bluuebunny/crossref_metadata_2025 huggingface dataset:
Velocity of neutral atoms emanating from the cathode of a steady-state low-pressure mercury arc
Authors: Eckhardt Gisela
Published: February 2004

The velocity of the neutral atoms emanating from the cathode of a steady-state low-pressure mercury-arc discharge has been studied by a gravimetric-calorimetric method. The results can be interpreted in a consistent way by attributing a superthermal rms velocity of (7.5±0.6)×103 m sec−1 to a first neutral flux component arising from cathode-spot action (and having a particle flux proportional to the arc current), and a thermal rms velocity of (2–10)×102 m sec−1 to a second neutral flux component comprising particles evaporated from the spot-free mercury surface. A model is proposed and discussed which explains the origin of the fast neutrals: It is suggested that the primary particles emerging in connection with the cathode spots are essentially all ions which have gained superthermal velocities in the vicinity of the cathode spots, and that a fraction of these ions subsequently becomes neutralized retaining most or all of its energy while, on the other hand, the primary particles evaporated from the spot-free mercury surface are all neutrals. It is shown that charge-exchange collisions were sufficiently frequent under the employed experimental conditions to account for an equilibrium between the various flux components; the existence of such an equilibrium is borne out by the experiments. While the experimental method employed did not permit a measurement of the velocity distribution, it did provide sufficient evidence to conclude that the stated neutral velocities are characteristic for the two neutral fluxes in the immediate vicinity of the cathode, and that the degree of velocity equilibration between them at distances on the order of a centimeter from the cathode should depend on various experimental parameters. The two limiting cases are discussed: that either complete velocity equilibration takes place between the two neutral flux components, or none at all.
Heating of Θ-pinch plasmas by pulsed CO2 lasers
Authors: Fuchs V.
Published: February 2004

The problem of heating a uniform Θ-pinch plasma by a pulsed CO2 laser is considered. The effort is concentrated on determining the final temperature of the plasma while taking into account its radial expansion against the confining magnetic field. It is shown how the final temperature scales with the pinch-tube filling factor and the ratio of the laser energy to the initial internal energy of the plasma. The results indicate that for large filling factors it is convenient to heat the plasma quasistatically with the use of laser pulses longer than the time it takes for an acoustic wave to traverse the plasma radius. For small filling factors, rapid heating becomes more efficient than quasistatic heating when the laser energy is much larger than the initial internal energy of the plasma.
Effect of structure and processing on electromigration-induced failure in anodized aluminum
Authors: Learn Arthur J.
Published: February 2004

The effect of barrier and porous anodizations, either singly or sequentially, on the electromigration resistance of aluminum films was characterized. Samples were tested for current densities in the 4×105−2×106-A/cm2 range and temperatures between 150 and 280°C with the median failure time being used as a basis for comparison of lifetimes. An initial barrier anodization was found to be necessary in order to consistently enhance lifetime. The addition of a porous layer as well led to the best result—an increase in lifetime by a factor of 23 at 227°C. All lifetime increases were attributable to increased activation energy for the electromigration-failure process. An increase of 0.14 eV was obtained for the double anodic structure. Results for structures having a barrier layer adjacent to aluminum were considered in terms of surface sealing of the aluminum and/or response to mechanical constraints of the overlayer. Direct porous anodization resulted in preferential oxidation at grain boundaries, thereby widening these regions, in pitting at grain boundaries, and in general cratering characteristic of this type of anodization. It was concluded that the widening phenomenon was most instrumental in reducing activation energy and lifetime.
Zero-order transverse mode operation of GaAs double-heterostructure lasers with thick waveguides
Authors: Paoli Thomas L. , Hakki B. W. , Miller B. I.
Published: February 2004

Fundamental (TE00 and TM00) transverse mode operation has been obtained from stripe-geometry GaAs double-heterostructure injection lasers with optical waveguides which are 2 μm thick. Selection of the zero-order mode perpendicular to the junction plane is achieved by providing a spatially nonuniform gain distribution within the waveguide. The nonuniformity is realized by locating the p-n junction within the waveguide such that the ratio of the thicknesses of the p and n regions is 2/1. For this choice of gain profile, the electronic gain of the zero-order mode is greater than that for higher-order modes by an amount sufficient to overcome the higher mirror loss of the zero-order mode. Along the junction plane, the stripe-geometry configuration provides zero-order mode operation. As a result, pure fundamental mode operation has been obtained at current levels up to 2.2 times threshold. Measurements are also reported for the internal stimulated efficiency, the bulk loss, and the electronic gain at threshold of the zero-order mode relative to the higher-order modes. Single-ended pulse output powers as high as 0.7 W (4×106 W/cm2 at the mirror) have been obtained from AR-coated devices without observable mirror damage.
Influence of tunneling processes on avalanche breakdown in Ge and Si
Authors: Groezinger O. , Haecker W.
Published: February 2004

The microplasma pulse rate of Ge and Si avalanche diodes has been investigated in the temperature range 30–300 K. It is shown that minority carriers which trigger the avalanche are created by tunneling at low temperatures. In Ge the turn-on probability of avalanche pulses can be explained by direct gap tunneling; contributions of indirect gap tunneling are small. At high temperature, thermal generation of minority carriers contributes to the turn-on probability. In Si on the other hand, (indirect gap) tunneling contributions are small and thermal generation determines the turn-on probability over the entire temperature range observed.
Carrier concentration profiles in Si-doped liquid-phase epitaxial Ga1−xAlxAs
Authors: Johnson W. J. , Rado W. G. , Crawley R. L. , Amey J. E.
Published: February 2004

The variation of carrier concentration with growth temperature in Si-doped Ga1−xAlxAs has been investigated as a function of the Al, As, and Si initial solution concentrations and the substrate's orientation for growth. Although all of the above parameters influence the temperature at which Si changes from an n- to p-type dopant, the temperature dependence of the carrier concentration profile was found to depend only upon the Si solution concentration and upon the substrate's orientation for growth.
Depth profile of concentration of deep-level impurities in vapor-phase epitaxial gallium-arsenide grown under various arsenic vapor pressures
Authors: Okamoto Hiroshi , Sakata Seizo , Sakai Kazuo
Published: February 2004

Vapor-phase homoepitaxial GaAs films were grown by using the Ga–As–HCl–H2 reaction system under various values of arsenic pressure PAs. Growth rate, electron mobility, shallow donor density ND, shallow acceptor density NA, and deep-level impurity density NT were measured and found to be in close relationship with PAs. Measurements of the concentration profile NT(x) of the deep-level impurities in the film were carried out by using the modified version of the transient C-V method developed by Senechal et al. Main results are (i) The energy level of these impurities is 0.89 eV from the conduction band, which is independent of growth condition, species of substrate and/or the depth position x in the film. (ii) Independently of the occurrence of the abnormal high-resistivity layer at the film-substrate interface, the concentration NT(x) in the region within a few microns from the interface is rather lower than that in the region far from it. (iii) In the film grown on the undoped substrate, the density NT(x) peaks at the transition point from the initial high-resistivity layer to the steady-state layer, whereas in the film grown on the Te-doped or Sn-doped substrate where the high-resistivity layer does not appear, no peak occurs in the profile NT(x). The energy level of 0.89 eV suggests these impurities to be copper. Most of the characteristics in the depth profile NT(x) mentioned above can be understood by taking into account the complicated behavior of copper in GaAs.
Crystal synthesis, electrical properties, and spontaneous and stimulated photoluminescence of In1−xGaxP:N grown from solution
Authors: Macksey H. M. , Holonyak N. , Dupuis R. D. , Campbell J. C. , Zack G. W.
Published: February 2004

The growth of In1−xGaxP from solution at constant temperature is described, and the distribution coefficient and incorporation of Ga in the crystal and also donor impurities are discussed. The variation of the measured mobility with composition indicates that the direct-indirect transition is near x=0.74. Photoluminescence data on direct and indirect In1−xGaxP:N are presented, and the energies of the band gap, nitrogen A line, and NN-pair peaks are plotted as a function of crystal composition. The nitrogen A line (EN) is degenerate with the Γ conduction-band minimum (EΓ) at a crystal composition of x ∼0.71. For x≤0.71 a resonant N-trap state exists above the fundamental conduction band edge. The resonant N-trap transition can be photoexcited into laser operation in x=0.69 In1−xGaxP:N at very high energy (2.246 eV–5520 Å, 77 °K) where, in fact, the recombination transition is enhanced (EN∼EΓ).
Effect of crystallization in polyethylene terephthalate electrets
Authors: Asano Yoshihiro , Suzuki Toshimasa
Published: February 2004

The crystallization has an effect on the decay lifetime of the homocharge and thermally stimulated currents (TSC) in polyethylene terephthalate electrets. The charge decay was measured over the temperature range from 100 to 140°C for the films with various degrees of crystallinity. TSC spectra were measured with the contactless electrode. The results indicate that the decay of the homocharge depends upon the dc electrical conduction process.
Observation of a core in an exploded lithium wire plasma by reflection of laser light
Authors: Leonard T. A.
Published: February 2004

A thin lithium wire which was extruded and exploded in vacuo was probed with a Q-switched ruby laser. Strong reflections of the ruby laser light were observed from a ``core'' in the plasma when the pressure was greater than 5 × 10−4 Torr. Changes in the plasma and discharge properties near this pressure suggested the possibility of a core of unvaporized wire due to current shunting through the surrounding air. The presence of this core was unexpected because of the relatively large discharge current and small wire diameter. When the pressure was below 5 × 10−4 Torr a ``core'' was never observed and there was no evidence of current shunting.
Mode-Grüneisen parameters of alkali halides
Authors: Madan M. P.
Published: February 2004

In the present paper, we examine the volume-dependent anharmonic interactions using the volume dependence of the long-wavelength optic mode phonon frequencies. The mode-Grüneisen parameters determined are shown to be in good agreement with the available experimental data.
Equivalent circuit and equipartition theorem in ideal dielectric and ferroelectric capacitors
Authors: van der Ziel A.
Published: February 2004

An ideal dielectric or ferroelectric is defined as a material involving only one time constant. The equivalent circuit for a capacitor made of such a material is derived and is used to evaluate the mean square value of the noise voltage V0 developed across the capacitor terminals. The reason for an apparent violation of the equipartition law is pointed out.
Ferroacoustic interaction in yttrium iron garnet with Rayleigh waves
Authors: Daniel Michael R.
Published: February 2004

The absorption of Rayleigh waves propagating on the surface of a YIG single crystal is reported. As a function of an external magnetic field the absorption exhibits a peak which is not believed to be ferroacoustic resonance. The strength of the interaction is at least two orders of magnitude lower than that encountered by bulk shear waves when undergoing resonance. It is attributed to Rayleigh waves on a magnetic medium being ``leaky'' rather than resonant.
Double injection in a large cylindrical p+-π-n+ germanium structure
Authors: Lee D. H.
Published: February 2004

Observation of radial double-injection semiconductor regime current in a forward biased hollow-core coaxial p+-π-n+ germanium device is reported. The cylindrical structure is an annulus with concentric p+ and n+ contacts at the inner and outer radii, respectively. Measurements of the current-voltage characteristic show linear behavior at low current and an I ∝ V2 relationship at higher injection levels. The magnitude of the double-injection current is greater than predicted from simple theory, which is attributed to diffusion effects at the carrier injecting boundaries. A correction for these effects is discussed in terms of effective radii approximations which can be conveniently incorporated into the first-order theory.
The diffusion of germanium in silicon
Authors: McVay G. L. , DuCharme A. R.
Published: February 2004

The diffusion of germanium in single-crystal silicon has been measured using the radioactive tracer 71Ge and a thin sectioning technique. The activation energy of 4.7 eV determined from the data is analyzed by considering the expected contribution due to the wrong-sized impurity ions. It is concluded that the high activation energy observed is expected from analogy to silicon self-diffusion.
Antiphase boundaries and their interactions with domain walls in ferroelastic-ferroelectric Gd2(MoO4)3
Authors: Barkley J. R. , Jeitschko W.
Published: February 2004

Antiphase boundaries (APB's) in ferroelastic-ferroelectric Gd2(MoO4)3 have been observed by etching single- and multiple-domain crystals. These boundaries form closed loops, or terminate on dislocations, external surfaces, or on domain walls. They can be generated and annihilated by moving domain walls. Space-group symmetry arguments show that APB's can exist in Gd2(MoO4)3. The crystals structure of ferroelastic-ferroelectric Gd2(MoO4)3 is discussed to describe the atomic distortions within domain walls and APB's. This qualitative analysis suggests that the free energy of an APB is of the order of the free energy of the domain wall.
Field ion microscope study on the interaction of gallium with metals. I. Pseudomorphic structure and superstructures on tungsten
Authors: Nishikawa O. , Utsumi T.
Published: February 2004

Gallium was deposited on a tip specimen of a field ion microscope by making contact in vacuum. Gallium deposited on a tip area and diffused from the tip shank at 350 to 500 °K was crystallized in the pseudomorphic structure on tungsten. The number of atomic layers of the pseudomorphic gallium was 2 to 3. The sharp helium image of the pseudomorphic gallium appeared at a voltage considerably lower than the helium best-image voltage for tungsten. The observed high evaporation field of the pseudomorphic gallium, 3.0–4.5 V/Å, may indicate that the gallium atoms in the pseudomorphic state are anomalously strongly bound to the substrate tungsten or are field evaporated as the doubly-ionized ions. Various superstructures were observed on the {112} areas after heating above 900 °K, but their detailed structures did not depend upon temperature or heating time. An unidentified underlayer may play a dominant role in determining the structure of the superstructures. No clear evidence of alloy formation was noticed in the temperature range 21 to 1500 °K.
Hardness of pure alkali halides
Authors: Gilman J. J.
Published: February 2004

An explicit expression is derived for the indentation hardness numbers of alkali halide crystals in terms of ionic binding, combined with the theory of plastic indentation. The resistance to indentation is caused by the electrostatic faults that exist at the cores of {100} 〈1̄10〉 dislocations. The theoretical hardness is given by (cgs units) H0=0.096(e2/εb4)= 1.2×10−2C44, where e is the electron charge, ε is the static dielectric constant, b is the Burgers displacement, and c44 is the elastic shear stiffness. The theoretical hardness for NaCl is 17 kg/mm2 compared with the observed value of 16.7 kg/mm2.
Studies of the thermoelectret and photoelectret states of Boswellia Glabra and ZnO-Boswellia Glabra mixtures and their applications in direct electrophotographic coatings
Authors: Pillai P. K. C. , Balakrishnan K. G.
Published: February 2004

The thermoelectret and photoelectret studies have been performed in detail in a natural plant product, Boswellia Glabra [BG(Y)] and its mixture with ZnO. Thermoelectret effect in this material is comparable with any other material. The permanent homocharge formation in the higher fields restricts the upper limit to which the photosensitive paper, with BG(Y) binders, can be charged. The photoelectret studies of this material show that it possesses a slow dark decay and a fast light decay when it is mixed with ZnO, which are the essential requirements for photosensitive mixtures. The ZnO-BG(Y) combination does not deteriorate the charge acceptance property of ZnO. Mixed with proper sensitizers for visible light, the ZnO-BG(Y) mixture is found to be suitable for photosensitive coating for direct electrophotographic-image processing systems.
Growth of silica and phosphosilicate films
Authors: Baliga B. Jayant , Ghandhi Sorab K.
Published: February 2004

Investigations of the reaction kinetics of the deposition of silica and phosphosilicate glasses were made to determine the parameters governing the rates of reactions. Dependence of deposition rates on substrate temperature shows that the reactions obey the absolute rate theory of heterogeneous reactions at a solid surface. The silane oxidation reaction is of half-order with respect to oxygen, of half-order with respect to silane, and of first-order over-all. The phosphine oxidation reaction is of second-order over-all. The unusual decrease in deposition rate with increasing oxygen concentrations, during the oxidation of silane, has been shown to originate from the adsorption of oxygen on the silicon substrates, retarding the reaction.
Coherent phonon generation by optical mixing in a one-dimensional superlattice
Authors: Yang K. H. , Richards P. L. , Shen Y. R.
Published: February 2004

With the help of the lattice momentum, phase-matched optical generation of coherent phonons with frequencies higher than 50 GHz appears feasible. We have considered two cases: (i) direct conversion of millimeter or submillimeter photons in a piezoelectric superlattice, (ii) optical mixing of two laser beams in a nonpiezoelectric superlattice.
Dislocation line kinetics as affected by high-temperature pulse irradiations
Authors: Simpson H.M. , Sosin A. , Johnson D.F.
Published: February 2004

Pulse experiments are described in which a pure copper sample was bombarded for 20 sec with 1-MeV electrons at temperatures between 293 and 430°K, then the continuing increase in accumulation of point defects at dislocations was monitored at temperature by internal friction and elastic modulus data. No discontinuity in the rate of arrival is found at the moment that the irradiation is discontinued, indicating that the arriving point defect must be characterized in its motion by an energy of 0.6 eV. The postirradiation kinetics are analyzed to show that the energy of migration of this defect along dislocations is ∼ 0.2 eV less than the energy for motion in the lattice, away from the dislocations. The above kinetic analyses are carried out with the aid of the recently formulated ``defect dragging'' theory of Simpson and Sosin and constitute further verification of this theory.
On the Steenbeck minimum principle for arc discharges and its comparison with the constant property arc
Authors: Cohen Ira M. , Whitman Alan M.
Published: February 2004

The foundations of the Steenbeck minimum principle for arc discharges are reexamined. The basis of its apparent experimental confirmation is also reexplored. It is shown that Steenbeck verified a consequence of either his minimum principle or the constant property arc by using measured values of arc radius. It is further shown that the arc radius obtained as a consequence of the minimum principle is at complete variance with experimental observations. However, the predictions of the constant property arc are shown to be in general agreement with experimental results. We conclude that Steenbeck's minimum principle is incorrect (even as an approximation), and that the constant property arc model provides an adequate description of electric arc discharges.
Electrical breakdown in a collision-dominated plasma sheath
Authors: Mikoshiba S. , Smy P. R.
Published: February 2004

The field strength at a cathode is increased by the presence of a moving plasma due to the formation of a cathode sheath in which the ion mobility is reduced by the high neutral density in the cold boundary layer formed around the electrode. If further field intensification due to surface irregularities is included, the field at the cathode reaches and exceeds 3×107 V/cm, the field emission threshold. This field can be achieved at an applied voltage between electrodes of 40 V, which is well below the Paschen minimum. This effect was studied experimentally using the argon plasma generated in electromagnetically driven shock tube for wide ranges of plasma density (109−1016cm−3), degree of ionization, and initial pressure (0.1–10 Torr). The results should form the basis for prediction of the reignition characteristics in the all important period immediately (1–10 μsec) after the cessation of an arc.
CO2 laser pulse shaping with saturable absorbers
Authors: Kleiman H. , Marcus S.
Published: February 2004

Time-dependent saturation of absorbing gases is used to alter the temporal development of pulses from an electron-beam CO2 laser. The gases used are SF6, CF2Cl2, and BCl3. Several pulse-shaping effects have been observed including ramp generation and elimination of the initial spike from a rectangular pulse.
Traveling wave oscillations in the optical region: a theoretical examination
Authors: Yariv Amnon , Armstrong Desmond R.
Published: February 2004

The interaction of an electron beam with the optical field of a periodically perturbed dielectric thin-film waveguide is considered. When the electron velocity is nearly equal to that of one of the spatial harmonics of the field, a coherent exchange of energy can take place. This interaction, which can lead in principle to a voltage-tunable optical oscillation, is examined in the light of presently available thin-film techniques. An estimate of the oscillation threshold is made.
Transient space-charge-perturbed currents following time-dependent injection
Authors: Hartmann George C. , Lipari Nunzio O.
Published: February 2004

The problem of space-charge-perturbed currents in dielectric media is studied for the case where the charge injection at one electrode is time dependent. An analytic approach is very difficult, and therefore we have solved numerically the equations governing the charge carrier dynamics. We have considered the special case where the injection has an exponential time dependence. A constant voltage boundary condition is assumed. Results are given for configurations consisting of one and two dielectric layers.
Photovoltaic properties and barrier heights of single-crystal and polycrystalline Cu2O–Cu contacts
Authors: Assimos J. A. , Trivich D.
Published: February 2004

The spectral distribution of the photovoltaic response of polycrystalline and single-crystal Cu2O–Cu contacts was measured at room temperature using a chopped light technique. The single-crystal contacts were formed by reducing the (111) surface of single-crystal Cu2O to copper using atomic hydrogen at room temperature. Prior to the reduction, a departure from stoichiometry was induced in the single crystals by treatment at 750 or 960°C in a known and controllable partial pressure of oxygen. The polycrystalline contacts were prepared from polycrystalline copper plate partially oxidized to Cu2O at 1000°C. The photoresponse measurements indicate that the dominant photovoltaic mechanisms in Cu2O–Cu contacts are hole photoemission from Cu into Cu2O when hv < Eg and electron injection from Cu2O into Cu when hv > Eg. Barrier heights determined from the threshold of the hole photoemission process measured 0.75±0.06 eV for the single-crystal contacts and 0.75±0.02 eV for the polycrystalline contacts. It is shown that the observed variation in the barrier height of the single-crystal contacts may be due to barrier lowering by the Schottky effect.
Scanning electron microscope study of laser-damaged beryllium thin films
Authors: Murr L. E. , Payne R. T.
Published: February 2004

Laser damage in Be films vacuum vapor deposited onto polished glass substrates was investigated in the scanning electron microscope. Surface scratches were observed to raise thermal gradients and promote premature melting and film degradation in Be films 0.1–0.3 μ thick for beam intensities of 40–55 MW. The damage zones were characterized by radially symmetric melting and evaporation consistent with a cross-sectional distribution of laser-beam energy. The results indicate that vaporization contributes prominently to Be film degradation by laser-beam irradiation.
IRQC parameters for Er3+ occupying sites of C2v and C3v symmetry in CdF2
Authors: Byer N. E. , Ensign T. C. , Mularie W. M. , Stokowski S. E.
Published: February 2004

Measurements have been made of the optical parameters relevant to the operation of the Er3+ infrared quantum counter (IRQC) proposed recently to detect 1.5-μm radiation. The CdF2:Er3+ crystals used for this purpose were prepared under specific conditions selected to provide different local site symmetries at the Er3+ ions. EPR measurements were employed to determine the site symmetries and the relative concentration of ions at the various sites. In particular, high concentrations of C2v sites were generated by double doping with NaF prior to crystalline growth [CdF2: (Er3+,Na+)], whereas C3v sites were generated preferentially by oxygen firing sodium-free crystals subsequent to growth [CdF2: (Er3+,O2−)]. Selective generation of these two sites permitted the unambiguous determination of their characteristic optical absorption, emission, and excitation spectra, as well as the lifetimes and radiative efficiencies of relevant excited states. In addition, double excitation using two ir sources simultaneously, was used to determine the cross section for transitions between the 4I13/2 and 4S3/2 excited states and the lifetime of the former state. The optical properties of the Er3+ ion were observed to be sensitive to the local environment associated with each site and, in particular, to the magnitude of the noncubic component of the crystalline field. Phase-lag measurements confirmed the successive-excitation model proposed to explain the conversion of 1.5-μm radiation to 540- or 660-nm radiation in the presence of an 840-nm pump. Cooperative-excitation processes, on the other hand, were observed to produce 660-nm emission when 790- or 970-nm pumps were employed. The dependence of the over-all IRQC quantum efficiency on pump flux and on the optical parameters of Er3+ is derived from solutions to the appropriate rate equations. The analysis indicates that the performance of the 1.5-μm Er:IRQC, utilizing an 840-nm pump, is nearly optimized for CdF2: (Er3+,O2−).
Proton-implanted GaP optical waveguide
Authors: Barnoski M. K. , Hunsperger R. G. , Wilson R. G. , Tangonan G.
Published: February 2004

Waveguiding in the visible spectrum has been observed in proton-implanted n-type GaP. The results obtained indicate that waveguide formation results from free carrier index change of the substrate refractive index with respect to that of the implanted layer.
``Vacuum reduction'' of rutile
Authors: Ohlsen W. D. , Johnson O. W.
Published: February 2004

Experimental results are presented demonstrating that the frequently observed ``vacuum reduction'' of rutile is, in fact, due to residual vacuum system impurities, and that no measurable reduction occurs in a clean vacuum at temperatures as high as 1000°C for times of [inverted lazy s] 100 h.
X-ray diffraction approach to grain boundary and volume diffusion
Authors: Unnam J. , Carpenter J. A. , Houska C. R.
Published: February 2004

A generalized two-dimensional diffusion model has been developed which consists of an array of boundaries coupled to the free surface and to the substrate lattice. The model makes use of three nonlinear partial differential equations which describe lattice, grain boundary, and surface diffusion. This two-dimensional model has been programmed for the IBM 360 computer using a finite-difference solution to give concentrations as a function of time. An x-ray intensity simulation program is developed to give integrated diffracted intensity for a given concentration distribution. This simulated intensity is compared with experimental intensity. Data are presented from a sample containing 8 μ of Ni on a (111)-oriented Cu crystal diffused for various times at 900°C and a similar sample with 6.5 μ of Ni diffused at 600°C. The simulations are in good agreement with experimental intensity bands. Activation energies and frequency factors are given for volume and grain boundary diffusion which are in good agreement with those literature values that are available. After a diffusion treatment at 600°C, it was found that pipe diffusion makes an important contribution to the volume diffusion coefficient. At 900°C this does not appear to be true. The contribution from pipe diffusion correlates with rocking curve data except for compositions close to that of the free surface.
Surface morphology of liquid-phase epitaxial layers
Authors: Saul R. H. , Roccasecca D. D.
Published: February 2004

The surface morphology of GaP liquid-phase epitaxial layers has been studied for a wide range of growth conditions in order to determine the origin of the commonly observed corrugated or lamellar surface structure. A double slider apparatus was used for decanting the melts to preserve the high-temperature morphologies and to permit controlled growth or meltback over selected areas of the substrate. The effect of melt supercooling was examined by varying the cooling rate and melt thickness. These results when combined with observations of the selected area meltback and regrowth experiments demonstrate that the lamellar morphology does not result from the action of capillarity forces on the last liquid to freeze or from interface instabilities associated with constitutional supercooling, as previously suggested. It is shown that the morphology is determined by the substrate orientation and is principally a manifestation of the microscopically layered nature of the liquid-solid interface.
Two-oscillator description of optical properties of oxygen-octahedra ferroelectrics
Authors: Uchida Naoya
Published: February 2004

Refractive index, birefringence, and linear electro-optic (EO) effect of BO6-type oxides have been analyzed using a two-term Sellmeier dispersion relation. Two oscillators correspond to two main transitions; the transition to dε conduction band with a transition energy of 4–6 eV and that to the dγ band with an energy of 9–11 eV. It is found that the contribution of the latter dγ transition to the refractive index in the visible to the infrared region is larger than that of the former, and that the dispersion energy Eidisp for the dγ transition is approximately equal to that for the average single oscillator. The birefringence and the linear EO effect are explainable by the polarization-induced changes in the position and the strength of the dε transition. In the ferroelectric phase, the change in the oscillator position is found to be proportional to the square of the spontaneous polarization Ps2. On the other hand, the change in the oscillator strength consists of the terms proportional to Ps2 and Ps4. The second term leads directly to two observed features: the quadratic EO coefficient depends on Ps; and a slight difference exists between the coefficients derived from the spontaneous birefringence and the linear EO effect.
Perturbation theory for the electric potential in a thin-film overlay acoustic surface-wave transducer
Authors: Wagers R. S.
Published: February 2004

A perturbation theory for the electric potential associated with a Rayleigh wave propagating on a layered surface is presented. The case analyzed is that of a thin piezoelectric film on a nonpiezoelectric substrate. The film is regarded as perturbing the Rayleigh wave of the substrate. The velocity, stress, and electric potential within the film are approximated by power series, and the coefficients of the series are found from Poisson's equation and the mechanical equations of motion in terms of the particle displacements of the unperturbed Rayleigh wave of the substrate. The results obtained using unperturbed Rayleigh wave displacements are shown to be in good agreement with exact calculations in the thin-film limit (kh≤0.2), while the use of exact particle displacements and phase velocity are shown to yield excellent agreement out to kh≤0.9. Generalities regarding the properties of the two media that control the coupling of thin-film overlay acoustic surface-wave transducers are obtained.
Stability of low-current break arcs between palladium contacts
Authors: Gray Eoin W. , Pharney Julian R.
Published: February 2004

The statistical distributions of break-arc durations have been examined as functions of arc current and number of operations under both ``clean'' and contaminated conditions. Exponential distributions were found for arcs between clean palladium electrodes operating below 0.9 A. At higher currents a Gaussian- (normal) type distribution was observed. Under highly contaminated conditions the Gaussian distribution was observed at all current levels examined. These distributions have been discussed in terms of the ``ionic-burst'' mechanism and thermionic emission. A model for the so-called activation or arc-duration enhancement of arcs is presented.
Point-cathode electron sources-electron optics of the initial diode region
Authors: Wiesner J. C. , Everhart T. E.
Published: February 2004

A realistic model of a point-cathode electron source is analyzed in this paper, and its electron optical properties are discussed. Both cathode and anode are modeled as equipotential surfaces of a sphere on orthogonal cone (SOC). The model predicts that the radius of the apparent electron source produced by this diode may be as small as 2–3 nm for field emitters and as small as 4–6 nm for strong-field Schottky emitters. This source is found to be a virtual image of the emitting area of the cathode. The image position and magnification are determined for different representative cathode shapes, and quantitative results are also presented on geometric aberrations, effects arising from the initial energies of emission, and on source current and current density. An optimum cathode apex radius for smallest source sizes is predicted to be about 200 nm for field emission and about 700 nm for Schottky emission. These results are compared with those from the often used, but less accurate, sphere model.
Effect of laser pulse rise time on heating of a magnetically confined plasma
Authors: Nguyen Duc-Long , Parbhakar Kanwal J.
Published: February 2004

For a magnetically confined plasma the effect of laser pulse rise time on heating is considered theoretically. The hydrodynamic equations are solved analytically in the asymptotic limit. We find that for a certain range the laser pulse energy requirement is quite sensitive to the rise time. By properly choosing the laser pulse rise time, the energy requirement can be decreased as much as 25%. The maximum radiation flux density is however not very sensitive and increases only slightly. It seems that fast-rising laser pulses are superior as far as flux is concerned but are inferior to slow-rising laser pulses from the point of view of energy requirement.
Magnetohydrodynamic boundary layer control with suction or injection
Authors: Wu Yung-Kuang
Published: February 2004

A steady two-dimensional magnetohydrodynamic boundary-layer control with uniform suction or injection is investigated. The transverse magnetic field is fixed to the semi-infinite flat plate and the electric field is assumed to be zero. A nonsimilar boundary-layer equation is solved numerically by a difference-differential method originated by Hartree and Womersley and improved by Katagiri. The velocity profiles and the coefficient of the skin friction are computed for various values of magnetic parameter and suction/injection parameter. The graphical plots indicate increasing boundary-layer thickness and decreasing skin-friction coefficient with increasing magnetic parameter, and also decreasing boundary-layer thickness and increasing skin-friction coefficient with increasing sunction/injection parameter. The magnetic field is found to be rather efficient in modifying the boundary layer, especially with the help of a proper seeding material.
Dwell times of thin exploding wires
Authors: Vlastós Antonios E.
Published: February 2004

Equations describing the dependence of the dwell times on the applied voltage of thin exploding wires whose restrikes are initiated at the exterior or the interior of the exploded wire are derived, using the energy equation for the ionized gas surrounding the wire and the Paschen law for the sparking potential, respectively. A comparison of the computed and the experimentally obtained dependences of dwell times on the applied voltage was made for thin constantan and tungsten wires.
Photographic studies of the transition between continuum and free molecular flow
Authors: Collins Frank G. , Sherman Frederick S. , Hurlbut Franklin C.
Published: February 2004

Sequences of pictures which show the evolution of two patterns between their continuum and free-molecule limits are presented. The first sequence examines the flow through an orifice as the orifice Knudsen number is decreased while the pressure ratio across the orifice is kept constant. The second sequence examines the flow about a washer placed at a fixed distance downstream of the orifice as the orifice Knudsen number is decreased. The effects of the first molecular collisions upon the flow pattern are clearly shown in both sequences of pictures. The photographs were obtained by employing the resonance scattering of sodium light by sodium vapor to make the flow visible in a rarefied-gas-dynamic wind tunnel.
Morphology and mechanical properties of crystalline polymers. I. Transcrystalline polyethylene
Authors: Wang Tsuey T.
Published: February 2004

A multistep analytical method is described for relating morphology to mechanical properties in crystalline polymers. The analysis is carried out at several microscopic scale levels to permit detailed consideration of morphological structures at each level. As an example, the elastic constants of transcrystalline polyethylene are determined and, upon transformation into complex moduli, the results agree well with the dynamic mechanical measurements of Takayanagi and of Kwei et al.
Emission spectra of laser-supported detonation waves
Authors: Wei P. S. P. , Hall R. B.
Published: February 2004

Laser-supported detonation waves are generated with a pulsed CO2 laser with energies up to 18 J, for a duration of 25 μsec and focused on solid surfaces in air. The time-integrated spectrum in the visible and near-uv range is found to consist mainly of N+ and O+. The temperature and the electron density in the plasma are estimated to be greater than 25 000 °K and 1.5×1017/cm3, respectively, through a theoretical analysis of the air composition.
Determination of magnetic bubble film parameters from strip domain measurements
Authors: Shaw Roger W. , Hill D. E. , Sandfort R. M. , Moody J. W.
Published: February 2004

Magneto-optical methods involving only strip domain patterns are proposed for the measurement of characteristic length l, saturation magnetization 4πMs, and domain wall energy density σw, in thin uniaxial magnetic films. Determination of l requires measurement of film thickness and the spatial period of the strip domain pattern in zero applied field as previously proposed by Fowlis and Copeland, while 4πMs and σw follow from additional measurements of M/Ms vs H as a hysteresis loop. The results of calculations which are necessary to put the methods to use are presented in detail. Experimental results are included which indicate reasonable agreement with other methods currently in use. The present method is of greater accuracy and convenience in certain cases. The effects of finite uniaxial anisotropy are quantitatively considered and shown to change the results by 6% or less for materials of practical interest.
Magneto-optic investigation of MnBi films
Authors: Lewicki G. , Guisinger J. E.
Published: February 2004

Another variation in the preparation of MnBi films from double layers of the constituents is reported. The dependence of Faraday and Kerr rotations on both composition and film thickness in these films suggests a model wherein a reacted double layer is made up of four separate layers. The variance in magneto-optic constants of MnBi reported here and previously is resolved in terms of this model.
Analog-computer studies of mixing and parametric effects in Josephson junctions
Authors: Hamilton C. A.
Published: February 2004

Analog-computer studies are made on a variety of mixing and parametric effects in Josephson junctions. The predictions of the constant-voltage model are compared with the more general behavior of a junction in a resistive circuit. A simple approximate method is developed for calculating frequency conversion efficiency and the matching condition for a junction operating in the oscillator mixer mode. A similar calculation is made for the second mode of operation, in which an external local oscillator is used. In either of these modes, frequency conversion gain is possible even in a purely resistive circuit. The conditions for parametric amplification without frequency conversion are also studied and it is found that gain occurs only when the self-oscillation frequency is near the signal frequency.
Comments on ``Behavior of simple screw dislocation arrays under an applied stress'' and ``Principles underlying the behavior of passing dislocations''
Authors: Hazzledine P. M. , Neumann P.
Published: February 2004

The limitations of the ``static equilibrium'' method for the simulation of dislocation motion are pointed out, emphasizing that the previously applied ``equation of motion'' method suffers from less severe restrictions.
Concentration-dependent diffusion of B and P in Si
Authors: Jain R. K. , Van Overstraeten R.
Published: February 2004

At high impurity concentrations, the boron and phosphorus diffusion coefficient is concentration dependent. In the present work Thai's results are modified, extended, and discussed in detail. The total diffusion enhancement factor is calculated assuming proper semiconductor degeneracy for the case of B and P diffusion in Si, for the concentration range 1017−1022 atoms cm−3 and for various diffusion temperatures. Theoretical results are compared with the available experimental results.
Charge buildup in electron-irradiated dielectrics
Authors: Gross Bernhard , Dow Julian , Nablo S. V.
Published: February 2004

Irradiation of dielectrics with nonpenetrating electron beams generates long-lasting space charges. A simple experimental and mathematical method is developed for the investigation of charge buildup during irradiation. Time-resolved charge measurements carried out with pulsed beams of 1-MeV electrons, pulse duration of 4×10−5 sec, and an average current density of 10−2 A/cm2 were used to analyze effects of charge leakage caused by radiation-induced conductivity and electron range reduction caused by retardation of the incident electrons in the internal space-charge field. Leakage is found to predominate in silica and borosilicate glass while range reduction predominates in polyethylene.
Study of aluminum oxide films by ion-induced x rays and Rutherford backscattering
Authors: Bauer Walter , Musket R. G.
Published: February 2004

Oxide films of about 0.5 and 48 μg (Al2O3)/cm2 on aluminum substrates were studied using 400-keV protons and He+ ions as probes. Energy analysis of the ion-induced x rays and the backscattered particles provided compositional information about the films. A Si(Li) detector was used to detect the O Kα and Al Kα,β x rays and a surface barrier detector was used to detect the backscattered particles. Since the samples and detectors were in the same high-vacuum chamber during all measurements, this approach afforded a direct in situ comparison of the two techniques. Owing to the energy resolution limitation of the surface barrier detector, only the ion-induced x-ray measurements provided quantitative thickness measurements of the thin oxide. For the thicker oxide both methods provided thickness information, and the stoichiometry of the oxide was obtained from the backscattering data. In addition proton stopping powers were obtained from the backscattering measurements.
Analysis of sputtering discharge by optical and mass spectrometry. I. Platinum and tantalum sputtered in argon
Authors: Westwood W. D. , Boynton R. J.
Published: February 2004

Optical emission and mass spectrometry techniques have been used to investigate the gas composition during the sputtering of platinum and tantalum in an argon discharge in a dc diode system. The optical emission technique shows that hydrogen is always present in the discharge although the mass spectrometer only detects hydrogen in the case of tantalum. For both metals, the hydrogen is due to dissociation of water vapor, either in the discharge or in the tantalum case by reaction with the tantalum, and its concentration depends on the sputtering conditions and duration and also on the sputtering and vacuum procedures used. The deposition rates of both metals increase as the hydrogen concentration decreases because a greater percentage of the discharge current is due to argon instead of hydrogen ions; changes of 20% in the deposition rate are observed due to this effect. The resistivity of the tantalum films increases with the hydrogen concentration in the discharge, if the hydrogen is due to dissociation of water vapor; no increase is observed when hydrogen is leaked into the sputtering system to increase the hydrogen concentration. It is proposed that the increase in resistivity is due to an increase in the oxygen concentration in the tantalum films, water vapor produced by outgassing being the source of oxygen. At 4.0 kV, changes in resistivity from 210 to 257 μΩ cm were observed and, at 3.0 kV, the resistivity changed from 382 to 560 μΩ cm. The optical emission technique shows promise as a tool for investigating processes taking place in a sputtering discharge without disturbing the system.