ALBERT

Notes: The evolution of stress and strain during the consolidation of a fluid-saturated porous elastic sphere subjected to a uniform normal surface traction is investigated. The solution of Cryer [Q. J. Mech. Appl. Math. 16, 401 (1963)] for the pore fluid pressure is extended by deriving and fully analyzing new analytical solutions for the strain tensor of the elastic skeleton, the total stress tensor, the trace-free stress deviator tensor, and the effective stress tensor. Asymptotic expansions for small values of time of the stress and strain components, which determine the behavior of these components during the initial stages of the consolidation, are derived. Computer-generated graphs of the exact analytical solutions are presented, which provide insights regarding the redistribution of stress and strain throughout the consolidation. As fluid is expelled from the outermost layers of the sphere, fluid discharge builds up quickly to a peak rate and then subsides slowly as successively deeper layers are drained. During this initial consolidation, the stresses, strains, deviator stresses, and effective stresses within the outermost layers all change very rapidly. The nature of the Mandel–Cryer effect (pore fluid pressure increase within the sphere during initial fluid expulsion) is illuminated. Two other quantities, the transverse component of the total stress tensor and the total mean normal pressure, also show changes of opposite sign in the near surface and deeper regions, respectively: diminution in the outermost layers and simultaneous increase in the deeper portions. All of these effects are derived from Biot's theory of poroelasticity, in which the dilatation satisfies the diffusion equation.

Notes: An experimental procedure has been developed to measure electron emission due to energetic ion bombardment during plasma source ion implantation. Spherical targets (radius=2 cm) of copper, stainless steel, graphite, titanium alloy (Ti-6Al-4V) and aluminum alloy (6061) were biased negatively to 20, 30, and 40 kV in argon and nitrogen plasmas. A Langmuir probe was used to detect the propagating sheath edge and a Rogowski transformer was used to measure the current to the target. The measurements of electron emission coefficients compare well with those measured under similar conditions [B. Szapiro and J. J. Rocca, J. Appl. Phys. 65, 3713 (1989)].

Notes: This paper addresses issues related to migration and acceptor neutralization of hydrogen (H) in crystalline Si. From spreading resistance measurements, it is shown that disordered regions, both surface and subsurface, directly inhibit the penetration of H. Further, these effects are shown to be independent of the kind of disorder and the method of hydrogenation. Secondary-ion mass spectrometry profiles of deuterated samples confirm the suppression of deuterium movement through the disordered regions. We observe that annealing of these hydrogenated damage regions results in generation of an acceptor deactivation profile which is persistent for temperatures up to 800 °C and durations up to 1 min. This sustained deactivation phenomenon results in up to four decade change in free-carrier concentration. Our results unequivocally suggests that H-soaked damage region acts as a source of atomic hydrogen under rapid thermal annealing.

Notes: Fast C-V measurement techniques are utilized to simultaneously probe both upper and lower interfaces of silicon-on-insulator/separation by implantation of oxygen buried oxide capacitors following exposure to pulsed ionizing irradiation. In addition to the relatively stable radiation-induced positive charge, reverse annealing is observed from both Si-SiO2 interfaces over the 200 μs to 300 s post exposure interval; this behavior is consistent with electron detrapping within the oxide. The dependence of electron detrapping on dc annealing bias is attributed to field-enhanced emission effects.

Notes: Capacitance and conductance measurements are presented for dc-driven Au/ZnS:Mn/p-Si electroluminescence metal-insulator-semiconductor (MIS) devices, where the ZnS:Mn films are deposited by radio frequency sputtering. Stable dc operation is achieved by introducing oxygen into the film during deposition and subsequently annealing. The effect of the post-deposition annealing upon the density of states at the ZnS:Mn/p-Si interface is investigated. As deposited, the devices show unusual MIS C-V characteristics, that indicate a very high interface state density. Annealing at 700 °C, normal C-V characteristics are observed, indicating that the very high density of states is greatly reduced. For these films the conductance technique has been used to measure the density of states at the interface between the ZnS:Mn and p-Si. The statistical model is found to describe most accurately the interface state conductance response. The interface state density consists of a tail of states that varies between 3.7×1013 cm−2 eV−1 at the silicon Fermi level and 1.1×1013 cm−2 eV−1 at the silicon mid-gap. A small peak is superimposed upon this tail at (−0.16±0.01) eV below mid-gap. The tail of states is believed to be intrinsic to the ZnS:Mn/p-Si interface, but evidence suggests that the small peak is due to the presence of oxygen, which is shown by secondary-ion mass spectrometry analysis to accumulate at the interface after annealing at 700 °C. It seems likely that the very high density of interface states in as deposited devices is a consequence of a plasma damage to the silicon surface during growth, creating defects such as silicon dangling bonds. One possible explanation for the decrease in this density is that by annealing at 700 °C, oxygen in the bulk of the film diffuses to the interface, where it mops up these defects by forming compounds such as SiOx. A simpler model of interface recrystallization is also suggested. The doping density in the depletion region of the silicon is calculated as (7.5±0.5)×1014 cm−3, and the interface state capture cross section for holes is found to have mean value of approximately 10−15 cm−2.

Notes: The correlations between structural quality and superconducting behavior in 1000-A(ring)-thick Ba2YCu3O7−δ (BYCO) films grown on LaAlO3(100) from the coevaporation of BaF2, Y, and Cu, followed by an optimized ex situ annealing process are reported. Epitaxial films with smooth, laminar morphology and excellent crystallinity can be grown to have critical current density Jc values nearly identical to single crystals. This finding contrasts with the typical observation that Jc values in thin films of BYCO are very high compared to those of single crystals. This is attributed to a greater density of flux pinning sites due to structural defects within the films. The most crystalline films presented here have penetration length λ∼2000 A(ring) with temperature dependencies described well by the Bardeen–Cooper–Schrieffer (BCS) theory. Material disorder of two types can be controlled by the high-temperature stage Ta of the annealing process. The first type is point defects and dislocations the same size or smaller than the coherence length ξab, which Rutherford backscattering/channeling suggests decrease in number with increasing Ta. The second is crevices, pinholes, and microcracks, which are at least one to two orders of magnitude larger than ξab. At Ta 〈 850 °C, crevices, which create areas of nonuniform thickness, occur due to incomplete epitaxial growth and correlate with the presence of weak links. Hence film resistivity is high, Tc is low, and λ is large. As Ta is increased, the film morphology becomes smoother and all electrical properties improve, except for Jc in nonzero applied magnetic fields, since the improved epitaxy correlates with reduced flux pinning. By Ta= 900 °C, the BYCO films are similar to single crystals in both cation alignment and Jc behavior. Above this annealing temperature, pinholes and microcracks develop and increase in both size and density with increasing Ta. Although these relatively large defects do not act as weak links, they do affect magnetic screening (and hence λ), to result in an anomalous temperature dependence that masks the intrinsic BCS behavior.

Notes: The changes in the real index of refraction and the optical absorption for conduction intersubband transitions in AlxGa1−xAs/GaAs/AlxGa1−xAs quantum wells are examined as a function of the carrier density. Various values for the input optical field and quantum well width are considered in the calculations. The linear contribution due to χ(1) as well as the nonlinear contribution from χ(3) is included. The relationship of the results to device applications such as waveguides and optical modulators is discussed.

Notes: In0.32Ga0.68P epitaxial layers doped with Te and Zn were grown on (100) GaAs0.61P0.39 epitaxial substrates by liquid-phase epitaxy using a supercooling method. The electrical properties of doped layers were determined by C-V measurements at 300 K. Room-temperature carrier concentrations ranging from 9×1016 to 2×1018 cm−3 for n-type and from 3×1016 to 6×1018 cm−3 for p-type dopants are obtained reproducibly. The full width at half maximum value of the 300 K photoluminescent spectrum increases with carrier concentration for Te- and Zn-doped layers. The relative intensity of 300-K photoluminescent peak presents the maximum values at 1×1018 and 6×1017 cm−3 for electron and hole concentrations, respectively. The 100-K photoluminescent spectra show three distinctive peaks and their relative intensities change with hole concentrations. Finally, the relationship between the acceptor ionization energy and hole concentration is described.

Notes: The magneto-optical polar Kerr rotation spectra and reflectivity spectra in the wavelength region 400–700 nm are studied for Fe/PbTe and Fe/Pb bilayer films. Large Kerr rotation enhancement with high reflectivity was observed. The experimental data of reflectivity are nearly consistent with theoretical calculation using Fresnel's equations. However, the observed Kerr rotation spectra behavior is quite different from that expected by macroscopic optical theory.

Notes: Metal transfer has been analyzed using both the static force balance method and the pinch instability theory. The influences of arc pressure as well as electromagnetic pressure in the development of instability in the cylindrical molten metal were considered. Using perturbation theory, the dispersion equation was obtained in terms of the arc current density, and the drop diameters were then calculated. The drop diameters, which were determined by considering the arc effect, were found to be greater than those drop diameters that were obtained without the arc effect. The transition current was obtained on the assumption that necking starts when the arc covers an entire drop, at which point spray transfer occurs as the molten droplet becomes cylindrical in shape. This explains why spray transfer or transition does not appear with carbon dioxide or helium shielding gas since the arc then exists only at the lower half of the droplet.

Notes: The photoquenching of EL2 in semi-insulating gallium arsenide is seen to be a complex process, where at low temperatures the initial slow quenching is followed by a switch to fast quenching. A possible explanation involving lattice strain mediated cooperative structural relaxation arising out of transition to the metastable state is proposed.

Notes: The critical temperature (Tc) of sintered and melt-textured YBa2Cu3O7+x samples carrying current with different rms values and frequencies were measured. The low-frequency self-field effect on the Tc value is reported here. For the sintered samples, Tc shifts with both the rms value and the frequency of applied transport current. A similar effect is not observed in the melt-textured samples.

Notes: Aluminum cluster ions Al+n are generated by a liquid metal ion source and observed up to n=10 using a magnetic mass analyzer. Relative integrated intensities of cluster ions as a function of n show a distinct step between n=7 and 8, which is explained by the electronic shell model. Cluster ions have lower kinetic energy compared with monomer ions which are accelerated to the full energy. Moreover, energy spread of cluster ions is larger than that of monomer ions. These results are attributed to the difference of ion formation mechanism. In addition to the fully accelerated monomer ions, at a high ion current region there also appear monomer ions with energy deficit which are formed in the same process as cluster ions.

Notes: Analytical approximations are derived for treating isotropic nonparabolic bands in the framework of the Joyce–Dixon approximation [W. B. Joyce and R. W. Dixon, Appl. Phys. Lett. 31, 354 (1977)]. The approximations are worked out for three-, two-, and one-dimensional idealized systems. Example calculations illustrate the utility of the methods for the narrow-gap III-V compounds, such as InAs and InSb, which are now being developed for device applications.

Notes: Modern techniques of functional minimization are applied to the one-dimensional profile inversion problem. The procedure is applied to profiles that can be represented as a series of linear ramps. A band-limited knowledge of the transmission function is used to determine the parameters that describe the profile. It is found that simple profiles can be readily determined. For more involved profiles, the method of simulated annealing proves to be helpful in obtaining the correct profile.

Notes: The uniform deposition of the oxide nitride oxide (ONO) film on the tunnel-structured polysilicon electrodes was examined by measuring the electrical characteristics of the capacitor and by using transmission electron microscopy. The conventional low pressure chemical vapor deposition method was adopted for the deposition of the nitride film of the ONO. The tunnel length is varied from 1.6 to 15.6 μm. The ONO film deposited over the entire tunnel of 15.6 μm showed good electrical characteristics, and the thickness uniformity as well. In addition to the maximum tunnel length which can accommodate the uniform ONO deposition, the growth mechanism of the ONO film inside of the tunnel is discussed.

Notes: Superconducting YBa2Cu3O7−x films have been deposited in situ onto III-V superlattice substrates. The substrates were GaAs/AlAs superlattices grown by molecular beam epitaxy onto GaAs substrates. For 5000-A(ring) -thick YBCO films grown at 615 °C substrate temperature, we have obtained Tc of 73 K. For thinner films the Tc's are lower, indicating poor interfaces. However, the onset of the superconducting transition is 90 K in all cases. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy (TEM) show these films to be polycrystalline. TEM shows an interaction layer of about 1000 A(ring) at the interface. Low-temperature cathodoluminescence measurements of the substrate show that atomic interdiffusion has intruded at least 5000 A(ring) below the interface.

Notes: Results of combined ac capacitance and conductance measurements on two-terminal metal-oxide-semiconductor-oxide-semiconductor capacitors fabricated in a silicon-on-insulator substrate formed by oxygen implantation are presented for the first time. We demonstrate the efficiency of the technique to investigate the presence of bulk traps presumably caused by metallic contaminants introduced during the high-energy oxygen implantation, as well as to determine the interface trap density at the buried oxide/Si substrate interface.

Notes: We have measured the tensor components c1111 and c1221 of third-order nonlinear optical susceptibility of two nematic liquid crystals, MBBA (p-methoxy-benzylidene p-n-butylaniline) and EBBA (p-ethoxy-benzylidene p-n-butylaniline), in the picosecond regime. We observed that the molecule with ethoxy group (EBBA) has a larger third-order nonlinearity than the one with methoxy group (MBBA) and present a model to explain this effect.

Notes: The thermally stimulated discharge current (TSD) behavior of native (dark rested) and irradiated amorphous selenium films (∼100 μm) has been studied in the temperature range 295–385 K. The TSD spectra of these films shows, in addition to the already reported relaxation at 310 K, a new relaxation peak in the temperature range 370–380 K. The origin of this relaxation is attributed to the trapping of charge carriers i.e., electron and holes at deep intrinsic and irradiation induced photostructural defect levels lying at ∼1.6 and 1.7 eV, respectively.

Notes: MeV He ion implantation is used to produce optical waveguides in KTa1−xNbxO3 (x=0.37). The detailed refractive index profiles of the implanted planar waveguides are reconstructed from the measured mode spectra at the wavelength of 632.8 nm. The absorption and the tunneling losses of the lowest mode of the waveguides are determined. Ionic collision is proposed to be the mechanism which causes the observed variation of the refractive index.

Notes: We observe that the crystallization of amorphous Si thin films in contact with a copper silicide layer occurs at a temperature of around 485 °C in the form of dendrites with a fractal dimension of 1.7. The in situ observation of both the silicidation reaction, forming Cu3Si, and the subsequent crystallization of the remaining amorphous silicon in the silicide matrix, were observed during annealing in a transmission electron microscope. We estimate the radial growth rate of these crystallites at 5 nm/s at this temperature. The fractal dimension of the dendrites indicates a growth process similar to one known as diffusion-limited aggregation.

Notes: A variety of diagnostics measure fluctuating quantities at a small number of locations. A common method to estimate the wave-number spectrum S(k) at a given frequency is to make many measurements of the "local'' wave number kl, which is the phase difference between two locations divided by their separation. The random-phase model allows the synthesis of a typical signal from a given S(k). We apply local wave-number analysis to such synthetic signals and show that, in the limit of small separation, the power-weighted mean of kl accurately reflects the mean of S(k), and the width of the distribution is exactly (large-closed-square) times smaller than the width of S(k). We also show that no information on the shape of S(k) exists in the measurements. Finally, we generalize these results to finite separations, finite measurement volumes, and any number of locations.

Notes: The effect of two-wavelength oscillation for short-optical-pulse generation in laser diodes by sinusoidal current modulation has been investigated using a rate equation analysis. A high peak power and short pulse without a tail can be generated at the shorter wavelength λ2 with the help of carrier damping through carrier-photon conversion at the longer wavelength λ1. This can be obtained provided that the cw threshold current for λ1 is lower than that for λ2 and the gain g2 larger than g1 at the high carrier excitation levels that occur under the conditions of gain switching.

Notes: This paper describes a computer simulation for oxygen precipitation in silicon crystals subjected to thermal treatments. In the simulation based on the classical nucleation theory, it is assumed that an oxygen precipitate is spherical and its nucleus is a carbon atom. In addition, to explain oxygen precipitation at high temperatures, the simulation takes into consideration coarsening of the precipitate, which is inferred from obtained three-step annealing results. Simulated results are compared with experimental results obtained from a complementary metal-oxide-silicon transistor thermal process in addition to the three-step annealings results. As a result, it is proven that the proposed simulation can predict the precipitated oxygen concentration in wafers subjected to various thermal treatments.

Notes: When crystalline solids are subjected to shock or impact the resulting plastic shear deformation is often concentrated in narrow-band-like regions. These regions are the sites of considerable energy localization and often determine the response of the crystal to the rapid deformation. Here, a theoretical account is given of this energy-localization plastic-deformation process. It is shown that the process is distinctly quantum mechanical. For mild shocks or impacts the energy dissipated within the bands can cause heating, material failure, and, where appropriate, chemical reactions. For high-amplitude shocks rapid multiphonon-stimulated internal molecular excitation can occur. This energy localization is responsible for both the initiation of chemical reaction in explosive crystals subjected to mild impact and the transition to detonation in these same crystals during high-amplitude shock loading.

Notes: We have developed a high-purity, intense, lithium ion beam source which operates at 500 kV and 120 A/cm2 with pulse widths of 125 ns full width half maximum. The beams were generated using a lithium chloride anode in planar magnetically insulated geometry. We have found that the combination of vacuum baking of the anode at 250 °C followed by the application of 100 W of pure argon, steady-state, glow discharge cleaning reduced the impurity concentration in the beam to approximately 10% (components other than chlorine or lithium were considered impurities). Although the impurities were low, the concentration of chlorine in the 1+ and 2+ charge states was significant (∼25%). The remaining 65% of the beam consisted of Li+ ions. Without the special cleaning process, over half the beam particles were impurities. It was determined that these impurities entered the beam at the anode surface but came originally from material in the vacuum chamber. After the cleaning process, recontamination was observed to occur in approximately 6 min. This long recontamination time, which was much greater than the expected monolayer formation time, was attributed to the elevated temperature of the anode. We also compared the electrical characteristics of the beams produced by LiCl anodes to those generated by a standard polyethylene proton source. In contrast to the polyethylene anode, the LiCl source exhibited a higher impedance, produced beams of lower ion current efficiency and had longer turn on times.

Notes: The existence of an absorbing layer, or buffer zone, of weakly ionized gas between the rear of the projectile and the front of the plasma arc armature in a plasma accelerator has been postulated. In the studies reported here a technique for finding the position of the projectile as a function of time is given and compared to the plasma armature position as determined by inductive probes. Analyses of these signals provide the basis for a description of the in-bore motion of the projectile with respect to the plasma arc armature. The experimental evidence appears to support the existence of a buffer zone.

Notes: For a cylindrical aluminum conductor, 0.2 cm in diameter and loaded by a current pulse from an overdamped discharge with an initial current rate of 490 kA/μs, dynamic pinch compression and temperature rise have been calculated. The numerical solution for the azimuthal distribution of the pinch pressure, obtained by applying Picard's method of successive iteration, consists of the superposition of a quasi-stationary and a transient term. In the very initial phase of pinching a steep, narrow pressure pulse is created below the surface of the wire which converges at the center, thereby broadening in width, growing in strength, and increasing in propagation velocity. Already in the early stage of current flow at about 0.4 μs, well before reaching maximum current and pinch pressure, the quasi-stationary term becomes dominant. Then the conductor is compressed quite homogeneously with the exception of a narrow shell below the surface where maximum pressure gradients exist. For applications on dynamic materials research various experimental aspects of dynamic pinch compression and possible high-speed methods of sample diagnostics are reviewed.

Notes: Compensation profile in ion-implanted GaAs has been analyzed by the simulation based on the Boltzmann transport equation. Comparing the simulations with experiments, we found that the compensation profile was originated in two types of defect distribution. One was created by deposited energy and the other was created by the implanted ions in the material. These two compensation profiles have two different energy levels, since the so-called L band splits into two peaks in deep level transient spectroscopy after annealing the sample. Based on the simulated results, we also introduced two different compensation yields of ion implantation.

Notes: The chemistry of an argon-ion-irradiated interface between an amorphous silicon dioxide film and a silicon single-crystal substrate was studied by determining the kind and depth distribution of compounds formed after nitrogen implantation at a depth more shallow than the SiO2 film thickness. With this study we intended to obtain some insight into the chemical and physical processes involved in the formation of silicon oxynitrides in silica as a consequence of nitrogen ion implantations. Samples were mainly characterized by x-ray photoelectron and Fourier-transform infrared spectroscopies. Scanning electron microscopy, Rutherford backscattering spectrometry, nuclear reaction analysis, and secondary-ion mass spectrometry techniques were also used to complete the set of results. The experimental evidences are consistent with a picture of an argon-induced radiation damage in terms of Si—O and Si—Si bond breaking in the SiO2 and in the silicon substrate regions, respectively. The subsequently implanted nitrogen atoms are drawn toward the interface by a chemical driving force, and there interact with unsaturated silicon bonds to produce SiOxNy or SiNz compounds. The formation of a large amount of these compounds at the interface is responsible for very rough surface morphological features.

Notes: The diffusion of iron and zinc in InP is studied with secondary-ion mass spectrometry (SIMS). Intentionally doped metalorganic-vapor-phase-epitaxy- (MOVPE-) grown layers as well as ion-implanted samples were investigated. In addition, resistivity measurements were performed on MOVPE-grown, iron-doped InP layers. The diffusion behavior of iron is strongly influenced by the presence of zinc and vice versa. In adjacent regions of iron and zinc-doped layers of InP there is a dramatic interdiffusion of both dopants. The interdiffusion process can be described with a kick-out mechanism in which iron interstitials kick out substitutional zinc. The diffusion of the iron interstitials is an extremely fast transport process in InP, but the concentration of iron interstitials remains below 5×1014 at cm−3. Due to this fast transport, the interdiffusion process proceeds even through barrier layers of (undoped) InP, while in the barrier layer itself the iron concentration remains below the SIMS detection limit (〈5×1014 at cm−3). A sulphur-doped, n-type layer of InP stops the diffusion of iron. The semi-insulating properties of iron-doped layers of InP are affected by the interdiffusion process of iron and zinc. Since sulphur-doped InP inhibits the interdiffusion, such a layer can be applied as a barrier layer to separate zinc-doped and iron-doped regions in InP and thus preserve the semi-insulating character of the iron-doped InP.

Notes: We use in situ photoluminescence (PL) to investigate recombination at (100)GaAs surfaces and GaAs/AlGaAs interfaces in a controlled crystal growth environment. PL was monitored for different GaAs surface reconstructions, after surface chemical modification, and during early stages of AlGaAs heteroepitaxy. Depositing ∼1 ML of Se to form a (2×1) surface increased the GaAs PL intensity 200 times. Surprisingly, it required 6 ML (15 A(ring)) of heteroepitaxial AlGaAs to achieve the same degree of surface passivation. We invoke lateral variations in interfacial AlGaAs composition to explain these results.

Notes: Phase formation and growth kinetics have been investigated with lateral diffusion couples in Cu-Si and Cu-Ge systems. Analytical electron microscopy was used to determine the crystal structures and chemical compositions of the growing phases. Cu3Si is found to be the dominant phase in the Cu-Si system. The growth of the silicide follows a (time)1/2 dependence with an activation energy of 0.95 eV in the temperature range of 200–260 °C. Cu3Ge is the only phase observed in Cu-Ge lateral diffusion couples with its length up to 20 μm. The growth of Cu3Ge is a diffusion controlled process at a rate similar to that of Cu3Si. The activation energy of Cu3Ge growth is 0.94 eV at 200–420 °C. In Cu-silicide or Cu-germanide formation, Cu appears to be the dominant diffusing species.

Notes: The critical volume fraction, at which the conducting component in conductor-insulator mixtures first becomes continuous or percolates, plays a very important role in both percolation theory and the generalized effective-media equation. The growth mechanism, by which very low (≤0.05) critical volume fractions for nearly spherical conducting powders in insulating hosts, such as polymers, are obtained, is not well understood. In this paper a simple model, based on the computer-generated model of Roberts and Schwartz [Phys. Rev. B 31, 5990 (1985)] for grain consolidation in porous media, for the very low critical volume fractions observed in some conductor-insulator mixtures is proposed.

Notes: Inelastic electron tunneling spectroscopy (IETS) is used to record the vibrational spectra of thin films of amorphous SiOx prepared by radio-frequency planar magnetron sputter deposition in argon. The SiOx films are incorporated as the insulating barriers in aluminium SiOx/lead tunnel junctions, with no prior or subsequent oxidation of the aluminium films. Peak assignments are presented by comparison with infrared, Raman, and neutron scattering data for bulk silica, and a plausible stoichiometry is proposed. The SiOx barriers can be considered as model glass substrates for further adsorption studies, and hence extend the analytical capabilities of IETS.

Notes: The long-term compositional stability of hydrogenated and deuterated amorphous germanium was studied by infrared absorption measurements. The results reveal for substrate temperatures below about 200 °C the growth of a void-rich material which is oxidized rapidly by ambient oxygen and water.

Notes: We present a method for characterizing liquid-solid phase transitions by using an acoustic shear horizontal (SH) plate mode sensor. The sensor consists of a Y-cut quartz plate provided with suitable interdigital transducers on the lower surface. To study the temporal evolution of a phase transition, the liquid is deposited in a thin layer on the upper surface and the SH mode attenuation is observed as a function of time during a programed temperature change. With this sensor the theoretical time resolution is about 1 μs. Experimental results are presented for the liquid-solid transition for deionized water, tap water, and 90%/10% mixture of tap water and ethanol, measured with an instrument time resolution of 50 ms.

Notes: The tunneling mechanism responsible for negative differential resistance in GaSb/AlSb/GaSb/AlSb/InAs double-barrier interband tunneling structures was studied systematically. It was found that the peak current results from resonant interband tunneling and that the spacers make a significant contribution to the valley current. Furthermore, the optimal thicknesses for the GaSb well and AlSb barriers were predicted to be 65 and 10 A(ring), respectively, which agrees fairly well with experimental results. Our theoretical results give some useful design principles for this type of interband tunneling device.

Notes: We have performed metalorganic chemical vapor deposition (MOCVD) on substrates of closed topologies, i.e., on a single cylindrical surface and on multiple cylindrical surfaces of ∼1000-A(ring)-diam rods. The side geometry of epitaxial growth can be controlled by rod direction, growth temperature, and ratio of the amount of group-V material to that of group-III materials. We have succeeded in growing mesoscopic multiply connected AlAs with multiplicity up to 6. The MOCVD growth on substrates with closed topology is of potential interest for fabrication of sophisticated mesoscopic structures.

Notes: Motivated by the recently developed experimental capability of ballistic-electron-emission microscopy (BEEM), we study the effect of phonon scattering and quantum mechanical reflection on the ballistic transport across the Schottky barrier from the metal into the semiconductor. We argue that, for the Schottky barrier formed by a metal overlayer on a semiconductor substrate, one can typically expect the quantum mechanical transmission probability to have an E1/2 dependence, where E is the electron kinetic energy in the final state. We make a distinction between the metallurgical metal/semiconductor interface and the Schottky barrier energy maximum resulting from image potential, and calculate the optical phonon scattering rate between the interface and the maximum. We compute the combined effect of optical phonon scattering and quantum mechanical scattering on the ballistic transport for an initially isotropic velocity distribution of electrons in the metal, and we show that the two scattering processes combine to give a much weaker energy dependence than for either effect alone for cases of the Au/Si and Au/GaAs at both 300 K and 77 K. We use our model to show that the magnitude of the BEEM current for Au/Si should be roughly 5 times larger than for Au/GaAs and that decreasing the temperature from 300 K to 77 K should increase the magnitude of the BEEM current for Au/GaAs by a factor of about 3. There is fairly good agreement between our predictions and the available experimental evidence.

Notes: The variation of the Schottky barrier height ΦB of Au/n-CdTe contacts with the Cd/Te ratio at the substrate's surface has been investigated. X-ray photoelectron spectroscopy measurements show that this ratio increases with the anneal temperature Ta up to 330 °C. The Schottky barrier height reaches a maximum for near stoichiometric substrates. Mixed regions of Te and Au, due to etching and subsequent surface disruption by Au, determine ΦB at low Ta. The ΦB value as expected for the ideal Au/n-CdTe contact (following the work-function model) is found for stoichiometric surfaces. At high Ta an increasing nonstoichiometry produces decreasing ΦB values. Our measurements show that the interfacial reactivity decreases with the number of defects. This offers us a general explanation for the observed ΦB behavior, based upon reactivity at nonstoichiometric surfaces.

Notes: A theory of phonon-assisted cyclotron resonance in quasi-two-dimensional semiconductor quantum-well structures is given. Using perturbation technique, expressions for absorption coefficients are obtained when the electrons are scattered by acoustic, nonpolar, and polar optical phonons. Extra peaks in the absorption spectrum due to transitions between Landau levels accompanied by emission and absorption of phonons are predicted. Numerical results for the frequency, magnetic field, and temperature dependence are given for parameters characteristic of GaAs.

Notes: Drag pressures of a levitation mechanism are investigated. The levitation mechanism consists of a high-Tc superconductor tile (type II superconductor) and a set of alternating-polarity bar magnets of the same size. Relationships of the drag pressure to the distance between the magnets and the superconductor tile and to the width of a bar magnet are investigated. The drag pressure becomes small rapidly with increasing distance. The drag pressure becomes large with the superconductor-magnets distance decreasing. If the distance is fixed there exist a width of a bar magnet providing a maximum drag pressure. The drag pressure is also measured when the superconductor is moved in the direction of the alternating polarity.

Notes: We measure the complex conductivity of thin superconducting niobium films using coherent time-domain terahertz spectroscopy. Both real and imaginary part of the conductivity are measured simultaneously without referring to the Kramers–Kronig relations. We also measure the superconducting band gap directly from the onset of absorption and compare our results with theory.

Notes: Three diphenyl-diacetylene nematic liquid-crystal homologs were synthesized and two mixtures formulated. Dielectric constant, threshold voltage, splay elastic constant, birefringence, order parameter, and rotational viscosity of these liquid crystals were evaluated at elevated temperatures. These highly conjugated liquid-crystal mixtures are found to exhibit a large birefringence, relatively low viscosity, wide nematic range, and modest dielectric anisotropy. Potential applications of these liquid crystals in high definition displays, infrared spatial light modulators, and high-speed light switches are foreseeable.

Notes: Boron nitride films prepared by reactive ion plating from a boron evaporation source were characterized structurally using three independent electron optical techniques: energy filtered electron diffraction with radial distribution function analysis; electron energy-loss spectroscopy of the near-edge structure of the boron K edge; and spectroscopy of the plasmon region of the energy-loss spectrum. Both specimens had a graded BNx layer between the BN layer and the silicon substrate and in addition one specimen had a titanium bonding layer underneath the BNx layer. The presence of c-BN in both specimens was confirmed by all techniques. The specimen with the titanium bonding layer was examined in cross section and showed essentially pure c-BN on the surface. A model for the formation of c-BN assisted by the compressive stress generated during deposition is proposed.

Notes: D-line luminescence at the photon energies of 0.81 and 0.87 eV in Czochralski silicon containing extended dislocation loops has been characterized. In samples containing a high-oxygen concentration and in tin-doped samples, the D-line luminescence was observed. In contrast, no D-line luminescence was detected in samples containing a low-oxygen concentration, except when the sample was deliberately contaminated with Cu. The results clearly indicate that the optical centers responsible for the D-line luminescence are associated with an interaction between the dislocations and impurities. It is hypothesized that the optical centers responsible for the D1 line at 0.81 eV could be associated with an interaction between the edge dislocation component of the dislocation loop and impurities, while the D2 line at 0.87 eV could be produced as a result of an interaction between the screw dislocation component and impurities.

Notes: In the growth of pseudomorphic strained layers, the critical thickness is the thickness up to which relaxation does not occur and beyond which relaxation occurs by plastic deformation of the layer. Previous theories have concentrated on the strain energy and kinetics of dislocation formation. We present a purely geometrical argument which predicts critical thicknesses and also predicts how relaxation progresses with increasing thickness. We find that the critical thickness, in monolayers, is approximately the reciprocal of the strain. Some relaxation occurs abruptly at critical thickness, and further relaxation is hyperbolic with thickness. The model can also handle multilayer structures. If all the layers have the same sign of strain, the model predicts that relaxation will occur at the lowest interface. These results are found to be in good agreement with experimental observations of dislocations in epitaxial structures of InGaAs grown on GaAs.

Notes: The production of stable vacancy-related point defects in silicon irradiated with 1.3 MeV protons has been studied as a function of ion flux (protons s−1 cm−2), while keeping the total fluence constant. Since the total fluence was very low (5 × 109 protons cm−2), no interference between neighboring ion tracks was expected. The defect concentrations have been measured by deep-level transient spectroscopy, and a decrease in the resulting defect density is found for increasing flux. This effect was unexpected and shows that there is an overlap between ion tracks, in spite of the low fluence. The behavior is attributed to the rapidly diffusing silicon interstitials, which overlap the vacancy distributions produced in adjacent ion tracks. When the ion flux is low, the distribution of vacancies from one ion becomes diluted and recombination with interstitials from ions impacting at a later time is rare. As the flux is increased the vacancy distribution from one ion will still be confined to a small volume when it is overlapped by interstitials from a later ion, leading to an increased recombination of vacancies and interstitials. Thus, within this low-fluence regime, the total concentration of stable vacancy-related defects decreases for a high flux. This result is supported by computer simulations of the defect generation kinetics.

Notes: Samples of R2Fe17CyNx (R=Y, Sm, Er, Tm) were prepared by arc melting appropriate amount of R, Fe, and C, vacuum annealing at 1373 K and finally annealing at 740 K in nitrogen for 10 h. The magnetic properties of these compounds were investigated by means of ac initial susceptibility, magnetization measurements, and x-ray diffraction. The thermal stability of the nitride phase was studied by differential scanning calorimetry. It was found that, when heated above 600 K, R2Fe17CyNx irreversibly decomposes N which is irrespective of the carbon concentration and rare-earth element. The Curie temperatures of R2Fe17CyNx are independent of the carbon concentration and are approximately 400 K higher than those of the corresponding pure R2Fe17 compounds. However, the Curie temperatures cannot be correlated to the composition x of the initial R2Fe17CyNx compounds at room temperature because some N was lost during the heating to Tc. In the Er and Tm compounds spin reorientation transitions were found, marking the change of the easy magnetization direction from the c axis to the basal plane with increasing temperature. The Tm compounds show an additional magnetic transition at low temperatures (below 40 K). A coexistence of the hexagonal and the rhombohedral structural modifications was found in Er2Fe17CyNx when y〈1.5, characterized by two different spin reorientation temperatures. The anisotropy fields of Sm2Fe17CyNx are higher than that of Sm2Fe17Nx. Indications of a magnetic phase transition were found also in Sm2Fe17C0.7Nx and Sm2Fe17C0.9Nx.

Notes: Films with a composition PbZr0.53Ti0.47O3 were prepared on different platinum bottom electrodes using a spin-coating process followed by metalorganic decomposition. The film morphology and structure were characterized by scanning electron microscopy and x-ray diffraction analysis. The morphology was strongly influenced by the heat cycle used to form the PbZr0.53Ti0.47O3 layer. Fast heating and high-fire temperatures produced smooth films, while slow heating and low-fire temperatures gave films having a rosette perovskite phase and an inter-rosette second phase. The films were characterized electrically by measuring hysteresis loops and capacitance and conductance versus bias voltage and by pulse-switching measurements. The dependence of the switched and nonswitched polarization on the number of switching cycles (i.e., the fatigue behavior) is found to be much better for fast-heated than for slowly heated films. Switching lifetimes exceeding 1011 cycles were measured. The type of platinum bottom electrode used was found to have a large influence on the ferroelectric properties of the lead zirconate titanate films.

Notes: Room-temperature measurements of linear and nonlinear photoconductivity in CaF2 containing trace amounts of yttrium, lanthanum, and several rare earths are reported and discussed. Linear spectral photoconductivity scans taken over the 1.55- to 6.20-eV range of photon energies produced significant photocurrents above 3 eV. The results are explained in terms of a combination of 4f-5d absorption in Ce+3 and Pr+3 and photoionization of interstitial F− in both nearest-neighbor charge-compensating defects and anion-Frenkel defects. Peak photocurrents induced by focused 950-ns-wide pulses from a 496.5-nm wavelength dye laser increased nonlinearly with increasing laser pulse energy. These results are interpreted as a transition from two-photon conductivity to electron avalanche and the asymptotic approach to the material's laser damage threshold at approximately 27 GW/cm2.

Notes: Excimer lasers are finding increasing use in the area of laser material processing. In this paper, near-threshold behavior of the ablation processes was investigated using light deflection spectroscopy as a detection method. The cumulative effects of polymethylmethacrylate near ablation threshold were studied in detail.

Notes: The kinetics of the amorphous-to-tetragonal transformation has been studied in sol-gel-derived thin films of zirconia deposited on alumina substrates. A rapid-thermal-annealing system was used which allowed good control of processing parameters such as temperature and heating rates. The effect of these two parameters on the transformation kinetics was studied and the experimental results were analyzed in terms of conventional nucleation and growth models. The use of two-step thermal processing cycles shows potential for the modification of the microstructural features of crystallized films and for a reduction in processing times.

Notes: Tungsten films have been deposited onto single-crystal silicon (Si) and silicon dioxide (SiO2) by plasma-enhanced chemical vapor deposition with WF6-SiH4-H2 chemistry: the annealing effect on these films has been investigated by rapid thermal annealing. The deposition rate of the tungsten films on both sides of Si and SiO2 is linearly dependent on the SiH4/WF6 ratio up to 1 and the deposition rate is not increased beyond this ratio (SiH4/WF6=1). Phase transition from α-W to β-W and silicidation are observed under the annealing at 900 °C for 15 s in W films on Si. On the other hand, resistivities of W films on SiO2 are decreased under the same annealing condition. The resistivity reduction in W films on SiO2 is believed to be the results of the grain growth and point, line defect removal, and out-diffusion of impurity atoms such as oxygen, fluorine, and silicon. In addition to this grain growth, the intensities of x-ray diffraction peaks are increased after the rapid thermal annealing. Etching process of the tungsten layer has been performed with a reactive ion etcher using CF4-O2 etchant. The etch rate of the as-deposited tungsten film is about 7800 A(ring)/min, and decreases with increase of annealing temperature to about 4600 A(ring)/min for the tungsten films annealed at 1000 °C for 15 s. This decrease in etch rate is believed to be caused by the decreases of the absorption site for etching sources due to grain growth and defect removal.

Notes: Mild steels which have been either thermally oxidized near 300 °C or implanted with nitrogen ions have been wear tested using a modified Falex Lubricant Testing machine. Both these treatments cause similar, much reduced wear rates which are about an order of magnitude better than in untreated samples. Specimens worn after treatments by both methods have been examined in detail using scanning electron microscopy and Auger spectroscopy. It is concluded that the wear induced by oxidation is the same as the wear induced by nitrogen ion implantation. Both of these treatments acted to initiate favorable sustained oxide wear and confirm the Initiator/Sustainer model. Additional studies have been done on oxidized samples using a variety of sample processing techniques and sequences including oxide layer stripping, wear recycling, and annealing. These studies clearly show that favorable wear results were caused by the grown oxide layer and not by the heat treatment. Also, it has been found that the favorable oxide wear can be stopped and started numerous times since it is able to reinitiate and sustain itself. However, if a worn oxide layer is stripped from a sample just prior to the wear run, favorable wear does not occur unless the sample was oxidized or favorably worn in the last few weeks. This occurs because wear favorable chemistry at the oxide/metal interface anneals at room temperature. Other discussions of the wear initiating and sustaining processes are presented.

Notes: A novel circuit is described which functions as an electronic analog of lumped element transmission line. The circuit requires only operational amplifiers, resistors, and capacitors. This module was coupled to a Josephson junction simulator and current voltage characteristics of the combined system were recorded. Steps were observed at voltages determined by the appropriate line resonances. When the transmission line was terminated with loads less than the characteristic impedance, chaos was seen in the lower steps. Similar results were obtained by numerical integration of the corresponding system of differential equations.

Notes: The performance of four overmoded (TE011 circular), two-cavity gyroklystron amplifier tubes operating in X band is reported. A summary of the theoretical design procedure is presented, followed by a description of the experimental setup. The stability and amplification properties of the four gyroklystron tubes are subsequently described, each being modified in sequence to improve performance. The fourth tube produced 2.0–2.7 MW pulses at 9.87 GHz for 0.5–1.0 μs, and exhibited gains of 17–19 dB and efficiencies of 5%. The results were obtained using electron beams with voltages, currents, and computed beam alphas (v⊥/vz) of 407–425 kV, 115–135 A, and 0.8–1.0, respectively. The presence of instabilities in the gun downtaper and drift tube prevented operation at the design point (500 kV, 160 A, and alpha 1.5). The effects of varying input frequency, input power, and beam parameters (voltage, current, magnetic compression) on the amplifier operation are reported. Detailed descriptions of the instabilities observed in the gyroklystrons are presented, and the use of lossy dielectrics to suppress the instabilities is discussed. The amplifier experimental performance is compared with simulations. Improvement schemes are summarized and follow-up experiments are outlined.

Notes: The relation between the flatband voltage shift of amorphous silicon nitride metal-insulator-semiconductor (a-SiN:H MIS) diodes and a-SiN:H deposition conditions is investigated. Significant hysteresis loops are observed in the capacitance-voltage (C-V) characteristics for some MIS diodes. This means that the bias scanning sequence and the a-SiN:H deposition conditions affect the flatband voltage. The dependence of the flatband voltage on bias stress time is also studied in connection with the deposition conditions. A logarithmic time dependence of the flatband voltage is seen for MIS diodes for which a-SiN:H was deposited at a high NH3/SiH4 gas ratio. These effects are induced from Si-dangling bonds which exist in a-SiN:H films.

Notes: Experimental determinations have been made of the peak optical gain as a function of spontaneous recombination current density for GaAs quantum wells of width 25 and 58 A(ring) bounded by AlGaAs barriers. These data were obtained from measurements of spontaneous emission spectra, observed through narrow windows in the 50-μm-wide contact stripes of oxide isolated lasers, using only a single reference value of the optical absorption coefficient above the band edge to calibrate the measurements in absolute units. These results are in good agreement with gain-current curves calculated using a model which includes unintentional monolayer well width fluctuations, band-gap narrowing and intraband carrier-carrier scattering. The characteristic intraband scattering time is calculated from first principles as a function of electron energy and carrier density on the basis of a 2-dimensional Auger-type process. This lifetime gives a much better representation of our observed spontaneous spectra than a lifetime which is simply dependent upon carrier density. The comparison between experiment and model calculation involves no adjustable parameters. For the 58-A(ring)-wide wells there is a difference between the experimental and calculated gain-current curves at low values of gain. We show that this is a consequence of applying the Einstein relations to a broadened spectrum in the process of deriving the gain from the observed spontaneous emission spectrum. A direct comparison of the shapes of experimental and calculated spontaneous emission spectra at several injection levels provides a more rigorous, yet equally valid, verification of the computer model.

Notes: The Pockels' effect has been demonstrated in thermally evaporated polycrystalline thin films of ZnS. The strongly (111)-oriented films were found to have an electro-optic constant of r41 = 3.3 × 10−13 m/V for fields perpendicular to the (111) planes. Extinction ratios of up to 85% have been observed in an optical waveguide modulator. Analysis indicates a stress-related birefringence that manifests itself upon temperature change. The temperature coefficient of stress in the polycrystalline films was found to be 3.0×105 N m−2/°C.

Notes: Cast iron can be viewed as a composite material. We use effective medium and other theories for the overall conductivity of a composite, expressed in the conductivities, the volume fractions, and the morphology of the constituent phases, to model the thermal conductivity of grey and white cast iron and some iron alloys. The electronic and the vibrational contributions to the conductivities of the microconstituents (alloyed ferrite, cementite, pearlite, graphite) are discussed, with consideration of the various scattering mechanisms. Our model gives a good account of measured thermal conductivities at 300 K. It is easily extended to describe the thermal conductivity of other materials characterized by having several constituent phases of varying chemical composition.

Notes: The H− negative ion thermal energy measured using the two-laser-pulse photodetachment technique is reported to be in the range from 0.1 to 0.7 eV for various conditions of volume ion source operation (pressure−from 2 to 7 mTorr, discharge current−from 1.5 to 20 A). The hydrogen pressure has a significant effect in lowering the negative ion temperature, while the increase of the discharge current leads to a rise in T−. It is found that T− is a fraction of the electron temperature, Te. This fraction is strongly dependent on the gas pressure. T− scales linearly with the electron temperature and exceeds the highest values predicted by the theory of dissociative attachment. The possible mechanisms for H− ion heating are discussed.

Notes: The presence and influence of translationally energetic ions in low-pressure etching discharges is well known. Neutral atoms and molecules, though known to be chemically reactive, are not generally considered to be otherwise activated in these plasmas. Neutral species may, however, become translationally hot through either charge exchange collisions or by dissociative excitation caused by electron impact. These species are important in etching discharges because they may bring an isotropic source of activation energy to the substrate which may compromise anisotropic etching mechanisms. In this paper we present a theoretical study of the sources and effects of translationally hot neutral atoms and molecules in CF4 etching plasmas. We find that ballistically hot F atoms comprise a significant fraction of the radical flux striking the substrate at pressures of 〈100 mTorr. In CF4 plasmas, the maximum flux of translationally hot F incident on the substrate of a parallel-plate rf etching discharge occurs between 10 and 100 mTorr. At these pressures the hot atom and ion fluxes to the substrate are comparable. The effects of translationally hot species on gas-phase plasma chemistry and surface reactions are discussed.

Notes: Defects produced in lightly doped crystalline silicon by 1-MeV electrons and 14-MeV neutrons are studied. Deep level transient spectroscopy (DLTS) and Hall voltage measurements have been used for investigating the energy depth, nature, and density of radiation-induced defects. The extent of damage caused by 14-MeV neutrons is found to be comparatively high as inferred from the continuous distribution of gap states in the DLTS measurement. Identical defects were observed in both cases where the A-center (Ec−0.17 eV), E-center (Ec−0.39 eV), and divacancy (Ec−0.23 eV) were prominent. An additional defect level (Ec−0.86 eV) was observed from DLTS for neutron-irradiated samples.

Notes: We present the first in situ measurement of the evolution of strain fields due to oxygen precipitation in silicon single crystals by means of high-resolution neutron backscattering. The integrated reflecting power R and the lattice parameter variations Δd/d which are directly related to the strain fields have been measured as a function of temperature and annealing time. In the temperature range from 300 to 1185 K, high purity float zone crystals maintain the R-values characteristic for perfect crystals. In contrast, Czochralski-grown crystals which contain on the order of 1018 oxygen atoms cm−3 (20 ppm), show a steep increase in reflectivity starting at 1160 K, and which goes through a maximum at 1350 K. At 1456 K, partial annealing occurs with a time constant of several hours.

Notes: In superconductors, cracks (of width w (approximately-greater-than) ξs) are effective in enhancing local supercurrent, and we calculate the size of these supercurrent hot spots as a function of the crack length a and the London penetration depth λ using the two-dimensional (2D) London theory. In the λ→∞ limit and constant injected current density, we show that this 2D solution is also exact for the current flow in a thin film containing a through crack. We argue that large local supercurrents near a surface crack nucleate vortex creation. If flux pinning is weak enough these vortices flow under the influence of the large local Lorentz force. The dissipation so produced can lead to a reduction in observed critical current. If flux pinning is moderate, the first additional vortices nucleated near the crack tip are pinned, in a region we label ρ, the flux pinning zone. In the case of a through crack in a thin film, we then argue that jc(a) reduces as jc(a)/jc(0) ∼ (ρ/a)x (for a/L(very-much-less-than)1), where L is the film width and x =1/2 for the simplest London theory. We compare this theory with the Bean (critical state) model, which predicts that the critical current is (approximately) determined by the cross section available for supercurrent, so that in a film containing a crack, jc(a)/jc(0) ∼ 1 − a/L (ignoring self-field effects). We argue that superconductors with sufficiently weak pinning should obey the hot-spot theory, while sufficiently hard superconductors should obey the critical-state model, and suggest experiments that should illustrate these two limiting cases.

Notes: Investigation of the 110-K Bi2Sr2Ca2Cu3Ox phase formation in superconducting thin films of Bi-based cuprates is reported. The films were dc magnetron sputtered from single Bi(Pb)-Sr-Ca-Cu-O targets of various stoichiometries, and subsequently annealed in air at high temperatures. The influence of the initial Pb content, annealing conditions, as well as the substrate material on the growth of the 110-K phase was investigated. We found that the films, fully superconducting above 100 K could be reproducibly fabricated on various dielectric substrates from Pb-rich targets by optimizing annealing conditions for each initial Pb/Bi ratio. Heavy Pb doping considerably accelerated formation of the 110-K phase, reducing the film annealing time to less than 1 h. Films containing, according to the x-ray measurement, more than 90% of the 110-K phase were obtained on MgO substrates, after sputtering from the Bi2Pb2.5Sr2Ca2.15Cu3.3Ox target and annealing in air for 1 h at 870 °C. The films were c-axis oriented, with 4.5-K-wide superconducting transition, and zero resistivity at 106 K. Their critical current density was 2 × 102 A/cm2 at 90 K, and above 104 A/cm2 below 60 K. The growth of the 110-K phase on epitaxial substrates, such as CaNdAlO4 and SrTiO3, was considerably deteriorated, and the presence of the 80- and 10-K phases was detected. Nevertheless, the best films deposited on these substrates were fully superconducting at 104 K and exhibited critical current densities above 2 × 105 A/cm2 below 60 K−one order of magnitude greater than the films deposited on MgO. We associate the presence of low-Tc phases in the films grown on epitaxial substrates with the intrinsic mechanism of the 110-K phase growth during the high temperature annealing process.

Notes: The validity of Kondorsky's switching field distribution for pinning magnets with rectangular hysteresis loops is extended to cases where the hysteresis loops are influenced by reversible rotation of the magnetization vectors in the domains. Caused by this influence, the monotonic Kondorsky function changes to modified Kondorsky functions HP(cursive-theta0) with minimal switching fields for orientation angles cursive-theta0(approximately-greater-than)0° when HP(cursive-theta0 = 0°) reaches the anisotropy field strength Ha. It is shown that the modified Kondorsky function is a more suitable description of experimental results in the literature than the Kondorsky function itself.

Notes: Co/Pd(111) and Ni/Pd(111) bilayer films were grown epitaxially on single crystal MgO (111) substrates by ultrahigh vacuum deposition. In situ observation of the strain of Co and Ni deposited on Pd (111) plane was performed by reflection high energy electron diffraction (RHEED) during fabrication. From RHEED patterns it was confirmed that the lattice constant of a Co film of 2 A(ring) in thickness deposited on Pd was about 3.7 A(ring), which was different from that of Pd (3.89 A(ring)). The strain (εCo) of the Co layer was rapidly released during further Co deposition. The strain εCo of the third Co monatomic layer on Pd is nearly equal to zero. The large strain of the Co layer is localized at about one or two monatomic layers of the interface between Co and Pd. On the other hand, a Ni film deposited on Pd was not strained from the beginning of the deposition. The relationship between the perpendicular magnetic anisotropy of Co/Pd and Ni/Pd compositionally modulated multilayer films and the strain of Co and Ni is discussed.

Notes: Nonlinear interactions in yttrium iron garnet cause complex, low-frequency signals seen during ferromagnetic-resonance experiments. Several methods from nonlinear dynamics have been used to measure quantities such as dimensions, Lyapunov exponents, and others, to characterize complex behavior that is measured by ferromagnetic resonance experiments. It is found that these quantities may be more useful in understanding the interactions in yttrium iron garnet than more commonly measured quantities such as oscillation frequency. Very simple numerical models are also used to suggest which quantities are most important in characterizing these spin-wave interactions.

Notes: Sm–Fe alloys have been produced by rapid quenching and the resulting phases have been investigated in the as-quenched state and after nitriding. Besides the well-known equilibrium phases of the binary Sm–Fe system (Fe, Sm2Fe17, SmFe3, SmFe2 and Sm), a hexagonal TbCu7-type phase shows up in melt spun ribbons (a=4.88 A(ring), c=4.23 A(ring)). Its stoichiometry is about Sm1Fe9 and it is formed only at wheel velocities above 15 m/s. The Curie temperature and the saturation polarization of this new phase is 210 °C and 1.25 T, respectively. At higher Sm concentrations or lower quenching rates the structure changes to the Th2Zn17-type. The Th2Zn17-type ribbons are magnetically soft whereas the TbCu7-type samples show moderate coercivities of up to 1.7 kA/cm. Nitrogenation leads to an expansion of the lattice and to an overall improvement of the hard magnetic properties for both phases. Their Curie temperatures are increased to 470 °C and the saturation polarizations are raised to 1.40 and 1.51 T for the TbCu7- and the Th2Zn17-type phases, respectively. The best hard magnetic properties for isotropic TbCu7-type material are obtained for quenched, annealed, and nitrided Sm10.6Fe89.4 which shows a coercivity, Hci, of 4.9 kA/cm, a remanence, Jr, of 0.86 T and an energy product, (BH)max, of 69.6 kJ/m3. For similarly treated Sm12Fe88, which crystallizes in the Th2Zn17 structure, a coercivity of 16.7 kA/cm, a remanence of 0.73 T and an energy product of 65.6 kJ/m3 are achieved.

Notes: InxGa1−xSb epitaxial layers have been grown on (100) GaSb substrates under TMSb/(TMIn+TEGa) ratio of 5.8 and system pressure of 170 Torr at different substrate temperatures (550–630 °C). From analyses of both the x-ray diffraction and photoluminescence (PL), the indium solid mole fraction was found to decrease with increasing growth temperature. The x-ray diffraction patterns degrade with increasing lattice mismatch (or with increasing In mole fraction in the solid). The photoluminescence peak wavelength decreases with increasing growth temperature. The optimum growth temperature is about 600 °C at which the good quality InxGa1−xSb epilayers with the most mirrorlike surface, narrowest PL full width at half-maximum (9 meV) and strongest PL intensity can be obtained. The narrowest full width at half-maximum value is only 9 meV. The full width at half-maximum of 10-K photoluminescence peaks was found to increase with increasing lattice mismatch due to the increasing misfit dislocations and strains existing at the lattice-mismatched interface.

Notes: Quantum wires were fabricated by selective intermixing of a GaAs/GaAlAs quantum well through masked Ga+ implantation and rapid thermal annealing. The evolution of the luminescence spectra of the wires with the width of the implantation masks, enabled us to characterize the lateral selectivity of our process as well as the degree of one-dimensional confinement. The lateral extent of the intermixing was estimated at 20 nm giving rise to an important penetration of aluminum into the wires. From numerical simulations of the spatial distribution of implantation-induced damage, it was concluded that some lateral diffusion of the defects occurred during annealing. However it has been possible to assess the confinement energies to be around 4 meV. The linewidth of the wires' emission turned out to increase with decreasing mask size, indicating the presence of some fluctuations of the confining potential along the wires. The roughness of the lateral definition of the wires was evaluated at 20 nm, of the same order of magnitude as the dimension of the intermixed region under the mask. Under these conditions optical excitation spectroscopy failed to detect the different one-dimensional subbands. Finally the potentialities of this method of fabrication of quantum wires are inspected.

Notes: Atomic hydrogen has been introduced from a plasma source into InAs layers grown by molecular beam epitaxy on GaAs substrates. It is shown that hydrogen diffuses very fast into this material. The presence of hydrogen modifies the electronic transport properties, the near-band-edge luminescence spectra, and the far-infrared reflectivity spectra. The most striking effect is that, unlike other III-V compounds, the free-carrier density increases by one order of magnitude after hydrogenation. These phenomena are reversible and thermal annealing restores the original properties of the samples. Finally, models are proposed to explain the experimental results.

Notes: An improved Monte Carlo model for ionized-impurity scattering is developed and used to calculate majority- and minority-electron mobilities in silicon. The model includes scattering cross sections derived from phase-shift analysis, implementation of the Friedel sum rule, and a simple phenomenological model for multiple-potential scattering. This model provides a very good fit to experiment using a single adjustable parameter. Electron mobilities in n- and p-type Si are calculated and fit to experimental data at 300 and 77 K. Experimental results for Si of μn(NA)/μn(ND) ≈ 2 at 300 K are reproduced and a value of 3 〈 μn(NA)/μn(ND) 〈 4 is predicted at 77 K.

Notes: A silicide anneal furnace, nominally oxygen and water free, has been used to anneal in the temperature range between 500 and 800 °C, in Ar or N2, silicon/oxide structures having a dielectric layer (thermal SiO2) about 7 nm thick. Quasistatic current-voltage measurements have pointed out a dramatic increase of the interface traps after just a few minutes anneal at T=700 °C. To prove that such an increase on interface-trap concentration could be correlated to a very low oxygen and/or water content inside the anneal chamber, the same oxide films have been annealed, before metal deposition, under ultrahigh vacuum (UHV)(10−8 Torr) in the same temperature range and for the same time intervals. Electron paramagnetic resonance (EPR) analysis has shown an increase of the Pb(111) and Pb1(100) defect centers, leaving unchanged the density of Pb0(100) defect centers. Experimental data on annealing efficiency and the strong similarity observed between results after anneals performed in the silicide anneal furnace and under UHV lend support to the idea that the cause of the Si-SiO2 interface degradation may be the Pb center reverse-passivation reaction. Also, EPR analysis has provided evidence of a different annihilation behavior of the Pb(111) and Pb0(100) centers. Finally, the comparison between the time-zero breakdown distribution after anneal in a silicide anneal furnace and under UHV has shown that (i) the Si-SiO2 interface degradation is not a precursor step of a more complex reaction process leading to the loss of the oxide integrity; (ii) for a thin oxide layer (in our case less than 10 nm), the electrical activation of macroscopic defects during anneal under vacuum happens at temperature much lower than previously reported.

Notes: A study has been made of the effect of hydrostatic pressure on an AlAs/GaAs/AlAs resonant tunneling diode in which the electrodes have been deliberately asymmetrically doped. In reverse bias, current is injected into the structure from a highly doped n+-GaAs electrode and in forward bias from a two-dimensional accumulation layer at the GaAs/AlAs interface. When large hydrostatic pressures are applied at 77 K, regions of negative differential resistance are induced in both bias directions. Current maxima with peak-to-valley ratios as large as 4 have been measured at 8 kbar. The intrinsic asymmetry of the structure aids in the identification of the origins of these features in terms of the X-point conduction-band minima of the device.

Notes: We have calculated the temperature dependence of the carrier density in epitaxial layers of semiconductors deposited on semi-insulating substrates when the potentials at the surface and the substrate interface are pinned. The results of these calculations are compared to experiments on thin, nominally undoped p-type layers of GaAs deposited epitaxially on EL2-dominated substrates. The theory predicts that as the temperature is lowered to some critical value the depletion layers at the edges of the epilayer overlap for thin, lightly doped samples. Below this value the carrier density decreases exponentially with inverse temperature with an activation energy which depends on the surface and interface potentials, as well as on the dopant concentration and the width of the layer. This activation energy can be derived analytically for strong depletion. In the intermediate range between negligible and complete depletion of the layer the carrier density must be obtained by numerical methods, and we present the results of such a calculation.

Notes: Thin films of Y1Ba2Cu3O7−x have been produced on MgO substrates by a chemical sol gel method. X-ray diffraction data indicate that the annealed films have the characteristic orthorhombic structure with lattice constants which are nearly the same as the values reported for the bulk specimen of Y1Ba2Cu3O7−x. Auger electron spectroscopy depth profiling measurements indicate that the films are uniform in thickness and composition. Measurements of electrical resistance of films 1–4.7 μm in thickness have been carried out between 12 and 300 K using a standard four-probe geometry. The films are superconducting with an onset temperature around 95 K and a full transition temperature as high as 79.5 K, and a critical current density of 2700 A/cm2 at 20 K. A theoretical analysis of the critical current density in Y1Ba2Cu3O7−x as a function of temperature has been made in order to determine the characteristics of the junctions between the superconducting grains. Theoretical models which describe the dependence of the critical current density on temperature have been presented and agreement has been found between these models and experimental values for sol gel films. The critical transport current has a temperature dependence which is characteristic of superconductor-normal metal-superconductor (S-N-S) type junctions. The magnitude of the resistance and thickness of the junctions has been determined from the theoretical models. Information regarding calculation of the oxygen content in Y1Ba2Cu3O7−x films is also presented.

Notes: The metalorganic chemical vapor deposition of Bi-Sr-Ca-Cu-O ultrathin films was performed on single-crystal (100) MgO substrates. An ultrathin film with average thickness of 3.5 nm was found to exhibit the full superconductivity at more than 60 K. The critical current density of a 5-nm-thick film was found to be strongly anisotropic for applied fields parallel and perpendicular to the film plane. In particular, in a field parallel to a film plane, the critical current density was constant up to 6 T even at 50 K, near the critical temperature. From the x-ray-diffraction patterns of ultrathin films prepared at the deposition rates of 3 and 0.3 nm/min, a Bi2Sr2CaCu2Ox (2212) phase was found to be formed at the first stage of deposition regardless of the deposition rate, while a Bi2Sr2Ca2Cu3Ox (2223) phase was found to be formed in the earlier stage of deposition when the deposition rate was decreased.

Notes: The microstructure of Mo-sheathed Chevrel-phase superconducting wires was investigated by high-resolution scanning electron microscopy (SEM). Excess Pb forms small nodules (10–30 nm) on the Chevrel-phase grains or wetting layers between the Chevrel grains. The critical current density Jc is strongly reduced when wetting layers are present. However, second-phase Mo exists as islands as large as 2–10 μm and has little harmful effect on Jc. Although some Mo-sheathed wires sintered at 700 °C show relatively high Jc ( ≥ 2 × 108 A/m2 at 8 T), the Chevrel phase in these wires has a very porous microstructure, and the Jc values measured with a magnetic field parallel to the current, Jc((parallel)), were only about 10% higher than the Jc values measured with a field perpendicular to the current, Jc(⊥). This clearly suggests that the transport current flows percolatively in these wires. Much denser microstructures were obtained by hot-isostatic-pressing (HIP) treatments at 1200 °C, and very high Jc values, (approximately-greater-than) 5 × 108 A/m2 at 8 T and 9.3 × 107 A/m2 at 23 T, which are of the order of the highest Jc values so far reported, were observed. High-resolution SEM observations of HIP'ed wires demonstrate that the interconnectivity between the Chevrel grains was much improved.

Notes: Single and multiple InAs/InP strained quantum wells have been grown by hydride vapor-phase epitaxy (HVPE). A compact set of vent/run valves monitored by manifold switches and a computer allowed the vapor species to be changed. InAs growth times of 4–24 s followed by etching times of 7–14 s, in an InCl, HCl, and H2 atmosphere, were used to control the thickness and interface abruptness. Low-temperature photoluminescence (PL) spectra have revealed emissions either in the form of a single peak or well-resolved multiple peaks attributed to monolayer variation in quantum-well thickness. The thinnest well obtained, observed for the first time by HVPE, has a PL energy transition at 1.28 eV. Experimental data agree well with theoretical calculations, taking into account strain effects on band structure and effective masses. The full widths at half maximum indicate good interfacial abruptness.

Notes: We report on experimental investigations of electro-optic polymers, carried out in connection with the development of a contactless measuring technique for electrical signals in printed circuit boards. We describe the preparation of the poled polymers and the measurement of the electro-optic properties. The polymer samples consist of poly methyl methacrylate doped with N,N-dihexyl-4-amino-4'-nitrostilbene (DHANS). For a sinusoidal electrical field with a frequency of 1.325 kHz applied to the polymer sample we observe a change of the refractive index linear in the electrical field, the poling field, and the DHANS concentration. Using a dc field, we obtain a considerably larger field-induced change of the refractive index which is quadratic in the field, linear in the DHANS concentration, and nearly independent of the poling field. For both cases a figure of merit is defined and experimentally determined. With the present experimental setup, a minimum detectable change of the refractive index requires an ac voltage amplitude of 85 V and a dc voltage of 20 V.

Notes: An analysis of silicon on insulator structures obtained by single and multiple implants by means of Raman scattering and photoluminescence spectroscopy is reported. The Raman spectra obtained with different excitation powers and wavelengths indicate the presence of a tensile strain in the top silicon layer of the structures. The comparison between the spectra measured in both kinds of samples points out the existence in the multiple implant material of a lower strain for a penetration depth about 300 nm and a higher strain for higher penetration depths. These results have been correlated with transmission electron microscopy observations, which have allowed to associate the higher strain to the presence of SiO2 precipitates in the top silicon layer, close to the buried oxide. The found lower strain is in agreement with the better quality expected for this material, which is corroborated by the photoluminescence data.

Notes: Spectrally resolved low-temperature cathodoluminescence (CL) imaging has been performed on thin, 250 A(ring), mismatched layers of GaAsxP1−x in between bulk GaP. The layers were grown on (111) oriented substrates by metalorganic vapor phase epitaxy, with layers ranging from perfectly strained to totally relaxed. CL imaging has proven to be a very sensitive technique for the study of the onset of the formation of misfit dislocations and is therefore useful for determination of the critical thickness [A. Gustafsson, M.-E. Pistol, M. Gerling, L. Samuelson, M. R. Leys and H. Titze, J. Appl. Phys. 70, 1660 (1991)]. For the use of perfectly strained layers, growth on (111) oriented substrates can be of interest since the critical thickness predicted by the mechanical equilibrium theory [J. W. Matthews and A. E. Blakeslee, J. Cryst. Growth 27, 118 (1974)] is about twice that for growth on (001) oriented substrates. In this work we show that the dislocations involved in the strain relief for the growth of mismatched layers on (111) oriented substrates are of the perfect 60° type and that the experimental critical thickness agrees well with the value expected from the mechanical equilibrium theory.

Notes: A steady-state model for ablation of materials by strongly absorbed long-pulse lasers is developed. Material is removed by a combination of evaporation and ejection of liquid due to evaporation-induced pressure gradients at the bottom of the ablation crater. The relative strength of the two processes depends on the details of the liquid flow. An explicit expression for the drilling velocity is derived. The model explains experimental drilling-depth and recoil data. It is applicable to materials that melt and vaporize.

Notes: An electron cyclotron resonance-excited Ar plasma completely removes CFx residue on Si resulting in a clean surface that is free of native Si oxide. In situ x-ray photoelectron spectroscopy verifies the absence of C and F on the surface, and the presence of what is thought to be a small amount of adsorbed or interstitially implanted O. Mechanistically, the Ar ion bombardment affects a nearly instantaneous ablation of F from the CFx surface followed in succession by a low average energy (100 eV) sputtering of the C-rich remnant, the native Si oxide, and the Si substrate. The etching rate of thick CFx residue is approximately 15 nm/min without any heat applied to the substrate.

Notes: Optical, in situ, real time control of surface processes during epitaxy is becoming increasingly important for the understanding and control of crystal growth. Here results are presented of in situ studies of the surface V/III balance using the reflectance-difference (RD) method during vacuum chemical epitaxy of (001) GaAs from arsine and triethylgallium. We have found a relationship between the RD signal and the V/III ratio, and we demonstrate the possibility for the use of this relationship for the optimization of growth. We have, by RD, detected a sharply defined, critical V/III ratio, below which the morphology and the photoluminescence intensity deteriorate dramatically, and which can be used to control the conversion from n-type to p-type conductivity. We believe that these observations will be of great importance for the in situ optimization of epitaxial growth, and in eliminating much of the uncertainties involved in reproducing surface V/III ratios.

Notes: High-energy Si implantations were performed into InP:Fe at energies ranging from 0.5 to 10 MeV for a dose of 3×1014 cm−2, and at 3 MeV for the dose ranging from 1×1014 to 2×1015 cm−2. The first four statistical moments of the Si-depth distribution, namely range, longitudinal straggle, skewness, and kurtosis, were calculated from the secondary-ion mass spectrometry (SIMS) data of the as-implanted samples. These values were compared with the corresponding trim-89 calculated values. SIMS depth profiles were closely fitted by Pearson IV distributions. Multiple implantations in the energy range from 50 keV to 10 MeV were performed to obtain thick n-type layers. Variable temperature/time halogen lamp rapid thermal annealing (RTA) cycles and 735 °C/10-min furnace annealing were used to activate the Si implants. No redistribution of Si was observed for the annealing cycles used in this study. Activations close to 100% were obtained for 3×1014-cm−2 Si implants in the energy range from 2 to 10 MeV for 875 °C/10-s RTA. Transport equation calculations were used to interpret low activation results for high dose Si implants. Polaron electrochemical C–V profiling was used to obtain carrier concentration depth profiles. The lattice quality of the as-implanted and annealed material was evaluated by performing x-ray rocking curve measurements.

Notes: An observed change in the photoacoustic signal frequency response upon the application of a transverse magnetic field across octylcyanobiphenyl samples in the nematic phase at 37 °C and 37.5 °C is reported. The application of a recent thermal-wave theory developed for depth profiling of continuously inhomogeneous condensed phases has given quantitative profiles of thermal diffusivity decreases extending to 20–30 μm below the liquid crystal surface. These decaying depth profiles are qualitatively consistent with earlier photoacoustic temperature scans of liquid crystals and are a measure of the extent of bulk reorientational effects due to the magnetic field, as well as the extent of the influence of the surface as a domain reorientation inhibitor in the kG range.

Notes: Molecular-beam-epitaxial growth of GaP incorporating isoelectronic N traps was achieved through coinjection of NH3 and PH3 which were dissociated into P2 and PN fluxes. The photoluminescence spectrum of a sample with a N concentration of ∼2×1019 cm−3 indicated that the dominant emission wavelength was at 5691 A(ring) (2.18 eV), which is characteristic of the nearest-neighbor pair transition NN1. The spectrum of a sample containing ∼2×1020 cm−3 N atoms also displayed strong NN1 pair luminescence in addition to much stronger emission line at 5846 A(ring) (2.121 eV), which is believed to be from a local mode outside the vibrational band. The peak intensity of this local mode was ∼25 times greater than the peak emission of the NN1 line from the lighter doped sample.

Notes: High doses (7×1016–1.3×1017/cm2) of 170-keV Er+ ions were implanted into single-crystal Si at an implantation temperature of Ti=520 °C. During Er implantation ErSi2 crystallizes as coherent precipitates within a crystalline Si matrix. During the subsequent annealing at 800 °C a discontinuous buried layer of the single crystalline ErSi2 is formed. Implanted and annealed samples were subsequently reimplanted with 170-keV Er+ ions at 250〈Ti〈520 °C. The second implantation results in a mesotaxial growth of the previously formed buried single-crystal ErSi2 layer for implantation temperatures Ti(approximately-greater-than)300 °C where ion beam induced, defect mediated diffusion of Er atoms in the Si matrix occurs during the implantation process.

Notes: In the present paper, the equation of state suggested by the authors has been applied in the case of plastics, rubbers, glasses, and polymers. The maximum pressure range and the minimum pressure range used in the present study are 0–100 and 0–24 kbar, respectively. A good agreement is found between the calculated and experimental values of V(P,T0)/V(0,T0) in case of all the materials studied here.

Notes: A microwave plasma discharge at very low temperatures (200–250 °C) has been used for the growth of thin silicon oxynitride films suitable for gate dielectric applications. The addition of CHF3 as a source of fluorine enhances the growth rate. A x-ray photoelectron spectroscopy study indicates the incorporation of fluorine (F/Si(approximately-equal-to)0.2) in the film. Electrical properties of the grown layers have been evaluated by the characterization of metal-insulator-semiconductor capacitors. Results have indicated the presence of negative charges in the insulator. The estimated charge density is lowest for the fluorinated film. The conduction mechanism in the films at room temperature appears to be Frenkel–Poole type.

Notes: YBa2Cu3O7−δ single crystals with Tc=90.5 K and different transition width have been irradiated with fast neutrons (E(approximately-greater-than)0.1 MeV) and a fluence of Φ⋅t=2×1017 cm−2. The flux-creep dM/dlnt at B=0.5 T is reduced at any temperature up to T=60 K by a factor of about 2. Correspondingly, the effective pinning potential Ueff is enhanced up to 100kBT at low temperatures and 50kBT at T=77 K, independent of an increase or decrease of the magnetization current density after irradiation. Therefore, the enhancement of Ueff may not in every case be related to a jc increase, which is also determined by the number of pinning centers or a certain defect structure, which may not necessarily show deep pinning potentials. The results can be explained within the conventional flux creep theory and are in a good agreement with recent considerations of the role of electronic anisotropy in the dissipative behavior of YBa2Cu3O7−δ.

Notes: A phase-shifted (PS) distributed-feedback (DFB) laser with linearly chirped grating (CG) was analyzed using the coupled-mode equations and rate equations. It was found that the mode instability of a DFB laser was caused by both the lasing-mode movement and the deterioration of the effective reflectivity spectrum of the corrugated-grating waveguide caused by the nonuniform carrier distribution under the injection. By suitable arrangement of the chirped factor of the PS-CG-DFB laser and the phase-shift value, PS-CG-DFB laser can overcome the effective reflectivity spectrum-deterioration problem and make the mode more stable under injection.

Notes: A transconductance spectroscopy method is introduced through computer modeling which provides an easy way to the determination of energy levels of surface states and bulk traps in a GaAs metal semiconductor field-effect transistor. It is shown that in the transconductance spectrum each trap will result in a peak at a frequency which is equal to the characteristic frequency of the trap. It is suggested that peaks due to surface states can be distinguished from those due to bulk traps in the gated channel region by the dependence of the surface-state peak height on the gate-source reverse bias. It is found that previous experimental reports of transconductance dependence on temperature and surface leakage current can be explained by the model developed in this study.