bluuebunny/crossref_metadata_2025 huggingface dataset:
Shallow diffusion profile analysis of phosphorus in silicon at 1100 °C and an empirical fit
Authors: Eranna G. , Kakati D.
Published: February 2003

A detailed study of a phosphorus diffusion profile in silicon at 1100 °C was made by repeated removal of silicon layers and resistivity measurements by observing the limitations of four-point probe voltage and currents [Solid-State Electron. 25, 611 (1982)]. The results confirmed that the phosphorus diffusion profile is not always given by an error function and on the contrary, a distinct kink and tail structure occurs in the profile. The observed data seems to agree with the concept of two diffusion coefficients proposed by Tsai [Proc. IEEE 57, 1499 (1969)] for temperatures below 1100 °C. Observed experimental data have been analyzed to give the values of the two diffusion coefficients and an empirical fit has been found. It is pointed out that two independent Gaussian profiles can be fitted for the phosphorus profiles by the two diffusion coefficients which lead to the apparent kink and tail structure of the profile.
A specific trap level at 78 meV in undoped liquid encapsulated Czochralski grown GaAs–SI materials
Authors: Fillard J. P. , Castagne M. , Bonnafe J. , de Murcia M.
Published: February 2003

In this paper we provided experimental evidence for the presence of a 78 meV trap which is specific of liquid encapsulated Czochralski grown semi-insulating GaAs. This trap gives rise to a well defined thermally stimulated current peak obeying a monomolecular recombination model and amendable to an accurate differential analysis. The Urbach parameter Ei/kTm is shown to lie well below the usual domain, as it was established for low temperature peaks. The deduced cross section is weak, whatever the polarity involved, and quite adapted to the case of a double acceptor. The thermal activation energy 78 meV is consistent with the optical transitions observed in absorption or photoluminescence whereas it looks different with the deep level transient spectroscopy or photo-induced transient spectroscopy or temperature dependant Hall results; this discrepancy is explained by the influence in these experiments of neighboring traps of larger cross section. Then it is confirmed that this 78-meV trap could originate in a well-defined lattice defect and plays a decisive role in the electrical equilibrium of the material.
Current transport in semiconductor-electrolyte barriers: Surface recombination and photovoltaic applications
Authors: El Guibaly Fayez , Colbow Konrad
Published: February 2003

A general analysis is given for the effects of illumination and surface recombination on the currents flowing in a semiconductor/conductor junction. The behavior of the electron and hole quasi-Fermi levels is examined and it is shown that a priori assumptions about their flatness in the depletion region leads to contradictions in the analysis. The two theories describing currents in a Schottky barrier junction, the thermionic emission theory and the diffusion theory of Shockley are shown to have their parallels in a semiconductor/electrolyte contact. A Shockley–Read–Hall model for surface recombination was employed in the analysis and it was shown that this model reduces to the expression for surface recombination often used in the literature under certain conditions.
Experimental comparison of atomic roughness and Hall mobility in p-Si inversion layers
Authors: Hahn P. O. , Henzler M.
Published: February 2003

Hall mobilities of Si(111) p-channel inversion layers have been measured at temperatures between 4.2 K and room temperature at metal-oxide semiconductors field-effect transistors MOS-FET’s with varying atomic roughness at the Si–SiO2 interface. The atomic roughness was determined on an atomic scale quantitatively with spot profile analysis of a low energy electron diffraction pattern (SPA-LEED). A strong correlation between Hall mobilities at high inversion and atomic roughness is found nearly with a proportionality. Even at room temperature the transistors with the low interface roughness exhibit the higher mobility. Additionally it is observed that the interface charge Qss as derived from Coulomb scattering for low carrier concentration is proportional to the mobility at high carrier concentration and therefore to step atom density, too.
Properties of NbN thin films deposited on ambient temperature substrates
Authors: Bacon D. D. , English A. T. , Nakahara S. , Peters F. G. , Schreiber H. , Sinclair W. R. , van Dover R. B.
Published: February 2003

The preparation of cubic NbN films by reactive dc magnetron sputtering is described. These superconductive films are deposited at a sufficiently low temperature (<90 °C) that photoresist liftoff techniques and can be used in fabricating Josephson junctions. The superconducting transition temperature has been measured as a function of gas composition and pressure. It reaches a maximum of 14.2 K at 15% N2–85% Ar and 1.06 Pa total pressure. The resistivity ratio of these films is close to unity. Structural studies by transmission electron microscopy and electron diffraction show that films 100-nm thick or less are randomly oriented, and noncolumnar with a crystallite diameter of 5 nm and a lattice parameter of 4.46 Å, which is significantly higher than the bulk value for cubic NbN. The films are dense with void diameters no larger than 0.7 nm. Films 300-400 nm thick show a small degree of texturing in x-ray studies with a Read camera. Auger analysis shows a monotonic increase in the N/Nb ratio with increase in the N2/Ar ratio in the sputtering ambient up to 30% N2. From 30% to 50% N2 in the sputtering mixture the N/Nb ratio is constant. Small amounts of carbon impurity are found in all films.
Magnetostriction and magnetic core loss at high frequency in amorphous Fe-Nb-Si-B alloys
Authors: Inomata K. , Hasegawa M. , Kobayashi T. , Sawa T.
Published: February 2003

Magnetostriction and magnetic core loss at high frequency up to 100 kHz were investigated together with crystallization temperature, saturation magnetization, and magnetic permeability for amorphous (Fe1−xNbx)zSi88−zB12 alloys. Crystallization temperature significantly rises with Nb addition, particularly in the high z region. Magnetostriction decreases with increasing Nb content and z value. Magnetic core loss decreases and magnetic permeability increases with decreasing magnetostriction. Magnetic core loss reduction due to Nb addition were analyzed to be mainly attributed to domain width reduction through the decrease of magnetostriction.
Corner clusters in thin soft magnetic layers. III. Conversions in corner clusters
Authors: van den Berg H. A. M.
Published: February 2003

The domain structure in thin soft magnetic films is considered as a concatenation of domain-wall clusters, being collections of domain walls that have one intersection line—the so-called cluster knot—in common. The transformations in the domain structure are accompanied by the addition and the disappearance of clusters to and from the configuration, respectively. The discussion is confined to the reversible conversions in the corner clusters, whose cluster knots coincide with corners in the magnetic film. The situation in corners is unique because a singularity in the field in this region can be generated by a moderate external stimulus. Only domain walls whose ‘‘feet,’’ or the part most adjacent to the corner, coincide with one of the edges of the corner can be present in these high-field regions. This feature of the field distribution is of decisive significance to the conversions in the magnetization distribution, which is accompanied by the penetration of domain walls into the non-field-free region near the corners whose bounding edges form angles η smaller than π. In corners with larger angles, conversion between two continuous magnetization modes is possible, one mode characterized by the singularity in the field and the other one by a rotation segment with sector angle η-π. In this rotation segment, being a sector in which the magnetization rotates circularly around the cluster knot, the same reversible conversions as those previously discussed for free clusters can take place. The theoretical findings are supported by experimental observations conducted with the Bitter technique in 3500-Å-thick permalloy layers.
rf planar magnetron sputtering and characterization of ferroelectric Pb(Zr,Ti)O3 films
Authors: Krupanidhi S. B. , Maffei N. , Sayer M. , El-Assal K.
Published: February 2003

Ferroelectric films of lead zirconate titanate (PZT) have been fabricated by rf planar magnetron sputtering. Films having a resistivity >106 Ω cm and a dielectric constant >800 at 300 K have been achieved using 100% oxygen as a sputtering medium, 10% excess PbO added to the target, and appropriate post-deposition annealing. The sputtering rate is in the range 0.2–1.0 μm/h and varies with sputtering pressure and substrate temperature. Post-deposition annealing affects both crystallinity and grain size, but incipient crystallization formed only in as-grown films deposited at substrate temperatures >400 °C is essential for this process to be effective. A clear ferroelectric transition is observed at 350 °C, while the activation energy for dc conductivity of around 0.8 eV is consistent with bulk properties of PZT. The spontaneous polarization and coercive field measured from ferroelectric hysteresis loops is 20.75 μC/cm2 and 10 kV/cm, respectively. The optical transmittance of the films is determined by a Pb–Pb charge transfer band near 400 nm and this is a sensitive test of film stoichiometry.
Calculation of potential distribution in homogeneous anisotropic nonlinear dielectrics
Authors: Lloris A. , Prieto A. , Torres J. C.
Published: February 2003

This paper presents an iterative procedure by relaxation for the calculation of potential distributions in nonlinear polar homogeneous and anisotropic dielectrics, using the finite difference method, in Cartesian coordinates and with Dirichlet boundary conditions. This procedure has been translated to a Fortran program limited for simplicity to two-dimensional problems, but can be easily expanded to three-dimensional problems. Some examples for different geometries are included.
Electron backscatter and impedance in one-dimensional space-charge limited diodes
Authors: Pereira N. R.
Published: February 2003

Megavolt electrons striking a high-Z anode/bremsstrahlung X-ray converter anode are partially reflected into the anode-cathode gap of the diode. The diode charge density is higher than without reflection, and the current density is lower. A quantitative estimate for one-dimensional flow yields a reduction from Child–Langmuir by up to 25% for unipolar flow. For bipolar flow, the ion current can increase twofold.
Monte Carlo simulation of the motion of electrons in SF6 in uniform electric fields
Authors: Dincer M. S. , Govinda Raju G. R.
Published: February 2003

The motion of electrons in SF6 in uniform electric fields is simulated using a Monte Carlo technique for the range of reduced electric fields 100≤E/p≤180 V cm−1 Torr−1. The swarm parameters evaluated are compared with the experimental results of drift velocity, ratio of diffusion coefficient to mobility, ionization, and attachment coefficients. The electron-molecule collision cross sections adopted in the simulation result in a good agreement with the experimental values over the range of E/p investigated.
Point defects in crystalline SiO2: Thermally stimulated luminescence above room temperature
Authors: Jani M. G. , Halliburton L. E. , Kohnke E. E.
Published: February 2003

Thermally stimulated luminescence from one natural and two synthetic samples of alpha-quartz has been investigated in the range from room temperature to 400 °C. Comparisons were made between unswept samples and others, taken from adjacent positions in the original stones, that were swept in a hydrogen atmosphere. Three sets of thermally stimulated luminescence (TSL) data were obtained from each sample, corresponding to initial electron irradiation at 77 K, at ice-bath temperature, and a double irradiation at ice bath plus 77 K. Electron spin resonance and infrared absorption data also were obtained from the same samples. A number of TSL peaks were found in the 60–130 °C region and they have been tentatively associated with hydrogen in the crystal. More intense peaks were found in the 200–300 °C region, but only in unswept samples after an ice-bath or ice-bath plus 77-K irradiation. These latter peaks are attributed to electron-hole recombination at [AlO4]0 centers as a result of electron release from alkali-associated electron traps.
Luminescence study of thallium implanted silicon
Authors: Swenson Orven F. , Luke Theodore E. , Hengehold Robert L.
Published: February 2003

Ion-implanted Si:Tl was characterized using photo- and cathodoluminescence. The same sharp line defects were found to be produced by the Tl heavy ions as were identified in previous light ion studies. The defects produced by the implantation were removed and the Tl was activated using a two-step anneal process. A high quality annealed implant layer was produced from which the four excited states of the Tl bound exciton no-phonon transition could be resolved. An unidentified bound exciton peak related to the Tl acceptor was observed for the first time in both ion-implanted Si:Tl and in a comparison sample of bulk grown Si:Tl. This is the first reported study of an implanted dopant in silicon using luminescence.
Quantification of dopant implants in oxidized silicon on sapphire using secondary-ion mass spectrometry
Authors: Dowsett M. G. , Parker E. H. C. , King R. M. , Mole P. J.
Published: February 2003

By measurement of ion and sputter yields from thermally grown SiO2 and single crystal Si it has been possible to quantify 11B range profiles measured by secondary-ion mass spectrometry from device-type silicon on sapphire wafers implanted through a gate oxide. Contrary to theoretical predictions, no step in 11B concentration is observed at the SiO2/Si interface after calibration. Measured ion ranges in SiO2 and Si agree well with those of other works and with theoretical predictions by Johnson and Gibbons and Biersack. Ranges in SiO2 are found to be around 20% greater than those calculated by Smith. Under 4-keV 16O2+ primary-ion bombardment, the relative yields (SiO2/Si) are found to be the following: sputtering, 2.05; 11B+ ion yield, 2.25; degree of 11B+ ionization, 1.10. The oxygen primary beam is apparently inert in the SiO2, but reacts with the Si to form a mix SiOm where m=1.95 under steady-state conditions.
Characterization of ion-implanted GaAs using cathodoluminescence
Authors: Cone M. L. , Hengehold R. L.
Published: February 2003

Cathodoluminescence is investigated as a method for determining the depth profiles of ion-implanted layers in GaAs. A computer simulation of the cathodoluminescence process is developed and used to study the sensitivity of the luminescence to changes in implant profile and electron beam energy. The results obtained for both uniformly doped layers and ion-implanted layers are then compared to experimental results from Mg-implanted GaAs. Clear differences are found to exist between the predicted luminescence curves for different types of layers suggesting that cathodoluminescence is a potentially useful diagnostic tool for use in profile determination.
Atomic resolution observations of nonlinear depleted zones in tungsten irradiated with metallic diatomic molecular ions
Authors: Pramanik Dipankar , Seidman David N.
Published: February 2003

Direct evidence, on an atomic scale, is presented for the enhancement of damage production per projectile ion in metallic diatomic molecular ion (dimer) irradiations of tungsten as compared to monatomic ion (monomer) irradiations. Irradiations were performed in situ at ≲10 K, in a field-ion microscope, employing 20 keV Ag+ and W+ ions and the results are compared with 40 keV W+2 and Ag+2 ion bombardments; the average energy per ion is 20 keV. The energy and mass of the dimers are such that the collision cascades are nonlinear. By directly counting the number of vacancies in individual depleted zones, produced by the different ions, it was demonstrated that the number of vacancies produced per incoming ion of the dimer is 1.55 times greater than the number of vacancies produced per monomer. The depleted zones produced in the near-surface region, by the W+2 dimers, give rise to void-like contrast effects. Whereas the W+ monomers do not produce the void-like contrast of the W+2 ions. This result can only be understood if significant rearrangement of vacancies had occurred after the dynamic development of the collision cascade. The presence of voids is explained employing a nucleation and growth model. The average diameter (〈λ〉) of the depleted zones created by 20 keV Ag+ and W+ monomers is 17.5 Å, while 〈λ〉 is 28.5 Å for the Ag+2 and W+2 dimers. Thus the depleted zones created by the dimers are larger than those produced by the monomers, but not twice as large. This indicates that the collision cascades, in the case of the dimer irradiations, overlapped to a certain degree. In addition, the radial distribution and the first nearest-neighbor clusters functions for the vacancies in the depleted zones are presented and compared for the monomer and dimer ion irradiations.
Studies of the spectral and spatial characteristics of shock-induced luminescence from x-cut quartz
Authors: Brannon P. J. , Konrad C. , Morris R. W. , Jones E. D. , Asay J. R.
Published: February 2003

Spatial and spectral studies of shock-induced luminescence from x-cut crystalline quartz as a function of stress level revealed the following information: Crystalline x-cut quartz has a threshold for emission near the dynamic yield point (about 6 GPa); the spatial distribution of the luminescence from x-cut quartz changes from an intersecting linear emission pattern to a uniform emission pattern as the stress level increases from 6 to 8 GPa; spectra from x-cut quartz are band-like rather than blackbody; crystalline x-cut quartz has emission peaks near 400 and 600 nm; a change in the 400-nm emission with time can be correlated to wave interaction times. A discussion of the luminous emission in terms of yielding and other physical mechanisms is given.
Disorder of an InxGa1−xAs-GaAs superlattice by Zn diffusion
Authors: Laidig W. D. , Lee J. W. , Chiang P. K. , Simpson L. W. , Bedair S. M.
Published: February 2003

Data are presented showing that Zn diffusion into an InxGa1−xAs-GaAs superlattice (240 Å/period) completely disorders the superlattice layers, resulting in InyGa1−yAs of uniform composition. X-ray diffraction data and sputter-Auger profiles are shown, comparing the as-grown superlattice with a partially disordered (1 h, 615 °C Zn diffusion) and a totally disordered (1 h, 680 °C Zn diffusion) superlattice.
Epitaxial growth of Si–Ge layers on Si substrates by plasma dissociation of SiH4 and GeH4 mixture
Authors: Suzuki Setsu , Itoh Tadatsugu
Published: February 2003

Silicon–germanium epitaxial layers were formed on (111) oriented Si substrates by the plasma dissociation of a mixture of SiH4 and GeH4. A growth rate of 33 Å/sec was obtained at a substrate temperature of 750 °C for Si–Ge epitaxial growth using 1×10−2 Torr of SiH4 and 1×10−4 Torr of GeH4 mixture as source materials. The introduction of GeH4 to SiH4 provided a good nucleation for epitaxy. Less than 1% of GeH4 is sufficient to reduce the concentration of the crystalline defects such as voids which form in the epitaxial layers at low substrate temperature with a high growth rate. The electron Hall mobility of layers coincided with that of bulk Si in the temperature range between 77 °K and room temperature.
Space-charge-limited currents: Refinements in analysis and applications to a-Si1−xGex:H alloys
Authors: Weisfield R. L.
Published: February 2003

A new algorithm is described for deriving the density of states N(E) from the Fermi energy EF upwards toward the conduction band edge. This refinement in the analysis of space-charge-limited currents (SCLC) enables the accurate determination of N(E) by implicitly accounting for the spatial variations of physical quantities across the thickness of the diode. SCLC is measured in NiCr/n+/a-Si1−xGex:H/Pt diode structures. For a-Si:H samples, SCLC values for N(EF) are compared to those derived from admittance measurements on the same diodes. The two determinations agree in samples where 1016<N(EF) <1018 eV−1 cm−3. Arguments are presented that densities of states between 3×1014 and 1016 eV−1 cm−3 found by SCLC methods are more accurate than higher densities found from admittance measurements. Structure in N(E) inferred from a number of investigations is discussed. SCLC in sputtered a-Si0.7Ge0.3:H is also investigated, as a function of hydrogen content cH, optical gap, and photoluminescence intensity IPL. In this alloy increasing cH causes N(EF) to decrease, to a minimum of 3×1016 for cH=14 at. %. IPL increases inversely with N(EF), confirming the sensitivity of SCLC to bulk nonradiative recombination centers. It is concluded that the SCLC measurement and analysis constitute a relatively simple, straightforward, and generally applicable method of obtaining the density of states in the gap of amorphous semiconductors.
Boundary limited nuclear spin relaxation of 3He liquid and vapor in high magnetic field
Authors: Samaratunga R. C. , Martin K. P. , Brooks J. S. , Zimmerman G. O.
Published: February 2003

We investigate the relaxation mechanisms of 3He nuclei and report here NMR measurements at high magnetic fields on both 3He vapor and liquid. The ranges of temperature and field are 4.3–1.3 K and 1–15 T. Both the gas and the liquid phases show a magnetic field dependent spin-lattice relaxation time (T1) which increases with field. Similar results have been reported for liquid 3He at low fields in porous media, but this is the first evidence for the field dependence of T1 in the bulk vapor. The vapor relaxation times also increase with density at constant field, in agreement with the results of other workers. We provide evidence that the field dependence of T1 in the case of the liquid originates from a field dependent surface relaxation time.
Electron scattering in semiconductor alloys
Authors: Rode D. L. , Fedders P. A.
Published: February 2003

Suitability of the Born approximation and the Boltzmann equation is demonstrated for the scattering of free-carrier electrons by random-alloy atomic potentials in semiconductor alloys. Composition dependences of alloy-scattering potential strengths are hypothesized and electron scattering rates are derived. ‘‘Order parameters’’ are derived from scattering theory and compared to those derived previously from statistical and thermodynamic arguments by Warren and Cowley. The treatment is generalized to include ternary, quaternary, and lattice-matched alloys which, in general, show more complicated order-parameter dependencies than the previously known x(1−x) dependence for ternary zincblende alloys. Electron-momentum relaxation-rate expressions are given, including nonparabolic Kane bands and admixed wave functions appropriate to small energy-gap semiconductors. Electron drift mobility, as determined by alloy scattering, is derived in the effective-mass limit which shows that any short-range alloy potential yields the experimentally observed 1/(m*5T)1/2 dependence reported in the literature. An effective-charge model for alloy scattering is compared to experiments on AlxGa1−xAs. The magnitude of the effective charge on isolated Al atoms in GaAs is found to be 0.145 electron charges.
Hot carrier injection of photogenerated electrons at indium phosphide–electrolyte interfaces
Authors: Cooper Gerald , Turner John A. , Parkinson Bruce A. , Nozik Arthur J.
Published: February 2003

Hot electron reduction of p-nitrobenzonitrile at (111) p-InP in acetonitrile electrolyte was observed as a supraband-edge redox reaction. The band-edge positions of the p-InP electrode were unequivocally established from Mott–Schottky data obtained as a function of light intensity and frequency. Special conditions of low light intensity and electrode potential were found wherein the semiconductor band edges were either fixed or had moved only very slightly with respect to redox potentials in the electrolyte, such that the respective supraband-edge redox reactions were definitely outside the band gap of InP.
Stimulated emission in strained-layer quantum-well heterostructures
Authors: Camras M. D. , Brown J. M. , Holonyak N. , Nixon M. A. , Kaliski R. W. , Ludowise M. J. , Dietze W. T. , Lewis C. R.
Published: February 2003

Stimulated emission data are presented on a large variety of strained-layer quantum-well heterostructures (QWH’s) and superlattices (SL’s) grown by metalorganic chemical vapor deposition (MOCVD). These structures consist of barrier-well combinations of thickness LB,Lz ≲150 Å made from GaAs-InGaAs, GaAsP-GaAs, and GaAsP-InGaAs. Also employed are higher band-gap confining layers of InxAlyGa1-x-yAs, AlyGa1−yAs1−xPx, and AlxGa1−xAs. All of the heterostructures are grown on a GaAs substrate with and, in some cases, without a graded layer. The strain range between 0.2 to 12.5×10−3 is examined. Photopumped, these heterostructures operate as continuous (cw) 300 K lasers, with thresholds of 1.6–7.5×103 W/cm2, for periods of time between 0.5 to >35 min. Under high-level excitation, the equivalent of Jeq∼103 A/cm2, laser operation fails or is quenched by networks of dislocations (with 〈110〉 Burger’s vectors) that are generated within the strained-layer region of the QWH’s or SL’s. These dislocation networks, which are revealed via transmission electron microscopy (TEM), occur at a more rapid rate in higher threshold samples and ones with higher built-in strain. The TEM data show, however, that no heterointerface defects (dislocations) are present in the as-grown strained-layer regions but are present in thick (bulk) graded regions.
Characterization of proton-exchange slab optical waveguides in z-cut LiNbO3
Authors: Clark D. F. , Nutt A. C. G. , Wong K. K. , Laybourn P. J. R. , De La Rue R. M.
Published: February 2003

We report the results of a systematic study on planar optical waveguides fabricated in z-cut LiNbO3 by proton exchange in benzoic acid. It was found that the refractive index varied with depth and could be accurately modeled by a step index profile with Δn=0.126. Diffusion coefficients have been calculated from mode effective refractive index measurements, assuming a step index profile, and hence a value for the activation energy for the proton exchange process has been deduced. The lowest measured optical propagation loss in single-mode waveguide at a 633-nm wavelength was 2.4 dB/cm.
Quantitative study of the aberrations for focused acoustic plane waves obliquely incident upon a plane interface
Authors: Frohly J. , Bruneel C. , Bridoux E.
Published: February 2003

The nonlinearity of Snell’s law induces aberrations for waves focused under oblique incidence. A detailed study of the phenomenon is given here for the case of a water-steel interface, on which mode conversion occurs. Two approaches are taken: first a coarse geometrical one and second a finer plane wave spectrum expansion. A comparison between the two models shows the validity of the geometrical approach. The fundamental parameters that must be taken into account and their respective influences are deduced, and limits are fixed over which the correction of aberrations prove necessary. The application of these conclusions has made possible the localization of defects inside a steel sample.
Thermal wave imaging of closed cracks in opaque solids
Authors: Grice K. R. , Inglehart L. J. , Favro L. D. , Kuo P. K. , Thomas R. L.
Published: February 2003

Thermal wave scattering from closed, slanted cracks is investigated both theoretically and experimentally. A Born approximation calculation is carried out for the particular case of gas-cell detection for three crack angles. Good agreement is found with experimental images of both the magnitude and phase of the gas-cell signal variation for cracks fabricated in an aluminum alloy at these same angles. Good agreement is also found between theory and experiment for the frequency dependence of the thermal wave scattering from a 45° crack. It is shown theoretically and confirmed experimentally that a strictly vertical, closed crack is not observable by gas-cell detection, but is easily seen by mirage-effect (optical beam probe) detection. The results for model cracks are applied to the case of brittle fractures in solids.
Differential laser Doppler interferometry for high surface velocity measurement
Authors: Kaplan Z. , Maron Y. , Katzir Y.
Published: February 2003

A single-beam Doppler interferometer is described, whereby light scattered by the diffuse target at slightly different directions interfere, producing a differential Doppler frequency which is much smaller than the Doppler shift of either beam. Due to the diffuse nature of the light scattered by the target, the conditions for alignment of the interferometer must include the effects of speckle decorrelation caused by both longitudinal and tilting motions of the target. Error sources, both systematic and random, are discussed. Ways to minimize the systematic error stemming from uncertainty in the actual direction of the motion, are discussed. The interference signals are processed digitally to minimize the effect of random errors, which can be reduced typically to 8% for the acceleration period and to a negligible degree for the constant velocity phase of the motion. A special exploding-foil accelerator was constructed to test the new measurement scheme. Experimental results show repeatable measurements of velocity profiles up to about 0.4 mm/μs.
Enhancement of ion beam currents through space-charge compensation
Authors: Feng Yu-Cai , Wilbur P. J.
Published: February 2003

Neutralization of the positive ion space charge between the grids of a positively charged-ion accelerator by injecting negative charges into this region has been studied theoretically. The current density of a beam of charged particles being accelerated between two parallel plate electrodes can be increased substantially by this injection. Multiple beams of oppositely charged particles can be used to produce the most substantial increases in the current density of the primary beam. The current density of this beam increases monotomically with the number of optimally selected, injected particle beams being used. There is an optimum injected particle current density and energy associated with each beam that yields the maximum extracted beam current density for a given number of injection stages. The total required injected particle current density, regardless of the number of stages used, is of the order of the ion current density times the square root of the extracted ion-to-injected particle mass ratio.
Model of positive ion sources for neutral beam injection
Authors: Chan Chun Fai , Burrell C. F. , Cooper William S.
Published: February 2003

A comprehensive model is presented to describe the physics of positive ion sources used to generate hydrogen isotope neutral beams for the heating of confined plasma in magnetic fusion energy programs. The model considers 11 important atomic and molecular reactions. A set of particle balance equations, together with those for the primary and secondary electrons in the sources, are solved simultaneously. Taking as input the source geometry, gas inlet flow rate, arc current and voltage, as well as the wall recombination coefficient and the measured temperatures of neutral atoms and molecules, the model gives as output the following information: the ion current densities available for extraction, primary electron density and energy distribution, and secondary electron density and temperature. These calculated results are compared with data of several Lawrence Berkeley Laboratory ion sources, both conventional and magnetic bucket types. Exploratory calculations are made for sources of different proposed designs with the aim of improving the source performance.
Nonlinear Bernstein–Greene–Kruskal wave equilibria subject to global energy and momentum conservation constraints
Authors: Davidson Ronald C. , Tsang Kang T.
Published: February 2003

The class of Bernstein–Greene–Kruskal (BGK) solutions to the nonlinear Vlasov–Poisson equations are examined within the context of the conservation of (spatially averaged) number, momentum and total energy, imposed as ancillary global constraints that connect the final saturated BGK state to a specified initial distribution function f(x,v,0). While imposing three conservation constraints of course does not uniquely determine the final BGK state, it does remove a large degree of ambiguity as to whether particular classes of solutions are accessible from given initial conditions. It also permits a determination of important features of the final BGK state (e.g., saturation amplitude, wave phase velocity, etc.) in terms of properties of the initial distribution function. The specific example of a low-density electron beam propagating through a background plasma with f(x,v,0)=(n0−nb)δ(v)+nbδ(v−Vb) is analyzed in detail assuming a saturated BGK state with monochromatic waveform φ0(x′)=φ̂0 cos kx′, and monoenergetic distribution of untrapped electrons with F±u(H)=n̂u(2mH0)1/2δ(H−H0) in the wave frame. Here, x′=x−(ω/k)t and H=(m/2)(v−ω/k)2−eφ0(x′) is the energy.
Modeling of thin film solar cells: Uniform field approximation
Authors: Crandall Richard S.
Published: February 2003

A model of a p-i-n thin-film solar cell is presented that can be easily used to analyze solar cell properties. The continuity equations are solved using the regional approximation, producing elementary solutions that give insight into the physics of the transport in the cell. The steady-state solutions are compared with measurements on typical hydrogenated amorphous silicon, a-Si:H, solar cells. The ac solutions are used to explain a new source of photocapacitance due to mobile carriers.
Atmospheric effects on projectile acceleration in the rail gun
Authors: Powell John D. , Batteh Jad H.
Published: February 2003

The manner in which projectile velocity in a rail gun is limited by the presence of atmosphere in the gun tube is studied. In particular, we solve the equation of motion for the acceleration of the armature and projectile, accounting for both the decelerating force exerted by the atmosphere and the time decay of the current profile. From the solution, a characteristic time is derived which indicates quantitatively when the effect of the atmosphere can be expected to be significant. Results of the calculation are then compared qualitatively with results from two recent experiments: one in which atmospheric effects are nearly negligible and one in which they are not.
Raman instability in longitudinally magnetized n-type piezoelectric semiconductors
Authors: Ghosh S. , Khan S.
Published: February 2003

Raman instability of the Stoke’s component of the scattered electromagnetic wave has been investigated analytically in an n-type nondegenerate piezoelectric semiconductor plasma subjected to a large longitudinal magnetostatic field. The general dispersion relation has been obtained following the coupled mode theory and considering that the scattering is due to both the molecular vibrations produced due to the pump wave at a frequency equal to that of the transverse optical phonons and the electron plasma wave. The dispersion relation has been solved for both cases of scattered electromagnetic waves (i.e., in the cases of left-hand and right-hand circularly polarized waves). The threshold value of the pump amplitude necessary for the onset of instability and the growth rate of the unstable mode well above the threshold have been obtained analytically for both the modes. The relevant experiment has not been reported. It is observed that with the increase in the longitudinal magnetostatic field, the threshold value of the pump amplitude increases while the growth rate decreases in both cases. Numerical estimates have been made for n-type InSb at 77 K irradiated with a pulsed 10.6-μm CO2 laser to obtain the necessary electric field. The analytical as well as numerical results have been compared with those of Ghosh [J. Appl. Phys. 52, 4667 (1981)] while studying the Brillouin instability in longitudianally magnetized n-type semiconductors.
Fourier transform approach to materials characterization with the acoustic microscope
Authors: Hildebrand J. A. , Liang K. , Bennett S. D.
Published: February 2003

A general method is presented for characterization of elastic properties of materials with the reflection acoustic microscope. The material acoustic reflectance function and the acoustic microscope focus curve [V(z)] are shown to be a Fourier transform pair. By measurement of both phase and amplitude, the complex V(z) curve can be recorded. These data can then be inverted to obtain an estimate of the reflectance function. This method allows calibration of individual acoustic lenses and is experimentally demonstrated with a 50-MHz acoustic microscope and a synchronous phase detection system.
Characterization of plasma-enhanced chemically-vapor-deposited silicon-rich silicon dioxide/thermal silicon dioxide dual dielectric systems
Authors: Yokoyama S. , Dong D. W. , DiMaria D. J. , Lai S. K.
Published: February 2003

Plasma enhanced chemically-vapor-deposited silicon-rich oxides (200 Å and 500 Å in thickness) of various excess silicon content were deposited onto thermal silicon dioxide (SiO2) layers (103, 207, and 530 Å in thickness) grown on a p-type silicon (Si) substrate. The dielectric constant, electron injection efficiency, current-voltage (I-V) reproducibility, and breakdown property of these composite structures were examined. The dielectric constants of Si-rich oxide were observed to increase with Si content from 3.8 for films deposited at a gas phase ratio (R0) of the concentration of nitrous oxide (N2O) to silane (SiH4) of 150 to ∼10 for films deposited with R0=0. The Si-rich oxides with R0≤5 were found to work as electron injectors. The average oxide field needed to induce a current of 4.8×10−7 A/cm2 through the SiO2 (530 Å in thickness) decreased about 40% in magnitude by adding a Si-rich oxide layer with the optimized R0(=1) compared to that of a control sample which had no Si-rich oxide layer. For thin SiO2 (103 Å and 207 Å in thickness) samples, the decrease of the average field was only 2% and 10% in magnitude with the optimized R0 (=2) layer, respectively, due to the relatively large voltage drop (≊−1 V) across the Si-rich oxide compared to that across the thermal oxide layer. The voltage drop across the oxide is discussed in terms of a dual dielectric model. The yeild, which was defined as the percentage of capacitors that required a field larger than 2 MV/cm to obtain a current of 9.6×10−4 A/cm2, on as-fabricated samples was larger than 90% for all samples with Si-rich oxide. The samples were not destroyed by the passage of a relatively high current density (1.21×10−2 A/cm2) through the oxide and subsequent measurements resulted in approximately the same field to produce the specified current as for the first measurement. The yield was found to have a maximum at R0=1–10 depending on the thickness of Si-rich oxides and SiO2. Current-voltage reproducibility was also found to be improved by the deposition of Si-rich oxide.
Experimental investigation of the magnetic behavior of superconducting-normal-superconducting Josephson junctions
Authors: Bures K. , Barnes S. E. , Baberschke K.
Published: February 2003

We have measured the magnetic field dependence of the supercurrent in micron-size medium and high current density superconducting-normal-superconducting Nb–Au–Nb Josephson junctions. We find good quantitative agreement between the experiment and a theory for the distributed Josephson effect in such junctions. For finite bias voltages, high current density junctions show a monotonic decrease in the effective critical current with increasing field in sharp contrast to the resistively shunted junction model which predicts the well-known Fresnel-type behavior. Our medium current density junctions represent an intermediate case, residual Fresnel behavior is observed at small bias voltages, but a monotonic decrease with the field is observed for higher bias voltages.
Influence of ternary additions and precipitation on the critical current density and other superconducting properties in Nb-65 wt. %Ti
Authors: Panek M. , Pattanayak D. , Meier-Hirmer R. , Küpfer H.
Published: February 2003

The superconducting behavior of Nb-65 wt. %Ti and their ternary alloys with 1 wt. % Mo, Re, Si, Ta, V, and Zr was studied with regard to precipitation. Transmission electron microscopy studies were carried out to determine the size and distribution of the precipitates. In contrast to the commerical Nb-Ti superconductor the alloys show a quadratic dependence of the pinning force on the field close to the upper critical field. With a suitable precipitate size distribution but without workhardening these alloys display high current densities which are comparable with commercial Nb-Ti.
Dielectric properties of plasma polymerized styrene film
Authors: Nakamura S. , Murata T. , Sawa G.
Published: February 2003

The dielectric loss tangent tan δ for the plasma polymerized styrene film has been investigated between room temperature and 250 °C over a frequency range of 102–104 Hz. As-polymerized films exhibited a noticeable peak on the tan δ temperature characteristic in vacuo. The temperature giving the maximum of tan δ shifted to a higher temperature with descending frequency and the peak disappeared once the sample was heated to 250 °C. These behaviors can not be understandable from the usual dielectric relaxation. As a candidate for their origin, the process of further polymerization of the residual low molecular moieties containing oxidized products by heating has been considered.
Sputtering of a polymer layer deposited on metal substrates
Authors: Emmoth B. , Mladenov G. M.
Published: February 2003

Substrates of Be, Si, Cr, and Mo were covered by a 400-nm thin film of the electron lithography resist poly(methyl methacrylate) (PMMA), and irradiated by Ar+ ions. The photon emission from sputtered deexciting particles ejected during the ion bombardment was detected. The spectral scans of observed photon radiation were different for PMMA on different substrates. This supports our conclusion that excitation and ejection processes are related to the collision cascades and possibly also to collective electronic excitations. The evaluated average sputtering rates for Ar+ bombardment of PMMA at ion energies 30 and 60 keV are 320 and 375 atoms/ion, respectively, or 1.85 and 2.20 Å cm2/μC correspondingly. The erosion mechanism is discussed against this background.
Computer simulation of ion beam penetration in amorphous target
Authors: Miyagawa Y. , Miyagawa S.
Published: February 2003

The formalism for a Monte-Carlo computer code using a liquid model is presented. One of the characteristic features of this program is a constant free flight path length between collisions and the other is the thoroughgoing usage of the fitting formula to the nuclear scattering cross section, minimum energy transfer, and free flight path shortening. This allows for a rapid and accurate assesment of an ion’s direction and energy loss resulting from nuclear collisions. For nuclear scattering, an approximation formula derived by Kalbitzer and Oetzmann was used and the results are compared with those obtained using the formula derived by Winterbon, Sigmund, and Sanders. Both results are compared with experiments, with the results obtained using gas-like model and also with other well-established programs marlowe and trim.
The microstructure and critical current characteristic of a bronze-processed multifilamentary Nb3Sn superconducting wire
Authors: Wu I. W. , Dietderich D. R. , Holthuis J. T. , Hong M. , Hassenzahl W. V. , Morris J. W.
Published: February 2003

The superconducting phase within a bronze-process, multifilamentary Nb3Sn superconducting wire is formed by reaction at the interface between the Nb filaments and the bronze matrix. The maximum current that can be carried by the wire is known to depend on the time and temperature of the heat treatment as well as on the transverse magnetic field. In the work reported here a commercial Airco wire containing 2869 Nb filaments of 3–5 μm diameter in a matrix with a bronze/Nb ratio of three was given a variety of reaction heat treatments. The microstructure of the reacted layer was analyzed as a function of heat treatment, and found to be divisible into three concentric shells that are morphologically distinct. The central shell consists of fine equiaxed grains. Its areal fraction, grain size, and composition depend on the heat treatment, and appear to determine the critical current. The best combination of grain size and composition, and the highest critical current, is obtained with an intermediate reaction temperature (700–730 °C). A further improvement in both microstructure and critical current is achieved by double-aging the wire, starting the reaction at 700 °C and finishing it at 730 °C. The relation between microstructure and heat treatment is interpreted in light of the apparent mechanism of the reaction, which is revealed by high resolution analyses of the reacted layer. The relation between microstructure and properties is consistent with current understanding of the influence of grain size and stoichiometry on the behavior of type II superconductors.
The effect of piezoelectrically coupled stresses on the junction characteristics of CdS-Cu2S solar cells
Authors: Bennett Murray S. , Kramer John J.
Published: February 2003

An investigation was conducted to determine the effects of piezoelectrically coupled stresses on the capacitance, open-circuit voltage, short-circuit current and I-V characteristics of CdS-Cu2S solar cells. The theoretical analysis suggests that only nonuniform stresses will result in changes in the open-circuit voltage and capacitance. This was consistent with measurements made under uniform and nonuniform stress. Furthermore the direction of the change was consistent with that expected for junctions formed on the polar S face or the Cd face. The short-circuit current and the I–V characteristics are, however, sensitive to both uniform and nonuniform stress but insensitive to the polar face on which the cell is formed. This suggests a nonpiezoelectric stress effect for these characteristics. The measurements were made at relatively low levels of stress (∼2 to 4×107 N/m2) and stress gradients (∼2×1010 N/m3). Under these conditions the measured changes are 1% or less. Thus the built-in stresses resulting from cell manufacture are not expected to have a significant effect on cell properties unless they are at least an order of magnitude larger.
Redistribution of chromium under annealed sulfur implants into chromium-doped GaAs
Authors: Wilson R. G. , Evans C. A. , Norberg J. C , Hopkins C. G. , Park Y. S.
Published: February 2003

The effect of sulfur implant fluence, ion energy, and annealing temperature on the redistribution accumulation of chromium during annealing of GaAs under SiO2 and Si3N4 caps and a capless condition is shown. The variation of the thickness of the heavily damaged or ‘‘amorphized’’ layer with implant fluence is shown and discussed. Three peaks are seen in the Cr accumulation profiles. When their integrated densities are plotted versus inverse annealing temperature, two peaks exhibit an activation energy for breakup of the Cr-defect complexes of 0.56 eV, and the third, of 1.8 eV. The nature or origin of these Cr-defect complexes is discussed. Sulfur migration or ‘‘diffusion’’ versus sulfur density is illustrated and discussed. The correlations of the two Cr peaks observed in 840 °C annealed depth distributions with capping environment and damage depth are discussed. Finally, these Cr accumulation profiles under sulfur implants are compared with those in self-amorphized GaAs.