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22 Nov 1999

Volume 75, Issue 21, pp. 3243-3419

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Patterning a surface on the nanometric scale by ion sputtering

S. Rusponi, G. Costantini, F. Buatier de Mongeot, C. Boragno, and U. Valbusa

Appl. Phys. Lett. 75, 3318 (1999); http://dx.doi.org/10.1063/1.125337 (3 pages) | Cited 54 times

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Surface etching by ion sputtering, besides producing equilibrium-oriented patterns similar to those obtained by molecular beam epitaxy (MBE), can also be used to pattern the surface along nonequilibrium orientations, thus extending the possibilities of MBE. By tuning the competition between ion erosion at grazing angles and diffusion-induced surface reorganization, it is, for example, possible to pattern a substrate characterized by a square symmetry with a well-ordered ripple structure running along any desired direction. © 1999 American Institute of Physics.
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81.65.Cf Surface cleaning, etching, patterning
68.35.B- Structure of clean surfaces (and surface reconstruction)
79.20.Rf Atomic, molecular, and ion beam impact and interactions with surfaces
81.15.Hi Molecular, atomic, ion, and chemical beam epitaxy
81.05.Bx Metals, semimetals, and alloys

Third-order optical nonlinearity in ZnO microcrystallite thin films

Weili Zhang, H. Wang, K. S. Wong, Z. K. Tang, G. K. L. Wong, and Ravinder Jain

Appl. Phys. Lett. 75, 3321 (1999); http://dx.doi.org/10.1063/1.125338 (3 pages) | Cited 25 times

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We report the measurement of third-order optical nonlinearity (χ(3)) of ZnO microcrystallite thin films near the excitonic resonance at various temperatures using the femtosecond degenerate four-wave-mixing technique. The measured χ(3) response times are 270, 240, and 160 fs at 4.2 K, 77 K, and room temperature, respectively. The values of χ(3) range from 10−7 to 10−4 esu. The maximum values of χ(3) always correspond to the absorption peaks at different temperatures. Room-temperature excitonic enhancement of χ(3) is also observed. © 1999 American Institute of Physics.
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42.70.Nq Other nonlinear optical materials; photorefractive and semiconductor materials
78.66.Hf II-VI semiconductors
42.65.An Optical susceptibility, hyperpolarizability
78.47.-p Spectroscopy of solid state dynamics
78.40.Fy Semiconductors
71.35.Gg Exciton-mediated interactions
42.65.Jx Beam trapping, self-focusing and defocusing; self-phase modulation

Interface properties of AlxGa1−xN/AlN heterostructures from optical waveguiding information

E. Dogheche, B. Belgacem, D. Remiens, P. Ruterana, and F. Omnes

Appl. Phys. Lett. 75, 3324 (1999); http://dx.doi.org/10.1063/1.125339 (3 pages) | Cited 14 times

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A complete optical characterization using the prism coupling technique is proposed for AlGaN/AlN heterostructures grown on sapphire substrates by metalorganic vapor-phase epitaxy. In this study, we have qualified the film behavior and the substrate-to-layer interface directly from the measured optical data. The experimental and theoretical approach used for this purpose is described in detail. The results have clearly shown essential changes in the refractive index profile at the interface, which may be related to structural defects, and indicate a good agreement with the trends observed by transmission electron microscopy analysis. © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
78.66.Fd III-V semiconductors
42.79.Gn Optical waveguides and couplers
78.20.Ci Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity)
81.15.Gh Chemical vapor deposition (including plasma-enhanced CVD, MOCVD, ALD, etc.)
68.55.Ln Defects and impurities: doping, implantation, distribution, concentration, etc.

Optical and structural properties of epitaxial MgxZn1−xO alloys

A. K. Sharma, J. Narayan, J. F. Muth, C. W. Teng, C. Jin, A. Kvit, R. M. Kolbas, and O. W. Holland

Appl. Phys. Lett. 75, 3327 (1999); http://dx.doi.org/10.1063/1.125340 (3 pages) | Cited 162 times

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The optical and structural properties of high-quality single-crystal epitaxial MgZnO films deposited by pulsed-laser deposition were studied. In films with up to ∼36 at. % Mg incorporation, we have observed intense ultraviolet band edge photoluminescence at room temperature and 77 K. The highly efficient photoluminescence is indicative of the excitonic nature of the material. Transmission spectroscopy was used to show that the excitonic structure of the alloys was clearly visible at room temperature. High-resolution transmission electron microscopy, x-ray diffraction, and Rutherford backscattering spectroscopy/ion channeling were used to verify the epitaxial single-crystal quality of the films and characterize the defect content. Post-deposition annealing in oxygen was found to reduce the number of defects and to improve the optical properties of the films. These results indicate that MgZnO alloys have potential applications in a variety of optoelectronic devices. © 1999 American Institute of Physics.
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78.66.Hf II-VI semiconductors
68.55.-a Thin film structure and morphology
78.55.Et II-VI semiconductors
78.40.Fy Semiconductors
71.55.Gs II-VI semiconductors
81.15.Fg Pulsed laser ablation deposition
71.35.Cc Intrinsic properties of excitons; optical absorption spectra
61.72.Cc Kinetics of defect formation and annealing
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Field emission study of gated GaN and Al0.1Ga0.9N/GaN pyramidal field emitter arrays

T. Kozawa, T. Ohwaki, Y. Taga, and N. Sawaki

Appl. Phys. Lett. 75, 3330 (1999); http://dx.doi.org/10.1063/1.125341 (3 pages) | Cited 16 times

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A self-aligned process has been proposed for fabrications of gated GaN and Al0.1Ga0.9N/GaN pyramidal field emitters with a small and precise distance between the gate electrode and the emitter tip. The sharp pyramidal emitters were obtained by a selective area growth technique. SiO2 and polyimide were used as the insulating layers between the emitters and the gate electrode. The gate-tip spacing and the tip protrusion through the gate openings were precisely controlled by adjusting the thickness of the SiO2 and polyimide layers. The turn-on voltage was reduced by narrowing the gate-tip spacing and by using Al0.1Ga0.9N/GaN emitter instead of GaN; the low onset gate voltage of 42 V was obtained for a gate-tip spacing of 0.4 μm. © 1999 American Institute of Physics.
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85.45.Db Field emitters and arrays, cold electron emitters

Room-temperature blue luminescence of thermally oxidized Si1−x−yGexCy thin films on Si (100) substrates

Xuemei Cheng, Youdou Zheng, Xiabing Liu, Lan Zang, Zhiyun Lo, Shunming Zhu, Ping Han, and Ruolian Jiang

Appl. Phys. Lett. 75, 3333 (1999); http://dx.doi.org/10.1063/1.125342 (3 pages) | Cited 1 time

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We measured at room temperature the photoluminescence spectra of the thermally oxidized Si1−x−yGexCy thin films which were grown on silicon substrates by plasma-enhanced chemical vapor deposition and then wet oxidized at 1100 °C for 20 min. The photoluminescence band with a peak at ∼393 nm under the exciting radiation of λ = 241 nm was observed. Possible mechanism of this photoluminescence is discussed. © 1999 American Institute of Physics.
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78.55.Hx Other solid inorganic materials
81.65.Mq Oxidation
78.66.Li Other semiconductors
81.05.Hd Other semiconductors

Ultrafast carrier trapping in Be-doped low-temperature-grown GaAs

A. Krotkus, K. Bertulis, L. Dapkus, U. Olin, and S. Marcinkevičius

Appl. Phys. Lett. 75, 3336 (1999); http://dx.doi.org/10.1063/1.125343 (3 pages) | Cited 18 times

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Time-resolved photoluminescence is used to study low-temperature-grown (LTG) GaAs with Be doping. It is observed that the carrier trapping time in the as-grown LTG GaAs increases with Be doping. Similar effect is observed also in the annealed samples doped with less than 3×1019 cm−3 of Be. At higher doping levels, the trapping time in these samples is abruptly reduced to below 100 fs. This behavior is attributed to changes in As antisite density and the compensation effect of Be. © 1999 American Institute of Physics.
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78.47.-p Spectroscopy of solid state dynamics
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
71.55.Eq III-V semiconductors
73.61.Ey III-V semiconductors
61.72.Cc Kinetics of defect formation and annealing
61.72.J- Point defects and defect clusters

Spatially resolved luminescence investigation of AlGaAs/GaAs single quantum wires modified by selective implantation and annealing

Xingquan Liu, Wei Lu, Zhi Feng Li, Yi Dong Chen, S. C. Shen, Y. Fu, M. Willander, Hark Hoe Tan, S. Yuan, C. Jagadish, J. Zou, and D. J. H. Cockayne

Appl. Phys. Lett. 75, 3339 (1999); http://dx.doi.org/10.1063/1.125344 (3 pages) | Cited 8 times

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Single Al0.5Ga0.5As/GaAs V-groove quantum wires (QWR) modified by selective implantation and rapid thermally annealing were investigated by spatially resolved microphotoluminescence (micro-PL). The PL from the necking region was clearly observed at room temperature. Optical properties of QWR and the adjacent quantum well structures were strongly degraded by the implantation. The recovery properties of the PL signals from all the structures were dependent on the implantation dose. A critical dose of 1×1013 cm−2 was found for the selective implantation, over which the PL from the necking region could not be recovered. Also the blueshifts of QWR and the necking-region PL peaks were observed for all the annealed samples. This blueshift is caused by the interface intermixing, which is very useful to increase the confinement of carriers in QWR region for optoelectronic device applications. © 1999 American Institute of Physics.
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78.66.Fd III-V semiconductors
78.55.Cr III-V semiconductors
61.72.uj III-V and II-VI semiconductors
61.72.Cc Kinetics of defect formation and annealing
73.21.-b Electron states and collective excitations in multilayers, quantum wells, mesoscopic, and nanoscale systems
68.35.Fx Diffusion; interface formation

Current transients in almost-ideal Czochralski silicon p–n junction diodes

A. Poyai, E. Simoen, and C. Claeys

Appl. Phys. Lett. 75, 3342 (1999); http://dx.doi.org/10.1063/1.125345 (3 pages) | Cited 2 times

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The nature of the reverse current transients in large-area nearly ideal p–n junction diodes fabricated on Czochralski silicon substrates is investigated. It is shown that they can be generated by an electrical or optical excitation pulse. A typical nonexponential behavior with time is observed. The best fit is found for a power-law function. The impact of the reverse bias and the temperature on the prefactor and on the exponent will be presented. From the observations, it is concluded that the capture of electrons is a necessary step for the generation of the transients. A discussion of the possible nature of the underlying defects is given, and the implications for practical current–voltage characterization will be discussed. © 1999 American Institute of Physics.
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85.30.Kk Junction diodes
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths

Ohmic contacts to p-type ZnSe using a ZnSe/BeTe superlattice

F. Vigué, P. Brunet, P. Lorenzini, E. Tournié, and J. P. Faurie

Appl. Phys. Lett. 75, 3345 (1999); http://dx.doi.org/10.1063/1.125346 (3 pages) | Cited 8 times

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Various configurations of pseudograded BeTe/ZnSe superlattices have been investigated to form a nonalloyed contact onto nitrogen-doped p-type ZnSe layers. Best results were obtained by using a fully N-doped superlattice with a 20-ML-thick pseudoperiod and with the thickness of individual layers in the pseudoperiod varying by 1 ML steps. A specific contact resistance of 6×10−2 Ω cm2 has been measured for a ZnSe p-type doping level of 2×1017 cm−3. Truly perfect ohmic contact is obtained. © 1999 American Institute of Physics.
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73.40.Ns Metal-nonmetal contacts
81.05.Dz II-VI semiconductors
73.40.Cg Contact resistance, contact potential
73.61.Ga II-VI semiconductors

Photoelectrical properties of a ferroelectric liquid crystalline photoconductor

Kyoko Kogo, Hiroki Maeda, Hiroaki Kato, Masahiro Funahashi, and Jun-ichi Hanna

Appl. Phys. Lett. 75, 3348 (1999); http://dx.doi.org/10.1063/1.125347 (3 pages) | Cited 4 times

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An organic ferroelectric photoconductor, 2-[(S)-4-(6-methylheptyloxy)phenyl]-6-decylnaphthalene, was prepared and its photoconductive and ferroelectric behaviors were characterized by steady-state and transient electrical measurements. This material exhibited fast carrier transport with an ambipolar mobility of 2.6×10−4 cm2/V s, independent of temperature and electric field. Under a polarized microscope, a fast switching with memory effect was observed visually and the spontaneous polarization was evaluated to be 0.6 nC/cm2 in chiral smectic C phase. © 1999 American Institute of Physics.
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72.40.+w Photoconduction and photovoltaic effects
77.84.Nh Liquids, emulsions, and suspensions; liquid crystals
77.22.Ej Polarization and depolarization
77.80.Fm Switching phenomena
72.30.+q High-frequency effects; plasma effects
72.20.Fr Low-field transport and mobility; piezoresistance
72.80.Le Polymers; organic compounds (including organic semiconductors)

Very low densities of localized states at the Fermi level in hydrogenated polymorphous silicon from capacitance and space-charge-limited current measurements

J. P. Kleider, C. Longeaud, M. Gauthier, M. Meaudre, R. Meaudre, R. Butté, S. Vignoli, and P. Roca i Cabarrocas

Appl. Phys. Lett. 75, 3351 (1999); http://dx.doi.org/10.1063/1.125348 (3 pages) | Cited 23 times

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The density of states at the Fermi level N(EF) has been measured on hydrogenated polymorphous (pm-Si:H) silicon samples using both capacitance measurements on Schottky barriers and space-charge-limited current measurements on n+/i/n+ structures. From both techniques, N(EF) values of 7–8×1014 cm−3 eV−1 have been obtained, which is significantly lower than reported in the literature for hydrogenated amorphous silicon (a-Si:H). Such values demonstrate that pm-Si:H is a very low defect density material which should be able to replace a-Si:H in the field of applications like photovoltaics. © 1999 American Institute of Physics.
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71.20.Mq Elemental semiconductors
71.55.Cn Elemental semiconductors
72.20.Ht High-field and nonlinear effects
73.30.+y Surface double layers, Schottky barriers, and work functions

Effect of initial surface reconstruction on the GaS/GaAs(001) interface

R. I. Pelzel, B. Z. Nosho, W. V. Shoenfeld, T. Lundstrom, P. M. Petroff, and W. H. Weinberg

Appl. Phys. Lett. 75, 3354 (1999); http://dx.doi.org/10.1063/1.125349 (3 pages) | Cited 2 times

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We have used photoluminescence of a GaAs/Al0.3Ga0.7As near-surface quantum well structure to study the quality of the interface between GaAs and GaS deposited in ultrahigh vacuum (UHV) using [(tBu)GaS]4. In addition to the luminescence of the near-surface and the deep/reference quantum wells, luminescence was observed for the GaAs cap following the deposition of 100 Å of GaS. This additional feature demonstrates the high quality GaS/GaAs interface achievable through the UHV deposition of this precursor. The ratios of the integrated luminescence intensity of both the GaAs cap and the near-surface GaAs quantum well to the deep/reference quantum well indicate that there are fewer GaS/GaAs interface states for deposition on the Ga-rich GaAs(001)-(4×2)/(2×6) surface compared to deposition on the As-rich GaAs(001)-(2×4) surface. Furthermore, GaS passivated samples exposed to ambient conditions for eight months exhibit no luminescence degradation for the near-surface quantum well confirming that these films provide adequate passivation longevity. © 1999 American Institute of Physics.
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68.35.Ct Interface structure and roughness
68.35.B- Structure of clean surfaces (and surface reconstruction)
81.15.-z Methods of deposition of films and coatings; film growth and epitaxy
78.55.Cr III-V semiconductors
78.66.Fd III-V semiconductors
81.65.Rv Passivation
81.05.Ea III-V semiconductors

Characterization of hydrogen-terminated Si(111) surfaces by sum-frequency surface vibrational spectroscopy

M. Y. Mao, P. B. Miranda, D. S. Kim, and Y. R. Shen

Appl. Phys. Lett. 75, 3357 (1999); http://dx.doi.org/10.1063/1.125350 (3 pages) | Cited 6 times

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Sum-frequency surface vibrational spectroscopy was used to characterize H-terminated Si(111) surfaces prepared by different methods. It was found that flash heating of a sample to 1500 K followed by H2 dosing at 900 K yields a surface as good in quality as a wet chemically treated surface. Both surfaces are far superior than that prepared by atomic H adsorption. © 1999 American Institute of Physics.
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68.35.Ja Surface and interface dynamics and vibrations
42.65.Ky Frequency conversion; harmonic generation, including higher-order harmonic generation
78.30.Am Elemental semiconductors and insulators
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
81.65.Rv Passivation
81.05.Cy Elemental semiconductors

SiO2/6H-SiC(0001)3×3 initial interface formation by Si overlayer oxidation

F. Amy, P. Soukiassian, Y.-K. Hwu, and C. Brylinski

Appl. Phys. Lett. 75, 3360 (1999); http://dx.doi.org/10.1063/1.125351 (3 pages) | Cited 29 times

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We investigate the initial oxidation and SiO2/6H-SiC interface formation by core level photoemission spectroscopy using synchrotron radiation. The results indicate that the direct oxidation of the 6H–SiC(0001)3×3 surface leads to SiO2 formation at low temperatures (500 °C) with a nonabrupt interface having significant amounts of mixed (Si–O–C) and intermediate (Si3+,Si2+,Si+) oxidation products. In contrast, C-free and a much more abrupt SiO2/6H-SiC(0001) interface formation is achieved when predeposited Si overlayer is thermally oxidized at low oxygen exposures and low temperatures (500 °C). © 1999 American Institute of Physics.
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81.65.Mq Oxidation
81.05.Hd Other semiconductors
73.20.At Surface states, band structure, electron density of states
82.80.Pv Electron spectroscopy (X-ray photoelectron (XPS), Auger electron spectroscopy (AES), etc.)
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Enhanced magnetic coercivities in Fe nanowires

N. Grobert, W. K. Hsu, Y. Q. Zhu, J. P. Hare, H. W. Kroto, D. R. M. Walton, M. Terrones, H. Terrones, Ph. Redlich, M. Rühle, R. Escudero, and F. Morales

Appl. Phys. Lett. 75, 3363 (1999); http://dx.doi.org/10.1063/1.125352 (3 pages) | Cited 142 times

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We describe a way of generating films (<2 mm2; <40 μm thick) of aligned Fe-filled carbon nanotubes. These Fe nanowires are usually composed of single Fe crystals, and have dimensions from 5–40 nm outer diameter and <10 μm in length. The carbon tubes, which coat the wires, have external diameters of ∼ 20–70 nm and are <40 μm in length. High-resolution electron energy loss spectroscopy, x-ray powder diffraction, and elemental mapping of the tubular structures reveal only characteristic metallic signals and the effective absence of oxygen (or any other nonmetallic element) within the wires. The material exhibits coercivities in the 430–1070 Oe range, i.e., greater than those reported for Ni and Co nanowires. © 1999 American Institute of Physics.
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68.65.-k Low-dimensional, mesoscopic, nanoscale and other related systems: structure and nonelectronic properties
61.46.-w Structure of nanoscale materials
75.50.Kj Amorphous and quasicrystalline magnetic materials
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.50.Vv High coercivity materials
75.70.Ak Magnetic properties of monolayers and thin films

An oxide-diluted magnetic semiconductor: Mn-doped ZnO

T. Fukumura, Zhengwu Jin, A. Ohtomo, H. Koinuma, and M. Kawasaki

Appl. Phys. Lett. 75, 3366 (1999); http://dx.doi.org/10.1063/1.125353 (3 pages) | Cited 18 times

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Epitaxial thin films of an oxide-diluted magnetic semiconductor, Mn-doped ZnO, were fabricated by pulsed-laser deposition technique. Solubility of Mn into ZnO exceeds thermal equilibrium limit as a result of nonequilibrium film growth process. As Mn content is increased, the lattice constants of both a and c axes of wurtzite Zn1−xMnxO films (x<0.35) increase and the band gap expands although considerable in-gap absorption develops. Itinerant electrons over 1019 cm−3 can be doped into the Zn1−xMnxO films by Al doping, in contrast to low carrier density in the other II–VI diluted magnetic semiconductors. The temperature dependence of the resistivity is almost metallic and considerable magnetoresistance is observed at low temperatures. © 1999 American Institute of Physics.
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81.15.Fg Pulsed laser ablation deposition
68.55.-a Thin film structure and morphology
73.61.Ga II-VI semiconductors
81.05.Dz II-VI semiconductors
72.80.Ey III-V and II-VI semiconductors
64.75.-g Phase equilibria
81.30.Mh Solid-phase precipitation
81.15.Kk Vapor phase epitaxy; growth from vapor phase
72.20.My Galvanomagnetic and other magnetotransport effects
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)

Room temperature La0.7Sr0.3MnO3 magnetoresistive prototype memory element

F. J. Cadieu, Li Chen, Biao Li, and T. Theodoropoulos

Appl. Phys. Lett. 75, 3369 (1999); http://dx.doi.org/10.1063/1.125354 (3 pages) | Cited 3 times

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Highly (110) textured La0.7Sr0.3MnO3 polycrystalline film strips in conjunction with a small interacting bias magnet have been used to construct a prototype room temperature memory element. The film strips were made by high laser pulse energy pulsed laser deposition such that the temperature of the resistance maximum was elevated to room temperature. Consequently room temperature operation did not require any temperature compensation. The magnetoresistance of such film strips exhibited highly anisotropic low field magnetoresistance with the largest response for applied fields in plane and parallel to the current direction. Perpendicular to the plane applied fields produced no response in the low field region. A simple bridge was configured in which the sensing element was a 100-μm-wide manganite strip made to exhibit a broad resistance maximum at room temperature. The memory element magnetoresistive response for field excursions approaching the intrinsic coercivity of the bias magnet exhibited two distinct zero applied field resistance values. Parallel versus antiparallel field excursions to 60 mT produced zero applied magnetic field voltage states separated by 18 mV at room temperature in a geometry investigated. © 1999 American Institute of Physics.
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75.70.Ak Magnetic properties of monolayers and thin films
75.47.De Giant magnetoresistance
85.70.Kh Magnetic thin film devices: magnetic heads (magnetoresistive, inductive, etc.); domain-motion devices, etc.
81.15.Fg Pulsed laser ablation deposition

Anomaly of Hall effect in magnetoresistive La0.67Ca0.33MnO3

X. W. Cao, J. Fang, Z. H. Wang, and K. B. Li

Appl. Phys. Lett. 75, 3372 (1999); http://dx.doi.org/10.1063/1.125355 (3 pages) | Cited 8 times

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We have simultaneously measured the longitudinal resistivity and the Hall resistivity for the magnetoresistive La0.67Ca0.33MnO3 thin films as a function of temperature in temperature region of colossal magnetoresistance at several magnetic fields. Two reversions of the Hall sign with reducting temperature have been observed. The temperature at which the reversion of the Hall sign occurs shifts to the higher temperature with the increase of applied magnetic field. It was argued that the coexistence of two types of conduction mechanisms, the itinerant electron and small polaron, competing with each other, might be responsible for the two reversions of the Hall sign. © 1999 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.50.Dd Nonmetallic ferromagnetic materials
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
73.61.Ng Insulators

Influence of a local magnetic field on the movement of a single vortex pinned in a niobium thin-film direct current superconducting quantum interference device

J. Gail, M. Mück, and C. Heiden

Appl. Phys. Lett. 75, 3375 (1999); http://dx.doi.org/10.1063/1.125356 (3 pages) | Cited 1 time

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To avoid pinning of many vortices, we prepared superconducting quantum interference devices (SQUIDs) with a square loop of only 1 μm linewidth. At one side of the SQUID, the loop widens to an area of 4 μm×5 μm, which offers enough space for a few vortices. If a vortex is trapped in this pinning area, it begins to migrate by thermally activated hopping between the pinning sites. It was possible to influence the hopping process via a Lorentz force on the vortex produced by a local magnetic field. We were able to show that the vortex was located in the extra area of the SQUID loop and not in any other part of the SQUID. © 1999 American Institute of Physics.
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85.25.Dq Superconducting quantum interference devices (SQUIDs)
74.25.Uv Vortex phases (includes vortex lattices, vortex liquids, and vortex glasses)
74.78.-w Superconducting films and low-dimensional structures
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)

Colossal magnetoresistance effect in perovskite-type La–Sn–Mn–O epitaxial films

Xiangxin Guo, Shouyu Dai, Yueliang Zhou, Guozhen Yang, and Zhenghao Chen

Appl. Phys. Lett. 75, 3378 (1999); http://dx.doi.org/10.1063/1.125357 (3 pages) | Cited 9 times

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La–Sn–Mn–O (LSnMO) thin films epitaxially grown on single-crystal substrates by pulsed-laser deposition are reported. The films have a perovskite structure and perform the colossal magnetoresistance effect with the maximum magnetoresistance (MR) ratio of 103% (at 233 K and 6 T). The dependence of electrical transport and magnetic properties on the film thickness has been studied. The analyses reveal that the electrical transport, in contrast with the magnetic phase transition, is more sensitive to the thickness of the films. © 1999 American Institute of Physics.
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75.47.Gk Colossal magnetoresistance
75.50.Dd Nonmetallic ferromagnetic materials
73.50.Jt Galvanomagnetic and other magnetotransport effects (including thermomagnetic effects)
75.30.Kz Magnetic phase boundaries (including classical and quantum magnetic transitions, metamagnetism, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
72.60.+g Mixed conductivity and conductivity transitions
81.15.Fg Pulsed laser ablation deposition

Nonlinear electrical conduction and broad band noise in the charge-ordered rare earth manganate Nd0.5Ca0.5MnO3

Ayan Guha, Arindam Ghosh, A. K. Raychaudhuri, S. Parashar, A. R. Raju, and C. N. R. Rao

Appl. Phys. Lett. 75, 3381 (1999); http://dx.doi.org/10.1063/1.125358 (3 pages) | Cited 26 times

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Measurements of the dc transport properties and the low-frequency conductivity noise in films of charge-ordered Nd0.5Ca0.5MnO3 grown on Si substrate reveal the existence of a threshold field in the charge-ordered regime beyond which strong nonlinear conduction sets in along with a large broad band conductivity noise. Threshold-dependent conduction disappears as T→TCO, the charge-ordering temperature. This observation suggests that the charge-ordered state gets depinned at the onset of the nonlinear conduction. © 1999 American Institute of Physics.
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73.61.Ng Insulators
73.50.Fq High-field and nonlinear effects
73.50.Td Noise processes and phenomena
71.45.-d Collective effects

The magnetism of a buried La0.7Sr0.3MnO3 interface

S. Stadler, Y. U. Idzerda, Z. Chen, S. B. Ogale, and T. Venkatesan

Appl. Phys. Lett. 75, 3384 (1999); http://dx.doi.org/10.1063/1.125359 (3 pages) | Cited 21 times

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Using x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) techniques, we have investigated the electronic structure and magnetic properties of La0.7Sr0.3MnO3 (LSMO) as a function of YBa2Cu3O7−δ (YBCO) cap layer thickness. The Mn L2,3 XAS and XMCD data clearly show that the magnetic properties and electronic structure of the LSMO are adversely affected by the YBCO overlayer caused by cation displacement/exchange that effectively reduces the concentration of the La atoms in the LSMO near the YBCO/LSMO interface. © 1999 American Institute of Physics.
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74.72.-h Cuprate superconductors
75.50.Dd Nonmetallic ferromagnetic materials
74.50.+r Tunneling phenomena; Josephson effects
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
78.20.Ls Magneto-optical effects
78.70.Dm X-ray absorption spectra
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
75.47.Gk Colossal magnetoresistance
71.20.Ps Other inorganic compounds

Vector imaging of supercurrent flow in YBa2Cu3O7−δ thin films using terahertz radiation

O. Morikawa, M. Yamashita, H. Saijo, M. Morimoto, M. Tonouchi, and M. Hangyo

Appl. Phys. Lett. 75, 3387 (1999); http://dx.doi.org/10.1063/1.125302 (3 pages) | Cited 11 times

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We demonstrated the vector mapping of the supercurrent flow in YBa2Cu3O7−δ thin films using a terahertz (THz) radiation imaging system. A wire-grid polarizer was employed to detect the vector components of the THz radiation. The two THz radiation images obtained through the polarizer tilted by +45° and −45° with respect to the detector’s orientation were successfully transferred into the vector image of the supercurrent distribution. The observed distributions in the current-biased and the vortex-penetrated films were qualitatively explained using Bean’s critical-state model [E. H. Brandt and M. Indenbom, Phys. Rev. B 48, 12893 (1993)]. © 1999 American Institute of Physics.
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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)
74.25.Ha Magnetic properties including vortex structures and related phenomena
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2–2 piezoelectric composites with high density and fine scale fabricated by interdigital pair bonding

Ruibin Liu, Kasia A. Harasiewicz, D. Knapik, N. A. Freeman, and F. Stuart Foster

Appl. Phys. Lett. 75, 3390 (1999); http://dx.doi.org/10.1063/1.125303 (3 pages) | Cited 1 time

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Interdigital pair bonding (IPB) is proposed as a means to fabricate piezoelectric composites used for ultrasonic transducers and arrays for medical imaging and nondestructive evaluation, especially in the high frequency range. This letter presents experimental results of prototype 2–2 piezoelectric composites made by IPB. Two composites with different lateral dimensions were fabricated using 70 and 40 μm thickness dicing saw blades. The widths of ceramic stripe and epoxy kerf for composite A are 53 and 12 μm, respectively, and are 36 and 4 μm for composite B. The thickness mode and lateral modes for both composites were investigated by impedance spectrum analysis. The kt for both samples is 0.64. The current designs permit the fabrication of composites for transducers operated up to approximately 50 MHz using conventional dicing saw blades. The extension of IPB to fabrication of 1–3 composite is discussed. © 1999 American Institute of Physics.
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77.84.Lf Composite materials
43.38.Hz Transducer arrays, acoustic interaction effects in arrays
43.38.Fx Piezoelectric and ferroelectric transducers
85.50.-n Dielectric, ferroelectric, and piezoelectric devices
81.05.Mh Cermets, ceramic and refractory composites
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