bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between resistivity and phosphorus concentration in silicon
Authors: Mousty F. , Ostoja P. , Passari L.
Published: February 2004

Accurate electrical and analytical measurements allowed us to determine a relationship between resistivity and phosphorus concentration in doped silicon. This relationship is compared with that obtained by other authors in the case of n-type silicon, and the differences due to the various doping agents are discussed. Differences between concentrations determined by analytical techniques and by Hall effect measurements are reported.
Laser drilling mechanics
Authors: Wagner R. E.
Published: February 2004

Many laser drilling applications require that the shape of the drilled hole be carefully controlled. In order to successfully do this it is necessary to understand the laser drilling process. This paper reports on a quantitative model which predicts the depth and shape of a hole drilled in alumina ceramic by a ruby laser. Both experimental and theoretical results indicate that the predominant drilling mechanism for this application is not one of surface absorption and conduction inward, but one in which laser energy is absorbed throughout the bulk of the ceramic. The depth and shape of holes drilled in ceramic have been accurately predicted from the measured beam energy density distribution. Finally, it is shown that the radiation pressure of the focused beam plays an important role in the romoval of molten material from the heated region.
Application of spall phenomena to gun explosion problem
Authors: Foltz J. V. , Grace F. I.
Published: February 2004

The authors apply knowledge of spall phenomena and a simple pressure wave propagation model as a tool in solving gun explosion problems. An example with an explosive-loaded cylinder serves to illustrate the approach.
Analysis of conversion efficiency of organic-semiconductor solar cells
Authors: Fang P. H.
Published: February 2004

The conversion efficiency of solar cells made of organic semiconductors with metallic electrodes on opposite surfaces is calculated on the basis of a model of two diodes connected in series, but with opposite polarity. We find that the intrinsic conversion efficiency would be two orders of magnitude higher than the conventional value of 10−5–10−6 if the presently used solar-cell configuration of organic semiconductors could be altered to have an Ohmic contact on one surface.
Relationship between stacking-fault energy and x-ray measurements of stacking-fault probability and microstrain
Authors: Reed R. P. , Schramm R. E.
Published: February 2004

Stacking-fault energies can be determined by measuring the positions and profiles of x-ray diffraction lines. Use of this method has been hampered by the uncertainty of the relationship between stacking-fault energy and the ratio of microstrain to stacking-fault probability. Microstrains and stacking-fault probabilities have been determined for five fcc metals by x-ray diffraction line profile analysis. For these metals, Ag, Au, Cu, Al, and Ni, stacking-fault energies have been estimated from a comprehensive updated review of the experimental literature. A linear correlation does exist between γ and 〈ε502〉111/α and thus, the x-ray technique can be applied more confidently. The possible role of elastic anisotropy is also considered.
Figures of merit of bismuth under conditions of strong phonon drag
Authors: Jacobson D. M.
Published: February 2004

Thermomagnetic effects are known to be large in bismuth near 4.2°K where strong phonon drag phenomena are believed to occur. The figures of merit of bismuth are analyzed in terms of the individual transport coefficients for varying extrinsic carrier concentrations and magnetic fields. Using available data and current theory, it is concluded that the figures of merit are insufficient to enable useful cooling to be obtained from a bismuth device operating in a temperature region of strong phonon drag.
Microparticle detector based on the energy gap disappearance of semiconductors (Se, I, Te, Bi, Ge, Sn, Si, and InSb) at high pressure
Authors: Rauser P.
Published: February 2004

A new rigid vibration-insensitive detector is described as suitable as a gauge in high-pressure techniques and as a registration device for small dust particles during space missions. The detector is based on sound physical principles and works as a go-no go (hit-no hit) detector. Its operation has been proved with a 2-MV dust-particle accelerator by shooting iron particles of mass around 10−10 g with velocities from 2.4 to 6.7 km/sec. In the considered range, the slope of the output signal versus particle mass is found to be 3.2 at ν=3.8±0.05 km/sec. The slope increases for smaller particle masses and higher velocities. The voltage output of the pressure-sensitive detector versus mass is more sensitive than that of the ion charge (slope≈0.9) which is collected from the plasma at impact. A rough model of the function of the device is given.
Narrowing of the emission spectrum of ruby laser by inhomogeneous pumping
Authors: Eichler H. J. , Eichler J.
Published: February 2004

A conventional ruby laser without mode selection emits spikes with frequencies distributed over a range of about 2×1010 Hz. By a suitable pump light distribution the frequency band of the emission was confined to about 0.3×1010 Hz. This effect can be explained by the model of spatial hole burning.
Relaxation-time measurement of CO2 laser by Q-switching technique
Authors: Kitazima I.
Published: February 2004

The present paper proposes that one can easily observe either the relaxation time of the 1000 level or that of the 0110 level in a CO2 laser system under cw excitation by use of rotating-mirror Q-switching techniques. It is mentioned here that the optimum repetition time Tropt for the laser pulse height corresponds to the relaxation time of the 0110 level (τ010) and the cutoff pulse interval Troff for the second pulse corresponds to the relaxation time of the 1000 level (τ100). When the CO2 (1.8 Torr)-He (7.2 Torr) mixture was sealed in a water-cooled Pyrex tube 20 mm in inside diameter and 170 cm in length, Tropt was measured to be 7 msec and Troff was 40 μsec, at a discharge current of 15 mA. These values were in satisfactory agreement with the values of τ010 and τ100 previously obtained by pulse-excitation techniques.
Wavelength measurements of simultaneously excited superradiance and laser emission from cryptocyanine dye
Authors: Sugiura Y. , Matsunaga Y. , Fujioka T.
Published: February 2004

The wavelengths of both superradiance and laser emission simultaneously excited from cryptocyanine are measured as functions of cell length and angle between the-two beams.
Theory of stripe-domain nucleation in garnet films
Authors: Muller M. W.
Published: February 2004

Micromagnetics predicts that domain nucleation in an in-plane field in mechanically rigid uniaxial films with easy axis normal to the faces should take the form of stripes parallel to the field. This prediction does not agree with observation in some real films. It has been shown previously that the magnetoelastic interaction in deformable films may cause the stripes to be perpendicular to the field when the films are thick enough. Quantitative assessment of this effect is difficult because the magnitudes of the magnetoelastic constants are not accurately known, and because high-quality epitaxial films are at least partly constrained from deforming. In this paper we discuss another interaction which can cause the stripes to be perpendicular to the field in a [111]-oriented cubic film, such as bubble-device garnet. The interaction energy is a dipolar energy brought into play by the effectively trigonal anisotropy. It vanishes when H is along [112̄] and is maximum when H is along [1̄10]. Quantitative evaluation shows that the interaction can account for a large part but not all of the behavior observed in recent experiments.
Third-order polarizabilities of long-chain molecules
Authors: Hermann J. P. , Ducuing J.
Published: February 2004

The third-order polarizabilities of several alkanes and polyenes have been deduced from third harmonic measurements. For satured hydrocarbons, γ increases linearly with the number of atoms, whereas for polyenes, a strong exaltation is found, with a superlinear increase. This behavior, attributed to delocalized π electron cloud, is in quantitative agreement with the results of a previous theoretical analysis. Large values of χ(3)≃10−12 esu are found in molten retinol and retinal.
The origin of non-Gaussian profiles in phosphorus-implanted silicon
Authors: Blood P. , Dearnaley G. , Wilkins M. A.
Published: February 2004

The origin of the tail on the distribution of phosphorus atoms implanted into misaligned silicon crystals has been established by measuring the number of phosphorus atoms transmitted through thin silicon crystals during implantation. Experiments on 〈110〉 and 〈100〉 crystals show that the tail is due entirely to atoms which are scattered into channels. The preparation of crystals 0.4–0.8 μm thick from epitaxial layers by selective electrochemical etching and ion beam thinning is described and the measurement of their thickness by backscattering techniques is discussed. It is suggested that the tails on the profiles of other dopants in silicon are also due to atoms which have entered channels in the crystals.
Acousto-optic properties of some chalcogenide crystals
Authors: Gottlieb M. , Isaacs T. J. , Feichtner J. D. , Roland G. W.
Published: February 2004

We report results of extensive measurements on the acousto-optic properties of several sulfosalt-type chalcogenide crystals. These materials typically are transparent from the near ir to the intermediate ir, with refractive indices ranging from 2.5 to 3. Their acoustic velocities are among the lowest of any material, and ultrasonic attenuation remains low for frequencies to 500 MHz. These properties lead to exceptionally high acousto-optic figures of merit.
Adsorption and condensation of Cu on W single-crystal surfaces
Authors: Bauer E. , Poppa H. , Todd G. , Bonczek F.
Published: February 2004

The adsorption and condensation of Cu up to several monolayers in thickness on tungsten {110} and {100} single-crystal surfaces are studied by combining low-energy electron diffraction, Auger electron spectroscopy, thermal desorption spectroscopy, work-function measurements, and quartz microbalance thickness measurements in one experimental system. The results show drastic differences in the evolution of the structure, work function, and desorption behavior between {110} and {100} surfaces. These differences are understandable in terms of the atomic roughness of the surfaces.
Traveling ionization disturbance during microwave breakdown of argon
Authors: McIntosh Robert E.
Published: February 2004

We report here the excitation of a propagating ionization disturbance during the transient microwave breakdown of argon. Evidence gathered from spectroscopic observations indicates that this disturbance travels away from the generating source at a velocity which depends on pressure and the magnitude of the microwave pulse.
Noise measurements on the floating diffusion input for charge-coupled devices
Authors: Emmons S. P. , Buss D. D.
Published: February 2004

A technique is presented for electrically introducing charge into a charge-coupled device (CCD) in a stable uniform low-noise manner. The technique utilizes a floating diffusion whose capacitance (Cfd) can be tailored for particular applications or monitored directly for noise measurements. Experimental results are presented which demonstrate that charge can be introduced into a CCD with a variance of kTCfd. This technique is particularly germaine to the introduction of a ``fat zero'' into a low-light-level surface channel CCD imager.
High-temperature Brillouin scattering in fused quartz
Authors: Bucaro J. A. , Dardy H. D.
Published: February 2004

Thermal Brillouin scattering has been studied in fused silica from room temperature, through the glass transition temperature (1200°C), and up to near the melting temperature of quartz (∼1700°C). The shear and longitudinal Brillouin shifts, the longitudinal linewidth, Pockel's coefficient, and the Landau-Placzek ratio are measured. From these the behavior of the elastic moduli and absorption coefficient with temperature are obtained. A significant change in the temperature dependence of the moduli and Pockel's coefficient is found to occur above 500°C. In addition, by using the Landau-Placzek ratio the first measurement in fused quartz of the equilibrium static compressibility above the glass transition has been obtained. Surprisingly little temperature dependence is observed.
Time-resolved spectroscopy of a pulsed H2–F2 laser with well-defined initial conditions
Authors: Nichols D. B. , Wrolstad K. H. , McClure J. Doyle
Published: February 2004

The time-resolved spectral output of a pulsed H2–F2 laser has been investigated as a function of initiating atomic fluorine concentration. Fast initiation, as well as variation of initial F-atom concentration, was accomplished by photodissociation of F2 in a flowing H2–F2–N2 mixture utilizing a variable-amplitude 30-nsec second harmonic pulse from a Q-switched ruby laser. Initial HF concentration due to prereaction was reduced to ∼0.01% of the final HF content by cryogenic cooling of the reagent premixer. The 30-cm-long reactor cell was contained within a 113-cm stable resonator cavity having a 70% output coupling coefficient. Lasing was observed on a number of P-branch transitions in the four lowest vibrational bands of HF for a gas mixture H2 : F2 : N2 = 7.5 : 7.5 : 75 Torr. For each of the nine dominant lines, variation of initiation time, pulse duration, peak intensity, and total energy was observed as a function of initiating F-atom concentration. Strong initial intensity transients observed for highest gain transitions are indicative of relaxation oscillation effects not included in conventional HF laser simulation codes based on the threshold gain constraint. Trends in temporal J progression predicted by such codes were observed, but simultaneous lasing on multiple lines within a given vibrational band indicates that usual assumptions of Boltzmann rotational distribution and gain saturation to threshold are overrestrictive. The observations show strong correlation between peak intensity and relative gain of the individual transition. Energy content of individual lines does not exhibit such correlation.
Crystal growth and electro-optical characterization of bismuth tri-iodide
Authors: Schieber Michael , Davies Terence J. , Schnepple Wayne F. , Randtke Peter T. , Carlston Richard C.
Published: February 2004

The purification and growth of BiI3 crystals from the vapor phase and some electro-optical characterization measurements are described. The sublimed boules had large single-crystalline pieces which could be cleaved to give areas of about 1 cm in diameter and about 1 mm in thickness. The complex index of refraction evaluated at a wavelength of 1 μm is N = 3.13−i(3.2×10−5).
Material content of binary physical mixtures as measured with a dual-energy beam of γ rays
Authors: Nofziger D. L. , Swartzendruber D.
Published: February 2004

The content of water and soil in physical intermixture was measured simultaneously and nondestructively by the attenuation of a dual-energy beam of γ rays. The beam, 1 mm by about 3 cm in cross section, was devised by placing a 280-mCi source of 137Cs behind a 389-mCi source of 241Am, with lead collimators suitably aligned in front of each source and the scintillation probe. The probe was connected in parallel to two-separate amplifier-analyzer-scaler systems, one being set in the integral mode to receive all pulses greater than 550 keV (for 137Cs, 662-keV peak), with the other being set in the differential mode to receive all pulses in a band 35–85 keV (for 241Am, 60-keV peak). When related to the count intensity in the high-energy range, the count intensity e caused by 137Cs in the low-energy band was empirically found to be independent of the material in the binary mixture (soil and/or water) placed in the beam for measurement. Also, e could be well expressed by a cubic polynomial that was then used along with a dead-time correction to determine the attenuated count intensity attributable to the 241Am source alone. Calibration of the system was then possible. Over-all measuring accuracy was on the order of ±0.01 cm3/cm3 in water content and ±0.02 g/cm3 in soil content (bulk density) for a counting period of 5 min; these changed to ±0.04 cm3/cm3 or g/cm3 for a counting period of 5 sec.
Correlation between the 337- and 311-μm line in a cw HCN laser
Authors: Mizuno K. , Kuwahara R. , Shimoe O. , Ono S.
Published: February 2004

Correlation between the 337- and 311-μm line in a cw HCN laser has been experimentally observed. Spectroscopic measurements have shown that the oscillation of the 337-μm line causes the reduction of the 311-μm line output, and the correlation between the same transverse modes for the both lines is larger than that between different modes.
Acoustic behavior of supercooled liquids
Authors: Mishra P. K. , Singh R. P.
Published: February 2004

An empirical relation between the maximum ultrasonic absorption and frequency of ultrasonic wave in supercooled liquids and mixtures, differing widely in molecular weight and chemical composition, is reported. The viscoelastic and ultrasonic relaxation in most of these liquids are describable in terms of the Barlow-Erginsav-Lamb model.
Thermal conductivity, electrical resistivity, and thermoelectric power of Pb from 260 to 550 K
Authors: Cook J. G. , Laubitz M. J. , Van der Meer M. P.
Published: February 2004

New data are given for the thermal and electrical conductivities and thermoelectric power of Pb from 260 to 550 K. Comparison of these data with literature values suggests that, contrary to some reports, there are no anomalous purity effects in the thermal conductivity at high temperatures and that some of the recently recommended values for this parameter may be some 2% too high.
Simple calculation of energy distribution of low-energy secondary electrons emitted from metals under electron bombardment
Authors: Chung M. S. , Everhart T. E.
Published: February 2004

A simple theoretical calculation is given in which the energy distribution of low-energy secondary electrons emitted from metals is derived. The main feature of the calculation is an energy-dependent electron mean free path. The theory predicts that the peak of the energy distribution occurs at a value of the secondary electron energy equal to φ/3, where φ is the metal work function.
Taylor instability in solids
Authors: Barnes John F. , Blewett Patrick J. , McQueen Robert G. , Meyer Kenneth A. , Venable Douglas
Published: February 2004

The growth of a sinusodial ``perturbation'' in the surface of a flat plate smoothly accelerated by expanding detonation products has been observed using the Los Alamos high-energy x-ray facility. Through modeling with a two-dimensional elastic-plastic numerical hydrodynamics code we have determined that amplitude growth is apparently largely governed by the dynamic yield strength of the material.
Amorphous bismuth-germanium thin films. II. Optical and photoelectrical properties
Authors: Vass R. W. , Anderson R. M.
Published: February 2004

Thin films of bismuth-germanium have been fabricated in vacuum by the method of codeposit vapor quenching onto liquid nitrogen or water-cooled substrates. In this paper, Paper II of a two-paper series, the optical and photoelectrical characterization of these films are reported. Transmittance, reflectance, and absorptance data are reported in the spectral range 0.2–3.0 μ for BixGe1−x thin films in the composition range 0 ≤ x ≤ 0.25. Ultraviolet/visible near-normal reflectance spectra for films in the amorphous phase (0 ≤ x ≤ 0.2) closely resemble the optical reflectance spectra of amorphous germanium. The reflectance spectra of the amorphous films were static and insensitive to an increase in bismuth concentration. Additionally the spectra were devoid of any optical remnants of the crystalline spectra of either germanium or bismuth. The reflectance spectra of a Bi0.25Ge0.75 film which was x-ray polycrystalline revealed a broad local maximum near 2 eV, indicating crystalline bismuth transitions and the existence of a pure Bi phase. Near-infrared transmittance, reflectance, and absorptance data indicate that the optical energy gap, Egopt(x) of the a-BixGe1−x thin-film system is reduced with an increase in bismuth concentration. An expression for Egopt(x) as a function of bismuth concentration is developed using the formulation of Cardona from calculated absorptance data. ac photoconductivity studies at room temperature and low temperature (T = 162°K) have been accomplished for a-BixGe1−x thin films in the composition range 0 ≤ x ≤ 0.03. The binary films in this set were found to be photoconductive with a response of the same order of magnitude and spectral shape as that of amorphous germanium films. The observed photoconductivity was present at room temperature and increased one to two orders of magnitude upon cooling to T = 162°K. The photoconductive spectral edge occurred at a photon energy between 0.6 and 0.8 eV for all films studied. An observed shift in the spectral edge with bismuth concentration is tentatively attributed to the optical band-gap dependence on the alloy concentration.
Point-obstacle representation of the dislocation-obstacle interaction
Authors: Morris J. W. , Syn C. K.
Published: February 2004

A general method is given for constructing the ``point-obstacle'' representation of the interaction between a dislocation and a physical obstacle. The equations of equilibrium are derived. The elastic interaction of a simple dislocation with a row of equispaced solute atoms which behave as repulsive barriers is treated as an illustration.
Electrical conductivity of disordered layers in GaAs crystal produced by ion implantation
Authors: Kato Y. , Shimada T. , Shiraki Y. , Komatsubara K. F.
Published: February 2004

The electrical conductivity of disordered layers in GaAs produced by ion implantation has been studied as a function of ion species, dose level, energy of implanted ions, and anneal temperature. The resistivity of the implanted layer, ρ, at room temperature can be expressed by a single relation, ρ=const×NDD−3, even for different masses and energies of implanted ions, where NDD is the total number of displacements of host atoms per unit volume due to nuclear collisions with implanted ions. At a temperature above 180 K the resistivity is proportional to exp(B/T) and below 180 K it changes as exp(B/T1/4). The conduction mechanism of the implanted layers is discussed based upon the hopping conduction in disordered or amorphous semiconductors. The annealing behavior of the implanted layers was also studied. The activation energy for recovery of the resistivity ρ was about 0.35 eV, which is quite small compared with the migration energies of stray atoms in ordered crystals. These results indicate that the implanted layer is in a disordered state rather than in a crystalline state containing the point defects.
Formation of stacking faults and enhanced diffusion in the oxidation of silicon
Authors: Hu S. M.
Published: February 2004

The phenomena of the formation of stacking faults and the enhanced diffusion during the oxidation of silicon are shown to be closely related and to have a common cause. A model is presented which at once can consistently explain various aspects of both phenomena; in particular, it is capable of explaining the crystal-orientation dependence of these phenomena and the parabolic growth of stacking faults. The model envisages a small incompleteness (∼ 10−3) of oxidation, producing silicon interstitials. A concept is introduced that these excess interstitials, as they supersaturate the lattice, will undergo surface regrowth. The rate of interface regrowth is proportional to the density of surface kinks, which is in turn dependent on the surface orientation. The dependence is described. Quantitative analyses are given for the excess interstitials, the growth of stacking faults, and the enhancement of diffusion. The analyses also show that the stacking-fault embryos are formed within a very short time of the start of oxidation, usually less than 1 sec, consequently leading to uniform stacking-fault size. The occasionally observed variation in the size of bulk stacking faults is attributed to a continuous formation of stacking-fault nuclei (e.g., oxide clusters and precipitates). The absence of a surface regrowth would predict a 1/4 power law of stacking-fault growth, in contradiction of the experiments.
Dislocation effects in smectic-A liquid crystals
Authors: Pershan P. S.
Published: February 2004

A method for calculating stress-strain fields around edge dislocations in smectic-A samples is discussed. In large part the method is isomorphic with the formalism for calculating magnetic fields around lines of electric current. The force law between dislocations that follows from the analogy is equivalent to the accepted force law between dislocations in crystals. In addition to rederiving the expression for the strain field surrounding an isolated edge dislocation that was first given by de Gennes, we present the solutions for the stress-strain fields surrounding dislocations near one or two boundaries and also the strain field surrounding an edge dislocation that is curved to form a circular loop. The stress-strain fields surrounding other defects with the same symmetries and boundary conditions can be expressed in terms of the above-mentioned solutions using Green's function techniques. The relative stability of dislocations in samples with different types of boundaries and also the effects of dislocations on the elastic properties of smectic samples are also discussed in some detail. We comment briefly on the relation between the analogy discussed here and an earlier one developed by de Gennes.
Inversion of a microwave line of NH3 in an infrared-microwave double-resonance experiment
Authors: Fourrier M. , Redon M.
Published: February 2004

Using the R(30) N2O laser line in order to saturate the infrared s a Q(9, 6, 9) (v2 = 0 ↔ v2 = 1) vibration-rotation line of NH3, the inversion of the microwave J = 9, K = 6, M = 9, v2 = 0, has been obtained. Exact coincidence between the laser line and the infrared NH3 transition is realized by Stark-effect tuning. The variation of the Stark field through the exact coincidence permits studying the evolution of the microwave line versus the frequency mismatch of the pumping radiation.
Electrically induced damage in NaCl
Authors: Grinberg A. , de Grinberg D. M. K.
Published: February 2004

In this paper some new observations on electrically induced damage in NaCl single crystals are presented. Microscopic studies made on surfaces normal and parallel to the applied electric field and inside the sample allowed us to determine the crystallographic and geometric characteristics of the breakdown channel, the nature of the different damaged zones around it, and their manifestations on the external surfaces of the sample. A mechanism based on the model of Bullough and Gilman is proposed to explain the experimental results. It is suggested that as a high amount of energy is transferred to the solid in a very short time compared with the elastic relaxation time, an interior implosion can be generated. An implosion of this kind would originate high-intensity shock waves, which would be responsible for the observed damage by causing intense heating, sublimation and decomposition of the material, spallation, and cleavage.
Influence of stoichiometry on the metal-semiconductor transition in vanadium dioxide
Authors: Griffiths C. H. , Eastwood H. K.
Published: February 2004

The structure and resistivity of vanadium dioxide films close to the metal-semiconductor transition have been studied as a function of stoichiometry. Unit-cell volume is shown to go through a minimum and the transition temperature and resistivity ratio through a maximum at the apparent stoichiometric oxygen level. The observed resistivities can be accounted for by an increased electron concentration due to vanadium interstitials in the low-oxygen films and by a second phase in the high-oxygen films. The variation of resistivity and transition temperature with electron concentration provides experimental support for the previous suggestion that the driving force of the transition is mainly an antiferroelectric distortion.
Luminescence in epitaxial GaN : Cd
Authors: Lagerstedt O. , Monemar B.
Published: February 2004

Investigations on luminescent properties of good-quality GaN single-crystalline epitaxial layers at temperatures in the range 1.6–300 K are reported. The high-energy region (3.27–3.48 eV) at 1.6 K is dominated by different bound exciton transitions. Peaks are observed at 3.469, 3.454, 3.447, 3.400, 3.377, 3.355, and 3.287 eV at 1.6 K in this region; their possible origin is discussed. At higher temperatures (T > 30 K) the free A-exciton emission is also clearly observed, and thus its position EAx=3.475±0.0005 eV at 1.6 K could be established (neglecting polariton effects) together with a value of 6.4±0.4 meV for the binding energy of an exciton to a neutral donor. The energy region 3.0–3.3 eV is dominated by the previously studied donor-acceptor pair spectra, which peak at 3.263±0.003 in all our good-quality samples (undoped and doped). From the assignment of a subsidiary high-energy peak as free-to-bound transitions, a value of 29±6 meV for the donor binding energy is experimentally determined, in good agreement with the theoretical effective mass value. The region below 3.0 eV is in Cd-doped material dominated by a broad band centered at 2.72 eV, unlike previous observations. This band is an envelope composed of several discrete series of emissions observable at low temperatures. The solubility of Cd in GaN appears to be rather low, and high-Ohmic single-crystalline material was not obtained, in contrast to our results from Zn-doping.
Wavelength-modulated spectra of some Fe3+ oxides
Authors: Blazey K. W.
Published: February 2004

The wavelength-modulated reflectivity spectra in the visible and near uv of GdIG, LuFeO3, FeBO3, Fe2O3, Fe[NiFe]O4, and BaFe12O19 are reported. Features of both the exciton sideband and the charge-transfer spectra are observed. Comparison of these spectra allows some site assignments to be made. In particular the octahedrally coordinated Fe3+ ion is found to contribute a characteristic charge-transfer spectrum that occurs at lower energies than the tetrahedral Fe3+ charge-transfer spectrum. A further charge-transfer process between octahedral and tetrahedral Fe3+ sites is suggested to explain the garnet spectra.
On surface preparation and measurement of niobium used in high-frequency cavities
Authors: Kneisel P. , Stoltz O. , Halbritter J.
Published: February 2004

The influence of several surface preparation techniques, such as electropolishing, chemical polishing, anodizing, and firing in an UHV furnace with different cool-down cycles, on Q0 values, peak rf fields, and surface mean free path ls have been studied in a welded S-band cavity having large beam tubes. With special treatments, peak fields up to 810 G at Q0≈1011 have been obtained, whereas the surface mean free paths stayed fairly short (≲300 Å ) not changing systematically with (surface) treatment. Hence, to obtain low rf losses and high rf fields, the purity is not important, but, as we will explain, the spatial homogeneity is very important. Measurements with Nb cylinders, processed like the cavities, showed that the variation of flux penetration depth λ(Hdc) with a dc magnetic field Hdc parallel to the cylinder surface changed markedly with surface treatment. This variation of λ(Hdc) shows several features, which are related to surface properties, namely, the reversibility near Hc1 and the signal at Hc2 as indications for roughness or oxygen in the surface sheath, the irreversibility between Hc1 and Hc2 as an indication for inhomogeneities, especially NbO precipitates, in a Nb surface layer. For example, by this method we observed that the usual cool down from 400 to 50°C in the UHV furnace deteriorates a Nb surface layer of several μ thickness. These surface properties obtained with λ(Hdc) are not only important for achieving better rf cavities but also for ac power transmission lines.
Output fluctuations of high-frequency pulse-pumped Nd:YAG laser
Authors: Jackson J. E. , Rice R. R.
Published: February 2004

The output fluctuations of a Nd:YAG laser have been determined for high-frequency pulse pumping using GaAlAs injection laser diodes. The results for a 100-mW-output laser show that a very high pump-pulse frequency (≥1 MHz) must be used to achieve quasi-cw output with low ripple amplitude.
Contribution to the equilibrium phase diagram of the Mn–Bi system near MnBi
Authors: Chen Tu
Published: February 2004

The phase diagram of the Mn–Bi system near the compound MnBi was studied with single crystals in the as-grown and heat-treated states. The results show that the high-temperature phase of MnBi is in fact a separate compound with chemical formula Mn1.08Bi, when grown from a Bi-rich solution. It was found that the transformation of MnBi at 355°C upon heating is associated with a peritectic decomposition of MnBi into Mn1.08Bi+liquid, and the transformation at 340°C upon cooling of the high-temperature phase is the result of decomposition of Mn1.08Bi to MnBi±Mn.
Raman spectra of glassy carbon
Authors: Nathan Marshall I. , Smith John E. , Tu K. N.
Published: February 2004

The Raman spectrum of glassy carbon has been measured. Two broad lines are observed at 1340 and 1590 cm−1. These results are consistent with the turbostratic structure, which has been suggested for glassy carbon, with a particle size La of approximately 30 Å.
Extrinsic absorption in 10.6-μm-laser-window materials due to molecular-ion impurities
Authors: Duthler C. J.
Published: February 2004

It is proposed that molecular-ion impurities that substitute for the halide ion in alkali-halide crystals constitute an important class of impurities limiting infrared transmission in laser-window materials. A survey of the experimental literature indicates that concentrations of less than 0.1 ppm of NO2−, HCO3−, SO42−, and CrO42− will yield an absorption coefficient β>10−4 cm−1 at 10.6 μm. Predicted temperature dependences of impurity-limited β(10.6 μm) are T1.6, nearly temperature independent, and decreasing β with increasing temperature depending on the particular ionic impurity.
Hall effect in silicon on sapphire
Authors: Hynecek J.
Published: February 2004

Variations of Hall mobility with gate bias in gated Hall measurements are explained by considering autodoping of silicon from the sapphire substrate. The method of obtaining the ``true'' electron Hall mobility for n -doped silicon is presented and the conductivity due to the p -type impurities is found.
ac equivalent circuits for MIM structures
Authors: Fonash Stephen J. , Roger Jean-Alain , Dupuy C.H.S.
Published: February 2004

The insulator in a metal-insulator-metal (MIM) structure, due to the fabrication procedures, is probably amorphous, or, at best, polycrystalline. Space charge may exist at the metal-insulator interfaces since it is very possible that there are states in the insulator gap. Thus contacts may play a significant role in determining the electrical properties of MIM structures. The ac properties of such devices can provide information on their band structure, conduction mechanisms, etc. Several ac equivalent circuits have been used to interpret ac data. The equivalent-circuit model derived here is developed assuming polarization at the interfaces dominates. The analysis indicates the significance of characteristic lengths, the significance of the relative magnitudes of the interface and interior electric fields, and the significance of the interior conduction mechanisms in determining the appropriateness of certain ac equivalent-circuit models. The results presented are valid for insulators with very short or very long dielectric relaxation times.
Fast capacitance transient appartus: Application to ZnO and O centers in GaP p-n junctions
Authors: Lang D. V.
Published: February 2004

New techniques and apparatus are presented which overcome some of the limitations of previous capacitance transient techniques and extend the useful range of capacitance transient measurements to intermediate depth impurity and defect states in semiconductors. This development greatly enhances the usefulness of capacitance techniques as a tool to study nonradiative recombination. These techniques and apparatus are used here to measure the electron-capture cross sections and concentrations of isolated oxygen donors and ZnO complex luminescence centers in p-type Zn- and O-doped GaP. These results agree with the donor-acceptor pairing theory and with the conclusion of previous capacitance measurements that the ioslated O donor is of negligible importance as a recombination center in these samples. Data is also presented which shows the effect of the junction electric field in greatly enhancing the thermal emission rate of electrons trapped in ZnO centers.
FMR spectrum of magnetostatic waves in a normally magnetized YIG disk
Authors: Yukawa Toshinobu , Abe Kenji
Published: February 2004

The absorption of microwaves in a normally magnetized YIG disk has been measured and analyzed. The absorption peaks are interpreted to be caused by magnetostatic waves propagating radially across the disk. The mode numbers of absorption peaks are determined by the aspect ratio of the disk, (ω/γ)2−Hi2 and BiHi −(ω/γ)2, where ω is the microwave angular frequency, γ is the gyromagnetic ratio, and Hi and Bi are internal magnetic fields and depend upon the applied magnetic field. The experimental values of the applied magnetic field at which the absorption peaks are caused are in good agreement with the theoretical values. It has been verified both theoretically and experimentally that the new mode absorptions due to the magnetostatic waves exist in the case of ω/γ−[Bi(0)Hi(0)]1/2 =dH > 0, where Bi(0) and Hi(0) are the internal fields at the disk center. These new mode abosrption peaks tend to shift toward the cutoff point of the usual absorption spectra as the incident microwave power is increased.
Analysis of response of pyroelectric optical detectors
Authors: Peterson R. L. , Day G. W. , Gruzensky P. M. , Phelan R. J.
Published: February 2004

Several configurations of pyroelectric optical-radiation detectors are mathematically modeled to determine their frequency response and current response to step-function heat inputs. Included in the analysis are heat losses by conduction and reradiation, effects of absorptive coatings, and an experimentally observed nonuniformity of polarization through the thickness of polymer pyroelectric films. Roll-off of the frequency response at both low and high frequencies is carefully examined. Curve fitting to response data allows a quantitative determination of the pyroelectric coefficient and the degree of nonuniformity of the polarization. The thermal conductivities of gold blacks used as absorbers are determined from the high-frequency data together with independent measurements of the black thicknesses and densities. The total emissivity of evaporated nickel films sometimes used as absorbers can be estimated from the low-frequency data. The difference in response to optical and electrical heat inputs is examined as a part of our effort in fabricating electrically self-calibrating optical detectors.
Pressure and temperature dependences of the elastic constants of compression-annealed pyrolytic graphite
Authors: Gauster W. B. , Fritz I. J.
Published: February 2004

Changes of ultrasonic transit times in compression-annealed pyrolytic graphite (CAPG) were measured as a function of temperature (4–300°K at atmospheric pressure) and of pressure (0–20 kbar at 295°K). From the low-temperature results, obtained for five independent acoustic modes, the temperature variations of all five elastic constants were calculated using the thermal expansion data of Bailey and Yates. From the high-pressure data, taken for four independent modes, the changes of all five elastic constants and of the unit cell dimensions with pressure were calculated under the assumption that the small a-axis compressibility is independent of pressure. The initial pressure derivatives of C33 and C44 are, respectively, about 25 and 35% lower than those obtained by Green et al. for CAPG. The pressure dependences of the volume and c-axis compressibilities are in good agreement with measurements on natural graphite crystals by Lynch and Drickamer and by Bridgman, and in less satisfactory agreement with data of Kabalkina and Vereshchagin. The results support the contention that CAPG has bulk elastic properties very similar to those of single-crystalline graphite.
Cross-sectional specimens for transmission electron microscopy
Authors: Abrahams M. S. , Buiocchi C. J.
Published: February 2004

Cross-sectional views of epitaxial structures yield much information when examined by transmission electron microscopy. Since the growth direction then lies in the plane of observation, rather than normal to it (as is usual), the overgrowth, original growth interface, and substrate can be imaged either simultaneously or individually. A realization of the suitable technique for preparing thin cross-sectional samples is described. Applications to continuously graded GaAsxP1−x/GaAs and step-graded InxGa1−xP/GaP are shown.
Mathematical-physical model of the streamer in nonuniform fields
Authors: Nasser E. , Heiszler M.
Published: February 2004

The initial electron avalanche created in the high nonuniform fields near an anode leaves behind it a space charge of positive ions that enhance the field farther away from the anode and, hence, produce the necessary conditions for successive electron avalanches to produce the streamer. A mathematical model of these processes has been derived and the minimum anode voltage required to satisfy these equations has been computed for different geometrical parameters. This streamer onset voltage agrees well with measured values. The conditions for streamer onset are found to exist whenever the average gradient of the field is higher than a certain value specified by the initial avalanche length.
Measurement of absorption and noise in an x-ray image intensifier
Authors: Swank Robert K.
Published: February 2004

Three experimental methods for measuring the noise-equivalent absorption of an x-ray image intensifier are described. In all cases, the image intensifier is irradiated with a source of x rays or γ rays, and the output is monitored with a photomultiplier. In one method the rms value of the photomultiplier current is observed as a function of the bandwidth of the measuring circuit. In the second method, the scintillation pulse spectrum is recorded, and its moments computed to give the required information. In the third method, the response to a series of short bursts of radiation is measured. The noise-equivalent absorption is determined from the standard deviation of a large number of observations, automatically recorded. The three methods are described and compared, and typical results are shown.
Evidence for Coble creep in the relaxation of surface-compressive stresses in tempered polycrystalline aluminum oxide
Authors: Krohn D. A. , Urick P. A. , Hasselman D. P. H. , Langdon T. G.
Published: February 2004

The kinetics of relaxation of surface-compressive stresses in tempered polycrystalline aluminum oxide were studied. Stress relaxation was observed at temperatures of 775°C and higher. Analysis of the data suggests that the relaxation occurred by Coble creep, which represents the first evidence, although indirect, of the existence of the Coble creep mechanism in ceramics.
Electromigration of Ti–Au thin-film conductors at 180° C
Authors: English A. T. , Tai K. L. , Turner P. A.
Published: February 2004

A total of 394 test stripes on sapphire substrates were subjected to constant current density [(2−8)×106A/cm2] at 180 °C. Resistance was measured periodically during the test. Sixty-eight percent of the samples were tested to open-circuit failure. For the remainder, lifetimes were predicted on the basis of the time-on-test and the lifetime statistics of the actual failures. The principal results are as follows: (i) Lifetime varied about as the inverse fourth power of the current density, and was almost independent of the stripe cross-sectional area per se. (ii) The initial slope of the resistance-time curve is highly correlated with, and varies inversely as, the lifetime. (iii) The distribution of failure times in this batch of test stripes was very broad, some 10% failing at times less than one-tenth the median time to failure (MTF), and about 4% at times greater than 10× the MTF. (iv) Estimates of performance under various conditions of service have been made. Operation at current densities above the mid 105 A/cm2 range at 100 °C are not recommended for high-reliability applications.
Photon recycling in semiconductor lasers
Authors: Stern Frank , Woodall J. M.
Published: February 2004

In a suitably designed semiconductor laser, spontaneously emitted photons with energies above the absorption edge can be reabsorbed in the active layer and can decrease the current density that must be supplied to reach the lasing threshold. The magnitude of the threshold reduction is estimated to be about 20% in a GaAs double-heterostructure laser at room temperature.
An 8% efficient layered Schottky-barrier solar cell
Authors: Anderson W. A. , Delahoy A. E. , Milano R. A.
Published: February 2004

An 8.1% efficient 1-cm2 Schottky-barrier solar cell has been fabricated in our laboratory using a layered Schottky barrier on <100> 2-Ω cm p-type silicon. Reproducible results have been obtained on the layered structure which involves 44-Å Cr adjacent to the silicon to obtain good photovoltaic voltage and a 58-Å Cu overlayer to decrease cell resistance. The layered structure provides good control of barrier height, resistance, and optical transmission. Application of this approach should produce a 15% efficient Schottky solar cell and be readily applied to thin-film silicon solar cells when high-quality thin silicon films have been developed.
Magnetization and magnetic entropy of Dy2Ti2O7
Authors: Flood Dennis J.
Published: February 2004

Isothermal measurements of the magnetic entropy, magnetization, and differential susceptibility of Dy2Ti2O7 have been made. Absolute values of magnetic entropy have been determined as a function of applied magnetic field for several temperatures in the range 2–20 K, and several isofield lines in the magnetic entropy-temperature plane have been determined. Magnetization measurements, which extended into the saturation region, yield a powder-average magnetic moment of 4.7±0.2 μB/ion. A van Vleck contribution to M was also observed. The results are consistent with the assumption of a nearly pure Jz = ± 15/2 ground-state Kramers doublet for the Dy+++ ion. Comments on the suitability of Dy2Ti2O7 for use in a magnetic refrigerator cycling between 4.2 and 20 K are included.
Self-heating hotspots in superconducting thin-film microbridges
Authors: Skocpol W. J. , Beasley M. R. , Tinkham M.
Published: February 2004

Heating effects in both long and short superconducting thin-film microbridges are described and analyzed. Except near Tc at low voltages where superconducting quantum processes occur, all of our experimental dc I-V characteristics can be satisfactorily understood on the basis of a simple model of a localized normal hotspot maintained by Joule heating. We consider approximations appropriate to the cases of long bridges, short bridges, and bridges coupled to microwave radiation. The analysis leads to analytic expressions for the I-V characteristics which agree well with the experimental data. We show that the formation of such a hotspot is the dominant cause of the hysteresis observed in the I-V characteristics at low temperatures. We also show that the growth of such a hotspot imposes a high-voltage limit on the ac Josephson effect in these devices, and we compare the importance of such heating effects at high voltages in various types of superconducting weak links.