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12 Jan 2004

Volume 84, Issue 2, pp. 161-308

Issue Cover Spotlight Figure

Appl. Phys. Lett. 84, 161 (2004); http://dx.doi.org/10.1063/1.1639505 (3 pages)

Hatice Altug and Jelena Vučković
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Two-dimensional coupled photonic crystal resonator arrays

Hatice Altug and Jelena Vučković

Appl. Phys. Lett. 84, 161 (2004); http://dx.doi.org/10.1063/1.1639505 (3 pages) | Cited 40 times

Online Publication Date: 7 January 2004

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We present the design and fabrication of photonic crystal structures exhibiting electromagnetic bands that are flattened in all crystal directions, i.e., whose frequency variation with a wave vector is minimized. Such bands can be used to reduce group velocity of light propagating in an arbitrary crystal direction, which is of importance for the construction of miniaturized tunable optical delay components and low-threshold photonic crystal lasers, and the study of nonlinear optics phenomena. © 2004 American Institute of Physics.
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42.55.Tv Photonic crystal lasers and coherent effects
85.60.Bt Optoelectronic device characterization, design, and modeling

Tuning quantum-cascade lasers by postgrowth rapid thermal processing

S. Anders, W. Schrenk, T. Roch, C. Pflügl, and G. Strasser

Appl. Phys. Lett. 84, 164 (2004); http://dx.doi.org/10.1063/1.1640463 (3 pages) | Cited 1 time

Online Publication Date: 7 January 2004

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We report on postgrowth heat treatment of quantum-cascade lasers. Intermixing of the atoms at the barrier–well interfaces in the temperature range between 850 and 875 °C shifts the energy levels and thus the gain of the structure. The achieved emission wavelength shift is from 10.3 to 11.9 μm. X-ray rocking curves confirm Al–Ga interdiffusion at the interfaces. A fit to the data yields interface widths of 1–2 nm. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Fc Modulation, tuning, and mode locking
81.40.Gh Other heat and thermomechanical treatments

High-efficiency tandem organic light-emitting diodes

L. S. Liao, K. P. Klubek, and C. W. Tang

Appl. Phys. Lett. 84, 167 (2004); http://dx.doi.org/10.1063/1.1638624 (3 pages) | Cited 151 times

Online Publication Date: 7 January 2004

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Tandem organic light-emitting diodes (OLEDs), with multiple electroluminescent (EL) units connected electrically in series, have been fabricated. Using an optically transparent doped organic p-n junction as the connecting unit between adjacent EL units, excellent light out-coupling and carrier-injection properties have been realized. The luminous efficiency is found to scale almost linearly with the number of EL units in the stack, giving values as high as 32 or 136 cd/A for a three-unit tandem OLED using a fluorescent or a phosphorescent emitter, respectively. © 2004 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
73.61.Ng Insulators
61.72.S- Impurities in crystals

Second-harmonic efficiency of ZnO nanolayers

Uwe Neumann, Ruediger Grunwald, Uwe Griebner, Günter Steinmeyer, and Wolfgang Seeber

Appl. Phys. Lett. 84, 170 (2004); http://dx.doi.org/10.1063/1.1639939 (3 pages) | Cited 36 times

Online Publication Date: 7 January 2004

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Pure and doped nanocrystalline ZnO films of 0.1–1.0 μm thickness were prepared by spray pyrolysis techniques. Structural properties of these thin films were investigated by electron microscopy, force microscopy, x-ray diffractometry, ellipsometry, and optical spectroscopy. Using Ti:sapphire laser pulses, the second-harmonic efficiency of the films was measured. A correlation between measured efficiency and the grain shape in the polycrystalline layers is reported. Moreover, measurements of the angular dependence of the second-harmonic intensity are indicative of the dominant role of bulk effects over surface effects for the second-harmonic generation in such films. © 2004 American Institute of Physics.
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81.07.-b Nanoscale materials and structures: fabrication and characterization
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation

Ultraviolet detection with ultrathin ZnO epitaxial films treated with oxygen plasma

Mingjiao Liu and Hong Koo Kim

Appl. Phys. Lett. 84, 173 (2004); http://dx.doi.org/10.1063/1.1640468 (3 pages) | Cited 52 times

Online Publication Date: 7 January 2004

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We have investigated the effects of oxygen plasma treatment on the UV detection properties of ultrathin ( ∼ 20-nm-thick) ZnO epitaxial films. Highly epitaxial ZnO films grown on sapphire were exposed to oxygen-radical-rich, inductively coupled plasma, and then their UV detection properties were characterized at 325 nm wavelength using a photoconductor structure. The oxygen plasma treatment is found to dramatically enhance the UV detection properties of ZnO, reducing the decay time constant (to below 50 μs) and increasing the on/off ratio of photocurrent (to over 1000) with high UV responsivity (1–10 A/W). This result, in conjunction with the microstructural and electrical characterization results, indicates that the plasma treatment efficiently suppresses the chemisorption sites (primarily the oxygen deficiency sites) on surface and also the oxygen vacancies in ZnO, therefore results in major reduction of the chemisorption effects and the dark current, respectively. © 2004 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
81.40.Tv Optical and dielectric properties related to treatment conditions
52.77.-j Plasma applications

Er3+–Yb3+ codoped polymeric optical waveguide amplifiers

W. H. Wong, E. Y. B. Pun, and K. S. Chan

Appl. Phys. Lett. 84, 176 (2004); http://dx.doi.org/10.1063/1.1640469 (3 pages) | Cited 36 times

Online Publication Date: 7 January 2004

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Codoping of erbium (Er3+) and ytterbium (Yb3+) rare-earth ions in polymer was studied for optical amplifier applications. The absorption spectrum confirms that the presence of Yb3+ ions enhances the absorption efficiency of Er3+ ions. Typical Er3+ luminescence at ∼1540 nm wavelength was observed, and the full width at half maximum bandwidth is ∼47 nm wide. Multimode Er3+–Yb3+ codoped polymeric channel waveguides were fabricated using electron beam direct writing. With an input signal power of <−18 dB m, an optical gain of 13 dB at a wavelength of 1533 nm was measured in an 18 mm long multimode channel waveguide. © 2004 American Institute of Physics.
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42.79.Gn Optical waveguides and couplers
61.72.up Other materials
42.82.Cr Fabrication techniques; lithography, pattern transfer
42.82.Et Waveguides, couplers, and arrays

Diode laser coupled to an atomic line by incoherent optical negative feedback

A. F. A. da Rocha, P. C. S. Segundo, M. Chevrollier, and M. Oriá

Appl. Phys. Lett. 84, 179 (2004); http://dx.doi.org/10.1063/1.1639502 (3 pages) | Cited 9 times

Online Publication Date: 7 January 2004

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We report on experiments using optical negative feedback with orthogonal polarization to control the emission frequency of single-mode AsAlGa diode lasers. We obtain linewidth reduction and absolute frequency stabilization by injecting into the semiconductor laser a beam whose intensity is controlled by a Cs–D2 absorption line shape. © 2004 American Institute of Physics.
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42.55.Px Semiconductor lasers; laser diodes
42.60.Da Resonators, cavities, amplifiers, arrays, and rings
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Measurement of ion flow in a negative ion source using a Mach probe

A. Tanga, M. Bandyopadhyay, and P. McNeely

Appl. Phys. Lett. 84, 182 (2004); http://dx.doi.org/10.1063/1.1638902 (3 pages) | Cited 9 times

Online Publication Date: 7 January 2004

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Measurements of ion flow in an ion source made for negative ion extraction are reported in this letter. The ion flow has been measured using the Mach probe as two single probes compared with the results as a double probe. The measured values of the Mach number lie between 0.2 and 0.4. The maximum value of the Mach number is observed near the radio-frequency excitation coil. The flow shows a dominant direction toward the extraction grid; however, the flow pattern, away from the central axis of the source, shows a direction reversal and, therefore, convection. The presence of an ion flow has a strong influence on negative ion motion toward the extraction grid and on the sheath potential. The ion flow will play a dominant role in the ion dynamics and negative ion beam overall efficiency. © 2004 American Institute of Physics.
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07.77.Ka Charged-particle beam sources and detectors
52.75.-d Plasma devices

Sensitive measurements of electric field distributions in low-pressure Ar plasmas by laser-induced fluorescence-dip spectroscopy

K. Takizawa, K. Sasaki, and A. Kono

Appl. Phys. Lett. 84, 185 (2004); http://dx.doi.org/10.1063/1.1639943 (3 pages) | Cited 15 times

Online Publication Date: 7 January 2004

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Laser-induced fluorescence-dip (LIF-dip) spectroscopy of Ar was used for measuring the distributions of sheath electric fields in low-pressure, inductively-coupled Ar plasmas. A sensitive detection limit of 3 V/cm obtained by LIF-dip allowed the measurement in the presheath region. The distributions of electric fields observed experimentally were compared with those of theoretical calculations based on a simple fluid model. As a result, reasonable agreement between the experiment and the theory was obtained in the electric fields in the sheath region, while the electric fields in the presheath region observed experimentally were higher than the theoretical results. © 2004 American Institute of Physics.
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52.70.Kz Optical (ultraviolet, visible, infrared) measurements
52.40.Kh Plasma sheaths
52.65.-y Plasma simulation
52.77.-j Plasma applications

A uniform glow discharge plasma source at atmospheric pressure

Se Youn Moon, W. Choe, and B. K. Kang

Appl. Phys. Lett. 84, 188 (2004); http://dx.doi.org/10.1063/1.1639135 (3 pages) | Cited 62 times

Online Publication Date: 7 January 2004

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An atmospheric-pressure, uniform, continuous, glow plasma was produced in ambient air assisted by argon feeding gas, using a 13.56 MHz rf source. Based on the measured current–voltage curve and optical emission spectrum intensity, the plasma showed typical glow discharge characteristics, free from streamers and arc. The measured rotational and vibrational temperatures were in the range of 490 to 630 K and 2000 to 3300 K, respectively, within the operation range of argon flow rate and rf power. From the spatial measurement of total optical emission intensity, and rotational and vibrational temperatures, the plasma shows very high uniformity (over 93%) in the lengthwise direction. The plasma size for this study was 200 mm×50 mm×5 mm, although a plasma was produced in the scaled-up version of 600 mm in length, aiming for large-area plasma applications. © 2004 American Institute of Physics.
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52.50.Dg Plasma sources
52.80.Hc Glow; corona
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Microcavity-coupled optical Stark effect: Application to ultrafast all-optical modulation

S. Sanchez, C. De Matos, and M. Pugnet

Appl. Phys. Lett. 84, 191 (2004); http://dx.doi.org/10.1063/1.1639134 (3 pages) | Cited 3 times

Online Publication Date: 7 January 2004

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We propose a modeling of the microcavity-coupled optical Stark effect that we compare to degenerate pump-probe experimental results obtained at room temperature on a bulk GaAs microcavity. The cavity energy mode is adjusted 15 meV below the edge of the GaAs bandgap. With a pump intensity as low as 0.4 MW/cm2, we could demonstrate an instantaneous reflectivity modulation with a 5:1 contrast ratio. The good agreement between experiment and modeling is promising to design structures well suited to all-optical modulation with low switching intensities. © 2004 American Institute of Physics.
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42.55.Sa Microcavity and microdisk lasers
78.66.Hf II-VI semiconductors

An angle modulation reflectance spectroscopy characterization of a GaAs/GaAlAs asymmetric microcavity structure

D. Y. Lin

Appl. Phys. Lett. 84, 194 (2004); http://dx.doi.org/10.1063/1.1639938 (3 pages)

Online Publication Date: 7 January 2004

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A GaAs/GaAlAs-based asymmetric microcavity structure was studied by an angle modulation reflectance (AMR) and reflectivity measurements at different angles of incidence (θinc) ranging from 10° to 65°. The AMR technique possesses the enhanced capability of showing only the angle-dependent cavity mode (CM) feature and interference features related to the properties of the distributed Bragg reflectors (DBRs). By comparison of the AMR spectra and the numerical first derivative (with respect to energy) of the R spectra, the relative strength and positions of the 1C–1H and 1C–1L excitonic transitions can be extracted through a careful line-shape fit. The resonance enhancement between the CM and excitonic transitions are also discussed. © 2004 American Institute of Physics.
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78.66.Fd III-V semiconductors
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
73.20.At Surface states, band structure, electron density of states

Narrow, deep level cathodoluminescence emission from semi-insulating GaAs

J. K. Radhakrishnan and G. Salviati

Appl. Phys. Lett. 84, 197 (2004); http://dx.doi.org/10.1063/1.1640471 (3 pages)

Online Publication Date: 7 January 2004

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Cathodoluminescence investigations on bulk undoped semi-insulating GaAs samples taken from different sources reveal the presence of a deep level emission at 0.9 eV at 77 K, with a narrow full width at half maximum of 8 meV. The temperature-dependent and beam-parameter-dependent studies indicate that, the probable origin for this emission may be some nanocluster/quantum-dot like structures with a band gap of 0.9 eV, present inside the semi-insulating GaAs crystal lattice. One possibility for such structures in semi-insulating GaAs are clusters/nanoprecipitates of arsenic. © 2004 American Institute of Physics.
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78.60.Hk Cathodoluminescence, ionoluminescence
71.20.Nr Semiconductor compounds
71.55.Eq III-V semiconductors

Infrared dielectric function and vibrational modes of pentacene thin films

M. Schubert, C. Bundesmann, G. Jacopic, H. Maresch, and H. Arwin

Appl. Phys. Lett. 84, 200 (2004); http://dx.doi.org/10.1063/1.1639129 (3 pages) | Cited 8 times

Online Publication Date: 7 January 2004

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Generalized infrared spectroscopic ellipsometry over the wave-number range from 300 to 2000 cm−1 is used for precise determination of the dielectric function, frequency, amplitude, and broadening parameters of 27 infrared active modes for polarization parallel to the growth surface of pentacene thin films obtained by molecular-beam deposition on glass. No in-plane anisotropy was detected, which is indicative for a random orientation of crystallites around the growth direction supporting previous x-ray diffraction results. © 2004 American Institute of Physics.
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77.22.Ch Permittivity (dielectric function)
78.30.Jw Organic compounds, polymers
68.55.-a Thin film structure and morphology
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
78.66.Qn Polymers; organic compounds
77.22.Ej Polarization and depolarization

Morphology and composition of highly strained InGaAs and InGaAsN layers grown on GaAs substrate

G. Patriarche, L. Largeau, J.-C. Harmand, and D. Gollub

Appl. Phys. Lett. 84, 203 (2004); http://dx.doi.org/10.1063/1.1639510 (3 pages) | Cited 38 times

Online Publication Date: 7 January 2004

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We have studied the morphology and the composition of highly strained InGaAs and InGaAsN quantum wells (QWs) by transmission electron microscopy. 002 dark-field images show that two symmetrical interfacial layers of about 1.5 nm border the QWs. The selected-area electron diffraction technique gives further evidence of these layers since two extra spots are always observed near the high-index spots on the diffraction patterns. From the position of these extra spots, we determine the strain of the interfacial layers as well as the strain of the middle part of the wells. The comparison of InGaAs and InGaAsN reveals that the morphology of the quaternary alloy QWs is deteriorated and its lateral fluctuation of composition is increased. © 2004 American Institute of Physics.
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85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
81.07.St Quantum wells

GaN quantum dots doped with Eu

Y. Hori, X. Biquard, E. Monroy, D. Jalabert, F. Enjalbert, Le Si Dang, M. Tanaka, O. Oda, and B. Daudin

Appl. Phys. Lett. 84, 206 (2004); http://dx.doi.org/10.1063/1.1637157 (3 pages) | Cited 29 times

Online Publication Date: 7 January 2004

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Molecular-beam-epitaxy growth of Eu-doped GaN quantum dots embedded in AlN has been achieved. The crucial issue of Eu location has been addressed by extended x-ray absorption fine structure measurements. By comparing the signature of the Eu short-range environment for several samples, it is concluded that Eu is mostly incorporated in GaN dots. Intense cathodoluminescence associated with Eu has been measured, with no GaN bandedge emission, evidence that carrier recombination mostly occurs through rare-earth ion excitation. Persistent photoluminescence of Eu-doped GaN quantum dots as a function of the temperature is suggested to be further confirmation of the recombination of confined carriers through Eu ion excitation. © 2004 American Institute of Physics.
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68.65.Hb Quantum dots (patterned in quantum wells)
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.07.Ta Quantum dots
61.72.uj III-V and II-VI semiconductors
78.67.Hc Quantum dots
78.70.Dm X-ray absorption spectra
78.60.Hk Cathodoluminescence, ionoluminescence
78.55.Cr III-V semiconductors

Diffusion phenomena in a Pt/IrO2/Ir/TiN/W multilayer structure during annealing in oxygen

A. Alberti, A. M. Borzì, and S. Ravesi

Appl. Phys. Lett. 84, 209 (2004); http://dx.doi.org/10.1063/1.1638899 (3 pages)

Online Publication Date: 7 January 2004

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The process generating hillock structures at the surface of a Pt/IrO2/Ir/TiN/W multilayer stack has been studied at a temperature of 700 °C. This phenomenon has been related to a structural modification of the barrier that involves iridium and platinum layers, and consists of platinum atoms diffusing downwards while iridium atoms move upwards. Once in the surface proximity, iridium has been oxidized forming large grains, the hillocks, that have grown and protruded up to the sample surface. Nevertheless, oxygen was not able to deeply penetrate the barrier stack, and therefore, the inner TiN and W layers have been preserved from oxidation. © 2004 American Institute of Physics.
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68.65.Ac Multilayers
66.30.Ny Chemical interdiffusion; diffusion barriers

Spectroscopic observation of oxidation process in InN

E. Kurimoto, M. Hangyo, H. Harima, M. Yoshimoto, T. Yamaguchi, T. Araki, Y. Nanishi, and K. Kisoda

Appl. Phys. Lett. 84, 212 (2004); http://dx.doi.org/10.1063/1.1639511 (3 pages) | Cited 28 times

Online Publication Date: 7 January 2004

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Spectroscopic observations of high-quality wurtzite InN have shown that oxygen is easily incorporated in the crystal by thermal treatments in the air. Incorporation of oxygen may play a key role in determining the apparent properties of InN including the bandgap and the lattice constant. It is shown that Raman scattering is a sensitive tool to probe the oxygen incorporation process and associated deterioration in crystallinity. © 2004 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.65.Mq Oxidation
81.40.Gh Other heat and thermomechanical treatments
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Correlation of charge transport to intrinsic strain in silicon oxynitride and Si-rich silicon nitride thin films

S. Habermehl and R. T. Apodaca

Appl. Phys. Lett. 84, 215 (2004); http://dx.doi.org/10.1063/1.1639132 (3 pages) | Cited 8 times

Online Publication Date: 7 January 2004

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Poole–Frenkel emission in Si-rich nitride and silicon oxynitride thin films is studied in conjunction with compositional aspects of their elastic properties. For Si-rich nitrides varying in composition from SiN1.33 to SiN0.54, the Poole–Frenkel trap depth (ΦB) decreases from 1.08 to 0.52 eV as the intrinsic film strain (ϵi) decreases from 0.0036 to −0.0016. For oxynitrides varying in composition from SiN1.33 to SiO1.49N0.35, ΦB increases from 1.08 to 1.53 eV as ϵi decreases from 0.0036 to 0.0006. In both material systems, a direct correlation is observed between ΦB and ϵi. Compositionally induced strain relief as a mechanism for regulating ΦB is discussed. © 2004 American Institute of Physics.
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72.20.Ht High-field and nonlinear effects
68.60.Bs Mechanical and acoustical properties
73.61.Ng Insulators
61.66.Bi Elemental solids
61.66.Dk Alloys

Transparent conducting Sb-doped SnO2 thin films grown by pulsed-laser deposition

H. Kim and A. Piqué

Appl. Phys. Lett. 84, 218 (2004); http://dx.doi.org/10.1063/1.1639515 (3 pages) | Cited 41 times

Online Publication Date: 7 January 2004

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Antimony-doped tin oxide (SnO2:Sb) thin films (100–480 nm thick) have been deposited by pulsed-laser deposition on glass substrates without a postdeposition anneal. The structural, electrical, and optical properties of these films have been investigated as a function of doping amount, substrate temperature, and oxygen partial pressure during deposition. Films were deposited at temperatures ranging from 25 to 600 °C in O2 partial pressures ranging from 10 to 100 mTorr. The films (300 nm thick) deposited at 300 °C in 45 mTorr of oxygen show electrical resistivities as low as 9.8×10−4 Ω cm, an average visible transmittance of 90%, a refractive index of 1.98 (at 550 nm), and an optical band gap of 4.21 eV.
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81.15.Fg Pulsed laser ablation deposition
78.66.Nk Insulators
72.80.Sk Insulators
68.55.-a Thin film structure and morphology

Metal/semiconductor superlattices containing semimetallic ErSb nanoparticles in GaSb

M. P. Hanson, D. C. Driscoll, C. Kadow, and A. C. Gossard

Appl. Phys. Lett. 84, 221 (2004); http://dx.doi.org/10.1063/1.1639932 (3 pages) | Cited 7 times

Online Publication Date: 7 January 2004

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We demonstrate the growth by molecular beam epitaxy of a metal/semiconductor composite consisting of epitaxial semimetallic ErSb particles in a GaSb matrix. The ErSb nucleates in an island growth mode leading to the spontaneous formation of nanometer-sized particles. These particles are found to preferentially grow along a [011] direction on a (100) GaSb surface. The particles can be overgrown with GaSb to form an epitaxial superlattice consisting of ErSb particles between GaSb spacer layers. The size of the ErSb particles increases monotonically with the deposition. The carrier concentrations in the superlattices are found to be dependent on both the size and density of the ErSb particles. Smaller particles and closer layer spacings reduce the hole concentration in the film. © 2004 American Institute of Physics.
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81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
73.40.Ns Metal-nonmetal contacts
68.65.Cd Superlattices
61.46.-w Structure of nanoscale materials

Tungsten inverse opals: The influence of absorption on the photonic band structure in the visible spectral region

Georg von Freymann, Sajeev John, Martin Schulz-Dobrick, Evangellos Vekris, Nicolas Tétreault, Sean Wong, Vladimir Kitaev, and Geoffrey A. Ozin

Appl. Phys. Lett. 84, 224 (2004); http://dx.doi.org/10.1063/1.1639941 (3 pages) | Cited 29 times

Online Publication Date: 7 January 2004

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We report on the fabrication and characterization of tungsten inverse opals for the visible and near-infrared spectral region. The crucial influence of the strong absorption in this spectral region is experimentally investigated by means of a gradient deposition technique and characterization with reflectance and transmittance spectroscopy. With increasing metal infiltration, we observe the breakdown of the photonic band structure, resulting first in a sphere-cavity-like behavior and finally in a behavior similar to that of a periodically structured metal surface. © 2004 American Institute of Physics.
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78.40.Kc Metals, semimetals, and alloys
78.30.Er Solid metals and alloys
78.20.-e Optical properties of bulk materials and thin films
42.70.Qs Photonic bandgap materials
42.86.+b Optical workshop techniques

Cross-sectional scanning tunneling microscopy and spectroscopy of InGaP/GaAs heterojunctions

Y. Dong, R. M. Feenstra, M. P. Semtsiv, and W. T. Masselink

Appl. Phys. Lett. 84, 227 (2004); http://dx.doi.org/10.1063/1.1638637 (3 pages) | Cited 10 times

Online Publication Date: 7 January 2004

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Compositionally abrupt InGaP/GaAs heterojunctions grown by gas-source molecular-beam epitaxy have been investigated by cross-sectional scanning tunneling microscopy and spectroscopy. Images inside the InGaP layer show nonuniform In and Ga distribution. About 1.5 nm of transition region at the interfaces is observed, with indium carryover identified at the GaAs–on–InGaP interface. Spatially resolved tunneling spectra with nanometer spacing across the interface were acquired, from which band offsets (revealing that nearly all of band offset occurs in the valence band) were determined. © 2004 American Institute of Physics.
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68.35.Dv Composition, segregation; defects and impurities
68.37.Ef Scanning tunneling microscopy (including chemistry induced with STM)
73.40.Kp III-V semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
68.35.Fx Diffusion; interface formation
73.20.-r Electron states at surfaces and interfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
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Simultaneous inductive determination of grain and intergrain critical current densities of YBa2Cu3O7−x coated conductors

A. Palau, T. Puig, X. Obradors, E. Pardo, C. Navau, A. Sanchez, A. Usoskin, H. C. Freyhardt, L. Fernández, B. Holzapfel, and R. Feenstra

Appl. Phys. Lett. 84, 230 (2004); http://dx.doi.org/10.1063/1.1639940 (3 pages) | Cited 28 times

Online Publication Date: 7 January 2004

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An inductive methodology simultaneously enabling the determination of grain- and intergrain critical current densities of YBa2Cu3O7−x coated conductors is developed. This noninvasive method is based on the identification of a clear peak in the reverse branch of the magnetization loop at a positive magnetic field, as a signature of the electromagnetic granularity inherent to these materials. A quantitative evaluation of the return magnetic field at the grain boundaries allows us to understand the existence of this magnetization peak and quantify the grain critical current density. This methodology is envisaged to sort out granularity effects from vortex pinning effects on coated conductors. © 2004 American Institute of Physics.
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74.72.-h Cuprate superconductors
74.25.Sv Critical currents
74.25.Ha Magnetic properties including vortex structures and related phenomena
61.72.Mm Grain and twin boundaries
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)

High thermal stability of magnetic tunnel junctions with oxide diffusion barrier layers

Yoshiyuki Fukumoto, Ken-ichi Shimura, Atsushi Kamijo, Shuichi Tahara, and Hiroaki Yoda

Appl. Phys. Lett. 84, 233 (2004); http://dx.doi.org/10.1063/1.1639128 (3 pages) | Cited 13 times

Online Publication Date: 7 January 2004

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We developed two types of magnetic tunnel junctions (MTJs) that showed high thermal stability. One is a PtMn exchange-biased spin-valve MTJ with a CoFe/Al-oxide (AlOx)/NiFe free layer and a CoFeTaOx/CoFe pinned layer, and the other is a pseudo-spin-valve (PSV) MTJ with a CoFe/AlOx/NiFe soft layer, where AlOx and CoFeTaOx act as barriers for Ni and Mn diffusion toward the tunnel barrier, respectively. After 390 °C-1H annealing, the PSV MTJs maintained 28% and the SV MTJs 39% of tunnel magnetoresistance. Transmission electron microscopy observation of the SV MTJs after 380 °C-1H annealing revealed that the migrated Mn atoms were trapped at the CoFeTaOx layer. © 2004 American Institute of Physics.
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75.47.Np Metals and alloys
68.35.Fx Diffusion; interface formation
81.40.Gh Other heat and thermomechanical treatments
75.50.Bb Fe and its alloys
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