ALBERT

Notes: A non-Fickian diffusion equation, which differs from the usual (Fickian) diffusion equation by having an additional, second-order derivative term in time, is considered to describe the dynamics of a Brownian particle. Some useful perspectives on this generalized diffusion equation are presented, particularly with respect to the effect of a potential field. Two quantities of physical interest, namely the mean square displacement and the particle flux at an absorbing boundary, are considered in the process of a comparative study of the two diffusion equations. We also discuss the applicability of the non-Fickian diffusion equation to some systems of physical and practical interest.

Notes: Thermal stresses induced during cooling from the fabrication temperature of a fiber with a noncubic superconducting ceramic coating are analyzed theoretically. The coating considered has a preferred crystallographic orientation such that the c axis of the coating material is perpendicular to the fiber surface which, in turn, results in different thermal expansion coefficients in the radial and the tangential directions in the coating. The thermal stresses are shown to result both from the mismatch between the fiber and the coating, and from the thermal expansion anisotropy of the coating. Stresses due to bending of the fiber/coating to form a superconducting component are also addressed. A critical radius of curvature of bending is obtained below which segmentation of the coating is predicted.

Notes: Diffusion profiles of gold in germanium were measured using the radiotracer as well as the spreading-resistance technique. Diffusion coefficients from both experimental methods show a good agreement and are described by an activation energy of 147±2 kJ mol−1 and a preexponential factor in the range (1–2)×10−6 m2 s−1. The results are interpreted within a generalized dissociative model allowing for interstitial-substitutional exchange with the aid of vacancies or interstitial Au-vacancy pairs. Solubility data taken from the boundary concentration of the penetration profiles reveal nonsignificant differences between the total Au concentration and that of substitutional Au atoms. Basic thermodynamic quantities were calculated from the temperature dependence of the solid solubility using data from the Au-Ge phase diagram.

Notes: A computer simulation of stripe deterioration under electromigration is developed with especial regard to the physical aspects of the process. A grain-boundary network is first established appropriate to a {111} grain-boundary texture by a Voronoi process. Stress relief through the motion of network vertices can be used to simulate the effects of annealing. In operation, two different situations are considered: (1) free-surface condition and (2) operation under a passivating surface containment. With the free-surface condition, voids grow internally while the extra material spreads over the surface. With the passivating condition, the matter is conserved and eventually a steady state ensues. The possibility of sideways extrusions or "spikes'' is considered. Many other possible applications of the model are indicated.

Notes: In the present paper, a dislocation dipole model is employed to simulate the nucleation of microvoids at the interface between a thin film and a substrate. In this model, the accumulation of dislocation dipoles plays a major role in the formation of a microvoid. The total free energy of the system increases with the fatigue cycle number due to the increase in elastic strain energy. It is shown that there exists a critical fatigue cycle number beyond which the initial state of dislocation dipole accumulation becomes energetically unstable, and the energy of this state will be released by the formation of a microvoid at the interface. The study can provide not only the S–N curves for the initiation but also their dependence on material parameters such as the thickness of the film, the grain size of the substrate, the shear moduli ratio, etc. The coalescence of those microvoids is expected to be one of the mechanisms of delamination of the thin film from its substrate.

Notes: The thermal stability of SiGe films deposited by ultrahigh-vacuum chemical vapor deposition was studied. Various Ge compositional profiles, including boxes, trapezoids, and triangles were examined. Planar-view transmission electron microscopy was performed following growth and after furnace annealing at 950 °C for 30 min to determine the presence and density of misfit dislocations. All profiles showed very similar stability behavior when expressed in terms of the total thickness of the film, heff, and the effective strain present in the layer, εeff. Following the anneal, misfit dislocations were observed when heff exceeded the critical thickness, as defined by Matthews and Blakeslee [J. Cryst. Growth 27, 118 (1974)], by a factor of ∼2.

Notes: The intermixing of GaAs/(Ga,Al)As heterointerfaces by Ga+ implantation and annealing has been investigated. The damage accumulation in a GaAs/AlAs superlattice turned out to be less rapid than in a GaAs/GaAlAs quantum-well structure. Low-temperature photoluminescence (PL) spectroscopy of a GaAs/AlAs superlattice could be performed for doses as high as 1 × 1016 ions/cm2. The photoluminescence spectra exhibited several emission bands on the high energy side. The number and energy of these blue shifted peaks were found to depend on the implanted dose and as confirmed by secondary ion mass spectrometry, they could be interpreted as the emission of several quantum wells of the superlattice, disordered with different mixing rates. Two regimes were evidenced; while the depth extension of the disordering has been directly related to the post-implantation defects distribution in the high dose regime, some diffusion of these defects during annealing has been pointed out in the low dose regime. Cross-sectional transmission electron microscopy observations have confirmed the influence of the structure of the implanted sample on damage accumulation. Moreover, the decrease of the PL intensity after annealing could be related to the presence of extended residual defects in the implanted layers. The study of the influence of annealing time at 760 °C, has shown that the photoluminescence intensity can be progressively recovered, while the intermixing saturates rapidly.

Notes: We have investigated the effects of disorder-induced band tailing on deep levels in compound semiconducting alloys, such as GaAs and AlxGa1−xAs. In particular, we have eliminated the assumption of Gaussian broadening of the defect density of states proposed earlier by others on the basis of the central-limit theorem. The expressions derived for the transient capacitance in the presence of the disorder-induced band tailing are quite different from previously published results and indicate that the form of the broadening function is quite sensitive to, and should closely reflect, the underlying physical environment. We applied this theory to the investigation of the deep-level transient spectra (DLTS) and isothermal capacitance transient spectra (ICTS) in GaAs and AlxGa1−xAs. Our results indicate that standard experimental measurements with DLTS and ICTS, in general, can underestimate the activation energy, capture cross section, etc., even in the case of weak disorder.

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: Bi-Sr-Ca-Cu-O (2212) and Bi-Pb-Sr-Ca-Cu-O (2223) superconductors were fabricated into silver-sheathed tapes by cold rolling and sintering. The resulting samples are compared in terms of microstructural alignment, critical current density, and strain dependence. Although both samples show good grain alignment, that of the 2212 phase is superior due to partial melting during heat treatment. This microstructural superiority is reflected in superior Jc as well. The single-filament and multifilament 2212 tapes have Jc (approximately-greater-than) 5 × 104 A/cm2 and Jc (approximately-greater-than) 1.5 × 104 A/cm2 at 20 T, respectively. Each material shows a similar dependence of Jc upon strain, with the 2223 phase exhibiting slightly more degradation. Furthermore, multifilamentary tapes were less affected by strain than single-filament tapes. A multifilamentary tape at 4.2 K, 0.5 T showed only a weak dependence upon strain, indicating that the strain dependence of the Bi system at low temperature may not be severe.

Notes: Bismuth- and aluminum-substituted yttrium iron garnet single-crystal films with the nominal composition of Y1.5Bi1.5Fe4.2Al0.8O12 (Bi,Al:YIG) were prepared by spin coating a gel on the (111) plane of (GdCa)3(GaMgZn)5O12 single-crystal garnet plates. Crystallinity of the films varies with temperature and time of heat treatment in air after gel coating. Single-crystal films were obtained at Ta=650 °C for 4 h. The onset temperature for crystal growth is about 560 °C, which is about 400 °C lower than that of liquid-phase epitaxy. The crystal-growth process of single-crystal Bi,Al:YIG films was examined by measuring crystallographic structures as well as the magneto-optical Faraday effect. The internal stress giving rise to magnetic uniaxial anisotropy to align the magnetization normal to the film plane plays an important role for completion of single-crystal growth throughout the film.

Notes: The index of refraction, the extinction coefficient, and the absorptance for gold and tin were measured in a temperature range from room temperature up to the melting point for the wavelength λ=10.6 μm. All measurements were performed under ultrahigh-vacuum conditions using a photometric infrared ellipsometer with a rotating analyzer. Measurements verify a discontinuous jump of the absorptance at the solid-to-liquid phase transition from 3.5 to 6.5% in the case of gold and from 4.9 to 9.2% in the case of tin. The experimental results derived for the clean solid surface are in good agreement with the theoretical prediction by a Drude model, if additionally appropriate effective masses and the anomalous skin effect are taken into account. This theory is much less accurate if applied to the molten state of gold and tin, as was already shown previously for liquid aluminum and copper.

Notes: The possibility of growing lattice-mismatched layers and quantum wells becomes more and more interesting for the fabrication of devices. For device performance it is necessary to control the formation of misfit dislocations within the mismatched layers. It is therefore essential to study the onset of misfit dislocations versus amount of mismatch and layer thickness. A preliminary cathodoluminescence (CL) investigation, performed on layers of GaAsxP1−x mismatched to GaP barriers, was presented [A. Gustafsson, J. Jönsson, M. Gerling, M. R. Leys, M.-E. Pistol, L. Samuelson, and H. Titze, Inst. Phys. Conf. Ser. No 100, 771 (1989)]. In this paper the critical thickness with respect to the composition, x, in GaAsxP1−x, is studied from a determination of the onset of the formation of dislocations as observed in the monochromatic CL images. The experimental values of the critical thickness are compared to theoretical predictions for the critical thickness, according to different theories. The best agreement is found with the mechanical equilibrium theory, which assumes that the barrier for the formation of dislocations is negligible.

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: X-ray diffraction analyses of chemically derived Pb1−xLax(Zr0.65Ti0.35)1−x/4O3 powders were combined with a phenomenological theory to investigate the corresponding single-crystal thermodynamic properties of compositions approaching the relaxor ferroelectric phase transition region (x=0–0.04). The temperature dependence of the electrostrictive strain component, x4, could be described by the Landau–Ginsburg–Devonshire phenomenological theory taking Tc = 357 °C independent of La content (x). The single-domain, single-crystal elastic Gibbs free-energy density was calculated as a function of temperature and composition. The calculated results were discussed in relation to a simple superparaelectric model of relaxor behavior involving the temperature stabilization of noninteracting polar microregions.

Notes: Single-crystal GexSi1−x/Si superlattices have been successfully fabricated using remote plasma-enhanced chemical vapor deposition, a novel low-temperature thin-film growth technique. Reflection high-energy electron diffraction, cross-sectional transmission electron microscopy (XTEM), plan view TEM, x-ray-diffraction, and secondary-ion mass spectroscopy techniques have been applied to study the crystallographic properties of the superlattice structures. Arrays of dislocation lines, which are either parallel or perpendicular to each other, have been observed in the superlattices for those cases in which the total layer thickness exceeds the critical layer thickness. The location, orientation, and Burgers vectors of the misfit dislocation lines have been analyzed. Possible mechanisms of the generation of the misfit dislocations are also discussed.

Notes: The downstream near afterglow region of a hydrogen plasma is used to decompose and convert trimethylarsine (TMAs) into methylarsine homologs [(CH3)3−xAsHx, where x=1,2,3] including that of arsine (x=3). Approximately 30%, 17%, and 10% of the TMAs is converted into dimethylarsine (DMAs), monomethylarsine (MMAs), and arsine, respectively, while 28% remains undecomposed. Hydrogen is replaced by deuterium to isotopically verify that the origin of the arsenic hydrogenation occurring during gas conversion arises from both the plasma gas and fragmented hydrogen from the TMAs. Deuterium tagging of the MMAs, DMAs, and hydrocarbon byproducts is consistent with TMAs decomposition via plasma initiated CH3 radical removal and explains why the predominant light stable hydrocarbon produced is methane while ethane and acetylene account for the main higher hydrocarbons.

Notes: Thin (3–300-nm) oxides were grown on single-crystal silicon substrates at temperatures from 523 to 673 K in a low-pressure electron cyclotron resonance (ECR) oxygen plasma. Oxides were grown under floating, anodic or cathodic bias conditions, although only the oxides grown under floating or anodic bias conditions are acceptable for use as gate dielectrics in metal-oxide-semiconductor technology. Oxide thickness uniformity as measured by ellipsometry decreased with increasing oxidation time for all bias conditions. Oxidation kinetics under anodic conditions can be explained by negatively charged atomic oxygen, O−, transport limited growth. Constant current anodizations yielded three regions of growth: (1) a concentration gradient dominated regime for oxides thinner than 10 nm, (2) a field dominated regime with ohmic charged oxidant transport for oxide thickness in the range of 10 nm to approximately 100 nm, and (3) a space-charge limited regime for films thicker than approximately 100 nm. The relationship between oxide thickness (xox), overall potential drop (Vox) and ion current (ji) in the space-charge limited transport region was of the form: ji ∝ V2ox/x3ox. Transmission electron microscopy analysis of 5–60-nm-thick anodized films indicated that the silicon-silicon dioxide interface was indistinguishable from that of thermal oxides grown at 1123 K.High-frequency capacitance-voltage (C-V) and ramped bias current-voltage (I-V) studies performed on 5.4–30-nm gate thickness capacitors indicated that the as-grown ECR films had high levels of fixed oxide charge ((approximately-greater-than)1011 cm−2) and interface traps ((approximately-greater-than)1012 cm−2 eV−1). The fixed charge level could be reduced to ≈4×1010 cm−2 by a 20 min polysilicon gate activation anneal at 1123 K in nitrogen; the interface trap density at mid-band gap decreased to ≈(1–2)×1011 cm−2 eV−1 after this process. The mean breakdown strength for anodic oxides grown under optimum conditions was 10.87±0.83 MV cm−1. Electrical properties of the 5.4–8-nm gates compared well with thicker films and control dry thermal oxides of similar thicknesses.

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: 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: In this work a new ammonia gas sensor is presented. Schottky barrier devices, Pt/n-GaAs, with discontinuous platinum films are sensitive detectors of ammonia gas in a wide temperature range (from room temperature to 150 °C). The effect of parameters such as operation temperature, thickness of the catalytic metal film, background atmosphere, and applied voltage bias on the device sensitivity are investigated. In addition, significant characteristics have been examined including sensitivity limits, linearity of response, and adsorption and desorption kinetics.

Notes: We describe a complete theoretical model to calculate the open circuit voltage, the light generated current density, and the conversion efficiency of thin and thick emitter silicon solar cells. We show the importance of the Fermi carrier degeneracy, in addition to the heavy doping effects such as band-gap narrowing and Auger recombination. For example, in contradiction to recent calculations, the conversion efficiency of thin passivated emitter solar cells is shown to be independent of the surface dopant concentration. Also, in agreement with experimental results, but contrary to old conventional cell designs, it is shown that the conversion efficiencies of thick emitter solar cells can be as high as those of thin emitter cells. The last result will occur whenever the emitter is well passivated and the surface impurity concentration is relatively low (Ns=1×1019 cm−3). For non-passivated solar cells it is better to have thin emitters and high surface dopant concentrations (Ns(approximately-greater-than)2×1020 cm−3) as usual in conventional solar cells.

Notes: A possibility to determine exciton energy levels in superlattices in a simple way based on the contactless photovoltaic effect measurement is demonstrated. Good agreement between results obtained from the photovoltaic effect and from the optical reflectivity measurements was found.

Notes: A new type of guided-wave electro-optical intensity modulator is proposed and analyzed. The waveguide consists of an N-type Si core layer on a P-type Si substrate. Foward bias on the N+-N-P-P+ diode decreases the refractive index of the core and displaces the fundamental guided mode downward into the substrate. However, the mode is not extinguished because the substrate is bounded by a P+ contact. A spatial filter at the output converts the mode displacement into optical intensity modulation. A Poisson and continuity equation solver and multilayer waveguide simulation were used to obtain numerical estimates of mode displacement in a realistic structure.

Notes: Glass particles having mean diameters of 20 μm were deposited onto substrates consisting of cross-linked polyurethane having Young's moduli of 2.5 and 32 MPa. The surface-force-induced contact radii were then determined, as a function of time for periods between 20 and 3600 min, using scanning electron microscopy. No changes in the contact radius with time was found with either substrate. This suggests that the 0.75 power dependence of the contact radius on particle radius, for particles in contact with polyurethane substrates, previously reported [D. S. Rimai, L. P. DeMejo, and R. C. Bowen, J. Appl. Phys. 66, 3574 (1989)] was not caused by viscous response of the substrate.

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.

Notes: Studies have been conducted on the etching characteristics of Si in a microwave plasma etching system having a pulse-modulated source. The experiments were performed at several pulse widths and duty cycles, as well as at cw, to determine how etch rate varied. Results indicate that the etch rate of Si increases and approaches that in a cw discharge as pulse width decreases even though total microwave energy is markedly reduced. Langmuir probe measurements suggest that these effects may be due to increased ionization early in the plasma pulse.

Notes: Based on detailed equation-of-state calculations, it is shown that the relationship between the shock-wave velocity Us and the particle velocity Up for shock-compressed dry air can be represented accurately by the linear relation Us = a(P0) + b(P0)Up in a wide range of Up (2≤Up≤9 km/s) and initial pressure P0 (10−6≤P0≤1 atm) where a and b are given by the cubic polynomials of log10P0. An accurate analytic expression for the adiabatic exponent is derived by utilizing the linear relation.

Notes: We report the two-photon photoelectric sensitivities of a granular silver film and a silver covered diffraction grating at the photon energy (h-dash-bar)ω=3.5 eV of a frequency-tripled Nd:YAG laser when surface plasmons are excited. Values higher than 3×10−15 A cm2 W−2 have been obtained with both structures which correspond to a one-photon quantum yield of 1×10−5 under a 1-GW-cm−2 incident laser power density. These photoemitters could be used as high current density electron sources by illuminating them with picosecond or subpicosecond lasers in the 2–4-eV spectral range.

Notes: We report a new theory for electronic conduction in thin (150 A(ring)) oxynitride films. The present experiment reveals that the electronic conduction mechanism in the oxynitride deviates from that in conventionally grown silicon oxide in the electric field ranging from 6 to 14 MV/cm and suggests that the electronic conduction is governed by three different mechanisms according to the strength of electric field. We suggest that the current conduction is trap-assisted at electric fields lower than 8 MV/cm. Specifically, the conduction is due the tunneling of electrons into the shallow traps in the insulator. In the high-field region ((approximately-greater-than)10 MV/cm), the Fowler–Nordheim (FN) effect becomes dominant and depends on the dielectrics preparation conditions. In the moderate-field region, traps can be filled by both FN current and direct tunneling of electron into the traps which result in a quasi-saturation in the leakage current. The experiment also shows a turnaround behavior in leakage current level, ledge in current-voltage characteristics, and field dependency of the current as the nitridation proceeds. These observations can be readily explained based on the proposed conduction mechanism.

Notes: Recently, Wu, Yang, and Evans [J. Appl. Phys. 68, 2845 (1990)] ascribed excess negative and positive capacitances at abrupt Schottky diodes to interface charges and a "waterfall'' of electrons "falling off the Schottky barrier cliff.'' This comment points out that such strange admittances are not related to interface charge at the front Schottky contact but to defective back contacts, as previously demonstrated [Phys. Rev. Lett. 60, 53 (1988) and Mater. Res. Soc. Symp. Proc. 91, 433 (1987)].

Notes: We have theoretically investigated the output performance of a pulsed discharge initiated H2/F2 chain first vibrational overtone HF chemical laser. The model used included rotational relaxation processes and simulated simultaneously both fundamental and overtone oscillations since the undesirable fundamental lasing cannot completely be suppressed during the experimental overtone oscillation. In the H2/F2 chain reaction system, which can produce the highly vibrationally excited HF(v) molecules up to vibrational level v=6, higher overtone output energy can be expected due to the increased vibrational overtone P branches, the increased transition probability of the first overtone transitions at the higher vibrational levels, and to the relative longer gain duration of a few tens microseconds. The overtone output energy of 2.73 J/l is obtainable from the laser gas mixture of F2/H2/He=10/4/786 (Torr). Adding He diluent gas can effectively suppress the undesirable fundamental lasing by pressure broadening; the overtone output energy is much less sensitive to this effect. The overtone output energy is found to be dependent on the residual reflectivity of the resonator mirrors over the fundamental lasing band.

Notes: The silicon integrated-circuits chip is built by contiguously embedding, butting, and overlaying structural elements of a large variety of materials of different elastic and thermal properties. Stress develops in the thermal cycling of the chip. Furthermore, many structural elements such as CVD (chemical vapor deposition) silicon nitride, silicon dioxide, polycrystalline silicon, etc., by virtue of their formation processes, exhibit intrinsic stresses. Large localized stresses are induced in the silicon substrate near the edges and corners of such structural elements. Oxidation of nonplanar silicon surfaces produces another kind of stress that can be very damaging, especially at low oxidation temperatures. Mismatch of atomic sizes between dopants and the silicon, and heteroepitaxy produce another class of strain that can lead to the formation of misfit dislocations. Here we review the achievements to date in understanding and modeling these diverse stress problems.

Notes: The quantum-well laser is described in terms of the appropriate quasi-Fermi levels and Einstein coefficient for stimulated emission. Emission frequencies, thresholds currents temperature dependencies, and linewidths are determined as a function of the quantum-well parameters, the photon lifetime, the temperature, and the emission coefficient. Correlation with existing data is demonstrated.

Notes: The reflection and transmission properties of finely divided fractal layers are investigated and characterized. The results for electromagnetic or optical waves normally incident upon generalized Cantor bar fractal multilayers are found for various fractal dimensions and stages of growth. A new exact self-similar algorithm is described which makes use of the self-similarity of the structures to clearly display the underlying physics. This fractal computational scheme provides the reflection and transmission coefficients for fractally distributed layers with extreme economy when compared to traditional approaches. Finally, a method for extracting fractal descriptors from scattered data is discussed. High- and low- frequency regimes are examined.

Notes: The role of the equation of state (EOS) is reviewed as an analytical vehicle to express material pressure as a function of density and temperature (or internal energy in the case of adiabatic transition). Starting from the fundamental laws of thermodynamics, three criteria are developed to measure the stability of equations of state, and are applied specifically to the Mie–Grüneisen EOS, with Hugoniot reference, to investigate the stability characteristics thereof. This EOS is singled out for study because of its relative importance in the computational modeling of shock transition. Results indicate numerous possibilities of instability under various circumstances. Various remedies are proposed to correct the observed instabilities and compared with existing models.

Notes: Elastic differential and total cross sections for positrons, from 5 eV to 10 keV, and for electrons, from 50 eV to 10 keV, scattered by bound gallium and arsenic atoms have been calculated using the method of partial waves. The optical potential consists of a static potential, a Buckingham-type polarization potential, and the Mittleman–Watson exchange potential (for electrons). Low-order partial wave phase shifts are computed by numerical integration of the radial part of the Schrödinger equation. For higher orders, a closed analytic expression is obtained in the first Born approximation for the phase shifts. The calculated total cross sections are parametrized in terms of the screened Rutherford cross section to be used in Monte Carlo transport codes.

Notes: The degradation during cw operation or under electron beam bombardment of the graded index separate-confining heterostructure laser devices grown on Si and on GaAs substrates was investigated. The induced current and the cathodoluminescence modes of a scanning electron microscope were used to observe the cleaved face of these devices as a function of the stage of degradation. Our findings strongly suggest that the degradation starts owing to a mechanism of donor annihilation and complex formation within the space-charge region of the device. Two different methods allowing the evaluation of the donor concentration within the depletion zone were developed. One method is based on the measurement of the direct bias necessary to recover the initial microscopic characteristics of a damaged device. The other one relies on a numerical calculation of the partition of nonequilibrium carriers which takes into account the detailed structure of the device. This calculation is based on a three-dimensional analytical function describing the energy losses of the primary electrons.

Notes: Quantitative measurements of ablated material from the surface of polyethyleneterephthalate (PET) by 248-nm excimer laser fluences up to 10 J/cm2 are performed by HeNe laser-beam deflection in vacuum and by photoacoustic depth profiling in air. HeNe laser-beam deflection measures the density of gas phase material present in the ablation plume. Photoacoustic depth profiling is a nonintrusive diagnostic that directly measures the etch depths from laser ablation. A hydrodynamic model consisting of a centered rarefaction wave that reflects off the PET surface is shown to describe the laser deflection signals. From these measurements an estimate of the initial temperature of the ablated species is found.

Notes: Tracer correlation factors have been calculated by simulating the diffusion of atoms and defects on a computer using a Monte Carlo technique. The correlated motion of the atomic species by a vacancy mechanism have been investigated for a binary random alloy with fcc structure. The tracer correlation factors for the atoms, fA and fB, and for the vacancies, fV, are calculated as functions of the jump frequencies, and the mixing ratio of A and B atoms for vacancy concentrations of cV = 0.001 and 0.1. The results are compared with theories and Monte Carlo simulations from the literature. Substantial discrepancies with previous Monte Carlo studies are observed. It is concluded that the correlation factors given in the literature are systematically too high because the jump sequences in those calculations were too short.

Notes: The production process for the formation of H− ions in a surface conversion source is sputtering of hydrogen atoms from the converter surface layers by incident positive ions, followed by electron attachment via resonant charge exchange with the converter surface. The sputtering process is in direct relation to the converter surface composition. New experimental data led us to identify two different classes of converters: metallic converters, like solid barium(binary) and adlayer converters, like cesium on tungsten (ternary). For a binary converter the hydrogen in the surface layers is directly sputtered by the incoming ions. Consequently, the negative ion yield scales with the hydrogen concentration in the surface layers. In the cesium/tungsten system (ternary) the hydrogen at the surface is believed to be sandwiched between the cesium adlayer and the tungsten surface. Hence, the negative ion yield scales with the sputter coefficient of hydrogen on adsorbed cesium. This is experimentally confirmed.

Notes: Gold films were deposited on quartz-crystal microbalances by decomposing C7H7F6O2Au (dimethyl gold hexafluoroacetylacetonate) with 2–10-keV Xe+, Kr+, Ar+, Ne+, or He+ ion beams. The number of molecules decomposed per incident ion (i.e., the total decomposition yield) was determined as a function of ion mass and energy. The total decomposition yield increases with increasing ion mass and ion energy, and is approximately proportional to the nuclear stopping power. A binary collision model and a thermal spike model are developed that relate the energy deposited by the ion, at the substrate surface, to the total number of molecules decomposed. Both models predict total decomposition yields that are in reasonable agreement with the experimental measurements; however, the variation of total yield with changes in ion mass and energy are best described by the binary collision model. The success of both models demonstrates that the energy deposited into the substrate surface through the ion-solid interaction is responsible for the decomposition of adsorbed molecules.

Notes: The refractory metal disilicides TiSi2 and TaSi2 were investigated for their usefulness as dopant diffusion sources. During furnace annealing and rapid thermal processing, strong decomposition reactions occur between the dopants D (B or As) and the respective silicide (MSi2) to form MxDy compounds. With the help of special sample preparation methods and various analytical techniques, the compound phases TiB2, TiAs, TaB2, and TaAs were unambiguously detected. The fraction of freely diffusing B in TaSi2 is determined to be below 5% of the total dose; by far, the major part of the dopant is bound within the TaB2 phase detected. Careful sample preparation and analysis of secondary-ion-mass spectrometry profiles is necessary to avoid artifacts caused by these compound particles. The MxDy-compound formation has detrimental consequences: The solubility of arsenic and even more of boron in TiSi2 and TaSi2 is limited to rather low-concentration levels (e.g., B in TaSi2: 4 × 1018 B/cm3 〈 CB(900 °C) 〈 1.6 × 1019 B/cm3) and the outdiffusion into poly- or monocrystalline silicon is strongly retarded. Also, the low interface dopant concentrations achievable result in unacceptably high values of contact resistance. The observations on metal-dopant- (M-D-) compound formation are demonstrated to agree well with the predictions from thermodynamic calculations on the respective M-Si-D system. The effects on junction formation are compared to the case of WSi2 and CoSi2, which, from a parallel study, are known not to form compounds. In all cases these comparisons support our statements on the tremendous impact of M-D-compound formation, because much improved data on diffusion and junction formation were obtained for CoSi2 and WSi2. The same holds for a comparison on contact resistances for silicide diffused junctions, which was performed for TiSi2 and CoSi2.

Notes: Viewing the brittle-to-ductile transition of fracture in intrinsically brittle solids as a crack tip initiated critical event of either nucleation of dislocation loops from the crack tip or the motion away of such dislocations from the crack tip, experiments have been devised to measure the critical activation energy of such events by measuring the arrest temperature of cleavage cracks with different velocities in experiments that were conducted on large Si single crystals subjected to a steep temperature gradient. While such experiments can provide precise information that can be related directly to mechanisms of crack tip bifurcation behavior, they are hampered by nontrivial perturbations that must be controlled. Here in the first of a series of communications we discuss the nature of these perturbations in Si single crystals, cleaving either on the {111} or the {110} planes.

Notes: The electrical and optical properties of AlGaAs grown by metalorganic molecular-beam epitaxy using triethylaluminum, tri-isobutylaluminum, and trimethylamine-alane are compared. It is found that tri-isobutylaluminum yields the lowest residual carbon incorporation in the layers (Na − Nd = 4 × 1015 cm−3) and the highest electron and hole mobilities. Photoluminescence spectra for the higher-quality AlGaAs, grown using TiBAl, show excitonic luminescence. However, this luminescence appears to be defect related.

Notes: Gold-hydrocarbon composite thin films with various metal volume fractions have been deposited by a combination of sputtering and plasma deposition in argon-propane plasma. Partial pressure control and optical spectroscopy of the gas phase have shown the growth processes to be partially dependent on the chemical reactions occurring on the substrate. The polymer matrix structure was analyzed by several techniques and found to consist of dense hydrocarbon with a density of 1.7. For low metal volume fractions, optical spectra of films show that the dielectric nature of the polymer predominates while the metallic phase governs the absorption phenomenon for gold-rich films. Electrical conductivity measurements have revealed the influence of graphitic structures in the film just above a metal volume fraction p=0.03, below which carbon-carbon sp2 bonds are more predominant. Similarly the percolation threshold has been found to occur at about p=0.3 and the conductivity exponent is evaluated at 1.55.

Notes: The titanium (Ti)/single-crystal silicon (Si) interface has been examined by cross-section high-resolution transmission electron microscopy (HRTEM) combined for the first time with 2-nm-diam probe, energy-dispersive spectrometry. HRTEM shows that thin Ti-Si alloy formation always occurs at the interfaces, even in the as-deposited state. The thickness of the reacted alloy depends on the crystallinity of the Si surface, but does not depend on impurities or doping level. Crystallization of the Ti-Si alloy depends on the annealing temperature; it remains in the amorphous phase after annealing at temperatures lower than 430 °C, and the C49 TiSi2 crystal phase was observed as the first crystalline phase after annealing at 460–625 °C. The composition of the Ti-Si alloy at the Si interface is close to TiSi2, and it remains amorphous with variable composition across the alloy. It seems that the electrical barrier height is determined by the degree of crystallinity of TiSi2 at the Si interface. The barrier height for TiSi2/p-type Si interface decreases from 0.73 to 0.57 eV, accompanied by the crystallization of TiSi2 at around 460 °C.

Notes: Tribological structural changes in plasma-produced fluoropolymers are investigated by polarized microinfrared spectroscopy. The olefinic structures, which arise from the defluorination of fluorocarbon frameworks by friction, are enhanced in the friction products remaining in the severely rubbed trace. The C—F bond softening, indicated by a downward shift in the C—F stretching peak, is confirmed in the friction products, comparing with unrubbed film. The degree of bond softening in the friction products increases with increasing the degree of rubbing severeness. Polarization analyses of the C—F stretching band reveal that the carbon frameworks of the friction products remaining in the vigorously rubbed trace are oriented in the rubbing direction.

Notes: A new class of bipolar-charge-transporting molecularly-doped polymers has been developed. The materials are ternary solid solutions comprised of 3,5-dimethyl-3',5'-di-tert-butyl-4,4'-diphenoquinone (MBDQ), N,N,N',N'-tetrakis (m-methylphenyl)-1, 3-diaminobenzene (PDA), and poly(4,4'-cyclohexylidenediphenyl carbonate) (PC-Z). No charge-transfer complexation occurs between the MBDQ and PDA. As a result the MBDQ and PDA function independently as electron and hole transport manifolds, respectively. Both electrons and holes can be injected into these materials from titanylphthalocyanine (TiOPc). In addition, it has been observed that the presence of MBDQ and PDA enhances the charge separation efficiency of the TiOPc.

Notes: Hall-effect measurements in magnetic fields up to 1.5 T are performed on β-FeSi2 films between 20 and 300 K. An anomalous low-field Hall coefficient R1 in addition to the normal high-field Hall coefficient R0 is detected at temperatures below 250 K. The temperature dependence of R0 is explained by a two valence-band model and an impurity level located close to the upper valence-band edge. The temperature dependence of R1 indicates that β-FeSi2 behaves as ferromagnetic below 100 K. Correlation between the coefficient Rs=R1−R0 and the electrical resistivity ρ indicates a drastic change in magnetic ordering at about 70 K.

Notes: At low oxygen potentials, YBa2Cu3O7−x decomposes by chemical reactions involving reduction. The results of this study show that the compound also decomposes at higher oxygen potentials. The initial decomposition products were found to be Y2BaCuO5 and a Ba-Cu oxide phase. The Ba-Cu phase was found to be a peroxide-type and the decomposition can be described by a chemical reaction involving oxidation: 4(YBa2Cu3O7−x)+(1/2 − 3/2δ +2x)O2(arrow-right-and-left)2Y2BaCuO5+3Ba2Cu3O6−δ+CuO. At 800 °C the equilibrium pressure for this reaction is slightly 〈1 bar, and the enthalpy change is ∼80-kJ/mol Y123. This result is not consistent with the conclusions drawn from some other studies of the stability of the superconducting Y-Ba-Cu-O compounds, and the differences are discussed.

Notes: The current-voltage (I-V) characteristics of silicon-incorporated polyethylene films fabricated by plasma polymerization have been measured at very high electric fields. The experimental results show that the electric conduction at high fields is due mainly to Fowler–Nordheim type tunneling injection of holes from the anode, and that the incorporation of silicon in polyethylene creates hole traps, thus suppressing the conduction current and enhancing the breakdown strength. The amount of positive space charge resulting from the hole trapping increases with increasing magnitude and duration of the applied field for a fixed silicon content, and increases with increasing silicon content for a fixed magnitude and duration of the applied field. This positive space charge tends to suppress the actual field at the hole injecting contact and to enhance the actual field at the electron injecting contact. For fields higher than a certain critical value, the rate of the current increase with field changes rapidly. This phenomenon is attributed to the onset of double injection. This means that the contribution of the electron current to the total current becomes significant due to the gradual enhancement of the field at the electron injecting contact by the large amount of accumulated positive space charge. It is concluded that silicon incorporated in polyethylene introduces new hole traps which in turn reduces the hole mobility and creates more positive trapped space charge. The overall effect would be to reduce the conduction current and to increase the breakdown strength of the polyethylene if a proper amount of silicon is incorporated in it.

Notes: A photoluminescence study has been made, at temperatures 2–300 K, on indium-alloyed semi-insulating GaAs subjected to bulk heat treatments. Heat treatments were made by slow and fast cooling following a 15 h, 950 °C soak. Two intrinsic acceptors at Ev + 0.069 eV and Ev + 0.17 eV are produced after heat treatments. The acceptor at Ev + 0.069 eV is attributed to the intrinsic pair defect GaAs−VGa and is produced more in the fast-cooled materials than in the slow-cooled materials. The deficiency of intermediate deep donors causes no drastic variation of the electron concentration after the heat treatments.

Notes: The influence of the physical properties of polymers on their plasma behavior has been investigated under O2 and Ar plasma treatments. The glass transition temperature (Tg) has been found to be an important parameter. A steplike increase in the etch kinetics in O2 plasmas has been correlated to the change in the heat capacity of the polymer occurring above Tg whatever the molecular weight of the polymer. Furthermore, above Tg, changes in the viscoelastic properties induce bulk polymer degradation if chain crosslinking cannot be achieved before or during plasma etching.

Notes: This paper presents a review devoted to the problem of how optical and structural properties of quantum-well heterostructures (QWH) can be correlated in detail, and how these properties may be connected with the parameters of the epitaxial growth process. It demonstrates how luminescence techniques, mainly photoluminescence (PL) and cathodoluminescence imaging (CLI), may be used for evaluation of the structural disorder on the atomic scale, which occurs at the growth surfaces creating the interfaces of the QWH. The physics of the excitonic luminescence in QWH (theory and experiment) is presented in detail in the first part of the review. This is followed by a comprehensive discussion of experimental aspects (hardware and software) of the luminescence techniques, as applied for studying QWH grown by molecular-beam epitaxy (MBE) and metalorganic vapor phase epitaxy (MOVPE). The specific features of both the epitaxial growth techniques, when used for growing QWH are presented in the next part of this review. Finally, the possibilities of application of PL and CLI to studies on growth of QWH by MBE and MOVPE are demonstrated on a couple of selected examples. The review concludes with a short discussion on possible interpretation mistakes which may occur when one applies the CLI to studies of interfaces in QWH without taking into account the basic parameters of the excitonic luminescence lines creating the CL images of the relevant interfaces.

Notes: We present a numerical investigation of all-optical switching of solitons in two- and three-core nonlinear fiber couplers. Both self-switching of solitons and phase-sensitive switching are considered. The extension of the results to multicore couplers is briefly discussed.

Notes: Output characteristics of an optically pumped tantalum vapor laser and the distribution of tantalum vapor generated by irradiation of a laser have been investigated experimentally. Ta vapor is generated by irradiation of a pulsed YAG laser and then the Ta atoms are optically pumped by a KrF excimer laser. It is observed that the maximum output energy is 160 nJ, the maximum optical conversion efficiency is 0.01%, and the ground-state Ta atoms are distributed not only in the luminous space of the vapor but also around it.

Notes: Pinch formation in fiber pinch experiments has been investigated in the lower terawatt regime. The main results are: (1) there are upper limits of breakdown voltage (∼700 kV) and current rise rate (∼20 kA/ns) beyond which leak discharges develop within the vacuum feed of the pulseline KALIF; (2) there is a lower limit of fiber radius (∼10 μm) below which pinch disruptions take place at a pinch current of (approximately-greater-than)300 kA; (3) the hot (Te≤1 keV) inhomogeneous pinch plasma develops typically 10 ns after local collapses (micropinches) at a pinch current (approximately-greater-than)400 kA and lives for more than 50 ns; (4) neutron emission (yield of CD2 fibers ∼1010) appears mostly isotropic; (5) all fiber pinches show global expansion with velocities reaching from typically 10 μm/ns (initial expansion) to (approximately-greater-than)100 μm/ns; and (6) the power requirements for the fiber ablation process are contradictory to those for the final pinch phase.

Notes: This paper deals with two major problems often encountered in analyzing the measured autocorrelation functions in photon correlation spectroscopy of semidilute polymer solutions and gels: partial heterodyning and the interpretation of slow relaxation modes. These topics are discussed in the context of measurements of semidilute aqueous polyacrylamide solutions and gels used as electrophoresis media. Following a review of basic principles of Rayleigh light scattering and photon correlation spectroscopy, data analysis procedures, including the constrained Laplace inversion program contin, are first re-examined by presenting the results from aqueous latex standard solutions. The method to analyze the partial heterodyne autocorrelation function is then presented and tested against the simulated partial heterodyne autocorrelation functions. Finally, the recently observed slow relaxation modes in polyacrylamide solutions are examined in detail with a test of contin against the simulated autocorrelation functions consisting of a trimodal distribution of relaxation rates. The results confirm that the slow relaxation modes detected in polyacrylamide solutions are indeed physical modes originating from structural relaxation and interdiffusion.

Notes: We have measured the photoreflectance spectra of a strained layer (001) In0.21Ga0.79As/GaAs single quantum well as a function of temperature in the range 10 K〈T〈500 K. The details of the lineshape of the fundamental conduction to heavy-hole feature (11H) demonstrates its excitonic nature even up to 500 K. From the temperature dependence of the 11H linewidth we have obtained important information about the quality of the material and interface. The variation of the 11H energy gap with temperature agrees with that of bulk material. Comparison of the energies of 11H and higher lying transitions with an envelope function calculation yields a conduction band offset parameter Qc=0.65±0.07.

Notes: Based on general rotationally invariant nonlinear electroelastic equations (energy balance equation and Gibbs function expansion), a complete and deductive derivation of constitutive equations for an electroelastic media upon mechanical or electrical bias has been presented. Bilinear constitutive relations for large quantities have been given and linear, but parametric constitutive formulas for small-field variables have been derived in the reference or intermediate frame. Equations of motion and boundary conditions in the respective configurations, required to solve dynamical problems, are also reported shortly for completeness. Presented reformulation of constitutive equations may be useful in solving nonlinear problems of electromechanical interactions in crystals, for example in analyzing sensors of nonelectric quantities with electric output or modulators.

Notes: A novel intense source of 2.45 MeV neutrons is described. Exploratory experiments with deuterated polyethylene fibers in an x-pinch configuration have been performed using 370-kA, 80-ns current pulses. Up to 4.5×108 neutrons per pulse have been produced. Compared to a z pinch, an x pinch produced about the same number of neutrons for the same current, but the x-pinch neutron source may be 1 mm or less in diameter.

Notes: The application of the magnetic discharge stabilization technique to high-pressure laser discharges is investigated. Scaling laws are developed with the help of Monte Carlo simulations for the transverse discharge velocity and for the magnetic field strength that is necessary for discharge stability. The results that are obtained indicate that the required magnetic field strength scales as the pressure squared. Unless a cost-effective means is found for implementing a very strong magnetic field into an electrode design, the magnetic discharge stabilization technique will be mainly relegated to low-pressure systems.

Notes: Polycrystalline thin films (1–10 μm) of the nonlinear material 2-methyl-4-nitroaniline were deposited on Ag, Cu, and Si by conventional and partially ionized beam deposition. The use of ions was seen to promote a highly oriented film, with only the single x-ray diffraction orientation (112) being observed at reduced temperatures (−50 °C). The effect of the ions on the physical microstructure of the films was to densify the film and reduce the size of the microcrystals. The films had powderlike optical properties and displayed a strong second harmonic from a Nd:YAG laser.

Notes: 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.

Notes: Formulas are derived for treating the carrier density and energy in isotropic nonparabolic bands using 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 as a function of spatial dimension, including the quasi-one-dimensional case of a bulk semiconductor in a homogeneous magnetic field. 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: We study the thermoelectric properties of a composite medium. Various approximations are developed for calculating the matrix Qˆe of the bulk effective transport coefficients of the medium, including exact upper and lower bounds for Qˆe under various conditions. Results are especially detailed for two-component composites, where a field decoupling transformation is used to reduce the thermoelectric problem to two uncoupled quasi-conductivity problems. Exact bounds are then obtained for the absolute thermopower αe and the thermoelectric figure of merit Ze in two-component composites. We prove that Ze of the composite can never exceed the largest value of Z in any component. Some of these results are extended to certain classes of multicomponent composites.

Notes: We determined the single particle relaxation time τs and the classical transport scattering time τt out of Shubnikov-de Haas (SdH) measurements at a GaAs-AlGaAs-GaAs double heterostructure consisting of a normal and an inverted interface. As a result we find that even in inverted heterostructures the classical scattering time τt is an order of magnitude larger than the single particle relaxation time τs. From a comparison with theoretical calculations including scattering from remote impurities, interface charges, and interface roughness, we conclude that the mobility in inverted heterostructures at low temperatures is dominated by Coulomb scattering from remote dopants and interface charges in the barrier, rather than interface roughness scattering. Nevertheless, the mobility of the inverted interface turns out to be significantly lower than that of a normal interface.

Notes: a-SiNx:H films of various composition x were deposited by rf glow discharge (GD). The deposition rate was analyzed for three ranges of gas flow ratio R = [NH3]/[SiH4] depending on the deposition mechanism. Properties of these films were measured by means of x-ray photoelectron spectroscopy (XPS), infrared (IR) absorption, optical absorption, and the temperature dependence of electrical conductivity. The composition x was determined by XPS. For large values of R, x was found to be saturated at 1.7. The variation of H content was detected by IR absorption. The variation of coordinating atoms of Si with increasing x was deduced from the variation of XPS spectra of the Si 2p core-level and the shift of Si-H stretching vibration frequency in IR absorption. Based on the random bonding model and assuming bonding units to the central Si atom to be Si, N, and NH, probabilities of Si tetrahedra with various coordinating units were obtained. The results indicate that there are many Si—Si bonds for the stoichiometric x=1.33 and that the concentration of Si—Si bonds diminishes at around the saturation value x=1.7. These results seem to imply that the presence of Si—Si bonds to some extent is a prerequisite condition for film deposition by GD. Experimental results of optical absorption analyzed by Tauc relation revealed the presence of two kinds of x region whose properties are quite different.For x〈1.5, its optical absorption is similar to a-Si:H modified by the presence of N. With increasing x, the optical band gap EO increases and B coefficient in the Tauc plot decreases. At about x=1.5, Si—Si bonding effectively disappears and the optical absorption abruptly changes to that similar to β-Si3N4. Considering these results, the change of electronic band structure with x was deduced on the basis of the atomic structure obtained above and by the tight binding approximation. For x〈1.5, the optical band gap is due to Si—Si bonding, the energy gap of which increases, and the linear band tail becomes broad with increasing x. From the observed temperature dependence of conductivity, variations of the activation energy and pre-exponential factor are obtained with x up to x=1.0. For the decrease of conductivity with x, the contribution from the pre-exponential factor is much larger than that from the activation energy. This result can be understood by a transport mechanism in the electronic band structure obtained above. Finally, it is concluded that the electronic properties of a-SiNx:H deposited by GD ran.

Notes: The effect of temperature and atmosphere on stability of the high-Tc phase in Bi1.8Pb0.4Sr2Ca2Cu3Ox superconductors has been investigated using ac susceptibility, x-ray diffraction, and Raman measurements. It is found that the high-Tc phase becomes unstable due to the structural phase transformation at temperature above 650 °C in O2 of 1 atm. The formation and the decomposition of the high-Tc phase is found to occur through the medium of the Ca2PbOx phase and depends on oxygen partial pressure at temperature above 650 °C.

Notes: The effect of fluorine on electron trapping in SiO2 films has been studied by avalanche electron injection. Samples are prepared by 25-keV fluorine implantation into dry oxides followed by a 1000 °C N2 ambient anneal. Bulk electron traps with capture cross sections on the order of 10−17–10−19 cm2, which are not due to implantation damage, are filled by avalanche electron injection. An optimum dosage of fluorine implantation to suppress the so-called turnaround effect during avalanche injection exists. This suggests that fluorine might passivate slow interface donor states or reduce bulk hydrogen diffusion. The observation that high-temperature (120 °C) injection can eliminate most fast and slow interface states for conventional oxides is also true for fluorinated oxides. Our results indicate an enhanced generation of fast donor states for oxides containing fluorine. These states contribute a positive charge when the Fermi level is in the lower portion of the band gap.

Notes: We report on the use of the scanning tunneling microscope (STM) for etching both single crystal and thin film, YBa2Cu3O7−x. Nanoscale features can be generated with the STM by ablation of atoms rastered by the microscope tip. The etching process can be controlled to remove layers of material which are multiples of the c axis (12 A(ring)). Various geometric features have been fabricated ranging from fine lines to square etch pits. The STM has also been used to study the growth mechanism and surface topography of thin films of YBa2Cu3O7−x produced by in situ laser deposition (Jc typically 1×106 A cm−2 at 77 K). Step features equal to the c axis of the material can be readily identified which form pinnacles or chip like morphologies at the surface. These surfaces can also be etched with the STM to reveal a more continuous substructure consistent with the high Jc's observed.

Notes: Intermetallic Sm(Fe1−xCox)2 compounds having the cubic MgCu2-type structure absorb a small quantity of hydrogen from the atmosphere under normal conditions. A magnetic annealing of such samples leads to the induction of a gigantic magnetic uniaxial anisotropy, which is linked to the ordered distribution of hydrogen into interstitial sites of the lattice. In this paper the induced magnetic anisotropy and spontaneous lattice distortions are studied as a function of both composition and hydrogen content. It is shown that the induced uniaxial anisotropy which adds to the initial cubic anisotropy gives rise to the occurrence of first-order magnetization processes (FOMP). In the temperature range where spin reorientation transitions take place a peculiar behavior of the FOMP is observed.

Notes: The electro-optic Kerr effect and its wavelength dispersion have been measured in glasses representing several compositional systems. The measured Kerr effect was found to be large for glasses having large refractive indices, including: (i) glasses containing high concentrations of the heavy metals Pb, Bi, and Tl; (ii) glasses with high Nb, Ta, and Ti content; and (iii) tellurite glasses. Comparison of the third-order nonlinear susceptibility, χeff(ω = ω + 0 + 0), obtained from the measured electro-optic data, to values estimated from literature values of the optical frequency value, χeff(ω = ω + ω − ω) suggest an opposition of the electronic and nuclear contributions to the low-frequency electro-optic effect for the glasses containing Ti, Ta, or Nb.

Notes: In previous work we have identified a near-gap photoluminescence in Ga0.52In0.48P which exhibits a strong dependence of emission energy on excitation intensity ("moving emission'') and correlated its presence and strength to conditions of growth. In this work we extend our investigations to the rise and decay lifetimes associated with the moving and nonmoving components of the emission. The two processes proceed simultaneously at the same energy. For the moving emission, the time constants scale approximately linearly with excitation intensity. Decaying luminescence can, in most cases, be well fitted with one or two exponentials with time constants as long as milliseconds. The rising luminescence is typically slower and in some cases has a nonmonotonic first time derivative. These results are discussed in terms of existing models of the microstructure of ordered Ga0.52In0.48P.

Notes: The intensity change in optical absorption at 3.8, 5.0, and 5.8 eV was measured for thermal treatment up to 1000 °C done on silica glass samples manufactured by various methods. It was found that these absorption bands change differently with heat, depending on the synthesis process of the sample. The 3.8-eV absorption band due to peroxy linkage is found to increase with high-temperature treatment when the sample contains dissolved oxygen molecules within the sample. For the sample with no oxygen molecules, high-temperaturetreatment does not alter the absorption intensity at 3.8 eV. The 5.0-eV absorption band is found to decrease by high-temperature treatment. In the case of an oxygen-containingsample, the reaction of oxygen molecules with oxygen vacancy sites is a cause of this decrease. The 5.1-eV band, which was thought to have no temperature dependence, is found to be annealed at a temperature region around 950 °C.

Notes: Novel photoconductive polyimides have been developed, whose monomer units are composed of a series of thiophenylene moieties, -C6H4S-, and imide groups. The most photosensitive polyimide shows an excellent photosensitivity of less than 1.0 μJ/cm2 in the visible light region, 400–570 nm. These photosensitive polyimide films are prepared by polymerizing the cast prepolymer films and annealing at the melting points of the polyimides. In this process their photosensitivities remarkably increase with the increase of crystallinity. From the structural studies by ultraviolet visible absorption, x-ray diffraction, infrared absorption, and x-ray photoelectron spectroscopy measurements, it is proposed that the coplanary conformation takes place in the crystallizing. The overlapped π orbitals, perpendicular to the polymer chains, lead to the more expanded conjugate system.

Notes: Intracavity laser absorption spectroscopy was used to measure the number density of neutral ground state barium atoms desorbed from an operating dispenser cathode. The measurement suggests an order of magnitude value of 108 atoms/cm3 at a distance of 5 cm from the emitting surface. This is the first direct state selective measurement of the barium density near to the surface of an operating cathode which can be directly traced to conventional multipass absorption spectroscopy. The value we obtain is consistent with results reported by other workers using less direct methods and allows more detailed statements to be made concerning the chemical state of the Ba at the instant of desorption.

Notes: A phenomenonological model of topographic contrast in secondary electron microscopy is presented. This model involves exponential attenuation of isotropically generated secondary electrons. The effect of primary beam diameter and the material dependent secondary electron attenuation length on secondary electron images is demonstrated by explicitly computing linescans of images of straight surface steps. These computed linescans are directly compared with those obtained from monatomic surface steps on Si(100) imaged at normal incidence in an ultrahigh-vacuum scanning transmission electron microscope. An asymmetry in the experimental linescan cannot be fit by any combination of model parameters suggesting that this contrast is not simply due to surface topography. A simple explanation for the contrast reversal observed in secondary electron images of surface steps when the primary beam changes direction from the upstairs to the downstairs direction is presented. The possibility of determining secondary electron emission parameters and extracting surface chemical and electronic information using high spatial resolution secondary and Auger electron imaging is briefly discussed.

Notes: Device-quality a-Si:H thin films, grown by rf magnetron sputtering, were annealed in the temperature range up to 850 °C and studied by in situ ellipsometry, spectroscopic ellipsometry, and thermal evolution measurements. Annealing causes a volume reduction which can be as high as 5%, and after annealing at T(approximately-greater-than)800 °C the material becomes microcrystalline with an average crystallite size that depends on the annealing temperature. A detailed analysis of the peak height of the imaginary part of the pseudodielectric function 〈ε(ω)〉, combined with the examination of the fundamental gap, the average gap (Penn gap), and the refractive index of a-Si:H, provides new insight on the role of hydrogen and the structural modifications induced by thermal annealing. Based on the presented experimental findings we propose the following: (a) annealing below Ts causes reduction of the isolated microvoids; (b) the weakly bound hydrogen is correlated with regions with a high density of microvoids; and (c) the evolution of weakly bound hydrogen does not drastically influence the optical properties of the film while evolution of isolated hydrogen does. The rate of change of the optical properties as a function of T is (a) nearly constant for TT〈 Ts, (b) increases for T (approximately-greater-than) Ts, and (c) decreases dramatically for T(approximately-greater-than)600 °C, therefore indicating irreversible structural changes at T (approximately-greater-than) Ts mainly due to isolated hydrogen loss.

Notes: The oxidation kinetics of copper thin films have been studied at temperatures below 200 °C in air. The protection of copper from oxidation can be achieved by alloying copper film with Ti, Pd, Cr, or Al. The influence of the composition and microstructure to the oxidation rate has been studied. The compounds Cu3Ti, Cu3Pd, and CuAl2 are stable in the oxidation ambient. The formation of Cr-oxide, which is a passive oxide, explains the inhibition of oxidation on Cu-Cr films. Compared with the crystalline phase, the amorphous Cu65Ti35 alloy film is more oxidation resistant. A TiN layer with oxygen incorporated is more effective in preventing copper oxidation than a TiN layer without oxygen incorporated. A passivating Si3N4 layer on copper thin films can prevent copper oxidation effectively at 350 °C in oxygen ambient.

Notes: Adsorption of Ba and its effect on the GaAs(110) surface oxidation has been studied by low energy electron diffraction (LEED) and Auger electron spectroscopy (AES). The Ba adsorption onto the surface results in a disordered interface of Ba and the GaAs surface at temperatures 〈500 °C. However, the reactivity of the GaAs surface to oxygen is dramatically enhanced by the adsorbed Ba atoms. This enhancement of the surface oxidation is proportional to the Ba exposure. Study of LEED and AES intensities has also revealed evidence of Ba-induced surface disorder on the GaAs.

Notes: The oxidation kinetics of reactively sputtered amorphous Ta36Si14N50 thin films are studied in dry and wet ambient in the temperature range of 650–850 °C by backscattering spectrometry, Dektak profilometer, and x-ray diffraction analyses. The dry oxidation is well described by a parabolic time dependence which corresponds to a process controlled by the diffusion of the oxidant in the oxide. The growth of the oxide in wet ambient is initially very rapid and then proceeds linearly which means that the process is reaction limited. Both oxidation rates are thermally activated. The activation energies are 2.0 eV for dry and 1.4 eV for wet ambient. The pre-exponential factors are 0.17×1016 A(ring)2/min and 7.4×108 A(ring)/min, respectively. Both the dry and wet oxidation of the amorphous ternary Ta36Si14N50 film result in the formation of an x-ray amorphous Ta14Si5.5O80 layer.

Notes: We have achieved phase-locked operation of a module consisting of up to seven relativistic magnetrons. The magnetrons are connected by waveguide in a peer/peer configuration, with no one magnetron acting as a master oscillator. The signals used for coupling are each a substantial fraction of a magnetron's radiated power. Total extracted power, at 2.8 GHz, was 2.0 GW with four magnetrons and 2.9 GW with seven. Several interconnection geometries were explored. One particular geometry was found to produce qualitatively better phase-locked operation than any other. This was in agreement with the predictions of a numerical model of the magnetrons as coupled van der Pol oscillators.

Notes: The strain tolerance of doctor blade tapes of the high-temperature superconductor Bi2Sr2Ca1Cu2O8−δ have been studied to determine the suitability of these materials for magnet conductors. Critical currents that are on the order of 150 000 A/cm2 in zero magnetic field fall by about 30% with 0.1% bending strain and by a factor of 6 with 0.2% bending strain. At 20 T, critical currents fall with strain by approximately the same factor as at 4.2 K, but the critical currents fall with field somewhat faster. These bending strain results have a character quite different from Nb3Sn bronze process material in that there is essentially no prestress from the Cu jacket and there seems to be only a very small reversible range where the sample is within the elastic limit.

Notes: The electro-optic response of polymer dispersed liquid-crystal (PDLC) films is reported as a function of frequency and amplitude of the applied voltage and size of the LC droplets. We found that the threshold voltage is minimum and sharpest at frequencies near a few kHz. Visual and optical response studies show that there are two types of PDLC films; type I, which exhibit large partial optical memory, and type II, which quickly regain their original levels of transmittance after switching off relatively small driving voltage. It was observed that both types of PDLC films, in general, exhibit a two-step decay involving fast and slow components. However, the order in which the two components appear as the voltage is increased is different for the two types of PDLC films. Observations under the polarizing microscope show that the LC droplets in the two types of PDLC films undergo different transformations as the applied voltage is changed.

Notes: We examine theoretically the role of thermodynamic spin fluctuations in optical guided waves propagating on a ferromagnetic film and undergoing Faraday rot ation. Using the equipartition theorem, we obtain the noise equivalent power (NEP) for these thermally excited magnetostatic spin waves, as a function of film thickness and applied magnetic field. These considerations place limiting sizes and modulation sensitivities on optical signal processing devices that are based on the Faraday effect. For example, if 1 mW of optical guided wave power propagates in a 1-μm film, then 46 pW of optical power are mode converted by these thermal spin waves and appear as optical noise. The NEP for all thermal spin waves in a 1-μm Bi-doped yttrium iron garnet film deposited on a gadolinium gallium garnet substrate is 30 nW and drops by a factor of two for a 10-μm film.

Notes: The coercivity of anisotropic cast–hot-pressed Pr19Fe74.5B5Cu1.5 magnets is investigated. The microstructure features and virgin magnetization curve reveal a nucleation-controlled coercivity mechanism. Regression analysis shows that the intrinsic coercivity varies inversely as the logarithm of the average grain size: iHc(kOe) = 21.7550 − 6.0517 ln d (μm), which is in good agreement with the nucleation statistical model. Investigation of Cu addition and Nd substitution shows that Cu mainly plays a role of suppressing grain growth during the final annealing. Higher coercivity is thus obtained with Cu addition. Nd19Fe74.5B5Cu1.5 magnets exhibit a much lower coercivity due to their coarse-grained cast structure.

Notes: Single-phase aluminum nitride thin films with preferred crystallographic orientations have been grown on single-crystal sapphire by pulsed-laser ablation. The orientation of the films was found to be determined by the atmosphere and the nitrogen pressure during deposition and the substrate temperature. The films were examined by x-ray diffraction, and scanning electron microscopy.

Notes: Using angle-resolved Auger electron spectroscopy, we show, nondestructively, a sequential variation of the composition from the outermost layer to the second layer of a Cu0.81Pt0.19 alloy and provide new evidence for ion bombardment-induced Gibbsian segregation in that alloy when it was sufficiently bombarded with 2.8-keV Ar ions at 10 and −80 °C.

Notes: Shock initiated chemical reaction experiments have been performed on a 1:1 atomic ratio mixture of 20- to 45-μm nickel and −325 mesh crystalline silicon powders. It has been observed that no detectable or only minor surface reactions occur between the constituents until a thermal energy threshold is reached, above which the reaction goes to completion. The experiments show the energy difference between virtually no and full reaction is on the order of 5 percent. Differential scanning calorimetery (DSC) of statically pressed powders shows an exothermic reaction beginning at a temperature which decreases with decreasing porosity. Powder, shock compressed to just below the threshold energy, starts to react in the DSC at 621 °C while powder statically pressed to 23% porosity starts to react at about 30 °C higher. Tap density powder starts to react at 891 °C. The DSC reaction initiation temperature of the shock compressed but unreacted powder corresponds to a thermal energy in the powder of 382 J/g which agrees well with the thermal energy produced by a shock wave with the threshold energy (between 384 and 396 J/g). (Thermal energies referenced to 20 °C.) A sharp energy threshold and a direct correlation with DSC results indicates that the mean thermal energy determines whether or not the reaction will propagate in the elemental Ni+Si powder mixture rather than local, particle level conditions. From this it may be concluded that the reaction occurs on a time scale greater than the time constant for thermal diffusion into the particle interiors.

Notes: Ionized cluster beam (ICB) deposition has received considerable attention since its introduction in 1972 by Takagi et al. at Kyoto University because of its potential for low-temperature film growth. While further investigation of many aspects of ICB deposition is warranted, it is first necessary to determine with some certainty whether large clusters are being produced. A complete analysis of the Eaton ICB source involving computer calculation of the potential fields and computer simulation of the electrons and ions as they react to and influence these fields provides an in-depth understanding of the dynamics that influence the final ion beam characteristics. A high-resolution time-of-flight mass spectrometer was developed to experimentally investigate the cluster size distribution. No evidence of large clusters was found down to a level more than two orders of magnitude below what the Kyoto University group has reported [T. Takagi, Ionized-Cluster Beam Deposition and Epitaxy, (Noyes, New Jersey, 1988)]. A computer analysis of the three Kyoto University cluster size experiments that form the foundation of ICB has shown that the potential fields in the ionization areas are critically distorted by either space-charge effects or design flaws, both of which are serious enough to invalidate the experiments. The theory behind large cluster production and the body of indirect evidence attributed to the presence of large clusters are not convincing by themselves so it is concluded that a Takagi-type source does not produce large clusters in quantities capable of affecting film growth.

Notes: The system consisting of an unintentionally doped GaAs epitaxial layer on a semi-insulating (SI) GaAs substrate forms a starting point for the GaAs integrated circuit technology. It is also the genesis of problems for GaAs field-effect transistors (FETs) in the form of back gating. Potentials applied to a point on the surface may propagate several millimeters to modulate the conduction of an FET built into the layer. In addition, the conductivity of the epilayer may be efficiently modulated by a potential applied to the back of the SI substrate. Well-developed p-channel FET characteristics have been observed in an epilayer on top of a 0.4-mm-thick SI substrate using the back of the substrate as a gate. Numerical simulations revealed that under some circumstances potentials may propagate across the substrate with little attenuation, giving a degree of modulation in agreement with experiment. Conditions for current transport then corresponded closely to those in a rectifying p-n junction. The parameter space was fully explored numerically and using an analytical model, and a simple set of conditions for rectification were developed.

Notes: It has been recently reported that the minority carrier radiative lifetime in thin layers sandwiched between degenerately doped barrier regions or heterojunction barriers is much reduced by the diffusion of majority carriers into the active layer from the barrier regions. We show here that the radiative lifetime is determined by the average majority carrier concentration which is dependent on active layer thickness and may be significantly higher than the dopant concentration in this layer. Our experimental results are in close agreement with this model. We have simulated a number of structures where the minority carriers are confined by either homojunctions or heterojunctions and have derived the radiative lifetime as a function of active layer thickness. This dependence of radiative lifetime on layer thickness is not embraced in the analysis normally used for example in interface studies but is shown to have a significant effect on the interpretation of results obtained from measurements of interface recombination velocity leading to erroneous conclusions if not taken into account.