bluuebunny/crossref_metadata_2025 huggingface dataset:
Ferroelectricity in polyvinylidene fluoride
Authors: Kepler R. G. , Anderson R. A.
Published: February 2003

Changes induced in the orientation of the axes of crystallites in thin films of polyvinylidene fluoride by the application of 6×107 V/m at 100 °C for 1/2 h have been observed. The changes were observed by measuring the intensity of x rays diffracted from the film as a function of the orientation of the film relative to the diffracting x-ray beam. A simple model calculation shows that the results are consistent with the assumption that the changes are induced by the interaction of the applied electric field with the dipole moments of the polyvinylidene fluoride molecules. The model uses the fact that the orthorhombic symmetry of the unit cell results from a small distortion of a hexagonal primitive lattice, the distortion being a 1% decrease in the separation between molecules in the direction of the dipole moments. This model is consistent with the assumption that polyvinylidene fluoride is ferroelectric.
Efficiency of the solid-state engine made with Nitinol memory material
Authors: Golestaneh A. A.
Published: February 2003

The thermal efficiency of the solid-state engine (SSE) based on the shape-recovery phenomenon accompanied by the martensite-parent-phase (M→P) transformation has been evaluated. Particular application is made for the memory components made with the Nitinol alloys. The result is expressed in terms of the hot and cold reservoir temperatures (T and T0), the latent heat of the M→P transformation, ΔH, the fraction of the M→P transformation, α, and a coefficient β that depends on the geometry and type of the deformation of the memory component. The relationship between the efficiencies of the SS and the Carnot engines is discussed. The factor α is expressed in terms of Tc, the critical temperature under an applied load, the degree of prestraining of the component, and the volume change involved in the M→P transformation. It is seen that the maximum of the thermal efficiency approaches that of the Carnot engine at an x=T−T0 value that depends on T0, ΔH, and α. Choosing T0=297 K and a Nitinol alloy with ΔH=2 cal/g, the maximum efficiency, about 20%, occurs at x=75 K. Moreover, for a steady-state heat-mechanical energy conversion, the critical temperature of the memory component is found in terms of the T and T0 temperatures. The engine efficiency in terms of the energy loss due to friction and the heat-transfer coefficient is analyzed and estimated to be about 16%. It is seen that higher thermal efficiency can be obtained if a Nitinol alloy with a larger H value than given above can be found.
Surface normalization of sensitized stainless steel by laser surface melting
Authors: Anthony T. R. , Cline H. E.
Published: February 2003

A scanning laser beam was used to melt and normalize the surface layer of sensitized 304 stainless steel. Subsequent Strauss tests indicated a complete resistance to intergranular corrosion. Mechanical testing at strains less than 15% also showed laser surface melting to indefinitely extend specimen life in a stress corrosion environment. At strains greater than 15%, the laser-scanned protective layer was breached by cracks. A maximum critical laser-scanning velocity compatible with normalization of the surface layer is calculated. Similarly, a minimum critical laser-scanning velocity required to avoid resensitization is determined. The stress distribution in a 304 stainless-steel specimen with a laser-melted and self-quenched surface layer is estimated and shown to be compatible with the observed appearance of martensite in the melted surface layer.
Determination of absolute transition probabilities and particle densities by saturated fluorescence excitation
Authors: Mailänder M.
Published: February 2003

The high spectral intensity of pulsed dye lasers makes possible the saturation of atomic and molecular optical transitions. Because of the low-intensity wings of the laser beam intensity distribution, the excited volume is only partially saturated. A mathematical procedure is described which yields a formal ’’saturated volume’’ which can experimentally be determined by measuring the degree of saturation using neutral optical filters in the path of the exciting laser beam. In this way, absolute transition probabilities and particle densities can independently be measured, and a mutual test on accuracy is possible. Preliminary results on CH and C2 produced in a low-pressure C3H8/air flame are presented.
The complex-dielectric constant of sea ice at frequencies in the range 0.1–40 GHz
Authors: Vant M. R. , Ramseier R. O. , Makios V.
Published: February 2003

A comprehensive and unique set of measurements of the complex-dielectric constant of sea ice, performed at several frequencies in the range 0.1–7.5 GHz, is described. In addition, a brief survey of previously published results is given and a set of dielectric models describing the complex-dielectric behavior of sea ice, over the frequency range 0.1–40 GHz, is discussed.
Different roll regimes in shear-excited NLC
Authors: Scudieri F. , Ferrari A. , Fedtchouk A.
Published: February 2003

Two different stationary regimes for roll instabilities in homeotropically oriented samples of nematic liquid crystals are observed. The roll pattern can develop parallel or perpendicular to the applied shear depending on the frequency of the imposed stress.
Selected crystal-field effects in rare-earth systems
Authors: Fulde Peter
Published: February 2003

Over the last years a considerable number of effects have been found in Rare-Earth (RE) systems which are caused by the crystalline–electric field (CEF) splitting of the RE-ions. This splitting is usually of the order of 1–100 cm−1 and involves the ground state J-multiplet of the incomplete 4f-shell. A discussion will be given of some of the observed phenomena by using simple physical arguments. One group of effects concerns the influence of the CEF-split ions on the transport properties of conduction electrons in case the matrix is metallic. The behavior of the thermoelectric power is here of special interest. Furthermore if the matrix is a superconductor the CEF-splitting shows up in the ability of the RE-ions to suppress superconductivity. A second group of effects concerns the coupling of lattice deformations (phonons) to CEF-levels. Special attention will be paid to phenomena which involve an applied magnetic field. Examples are the Faraday rotations of the phonon-polarization vectors or the Cotton-Mouton effect. Analogous effects occur for optical phonons. They can be detected by Raman-scattering experiments.
Effect of magnetic field on the 3d ordering and spin correlations of the linear antiferromagnet TMMC
Authors: Borsa F. , Boucher J-P. , Villain J.
Published: February 2003

We present an investigation of the effect of an applied external magnetic field on the low temperature magnetic properties of the linear Heisenberg antiferromagnet (CH3)4NMnCl3(TMMC). The proton and deuteron spin-lattice relaxation rate T−11 has been measured in the temperature interval 1.3–4.2 K and for applied field ranging from 1 kG to 88 kG. Large effects are observed both for the field parallel and perpendicular to the chain axis c. In particular, for H⊥c, a peak in T−11 occurs at the 3d ordering temperature TN. In this way the investigation of the field dependence of TN reported by Dupas and Renard up to 10 kG is extended to 88 kG. In this paper we limit the discussion to the effect of H on TN, for H⊥c. The results are explained by considering the effect of both the dipolar anisotropy and the magnetic field on the spin correlations. It is shown that for H⊥c the system should be described by an XY model for T<20 K and it crosses over to an Ising model for kT∼gμB[S (S+1) H]1/2. The corresponding changes in the correlation length are responsible for the strong field dependence of TN. At low fields we obtain theoretically the correct H2 dependence of TN. For high fields one suggests that the correlation length and hence TN are affected by the crystal defects.
The effects of lateral current spreading, carrier out-diffusion, and optical mode losses on the threshold current density of GaAs-AlχGa1−χAs stripe-geometry DH lasers
Authors: Tsang W. T.
Published: February 2003

A calculation of the effect of stripe width on the threshold current density of stripe-geometry GaAs-AlχGa1−χAs DH lasers is given. This calculation includes the effects of lateral current spreading, carrier out-diffusion from the stripe, and optical mode losses. The relative importance of each of these effects is determined and threshold calculations are done for a variety of typical laser parameters such as Al content of the cladding layers, sheet resistance of the layers above the active layer, active layer thickness, and carrier diffusion length of the minority carriers in the active layer. Calculated curves for the variation of the threshold current density with stripe width and active layer thickness are compared to experimental data for a variety of types of stripe-geometry lasers. The agreement obtained between theory and experiment is excellent in all cases.
Superconducting transition temperatures of glassy and partially crystalline Be-Nb-Zr alloys
Authors: Hasegawa R. , Tanner L. E.
Published: February 2003

Superconducting transition temperatures of noncrystalline and partially crystalline Be-Nb-Zr alloys obtained by liquid quenching are reported. An increase of the transition temperature Tc to about 7 K from about 3 K was achieved in a partially crystalline Be20Nb15Zr65 alloy. The enhancement of Tc is attributed to a proximity effect in a glassy Be-Zr base matrix containing superconducting crystalline particles.
A superconducting fault-current limiter
Authors: Gray K. E. , Fowler D. E.
Published: February 2003

A conceptual design is presented for a fault-current limiter for the electrical power utilities which utilizes a superconducting element to commutate the fault current into a shunt resistor. The technical feasibility of the concept is supported by a computer simulation of the switching. A three-phase 145-kV 2-kA electrical system is considered in detail for ease of comparison with other fault-current limiters. Finally, the important advantages of such a fault-current limiter are pointed out, and the areas of additional research for the immediate future are indicated.
Lattice location of Te in laser-annealed Te-implanted silicon
Authors: Foti G. , Campisano S. U. , Rimini E. , Vitali G.
Published: February 2003

Backscattering of a 2.0-MeV He+ ion beam and channeling-effect techniques have been used to investigate the lattice location of Te in laser-annealed Te-implanted silicon. After Q-switched ruby-laser irradiation, an attenuation of 85% has been found in the Te signal for beam incidence along the 〈111〉 and the 〈110〉 axes of a Si crystal implanted with 400-keV Te to a dose of 1015 ions/cm2. The damaged amorphous layer recrystallizes completely after a 50-MW/cm2 pulse of 50-nsec duration for 〈111〉-oriented specimens; a lower power density is sufficient for 〈100〉 specimens. The Te profile broadens and shows accumulation at the Si surface for a power density of 60 MW/cm2 on a 〈100〉 specimen.
Correlation between lattice damage and electrical activation of phosphorus-implanted silicon
Authors: Miyao M. , Yoshihiro N. , Tokuyama T. , Mitsuishi T.
Published: February 2003

Quantitative comparision between the profiles of damage density before annealing and carrier concentration after annealing were examined for a wide range of phosphorus-implantation dose (1013–1016 cm−2). Electrical-activation mechanisms during low-temperature (around 500 °C) annealing before epitaxial regrowth occurs were found to be different in the different damaged regions (very low, ∼20%, 20–75%, 75%∼damage density).
Electrical switching in metal-EuS contacts
Authors: Peña J. L. , Sinencio F. Sánchez , Helman J. S. , Abraham S. , Kaldis E.
Published: February 2003

Experimental results where the resistance of samples of EuS single crystals prepared with two metallic contacts changes abruptly up to seven orders of magnitude, as a function of voltage, are presented. It is shown that this switching effect is associated with an insulating thin film that appears at the electrical contact between the metal and the semiconductor. The nature of the insulating film was studied by the SIMS technique.
Migration on fine molten wires in thin silicon wafers
Authors: Cline H. E. , Anthony T. R.
Published: February 2003

A series of molten Al-rich wires between 10 and 500 μ wide were translated through thin (100) and (111) silicon wafers in a thermal gradient to produce vertical p-n junctions, which are sufficiently narrow to be considered for some integrated-circuit applications. Thermal gradients were generated by heating the silicon wafers with either a scanning electron beam in vacuum or a hot tungsten filament in various atmospheres. The migration rate rapidly increased with the wafer temperature in agreement with calculations of the temperature gradient through the wafer. A reduction in the magnitude of the gradient near the colder wafer surface was explained by radiative-heat transport through the semitransparent silicon wafer. The width of the resulting doped region was finer in (100) wafers than in (111) wafers, because the shape of the liquid wire was narrower for the (100) orientation. A relationship between the linewidth, wafer temperature, and Al film geometry was derived to predict the linewidths from 30 to 140 μ in (100) wafers.
Laser-shock-induced microstructural changes and a comparison with explosive-shock-induced phenomena in metals: Field-ion and electron microscopic studies
Authors: Inal O. T. , Murr L. E.
Published: February 2003

Annealed etched molybdenum and tungsten wires were field evaporated to perfection in a specially designed field-ion microscope through which a laser beam could be focused onto the perfect metal emission end form or along the wire shank. Irradiation utilizing a Q-switched laser at fluences between 22 and 35 J/cm2 produced residual effects ranging from increasing numbers of lattice vacancies and vacancy clusters to massive deformation, cavitation and spallation, and melting. The results of increasing vacancy concentration with increasing laser fluence for molybdenum and tungsten were compared to similar observations in explosively shock-loaded molybdenum in concluding that laser shocking can produce residual effects approximately up to several hundred kbar peak pressure. Laser irradiation of electron transparent molybdenum foils also confirmed the attendant features of laser irradiation including vaporization, melting, and shock-induced spallation by direct observations in the transmission electron microscope. Dislocation substructures identical to those observed following explosive shock loading of molybdenum were also observed in the laser-irradiated molybdenum foils.
A ’’photocurrent-inversion effect’’ of sintered AgBr microcrystals at room temperature
Authors: Fujiwara Shin-ichi , Hada Hiroshi , Armiento C. A.
Published: February 2003

The photocurrent of sintered AgBr microcrystals of high dark conductivity has been measured at room temperature by using a polarization technique of mobile silver ions. Under the condition in which mobile silver ions were polarized, first, a negative photocurrent was observed and, consequently, this negative photocurrent was reversed to a positive one; that is, a ’’photocurrent-inversion effect’’ has been found. This negative photocurrent and the inversion effect of the current were explained by the theory of photographic sensitivity and the experimental estimation of the range of photoelectrons (?5×10−4 cm) in this sintered AgBr. It has been concluded that excess silver ions could be regarded not only as being significant for the electron traps in the surface region, but also as being the electron traps whose distribution could be varied by external voltage.
Dynamics of double-Josephson-junction interferometers
Authors: Blackburn James A. , Smith H. J. T.
Published: February 2003

The behavior of a superconducting loop containing two Josephson junctions has been studied by means of computer simulations. It is found that a current-biased system can exhibit various dynamical modes in which flux quanta alternately enter and leave the loop through the junctions. The nature of these coupled oscillations and their dependence on device parameters are discussed.
The hydrogen content of plasma-deposited silicon nitride
Authors: Lanford W. A. , Rand M. J.
Published: February 2003

The hydrogen content of glow-discharge-deposited silicon nitride (SiN) films made at 330–350 °C has been determined. Preparation conditions were varied to produce a range of compositions of Si/N=0.7–1.4. Quantitative hydrogen profiling of the samples was carried out using the resonant nuclear reaction 15N+H→12C+4He+γ ray. Calibration factors for Si-H (2160 cm−1) and N-H (3350 cm−1) absorption-band areas or absorbances have also been determined, enabling infrared transmission spectra to be used for hydrogen analyses of these films. All samples were homogeneous in hydrogen content and were in the range (1.6–2.1) ×1022 H atoms/cm3, or about 20–25 at.% H. Roughly three-quarters of the H is bonded to Si, the remainder to N. One plasma SiO2 sample made at 300 °C from SiH4 and N2O was measured also, and contained 5.7 at.% H, all as OH. Although there was little variation in the H content of SiN, there is a correlation between the total H concentration and the buffered HF etch rate. Some observations on the effects of the 15N ion beam (6–8 MeV) on the SiN are reported. Many Si-H and N-H bonds are broken, but the liberated H atoms or ions are unable to diffuse out of the film.
Oxygen pressure dependence of the retrogrowth of oxidation-induced stacking faults in (100) silicon
Authors: Murarka S. P.
Published: February 2003

Oxygen partial-pressure dependence of the length (L) of the oxidation-induced stacking faults (OISF) in (100) silicon has been investigated in the temperature range 1150–1250 °C (so-called retrogrowth range of temperatures). It has been observed that for a given time of oxidation the maximum temperature (TM), above which OISF start shrinking instead of growing decreases with decreasing partial pressure (pO2) of oxygen in the oxidizing ambient. On the other hand, for a given pO2, TM decreases with increasing time of oxidation. Based on the present results, the constant K′ in the equation L=K′pmO2tn exp(−Q/kT) has been calculated (where m and n are number exponents, Q is the activation energy, and T is the temperature). K′ has been found to decrease rapidly at temperatures above 1150 °C. These results agree reasonably well with the quantitative model proposed by this author and the observation that the temperature at which OISF start vanishing could be lowered by reducing the oxidation rate constant of silicon (as done in present experiments by lowering pO2).
A passive nonresonant technique for pulse contrast enhancement and gain isolation
Authors: Sala K. , Richardson M. C.
Published: February 2003

A passive aperture-scalable device is described which provides high contrast enhancement of a laser pulse over baseline optical noise while maintaining efficient net transmission of the principal laser pulse. The technique, which is based upon the nonresonant phenomenon of self-induced ellipse rotation, is capable of providing effective gain isolation for virtually any high-power laser system. The constrast enhancement capabilities of the device are demonstrated experimentally using a single ultrashort laser pulse obtained from a cavity-dumped passively mode-locked Nd : glass laser. In addition, a discussion is given concerning the ability of the device to temporally compress or stretch the optical pulse.
Active-passive mode-locked oscillators at 1.054 μm
Authors: Seka Wolf , Bunkenburg Joachim
Published: February 2003

We report on the characteristics of active-passive mode-locked phosphate-glass oscillators. These highly reliable oscillators operate at 1.054 μm and are characterized by the absence of satellite pulses for pulse durations tp≳80 psec. They have very high peak-to-background contrast of 107 to 108. Transform-limited pulse widths between 80 and 600 psec are reliably generated using a pair of intracavity etalons. The reproducibility of the pulse durations is better than ±10%, that of the pulse-train maximum about ±10 to 20%. Single-pulse selection with ±5% amplitude fluctuation has been achieved with threshold-pulse selectors. For pulses shorter than 50 psec, satellite pulses are occasionally observed. A theoretical explanation for this observation is given.
Nd : Y2O3 single-crystal fiber laser: Room-temperature cw operation at 1.07- and 1.35-μm wavelength
Authors: Stone J. , Burrus C. A.
Published: February 2003

Single-crystal fibers have been grown from high-purity 1.5 wt% Nd2O3 : Y2O3 powder mixtures, and short lengths of the fiber in dielectric mirror resonators have been evaluated as lasers at both 1.07- and 1.35-μm wavelength. The laser transition cross sections were approximately equal at the two wavelengths, and they were about two-thirds the cross section of Nd : YAG at 1.31 μm. The fluorescence lifetime of the laser samples was 340 μsec. Loss in the material was approximately 3% per cm. The absorption spectrum from 0.7 to 1.0 μm and fluorescence spectra for the 4F3/2→4I9/2, 4F3/2→4I11/2, and 4F3/2→4I13/2 manifolds of Nd3+ in Y2O3, taken with fiber samples, are reproduced in detail. The resultant energy levels are given. With a Kr laser operating at 0.7525 μm as the end pump, minimum observed laser threshold was 0.57 mW absorbed pump power for a 100-μm-diam 2.5-mm-long fiber operating cw in room-temperature air at 1.07 μm. The lasers operated in one or two transverse modes and had active linewidths of approximately 2 Å.
Generalized theory of the photoacoustic effect
Authors: McDonald F. Alan , Wetsel Grover C.
Published: February 2003

The theory of the photoacoustic effect is extended to include the contribution of mechanical vibration of the sample. Coupled equations for thermal and acoustic waves are solved in both sample and gas. It is shown that the pressure signal in the gas may be significantly affected by acoustic coupling in the sample, and experimental confirmation of this extended theory is given. The results of the fully coupled treatment are shown to be accurately reproduced by an extension of the Rosencwaig piston model: the pistonlike motion of the gas boundary layer adjoining the sample is superimposed on the mechanical vibration of the sample surface to give a composite piston displacement which then produces the pressure signal in the gas. The composite-piston model provides relatively simple algebraic results applicable to many cases of physical interest.
Aerosol impactors: A study of a fluid jet impinging upon a void
Authors: Forney L. J. , Ravenhall D. G. , Winn D. S.
Published: February 2003

The theoretical analysis of a two-dimensional jet of ideal fluid impinging normally upon a void has been made and compared with experimental observations. Using a scaled-up water model with a fixed-jet Reynolds number of 750, general features of the flow such as streamline positions and fluid velocities are in good agreement with theoretical predictions. Moreover, theoretical limitations on the void-space opening ratio h/w for a given jet spacing ratio s/w covering a range from 0 to 2 correlate well with the onset of irregularities in the observed flow pattern. Finally, experimental precautions are outlined necessary to minimize fluid instabilities and concurrent fluid flux into the void space.
One-dimensional numerical simulation of ac discharges in a high-pressure mixture of Ne+0.1% Ar confined to a narrow gap between insulated metal electrodes
Authors: Sahni O. , Lanza C. , Howard W. E.
Published: February 2003

The present work is concerned with a one-dimensional dynamic simulation, incorporting a self-consistent treatment of space-charge effects, of the buildup and decay of ac discharges in a high- (≳100 Torr) pressure mixture of Ne+0.1% Ar confined to a narrow gap (∼10−2 cm) between insulator (MgO) covered metal electrodes. Numerical modeling has been done of the dynamics of successive avalanches triggered by the electric-field-dependent secondary emission of electrons at the cathode due to ionic species, metastables, and photons. The basic continuity equations of the problem deal with the following collisional phenomena in the gas volume: (i) electron impact excitation and ionization of neon atoms, (ii) collisional ionization involving excited neon states, (iii) two-body and three-body collisional processes involving energy transfer, and (iv) absorption and reemission of imprisoned resonant radiation. The computed results show a satisfactory agreement with measured parameters on a single cell of a specially constructed ’’one-dimensional’’ ac plasma panel whose electrode linewidths were made an order of magnitude larger than the gas gap. Neon ions were found to play a dominant role in the secondary electron emission from the MgO surfaces, while photoemission was negligible. The theoretical and experimental results were fitted to yield a value of 0.45 for the intrinsic secondary-emission coefficient of MgO surfaces caused by the arrival of neon ions under vacuum conditions. Finally, sample results are presented for the spatial and temporal profiles of the electric field, charged particle concentrations, and the volume density of various excited species of the host gas.
A metal cluster generator for gas-phase electron diffraction and its application to bismuth, lead, and indium: Variation in microcrystal structure with size
Authors: Yokozeki Akimichi , Stein Gilbert D.
Published: February 2003

An oven has been designed and built for the production of metal microcrystals via nucleation and growth of the metal vapor in an inert-gas atmosphere. It has a flowing-argon double-orifice sampling system producing a supersonic free-jet mixture which crosses a 40-keV electron beam. Debye-Scherrer diffraction patterns are obtained from the metal cluster samples which range in size from 40 to 95 Å in diameter with estimated concentrations of 1012–1013 cm−3 at the electron beam location. The average cluster size produced in the oven for all three metals studied correlated well with the product of oven pressure times metal evaporation temperature p0T0m. As p0T0m increases, average size increases and cluster concentration decreases, in qualitative agreement with other metal evaporation research and with nucleation studies of vapor–inert-gas expansions in supersonic nozzles. Analyses of the diffraction patterns reveal changes in crystal structure from that of the bulk in the neighborhood of 50–60 Å in diameter (2000–4000 atoms per cluster). The differences are most pronounced in indium which changes from tetragonal to face-centered cubic as the size decreases. Cluster temperatures at the electron beam location have been estimated from Debye-Waller factors, from extrapolation to bulk structure, and from calculated values of the argon-gas temperature in the free jet. The three methods yield consistent results, and the hotter the clusters are prior to the free-jet expansion, the greater is the temperature difference between the clusters and the argon gas when the mixture becomes collisionless (i.e., no further change in the temperature of gas or custer).
High-power photopreionization-stabilized carbon dioxide waveguide lasers operating at gas pressures of up to 13 atm
Authors: Brink D. J. , Hasson V.
Published: February 2003

A simple photopreionization-stabilized waveguide laser is energized effectively by fast Blumlein-type pulsers and operates at pressures of up to 13 atm. The laser has an active plasma volume of ∼0.2 cm3 and provides 20 ns gain-switched pulses with beam energies of 10 mJ. The maximum pressures and beam energies are more than an order of magnitude higher than those published previously; the peak power is enhanced by two orders of magnitude.
Conduction mechanism of non-Ohmic zinc oxide ceramics
Authors: Eda Kazuo
Published: February 2003

The conduction mechanism of non-Ohmic ZnO ceramics is investigated. In order to explain the non-Ohmic property, a new energy-band model composed of a thin intergranular layer with traps sandwiched between Schottky barriers formed opposite each other is proposed. According to the newly proposed energy-band model, the non-Ohmic property of ZnO ceramics is mainly governed by field emission for the reverse-biased Schottky barrier in the voltage region above the threshold voltage in the V-I curve and by thermionic emission in the voltage region below the threshold voltage. The energy-band model and the conduction mechanism discussed in this paper are appropriate for the explanation of experimental results, not only those presented in previous papers, such as the effect of additives, the V-I curve and its temperature dependence, but, additionally, the dielectric properties, the asymmetrical degradation of the V-I curve, and the thermally stimulated current.
Dual implantation of C and Ga ions into GaAs
Authors: Shin B. K. , Ehret J. E. , Park Y. S. , Stefiniw M.
Published: February 2003

Dual implants of C+ and Ga+ ions in GaAs have been investigated by sheet-resistivity and Hall-effect measurements. Efficient doping has been achieved by dual implantation, even at an annealing temperature of 700 °C. Analysis of electrical profiles indicates that the concentration of substitutional atoms in As sites is less than the implanted dose; the remaining C atoms are believed to out-diffuse through encapsulation during annealing. Although the doping efficiency for the dual implants is higher than that of the single implants, the effective compensation ratio is about the same, which suggests that ’’self-compensation’’ may be the predominant mechanism in the implanted samples.
Colloidal metal in aluminum-oxide
Authors: Goad David G. W. , Moskovits M.
Published: February 2003

The nature of the origin of the color in anodized aluminum colored by ac electrolysis in electrolytes containing nickel, copper, silver, gold, and molybdenum salts is investigated. The measured specular reflectance spectra in the region 350–750 nm can be adequately explained by assuming that small metallic particles are incorporated in the anodic film as a colloid. By calculating the optical constants of such a system, specular reflectance spectra can be deduced. A detailed comparison of the calculated and experimental reflectance spectra yields good agreement. It is concluded that metals which do not possess interband transitions or plasma resonance absorptions in or near the visible region of the spectrum will produce brown or bronze colored anodic films when incorporated as a colloid.
Epitaxy of MgO on alkali halides with NaCl-type structure
Authors: Aboelfotoh M. O.
Published: February 2003

Reflection high-energy electron diffraction has been used to examine the growth of MgO on (001) surfaces of LiF, NaCl, and KCl in the temperature range 25–250 °C. MgO grew initially with parallel orientation, i.e., (001)MgO∥ (001)s and [100]MgO∥[100]s. The substrate temperature at which parallel orientation occurred depended on the nature of the substrate, increasing in the sequence LiF, NaCl, and KCl. The mode of MgO growth did not depend on the substrate temperature and the lattice misfit. MgO initially formed three-dimensional nuclei. At high substrate temperatures (250 °C) the range of film thickness over which parallel orientation persisted depended on the nature of the substrate, decreasing in the sequence LiF, NaCl, and KCl. For a given substrate this range of film thickness increased with increasing substrate temperature. Infrared spectra obtained for films deposited on substrates at 25–250 °C showed the presence of hydroxyl groups only in films deposited on substrates at low temperatures (25 °C). These results suggest that (1) the range of film thickness over which parallel orientation persists is influenced by the misfit between the MgO and the substrate lattice, decreasing with increasing lattice misfit and (2) the parallel orientation is also influenced by the incorporation of impurities such as hydroxyl groups into the growing film at later stages of growth on substrates at low temperatures.
Junction current and luminescence near a dislocation or a surface
Authors: Lax M.
Published: February 2003

Closed-form solutions (integral representations) are obtained for the charge density and current density in the vicinity of a dislocation or a surface which pierces a junction at right angles. The total reduction in luminescence and increase in junction current are obtained as functions of two dimensionless ratios, ε, the recombination-length/diffusion-length ratio, and η, the radius-of-dislocation/diffusion-length ratio, where recombination length a=D/s is the diffusion constant over surface-recombination velocity.
Charge transfer in ZnO surfaces in the presence of photosensitizing dyes
Authors: Lagowski J. , Gatos H. C. , Balestra C. L.
Published: February 2003

The charge transfer associated with the presence of photosensitizing dyes (fluorescein, erythrosin B, and rose bengal) was investigated on single-crystal ZnO surfaces employing surface photovoltage spectroscopy. It was found that the charge transfer takes place via electron transitions from the surfaces to the conduction band. The energy necessary for these transitions is transferred to the surface states from excited states of the photosensitizing dyes. The surface states were found to be related to chemisorbed oxygen and their density is (2–4) ×1010/cm2 under atmospheric pressure at room temperature.
Dember-effect theory
Authors: Goldman S. Robert , Kalikstein Kalman , Kramer Bernard
Published: February 2003

A theoretical investigation of the photovoltage produced in insulated CdS-type crystals excited by strongly absorbed radiation has been carried out, taking into account trapped electrons and trapped holes in addition to free electrons. Expressions for the photovoltage dependence on intensity for isolated crystals have been obtained over a wide range of excitation levels. A plot of typical density profiles for the free electrons, trapped electrons, and trapped holes as functions of position is given. It is shown that the results can readily be extended to nonisolated crystals.
Investigation of mobile ions in MOS structures using the TSIC method
Authors: Nauta P. K. , Hillen M. W.
Published: February 2003

Mobile ions in SiO2 layers of MOS structures have been investigated with the thermally stimulated ionic current (TSIC) method. Two distinct peaks were observed in the temperature range 30–350 °C, the first at about 150 °C and the second at about 300 °C. Measurements on samples intentionally contaminated with either sodium or potassium show that the first peak is due to the motion of sodium ions, whereas the second peak results from the motion of potassium ions. The surface-trapping model describes the curves well when a Gaussian spread in activation energy is assumed. When a physically plausible value for the emission time constant is assumed (10−12 s), an activation energy is found that is consistent with an emission-limited process.
A method for studying interface states in MIS structures by thermally stimulated surface potential
Authors: Yamashita Ken , Iwamoto Mitsumasa , Hino Taro
Published: February 2003

A thermally stimulated surface potential (TSSP) method has been developed to estimate the parameters of the insulator-semiconductor interface in MIS structures. As TSSP is measured in the open-circuit condition, charge on the gate electrode and voltage applied across the insulating layer are both constant in the measurement. For the above reasons, the analysis of TSSP is simplified, and theoretical TSSP curves can be calculated under non-steady-state and steady-state conditions. The samples used for our experiments are Al-SiO2-Si MIS structures. To estimate the energy distribution of interface states, the temperature-vs-potential characteristic is used, particularly the point where the interface changes from non-steady-state to steady state. The characteristic can be clearly and easily obtained by a convenient method devised in the present work. The total amount of interface states, their energy distribution, and their lifetime are estimated in a wide energy range from the characteristic by simple calculation. Further, the relaxation mechanisms of the interface are discussed for samples having substrates of both p- and n-type Si.
Dielectric properties of aluminum oxide films
Authors: Birey H.
Published: February 2003

This paper presents the results of an investigation on the dielectric properties and discusses the observed ac and dc electrical characteristics of aluminum oxide thin films. ac properties are deduced from the capacitance measurements at intermediate and high frequencies. Measurements indicate the existence of two relaxation mechanisms. Hopping polarization of charge carriers is responsible for the high-frequency dissipation mechanism. This polarization is influenced by an additional mechanism at low frequencies. dc current-voltage characteristics are obtained from the steady-state region of the current transients for various step voltages. They exhibit two distinct types of conduction mechanisms depending on the applied voltage: (a) Ohmic conductivity at low voltages and (b) space-charge-limited current (SCLC) at high voltages. Specimens are polarized in the upper limit of the Ohmic region. According to the additional effect of the polarization field in a formed sample with respect to applied field, two alternative types of current transients are posible, which are called ’’same’’ and ’’reverse’’ polarity transients. Relaxation frequencies, obtained by means of the current transient data using Hamon’s equation, depend on the applied electrical field. The polarization field also moderates the relaxation frequencies.
Optical birefringence of ultrathin AlxGa1−xAs-GaAs multilayer heterostructures
Authors: van der Ziel J. P. , Gossard A. C.
Published: February 2003

The measured birefringence of ultrathin AlxGa1−xAs-GaAs multilayers grown by molecular beam epitaxy is shown to result from the difference in the effective refractive indices for transverse electric and magnetic polarizations and from the quantum-size effect of the one-dimensionally confined carriers in the GaAs potential wells.
High-resolution composition profiling of GaAs-AlxGa1−xAs double-hetero-laser structures with photoluminescence
Authors: Ḿonemar B.
Published: February 2003

Measurements of composition of multilayer semiconductor laser wafers were performed with the aid of photoluminescence spectra. Reliable depth profiling of composition is difficult in as-grown wafers, even at low temperature, because the excess-carrier diffusion length is comparable to the layer thicknesses. With adequate reduction of the diffusion length, which in our case was done with ion implantation, the origin of photoluminescence could be restricted to a narrow region close to the excited surface. Samples were prepared for profiling by an angle-etching technique, leaving a controlled angle as small as 0.01° across the wafer, which greatly simplifies profiling measurements. Results from composition profiling of a conventional five-layer GaAs-AlxGa1−xAs DH-laser wafer with a depth resolution better than 0.1 μm are presented.
Positive gain measurements on the 470-nm continuum band of CdHg
Authors: McGeoch M. W. , Fournier G. R.
Published: February 2003

Optical gain has been observed on the 470-nm continuum band of CdHg following the flashlamp excitation of vapor mixtures of Cd and Hg. An argon ion laser was used to monitor gain signals at wavelengths ranging from 457.9 to 514.5 nm.
Noncollinear three-phonon interaction in an isotropic plate
Authors: Brower Neal G. , Mayer Walter G.
Published: February 2003

Two noncollinear pump modes of 5 and 7 MHz have been excited in an isotropic plate of brass. For certain pump-mode configurations, the pump modes could interact via the nonlinearities of the medium to produce a third Lamb mode at the sum frequency of 12 MHz. The three-phonon interaction has been detected using an optical probe for two pump-mode configurations. pressure,discharge energies, and translational temperature of the
Reflection of an impulsive plane wave by a plasma half-space moving perpendicular to the plane of incidence
Authors: Kalluri Dikshitulu , Prasad R. C.
Published: February 2003

Reflection of an obliquely incident impulsive plane electromagnetic wave from lossless, cold, isotropic, and uniaxial plasma half-spaces moving perpendicular to the plane of incidence is considered. The analytical solutions are obtained by inversion of the appropriate Laplace transforms. The analysis shows that in the case of uni-x plasma both the pulse height and loop width of the reflected field decrease with increase in the medium velocity. However, in the case of uni-y plasma (perpendicular polarization) the pulse height decreases and loop width increases with increase in the medium velocity. Also, some more results are presented and discussed in the text.
Ring-shaped stacking faults induced by oxide precipitates in silicon
Authors: Plougonven C. , Leroy B. , Arhan J. , Lecuiller A.
Published: February 2003

Repeated heat treatments at 1100 °C on CZ-grown wafers result in the nucleation and growth of stacking faults in the vicinity of oxygen precipitates. During the high-temperature treatment, the precipitates and the stacking faults grow. During the cooling, new precipitates form on the SF bounding partial which by their subsequent growth can generate a ring-shaped stacking fault on top of the first one. Possible mechanisms involve interstitial condensation at the SF partial or vacancy generation by the partial climb. Models of the growth kinetics are discussed and take into account both mechanisms.
Proton-enhanced diffusion and vacancy migration in silicon
Authors: Masters B. J. , Gorey E. F.
Published: February 2003

Single crystals of silicon containing prediffused arsenic, boron, and phosphorus profiles are bombarded at 600–900 °C with 250–360-keV protons. Under conditions approaching ideality (low impurity concentration and less than 1013 protons/cm2 sec) enhanced impurity diffusion appears to proceed in an uncomplicated manner which is well described by steady-state kinetic treatment. At high temperatures and very low bombardment fluxes the enhanced-diffusion coefficients are observed to be temperature independent and first-order dependent upon flux. At moderately increased damage rates, particularly at lower temperatures, the diffusivities become temperature dependent and a half-order flux dependence is observed. The results are explained by assuming proton-enhanced diffusion to be controlled by the migration of split monovacancies (semivacancy pairs). Consistency with annealing studies of radiation-induced defects at much lower temperatures and with thermally activated diffusion studies at higher temperatures is attained by assuming a 1.47-eV migrational enthalpy and a 3.66-eV enthalpy of formation for the uncharged defect.
Volume expansion and annealing compaction of ion-bombarded single-crystal and polycrystalline α-Al2O3
Authors: Krefft G. B. , EerNisse E. P.
Published: February 2003

Radiation damage of α-Al2O3 was systematically investigated as a function of incident ion mass and energy partitioning into atomic and electronic processes by measuring the resulting stress in the ion-bombarded layer with a cantilever beam technique. Heavy-ion-bombardment-induced expansion in the implanted surface layer shows strong anisotropy which appears to be related to the higher defect production rate along the c axis. Stress relief is observed at fluences above 1×1015 Ar/cm2 for the [0001] orientation only and is attributed to basal slip. Hydrogen bombardment subsequent to heavy-ion bombardment results in compaction which is also anisotropic. The anisotropy of both the expansion and the compaction point to structure sensitive defects. Approximately 80% of the radiation damage is annealed at 900 °C for the [0001] orientation and 60% for the [011̄0] orientation. A similar expansion-compaction response is found in argon- and hydrogen-bombarded polycrystalline Al2O3.
Electrical properties of Si-N films deposited on silicon from reactive plasma
Authors: Sinha A. K. , Smith T. E.
Published: February 2003

Because reactive-plasma-deposited Si-N films might offer certain advantages in silicon integrated-circuit technology, we have evaluated their electrical properties and compared them with those of CVD Si3N4. Various films with compositions in the range 0.75?Si/N?1.9 were studied using C-V and I-V measurements, the latter at temperatures up to 200 °C. The dominant conduction mode appears to be Frenkel-Poole emission; this is consistent with the observed linear I-vs-V1/2 relationship and magnitudes of various parameters. The resistivities (range 104–1021 Ω cm at 2×106 V/cm) and dielectric strengths (range 0.8×106 to 8×106 V/cm) are found to depend upon the film composition and on an as yet undefined structural parameter (for Si/N?0.75). The interface between Si-N and Si is associated with a high density of surface charge (≳1012 cm−2) and a large trapping instability.
Structure of the LaB (001) surface studied by angle-resolved XPS and LEED
Authors: Aono M. , Oshima C. , Tanaka T. , Bannai E. , Kawai S.
Published: February 2003

The atomic structure of the LaB6 (001) clean surface has been studied by angle-resolved x-ray photoelectron spectroscopy (XPS) and low-energy electron diffraction (LEED). The results indicate that the outermost layer of the surface is a lanthanum layer which is in a (1×1) ordered state.
The resistive phase of a high-voltage water spark
Authors: VanDevender J. Pace
Published: February 2003

The resistive phase of self-breaking water-dielectric spark gaps in a high-current relativistic electron-beam accelerator is investigated experimentally. For gaps that withstand voltages V?1.8 MV and mean electric fields between 2×107 and 5×107 V/m, both the current rise time and the energy dissipated in the discharge are adequately described by the semiempirical relations of Martin. In contrast to the results reported in lower-energy experiments, no evidence was found of a slowly varying resistive phase with a gap resistance comparable to the circuit impedance after t=2.5τr. Approximately 8±3% of the energy dissipated in the gap is coupled into a shock wave generated by the discharge. Light emission from the arc channels indicated that the light was strongly filtered by the highly excited water surrounding the channel, and the light emission cannot be analyzed to determine the plasma properties of the arc channel unambiguously.
Absolute efficiency of (ZnCd)S : Ag phosphor under fluoroscopy conditions
Authors: Nomicos Constantine D. , Giakoumakis George E. , Euthymiou Paraskevi C. , Sandilos Panayotis X.
Published: February 2003

The absolute x-ray efficiency of (ZnCd)S : Ag phosphor screens was measured under fluoroscopy conditions as a function of x-ray tube voltage and for different screen weights. The screens were prepared by sedimentation. Two types of grain size were used, i.e., 2–3 and 10 μm. The authors calculated the matching factor of some phosphor-photocathode combinations.
The stress-enhanced diffusion of boron in silicon
Authors: Todokoro Yoshihiro , Teramoto Iwao
Published: February 2003

The stress effect on diffusion of impurities in the fabrication of silicon avalanche photodiodes was found when thick diffusion masks of SiO2 were used. The observation of the avalanche multiplication profile showed that nonuniform diffusion occurs over the window area of the mask. From the qualitative analysis, it is concluded that the diffusion coefficient is represented by the sum of the zero-stress term and the stress-induced term.