bluuebunny/crossref_metadata_2025 huggingface dataset:
Photoconductivity in germanium doped with gold
Authors: Jayakumar V. , Ashley K. L.
Published: February 2004

Detailed correlation between theoretical and experimental behavior of photoconductivity in p-type Ge:Au is presented. The electron capture coefficient of Au in the donor state, γn+, is obtained as 5.0×10−7cm3 sec−1. The theoretical spatial distribution of excess free carriers and impurities in the various ionized states, for surface generation of electron-hole pairs, is presented. The influence of surface recombination on photoconductive characteristics is considered. The excitation source was a spontaneous-emitting GaAs diode which allowed the intensity of infrared emission to be easily and accurately controlled.
Theory of pulsed internal optical parametric oscillators
Authors: Davis J. I. , Krupke W. F.
Published: February 2004

A model has been developed to describe the transient behavior of the triply resonated internal optical parametric oscillator (IOPO). Pump, signal, and idler fluxes are expressed as Gaussian eigenmodes of the laser and parametric oscillator resonators, and the resulting equations of motion are parameterized in terms of the Boyd-Kleinman integrals with equal confocal parameters for all waves. Effects of cavity mode-pulling and laser-medium dispersion have been included in the analysis. The transient behavior of IOPO devices driven by a cw-pumped, repetitively Q-switched Nd:YAG laser medium and using parametric materials of both low and high nonlinearity has been computed. The influence of mode pulling and laser-medium dispersion on the dynamic response of the IOPO was explored with respect to (i) exchange of energy between pump wave and signal and idler waves, (ii) approach to the steady state, and (iii) operation in the ``efficient'' pulsing regime.
Computer studies of cylindrical magnetic domains
Authors: Chou S. C.
Published: February 2004

The dimensions of stable isolated elliptical-shaped cylindrical domains allowed in the presence of domain-wall coercivity and varying amounts of wall energy anisotropy are obtained numerically.
Magnetic behavior of quenched and aged CoFe2O4–Co3O4 alloys
Authors: Takahashi Masatake , Fine Morris E.
Published: February 2004

The saturation magnetization (Ms) and intrinsic coercive force (Hc) of spinel-structured CoFe2O4–Co3O4 samples were measured in the quenched condition and also after aging inside the miscibility gap which is present below 860°K in this system. Magnetic properties were interpreted through correlation with the sample's microstructures. The isothermal Ms of as-quenched samples decreases approximately linearly with Co content. At low temperatures compensation compositions exist near 25 cation% Fe. From the composition dependence of Ms at low temperatures, and assuming Néel's model, it was concluded that the addition of Co to CoFe2O4 made the cation distribution more normal and that Co3+ entered B sites diamagnetically replacing Fe3+. The intrinsic coercive force of as-quenched samples were small at room temperature but those at low temperatures were very large; Hc values at 77°K were 22, 15, and 4.8 kOe for 30, 35, and 50 cation% Fe samples, respectively. This was attributed to the presence of compensated M=0 regions in the samples due to composition fluctuations arising from spinodal decomposition which occurred during the quench. It was suggested that these act as large energy barriers to domain-wall motion by a process similar to exchange anisotropy. Compensation does not occur at temperatures higher that 200°K; thus Hc at room temperature is small. The Hc values of samples fully aged at 500°C measured at room temperature were 7 and 4.5 kOe for 35 and 50 cation%Fe, respectively, while those measured at 77°K were 22 and 12.5 kOe. The maximum energy products (BH) at room temperature were 0.25 and 1.0×106 G Oe. Aging of 45 and 50 cation % Fe samples at 700°C did not cause any large increase in Hc because 700°C is outside the spinodal. The large Hc can be explained by single-domain precipitates of composition near CoFe2O4 (which has a large crystalline anisotropy) produced by spinodal decomposition where isolated regions are formed due to the wavelike nature of the decomposition product. The small Hc obtained on aging outside the spinodal is interpreted by classical nucleation and growth decomposition which does not produce isolated ``CoFe2O4'' precipitates when it is the major component.
Radial conduction effects in the pulse method of measuring thermal diffusivity
Authors: Donaldson A. B.
Published: February 2004

This paper discusses the effects of radial conduction on thermal diffusivity measurements obtained by the pulse method. The solution to the mathematical problem of transient two-dimensional conduction which follows an instantaneous disk source of energy at one surface of an infinite slab is used to determine the half-time as a function of boundary heat losses. This value is then compared with the half-time obtained when radial conduction is neglected. The magnitudes of the effects for various ratios of pulse radius to slab thickness are tabulated.
Full-range solution for the measurement of thin-film surface densities with proton-excited x rays
Authors: Reuter F. William , Smith Harold P.
Published: February 2004

A Fredholm-integral expression for characteristic x-ray production by proton bombardment is developed relating multicomponent elemental thin-film concentration profiles to proton-stopping power, x-ray-production cross section, and x-ray attenuation. The thickness of Al2O3 and Ta2O5 films on their respective metallic substrates were measured with 20- to 80-keV protons with an accuracy of 5% for thick films (1200 Å) and 25% for thinner films (30 Å). Nonlinear regression analysis of the data indicated that all parameters of interest, including the zero-voltage anodization potential, can be determined from the raw data. With exception to the oxygen K-shell x-ray attenuation coefficient, the parameters were determined with good to reasonable accuracy. A general concentration profile could not be determined by numerical methods as a result of insufficient variation in the kernel of the integral equation.
Determination of the surface energy of naphthalene crystals by cleavage method
Authors: Maugis D. , Andarelli G.
Published: February 2004

Results of Skvortsov et al. are reexamined, including correction factors neglected by the authors.
Ultrasonic hysteresis absorption in polymers
Authors: Hartmann Bruce , Jarzynski Jacek
Published: February 2004

Ultrasonic absorption measurements were made in polymethylmethacrylate, polyethylene, and polyethylene oxide as functions of frequency, temperature, and strain. At room temperature, all three polymers show a hysteresis-type absorption that extends at least over the frequency range from 1 to 107 Hz, as shown by using literature values for results at 1 Hz. There is no strain dependence to the absorption in any of the polymers in the strain range from 10−9 to 10−6. The mechanism responsible for the hysteresis absorption is postulated to be the trapping of the polymer in one of its many local metastable potential-energy minima. This mechanism leads to the prediction that the hysteresis absorption should be a linearly decreasing function of volume and this prediction is in reasonable agreement with the experimental data.
Investigation of film-thickness determination by oscillating quartz resonators with large mass load
Authors: Lu Chih-Shun , Lewis Owen
Published: February 2004

A one-dimensional acoustical composite-resonator model is used to study the behavior of a quartz-crystal resonator with large mass load. On the basis of this model, it is found that the exact relationship between the frequency shift and the added mass depends on the acoustic impedance of the deposited material. The experimental data for three materials (silver, copper, and lead) with different acoustic impedances are shown to be in good agreement with the theoretical predictions. The validity and limitations of the presently used equations for thickness determination by quartz-crystal resonators are also discussed.
Thermomigration of aluminum-rich liquid droplets in silicon
Authors: Cline H. E. , Anthony T. R.
Published: February 2004

Aluminum-rich liquid droplets migrating in a thermal gradient in the 〈111〉 direction in silicon form flattened triangular platelets bounded by (111) planes and leave behind p-type trails in n-type silicon. The droplet migration rate decreases with decreasing droplet size because of processes at the solid-liquid interface. Above 700°C the migration rate is an Arrhenius function of temperature and is consistent with a liquid diffusion coefficient D=4×10−3 exp(−[7.1 kcal/mole °K]/RT) cm2/sec. Below 700°C, an aluminum-oxygen interaction causes a large decrease in droplet velcotiy. Droplet migration up a temperature gradient in the Al–Si system generates a hydrostatic tension in the droplet liquid which exceeds the yield stress of silicon after the droplet has traveled 7°C. On cooling a sample and solidifying a droplet, a large positive pressure is produced in the solidified droplet which causes yielding or cracking in the surrounding silicon matrix.
Processes involved in the triggering of vacuum breakdown by low-velocity microparticles
Authors: Chatterton P. A. , Menon M. M. , Srivastava K. D.
Published: February 2004

The role of low-velocity microparticles (diameters < 100 μm; velocities ∼ 10–50 m/sec) in inducing breakdown in a high vacuum gap is investigated. On the basis of a simple model, it is shown that as an anode initiated microparticle approaches the cathode, fields sufficient to cause appreciable field emission (> 109 V/m) are possible at the cathode surface. The emission current not only causes partial neutralization of the initial charge on the microparticle, but also raises the temperature (> 2000°K) of the particle surface. As a consequence, a significant increase in gas pressure (∼ 100 Torr) in the microvolume between the cathode and the particle is possible, resulting in a discharge between the two. Such a discharge could act as a trigger for the breakdown of the main gap. Other possible processes that could arise due to the onset of melting or boiling of the bombarded surface, and which may lead to breakdown of the entire gap, are also discussed.
Transverse ion temperature in an ionospheric wind tunnel
Authors: Fournier Gérard , Pigache Daniel
Published: February 2004

The transverse ion temperature Ti⊥ of a collisionless plasma stream which simulates the ionospheric plasma has been measured by two independent means: a long cylindrical probe and a collimator-collector device. Results with the long probe provide an experimental verification of the known end-effect theories. Reliable measurements of Ti⊥ have been performed by these two methods, which are evaluated and compared. Ti⊥ can be varied by means of a negatively biased grid immersed in the plasma stream, the grid mesh being larger than about three Debye lengths. The achieved values are typical of the ionospheric conditions; Ti⊥ was the last parameter to be simulated with its actual value in ionospheric wind tunnels. Examples of cylinder wakes in such conditions are given.
Gas-temperature measurement in pulsed H2O laser discharges
Authors: Pichamuthu J. P. , Hassler J. C. , Coleman P. D.
Published: February 2004

A spectroscopic technique of temperature measurement with submicrosecond time resolution, using ultraviolet OH emission, is described. The time varying gas temperature was measured during a 4-μsec 150-A current pulse through H2O. The gas temperature rose to 2000°K during the current pulse in pure H2O but to only 550°K in H2O–He discharges. The 2ν2 mode, which contains several lower laser levels, is pumped due to the gas heating. This tends to switch off the gain, attenuate the laser pulse, and make the medium lossy in the afterglow. Helium alleviates these problems by maintaing a low gas temperature.
Electronic charge trapping in chemical vapor-deposited thin films of Al2O3 on silicon
Authors: Mehta D. A. , Butler S. R. , Feigl F. J.
Published: February 2004

Electronic charge trapping in 200-nm thick films of Al2O3 has been investigated by photoinjection-photodepopulation and capacitance-voltage measurements. The Al2O3 films were chemically vapor deposited on (100) silicon substrates by hydrolysis of AlCl3 at 900 °C in the presence of H2 and CO2. Released charge during monochromatic depopulation at 480 nm was measured as a function of applied voltage. Analysis of these results gave (a) optically releasable charges (1.5×1017 cm−3) and (b) fixed charges introduced during photoinjection (4.90×1017 cm−3). The centroid of these charges was determined to be 140 nm from the metal-Al2O3 interface. The charge densities calculated from these measurements and the C-V measurements showed excellent internal consistency. The photodepopulation current measurements as a function of wavelength were carried out in the range 700–350 nm. These results indicated that the trapping states are continuously distributed in this spectral energy range in a nonuniform manner. These results combined with optical bleaching measurements indicated dynamical broadening of the individual trapping states. A phenomenological model of electron traps in Al2O3 is proposed which is consistent with the results obtained in this research. According to this model, one distribution of trapping states describes both the optically releasable and the fixed charges.
Recombination studies on gamma-irradiated n-type silicon
Authors: Curtis O. L. , Srour J. R. , Rauch R. B.
Published: February 2004

Results of a detailed investigation of recombination in phosphorus-doped Co60 γ-irradiated n-type silicon are reported. An analytical procedure is employed which allows, in principle, a complete and unambiguous determination of parameters associated with recombination centers. Properties of two recombination centers are determined. The level most important at low excess densities is determined to be 0.40 ±0.015 eV from the conduction band. cn varies as exp(0.06±0.015eV/kT), and cp varies as exp(0.03±0.015eV/kT). The capture-probability ratio cp/cn varies from 8 ± 1 at 303°K to 9.5 ± 1 at 370°K. The level dominant at high excess densities is placed at 0.21 ± 0.03 eV below the conduction band with cn ∼exp(0.01±0.01eV/kT) and cp ∼exp(−0.05±0.03eV/kT). The corresponding capture probability ratio, cp/cn, varies from ∼5.6 at 303 °K to ∼8 at 370 °K. Based upon dependence on phosphorus concentration and annealing behavior, the deeper level appears to belong to the E center. There is some evidence that the other level is also associated with phosphorus-containing defects.
Recombination instabilities in semiconductors doped with deep two-level traps
Authors: Antognetti P. , Chiabrera A. , Ridella S.
Published: February 2004

This paper presents a general theory of the recombination-wave diode, i.e., of a bulk semiconductor doped with deep two-level traps. Such theory includes other proposed models as particular cases. The range of validity of such models is discussed. The high-frequency carrier lifetimes are compared with the dc lifetimes and with experimental values on gold-doped silicon. A limiting condition to obtain oscillations is determined on the semiconductor doping. The theoretical results concerning the oscillation frequency and the threshold voltage are compared with experimental data on gold-doped silicon.
Vapor deposition of platinum using cw laser energy
Authors: Hess Milton S. , Milkosky John F.
Published: February 2004

The fabrication of beam lead silicon integrated-circuit devices involves the vapor deposition of platinum, which is generally accomplished by electron-beam bombardment or by low-voltage sputtering. In an effort to develop alternative platinum-deposition techniques, we have evaluated the feasibility of using a cw laser as the energy source for a thermal-evaporation process. Using a 20-W-output YAG laser, uniform platinum films were successfully deposited in a stable easily controlled process. Films deposited on oxidized silicon slices evidenced no space-charge buildup in the oxide, the change in flat-band voltage following platinum deposition being negligible. Although the evaporation rate that was obtained is but 0.2 Å/min at a 6-cm source-to-substrate distance, it is concluded that this is entirely a result of the limited power output of the particular laser that was used. No theoretical limitation to the utilization of a laser in vapor-deposition processes was encountered in this study.
Laser writing and erasing on chalcogenide films
Authors: von Gutfeld R. J. , Chaudhari P.
Published: February 2004

Optical switching from the mostly crystalline to the amorphous state has been studied in TeGeAs alloy films using ∼ 5-nsec pulses from a nitrogen laser pumped dye laser. These ``reverse-mode'' written spots were switched (erased) by both optical and thermal means. Microscopic examination of the films, thermally crystallized before optical writing, indicates the existence of a two-phase system consisting of Te crystallites in a background of amorphous Ge-rich material. A similar condition is again found after a write-erase cycle has occurred. Computer calculations on the thermal history of the crystalline film resulting from a 5-nsec pulse indicate initial cooling rates of the order of 1010°C/sec.
A Mössbauer investigation of mechanically induced magnetic anistropy in natural hematite
Authors: Keeling Rolland O.
Published: February 2004

The magnetic structure of hematite is affected by the mechanical processes of cutting and lapping thin slices or plates of natural single crystals for Mössbauer absorption measurements. The effect, as observed in plates perpendicular to the basal plane, is to produce an anisotropic Fe3+ spin distribution in which the total spin component in the plane of the plate is less than that normal to the plate. The anisotropy is removed by annealing. Magnetic fields of 10 kOe produce no remanent changes in the spin distribution either before or after annealing. This implies, and measurements confirm, the existence of an accompanying directional dependence in the remanent magnetization. The effect is attributed to deformation twinning which results from stresses imposed during sample preparation.
New approach to Lorentz approximation in micromagnetism
Authors: Adam Gh. , Corciovei A.
Published: February 2004

Hoffmann showed that the variational theory of magnetization ripple and related phenomena is greatly simplified if magnetostatic interactions inside a finite range (the main part of the magnetostatic interaction) are retained, while interactions outside this range (the residual part) are neglected. [The critical range is several orders of magnitude larger than the cutoff of short-range (e. g., exchange) interactions.] Hoffmann's way of deriving the main part of the magnetostatic energy rests, however, on dubious approximations whose validity cannot be settled within the Lorentz approach to micromagnetic evaluation of dipolar sums. An alternative approach to that of Lorentz is developed here which permits the main part of the magnetostatic interaction to be calculated directly from dipolar sums The result is different from that of Hoffmann. It is shown the the Lorentz approximation is not responsible for this difference, which stems rather from the use by Hoffmann of an inappropriate expression for the potential created by an assembly of dipoles. As a consequence, serious implications for several micromagnetic calculations are to be expected.
Compression of NaCl and CsCl to 32 kbar
Authors: Decker D. L. , Worlton T. G.
Published: February 2004

The compression of NaCl and CsCl has been measured to 32 kbar using time-of-flight neutron-diffraction techniques. These measurements indicate that Decker's equation of state for CsCl yields pressures which are about 2% lower than does his equation of state for NaCl over this range of pressures.
Effect of substrate bias and deposition temperature on the properties of thick sputtered chromium deposits
Authors: Patten J. W. , McClanahan E. D.
Published: February 2004

Several thick dc-sputtered pure-chromium deposits were examined for variations in hardness, crystallographic orientation, and microstructure as a function of substrate bias and deposition temperature. Deposit hardness increased to a maximum of approximately 700 DPH at −50 V substrate bias and then decreased for higher bias. Hardness also decreased with increasing deposition temperature. Bias had no effect on orientation but increasing temperature favored random rather than highly textured orientation. Microstructure changes corresponding to hardness changes were observed. Some tensile ductility was noted in a 400 °C deposit sputtered using a −50 bias.
Silicon in LPE-grown Ga1−xAlxAs: effect of the arsenic solution concentration
Authors: Rado W. G. , Crawley R. L.
Published: February 2004

Additional data are obtained concerning the differences in the amphoteric behavior of Si in liquid-phase epitaxially (LPE) grown Ga1−xAlxAs on (111)-As and (111)-Ga face GaAs substrates. For growth on (111)-As face substrates the logarithmic dependence of the Si n-to-p transition temperature, Ttr, on the initial Al-to-As concentration ratio in solution is further substantiated. However, it is found that for growth on (111)-Ga face substrates, Ttr can be predicted more accurately based on the initial As concentration in solution only. For (111)-Ga face growth, it is found that Ttr is virtually independent of initial Al and only slightly dependent on the initial Si concentration in the solution.
Potential due to a double lamina
Authors: Kanwal R. P. , Sachdeva B. K.
Published: February 2004

A solution for the electrostatic field due to an inner lamina at a constant potential surrounded by an annular ring at another constant potential is presented. Two cases are considered. The first is a double circular disk and the second is a double spherical cap.
Positive column of a helium discharge in transition from the homogeneous to the striated state
Authors: Wellenstein H. F. , Robertson W. W.
Published: February 2004

The critical conditions for appearance or disappearance of striations in the positive column of a helium discharge are expressable in terms of discharge current, gas pressure, and tube radius as I=A/(pR)5. For I in mA, P in Torr, and R in cm, A ranges from 160 to 30, depending upon position of observation from cathode to anode end of positive column.
Electrical resistivity of conducting particles in an insulating matrix
Authors: Bueche F.
Published: February 2004

When conducting particles are added to a nonconducting matrix, conductivity increases abruptly at a critical concentration. The theory of infinite chains is used to predict the variation of conductivity with particle concentration. Factors which determine the critical concentration are discussed.
Alignment of carbon and other man-made fibers by magnetic fields
Authors: Timbrell V.
Published: February 2004

High-modulus carbon fibers in liquid suspension are aligned precisely by magnetic fields. Other man-made fibers can also be aligned after coating with iron. This response has many applications in light-scattering experiments and in the preparation of composites. Thin films of aligned fibers offer advantages in determinations of diameter and length distributions and in other types of examination.
Scattering of a transverse elastic wave by an elastic sphere in a solid medium
Authors: McBride Robert J. , Kraft David W.
Published: February 2004

Cross sections are computed for the scattering of a plane transverse elastic wave by an elastic sphere in an infinite isotropic homogeneous elastic solid. Analytic expressions are derived for the matrix elements indicated by Einspruch, Witterholt, and Truell, and the resulting matrix equations are solved numerically. The dependence of the scattering cross section upon K1a (K1 is the transverse propagation constant, a is the obstacle radius) over the range 0.01–10 is computed for various combinations of host and scatterer materials. The sensitivity of the cross section and its component terms to the elastic properties of the host and scatterer materials, and their behavior in the Rayleigh limit approximation are discussed. The calculations include the case of a constant host with a varying obstacle, and a constant scatterer in a varying host medium. It is found that most of the examples tested can be grouped conveniently into four classes, with a fifth category containing unstable results; this classification scheme is based on the general shape and specific peaking behavior of the cross-section curves. The peaking behavior is related to the occurrence of zeros in the spherical Bessel and Neumann functions.
Expansion, crazing and exfoliation of lithium niobate on ion bombardment and comparison results for sapphire
Authors: Primak William
Published: February 2004

Surface deformation and destruction resulting from bombardment with respective 140-keV ions H+, D+, He+, and Ne+ were observed. Following bombardment, spontaneous secular changes occurred over a period of many months at room temperature. Optical absorption curves of the specimens showed interference effects. Calculations of optical interference patterns caused by blistering are given. Some bombarded lithium niobate surfaces became crazed. The patterns consisted of fractures parallel to the ZY plane, despite no evidence of cleavage. Exfoliation occurred by material from the areas between the fractures breaking away. The surface deformation of a proton-bombarded specimen annealed below 300°C simultaneously with the intense optical absorption caused by the hydrogen. Calculations of effects to be expected from neutron irradiation are given. The depths of the effects are compared with the particle ranges and appear to be close to their median projected ranges. The depths are greatly in excess of the ranges calculated from Lindhard's theories, which overestimate the electronic stopping power at these energies. The radiation effects along the range are important in determining the blistering behavior. The piezoelectric effect may be the cause of the crazing paralle to Y.
Phenomenological theory of antiferroelectricity and ferroelectricity applied to NaNbO3 and the system KNbO3–NaNbO3
Authors: Darlington C. N. W.
Published: February 2004

Cross has applied the Kittel-Devonshire phenomenological treatment of ferroelectricity and antiferroelectricity to NaNbO3 and the system NaNbO3–KNbO3. Recent experimental work has shown that the low-temperature form has rhombohedral symmetry with space group R3c, and that therefore this phase is a ``line ferroelectric'', rather than a ``cone ferroelectric'' with canted polarization, as had been supposed by Cross. The amendments to the phenomenology are discussed, and it is shown that the agreement with observation is improved using the correct low-temperature form.
Calculation of laser-induced stresses in water
Authors: Feiock F. D. , Goodwin L. K.
Published: February 2004

Pressure profiles in water due to absorption of CO2 laser radiation are computed using a hydrodynamic computer code incorporating thermal conductivity and an equation of state which allows vaporization. In the absence of vaporization, the numerical results agree with the analytic solution which gives a thermal-expansion pulse of a fraction of 1 kbar. At longer times, a vaporization pulse is formed which approaches 1.8 kbar in 0.3 μsec. This gives an electromagnetic-to-acoustic-energy conversion efficiency in excess of 1.3% which is an order of magnitude greater than that obtained without vaporization.
Indirect, Γ8v-X1c, band gap in GaAs1−xPx
Authors: Onton A. , Foster L. M.
Published: February 2004

The indirect band gap of GaAs1−xPx has been determined accurately over a large alloy composition range. The results were obtained with a wavelength derivative technique in optical absorption on material grown under complete equilibrium conditions. Zero-phonon as well as momentum-conserving phonon-assisted free-exciton transitions were observed. A distinct curvature in the direct band gap-vs-alloy composition curve is determined. Photoluminescence measurements of the same samples, together with the absorption edge data, give the alloy composition dependences of the energies of donor-acceptor pairs and bound excitons; thus the intrinsic nature of the transitions observed in absorption is established.
Magnetophotoconductivity of semi-insulating GaAs and its behavior upon electron bombardment
Authors: Nomicos C. D. , Euthymiou P. C.
Published: February 2004

The effect of a magnetic field on the photoconductivity of semi-insulating p-type GaAs single crystals mounted in the Voigt geometry has been investigated within the temperature region 260–350 °K. If the magnetic field deflects the photocarriers toward the volume of the specimen, a decrease of the photoconductivity is obtained for weak electric field and an increase for high electric field under constant magnetic field. The decrease is attributed to the combination of photoconductivity and photomagnetoelectric effect while the increase is attributed to the difference in the values of lifetime across the specimen thickness. From photoconductivity measurements with and without the application of magnetic field, the carrier lifetimes were determined. Bombardment of the specimen with 1-MeV average energy β particles resulted in a decrease of the magnetophotoconductivity at high electric fields.
Resonant enhancement of the recombination probability associated with isoelectronic trap states in semiconductor alloys: In1−xGaxP:N laser operation (77 °K) in the yellow-green (λ≲5560 Å, ℏ ω≳2.23 eV)
Authors: Duke C. B. , Smith D. L. , Kleiman G. G. , Macksey H. M. , Holonyak N. , Dupuis R. D. , Campbell J. C.
Published: February 2004

Calculations of the recombination probability of an electron and hole in III-V ternary alloys containing short-range isoelectronic traps indicate its resonant enhancement when by varying the alloy composition, the electronic trap state is made degenerate with the direct (Γ) minimum in the conduction band. This result is consistent with observations of strong photostimulated laser operation of the N-trap transition in In1−xGaxP (0.6≤x≤0.7) in cases for which this state occurs near and above the direct band gap. These results lead to III-V semiconductor laser operation at wavelengths as short as or shorter than 5560 Å (2.23 eV, 77 °K), with the ultimate limit in In1−xGaxP:N being about EN ≈EΓ=2.27 eV (5470 Å).
Magnetic transitions in the insulator nickel squarate dihydrate, NiC4O4·2H2O
Authors: Gerstein B. C. , Habenschuss M.
Published: February 2004

The real and imaginary initial susceptibilities of two samples of nickel squarate dihydrate, NiC4O4·2H2O have been measured in the range 1.2–4°K. Both samples exhibited deviations from Curie-Weiss behavior and magnetic losses characteristic of ferromagnetic ordering. Magnetic transitions were found in both samples in the neighborhood of 1.6 and 1.9°K, the higher temperature transition occuring at 1.8°K in a sample grown from an alcohol-water solution, and at 2.1°K in a sample grown from a pure water solution. The difference in magnetic behavior of the two samples is thought to be related to the type of solvent molecule clathrated by the open NiC4O4·2H2O structure.
Reduced Phonon Noise in the Acoustoelectric Amplifier
Authors: Schulz M. , Reik H. G.
Published: February 2004

In long acoustoelectric amplifiers, the phonon noise at a frequency of maximum acoustoelectric gain in the gigahertz regime is reduced to 110 of the thermal noise level if GaAs is used as the amplifying material and to ½ of the thermal level for CdS. The reduction is quantitatively measured by a double-pulse technique. In order to obtain a large gain within the linear regime of the device, long and thin piezoelectric semiconductor rods having a high mobility and a weak piezoelectric coupling, must be used for the amplifier. In a GaAs amplifier an over-all linear gain of 90 dB can be obtained, before nonlinear effects set in.
Transient Plasma Diagnostics Using Simultaneous CO2 Laser Interferometry and Absorption
Authors: Offenberger A. A. , Kerr R. D.
Published: February 2004

A plasma diagnostic technique using simultaneous CO2 laser interferometry and absorption is described which allows temporal determination of both electron density ne and temperature Te. Results are given for the case of a transient plasma produced by focusing TEA CO2 laser radiation into argon. Application of these diagnostics to laser-produced plasmas provides a method for recombination coefficient measurements. Time dependence of average ne and Te along with a recombination coefficient for argon are reported.
Electrical Behavior of Composite Discontinuous Films
Authors: Tick Paul A. , Fehlner Francis P.
Published: February 2004

Composite discontinuous films of gold-rich islands grown on palladium nucleii exhibit two distinctly different regions of temperature-dependent conductivity. At low temperatures, film properties are dominated by a process characteristic of large gold-rich islands which are closely spaced. This results in a film with a high resistivity and a low activation energy. At higher temperatures, the process abruptly changes and the conductivity of the film begins to increase rapidly with temperature. The dominant transport process in this conductivity region is attributed to activated tunneling between the small palladium-rich islands.
Measurements of the Effect of a Thin Plasma Layer on the Near Field of an Aperture Antenna
Authors: Rudderow W. H.
Published: February 2004

Measurements of the X-band microwave attenuation produced by a high-density air plasma slab coating an aperture antenna were performed. The plasma was produced in a rectangular shock tube using the conical driving technique. Measured shock velocities varied from 2.4 to 5.0 mm/μ sec at initial pressures of 10–50 Torr. Plasma slabs with a thickness of 3.175 and 12.7 mm were utilized in the experiments. Attenuation measurements are in reasonable agreement with impedance sheet theoretical predictions. Additional measurements were made of the effectiveness of sulfur hexafluoride as a plasma alleviant in a high-temperature oxidizing environment. Significant reduction in microwave attenuation was observed for high-temperature air plasmas containing small mole fractions of sulfur hexafluoride.
Laser-Induced Stress Waves in Quartz Phenolic
Authors: Anderholm N. C. , Boade R. R.
Published: February 2004

Observations of stress-wave generation in quartz phenolic by laser irradiation are reported. A value of the Grüneisen parameter of 0.22±0.05 is found at wavelengths of λ=0.6943 and 1.06 μ.
Measurement and Interpretation of Long Spontaneous Lifetimes in Double Heterostructure Lasers
Authors: Dyment J. C. , Ripper J. E. , Lee T. P.
Published: February 2004

From measurements of stimulated emission time delays, values of the spontaneous carrier lifetime at the lasing threshold for double heterostructure (DH) lasers have been determined in the temperature range 77–400°K. Typical lifetime values are found to decrease from 10 to 15 nsec at 77°K to about 2–4 nsec near 400°K. These lifetimes are longer by factors of 3 and 6 than in single heterostructure (SH) lasers and homostructure (diffused) lasers, respectively. It is shown theoretically that this increased lifetime alone contributes to lowering the threshold current density for DH lasers by about a factor of 2. It is also shown how the long delay times can be reduced by prepumping the laser in order to increase the maximum allowable repetition rate in pulsed operation. Finally, it is suggested that the longer lifetime values in DH lasers are a result of the growth conditions used to form the Si-doped active regions. These conditions produce a high degree of compensation in DH lasers which is not present in the diffused active regions of either SH or homostructure lasers.
Effects of Impurity Compensation on Electrical Properties of p-Type Germanium under Hydrostatic Pressure
Authors: Kanda Yozo , Kato Yoshiki , Narita Koziro
Published: February 2004

The fractional change of resistivity Δρ/ρ0 under hydrostatic pressure up to 30 kbar and Hall effect up to 10 kbar have been measured in Cu-doped germanium samples with acceptor concentration Na ranging from 1013 to 3.96 × 1016 cm−3, and with compensation ratios K from 0.38 to 0.968. Δρ/ρ0 increases from negative to positive values with increasing K. The experimental behavior of Δρ/ρ0 with hydrostatic pressure P is divided into four categories: (i) negative and linear for Na ∼ 1015 cm−3 and small K; (ii) positive and linear for Na ≥ 3.4 × 1015 cm−3 and 0.7 ≤ K ≤ 0.968; (iii) sublinear for Na < 3 × 1014 cm−3 and any K; and (iv) superlinear (or exponential) and positive for Na ∼ ni, where ni is the intrinsic carrier concentration. These features were analyzed theoretically. A good agreement between analytical calculations and the data is obtained if the values d(lnμhL)/dP = 6.2 × 10−3 kbar−1 and d(lnμhI)/dP = −14.4 × 10−3 kbar−1 are used, where μhL and μhI are the lattice and ionized impurity scattering mobility of hole, respectively. The present experiment suggests that samples with Na ≥ 1016 cm−3 and 0.9 ≤ K ≤ 0.96 can be used as hydrostatic pressure sensors around room temperature.
Lasing Action in Electron-Beam-Pumped ZnO
Authors: Shewchun J. , Garside B. K. , Kawasaki B. S. , Efthymiopoulos T.
Published: February 2004

Results of a detailed investigation on the time dependence of the stimulated emission from electron-beam-pumped ZnO are reported. Unlike the behavior found in CdS, CdSe, and GaAs, no rapid tuning with time of the stimulated emission to longer wavelengths has been observed. A small tuning is observed which is consistent with thermal variation of the band gap. Furthermore, no temporal variation of the angular position of the spatial mode has been observed as is the case with CdSe and GaAs. More conclusive evidence for the presence of lasing action is presented; in particular, the first observation of very-high-visibilitv frequency modes is reported.
Gamma-Radiation Damage in Epitaxial Gallium Arsenide
Authors: Brehm G. E. , Pearson G. L.
Published: February 2004

Electrical and photoluminescence measurements were carried out on liquid epitaxial GaAs single crystals after irradiation at room temperature by 1.25-MeV 60Co γ rays. Following each of a series of irradiations, Hall measurements were made on both n- and p-type crystals as a function of temperature between 77 and 300°K. The n-type crystals exhibited energy levels 0.13, 0.16, and 0.30 eV below the conduction band minimum after irradiation. The 0.13- and 0.16-eV levels were introduced during irradiation at roughly one-half the rate at which compensating deep acceptors were introduced. The p-type crystals showed energy levels 0.059 and 0.10 eV above the valence band maximum. Before irradiation, these p-type crystals had energy levels in the lower 0.20 eV level of the band gap. It is, therefore, not possible to determine whether the 0.059 and 0.10 eV were produced by irradiation or were merely uncovered as the free-hole density was reduced by radiation-induced deep donors. The carrier removal rate at 77°K was 0.012 cm−1 for p-type crystals. Photoluminescence measurements on irradiated material revealed additional energy levels near the center of the band gap.
Current Oscillations in n-Type Ge at Low Temperatures
Authors: de Biasi Ronaldo S. , Yee S.S.
Published: February 2004

Measurements were performed in high-purity n-type germanium in the temperature range 15–30 K with the electric field applied in the [111], [110], and [100] directions. A large anisotropy of the conductivity was observed. In the case of the [111] orientation, current oscillations in the megahertz range were observed in the electric field range 3–20 V/cm. The results are consistent with the theory of electron transfer among 〈111〉 valleys of the conduction band in germanium.
Investigation of Ferrimagnetic Cobalt-Doped Gamma-Ferric Oxide Micropowders
Authors: Khalafalla Dorothy , Morrish A. H.
Published: February 2004

The magnetic properties of cobalt-doped γ-Fe2O3 were investigated, and the crystallographic properties were examined using the Mössbauer technique and x-ray diffraction. An increase in lattice parameter with cobalt concentration was observed. A large increase in coercive force, especially pronounced at low temperatures, was proportional to cobalt concentration, and may be accounted for by single-ion anisotropy. The magnetic moment changed very little. Measurements on partially aligned particles indicated that the particles were single domain. The Mössbauer spectra provided no evidence for the presence of Fe2+ or Fe4+ ions. Also, at helium temperature the anisotropy was such that the samples were not saturated at 50 kOe. The experimental data are consistent with the hypothesis that the cobalt ions replace iron on B sites and also fill B-site vacancies. Conversion to α-Fe2O3 on heating was never attained completely, and it is proposed that cobalt ferrite is present in the heated samples.
Degradation and Reenhancement of the Peak Critical Current in Superconducting Lead
Authors: Winter J. J. , Leupold H. A. , Breslin J. T.
Published: February 2004

Certain samples of the type discussed in a previous article have been shown to exhibit greatly broadened I-R transitions. Although the axial asymmetry of the sample appears to induce the broadening, the transition can be made to approach that of a right circular cylinder of lead by certain surface treatments or by flux trapping. A simple qualitative model is outlined to correlate these phenomena.
Feedback Control Scheme for Scanning X-Ray Topography
Authors: van Mellaert L. J. , Schwuttke G. H.
Published: February 2004

Feedback control of scanning x-ray topography is described. A control scheme is developed that maintains the x-ray topography system at all times at the peak of the rocking curve I(β). The mathematical control scheme is implemented through an angular derivative generator capable of generating the signal dI/dβ on a continuous basis. Circuit requirements to measure dI/dβ continuously are established. Actual measurement of the command signal dI/dβ is accomplished through a modulation technique. Circuit design details are given and the operation of the system is discussed.
Ortho-Positronium Annihilation and the Glass Transition of Nylon 6
Authors: Chuang S. Y. , Tao S. J. , Wilkenfeld J. M.
Published: February 2004

The mean life τ2 or ortho-positronium annihilating in samples of Nylon 6 both dried and containing 0.5% of H2O has been measured as a function of temperature from 15°C up to 100°C. A sudden change of τ2 in the lifetime-vs-temperature curve was found at the glass-transition temperature. The main glass transition for the dry sample is determined to be 50°C and for the sample containing water, 33°C. The Tg measured by this method is lower than that measured by other methods. This agrees well with the result for polystyrene observed by Stevens and Mao.
Unsteady Tangential Newtonian Flow in a Porous Annulus
Authors: Shah Y. T. , AuYong K. S.
Published: February 2004

This communication presents the analytical solutions for the velocity and the pressure distributions for an unsteady tangential Newtonian flow in an annulus of two infinite porous-wall concentric rotating cylinders.
Optically Pumped In1−xGax P Platelet Lasers from the Infrared to the Yellow (8900−5800 Å, 77°K)
Authors: Scifres D. R. , Macksey H. M. , Holonyak N. , Dupuis R. D.
Published: February 2004

The laser operation (77°K) of optically pumped thin platelets of In1−xGaxP over the composition range x=0–0.59 (8900−5800°A) is demonstrated. The samples are prepared from material grown at constant temperature (900–1000°C) from In solution with source InP and GaP introduced at slightly higher temperature. The dependence of the laser photon energy upon composition agrees well with the Γ−χ curves of Lorenz and Onton and confirms the belief that the direct-indirect transition is at x∼0.74. In addition, unique spectral data on In1−x Gax P (x=0.27) are presented that show the mode development from spontaneous to high-level stimulated emission.
Radiation-Induced Extrinsic Photoconductivity in Li-Doped Si
Authors: Fenimore E. , Mortka T. , Corelli J. C.
Published: February 2004

A brief description is given of instrumentation and methods used in the study of radiation damage in lithium-diffused Si. Infrared photoconductivity (1 to 10 μ) and infrared spectroscopy (1 to 50 μ) were used as the probes. The defects were induced in the material by 1.5- MeV electrons with the sample temperature at 300°K during irradiation; one irradiation experiment was run at ∼110°K. No infrared-active defect bands were induced by electrons of E≲5 MeV up to radiation fluences of 3.3×1017 e/cm2. All samples studied which have lithium concentrations in the range 9×1015−2×1017 cm−3 exhibit sharp increases in resistance after heat treatment in the range 200 to 700°K. Dominant radiation-induced photoconductivity arises from levels at Ec=0.2, Ec−0.39, Ec−0.54, Ec−0.6, Ec−0.7, and Ec−0.8 eV in oxygen-rich Si and at Ec−0.2, Ec−0.54, Ec−0.8, Ec−0.92, and Ec−1.0 eV in oxygen-lean Si. The levels are found to disappear and in some cases shift with annealing in the 100–450°C temperature range. In all cases the spectrum is dominated by three or four energy levels after irradiation and after various anneals. Energy levels obtained by other workers using carrier concentration, minority carrier lifetime, and photoluminescence as the probes are compared to our measurements. Due to the complexity of the system and the present lack of adequate theory, no complete analysis of the data can be made.
Possible Field-Assisted Infrared Photocathode
Authors: Dalal Vikram L.
Published: February 2004

The possibility of making field-assisted semiconductor photocathodes in the infrared range is analytically considered. The conditions for efficient and feasible photoemission from reversebiased pn junctions are discussed. Narrow band-gap materials, such as InAs, InSb, and HgCdTe are evaluated as possible materials for such photocathodes. Tunneling and avalanche phenomena are considered and possible design criteria and fabrication techniques are presented.
Current-Voltage Characteristics of Pb Dayem Bridges
Authors: Chen J. T. , Kim S. H. , Kim Y. W.
Published: February 2004

We have investigated the negative-resistance region in the current-voltage characteristics of Pb Dayem bridges. The conditions for observing the negative-resistance region agree with the recent theoretical predictions of Warman and Blackburn who have taken into account the effect of bias-source resistance on the current-voltage characteristics.
Range Distribution Theory Based on Energy Distribution of Implanted Ions
Authors: Furukawa Seijiro , Ishiwara Hiroshi
Published: February 2004

This paper presents a new analysis concerning the range distribution of implanted ions in amorphous substrates. In this analysis, energy distributions of an ion are calculated at steps of collisions in the substrate to determine the range distribution, instead of solving integral equations for the moments of the range which is essential in the theory of Lindhard, Scharff, and Schiott. The validity of this analysis is shown for both single- and multiple-element substrates by assuming a screening function proportional to 1/r and by comparing with the theory of Lindhard et al. The range distribution for the case of multiple-layer substrates, which cannot be calculated by usual theories, is also considered. The special features obtained for this case are (i) there can be discontinuities in ion concentration at the boundaries of the layers and (ii) for even the same dose, the maximum ion concentration can become higher by depositing an appropriate surface layer on a substrate.
Thermoelectric Properties of the Uranium Oxide U3O8
Authors: Djerassi H. , Sorriaux A. P.
Published: February 2004

Thermoelectric power and electrical conductivity results between 300 and 1450°K show that U3O8 (sintered) exhibits an intrinsic semiconducting behavior at high temperature. The energy gap is estimated to be about 0.48 eV.