bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of microscopic distribution of magnetic fields by electron holography
Authors: Matsuda Tsuyoshi , Tonomura Akira , Zuzuki Ryo , Endo Junji , Osakabe Nobuyuki , Umezaki Hiroshi , Tanabe Hideo , Sugita Yutaka , Fujiwara Hideo
Published: February 2003

A newly devised method for measuring magnetic fields localized in a submicron region is described. In this method, magnetic lines of force are observed as the contour lines for the transmitted electron phase with two neighboring lines containing the constant magnetic flux of h/e. Actual microscopic distributions of magnetic fields which were inaccessible by any other method, such as stray fields from a fine ferromagnetic particle, are measured.
Madey’s gain-spread theorem for the free-electron laser and the theory of stochastic processes
Authors: Krinsky S. , Wang J. M. , Luchini P.
Published: February 2003

We elucidate the correspondence between Madey’s gain-spread theorem for the free-electron laser, and a similar theorem obtained for the Brownian motion of a stochastically driven oscillator. By using suitable changes of variables, these two different theorems can be shown to be special cases of a more general result valid for a mechanical system described by a Hamiltonian of the form H = H0(p,t)+λH1(q,p,t). For such a system, when terms up to second order in λ are kept, under certain specified conditions it follows that 〈Δp〉 = (1/2) (∂/∂pi) 〈(Δp)2〉, where Δp is the change in p in time Δt, and the average is over the initial value of the coordinate qi, for fixed time and initial momentum pi. In the case of the free-electron laser, the canonical momentum p must be chosen as the total energy E of the electron, while for the driven oscillator, the necessary choice is the action variable J corresponding to the unperturbed periodic motion.
Improved performance of a ballast resistance helical transversely excited CO2 laser with water vapor and low ionization potential additives instead of helium
Authors: Nath A. K. , Biswas D. J.
Published: February 2003

Increased laser energy, peak power, and number of lasing rotational lines are reported in a ballast resistance TE CO2 laser, with small amounts of water vapor and low ionization potential additives in place of helium.
Thermal behavior of NdP5O14 lasers
Authors: Chinn S. R. , Zwicker W. K. , Colak S.
Published: February 2003

Thermally induced changes in the output behavior of a quasi-cw NdP5O14 laser under different pump duty cycles have been studied both theoretically and experimentally. With a cavity design which supports thermally stable Gaussian modes, no anomalous mode or spectral changes were observed under different heating or drive conditions. The magnitude of the remaining thermal effects on the microscopic lasing properties of the material are reviewed and compared. The decrease of laser output power at high average excitation levels is attributed mainly to a terminal state population increase with rising temperature, and results calculated from this model are in good agreement with the experimental data.
Single-crystal CsBr infrared fibers
Authors: Mimura Y. , Okamura Y. , Ota C.
Published: February 2003

Using a modified pulling down technique originally developed for drawing single-crystal fibers, single-crystal CsBr fibers have been prepared with total losses of 2–5 dB/m at 10.6 μm. The major sources of these losses were absorption by molecular impurities and scattering from surface imperfections. From spectral loss measurements it was found that the impurity which absorbed most strongly at 10.6 μm was the SO = 4 ion contained in the raw materials. The result of tensile testing has shown that 〈001〉 oriented fibers are most excellent from the viewpoint of mechanical strength.
Shear waves and ’’internal viscosity’’ in cylindrical gels
Authors: Nossal R. , Jolly M.
Published: February 2003

The torsional excitation modes of gels formed in cylindrical containers are expounded by solving a set of modified elasticity equations. These equations have been modified to contain terms which account for dissipation of mechanical energy by rearrangements of microscopic gel structures. Results are used to interpret dynamic light scattering measurements of the shear modulus G and internal viscosity η of bulk gel. Illustrative data are presented which show the concentration dependence of G and η for a series of agarose gels. A simple device for exciting observable shear modes in light scattering cuvettes is described.
Plasma etching of sputtered Mo and MoSi2 thin films in NF3 gas mixtures
Authors: Chow T. P. , Steckl A. J.
Published: February 2003

Plasma etching characteristics of sputtered molybdenum and MoSi2 thin films using various NF3 gas mixtures in a planar reactor are presented. Anisotropic (vertical-to-lateral etch ratio of ∼3) edge profiles were obtained. The etch rates of Mo, MoSi2, doped poly-Si, and SiO2 were determined as a function of rf current, reactor pressure, and NF3 concentration. At 1 A and 100 mTorr in 100% NF3, etch rates of 2490, 3440, 14000, and 670 Å/min were measured for Mo, MoSi2, doped poly-Si, and SiO2, respectively. Also, the etch rate ratios of Mo, MoSi2, doped poly- Si over SiO2 were 1.5–4, 4–8, and 12–24, respectively. Diluting the NF3 plasmas with argon or helium decreased the etch rates for all the materials studied here. At 200 mTorr and 1 A, the Mo etch rate dropped from 1800 Å/min in 100% NF3 to 540 Å/min in 20% NF3/80% Ar, while the corresponding silicide etch rate decreased from 7850 to 1130 Å/min. Auger spectroscopy measurements inferred that the desorption of molybdenum products, but not the silicon ones, may be the rate-limiting step in the etching process. Furthermore, dc voltage measurements on the rf electrode indicated a higher degree of ion bombardment at low pressures (<150 mTorr) and in NF3 plasmas diluted with inert gases.
Reply to ’’Comment on ’A photoluminescence study of beryllium-doped GaAs grown by molecular beam epitaxy’ ’’
Authors: Scott G. B. , Dobson P. J. , Duggan G. , Dawson P.
Published: February 2003

After noting Ploog, Künzel, and Collins’ criticism of that part of our earlier paper dealing with the low temperature (6.5 K) photoluminescence of Be-doped GaAs grown by molecular beam epitaxy (MBE), we have repeated our low temperature study of the samples used previously but using a lower excitation density. One sample, MBE 89, shows marked changes in its spectral features including the appearance of the Be-related line at 1.5108 eV. The other two samples remain essentially unchanged and still do not show the excitonic features observed by Künzel and Ploog between 1.504 and 1.511 eV. In order to demonstrate that this is not a limitation set by our experimental arrangement, the appearance of these features is shown in one additional sample studied.
Photoluminescence evaluation of semi-insulating GaAs grown by the liquid encapsulated Czochralski technique
Authors: Swaminathan V. , Von Neida A. R. , Caruso R. , Young M. S.
Published: February 2003

Semi-insulating (SI) GaAs crystals were grown by the liquid encapsulated Czochralski (LEC) technique and evaluated by low temperature photoluminescence and secondary ion mass spectroscopy (SIMS). The purpose of this work was to evaluate a condition in which SI crystals were sometimes not obtained even though the growth conditions were carefully reproduced. In such crystals which were n type and conducting, a strong donor related band-edge luminescence was observed. Correlated with the photoluminescence, SIMS indicated the presence of a high density of shallow donors. The primary source of these donors was identified as group VI impurities, S and Se, present in the elemental As used in the synthesis of GaAs. Silicon, another major donor impurity, was introduced mainly by reduction of silica crucibles. By carefully choosing As of high purity and by using direct synthesis of GaAs the total shallow donor concentration was reduced. This paper emphasizes the importance of the purity of the starting material and the advantage of the direct synthesis LEC for achieving reproducible growth of SI crystals. Furthermore, it shows that photoluminescence is valuable for rapid evaluation of such crystals.
Second and third harmonic generation in the presence of a direct current
Authors: Ahluwalia H. S. , May E. J. P. , Vandamme L. K. J.
Published: February 2003

The passage of a single-frequency ac through a nonlinear resistor produces a small voltage at the harmonic frequencies of the exciting signal. The effect of a simultaneously applied dc on the second and third harmonic voltages has been reported. An empirical model is proposed to explain the behavior of the first two harmonic voltages with dc. A physical explanation is put forward based on temperature-induced changes in mobility. It is shown that this leads to an expression of the same form as the basis of the empirical model.
A new formula for calculating the inductance of a superconducting strip transmission line
Authors: Jia-shan Bao , Jian Qian
Published: February 2003

This paper presents an accurate analytical formula for calculating the inductance of a superconducting strip line with a finite width and thickness. It is derived by the standard potential theory and the total magnetic free energy including both the static magnetic energy and the kinetic energy of the superelectrons. The inductance thus calculated is very close to that obtained by the numerical method even for small width-height and width-thickness ratios. This formula is proved to be accurate, convenient, and functional.
Piezoelectricity of a vinylidene fluoride-trifluoroethylene copolymer
Authors: Yamada Takeshi
Published: February 2003

A vinylidene fluoride-trifluoroethylene copolymer was studied to determine its piezoelectricity. The Curie temperature at 65 °C made it easy to polarize this material. The piezoelectric constant was proportional to the polarization. The piezoelectric constant was 22×10−12 C/N for a sufficiently polarized copolymer film with 51 mole % of VDF. The copolymer with 55 mole % of VDF had the largest piezoelectric constant under an appropriate poling condition. The piezoelectricity of the VDF-TrFE copolymer was discussed by a phenomenological theory based on dipole orientation.
High-sensitivity silicide films for optical recording
Authors: Ahn K. Y. , DiStefano T. H. , Herd S. R. , Mazzeo N. J. , Tu K. N.
Published: February 2003

The laser writing power for near-noble metal silicide films has been reduced significantly by several techniques including amorphization of the thin metal films and fabrication of trilayers. Rh films alloyed with B by thermal evaporation from an alloy slug (containing 10 wt. % B) show no crystalline structure. In bilayer structures consisting of RhB (250 Å) and Si, the characteristic reflection minimum is found to decrease in magnitude and to shift toward longer wavelength: 20% at 6000 Å for 150-Å-thick Si to 8% at 10 000 Å for 400-Å-thick Si. Static laser writing power on samples deposited on polymethyl methacrylate substrates for half-saturation of contrast with 50 ns pulse width at 6417 Å is 18 mW. Further reduction in writing power was achieved by fabrication of a trilayer structure consisting of Al(300 Å)-SiO2(900 Å)-Au(60 Å)-Si(60 Å). Typical writing power is below 10 mW for spot size slightly smaller than 1 micron.
Field ion microscopy and pulsed laser atom-probe mass spectroscopy of insulating glasses
Authors: Kellogg G. L.
Published: February 2003

Field ion microscopy and atom-probe mass spectroscopy of insulating glasses are reported for the first time. Procedures for preparing, field ion imaging, and atom-probe mass analyzing samples of pyrex (Corning 7740 glass) and fused quartz are presented.
Resonance in two coupled circular microstrip disk resonators
Authors: Ali S. M. , Habashy T. M. , Kong J. A.
Published: February 2003

A rigorous formulation to the problem of two coupled circular microstrip disk resonators is presented. Using the vector Hankel Transform, the problem is formulated in terms of a set of vector integral equations. The resonance in the two coupled resonators is then analyzed using two approaches: Galerkin’s method and a perturbative approach. It is shown that the structure can support four different resonant modes: even symmetric, even antisymmetric, odd symmetric, and odd antisymmetric. Using the vector Hankel transform and Galerkin’s method, it is also shown that the perturbation formula can be derived as a special case of the rigorous equations when the dielectric substrate is thin compared to the radius of the smaller disk. Numerical results are presented for several cases.
Switching dynamics of ac superconducting quantum interference devices and determination of rest currents
Authors: Murayama Y. , Asano A. , Kotera N.
Published: February 2003

Switching dynamics have been considered for a simple closed loop composed of a Josephson junction and inductors (an ac superconducting quantum interference device). The rest current which remains in the junction after self-resetting was calculated by either (1) assuming that the junction closes instantaneously after its current is reduced to below Imin, or (2) by means of simulation for t→∞. It is shown from a free energy viewpoint that the introduction of flux quanta is favorable. However, the final state is not the absolute minimum energy, but a metastable state.
Isothermal equations of state for H2O-VII and D2O-VII
Authors: Munro R. G. , Block S. , Mauer F. A. , Piermarini G.
Published: February 2003

Lattice parameters and cell volumes at room temperature are reported for H2O-VII to 36 GPa and for D2O-VII to 32 GPa. The data are fitted to seven isothermal equations of state from which are derived averaged values of the isothermal bulk moduli (B) and their pressure derivatives (dB/dP) as a function of pressure. For H2O over the range 2.33⩽P⩽30.9 GPa, B increases from 22.3 to 141.0 GPa while dB/dP decreases from 4.9 to 3.7. For D2O over the range 2.8⩽P⩽30.27 GPa, B increases from 30.0 to 129.0 GPa while dB/dP decreases from 4.1 to 3.1. An independent determination of B and dB/dP using a piecewise regression analysis gives B = 15.78+4.11 P, GPa with no distinction between H2O and D2O over the observed pressure ranges. The procedures employed for treating the data and the reliability of the derived results are assessed for both materials.
Au diffusion in amorphous and polycrystalline Ni0.55 Nb0.45
Authors: Doyle B. L. , Peercy P. S. , Wiley J. D. , Perepezko J. H. , Nordman J. E.
Published: February 2003

Diffusion of Au in amorphous and polycrystalline Ni0.55 Nb0.45 has been studied by Rutherford backscattering spectroscopy of heat-treated Au/NiNb couples. The diffusion process is characterized by interdiffusion of Nb and Au with NiNb showing a Au miscibility of ∼20 at. %. The Au diffusion coefficient in polycrystalline NiNb at 400 °C was found to be 1.6×10−15 cm2/s. The diffusion coefficient for Au in amorphous NiNb was found to be substantially less, ∼10−21 cm2/s at 400 °C. These results support the concept of using amorphous films as metallizations or diffusion barriers in high-temperature solid-state device applications.
Epitaxial regrowth of (100) InP layers amorphized by ion implantation at room temperature
Authors: Auvray P. , Guivarc’h A. , L’Haridon H. , Pelous G. , Salvi M. , Henoc P.
Published: February 2003

The formation and the annealing of InP amorphous layers obtained by implantation of Be (400 KeV), Cr, and Se (800 KeV) ions at room temperature are studied using Rutherford Backscattering, reflection high energy electron diffraction, transmission electron diffraction and microscopy, x-ray diffraction techniques. The reordering of (100) InP during anneal at temperatures up to 800 °C is seen to be mainly governed by the thickness of the amorphous layer, the maximum thickness of good reepitaxy from a single crystal being limited to about 2000 Å. Two cases must be considered. When the sample is amorphized up to the surface, a 2000-Å-thick regrowth occurs from the bulk only. When a crystalline layer remains at surface, the regrowth occurs from both substrate and surface so that the total thickness of the reepitaxied layer can reach 4000 Å. A schematic description of regrowth is proposed. The phenomena limiting the thickness of the reepitaxied layer and the consequences of the cold-hammered and polycrystalline layers resulting from an incomplete regrowth are discussed.
Crystallization and resistivity of amorphous titanium silicide films deposited by coevaporation
Authors: Kemper M. J. H. , Oosting P. H.
Published: February 2003

Films of titanium silicide were deposited on oxidized silicon wafers by means of the coevaporation of titanium and silicon. The atomic concentration range 0?Si/Ti?4 was studied. The films were annealed in hydrogen ambient in the temperature range 300–1000 °C. For Si/Ti≊2, annealing between 800 and 900 °C results in the formation of TiSi2 with a resistivity as low as 15–25 μΩcm and a grain size of 200–500 Å. In situ annealing in a transmission electron microscope and differential thermal analysis show that the crystallization of the silicide starts at 350 °C. The properties of the as-deposited amorphous (Ti+Si) films were found to be consistent with theories for disordered metal-metal alloys. The resistivity behavior (a low temperature coefficient, which is independent of temperature and composition) can be described in terms of Mooij’s rule. The crystallization temperature of 350 °C is in agreement with a model proposed by Buschow.
Minority-carrier lifetime in gold-diffused silicon at high carrier concentrations
Authors: Schmid W. , Reiner J.
Published: February 2003

In this paper the influence of gold doping in n- and p-type silicon on the minority-carrier lifetime is investigated for majority-carrier concentrations between 1017 and 1019 cm−3. In p-Si the data can be explained by two recombination mechanisms: recombination via the Au acceptor (Shockley-Read-Hall, SRH) and band-to-band Auger recombination. In n-Si a third mechanism with a probability ∼n occurs which is ascribed to the hole capture of the Au donor by an Auger process. The observed temperature dependence of the lifetime in the SRH region deviates considerably from Bemski’s results; however, it agrees well with recent data of Wu et al.
Capacitance spectroscopy of localized states at metal-semiconductor interfaces. I. Theory
Authors: Muret P. , Deneuville A.
Published: February 2003

The influence of interface states on some electrical properties of Schottky diodes is studied. Assuming that Shockley-Read-Hall statistics and tunnelling-like mechanism controls the flows between interface states and the semiconductor and metal bands, the occupancy of interface states is derived for two limiting cases: The discrete level and the rectangular band. The role of demarcation levels is demonstrated. The particular range consisting of forward bias is explored because its ability to vary the interface states population owing to the carrier concentration changes at the interface. The small signal admittance due to interface state is then obtained, and the behavior of the parallel capacitance Cp is peculiarly analyzed versus the frequency f and the difference between the quasi-Fermi levels of the semiconductor and metal Fn−Fm. Eventually, a method for the determination of the interface states parameters is developed. It is shown that the experimental results are to be analyzed by studying the slopes d log Cp/d log f versus normalized quasi-Fermi level position x = Fn−Fm/kT and d log Cp/dx vs x.
Capacitance spectroscopy of localized states at metal-semiconductor interfaces. II. Experiments about Ag, Au, and Ni on crystalline (111) Si surfaces
Authors: Muret P.
Published: February 2003

Metal-(111) silicon interfaces obtained by electron gun evaporation onto a clean cleaved n-doped Si surface are studied at various constant temperatures by small-signal capacitance measurement under both forward and reverse bias. The model described in the previous paper is applied and the slopes of the logarithmic capacitances or their cutoff frequencies versus junction voltage generally take the integer values which were estimated before. Moreover, these results bear out the identity of the quasi-Fermi level of electrons in the neutral region and near the interface. Thus a spectroscopy of the interface states is possible and results are interpreted owing to the model of the preceding paper. Both recombinations with the metallic electrons and the silicon holes are found, respectively, in Ni/Si and Ag/Si interfaces. Each interface shows distinct features which are tentatively correlated to the interface physical nature and metals band structures.
Silicide and Schottky barrier formation in the Ti-Si and the Ti-SiOx -Si systems
Authors: Taubenblatt Marc A. , Helms C. R.
Published: February 2003

Silicide and Schottky barrier formation has been characterized for Ti deposited on the Si(100) surface, both with and without surface oxides present. Reactions were carried out in ultrahigh vacuum, while observing electronic and chemical changes with ultraviolet photoemission spectroscopy and Auger electron spectroscopy. Ti deposited on Si shows a sharp interface, no change in Fermi level position, and no silicide formation until heated to 400–500 °C. Ti deposited on thin oxides (<20 Å) frees silicon at the interface and reacts through the oxide to form a silicide when heated to 400–500 °C. Ti deposited on thick thermal oxides also frees Si, but no further reaction occurs until heated to 700–900 °C, at which point TiOx forms near the surface. This differing behavior of thin and thick oxides is shown to be consistent with bulk thermodynamic data.
Superconducting lead particles produced by chemical techniques
Authors: Fariss T. L. , Nixon W. E. , Bucelot T. J. , Deaver B. S. , Mitchell J. W.
Published: February 2003

The superconductivity of extremely small lead particles has been studied as a function of size, surface condition, and connectivity using chemical techniques to produce particles of well-controlled size and shape suspended in insulating media. Approximately monodisperse suspensions of equiaxed, rod, and lath-shaped particles of lead halides and other lead compounds suspended in gelatin, polyacrylamide, polyvinylpyrrolidone, polyvinyl alcohol, methyl cellulose, and hydroxyethyl cellulose have been produced. These particles have been reduced to pseudomorphs of lead in the liquid phase or the suspensions have been coated on substrates and dried before reduction. Reducing solutions containing aminoiminomethanesulfinic acid are effective with particles of lead halides, lead phosphate, lead sulfate, and lead tartrate. Suspensions of smaller discrete lead particles have also been produced by direct reduction of solutions of soluble lead salts containing suitable polymers, chelating, and stabilizing agents. Dispersions with mean particle dimensions between 3 nm and 5 μm, and a narrow size-frequency distribution, have been produced. The superconductivity of the particles has been characterized by measurements of the magnetization as a function of temperature and magnetic field. The larger particles have a transition temperature of 7.2 K, the same as bulk lead; however, for particles of characteristic dimensions less than 20 nm, the transition temperature is lower by ∼0.1 K.
High pressure measurements on AlxGa1−xAs-GaAs (x = 0.5 and 1) superlattices and quantum well heterostructure lasers
Authors: Kirchoefer S. W. , Holonyak N. , Hess K. , Meehan K. , Gulino D. A. , Drickamer H. G. , Coleman J. J. , Dapkus P. D.
Published: February 2003

Absorption data on AlAs-GaAs and AlxGa1−xAs-GaAs superlattices (SL’s) and emission data on AlxGa1−xAs-GaAs quantum well heterostructure (QWH) laser diodes subjected to hydrostatic pressure (0–10 kbar) at 300 K are presented. Superlattice absorption data show that the confined-particle transitions, which partition and ’’label’’ the Γ energy band high above the band edge, all move with the same pressure coefficient of 11.5 meV/kbar. (For bulk GaAs, the pressure coefficient is 12.5 meV/kbar.) The effect of the L indirect minima on the highest observed confined-particle transitions is small; the effect of the X minima is large. At lower pressures, QWH diodes exhibit a pressure dependence similar to that of the free (unconstrained) SL’s. The data on QWH diodes demonstrate, however, a size-dependent [Lz(GaAs)<500 Å] shift in slope to a lower (8.5 meV/kbar) energy gap versus pressure coefficient at higher pressures. This change in slope can be explained by considering the effect on the light- and heavy-hole subbands of shear stresses generated within the p-n diode heterostructure.
Analysis and performance of a picosecond dye laser amplifier chain
Authors: Koch T. L. , Chiu L. C. , Yariv A.
Published: February 2003

A mathematical analysis is presented for dye laser amplifier chains used to amplify cw mode-locked dye laser pulses up to the gigawatt regime. The model permits a discussion of the important aspects of the problem such as gain saturation, pulse shaping, and the optimization of pumping efficiencies. Experimentally, an amplifier chain has been demonstrated which is simple in design and operation without sacrificing high performance. A frequency doubled Q-switched Nd:YAG oscillator alone is used to longitudinally pump three identical Brewster cells with the same flowing dye solution in each. The amplifier boosts the output of a synchronously mode-locked dye laser to obtain ∼0.5 mJ≲1 psec pulses over a ∼400 Å bandwidth. These pulses are suitable for efficient Raman shifting, frequency mixing, and continuum generation to vastly extend the spectral range of the system. Some experimental results are presented to support the mathematical model.
Diode array images of linear laser sparks
Authors: Schmieder Robert W.
Published: February 2003

The dependence of time-integrated diode array images of linear striated filamentary laser sparks on gas pressure and laser energy is described. For sparks in air, it was found that the pressure regime 100–300 Torr produces images of minimum diameter (about 150 μm) and maximum sharpness. Diode array images exhibit longitudinal and transverse luminosity profiles which differ from photographic images due to different spectral sensitivities. These data are of value in using the linear laser spark as an imaging probe of inhomogeneous gases such as turbulent reacting flows and diffusion flames.
Polarization absorption spectroscopy: Determination of the direction and degree of orientation of absorption transitions
Authors: Daniels J. M. , Cladis P. E. , Finn P. L. , Powers L. S. , Smith J. C. , Filas R. W. , Goodby J. W. , Leslie T. M.
Published: February 2003

In an ordered, directional medium, such as liquid crystals or biological membranes, it is often desirable to determine both the degree of ordering (i.e., order parameters) and the directions in space which most aptly characterize it. Here, a method is presented for determining these quantities relative to a laboratory frame. It consists in measuring changes in the light absorbed by a pleochroic dye dissolved in dilute quantity in a directionally ordered medium (e.g., nematic liquid crystal or lipid bilayer) as functions of polarization and angles of incidence. The results of testing this method on a model system of dilute mixtures of dyes in a room temperature nematic liquid crystal are presented. In principle, only six such measurements are necessary to make these determinations; however, some redundancy is desirable to obtain sufficiently accurate results. We show that an accuracy of 5% or better can be obtained from nine measurements. A detailed discussion of the errors that can be expected is given.
A real time spectrum characteristic technique for diode lasers
Authors: Halido D. , Lindström C.
Published: February 2003

A real time technique to observe the spectrum of diode lasers on a regular video monitor is described. The linear spectral dispersion in this technique allows us to determine the true mode picture of multimode diode lasers. The resolution of the experimental setup used is 0.3 Å.
Ion beam extraction with ion space-charge compensation in beam-plasma type ion source
Authors: Ishikawa Junzo , Sano Fumimichi , Takagi Toshinori
Published: February 2003

The beam-plasma type ion source that we have developed has an original ion- beam extraction mechanism. An ion beam is formed with an ion space-charge compensation by electrons which are distributed by force in the extraction region. The electrons are used in order to ameliorate an ion space-charge effect, which might be an obstacle for high-current ion-beam extraction. The space charge of ions is effectively neutralized by many kinds of energetic electrons; that is, a primary electron beam, a secondary electron beam, and high-energy plasma electrons. When the ion space-charge compensation by these electrons is effective, theoretically, the divergence of an ion beam is suppressed, the space-charge limitation of an extractable ion current is relaxed, and the shape of the ion-emission surface is improved. Therefore, a high-current ion beam with good quality can be extracted, even at a low-extraction voltage. In the experiment, the current of more than 0.1 A at the extraction voltage of 1–5 kV, which was more than ten times the normal space-charge limited current, was extracted from a single aperture under the ion space-charge compensation condition.
Cavity dumping and coupling modulation of an etalon-coupled CO2 laser
Authors: Marcus S.
Published: February 2003

A novel technique for cavity dumping or coupling modulation of a CO2 laser, has been implemented. This technique, which employs an electro-optically tuned etalon as an output coupler, offers improved efficiency as compared to conventional Brewster-angle coupling, and it provides convenient end-mirror outcoupling.
Al0.3Ga0.7P0.01As0.99 GaAs laser heterostructures grown by molecular beam epitaxy
Authors: Wagner W. R. , Cho A. Y.
Published: February 2003

Stresses commonly present in AlGaAs/GaAs laser heterostructures were reduced using Molecular Beam Epitaxy grown Al0.3Ga0.7P0.01As0.99 cladding layers. The Al0.3Ga0.7P0.01As0.99 alloy was grown using an incident P2 flux of ≊1×1014/cm2 indicating a sticking coefficient of 0.1 at a substrate temperature of 600 °C. X-ray automatic Bragg angle control curvature measurements were used to monitor the residual heteroepitaxial stress. Broadened double crystal x-ray linewidths indicated the occurrence of alloy grading and broadened interfaces. The effects of P concentration and film thickness on stress and on the existence of a misfit dislocation grid are discussed.
Effects of ion-implantation-induced damages and impurity on platinum silicide formation
Authors: Mashiko Y. , Koyama H. , Kawazu S. , Kashiwaki T.
Published: February 2003

The present paper describes the effects of damages and impurity on the formation of platinum silicide prepared on polycrystalline substrate. Damages and impurities have been introduced into polycrystalline silicon by ion implantation prior to preparing metal layer. The major analytical techniques employed are Auger electron spectroscopy, secondary ion mass spectrometry, and scanning electron microscopy. The observation indicates a formation of irregular and nonplanar structure at the platinum silicide-silicon interface caused by the damages. Also, voids at the silicide-silicon interface are observed in the sample containing implanted argon. Direct evidence that the voids are filled with argon is obtained by mass spectrometry. Mechanism of the anomalous interface formation is discussed.
A probe technique for determining the electrical potentials in an ionized corona field for the measurement of resistivity of electrostatically precipitated deposits
Authors: Goard P. R. C.
Published: February 2003

In order to determine the resistivity of an electrostatically precipitated particulate layer of high resistivity material, a new technique is described using a conducting potential probe. The space-charge potentials are first determined by the probe in a small parallel plate precipitator with wire-to-plate spacing of 75 mm at several distances from the collector plate, and a short extrapolation gives the potential at the dust surface. Using this potential and the associated measurements of collected layer thickness and current density, the operational resistivity ρf of such a layer is determined while subject to the corona currents and high electric fields of normal electrostatic precipitator operation. The theory is given for the conducting potential probe in a unidirectional ionized field of a single wire to parallel plate unit. An example of the field dependence of the operational resistivity of a fly ash is given.
Self-consistent theory for crossed-field diode current fluctuations
Authors: Rosenthal S. E. , Crawford F. W. , Harker K. J.
Published: February 2003

Applying a perturbation expansion to the self-consistent Poisson equation for a planar, space-charge-limited crossed-field diode, we have derived four universal diode functions (independent of any particular diode specification), in addition to the usual Fry-Langmuir function for unperturbed, unmagnetized planar diodes. A crossed-field diode is completely specified by three external parameters: its normalized width X = xa/λDb, anode voltage V = φa/φTb, and magnetic field Ω = ωc/ωpb. Here a and b, respectively, denote anode and cathode quantities, λDb is the electronic Debye length, ωpb is the plasma frequency, φTb is the electron temperature in volts, and ωc is the electron gyrofrequency. Evaluating the universal functions at abscissas appropriate for a particular set of X, V, and Ω then allows the calculation of the anode noise power (mean square current fluctuation at the anode) as a function of X, V, and Ω. The range of external parameters for which the theory is applicable is specified by a simple constraint relation for X, V, and Ω, which ensures that the diode is space-charge limited both with and without the applied magnetic field. The results of our analysis show that the noise level of a space-charge-limited diode increases monotonically from the reduced level at zero magnetic field. These results are for a range of magnetic fields well below the threshold where the diode enters the regime of magnetic-field-limited flow in which the noise power reaches the temperature-limited level. Thus the range of the space-charge-limited regime studied is always associated with a reduced noise level which is, nevertheless, greater than the unmagnetized space-charge-limited level.
Feasibility of dc to visible high-power conversion employing a stimulated Compton free electron laser with a waveguided CO2 laser pump wave and an axial electric field
Authors: Gover A. , Tang C. M. , Sprangle P.
Published: February 2003

We examine the feasibility of high power generation of visible radiation by a process of applying an axial accelerating electric field on electrons trapped in the ponderomotive potential of a Compton scattering free electron laser. We consider a scheme where the pump (wiggler) field is produced by a high-power pulsed CO2 laser and the signal wave is the radiation of a high-power pulsed dye laser. We propose to use a hollow dielectric waveguide in order to overcome the pump wave diffraction and obtain a long interaction length.
Theoretical studies of output performance dependence on excitation rate for electron-beam excited KrF laser
Authors: Kannari F. , Obara M. , Fujioka T.
Published: February 2003

We have developed a comprehensive computer code to analyze output performance of KrF laser excited by an intense electron beam. Especially for short pulse (<100 ns) and high excitation rate (≳1 MW/cm3) pumping, and under realizable conditions, we have calculated the intrinsic laser efficiency as a function of excitation rate. The results were compared with some experimental results which have been already reported by other groups, and a fairly good agreement was obtained. At an excitation rate of 1.5–2 MW/cm3, and at a total gas pressure of near 1.5–2 atm, an intrinsic efficiency of up to 11.5% is found to be attainable. At 3–4 atm, even at an excitation rate of near 7 MW/cm3, the efficiency of 9% is obtainable. We have also calculated the KrF* production efficiency and the laser extraction efficiency, and explained the output performance in terms of excitation rate.
Calculation of the threshold current of stripe-geometry double-heterostructure GaAs-Ga1−xAlxAs lasers, including a self-consistent treatment of the current-temperature dependence
Authors: Mattos T. J. S. , Patel N. B. , Nunes F. D.
Published: February 2003

The threshold current density of a stripe-geometry GaAs double-heterostructure laser has been calculated taking into account the influence of the dynamical processes occurring along the junction plane. The calculation includes the effects of a temperature profile, current spreading, carrier diffusion and optical mode losses. The junction current density J, which causes heat generation, is assumed to be temperature dependent. The interdependence between them is taken into account in a self-consistent way. The temperature effect is shown to be particularly important for lasers with narrow stripe widths (<20 μm).
Optimal staging of endoreversible heat engines
Authors: Rubin Morton H. , Andresen Bjarne
Published: February 2003

One way to classify performance indices of irreversible heat engines is according to how the indices change when one engine is replaced by two (or more) of the same kind in series. We investigate the performance of two endoreversible engines (i.e., heat engines with the only irreversibility being heat resistance to the surroundings) which are put in series to form a single engine, whose power output is maximized. In this unconstrained optimization the interface between the two stages, which for the present model is the intermediate temperature and the relative timing of the two engines, is arbitrary and can be used to satisfy other, nonthermodynamic constraints. Adding any constraint on the volume of the working gas does not lift this indeterminacy. The optimum composite system is equivalent to a single endoreversible engine, thus displaying a sequencing property similar to Carnot engines.
Two-photon-ionization coefficients of propane, 1-butene, and methylamines
Authors: Lee Long C. , Bischel William K.
Published: February 2003

Ion currents produced by two-photon ionization were investigated for several organic molecules. At low charge density, the ion current is proportional to the product of gas pressure and the square of laser intensity. At high gas pressure and high laser intensity, the ion current saturates. The saturation effect is well interpreted by a model including electron attachment and charge recombination processes. The two-photon-ionization coefficients were determined from the low ion current data. Among the molecules studied, trimethylamine has the highest coefficient of 3.6×10−26 cm4/W at the KrF laser wavelength of 248 nm. Such a high photoionization coefficient indicates that trimethylamine could be used to produce a high density of initial electrons for laser-controlled switches. The present results could also be used to develop new techniques for investigating the electron attachment and charge recombination processes at high gas pressures.
Effect of radiation losses on scaling laws in laser-produced plasmas
Authors: Goel S. K. , Gupta P. D. , Bhawalkar D. D.
Published: February 2003

The effect of radiation losses in determining scaling laws of electron temperature on laser flux Φ is discussed for moderate Z plasmas created by lasers in the flux range 1011–1013 W/cm.2 Temperature scaling slower and faster than Φ4/9, observed by various authors, is explained by including radiation losses in a self-regulatory model. Results of experiments on carbon plasma produced by 1-GW, 5-nsec Nd: glass laser show temperature scaling Φ0.25 and Φ0.75 , and are in good agreement with the predicted behavior.
Ion temperature and the density distribution in the corona of a dense z pinch
Authors: Finken K.-H. , Ackermann U.
Published: February 2003

Magnetic field measurements, which are performed at a dynamic z-pinch experiment, yield the ion temperature of the dense plasma column. The value of the ion temperature is consistent with results obtained from the speed of signal propagation, from the equilibrium of the pressure of the plasma boundary and from a consideration of the balance of energy. From an analysis of the speed of compressional Alfvén waves in the region between the wall and the compressed plasma channel, the density outside the dense column is derived. The electron density in the corona is about three orders of magnitude smaller than in the core.
Neutron diffraction studies of Nd2(CoxFe1−x)17 alloys: Preferential site occupation and magnetic structure
Authors: Herbst J. F. , Croat J. J. , Lee R. W. , Yelon W. B.
Published: February 2003

Rietveld analyses of room-temperature neutron powder diffraction data for seven Nd2(CoxFe1−x)17 alloys (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, 1) are reported. In the ternary systems we find that the c-type transition metal sites are preferentially occupied by Fe ions; concomitantly, the d and h sites have Co occupations larger than those predicted by stoichiometry, while the f sites deviate only slightly from random occupation. The magnetic moments obtained from the data refinements indicate a transition from a low to a high spin state on the d,  f, and h sites as Fe is incorporated into the structure; a reverse trend is exhibited by the moments on the c site.
Optical spectra of MgAl2O4 crystals exposed to ionizing radiation
Authors: White G. S. , Jones R. V. , Crawford J. H.
Published: February 2003

Exposure of MgAl2O4 crystals to 137Cs γ rays produces a broad absorption complex centered near 3 eV and at the same time destroys absorption at 4.8 and 6.4 eV which is attributed to charge transfer transitions on octahedral Fe3+ impurity ions. Thermal and optical bleaching of the 3-eV absorption complex in crystals with different Fe3+ concentration reveal that this complex is composed of absorption bands located at 2.8, 3.1, 3.6, and possibly at 3.9 eV. Analysis of the intense, persistent afterglow and conductivity after γ-ray exposure and thermally stimulated conductivity discloses a very high concentration of shallow electron traps with a prominent set of these traps having a thermal depth of ∼0.9 eV. It is proposed that antistructure disorder, e.g., Al3+ ions on tetrahedral sites, is responsible for a substantial portion of these electron traps.
Capacitance and its upper and lower bounds by the method of optimized simulated images
Authors: Chow Y. L. , Lan Y. F. , Fang D. G.
Published: February 2003

Like the classical charge image method, the optimized simulated image method gives very simple expressions for the capacitance of a conducting body and the potential field around it. Unlike the former method, however, it can be applied to arbitrary conducting bodies. Also, the simple expressions for the potential field are found to be well suited for calculating the capacitance bounds of Payne and Weinberger. These two nice properties are derived, and are demonstrated by examples. The examples are the capacitance of (i) a conducting cube and (ii) a series of conducting cylinders of finite lengths.
Ultra-small metal particle arrays produced by high resolution electron-beam lithography
Authors: Craighead H. G. , Mankiewich P. M.
Published: February 2003

Arrays of silver and gold-palladium particles smaller than 10 nm in diameter and center-to-center spacings as low as 25 nm have been fabricated by electron-beam contamination lithography in a scanning transmission electron microscope and ion milling.
Kinetic processes in the HgBr(B→X)/HgBr2 dissociation laser
Authors: Nighan William L. , Brown Robert T.
Published: February 2003

Results are reported of an investigation of fundamental kinetic processes influencing discharge and laser properties typical of the 502-nm HgBr(B→X)/HgBr2 dissociation laser. Specific attention is focused on conditions representative of electron-beam-controlled discharges. Experimental results and corresponding analysis and interpretation are presented for several laser mixtures, focusing particularly on the factors affecting discharge characteristics and HgBr(B) formation. A set of phenomenological electron-HgBr2 cross sections inferred on the basis of analysis of experimental observations is presented, along with a discussion of the effect of electron-electron collisions on medium properties at the level of fractional ionization typical of the HgBr(B)/HgBr2 laser.
Carrier transport in double-heterostructure active layers
Authors: Joyce W. B.
Published: February 2003

Use of the diffusion equation (with an effective coefficient De) for describing carrier diffusion and drift parallel to the junction in the active layer of a semiconductor double-heterostructure is justified under commonly encountered conditions, and the effective De is evaluated. This equation is basic to the description of any laser or light emitting diode phenomenon where the injected carrier density is nonuniform. UFoff
Collinear acoustico-optic diffraction using a diffuse acoustic field
Authors: Ivanov Dentcho , Burov Julian
Published: February 2003

The acoustic waves propagating in a low-loss crystal travel long distances after numerous reflections by the walls before vanishing and thus form a complex sound field in the crystal. From this sound field called ’’diffuse’’ it is possible to select different acoustic modes at given frequencies by means of flat and parallel, disposed normally to pure-mode axes of the crystal, pairs of reflecting walls which form acoustic Fabry-Perot interferometers. Some acoustic modes selected from the diffuse field are used for realizing collinear acousto-optic diffraction and thus, it is shown that the overlapping in space of acoustic and light beams may be achieved in this way. A model for determining the intensities of the selected modes is established. The model is used for calculating the efficiency of the collinear diffraction.
The effects of self-ion bombardment (30–500 keV) on the surface topography of single-crystal germanium
Authors: Wilson I. H.
Published: February 2003

High-resolution scanning electron microscopy has been used to observe the effects of self-ion bombardment on the topography of germanium surfaces. Holes (mean separation 400 Å) appeared in the surface at doses above 2×1015 ions/cm2 (ion energy 50 keV). These enlarged with increasing ion dose and developed into a complex cell structure. This structure underwent no further gross change for doses above 1×1017 ions/cm2, where the mean cell diameter was ∼1200 Å. The surface preparation was found to have no influence on the appearance of this cellular structure. Some specimens were fractured after bombardment to observe a section of the bombarded surface. A porous layer of thickness 2.5 times the projected range (Rp) was observed at doses just below those where changes in surface topography were first observed. At the highest dose (4×1017 ions/cm2) the thickness of this layer was 6Rp. The cellular surface structure was observed at all ion energies chosen so long as the energy deposited in the surface by the ion beam was kept below 0.5 W cm−2. The observed effects can be qualitatively explained by the formation of large voids. When these intersect the surface the effects of sputter etching and redeposition combine to enlarge the cell structure. At surface loadings above 0.6 W cm−2 different topographies were observed, as a consequence of the surface temperature exceeding the amorphous/crystalline transition temperature during bombardment.