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A systematic study of the effects of lateral magnetostatic coupling of closely packed pseudo-spin-valve Ni80Fe20(10 nm)/Cu(tCu)/Ni80Fe20(80 nm) nanowire arrays with varied Cu film thicknesses is investigated. Nanowire arrays with a width of 185 nm and edge-to-edge spacings of 35 and 185 nm, respectively, were fabricated using deep ultraviolet lithography at 248 nm exposing wavelength. When the Cu spacer layer thickness is comparable to the edge-to-edge spacing of the closely packed wires, marked changes in the magnetization reversal process are observed for the nanowire array with edge-to-edge spacing of 35 nm, due to the competition between the dipolar coupling between the neighboring nanowires and interlayer magnetostatic coupling between the thick and thin Ni80Fe20 layers. [ABSTRACT FROM AUTHOR]

We have generated shift and injection currents in unstrained, undoped (110)-grown GaAs/Al0.3Ga0.7As quantum wells with a single optical pulse and detected them via free-space terahertz experiments. By properly choosing the polarization state of the excitation pulse, it is possible to generate both currents alone along certain crystal directions or to simultaneously generate them along the same crystal direction. A comparison of injection and shift currents allows us to estimate the strength of the injection current. At an excitation energy of 1.53 eV the injection current tensor element is ≈i2×107 A/(V2 s). This corresponds to an injection of electrons with an average velocity of ≈10 km/s. Moreover, a comparison of the intensity dependence of shift and injection currents under identical experimental conditions demonstrates a stronger saturation of the shift current. [ABSTRACT FROM AUTHOR]

The 87Rb spin-lattice relaxation time T1 and spin-spin relaxation time T2 of RbCdCl3 and Rb4CdCl6 single crystals grown by the slow evaporation method were measured over the temperature range of 160–410 K. In the case of the RbCdCl3 crystal, changes were observed in the 87Rb T1-1 near 340, 363, and 395 K, which correspond to phase transitions. The abrupt decrease in T1-1 observed at 395 K is due to a shortening in the c direction as a result of a phase transition from a tetragonal to a cubic structure. We suggest that the cubic Rb environment is favored above 395 K, which causes relaxation and averages out the quadrupolar splittings. On the other hand, the 87Rb T1 in Rb4CdCl6 decreased with increasing temperature, and no phase transitions were observed in the temperature range considered. For both RbCdCl3 and Rb4CdCl6, the relaxation rate of Rb was found to be proportional to the square of the temperature, indicating that the relaxation proceeds via a Raman process. This behavior for the electric-quadrupolar-type RbCdCl3 and Rb4CdCl6 crystals stands in contrast to a previous report that the relaxations in Cs2CuCl4 and Cs2CoCl4 crystals with the magnetic relaxation type proceed via single-phonon processes. Therefore, the relaxation mechanism in crystals with an electric quadrupolar NMR interaction mechanism is completely different from that in crystals with magnetic-type NMR behavior. [ABSTRACT FROM AUTHOR]

Luminescence properties of ZnO films, which have been epitaxially grown on c-sapphire (0001) substrates by plasma-assisted molecular beam epitaxy, are investigated by means of different excitation sources and their measurement conditions. With the increase of measurement temperature, photoluminescence spectra clearly present, the appearance of different bound-exciton peaks (I10 line) with an abrupt increase of emission intensity at the measurement temperature of 30-50 K. Hypothetical explanations on the basis of thermalization effects, vibronic/rotational resonance states, and the involvement of the B-valence level in emission are given. In cathodoluminescence (CL), the deep level emission intensity was enlarged with the electron beam penetration depth due to the higher defect density near the interface between ZnO and the sapphire. From the CL image of the ZnO film, the dislocation density was estimated as 6×108-3×109/cm2. The lasing phenomenon was observed at the threshold power density of 1.3 MW/cm2 at 300 K. [ABSTRACT FROM AUTHOR]

Shift and injection currents are generated in the wurtzite semiconductors CdSe and CdS at 295 K using above-band-gap (hω>Eg) femtosecond pulses and detected via the emitted terahertz radiation; the optical beams are normally incident on samples with the optic axis in the plane of the surface. For optical intensities up to 75 MW cm-2 (or carrier density <1018 cm-3) the terahertz radiation amplitude shows the expected linear dependence and also varies with optical polarization and sample orientation consistent with the third-rank tensors that govern the current generation processes in the wurtzite structure. The largest shift currents are generated along the optical axis for light polarized along that axis. In CdSe with hω=1.80 eV (690 nm), the electron shift distance is ∼40% of the 0.25 nm bond length and the peak current density is 5 kA cm-2 for an optical intensity of 10 MW cm-2; for CdS the corresponding experiment at hω=3.0 eV (410 nm) gives a shift distance ∼80% of the 0.26 nm bond length with a peak current density of 50 kA cm-2 for an incident intensity of 75 MW cm-2. For injection current produced in CdSe with circularly polarized 690 nm excitation, electrons are injected with an average speed of 9 km s-1; this is ∼3% of the group velocity for electrons excited with the same energy. The corresponding values for CdS excited at 410 nm are 20 km s-1 and 2%. From the temporal characteristics of the terahertz emission for injection currents in CdS we deduce that the electron momentum scattering time is <100 fs, consistent with mobility studies. [ABSTRACT FROM AUTHOR]

A systematic investigation of the magnetization reversal process of diamond-shaped Ni80Fe20(10 nm)/Cu(tCu nm)/Ni80Fe20(40 nm) pseudo-spin-valve nanostructures is presented. The structures were fabricated on silicon substrate using deep ultraviolet lithography at 248 nm exposing wavelength. By carefully selecting two ferromagnetic layer thicknesses, with different reversal mechanisms, we have created a magnetic structure with unique magnetic properties. We observed that the magnetization reversal process of the spin valve is strongly influenced by the Cu spacer layer thickness. Our experimental results were substantiated with a three-dimensional micromagnetic simulation. [ABSTRACT FROM AUTHOR]

The 87Rb spin-lattice relaxation time of Rb2CoCl4 single crystals grown using the slow evaporation method was measured using nuclear magnetic resonance. The recovery trace for the central line of 87Rb with dominant magnetic relaxation cannot be represented with a single exponential function, but can be represented with a linear combination of two exponential functions. The change in the 87Rb spin-lattice relaxation rate near Tc1 corresponds to the ferroelectric to incommensurate phase transition. There is a weak anomalous contribution to T1, and this seems to be the only detectable influence of a structural phase transition. The temperature dependence of T1 -1 near Ti is more or less continuous and is not affected by the normal-incommensurate phase transition. For T>Ti, the spin-lattice relaxation rate is governed by molecular motion as described by the Bloembergen-Purcell-Pound theory. This behavior is different to that found for Rb in Rb2ZnCl4. The phase-transition temperatures of the Rb2CoCl4 and Rb2ZnCl4 single crystals are quite similar, but their phase-transition mechanisms are different. The nuclear-magnetic-resonance (NMR) interaction mechanism in Rb2ZnCl4 is well known to be of the electric quadrupolar type whereas in Rb2CoCl4 it is of magnetic origin. Therefore a completely different NMR behavior is obtained in the two crystals. [ABSTRACT FROM AUTHOR]

The semiconductor ZnO has gained substantial interest in the research community in part because of its large exciton binding energy (60 meV) which could lead to lasing action based on exciton recombination even above room temperature. Even though research focusing on ZnO goes back many decades, the renewed interest is fueled by availability of high-quality substrates and reports of p-type conduction and ferromagnetic behavior when doped with transitions metals, both of which remain controversial. It is this renewed interest in ZnO which forms the basis of this review. As mentioned already, ZnO is not new to the semiconductor field, with studies of its lattice parameter dating back to 1935 by Bunn [Proc. Phys. Soc. London 47, 836 (1935)], studies of its vibrational properties with Raman scattering in 1966 by Damen et al. [Phys. Rev. 142, 570 (1966)], detailed optical studies in 1954 by Mollwo [Z. Angew. Phys. 6, 257 (1954)], and its growth by chemical-vapor transport in 1970 by Galli and Coker [Appl. Phys. Lett. 16, 439 (1970)]. In terms of devices, Au Schottky barriers in 1965 by Mead [Phys. Lett. 18, 218 (1965)], demonstration of light-emitting diodes (1967) by Drapak [Semiconductors 2, 624 (1968)], in which Cu2O was used as the p-type material, metal-insulator-semiconductor structures (1974) by Minami et al. [Jpn. J. Appl. Phys. 13, 1475 (1974)], ZnO/ZnSe n-p junctions (1975) by Tsurkan et al. [Semiconductors 6, 1183 (1975)], and Al/Au Ohmic contacts by Brillson [J. Vac. Sci. Technol. 15, 1378 (1978)] were attained. The main obstacle to the development of ZnO has been the lack of reproducible and low-resistivity p-type ZnO, as recently discussed by Look and Claflin [Phys. Status Solidi B 241, 624 (2004)]. While ZnO already has many industrial applications owing to its piezoelectric properties and band gap in the near ultraviolet, its applications to optoelectronic devices has not yet materialized due chiefly to the lack of p-type epitaxial layers. Very high quality what used to be called whiskers and platelets, the nomenclature for which gave way to nanostructures of late, have been prepared early on and used to deduce much of the principal properties of this material, particularly in terms of optical processes. The suggestion of attainment of p-type conductivity in the last few years has rekindled the long-time, albeit dormant, fervor of exploiting this material for optoelectronic applications. The attraction can simply be attributed to the large exciton binding energy of 60 meV of ZnO potentially paving the way for efficient room-temperature exciton-based emitters, and sharp transitions facilitating very low threshold semiconductor lasers. The field is also fueled by theoretical predictions and perhaps experimental confirmation of ferromagnetism at room temperature for potential spintronics applications. This review gives an in-depth discussion of the mechanical, chemical, electrical, and optical properties of ZnO in addition to the technological issues such as growth, defects, p-type doping, band-gap engineering, devices, and nanostructures. [ABSTRACT FROM AUTHOR]

We have investigated the low-temperature magnetoresistance (MR) behavior of Co nanowires with varying widths between 40 nm and 5.2 μm prepared by high-resolution electron-beam lithography. The wires have a thickness of 20 nm and are protected from oxidation by a 10 nm carbon cap layer. The magnetoresistance—for magnetic fields applied transversal or perpendicular to the wire—is negative and can be attributed to anisotropic magnetoresistance. The MR curves exhibit a strong dependence on the wire width from which the shape anisotropy and the demagnetizing factors can be deduced. The experimental results are in perfect agreement with the theoretical values for the demagnetization tensor of the general ellipsoid. During the magnetization rotation process a minor contribution from domain-wall nucleation and annihilation occurs. [ABSTRACT FROM AUTHOR]

With few exceptions, YBa2Cu3O7-δ thin films have been shown to be heavily microtwinned. Conflicting reports of twin-free films, however, have been presented when using the (0 0 1) NdGaO3 substrate. In this report, we address this issue as well as investigate the epitaxial relationship between YBa2Cu3O7-δ and this substrate. We find no evidence that the films are twin-free, but instead provide corroborative support for other work showing that the films are preferentially twinned. This work also establishes the epitaxial relationship between the film and substrate; a relationship consistent with the formation of preferential twins. [ABSTRACT FROM AUTHOR]

The controlled synthesis of materials by methods that permit their assembly into functional nanoscale structures lies at the crux of the emerging field of nanotechnology. Although only one of several materials families is of interest, carbon-based nanostructured materials continue to attract a disproportionate share of research effort, in part because of their wide-ranging properties. Additionally, developments of the past decade in the controlled synthesis of carbon nanotubes and nanofibers have opened additional possibilities for their use as functional elements in numerous applications. Vertically aligned carbon nanofibers (VACNFs) are a subclass of carbon nanostructured materials that can be produced with a high degree of control using catalytic plasma-enhanced chemical-vapor deposition (C-PECVD). Using C-PECVD the location, diameter, length, shape, chemical composition, and orientation can be controlled during VACNF synthesis. Here we review the CVD and PECVD systems, growth control mechanisms, catalyst preparation, resultant carbon nanostructures, and VACNF properties. This is followed by a review of many of the application areas for carbon nanotubes and nanofibers including electron field-emission sources, electrochemical probes, functionalized sensor elements, scanning probe microscopy tips, nanoelectromechanical systems (NEMS), hydrogen and charge storage, and catalyst support. We end by noting gaps in the understanding of VACNF growth mechanisms and the challenges remaining in the development of methods for an even more comprehensive control of the carbon nanofiber synthesis process. [ABSTRACT FROM AUTHOR]

The high frequency magnetoimpedance (MI) has been measured in NiFe/Au/NiFe narrow sandwich thin films with transverse, longitudinal, and crossed magnetic anisotropies over a frequency range of 50–500 MHz. The MI elements have an opened structure with lengths of 2 or 5 mm, widths of 50–200 μm and a total film thickness of 1.5 μm. The magnetoimpedance characteristics with different field curve shapes, including asymmetrical, have been realized for certain magnetic anisotropy using a dc bias current. Initially the different MI field characteristics have been demonstrated in ferromagnetic microwires with circumferential, helical, and longitudinal anisotropies. Here we have reintroduced these field characteristics for the MI sandwich thin film elements. In an attempt to induce a particular anisotropy in the films the magnetic layers were rf sputtered in the presence of a strong magnetic field, with a further thermal restress treatment of the final MI elements. The use of thin film technology for MI is preferable in many applications because of its compatibility with integrated circuit technology which enables miniaturization, avoiding alignment issues, and wire soldering. [ABSTRACT FROM AUTHOR]

The optical and morphological characteristics of vanadium dioxide nanoparticles and thin films during their nucleation and growth phases have been studied by correlating the temperature and sharpness of the transition with the processing parameters. Thermal annealing results in grain growth and improved crystallinity. Normally, larger crystallites show smaller hysteresis, as there is a greater probability of finding a nucleating defect in the larger volume. But at the same time, this improved crystal perfection, which accompanies the thermal annealing and grain growth, tends to a larger hysteresis, as there are fewer nucleating defects within the volume. We show that the width and shape of the hysteresis cycle are thus determined by the competing effects of crystallinity and grain size. [ABSTRACT FROM AUTHOR]

The influence of second-order magneto-optic effects on Kerr effect magnetometry of epitaxial exchange coupled Fe 50 Mn 50/Ni 81 Fe 19-bilayers is investigated. A procedure for separation of the first-and second-order contributions is presented. The full angular dependence of both contributions during the magnetization reversal is extracted from the experimental data and presented using gray scaled magnetization reversal diagrams. The theoretical description of the investigated system is based on an extended Stoner-Wohlfarth model, which includes an induced unidirectional and fourfold anisotropy in the ferromagnet, caused by the coupling to the antiferromagnet. The agreement between the experimental data and the theoretical model for both the first-and second-order contributions are good, although a coherent reversal of the magnetization is assumed in the model. [ABSTRACT FROM AUTHOR]

Optical propagation losses from ZnO thin films grown on c-cut sapphire were measured for 632.8 nm light using prism coupling and a charge coupled device detection method. Propagation losses varied according to growth temperature and growth rate. No relationship between the distribution of crystallographic orientation and propagation losses was observed. However, propagation losses were found to be insensitive to changes in the distribution of grain orientations. Neither the depth of surface roughness nor the mean interval of the surface undulations was found to be a dominant factor contributing to the losses. A mean angle of surface roughness, α, is proposed as a parameter to comprehensively characterize both effects. Loss is found to depend on α for propagation of both TE[sub 0] and TE[sub 1] modes. This demonstrates that the parameter α effectively characterizes surface morphology for optical device applications. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Differential phase contrast (DPC) scanning transmission electron microscopy was applied to investigate the magnetic structures of Fe granular films. The DPC images showed a cluster-like contrast of 200 nm in the lateral size, which could not be observed by Lorentz transmission electron microscopy in the Fresnel mode. The magnetization vector map reproduced from the DPC images indicated that a magnetization loop generally intersects several isolated particles of 20–40 nm in diameter. The films composed of densely dispersed magnetic particles showed larger magnetization loops, while more separately dispersed films tended to have smaller loops, or magnetization closures in one particle. The loop size is associated with the strength of magnetic interaction between magnetic particles. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Previous work [Vanheusden and Devine, Appl. Phys. Lett. 76, 3109 (2000)] has reported that subjecting Si/SiO[sub 2]/Si capacitors to a 450 °C preanneal in hydrogen impedes formation of protons in the buried oxide during the subsequent generation anneal at 600 °C in H[sub 2]. In interpreting, a key role in proton generation was assigned to Si dangling bond (P[sub b]-) type defects, yet with unusual assumptions as to their atomic hydrogen production nature. Here, an explanation of the preanneal effect is offered based on annealing induced structural relaxation of (P[sub b]-type) interface defects residing in edge regions of the capacitor, affecting their atomic hydrogen generation efficiency through altering the spreads in the defect activation energies for passivation in H[sub 2] and dissociation. Thus the preannealing effect is seen as a direct result of the occurrence of substantial spreads in regions of enhanced strain. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We report all-optical injection and coherent control of a ballistic charge current in GaAs/AlGaAs quantum wells. This current arises through quantum interference of one- and two-photon absorption of ∼100 fs pulses with parallel linear polarizations, and its magnitude can be controlled by adjusting the relative phase of the incident pulses. By monitoring differential transmission using a spatially resolved optical pump–probe technique, we observe evidence of carrier motion associated with this ballistic current. Results are consistent with a theoretical treatment specific to quantum wells, and are qualitatively similar to previous measurements in bulk GaAs. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Mechanisms of the generated positive charge and the charge trapping during the high-field electron injection at constant voltage regime in buried oxide (BOX) of silicon-on-insulator (SOI) structures fabricated by UNIBOND and single implanted separation by implanted oxygen (SIMOX) technologies are studied by capacitance-voltage characteristics. It is found, that considerable positive charge is accumulated near the buried oxide/substrate interface independently from direction of the injection (from film or from silicon substrate) for both kinds of structures. Comparison of the theory and experimental data allows to suggest that in the case of the UNIBOND buried oxide a positive charge is generated by two mechanisms—anode hole injection and band-to-band impact ionization. In the case of the SIMOX SOI material at the high-field electron injection in the buried oxide the anode hole injection with defect creation at precursor sites in the strained structure of oxide network is supposed to appear. It is shown, that the positive charge in the UNIBOND BOX can be completely annealed at a temperature of 400 °C while in the SIMOX BOX it is much more stable and the annealing temperature increases with the electron injection electric field rising. [ABSTRACT FROM AUTHOR]

Bottom-gate-type thin film transistors using ZnO as an active channel layer (ZnO-TFT) have been constructed. The ZnO layers were deposited using pulsed laser deposition at 450°C at an oxygen pressure of 3 m Torr, and the material that was formed had a background carrier concentration of less than 5 × 10[sup 16] cm[sup -3]. A double layer gate insulator consisting of SiO[sub 2] and SiN[sub x] was effective in suppressing leakage current and enabling the ZnO-TFT to operate successfully. The I[sub on]/I[sub off] ratio of ZnO-TFTs fabricated on Si wafers was more than 10[sup 5] and the optical transmittance of ZnO-TFTs fabricated on glass was more than 80%. These results show that it is possible to fabricate a transparent TFT that can even be operated in the presence of visible light. [ABSTRACT FROM AUTHOR]

We report a study of the effect of magnetocrystalline anisotropy in the magnetization reversal of submicron Co rings fabricated by nanoimprint lithography. For weak magnetocrystalline anisotropy, the complete reversal takes place via a transition from saturation at large negative fields, into a vortex configuration at small fields, and back to reverse saturation at large positive fields. When the anisotropy strength is increased to a critical value, the intermediate vortex configuration no longer exists in the magnetization reversal along the easy axis; instead, the reversal occurs through a rapid jump. However, when the applied field direction is far from the easy axis, the presence of the magnetocrystalline anisotropy favors local vortex nucleation, and this leads to a similar switching process as found for low anisotropy. Micromagnetic simulations indicate that the magnetization reversal process of the rings, starts from a buckling-like reverse domain nucleation, followed by local vortex formation and an avalanche process of local vortex nucleation. [ABSTRACT FROM AUTHOR]

The segregation behavior in 3 and 10 mol % polycrystalline yttria stabilized zirconia (YSZ), calcined at temperatures ranging from 300 to 1600°C, is characterized using low-energy ion scattering (LEIS). In order to be able to separate the Y and Zr LEIS signals, YSZ samples have been prepared using isotopically enriched [sup 94]ZRO[sub 2] instead of natural zirconia. The samples are made via a special precipitation method at a low temperature. The segregation to the outermost surface layer is dominated by impurities. The increased impurity levels are restricted to this first layer, which underlines the importance of the use of LEIS for this study. For temperatures of 1000°C and higher, the oxides of the impurities Na, Si, and Ca even cover the surface completely. The performance of a device like the solid oxide fuel cell which has an YSZ electrolyte and a working temperature around 1000°C, will, therefore, be strongly hampered by these impurities. The reduction of impurities, to prevent accumulation at the surface, will only be effective if the total impurity bulk concentration can be reduced below the 10 ppm level. Due to the presence of the impurities, yttria cannot accumulate in the outermost layer. It does so, in contrast to the general belief, in the subsurface layer and to much higher concentrations than the values reported previously. The difference in the interfacial free energies of Y[sub 2]O[sub 3] and ZrO[sub 2] is determined to be -21 ± 3 kJ/mol. [ABSTRACT FROM AUTHOR]

On annealing a boron implanted Si sample at ∼800 °C, boron in the tail of the implanted profile diffuses very fast, faster than the normal thermal diffusion by a factor 100 or more. After annealing for a sufficiently long time, the enhanced diffusion saturates. The enhanced diffusion is temporary, on annealing the sample a second time after saturation, enhanced diffusion does not occur. It is therefore designated as transient enhanced diffusion (TED). The high concentration peak of the implanted boron profile, which is electrically inactive, does not diffuse. TED makes it difficult to fabricate modern Si based devices, in particular TED produces the parasitic barriers which degrade the performance of the SiGe heterostructure bipolar transistors and TED can limit the fabrication of shallow junctions required for sub-100 nm complementary metal-oxide-semiconductor technology. The mechanisms of TED have been elucidated recently. A Si interstitial "kicks out" the substitutional boron atom to an interstitial position where it can diffuse easily. Alternatively the interstitials and boron atoms form highly mobile pairs. In both cases Si interstitials are required for the diffusion of boron. Therefore the enhanced boron diffusivity is proportional to the concentration of the excess Si interstitials. The interstitials are injected during implantation with Si or dopant ions. The interstitials are also injected during oxidation of the Si surface. Therefore the diffusivity increases temporarily in both cases. Even at relatively low annealing temperatures (∼800 °C) the mobility of the interstitials is high. The TED at this temperature lasts for more than 1 h. This large TED time can be explained by the presence of interstitial clusters and interstitial-boron clusters. The interstitial clusters are the {311} extended defects and dislocation loops. The precise structure of interstitial-boron clusters is not yet known though several models have been proposed.... [ABSTRACT FROM AUTHOR]

Vacancy-type defects in separation-by-implanted oxygen wafers were probed using monoenergetic positron beams. We measured the Doppler broadening spectra of annihilation radiation and the lifetime spectra of positrons. The species of the defects in Si-on-insulator (SAT) layers were identified as oxygen clusters or small oxygen precipitates, and the positrons are considered to be trapped by open spaces adjacent to such defects. The mean size of the open spaces was estimated to be larger than that of a hexavacancy. After annealing in a hydrogen atmosphere at 600 °C, both the lifetime of positrons trapped by the defects and the annihilation probability of positrons with high-momentum electrons decreased. These facts were attributed to the trapping of hydrogen atoms by the open spaces. The defects in bond-and-etchback SaT wafers and their interaction with hydrogen were also studied. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL) imaging and temperature-dependent cathodoluminescence spectroscopy (CLS) have been used to probe the spatial distribution and energies of electronic defects near GaN/A1[sub 2]O[sub 3] interfaces grown by hydride vapor phase epitaxy (HVPE). Cross sectional secondary electron microscopy imaging, CLS, and CL imaging show systematic variations in defect emissions with a wide range of HVPE GaN/sapphire electronic properties. These data, along with electrochemical capacitance-voltage profiling and secondary ion mass spectrometry provide a consistent picture of near-interface doping by O out-diffusion from A1[sub 2]O[sub 3] into GaN over hundreds of nanometers. Low-temperature CL spectra exhibit a new donor level at 3.447 meV near the interface for such samples, characteristic of O impurities spatially localized to the nanoscale interface. CLS emissions indicate the formation of amorphous A1-N-O complexes at 3.8 eV extending into the A1[sub 2]O[sub 3] near the GaN/sapphire interface. CLS and CL images also reveal emissions due to excitons bound to stacking faults and cubic phase GaN. The temperature dependence of the various optical transitions in the 10-300 K range provides additional information to identify the near interface defects and impurity doping. [ABSTRACT FROM AUTHOR]

We demonstrate coherent all-optical injection and control of a ballistic spin-polarized current in bulk, low-temperature-grown GaAs at room temperature. The spin current is injected by interfering the two-photon absorption of the fundamental (1.55 µm) and the single photon absorption of the second harmonic (0.775 µm) of ∼180 fs pulses that propagate collinearly and have the same circular polarization. Adjusting the relative phase of the two pulses controls the direction of this current. The component of the electrical current transverse to the pulse propagation direction is investigated by monitoring charge collection across a pair of gold electrodes deposited on the GaAs surface. Results are in agreement with recent theoretical predictions. [ABSTRACT FROM AUTHOR]

Time-resolved nonlinear optics are used to study the propagation of magnetic flux pulses in a 250 nm Permalloy film. The flux is generated in the film by coupling it to a coplanar waveguide structure driven with broadband voltage pulses. Flux pulses propagated in the film with a phase velocity of 4.2×10[sup 5] m/s and a group velocity of 1.5×10[sup 5] m/s. Both velocities are consistent with the predictions of Damon–Eshbach theory for magnetostatic surface waves with 200–300 μm wavelengths. Within 100 μm of the excitation source, flux pulses decayed monotonically but with no measurable delay. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Large angle picosecond reorientation of the magnetization has been studied in circular Ni[sub 81]Fe[sub 19] thin-film elements of 30 μm diameter and 500 Å thickness by means of an optical pump–probe technique. The sample was pumped by an optically triggered magnetic field pulse and probed by a time resolved magneto-optical Kerr effect measurement. The temporal profile of the pulsed field and the in-plane uniaxial anisotropy of the element were first determined from measurements made in large static fields where the magnetization exhibited small amplitude ferromagnetic resonance oscillations. Measurements of large amplitude oscillations were then made in a smaller static field that was still larger than the in-plane uniaxial anisotropy field and sufficient to saturate the sample. Using the measured temporal profile of the pulsed field, the Landau–Lifshitz–Gilbert equation was used to model the motion of the magnetization as a coherent rotation process. The same values of the anisotropy and damping constants provided an adequate simulation of both the high and low field data. The magnetization was found to move through an angle of up to about 30° on subnanosecond time scales. The dependence of the reorientation upon the direction of the static applied field and observed deviations from the coherent precession model are discussed. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The depth distributions of oxygen-related defects in separation-by-implanted oxygen wafers were determined from measurements of Doppler broadening spectra of the annihilation radiation. Vacany-oxygen complexes were introduced by implanting 180-keV oxygen at (2–6) × 10[sup 17] cm[sup -2] into Si substrates. Their sizes decreased below the subsurface region (<100 nm) because an agglomeration of vacancy-type defects was suppressed by the interaction between vacancies and oxygen atoms. As the dosage was increased, in the region near the projected range of oxygen, atomic rearrangement of vacancy-type defects occurred, and this rearrangement is considered to introduce SiO[sub x] (x<2) that is stable at high annealing temperatures. Oxygen-related defects were presented in the superficial Si layer even after annealing at 1350 °C. The concentration of such defects was low when the substrate was implanted with a dose of 4 × 10[sup 17] cm[sup -2]. [ABSTRACT FROM AUTHOR]

Transmission electron microscopy and high resolution x-ray diffraction are used to characterize defects in ZnO layers grown by plasma-assisted molecular-beam epitaxy on (0001) sapphire. Two- and three-dimensional types of growth modes are described and the observed mosaic structure is analyzed in each case. It is found that two-dimensional layers exhibit a roughness as low as 6 nm. Their subdomains have small lateral coherence lengths and a mean in-plane misorientation of ±0.4°, leading to an important dislocation density of 1–4×10[sup 10] cm[sup -2]. On the contrary, it is demonstrated that, through numerous interactions between dislocations, the three-dimensional growth mode leads to a better structural quality with a larger lateral coherence length and a smaller in-plane mosaic spread of ±0.07°. The total dislocation density is consequently reduced by 1 order of magnitude down to 3–5×10[sup 9] cm[sup -2] and the radical modification of the structure results in a change of the dislocation distribution. Our results thus demonstrate that two-dimensional growth mode and low full width at half maximum for symmetric x-ray diffraction are a not reliable indicator of a good structural quality. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Several different models have been employed for modeling the dielectric function of hexagonal GaN in the range from 1 to 10 eV. Models are compared in terms of number of parameters required, intricacy of model equations, and possibility of accurate estimation of important physical parameters, such as energies of critical points and exciton binding energies. Shortcomings and advantages of each model are discussed in detail. Excellent agreement with the experimental data for GaN has been achieved with three of the investigated models. It has also been shown that an assumption of adjustable broadening instead of a purely Lorentzian one improves the agreement with the experimental data and enables elimination of excessive absorption below the gap which is inherent to the models with Lorentzian broadening. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A theoretical approach for calculating the impedance of a three-layer sandwich, consisting of two metallic ferromagnetic layers separated by a non-magnetic conductive layer, is presented. The Maxwell equations for the electromagnetic field coupled with the Landau-Lifshitz equations for the magnetization dynamics are solved, which enables one to describe the system over a wide frequency range, including the ferromagnetic resonance. Two sandwich strip structures are analyzed, both having thickness much less than the width, and the width much less than the length: a "closed" structure with the magnetic film closing at the edges along the width, and an "open" structure without flux closures where all the layers have the same width. The impedance for the two structures is calculated and analyzed as a function of the physical parameters of the device and frequency. The "closed" structure is more efficient magnetically and exhibits a highly inductive response to much higher frequencies than the "open" structure. The analytical results obtained are directly applicable to practical design of GHz inductive components. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Discusses the principles of strain relaxation in heteroepitaxial films growing on compliant substrates. Concept and misconceptions regarding elastic relaxation; Plastic relaxation; Relaxing modes of film growth.

Investigates the properties of double barrier resonant tunneling diodes (RTD) in quantum wells containing self-assembled quantum dots. Use of resonant tunneling and photoluminescence spectroscopy; Effect of quantum dots on electronic states and charge distribution on RTD; Possibility of using dot photoluminescence as a probe of carrier dynamics in RTD.

Investigates the microstructural effects on the magnetic behavior of rf-sputtered CoFe-AgCu granular alloys through the study of the in-plane remanence-to-saturation magnetization ratio. Microstructure and magnetic anisotropy; Temperature decay of the remanence and low field susceptibility.

Reports that the magnetization reversal processes of an epitaxial Fe/GaAs(001) film are modified by controlling the lateral dimensions of the continuous film to create rectangular microstripes. Description of fabrication and measurement techniques; Size dependent transitions; Model of the effective anisotropy energy contributions.

Studies the intersubband emission at far-infrared wavelengths from semiconductor superlattices with parabolically graded quantum wells. Production of light emission by sequential resonant tunneling injection of electrons into higher energy levels of quantum wells; Resonant tunneling diodes.

Deals with a study which investigated oscillations in the frequencies and coupling strengths of two-dimensional plasmons induced by grating couplers. Experimental methods; Experimental results; Conclusions.

Focuses on a study on the rapid thermal oxidation of Czochralski-grown silicon in either oxygen or nitroxide atmospheres using spectroellipsometry and Auger electron spectroscopy. Description of rapid thermal oxidation; Experimental setup; Optical models; Results and discussion.

Presents a study that measured the orientation of the electric-field gradients due to vacancy trapping by substitutional indium donors in the semiconductor mercury-cadmium-tellurium. Use of perturbed angular correlation technique; Background on the semiconductor; Equations used in the study.'

Focuses on a study on hydrogen-atom spectroscopy of the ionizing plasma containing molecular hydrogen, considering line intensities and ionization rate. Introduction to collision-radiative model; Characteristics of line intensities; Derivation of equations.

Presents a study which demonstrated that differing transistor characteristics in material systems can be explained by the defect pool model applied to the defects near the interface of hydrogenated amorphous silicon thin film transistors. Theoretical background; Description of the experimental setup; Results.

Presents a study which monitored defects in silicon-on-insulator structures, formed either by single or multiple-step implantation of oxygen, during the processing steps using K-band electron spin resonance. Introduction to the separation by implantation of oxygen technique; Experimental details; Results and discussion.

Focuses on a study that discussed chemical etch rates in diluted hydrogen fluoride (HF) or a mixture of HF, water and HNO[sub3] on conventional thermal silicon oxides. Features of the multi-implanted samples; Implication of accurate mechanical thickness measurements; Function of oxide thickness.

Focuses on thin films suitable for horizontal recording. Details on thin-film recording media; Theoretical background on making recording media from thin metallic films; Description of a typical thin-film medium; Information on thin-film media noise; Effect of anisotropy on thin-film disks; Discussion on magnetic alloys and microstructures.

Presents conductivity measurements on hydrogenated amorphous silicon nin devices with several i-layer thicknesses. Discussion on the Meyer-Neldel rule (MNR); Examples of the current-voltage characteristics of nin's; Influence of doping on the MNR parameters.