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7 Jul 1997

Volume 71, Issue 1, pp. 1-148

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Ultrafast hole–phonon interactions in GaAs

N. Del Fatti, P. Langot, R. Tommasi, and F. Vallée

Appl. Phys. Lett. 71, 75 (1997); http://dx.doi.org/10.1063/1.119472 (3 pages) | Cited 2 times

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Ultrafast heating of cold holes is investigated in bulk GaAs using a high-sensitivity two-color absorption saturation technique. Measurements performed as a function of the lattice temperature and of the carrier excess energy show that absorption of optical phonons is the main hole heating mechanism for the investigated temperatures in the range 100–300 K. Using a numerical model for carrier dynamics, the optical deformation potential is estimated to be d0 ∼ 40 eV. © 1997 American Institute of Physics.
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72.80.Ey III-V and II-VI semiconductors
71.38.-k Polarons and electron-phonon interactions
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)

GaAs/AlGaAs quantum-well infrared photodetectors on GaAs-on-Si substrates

D. K. Sengupta, W. Fang, J. I. Malin, J. Li, T. Horton, A. P. Curtis, K. C. Hsieh, S. L. Chuang, H. Chen, M. Feng, G. E. Stillman, L. Li, H. C. Liu, K. M. S. V. Bandara, S. D. Gunapala, et al.

Appl. Phys. Lett. 71, 78 (1997); http://dx.doi.org/10.1063/1.119473 (3 pages) | Cited 3 times

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In this letter, we describe the characteristics of molecular beam epitaxy GaAs/AlGaAs quantum-well infrared photodetectors (QWIP’s) grown on a GaAs substrate, and on a GaAs-on-Si substrate produced by metalorganic chemical-vapor deposition. Important issues for QWIP applications such as dark current, spectral response, and absolute responsivity are studied. We find that compared to a similar detector structure grown on a GaAs substrate, the detector grown on a GaAs-on-Si substrate exhibits similar dark current and absolute responsivity while displaying a small blueshift in the spectral response. © 1997 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
72.40.+w Photoconduction and photovoltaic effects
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
07.57.Kp Bolometers; infrared, submillimeter wave, microwave, and radiowave receivers and detectors
72.80.Ey III-V and II-VI semiconductors
81.05.Ea III-V semiconductors
68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
73.61.Ey III-V semiconductors
85.35.Be Quantum well devices (quantum dots, quantum wires, etc.)
78.66.Fd III-V semiconductors

Characterization of SrBi2Ta2O9 ferroelectric thin films deposited at low temperatures by plasma-enhanced metalorganic chemical vapor deposition

Nak-Jin Seong, Soon-Gil Yoon, and Seaung-Suk Lee

Appl. Phys. Lett. 71, 81 (1997); http://dx.doi.org/10.1063/1.119475 (3 pages) | Cited 27 times

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Ferroelectric bismuth-layer SrBi2Ta2O9(SBT) thin films were prepared on Pt/Ti/SiO2/Si substrate by plasma-enhanced metalorganic chemical vapor deposition. The films were crystallized at temperatures between 500 and 600 °C. The dielectric constant and dissipation factor of SBT films were 320 and 0.04 at an applied frequency of 1 MHz, respectively. The remanent polarization (Pr) and the coercive field (Ec) obtained for a 200 nm thick Sr0.9Bi2.3Ta2.0O9 films deposited at 550 °C were 15 μC/cm2 and 50 kV/cm at an applied voltage of 3 V, respectively. The leakage current density was about 5.0×10−8 A/cm2 at 300 kV/cm. The films showed fatigue-free characteristics up to 1.0×1011 switching cycles under 6 V bipolar pulse. © 1997 American Institute of Physics.
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77.80.-e Ferroelectricity and antiferroelectricity
77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.55.-g Dielectric thin films
77.22.Ch Permittivity (dielectric function)
52.77.Bn Etching and cleaning
52.77.Dq Plasma-based ion implantation and deposition
68.55.-a Thin film structure and morphology
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
77.22.Ej Polarization and depolarization

Effects of high hydrogen dilution at low temperature on the film properties of hydrogenated amorphous silicon germanium

Masaki Shima, Akira Terakawa, Masao Isomura, Makoto Tanaka, Seiichi Kiyama, and Shinya Tsuda

Appl. Phys. Lett. 71, 84 (1997); http://dx.doi.org/10.1063/1.119476 (3 pages) | Cited 7 times

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The effects of hydrogen dilution of up to 54:1 ( = H2:SiH4) on hydrogenated amorphous silicon germanium (a-SiGe:H) was investigated at a low substrate temperature, while keeping the optical gap (Eopt) constant. It was found that deterioration of the film properties, when substrate temperature decreases, can be compensated by the high hydrogen dilution method. As the substrate temperature decreases from 230 to 180 °C, the high photoconductivity, high photosensitivity, and low silicon dihydride content of a-SiGe:H can be maintained with a high hydrogen dilution ratio of 54:1, although these properties becomes worse with conventional low hydrogen dilution ratios. Probably, hydrogen radicals substitute for the surface reaction energy lost by decreasing the temperature. Besides, a-SiGe:H films deposited under higher hydrogen dilution have more germanium and less hydrogen content than those of the conventional films, despite having the same Eopt. One possible explanation for why Eopt can be kept constant is the suppression of the formation of Ge–Ge bonds at the growing surface by the energy supplied by the hydrogen radicals. © 1997 American Institute of Physics.
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81.05.Gc Amorphous semiconductors
72.80.Ng Disordered solids
73.61.Jc Amorphous semiconductors; glasses
61.66.Bi Elemental solids
61.66.Dk Alloys
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
72.40.+w Photoconduction and photovoltaic effects
73.50.Pz Photoconduction and photovoltaic effects
82.65.+r Surface and interface chemistry; heterogeneous catalysis at surfaces
82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.-a Thin film structure and morphology

Determination of interface layer strain of Si/SiO2 interfaces by reflectance difference spectroscopy

Z. Yang, Y. H. Chen, Jacob Y. L. Ho, W. K. Liu, X. M. Fang, and P. J. McCann

Appl. Phys. Lett. 71, 87 (1997); http://dx.doi.org/10.1063/1.119477 (3 pages) | Cited 4 times

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Detailed studies of the often-observed resonance feature near 3.4 eV in the reflectance difference spectrum of Si/SiO2 interfaces and Si surfaces show that the resonance is due to the intrinsic local-field effect, and that its energy position coincides with the E1 energy of bulk Si. Using the energy position of the resonance of the pseudomorphically grown Si/CaF2 interfaces as a reference point, the strain-induced resonance energy shift of the Si interface layer at several Si/SiO2 interfaces are obtained and the strain in these layers is determined. The results show that the interface layers are highly strained with an equivalent hydrostatic pressure of 0.79 GPa, but still maintain a high degree of order. © 1997 American Institute of Physics.
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68.35.Ct Interface structure and roughness
62.20.F- Deformation and plasticity
81.05.Cy Elemental semiconductors

Ionization rates and critical fields in 4H silicon carbide

A. O. Konstantinov, Q. Wahab, N. Nordell, and U. Lindefelt

Appl. Phys. Lett. 71, 90 (1997); http://dx.doi.org/10.1063/1.119478 (3 pages) | Cited 88 times

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Epitaxial p-n diodes in 4H SiC are fabricated showing a good uniformity of avalanche multiplication and breakdown. Peripheral breakdown is overcome using the positive angle beveling technique. Photomultiplication measurements were performed to determine electron and hole ionization rates. For the electric field parallel to the c-axis impact ionization is strongly dominated by holes. A hole to electron ionization coefficient ratio of up to 50 is observed. It is attributed to the discontinuity of the conduction band of 4H SiC for the direction along the c axis. Theoretical values of critical fields and breakdown voltages in 4H SiC are calculated using the ionization rates obtained. © 1997 American Institute of Physics.
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73.40.Lq Other semiconductor-to-semiconductor contacts, p-n junctions, and heterojunctions
73.61.Le Other inorganic semiconductors
72.20.Ht High-field and nonlinear effects
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems

Pressure-induced intra-4f luminescence in GaAs:Er,O

K. Takarabe, T. Mizushima, S. Minomura, R. A. Hogg, A. Taguchi, and K. Takahei

Appl. Phys. Lett. 71, 93 (1997); http://dx.doi.org/10.1063/1.119479 (3 pages) | Cited 3 times

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In metalorganic chemical vapor deposition grown GaAs:Er,O samples, at ambient pressure, only the ErGa−2O center is excited by above band gap host photoexcitation (host excitation) and shows a sharp infrared luminescence spectra due to intra-4f transitions in the Er3+ ion. It is found, at high pressure, that at least two other Er centers become optically active by host excitation. One of these pressure-induced centers is assigned to a specific Er center having slightly different atomic configuration than the ErGa−2O center by comparing the pressure-induced photoluminescence (PL) spectra with the site-selective PL spectra. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
73.20.Hb Impurity and defect levels; energy states of adsorbed species
71.55.Eq III-V semiconductors
81.05.Ea III-V semiconductors
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)

Electroluminescence of erbium-doped silicon films as grown by ion beam epitaxy

Morito Matsuoka and Shun-ichi Tohno

Appl. Phys. Lett. 71, 96 (1997); http://dx.doi.org/10.1063/1.119480 (3 pages) | Cited 16 times

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Sharp and well-split electroluminescence has been achieved from light-emitting diodes (LEDs) fabricated from as-grown erbium–oxygen codoped silicon films, where all elements were in situ incorporated during film growth. The LEDs were fabricated using ion beam epitaxy with an electric mirror sputtering-type metal ion source in an ultrahigh vacuum. Electroluminescence was observed from the LEDs under both forward and reverse biases. Each luminescence line corresponded well to the intra-4f transitions of Er+3 ions with almost single local coordination. The electroluminescence quenching factor with temperature under a forward bias was similar to that for photoluminescence. Sharp luminescence was, however, still observed even at room temperature under a forward bias. Under a reverse bias, strong electroluminescence was observed at room temperature without quenching. © 1997 American Institute of Physics.
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85.60.Jb Light-emitting devices
78.60.Fi Electroluminescence
81.05.Cy Elemental semiconductors
81.15.Kk Vapor phase epitaxy; growth from vapor phase
81.15.Cd Deposition by sputtering
78.66.Db Elemental semiconductors and insulators

Numerical analysis of excimer-laser-induced melting and solidification of thin Si films

Vikas V. Gupta, H. Jin Song, and James S. Im

Appl. Phys. Lett. 71, 99 (1997); http://dx.doi.org/10.1063/1.119481 (3 pages) | Cited 21 times

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We have developed an efficient two-dimensional numerical model, based on the finite difference method and utilizing the alternate-direction explicit scheme, that can simulate excimer laser melting and solidification of thin Si films on SiO2. The model takes into account important aspects of the process such as undercooling and the temperature-dependent velocity of the solidifying interface, supercooling of liquid Si, and the inert nature of the underlying oxide interface. We demonstrate the unique capability of the model by simulating spatially confined beam-induced localized complete melting of the irradiated portion of the film, and the ensuing lateral solidification, which initiates from the unmelted regions of the film into the completely molten area. © 1997 American Institute of Physics.
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81.05.Cy Elemental semiconductors
64.70.D- Solid-liquid transitions
68.55.-a Thin film structure and morphology
68.35.Rh Phase transitions and critical phenomena
79.20.Ds Laser-beam impact phenomena

Growth of epitaxial GaN films by pulsed laser deposition

R. D. Vispute, V. Talyansky, R. P. Sharma, S. Choopun, M. Downes, T. Venkatesan, K. A. Jones, A. A. Iliadis, M. Asif Khan, and J. W. Yang

Appl. Phys. Lett. 71, 102 (1997); http://dx.doi.org/10.1063/1.119441 (3 pages) | Cited 31 times

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High crystalline quality epitaxial GaN films with thicknesses 0.5–1.5 μm have been successfully grown directly on Al2O3(0001) substrate by pulsed laser deposition (PLD). For films grown at 950 °C, we obtained an x-ray diffraction rocking curve linewidth of 7 arc min. The ion channeling minimum yield in the near-surface region ( ∼ 2000 Å) for a 0.5 μm thick film was ∼ 3%–4% indicating a high degree of crystallinity. The optical absorption edge measured by UV-visible spectroscopy was sharp, and the band gap was found to be 3.4 eV. The crystalline properties of these PLD GaN films are comparable to those grown by metalorganic chemical vapor deposition and molecular beam epitaxy. © 1997 American Institute of Physics.
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81.05.Ea III-V semiconductors
81.15.Fg Pulsed laser ablation deposition
85.40.Sz Deposition technology
81.15.Kk Vapor phase epitaxy; growth from vapor phase
72.80.Ey III-V and II-VI semiconductors

Calculation of unstable mixing region in wurtzite In1−x−yGaxAlyN

Takashi Matsuoka

Appl. Phys. Lett. 71, 105 (1997); http://dx.doi.org/10.1063/1.119440 (2 pages) | Cited 78 times

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The wurtzite structure In1−x−yGaxAlyN quaternary system with a wide band gap, which is useful for light emitters in the wavelength region shorter than green, is studied with respect to the unstable region in mixing. This unstable region in mixing is calculated from the free energy of mixing using the strictly regular solution model. The interaction parameter used in this calculation is obtained using the delta-lattice-parameter method. From this calculation, the ternary alloys of InAlN, InGaN, and GaAlN are, respectively, predicted to always, sometimes, and hardly ever have a unstable mixing region at the temperature lower than 3000 °C. © 1997 American Institute of Physics.
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61.66.Fn Inorganic compounds
64.75.-g Phase equilibria
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Relationship between storage media and blue photoluminescence for oxidized porous silicon

A. Loni, A. J. Simons, P. D. J. Calcott, J. P. Newey, T. I. Cox, and L. T. Canham

Appl. Phys. Lett. 71, 107 (1997); http://dx.doi.org/10.1063/1.119442 (3 pages) | Cited 9 times

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Blue photoluminescence is observed, with nanosecond decay time, from rapid thermally oxidized porous silicon as a result of accelerated aging in plastic containers. Photoluminescence measurements, combined with chemical analyses of the “aged” porous silicon, indicate that the emission is a consequence of the incorporation of trace organic (hydrocarbon) contamination from the plastic containers as they outgas at a mildly elevated temperature (80 °C) and, albeit at a reduced rate, at room temperature. Such carbonaceous contaminants can subsequently be removed by high-temperature annealing, a process which also quenches the blue photoluminescence. Consequently, it is important to take into consideration the storage medium used when making comparative luminescent and compositional studies of porous silicon and, perhaps, porous materials in general. © 1997 American Institute of Physics.
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78.55.Mb Porous materials
78.55.Ap Elemental semiconductors
81.65.Mq Oxidation
68.35.Dv Composition, segregation; defects and impurities
81.40.Gh Other heat and thermomechanical treatments
81.40.Tv Optical and dielectric properties related to treatment conditions

Band gap states of Ti, V, and Cr in 4H–silicon carbide

Norbert Achtziger and Wolfgang Witthuhn

Appl. Phys. Lett. 71, 110 (1997); http://dx.doi.org/10.1063/1.119485 (3 pages) | Cited 18 times

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Band gap states of Ti, V, and Cr in n-type 4H–SiC were investigated by radiotracer deep level transient spectroscopy (DLTS). Doping with the radioactive isotopes mathV and mathCr was done by recoil implantation followed by annealing (1600 K). Repeated DLTS measurements during the elemental transmutation of these isotopes to mathTi and mathV, respectively, reveal the corresponding concentration changes of band gap states. Thus, six levels are identified in the band gap: Cr levels at 0.15, 0.18, and 0.74 eV, one V level at 0.97 eV, and two Ti levels at 0.13 and 0.17 eV below the conduction band edge. © 1997 American Institute of Physics.
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71.55.Ht Other nonmetals
61.72.up Other materials
61.80.Jh Ion radiation effects
61.72.Cc Kinetics of defect formation and annealing
81.40.Gh Other heat and thermomechanical treatments

Selective Stark-ladder transitions in an asymmetric double-well GaAs/AlAs superlattice

Kenzo Fujiwara, Shin-ichi Hinooda, and Kenji Kawashima

Appl. Phys. Lett. 71, 113 (1997); http://dx.doi.org/10.1063/1.119444 (3 pages) | Cited 8 times

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Optical transitions in a novel biperiodic GaAs/AlAs superlattice consisting of asymmetric double quantum wells have been investigated as a function of an applied electric field by photocurrent spectroscopy. Due to the existence of two different heavy-hole localized states under the applied field, two types of Stark-ladder transitions are possible in the superlattice. It is found that, among four possible indirect ladder transitions between the nearest neighbor wells, two of them have larger oscillator strengths. This selectivity of the indirect ladder transitions is rigorously explained by selective resonance coupling between the inequivalent neighboring wells because of the introduced structural asymmetry. © 1997 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.20.Jq Electro-optical effects
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
73.20.Fz Weak or Anderson localization
73.50.Pz Photoconduction and photovoltaic effects
73.61.Ey III-V semiconductors

The electrical conductivity of levitated liquids

J. E. Enderby, S. Ansell, S. Krishnan, D. L. Price, and M.-L. Saboungi

Appl. Phys. Lett. 71, 116 (1997); http://dx.doi.org/10.1063/1.119445 (3 pages) | Cited 11 times

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The electrical conductivities of aerodynamically levitated liquid spheres have been determined by an electrodeless method. It is shown that this technique is reliable over a wide range of temperatures; results are presented for a variety of systems including metals, semiconductors at room temperature and at their melting points, and solid and liquid Al2O3. © 1997 American Institute of Physics.
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72.15.Cz Electrical and thermal conduction in amorphous and liquid metals and alloys
72.20.Fr Low-field transport and mobility; piezoresistance

Normal incident long-wavelength quantum well infrared photodetectors using electron intersubband transitions

S. Y. Wang and C. P. Lee

Appl. Phys. Lett. 71, 119 (1997); http://dx.doi.org/10.1063/1.119446 (3 pages) | Cited 9 times

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Grating-free quantum well infrared photodetectors (QWIPs) for 8–10 μm applications have been fabricated. The QWIPs fabricated with InGaAs/GaAs quantum wells show excellent performance with normal-incident infrared radiation. A detectivity of 2×1010 cm Hz1/2/W and a responsivity of 0.23 A/W have been obtained for these devices. The devices were compared with QWIPs with 1D and 2D surface gratings. No significant improvement in responsivity is observed for devices with 1D gratings. Devices with 2D gratings have significantly higher peak responsivity but only in a very limited spectral range. The GaAs/AlGaAs QWIPs in the similar spectral range have also been fabricated and, however, shown much weaker TE absorption. © 1997 American Institute of Physics.
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85.60.Gz Photodetectors (including infrared and CCD detectors)
78.66.Fd III-V semiconductors

Strain effects in Nb3Al multifilamentary conductors prepared by phase transformation from bcc supersaturated-solid solution

T. Takeuchi, Y. Iijima, K. Inoue, H. Wada, B. ten Haken, H. H. J. ten Kate, K. Fukuda, G. Iwaki, S. Sakai, and H. Moriai

Appl. Phys. Lett. 71, 122 (1997); http://dx.doi.org/10.1063/1.119447 (3 pages) | Cited 38 times

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Strain effects on critical current densities have been examined for conductors containing nearly stoichiometric Nb3Al filaments with fine grains. The Nb3Al phase in these multifilamentary conductors are prepared by phase transformation from supersaturated Nb(Al) bcc solid solution and show high-field critical current densities much larger than those for conventionally prepared Nb3Al conductors, where the Nb3Al phase is known to be off-stoichiometric. The degradation of critical current densities with −0.7% intrinsic strain is ca. 20% at 12 T, comparable with those for conventional Nb3Al conductors of high strain tolerance. © 1997 American Institute of Physics.
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74.25.Sv Critical currents
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
84.71.Mn Superconducting wires, fibers, and tapes

Electron beam irradiation of Y1Ba2Cu3O7−x grain boundary Josephson junctions

F. Tafuri, S. Shokhor, B. Nadgorny, M. Gurvitch, F. Lombardi, and A. Di Chiara

Appl. Phys. Lett. 71, 125 (1997); http://dx.doi.org/10.1063/1.119448 (3 pages) | Cited 13 times

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The properties of the Y1Ba2Cu3O7−x biepitaxial Josephson junctions were reproducibly modified by a focused electron beam irradiation of the interface region. The junctions were fabricated by depositing Y1Ba2Cu3O7−x thin film by cylindrical magnetron sputtering technique on the (110) SrTiO3 substrate, partially covered by a pregrown MgO seed layer. The junction parameters can be adjusted controllably by applying an appropriate dose. Electron irradiation decreased the critical current of the junctions IC and increased the normal state resistance times area to values of the order of 1(μ Ω cm2). Some other effects, such as the disappearance of the excess current, were also observed. The original properties of the junctions could be partly restored by isothermal annealing. We also speculate that some aspects of the nature of the grain boundary barriers can be better understood from the study of the properties of irradiated junctions. © 1997 American Institute of Physics.
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74.50.+r Tunneling phenomena; Josephson effects
74.78.-w Superconducting films and low-dimensional structures
74.72.-h Cuprate superconductors
61.80.Fe Electron and positron radiation effects
61.72.Mm Grain and twin boundaries
81.15.Cd Deposition by sputtering
81.15.Kk Vapor phase epitaxy; growth from vapor phase
74.25.Sv Critical currents
81.40.Gh Other heat and thermomechanical treatments
81.40.Rs Electrical and magnetic properties related to treatment conditions
81.05.Je Ceramics and refractories (including borides, carbides, hydrides, nitrides, oxides, and silicides)

Superconducting single flux quantum 20 Gb/s clock recovery circuit

V. Kaplunenko, V. Borzenets, N. Dubash, and T. Van Duzer

Appl. Phys. Lett. 71, 128 (1997); http://dx.doi.org/10.1063/1.119449 (3 pages) | Cited 13 times

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A clock recovery circuit has been successfully tested at frequencies up to 20 GHz. This cell is designed for a rapid-single-flux-quantum (RSFQ) telecommunication data switch. It serves to set the receiver clock in phase with the incoming digital signal. The circuit consists of a dc-to-SFQ converter, ring oscillator [(RO) is a closed-loop RSFQ Josephson transmission line], confluence buffer, and an 8-bit binary counter. The input signal transforms to SFQ pulses, and each pulse resets the phase of the ring oscillator, giving a locking time of 1 bit. Thus, the pull-in (capture) range and hold-in (tracking) range are the same, and strictly depend on the encoding of the input signal. This range is estimated to be about 1 GHz at frequency 20 GHz, if the sequence of consecutive ONEs or ZEROs does not exceed 20 bits. The quality factor QRO of ring oscillator is about 2000, which gives a jitter of 50 fs for a 35-junction RO. A sampling technique was used to demonstrate phase recovery (phase locking) with only one incoming pulse per 512 clock periods. © 1997 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
84.40.Ua Telecommunications: signal transmission and processing; communication satellites
84.30.-r Electronic circuits

Unshielded use of thin-film Nb dc superconducting quantum interference devices and integrated asymmetric gradiometers for nondestructive evaluation

M. E. Walker, H. Nakane, A. Cochran, R. G. Weston, U. Klein, C. M. Pegrum, and G. B. Donaldson

Appl. Phys. Lett. 71, 131 (1997); http://dx.doi.org/10.1063/1.119450 (3 pages) | Cited 2 times

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Novel nondestructive evaluation measurements made using niobium dc superconducting quantum interference devices with integrated asymmetric first-order gradiometers are described. Comparative theoretical and experimental studies of their spatial response have been described, and it is shown that the gradiometric response makes operation possible in an unshielded and electromagnetically noisy environment. As a demonstration of their capabilities, subsurface defects in a multilayer aluminum structure have been located and mapped using induced eddy currents at 70 Hz, with no magnetic shielding around the specimen or cryostat. © 1997 American Institute of Physics.
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74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.78.-w Superconducting films and low-dimensional structures
81.70.Ex Nondestructive testing: electromagnetic testing, eddy-current testing
07.55.Nk Magnetic shielding in instruments

Direct imaging of current sharing in (BiPb)2Sr2Ca2Cu3Ox composite conductors

T. B. Peterson, U. Welp, G. W. Crabtree, N. Vasanthamohan, J. P. Singh, M. T. Lanagan, V. K. Vlasko-Vlasov, and V. I. Nikitenko

Appl. Phys. Lett. 71, 134 (1997); http://dx.doi.org/10.1063/1.119451 (3 pages) | Cited 8 times

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Using a high-resolution magneto-optical imaging technique, we study the flow of transport currents around cracks in monofilament (BiPb)2Sr2Ca2Cu2Ox composite conductors. Shunting through the Ag clad is directly observed. The current in the silver decays exponentially with distance from the crack as expected in a one dimensional distributed resistance model. At 77 K, the transfer length, λ, is approximately 0.56 mm, implying an interface resistivity of 7.5×10−8 Ω cm2. This transfer length is found to increase slightly with increasing temperature. © 1997 American Institute of Physics.
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74.72.-h Cuprate superconductors
84.71.Mn Superconducting wires, fibers, and tapes
74.25.Sv Critical currents
78.20.Ls Magneto-optical effects

Enhanced Jc and improved grain-boundary properties in Ag-doped YBa2Cu3O7−δ films

P. Selvam, E. W. Seibt, D. Kumar, R. Pinto, and P. R. Apte

Appl. Phys. Lett. 71, 137 (1997); http://dx.doi.org/10.1063/1.119452 (3 pages) | Cited 12 times

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A large increase ( ∼ 8×) in critical current density, Jc, was achieved for in situ laser ablated YBa2Cu3O7−δ–Ag films. High-resolution Auger electron spectroscopic investigation indicates that the Ag-doped films are stoichiometric with a relatively low grain-boundary extension (8 nm) in contrast to undoped YBa2Cu3O7−δ films (32 nm). Further analysis suggests that the doped film contains a much lower silver content (<0.15 wt %) than in the target material (5 wt %). These observations are in excellent agreement with the temperature dependence of Jc, the room-temperature resistivity, and the surface resistance results. Thus, Jc enhancement in Ag-doped films can be attributed to their superior properties, viz., improved microstructure characteristics and the reduced resistive grain boundaries. © 1997 American Institute of Physics.
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74.78.-w Superconducting films and low-dimensional structures
74.62.Dh Effects of crystal defects, doping and substitution

The role of strain in magnetic anisotropy of manganite thin films

Y. Suzuki, H. Y. Hwang, S-W. Cheong, and R. B. van Dover

Appl. Phys. Lett. 71, 140 (1997); http://dx.doi.org/10.1063/1.119454 (3 pages) | Cited 149 times

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We show the importance of the role of strain in La0.7Sr0.3MnO3 films by revealing the dominance of stress anisotropy effects over magnetocrystalline anisotropy effects in the magnetic anisotropy of these films. Magnetic anisotropy measurements of (001) and (110) La0.7Sr0.3MnO3 thin films on SrTiO3 and LaGaO3 substrates, with excellent structural quality, reveal twofold symmetry on (110) La0.7Sr0.3MnO3 films and fourfold symmetry on (001) films. Such symmetries can only be explained by stress anisotropy contributions in the plane of the film. In conjunction with the thickness dependence of the magnetic properties, the results indicate the dominant role of strain in the magnetic properties of these doped manganites. © 1997 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.80.+q Magnetomechanical effects, magnetostriction
75.30.Gw Magnetic anisotropy
75.50.Dd Nonmetallic ferromagnetic materials

Submicron GaMn quasicrystals in ferromagnetic GaAs

J. P. Zhang, A. K. Cheetham, K. Sun, J. S. Wu, K. H. Kuo, J. Shi, and D. D. Awschalom

Appl. Phys. Lett. 71, 143 (1997); http://dx.doi.org/10.1063/1.119486 (3 pages) | Cited 8 times

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GaMn icosahedral particles with quasicrystalline order have been found in Mn implanted and rapidly annealed GaAs by means of selected-area electron diffraction, high-resolution, and dark-field electron microscopy. The orientation relationship between the submicron quasicrystals with the icosahedral (2/m mathmath) symmetry and the face-centered cubic (fcc) GaAs matrix is determined to be: imath (the fivefold inversion axis in (2/m mathmath))//[110]GaAs, imath (the threefold inversion axis)//[11math]GaAs, and i2 (the twofold axis)//[12math]GaAs. The statistics of these structural studies, combined with magnetic force microscopy, indicate that the submicron quasicrystals are ferromagnetic. © 1997 American Institute of Physics.
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61.72.uj III-V and II-VI semiconductors
61.44.Br Quasicrystals
75.50.Kj Amorphous and quasicrystalline magnetic materials
81.05.Ea III-V semiconductors
75.50.Dd Nonmetallic ferromagnetic materials
75.50.Pp Magnetic semiconductors

Imaging of domain-inverted gratings in LiNbO3 by electrostatic force microscopy

H. Bluhm, A. Wadas, R. Wiesendanger, A. Roshko, J. A. Aust, and D. Nam

Appl. Phys. Lett. 71, 146 (1997); http://dx.doi.org/10.1063/1.119455 (3 pages) | Cited 21 times

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Ferroelectric domains in LiNbO3 have been investigated by means of electrostatic force microscopy. Polarization-inverted gratings with 4 μm periodicity were fabricated by titanium diffusion into both +c and −c faces of single-domain LiNbO3 crystals. The distribution of the electric field in the vicinity of the sample surface was measured using scanning probe microscopy. The electrostatic force image was found to correlate with the shape of the domain-inverted profile observed by scanning electron and optical microscopies. © 1997 American Institute of Physics.
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77.84.Ek Niobates and tantalates
77.84.Cg PZT ceramics and other titanates
77.80.Dj Domain structure; hysteresis
66.30.J- Diffusion of impurities
42.79.Dj Gratings
77.22.Ej Polarization and depolarization
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