bluuebunny/crossref_metadata_2025 huggingface dataset:
PbTe-Pb1−xSnxTe superlattices prepared by a hot wall technique
Authors: Kinoshita H. , Fujiyasu H.
Published: February 2003

The PbTe-Pb0.8Sn0.2Te superlattices were made by the hot wall technique on BaF2 substrates. Two superlattices with the period thickness of 100 and 200 Å were analyzed by sputtering-Auger electron spectroscopy and good results were obtained. The interdiffusions of Pb and Sn across the junction were also investigated and the diffusion coefficients of Pb and Sn at 300 °C were found to be 1.8 and 2.9×10−17 cm2/sec, respectively.
Effects of annealing on Hg0.79Cd0.21Te epilayers
Authors: Chu M.
Published: February 2003

The dependence of conduction types and carrier concentrations of Hg0.79Cd0.21Te epilayers on annealing temperature and annealing pressure was studied. At 410 °C, a relation of p∝P−1Hg was observed which was explained by a defect equilibrium model. Detailed analysis of the temperature-dependent Hall coefficients indicated that the hole concentrations of the samples annealed under the above conditions were a result of close compensation of acceptors and donors on the order of 1×1017 cm−3. From Hall measurement, the acceptor ionization energies of the p-type annealed layers were found to be from 1 to 5 meV. Experiments also showed that n-type epilayers with electron concentrations on the order of 1014 cm−3 can be achieved by annealing at low temperature under Cd or Hg pressures.
Comparison of two high-repetition-rate pulsed CO2 laser discharge geometries
Authors: Faszer Wayne , Tulip John , Seguin Herb
Published: February 2003

Two discharge geometries are commonly used for pumping high-repetition-rate transversely excited atmosphere (TEA) lasers. One uses solid electrodes with preionization provided by downstream spark pins. The other uses a solid electrode and a screen electrode with preionization provided by an auxiliary discharge behind the screen. In this study the performance of the two systems was compared. The repetition rate at which arcing occurs was found to increase linearly with flow velocity but decrease with increasing energy density. It was also dependent on system geometry and the spark pin preionized system performed better than the auxiliary discharge preionized system. Data are given for discharges in N2, CO2, He, and a CO2 laser mixture.
Laser oscillator and parametric oscillator under external injection
Authors: Dutta N. K.
Published: February 2003

The laser oscillator and parametric oscillator are analyzed in the presence of an externally injected signal. Synchronization to the external signal is possible only if it is larger than a certain magnitude. In the weak synchronization limit, expressions for the oscillator frequency and linewidth as a function of detuning (Δi) are obtained. An exact expression for the stationary probability distribution is obtained for Δi=0. It is shown that laser noise due to reflected signal may result from the repetitions of the ’’locked’’ and ’’unlocked’’ state arising from temperature variation within the laser itself.
Nonlinear oscillations of a polar-liquid column under unipolar-ion injection
Authors: Suzuki Makoto , Sawada Yasuji
Published: February 2003

A nonlinear oscillation of the level and of the current is theoretically predicted and experimentally observed in a U-tube system containing a polar liquid with a capillary whose diameter is as large as 1 mm, and which is equipped with an electrode injecting unipolar ions. The observed critical potential difference, amplitude, period, and waveforms of the level oscillation agree qualitatively and quantitatively with the theoretical results. The experimental amplitude of the current oscillation is larger than the theoretical one, and it is suggested that the discrepancy might be due to the high-field dissociation current of neutral impurities.
Energy losses due to an ion-acoustic wave instability in a plasma
Authors: Anastassiades A. J. , Sideris E.
Published: February 2003

We have studied the relation of energy loss with the amplitude of a spontaneously excited ion-acoustic wave instability in a current-carrying plasma. A simple model gave a very good fit with the experimental data and led us to the conclusion that the energy loss comes from the drift motion of the particles interacting with the wave and not from the wave motion which suffers much lower energy loss in the system.
Solutions of potential problems using the reduction to Fredholm integral equations
Authors: Caldwell James
Published: February 2003

The numerical solution of potential problems using a method which reduces them to Fredholm integral equations of the first and second kinds is considered. The method is illustrated for potential problems of the Dirichlet type and solutions have been obtained for the case of a unit sphere. This method provides an alternative approach to the classical finite-difference methods which have been widely used in the past. It overcomes some of the difficulties associated with the classical approach.
Picostrain measurements with piezoelectric transducers
Authors: Forward Robert L.
Published: February 2003

Piezoelectric ceramic strain transducers are shown to have a linear response to strain down to a strain level of 10−11 (10 picostrain) at a frequency of 20 Hz. For measurement of vibrational resonances, their sensitivity to strain is 50 000 times greater than that obtainable from a comparably sized resistive strain gauge.
Transmission electron microscopy and Rutherford backscattering studies of different damage structures in P+ implanted Si
Authors: Sadana D. K. , Stratham M. , Washburn J. , Booker G. R.
Published: February 2003

Cross-sectional transmission electron microscopy (TEM) and MeV He+ channelling methods have been used to examine different damage structures present under the color bands visible at the surface of a high-dose-rate P+ implanted (111) Si implanted to a dose of 7.5×1015 ions/cm2. TEM and channelling results obtained from individual colored regions showed a good qualitative correlation in that discrete damage layers observed in the cross-sectional TEM micrographs appeared as discrete peaks in the channelled spectra. The mean depths of the damage layers obtained from these two methods were in agreement. However, the widths of the deeper lying damage layers calculated from the channelling measurements were always greater than the widths observed by TEM. An empirical method based on subtraction of dechannelling background in the channelling spectra gave damage layer widths that were in close agreement with the TEM results.
Microstructure and normal grain growth in metals and ceramics. Part I. Theory
Authors: Kurtz S. K. , Carpay F. M. A.
Published: February 2003

By extending the theory of Feltham and combining it with the work of Rhines and Craig, a detailed statistical theory of normal grain growth has been constructed. The theory exhibits all four attributes of normal grain growth: uniformity, scaling, stability, and lognormality. A prime new feature of the theory is the division of the grains into topological classes (14 planar, 34 spatial), each with a lognormal distribution of grain sizes. Growth is found to be controlled by the rate of loss of grains from the lowest topological class. Complete solutions are found for the grain growth kinetics of each class, as well as the transfer rates between classes. The latter result is used to explain how the median diameter of those classes in which grains are shrinking still manages to increase in the manner required to keep their number a constant fraction of the total population. A parabolic growth law is found for the median grain size of the whole population as well as the median grain size in each topological class. The growth constant for each class is found to increase approximately as the cube of the planar topological parameter or the square of the spatial topological parameter. The Rhines-Craig structural gradient is shown to be independent of time and hence a basic constant of normal grain growth. Stability is due to a maximum in the grain boundary velocity with increasing grain size. The ratio of the maximum to median grain diameter is found to be e(=2.718). A comparison of the present theory is made with that of Hillert. Possible origins of the lognormality are discussed.
Microstructure and normal grain growth in metals and ceramics. Part II. Experiment
Authors: Kurtz S. K. , Carpay F. M. A.
Published: February 2003

An extensive set of measurements on the grain growth and microstructure evolution of a series of high-density Ni-Zn ferrites annealed over periods ranging from 1/4 to 48 h is reported. A comparison of the data with predictions of the statistical multiple-lognormal theory of normal grain growth presented in Part I is made. The time invariance of the standard deviations of both the grain size and population of individual topological classes is confirmed, demonstrating that the scaling and stability of normal grain growth are critically related to the dispersion of the grain sizes and that at least two parameters are needed to characterize a given microstructure. A parabolic growth law for the median diameter in both two and three dimensions is confirmed as well as the predicted power law dependence of the growth constants for each class on the topological index. A series of sectioning experiments verifies the near equivalence of the planar and spatial size parameters.
Interference with negative particle sampling due to formation of positive ions in a quadrupole mass spectrometer
Authors: Kuehn D. G. , Chanin L. M.
Published: February 2003

A quadrupole mass spectrometer has been utilized to study active discharges containing Cs vapor. Production of positive ions by electron impact within the mass spectrometer and subsequent secondary electron emission from cesiated surfaces produced spurious or pseudonegative ion signals which interfered with attempts to sample negative ions from the plasma. These effects may also occur in other gas discharge systems.
The generation of electron-hole pairs in very thin solar cells possessing an optical back-surface reflector
Authors: von Roos Oldwig
Published: February 2003

It is pointed out that very thin solar cells (1 μm thick or less) as, for example, amorphous silicon or cadmium sulfide cells, possessing a back-surface reflector should be regarded as Fabry-Perot cavities as far as the generation of electron-hole pairs by light is concerned. The generation rate of electron-hole pairs as a function of distance from the front surface exhibits characteristic interference patterns which are not negligible and must be accounted for in an analysis of the performance of such a cell.
Recombination mechanisms in amorphous silicon-based alloys
Authors: Adler D. , Silver M. , Madan A. , Czubatyj W.
Published: February 2003

Photoconductivity has been measured as a function of temperature, photon energy, and electric field strength for amorphous Si:F:H alloys. The results clearly show that geminate recombination is not important in the visible region of the spectrum in these materials. The significance of these results for efficient solar photovoltaic energy conversion is discussed.
An improved technique for selective etching of GaAs and Ga1−xAlxAs
Authors: LePore J. J.
Published: February 2003

An improved technique is described for selectively etching ’’windows’’ in GaAs crystals with Ga1−xAlxAs (0.30⩽x⩽ 0.80) epitaxial layers. A reduction factor of 10–50 in the sample preparation time is achieved with a good reproducibility.
Quantitative studies of thermally generated elastic waves in laser-irradiated metals
Authors: Scruby C. B. , Dewhurst R. J. , Hutchins D. A. , Palmer S. B.
Published: February 2003

Quantitative experimental measurements have been made in the study of thermoelastic generation of elastic waves in a metal by unfocused laser radiation. A calibrated wide-band detection system, incorporating a capacitance transducer, has enabled acoustic waveforms to be recorded with a minimum of distortion. From these measurements, a theoretical model has been developed. The transfer function of the metal block has been deconvoluted to give the acoustic source function, which was modeled as a rapidly expanding point volume of material. The thermoelastic source generated longitudinal (L) and (S) waves, but the latter predominated at the epicenter, where, in experiments presented here, both wave amplitudes L and S were proportional to the total absorbed energy in the laser pulse.
Effect of hydrogen on the temperature dependence of the elastic constants of palladium single crystals
Authors: Salama K. , Ko C. R.
Published: February 2003

The changes in the absolute values as well as in the temperature dependences of the elastic constants C11, C44, C′, and CL as a function of dissolved hydrogen up to 1.7 at. %, in palladium single crystals have been determined. The measurements were performed in the temperature range between 140 and 310 K, using both longitudinal and shear 10-MHz ultrasonic waves. In the α phase, the changes in the absolute values of the elastic constants C11, C44, and CL were very small, while a larger effect of −1.2%/ at. % H was obtained in the case of the shear constant C′. The relative changes in the computed bulk modulus and Voight-Reuss average Young’s modulus in that phase are, respectively, +0.2% and −0.5%/ at. % H. The effects of hydrogen in the α phase on the temperature dependences of the elastic constants, however, are found to be significantly large in the case of C11 and CL and small in the case of the shear constants C′ and C44. These effects are discussed in terms of the volume expansion due to H in Pd, the possible electronic effect due to the addition of H to Pd, and finally the hydrogen contributions to the higher-order elastic constants. From this analysis, it is concluded that hydrogen in the α phase contributes primarily to the short-range ion core repulsive interactions in palladium.
The effect of noncrystallinity on the α→ε transition of Fe85B14Si1 alloy
Authors: Dunn K. J. , Bundy F. P. , Walter J. L.
Published: February 2003

The electrical resistance behavior under pressure of an Fe85B14Si1 alloy in the as-cast amorphous condition and in three different annealed states with different degrees of crystallinity was studied. We found that in the as-cast amorphous sample there is no measurable resistance-jump with application of pressure up to about 300 kbar. Subsequent annealing of the amorphous sample for different lengths of time results in the reappearance of the resistance-jump with different amplitudes.
Automatic x-ray diffraction measurement of the lattice curvature of substrate wafers for the determination of linear strain patterns
Authors: Segmüller Armin , Angilelo J. , La Placa Sam J.
Published: February 2003

An x-ray diffraction topography goniometer (Lang camera) under computer control has been used to measure localized bending of silicon wafers. The wafer, mounted free from external stresses, is set for Bragg reflection in transmission by lattice planes perpendicular to the surface (Laue case) and it traverses across the x-ray beam in steps of 0.01 mm or multiples thereof. At each step the angular position and the intensity of the peak of the Bragg reflection is determined by least-squares methods from the peak profile with a precision better than the minimum angular step of 0.001°. The lattice curvature obtained from the peak shift is a direct measure of the magnitude of the strains imposed on the wafer by oxide layers, thin films, implantation, and other manufacturing processes. Therefore linear strain maps, showing, for instance, strain gradients occurring at film edges, can be measured quantitatively with high resolution, fully automatically and nondestructively in several direction across a substrate wafer. Measuring substrates of high crystalline perfection and controlling the ambient temperature, the radius of curvature R (in meters) of a uniformly curved substrate can be measured with a probable relative error ΔR/R=R/(1700 m).
Energy and electric field dependence of Si-SiO2 interface state parameters by optically activated admittance experiments
Authors: Poon T. C. , Card H. C.
Published: February 2003

By means of a recently developed experimental technique, the dependence on the energy and electric field of Si-SiO2 interface state capture cross sections has been measured for Al-SiO2-nSi structures with an oxide thickness ?800 Å. The capture cross section for holes,σp, has been observed to be several orders of magnitude larger than that for electron, σn, and further it has been observed to show a strong dependence on energy in the upper half of the silicon energy gap. This apparent dependence of σp on energy has been shown to arise primarily from a dependence on the electric field at the semiconductor surface. For the same electric field, interface states at different energies in the gap are observed to have very nearly the same magnitude of capture cross section.
Electrical analysis methods for metal insulator semiconductor structures on GaAs
Authors: Schuermeyer Fritz L. , Hartnagel Hans L.
Published: February 2003

Capacitance-voltage measurements on GaAs metal insulator semiconductor structures are plagued by charging problems. Additionally, it seems that accumulation cannot be reached owing to Fermi-level pinning and consequently the insulator capacitance cannot be determined. Furthermore, it is difficult to determine semiconductor characteristics in these MIS structures, which may have changed during annealing. In this paper, a measurement technique is described which eliminates the effect of the charging, allowing the measurement of insulator capacitance, surface potential, and semiconductor doping. This measurement technique is based on the study of transient photovoltage, transient capacitance, and the charging characteristics. This new measurement technique is used to evaluate GaAs MIS diodes and test results are presented.
Surface charge and specific ion adsorption effects in photoelectrochemical devices
Authors: Singh P. , Singh R. , Gale R. , Rajeshwar K. , DuBow J.
Published: February 2003

The importance of specific ion adsorption and surface charge effects in the design and operation of photoelectrochemical (PEC) devices is demonstrated by experimental data on the n-GaAs/electrolyte and n-Si/electrolyte interface. The electrolyte chosen for the present study was an ambient temperature molten salt comprising mixtures of aluminum chloride and n-butyl pyridinium chloride in varying molar ratios. A direct correlation between specific adsorption effects and photovoltaic output parameters is presented for the n-GaAs PEC system. Evidence for specific adsorption of Cl− ions in this system is found in the systematic shift observed in flat-band potentials Vfb towards negative values with increasing concentration of free Cl− ions in the AlCl3-BPC electrolyte. The magnitude of the slope of Vfb versus pCl (=−log[Cl−]) plots [∼0.13 V or 2(2.3kT/q) V] is consistent with that expected from Esin-Markov adsorption behavior. Anomalous PEC behavior is observed at the n-Si/AlCl3-BPC interface brought about by modifications in electrostatics across the electrode/electrolyte interphasial region. These modifications arise from either specific adsorption effects or by electrodeposition of aluminum on the n-Si electrode surface. Either process results in a net lowering of the band structure in n-Si on the energy scale relative to the redox levels. An examination of literature data on high-efficiency PEC systems reveals that similar shifts in the relative positions of the semiconductor energy levels and redox energies may play an important role in ensuring a more favorable photoresponse than that predicted from idealized models.
Dispersive optical constants of amorphous Se1−xTex films
Authors: Adachi Hiroshi , Kao Kwan C.
Published: February 2003

Optical constants of amorphous Se1−xTex films have been measured for 0⩽x⩽0.45 at wavelengths from 0.35 to 2 μm using both an ellipsometer and a spectrophotometer. The results show that the optical transmission cutoff wavelength, the refractive index, and the extinction coefficient vary linearly with x (the Te content). The optical constants are dispersive. The dispersion is attributed to the optical transition of electrons from the valence band to the conduction band. All results can be consistently explained on this basis. The substitution of Te atoms for Se atoms in Se1−xTex films increases the density and enhances the tailing of the localized states into the mobility gap, thus resulting in the change of optical constants with x in Se1−xTex films.
Composition dependence of Nd3+ homogeneous linewidths in glasses
Authors: Pellegrino J. M. , Yen W. M. , Weber M. J.
Published: February 2003

Optical homogeneous linewidths of the 4F3/2–4I9/2 transition of Nd3+ in oxide and fluoride based glasses are measured for host composition ranging from simple binary to multicomponent glasses. Homogeneous linewidths at 300 K exhibit a broad range of values, varying by approximately a factor of 4. The ratio of homogenous to inhomogeneous linewidth also varies over a broad range, from 0.16 for a sodium barium borate glass to 1.86 for a rubidium phosphate glass. In addition, the homogeneous linewidth is inversely dependent to the ∼2.5 power of the velocity of sound from host to host. This dependence is not predicted by existing theories of the line broadening process.
Electron diffraction study of newly discovered nickel phosphides in partially crystallized amorphous electrodeposited Ni-P thin films
Authors: Vafaei-Makhsoos E.
Published: February 2003

Amorphous electrodeposited thin films of nickel phosphides, containing 20 and 22 at. % P were studied by electron microscopic methods. Upon beam heating the amorphous phase transformed into Ni12P5 and several other new crystalline phases, with or without additional metallic nickel. The following crystallizations from the electrodeposited Ni-P films were observed: (1a) Amorphous Ni-P→NixPy(Ni)+Ni. The probable values of x and y are 5 and 2, respectively. The lattice parameters are a=6.61 and c=12.31 Å. Upon further beam heating (1a) transforms to: (1b) NixPy(Ni)+Ni→Ni3P+Ni. The body-centered tetragonal unit cell dimensions of Ni3P are a=8.93 and c=4.39 Å. (2) Amorphous Ni-P→Ni12P5. The unit cell of Ni12P5 is again body-centered tetragonal, with a=8.64 and c=5.07 Å. (3) Amorphous Ni-P→Ni3P. The hexagonal unit cell parameters are a=5.00 and c=8.66 Å. (4) Amorphous Ni-P→Ni3P+Ni. The unit cell is again body-centered tetragonal, like that of (1b). However, the dimensions are a=6.10 and c=5.04 Å. (5) Amorphous Ni-P→Ni3P. The body-centered unit cell dimension is a=6.10 Å. The observation of such a number of crystalline phases implies that the crystallization of the amorphous Ni-P films is more complex than expected and it must depend on a number of factors, including rates of electron beam heating, temperature gradients, and the homogeneity of the as-deposited sample. Although the unit cell dimensions of various phases are distinct, there is an apparent geometric relationship between the magnitudes of individual unit translations. This observation indicates that the primary structures of these phases must be simple closed-packed structures derivable from hcp, fcc, and bcc structures. Interestingly, while the transformation from the amorphous Ni-P to the equilibrium two-phase mixture of (1b) occurred through the crystallization of the intermediate metastable two-phase mixture of (1a) in accordance with the Ostwald rule, the transformation from the amorphous Ni-P to the equilibrium phases of 2, 3, 4, and 5 underwent no subsequent transformation, therefore violating the Ostwald rule.
Oxide growth in an rf plasma
Authors: Fromhold A. T. , Baker John M.
Published: February 2003

A mechanism is considered for oxide growth on an electrically isolated metal sample in the presence of an rf-excited oxygen plasma. The assumption is made that the rate of rf oxidation is limited by transport of ionic species through the already-formed oxide layer. Thermally activated hopping of ionic defects in the presence of electric fields due to the surface potential established by the rf discharge and modified by the space charge of the mobile ionic defects is hypothesized. The origin of the voltage across the oxide is discussed in terms of a balance between the transport of negatively charged O ions and transport of electron holes created by ion neutralization of positive ions from the plasma. This model is developed analytically and evaluated numerically by employing the continuum limit of hopping transport equations valid for the very-high-field limit. A three parameter fit gives excellent agreement of the theory with the published data of Greiner for the rf oxidation of lead. The fitting parameters are the voltage across the oxide film, the ionic diffusivity, and the rate at which the oxide is removed by sputtering. The resulting parameter values are shown to be in reasonable accord with available experimental data. Parametric curves are presented to illustrate the dependence of the kinetics on the various microscopic parameters. The dependence of the limiting thickness on the primary parameters is likewise presented. It is shown that the growth rate may be significantly retarded by high levels of space charge in the oxide.
Pumping mechanism of mercury-ion laser
Authors: Ninomiya H. , Osumi H. , Horiguchi S.
Published: February 2003

In a pulsed discharge in a He-Hg gas mixture favorable for laser oscillation of Hg ion at the green line, the temporal and spatial behavior of the population densities of Hg(63P2) and He(21S0) atoms has been studied experimentally. These reactants are thought to be responsible for the Penning-like excitation process. It is found that the depression of the population of reactants coincides in space and time with the occurrence of the laser oscillation.
Calculated absorption, emission, and gain in In0.72Ga0.28As0.6P0.4
Authors: Dutta N. K.
Published: February 2003

The absorption, emission, and gain spectra of In0.72Ga0.28As0.6P0.4 (λg =1.3 μm), which lattice matches InP, is calculated using a Gaussian fit to Halperin-Lax band tails and Stern’s matrix element. The calculation is done both for p- and n-type material at various impurity concentrations. The spectral width of emission increases both with increasing doping and impurity concentration. All results are for 297 K. The gain-versus-excitation rate is given by the equation g (cm−1)=0.057 (Jnom −2400), where Jnom is the nominal current density in the active layer expressed in A/cm2 μm. Also, the photon energy at maximum gain increases with increasing excitation rate.
Field-dependent grain-boundary diffusion in polycrystalline material
Authors: Saha H. , Mukhopadhyaya K.
Published: February 2003

The generalized analysis of the grain-boundary diffusion by surface accumulation method has been extended by incorporating the effects of an electric field along the grain boundary. General expressions for the average surface concentration have been derived and the effects of an electric field on its time dependence have been investigated in some detail.
Stress-enhanced crystallization in amorphous selenium films
Authors: Stephens R. B.
Published: February 2003

One of the singular features of amorphous selenium films is their position-dependent crystallization rates. A new model is proposed which attributes the 100-fold variation in rate to stress fields surrounding some of the polycrystalline cylindrites. The mechanism by which these fields can enhance the crystallization rate is discussed and some critical tests are suggested.
Studies of the formation of slow positrons in MgO-coated moderators
Authors: Zitzewitz Paul W.
Published: February 2003

Studies have been made of the production of slow (∼1 eV) positrons by high-energy positrons from a radioactive source. Moderators consisting of thin metallic foils coated with MgO smoke were used in the transmission mode. The thinnest foils gave the largest fluxes of slow positrons. A double moderator, consisting of a MgO-coated grid following the MgO-coated thin foil, gave a flux almost double that of either the foil or grid alone. The positron beam machine used is described. It has electrostatic optics for the collection, analysis, and transmission of the slow positrons.
SEM observations of domain configurations in thin-film head pole structures
Authors: Mee Peter B.
Published: February 2003

An investigation was made of the domain configurations in uniaxial anisotropic permalloy pole structures for integrated thin-film heads utilizing the SEM type-II magnetic contrast mode. The technique was compared with other viable methods including Kerr magneto-optics and the ferrofluid colloid. Type II was found to be superior for dynamic and high-magnification studies. ac demagnetized, partially saturated, and remanent configurations were observed in poles of different geometries, after magnetization in both easy and hard directions. A comparison was made with the domain configuration in double-layer permalloy structures. In the study of complete integrated heads, only the top pole domain configuration was observable using the ferrofluid colloid method, while with 200-keV type II, the complete magnetic circuit domain structure was imaged. The effect of subsequent head processing on easy axis alignment was found to be minimal.
Coupled dipole oscillations in an intense relativistic electron beam
Authors: Davidson Ronald C. , Uhm Han S.
Published: February 2003

The stability properties of coupled dipole resonance oscillations in a relativistic electron-beam–plasma system are investigated within the framework of a rigid beam model. The analysis is carried out assuming sharp-boundary rectangular density profiles, and distinguishing the two cases: (a) beam-electron–plasma-electron dipole resonance oscillations and (b) the ion resonance instability for an intense relativistic electron beam partially charge neutralized by background ions. In case (a), it is shown that the system is most unstable for zero fractional charge neutralization and that the instability growth rate can be significantly reduced by increasing the density ratio ?e’/?e, where ?e’ and ?e are the beam-electron and plasma-electron densities, respectively. Moreover, the characteristic growth rate for the electron-electron dipole resonance instability can be a substantial fraction of the beam-electron cyclotron frequency. In case (b), it is found that the instability growth rate is enhanced considerably by increasing the beam density and energy and that, for sufficiently small fractional charge neutralization, the most unstable mode occurs for long axial wavelengths (kz=0). The characteristic growth rate for the ion resonance instability is also found to be a substantial fraction of the beam-electron cyclotron frequency.
Parametric studies of uv preionization in TEA CO2 laser
Authors: Yamabe Chobei , Matsushita Toshio , Sato Saburo , Horii Kenji
Published: February 2003

The discharge characteristics of an electrical circuit for uv preionization in TEA CO2 laser are described. The suitable size of an electrode for uniform volumetric preionization of a laser gas is decided. The mechanisms of the ionization and the generated total initial electrons by uv photons are discussed. Moreover, both the effects of circuit parameters R, L on the intensity of uv radiation and the endurance test of the electrode for repeated discharges are also described.
Effects of dc electric fields on a dye laser amplifier
Authors: Urisu Tsuneo , Sugeta Takayuki , Mizushima Yoshihiko
Published: February 2003

Electric field dependence of the output polarization was investigated in the dye laser light amplifier, using the dimethyl sulfoxide (DMSO) solution of coumarin 30, which was found to have a large Kerr coefficient and a high resistivity. Output polarization was found to be determined by the Kerr effect of the solvent DMSO and the anisotropic gain due to the anisotropic orientation distribution of excited dye molecules. The nonlinear electric susceptibility ‖χxxxx−χzzxx‖ of DMSO was estimated to be 9.5×10−12 cgs esu. The orientational distribution time constant τr for coumarin 30 dissolved in DMSO was estimated to be about 1.3×10−9 s.
Degradation mechanisms of Ga1−xAlxAs visible diode lasers
Authors: Kajimura T.
Published: February 2003

Degradation of Ga1−xAlxAs visible diode lasers in the 0.7-μm wavelength region is investigated through room-temperature life tests. A marked dependence of laser life on lasing wavelength is observed. In particular, degradation proceeds faster for shorter-wavelength lasers. It is shown that the degradation of lasers radiating at wavelengths below 730 nm can mainly be attributed to the rapid formation of dark regions and dark-line defects during aging. A notable improvement in life is obtained for these shorter-wavelength lasers by Te doping of the active layer. On the other hand, degradation at above 740 nm results from enhanced facet oxidation due to high AlAs mole fractions in the active and cladding layers. This facet oxidation is effectively suppressed by facet coatings with SiO2 films. As a result, stable operations, exceeding 4000 h, are achieved in the 740–770-nm wavelength region.
Measurements of a spherical potential profile produced by electrostatically focused ions
Authors: Ham Mooyoung , Robinson James W.
Published: February 2003

An electrostatic potential well was produced by injecting positive zinc ions into a hollow cathode. The apparatus consisted of two concentric spherical electrodes with the inner wire-mesh electrode being 91% transparent. Ion current pulses as high as 40 mA were injected by a vacuum-arc source located between the spheres. The outer sphere was biased at 4 kV and the inner sphere from 0 to −1.5 kV so that the ions would circulate between the spheres and be drawn toward the inner sphere. Current pulses lasted up to 20 μs and during the current pulses, potential wells of up to 200 V were formed by the accumulation of ions within the inner electrode. The well profile was computed from the deflection of a 2-nA swept electron beam. The deflection was measured with a many-slotted circumferential detector which intercepted the beam after it traversed the space-charge region. Each profile was calculated from data recorded during a single 2-μs sweep of the probing beam.
Plasma quiescence in a reflex discharge
Authors: Jerde L. , Friedman S. , Carr W. , Seidl M.
Published: February 2003

A thermionic cathode reflex discharge and the plasma it produces are studied. It is found that extremely quiescent plasmas can be produced when the electron-loss rate due to classical diffusion is equal to the ion-loss rate. Particle and power balances for the quiescent plasma are obtained, and the average electron energy loss per ion produced is determined.
Application of Lindhard’s dielectric theory to the stopping of ions in solids
Authors: Iafrate G. J. , Ziegler J. F. , Nass M. J.
Published: February 2003

Lindhard’s dielectric theory of energy loss is applied to the stopping of energetic ions in solids. The Lindhard formalism, in combination with the local density approximation and the concept of effective charge, is used to calculate the stopping powers of heavy ions in many targets and over a wide range of projectile energies. Theoretically calculated stopping powers are compared with available experimental data.
Electroepitaxy of multicomponent systems: ternary and quarternary compounds
Authors: Bryskiewicz T. , Lagowski J. , Gatos H. C.
Published: February 2003

A theoretical model is presented which accounts for the electroepitaxial growth kinetics and composition of multicomponent compounds in terms of mass transport in the liquid and phase diagram relationships. The mass transport in the interface is dominated by electromigration in the absence of convection and by diffusion in the presence of convection. The composition of the solid is controlled by the Peltier effect at the growth interface and by the diffusion and mobility constants of the solute components and the growth velocity (current density). Thus, for a given solution composition, the composition of the solid can be varied by varying the current density. For a given current density the composition remains constant even in the case of relatively thick epitaxial layers. All aspects of the model were found to be in good agreement with the growth and composition characteristics of Gax−1AlxAs layers.
Optical absorption in polymer glasses by laser calorimetry
Authors: Crist B. , Marhic M. E. , Raviv G. , Epstein M.
Published: February 2003

Optical absorption in polystyrene and poly(methyl methacrylate) was measured in the visible region of radiation. Two methods of data evaluation yield consistent results to indicate that near λ=500 nm, the absorption coefficient is approximately 2×10−4 cm−1, or less than 100 dB/km, for both materials.
Pulsed-laser atom-probe field-ion microscopy
Authors: Kellogg G. L. , Tsong T. T.
Published: February 2003

A time-of-flight atom-probe field-ion microscope has been developed which uses nanosecond laser pulses to field evaporate surface species. The ability to operate an atom-probe without using high-voltage pulses is advantageous for several reasons. The spread in energy arising from the desorption of surface species prior to the voltage pulse attaining its maximum amplitude is eliminated, resulting in increased mass resolution. Semiconductor and insulator samples, for which the electrical resistivity is too high to transmit a short-duration voltage pulse, can be examined using pulsed-laser assisted field desorption. Since the electric field at the surface can be significantly smaller, the dissociation of molecular adsorbates by the field can be reduced or eliminated, permitting well-defined studies of surface chemical reactions. In addition to atom-probe operation, pulsed-laser heating of field emitters can be used to study surface diffusion of adatoms and vacancies over a wide range of temperatures. Examples demonstrating each of these advantages are presented, including the first pulsed-laser atom-probe (PLAP) mass spectra for both metals (W, Mo, Rh) and semiconductors (Si). Molecular hydrogen, which desorbs exclusively as atomic hydrogen in the conventional atom probe, is shown to desorb undissociatively in the PLAP. Field-ion microscope observations of the diffusion and dissociation of atomic clusters, the migration of adatoms, and the formation of vacancies resulting from heating with a 7-ns laser pulse are also presented.
Degradation of GaAs0.9P0.1 light-emitting diodes for optical fiber communication with internal stress
Authors: Shimano Noriyuki , Kawai Yoshio , Sakuta Masaaki
Published: February 2003

Degradation mechanisms of GaAs0.9P0.1 light-emitting diodes for optical fiber communication systems were studied to elucidate the effects of internal compressive stress (on the order of 107–108 dyn/cm2) on initial rapid degradation. The diodes were fabricated from wafers with various phosphorus composition gradients (?0.7%/μm) in the tapered layer.Experimental results from the degradation of the diodes operating at 660 A/cm2 showed that the lifetimes of the diodes increased with decreasing the compositional grading in the crystals. The improved lifetime is due not only to the suppression of 〈110〉 dark-line defects but also to the slow growth velocities of 〈100〉 dark-line defects and due to slow accumulation rates of nonradiative recombination centers near the PN junctions at low internal stress. For the first time, the growth velocities of 〈100〉 dark-line defects during initial rapid degradation were observed to depend on the internal compressive stress.
Interferometric investigation of shock waves induced by a TEA-CO2 laser-produced plasma in air in front of a solid target
Authors: Apostol D. , Apostol I. , Cojocaru E. , Draganescu V. , Mihailescu I. N. , Morjan I. , Konov V. I.
Published: February 2003

The shock waves induced in the surrounding atmosphere by an air plasma were investigated by laser interferometry. The air-breakdown plasma was produced by a TEA-CO2 laser in front of a solid target. The results were compared to the predictions of the theory of intense explosions in gases and a good agreement was inferred. It was also determined that the symmetry of the expansion of the initial shock wave is determined by the plasma-source shape and, accordingly, depends on the laser power density incident on the target surface. However, for further stages all the shock waves expand spherically.
Variation of the ideality factor in the curent-voltage characteristics of double-heterostructure diodes
Authors: Yang E. S. , Wu C. M. , Hung R. Y.
Published: February 2003

The low-current I-V characteristics of AlxGa1−xAs-GaAs DH laser diodes have been investigated. The variation of the ideality factor is explained by taking into account the interaction of the thermionic-field emission and interface charge. Both theoretical calculations and experimental data are presented here to show the validity of our model.
Electrical and optical properties of n-type semiconducting chalcogenide glasses in the system Ge-Bi-Se
Authors: Tohge Noboru , Minami Tsutomu , Yamamoto Yoshitaka , Tanaka Masami
Published: February 2003

The glass-forming region was determined for the system Ge-Bi-Se; 13 at.% Bi was found to be incorporated at its maximum content into glasses, the Ge content of which was 20 at.%. Electrical resistivity, thermoelectric power, and optical absorption coefficient were measured mainly on a series of Ge20BixSe80−x glasses (x=0 –13). The resistivity decreased by about four orders of magnitude between x=9 and 10, and remained almost constant for x?10. The thermoelectric measurement showed the change of conduction type from p to n, accompanied by the above-mentioned abrupt decrease of resistivity. In n-type glasses, hopping conduction in the tail of localized states was proposed in parallel with conduction in extended states. The optical band gap was very slightly changed with the incorporation of more than 2.5 at.% Bi, in contrast to the remarkable decrease in the activation energy for conduction between x=9 and 10. The discussion based on the concentration of covalent bonds formed in the glasses led to the conclusion that the formation of a fairly large number of Bi-Se bonds and the disappearance of Se-Se bonds near x=10 were closely related to the composition dependence of the electrical and optical properties of the glasses in the present system.
Improved characterization of impurities in semiconductors from thermal carrier measurements
Authors: Blakemore J. S.
Published: February 2003

Conditions are discussed for which the concentration, binding energy, and compensation of a set of impurities can be deduced from the temperature dependence of the thermal free-carrier population. Improved methods for verifying the quality of a numerical fit to the mass-action equations are illustrated with data for germanium doped with indium or mercury acceptors. The graphical methods illustrated permit a critical assessment of whether the data really conforms to the generally used equations, and how various forms of error or inapplicability can be observed. It is pointed out that these same techniques can be useful in analysis of thermal emission data under nonequilibrium conditions.
Static compression of silicon in the [100] and in the [111] directions
Authors: Gupta Mool C. , Ruoff Arthur L.
Published: February 2003

High pressures were generated using a diamond indentor technique. The phase transition in silicon loaded in the [100] direction and silicon loaded in the [111] direction under high pressure was studied. From the behavior of electrical resistance of silicon loaded in the [100] direction, it was found that it becomes metallic at about 12.0 GPa in agreement with the previously reported results on silicon using different techniques. However, silicon loaded in the [111] direction becomes metallic at a lower pressure. The silicon transition is highly sensitive to the type of stress applied.
Current transport in GaAs Schottky barrier diodes subject to high neutron fluence
Authors: Ashok S. , Borrego J. M. , Gutmann R. J.
Published: February 2003

The electrical characteristics of GaAs Schottky barrier diodes are investigated after fast-neutron irradiation at fluences causing appreciable (≳75%) carrier removal. A significant change is seen in the forward current-voltage (I-V) characteristics, with one-carrier space-charge-limited (SCL) current in the presence of distributed traps becoming the dominant conduction mechanism. Depending on preirradiation doping level and neutron fluence, both power law and exponential forward I-V characteristics are obtained, signifying exponential and uniform trap distributions respectively. The trap parameters are evaluated from analysis of I-V data taken over a wide temperature range.
Electron trapping and detrapping characteristics of arsenic-implanted SiO2 layers
Authors: DeKeersmaecker R. F. , DiMaria D. J.
Published: February 2003

The electron trapping and detrapping properties of As+-implanted thermally grown SiO2 layers incorporated into metal-silicon dioxide-silicon (MOS) structures have been studied. The samples were charged using avalanche injection from the silicon substrate or internal photoemission from either interface. The charge state of the MOS devices was investigated using capacitance-vs-voltage (C-V) and photocurrent-vs-voltage (photo I-V) measurements. After a 1×1013 As+/cm2 implant and a 1000 °C anneal in N2 for 30 min, a dominant (in terms of trapping probability) trapping center with a capture cross section of (1–2) ×10−15 cm2 is found, together with various other centers with cross sections of (1–4) ×10−17, (2–5) ×10−16, and (0.4–1.6) ×10−14 cm2, respectively. The sum of the trap densities for the various centers with cross sections in the range 10−15–10−16 cm2 is equal to 0.7–1 times the ion fluence, independent of ion energy (10–100 keV), avalanche injection current (5×10−11–5×10−10 A), and oxide thickness (490–1430 Å). The dominant trap density is proportional to the ion fluence over our experimental range (3×1012–1×1014 As+/cm2). Increasing the anneal temperature from 600 to 1100 °C gradually decreases the electron trapping rate, without extensively changing the dominant-trap parameters. The negative-charge distribution centroid (measured with respect to the Al-SiO2 interface) is shown to be proportional to the ion energy but does not depend on trapped charge density (4×1011−1×1013 cm−2), ion fluence (3×1012−1×1014 cm−2), injection mechanism (avalanche injection or internal photoemission), oxide thickness (490–1430 Å), anneal temperature (600–1100–°C), or ambient temperature (83–295 K). The charge centroids were found to be in excellent agreement with the experimentally determined (SIMS) ion distribution centroids, but systematically larger (up to 40%) than the values predicted by the theory of Lindhard, Scharff and Schio/tt (LSS). It is shown that optical excitation removes the trapped negative charge from the trapping centers in a homogeneous way (i.e., with constant charge centroid). From the detrapping experiments, an effective photoionization cross section is determined as a function of photon energy with an absorption threshold of 3.3 eV. This is corroborated by a model which assumes that the electron trapping is related to the implanted arsenic ions, incorporated into the SiO2-network at oxygen-sites. Isothermal detrapping experiments (in the range 100–250 °C) and thermally stimulated current measurements are reported. Both experiments can be modeled by assuming a Gaussian trap distribution around a median thermal trap depth Em=1.2–1.3 eV with a standard deviation ΔE=0.2 eV.