bluuebunny/crossref_metadata_2025 huggingface dataset:
On cyclotron waves in a bounded magnetoplasma
Authors: Das S. K. , Basu J.
Published: February 2003

The paper presents a study of the cyclotron waves in a plasma column enclosed in a conducting cylinder and placed in an axial static magnetic field. The cutoff frequencies of the waves are investigated with special reference to the role of the plasma radius a in the wave propagation. The cyclotron modes discussed cover all the possible types, namely, circularly symmetric Com modes and asymmetric Cnm modes with n?1, each Cnm mode being split into two, designated as C−nm and C+nm modes, corresponding to two different polarizations of the field components. The upper and lower limits of the cutoff frequencies of the various modes as a tends to zero and infinity, respectively, are derived. It is found that cyclotron modes can broadly be divided into the following two categories: (1) C+n1 modes, the limiting cutoff frequencies of which are the electron cyclotron frequency ωce and lower hybrid frequency ωlh, and (2) modes other than C+n1 modes, the limiting frequencies being the upper hydrid frequency ωuh and a frequency ω0 which is a function of electron and ion plasma frequencies, ωpe and ωpi, as well as electron and ion cyclotron frequencies, ωce and ωci. The modes belonging to the first category represent, in all cases, forward waves while those of the second category may represent backward or forward waves, depending essentially on a if ωpe and ωce are kept constant. The critical radii at which the change takes place for the lowest-order modes are derived. The effect of plasma ions on the propagation of the C+n1 modes is found to be considerable if a is sufficiently large. For other modes the effect can be considerable if both a and ωce have sufficiently high values.
Electrical properties of Si implanted with As through SiO2 films
Authors: Hirao T. , Fuse G. , Inoue K. , Takayanagi S. , Yaegashi Y. , Ichikawa S. , Izumi T.
Published: February 2003

The effects of the recoil implantation of oxygen on the electrical properties of Si heavily implanted with As through SiO2 films have been investigated as a function of annealing temperature, in correlation with the crystal orientation. The concentration profiles of the electrically active As in Si have been compared with those of total As and recoil implanted oxygen measured by secondary-ion mass spectrometry. It is shown that at temperatures between 650 and 850 °C, both the restriction in the electrical activation and the reduction of mobility are observed in the region where the oxygen concentration exceeds ∼1020 O/cm3 in (111) -oriented Si, while the recoil implantation of oxygen has much less influence on the electrical properties of Si in (100) -oriented Si. At 1000 °C the only effect of the recoil implantation is the reduction of mobility in the surface region in (111) -oriented Si. The analysis of the defect structures by transmission electron microscopy indicates that the defects in (111) -oriented Si after annealing are much denser than those in (100) -oriented Si. The isochronal annealing are much denser than those in (100) -oriented Si. The isochronal annealing behavior of carrier concentration is correlated with that of defects measured by ESR method.
Temperature distributions produced in semiconductors by a scanning elliptical or circular cw laser beam
Authors: Nissim Y. I. , Lietoila A. , Gold R. B. , Gibbons J. F.
Published: February 2003

Temperature profiles induced by a cw laser beam in a semiconductor are calculated. The calculation is done for an elliptical scanning beam and covers a wide range of experimental conditions. The limiting case of a circular beam is also studied. This calculation is developed in the particular cases of silicon and gallium arsenide, where the temperature dependence of the thermal conductivity has been taken into consideration. Using a cylindrical lens to produce an elliptical beam with an aspect ratio of 20, a 1-mm-wide area of an ion-implanted silicon wafer was annealed in a single scan. The experimental data are consistent with the extrapolation of solid-phase epitaxial regrowth rates to the calculated laser-induced temperatures.
Dynamics of the field-induced transition to the polar α phase of poly(vinylidene fluoride)
Authors: Dvey-Aharon H. , Taylor P. L. , Hopfinger A. J.
Published: February 2003

A mechanism for the poling of α-phase poly(vinylidene fluoride) into its polar form is studied in which a 180° twist or kink is propagated along a chain. Results are obtained by analytical approximation and by computer experiment for the field and temperature dependence of the poling time. Intrachain and interchain potentials used in this calculation are obtained by conformational analysis. The results are compared with experimental data.
The pressure dependence of the pyroelectric response of poly (vinylidene fluoride) films
Authors: Scheinbeim J. I. , Chung K. T. , Pae K. D. , Newman B. A.
Published: February 2003

The pressure dependence of the pyroelectric coefficient Py was determined from atmospheric pressure to 7 kbar over a temperature range from −80 to +48 °C for poled uniaxially oriented poly (vinylidene fluoride) film. The effect of the glass transition on Py as a function of pressure is compared to the pressure dependence of the glass-transition temperature obtained from dielectric studies. The ratio of dp, the hydrostatic pressure piezoelectric coefficient, to Py is presented as a function of both temperature and pressure. The details of a high-pressure system design for these measurements are also presented.
Epitaxial polymerization of (SN)x: Chemical defects
Authors: Ishida Hatsuo , Rickert Scott E. , Hopfinger Anton J. , Lando Jerome B. , Baer Eric , Koenig Jack L.
Published: February 2003

Epitaxially polymerized (SN)x on various substrates has been studied by Fourier-transform infrared spectroscopy (FT-ir). Those substrates include Pt-shadowed KI, AgCl, NaCl, KCl, KI, KBr, RbI, and NaI. All samples of the polymer contained significant amounts of chemical defects, mostly as NH and S=O groups. The spectral variation observed with (SN)x polymerized on various substrates appeared to be due to differences in its degradation by water. There are at least two distinct degradation mechanisms. One is the degradation by water incorporated into the S2N2 crystals prior to the polymerization, and the other is the attack of moisture on the polymer. The nature of the chemical defects were studied by deuterium exchange and degradation by H2 18O as well as H2 16O. The band at 1400 cm−1 was assigned to the NH group while two bands at 1220 and 1090 cm−1 were assigned to S=O groups with different chemical environments. The band at 1220 cm−1 is related to a structure produced during the early stages of degradation in the preparative vacuum chamber, but the band at 1090 cm−1 is thought to arise from a structure formed at a later stage of degradation after sample preparation by atmospheric water.
Stability conditions for a diffusion-controlled plasma column in the presence of stepwise ionization processes
Authors: Gilardini Aldo L.
Published: February 2003

The case of a cylindrical diffusion-controlled plasma column with electron production rates linear and quadratic in electron density is discussed. The amount of plasma constriction is evaluated numerically as a function of an appropriate parameter related to the discharge current. The onset of plasma instability due to the presence of the quadratic electron production term is studied by the perturbation method, which leads to a homogeneous differential equation having eigenvalue solutions. A stabilizing resistance is placed in between the voltage supply and the plasma; the eigenvalues then provide, for given plasma parameters, the minimum ratio for stability of this outer resistance to the plasma resistance. The proper variables of the problem are defined, and numerically computed values of the instability limits, in particular the minimum resistance ratio for a neon plasma, are given and discussed.
Radial distribution of excited atoms in a new coaxial line type microwave cw discharge tube
Authors: Kato Isamu , Tsuchida Hisazumi , Nagai Masaru
Published: February 2003

A study has been made of a new microwave discharge method to obtain a plasma suitable for a gas laser medium and plasma chemical vapor deposition. When the plasma frequency is higher than that of the microwave power supplied to the plasma in the coaxial line mode, the plasma plays an important role as the inner conductor of the coaxial line. Therefore a cylindrical plasma of the arbitrary size which is uniform along the circumference and in the radial direction can be produced. The radial distribution of the excited atom density of the plasma has been measured using the side-light method. It is shown that the microwave discharge has the proper distribution. The distribution is not bell-shaped, but is either trapezoidal in shape or has a central dip.
Ion-beam-induced metastable Pt2Si3 phase. II. Kinetics and morphology
Authors: Tsaur B. Y. , Mayer J. W. , Graczyk J. F. , Tu K. N.
Published: February 2003

The transformation behavior of the ion-beam-induced amorphous Pt2Si3 alloys has been studied by using resistivity measurements. Two distinct stages of transformation were observed as revealed by a rapid change of resistivity with increasing annealing temperature. In the first state a transfrom from the amorphous to a metastable crystalline Pt2Si3 phase occurred in a narrow temperature range around 400 °C. The second stage, which appeared gradually near 550 °C, involved the transformation to the equilibrium two-phase state of PtSi and Si. The kinetics of the amorphous to metastable crystalline transformation has been determined by isothermal treatment over the temperature interval 376–392 °C. The results are interpreted in terms of a classical nucleation and growth mechanism with a t4 (time) dependence and an apparent activation enthalpy of (108±5) kcal/mol. The microstructure of the alloys at various stages of transformation was studied by transmission electron microscopy and diffraction. The correlation between the kinetics and the microstructures of the alloyed layers is given and discussed.
Secondary ion mass spectrometry and ion scattering spectrometry determination of iodide distribution in Ag(Br,I)
Authors: Furman B. K. , Morrison G. H. , Saunders V. I. , Tan Y. T.
Published: February 2003

The spatial distribution of iodide in Ag(Br,I) (6 mol % I) sheet crystals has been determined with ion scattering spectrometry and secondary ion mass spectrometry. The results of both techniques show an enchancement of the iodide concentration at one surface, which results from the method of crystal growth.
Crystal structure and isothermal compression of Fe2O3, Cr2O3, and V2O3 to 50 kbars
Authors: Finger Larry W. , Hazen Robert M.
Published: February 2003

Crystal structures of several of the corundum-type oxides have been determined at pressures to 50 kbars. All materials have linear compression within the pressure range and precision of the techniques used. Compression of Cr2O3 and Al2O3 is essentially isotropic (c/a remains constant), Fe2O3 has a slightly anisotropic compression, with c/a decreasing slightly with pressure, and V2O3 is very anisotropic, with the a axis nearly three times more compressible than c. Similar differences are observed in the structural parameters. Aluminum, iron, and chromium sesquioxides simply scale, whereas atomic positions in V2O3 approach an ideal HCP arrangement with increasing pressure. The differences in structural variation with pressure for these ’’isostructural’’ compounds emphasize the difficulty in using simple bonding parameters to predict details of crystal structures under nonambient conditions.
Cosputtered molybdenum silicides on thermal SiO2
Authors: Murarka S. P. , Fraser D. B. , Retajczyk T. F. , Sheng T. T.
Published: February 2003

The silicides of molybdenum have been formed by cosputtering mixtures of molybdenum and silicon on oxidized silicon wafers. Alloys with as-deposited Mo/Si nominal atomic ratios of 0.25 to 4 were sintered in a hydrogen ambient in the temperature range of 900–1150 °C. The formation of the silicide in these films was followed by the use of sheet resistance, by x-ray diffraction and stress measuring techniques, and by the use of transmission electron microscopy. The resistivity was found to decrease with increasing molybdenum content, the lowest being ∼60 μ Ω cm. The stress was highest in films richer in the intermetallic MoSi2. The coexistence of the three phases Mo3Si, Mo3Si2, and MoSi2 led to lower stresses due to void formation in the film. A comparison of the resistivity and the sintering behavior in Mo-Si films has been made with that observed in Ta-Si and Ti-Si films. The role of the oxygen contamination has been emphasized as one of the rate controlling factors in the silicide formation.
Effectiveness of SiO2 for preventing silicon -metal reactions at high temperatures
Authors: Bevolo A. J. , Campisi G. J. , Shanks H. R. , Schmidt F. A.
Published: February 2003

Silicon dioxide layers, deposited by rf sputtering and measuring less than 1000 Å thick, were found to prevent silicide formation between evaporated silicon films and molybdenum substrates after annealing for 1 h at 1250 °C. Silicon grain size ranged from 0.2 to 2.5 μ in cross section. In situ Auger electron spectroscopy (AES) was used in the silicon deposition chamber to monitor the heat treated Si/SiO2/Mo samples for silicide formation. Composition depth profiling by ion beam sputtering and AES analysis was used to measure oxygen diffusion into the silicon and metal phases. This technique established that the breakdown of SiO2 as a reaction barrier between the molybdenum and silicon occurred because of oxygen diffusion from the SiO2 layer into the silicon. A similar behavior is expected between SiO2 and tungsten. However, when SiO2, deposited on tantalum, was heated to 1100 °C, the oxygen was found to have migrated into the metal resulting in the breakdown of the oxide layer.
Conformational recovery of poly(vinyl chloride) glasses prepared under pressure
Authors: O’Reilly James M. , Mosher Ralph A.
Published: February 2003

The recovery of polyvinyl chloride glasses prepared at high temperature and pressure (120 °C, 7 kbar) have been observed using Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). Changes in absorbance associated with conformational reequilibration occur above 80 °C, the normal glass temperature of polyvinyl chloride (PVC). Peaks are observed in Cp 15–20 °C below Tg which are attributed to relaxation of volume strain or holes. Since the enthalpy and the conformational recovery occur at different temperatures and time scales, we conclude that neither free volume models nor flexed bond models are adequate to explain the properties of glasses prepared at high pressure.
Additive properties of some crosslinked epoxies
Authors: Hartmann Bruce , Lee Gilbert F.
Published: February 2003

The assumption of additive properties was applied to a series of eight crosslinked epoxy/amine polymers. The thermodynamic properties of the four independent structural components of these polymers were determined from experimental measurements on the polymers. This approach was applied to: density, thermal expansion, bulk modulus, and heat capacity. Using the component values, polymer properties were then calculated with the result that the predictions agree on the average with the measurements to within the accuracy of the measurements.
Structure of the in-plane 90° charged magnetic domain wall in double-layer magnetic films
Authors: Henry G. R.
Published: February 2003

We consider a double-layer magnetic film with magnetization in one layer lying in the film plane and magnetization in the other layer orthogonal to the film plane. An analytic solution is obtained for the transition structure, which takes the form of a 90° charged wall in the film plane.
Magnetic loss and domain-wall mobility in magnetic bubble garnet films
Authors: Ikeda T. , Ohta N. , Ishida F. , Sugita Y.
Published: February 2003

Magnetic loss and domain-wall mobility have been studied in the bubble garnet system (YSmLuCa)3(FeGe)5O12 and in large gyromagnetic ratio (high-g) garnets such as (LaTmCa)3(FeGe)5O12, (YErCa)3(FeGe)5O12, and (YEuCa)3(FeGeSi)5O12. The resonance line width ΔH increases as the concentration of the rare-earth ion in the film increases and decreases as the saturation induction 4πMs increases. The product MsΔH depends only on the rare-earth ion in the film and its concentration. We consider this product as a magnetic loss parameter because it is proportional to the concentration of the rare-earth ion, which is closely related to the magnetic loss energy of the garnet system. The modified Landau-Lifshitz damping parameter Λ(≡λ/γ2; λ: normal Landau-Lifshitz damping parameter; γ: gyromagnetic ratio) is found to be proportional to MsΔH. It is shown that Λ is preferable to the Gilbert damping parameter α and λ itself in studying the dynamic properties such as domain-wall mobility.
Stimulated electron radiation in a medium due to wiggler magnet
Authors: Šoln Josip
Published: February 2003

The stimulated radiation when an electron interacts with a static wiggled magnetic field in a dielectric medium is analyzed with the help of the S matrix resulting from the previously developed PDECC (partial differential equations with respect to coupling constants) formalism. From the vacuum-to-vacuum S matrix transition, the power spectrum P (ω), is derived from which the total radiated power WT can be evaluated. Assuming specifically that an electron of about 100 keV passes close to the quartz surface (the index of refraction n?1.7) when interacting with the wiggled magnetic field with a wavelength of λ?1 cm, we find that kinematically the near-millimeter radiation will occur around an angle of 6° with respect to the electron velocity. Furthermore, if the interaction region is about 1 m and the peak value of the magnetic field is about 1 kG, we find that an efficiency of the order of 10% can be easily achieved.
The effect of O2 on reactively sputtered zinc oxide
Authors: Aita C. R. , Purdes A. J. , Lad K. L. , Funkenbusch P. D.
Published: February 2003

The rf diode sputtering of a ZnO target using an Ar/O2 gas mixture was studied as a function of the O2 content of the sputtering gas. Films sputtered using gas mixtures containing 0–100% O2 were investigated. Glow discharge spectrometry was used to monitor the ionized species present in the various Ar/O2 plasmas. The crystallographic orientation of the films was found to be highly correlated with the ratio of the number of Zn to ZnO ions in the plasma. The most highly ordered films were obtained when the Zn to ZnO ion ratio was at a minimum which occurred when a 75% Ar/25% O2 gas mixture was used. This result can be explained in terms of the relative degree of oxidation of the ZnO target surface and the number of secondary electrons in the plasma for the various Ar/O2 sputtering gas mixtures.
The electric field distribution in the field ion microscope as a function of specimen shank
Authors: Gipson G. S. , Eaton H. C.
Published: February 2003

A new empirical field calibration equation is presented. This relationship is obtained from a detailed numerical study of the field distribution within a real field ion microscope. The equation separates the important shank angle effect from the other geometric influences. Comparison is made of the predicted field with actual values.
Effect of pressure on the spectral distribution of a transversely excited atmosphere CO2 laser oscillator
Authors: Nath A. K. , Chatterjee U. K.
Published: February 2003

Simultaneous oscillation was observed on several rotational lines from P(14) to P(26) of the 10.6-μm band in a transversely excited atmosphere CO2 laser at low gas pressures. With the increase of pressure, the number of lasing lines reduced and the P(20) line became more dominant. Theoretical analysis has revealed that the changes in the rotational relaxation rate and the stimulated emission rate with gas pressure could account for the observed variation in the laser spectrum.
Suppression of semiconductor laser pulsations using optical feedback from a fiber
Authors: Dyment J. C. , Chik K. D.
Published: February 2003

A novel optical feedback method is described for suppressing self-sustained pulsations in semiconductor lasers. Using an external cavity formed from a single segment of optical fiber about 1 cm long, a few percent of the light is coupled back into the laser cavity. All pulsations are suppressed, independently of the pulsation frequency. This behavior is predicted by a model which incorporates saturable absorption centers in the laser cavity.
Early expansion in exploding multiple wire arrays
Authors: Bloomberg H. W. , Lampe Martin , Colombant D. G.
Published: February 2003

A simple model is developed for the initial stage (blow-off and the onset of pinching) of a multiple exploded wire array. With obvious modifications the model can also be applied to single wires or other self-pinched plasma columns. Each wire in the array is modeled as a plasma cylinder undergoing self-similar radial motion, and the whole array is coupled self-consistently to an external circuit. The plasma expands initially; the onset of self-pinch is shown to be coincident with the plasma conductivity reaching a value large enough for skin effect to occur. The model is run for a variety of system parameters, and the choice of machine and wire parameters to attain particular objectives (e.g., rapid current rise, limited wire expansion, etc.) is discussed.
Resistive wall interaction of axially moving field-reversed E layers or plasma rings
Authors: Rej D. J. , Larrabee D. A. , Fleischmann H. H.
Published: February 2003

Calculations are performed of the interaction force between an axially moving current carrying plasma ring or E layer with a resistive wall for a variety of parameters relevant to various moving-ring fusion schemes and experiments. Various wall configurations are considered: (i) For a thin resistive wall, the interaction force Fr(vz) is found to be proportional to the axial speed vz or to (1/vz) for small or large velocities, respectively, and to be strongly dependent on the ratio of the effective ring radius R to wall radius Rw. In contrast, the force dependence on the ring thickness δR is found small when rings with similar external field distributions are compared. For fusion-relevant ratios R/Rw≲0.7, and L/R=1–2 (L=ring length), the energy losses for moving the rings an axial distance equal to L may amount to 25% of the rings’ magnetic self-energy. However, this energy can be strongly reduced by proper choice of parameters. (ii) The addition of a fully flux-conserving wall at a radius Rc≳Rw is also found to lead to significant reductions of Fr(v) in the low-velocity regime, dependent in size on the ratio α=Rc/Rw. (iii) A finite wall thickness mainly will lead to increases in Fr(v) at large vz, where the transit time of the rings tt?(R2w+L2)1/2/vz becomes shorter than skin-depth time of the wall. In this case, Fr(v) ∼v−1/2z is obtained.
Two-electron group model and electron energy balance in low-pressure gas discharges
Authors: Ligthart F. A. S. , Keijser R. A. J.
Published: February 2003

The two-electron group model (2-EGM) provides a simple and powerful method to account for deviations from a Maxwellian shape of the electron energy distribution function in calculations on the positive column of low-pressure gas discharges. An analysis is given of the electron energy balance in this 2-EGM. Analytical expressions are obtained for the electron energy flow terms due to electron-electron interactions, elastic collisions, and the external electric field. The results obtained differ from those used thus far. The 2-EGM is applied in a simplified calculation for a low-pressure Hg-Ar discharge to obtain excited state densities. Good agreement is obtained with experimental data from literature.
Two-electron-group model and Boltzmann calculations for low-pressure gas discharges
Authors: Morgan W. L. , Vriens L.
Published: February 2003

For Ne, Ar, and Cs-Ar positive column plasmas a comparison is presented between Boltzmann and two-electron-group model (2-EGM) calculations. This 2-EGM is an approximation method to account for deviations from a Maxwellian electron energy distribution in plasma modeling. The comparison makes it possible to obtain in the 2-EGM an accurate normalization function for the high-energy tail of the electron energy distribution. The 2-EGM is found to give electron impact collision and energy transfer rates that agree well with those from the Boltzmann calculation over a wide range of currents and pressures.
Nonlatching Josephson interferometer made with small-area junctions
Authors: Howard R. E. , Hu E. L. , Jackel L. D. , Fetter L. A.
Published: February 2003

A 1:2:1 Josephson interferometer has been fabricated with small-area, high–current-density tunnel junctions. The short intrinsic RC times of these junctions result in device I-V characteristics with reduced hysteresis suitable for use in nonlatching logic circuits. The control current for this interferometer was fed directly, and asymmetrically, into the base electrode. Critical current versus control current measurements indicate that this device has a current gain greater than unity. The interferometer described represents an exploratory study of circuit design incorporating low-hysteresis junctions.
Convergence of the calculations of elastic constants from wave velocities in cubic crystals
Authors: Neighbours John R.
Published: February 2003

Elastic constants were determined from wave velocities by iteration of the perturbation expansion of the secular determinant. Calculations, carried to twenty iterations, were performed for many propagation directions in cubic nickel. Convergence was best along the boundaries of the unit triangle. Within the interior, the percentage difference between the true elastic constants and the final iterated values was never larger than 3200 ppm.
Permanent-magnet material obtained by sintering the hexagonal ferrite W=BaFe18O27
Authors: Lotgering F. K. , Vromans P. H. G. M. , Huyberts M. A. H.
Published: February 2003

The hexagonal ferrite W=BaFe2+2Fe3+16O27 has a saturation magnetization about 10% higher than the widely used permanent-magnet material M=BaFe3+12O19 and the anisotropy field is about equal. This opens up the possibility of using W as a permanent-magnet material with a higher remanence Br and energy product BHm. This paper describes the sintering of W having a slight deviation from the stoichiometric composition and containing a trace of SiO2 at, e.g., 1220 °C in a reducing atmosphere to 92–95% of the x-ray density and containing well-oriented grains of 2–8 μm. Samples with coercive forces Hc=1.5–2.1, Br=4.4–4.7, and BHm=3.7–4.3 (B in kG, H in kOe) were obtained, which may be compared with Hc=2.1, Br=4.0, and BHm=3.4 found from our own measurements on high-quality commercial M. We found surprisingly that the pickup of a trace iron during grinding increases the sintering density considerably, and this is therefore essential for the preparation of useful material.
Ga-In-As solidus isotherms developed by the step-grading technique
Authors: Bedair S. M. , Morrison C. , Fang R. , El-Masry N. A.
Published: February 2003

Liquidus and solidus data are presented for the 650, 700, and 800 °C isotherms in the In-rich corner of the Ga-In-As ternary system. The step-grading technique has been applied to accommodate large lattice mismatch and thereby obtain extended solidus data up to 60% InAs. LPE has been used to grow eight successive step layers of Ga1−xInxAs on GaAs substrate material, and each one of these layers provides a solidus data point for this ternary. The present technique predicts the conditions for successful lattice matched growth of Ga1−xInxAs on InP substrates. The accurate knowledge of the solidus and liquidus isotherms resulted in epitaxial growth of Ga1−xInxAs (0<X<0.3) with quality better than that previously obtained by VPE and LPE techniques. The simple solution model, successfully applied before for limited solidus data, does not seem to be adequate for the present extended data.
Damped surface modes in thick yttrium iron garnet films
Authors: Borghese Camillo , De Gasperis Paolo
Published: February 2003

Damped surface modes in thick YIG epilayers which appear at low fields close to the Damon-Eshbach limit in microwave spectra with the dc magnetic field parallel to the surface have been investigated. The results are explained in terms of the De Wames–Wolfram model, when a surface anisotropy energy due to the effect of a diffusion layer on the spins at the substrate/film interface is taken into account. In accordance with the experimental results, the above theoretical assumption leads to a low value of the parallel wave vector ky for which those modes can be excited (≲103 cm−1).
Deep electron traps in organometallic vapor phase grown AlxGa1−xAs
Authors: Wagner Elmar E. , Mars Dan E. , Hom Gil , Stringfellow G. B.
Published: February 2003

Deep electron traps have been studied by means of deep level transient spectroscopy in n-type nominally undoped and intentionally Te-doped AlxGa1−xAs epitaxial layers which were grown by vapor phase epitaxy from organometallic compounds (OMVPE). Three main deep electron levels are present in undoped material: a trap with an activation energy of 0.8 eV, which is also found in GaAs grown by conventional VPE, and two levels specific to OMVPE with activation energies of 0.32 and 0.38 eV, respectively. The concentration of the 0.8 eV level is found to be independent of the aluminum content x, supporting the assumption that it is not related to substitutional oxygen. The other levels, however, exhibit a very strong dependence of concentration on the composition, varying by four orders of magnitude in the range of 0⩽x⩽0.35. In Te-doped samples, a level with an activation energy of 0.23 eV has been identified, which is thought to be related to an IR emission found in photoluminescence in OMVPE as well as in liquid phase epitaxial material.
Gain broadening mechanism in various GaAlAs laser structures
Authors: Rühle W. , Brosson P.
Published: February 2003

Coupling of an external grating to a GaAlAs laser results in a strong enhancement of the selected mode and a reduction of the nonselected modes. The spectral form of this reduction is measured with a new sensitive experimental arrangement for three types of laser structures: proton bombarded stripe geometry, V-groove and CSP lasers. This spectral form is determined by the gain curve of the laser only and is independent on the position of the selected mode, i.e., no spectral hole burning is observed at room temperature.
Ablation of materials subjected to laser radiation and high-speed gas flows
Authors: Crane K. C. A. , Garnsworthy R. K. , Mathias L. E. S.
Published: February 2003

This paper presents results of investigations of the steady-state ablation that takes place when materials are irradiated by high-intensity laser radiation in high-speed gas flows. Materials investigated were stainless steels 304 and 310, carbon steel 1020, titanium 6Al-4V alloy, commercially pure titanium, and a glass fiber reinforced polyester. Four gases were used: air, a mixture of 40% oxygen and 60% nitrogen, argon, and nitrogen. Target samples were subjected to continuous-wave irradiation by a carbon-dioxide laser, and to tangential subsonic gas flows at a static pressure of 1 atm. The quantities measured included the ablation rates and surface temperatures. Analysis of the data for the metals yields values for the surface absorptances at 10.6 μm and values for the net contribution to the heat input provided by combustion and cooling. Information is also provided on the mechanism of melt removal and on the surface oxidation processes. For the nonmetal, the enthalpy required for ablation was obtained. These results, which are applicable to the upstream regions of irradiated areas, may be used to predict ablation characteristics for the gas-assisted laser cutting of plates, and the production of large holes in plates.
The reverse laser drilling of transparent materials
Authors: Anthony T. R. , Lindner P. A.
Published: February 2003

Within a limited range of incident laser-beam intensities, laser drilling of a sapphire wafer initiates on the surface of the wafer where the laser beam exits and proceeds upstream in the laser beam to the surface where the laser beam enters the wafer. This reverse laser drilling is the result of the constructive interference between the laser beam and its reflected component on the exit face of the wafer. Constructive interference occurs only at the exit face of the sapphire wafer because the internally reflected laser beam suffers no phase change there. A model describing reverse laser drilling predicts the ranges of incident laser-beam intensity where no drilling, reverse laser drilling, and forward laser drilling can be expected in various materials. The application of reverse laser drilling in fabricating feed-through conductors in silicon-on-sapphire wafers for a massively parallel processor is described.
Silane silicidation of Mo thin films
Authors: Chow T. P. , Brown D. M. , Steckl A. J. , Garfinkel M.
Published: February 2003

Silicidation of molybdenum thin films has been obtained for the first time from the reaction of molybdenum with silane (SiH4). Auger electron spectroscopy measurements indicate a uniform MoSi2 film has been grown. X-ray diffraction data show that films silicidized at relatively high flow rates have a dominant Mo component along with a significant hexagonal MoSi2 phase. Post-reaction annealing in H2 results in the complete disappearance of Mo with the concurrent increase of various silicide phases (MoSi2, Mo3Si). The growth kinetics were investigated as a function of reaction time and temperature and reactant flow rate. The sheet resistance of the reacted films can be controllably varied between that of Mo and of MoSi2. Post-silicidation annealing behavior was found to be strongly ambient dependent. Oxidation of the reacted films resulted in a uniform SiO2 overlayer.
Laser glazing of sprayed metal coatings
Authors: Pangborn R. J. , Beaman D. R.
Published: February 2003

The outer portion of a plasma sprayed, metal film 50 μm thick has been fused by means of laser scanning. The porosity of the film is thus sealed while the high-power density and rapid quench rates characteristic of laser melting preclude solid solution or compound formation at the film-substrate interface. The corrosion resistant properties of metals such as titanium may thus be economically imparted to a variety of substrates.
Scanning light-spot analysis of the carrier collection in liquid-junction solar energy converters
Authors: Furtak T. E. , Canfield D. C. , Parkinson B. A.
Published: February 2003

A scanning laser-spot system has been developed for the in situ evaluation of carrier collection in liquid-junction solar cells. The system was applied to the identification of topological features and the correlation of these features to the carrier collection efficiency on several materials presently being considered as solar energy converters in the liquid-junction cell configuration.
Evidence of minority-carrier injection in (n-n) SnO2-Ge heterojunction diodes
Authors: Legge R. N. , Wang E. Y.
Published: February 2003

Heterojunction diodes with rectifying current-voltage characteristics have been fabricated by chemical vapor deposition of n-type SnO2 onto chemically polished substrates of n-type Ge and Si. Observation of the diode recovery time as the samples are pulsed from forward bias to reverse bias indicates the existence of minority-carrier injection for the case of n-Ge, but not for n-Si. This is in agreement with predictions bases on the appropriate energy-band diagram for each structure.
Observation of a possible fringing field effect on the threshold voltage variation of the short-channel MOSFET
Authors: Chang Hsien-Liang , Yu S.-Y.
Published: February 2003

A very thick gate oxide layer 1.1 μm is intentionally used to enhance the fringing field effect around the edge of oxide layer. Then, the slopes of the Id-VG curves in the linear region are obtained for various substrate reverse-biased voltages VBG. The slopes are an increasing function of ‖VBG‖, which indicates that the effective capacitance per unit area of the oxide layer also increases with ‖VBG‖.
Dual implantation of Ga and Ge into GaAs
Authors: Pedrotti F. L. , Yeo Y. K. , Ehret J. E. , Park Y. S.
Published: February 2003

The electrical properties of GaAs, doubly implanted with Ge+Ga, have been studied by the van der Pauw–Hall-effect/sheet-resistivity technique. In all cases both species of the dual implants were implanted sequentially at the same ion energy of 120 keV and at the same dose, with doses ranging from 1×1013 to 3×1015 cm−2. Implanted samples were annealed with pyrolytic Si3N4 encapsulants at temperatures ranging from 700 to 1000 °C. The addition for Ga ion implants to GaAs:Ge produces p-type conductivity for all doses up to an anneal temperature of 900 °C. The p-type electrical activity of Ge in GaAs:Ge+Ga was found to increase significantly over that of GaAs:Ge for doses of 3×1014 cm−2 or below, while the original n-type activity of Ge single implants was found to change to p type for doses of 1×1015 cm−2 or above, except for anneal temperatures higher than 900 °C. The maximum electrical activation efficiency obtained with the dual implantation was 61% at a dose of 1×1013 cm−2 and an anneal temperature of 950 C.
Modification of the amphoteric activity of Ge implants in GaAs by dual implantation of Ge and As
Authors: Yeo Y. K. , Pedrotti F. L. , Park Y. S.
Published: February 2003

The electrical properties of Ge in Cr-doped semi-insulating GaAs implanted with both Ge and As have been studied by the van der Pauw Hall-effect/sheet-resistivity technique. In all cases, room-temperature implantation of both ion species was performed sequentially at the same ion energy (120 keV) and at the same dose (ranging from 1×1013 to 3×1015/cm2). Implanted samples were annealed with pyrolytic Si3N4 encapsulants at temperatures ranging from 700 to 1000 °C. Compared with Ge single implants in GaAs, the addition of As ion implants to GaAs:Ge has been found to produce a significant enhancement of the n-type electrical activity for ion doses of ?1×1015/cm2, a conductivity type conversion for intermediate doses, and little effect upon p-type activity for ion doses of ?3×1013/cm2. In most cases, the electrical activation continues to increase with annealing temperature up to 1000 °C. The maximum electrical activation efficiency obtained for these dual implants was 50% at an ion dose of 1×1013/cm2 for the p-type samples and 24% at an ion dose of 3×1014/cm2 for the n-type samples.
Evolution of shock waves in a one-dimensional lattice
Authors: Tasi James
Published: February 2003

A normal impact problem for a lattice is considered. A solution is formulated for an arbitrary interaction potential between particles at the two impact ends and simple linear force interaction between particles within each lattice. Asymptotic response of a lattice to impact with truncated interaction and to different end accelerations applied to achieve a shock velocity are considered and related to the response to a step jump in velocity. The essential difference in the asymptotic head of the pulse response for different shock excitations is a constant phase shift in the arrival time of the dispersive oscillations relative to the step jump response. Then, weakly nonlinear interactions of quadratic form are considered within a lattice. A modification is made for the far-field evolution equation previously obtained [J. Appl. Phys. 44, 4569 (1973)] for the asymptotic first-order frequency dispersion and nonlinear response to a step jump in velocity. Comparison is made with numerical solutions of the lattice equations of motion and the differences are discussed. For different end accelerations applied to achieve a shock velocity, the asymptotic nonlinear dispersive oscillations are determined by a phase shift in response relative to the nonlinear response to a step jump in velocity. The amount of the phase shift is the same as in the case of linear interaction.
Electronic structure and surface oxidation of LaNi5, Er6Mn23, and related systems
Authors: Weaver J. H. , Franciosi A. , Wallace W. E. , Smith H. Kevin
Published: February 2003

Photoelectron spectroscopy using synchrotron radiation and bulk samples cleaved in situ has been used to determine the electronic structure of LaNi5, LaNi5Ti0.1, LaNi5Zr0.1, and Er6Mn23. Comparison to analogous measurements of elemental Ni and Mn shows that the occupied states are dominated by the Ni- and Mn-derived d bands. Exposure to oxygen (up to ∼100 L of O2 at 300 °K) unambiguously results in an oxidized state for Ni and Mn at the suface.
Photoelectric properties of ZnSe/GaAs heterojunctions prepared by the close-spaced technique
Authors: Mizuno Hideaki , Nakamura Hiroshi , Shirakawa Yasuhiro , Kukimoto Hiroshi
Published: February 2003

Heterojunctions between n-ZnSe layers and p-GaAs substrates have been prepared by the close-spaced technique. The treatment of the diodes with Zn vapor has improved the spectral response as well as photoelectric conversion efficiency. These effects are explained by the reduction in the resistivity of the ZnSe layers. The best device demonstrates a nearly flat photoresponse spectrum ranging from 470 to 830 nm and a conversion efficiency of ∼5% under the solar irradiation (82 mW/cm2).
Increase in photoconductivity of polycrystalline silicon by plasma annealing
Authors: Makino T. , Nakamura H. , Nakashita T.
Published: February 2003

Absorption coefficient and photoconductivity of CVD prepared polycrystalline silicon were measured in the photon energy range between 0.6 and 2.4 eV. The photoconductivity is increased by plasma hydrogen annealing at 300 °C by a factor of more than 1000 to about 10−3 (Ω cm)−1/1015 photons cm−2 sec−1 at 2 eV. Beyond 1 eV the absorption coefficient is scarcely affected by the plasma annealing. The lifetime is estimated from the photoconductivity, resulting in about 10−5 sec for hydrogenated polycrystalline silicon.
Admittance measurements of Si-SiO2 interface states under optical illumination
Authors: Poon T. C. , Card H. C.
Published: February 2003

A new experimental technique is presented for the investigation of the localized electronic states at the silicon-silicon dioxide (Si-SiO2) interface, in which the ac conductance and capacitance of metal-oxide semiconductor structures is measured as a function of bias voltage and measurement frequency in the presence of a uniform background of optical illumination. The illumination is of photon energy in excess of the silicon energy gap, and provides for the photogeneration and supply of minority carriers to the silicon surface. The density of interface states and their capture cross sections for both majority and minority carriers can be obtained by this method, as well as possible dependencies of the cross sections on electric field at the semiconductor surface. Results obtained by conductance and capacitance measurements under illumination are in agreement with each other, and the capture cross section for minority carriers (electrons in our case) is observed to fall with increases in interface state energy towards the conduction band edge, in agreement with other workers.
Transport measurements on InP inversion metal-oxide semiconductor transistors
Authors: Klitzing K. v. , Englert Th. , Fritzsche D.
Published: February 2003

Using recently developed InP metal-oxide-semiconductor field-effect transistors with SiO2 gate insulation, the transport properties of electrons in (100) inversion layers are investigated for surface carrier densities up to 7×1012 cm−2. Conductivity and magnetoconductivity measurements are analyzed in magnetic fields up to 19.7 T at 4.2 K. The depletion charge is varied in the range 0.56–1.66×1012 cm−2. The carriers in the surface channel behave like a quasi two-dimensional electron gas. From the surface quantum oscillations, it is possible to determine the density of free carriers in the surface layer and the threshold voltage. A second electric subband is occupied at surface carrier concentrations above Ninv =4.5×1012 cm−2. The effective mobility is dominated by Coulomb and surface roughness scattering. The characteristic parameters for the two scattering mechanisms are evaluated.
Feedback sharpening of Josephson interferometer switching characteristics
Authors: Howard R. E. , Jackel L. D. , Epworth R. W.
Published: February 2003

Transfer characteristics of Josephson interferometers made with nonhysteretic junctions can be improved using positive feedback. Numerical calculations show that an interferometer’s continuous current transfer characteristic can be sharpened to a step function by sending some of the output current back through a control current path. Logic circuits using feedback should have fairly wide operating margins. In some configurations parallel fanout is possible.
Influence of oxygen adsorption on perpendicular anisotropy in amorphous Gd-Fe and Gd-Co films
Authors: Tsunashima S. , Shinoda T. , Miyatake H. , Uchiyama S.
Published: February 2003

Influence of oxygen adsorption on the perpendicular anisotropy in vacuum-deposited amorphous Gd-Fe and Gd-Co films was studied. The films, typically 500 Å thick, were prepared by coevaporation technique. As for oxygen-free films, a perpendicular anisotropy of 3×105 erg/cm3 was found, but in oxygen-adsorbed films the perpendicular magnetization was not found. This difference is due to the increase of the magnetization as well as the decrease of the anisotropy resulting from the oxidation of the surface layer. It was further found that Gd-Fe films of only 100 Å in thickness exhibit the perpendicular magnetization if the films are not exposed to the air. As for Gd-Co films, the magnetization was in-plane in as-deposited samples, but slight increase of the anisotropy was found in oxygen-adsorbed films during annealing at 200–300 °C.
High-frequency electromechanical properties of piezoelectric ceramic/polymer composites in broadband applications
Authors: Bowen Leslie J. , Gururaja Turuvekere R.
Published: February 2003

Composites of piezoelectric ceramic (lead zirconate titanate) rods aligned in an epoxy resin matrix have been evaluated for broadband transducer applications. The rods are driven at their longitudinal mode resonance frequency and bandwidth is increased by fabricating the composite in a wedge configuration. The passband can be tailored as required by altering the surface profile of the device, and in principle bandwidths of almost 100% are possible. Dimensional parameters governing the design and performance of the device are presented. The attenuation properties of the polymer phase are of prime importance in mechanically decoupling adjacent piezoelectric elements. Acoustic signal attenuation in the polymer is accomplished by the series combination of acoustic impedence mismatch and classical transmission line attenuation. Experimental and theoretical considerations suggest the mechanical Q of the polymer is so low that the active elements are insignificantly damped. As a corollary, linear theory is not reliable for the prediction of dynamic mechanical properties of piezoelectric composites.
Mechanisms of radical production in radiofrequency discharges of CF3Cl, CF3Br, and certain other plasma etchants: Spectrum of a transient species
Authors: Flamm Daniel L.
Published: February 2003

Radiofrequency discharges in CF3Cl, CF3Br, and C2F6 emit a broad continuum centered at ∼614 nm. The variation of emission intensity with residence time, oxygen additions, power and pressure are evidence that this continuum originates from a common excited species produced by electron impact dissociation of the halocarbon feed gases. The hypothesis that this species is an excited state of the CF3 radical, which undergoes a transition to a repulsive state to yield CF2+F, is consistent with the spectral evidence and explains the presence of CF2 and unsaturated fluorocarbons in these discharges.