bluuebunny/crossref_metadata_2025 huggingface dataset:
The high-pressure behavior of α-quartz, oxynitride, and nitride structures
Authors: Cartz L. , Jorgensen J.D.
Published: February 2003

The high-pressure behavior of α-quartz SiO2 and GeO2, oxynitrides Si2N2O and Ge2N2O and α- and β-Si3N4 depends markedly on the nature of the linking of the coordination polyhedra in their crystal structures. Where bond angles can vary between neighboring polyhedra linked at one corner, relative tilting or rotations can occur modifying the aspect of the three-dimensional framework. Such fine structural rearrangements can dominate the reponse of the crystal structure to applied stresses as induced by the application of high pressures or by temperature changes. Direct evidence for this is available from structural measurements at high pressure using time-of-flight neutron diffraction with multicomponent profile refinement procedures, where atomic position changes have been determined up to pressures of ∼3×109 Pa. The crystal structures studied are the flexible α-quartz structures of SiO2 and GeO2, the partially flexible structures Si2N2O and Ge2N2O, and the rigid structures α- and β-Si3N4. The volume compressibility coefficients Kv are greatest for α-quartz SiO2 (274 × 10−13 Pa−1 ) and GeO2 (256×10−13 Pa−1) with the Si-O-Si and Ge-O-Ge angles varying the most; Kv is intermediate for Si2N2O (79 × 10−13 Pa−1 ) and Ge2N2O (99×10−13 Pa−1 ) where the Si-O-Si and Ge-O-Ge angles vary appreciably while the bond angles to the nitrogens change only slightly; Kv is least for α-Si3N4 (35.5 × 10−13 Pa−1 ) and β-Si3N4 (27.5×10−13 Pa−1 ) where no bond angles vary appreciably. For all of the structures examined, bond length changes with pressure are very small in comparison to bond angle changes, which can be an order of magnitude greater. Each structural type behaves in a characteristic way. For example, Si2N2O and Ge2N2O exhibit almost identical responses to pressure.
Dark current reduction in AlxGa1−xAs-GaAs heterojunction diodes
Authors: Lee S. C. , Pearson G. L.
Published: February 2003

The addition of a thin, high band-gap P(N)-type AlxGa1−xAs layer into a conventional AlyGa1−yAs-GaAs N-p (P-n) heterojunction is found to significantly reduce the 2kT recombination current, thereby permitting the bulk diffusion current to dominate at current densities as low as ∼10−5 A/cm2. Experiment indicates that the 2kT current is due to surface-recombination processes and originates in a very narrow region near the p-n junction, presumably due to the small minority-carrier surface-diffusion length.
Discrimination between two noise models in metal-oxide-semiconductor field-effect transistors
Authors: Park H. S. , van der Ziel A. , Zijlstra R. J. J. , Liu S. T.
Published: February 2003

In order to discriminate between the number-fluctuation and the mobility-fluctuation noise models of 1/f noise in metal-oxide-semiconductor field-effect transistors, the drain-flicker-noise spectral intensity SId (f) was measured as a function of drain bias Vd from low values of Vd through saturation (Vd≳Vds). Chiefly because of the hot-electron effects in mobility-fluctuation noise at high fields, discovered by Bosman, Zijlstra, and Van Rheenen, the theoretically predicted dependence of SId (f) upon Vd differs for the two models. Data on some metal-oxide semiconductor (MOS) devices agree better with the number-fluctuation model, whereas other MOS devices, e.g., those made by shallow ion implantation, agree best with the mobility-fluctuation model. In these cases the temperature dependence of the noise also agrees with the mobility-fluctuation model.
Coadsorption of cesium and oxygen on iridium and lanthanum hexaboride
Authors: Danielson L. R.
Published: February 2003

The coadsorption of cesium and oxygen on iridium and lanthanum hexaboride has been studied by measurements of elemental surface concentrations, work functions, and electron reflectivities. The elemental surface concentrations were determined by Auger electron spectroscopy and the work functions and reflectivities by the field emission retarding potential technique. Simultaneous deposition of cesium and oxygen on iridium or lanthanum hexaboride substrates produced a thick oxide layer. For both substrates this oxide layer possessed a work function of 1.0±0.05 eV and an electron reflectivity at threshold of 0.45±0.10 eV. Brief stepwise heatings of this layer on LaB6 showed stability to 390 K. The threshold reflectivity for some higher work function surfaces depended strongly on whether the final deposition was cesium or oxygen.
Thin palladium silicide contacts to silicon
Authors: Kritzinger S. , Tu K. N.
Published: February 2003

A new approach to the development of very thin Pd2Si-to-Si contacts for possible future use in ultrasmall devices is described. It is based on the principle of diluting the silicide-forming metal (Pd in this case) with Si, by codeposition of these two elements onto a single-crystal Si substrate. The composition of the codeposited layer has been chosen as Pd80Si20, which is a metastable alloy with an amorphous structure. During annealing of the layered structure, Pd is extracted from the amorphous alloy to form the metal-rich and very stable compound Pd2Si at the interface. At the same time, the decomposing Pd80Si20 is also converted in Pd2Si. In this way a silicide is formed for which only ∼50% of the required Si need be supplied by the Si-substrate, resulting in a very shallow silicide contact. In the illustrated case, with 400 Å of Pd80Si20 on Si〈100〉, only ∼80–100 Å of substrate Si is consumed. The microstructural properties of the formed silicide have been studied by in situ transmission electron microscope experiments, while the electrical characteristics of Pd2Si-to-Si Schottky diodes, fabricated by this technique, have been studied by Schottky barrier height (SBH) measurements from the current-voltage curves. By choosing the annealing treatments of these two sets of identical specimens, the microstructural and electrical properties could be correlated. It is shown that overannealing of a Pd2Si-to-Si contact formed in this way should be avoided, since this gives rise to a lowering of the SBH. Finally, it is demonstrated that initially bad Schottky diodes (ideality factor n≳1) can be restored to a good n?1 condition by annealing.
A model of interface states and charges at the Si-SiO2 interface: Its predictions and comparison with experiments
Authors: Ngai K. L. , White C. T.
Published: February 2003

We develop a model for states and charges at the Si-SiO2 interface based on the expected existence at this interface of threefold coordinated Si atoms, strained Si-Si bonds, etc. The associated electronic states are studied by using a generalized bond orbital approximation (supplemented in some cases by multiband cluster Bethe lattice calculations), where the various configurations ofinterest are allowed to relax in order to minimize the energy of the system. It is shown that the reconstructing character of interface states so obtained has a number of interesting experimental implications, and in particular it is found that by including reconstruction effects one is able to understand and in some cases correlate many different experimental results. Among others, these include some observed metal-oxide-semiconductor device instabilities, the dependence of the interface density of states on the conductivity type of the semiconductor substrate, and the amphoteric character of interface states.
Resonances of dielectrically coated conducting spheres and the inverse scattering problem
Authors: Gaunaurd G. , Überall H. , Moser Philip J.
Published: February 2003

The resonance theory of scattering, recently developed for the diffraction of acoustic and elastic waves, is applied here to radar scattering from penetrable targets, with a view toward solving the inverse scattering problem. For the example of a dielectrically coated conducting sphere, it is shown that the thickness and the dielectric constant of the target can be obtained from a determination of the spacing and of the widths of the scattering resonances in the radar echo returns.
Electric field gradient and mean square displacement of iron sites in cubic iron sulphide
Authors: Garg V. K.
Published: February 2003

Mössbauer absorption of Fe57, for four equivalent but differently oriented sites, in naturally occuring single crystals of FeS2 (pyrite) has been studied as a function of the orientation of the crystal axes with respect to the γ-ray beam from a Co57/Pd source. Polarization effects for our absorbers of ∼0.1 mm thickness were found not to be appreciable. Experimental peak area ratio of ∼1 in the case of powdered absorber and monocrystalline absorbers in (111), (110), and (100) planes has been analyzed to obtain the principal axes of the electric-field-gradient and the mean-square displacement as ‖1,1,1‖, ‖−1,1,1‖, ‖1,1,−1‖, and ‖1,−1,1‖ direction for the Fe sites corresponding to 000, 1/2   1/2  0, 1/2  0  1/2 , and 0  1/2   1/2, respectively. The angular independent recoilless fraction at 298 K has been obtained to be 0.20±0.02 and for the mean-square displacement 〈x2〉=〈 y2〉=〈z2〉, and its value at 298 K is 4.34±0.23×10−19 cm2.
A four-phase complex refractive index model of ion-implantation damage: Optical constants of phosphorus implants in silicon
Authors: Delfino M. , Razouk R. R.
Published: February 2003

A four-phase complex refractive index-model approximation coupled with multiple-angle-of-incidence ellipsometric measurements is utilized in an analysis of ion-implantation damage in silicon. The four phases refer to the ambient, native oxide, implant layer, and substrate. The analysis is applied to phosphorus implants as functions of various ion-dose ranging from 5×1012 to 1×1016 ions cm−2, and effective energies from 36 to 120 KeV, for both monomer (P+) and dimer (P+2) species. Implant depths are found to be related to the implant parameters and are found to be equal to RP +1.08 ΔRP where RP is the projected range and ΔRP is the projected standard deviation of the implanted ion. This relationship is invariant with respect to effective energy, ion dose, and species. Changes in refractive index, extinction coefficient, and reflectivity are readily detected at doses as low as ∼1013 ions cm−2. A decrease in extinction coefficient at high doses suggests that ion-beam annealing is occurring. In general, changes in optical constants reflecting implant damage are larger for the dimer than the monomer, increase with ion dose, and decrease as the effective energy decreases.
Free-carrier absorption in quantizing magnetic fields: Transverse configuration
Authors: Rynne Timothy M. , Spector Harold N.
Published: February 2003

The theory of free-carrier absorption in nondegenerate semiconductors in the presence of quantizing magnetic fields is used to calculate the absorption of electromagnetic radiation polarized perpendicular to the magnetic field direction. We find that using the Born approximation, the absorption coefficient diverges logarithmically for radiation polarized transverse to the magnetic field whenever the photon frequency is an integral multiple of the carrier cyclotron frequency, i.e., when Ω=nωc. The magnetic field dependence of the absorption for the transverse configuration, like that for the longitudinal configuration, can be explained in terms of phonon-assisted transitions between the various Landau levels of the carriers.
Strain effects on surface acoustic wave velocities in modified PbTiO3 ceramics
Authors: Takeuchi Hiroshi , Yamauchi Hisao
Published: February 2003

The effect of substrate strains upon surface acoustic wave (SAW) velocities were determined for piezoelectric PbTiO3 ceramics that were modified by adding Nd2O3, In2O3, and MnO2. SAW velocity variations were measured against uniaxial bending strain in the direction of propagation. It was found that the relationship between fractional SAW velocity change and uniaxial strain reveals strong nonlinearity, which contrasts with the case for single-crystal substrates. The present ceramics were also found to have an anomalously large SAW velocity strain coefficient (∼10) at a highly strained condition (∼8×10−5).
The effect of substrate growth temperature on deep levels in n-AlxGa1−xAs grown by molecular beam epitaxy
Authors: McAfee S. R. , Tsang W. T. , Lang D. V.
Published: February 2003

The deep level transient spectroscopy (DLTS) technique has been used to study changes in electron trapping centers as a function of substrate growth temperature (550 °C≲Tsub≲675 °C) in n-Al0.25Ga0.75As Schottky barriers grown by molecular beam epitaxy (MBE). The principal result is a deep level at Ec−0.78 eV which decreases by over an order of magnitude in concentration as the growth temperature is increased from 575 to 675 °C.
Comparison of characterization methods for As-doped silicon
Authors: Wagner Hans H. , Schaefer Rolf R. , Kempf Juergen E.
Published: February 2003

Silicon wafers implanted with arsenic doses from 1×1015 to 2×1016 As/cm2 were characterized with the following methods: four point probe, bevel and stain, secondary ion mass spectroscopy, spreading resistance, incremental sheet resistance, and infrared transmittance and reflectance. The results are compared and the capability of each method is discussed.
Integral equation method for calculating entropy of confined chains
Authors: Priest R. G.
Published: February 2003

An important aspect of the thermodynamic properties of chain molecules in solids is the amount of entropy that is associated with rotations about bonds. Of particular interest is the high-pressure hexagonal phase of polyethylene. This system is modeled for the purpose of this calculation as an assembly of chains confined to small cylinders. This paper describes an integral equation approach to the problem that may be viewed as a continuum limit of the transfer matrix technique. Two cases are solved: (1) the freely jointed chain confined to a cylinder small enough to prevent the chain from folding back on itself, and (2) the fixed bond angle chain confined to the same type of cylinder. The result of calculation (2) is discussed in light of a model for the high-pressure hexagonal phase of polyethylene.
Conformational and lattice packing analyses of poly(acetylene)
Authors: Orchard B. J. , Tripathy S. K. , Hopfinger A. J. , Taylor P. L.
Published: February 2003

The intra- and inter-chain structural analyses of proposed poly (acetylene) (PA) valence geometries were performed. The semi-empirical molecular methods CNDO/2, MINDO/3, and NDDO were used in the intramolecular conformational analysis. A molecular-mechanics based lattice packing formalism was used to compute the interchain energies. The structures proposed by Baughman and coworkers are predicted to be most stable in observed orthorhombic lattices. The all-trans chain packs with the lowest energy and the trans-cisoid structure is more stable than the cis-transoid. However, a monoclinic set of lattices, not yet observed, are predicted to be about 50% lower in energy than the corresponding orthorhombic lattices for all three chain conformations.
A theory crack healing in polymers
Authors: Wool R. P. , O’Connor K. M.
Published: February 2003

A theory of crack healing in polymers is presented in terms of the stages of crack healing, namely, (a) surface rearrangement, (b) surface approach, (c) wetting, (d) diffusion, and (e) randomization. The recovery ratio R of mechanical properties with time was determined as a convolution product, R = Rh (t)*φ(t), where Rh (t) is an intrinsic healing function, and φ(t) is a wetting distribution function for the crack interface or plane in the material. The reptation model of a chain in a tube was used to describe self-diffusion of interpenetrating random coil chains which formed a basis for Rh (t). Applications of the theory are described, including crack healing in amorphous polymers and melt processing of polymer resins by injection or compression molding. Relations are developed for fracture stress σ, strain ε, and energy E as a function of time t, temperature T, pressure P, and molecular weight M. Results include (i) during healing or processing at t<t∞, σ,ε∼t1/4, E∼t1/2; (ii) at constant t<t∞, σ,ε∼M−1/4, E∼M−1/2; (iii) in the fully interpenetrated healed state at t = t∞, σ,ε∼M1/2, E∼M; (iv) the time to achieve complete healing, t∞ ∼M3, ∼exp P, ∼exp 1/T. Chain fracture, creep, and stress relaxation are also discussed. New concepts for strength predictions are introduced.
Fatigue of high impact polystyrene and influence of surface treatments
Authors: Sauer J. A. , Habibullah M. , Chen C. C.
Published: February 2003

The fatigue endurance of unnotched samples of a rubber modified, high impact polystyrene (HIPS) was determined under tension-compression cycling. The role of the rubber phase inclusions in the fatigue fracture process was further studied by detailed examination of the fracture surfaces by optical methods and by scanning electron microscopy. The observed morphology is compared with that obtained on HIPS samples subject to simple tension bonding and with that obtained on the unmodified polystyrene homopolymer. The dispersed rubber phase particles lead to an increased fatigue crack propagation resistance and, if comparison is made on the basis of the same relative stress, the rubber modified polymer leads also to increased fatigue lifetimes. The influence of various environmental variables such as elevated temperature annealing, surface condition, and surface treatments is discussed. Silicon oil coatings of low viscosity tend to significantly reduce fatigue lifetimes, but lifetimes increase with increased viscosity of oil coating. Significant enhancement in fatigue endurance can be realized by use of elastomeric coatings, such as a thin layer of nitrile rubber.
First-order Raman coefficient as related to elasto-optic, linear electro-optic, and second-harmonic-generation coefficients in zinc-blende crystals
Authors: Varshney Subhash C. , Gundjian Arshavir A.
Published: February 2003

This paper evaluates the first-order Raman coefficient for a large number of zinc blende crystals from the measured values of two different sets of coefficients, namely, the elasto-optic and the electro-optic coefficients. First it validates after correction a previously obtained relation of the Raman coefficient with the elasto-optic coefficients. Then it presents a lattice dynamical relation for its evaluation from the linear electro-optic and the second-harmonic-generation coefficients. The two predictions of the first-order Raman coefficient are in agreement and compare favorably with available calculated values. The Raman coefficient is observed to be negative in all II-VI and III-V zinc blende crystals, and positive in the I-VII case.
Direct observation of thermionic emission pattern of hemispherical single-crystal LaB6
Authors: Shimizu R. , Onoda H. , Hagiwara H. , Ishii S.
Published: February 2003

Thermionic emission pattern from a hemispherical LaB6 cathode of 〈110〉 orientation was made using an experimental setup similar to Martin’s experiment. The emission pattern from a clean surface has clearly indicated that the bright region consists of (100) spot surrounded by four (210) spots. This suggests that the bright spots (except for the center spot in the cross-over images observed for 〈100〉, 〈110〉, and 〈111〉 LaB6 cathodes correspond to (210) spots as deduced by Oshima et al. Emission patterns at different vacuum conditions are also observed to find that a specific emission pattern appears with good reproducibility corresponding to the change of vacuum condition, leading to existence of enhanced thermionic emission.
Saturation characteristics of laser-induced Na fluorescence in a propane-air flame: The role of chemical reaction
Authors: Iino M. , Yano H. , Takubo Y. , Shimazu M.
Published: February 2003

Saturation curves for laser-induced sodium fluorescence in a propane-air flame under the cw and the pulsed excitations were measured to examine the contribution of chemical reaction via the excited states of sodium atom to saturated fluorescence. Saturation behavior for the pulsed excitation of ns duration is interpreted by the ordinary two-level model taking account of spatial and temporal distribution of the laser intensity. The fluorescence intensity under the cw excitation levels off at much lower intensity than the ordinary saturation intensity. Consideration of species distributions in the flame indicates that the hydroxide formation process results in the saturation of the cw fluorescence. From the time-resolved fluorescence measurement, the rate constant for this molecular formation is estimated to be around 1×107 s−1.
Meltback and pullover as causes of disturbances in liquid-phase epitaxial growth of InGaAsP/InP 1.3-μm laser material
Authors: Ladany I. , Smith R.T. , Magee C.W.
Published: February 2003

InGaAsP/InP 1.3-μm laser material grown by liquid-phase epitaxy occasionally exhibits an anomalous x-ray diffraction pattern and may also have a high threshold current density. The origin of this effect is shown to be the contamination of the normal p-type InP cladding layer with Ga and As. A typical composition of this quaternary cladding layer is determined, and secondary-ion mass-spectrometry analyses are used to show the contamination is most likely caused by pullover from the previous melt.
Facet degradations in Ga1−xAlxAs/Ga1−yAlyAs double-heterostructure lasers
Authors: Hayakawa T. , Yamamoto S. , Sakurai T. , Hijikata T.
Published: February 2003

Degradation phenomena in Ga1−xAlxAs/Ga1−yAlyAs double-heterostructure lasers with AlAs mole fractions x of 0–0.17 in the active layer have been investigated. Degradation rate was found to markedly depend upon x and is a minimum value at x = 0.08. It is shown that the degradation in the lasers with x below 0.08 is primarily caused by the dark defects formation in the vicinity of the mirror surfaces, which is suppressed with increasing x. The degradation in the region of x = 0.08–0.17 results from the facet oxidation, which is enhanced with increasing x. This degradation was found to be affected by the humidity of the operating ambient and was effectively suppressed with the Al2O3 facet coatings. In particular, the long-term degradation in the lasers with x = 0.08 was suppressed with increasing the humidity. Auger analysis revealed that the native oxide formed at the facet was only partially oxidized and the enhanced oxidation for larger x had its origin in the initial stage of oxidation, where the faster oxidation rate of Al than that of Ga enhanced the oxidation. In addition, oxidation is diffusion controlled in the oxide after more than 102-Å thick oxide is formed.
Operation of a laser-heated thermal diffusion column
Authors: Klein F. S. , Duval V. , Glatt I. , Steinfeld J. I.
Published: February 2003

Separation of N16O and N18O has been measured in a thermal diffusion column heated by resonant absorption of CO laser photons. For the most part, the behavior of the laser-heated column can be adequately explained as a simple thermal effect, although the separation efficiency at low-input powers is higher in the laser-heated column than in a comparable hot-wire experiment.
Influence of supersaturated melt for InP growth on InP-InGaAsP interface of double-heterostructure laser wafers
Authors: Takahashi Shin-ichi
Published: February 2003

Liquid-phase epitaxial growth with higher supersaturated InP growth melt could be successfully used in fabricating InGaAsP/InP double heterostructure (DH) lasers emitting in the 1.50–1.55-μm wavelength region. InP-InGaAsP interface characterization has been carried out with scanning electron microscope (SEM), transmission electron microscope, photoluminescence (PL) measurements, and Auger spectroscopy. From the dissolution depth measurements, it was found that there is a slight dissolution on the surface of the InGaAsP layer, even in the 1.3-μm wavelength region during an InP layer growth with 16° supersaturated melt. Although the amount of dissolution increases as the composition of the quaternary active layer becomes a longer wavelength, as a result of this dissolution, the transition region does not catastrophically affect the laser performances at a wavelength shorter than 1.55 μm. It was found that the InP-InGaAsP interface at 1.59-μm wavelength shows rugged configuration under high-resolution SEM observation and the half-width of PL spectrum becomes wider than that for DH wafers at a wavelength shorter than 1.55 μm. This was confirmed by Auger line profile measurements.
Comparison of cw laser-annealed and electron-beam annealed Si
Authors: Mizuta Masashi , Sheng Neng-Haung , Merz James L.
Published: February 2003

Si samples implanted with As+ have been annealed with a modified commercial scanning electron microscope and with a scanning cw Ar+ laser. A comparison of these two techniques is presented, using electron-beam-induced current as a probe of minority-carrier effects. With a minimum of parameter optimization, it is found that electron-beam annealing is usually superior to laser annealing with respect to both lateral and vertical uniformity.
Comment on ’’Normal modes of semiconductor p-n junction devices for material-parameter determination’’
Authors: Muralidharan R. , Jain S. C.
Published: February 2003

During the open circuit voltage decay (OCVD) in a diode with τB/τE≫1 (τB and τE are the lifetimes of the minority carriers in the base and emitter, respectively), the quasistatic approximation is found to be valid in the emitter but not in the base. If the band-gap narrowing ΔEg is significant, τE,τB, as well as ΔEg determine the OCVD for t<τB. For t≫τB [and exp (qV/kT)≫1] OCVD vs t plot is approximately linear with its slope ∼1/τB, irrespective of the magnitude of ΔEg.
p-GaAs/P-Ga1−xAlxAs isotype heterojunctions in doubleheterostructure laser material
Authors: Hakki B. W
Published: February 2003

The p-GaAs/P-Ga1−xAlxAs isotype heterojunction, that occurs in doubleheterostructure laser material, is studied experimentally and theoretically. In good quality liquid phase epitaxially grown material, carrier-concentration profiles show the presence of hole accumulation in the small band-gap material and hole depletion in the large band-gap material. When either the layer thickness varies across the diode or the heteroboundaries are not abrupt, the profile across the isotype heterojunction becomes smeared. Hence, this profiling method can provide a sensitive measure of material quality. Furthermore, the analysis accounts for the possible presence of interface states, which can affect band bending at heteroboundaries. It is shown that this band bending can affect the recombination of carriers, and therefore their lifetimes and efficiency.
Thermal cycling-induced changes in the electrical transport properties of (111) epitaxial, n-type PbTe films
Authors: Restorff J. B. , Allgaier R. S. , Houston Bland
Published: February 2003

Weak-field magnetoresistance measurements at 297 K were used in conjunction with an appropriate band structure model to detect the substrate-induced strain in n-type PbTe epitaxial films grown on BaF2. Evidence of strain in as-grown films was found. The temperature of the sample was repeatedly cycled from 297 to 4.2 K and back, and the 297-K strain was found to decrease. At the same time, Hall effect and resistivity measurements show that the 4.2-K mobility dropped and the 297- and 4.2-K carrier concentrations increased. The observed effects are ascribed to an extended defect density which grows larger as the number of thermal cycles increases.
Thermally stimulated currents in amorphous selenium: Relationship to trapping levels and the noncrystalline state
Authors: Hoshino Yasushi , Miyata Hiroyuki
Published: February 2003

Deep traps in amorphous selenium are measured using a thermally stimulated current (TSC) technique. A peak is found in the TSC curve, which arises from the thermal liberation of trapped carriers in the bulk of amorphous selenium. It is found that the trapped carriers are mainly positive holes in the temperature range 170∼310 °K. Three methods (Grossweiner’s method, initial rise plot method, and varying temperature rising rate method) are applied to obtain the trap activation energy. It is concluded that the trap activation energies are distributed from 0.6 to 1.1 eV.
Infrared quenching of photocapacitance in CuxS/CdS solar cells
Authors: Suda Toshikazu , Bube Richard H.
Published: February 2003

Copper diffusion into CdS substrates normally occurs in CuxS/CdS solar cells during fabrication, and may cause degradation of solar efficiency because of a decreased proportion of copper in the CuxS. In order to obtain information about deep Cu-acceptor levels in CuxS/CdS solar cells prepared by both the wet and dry methods on CdS single crystals, an infrared quenching of photocapacitance (PHCAP IR quenching) method has been used. A theory for the description of the PHCAP-IR quenching, and also for a doping profile by a modified C-V method using PHCAP-IR quenching, has been developed to obtain energy levels, photoionization cross sections, and concentration profiles of Cu levels in CdS. Two transitions of 1.08 and 0.86 eV, corresponding to the transition (3d9)Cu2+→(3d10)Cu+, and an internal transition in (3d9)Cu2+, respectively, were measured at room temperature. The photocapacitance quenching level of 0.86 eV disappears at low temperature, and only a 1.20-eV transition was measured at 91 K, corresponding to the internal transition (3d9)Cu2+[E5/2(2T2)]→(3d9)Cu2+[G( 2E)]. Spectral distributions of photoionization cross sections σ0pv corresponding to the transition (3d9)Cu2+→(3d10)Cu+ were obtained; the peak value was 1.1×10−16 cm2. The doping profile of Cu shows that a density of Cu up to one half of the majority-carrier density diffused into CdS after heat treatments at 200 °C for a few minutes.
A model of impact ionization through surface states
Authors: Hamasaki M. , Taira K.
Published: February 2003

Impact ionization in N channel metal-oxide-semiconductor field-effect transistors (MOS)(FET’s) was investigated. Experimental observation indicates that impact ionization is related to surface-state density. A simple model and supporting experimental evidence are presented.
Chaotic states of rf-biased Josephson junctions
Authors: Kautz R. L.
Published: February 2003

The existence of chaotic solutions to the rf-driven Stewart-McCumber model of a Josephson junction has recently been demonstrated. The present paper describes more fully the range of junction parameters and frequencies for which chaotic solutions occur, details the connection between chaotic states and instabilities in phase-lock, and shows that chaotic noise can be much larger than the thermal noise of a junction.
Effect of strain on the critical current of Nb-Hf/Cu-Sn-Ga multifilamentary superconductors
Authors: Ekin J. W. , Sekine H. , Tachikawa T.
Published: February 2003

The critical current of multifilamentary Nb-Hf/Cu-Sn-Ga has been determined as a function of both field and strain at fields from 4 to 19 T. The strain dependence of the critical current is significantly reduced compared with that of commercial multifilamentary Nb3Sn superconductors. This reduced strain sensitivity, coupled with an enhanced critical-current density above 12 T, make this a candidate material for economic high-field magnet construction. An analysis of the data in terms of the strain scaling law indicates that the Hf and Ga additives do not produce this improvement through a decrease in the strain sensitivity of the bulk upper critical field B*c2. Rather, they reduce the strain sensitivity of the critical current through a changed shape of the flux pinning curve and an enhancement in the strain-free maximum value of B*c2 (B*c2m = 25 T for Nb-Hf/Cu-Sn-Ga versus 21 T for Nb3Sn).
Depth dependence of piezoelectric activity in poly(vinylidene fluoride) transducers: Control and measurement
Authors: Marcus Michael A.
Published: February 2003

Double-layer and multilayer poling experiments have been performed to determine the depth dependence of piezoelectric activity in poly (vinylidene fluoride) (PVF2) films. The depth dependence of activity is highly dependent on poling field and time. Removal of the poling field before cooling alters the activity distribution. When central conductive layers are present during poling, cathode activity is increased. When a thermal gradient occurs across the sample’s thickness during poling, the cool side is the more active. A bulk measurement of activity asymmetry in transducer films is described, and use of asymmetric films as flexure devices is discussed. Reversing the field during poling is useful in increasing asymmetric activity.
Photoacoustic chopping frequency studies on sapphire
Authors: Fernelius Nils C.
Published: February 2003

Experimental photoacoustic (PA) signal amplitude and phase angle data were obtained as a function of chopping frequency on single-crystal sapphire Al2O3 windows using a 1.3-μm laser with about 4 W incident power. The PA signal amplitude had a f−n dependence with n = 1.10 on one run and n = 1.07 on another. Somewhat noisy phase angle plots yielded a phase angle difference between 1000 and 100 Hz of 12 ° and 8.5 °; between 500 and 100 Hz of 10 ° and 7.5 °. Laser rate calorimetry on these samples yielded an average effective optical absorption coefficient βeff = βB +2βs /l = 0.745×10−3 cm−1. βB is the bulk optical absorption coefficient in cm−1 and βs the dimensionless surface optical absorption. l is the sample thickness = 0.78 cm. Theoretical calculations were made using several PA theories and parameters relevant to sapphire. The Rosencwaig-Gersho (R-G) theory calculations yielded results that differed greatly with experiment. Calculations using the McDonald-Wetsel composite-piston model, an extension of the R-G theory, yielded results closer to experiment. A comparison of various calculations using the Bennett-Forman theory indicated that the surface-to-bulk optical absorption ratio r≡βs /βB was between 0.015 and 0.020 cm. Using r = 0.020 cm yields βB = 0.709×10−3 cm−1 and βs = 0.000014. Thus for these samples 95% of the measured βeff is due to βB .
Impurity effects in a-Si:H solar cells due to air, oxygen, nitrogen, phosphine, or monochlorosilane in the plasma
Authors: Delahoy A. E. , Griffith R. W.
Published: February 2003

It is demonstrated that solar cells fabricated using plasma-deposited a-Si:H alloys can be seriously degraded by the incorporation of certain impurities during deposition of the a-Si:H materials. Nominally intrinsic layers are adversely affected by the addition to the plasma of air, N2+O2 mixtures (although by neither N2 nor O2 separately), PH3, or SiH3Cl (monochlorosilane). For example, the conversion efficiency of Pd/p-i-n solar cells is lowered from 3.1% to 1.5% by the presence in the plasma of 3000 ppm air during deposition of the i-layer. In this case modification of the a-Si:H gap-state density owing to synergistic effects of oxygen and nitrogen in the plasma leads to a collapse of the space-charge region and a reduction of the μτ product for holes. The deleterious effects on device performance of phosphine and monochlorosilane are also discussed.
Vertical solar cell and internal electric field
Authors: Yang Yu-Tung
Published: February 2003

The fact that a vertical solar cell reacts differently with different monochromatic light enables us to estimate the pattern of the built-in electric field distribution within the cell. The technique may be useful for quality control.
The equivalence of electromagnetic coils for electron optics
Authors: Vassell M. O.
Published: February 2003

The theoretical basis is discussed, and a stable, accurate, and efficient numerical procedure given for calculating the winding distribution that is needed on a designated target yoke so that the magnetic field it produces in a specified region of space is identical with that generated by a given primary yoke. This capability is useful for characterizing the mapping properties of equivalent electromagnetic coils, a central issue in the synthesis and design of yokes for color television and monitor tubes. The formulation incorporates and generalizes the conventional integral equation method of magnetostatics. In common with the latter method, it is based on the linear integral relation between the magnetic potential and its two sources: the ’’effective charge density’’ on core surfaces and the current distribution on winding surfaces. However, whereas the conventional method seeks to determine the former source (given details of the latter source) from a single Fredholm equation of the first kind, the present method is designed, in addition, to determine (if desired) both sources simultaneously as the solution of a pair of such integral equations. Although the formal statement of solution is valid for arbitrary coil geometry, the numerical procedure for applying it is given here only for coil geometries of axial symmetry, where the ability to expand the field quantities in angular harmonics allows one to resolve the problem into a sequence of two-dimensional problems, one for each harmonic. It is demonstrated that the known proneness of Fredholm equations of the first kind to be ill conditioned is heightened in the present method, more so than in the conventional problem. The core of the numerical procedure is thus a smoothing algorithm for suppressing high-frequency, large-amplitude oscillations that are an unwanted feature of any direct solution of such an ill-conditioned system.
InGaAsP n-channel inversion-mode metal-insulator-semiconductor field-effect transistor with low interface state density
Authors: Shinoda Yukinobu , Kobayashi Takeshi
Published: February 2003

n-channel inversion-mode metal-insulator-semiconductor field-effect transistors (MISFET’s) were fabricated on In1−xGaxAsyP1−y quaternary alloy (y≃2.2x) with chemical vapor deposition (CVD) Al2O3 gate insulator. The InGaAsP MISFET exhibited compositional dependence of the effective mobility μeff. μeff monotonically increased with increasing As molar fraction y in the 0⩽y⩽0.55 experimental range. The highest mobility obtained so far was 2300 cm2/V s at room temperature, higher than that of InP MISFET devices fabricated in this laboratory (400–800 cm2/V s). Very large temperature variation in threshold voltage and zero temperature coefficient of μeff were observed on InP(y = 0) devices. Contrasting to this, small temperature variation in the threshold voltage and the clear dependence of μeff on temperature, similar to that of the bulk mobility, were seen on InGaAsP MISFET’s. These excellent characteristics of the quaternary device appeared to be brought about through reduction in the interface states near the conduction band edge. The interface state density was estimated to be 1×1012/cm2eV, as compared to 1×1013 at the InP interface. A simple analysis, including the effect of the interface state on MISFET characteristics, explained the experimental results with good consistency.
Quasi-optics of the coupling of guided magnetic waves for the normal magnetization
Authors: Seshadri S. R. , Tsai Ming-Chi
Published: February 2003

The coupled mode equations governing the interaction of the guided magnetic waves propagating in opposite directions along a ferrimagnetic film having a periodic array of shallow rectangular grooves on one of its surfaces are deduced using quasi-optical techniques for the case in which the magnetization is normal to the surfaces of the film. Effects caused by the deviation of the wave frequency from the Bragg frequency and by the presence of small magnetic losses are also taken into account. For a surface corrugation extending only for a finite length along the film, the longitudinal boundary value problem is solved to obtain the reflection, the transmission, and the absorption coefficients. The coupled mode equations are found to yield correctly the power conservation relation.
Finite difference solution for biopotentials in a multisphere volume conductor
Authors: Sjo/ntoft Erik
Published: February 2003

A three-dimensional finite difference computer simulation has been used to model an entire spherical volume conductor. The model permits conductivity to be dependent on distance from the center of the sphere. The method of successive overrelaxation is employed to solve the finite difference equations in a spherical nonhomogeneous, nonequidistant net. A new method of using successive overrelaxation along each space direction is presented. This method is very suitable for giving starting potentials of the normal successive overrelaxation.
Effect of slot ends on ion extraction optics
Authors: Wooten J. W. , Whealton J. H. , McCollough D. H.
Published: February 2003

A preliminary result is given for the transverse and longitudinal root mean square divergence angles for an ion beam traversing a sample finite slot accelerator design. The result is obtained using a finite element code to achieve a three-dimensional explicit solution for the extraction sheath resulting from the solution of the Poisson Vlasov equation. This is the first three-dimensional explicit sheath solution for a possible neutral beam accelerator electrode design.
Direct evidence for spontaneous precipitation of helium in metals
Authors: Thomas G. J. , Bastasz R.
Published: February 2003

Using transmission electron microscopy, we have observed helium bubbles and interstitial dislocation loops in gold implanted with helium at below the displacement threshold energy. These results indicate that helium clusters may spontaneously form Frenkel-pair defects in metals.
Experimental investigation of CO chemical laser produced by supersonically mixing CS/S with O2 in a shock tunnel
Authors: Stricker J. , Tilleman M.
Published: February 2003

Experimental results of small-signal gain in CO chemical laser, operating with very high values of CS:CS2 and S:CS, are presented. The laser is produced in a shock tunnel where complete thermal dissociation of CS2 into CS+S is accomplished by a reflected shock wave. The dissociated products, diluted in Ar, expand through a supersonic nozzle into a combustion chamber, where molecular oxygen is supersonically injected. The two streams react, and vibrationally excited CO is produced. The experimental data are compared with a numerical model developed for this laser. A fairly good agreement between calculations and experiments was found, which enables the utilization of the mathematical model for better understanding of the processes involved in laser operations. Gains for P7(14) and P5(18) were measured at distances of 5.5 and 11.5 cm downstream from oxygen injectors. Stagnation pressure of 25 atm was kept constant in all experiments. Stagnation temperatures were varied in the range of 2500–4600 °K, and mixtures of CS2:Ar between 5:90 and 30:70 were tested. A maximum of small-signal gain was observed for each of the parameters investigated. The maximum gain measured for P7(14) was 8% cm−1 for CS2:Ar = 20:80 and stagnation temperature of 4000 °K. For these operating conditions, laser oscillations were observed in an 8-cm-long active cavity. The resonator consists of a full reflector and a 42% reflective coupling mirror.
Laser chemical vapor deposition: A technique for selective area deposition
Authors: Allen S.D.
Published: February 2003

Laser chemical vapor deposition (LCVD) uses a focused laser beam to locally heat the substrate and drive the CVD deposition reacton. Several different deposition reactions and substrates have been examined as a function of intensity and irradiation time using a CO2 laser source: Ni on SiO2, TiO2 on SiO2, TiC on SiO2, and TiC on stainless steel. LCVD film thicknesses range from <100 Å to ≳20 μm. Deposition rates of mm/min have been observed for LCVD Ni and 20 μm/min for LCVD TiO2. The diameter of the deposited films is dependent on irradiation conditions and can be as small as one tenth of the laser beam diameter. The LCVD films exhibit excellent physical properties such as adherence, conductivity, hardness, and smoothness.
A finite material temperature model for ion energy deposition in ion-driven inertial confinement fusion targets
Authors: Mehlhorn Thomas A.
Published: February 2003

We have developed a model for use in ion-driven inertial confinement fusion (ICF) target design to describe the deposition of energy by an arbitrary ion traversing a material of arbitrary composition, density, and temperature. This model particularly emphasizes the deposition physics of light ions having specific energies of 3 MeV/amu or less. However, the model is also applicable to heavy ion fusion problems where there are specific energies in excess of 10 MeV/amu. We have found that an accurate description of the cold material stopping power must include both shell corrections to the Bethe theory as well as the alternative LSS (Linhard-Scharff-Schio/tt) model at low energies. We have incorporated finite temperature effects by scaling the relevant bound electron parameters with the degree of material ionization as well as by including the free-electron stopping power. We discuss both the phenomenon of range shortening and range relengthening in heated material. Our preliminary calculations indicate that the minimum ion range in heated material is approximately one-half that in cold dense targets, independent of the identities of the projectile ion and the host material.
Cherenkov radiation from a relativistic annular electron beam propagating through a dielectric loaded waveguide
Authors: Uhm Han S.
Published: February 2003

Stability properties of the free-streaming mode (space-charge wave) in a relativistic annular electron beam with radius R0 propagating through a dielectric loaded waveguide is investigated, in connection with the Cherenkov radiation. The stability analysis is carried out within the framework of the linearized Vlasov-Maxwell equations for an electron distribution function, in which all electrons have a Lorentzian distribution in the axial canonical momentum. One of the most important features of the analysis is that, for some ranges of physical parameters, a strong mode coupling between the vacuum dielectric waveguide and free streaming modes occurs, exhibiting possibilities of a Cherenkov radiation. The typical maximum growth rate of instability is a few percent of c/R0, where c is the speed of light in vacuo. However, the growth rate and bandwidth of instability are substantially reduced by increasing the axial momentum spread.
Striated jets due to the nonlinear force and spontaneous magnetic field in laser-induced plasmas
Authors: Dragila R.
Published: February 2003

The interaction of a spontaneous dc magnetic field and nonlinear force-induced striated motion of plasma caused by an obliquely incident p-polarized electromagnetic plane wave upon an inhomogeneous plasma is investigated and consequent additional deconfining pressure is evaluated.
A study of unipolar arcs in a low-pressure mercury discharge
Authors: Johnson C. T. , Lee A. , Smeltzer G. S.
Published: February 2003

An experimental study of unipolar arcs was conducted in a low-pressure mercury rf-generated plasma. The results were found to be consistent with the concept of a sheath mechanism for driving the unipolar arcs. Floating double-probe measurements yielded electron temperatures of ∼2 eV and electron-number densities of ∼1×1011 cm−3. The variation of the unipolar arc current with (1) the electron temperature and density and (2) the metal surface area exposed to the plasma verified the predicted dependence of the arc current on the plasma parameters and the metal surface area. Finally, alternative mechanisms for sustaining the observed arcs by high-frequency rectification were ruled out on the basis of the recorded current waveforms of the unipolar arcs.