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15 Oct 2007

Volume 91, Issue 16, Articles (16xxxx)

Issue Cover Spotlight Figure

Appl. Phys. Lett. 91, 162101 (2007); http://dx.doi.org/10.1063/1.2794995 (3 pages)

D. J. Reilly, C. M. Marcus, M. P. Hanson, and A. C. Gossard
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High porosity metallic glass foam: A powder metallurgy route

Marios D. Demetriou, Joseph P. Schramm, Chris Veazey, William L. Johnson, Jay C. Hanan, and Nicholas B. Phelps

Appl. Phys. Lett. 91, 161903 (2007); http://dx.doi.org/10.1063/1.2799248 (3 pages) | Cited 9 times

Online Publication Date: 15 October 2007

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A powder metallurgy route to the fabrication of metallic glass foam is introduced. The method involves consolidating metallic glass powder blended with blowing agent particulates to produce expandable precursors, capable of yielding foams with porosities as high as 86%. The foams are found to inherit the strength of the parent metallic glass and to be able to deform heavily toward full densification absorbing high amounts of energy.
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82.70.Rr Aerosols and foams
81.20.Ev Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation

In situ investigation of growth modes during plasma-assisted molecular beam epitaxy of (0001) GaN

G. Koblmüller, S. Fernández-Garrido, E. Calleja, and J. S. Speck

Appl. Phys. Lett. 91, 161904 (2007); http://dx.doi.org/10.1063/1.2789691 (3 pages) | Cited 26 times

Online Publication Date: 15 October 2007

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Real-time analysis of the growth modes during homoepitaxial (0001) GaN growth by plasma-assisted molecular beam epitaxy was performed using reflection high energy electron diffraction. A growth mode map was established as a function of Ga/N flux ratio and growth temperature, exhibiting distinct transitions between three-dimensional (3D), layer-by-layer, and step-flow growth modes. The layer-by-layer to step-flow growth transition under Ga-rich growth was surfactant mediated and related to a Ga adlayer coverage of one monolayer. Under N-rich conditions the transition from 3D to layer-by-layer growth was predominantly thermally activated, facilitating two-dimensional growth at temperatures of thermal decomposition.
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81.05.Ea III-V semiconductors
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
68.55.A- Nucleation and growth
52.77.Dq Plasma-based ion implantation and deposition
68.35.B- Structure of clean surfaces (and surface reconstruction)
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)

Effect of backing layer thickness on adhesion of single-level elastomer fiber arrays

Seok Kim, Metin Sitti, Chung-Yuen Hui, Rong Long, and Anand Jagota

Appl. Phys. Lett. 91, 161905 (2007); http://dx.doi.org/10.1063/1.2801371 (3 pages) | Cited 16 times

Online Publication Date: 15 October 2007

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The effect of the backing layer thickness on adhesion was investigated for single-level elastomer fibrillar adhesives. Polyurethane microfiber arrays with spatulated tips on a 160 μm thick backing layer show nine times greater adhesion strength (around 22 N/cm2) than those with a 1120 μm thick backing. A theoretical model is proposed to explain this difference in which very thin backing layers promote equal load sharing, maximizing adhesion, while very thick backings can lead to reduced adhesion due to edge stress concentration. Therefore, backing layer thickness should be considered as a significant parameter for design of high performance fibrillar adhesives.
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82.35.Gh Polymers on surfaces; adhesion
62.20.-x Mechanical properties of solids
81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties

Initial interactions between water molecules and Ti-adsorbed carbon nanotubes

Yang Lei, Zheng Xiao Guo, Wenguang Zhu, Sheng Meng, and Zhenyu Zhang

Appl. Phys. Lett. 91, 161906 (2007); http://dx.doi.org/10.1063/1.2793182 (3 pages) | Cited 5 times

Online Publication Date: 16 October 2007

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Spin-polarized first-principles calculations were employed to study the initial stages of water interactions with Ti-doped carbon nanotubes (CNTs), aiming to explore their potentials for water splitting to generate hydrogen or as practical hydrogen storage systems involving moisture. The rate-limiting barrier for splitting the first H2O is 0.48 eV on a semiconducting (8,0) CNT, and 0.41 eV on a metallic (5,5) CNT. The barrier for splitting the second H2O is only 0.12 eV, accompanied by the formation and release of a H2 molecule.
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68.43.Mn Adsorption kinetics
84.60.-h Direct energy conversion and storage

Cross-sectional scanning tunneling microscopy study on II–VI multilayer structures

A. Wierts, J. M. Ulloa, C. Çelebi, P. M. Koenraad, H. Boukari, L. Maingault, R. André, and H. Mariette

Appl. Phys. Lett. 91, 161907 (2007); http://dx.doi.org/10.1063/1.2799254 (3 pages)

Online Publication Date: 17 October 2007

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Cross-sectional scanning tunneling microscopy is used to study in the atomic scale the structural properties of ZnSeTe/ZnTe multiple quantum wells and N:ZnTe delta-doped structures. Some peculiar effects are found on the cleaved (110) ZnTe surface plane, which have not been observed in III–V semiconductors. In particular, cleavage induced monatomic wide vacancy chains are always present on the Te sublattice. Furthermore, the semiconductor surface is manipulated when certain positive voltages are applied to the sample. Regarding the heterostructures, the ZnSeTe/ZnTe quantum wells are found to have abrupt interfaces and the Se concentration is determined to be significantly larger than the nominal value.
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68.65.Fg Quantum wells
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)

Low-temperature formation of SiO2 layers using a two-step atmospheric pressure plasma-enhanced deposition-oxidation process

Hiroaki Kakiuchi, Hiromasa Ohmi, Makoto Harada, Heiji Watanabe, and Kiyoshi Yasutake

Appl. Phys. Lett. 91, 161908 (2007); http://dx.doi.org/10.1063/1.2801516 (3 pages) | Cited 1 time

Online Publication Date: 17 October 2007

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Silicon oxide (SiO2) layers were fabricated at low temperatures ( ⩽ 400 °C) by combining the deposition of hydrogenated amorphous Si (a-Si:H) with its oxidation using atmospheric pressure plasmas excited by a 150 MHz very high-frequency (VHF) power. The surface excitation by the atmospheric pressure VHF plasma was capable of reducing the temperature for the hydrogen effusion from a-Si:H. As a result, a porous a-Si:H film containing a large amount of hydrogen could be transformed into a stoichiometric SiO2 with an approximately 24% increase in oxidation rate compared with the oxidation of Si(001) at a temperature of 400 °C.
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61.66.Bi Elemental solids
61.66.Dk Alloys
81.65.Mq Oxidation
81.15.Jj Ion and electron beam-assisted deposition; ion plating
61.43.Gt Powders, porous materials
61.43.Dq Amorphous semiconductors, metals, and alloys
52.77.Dq Plasma-based ion implantation and deposition

Nonlinear behavior of the energy gap in Ge1−xSnx alloys at 4 K

H. Pérez Ladrón de Guevara, A. G. Rodríguez, H. Navarro-Contreras, and M. A. Vidal

Appl. Phys. Lett. 91, 161909 (2007); http://dx.doi.org/10.1063/1.2800296 (3 pages) | Cited 6 times

Online Publication Date: 17 October 2007

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The optical energy gap of Ge1−xSnx alloys (x ⩽ 0.14) grown on Ge substrates has been determined by performing transmittance measurements at 4 K using a fast fourier transform infrared interferometer. The direct energy gap transitions in Ge1−xSnx alloys behave following a nonlinear dependence on the Sn concentration, expressed by a quadratic equation, with a so called bowing parameter b0 that describes the deviation from a simple linear dependence. Our observations resulted in b0RT = 2.30±0.10 eV and b04 K = 2.84±0.15 eV, at room temperature and 4 K, respectively. The validity of our fit is limited for Sn concentrations lower than 15%.
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71.20.Nr Semiconductor compounds
78.30.Hv Other nonmetallic inorganics
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

Decoherence of exciton complexes in single InAlAs quantum dots measured by Fourier spectroscopy

S. Adachi, N. Yatsu, R. Kaji, S. Muto, and H. Sasakura

Appl. Phys. Lett. 91, 161910 (2007); http://dx.doi.org/10.1063/1.2800373 (3 pages) | Cited 13 times

Online Publication Date: 17 October 2007

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We report the single-photon Fourier spectroscopy of exciton and exciton complexes in single self-assembled InAlAs/AlGaAs quantum dots. A Michelson interferometer was inserted in the photoluminescence path for measuring the coherence length of the time-averaged emission of neutral excitons and their complexes. The effects of exchange interactions and fluctuations in the surrounding excess charges were estimated by comparing the coherence times and the excitation energies of the excitons and their complexes.
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78.67.Hc Quantum dots
73.21.La Quantum dots
78.55.Cr III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra

Free exciton emission and dephasing in individual ZnO nanowires

Yang Zhang, Dai-Jang Chen, and Ching-Ting Lee

Appl. Phys. Lett. 91, 161911 (2007); http://dx.doi.org/10.1063/1.2793178 (3 pages) | Cited 7 times

Online Publication Date: 17 October 2007

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We report on systematic measurements of the dephasing of the free excitonic transition in individual ZnO nanowires with a diameter of about 70 nm. The temperature-dependent intensity of the free exciton (FX) emission is well reproduced by a thermally activated behavior having two constant activation energies of 5.98 and 30.63 meV. The FX linewidth broadening with temperature reveals the dephasing of FX scattered by acoustic phonons rather than longitudinal optical phonons. These findings indicate that the dephasing mechanism scattering from acoustic phonons in individual ZnO nanowires result from the compensation of acoustic phonons to the nonconservation of crystal momentum.
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78.67.-n Optical properties of low-dimensional, mesoscopic, and nanoscale materials and structures
78.55.Et II-VI semiconductors
71.35.-y Excitons and related phenomena
63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.22.-m Phonons or vibrational states in low-dimensional structures and nanoscale materials

White light-emitting diodes based on a single InGaN emission layer

X. H. Wang, H. Q. Jia, L. W. Guo, Z. G. Xing, Y. Wang, X. J. Pei, J. M. Zhou, and H. Chen

Appl. Phys. Lett. 91, 161912 (2007); http://dx.doi.org/10.1063/1.2800797 (3 pages) | Cited 9 times

Online Publication Date: 18 October 2007

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White light-emitting InGaN/GaN diode with an InGaN underlying layer grown on the (0001) sapphire substrate was fabricated by low pressure metal-organic vapor phase epitaxy. The electroluminescence measurements show that the emitted white light is composed of blue and yellow lights, centered at around 440 and 570 nm, respectively, for an injection current of 20 mA. Cross-sectional transmission electron microscopy reveals that In-rich quantum dots were formed in InGaN wells due to phase separation of indium. It is suggested that the yellow and blue lights come from In-rich quantum dots and the low-indium regions, respectively, in InGaN quantum wells.
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85.60.Jb Light-emitting devices
81.15.Kk Vapor phase epitaxy; growth from vapor phase
78.60.Fi Electroluminescence
78.67.Hc Quantum dots
78.66.Fd III-V semiconductors

Sample size effect and microcompression of Mg65Cu25Gd10 metallic glass

C. J. Lee, J. C. Huang, and T. G. Nieh

Appl. Phys. Lett. 91, 161913 (2007); http://dx.doi.org/10.1063/1.2800313 (3 pages) | Cited 58 times

Online Publication Date: 19 October 2007

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Micropillars with diameters of 1 and 3.8 μm were fabricated from Mg-based metallic glasses using focus ion beam, and then tested in compression at strain rates ranging from 6×10−5 to 6×10−1 s−1. The apparent yield strength of the micropillars is 1342–1580 MPa, or 60%–100% increment over the bulk specimens. This strength increase can be rationalized using the Weibull statistics for brittle materials, and the Weibull modulus of the Mg-based metallic glasses is estimated to be about 35. Preliminary results indicated that the number of shear bands increased with the sample size and strain rates.
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81.40.Lm Deformation, plasticity, and creep
61.43.Fs Glasses
62.20.F- Deformation and plasticity
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Fast single-charge sensing with a rf quantum point contact

D. J. Reilly, C. M. Marcus, M. P. Hanson, and A. C. Gossard

Appl. Phys. Lett. 91, 162101 (2007); http://dx.doi.org/10.1063/1.2794995 (3 pages) | Cited 31 times

Online Publication Date: 15 October 2007

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We report high-bandwidth charge sensing measurements using a GaAs quantum point contact embedded in a radio frequency impedance matching circuit (rf-QPC). With the rf-QPC biased near pinch-off where it is most sensitive to charge, we demonstrate a conductance sensitivity of 5×10−6 e2/h Hz−1/2 with a bandwidth of 8 MHz. Single-shot readout of a proximal few-electron double quantum dot is investigated in a mode where the rf-QPC back action is rapidly switched.
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73.63.Rt Nanoscale contacts
73.63.Kv Quantum dots
73.21.La Quantum dots
85.35.Gv Single electron devices

Efficient visible light detection using individual germanium nanowire field effect transistors

Y. H. Ahn and Jiwoong Park

Appl. Phys. Lett. 91, 162102 (2007); http://dx.doi.org/10.1063/1.2799253 (3 pages) | Cited 30 times

Online Publication Date: 15 October 2007

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We report photoconductivity (PC) in individual germanium nanowire field effect transistors (GeFETs). PC measurements with a global illumination reveal that GeFETs can be used as a polarization-sensitive nanoscale light detector in the visible range. It is also found that the PC shows sensitive optical response especially in the low intensity regime. We observe a high internal gain in PC in conjunction with strong saturation behavior, which is attributed to the filling of surface trapping states. This mechanism for high internal gain is consistent with spatially resolved scanning photocurrent measurements, whose results confirm that optical absorption is in the linear regime.
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73.63.Bd Nanocrystalline materials
73.50.Pz Photoconduction and photovoltaic effects
85.30.Tv Field effect devices
73.63.Nm Quantum wires
73.40.-c Electronic transport in interface structures

Low-resistance Ni-based Schottky diodes on freestanding n-GaN

L. Lewis, B. Corbett, D. O Mahony, and P. P. Maaskant

Appl. Phys. Lett. 91, 162103 (2007); http://dx.doi.org/10.1063/1.2799739 (3 pages) | Cited 3 times

Online Publication Date: 15 October 2007

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Schottky diodes formed on a low doped (5×1016 cm−3) n-type GaN epilayer grown on a n+ freestanding GaN substrate were studied. The temperature dependent electrical characteristics of Ni contacts on the as-grown material are compared with an aqueous, potassium hydroxide (KOH) treated surface. In both cases the diodes are dominated by thermionic emission in forward bias, with low idealities (1.04 at room temperature) which decrease with increasing temperature, reaching 1.03 at 413 K. The Schottky barrier height is 0.79±0.05 eV for the as-grown surface compared with 0.85±0.05 eV for the KOH treated surface at room temperature. This is consistent with an inhomogeneous barrier distribution. The specific on-state resistance of the diodes is 0.57 mΩ cm2 The KOH treatment reduces the room temperature reverse leakage current density at −30 V to 1×10−5 A cm−2 compared to 6×10−2 A cm−2 for the as-grown samples.
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85.30.Kk Junction diodes
85.30.Hi Surface barrier, boundary, and point contact devices
85.30.De Semiconductor-device characterization, design, and modeling

Determination of the valence band offset of wurtzite InN/ZnO heterojunction by x-ray photoelectron spectroscopy

Riqing Zhang, Panfeng Zhang, Tingting Kang, Haibo Fan, Xianglin Liu, Shaoyan Yang, Hongyuan Wei, Qinsheng Zhu, and Zhanguo Wang

Appl. Phys. Lett. 91, 162104 (2007); http://dx.doi.org/10.1063/1.2800311 (3 pages) | Cited 18 times

Online Publication Date: 17 October 2007

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The valence band offset (VBO) of the wurtzite InN/ZnO heterojunction is directly determined by x-ray photoelectron spectroscopy to be 0.82±0.23 eV. The conduction band offset is deduced from the known VBO value to be 1.85∓0.23 eV, which indicates a type-I band alignment for InN/ZnO heterojunction.
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71.20.Nr Semiconductor compounds
73.20.At Surface states, band structure, electron density of states
79.60.Bm Clean metal, semiconductor, and insulator surfaces
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)

Conductivity fluctuation within a crystalline domain and its origin in pentacene thin-film transistors

Noboru Ohashi, Hiroshi Tomii, Ryousuke Matsubara, Masatoshi Sakai, Kazuhiro Kudo, and Masakazu Nakamura

Appl. Phys. Lett. 91, 162105 (2007); http://dx.doi.org/10.1063/1.2799743 (3 pages) | Cited 13 times

Online Publication Date: 18 October 2007

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Surface topography and high-resolution potential images in a thin-film transistor with a polycrystalline pentacene active layer have been measured by atomic-force-microscope potentiometry. A potential fluctuation independent of topographic features was found in large flat molecular terraces. The origin of the potential fluctuation was concluded to be the fluctuation of the top level of the highest-occupied-molecular-orbital band, which results in the variation of local carrier concentration. The full width at half maximum of the band fluctuation was estimated to be 12 meV, which might reduce the mean carrier velocity in crystalline domains.
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85.30.Tv Field effect devices

Forming single molecular junctions between indium tin oxide electrodes

Fang Chen, Zhifeng Huang, and Nongjian Tao

Appl. Phys. Lett. 91, 162106 (2007); http://dx.doi.org/10.1063/1.2800303 (3 pages) | Cited 7 times

Online Publication Date: 18 October 2007

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We have demonstrated that indium tin oxide (ITO) can be used as contact electrodes to form molecular junctions via ITO-carboxylic acid bonds. We measured the conductance of n-alkane terminated with dicarboxylic acids using conducting atomic force microscope break junction. The conductance decreases exponentially with molecular length with a decay constant of ∼ 0.80 Å−1, which is similar to that of Au-carboxylic acid junctions. However, the contact conductance of ITO-carboxylic acid is smaller than that of Au-carboxylic acid, reflecting different electronic couplings between the linker group and electrodes. From the average breakdown force and stretching length, we estimated the binding energy of ITO-carboxylic acid.
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73.40.Ns Metal-nonmetal contacts

Nonvolatile programmable metallization cell memory switching element based on Ag-doped SbTe solid electrolyte

Young Sam Park, Seung Yun Lee, Sung Min Yoon, Soon Won Jung, Byoung Gon Yu, Soo Jin Lee, and Soon Gil Yoon

Appl. Phys. Lett. 91, 162107 (2007); http://dx.doi.org/10.1063/1.2789663 (3 pages) | Cited 4 times

Online Publication Date: 18 October 2007

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We report that industrially qualified SbTe chalcogenide film can be applied to programmable metallization cell memory switching device. To fabricate the switching device, Sb35Te65, Ag, and W (top electrode) were consequently sputtered on TiW (bottom electrode)/SiO2/Si substrate, and Ag diffusion process was not added. During Ag sputtering, it is apparent that Ag is diffused into Sb35Te65 film to form Ag-doped Sb35Te65 solid electrolyte, and that some of the diffused Ag reacts with Te to form Ag–Te bond in the solid electrolyte.
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84.32.Dd Connectors, relays, and switches
84.30.Sk Pulse and digital circuits
85.30.-z Semiconductor devices

Investigation on the diffusion barrier properties of sputtered Mo/W–N thin films in Cu interconnects

Prodyut Majumder and Christos G. Takoudis

Appl. Phys. Lett. 91, 162108 (2007); http://dx.doi.org/10.1063/1.2800382 (3 pages) | Cited 21 times

Online Publication Date: 18 October 2007

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Mo/W–N bilayer thin film structures deposited on Si using sputtering have been studied as a copper diffusion barrier. The thermal stability of the barrier structure after annealing Cu/Mo/W–N/〈Si〉 samples in N2 for 5 min is studied using x-ray diffraction (XRD), scanning electron microscopy/energy dispersive spectroscopy, and four point probe measurements. The failure of the barrier structure is indicated by the abrupt increase in sheet resistance value and the formation of Cu3Si phase as probed by XRD. Our results suggest that the Mo (5 nm)/W–N (5 nm) barrier is stable and can prevent the formation of Cu3Si at least up to 775 °C.
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68.55.-a Thin film structure and morphology
81.15.Cd Deposition by sputtering
61.72.Cc Kinetics of defect formation and annealing
85.40.Ls Metallization, contacts, interconnects; device isolation
82.80.Ej X-ray, Mössbauer, and other γ-ray spectroscopic analysis methods
66.30.Fq Self-diffusion in metals, semimetals, and alloys

Memory effect of nonvolatile bistable devices based on CdSe/ZnS nanoparticles sandwiched between C60 layers

Fushan Li, Dong-Ick Son, Jung-Hun Ham, Bong-Jun Kim, Jae Hun Jung, and Tae Whan Kim

Appl. Phys. Lett. 91, 162109 (2007); http://dx.doi.org/10.1063/1.2801357 (3 pages) | Cited 18 times

Online Publication Date: 19 October 2007

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Current-voltage and conductance-voltage (G-V) measurements on three-layer Al/C60/CdSe nanoparticles/C60/indium tin oxide (ITO) structures fabricated by using a spin-coating method showed a nonvolatile electrical bistable behavior. Capacitance-voltage (C-V) measurements on Al/C60/CdSe nanoparticles/C60/ITO structures showed a clockwise hysteresis with a flatband voltage shift due to the existence of the CdSe nanoparticles, indicative of memory effects in the devices. Current-time measurements showed that the devices exhibited excellent memory retention ability at ambient conditions. Possible operating mechanisms for the memory effects in the Al/C60/CdSe nanoparticles/C60/ITO devices are described on the basis of the G-V and the C-V results.
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85.30.-z Semiconductor devices
73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.63.Bd Nanocrystalline materials

The metal-insulator transition in VO2 studied using terahertz apertureless near-field microscopy

Hui Zhan, Victoria Astley, Michael Hvasta, Jason A. Deibel, Daniel M. Mittleman, and Yong-Sik Lim

Appl. Phys. Lett. 91, 162110 (2007); http://dx.doi.org/10.1063/1.2801359 (3 pages) | Cited 11 times

Online Publication Date: 19 October 2007

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We have studied the metal-insulator transition in a vanadium dioxide (VO2) thin film using terahertz apertureless near-field optical microscopy. We observe a variation of the terahertz amplitude due to the phase transition induced by an applied voltage across the sample. The change of the terahertz signal is related to the abrupt change of the conductivity of the VO2 film at the metal-insulator transition. The subwavelength spatial resolution of this near-field microscopy makes it possible to detect signatures of micron-scale metallic domains in inhomogeneous VO2 thin films.
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71.30.+h Metal-insulator transitions and other electronic transitions
68.55.-a Thin film structure and morphology
68.37.Uv Near-field scanning microscopy and spectroscopy
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Influence of growth temperature on critical current and magnetic flux pinning structures in YBa2Cu3O7−x

D. M. Feldmann, O. Ugurlu, B. Maiorov, L. Stan, T. G. Holesinger, L. Civale, S. R. Foltyn, and Q. X. Jia

Appl. Phys. Lett. 91, 162501 (2007); http://dx.doi.org/10.1063/1.2799875 (3 pages) | Cited 20 times

Online Publication Date: 15 October 2007

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We have studied the critical current density (Jc) as a function of applied magnetic field (H) magnitude and orientation for ∼ 1-μm-thick YBa2Cu3O7−x films grown by pulsed laser deposition at growth temperatures (Tg) from 730 to 870 °C. With changing Tg, alternately a high density of planar defects (YBa2Cu4Ox intergrowths) or columnar defects (Y–Cu–O nanocolumns) are introduced. These defects produce a maximum for Jc(H ∼ 1 T) parallel to the plane of the film or the film normal, respectively. For Tg ≥ 830 °C, we present evidence of a Ba–Cu–O liquid phase during growth, which results in a dramatic change in both the microstructure of the films and magnetic field orientation dependence of Jc.
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74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
81.15.Fg Pulsed laser ablation deposition
68.55.A- Nucleation and growth

Off-track margin in bit patterned media

Andreas Moser, Olav Hellwig, Dan Kercher, and Elisabeth Dobisz

Appl. Phys. Lett. 91, 162502 (2007); http://dx.doi.org/10.1063/1.2799174 (3 pages) | Cited 16 times

Online Publication Date: 15 October 2007

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When two dimensional patterns are written into bit patterned media the off-track margin is of great importance. Using a static write/read tester we measure the hard error rate (written-in errors) as a function of the distance from the track center. We observe three different segments. In the track center, the head writes very well and almost no hard errors are observed. At the track edges the hard error rate increases linearly over an interval, which is shown to relate to the off-track margin of the recording system. At larger distances from the track center, no islands are switched.
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02.60.-x Numerical approximation and analysis

X-ray absorption and magnetic circular dichroism characterizations of Mn doped ZnO

P. Thakur, K. H. Chae, J.-Y. Kim, M. Subramanian, R. Jayavel, and K. Asokan

Appl. Phys. Lett. 91, 162503 (2007); http://dx.doi.org/10.1063/1.2794764 (3 pages) | Cited 34 times

Online Publication Date: 15 October 2007

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We report the near-edge x-ray absorption fine structure (NEXAFS) and x-ray magnetic circular dichroism (XMCD) experiments on well characterized Mn doped ZnO thin films that show ferromagnetism at room temperature. The NEXAFS measurements at O K edge clearly exhibit a preedge spectral feature which evolves with Mn doping, similar to one observed in hole-doped cuprates and manganites. The Mn L3,2 edge NEXAFS spectra exhibit divalent Mn apart from mixed valent Mn3+/Mn4+ states. The spectral features of XMCD at Mn L3,2 edge demonstrate that ferromagnetism comes from Mn2+ ions and its dichroism shape is independent of Mn concentration.
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78.70.Dm X-ray absorption spectra
78.20.Ls Magneto-optical effects
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors

Influence of oxygen contents of carbohydrate dopants on connectivity and critical current density in MgB2 tapes

Zhaoshun Gao, Yanwei Ma, Xianping Zhang, Dongliang Wang, Huan Yang, Haihu Wen, and K. Watanabe

Appl. Phys. Lett. 91, 162504 (2007); http://dx.doi.org/10.1063/1.2790381 (3 pages) | Cited 10 times

Online Publication Date: 16 October 2007

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More recently, it has been reported that carbohydrate doping resulted in an effective substitution of carbon for boron in MgB2, and hence achieved significant flux pinning enhancement. However, the authors found that the oxygen amount in carbohydrate additives played an important role in improving Jc-B performance in MgB2. In this work, the effect of maleic anhydride (C4H2O3) and maleic acid (C4H4O4) dopants on the superconducting properties of in situ MgB2 tapes has been studied. Compared to the undoped counterpart, both doped tapes showed an enhancement of Jc values by more than an order of magnitude in high-field region; however, the transport Jc of C4H4O4 doped tapes was apparently lower than that of C4H2O3 added samples. The poor grain connectivity as a result of more MgO and voids formed during the reaction in C4H4O4 doped samples can be responsible for the reduced Jc values.
Show PACS
74.25.Sv Critical currents
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
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