetometric measurements and magnetic force microscopy scans. Increasing x promotes the loss of the four-fold magnetic-crystalline anisotropy associated to an Fe-like behavior, which is lost completely above x = 0.20. Stripe domains with rotatable anisotropy are observed even in samples in which the theoretical conditions for stripe appearance are not completely fulfilled. An unexpected “saw-tooth” stripe structure has been found under certain conditions.
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75.70.Kw Domain structure (including magnetic bubbles and vortices)
75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy

Spin-wave excitations induced by spin current through a magnetic point contact with a confined domain wall

Hiroko Arai, Hiroshi Tsukahara, and Hiroshi Imamura

Appl. Phys. Lett. 101, 092405 (2012); http://dx.doi.org/10.1063/1.4745777 (3 pages)

Online Publication Date: 28 August 2012

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Using micromagnetic simulations, we studied spin-wave excitations induced by spin current through a nanometer-sized magnetic point contact with a confined domain wall. We found that the spin-wave excitations could be classified into three different modes by their spatial distribution profiles and oscillation frequencies. One is a localized mode while the other two are spreading modes. The oscillation frequency of the localized mode can be controlled in a wide range from 5 GHz to 147 GHz by varying the applied current density.
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75.30.Ds Spin waves
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.50.Tt Fine-particle systems; nanocrystalline materials
75.60.Ch Domain walls and domain structure
75.78.Cd Micromagnetic simulations
75.78.Fg Dynamics of domain structures

Low-temperature ordering of FePt thin films induced by glow-discharge ion bombardment

F. T. Yuan, Jen-Hwa Hsu, A. C. Sun, S. N. Hsiao, and H. Y. Lee

Appl. Phys. Lett. 101, 092406 (2012); http://dx.doi.org/10.1063/1.4749274 (5 pages)

Online Publication Date: 30 August 2012

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This study investigates the effect of glow-discharge induced ion bombardment (IB) on low-temperature ordering in FePt films. H, He, and Ar ions are used. Extensive ordering occurs at 300 °C via IB at energy below sputtering threshold, achieving the degree of ordering comparable to 400 °C of thermal annealing. Distinct ordering mechanism is identified. H-IB films undergo grain-growth-dominated transformation, similar to thermal annealing. However, Ar-IB modifies diffusion behavior causing nucleation-controlled process, realizing high ordering and refined microstructure simultaneously. The mechanisms can be thoroughly elucidated by diffusion-modified nucleation-growth kinetics. The results significantly contribute to efforts in microstructure engineering for advanced thin film devices.
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79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
82.33.Xj Plasma reactions (including flowing afterglow and electric discharges)
61.80.Jh Ion radiation effects
61.82.Bg Metals and alloys
68.55.A- Nucleation and growth
81.40.Gh Other heat and thermomechanical treatments

Nanostructured thin manganite films in megagauss magnetic field

S. Balevičius, N. Žurauskienė, V. Stankevič, S. Keršulis, V. Plaušinaitienė, A. Abrutis, S. Zherlitsyn, T. Herrmannsdörfer, J. Wosnitza, and F. Wolff-Fabris

Appl. Phys. Lett. 101, 092407 (2012); http://dx.doi.org/10.1063/1.4749820 (4 pages) | Cited 1 time

Online Publication Date: 30 August 2012

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We report on the use of the colossal magnetoresistance (CMR) effect in manganites for the measurement of pulsed magnetic fields up to the megagauss limit. To increase the application range in a magnetic field, we fabricated nanostructured La-Sr-Mn-O films consisting of nanocrystallites cummulated into clusters separated by highly amorphous inter-cluster boundaries. We demonstrate that the CMR effect does not saturate in these films at 77 K up to 91.4 T. Moreover, the magnetoresistance behavior at 290 K shows that nanostructured manganite films are promising candidates for the development of magnetic field scalar sensors operating in wide field and temperature ranges.
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81.16.-c Methods of micro- and nanofabrication and processing
75.75.Cd Fabrication of magnetic nanostructures
75.70.Ak Magnetic properties of monolayers and thin films
75.47.Gk Colossal magnetoresistance
81.07.Bc Nanocrystalline materials
75.47.Lx Magnetic oxides
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Low-frequency critical current noise in Josephson junctions induced by temperature fluctuations

S. M. Anton, C. D. Nugroho, J. S. Birenbaum, S. R. O’Kelley, V. Orlyanchik, A. F. Dove, G. A. Olson, Z. R. Yoscovits, J. N. Eckstein, D. J. Van Harlingen, and John Clarke

Appl. Phys. Lett. 101, 092601 (2012); http://dx.doi.org/10.1063/1.4749282 (4 pages) | Cited 2 times

Online Publication Date: 30 August 2012

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We demonstrate a spurious contribution to low-frequency critical current noise in Josephson junctions—normally attributed to charge trapping in the barrier—arising from temperature instabilities inherent in cryogenic systems. These temperature fluctuations modify the critical current via its temperature dependence. Cross-correlations between measured temperature and critical current noise in Al-AlOx-Al junctions show that, despite excellent temperature stability, temperature fluctuations induce observable critical current fluctuations. Particularly, because 1/f critical current noise has decreased with improved fabrication techniques in recent years, it is important to understand and eliminate this additional noise source.
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74.40.De Noise and chaos
74.50.+r Tunneling phenomena; Josephson effects
74.25.Sv Critical currents
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Dielectric enhancement in amorphous TaxGe1−xOy thin films

Taro A. Naoi, Sara C. Barron, Maxim M. Noginov, and R. B. van Dover

Appl. Phys. Lett. 101, 092901 (2012); http://dx.doi.org/10.1063/1.4748158 (3 pages)

Online Publication Date: 27 August 2012

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We report that the dielectric constant can be increased in amorphous thin film TaxGe1−xOy over pure amorphous Ta2O5. With only 3% substitution of Ge for Ta the relative dielectric constant εr rises to 30.5, a 40% increase over the value obtained for pure amorphous Ta2O5 films deposited under identical conditions (εr = 22). No enhancement is observed in the optical dielectric constant (i.e., refractive index). This suggests that the enhancement is dominated by the effects in the ionic polarizability rather than the electronic polarizability. This system represents a valuable opportunity to explore the sensitive relationship between bonding and electronic properties in amophous oxides.
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77.22.Ch Permittivity (dielectric function)
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
77.22.Ej Polarization and depolarization
78.66.Jg Amorphous semiconductors; glasses
73.61.Jc Amorphous semiconductors; glasses

Screening of ferroelectric domains on BaTiO3(001) surface by ultraviolet photo-induced charge and dissociative water adsorption

J. L. Wang, B. Vilquin, and N. Barrett

Appl. Phys. Lett. 101, 092902 (2012); http://dx.doi.org/10.1063/1.4748330 (3 pages) | Cited 1 time

Online Publication Date: 27 August 2012

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The surface potential contrast between oppositely polarized ferroelectric domains of a BaTiO3(001) single crystal under ultraviolet (UV) illumination before and after the dissociative adsorption of water is measured using the transition from mirror electron microscopy to low-energy electron microscopy. Both photo-generated free charge carriers and dissociative adsorption of water are effective screening mechanisms of the surface polarization charge. The screening rate is dominated by drift, whereas the relaxation in the absence of UV light is driven by thermal diffusion. Surface chemistry plays an important role in the surface charge dynamics.
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77.80.Dj Domain structure; hysteresis
68.43.Mn Adsorption kinetics
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
68.43.Jk Diffusion of adsorbates, kinetics of coarsening and aggregation
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
77.22.Ej Polarization and depolarization

Colossal intrinsic magnetoelectric effect in Pb(Fe2/3W1/3)0.83Ti0.17O3

B. Fraygola, Adelino A. Coelho, D. Garcia, and J. A. Eiras

Appl. Phys. Lett. 101, 092903 (2012); http://dx.doi.org/10.1063/1.4748819 (3 pages)

Online Publication Date: 27 August 2012

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Dielectric and magnetic properties were investigated in Pb(Fe2/3W1/3)0.83Ti0.17O3 ceramics. The dielectric constant in these samples exhibits colossal changes at the magnetic ordering temperature under the presence of bias external electric fields, which presents a close connection with magnetoelectrics effects (ME), confirming the possibility to control magnetic proprieties with electric fields. The ferroelectromagnetoelastic coefficient was determined from the dielectric response as a function of the electric field. The analysis of magnetic and dielectric susceptibilities based on the Landau-Devonshire thermodynamic formalisms indicates that the ME effects is a contribution of intrinsic ME coupling and a field dependent term.
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75.85.+t Magnetoelectric effects, multiferroics
77.22.Ch Permittivity (dielectric function)
81.40.Jj Elasticity and anelasticity, stress-strain relations
62.20.de Elastic moduli
75.30.Cr Saturation moments and magnetic susceptibilities
65.40.G- Other thermodynamical quantities

Surfactant assisted growth of MgO films on GaN

E. A. Paisley, T. C. Shelton, S. Mita, R. Collazo, H. M. Christen, Z. Sitar, M. D. Biegalski, and J.-P. Maria

Appl. Phys. Lett. 101, 092904 (2012); http://dx.doi.org/10.1063/1.4748886 (4 pages)

Online Publication Date: 28 August 2012

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Thin epitaxial films of 〈111〉 oriented MgO on [0001]-oriented GaN were grown by molecular beam epitaxy and pulsed laser deposition using the assistance of a vapor phase surfactant. In both cases, surfactant incorporation enabled layer-by-layer growth and a smooth terminal surface by stabilizing the {111} rocksalt facet. Metal-insulator-semiconductor capacitor structures were fabricated on n-type GaN. A comparison of leakage current density for conventional and surfactant-assisted growth reveals a nearly 100× reduction in leakage current density for the surfactant-assisted samples. These data verify numerous predictions regarding the role of H-termination in regulating the habit of rocksalt crystals.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
84.32.Tt Capacitors
81.15.Fg Pulsed laser ablation deposition
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