bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of the resistivity of inhomogeneous conducting ``fine lines''
Authors: Kirkpatrick E. S. , Mayadas A. F.
Published: February 2004

The mechanisms contributing to the resistivity of the Al–Cu thin-film conducting stripes used as connections on chip microcircuitry are analyzed. The excess resistivity due to the presence of copper in the stripe, both in solution and as a precipitated compound, is studied here by a general theory of mixtures and by computer simulations. Consequences of the finite size of a strip are predicted, leading to systematic increases in resistivity and variations of the resistance within populations of similarly prepared stripes. We obtain some quantitative estimates of the conditions under which such size effects became significant, and analyze the role of different preparation techniques on these size effects.
Consideration of lattice translations in computer studies of grain-boundary coincidence
Authors: Bruggeman G. A. , Bishop G. H.
Published: February 2004

The proposal that boundaries between crystals related by a high-density coincidence misorientation will not contain shared atom sites is examined. The rigid lattice translations which reputedly destroy boundary coincidence in computer-simulated minimum-energy grain-boundary configurations are compared with the set of special displacements which conserve the pattern of coincidence sites. The lattice of all such displacements has been termed the ``DSC lattice''. It is shown that most of the computed translations cited as evidence in support of the proposal are very nearly DSC lattice vectors, and hence shared atoms are still present in the boundaries, in most cases, after the translations. Therefore, little justification for discarding the concept of atom sharing in grain-boundary structures is provided by the computer calculations performed thus far. The importance of considering the properties of the DSC lattice in computer modeling of coincidence boundaries, both in setting up the computer program and in evaluating its results, is clearly indicated.
Decay and thermal reignition of low-current cylindrical arcs
Authors: Kimblin C. W. , Lowke J. J.
Published: February 2004

Measurements have been made of the critical reignition fields for decaying 5-mm-diam plasmas formed initially from steady-state wall-stabilized arcs of from 12 to 36 A in air. It is found that the reignition field for a given plasma conductance (a) is independent of the initial temperature profile of the plasma and (b) corresponds closely to the field given by the steady-state arc characteristic. These results suggest that the temperature profiles of the decaying plasmas from low-current arcs correspond closely to the steady-state temperature profiles which have the same conductance. The effects are consistent with theoretical predictions made using the energy-balance equation, assuming local thermodynamic equilibrium.
Effect of thermal history on helium diffusion and solubility in vitreous B2O3 and sodium borate glasses
Authors: Shelby J. E.
Published: February 2004

Helium diffusivity and solubility in vitreous B2O3 and sodium borate glasses (0–7 mol% Na2O) can be decreased by as much as 30% by thermal annealing. It is concluded that this decrease is due to thermally induced volume relaxation. Since these measurements can be made while the sample is being annealed, they can be used to determine the time dependence of the volume relaxation process. The relaxation time at 182°C for vitreous B2O3 as determined from the time dependence of the helium diffusion coefficient is approximately 6 × 104 sec.
Defect structure and electronic donor levels in stannic oxide crystals
Authors: Samson S. , Fonstad C. G.
Published: February 2004

By measuring the conductivity of stannic oxide crystals as a function of oxygen partial pressure at elevated temperatures, it is shown that the dominant native defect in SnO2 is a doubly ionizable oxygen vacancy. Both donor levels of this defect, the first 30 meV deep and the second 150 meV deep, are identified and a model is presented that explains previous results. The behavior in hydrogen is contrasted to that in oxygen, and preliminary results are presented indicating that hydrogen introduces a donor 50 meV deep.
Radiative tunneling in parallel and cross electric-magnetic fields in InSb
Authors: Tsai Tung-Iin , Thomas G.
Published: February 2004

A theoretical analysis of a model for the emission of radiation from InSb at very low temperatures is presented. The model assumed a depletion region, such as would be caused by non-Ohmic contacts, and a bulk region. The presence of a magnetic field causes different quantization conditions in the two regions which can give rise to current instabilities and radiation emission. In the case of parallel magnetic and electric fields, the wave function is solved ``exactly'' (neglecting losses) by matching boundary conditions at the interface between the two regions. In the cases of cross magnetic and electric fields, the Hamiltonian is transformed into the familiar double harmonic oscillator Hamiltonian and well-known results applied. Finally, the threshold for instabilities is calculated by means of a photon generation and loss rate equation.
Predicted electron transport coefficients and operating characteristics of CO2–N2–He laser mixtures
Authors: Lowke J. J. , Phelps A. V. , Irwin B. W.
Published: February 2004

Calculations have been made of transport coefficients of electrons in gas mixtures for ratios CO2:N2:He of 1:1:8, 1:2:3, 1:7:30, and 1:0.25:3. New cross sections for CO2 derived from swarm experiments are used together with previously published cross sections for N2 and He. Curves are presented of the predicted electron drift velocity, transverse and longitudinal diffusion coefficients, and ionization and attachment coefficients for E/N values ranging from 10−18 to 1 × 10−15 V cm2; E is the electric field strength and N the gas number density. Examples are given of derived distribution functions and comparisons are made with a Maxwellian distribution function. The percentage of the input electrical power which excites vibrational processes coupled to the 001 upper laser level of CO2 is given as a function of E/N. The maximum efficiency from these calculations increases for increasing ratios of N2:CO2, because the proportion of energy used to excite the bending and stretching modes of CO2 is then reduced. By assuming a recombination coefficient of 10−7 cm3 sec−1, the operating E/N for self-sustained glow discharges is predicted as a function of current density for various laser mixtures by equating the ionization rate to the attachment and recombination rate.
Stationary charge transport in metal-semiconductor-metal (MSM) structures
Authors: El-Gabaly M. , Nigrin J. , Goud P. A.
Published: February 2004

Important physical processes affecting charge transport in the metal-semiconductor-metal (MSM) structure have been studied from the diffusion theory point of view, in combination with boundary conditions based on thermionic emission theory. At current densities exceeding about 0.1 A cm−2, the stationary unipolar charge transport of injected charge carriers, to which the problem reduces if thermal and avalanche generation of electron-hole pairs can be neglected, is described by the conduction current equation and Poisson's equation. Charge conduction through a semiconductor with nonuniform electric field and mobile-charge distribution is described using the low-field diffusion constant and field-dependent mobility. The current-dependent concentration of mobile charges at the M-S interfaces represent the boundary conditions. Physical processes in four MSM structures (PtSi-n Si–PtSi), differing in doping concentration (ND = 4.4 and 12 × 1014 cm−3) and semiconductor width (L = 4 and 10 μm), have been investigated numerically at two different temperatures (Tc = 300 and 423°K). At current densities exceeding about 5 A cm−2, the investigated structures can be regarded as trap free, if they have a semiconductor trap density of the order of 1012 cm−3 or lower. The diffusion and space charge of injected carriers significantly affect the electrical characteristics of the structures. Depending on the semiconductor temperature, donor concentration, and current density, the width of the diffusion-affected region of the semiconductor varies from 0.2 to 0.8 μm. At small current densities, the structure current increases exponentially with applied voltage; at current densities exceeding 1–5 A cm−2, this current increase is significantly reduced because of the space-charge effect of the mobile carriers. For still greater applied voltages, the I-V characteristic levels off almost completely. In comparison with the room-temperature characteristic, the high-temperature characteristic is shifted towards slightly lower voltages at small currents, while the large space-charge effect of the mobile carriers at high current levels can cause these I-V characteristics to intersect.
Auger recombination in a semiconductor under a magnetic field
Authors: Takeshima Masumi
Published: February 2004

The Auger recombination lifetime of the excess carriers in a semiconductor under an applied magnetic field is calculated on the basis of a simple two-band model. It is predicted that the magnitude of the lifetime shows an oscillation with the change of the magnetic field when the cyclotron energy and the band-gap energy are of comparable order of magnitude.
Angular selectivity of lithium niobate volume holograms
Authors: Gaylord T. K. , Tittel F. K.
Published: February 2004

The angular selectivities for the reconstruction of volume-phase holograms in doped and nominally pure LiNbO3 crystals have been measured. The half-power angular widths for reading were found for the cases studied to be in agreement with theoretically predicted values.
Magnetic resonance spectrometer measurements of atomic hydrogen surface recombination
Authors: Mandl A. , Salop A.
Published: February 2004

Measurements have been made of the recombination efficiency γ of atomic hydrogen on Vycor, borosilicate glass, fused quartz, and Dri-Film surfaces using a pulse-sampling magnetic resonance technique. The values obtained were of the order of 10−4 for all surfaces except fused quartz, for which the recombination efficiencies were about 6 × 10−4.
Determination of dielectric parameters for films at microwave frequencies
Authors: Dube D. C. , Natarajan R.
Published: February 2004

A technique for measuring the dielectric constant and loss of isotropic films by mounting the specimen longitudinally at the center of a rectangular waveguide is proposed. Experiments have been performed at 9.375 GHz on the samples of Mylar and Teflon films ranging in thickness from 75 to 250 μm. The experimental results agree well (within 1–2%) with the accepted values. Analytical numerical results for typical samples are also given.
Temperature dependence of photoluminescence from germanium-doped and undoped gallium arsenide
Authors: Dingle R.
Published: February 2004

Changes in photoluminescence intensities, energies, and band shapes as a function of temperature in the range 4.2–300 K lead to the identification of germanium as a 40 ± 2 meV deep acceptor in GaAs. Luminescence due to this acceptor quenches near 200 K in favor of a high-energy band that grows out of the low-temperature bound and free-exciton structure. The origin of the 300 K luminescence is considered and it is attributed to band-to-band recombination.
Superconductivity transition temperatures of rf reactively sputtered NbN Films
Authors: Buttig K. , Liemersdorf H. , Kinder H. , Reichelt K.
Published: February 2004

Niobium nitride films of a thickness ranging from 500 to 3000 Å have been deposited by reactive rf sputtering of niobium in a nitrogen/argon atmosphere. A water-cooled substrate holder was used. The partial pressure of nitrogen was varied systematically between 0 and 10−3 Torr at two different argon pressures. Generally, the substrate was set on anode potential but in some cases a bias voltage was applied. The experiments showed that the transition temperature was strongly dependent upon the partial pressures of nitrogen and argon. In the sputtering experiments without bias very steep transition curves were obtained. The highest transition temperature was Tc = 14.5 K. The structures of films were examined by x-ray and TEM transmission methods. The investigations made evident that rf sputtering is a method by which high transition temperatures can be obtained, even at high residual gas pressures and unheated substrates.
Low-energy sputtering yield of the (111) and (1̄1̄1̄) faces of GaAs
Authors: Cooper C. Burleigh , Hart Robert G. , Riley James C.
Published: February 2004

The sputtering yields of the (111) and (1̄1̄1̄) faces of a GaAs crystal under normal bombardment by 100-eV Ar+ ions were measured by target weight loss. The yield for the (111) face was found to be 0.169 molecules/ion and for the (1̄1̄1̄) face about 6% less.
Dielectric constants of quartz. I. Theory
Authors: Pradoux Denise , Blanc Franc̊ois , Fanguin René , Raoult Gaston
Published: February 2004

We have theoretically studied the propagation of guided waves in anisotropic media, and have obtained approximate results for two particular planes. The two waves that can propagate have a structure very close to classical waves, and the difference in wavelength for every mode is given.
Application of molecular-beam techniques to the study of neutral particles in thermal plasmas
Authors: Gersh Michael E. , Sides Gary D. , Tang S.Y. , Muschlitz E.E.
Published: February 2004

The application of low-energy molecular-beam techniques to the analysis of the neutral (metastable and ground-state) particles emitted by a thermal plasma is described. The technique is illustrated with the use of an apparatus that contains a rotating slotted-disk velocity analyzer and an inhomogeneous-field deflecting magnet. The beam source is a hot-cathode low-voltage continuous discharge in a rare gas. With this apparatus the Landé g factor was found to be 1.51 ± 0.01 for Ne 3P2 and 1.50 ± 0.02 for Ar 3P2, in accord with theory. In addition, measurement of the velocity distributions of the two Ne metastable atoms (3P0 and 3P2) demonstrated that they could be characterized by Maxwell-Boltzmann distribution functions with different temperatures for the two states.
Current to a moving cylindrical electrostatic probe
Authors: Hoegy W. R. , Wharton L. E.
Published: February 2004

The current collection characteristics of a moving cylindrical Langmuir probe are evaluated for a range of probe speeds and potentials which are applicable to earth and planetary measurements. The current expressions derived include the cases of the general accelerated current, sheath area limited current, orbital motion limited current, and retarded current. For the orbital motion limited current, a simple algebric expression is obtained which includes and generalizes the Mott-Smith and Langmuir expressions for both a stationary probe and a rapidly moving probe. For a rapidly moving probe, a single formula adequately represents both the accelerated and the retarded current.
High-efficiency Nd3+ : LiYF4 laser
Authors: Sharp E. J. , Horowitz D. J. , Miller J. E.
Published: February 2004

Pulsed room-temperature laser action has been observed in Nd3+ : LiYF4 at 1053 nm. A threshold of 8 J and a slope efficiency of 0.82% was obtained with a 60% reflectivity output mirror. These results are compared to Nd3+ : YAG data taken in the same cavity. Loss coefficients are calculated for each material and are compared.
Spectral emissivity of nonisothermal semi-infinite slabs of transparent materials
Authors: Madjid A. H.
Published: February 2004

The expressions for the normal and the directional spectral emissivity of effectively infinite slabs (that is, slabs that are virtually opaque to radiation) of transparent materials in the presence of constant temperature gradients normal to the surface are derived; the results are related to the isothermal emissivities, and conditions are specified under which the effects of the temperature gradient may be neglected. The ambiguity, which rests in the fact that the slab is not at the same temperature throughout, is resolved by defining the emissivities in relation to a comparison blackbody which is at the surface temperature of the slab.
Injection and removal of ionic charge at room temperature through the interface of air with SiO2
Authors: Woods M. H. , Williams R.
Published: February 2004

A method has been found for introducing ions into SiO2 that are highly mobile at room temperature. This is done by contaminating the surface of the oxide with a salt containing the ion to be introduced, followed by charging with a corona discharge. Positive ions move rapidly through a thin layer of oxide and accumulate at the silicon interface where their presence is detected by means of C-V measurements. Charge introduced in this way can be subsequently removed by charging with a negative corona, followed by washing in water and annealing.
Pumping of GaAs1−x Px : N (at 77 °K, for x≲0.53) by an electron beam from a gas plasma
Authors: Holonyak N. , Campbell J. C. , Lee M. H. , Verdeyen J. T. , Johnson W. L. , Craford M. G. , Finn D.
Published: February 2004

The design features and operating parameters of a cold-cathode gas plasma electron beam apparatus for bombardment excitation of semiconductor samples is described. The gas plasma apparatus is capable of electron beam energies > 50 keV and current densities ≳50A/cm2, which are sufficient for semiconductor laser operation. Although photopumping and high surface losses do not permit the observation of an A-line peak in 0.41019/cm3), the deeper pumping of the gas plasma electron beam source permits observation of the A-line, as is demonstrated on x = 0.53 material. The deeper excitation afforded by the gas plasma electron beam apparatus, and lower over-all surface losses have permitted laser operation of indirect crystal (x > xc) made quasidirect by the N trap, as is shown (77 °K) on the A-line transition in x = 0.47 (x > xc ≈ 0.46) GaAs1-x Px : N− (N < 1019/cm3).
LPE GaAs/(Ga, Al)As/GaAs transmission photocathodes and a simplified formula for transmission quantum yield
Authors: Liu Y. Z. , Hollish C. D. , Stein W. W. , Bolger D.E. , Greene P.D.
Published: February 2004

GaAs/(Ga,Al)As/GaAs transmission photocathodes were fabricated by a multiple layer liquid epitaxy technique using GaAs substrates. The GaAs substrate was subsequently removed by bubble etching. Transmission mode white light sensitivity of 340 μA/lm and an electron diffusion length of 5 μm or more can be routinely achieved. The reflection sensitivity was found to be lower than that of a similarly prepared layer grown directly on the GaAs substrate. The spectral response, when analyzed with the yield formula, indicated negligible recombination at the GaAs / (Ga,Al)As interface. Also, despite the almost perfect lattice match between GaAs and AlAs, some bowing of the GaAs / (Ga,Al)As samples was observed, suggesting the presence of internal stresses. A simplified formula is derived for the transmission quantum yield which enables graphic solution of surface recombination velocity at the photocathode input surface and the ratio of photocathode thickness to the electron diffusion length without tedious computer calculations.
Grüneisen data from the free surface velocity of thermoelastic materials
Authors: Oswald R. B. , McLean F. B. , Schallhorn D. R. , Oldham T. R.
Published: February 2004

A technique is presented for the measurement of the Grüneisen parameter Γ of a solid from the free surface velocity induced by pulsed energy deposition. The technique is applied to both energy -(internal energy density) dependent and energy-independent Grüneisen data. The measurements employ a velocity interferometer to determine the free surface velocity of solids exposed to a pulsed electron beam. For the cases where Γ is independent of temperature, or energy density, the Γ values are obtained from the maximum free surface velocity as a function of incident fluence. Energy-dependent Grüneisen data are extracted by an analysis based on the differentiation of the free surface velocity with respect to the initial energy density of the solid. The analysis takes into account the effects of both the finite exposure time of the electron pulses and the delay time of the interferometer. Results are presented for Al, Cu, Ge, and Si in a temperature range where Γ is constant. In addition, for silicon Γ is measured as a function of energy over the temperature range 50–300°K, where Γ is strongly energy dependent. In all cases the results are in excellent agreement with the thermodynamic values.
Damage produced by high-speed liquid-drop impacts
Authors: Engel Olive G.
Published: February 2004

The state of knowledge regarding the pressure that develops and the pressure distribution that exists between an impinging liquid drop and a planar solid as a consequence of impact is reviewed. Experimental evidence is cited which indicates that radial jetting flow of drop liquid occurs at a later time than that indicated by theoretical treatments. The criterion for termination of the no-flow regime is developed analytically, and the regime that sets in after this criterion is realized is explored phenomenologically.
Change of vibrational temperature due to laser action in CO2 lasers
Authors: Avivi P. , Dothan-Deutsch F. , Keren H. , Ben-Yosef N.
Published: February 2004

The influence of laser action on the change of the vibrational temperature Tν of the asymmetric stretch mode of CO2 in the discharge of an electrically excited CO2 laser is investigated, employing a periodically switched laser. The vibrational temperature change ΔTν is calculated from the measured excess of vibrational energy stored in a nonlasing discharge as compared to that in the gas under lasing conditions. Results are presented for ΔTν as a function of Tν for different values of discharge currents. The gas compositions were CO2–He and CO2–He–N2.
Properties of a single-level surface state induced by Be implantation into Si–SiO2 interfaces
Authors: Fahrner W. , Goetzberger A.
Published: February 2004

Be ions implanted in an Si–SiO2 interface constitute the first measured single-level surface state at Ec − E=0.70 eV. Time constant dependence on surface potential was in good agreement with theory. Capture cross sections were determined σp=10−13 cm2 for holes and σn=10−10 cm2 for electrons. The Be ions form an efficient recombination center.
Anomalously high ``mobility'' in GaAs
Authors: Wolfe C. M. , Stillman G. E. , Spears D. L. , Hill D. E. , Williams F. V.
Published: February 2004

A high-purity GaAs sample with a measured room-temperature mobility of 15 200 cm2/V sec is examined in detail. Resistivity and Hall measurements are in reasonable agreement with a previously developed model which shows that conducting inhomogeneities can result in anomalously high measured mobilities. A sizeable number of precipitates (probably gallium) are observed in the sample.
Characteristics of infrared photodetectors produced by radiation doping
Authors: Gross Chris , Mattauch Robert J. , Viola Thomas J.
Published: February 2004

High-energy electrons (≈7 MeV) were used to radiation dope extrinsic silicon. Both n- and p-type silicon photodetectors were fabricated using this doping technique. The 500°K blackbody responsivity, spectral response, and peak detectivity were determined for these devices. The peak detectivity values measured were 4.8×1011 cm Hz1/2 W−1 at 2.15 μ for 0.1-Ω cm n-type devices and 3.7×1011 cm Hz1/2 W−1 at 40 μ for 10-Ω cm p-type detectors. A comparison of the thermally generated background majority carrier concentration for radiation-doped and conventional impurity-doped detectors is made.
Proposal of periodic layered waveguide structures for distributed lasers
Authors: Wang Shyh
Published: February 2004

Here new periodic structures are proposed for distributed lasers, utilizing the thickness variation introduced in a multilayer thin-film optical waveguide. Wave propagation in such structures is analyzed. Expressions are derived for the amount of distributed feedback and possible scattering losses. From the coupled-wave equations, the laser-oscillation conditions are set up. Computational results for the GaAs–GaxAl1−xAs and dye lasers are presented. The applicability of the proposed scheme for distributed feedback to semiconductor, dye, and solid-state lasers is discussed.
Relation between apparent and true activation area
Authors: Baskes Michael I. , Thompson Anthony W.
Published: February 2004

It is shown that the true activation area A* is less than the apparent activation area B*, and the difference between A* and B* is calculated in terms of quantities obtainable in a tensile test. This result depends on the assumptions discussed in the paper, but represents a generalization of previous work in the sense that a sinusoidal stress field need not be assumed.
Comments on ``Grain boundary contrast in field-ion microscope images''. I
Authors: Smith D. A. , Smith G. D. W.
Published: February 2004

The work of French and Bishop is compared critically with previous attempts to explain the images of grain boundaries in field-ion micrographs. It is argued that the assumption that the regions adjacent to a boundary behave as rigid bodies is unrealistic for low-angle boundaries and dubious for high-angle boundaries in the light of existing theories and experimental observations. In the absence of relaxation it is difficult to relate stepped spiral contrast in the field-ion image to dislocations unless they have very wide cores. Combined transmission electron microscopy and field-ion microscopy can be used to clarify the nature of grain boundary dislocations.
Calculation of transient photocurrents in insulators with trapped space charge
Authors: Hermann A. M.
Published: February 2004

The transit times and pulse shapes of photoinjected carriers moving in the presence of trapped space charge are derived. Two distributions are considered: uniformly trapped space charge, and trapped space charge decreasing exponentially in position from the injecting electrode. The pulse shapes are in some cases similar to those arising from transient space-charge-limited currents. The results in the case of the exponentially trapped space charge may have application in analysis of pulses taken in the presence of space charge trapped in the excitation layer or on the surface of insulators.
In-pile migration of fission product inclusions in mixed-oxide fuels
Authors: Michels L. C. , Poeppel R. B.
Published: February 2004

Migration velocities of fission-gas bubbles and solid fission-product inclusions in uranium-plutonium mixed oxide under irradiation have been obtained. Trails behind migrating second-phase particles are observed upon etching a polished metallographic section from an irradiated fuel pin. It was determined from the microstructure and the reactor power history that these trails were produced during one reactor power cycle of known duration. Particle velocity was computed from the observed trail length and the duration of the power cycle. Velocities varied between 1 and 10 Å/sec for particles with diameters between 1 and 10 μ. The temperature was between 1585 and 1850°C, and the average temperature gradient was [inverted lazy s]5400∘C/cm. In all cases, the particles moved in the direction of increasing temperature. The measured velocities for both bubbles and solid inclusions are shown to be in agreement with the calculated velocities based on a surface-diffusion mechanism with Qs*, the surface heat of transport, equal to 100 kcal/mole.
Pressure and temperature dependence of the elastic constants of LiBr and LiCI
Authors: Ching L. S. , Day J. Paul , Ruoff Arthur L.
Published: February 2004

Measurements of the pressure and temperature dependence of the second-order elastic constants of LiBr and LiCl single crystals have been made by the ultrasonic interferometric technique at temperatures from 220 to 340°K, and pressures up to 3.5 kbar. The adiabatic elastic constants (in units of 1011 dyn/cm2) and the isothermal pressure derivative of the adiabatic constants (unitless) at 295°K are as follows (where C00=(1/2)[C11 + C12 + 2C44]): For LiBr, C11 = 3.959, C44 = 1.909, C00 = 4.843, dC11/dP = 10.42, dC44/dP = 1.67, dC00/dP = 8.27. For LiCl, C11 = 4.963, C44 = 2.503, C00 = 6.124, dC11/dP = 10.42, dC44/dP = 1.70, dC00dP = 8.34. The three measured quantities C11, C44, and C00 are given, respectively by ρν112, ρν442, and ρν002, where ρ is the density and the v's are the sound velocities at a specific pressure and temperature. The Deybe temperatures are calculated from the second-order elastic constants at four temperatures on the interval 220–340°K.
Conduction, permittivity, internal photoemission, and structure of electron-beam-evaporated yttrium oxide films
Authors: Riemann E. , Young L.
Published: February 2004

A study has been made of thin electron-beam-evaporated yttrium oxide films. The oxide structure was found to be polycrystalline, with grain sizes of the order of 100 Å, by electron microscopy. dc conduction measurements were made and a Frenkel-type of conduction mechanism was proposed. Step response and bridge dielectric loss measurements were compared. Internal photoemission was used to obtain metal/oxide barrier heights of 3.14 and 3.72 eV in an Al-Y2O3-Al structure.
Grain boundary friction in copper subjected to neutron irradiation and fatigue
Authors: Strible Fred C. , Cady James R.
Published: February 2004

The grain boundary friction of pure (99.999%) annealed, polycrystalline copper has been investigated as a function of neutron irradiation and fatigue. Neutron irradiation was found to suppress the magnitude of the grain boundary peak as observed by measurements of internal friction. This result is attributed to inhibited grain boundary movement caused by the interaction between irradiation-generated defects and the grain boundaries. After intensive irradiation, the grain boundary peak is completely eliminated. Fatigue also suppressed the magnitude of the grain boundary peak. The fatigue effect is attributed both to reduced grain boundary viscosity, and to peak broadening caused by an increased spectrum of relaxation times. The effects of neutron irradiation and fatigue appear to be additive at the lower levels of irradiation. However, after intensitive irradiation, fatigue causes the material to soften, probably by mechanisms similar to those causing fatigue softening of cold worked materials. The latter effect is reflected in a large increase in background friction and restoration of a slight grain boundary peak.
Frequency response of acoustic surface wave filters. I
Authors: Ganguly A. K. , Vassell M. O.
Published: February 2004

The transfer function of an acoustic surface wave filter is derived from first principles by calculating the current induced on the receiver transducer when an impressed voltage is applied to the generator transducer. By manipulating the equations of motion and the boundary conditions that govern the mechanical and electromagnetic variables, it is shown that the normal component of the electric displacement inside the substrate, and ultimately the surface charge density, can be related to the Fourier transform of the electric potential outside the substrate by means of a dielectric response function. An exact expression for the latter function containing full piezoelectric coupling is deduced, and a numerical prescription given for calculating from it the three important material parameters of the theory—effective relative dielectric constant, effective electromechanical coupling constant, and surface wave velocity. Difficulties associated with solving the mixed boundary value problem for the electric potential outside the substrate are discussed, and an approximate solution is offered. The transfer function calculated within this approximation is related to that obtained from the equivalent circuit model. The phenomenon of the triple transit echo is included in the theory in an empirical way by introducing the reflection coefficient of the transducer as a parameter. The fine structure observed experimentally in the frequency response is explained as an interference effect between the direct wave and the triple transit echo. Frequency response characteristics are calculated for some specific filter designs some of which employ varying finger overlap and varying finger width. There is good agreement between theory and experiment.
Frequency response of acoustic surface wave filters. II
Authors: Zucker J. , Ganguly A. K.
Published: February 2004

For comparison with the theory of Ganguly and Vassell we measured the transfer functions of three types of surface wave filters, each composed of two or more interdigital transducers. In one type the transducers had both period and finger length constant, in the second there was a logarithmically varying period and in the third finger length varied with position as sinx/x. For all three types there was good agreement of experiment with theory on the shape of the transfer function but only fair agreement on the absolute magnitude of insertion loss, since diffraction effects, resistive losses, and propagation losses were neglected in the calculations.
Velocity modulation of propagating waves
Authors: Landauer R. , Peng S. T.
Published: February 2004

Propagation in a dispersionless linear medium whose dielectric constant varies slowly in space and time is analyzed. The medium is represented as a series of small and moving dielectric constant discontinuities, with a uniform medium between adjacent moving steps. In the simplest approximation the reflections generated at the steps are ignored but the change in transmitted amplitude is taken into account. This extends earlier work by Tsai and Auld and shows that the electric field is proportional to (ωk/ε)1/2 as ω, k, and ε vary along the path taken by a given phase of the propagating wave. This amplitude variation is shown to be equivalent to the conservation of photon numbers. The neglected higher-order multiple reflections are discussed in an evaluation of the validity of the approximation. We also review the solution for the truly nonlinear problem. In this case, the same nonlinearities which couple a large pump wave and a small signal cause different portions of the pump wave to travel with different velocities. A given portion of the small signal stays with a particular value of the dielectric constant and therefore no reflections are generated. The E∼(ωk/ε)1/2 result then becomes exact. Finally, a novel amplifying device called ``radiation klystron'' is discussed. In this device the small signal to be amplified controls the propagation of a high-level high-frequency signal.
Significant loss mechanisms in gas breakdown at 10.6 μ
Authors: Chan C. H. , Moody C. D. , McKnight W. B.
Published: February 2004

An experimental study of the breakdown of various gases under intense radiation of 10.6 μ was made, and a theoretical model for the development of gas breakdown is presented. The gases under investigation were He, Ne, Ar, O2, and air. The pressure range was from 0.3 to 13 atm and the focal diameter from 0.75 × 10−2 to 3.0 × 10−2 cm. It was found that for all gases studied, the threshold power density decreases as the focal volume increases and that it decreases as the pressure increases, in the pressure range considered. The rate of decrease with pressure was found to vary with different gases and focal volumes. This reduction of threshold with increased pressure is less sharp as the focal volumes become larger. The theoretical model is based on classical microwave cascade theory. The importance of loss terms other than the electron diffusion loss is discussed. The theoretical model predicts that even for large beams some loss terms are still important and the breakdown threshold is not completely time dominated. The threshold value is predicted to be higher than the one predicted based on a loss-free calculation.
Effect of phosphorus concentration on the atomic distribution function of amorphous Pd–Ni–P alloys
Authors: Dixmier Jean , Duwez Pol
Published: February 2004

The effect of the phosphorus concentration on the atomic distribution function in amorphous alloys (Pd50–Ni50)100−xPx in which x varies from 15 to 27.5 was investigated. The alloys were obtained by rapid quenching from the liquid state. The intensity of the first peak of the interference function decreases with increasing phosphorus content. The second peak has a definite shoulder on the right side for alloys low in phosphorus and this shoulder progressively disappears as the P concentration is increased. This feature was not found before in binary Ni–P alloys obtained by electrodeposition. From the atomic distribution functions it was possible to determine the metal-to-metal distances and the approximate metal-to-phosphorus distances.
Experimental properties of injection lasers: modal distribution of laser power
Authors: Sommers H.S.
Published: February 2004

The paper reports extensive measurements and analysis in terms of physical parameters of the frequency and spatial distribution of the radiation from GaAs injection lasers operated at room temperature. Covered are most of the internal configurations found in modern structures. All cavities have similar lengths and widths, cleaved uncoated facets, and sawed sidewalls. The power ranges from threshold to full drive as set by the limit for facet damage. Qualitatively the beam and spectral widths grow almost discontinuously with current near threshold and more slowly at higher drive, with up to a thousand cavity modes sharing the power at full output. Quantitative analysis is enabled by a new model of a laser cavity with sawed sidewalls and by a new equation for the modal power distribution function, which has the form of a sum over the normal modes of the cavity. Summing gives new predictive expressions for the beam shape and for the dependence of half-width on current, both of which are found to be obeyed by all the lasers, and an expression in terms of observables for the critical power associated with the nonlinearity which spreads the coherent radiation among the normal modes. For all the lasers studied, the critical parameter is of the order of 10 mW per normal mode. It is speculated that the observed behavior is representative not only of GaAs injection lasers but of the entire class of semiconductors, that the critical parameter power per mode is a material constant associated with the onset of nonlinear absorption/emission, and that its low level is to be expected in semiconductors.
Estimation of Debye temperatures by averaging elastic coefficients
Authors: Ledbetter H. M.
Published: February 2004

Elastic Debye temperatures θ were calculated by averaging elastic stiffness coefficients. For cubic symmetry, eight averaging methods were evaluated with respect to a computationally exact θ. Reuss's θ, corresponding to uniform stress, gave better agreement than Voigt's θ, corresponding to uniform strain. Hill's geometrical θ gave the best agreement.
Electric field, transfer, and spread functions in xerographic image studies
Authors: Kao Cheng C.
Published: February 2004

The general solution to the problem of computing the electric field associated with any charge distribution on the surface of a photoconductor has been solved. The model includes the case where an interposition film is present. Use of the concept of the point spread function and the transfer function in the modeling of this step of the xerographic process is discussed with reference to particular examples.
Electrical transport phenomena in amorphous gallium phosphide films
Authors: Barbe D. F. , Saks N. S.
Published: February 2004

Conduction processes in 50 amorphous GaP films were studied over the temperature range 77 ≤ T ≤ 400°K, for sample thicknesses from 0.1 to 2 μ, for electric fields up to 106 V/cm, and for frequencies up to 106 Hz. Contact effects were shown to be negligible; therefore, all conduction processes reported here are bulk limited. ac and dc conduction is Ohmic for fields up to 104 V/cm. The dc activation energy at 300°K is 0.55 eV which is approximately half the optical band gap. Above 105 Hz, the ac conductivity at 300°K increases as ω0.9, indicating hopping conduction. dc conduction at fields greater than 104 V/cm exhibits Poole-Frenkel behavior. Calculation of the dielectric constant by means of the Poole-Frenkel constant yields K=9.84, in agreement with the optically determined dielectric constant. For JE≥1.4×104 W/cm3, the Poole-Frenkel current is enhanced due to Joule heating.
Photoelectronic properties of p-ZnTe
Authors: Fischer J. R. , Khosla R. P. , Tan Y. T. , Ranadive D. K.
Published: February 2004

Highly photosensitive single crystals of ZnTe have been prepared by annealing in an atmosphere containing Zn and Ga or In and quenching to room temperature. The material remains p type under illumination and displays many of the characteristics of other II-VI photoconductors, including strong trapping and thermal quenching. An electron-trapping level at about 0.24 eV below the conduction band is inferred from the data and associated with the Ga or In impurity. The peak sensitivity is comparable to that of the better CdS or CdSe photoconductors. Acceptor levels at about 0.06, 0.13, and 0.22 eV are also observed.
Effect of γ irradiation on the magnetic properties of ruby
Authors: Blunt R. F. , Candela G. A. , Forman Richard A.
Published: February 2004

The magnetic susceptibilities of ruby samples (Cr3+ in α-Al2O3) were measured before and after Co60 γ irradiation. Within the experimental error the magnetic susceptibility was found to be unchanged by the irradiation. The degree of microwave saturation possible for the Cr3+ spin system, when at the resonance condition for complete saturation, showed a marked decrease after irradiation. Together, these results indicate that the γ irradiation has changed the resonance condition for approximately 10–15% of the Cr3+ in a 0.05 wt% Cr2O3 sample. A likely inference is that the oxidation state of at least 99% of the chromium is unaltered, and that less than 10 ppm Cr has valence differing from three in the irradiated sample. These experiments are in essential agreement with other experiments on ruby.
Observations on electron loading in superconducting cavities
Authors: Kneisel P. , Stoltz O. , Halbritter J.
Published: February 2004

Electron loading has become a severe drawback for the high-field application of good superconducting cavities. In this paper we have analyzed different experimental forms of electron loading. We found both qualitatively new forms of resonant trajectories causing multipactor barriers and multipactor barriers at electron impact energies, where clean metal surfaces would give no gain of electrons.
Semihard magnetic material of the Fe–Cu–Mn system
Authors: Ogawa Koichi , Kawaguchi Toranosuke
Published: February 2004

A Fe–Cu–Mn ternary alloy has been developed for use as a switching reed material. The qualities of coercivity and squareness are improved by the process of first cold drawing the material and then subjecting it to heat treatment. The 80Fe-1.7Mn–Cu alloy obtains a coercivity of 20–50 Oe, a remanence of 14–15.5 kG and a squareness (Br/B200) of 0.9–0.96 when heated at 500–600°C after being cold drawn. Hysteresis curves of the Fe–Cu–Mn alloy become very square after the heat treatment. This is due to an increase in uniaxial anisotropy which is induced by the combination of cold drawing and heat treatment. Very little deterioration is observed in the magnetic properties of an alloy that has already been aged when the alloy is heated again at 600–800°C for a short time. The thermal-expansion coefficient of the alloy, which is 115×10−7/°C, closely approximates that of the new sealing glass and the alloy has good electrical conductivity.
Quenching of fluorescence at the nematic-isotropic phase transition
Authors: Baur G. , Stieb A. , Meier G.
Published: February 2004

Polarized fluorescence of doped nematic liquid crystals is observed in the nematic phase and at the nematic-isotropic phase transition. We find a large change in the quantum yield of the fluorescence in the nematic and isotropic phases due to different quenching rates. The order parameter cannot be easily calculated from the fluorescence intensities because of these quenching effects.
Adiabatic third-order elastic constants of fused silica
Authors: Yost W. T. , Breazeale M. A.
Published: February 2004

Results of ultrasonic harmonic generation are combined with those of ultrasonic beam mixing [R. W. Dunham and H. B. Huntington], to obtain a complete set of truly adiabatic third-order elastic constants of a strain-free sample of G.E. type 151 fused silica: C111+64.8±0.5×1011 dyn/cm2; C144=+5.4±0.3×1011 dyn/cm2; and C456=−1.32±0.08×1011 dyn/cm2. Differences among values of the third-order elastic constants for different samples are great enough that care in sample selection is necessary for consistent results.
Observation of misfit dislocations in GaP–GaAs heterojunctions
Authors: Tamura Masao
Published: February 2004

Transmission electron microscope observations have been made on vapor-grown epitaxial GaP films on Ga (111) faces of GaAs substrates. The epitaxial films contained an ordered array of dislocation networks running parallel to three sets of 〈110〉 directions at the interface. It is believed that these dislocations in the interface region result from a partial accommodation of the lattice mismatch between GaP and GaAs.
Spontaneous magnetization of aluminum at cryogenic temperatures
Authors: Acosta Virgilio , Roy Thomas N.
Published: February 2004

Different specimens of aluminum, when immersed in liquid nitrogen at atmospheric pressure, produced transient magnetic fields of 10 nT (γ) at 15 cm, lasting less than 60 sec. This effect was first seen in 1968 during a lunar magnetometer calibration done at the Magnetic Test Facility (GSFC). Subsequent to the calibration, experimental work was conducted in zero ambient magnetic field and preliminary experimental results are presented.
Exploding wires in strong axial magnetic fields
Authors: Honig E. M. , Kristiansen M. , Hagler M. O.
Published: February 2004

Thin copper wires, typically No. 27 and No. 33, were exploded in magnetic fields up to 72 kG. The ambient gas was atmospheric pressure air. The wire lengths were 0.5–1.35 cm, the applied voltage 3–7 kV, the peak currents 3.5–39 kA, and the ringing frequency 300 kHz. The effect of the magnetic field was generally to increase the pause length and to damp the ringing discharge more.
Impossibility of obtaining coefficients of thermal expansion of a solid from ultrasonic wave-velocity measurements
Authors: Dandekar D. P.
Published: February 2004

It is shown that thermal-expansion coefficients of a material cannot be measured by using an ultrasonic cw spectrometer.
Magnetic iron sulfide of the γ-Al2O3 type
Authors: Yamaguchi S. , Wada H.
Published: February 2004

Ferromagnetic iron sulfide Fe2S3 of spinel-type structure was synthesized chemically. The crystal structure of this sulfide was geometrically similar to that of γ-Al2O3 and γ-Fe2O3 containing vacancies. The formula FeIII (□1/3Fe5/3III)S4 was postulated as a vacancy structure isomorphous with FeIIFe2IIIS4. The magnetic characteristics of this sulfide were similar to those of greigite Fe3S4.