bluuebunny/crossref_metadata_2025 huggingface dataset:
Mode coupling in modified lead titanate/polymer 1–3 composites
Authors: Chan Helen L. W. , Unsworth Joe , Bui Tuan
Published: July 2002

Modified lead titanate/polymer 1–3 composites are fabricated and their resonance characteristics determined. The mode coupling theory is applied to the pillar-shaped ceramic elements inside the 1–3 composite. Coupling of lateral and thickness mode vibrations occurs as the width to thickness ratio increases. The experimental results agree well with the mode coupling theory predictions. It is found that the piezoelectric properties of PbTiO3/epoxy composites are similar to that of lead zirconate titanate (PZT)/epoxy composites, except that the coupling constants of lead titanate are very small due to ceramic anisotropy. The thickness mode resonant frequency times the thickness value, fH, stays steady and close to the uncoupled value as the configurational (width/thickness) L/H ratio is increased from 0.1 to 1.0. In the range L/H=1.0–1.5, the thickness and lateral mode vibrations couple. Above L/H=1.5, these modes decouple and are easily resolved. The thickness mode becomes again close to the uncoupled value. Lead titanate/epoxy composites geometries can therefore be selected with L/H>1.5. This produces better medical ultrasonic transducers than PZT/epoxy types.
Solenoid gas puff imploding liner x-ray source
Authors: Lougheed G. D. , Kekez M. M. , Lau J. H. W. , Gupta R. P.
Published: July 2002

There is a worldwide effort to produce a soft x-ray source for submicron microlithography to manufacture future generation large scale integrated microchips. The gas puff plasma discharge has been suggested as a viable alternative for low volume facilities which require relatively low throughputs with a single aligner station. The repetition rate for such systems is limited by the large gas flow into the vacuum system with the standard electromechanical puff valve. A unique puff arrangement is being developed which will limit the dead gas flow and, in principle, will allow for the development of high repetition rate systems. In this arrangement, the gas flows continuously from a low-pressure plenum through an annular aperture into the Z-pinch electrode gap. A discharge through a single turn solenoid coil mounted on the outside of the plenum inductively heats the gas, temporarily increasing the mass flow to produce a low mass (<1 μg), preionized liner which is imploded by a Z-pinch current discharge. (Multiturn coils have also been used. However, all the experiments reported in this paper used a single turn configuration.) Experiments were carried out with a variety of low-energy (<2.5 kJ) drivers including capacitor banks, peaking capacitors, and dc charged paper/castor oil Blumleins. Radiation measurements in the ultrasoft and soft x-ray regions were made using x-ray diodes, p-i-n diodes, and a time integrated pinhole camera. A slug model coupled to a capacitor bank or Blumlein circuit solver is used to estimate the liner dynamics as well as the load current and voltage.
X-ray photoelectron spectroscopy study of Si-C film growth by chemical vapor deposition of ethylene on Si(100)
Authors: Taylor P. A. , Bozack M. , Choyke W. J. , Yates J. T.
Published: July 2002

The growth of a thin film of SiC grown by chemical vapor deposition (CVD) of ethylene on Si(100) at 970 K was studied by x-ray photoelectron spectroscopy (XPS). The growth of the film was observed through the behavior of the Si(2p) and C(1s) core levels and their plasmon losses. A 1.2-eV (towards higher binding energy) shift is observed for the Si(2p) binding energy between silicon in Si(100) and silicon in SiC. The plasmon loss energies measured as a function of film thickness below the C(1s) emission indicate that the C/Si ratio of the Si-C film throughout the CVD process is fairly constant.
Picosecond nonlinear optical response of three rugged polyquinoxaline-based aromatic conjugated ladder-polymer thin films
Authors: Cao X. F. , Jiang J. P. , Bloch D. P. , Hellwarth R. W. , Yu L. P. , Dalton L.
Published: July 2002

We have fabricated the first optical quality polymer films of aromatic ladder polymers having an unbroken conjugated backbone, and find third-order nonlinear susceptibilities two orders of magnitude larger than CS2. The nonlinearities respond in less than 6 ps. Although we find their space symmetry to agree with that expected for a nonresonant electronic nonlinearity, the mechanism may well depend on lattice motion. The polymers are stable and rugged at room temperature. We also develop and analyze a simple form of degenerate four-wave mixing for the measurements, finding expressions for the effects of uncertainties in the spatial and temporal pulse profiles.
An analysis of complex spectra from deep level transient capacitance measurements
Authors: Di Zitti Ermanno , Bisio Giacomo M. , Fuochi Pier Giorgio , Passerini Bruno V. , Zambelli Mauro
Published: July 2002

The effect of complex sets of single- and double-level traps on deep level transient spectroscopy (DLTS) spectra is critically discussed using a numerical simulator. The simulation takes into account: the partial trap ionization, the effect of base doping, the dynamics of charged traps, and the depletion layer effect. The modeling of the capacitance transient has been extended when many traps are present. The simulator has been used for the analysis of DLTS spectra of platinum-doped and high-energy (12 MeV) electron-irradiated silicon diodes. These examples evidence how the simulation method increases the resolution of the DLTS technique. A detailed analysis of the emission kinetics of two energy level traps is also presented.
Structural studies of artificial Si/Nb superlattice films
Authors: Song S. N. , Li D. X. , Ketterson J. B. , Hues S. M.
Published: July 2002

Amorphous Si/Nb superlattices with modulation wavelengths ranging from 20–200 Å have been grown on sapphire substrates at 100–150 °C by dual e-beam evaporation in an ultra-high-vacuum (UHV) system. The low-angle x-ray diffraction data can be accounted for by a symmetric trapezoidal composition profile model. The intermixing at the layer interfaces is estimated to be 6–12 Å, depending on the substrate temperatures. In the film growth direction, the coherent domain size of the polycrystalline Nb layers scales with the Nb layer thickness. High-resolution transmission electron microscopy reveals the existence of microcrystallites in the 20-Å-thick amorphous Nb layers; also resolved are the microstructure of the substrate/superlattice and superlattice/thick-Nb layer interfaces. In addition, Auger depth profiling results are also consistent with the expected composition modulation.
On the mechanisms of strain release in molecular-beam-epitaxy-grown InxGa1−xAs/GaAs single heterostructures
Authors: Drigo A. V. , Aydinli A. , Carnera A. , Genova F. , Rigo C. , Ferrari C. , Franzosi P. , Salviati G.
Published: July 2002

Inx Ga1−x As/GaAs single heterostructures have been grown by molecular-beam epitaxy with different growing rates and In molar fractions. Indium composition, layer thickness, and residual strain have been measured mainly by Rutherford backscattering/channeling spectrometry and the results on selected samples compared with the results of other techniques like Auger electron spectroscopy and single- and double-crystal x-ray diffraction. Cathodoluminescence, x-ray topography, transmission electron microscopy, and ion dechanneling have been employed to observe dislocations and to characterize their nature and density. While the onset of misfit dislocations has been found to agree with the predictions of the equilibrium theory, the strain release has been found to be much lower than predicted and the results are compared with the available metastability or nucleation models. Present results are in best agreement with nucleation models. Moreover, annealing experiments show that these heterostructures are at (or very close to) thermodynamic equilibrium.
Observation and characterization of deep donor centers (D
X centers) in Si-doped AlAs
Authors: Kasu Makoto , Fujita Shizuo , Sasaki Akio
Published: July 2002

We find the DX centers in Si-doped AlAs for the first time. The activation energy is measured as 0.56 eV from deep level transient spectroscopy (DLTS). The DX centers in n-AlAs exhibit a large capture energy 0.5 eV and a persistent photoconductivity. These properties are similar to those of the DX centers in AlxGa1−xAs with x∼0.3. However, the carrier concentration in the DX centers revealed by DLTS is not linearly proportional to Si donor concentration. This result is interpreted by the band structure that the DX center level lies at 30 meV above the X-conduction band (CB) minima and at 150 meV below the L-CB minima. The DX center is found not to be associated with the X-CB minima, but the L-CB minima.
Thermally induced reactions of thin Ti and Nb films with SiO2 substrates
Authors: Wang S. Q. , Mayer J. W.
Published: July 2002

The reactions between thin refractory metal Ti or Nb films and SiO2 substrates in the temperature range 650–1000 °C in a vacuum have been studied by Rutherford backscattering spectrometry and glancing angle x-ray diffraction. The reactions started with the growth of measureable phases at 700 and 900 °C and completed with the configurations of SiO2 /Ti5 Si3/ TiO and SiO2 /Nb5 Si3 /NbO. Marker experiments indicated that the Ti atoms were the dominant diffusing species in the formation of Ti5 Si3 in the SiO2 /Ti reaction. The formation rate of the Ti5 Si3 layer was thickness dependent: The thicker the original thin Ti film, the higher the rate.
Actinide-activated luminescence in uranium-implanted III-V semiconductors
Authors: Pomrenke Gernot S. , Hengehold Robert L. , Yeo Yung Kee , Brown Ian G. , Solomon James S.
Published: July 2002

An actinide was successfully introduced into III-V semiconductors and investigated with photoluminescence and secondary ion mass spectrometry (SIMS). The implanted uranium ion gives rise to relatively strong and sharp emissions between 1.60 to 1.69 μm in GaAs and at 1.67 μm in InP. The implantation was performed at an ion mean energy of 131 keV using a new type of high-current metal ion source; the predicted depth profile of uranium was confirmed with SIMS. The emissions are a result of transitions between specific crystal-field split spin-orbit levels of possibly trivalent uranium (U3+) but most likely tetravalent uranium (U4+). The half-width of the main 1601-nm line in GaAs and the 1670-nm line in InP is less than 0.46 meV at 6 K. Temperature-dependent studies indicate that the emissions are associated with one center, and the luminescence is observed in GaAs and InP up to a temperature of 100 K after which it rapidly quenches.
Superconducting hysteresis and the Preisach model
Authors: Mayergoyz I. D. , Keim T. A.
Published: July 2002

It is suggested to use the Preisach hysteresis model for the description of superconducting hysteresis. It is shown that the Bean (critical state) model and its further generalizations are very particular cases of the Preisach model. It is also shown that noncyclic hysteresis losses in superconductors can be evaluated by using the Preisach model and experimentally measured first-order transition curves.
Applications of amorphous magnetic materials at very-high magnetization rates (invited)
Authors: Smith Carl H.
Published: July 2002

Amorphous ferromagnetic alloys are finding increased application in high-energy pulse-power systems and in high-frequency switched-mode power supplies. The peak powers in these applications differ by several orders of magnitude as do the core sizes; however, these applications do share similar very-high magnetization rates often measured in teslas per microsecond. In this paper the important characteristics of amorphous magnetic materials used at high magnetization rates are reviewed. Domain models for very-high magnetization rates are discussed. The effects on magnetic losses of differing voltage waveform excitations are calculated for applications which require nonconstant rates of dB/dt. Finally, several applications utilizing magnetic amorphous alloys at high magnetization rates, in both research devices and potential commercial applications, are described. Pulse-power devices based on amorphous alloy cores have already reached multiterawatt peak output power levels with pulses shorter than 100 ns. Petawatt peak-power devices are on the drawing boards.
High spatial resolution quantitative micromagnetics (invited)
Authors: Scheinfein M. R. , Unguris J. , Pierce D. T. , Celotta R. J.
Published: July 2002

Magnetization profiles at surfaces are observed with scanning electron microscopy with polarization analysis (SEMPA). This technique allows for quantitative analysis of the vector magnetization profile with 70 nm spatial resolution. Magnetization profiles in surface Néel walls which terminate bulk 180° Bloch walls at surfaces have been calculated by solving the micromagnetic equations using energy minimization. The micromagnetic calculations show that the surface Néel wall penetrates a distance from the surface comparable to a Bloch wall width and that the surface Néel wall width is at least twice the bulk Bloch wall width. The dependence of the domain wall magnetization on sample thickness is calculated for Fe, and model predictions of the wall widths that would be determined by transmission Lorentz microscopy are compared with the experimental results. The magnetic field outside of the sample, which gives rise to contrast with the Bitter technique and magnetic force microscopy (MFM), is a complicated superposition of contributions from both bulk and surface walls. Moreover, a strong mutual interaction between the sample and the MFM tip may alter the sample magnetization.
High-temperature ion beam synthesis of cubic SiC
Authors: Martin P. , Daudin B. , Dupuy M. , Ermolieff A. , Olivier M. , Papon A. M. , Rolland G.
Published: July 2002

The β-SiC (or 3C-SiC) synthesis through high-dose carbon implantation into a silicon substrate heated at high temperature is studied by means of cross-sectional transmission electron microscopy, x-ray diffraction, infrared absorption spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, channeling, and nuclear reaction analysis. It is shown that a thick buried layer of β-SiC (about 300 nm) is directly formed after multiple implantations at 860 °C without post-implantation annealing. This layer is not continuous but consists of small monocrystalline grains (average size ∼7 nm) in a near-perfect epitaxial relationship with the silicon matrix. These grains are only slightly misorientated (∼3.5°) but are severely twinned on {111} planes.
Hole trapping phenomena in the gate insulator of As-fabricated insulated gate field effect transistors
Authors: Lipkin L. , Reisman A. , Williams C. K.
Published: July 2002

Hole trapping phenomena in SiO2 were examined using an optically assisted hot carrier injection technique on p-channel insulated gate field effect transistors. It was found that only a single, field-dependent, capture-cross-section hole trap is present. The capture cross section of these hole traps at a field of 4 mV/cm across the gate insulator, corresponding to a gate voltage just above the threshold voltage, was found to be 8.5×10−14 cm2. Injected holes were found to trap with an initial efficiency of approximately 60% at this gate field. Depopulation of trapped holes at room temperature was also examined, and found to be significant. The neutral hole trap density in unirradiated device gate insulators after post-metal annealing was found to be approximately 7.0×1012 cm−2. Based on a study of the threshold voltage shift as a function of gate insulator thickness, coupled with the model recently proposed by Walters and Reisman for determining charge centroid, it appears that for oxides with thicknesses greater than 10 nm, the hole traps lie in a band of finite thickness with a charge centroid 5 nm from the substrate-SiO2 interface. In addition, there exists a layer approximately 3.7 nm thick at each interface that appears void of trapped charge. Therefore, oxides less than 7.4 nm thick should not trap charge, which was found to be the case experimentally. This implies that as devices are scaled down, hole trapping will disappear, which is of particular significance in oxides subjected to ionizing irradiation, either during processing or during use.
Reduced light-induced changes of photoconductivity in duterated amorphous silicon
Authors: Ganguly G. , Suzuki A. , Yamasaki S. , Nomoto K. , Matsuda A.
Published: July 2002

The light-induced decrease of the photoconductivity in deuterated amorphous silicon is a factor of 3 less even though the defect density increase is greater than in hydrogenated material having equivalent as-deposited properties. Consequent changes in the average recombination cross section of the defects is illustrated. Since the differences in the light soaking behavior upon isotopic substitution has been found to disappear in films deposited at low temperatures, the changes are thought to arise from differences in the silicon network occurring during growth.
Surface-force-induced deformations of monodisperse polystyrene spheres on planar silicon substrates
Authors: Rimai D. S. , DeMejo L. P. , Bowen R. C.
Published: July 2002

The contact radii between polystyrene spheres, having diameters between approximately 1.5 and 12 μm, and polished silicon wafers, arising from adhesion forces, were determined using scanning electron microscopy. It was found that the contact radius varied approximately as the square root of the particle radius. This dependence is consistent with nonelastic response models of adhesion, such as those proposed by Krupp [H. Krupp, Adv. Colloid Interface Sci. 1, 111 (1967)] and by Maugis and Pollock [D. Maugis and H. M. Pollock, Acta Metall. 32, 1323 (1984)], but is inconsistent with various elastic response models which assume Hertzian deformations. The experimentally determined contact radii are also compared to those obtained for polystyrene spheres on a polyurethane substrate [D. S. Rimai, L. P. DeMejo, and R. C. Bowen, J. Appl. Phys. 66, 3574 (1989)].
Time-dependent electron emission from ferroelectrics by external pulsed electric fields
Authors: Gundel H. , Hańderek J. , Riege H.
Published: July 2002

Results of experiments investigating the influence of the amplitude, the growth rate, and the repetition rate of the exciting electric field pulses on the electron current and charge density emitted from ferroelectrics are reported. The behavior of two types of lead-lanthanum-zirconium-titanate (PLZT) ceramics, 2/95/5 and 8/65/35, was studied. The temporal shift between the applied HV pulses and the emitted electron current pulses was different for the two materials. Regular electron emission was observed at repetition rates of up to 2 MHz in the PLZT-2/95/5 material, showing that the recovery of the emitting sample back to the original state may happen in less than a microsecond.
Measurement of ion impact energy and ion flux at the rf electrode of a parallel plate reactive ion etcher
Authors: Manenschijn A. , Janssen G. C. A. M. , van der Drift E. , Radelaar S.
Published: July 2002

An experimental study on the ion impact energy distribution and the total ion flux at the driven electrode of a parallel plate reactive ion etcher is presented. Results are shown for 13.56 MHz discharges in Ar, Ar/H2, N2, O2, Cl2, and SF6/He over a pressure range of 0.3–40 Pa. The ion impact energy distribution consists of a collision-free part and a collision-induced part. It is observed that in Ar, N2, O2, and Cl2 the collision-induced part contains single and double peaks at regular energy intervals. This peaked structure is attributed to charge exchange processes in the sheath. Both the collision-free part and the collision-induced part of the ion impact energy distribution are well described by a model based on a constant sheath width, a sinusoidal sheath voltage, and a power law for the electric field in the sheath. The only adjustable parameter in the model is the sheath thickness. The sheath thickness has also been determined independently from the total ion current density using the Child–Langmuir law. The obtained values are in good quantitative agreement with each other and with the observed optical sheath thickness, demonstrating the overall consistency of the present approach.
Kerr effect from Pt/Co superlattices and the role of the magneto-optic activity of Pt
Authors: Moog E. R. , Zak J. , Bader S. D.
Published: July 2002

The magneto-optic response of Pt/Co superlattices is simulated to gain insight into the recent experimental findings of favorable information-storage characteristics. Major trends are reproduced qualitatively, and the calculations indicate that the Pt contributes significantly to the short-wavelength polar Kerr signal (at 4 eV). The influences of the wavelength, angle of incidence, component thicknesses, overcoat, and substrate on the rotation, ellipticity, and reflectivity are evaluated.
An infrared study of thin-film formation on Si and Ge surfaces treated with aqueous NH4F and HF
Authors: Yota J. , Burrows V. A.
Published: July 2002

The surface chemistry of Si and Ge after treatment with hydrofluoric acid buffered with ammonium fluoride (BHF) was studied using surface infrared spectroscopy. For each of these materials, the BHF not only dissolved the native oxide, but also deposited a thin inorganic film comprised of ammonium salts (NH4F and NH4F.HF). Through one or more complex reactions with the substrate, these salts slowly disappear as the thermodynamically very stable hexafluorometallate compounds [(NH4)2SiF6 and (NH4)2GeF6] form. The NH4F.HF disappearance correlates directly with the hexafluorometallate formation. Though the original fluoride and bifluoride salts are quite soluble in alcohols as well as in aqueous solutions, the hexafluorometallates are completely insoluble in alcohols, and can only be removed by thorough water rinse.
Temperature dependence of magnetoresistance in Fe-Cr-Fe sandwiches
Authors: Chaiken A. , Tritt T. M. , Gillespie D. J. , Krebs J. J. , Lubitz P. , Harford M. Z. , Prinz G. A.
Published: July 2002

Resistivity measurements have been performed as a function of temperature (1–300 K) and magnetic field (0–10 T) on antiferromagnetically coupled Fe-Cr-Fe sandwiches. Two types of samples were studied: MBE-grown sandwiches deposited epitaxially on the ZnSe (100) surface, and evaporated polycrystalline sandwiches deposited on glass substrates. The magnetic saturation field Hs determined from the resistivity ρ(H,T) is linear with temperature throughout the full temperature range for all samples. In the polycrystalline sandwiches, where the observed in-plane magnetic anisotropy is small, the linearity of Hs(T) implies that the antiferromagnetic interlayer exchange coupling A12 is also linear with temperature. The magnetoresistance of the sandwiches is constant at low temperature, and decreases linearly with increasing temperature above about 70 K.
Computer simulation of magnetization reversal in fine hexagonal platelet particles with defects
Authors: Uesaka Yasutaro , Nakatani Yoshinobu , Hayashi Nobuo
Published: July 2002

The Landau–Lifshitz–Gilbert equation is used to investigate the switching fields and mechanisms of fine hexagonal platelet particles which have three types of defects in comparison with a nondefect particle. Two of the defects are surface defects, one with an area more than 50% of the hexagon and the other much less than 50%. The third defect is not a surface defect but a defect which extends from the top to bottom surface. The differences between the switching fields of these particles are small, at most 12%. The angular dependence of the switching fields of these particles is similar to the ones derived from the coherent rotation mode. The switching mechanisms of the particles change with applied field. The nondefect particle switch in a normal vortex mode and the particles with defects switch in a mixture of normal vortex and coherent rotation-like mode at the applied field=Hsw (switching field). Most of them switch in a twisted vortex mode at the applied field=3 × Hsw. But in surface defect particles, whose defect area is more than 50% of the hexagon, the switching mechanism hardly changes from a coherent rotation-like mode.
Plasma-deposited germanium nitride gate insulators for indium phosphide metal-insulator-semiconductor field-effect transistors
Authors: Johnson Gregory A. , Kapoor Vik J.
Published: July 2002

Germanium nitride (Ge3N4) films were deposited on indium phosphide (InP) compound semiconductor substrates using plasma-enhanced chemical vapor deposition. The depositions were performed in a capacitively coupled parallel-plate reactor using two different processes. In the first process, germane (GeH4), nitrogen (N2), and ammonia (NH3) reactant gases were used. In the second process, germane and pure nitrogen were used as reactant gases. The films were deposited using 13.56 MHz rf excitation to a typical thickness of 800 Å with a refractive index of 2.11–2.16. The breakdown field strength of the films was greater than 106 V/cm. Auger electron spectroscopy did not indicate significant chemical composition differences between the two deposition processes. In order to study the feasibility of plasma-deposited germanium nitride as a gate insulator, metal-insulator-semiconductor field-effect transistors (MISFETs) with 2-μm channel lengths were fabricated on InP. The device transconductance and threshold voltage for the GeH4/N2/NH3 process were 17 mS/mm and −3.6 V, respectively. The drain-source breakdown voltages were greater than 10 V. The GeH4/N2/NH3 deposition process was preferred over the GeH4/N2 process because of enhanced thickness uniformity, increased deposition rate, increased resistivity, reduced interface state density, and comparable MISFET electrical characteristics.
Photon-gated persistent spectral hole burning by donor-acceptor electron transfer in tetraphenylporphine/halogenated anthracene systems
Authors: Suzuki H. , Shimada T. , Hiratsuka H.
Published: July 2002

Photon-gated persistent spectral hole burning was observed for metal-free tetraphenylporphine with halogenated anthracene derivatives in poly(methylmethacrylate) or poly(ethylene) at liquid-helium temperatures. The hole formation yield was markedly dependent on the polymer matrices and the sample composition as well as on the gating wavelength. The irreversible broadening of holes in the systems measured by temperature cycling experiment was smaller than that by proton tautomerization of tetraphenylporphine. We concluded that the hole formation mechanism is donor-acceptor electron transfer on the basis of combined analysis of the matix and acceptor concentration dependence of hole formation yield, the action spectrum of the gating photon and the photoproduct spectrum.
Backscattering of an electromagnetic missile by a perfectly conducting sphere
Authors: Geyi Wen , Ruan Chengli , Lin Weigan
Published: July 2002

It has been shown recently that when an electromagnetic (EM) missile with an energy decreasing as r−ε is incident upon a perfectly conducting plate, the reflected energy will decrease as r−ε with the same exponent as the EM missile. The question of studying the backscattering properties of an EM missile by other objects is then left open to further investigation. In this paper we make a study of backscattering of an EM missile with an energy decreasing as r−ε by a perfectly conducting sphere, and the analysis indicates that the rate of energy decay for the backscattered field far from the sphere is proportional to r−(2+ε) (0<ε<2), which is faster than r−ε for plate scattering but slower than the usual energy decay r−4 for a three-dimensional backscattered field.
The maximum possible conversion efficiency of silicon-germanium thermoelectric generators
Authors: Slack Glen A. , Hussain Moayyed A.
Published: July 2002

The thermoelectric properties of N-type and P-type Si-Ge alloys have been reviewed and detailed calculations for the efficiency of a thermoelectric generator made from a 70% Si-30% Ge alloy have been made over the temperature range from 300 to 1300 K. A model employing one valence band and two conduction bands has been used. A generator of standard material, optimally doped, and infinitely segmented will have an efficiency of 12.1% operating over this range. If the lattice thermal conductivity can be reduced to its minimum value without upsetting the electrical properties, then the efficiency can be raised to an ultimate maximum of 23.3%. A more modest increase in efficiency to 14.7% could be obtained by a 2.4 volume percent of finely dispersed second-phase precipitates which would act as phonon scatterers. The utility/futility of GaP additions and grain-boundary scattering as methods to increase the efficiency is discussed.
Grain boundary scattering in CuInSe2 films
Authors: Sanyal I. , Chattopadhyay K. K. , Chaudhuri S. , Pal A. K.
Published: July 2002

Electrical conductivity and Hall mobility of CuInSe2 films were measured in the temperature range of 77–400 K. The films were deposited with different Cu/In ratios ranging from 0.7–0.9 and at substrate temperatures of 620–720 K. Effects of grain boundary scattering on the electron transport properties were studied carefully and it was observed that scattering at the grain boundaries is a predominant factor controlling the electron transport properties at lower temperatures while complex scattering mechanisms become operative at higher temperatures. The energy values of trap levels and the densities of trap states were also obtained.
Sidegating in GaAs metal-semiconductor field-effect transistors under low-level injection
Authors: Shulman Dima D. , Young Lawrence
Published: July 2002

Sidegating in GaAs metal-semiconductor field-effect-transistors (MESFETs) is widely attributed to space-charge-limited (SCL) conduction through the semi-insulating (SI) substrate. But often sidegating is accompanied by low sidegate currents and occurs at sidegate voltages that are too small to initiate SCL conduction. We suggest that this is due to low-level hole injection from a MESFET into the substrate. An analytical treatment of carrier, field, and potential distribution in a SI substrate under conditions of low-level injection shows that an electric field overshoot may develop in the vicinity of the MESFET when hole injection occurs. This results in a large portion of the applied voltage being dropped across the channel-substrate interface and, consequently, in sidegating. One result for short structures is the electric field outside the narrow region of overshoot is below the value expected for ohmic conduction. Consequently, over a wide range of applied voltages the field in most portions of the structure is below the critical value required for intervalley electron transfer.
Phase transitions in KH2PO4 and RbH2PO4 to 14 GPa observed by capacitance change in a diamond anvil cell
Authors: Bao Z. X. , Schmidt V. Hugo , Howell Francis L.
Published: July 2002

Phase transitions in KH2PO4 (KDP) and RbH2PO4 (RDP) at room temperature for pressures up to 14 GPa have been determined by means of capacitance measurements using a diamond anvil cell. Phase transitions occur in KDP near 2.5 and 7.0 GPa. In RDP, a transition was detected near 5.4 GPa.
The process-controlled magnetic properties of nanostructured Co/Ag composite films
Authors: Liou S. H. , Malhotra S. , Shan Z. S. , Sellmyer D. J. , Nafis S. , Woollam John A. , Reed C. P. , DeAngelis R. J. , Chow G. M.
Published: July 2002

Nanostructured Co/Ag composite films were prepared by magnetron sputtering using a single target. The average crystallite sizes of Co and Ag in the films depend on the deposition conditions. As the substrate temperature increases from 100 °C to 600 °C, the average Ag crystallite size increases from 39 to 452 Å, and the average Co crystallite size increases from <30 to 297 Å in the film with 39 vol. % of Co. The films with 39 vol. % of Co and prepared at 400 °C substrate temperature showed a maximum magnetic coercivity of 565 Oe at 6 K. We have studied the correlation between the structure and magnetic properties of these films.
Characterization of the interaction between a hollow cathode source and an ambient plasma
Authors: Vannaroni G. , Dobrowolny M. , Melchioni E. , De Venuto F. , Giovi R.
Published: July 2002

The laboratory characterization of the interaction between a hollow cathode plasma source and an ambient plasma of ionospheric type is reported. The investigation was carried out by means of Langmuir probes for various positive polarization levels of the source with respect to the ambient plasma in absence of magnetic field. Measurements put into evidence the formation of a double layer that dominates the current collection process on the hollow cathode source. The electron energy distribution function, derived along the axis of the current path, indicates the presence of an anomalous collisional mechanism due to the bump-in-tail instability in the region between the double layer and the source. The experimental data were also compared with the results of a one-dimensional theoretical model of the interaction; taking into account the approximation of the model, such a comparison indicates that both the position and the voltage drop associated to the double layer match rather well the theoretical predictions.
On extrinsic effects in the surface impedance of cuprate superconductors by weak links
Authors: Halbritter J.
Published: July 2002

The reported rf surface impedance of superconducting cuprates continues to drop with 2 years of improving material quality. As leading indicator for quality the weak-link critical current jcJ(T≊ 0, B ≊ 0) has grown from 102 to 106 A/cm2 and thus the Josephson penetration depth λJ ∝ 1/√jcJ and the excess normal (leakage) tunnel current jbl are shrinking. This jcJ growth has now saturated, whereas the rf residual surface impedance Zres is still shrinking with material improvements. This shows clearly that Zres is an extrinsic property. Evidence that Zres is due to the large leakage current jbl and the small jcJ of weak links, where the latter destroys the intrinsic shielding from a λI thin-seam λJ deep into the bulk, is presented. This causes rf residual losses Rres ≊ (ωμ0)2λJ3σbl/2. Rres stays finite at T ≂ 0 by σbl(T → 0) ≊ σbl (∝jbl) being amplified by (λJ/λI)3 ≳ 103 as a weighting factor. With slow crystal growth weak links are improved and their density is reduced so that Rres values better than RNb(4.2 K) are now obtainable. The jcJ(T,B) values explain λres and Rres quantitatively and in temperature proportional to (a + Tm); m ≊ 1, T < Tc/2, and proportional to (b + Hn), n ≊ 1; H ≳ Hc1J in field dependence. Here Hc1J is the field where flux enters into weak links as Josephson fluxons having negligible viscous losses, but act by enhancing the penetration depth.
Generation of relativistic photoelectrons induced by an ultraviolet laser and their propagation characteristics in a longitudinal guiding magnetic field
Authors: Kawamura Y. , Toyoda K. , Kawai M.
Published: July 2002

Photoelectrons from a metal surface irradiated by a pulsed ultraviolet laser were accelerated to relativistic energy to obtain a very cold and relatively high-current electron beam. Typical values of the transverse velocity component β⊥/β∥ were measured to be less than 8×10−3, which leads to a spread of the parallel energy component Δγ∥ /γ∥ of 1×10−4 or less. Propagation characteristics in a longitudinal guiding magnetic field were investigated. A nonadiabatic factor was defined to estimate the conservation of the magnetic moment of the electrons moving along the magnetic flux, and this was shown experimentally to be reasonable. Spacial controllability of the cross section of this electron beam was demonstrated.
Modeling the direct current superconducting quantum interference device coupled to the multiturn input coil. II
Authors: Enpuku K. , Cantor R. , Koch H.
Published: July 2002

A complete circuit model of a dc superconducting quantum interference device (SQUID) coupled to a multiturn input coil has been developed. With this model, it is shown that the rf properties of the coupled SQUID can be calculated using only the given parameters of the SQUID. There are no adjustable parameters. The resonant structures in the SQUID characteristics caused by the presence of the input coil have been quantitatively studied. Methods to suppress the resonant structures have also been investigated. It is shown that the present circuit model explains well the experimentally observed rf properties of coupled SQUIDs. The present circuit model is therefore useful for the design of highly sensitive SQUIDs.
Geometrical optics analysis of electromagnetic-missile backscattering
Authors: Ren Wei , Wan Changhua , Lin Weigan
Published: July 2002

In this paper, the backscattering of an electromagnetic (EM) missile the energy of which decays as r−ε by arbitrary three-dimensional (3D) and two-dimensional (2D) targets, such as perfect conductors, dielectrics, and a perfect conductor coated with dielectric, is analyzed by using geometrical optics. The analysis shows that the backscattered energy of the EM missile by arbitrary 3D and 2D targets is proportional to r−εR1R2/[(R1+2r)(R2+2r)] and r−εR/(R+2r), respectively, where R1 and R2 are the two principal radii of curvature of the 3D surface at the specular point and R is the radius of curvature of the 2D surface at the specular point. This general result includes several special examples available, such as plates, perfectly conducting elliptical cylinders, and spheres. It is seen that the rate of energy decrease of the backscattered EM missile is slower than those for conventional 3D and 2D backscattered fields.
Thickness dependence of the anisotropic magnetoresistance in epitaxial iron films
Authors: Tondra Mark , Lottis Daniel K. , Riggs K. T. , Chen Youjun , Dahlberg E. Dan , Prinz G. A.
Published: July 2002

The anisotropic magnetoresistance (AMR) has been measured at room temperature on a series of epitaxial iron films of various thicknesses. Seven of the films range in thickness from 5 to 20 nm, and one is 500 nm thick. The resistivity of the films was measured with current along photolithographically defined paths parallel to three directions of high symmetry in the single crystal films ([001], [110], and [111]). It was determined that the magnitude of the AMR depends upon the direction the current is applied and that this directional dependence increases with film thickness until saturating near 20 nm. The AMR is roughly 0.15% for all crystal directions in the thinnest films, while in the thickest film, the AMR is 0.08% with current along the [001] direction, 0.35% along the [110] direction, and 0.51% along the [111] direction. These values are to be compared with the AMR of bulk polycrystalline iron which is 0.2%; a weighted average over the different crystallographic directions.
A study of point defect detectors created by Si and Ge implantation
Authors: Meng H. L. , Prussin S. , Law M. E. , Jones K. S.
Published: July 2002

Short-time/low-temperature thermal oxidation is known to lead to point defect perturbations in silicon. This study investigates the interaction between oxidation-induced point defects and type II dislocation loops intentionally introduced in silicon via ion implantation. The type II (end-of-range) dislocation loops were introduced via implantation of either Si+ ions at 50 keV or Ge+ ions at 100 keV into <100≳Si wafers at doses ranging from 2×1015 to 1×1016/cm2. Furnace anneals were done at 900 °C for times between 30 min and 4 h in both a dry oxygen and nitrogen ambient. The change in atom concentration bound by dislocation loops as a result of oxidation was measured by plan-view transmission electron microscopy. The results show type II dislocation loops can be used as point defect detectors. When Ge+ implantation was used to form the dislocation loops, a decrease in trapped atom concentration relative to the control was observed upon oxidation. These results imply that oxidation of high dose Ge+ implanted silicon results either in vacancy injection or provides an excellent sink for interstitials. It is also shown that when Si+ implantation is used to form the dislocation loops, the measured net interstitial flux trapped by dislocation loops is linearly proportional to the total supersaturation of interstitials determined by oxidation-enhanced diffusion studies done by Packan and Plummer [J. Appl. Phys. 68, 4327 (1990)].
Determining energy-band offsets in quantum wells using only spectroscopic data
Authors: Koteles Emil S.
Published: July 2002

We have developed an experimental technique for accurately determining energy-band offsets in semiconductor quantum wells (QW) based on the fact that the magnitude of the ground-state light-hole (LH) energy is more sensitive to the depth of the valence-band well than is the ground-state heavy-hole (HH) energy. In a lattice-matched, unstrained QW system, this behavior causes the energy difference between the LH and HH excitons to go through a maximum as the well width, Lz, increases from zero. Calculations show that the position, and more importantly, the magnitude of this maximum is a sensitive function of the valence-band offset, Qv, the parameter which determines the depth of the valence-band well. By using Qv, or alternatively Qc=1−Qv, as an adjustable parameter and fitting experimentally measured LH-HH splittings as a function of Lz, an accurate determination of band offsets can be derived. However, we further reduce the experimental uncertainty by plotting LH−HH as a function of HH energy (which is, itself, a function of Lz) rather than Lz, since then all of the relevant data values can be precisely determined from absorption spectroscopy alone. Using this technique, we have derived the conduction-band offsets for several material systems, including lattice-mismatched systems and, where a consensus has developed, have obtained values in good agreement with other determinations.
Topographic effect of surface roughness on thin-film flow
Authors: Kim J. S. , Kim S. , Ma F.
Published: July 2002

This article addresses the effect of topographic structure of surface roughness on the flow of a thin film over a rotating disk. Six factors, namely centrifugation, surface tension, viscosity, air-shear, disjoining pressure, and surface roughness, that affect the depletion of the film are considered. Depletion histories of a thin film are given for cases involving deterministic as well as stochastic descriptions of surface roughness. It has been found that surface roughness of the disk plays a significant role in thin-film flow, and different topographic structures of the surface roughness lead to different asymptotic limits of liquid retention. The interplay of topographic parameters such as the height, skewness, and frequency of surface asperities on lubricant retention is also investigated.
Photoluminescence of ZnSe/ZnMnSe superlattices under hydrostatic pressure
Authors: Tuchman Judah A. , Sui Zhifeng , Kim Sangsig , Herman Irving P.
Published: July 2002

Photoluminescence near 4450 Å (violet) and 5900 Å (yellow) from ZnSe/Zn1−xMnxSe strained-layer superlattices (SLS) is studied as a function of applied hydrostatic pressure up to ∼90 kbar for x=0.23, 0.33, and 0.51 at 9 K. For each of the three SLSs, the peak energy of the near-band-gap violet photoluminescence (PL) from exciton recombination increases sublinearly with pressure, and closely follows that of ZnSe. The observed dependence is consistent with type-I band alignment, at least at pressures where the violet PL intensity remains strong. For the x=0.23 SLS, the energy of the biexciton PL increases faster than that of the exciton, which suggests decreased confinement. The yellow PL is due to the 4T1 →6A1 intraionic transition in Mn2+ and the nearly linear decrease of the peak energy of this signal with pressure is explained by crystal-field theory. In most cases examined, the intensities of the violet and/or yellow PL decrease abruptly above a certain pressure that increases with x from ∼65 to ∼90 kbar. For the different cases, this suggests either the occurrence of a phase transition in the ZnxMn1−xSe layers or a band crossing.
Illumination-dependent dynamic resistance of Hg1−xCdxTe heterojunction photodiodes
Authors: Graft R. , Fischer T. , Gray A. , Kennerly S.
Published: July 2002

Experimental data are presented on the illumination dependence of the dynamic resistance of long-wave infrared heterojunction photodiodes and the results are interpreted using a numerical drift/diffusion device model. The diodes are double-layer heterojunctions grown by liquid-phase epitaxy; nominal cutoff wavelength, zero-bias quantum efficiency, and resistance area product are 10.6 μm, 76%, and 210 Ω cm2 (77 K), respectively. It is shown that for a single-sided p-on-n heterojunction, the illumination dependence is due to an increase in hole current resulting from a voltage-dependent increase in the base layer diffusion current. Calculated results are provided as a function of relative hetero- and p-n junction location and applied reverse bias. The results are compared with experimental data obtained on back-illuminated HgCdTe heterojunction diodes. An interpretation based upon the voltage dependence of the hole concentration at the depletion edge is presented and contrasted with recent models appearing in the literature.
Radio frequency sputtered cobalt oxide coating: Structural, optical, and electrochemical characterization
Authors: Estrada W. , Fantini M. C. A. , de Castro S. C. , Polo da Fonseca C. N. , Gorenstein A.
Published: July 2002

Cobalt oxide thin films (thickness 2000 Å) with different stoichiometries were deposited by reactive rf sputtering. The variation of the oxygen partial pressure lead to films with compositions varying from metallic cobalt to CO3O4, as determined by x-ray diffraction and x-ray photoelectron spectroscopy. The electrochromic properties of the films were investigated in aqueous electrolytes (0.1 M KOH). The initial electrochemical behavior of the films is strongly dependent on the film deposition conditions, but after cycling the electrochemical/electrochromic characteristics of the different deposits were quite similar. Transmittance changes and electrochromic efficiency are discussed.
In situ scanning-tunneling-microscopy studies of current driven mass transport in Ag
Authors: Levine L. E. , Reiss G. , Smith D. A.
Published: July 2002

We present the results of an ultrahigh vacuum (UHV) scanning-tunneling-microscopy study of large scale mass transport in current carrying metal films. Scans were taken in situ on a current carrying 2100-Å-thick Ag film with current densities ranging from 5.0×104 A/cm2 up to 3.2×105 A/cm2, at which point the sample failed due to a runaway thermal fusing mechanism. Axial UHV inchworms allowed us to obtain data from the same 2-μm-square region of the sample throughout the experiment in spite of large temperature-induced drifts. Calculations of the driving forces demonstrate that the electromigration driving force was dominant for this current range. Significant topographical changes were observed including current aligned grain growth, current induced faceting, and complex mass flow divergences. A model that explains the observed divergences is presented. It is based upon diffusion in the presence of local inhomogeneities of the electric field.
Photorefractive effect in a poled polymer containing the tricyanovinylcarbazole group
Authors: Kippelen B. , Tamura K. , Peyghambarian N. , Padias A. B. , Hall H. K.
Published: July 2002

The photorefractive properties of a poled polymer containing the tricyanovinylcarbazole group with an alkylene spacer are investigated by four-wave mixing experiments and Mach–Zehnder type electro-optic measurements. The photorefractive effect is demonstrated in a polymer that shows both the photoconductivity and the electro-optic effect intrinsically.