bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-current blocking temperature writing of double barrier magnetic random access memory cells
Authors: Wang Jianguo , Freitas P. P.
Published: February 2004

A magnetic random access memory cell architecture is fabricated where the pinned layer is reversed by heating above a reduced blocking temperature with a current pulse crossing the junction, and cooled under an external applied field (word line), minimizing half-select switching of nonaddressed bits. In order to improve Joule heating and increase breakdown voltage, a double barrier structure was used, with a common antiferromagnetic layer (60 Å MnIr) two pinned 30 Å CoFe layers, and two free layers incorporating nanooxide structures. The blocking temperature was reduced to 120 °C. A TMR of 25% was achieved for both single barrier and double barrier tunnel junctions with resistance×area products of ∼40 Ω×μm2 and ∼280 Ω×μm2, respectively. Pinned layer writing allows the definition of a three-state memory, requiring, however, a destructive read out. A significant improvement of writing efficiency is observed with the double barrier structure. A 10 ns current pulse of 9 mA/μm2 is sufficient to heat the double barrier junctions above the blocking temperature and induce pinned layer switching.
Correlations between pressure and bandwidth effects in metal–insulator transitions in manganites
Authors: Cui Congwu , Tyson Trevor A.
Published: February 2004

The effect of pressure on the metal–insulator transition in manganites with a broad range of bandwidths is investigated. A critical pressure is found at which the metal–insulator transition temperature, TMI, reaches a maximum value in every sample studied. The origin of this universal pressure and the relation between the pressure effect and the bandwidth on the metal–insulator transition are discussed.
AlGaN-based ultraviolet light-emitting diodes grown on bulk AlN substrates
Authors: Nishida Toshio , Makimoto Toshiki , Saito Hisao , Ban Tomoyuki
Published: February 2004

We have confirmed the potential of a bulk AlN substrate for high current operation of nitride ultraviolet-light-emitting diodes (UV-LEDs). For the high flux UV extraction from nitride UV-LEDs, transparency and high thermal conductivity of the substrates are important issues. The bulk AlN is one of the best candidates, because it satisfies requirements above, and has the same crytallographic symmetry with those of AlGa(In)N families, which is beneficial to the high-quality crystal growth of the nitride device structures. We formed AlGaN-based UV-LEDs on a bulk AlN substrate and compared its performance with that of a reference device grown on an AlN-template grown on a sapphire substrate. The output power linearly increases with a saturation injection current of 300 mA, which is two times higher than that of the reference device. The emission spectrum under high current injection is much more stable than that of conventional substrate.
ELECTRON DIFFUSION EFFECTS DURING HOLOGRAM RECORDING IN CRYSTALS
Authors: Amodei J. J.
Published: February 2004

Diffusion effects are shown to give rise to strong electric fields when insulators with trapped carriers are exposed to holographic interference patterns. A simple physical model is used to calculate the field generated by sinusoidal light intensity distributions of typical wave-lengths. This phenomenon can be utilized for recording phase holograms in electro-optic crystals and as means of enhancing the efficiency and permanence of absorption holograms in photochromic materials.
HOW TO MEASURE SUBNANOSECOND LASER PULSES AT 10.6μ
Authors: Patel C. K. N.
Published: February 2004

This letter describes techniques for measurement of widths of subnanosecond pulses at 10.6μ obtained from mode-locked high-pressure CO2 lasers. Two novel linear correlation techniques are proposed. These are based upon (1) the effect of photon flux on free carriers in semiconductors and (2) a fast shutter produced in a semiconductor.
INDIRECT ELECTRON DRIFT VELOCITY VERSUS ELECTRIC FIELD MEASUREMENT IN GaAs
Authors: Bastida E. M. , Fabri G. , Svelto V. , Vaghi F.
Published: February 2004

A measurement of the drift velocity versus electric field in GaAs has been determined for electric fields between 15 and 90 kV/cm. The experimental values were obtained from the measurement of the current-voltage characteristic of a Gunn diode, done during the transit time of a domain.
BIREFRINGENCE COMPENSATION AND TEM00 MODE ENHANCEMENT IN A Nd: YAG LASER
Authors: Scott W. C. , de Wit M.
Published: February 2004

A Nd: YAG laser has been operated under strong thermal focusing and birefringent conditions and has yielded both linearly polarized output with negligible power loss and TEM00 output of 50–70% of the multimode power. The laser consisted of two Nd: YAG rods separated by a 90° crystal quartz polarization rotator together with a convex mirror and used no special cooling techniques. The performance of this laser, which agreed with theoretical predictions, indicates that this design approach may be generally applicable to the problem of thermally induced aberrations in such systems.
PLASMA DIAGNOSTICS OF AN rf-SPUTTERING GLOW DISCHARGE
Authors: Coburn J. W. , Kay Eric
Published: February 2004

The positive ions incident on the substrate plane in a planar diode discharge system are observed with an electrostatic deflection energy analyzer and a quadrupole mass spectrometer. Several targets have been rf sputtered in rare-gas discharges and the mass spectra that are obtained indicate that the sputtered species, which leave the target predominantly as neutrals, are subsequently ionized in the discharge by Penning ionization rather than by electron-impact ionization or other ion-molecule reactions.
DIRECT DETERMINATION OF OPTICAL GAIN IN SEMICONDUCTOR CRYSTALS
Authors: Shaklee K. L. , Leheny R. F.
Published: February 2004

We report a new technique for measuring the stimulated emission spectrum and optical gain of semiconductor materials. Amplified spontaneous emission is used to determine the gain factor by relating the measured variation in light output to variation in the length of the excitation beam. Results for CdS crystals at 2°K are presented that indicate net gains as high as 160 cm−1 at λ = 4907 Å are possible with ∼ 12-MW/cm2 optical pump power density from a nitrogen laser.
NEW cw LASER TRANSITIONS IN Se II
Authors: Klein M. B. , Silfvast W. T.
Published: February 2004

We have observed 22 new laser transitions in singly ionized selenium, ranging in wave-length from 4467 Å to 1. 26 μ. Output powers varying from 3 to 50 mW have been measured over the entire spectral range of operation in a 2-m discharge tube. This same tube produces a combined output power of 250 mW on the six strongest blue-green transitions. We have also studied the current saturation behavior of the laser and the effects of isotope structure on the laser output.
THE ADJUSTMENT OF MOS TRANSISTOR THRESHOLD VOLTAGE BY ION IMPLANTATION
Authors: Pherson M. R. Mac
Published: February 2004

Two new techniques have been demonstrated to set the threshold voltage of p-channel MOS transistors and integrated circuits. Both processes employ ion implantation to alter the doping profile near the Si–SiO2 interface. The first centers the ion distribution at the interface while the second places it well inside the silicon. Thresholds may be modified from enhancement through depletion mode. Either method is compatible with standard MOS processes.
DETERMINATION OF OPTICAL GAIN FOR CO TRANSITIONS IN A CS2–O2 FLAME BY OSCILLATION-RANGE MEASUREMENTS
Authors: Djeu N. , Pilloff H. S. , Searles S. K.
Published: February 2004

Optical gain in the neighborhood of 2% has been measured in CO vibration-rotation transitions P(12)–P(14) in the bands 8–7, 9–8, and 10–9 in a free-burning CS2–O2 flame. The flame was inside a single-transition single-mode CO laser cavity. Gain was determined from the change in the oscillation range of the frequency-tuning curve. This method is particularly useful for the measurement of small optical gains and losses.
VOLTAGE-DEPENDENT OPTICAL ACTIVITY OF A TWISTED NEMATIC LIQUID CRYSTAL
Authors: Schadt M. , Helfrich W.
Published: February 2004

A new electro-optical effect in twisted nematic liquid crystals is described which allows variation of the rotation of linearly polarized light continuously from 0° to 90°. It requires lower voltages than other electro-optic effects.
GROWTH-INDUCED ANISOTROPY BY PREFERENTIAL SITE ORDERING IN GARNET CRYSTALS
Authors: Callen Herbert
Published: February 2004

The noncubic anisotropy observed under growth faces of certain mixed garnet crystals is explained in terms of the preferential occupation (by one of the two types of rare-earth ions) of particular rare-earth sites. The effect depends on the coordination of the rare-earth ion with its second-nearest tetrahedral iron neighbors. The theory is related to, but different from, the pair-ordering theory of Rosencwaig and Tabor, and the difference is discussed.
MONOLITHIC ACOUSTIC SURFACE-WAVE AMPLIFIER
Authors: Coldren L. A. , Kino G. S.
Published: February 2004

The characteristics of a monolithic surface-wave acoustic amplifier are described. Using indium antimonide vacuum-deposited on lithium niobate, electronic gain of 70 dB with a terminal gain of 24 dB has been obtained at 660 MHz.
TYPE CONVERSION AND n-p JUNCTION FORMATION IN Hg1−xCdxTe PRODUCED BY PROTON BOMBARDMENT
Authors: Foyt A. G. , Harman T. C. , Donnelly J. P.
Published: February 2004

We have fabricated n-p junction photovoltaic detectors in Hg1−xCdxTe with x=0.50, 0.31, and 0.25 using proton bombardment to create the n-type layer. Peak detection sensitivities were in the wavelength range 1.6–6 μm. Although high-sensitivity photodiodes were obtained with each composition, the best results were obtained with the x=0.31 material, which has a peak response at 3.8 μm. At 77°K, 15-mil×15-mil diodes made with this material had zero-bias impedances of several megaohms. The peak detectivity at 3.8μ was 9×1011 cmHz1/2/W in reduced background and the quantum efficiency at the peak was 29%.
SIGNAL GENERATION VIA NONLINEAR INTERACTION OF OPPOSITELY DIRECTED SONIC WAVES IN PIEZOELECTRIC SEMICONDUCTORS
Authors: Wang W. C.
Published: February 2004

When an ultrasonic wave propagates in a properly oriented piezoelectric semiconductor, it gives rise to both an electric field wave and a space-charge wave. The rf signal developed across the crystal by the propagating wave is quite small. However, if one launches ultrasonic waves from the opposite ends of a properly oriented piezoelectric crystal so that the two waves travel toward each other, when the two waves meet, a rf signal of large amplitude, twice the frequency of the ultrasonic wave, will be developed across the crystal and the envelope (time function) of the double-frequency rf signal represents the convolution integral between the two envelopes of the ultrasonic waves which were launched into the crystal from the opposite ends.
TUNABLE DISTRIBUTED-FEEDBACK DYE LASER
Authors: Shank C. V. , Bjorkholm J. E. , Kogelnik H.
Published: February 2004

Efficient broadly tunable dye-laser action with a narrow line output has been demonstrated with a mirrorless laser system using distributed feedback. The feedback was obtained from a spatial modulation of both gain and index of refraction, induced by pumping a liquid organic dye solution with fringes formed by the interference of two coherent light beams. The device was tunable over 640 Å either by varying the angle between interfering pump beams or the refractive index of the dye solvent. Linewidths less than 0.01 Å were measured and a peak power of 36 kW was observed.
Dislocation Stresses in a Thin Film Due to the Periodic Distributions of Dislocations
Authors: Saito K. , Bozkurt R. O. , Mura T.
Published: February 2004

The state of stresses and displacements in thin films due to the presence of a periodic distribution of screw dislocations and edge dislocations is investigated by the method of continuously distributed dislocations and the three-dimensional theory of elasticity. The dislocations are straight and pierce obliquely the surfaces of the thin films in both cases. As a special case the exact solution is presented for a straight-edge dislocation piercing normally the surfaces of the films. Emphasis is placed upon the stress relaxation caused by the presence of free surfaces. The result will be useful for the contrast study of dislocation images in electron microscopy.
Nondestructive Analysis for Trace Amounts of Hydrogen
Authors: Cohen B. L. , Fink C. L. , Degnan J. H.
Published: February 2004

A method is described and demonstrated for a nondestructive determination of the hydrogen content inside materials in sheet form by measurement of the energy-loss distribution from proton-proton scattering events. The method is absolutely specific for hydrogen, and has a sensitivity of 1 ppm (atomic), or better. Materials analyzed (with ppm of hydrogen in parentheses) were: Ti (4200), Zr (5000), Al (20), Fe (∼ 10), C (13000), and Teflon (220). In the titanium and zirconium samples, the hydrogen content drops off near the surfaces. The method also detects oil or moisture on surfaces for thicknesses down to about 1 Å; all materials studied had such surface films several hundred Å thick.
Analysis of Data Gathered with Incomplete Coverage
Authors: Elmore W. C.
Published: February 2004

The task of calculating the position, width, and area associated with a Gaussian-like curve often occurs in data reduction. The present analysis examines the systematic error in these quantities arising from the spacing of data points at which local average values of the dependent variable are observed. The analysis has important applications in nuclear spectroscopy and in statistics.
Optimum Charged Aerosols for Power Conversion
Authors: Marks Alvin M.
Published: February 2004

Charged aerosols capable of efficient power transduction in power conversion devices are discussed. These charged aerosols comprise charged liquid droplets, submicron solids, or large molecules in a carrier gas. To achieve efficient transduction, the charged particles must have an optimum ratio of the radius to the number of charges. This optimum ratio is derived for various operating conditions. Processes and devices are described for producing charged particles having an optimum ratio. Elongated conductive particles, such as elongated liquid rodlike submicron microcrystals or long molecules, may be employed to increase the apparent dielectric constant and decrease the space charge of the conversion space, and thus increase output current and power density. A mathematical-physics analysis provides optimum ratios r/N as a function of relative gas density and a lumped parameter. The conditions for five cases are distinguished and discussed.
Total Melting Time in the Ablating-Slab Problem
Authors: Glen J. W.
Published: February 2004

The result obtained by Rogerson and Chayt is derived more simply from the conservation of energy.
High-Frequency Fatigue in Aluminum
Authors: Chevalier J. L. , Gibbons D. F. , Leonard L.
Published: February 2004

High-frequency (15-kHz) low-strain fatigue measurements have been carried out on high-purity polycrystalline aluminum, using a piezoelectrically driven exponential horn. The data show that ``channeling, similar to that observed in the deformation of irradiated metals, occurs prior to fatigue failure. Estimates show that the point-defect concentration produced during high-frequency fatigue can easily reach the critical concentration necessary for channel formation which has been found for irradiated metals. These observations suggest, therefore, that point defects may also play a critical role in the mechanisms of normal low-frequency fatigue processes.
Diffusion of Impurities in Polycrystalline Silicon
Authors: Kamins T. I. , Manoliu J. , Tucker R. N.
Published: February 2004

The diffusion of electrically active impurities into polycrystalline silicon deposited by the thermal decomposition of silane has been studied. Both boron and phosphorus have been found to diffuse more rapidly into polycrystalline silicon than into single-crystal silicon. The diffusivity is greatest in films deposited at about 1000°C although this maximum is a function of the deposition rate, film thickness, and substrate material as well as the deposition temperature. The maximum diffusivity is associated with a structure which has the maximum {110} texture. Although most of the films have been deposited onto amorphous SiO2, a nucleating layer of polycrystalline silicon has been found to influence the diffusion of impurities into a thick layer of polycrystalline silicon deposited over the nucleating layer. An optimum structure is obtained with a nucleating layer containing maximum {110} texture. The enhanced diffusion is tentatively attributed to diffusion down defects in the polycrystalline silicon. The activation energy for diffusion of impurities into the polycrystalline silicon is less than that for diffusion into single-crystal silicon.
Mechanism of the TiNi Martensitic Transformation and the Crystal Structures of TiNi-II and TiNi-III Phases
Authors: Wang Frederick E. , Pickart Stanley J. , Alperin Harvey A.
Published: February 2004

Based on combined x-ray and neutron-diffraction data, an inference for the coexistence of the B2(CsCl) and P3̄m1 structures in the TiNi-II phase is made. Other experimental evidence indicates the proportion of the B2 to P3̄m1 structures to depend critically on the thermal and mechanical history of the alloy. Through a mechanism of an inhomogeneous-but-cooperative atomic shear in the 〈111〉B2 direction and a factor sequence, −(0−1−1̄)n− in the (110)B2 plane, the B2 and P3̄m1 structures transform into P1̄ abd P6/m structures, respectively, during the TiNi-II to TiNi-III martensitic transformation. Subsequent submicrotwinning at atomic level of the P1̄ structure leads to the P1 structure. Therefore, the TiNi-III (``martensite'') phase may consist of the P1̄, P1, and P6/m structures.
Electric and optic behavior of aligned samples of nematic liquid crystals
Authors: Bertolotti M. , Scudieri F. , Sette D. , Bartolino R.
Published: February 2004

The orientation behavior of nematic liquid crystals was studied by measurements of I vs V and I vs T combined with observation of their optical behavior. The measurements were performed at low dc voltages in the region around the Helfrich threshold for the formation of domains. A voltage region in which the electric conductivity decreases by increasing the electric field is found. It is also observed that in certain cases the whole crystal orientates itself through a cooperative motion. The change in conductivity with increasing electric field can be partially accounted for by the anisotropy properties of the material, although other phenomena, such as the flow of the material and charge injection at the electrodes, may play a role. The temperature behavior of I gives an indication that charge carrier velocity is governed by the same processes as viscosity.
Diffusivity of sodium in lead
Authors: Owens C. W. , Turnbull David
Published: February 2004

The rate of diffusion of 22Na in lead has been measured at temperatures between 249 and 313°C by sectioning diffusion couples prepared by pressure welding a sodium-lead alloy with pure lead. Over the observed temperature range the 22Na diffusivity is three to four times that of lead self-diffusivity, and the activation energy for sodium diffusion is approximately equal to that for lead self-diffusion. These results indicate that Na diffuses in lead predominantly via a vacancy mechanism. The contrast between this behavior and that of the monovalent noble metal solutes suggests that a necessary condition for appreciable interstitial solution in hosts such as lead is that the size of the interstices delineated by the host ions should be equal to or larger than the metallic volume of the solute atom.
Cadmium selenide films deposited at high substrate temperature as tunneling barriers between tin electrodes
Authors: Lubberts G. , Shapiro Sidney
Published: February 2004

Very thin films of CdSe have been prepared as tunneling barriers in Sn–CdSe–Sn tunnel junctions. The CdSe barriers were prepared at a substrate temperature of 115°C. High substrate temperatures were used since under such conditions dielectric films of CdSe can be produced. Conductance measurements on these junctions at 300°K as well as 77°K showed that the conductance depended exponentially on the thickness of the CdSe barrier within the thickness range studied, 50–100 Å. This result is consistent with tunneling theory. In addition, at 1.4°K a sudden jump in current occurred at a voltage corresponding to the Sn superconducting energy gap. The magnitude of the current jump agrees with the theory of quasi-particle tunneling. The shape of the I-V curve as well as its weak dependence on temperature also indicate that tunneling is the conduction mechanism in these junctions. Since thin CdSe films are usually not continuous, it is necessary to oxidize those areas of the Sn electrode where no CdSe is present. A method is given for determining the pinhole area. From a knowledge of the pinhole area, one can estimate the fraction of the total current which flows through the CdSe. Our results indicate that essentially all the current flows through the CdSe. This conclusion is supported by the pronounced longitudinal optical (LO) phonon structure in the tunneling data. The LO phonon structure is characteristic of the CdSe barrier. Typical changes of 20% in conductance are observed as a result of excitation of LO phonons in the CdSe layer by the tunneling electrons. Measurement of the conductance as a function of the CdSe thickness show that the conductance of the tunnel junctions can be controlled in a fairly reproducible manner by varying the thickness of the CdSe layer.
Bow-shock effects on probe measurements
Authors: Lee S. , Sandeman R. J.
Published: February 2004

Probe measurements of pressure and magnetic field are of importance in electromagnetic-shock-tube diagnostics. The effect of the bow shock on such measurements, in transverse shock waves in the ionizing-hydromagnetic regimes, is considered. The bow-shock jump equations are first solved, then the total stagnation pressure is obtained assuming an isentropic compression towards the stagnation point. The pressure measured at the stagnation point of the probe is seen to be less than the free-stream total gas pressure. The magnetic field is considered in terms of a simple model taking into account the field and flow distributions outside of the stagnation streamline. This analysis shows that the magnetic field measured at a coil is also less than the free-stream magnetic field.
Transient behavior of a cavity
Authors: Faust William R.
Published: February 2004

An expression for the transient electric field setup in a lossless cylindrical cavity by a short pulse of electrons has been derived by means of the Laplace transformation. It is found that longitudinal and radial fields are set up in the cavity. Expressions for the electric field have been evaluated as a function of time for several different points within a representative cavity.
Radiative recombination mechanisms in GaAsP diodes with and without nitrogen doping
Authors: Craford M. G. , Shaw Roger W. , Herzog A. H. , Groves W. O.
Published: February 2004

The electroluminescent properties of GaAs1−xPx light-emitting diodes with and without nitrogen doping have been studied at temperatures from 77 to 300 °K. The radiative transitions in the indirect band-gap region have been identified by a comparison of the emission spectra with those obtained in GaP. At 77 °K nitrogen-free GaAsP recombination consists of three peaks, shallow donor-acceptor pair transitions, free-exciton transitions (which are not observed in pure GaP), and LA phonon-assisted free-exciton transitions. As the temperature is increased, the free excitons and/or free electron-hole transitions become dominant. The indirect energy band gap has been found to exhibit appreciable curvature. The alloy composition at which the direct-indirect energy band-gap transition occurs has been found to be xc=0.46 at 77 °K and 0.49 at 300 °K. In nitrogen-doped GaAsP the 77 °K emission is dominated by transitions associated with nitrogen. For alloy compositions near GaP (x ≥ 0.9) a series of distinct peaks are observed, corresponding to the sharp-line nitrogen spectrum commonly observed in GaP. For x<0.80 the distinct peaks converge into a single broad band. Optical-absorption measurements indicate that both the depth and width of the nitrogen absorption band increase with increasing As concentration. The electroluminescent recombination for x < 0.80 has been found to occur primarily in a NN pair band, the high-energy onset of the EL band corresponding roughly to the center of the absorption band.
High-intensity injection luminescence in CdS single-crystal optical cavities
Authors: Nicoll F. H.
Published: February 2004

Injection luminescence has been examined in CdS samples having two different forms of optical cavity with the electrode configuration chosen to suit the cavity. For a total internal reflection cavity, the electroluminescent spectrum has characteristics very similar to the spectrum of the same sample pumped by an electron beam to near laser threshold. Under low-duty-cycle pulsed operation (70-nsec pulses) rise and decay times <20 nsec are observed and there are indications that stimulated emission may be occurring at the highest drive. There is also some evidence of this in the spectra from a Fabry-Perot cavity. Our inability to observe well-defined laser action with all its attributes is discussed in terms of our knowledge of the injection-luminescence behavior and electron-bean pumping of similar samples of CdS.
Influence of plastic deformation and recrystallization upon permeability anomalies in gadolinium metal
Authors: Milstein Frederick , Zyvoloski George
Published: February 2004

Studies of the influence of plastic deformation by rolling and of recrystallization annealing upon the weak-field ac permeability of ferromagnetic materials are of technological importance and of fundamental interest. In this study, polycrystalline gadolinium metal was plastically deformed by a cold-rolling technique and measurements were subsequently made of the weak-field ac relative permeability as a function of temperature. The Gd was then subjected to a recrystallization anneal, and the magnetic measurements were repeated as a function of temperature. The salient experimental results which were observed are (i) in the annealed state, the permeability passes through an anomalous ``hump'' in the neighborhood of the Curie temperature; this anomaly is absent in the plastically deformed state, (ii) in a range of temperatures below the Curie temperature, the relative permeability in the work-hardened state is greater than that in the annealed state and (iii) at a lower temperature (about 240°K), the relative permeability in the annealed state undergoes a further, sharp increase which is much greater than that which occurs at the Curie point; this lower temperature increase in relative permeability is largely suppressed in the work-hardened state. The experimental results are discussed in terms of the influence of the cold-rolling process upon magnetocrystalline anisotropy and in terms of the relative importance of domain rotation and domain-wall movement in the plastically deformed and in the annealed state.
Discussion on ``Magnetoacoustic amplification in extrinsic nondegenerate semiconductors''
Authors: Ishii T.
Published: February 2004

Important and significant revisions in the theory of Abe and Mikoshiba are made, with great emphasis on the first-order particle trajectory in the integral expressions of the solution to the Boltzmann equation. Finally correct expressions are obtained for the amplification constant.
Hardening of CaF2 single-crystal surfaces due to contamination by atmospheric oxygen
Authors: Sashital S. R. , Vedam K.
Published: February 2004

Edge dislocation mobility and Vickers microhardness measurements have been made on pairs of matching, cleaved {111} surfaces of CaF2 single crystals. While one part of each pair was preserved in the contamination-free condition by immersion in a nonpolar liquid ambient, the matching counterpart surface was aged at room temperature in various ambients such as air, oxygen, nitrogen, or a moisture-saturated atmosphere. Comparison of microhardness and edge dislocation mobility of the matching surfaces indicate that the atmospheric oxygen is mainly responsible for the observed surface hardening of the contaminated crystal. Oxygen contamination of ``air''-aged surfaces is attributed to possible diffusion of O2− ions into surface layers along dislocations, while the observed hardening is attributed to interactions between associated O2− impurity-F− vacancy complexes in the surface layers.
Ultrasonic attenuation studies in deuterated and undeuterated chromium potassium alum
Authors: Miller R. E. , Norwood M. H. , Marshall B. J.
Published: February 2004

The attenuation of 10- and 30-MHz sound waves in deuterated and undeuterated chromium potassium alum have been measured over the temperature range 300–4.2 K. A very large attenuation peak occurs in the temperature range 70–160 K. It is believed that this is associated with phonon-phonon scattering.
Acousto-optic light deflectors using optical activity in paratellurite
Authors: Warner A. W. , White D. L. , Bonner W. A.
Published: February 2004

Light deflector designs which use the anomalously low shear wave acoustic velocity and high acousto-optic figure of merit in single-crystal paratellurite, first proposed by Uchida and Ohmachi, have been made practical by exploiting this material's birefringence to circularly polarized light. Dixon's equations for Bragg interaction in birefringent materials are found to be equally applicable to optically active materials when linearly polarized propagation modes are replaced by circularly polarized modes. For specific ratios of sound-to-light wavelengths, there is a substantially expanded angular range over which Bragg interaction can take place. One effect of this increased range is to permit longer interaction lengths between light and sound, which greatly reduces the acoustic power required. In paratellurite, for visible light, this expanded range occurs for sound frequencies below 100 MHz, in the region of acceptable acoustic loss. Examples of possible designs include a deflector only 3×5×7 mm having a capacity of 500 linearly resolvable spots with a random access time of 10 μsec, with 50% of the incident light being deflected at 35-mW acoustic power.
Growth of nearly stoichiometric MgAl2O4 spinel single crystals by a gradient furnace technique
Authors: Viechnicki D. , Schmid F. , McCauley J. W.
Published: February 2004

Nearly stoichiometric MgAl2O4 spinel single crystals can be grown by a gradient furnace technique in molybdenum crucibles with an inert-gas atmosphere of industrial-grade argon, high-purity argon, or technical-grade helium. There is a reaction between MgO in the melt and the molybdenum crucibles which results in bands of molybdenum metal inclusions in the boule, although molybdenum concentration away from the bands is less than 100 ppm. This reaction can be minimized by ensuring that the starting materials are well reacted by high-temperature heat treatment to form MgAl2O4 before melting. Similarly, a greenish-brown discoloration which arises from oxygen deficiency in the boules may be eliminated by reacting the starting materials completely to MgAl2O4. A loss of nearly 2 mole% MgO generally occurs during the growth of a boule. This loss results in the formation of a ``skin'' of nonstoichiometric spinel on the outside of the boule. This ``skin'' is the last material to solidify and is highly strained upon cooling. It cracks and these cracks propagate throughout the boule. The loss of MgO also causes the formation of a second phase, α-Al2O3, when the spinel is annealed at 1150 and/or 1550°C for periods of time that are less than 30 h. This second-phase precipitate causes variations in the Knoop100 hardness of spinel between 1360 and 1820 kg/mm2. Because of the difficulty in controlling composition, cracking, and the changes in hardness upon annealing at temperatures where silicon is commonly deposited on single-crystal insulating substrates, it is questionable whether spinel will find widespread applicability as an insulating substrate material.
Far-infrared plasma reflectometry and instability detection
Authors: Jassby D. L. , Marhic M. E.
Published: February 2004

A focused cyanide laser beam at 337 μ is used to study a steady-state highly ionized plasma column operating at densities up to 1.5×1016 cm−3 in an axial magnetic field up to 10 kG. A reflectometer measures the energy reflected from the cutoff layer. A strong coherent m=1 instability in the plasma is detected by amplitude modulation of either an off-axis transmitted beam or an on-axis reflected beam. This technique allows electrodeless probing of the stability characteristics of a high-energy-density plasma.
Infrared absorption spectra of sodium silicate glasses at high pressures
Authors: Ferraro John R. , Manghnani Murli H.
Published: February 2004

Infrared absorption spectra of 12 sodium silicate glasses of varying composition (10 to 45 mole% Na2O) are examined at varying pressures to 58.8 kbar. The pressure dependences of all the infrared absorption frequencies studied are found to be positive. Grüneisen γ's are evaluated from the pressure dependence of the infrared vibrations and elastic parameters. The results are compared with those obtained from previous high-pressure studies of α-quartz and several other silicate glasses.
Free-carrier reflectivity in optically inhomogeneous silicon
Authors: Lambert L. M.
Published: February 2004

Interpretation of reflectivity data from the surface of a semiconductor containing an impurity gradient and, in particular, a p-n junction is of practical importance. Current theories predict a shift in the wavelength of the reflection minimum to shorter wavelengths. In this theory and subsequent measurements, such behavior was not observed; in fact, almost no shift of wavelength occurred even for the most lightly doped and shallow junction samples. The results obtained indicate that the surface free-carrier concentration can be obtained directly from a reflectivity measurement.
A scanning device for measurement of doping homogeneity in GaP
Authors: Seman J. A. , Wiley J. D.
Published: February 2004

This paper describes a device for investigating doping homogeneity in bulk GaP. It utilizes a laser scanning technique to measure changes in the infrared free-carrier absorption. Both p- and n-type material grown by the liquid-encapsulated Czochralski (LEC) technique were investigated. In the case of one selenium-doped boule a central core of higher carrier concentration which increased in diameter and depth from seed to tail was observed. A longitudinally sliced GaP boule was also scanned in order to demonstrate the feasibility of studying seed-to-tail inhomogeneities by this technique. It was noted that apparently homogeneous cross-sectional slices can have significant longitudinal inhomogeneities. The advantages and disadvantages of using a laser for infrared transmission measurements are discussed and it is shown that the laser scanning apparatus is much simpler to use for homogeneity studies than conventional techniques such as Hall effect.
Some theoretical aspects of spin-disorder resistivity of rare-earth alloys
Authors: Yang Tien-Tsai , Robinson Lawrence Baylor
Published: February 2004

A theoretical expression for the spin-disorder resistivity of binary rare-earth alloys at temperatures above the magnetic transition point has been derived by Dekker. Some experimental results have been obtained by Bozorth and Suits and also by Yang and Robinson. A comparison of theory and experiment has been made in this note. According to Dekker's theory, the spin-disorder resistivity ρd for a binary alloy containing two magnetic components can be expressed approximately as ρd = c1x(1 − x)+(c2 − c3)x + c3, where c1, c2, and c3 are some constants and x is the percentage composition of one of the components. The experimental spin-disorder resistivity of the Gd–Dy system conforms to this theoretical expression. The constants c1, c2, and c3 have a theoretical basis.
Theory of anisotropy skew in magnetostrictive thin films
Authors: Hornreich R. M. , Rubinstein H.
Published: February 2004

In magnetostrictive thin films, distinctive types of anisotropy skew patterns are found. These patterns depend on (i) the sign of the film's magnetostriction constant and (ii) the coefficient of thermal expansion of the film relative to that of its substrate. It is shown that these effects can be explained by the presence of thermal gradients in the film-substrate structure during and following the deposition process. Using the theory of magnetostrictively induced anisotropy in thin films, expressions for the variation in anisotropy field and easy-axis direction due to temperature gradients are derived and compared with those found experimentally. In order to restrict magnetostrictively induced easy-axis skews to ±0.5°, temperature gradients must be less than 0.5°K/cm.
Use of divergent-beam x-ray diffraction to measure lattice expansion in LiF as a function of thermal-neutron dose up to 6 × 1016 nvt
Authors: Yakowitz Harvey
Published: February 2004

The lattice expansion of LiF was measured by means of the divergent-beam (Kossel) x-ray diffraction method at three levels of thermal-neutron dose, 0.45, 2, and 6 × 1016 nvt, respectively. The lattice parameter of LiF increases due to the production of Frenkel defects resulting from the Li6(n, α)H3 reaction. At 6 × 1016 nvt, the lattice expansion was found to be 0.13±0.02% which is in good agreement with previously reported values.
Round-trip amplification of ultrasonic waves in n-InSb
Authors: Ogawa Fumihiro , Aoki Takeshi , Arizumi Tetsuya
Published: February 2004

Round-trip amplification of ultrasonic waves of 210 MHz was observed in n-InSb under a transverse magnetic field at 77 K. Its maximum gain increased with the magnetic field, amounting to 6.2 dB/cm at 8 kG.
Proton irradiation at 30°K and isochronal annealing of reactively sputtered Ta thin-film resistors
Authors: Shewchun J. , Hardy W.R. , Pronko P.P.
Published: February 2004

Tantalum thin-film resistors reactively sputtered in oxygen and nitrogen simultaneously have been irradiated by 150-keV protons at 30°K. The observed conductance increase of the films is ascribed to radiation-produced defect levels within the inter-island regions of Ta2O5 in these discontinuous films. The nonlinearity of the conductance increase with fluence may be accounted for by a nonlinear rate of defect production due to a combination of spontaneous recombination and close-pair thermal annealing. The number of unstable sites surrounding each defect is found to be equal to or greater than four for crystalline Ta2O5. Thermal recovery of the damage proceeds in two main stages: Stage A (34–150°K) possesses some substructure and is attributed to close-pair or correlated recombination; stage B (150–300°K) is very broad and structureless and is attributed to uncorrelated annihilation of defects at the gap-island interface. Negative annealing stages (characterized by a conductance increase) indicate a metallic conduction process via connected metallic islands.
Spall fracture in aluminum monocrystals: a dislocation-dynamics approach
Authors: Stevens A. L. , Davison Lee , Warren W. E.
Published: February 2004

High-purity monocrystalline aluminum disks of three crystallographic orientations were subjected to carefully controlled planar impact producing low levels of spall damage. This damage was observed by optical and scanning electron microscopy of sections through the recovered disks, and was found to consist of voids of essentially octahedral form having {111} planes as faces. To describe the growth of these voids we propose a kinematical model based on the motion of edge dislocations. Dynamical equations describing the rate of growth of an individual void are obtained by applying established concepts of dislocation mechanics to the kinematical model. Finally, the dynamical void growth model is combined with an empirically established nucleation model to yield equations for calculating the total volume growth rate in a spalling sample. Extension of these results to other ductile fracture phenomena is suggested.
Positive-ion bombardment of substrates in rf diode glow discharge sputtering
Authors: Coburn J. W. , Kay Eric
Published: February 2004

The plasma potential and the potential of an electrically isolated surface are measured in an rf diode sputtering glow discharge. The influence on these potentials of both the geometry enclosing the discharge volume and of a positively biased auxiliary electrode in contact with the discharge is investigated. It is shown that confining the discharge increases the plasma potential and the energy of positive ions incident on electrically isolated substrates, whereas applying a positive voltage to an auxiliary electrode also increases the plasma potential but does not significantly increase the energy of ions incident on electrically isolated substrates. The effect of rf modulation on the ionic energy distributions is demonstrated. This occurs as the ions pass through the plasma-substrate sheath and results in a large broadening of the energy distributions of low-mass species.
Growth of electromagnetic waves on the surface of a negative differential conductance material
Authors: Matthews D. B. , Frey Jeffrey
Published: February 2004

In order to determine the usefulness in device applications of semiconducting materials which exhibit a bulk differential negative conductivity, but which may be fabricated most easily in the form of thin sheets, a study is performed of the propagation of electromagnetic surface waves along the interface between such materials and free space. The dispersion relation of the system is determined for waves traveling with phase velocities comparable to the velocity of light, so that the quasistatic approximation is not made. rf charge concentration at the surface is accounted for in a manner similar to that used in the study of scalloped electron beams. Numerical solution of the dispersion relation is made for possible values of parameters for one relevant class of semiconducting materials, viz., compound semiconductors in which crystalline superlattices have been formed. Growth rates up to several decades of dB/cm at frequencies up to 1012 Hz are seen to occur for reasonable superlattice parameters for gallium arsenide and indium antimonide.
Theoretical tunneling current characteristics of the SIS (semiconductor-insulator-semiconductor) diode
Authors: Shewchun J. , Temple V. A. K.
Published: February 2004

The dc current-voltage characteristic of the SIS (semiconductor-insulator-semiconductor) diode is calculated using a simple two-band model for the insulating barrier. The effect of various parameters such as insulator thickness, image force barrier reduction, interface charge, temperature, and semiconductor doping density are investigated as well as the effect of current tunnelling through the semiconductor space-charge region. Several interesting results are observed including the negative resistance feature for the degenerate p-i-n system. This negative resistance is more pronounced than that of the p-n tunnel diode and exhibits some unusal temperature behavior.
Analysis of the CO2 TEA laser
Authors: Manes K. R. , Seguin H. J.
Published: February 2004

A five-temperature model for the CO2–N2–He system has been employed to predict the output-power pulse shape from a TEA laser. Theoretical predictions are compared to experimental data for several gas mixtures, cavity configurations, and excitation levels with good agreement. This model should be useful in the evaluation of alternative pumping schemes and in the understanding of CO2 TEA laser dynamics when nonlinear media are placed in the optical cavity.
Spatially resolved spectroscopic profiles of plasmoidal rf discharges
Authors: Bruce C. W. , Miller A.
Published: February 2004

The intensities of prominent visible emissions from rf-excited plasmoidal discharges consisting of gaseous oxygen, oxygen/nitrogen mixtures, nitrogen, oxygen/carbon monoxide mixtures, and carbon monoxide have been recorded. In each case the radial dependence of the luminous output from a spherically symmetric discharge was obtained by deconvolution of the spatially resolved intensity data. Only the emissions associated with transitions between the relatively long lived excited states of the ions, i.e., (O2+)* and (CO+)* revealed the anomaly known as the dark sheath in the discharge. Further, the dark sheath was only observed when oxygen was present in the discharge. These results are in agreement with the ``delayed-emission'' theory proposed by Kregel and Miller which associates the dark sheath with relatively long lifetimes for the excited states of the ions as well as with a coincident region of high electric field (peculiar to electronegative gases such as oxygen). Discharge pressures ranged from 10−4 and 10−3 Torr and the frequency of the applied rf field was 27.120 MHz.
Optimum thickness for thermomagnetic writing
Authors: Silverman B. D.
Published: February 2004

It is shown that there is an optimum film thickness for laser writing. This thickness depends on the thermal properties of the film and substrate as well as on the optical properties. Calculations are presented for Fe-doped EuO.
Structural and magnetic studies on DyFe2–DyAl2 and DyCo2–DyAl2
Authors: Oesterreicher H. , Pitts Roland
Published: February 2004

Both pseudobinary systems are constituted of broad homogeneous regions of cubic and hexagonal Laves phase type. Ordering tendencies on crystallographic sites between Al and the transition metal are studied in the hexagonal type. Magnetic investigations have been carried out only in the ordered regime. It is found that electron transfer from Al to the transition metals quenches their moments to the effect that they become nonmagnetic at high Al concentrations. At cryogenic temperatures the magnetization behavior of powdered specimens is complex in the intermediate region of concentration. Considerable magnetic hardness and anisotropy develops, and in DyFe2–DyAl2 pronounced spontaneous increases in magnetization with field occur as a result of the presence of highly energetic domain walls. The complex interplay of effects from disordered magnetic components, the crystalline electric field, and domain-wall effects is discussed and compared with findings in related systems.
Reflections from a plasma sphere and relationship between plasma frequency and the classical electron radius
Authors: Hershberger W. D.
Published: February 2004

Plasma frequency, ωp, may be expressed in terms of the classical electron radius re by the relationship: ωp2=4πc2Nre. The use of this relationship permits the reflection cross section of a spherical cluster of electrons to be expressed in terms of electron radius, when this is convenient, or alternately, in terms of macroscopic quantities such as plasma frequency and the radius of the electron cluster.
Observation of the amorphous-crystalline phase transition in the Ovonic semiconducting glass Te81Ge15As4 by the Mössbauer effect in Te125 and I129
Authors: Hafemeister D. , deWaard H.
Published: February 2004

Mössbauer spectra obtained with absorbers of Te81125Ge15As4 and a ZnTe125m source indicate that tellurium atoms are in an environment similar to that in tellurium metal. These spectra as well as those obtained with sources of Te81129mGe15As4 and a CuI129 absorber indicate that the amorphous phase has a higher charge asymmetry than the crystalline phase which is consistent with the concept of ``dangling'' chemical bonds. Because of the great difference in the I129 spectra of the amorphous and crystalline phases it appears of interest to investigate Ovonic devices prepared with Te129m in order to see if voltage-dependent phenomena can be observed in the I129 Mössbauer spectra.