bluuebunny/crossref_metadata_2025 huggingface dataset:
Optogalvanic signals generated in a neon positive column discharge by resonant chopped cw radiation at 588.2 nm
Authors: Kane D. M.
Published: February 2003

The optogalvanic line profile for the 1s5-2p2 transition (Paschen notation) in a neon positive column discharge has been studied as a function of dye laser power (0–300 mW) and discharge conditions (2–20 mA, 1–2.5 Torr) for a variety of experimental arrangements, incorporating simultaneous absorption and emission studies. Under certain discharge conditions the sign of the optogalvanic signal changes as a function of dye laser power. A set of four rate equations describing the populations of the 1s5, 1s4, 1s3, and 2p2 levels in neon with and without resonant laser irradiation on the 1s5-2p2 transition at 588.2 nm are solved in the steady state. The steady-state values are used as initial values for numerical integration of the rate equations to show the time evolution of the various populations as the laser is switched on and off. A qualitative interpretation of the expected optogalvanic signal may be made from the results. In particular, it is seen that buildup in the 1s3 metastable density with laser irradiation on the 588.2-nm transition can explain the above observations of a sign reversal in a neon positive column discharge.
A vacuum-ultraviolet Čerenkov radiation source
Authors: Sheppard J. C. , Gearhart R. A. , Rothbart G. B. , Pantell R. H. , Piestrup M. A.
Published: February 2003

We report on measurements performed to characterize vacuum-ultraviolet Čerenkov radiation generated with a gas cell and optical system, installed in a primary beam line of the Stanford Linear Accelerator Center 20-GeV electron linac. Variation of the helium pressure in the cell resulted in collected radiation which was tuneable from 800 Å through the visible, had a bandwidth of ≂4% at 1000 Å, a photon flux of ≂1012 photons/sec mA of beam current, and a time structure identical to that of the electron beam. Measured radiation properties are compared to calculated predictions to indicate where improvements in the system design and fabrication could be made.
Electromagnetic induction in accelerated conductors with frontal compression and rear dilution of magnetic flux
Authors: Wilhelm H. E.
Published: February 2003

The initial-boundary-value problem for the electromagnetic induction in an accelerated conductor (σ<∞) located at s(t)≤x≤s(t)+a, and (i) the compression of the transverse magnetic field ahead and (ii) the dilution of the transverse magnetic field behind the moving conductor is treated in presence of fixed liners of ideal conductivity (σ=∞) in the end planes x=−b and x=+d, where −b≤s(t)≤+d−a. Two initial (t=0) configurations are considered assuming (I) a field-free conductor embedded by the magnetic gap fields B0(x)={0,B10,0} for −b<x<s0 and B0(x)={0,B20,0} for s0+a<x<+d, and (II) a magnetic field which is uniform throughout the conductor and gaps, B0(x)={0,B0,0} for −b<x<+d. By means of the time-dependent coordinate transformation ξ=[x−s(t)]/a and eigenfunction expansions, the electromagnetic fields in the moving conductor are represented as integral functionals of the boundary-values B1(t) and B2(t), where the gap fields B1(t) and B2(t) are determined analytically as solutions of two coupled Volterra integrodifferential equations. Since wave phenomena associated with the electric displacement current are neglected, the theoretical results are valid for arbitrary but nonrelativistic conductor motions, ‖ṡ(t)‖≪c. This condition is in general satisfied for explosion driven conductors.
Carrier diffusion and recombination influencing gain and current profiles in planar injection lasers
Authors: Shore K. A.
Published: February 2003

Carrier diffusion and spontaneous recombination processes are analyzed within the framework of a consistent treatment for lateral current spreading in injection lasers. The formalism allows analysis of the above-threshold behavior of the device and results of relevance to mode stability properties are obtained. The extension of the model to the analysis of three-dimensional effects following from longitudinal nonuniformities in the laser is briefly considered.
Laser triggering of a 500-kV gas-filled switch: A parametric study
Authors: Woodworth J. R. , Hargis P. J. , Pitchford L. C. , Hamil R. A.
Published: February 2003

We have investigated neodymium: yttrium aluminum garnet (Nd:YAG) laser triggering of a 500-kV, SF6-insulated gas switch for a range of laser parameters. Laser wavelengths of 266 nm and 1064 nm with nominal pulse lengths of 2- and 4-nsec full width at half maximum (FWHM) were used to trigger the switch. The switch was triggered by focusing the laser to form a breakdown arc in the gas between the electrodes. Subnanosecond jitter in the operation of the switch was obtained for 266-nm laser pulse energies as low as 5 mJ. Results obtained with the Nd:YAG laser are compared to earlier data in which the switch was triggered with a krypton-fluoride laser operating at 248 nm with a pulse length of 20-nsec FWHM. Our experimental results show that ultraviolet laser triggering gives results which are a dramatic improvement over infrared laser triggering in terms of lower jitter and smaller change in delay time with variations in applied voltage. We also see indications that the optimum laser pulse length is equal to or greater than the closure time of the switch.
Determination of stress-time histories in axially symmetric impacts with the two-gauge technique
Authors: Rosenberg Z. , Partom Y. , Mayseless M. , Falcovitz J.
Published: February 2003

We present an experimental technique for the direct measurement of stress-time histories in axially symmetric dynamic impacts, where the state of strain is not uniaxial. The technique is based on placing two different well-calibrated piezoresistance gauges in the desired location on the symmetry axis. The two measured resistance changes are then substituted in a system of two equations with two unknowns from which one obtains the axial stress and the lateral strain histories. We demonstrate the technique with manganin and constantan gauges which were calibrated both under uniaxial strain and hydrostatic conditions. As an example we bring the results of stress measurements inside thick polymethyl methacrylate targets which were impacted by thick copper discs. The measured stress-time history is then compared to that predicted by a two-dimensional Lagrangian code.
A new model for the growth of silicon dioxide layers
Authors: Lu Y. Z. , Cheng Y. C.
Published: February 2003

A new model is proposed to account for the growth of both thin and thick silicon dioxide layers. The main assumption of the model is the presence of an exponential distribution of total net charges during oxidation, which strongly affects the oxidation kinetics if the oxidizing species is in ionic form. Theoretical calculation, taking into account the influence of this internal electric field, agrees reasonably well with experimental data covering both thin and thick oxides. The model can be reduced to the well-known formula of Deal and Grove in the limit of thick oxide, and can also explain satisfactorily the effect of an external field on the oxidation rates.
Influence of ambient media on the out-diffusion of S from InP:S
Authors: Dutt B. V. , Chin A. K. , Camlibel I. , Bonner W. A.
Published: February 2003

Liquid-encapsulated Czochralski-grown InP:S samples annealed for short times of 30 min in various ambients at 550 °C show diffusion fronts suggesting an extremely rapid out-diffusion of S. In phosphorus ambient, the effective diffusion coefficient is inversely proportional to the phosphorus vapor pressure. Such a strong dependence on phosphorus vapor pressure is at variance with the generally accepted substitutional-interstitial model. The out-diffusion is fastest in vacuum, followed by hydrogen and forming gas mixtures. In inert gas medium (He), it is substantially slower. Annealing in air suggests the rapid formation of an oxide mask with little or no out-diffusion. An Arrhenius plot of the temperature dependence of the diffusion coefficient D in vacuum anneals, yields a D of 4×105 exp(−2.16 eV/kT) in the temperature range of 350–500 °C. Anneals in vacuum at 450 °C with different orientations showed that the out-diffusion is nearly orientation independent except for the observed absence of diffusion from 〈111〉-In face. The kinetics of surface reactions appear to play a significant role on the rates of diffusion.
The dynamics of photoexcited carriers in microcrystalline silicon
Authors: Komuro Shuji , Aoyagi Yoshinobu , Segawa Yusaburo , Namba Susumu , Masuyama Akio , Matsuda Akihisa , Tanaka Kazunobu
Published: February 2003

Dependences of the diffusion coefficient and the lifetime of photoexcited carriers in undoped microcrystalline silicon ( μc-Si) on the volume fraction and the grain size were observed by a transient grating method and the dynamics of photexcited carriers is discussed. Under the condition of a constant grain size, the lifetime decreases with the increase of the volume fraction but the diffusion coefficient increases with the increase of the volume fraction for any fraction larger than 0.2. The dependence of the lifetime was explained well by a carrier recombination at grain boundary regions. The dependences of the diffusion coefficient and the dark conductivity were interpreted by a percolation process.
Oxygen-related thermal donors in silicon: A new structural and kinetic model
Authors: Ourmazd A. , Schröter W. , Bourret A.
Published: February 2003

A structural model for the oxygen-related thermal donors produced at moderate temperatures (<500 °C) is presented, where electrical activity commences with clusters containing five or more oxygen atoms and arises from a silicon atom at the center of the cluster. The donor activity of a cluster is terminated upon the ejection of this central silicon atom in order to bring about stress relaxation. A large number of electrically active donor species are predicted, differing only in the number of oxygen atoms each species contains. This structural model satisfies the stringent symmetry requirements of electron paramagnetic resonance (EPR), explains the lack of hyperfine interaction with Si29 or O17 nuclei and the large multiplicity in the number of donor species observed by infrared spectroscopy and EPR. The proposed clusters are shown to be embryonic forms of the much larger rodlike defects examined in detail by electron microscopy. Chemical reaction theory is used to deduce the kinetic consequences of the structural model. Both approximate analytic and numerical solutions of the resulting coupled, nonlinear equations are presented. The numerical results provide a good description of the detailed infrared kinetic data on the growth of the individual donor species and, in addition, reproduce the well-known average kinetic data from resistivity measurements. In order to explain the dependence of the oxgyen diffusivity on the sample thermal history and the well-known diffusivity enhancement, a highly mobile oxygen-silicon interstitial complex is proposed, which provides a satisfactory description of the results of dichroic recovery experiments. It is shown, however, that the values of diffusivity deduced from donor formation studies are, in addition, strongly influenced by inhomogeneities in the oxygen distribution as well as by the presence of small, electrically inactive oxygen clusters prior to the anneal. It seems necessary to consider all these possibilities to explain the experimental data.
Electrical properties of halogen lamp recrystallized silicon films on SiO2
Authors: Vu D. P. , Chantre A. , Mingam H. , Vincent G.
Published: February 2003

The electrical properties of halogen lamp recrystallized silicon films on oxide-coated Si substrates have been investigated by capacitance technique and transport measurements. Bulk and interface defect densities revealed by deep level transient spectroscopy are lower than 5×1011 cm−3 and 1010 eV−1 cm−2, respectively. However, the generation lifetimes on the order of 0.1 μs, obtained from pulsed metal-oxide-semiconductor (MOS) capacitor techniques, cannot be accounted for by bulk or surface generation, given the very low defect densities observed. The source of defects may be the subgrain boundaries. Electron mobility measured from depletion-mode MOS transistors ( μ=700 cm2/V s) is comparable to that obtainable in bulk-type material. Subgrain boundaries do not appear to have a significant effect on carrier transport.
On the weak-field magnetoresistance of holes in Ge and Si
Authors: Nakagawa Hidemoto , Zukotynski Stefan , Reggiani Lino
Published: February 2003

The weak-field magnetoresistance in p-type Ge and Si is studied theoretically in the range from 77 to 300 K. The energy band model is based on the k⋅p perturbation calculations of Kane and includes both the nonparabolicity and the warped nature of the valence band. Light and heavy holes are included. Acoustic phonon, nonpolar optical phonon, and impurity scattering are considered. No adjustable parameters are introduced into the calculations and the material parameters are those applied successfully before to the low field mobility and Hall factor. Satisfactory agreement between theory and available experimental data is obtained. For Ge the agreement is quantitative throughout the temperature and impurity concentration ranges. For Si the agreement is good at 300 K. At 77 K the agreement in Si is satisfactory.
Irreversible and reversible annealing of paramagnetic oxygen vacancies (E′1 centers) in oxygen-implanted amorphous SiO2
Authors: Golanski A. , Devine R. A. B. , Oberlin J. C.
Published: February 2003

The creation/annihilation dynamics of E1 defects induced in thermal SiO2 by implantation of N+ and O+ ions has been studied using electron paramagnetic resonance. A new effect of the irreversible self-annealing of E′1 defects has been observed for RT O+ implants. This effect correlates with the average concentration of implanted oxygen atoms within the saturated damage volume. Low-temperature (100<T<300 °C) E1 defect annealing behavior appears to correspond to reversible oxygen vacancy charge transformation E′1⇄B2 via a hole release/trapping process. Irreversible thermal annealing of E1 centers is observed at temperatures T>500 °C. However, the isochronal annealing behavior does not correspond to Waite’s model based on the molecular oxygen diffusion mechanism.
The role of compound formation and heteroepitaxy in indium-based ohmic contacts to GaAs
Authors: Lakhani Amir A.
Published: February 2003

Ohmic contacts to n-GaAs formed by the heat treatment of In films have been investigated. The widely-accepted model for ohmic contact formation, involving the establishment of a heavily-doped layer, fails in this case because In is not a n-type dopant in GaAs. It is shown that the heat treatment results in the formation of a graded InxGa1−xAs (0≤x<1) heterojunction. This heterojunction is responsible for the ohmic behavior.
Secondary ion mass spectrometry analysis of impurity distributions across liquid-encapsulated Czochralski GaAs wafers
Authors: Homma Y. , Ishii Y.
Published: February 2003

The impurity distributions in liquid-encapsulated Czochralski-grown GaAs were studied using secondary ion mass spectrometry along the diameter of circular wafers. Si and Al concentrations gradually decrease from the center to the edge of the wafer, while B has an inverse profile with respect to Si and Al. On the other hand, Cr concentration is almost constant across the wafer. To explain the impurity profiles across the wafer, we propose a model which shows that the nonuniform impurity distributions in the GaAs melt near the solid-liquid interface during crystal growth is due to the reducing reaction of the encapsulant B2O3.
Anodic oxidation of AlxGa1−xAs
Authors: Yu Jinzhong , Aoyagi Yoshinobu , Iwai Sohachi , Toyoda Koichi , Namba Susumu
Published: February 2003

A new anodic oxidation technique for AlxGa1−xAs is developed. N-methylacetamide adjusted to a pH value of 8.0–8.5 by NH4OH can be used as an electrolyte. The oxide growth rate of AlxGa1−xAs and the amount of AlxGa1−xAs consumed in the process are independent of the mole fraction x of AlAs in AlxGa1−xAs solid, and they are 22.9 and 14.3 Å/V, respectively, when grown at a constant current density of 0.5 mA/cm2.
Growth of Sr1−xBaxF2 films on InAs by molecular beam epitaxy
Authors: Sugiyama Koichi
Published: February 2003

Heteroepitaxial films of Sr1−x BaxF2 have been deposited onto (001), (110), and (111)B oriented InAs substrates by molecular beam epitaxy. The epitaxial growth was studied by reflection high energy electron diffraction (RHEED), electron microscopy, x-ray diffraction, and secondary ion mass spectrometry (SIMS). The films grown epitaxially on the (001) and (110) substrates exhibit {111} faceting, and smooth and featureless growth occurs only on the (111)B oriented substrates. Single crystalline Sr1−x BaxF2 films lattice-matched to the InAs substrates are grown at temperatures higher than 200, 450, and 400 °C on the (001), (110), and (111)B faces, respectively. SIMS profiles indicate that the interdiffusion between epitaxial film and substrate is rather small even at a growth temperature of 520 °C. The change in RHEED patterns during the thermal cleaning of substrate surfaces is also described.
A characteristic study of the superconducting phase in the niobium-aluminum-germanium system
Authors: Kannatey-Asibu E.
Published: February 2003

A study has been made of the time and temperature dependence of the growth of the superconducting A-15 phase and its grains in the Nb-Al-Ge system. In addition, changes in the microstructure and composition of the A-15 phase have been studied using energy dispersive analysis of x rays. The data obtained have been plotted and compared with theory. The results have been used to explain the variations in the superconducting properties of this system as observed in earlier work.
A magnetostatic wave model for domain-wall collective excitations
Authors: Stancil D. D.
Published: February 2003

An analysis of collective excitations of stripe domains is presented which is similar to that used with magnetostatic waves in single-domain films. The analysis is valid when both the wavelength and film thickness are large compared to the stripe width. It is shown that the backward wave character of the waves results from the anisotropic nature of the effective susceptibility of the film obtained by averaging over many domains. Specifically, the susceptibility components parallel to the wall motion are found to be positive and constant whereas the perpendicular component is frequency dependent and can be negative. Expressions are also given for the electromagnetic fields associated with the waves.
Structure and dielectric properties of amorphous LiNbO3 thin films prepared by a sputtering deposition
Authors: Kitabatake Makoto , Mitsuyu Tsuneo , Wasa Kiyotaka
Published: February 2003

Thin films of amorphous LiNbO3 were prepared by a sputtering deposition technique. Their structure and dielectric properties were studied. The as-sputtered amorphous LiNbO3 exhibited a dielectric anomaly close to the crystallization temperature. The dielectric anomaly was explained by the dielectric relaxation and the change in microscopic structure. The high dielectric constant and the dielectric relaxation were attributed to the Li ion transfer to the adjacent O-octahedron unit in the micronetwork which is similar to the crystalline LiNbO3.
Reflectance of AlAs-GaAs and In0.28Ga0.72As-GaAs superlattices
Authors: Laidig W. D. , Blanks D. K. , Schetzina J. F.
Published: February 2003

Reflectance measurements are reported for In0.28Ga0.72As-GaAs and AlAs-GaAs superlattices over the wavelength range 300–500 nm. Superlattice layer thicknesses ranged from 46 to 368 Å for the In0.28Ga0.72As-GaAs film samples and from 77 to 612 Å for the AlAs-GaAs specimens. Peaks corresponding to the E1 and E1+Δ1 transitions of GaAs are present in all of the AlAs-GaAs spectra. Size quantization is found to have little effect on the energy positions of these peaks because of the large effective mass and parallel curvature of the conduction band near the L valleys in this semiconductor. The AlAs E1 transition, observed previously in electroreflectance studies, also appears in the AlAs-GaAs superlattice reflectance and increases in energy as the superlattice layer thickness decreases. The In0.28Ga0.72As-GaAs reflectance spectra for superlattice layer thicknesses less than 150 Å contain peaks similar to the E1 and E1+Δ1 transitions for In0.28Ga0.72As and GaAs. The lower energy peak occurs around 2.8 eV, which is intermediate between the E1 transitions for In0.28Ga0.72As (2.67 eV) and GaAs (2.92 eV). Similarly, the higher energy peak at 3.03 eV falls between the E1+Δ1 peaks for In0.28Ga0.72As (2.90 eV) and GaAs (3.14 eV). For superlattice layer thicknesses greater than 150 Å, a third peak appears near the In0.28Ga0.72As E1+Δ1 transition.
The range of light ions in polymeric resists
Authors: Adesida Ilesanmi , Karapiperis Leonidas
Published: February 2003

The technique of ion beam lithography coupled with calculations using a Monte Carlo computer program for ion penetration in solids have been used to obtain various range parameters of hydrogen, helium, lithium, beryllium, boron, and carbon ions in polymethyl methacrylate resist. In the experiment, the resist is bombarded with ions and then developed in a 1 : 1 solution of methyl isobutyl ketone and isopropyl alcohol with the developed depth monitored as a function of time. The saturated developed depth is approximated as the mean path length of the ion in the resist. The physical basis of this approximation is discussed. The projected ranges and straggles of the specified ions at energies of 5–300 keV obtained by fitting the experimental data to the total range using a Monte Carlo program are presented. These range data can be used as guidelines to determine the resist mask thickness for ion implantation and for choosing resist thickness in ion beam lithography.
A study of hydrogenated amorphous silicon deposited by rf glow discharge in silane-hydrogen mixtures
Authors: Vanier P. E. , Kampas F. J. , Corderman R. R. , Rajeswaran G.
Published: February 2003

The rf glow discharge deposition of hydrogenated amorphous silicon from silane-hydrogen mixtures has been studied as a function of silane fraction. Discharge processes were investigated using optical emission spectroscopy and mass spectrometry. The deposited films were characterized using UV and IR spectroscopy, dark conductivity, and photoconductivity. The dilution of silane in hydrogen resulted in an increase in deposition rate by as much as an order of magnitude over the rate for pure silane, for constant values of total flow rate, pressure, substrate temperature, and rf power. The dependence of deposition rate on silane fraction is attributed to changes in the electron energy distribution in the plasma. The hydrogen content and optical gap of the films are independent of the silane fraction. Photoconductivity values, corrected for slight variations of the Fermi level, increase with silane dilution.
Collection efficiency and short circuit current in polycrystalline solar cells
Authors: Sen K.
Published: February 2003

Theoretical investigations of the influence of grain size on collection efficiency and short circuit current are made. It is found that the dominant mechanism of photogenerated carrier collection at small grain size (<5 μm) is the built-in field collection, whereas at higher grian sizes (>10 μm) the collection is dominated by diffusion of carriers.
Rapid thermal annealing of modulation-doped AlxGa1−xAs/GaAs heterostructures for device applications
Authors: Pearah P. , Henderson T. , Klem J. , Morkoç H. , Nilsson B. , Wu O. , Swanson A. W. , Ch’en D. R.
Published: February 2003

High-quality molecular beam epitaxial modulation-doped heterostructures were flash annealed at several temperatures TA:750 °C≤TA≤900 °C using a rapid thermal annealing technique. Samples of bulk GaAs and bulk AlGaAs were also included in the study. Structural parameters were varied for the purpose of optimization and to determine mechanisms of electronic degradation. Layers were characterized by measurements of electron mobility (μ), sheet carrier density (ns), and by photoluminescence (PL) spectra. In all cases, the modulation-doped heterostructures displayed decreases in μ, ns and PL intensity with increasing TA above 850 °C. These trends are attributed to vacancies and traps formed during the annealing process and to transfer of the amphoteric Si dopant from donor to acceptor lattice sites in the n-AlxGa1−xAs layer. At TA=800 °C, the minimum temperature at which sufficient implant activation has been achieved, we have demonstrated that the most heat tolerant of the modulation-doped structures studied retains over 95% of its original mobility and sheet carrier density, with no fundamental changes in the PL spectrum. This constitutes a primary technological advance towards high performance self-aligned modulation-doped GaAs/AlxGa1−xAs field effect transistors.
Be-implanted In0.53Ga0.47As diodes with ideal forward current-voltage characteristics
Authors: Zemel A. , Tell B. , Leheny R. F. , Harrison T. , Bridges T. J. , Burkhardt E. G. , Liao A. S. H. , Beebe E. D.
Published: February 2003

The temperature dependence of the forward current-voltage characteristics of Be-implanted p+-n junctions in In0.53Ga0.47As is presented. The results are interpreted on the basis of a diffusion current component and a recombination current component. The best diodes obey a pure diffusion current equation, J=J0(T)exp(qV/kT) for a current range of five decades and for temperatures above 200 K.
Hardness anisotropy of III-V semiconducting compounds and alloys
Authors: Watts D. Y. , Willoughby A. F. W.
Published: February 2003

Knoop hardness anisotropy measurements have been carried out on {100} samples of InP, both undoped and doped with sulfur to 1019 cm−3, InGaAs and InGaAsP, the latter two being in layer form. The results show that the ternary and quaternary alloys share similar hardness anisotropy characteristics characterized by two maxima at about 20° from the 〈110〉 direction, and a minimum close to the 〈100〉 direction, whereas InP shows a single maximum near the 〈100〉 direction and two minima about 6–8° from 〈110〉. Sulfur doping increases the general hardness of InP, but the shape of the curve is maintained. The relative hardness curves are discussed in relation to deformation mechanisms.
Variation in the diode quality factor with the insulator layer thickness for a metal-insulator-n-semiconductor solar cell
Authors: Goel Anju , Sharma T. P.
Published: February 2003

The theoretical calculations for the diode quality factor ‘‘n’’ for a metal-insulator-n-semiconductor solar cell in the dark are presented here by taking proper account of the effective mass for the holes. These calculations show that in the dark the diode quality factor ‘‘n’’ increases with increasing insulator layer thickness ‘‘d.’’ Results of the calculations agree well with experimental values observed by Card [Solid State Electron. 20, 971 (1977)].
Local bonding arrangements of boron in doped hydrogenated amorphous silicon
Authors: Greenbaum S. G. , Carlos W. E. , Taylor P. C.
Published: February 2003

Analysis of boron-11 NMR linewidths in films of boron-doped hydrogenated amorphous silicon yields structural information concerning coordination and nearest-neighbor bonding of the dopant atoms. A heavily doped (10 at. %, B) film exhibits two distinct boron sites, both of them being threefold coordinated. A second sample containing 0.7 at.% B shows only one boron site, also threefold coordinated. Annealing studies of the latter sample suggest the formation of B-Si bonds as the hydrogen is driven off. The 11B linewidth of a compensated film (containing 0.7 at. % B and 0.6 at. % P) is comparable to that of the uncompensated sample. 11B spin-spin relaxation (T2) measurements indicate that the boron sites are clustered in all three materials.
Direct measurement of the maximum depth phase change of crystal silicon under pulsed laser irradiation
Authors: Toulemonde M. , Heddache R. , Nielsen F. , Siffert P.
Published: February 2003

Irradiation of silicon by a pulsed laser induces a surface phase change above a certain threshold. The maximum depth of this phase change has been measured by using the diffusion of dopants in the phase change. By repetitive pulsed illumination the dopant will progressively diffuse towards the maximum depth and will be homogeneously distributed through the thickness of the modified phase. Experimentally, we used a pulsed ruby laser with a 20-ns pulse duration and a repetition rate of 0.16 and 0.03 Hz. A successful comparison with our thermal model calculations was established. This model considers both the temperature dependence of optical and thermal properties of silicon.
Optimum partial pressure of cesium over negative electron affinity surface of GaP-Cs
Authors: Hagino M. , Itoh H. , Miyao M.
Published: February 2003

Optimum vapor pressures of cesium over a negative electron affinity (NEA) GaP-Cs emitter at different temperatures are determined under an equilibrium condition of cesium vapor from the emitter and metallic cesium. The activation energy of cesium desorption from the NEA GaP-Cs surface with an optimum cesium coverage is 0.98 eV. The optimum value of cesium vapor pressure over the NEA GaP-Cs emitter at room temperature is estimated to be about 3×10−13 Pa by extrapolating the vapor pressure values measured at higher temperatures. It is proposed that the coexistence of a Cs-Sb film with the NEA GaP-Cs emitter is useful for maintaining the optimum cesium vapor pressure over the NEA emitter.
Atomic mixing and electron range effects in ultrahigh-resolution profiles of the Ta2O5/Ta interface by argon sputtering with Auger electron spectroscopy
Authors: Seah M. P. , Hunt C. P.
Published: February 2003

An assessment is made of the effects of atomic mixing and electron range on the profile shape and interface resolution measured in the composition depth profiling of elemental layers on elemental substrates, using Auger electron spectroscopy. A practical method is derived for extracting these two parameters. For compound overlayers, preferential sputtering and pileup effects are included and this can sharpen the interface, as demonstrated by measurements in the Ta2O5/Ta system. The profiles for oxygen show resolutions of 1.41±0.07 nm at 28.4 nm and 1.74±0.10 nm at 96.3 nm. These resolutions involve atomic mixing contributions of 0.66 and 0.83 nm, respectively, in close agreement with the predictions of Lindhard, Scharff, and Schio/tt’s theory.
Theory of sedimentation of aggregated particulate systems
Authors: Zimmels Y.
Published: February 2003

Sedimentation of mono- and polydispersed aggregated particulates is considered with due regard to effects of volume changes which follow aggregation. It is shown that velocities and flux densities depend on volume fractions occupied by particles in slurry and within aggregates, if they are monodispersed, and also on size and volume fraction distributions if they are polydispersed. Velocities of smaller and lighter aggregates may be reversed due to motion of larger and heavier ones. Increase of total volume fraction occupied by particles in slurry, decrease of their volume fraction in aggregates, and increase of standard deviation of related distributions enhance reversal of velocities of larger and heavier aggregates. In continuous steady-state sedimentation velocity of slurry must be adjusted so as to offset negative velocities which may occur in the slurry. Illustration of numerical examples is provided and significance of results discussed.
Performance of a novel injection-locked excimer laser
Authors: McKee Terrence J. , Hastie S. D. , Weeks R. W.
Published: February 2003

Improvements in temporal and spatial coherence of XeCl and KrF excimer laser emission using pulsed injection locking are described for a novel discharge circuit contained within a single laser. Using standard techniques, spectral linewidths of 0.005 nm with divergence of 0.15 mrad are observed, providing an improvement of approximately 3×104 in brightness over a standard excimer laser of similar active volume.
Reliability of the isothermal bulk modulus deduced from model equations of state
Authors: Munro R. G. , Block S. , Piermarini G. J.
Published: February 2003

The evaluation of the isothermal bulk modulus of a material by the technique of fitting model isothermal equations of state to experimental data is discussed. A sometimes serious difficulty in this application of model equations is identified, and the relationship between the error in the measured lattice parameter or the pressure and the error in the deduced value of the bulk modulus is investigated.
Optically pumped InGaAsP/InP distributed feedback lasers
Authors: Temkin H. , Dolan G. J. , Logan R. A.
Published: February 2003

Electron beam writing and wet chemical etching have been used to form high-quality first- and second-order diffraction gratings on InGaAsP/InP laser structures. Optical pumping of a set of small, 50×200-μm gratings with the period changing in 25 Å increments yields a tunable array of single-mode lasers operating in the 1.5-μm region with a peak power of ∼5 W/facet. The wavelength tunability range of ∼270 Å corresponds to the width of the gain curve of the quaternary structure. Comparison of the first- and second-order gratings fabricated on the same wafer indicates superior performance of the latter.
A bismuth layer-structured ferroelectric ceramic bulk-wave oscillator
Authors: Toda Kohji , Takenaka Tadashi , Sakata Koichiro
Published: February 2003

A bismuth layer-structured ferroelectric ceramic is described as a substrate material for a bulk-wave oscillator. The oscillator of the delay-line type consists of two interdigital transducers and an amplifier for constructing a feedback loop. The oscillator has application to moderately high-frequency operation because of the use of interdigital electrodes and the fast wave velocity of 4270 m/s in a hot-forged ceramic Pb0.15(NaBi)0.425Bi4Ti4O15.
Study of the variation of refractive index and material dispersion with wavelength from attenuation data
Authors: Datta Arup K. , Paul A. , Sanyal G. S.
Published: February 2003

Variation of refractive index, extinction index, and material dispersion of a sodiumborosilicate glass with wavelength has been studied between 800 and 1800 nm from attenuation data obtained for samples of different thicknesses. Both the refractive index and the extinction index curves show that the OH stretching vibrational overtone near 1410 nm gives rise to Sellmeier-type oscillation (anomalous dispersion) superposed on the normal dispersion curve for the glass. The estimated normal dispersion curve of the glass obtained by drawing the base line through the impurity oscillations fits well into a single oscillator Sellmeier equation. The oscillator and the dispersion energy parameters were obtained by extrapolating the (n2−1)−1 vs λ−2 straight line. The material contribution to the time delay dispersion for signal propagation was estimated from these values.
Calculation of electromagnetic field strength, reflectivity, transmission, and absorption of n-layer thin metallic films
Authors: Tien Z. J. , Lyons K. B.
Published: February 2003

We present a calculation of the fields within a metallic heterostructure system for the purpose of optimizing the scattering efficiency of one component. The example chosen is a Ge-Bi heterostructure. The calculation, carried out by a new technique which results in considerable simplification for the case of absorbing media, yields as well the field value within each layer of the heterostructure.
Estimating effects of processing conditions and variable properties upon pool shape, cooling rates, and absorption coefficient in laser welding
Authors: Chande T. , Mazumder J.
Published: February 2003

This paper examines the role of traverse speed, Beer–Lambert absorption coefficient β, surface reflectivity, and changing liquid thermal conductivity upon the shape of the melt pool and the cooling rates that occur. The dependence of β upon processing conditions is also examined. A three-dimensional variable property, moving heat source, quasi-steady-state, finite difference model for heat conduction into the substrate during laser welding is used. With an increase in traverse speed, the pool flattens out and is swept back, and cooling rates increase. An increase in β sharply decreases the depth of penetration. With the onset of melting, changes in reflectivity did not change pool shape significantly. An increase in effective liquid metal thermal conductivity increases melt pool aspect ratio. Cooling rates increased as the energy density in the pool decreased. A dimensionless melt front velocity Φ is defined such that cooling rates exceed 1000 K/s as Φ approaches unity. The product βz, where z is the depth of penetration, is shown to vary linearly with the natural logarithm of Φ. These results imply that β affects depth of penetration more than the width, that an upper bound for β may be deduced from Φ, that variations in surface reflectivity are less critical in laser welding, that the maximum thickness that can be welded in a single pass decreases as fluid flow becomes more dominant in the melt pool, and that cooling rates increase as pool energy density decreases, especially for values of Φ<100.
Radiation-induced thermal noise in optoacoustic detection cells
Authors: Stewart R. B. , Diebold G. J.
Published: February 2003

When radiation is strongly absorbed in an optoacoustic detection cell, fluctuations in the radiation intensity give rise to thermal noise within the cell. The spectral density of the thermal noise thus generated is dependent on both the frequency response of the cell and the power spectral density of the radiation source. The frequency response function for the spectrophone cell is determined by application of elementary linear response theory to a solution of the heat equation for a uniformly heated cylinder. The power spectral density of coherent and incoherent radiation sources can be determined from their respective intensity autocorrelation functions. Radiation sources are discussed with regard to obtaining the smallest root-mean-square temperature fluctuations in the spectrophone cell. It is shown that optoacoustic noise is minimized by using a stabilized laser operating well above threshold.
Generation of negative ions in tandem high-density hydrogen discharges
Authors: Hiskes J. R. , Karo A. M.
Published: February 2003

An optimized tandem two-chamber negative-ion source system is discussed. In the first chamber high-energy (E>20 eV) electron collisions provide for H2 vibrational excitation, while in the second chamber negative ions are formed by dissociative attachment. The gas density, electron density, and system scale length are varied as independent parameters. The extracted negative ion current density passes through a maximum as electron and gas densities are varied. This maximum scales inversely with system scale length R. The optimum extracted current densities occur for electron densities nR=1013 electrons cm−2 and gas densities N2R in the range 1014–1015 molecules cm−2. The extracted current densities are sensitive to the atomic concentration in the discharge. The atomic concentration is parametrized by the wall recombination coefficient γ and scale length R. As γ ranges from 0.1 to 1.0 and for system scale lengths of 1 cm, extracted current densities range from 8.0 to 80 mA cm−2. The relative negative-ion yields from single-chamber and tandem two-chamber systems are compared. Estimates are made for the rates of polar dissociation of H2 molecules and H+3 ions, and these rates are compared with the dissociative attachment rates.
Stark effect of atomic sodium measured in a hollow cathode plasma by Doppler-free spectroscopy
Authors: Moreno F. , Alvarez J. M. , Amaré J. C. , Bernabeu E.
Published: February 2003

The Stark widths of the 5896-Å (3 2P1/2→3 2S1/2) neutral sodium hyperfine lines in the presence of charged perturbers were measured by means of laser saturation spectroscopy. The plasma containing the sodium atoms and the perturbers was generated in a hollow cathode discharge. The Baranger and Brechot theories for the line shape of neutral atom transitions in a plasma has been extended to hyperfine structure and applied to the hyperfine components of sodium D1 line. The theoretical and experimental results were compared and the electronic density and temperature in the discharge were evaluated.
Effect of dephasing on the molecular absorption in a two-frequency field
Authors: Nayfeh Munir H. , King Kevin K. , Shobaki J.
Published: February 2003

The absorption of a molecule in the field of a fixed frequency coherent wave is studied using a simple, classical one-dimensional anharmonic oscillator model. The absorption is found to develop structure in the presence of a second mode of varying frequency. The structure is found to be sensitive to the intensity and wavelength of the tunable field and to wash out in the presence of collisions.
Excitation of electromagnetic waves by an axial electron beam in a slow wave structure
Authors: Tripathi V. K.
Published: February 2003

An axial electron beam passing through a slow wave structure is unstable to an electromagnetic perturbation whose phase velocity equals the velocity of the beam. This phenomenon of Čerenkov emission is the basis of all traveling wave tubes. In this paper a simple treatment of excitation of electromagnetic waves in a slow wave structure, viz., two parallel planes partially loaded with a dielectric is presented. When the effects of a guide field or a background plasma are ignored, the dispersion relation is quite simple. It is in the form of a coupling between a TM mode of a stationary electron plasma-filled slow wave structure and the beam mode. In the presence of a guide magnetic field, the electron motion is predominantly one-dimensional and the growth rate of instability is considerably modified. At relatively higher gas pressures, when a background plasma is created by the beam, the mode structure is considerably modified, leading to a reduction in the growth rate, hence to the efficiency of the device.
Two-photon laser-induced fluorescence monitoring of O atoms in a plasma etching environment
Authors: DiMauro L. F. , Gottscho Richard A. , Miller Terry A.
Published: February 2003

Atomic radicals are usually the most important reactants in plasma processing. For example, in dry etching or development of organic photoresists, O2 plasmas are used to generate O atoms which can etch the resist spontaneously. However, concentration measurements of these reactive atoms have been limited largely to indirect and often unverifiable methods such as emission spectroscopy, making process optimization difficult. We demonstrate the applicability of two-photon laser-induced fluorescence to monitor atom concentrations in situ by exciting O atoms at 226 nm and detecting fluorescence at 845 nm. A detection limit of <1013 atoms cm−3 is determined using downstream electron paramagnetic resonance spectroscopy. Noise from background plasma-induced emission is eliminated by firing the laser at a time when the applied voltage crosses zero and the emission is extinguished. From the relative intensities of the O(2p4 3P) fine-structure components, the plasma temperature is found to be thermalized with the ambient walls. This technique should also be applicable to detection of other atoms found in plasma reactors, such as N, Cl, S, and H.
Forbidden (M1) lines in the spectra of titanium, vanadium, chromium, iron, and nickel observed in a tokamak plasma
Authors: Finkenthal M. , Bell R. E. , Moos H. W. , Group TFR
Published: February 2003

A time-resolving spectrograph has been used to survey the forbidden magnetic dipole emissions of titanium, vanadium, chromium, iron, and nickel ions injected into the TFR (Tokamak de Fontenay-aux-Roses) plasma. A number of magnetic dipole transitions within the n=2 ground configuration of the isoelectronic sequences from FI to BI were identified in the tokamak spectra; in some cases, experimental values of the wavelength were measured for the first time. The spectrograph had a photoelectric multispectral detector and a calibrated linear photometric sensitivity; thus, reliable determinations of the brightnesses in typical tokamak discharges could be made for these lines.
Enhanced penetration of field-aligned currents into a Lorentz plasma in a stochastic magnetic field
Authors: Jacobson Abram R. , Moses Ronald W.
Published: February 2003

We show that anomalously fast current penetration into a plasma can result from the nonlocal electrical conductivity caused by a stochastic magnetic field. We calculate the admittance of a plasma slab subjected to an oscillating surface electric field along B. The effect of increasing stochasticity (or of increasing electron mean free path) is to make the admittance less dissipative and more inductive.
Thermal properties of some lubricants under high pressure
Authors: Richmond J. , Nilsson O. , Sandberg O.
Published: February 2003

The thermal conductivity λ, specific-heat capacity ρcp, and the point of glass transition have been determined for a range of lubricants. These included Santotrac 40; LAD 2201, a naphtenic mineral oil; Oxilube 50/150; and 5P4E, a polyphenyl ether. The thermal properties were determined by a hot-wire probe method. Pressure was varied from 0–1.5 GPa and the range of temperature covered was in general 20–110 °C although Oxilube was taken down to −24 °C. The thermal conductivities at 1.5 GPa were found to be roughly twice that of the oils at atmospheric pressure. The temperature dependence of the glass formation pressure was found to be quite different for the oils studied. The results obtained will be particularly useful for people studying elastohydrodynamic lubrication.
Au/Ti resistors used for Nb/Pb-alloy Josephson junctions. II. Thermal stability
Authors: Murakami Masanori , Kim K. K.
Published: February 2003

In the preceding paper bilayered Au/Ti resistors were found to have excellent electrical stability during storage at room temperature after preannealing at an elevated temperature, which is essential to design logic and memory circuits of Nb/Pb-alloy Josephson junction devices. The resistors could contact directly with the Pb-alloy control lines in which Pb and In atoms which are known to intermix easily with Au atoms are contained. Since Pb and In atoms in the control lines are separated from Au atoms of the resistors by thin Ti layers, thermal stability at the contacts is a major concern for use of the Au/Ti resistor material in the Josephson devices. In the present study, surface morphology change and diffusion mechanism at the resistor/control-line contacts were studied using x-ray diffraction and scanning electron microscopy for square-shaped Au/Ti resistors covered by Pb-In layers. The samples were isothermally annealed at temperatures ranging from 353 to 423 K. The diffusion did not occur immediately after annealing at these temperatures. After the incubation period, the interdiffusion was observed to initiate at the edges of the resistors facing to the center of the cathode. Significant amounts of the In atoms in the Pb-In layers were observed to diffuse into the Au layers of the resistors, forming AuIn2 compounds under the Ti layers. By measuring growth rates of the AuIn2 layers, the diffusion coefficients and the activation energy for the layer growth were determined. Also, by analyzing changes in the In concentration in the Pb-In layers during annealing, interdiffusion coefficients of In atoms in the Pb-In layers were determined using a computer simulation technique. The activation energy was about 1.1 eV. Since these diffusion coefficients were found to be very close to those determined previously in bulk materials, the diffusion kinetics is believed to be controlled by the lattice diffusion. Based on the present results, several methods to reduce the interdiffusion between Pb-alloy and Au/Ti resistors were proposed.