bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrical properties of Si films doped with 200-eV In+ ions during growth by molecular-beam epitaxy
Authors: Noël J.-P. , Hirashita N. , Markert L. C. , Kim Y.-W. , Greene J. E. , Knall J. , Ni W.-X. , Hasan M. A. , Sundgren J.-E.
Published: July 2002

A single-grid ultra-high-vacuum-compatible ion source was used to provide accelerated In+-dopant beams during Si(100) growth by molecular-beam epitaxy. Indium incorporation probabilities σ, determined by secondary ion mass spectrometry, in films grown at Ts=800 °C were too low to be measured for thermal In (σIn was <3×10−5 at Ts>550 °C) . However, for accelerated In+ doping, σIn+ at 800 °C ranged from 0.03 to ∼1 for In+ acceleration energies EIn+ between 50 and 400 eV. Temperature-dependent Hall-effect and resistivity measurements were carried out on In+-doped Si films grown at Ts =800 °C with EIn+=200 eV . Indium was incorporated substitutionally into electrically active sites over a concentration ranging from 2×1015−2×1018 cm−3, which extends well above reported equilibrium solid-solubility limits. The acceptor-level ionization energy was 156 meV, consistent with previously published results for In-doped bulk Si. Room-temperature hole mobilities μ were in good agreement with the best reported data for B-doped bulk Si and were higher than previously reported values for annealed In-implanted Si. Temperature-dependent (77–400 K) mobilities μ(T) were well described by theoretical calculations, with no adjustable parameters, including lattice, ionized-impurity, neutral-impurity, and hole-hole scattering. Lattice scattering was found to dominate, although ionized-impurity scattering was still significant, at temperatures above ∼150 K where μ varied approximately as T−2.2 . Neutral-impurity scattering dominated at lower temperatures. Plan-view and cross-sectional transmission electron microscopy observations showed no indications of dislocations or other extended defects. Considering the entire set of results, there was no evidence of residual ion-bombardment-induced lattice damage.
Organometallic vapor-phase epitaxy of high-quality Ga0.51In0.49P at high growth rates
Authors: Cao D. S. , Kimball A. W. , Chen G. S. , Fry K. L. , Stringfellow G. B.
Published: July 2002

High-quality Ga0.51In0.49P, lattice-matched to GaAs, has been grown by atmospheric pressure organometallic vapor-phase epitaxy. The growth was performed at a temperature of 680 °C and a growth rate of about 12 μm/h. The indium distribution coefficient was found to be unity at this growth temperature. At a V/III ratio of 148, the Ga0.51In0.49P epilayers had photoluminescence (PL) half-widths of 35 and 7.2 meV at 300 and 10 K, respectively, the best reported results to date. As the V/III ratio was changed from 94 to 240, the 300-K energy band gap measured by PL varied only from 1.897 to 1.912 eV, values close to that of Ga0.51In0.49P grown by liquid-phase epitaxy. An ordered arrangement of gallium and indium atoms on the column III sublattice with a Cu-Pt structure was observed in transmission electron diffraction patterns for all samples. Our results show that the phenomenon of changing energy band gap with varying V/III ratio does not occur at these high growth rates.
Tunneling-injection-induced turnaround behavior of threshold voltage in thermally nitrided oxide n-channel metal-oxide-semiconductor field-effect transistors
Authors: Ma Z. J. , Lai P. T. , Liu Z. H. , Fleischer S. , Cheng Y. C.
Published: July 2002

The threshold voltage (VT) degradation metal-oxide-semiconductor field-effect transistors (MOSFETs) with thermally nitrided oxide or pure oxide as gate dielectric was determined under Fowler–Nordheim (FN) stressing. A typical VT turnaround behavior was observed for both kinds of devices. The VT for nitrided oxide MOSFETs shifts more negatively than that for pure oxide MOSFETs during the initial period of FN stressing whereas the opposite is true for the positive shift after the critical time at turnaround point. The discovery that the shift of substrate current peak exhibits similar turnaround behavior reinforces the above results. In the meantime, the field-effect electron mobility and the maximum transconductance in the channel for nitrided oxide MOSFETs are only slightly degraded by stressing as compared to that for pure oxide MOSFETs. The VT turnaround behavior can be explained as follows: Net trapped charges in the oxide are initially positive (due to hole traps in the oxide) and result in the negative shift of VT. With increasing injection time, trapped electrons in the oxide as well as acceptortype interface states increase. This results in the positive shift in VT. It is revealed that VT degradation in MOSFETs is dominated by the generation of acceptortype interface states rather than electron trapping in the oxide after the critical time.
Barrier inhomogeneities at Schottky contacts
Authors: Werner Jürgen H. , Güttler Herbert H.
Published: July 2002

We present a new analytical potential fluctuations model for the interpretation of current/voltage and capacitance/voltage measurements on spatially inhomogeneous Schottky contacts. A new evaluation schema of current and capacitance barriers permits a quantitative analysis of spatially distributed Schottky barriers. In addition, our analysis shows also that the ideality coefficient n of abrupt Schottky contacts reflects the deformation of the barrier distribution under applied bias; a general temperature dependence for the ideality n is predicted. Our model offers a solution for the so-called T0 problem. Not only our own measurements on PtSi/Si diodes, but also previously published ideality data for Schottky diodes on Si, GaAs, and InP agree with our theory.
‘‘Designer’’ interfaces in II-VI/III-V polar heteroepitaxy
Authors: Farrell H. H. , Tamargo M. C. , de Miguel J. L. , Turco F. S. , Hwang D. M. , Nahory R. E.
Published: July 2002

The development of composite materials incorporating both II-VI and III-V compound semiconductors, such as ZnSe and GaAs, leads to the possibility of a variety of new devices of potential importance to the communications industry. In many cases, such as those involving resonant tunneling junctions and quantum well structures, the quality of the interface between the different compound semiconductors determines the ultimate quality of the device itself. Therefore, we have investigated the factors determining this interface quality for the GaAs/ZnSe system as prepared by molecular beam epitaxy. In this system, the stoichiometry of the substrate is of paramount importance. An excess of one constituent leads to high local electrical fields and poor interface morphology. Optimum growth of ZnSe on GaAs is achieved with GaAs substrate surfaces having a stoichiometry intermediate between the As- and Ga-rich extremes. We will describe a model that defines the conditions for good interface formation and summarize experimental evidence which supports the validity of this model.
Diffusion barrier performance of pulsed laser deposited amorphous tungsten carbide films
Authors: Ghaisas Smita
Published: July 2002

The performance of pulsed laser deposited tungsten carbide films as diffusion barriers between a 〈100〉 Si substrate and an Al overlayer has been investigated. Four-point probe measurement of resistance is employed to monitor the electrical stability of the Al/WC/Si metallization schemes upon thermal annealing in a vacuum for 30 min in a temperature range from 100 to 500 °C. The Glancing angle x-ray diffraction technique has been used to characterize the as-deposited as well as annealed samples. To study the metallurgical interaction between Al overlayer and the barrier film, experiments on isothermal annealings are carried out. The data obtained have been used to estimate the activation energy for the formation of the intermetallic compound WAl12. Morphological features of the annealed samples have been obtained by employing the technique of scanning electron microscopy.
Temporal evolution of the electron distribution function in an electron cyclotron resonant discharge
Authors: Brown M. R. , Sheridan T. E. , Hayes M. A.
Published: July 2002

We present time-resolved experimental measurements of the electron distribution function f(v∥,v⊥,t) in a pulsed, partially ionized, electron cyclotron resonance (ECR)-produced plasma. The discharge has some characteristics similar to those used in plasma processing applications. These properties include ECR production in a strong magnetic field and low electron temperature (Te<5 eV). In addition, electron-neutral collisions play an important role. A novel analyzer is used to study the dependence of f(v∥,v⊥,t) on velocities both parallel and perpendicular to the magnetic field. This information cannot be obtained with a simple Langmuir probe. The temporal evolution of f(v∥,v⊥,t) is examined during plasma formation, with the source biased, with the source grounded and in the afterglow.
Plasma etching of Ti in fluorine-containing feeds
Authors: d’Agostino R. , Fracassi F. , Pacifico C. , Capezzuto P.
Published: July 2002

The detailed chemistry of the process of etching of titanium in CF4-O2 plasmas has been studied in the gas phase as well as at the substrate surface. A triode reactor has been utilized to research the role of key parameters such as feed composition, pressure, substrate bias, and temperature, by means of emission spectroscopy and quartz-crystal microbalance technique. Byproducts provided by this research are the principles for using and calibrating quartz microbalances in a broad temperature range (50–300 °C). A diode reactor connected under high vacuum to an x-ray photoelectron spectrometer has been used to characterize the surface chemistry during the etching process in the absence of any external contamination.
High structural quality Ga1−xInxSb/InAs strained-layer superlattices grown on GaSb substrates
Authors: Miles R. H. , Chow D. H. , Hamilton W. J.
Published: July 2002

Strained Ga1−xInxSb/InAs superlattices exhibiting a high degree of structural perfection have been grown on GaSb substrates. The superlattices display ideal, defect-free structure, to within the resolution limits of transmission electron microscopy (TEM) and high-resolution x-ray diffraction. Cross-sectional micrographs reveal the layers to be highly planar, regular, and coherently strained to the GaSb substrates. No crystalline defects were observable by TEM, despite an internal lattice mismatch of almost 2%. Planarity of the layers is confirmed by the presence of Pendellösung fringes in high-resolution x-ray diffraction, while the observation of numerous sharp satellite peaks indicates little or no interdiffusion within the superlattices. Observed x-ray diffraction is closely fit by simulations based on a kinematical model which accounts properly for the highly strained interfaces and absence of strict translational symmetry in the superlattice growth direction. Based on this fit, an InSb-rich character is assigned to the interfaces, yielding superlattice layer thicknesses and compositions that are in quantitative agreement with those derived from independent growth rate calibrations.
Thermal stability and grain growth behavior of mechanically alloyed nanocrystalline Fe-Cu alloys
Authors: Eckert J. , Holzer J. C. , Johnson W. L.
Published: July 2002

X-ray diffraction, transmission electron microscopy, and differential scanning calorimetry were used to study the thermal stability of highly supersaturated nanocrystalline FexCu100−x alloys (10≤x≤95) synthesized by mechanical alloying. Alloys with x<60 exhibit single-phase fcc structure while single-phase bcc alloys form for x≳80. For 60≤x≤80 fcc and bcc phases coexist. Heating to elevated temperatures leads to structural relaxation, phase separation, and grain growth of the metastable nanocrystalline solid solutions. Single-phase fcc and bcc alloys undergo significant strain release but no appreciable grain growth prior to phase separation. After phase separation pronounced grain growth sets in. In contrast, samples in the two-phase region show some grain growth and significant chemical redistribution even at low temperatures. The phase separation of single-phase fcc and bcc alloys proceeds via different mechanisms: fcc solid solutions decompose by forming small Fe precipitates, while demixing in bcc alloys starts by segregation of Cu atoms to bcc grain boundaries before nucleation of Cu precipitates. These results show that the stability and grain growth behavior of nanocrystalline alloys is strongly affected by the microstructure of the material.
Electrical conductivity of annealed polyaniline
Authors: Kobayashi Atsushi , Ishikawa Hitoshi , Amano Kosuke , Satoh Masaharu , Hasegawa Etsuo
Published: July 2002

The electrical conductivity of chemically synthesized and annealed polyaniline has been investigated. The room-temperature conductivity varies with the time and the temperature of annealing, and exhibits a maximum peak on its time-dependence curves for the polymer annealed above 120 °C. The time showing the maximum peak of the conductivity shifts to the shorter side with higher annealing temperature. The linear dependence of the conductivity on temperature with T−1/2 is observed in all samples as explained for this polymer with the quasi-one-dimensional variable-range-hopping processes. In the initial stage of annealing, the conductivity increases in the whole temperature range without varying the exponential factor of the variable range hopping. This indicates that the density of states remains unchanged in this stage. The results concerning the pre-exponential factor of the quasi-one-dimensional variable-range-hopping mechanism demonstrate the increase of the mean free time, the transverse localization length, and the interchain transfer integral with annealing. X-ray-diffraction patterns exhibit the generation of regularized amorphous structure in annealed samples, which leads to the enlargement of the interchain interaction. The results show the increase of regularity of the polymer chain at first, and the phase transition to the loose-packed and ordered structure in next stage of annealing.
Plasma remediation of trichloroethylene in silent discharge plasmas
Authors: Evans Diane , Rosocha Louis A. , Anderson Graydon K. , Coogan John J. , Kushner Mark J.
Published: July 2002

Plasma destruction of toxins, and volatile organic compounds in particular, from gas streams is receiving increased attention as an energy efficient means to remediate those compounds. In this regard, remediation of trichloroethylene (TCE) in silent discharge plasmas has been experimentally and theoretically investigated. We found that TCE can be removed from Ar/O2 gas streams at atmospheric pressure with an energy efficiency of 15–20 ppm/(mJ/cm3), or 2–3 kW h kg−1. The majority of the Cl from TCE is converted to HCl, Cl2, and COCl2, which can be removed from the gas stream by a water bubbler. The destruction efficiency of TCE is smaller in humid mixtures compared to dry mixtures due to interception of reactive intermediates by OH radicals.
Gas source molecular beam epitaxy/migration enhanced epitaxy growth of InAs/AlSb superlattices
Authors: Seta Masumichi , Asahi Hajime , Kim Song Gang , Asami Kumiko , Gonda Shun-ichi
Published: July 2002

We report on the gas source molecular beam epitaxy/migration enhanced epitaxy (MEE) growth of InAs/AlSb superlattices. The incorporation behavior of constituent group III and group V atoms during growth is investigated in detail using reflection high energy electron diffraction. In and Sb atoms are found to move towards the surface during MEE growth, although the movement of In atoms can be reduced by lowering the growth temperature. Raman scattering measurement of InAs/AlSb superlattices shows that the formation of atomically controlled heterointerfaces (InSb- or AlAs-type interfaces in InAs/AlSb superlattices) is difficult. However, photoluminescence (PL) measurement shows that the optical properties of quantum well structures are strongly dependent on the shutter sequence at the interfaces. 77 K PL from InAs/AlSb quantum well structures with an InSb-type interface shutter sequence is one order of magnitude stronger than that of the AlAs-type interface.
Glow-discharge enhanced permeation of oxygen through silver
Authors: Wu D. , Outlaw R. A. , Ash R. L.
Published: July 2002

The permeation of oxygen through Ag0.05Zr over the temperature range of 300–650 °C under glow-discharge conditions has been studied and compared to the permeation of thermally dissociated molecular oxygen. A low-energy dc glow-discharge in O2 has been employed which produced approximately 10% atoms. The permeation rate during the glow discharge was found to be much higher (a factor of ∼10) than without the glow discharge. The small fraction of oxygen atoms generated appears to dominate the permeation because of much higher solution probabilities. Below 500 °C, the activation energy for the permeation with glow discharge was found to be 15.5 kcal/mol compared to 22.0 kcal/mol without glow discharge (molecular oxygen). Above 500 °C, the enhanced permeation with glow discharge gradually diminishes with increasing temperature and approaches that observed without the glow discharge at high temperature; the reason for this is primarily because of the thermal instability of the supersaturated high-pressure interface where atoms recombine and desorb back into the gas phase.
Optical emission characterization of CH4+H2 discharges for diamond deposition
Authors: Gomez-Aleixandre C. , Sanchez O. , Castro A. , Albella J. M.
Published: July 2002

Methane and hydrogen discharges has been studied at different discharge frequencies (35 kHz, 13.56 MHz, and 2.45 GHz) and feeding gas ratios (up to 100% of methane) during diamond and diamond-like deposition by plasma chemical vapor deposition techniques. Optical emission spectroscopy shows that the intensity of atomic hydrogen line (Hα) is the highest at the microwave frequency (2.45 GHz). In addition, at this frequency and low methane concentrations (<7.5%) the emission of CH+ species is also detected, which has been associated to the presence of the diamond phase in the films. On the contrary, at the lower frequencies (35 kHz and 13.56 MHz), the emission spectra are dominated by neutral CH species that are supposed to be the precursor species in the diamond-like films deposited at these frequencies.
Low core losses of nanocrystalline Fe–M–B (M=Zr, Hf, or Nb) alloys
Authors: Suzuki Kiyonori , Makino Akihiro , Inoue Akihisa , Masumoto Tsuyoshi
Published: July 2002

Magnetic core properties, core loss, permeability, and saturation magnetic induction of bcc-nanocrystalline Fe–M–B (M=Zr, Hf, and Nb) alloys produced by annealing a melt-spun amorphous phase were investigated in a ring-shaped form with the aim of clarifying the application potential as a core material. The bcc alloys exhibit high saturation induction (Bs) from 1.49 to 1.63 T combined with high permeability (μe) from 22 000 to 32 000 at 1 kHz and 0.4 A/m. The bcc Fe–M–B (M=Zr, Hf, or Nb) alloys also show low core losses (W) from 1.4×10−1 to 2.1×10−1 W/kg at 50 Hz and 1.4 T and from 1.70 to 2.50 W/kg at 1 kHz and 1.0 T. The W values attained for the bcc Fe–M–B (M=Zr, Hf, and Nb) alloys are smaller by 60%– 90% at 50 Hz and 1.4 T and 50%–70% at 1 kHz and 1.0 T, as compared with those for an amorphous Fe78Si9B13 alloy in practical use as a transformer core material. The low W values for the bcc-nanocrystalline alloys are presumably due to the small anomaly factor comparable to a Co-based amorphous alloy. The comparison of the present data with those for the amorphous Fe78Si9B13 alloy indicates that the bcc-nanocrystalline Fe–M–B (M=Zr, Hf, and Nb) alloys are promising for practical use as core materials.
Quantitative characterization of modulation-doped strained quantum wells through line-shape analysis of room-temperature photoluminescence spectra
Authors: Brierley Steven K.
Published: July 2002

Room-temperature photoluminescence (PL) has been used to characterize modulation-doped AlGaAs/InGaAs/superlattice strained layer quantum wells. A phenomenological line-shape model has been developed which can be fitted to PL spectra in order to obtain key parameters such as the subband energies, Fermi energy, and transition amplitudes. Quantum well sheet densities calculated from fits to the PL spectra (taken at both room temperature and 77 K) have been compared to sheet densities obtained from low-temperature Hall measurements. It has also been shown how variations in quantum well composition, width, and symmetry can be characterized by shifts in values of the relevant fitting parameters.
Influence of defect passivation by hydrogen on the Schottky barrier height of GaAs and InP contacts
Authors: Van Meirhaeghe R. L. , Laflere W. H. , Cardon F.
Published: July 2002

The change in barrier height caused by sputter metallization of contacts on both GaAs and InP substrates, and using evaporated contacts as a reference, is investigated. It has been found that by annealing, the reference barrier height can be restored. A model is proposed, wherein sputter metallization leads to passivation of interfacial defects by hydrogen. Accordingly, the Fermi level pinning caused by these defects is removed and the barrier height changes and is determined by other mechanisms. Annealing produces a removal of hydrogen and reactivates the amphoteric defects. Additional evidence is given for the assumption that sputter metallization leads to passivation, by hydrogen, of dopants and defects in the semiconductor.
Crystalline structure and symmetry dependence of acoustic nonlinearity parameters
Authors: Cantrell John H.
Published: July 2002

A quantitative measure of elastic wave nonlinearity in crystals is provided by the acoustic nonlinearity parameters. The nonlinearity parameters are defined for arbitrary propagation modes for solids of arbitrary crystalline symmetry and are determined along the pure mode propagation directions for 33 crystals of cubic symmetry from data reported in the literature. The magnitudes of the nonlinearity parameters are found to exhibit a strong dependence on the crystalline structure and symmetries associated with the modal direction in the solid. Calculations based on the Born–Mayer potential for crystals having a dominant repulsive contribution to the elastic constants from the interatomic pair potential suggest that the origin of the structure dependence is associated with the shape rather than the strength of the potential. Considerations based on variations in crystal symmetry during loading along pure mode propagation directions of face-centered-cubic solids provide a qualitative explanation for the dependence of the acoustic nonlinearity parameters on modal direction.
Study of mechanical and dielectric losses contribution to the surface-acoustic-wave attenuation in piezoelectric ceramics
Authors: Feuillard G. , Tran-Huu-Hue L. P. , Tessier L. , Millar C. E. , Lethiecq M.
Published: July 2002

The surface-acoustic-wave (SAW) propagation losses of two ceramics, a lead zirconate titanate composition and a modified lead titanate composition, are studied. Contrary to crystals, where only mechanical losses contribute, dielectric losses and scattering at the grain boundaries have to be taken into account. A first-order perturbation theory is extended to include dielectric losses to calculate the surface attenuation. Based on the measurement of the mechanical and the dielectric losses of the two ceramics as a function of frequency, the frequency behavior of the SAW propagation losses of each material is theoretically calculated and values are compared to those obtained experimentally at 25 MHz. Both results show that the modified lead titanate ceramic has low SAW propagation losses, 0.22 dB/mm at 25 MHz, while the lead zirconate titanate has propagation losses of 2 dB/mm at 25 MHz. Using results published in literature, the effect of the scattering contribution is evaluated. Finally, other SAW properties of ceramics, i.e., the free-surface-wave velocity, the surface coupling coefficient, and the surface permittivity are measured and reported. All these results are discussed and the suitability of both materials for SAW applications is examined.
Ferroelectric properties of Bi2VO5.5 thin films on LaAlO3 and SiO2/Si substrates with LaNiO3 base electrode
Authors: Satyalakshmi K. M. , Varma K. B. R. , Hegde M. S.
Published: July 2002

Ferroelectric bismuth vanadate Bi2VO5.5 (BVO) thin films have been grown on LaAlO3 (LAO) and SiO2/Si substrates with LaNiO3 (LNO) base electrodes by the pulsed laser deposition technique. The effect of substrate temperature on the ferroelectric properties of BVO thin films, has been studied by depositing the thin films at different temperatures. The BVO thin films grown on LNO/LAO were textured whereas the thin films grown on LNO/SiO2/Si were polycrystalline. The BVO thin films grown at 450 °C exhibited good ferroelectric properties indicating that LNO acts as a good electrode material. The remanent polarization Pr and coercive field Ec obtained for the BVO thin films grown at 450 °C on LNO/LAO and LNO/SiO2/Si were 2.5 μC/cm2, 37 kV/cm and 4.6μC/cm2, 93 kV/cm, respectively.
Piezoelectric and ferroelectric properties of polyurea-5 thin films prepared by vapor deposition polymerization
Authors: Hattori Takeshi , Takahashi Yoshikazu , Iijima Masayuki , Fukada Eiichi
Published: July 2002

Submicron films of aliphatic polyurea-5 were synthesized by vapor deposition polymerization. The structure of films depended on the partial pressure ratio of evaporated monomers. Excess of diamine monomer over diisocyanate monomer yielded lower crystalline structure, to be poled easier at low temperatures. The maximum value of the piezoelectric stress constant e31 was 10 m C/m2, twice that of polyurea-9. The pyroelectric constant was about 15 μC/m2 K. Ferroelectric D-E hysteresis was observed. Three relaxations were observed for the temperature dependence of the elastic constant, the dielectric constant, and the piezoelectric constant. The poling dynamics involving urea dipoles and ionic species was discussed.
Comparison of gain and threshold current density for InGaAsP/GaAs (λ=808 nm) lasers with different quantum well thickness
Authors: Yi H. J. , Diaz J. , Eliashevich I. , Lukas G. , Kim S. , Wu D. , Erdthmann M. , Jelen C. , Slivken S. , Wang L. J. , Razeghi M.
Published: July 2002

We investigated the quantum-size effects of quantum well (QW) on gain and threshold current density for InGaAsP/GaAs (λ=808 nm) laser diodes. In this work, a comparison is made of lasers with different QW thickness while keeping the optical confinement factors constant. We found that the threshold current density and differential efficiency were not affected by narrowing the QW thickness. The theoretical model taking into account the mixing of the valence bands and momentum relaxation for InGaAsP/GaAs lasers with spontaneous emission (optically pumped) measurement shows that the absence of difference between these structures can be attributed to the high relaxation rate.
Optical and photoelectrical properties of ReS2 single crystals
Authors: Friemelt K. , Kulikova L. , Kulyuk L. , Siminel A. , Arushanov E. , Kloc Ch. , Bucher E.
Published: July 2002

Optical absorption, photoacoustic spectroscopy and photoconductivity were investigated in ReS2 single crystals in the temperature range 50–300 K. The energy gap (1.55 eV at 80 K) and its temperature dependence, the value of the average phonon energy (17 meV) and the electron phonon coupling parameter (S=2.40) as well as the electron-hole mobility due to lattice scattering were determined.
Application of exceptional wave theory to materials used in surface acoustic wave devices
Authors: Naumenko N. F.
Published: July 2002

The exceptional wave theory developed in the last two decades is applied to trigonal crystals, widely used in surface acoustic wave devices: quartz, lithium niobate, and lithium tantalate. For quartz all crystallographic orientations where one of bulk acoustic waves satisfies the stress-free mechanical boundary conditions, have been found and plotted on the stereographic projection of a unit wave normal sphere as ‘‘exceptional wave lines.’’ The possibility of existence and the main features of pure shear, quasishear, and quasilongitudinal exceptional waves are examined in three cut families with Euler angles (0°,θ,0°), (90°,90°,ψ), and (0°,θ,90°). These orientations are analyzed both without and with piezoelectric effect by means of analytical and numerical techniques. The obligatory existence of undamped surface skimming bulk waves or leaky waves is proved for selected cuts of trigonal crystals, such as a well-known 41°-rotated Y cut of lithium niobate. The behavior of these waves is compared in three crystals. A simple relation between elastic moduli of trigonal crystals with point symmetry of 32 or 3m has been derived, which allows the existence of a longitudinal type of exceptional waves. Such waves have been discovered in quartz. They are similar to those found earlier in lithium tetraborate and in both crystals they give rise to piezoelectrically coupled high velocity leaky waves with small attenuation.
Effects of ion energy and arrival rate on the composition of zirconium oxide films prepared by ion-beam assisted deposition
Authors: Matsuoka M. , Isotani S. , Miyake S. , Setsuhara Y. , Ogata K. , Kuratani N.
Published: July 2002

Thin zirconium oxide films were grown using the ion-beam assisted deposition method. Zirconium metal was evaporated by an electron beam and condensed on a Si substrate, while oxygen ions were directed simultaneously onto the substrate, allowing the fundamental deposition parameters of ion energy and arrival rate ratio ARR(O/Zr) to be measured and controlled easily. X-ray photoelectron spectroscopy (XPS) was used to study the oxidation and the composition of the films. XPS analyses indicated the presence of four oxidation states of zirconium (Zr4+−Zr1+) in Zr 3d spectra and two peaks in O 1s spectra; Zr4+ is a predominant ion in all the films and the two peaks in O 1s spectra are related to the oxide and to hydroxyl groups and/or carbonates, respectively. Composition analyses of the films suggested that these oxygen-associated species may be bound to zirconium. The variation of composition as a function of ion energy (from 2 to 20 keV) and ARR(O/Zr) (at 0.54 and 1.09) could be explained with the preferential sputtering of zirconium from the growing film by incoming oxygen ions and the incorporation of oxygen ions into the film.
In-vacuum cleaving and coating of semiconductor laser facets using thin silicon and a dielectric
Authors: Tu L. W. , Schubert E. F. , Hong M. , Zydzik G. J.
Published: July 2002

We propose and demonstrate a novel approach to the coating of semiconductor laser facets. In this approach, processed semiconductor lasers are cleaved in a high-vacuum system immediately followed by coating of the vacuum-exposed facet with a very thin Si layer (≤100 Å) and a large band gap dielectric (Al2O3) layer. The Si layer is sufficiently thin to avoid the formation of quantized bound states in the Si. GaAs coated with thin Si and Al2O3 have a higher luminescence yield and a lower surface recombination velocity than bare GaAs surfaces as well as GaAs surfaces coated with Al2O3 only. A surface recombination velocity of 3×104 cm/s has been obtained using a modified dead layer model for the Si/Al2O3 sample. It is also shown that lasers which are cleaved in vacuum and subsequently coated with Si and Al2O3 have improved properties including an increased threshold for catastrophic optical damage.
Suspended epitaxial YBaCuO microbolometers fabricated by silicon micromachining: Modeling and measurements
Authors: Méchin Laurence , Villégier Jean-Claude , Bloyet Daniel
Published: July 2002

Suspended epitaxial YBaCuO microbolometers were successfully fabricated by two silicon micromachining techniques. The first one used the reactive ion etching (RIE) of Si substrates and the second one the etching of the SiO2 layer in separated by implanted oxygen (SIMOX) substrates. This work aims at the modeling and the measurement of the bolometric performances of IR pixels (100×100 μm2 detection area) constituted by suspended bridges in series. The influence of both the dimensions and the thermophysical properties of the materials constituting the membrane is discussed. Thermal conductances and time constants were measured as functions of the length and the width of different suspended bridges fabricated by RIE. Comparison of a “RIE type” bridge with a bridge of same dimensions fabricated from a SIMOX substrate shows that the sensitivity-bandwidth product of the SIMOX bridge is improved by one order of magnitude. All measurements on suspended bridges are consistent with calculations from thermal model. The specific detectivity D* of a 4-μm-wide suspended meander line, measured at 85 K under irradiation from a blackbody, is 2.5×109 cmHz/W, with a thermal time constant of 564 μs. These performances are among the best reported for YBaCuO microbolometers.
Magnetic linear dichroism effects in reflection spectroscopy: A case study at the Fe M2,3 edge
Authors: Höchst Hartmut , Rioux Dennis , Zhao Dai , Huber David L.
Published: July 2002

Magneto-optical measurements are strongly dependent on the polarization of the radiation as well as the interaction geometry of the light with respect to the relative orientation and direction of the magnetization M. We performed magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) measurements around the Fe M2,3 transition by measuring the difference between the reflected intensities of right and left circular polarized light (MCD) and the difference between the reflected intensities for opposite magnetization directions (MLD). From the angular variations of the MCD measurements we extracted the dielectric tensor ε(ω) which was then used as an input parameter to calculate the magneto-optical response of Fe in reflection MLD spectra. The experimental data around the M2,3 edge show good agreement with model calculations.
Secondary electron emission from diamond surfaces
Authors: Shih A. , Yater J. , Pehrsson P. , Butler J. , Hor C. , Abrams R.
Published: July 2002

Diamond exhibits very high, but widely varying, secondary-electron yields. In this study, we identified some of the factors that govern the secondary-electron yield from diamond by performing comparative studies on polycrystalline films with different dopants (boron or nitrogen), doping concentrations, and surface terminations. The total electron yield as a function of incident-electron energy and the energy distribution of the emitted secondary electrons showed that both bulk properties and surface chemistry are important in the secondary-electron-emission process. The dopant type and doping concentration affect the transport of secondary electrons through the sample bulk, as well as the electrical conductivity needed to replenish the emitted electrons. Surface adsorbates affect the electron transmission at the surface-vacuum interface because they change the vacuum barrier height. The presence of hydrogen termination at the diamond surface, the extent of the hydrogen coverage, and the coadsorption of hydrocarbon-containing species all correlated with significant yield changes. Extraordinarily high secondary-electron yields (as high as 84) were observed on B-doped diamond samples saturated with surface hydrogen. The secondary electrons were predominantly low-energy quasithermalized electrons residing in the bottom of the diamond conduction band. Two key reasons for the unusually high yields are (1) the wide band gap which allows the low-energy secondary electrons to have long mean-free paths, and (2) the very low or even negative electron affinity at the surface which permits the low-energy quasithermalized electrons that reach the surface to escape into vacuum.
Material strength and inelastic deformation of silicon carbide under shock wave compression
Authors: Feng R. , Raiser G. F. , Gupta Y. M.
Published: July 2002

In-material, lateral, manganin foil gauge measurements were obtained in dense polycrystalline silicon carbide (SiC) shocked to peak longitudinal stresses ranging from 10–24 GPa. The lateral gauge data were analyzed to determine the lateral stresses in the shocked SiC and the results were checked for self-consistency through dynamic two-dimensional computations. Over the stress range examined, the shocked SiC has an extremely high strength: the maximum shear stress supported by the material in the shocked state increases from 4.5 GPa at the Hugoniot elastic limit (HEL) of the material (11.5 GPa) to 7.0 GPa at stresses approximately twice the HEL. The latter value is 3.7% of the shear modulus of the material. The elastic–inelastic transition in the shocked SiC is nearly indistinctive. At stresses beyond twice the HEL, the data suggest a gradual softening with increasing shock compression. The post-HEL material strength evolution resembles neither catastrophic failure due to massive cracking nor classical plasticity response. Stress confinement, inherent in plane shock wave compression, contributes significantly to the observed material response. The results obtained are interpreted qualitatively in terms of an inhomogeneous deformation mechanism involving both in-grain microplasticity and highly confined microfissures.
Structural and magnetic properties of ball milled copper ferrite
Authors: Goya G. F. , Rechenberg H. R. , Jiang J. Z.
Published: July 2002

The structural and magnetic evolution in copper ferrite (CuFe2O4) caused by high-energy ball milling are investigated by x-ray diffraction, Mössbauer spectroscopy, and magnetization measurements. Initially, the milling process reduces the average grain size of CuFe2O4 to about 6 nm and induces cation redistribution between A and B sites. These nanometer-sized particles show superparamagnetic relaxation effects at room temperature. It is found that the magnetization is not saturated even with an applied field of 9 T, possibly as the result of spin canting in the partially inverted CuFe2O4. The canted spin configuration is also suggested by the observed reduction in magnetization of particles in the blocked state. Upon increasing the milling time, nanometer-sized CuFe2O4 particles decompose, forming α-Fe2O3 and other phases, causing a further decrease of magnetization. After a milling time of 98 h, α-Fe2O3 is reduced to Fe3O4, and magnetization increases accordingly to the higher saturation magnetization value of magnetite. Three sequential processes during high-energy ball milling are established: (a) the synthesis of partially inverted CuFe2O4 particles with a noncollinear spin structure, (b) the decomposition of the starting CuFe2O4 onto several related Fe–Cu–O phases, and (c) the reduction of α-Fe2O3 to Fe3O4.
Electrical signatures and thermal stability of interstitial clusters in ion implanted Si
Authors: Benton J. L. , Halliburton K. , Libertino S. , Eaglesham D. J. , Coffa S.
Published: July 2002

Deep level transient spectroscopy (DLTS) investigations have been used to characterize the electrical properties of interstitial clusters in ion-implanted Si. Both n- and p-type samples were implanted with 145 keV–1.2 MeV Si ions to doses of 1×1010–5×1013 cm−2 and annealed at 450–750 °C. On samples annealed at temperatures above 550 °C, the residual damage is dominated by two hole traps (B lines) in p-type and five electron traps (K lines) in n-type samples. Analyses of the spectra and defect depth profiles reveal that these signatures are related to Si self-interstitial clusters, and experiments confirm that these clusters do not embody large numbers of impurities such as C, O, B, or P. Four deep level signatures exhibit similar annealing behavior, suggesting that they arise from the same defect structure. On the other hand, the remaining signatures exhibit different annealing behaviors and are tentatively associated with different cluster configurations. We have found that the thermal stability of the clusters is enhanced by either increasing the Si dose or by reducing the impurity content of the substrate. The explanation of these effects proposes that bigger and more stable clusters are formed when the concentration of free interstitials available for clustering is increased and the competing interstitial trapping at impurities is inhibited. Finally, in samples implanted at doses of ⩾1×1013 cm−2, most of the DLTS signals exhibit a complex and nonmonotonic annealing behavior providing evidence that the clusters can transform between electronic configurations.
Exchange-biased magnetic tunnel junctions and application to nonvolatile magnetic random access memory (invited)
Authors: Parkin S. S. P. , Roche K. P. , Samant M. G. , Rice P. M. , Beyers R. B. , Scheuerlein R. E. , O’Sullivan E. J. , Brown S. L. , Bucchigano J. , Abraham D. W. , Lu Yu , Rooks M. , Trouilloud P. L. , Wanner R. A. , Gallagher W. J.
Published: July 2002

Exchange biased magnetic tunnel junction (MTJ) structures are shown to have useful properties for forming magnetic memory storage elements in a novel cross-point architecture. MTJ elements have been developed which exhibit very large magnetoresistive (MR) values exceeding 40% at room temperature, with specific resistance values ranging down to as little as ∼60 Ω(μm)2, and with MR values enhanced by moderate thermal treatments. Large MR values are observed in magnetic elements with areas as small as 0.17 (μm)2. The magnetic field dependent current–voltage characteristics of an MTJ element integrated with a silicon diode are analyzed to extract the MR properties of the MTJ element itself.
Band-structure effects in the spin relaxation of conduction electrons (invited)
Authors: Fabian J. , Sarma S. Das
Published: July 2002

Spin relaxation of conduction electrons in metals is significantly influenced by the Fermi surface topology. Electrons near Brillouin zone boundaries, special symmetry points, or accidental degeneracy lines have spin flip rates much higher than an average electron. A realistic calculation and analytical estimates show that these regions dominate the spin relaxation, explaining why polyvalent metals have much higher spin relaxation rates (up to three orders of magnitude) than similar monovalent metals. This suggests that spin relaxation in metals can be tailored by band-structure modifications like doping, alloying, reducing the dimensionality, etc.
Aberrations and allowances for errors in a hemisphere solid immersion lens for submicron-resolution photoluminescence microscopy
Authors: Baba Motoyoshi , Sasaki Takeaki , Yoshita Masahiro , Akiyama Hidefumi
Published: July 2002

We have analyzed the aberrations and allowances for an aspheric error, a thickness error, and an air gap in a hemisphere solid immersion lens for photoluminescence microscopy with submicron resolution beyond the diffraction limit, where light with large ray angle and the effect of an evanescent field play important roles.
Structure of copper- and H2-phthalocyanine thin films on MoS2 studied by angle-resolved ultraviolet photoelectron spectroscopy and low energy electron diffraction
Authors: Kamiya Okudaira Koji , Hasegawa Shinji , Ishii Hisao , Seki Kazuhiko , Harada Yoshiya , Ueno Nobuo
Published: July 2002

Angle-resolved ultraviolet photoelectron spectra (ARUPS) of copper phthalocyanine (CuPc) and metal-free phthalocyanine (H2Pc) films (thickness from monolayer to 50–80 Å) on cleaved MoS2 substrates were measured using monochromatic synchrotron radiation. Observed take-off angle (θ) and azimuthal angle (φ) dependencies of the top π band intensity were analyzed quantitatively by the single-scattering approximation theory combined with molecular orbital calculations. The analysis indicated that the molecules lie flat on the MoS2 surface in monolayer films of CuPc and H2Pc. The azimuthal orientation of the molecules (angle between molecular axis and surface crystal axis of MoS2), was found to be about −7°, −37°, or −67° for both monolayer films of CuPc and H2Pc. In the azimuthal orientation, the analyses indicated that there are only molecules with conterclockwise rotation, although both clockwise and counterclockwise rotations are expected. From the low energy electron diffraction, the two-dimensional lattice structure of the monolayer film was obtained. On the basis of these two kinds of experimental results, the full structure of the monolayer film, the two-dimensional lattice and the molecular orientation at the lattice points, was determined. Furthermore, for the thick films it is found from the analyses of ARUPS that CuPc and H2Pc molecules tilt about 10° from the surface plane.
Surface energy and polarity of treated indium–tin–oxide anodes for polymer light-emitting diodes studied by contact-angle measurements
Authors: Kim J. S. , Friend R. H. , Cacialli F.
Published: July 2002

We present contact-angle hysteresis and surface energy of differently treated indium–tin–oxide (ITO) thin films obtained from contact angles for liquids with different polar character. We find that the hysteresis and the polar and dispersion component of the surface energy depend strongly on the surface treatments. Oxygen-plasma treatments induce the highest polarity and the highest total surface energy, and we suggest that this improves the interface formation with polymers, and therefore, the performance of light-emitting diodes. We discuss the results in relation to the ITO surface roughness and chemical heterogeneity modified by the different treatments.
The grain size dependence of the resistance behaviors in doped lanthanum manganite polycrystalline films
Authors: Liu Xiangdong , Jiao Zhengkuan , Nakamura Keikichi , Hatano Takeshi , Zeng Yuewu
Published: July 2002

Using the sol–gel spin-coating method, La0.67Sr0.33MnO3 and La0.7Ca0.3MnO3 polycrystalline films have been prepared. The polycrystalline films show much lower resistivity peak temperature Tp than that of the corresponding epitaxial film, and Tp shifts to higher temperature when the annealing temperature increases. The magnetization measurement reveals that all of the polycrystalline films have the same magnetic transition temperature as the corresponding epitaxial films. These results are different from the previous works. We ascribe the difference to the grain size of our polycrystalline samples being much smaller, so the conduction through the grain boundaries predominates over the intragrain conduction. In this case, spin disorder and magnetocrystalline anisotropy should be taken into account in explaining the magnetotransport behavior.
Optical and photoelectric study of mirror facets in degraded high power AlGaAs 808 nm laser diodes
Authors: Andrianov A. V. , Dods S. R. A. , Morgan J. , Orton J. W. , Benson T. M. , Harrison I. , Larkins E. C. , Daiminger F. X. , Vassilakis E. , Hirtz J. P.
Published: July 2002

Mirror facets of broad area AlGaAs SQW 808 nm lasers with fast degradation of the output power have been investigated by photoluminescence microscopy (PLM), electroluminescence microscopy, and micro-photocurrent spectroscopy techniques. Over 2000 images of the photoluminescent light emitted from the facets of approximately 20 degraded laser bars have been made. Repeating patterns associated with the degradation have been noted and classified. Degraded lasers have dark lines on the mirror facet surface which are inclined from the epitaxial plane by 55°. Pairs of such lines often form V-shaped patterns. The orientation of the observed features suggest they are planar or line defects lying the the {111} crystallographic planes. The defects demonstrate a reduction in the lifetime of nonequilibrium electron–hole pairs and increased density of states in the forbidden gap of the active region of the laser structure, and are directly related to laser failure. Observations of the evolution in size and contrast of PLM patterns with ageing suggest the defects were initially created in the active region side of the laser structures during crystal growth or during the mounting procedure, and later propagate in the {111} planes, stimulated by the lasing action. We interpret the V formation to be a way to relax a compressive strain in the epitaxial plane. A dislocation on the {111} planes could actually translate the portion of the crystal bounded by the V upwards (away from the mounting of the crystal), in response to compressive strain.