bluuebunny/crossref_metadata_2025 huggingface dataset:
Bragg reflection of millimeter waves by a corrugated ferrite slab
Authors: Tsutsumi Makoto , Kumagai Nobuaki
Published: February 2003

Bragg reflection characteristics of millimeter waves from a corrugated ferrite slab are investigated theoretically and experimentally. Theoretical analysis is performed by using a singular boundary perturbation procedure. Experiments are carried out at millimeter wave frequency with a corrugated polycrystalline yttrium iron garnet slab. Typical results obtained are stop bandwidth of 600 MHz at a Bragg frequency of 46.7 GHz with a 2.5-dB insertion loss. The Bragg frequency is tunable over the range of 1.2 GHz by changing the applied dc magnetic field. Experimental results show satisfactory agreement with theoretical predictions.
Comment on ‘‘Thermocouple temperature measurements in shock-compressed solids’’
Authors: Rosenberg Z. , Partom Y.
Published: February 2003

We disagree with the interpretation offered in the above comment. The suggestion was made that the anomalously fast response of thin-foil thermocouples reported previously is the result of strain dependence of the thermocouple response and not shock enhanced thermal equilibration. Although the emplacement geometry has a profound effect on the response of embedded thin-foil temperature gauges as noted in the above comment, the evidence presented, along with recent results discussed in this reply, do not support the conclusions presented in the above comment.
Reply to ‘‘Comment on ‘Thermocouple Temperature measurements in shock-compressed solids’ ’’
Authors: Bloomquist D. D. , Sheffield S. A.
Published: February 2003

We present several arguments and experimental support for a different interpretation of the dynamic response of embedded thermocouples. These were interpreted recently as temperature histories, whereas we suggest that longitudinal strain is responsible for much of the output emf of these gauges.
Chromium and iron impurities in liquid encapsulated Czochralski gallium arsenide
Authors: Clegg J. B.
Published: February 2003

Residual impurities in GaAs crystals grown by the Liquid Encapsulated Czochralski method have been measured using calibrated Secondary Ion Mass Spectrometry. It is shown that Cr and Fe are not dominant compensating impurities in undoped crystals, and typical concentrations are 3×1013 cm−3 (Cr) and 2×1014 cm−3 (Fe). Carrier compensation may be explained by the presence of carbon and a deep electron trap.
Cathodoluminescence studies of postrange defect introduction from ion implantation in CdSe
Authors: Norris C. B.
Published: February 2003

Cathodoluminescence measurements in conjunction with layer removal by chemical etching show that shallow 200-keV Xe+ ion implantations cause significant postrange defect introduction in CdSe. Strong spectral changes are present at depths an order of magnitude beyond the calculated projected ion range (∼500 Å). There is significant residual damage at depths greater than a micron in some instances. Implantation at 80 K yields deeper and more severe 300- K stable postrange defect introduction than does implantation at 300 K. One component of the postrange damage enhances nonradiative (<1 eV) recombination. The introduction of, or increased prominence in, deep-center luminescence near 1.4 eV is tentatively associated with cadmium vacancy (VCd) introduction in the postrange zone. The simultaneous strong growth in the prominence of luminescence near 1.7 eV is explained by the novel interpretation that incumbent interstitial alkali impurities (Na, Li) are reacting with ion-implantation-induced VCd to enhance the substitutional alkali concentration in the postrange zone. There is no evidence, though, that Cd interstitials from the range-zone implant damage are a significant component of the postrange damage.
Experimental results on the stability of ac thin-film electroluminescent devices
Authors: Alt P. M. , Dove D. B. , Howard W. E.
Published: February 2003

Experimental results on the stability of ac-coupled thin-film electroluminescent devices are presented. The luminance-voltage characteristics of ZnS:Mn devices, including both memory and nonmemory types, were measured throughout constant luminance aging experiments. Deposition conditions were varied, and post-deposition treatments by ion implantation and thermal annealings were investigated. We find a pervasive shift in the threshold voltage, and a corresponding loss of hysteresis in memory devices. We postulate that memory loss results from the creation of shallow interface states. The responsible physical mechanism is very sensitive to both hydrogen and oxygen incorporation in the ZnS film; in similar fashions, H or O increases the rate of memory loss. By comparison, the devices were insensitive to common contaminants such as Na, Cl, and F. We have found that hydrogen is generated during the deposition process. Even so, some of our devices exhibited significant memory for several thousand hours.
New method for the optimization of thermoluminescence sensitivity in LiF:Mg,Ti
Authors: Wachter W.
Published: February 2003

Glow curve shape and thermoluminescence (TL) sensitivity in LiF:Mg,Ti single crystals have been studied as a function of Mg2+ and Ti3+ concentrations. A detailed method for TL optimization is presented, along with a simplified scheme which relies on the ratio of peak 5 height to peak 4 height (or ratio of peak 5 to peak 3) and the height of peak 3. In addition, the role of hydroxyl (OH−) impurities has been investigated and it has been found that some Mg ions are removed from the TL process by forming magnesium-hydroxyl complexes Mg(OH)n. This may explain prior discrepancies in Mg and Ti concentrations for optimum TL sensitivity.
Correlation between the thermoluminescence property and thermal activation energies of the carrier-capture process during irradiation of thermoluminescence phosphors
Authors: Nakajima Toshiyuki
Published: February 2003

It is theoretically and experimentally established that changes in the ’’proper’’ thermoluminescence sensitivity of a phosphor can be approximated by a quadratic equation in terms of the reciprocal of the irradiation temperature, when the phosphor is irradiated in the region of high temperatures, with low linear energy transfer (LET) radiation to a low dose; moreover, the curve of the ’’proper’’ sensitivity shifts toward the lower side of the irradiation temperature with a decreasing rate of energy absorption. A method is presented for evaluating the activation energy describing the carrier-capture reaction during irradiation. Experimentally determined values of the activation energies are given for Mg2SiO4(Tb), CaSO4(Tm), and LiF(Mg,Cu,P) phosphors. The carrier-capture reaction of these phosphors during irradiation is shown to be exothermic, and it is demonstrated that thermoluminescent dosimeter (TLD) phosphors, intended for high sensitivity measurements, should present the relationship expressed by Ed ≳E2≳E1 = 0, where E1, E2, and Ed are the thermal activation energies for carrier trapping, for carrier escape, and for carrier disappearance, respectively. The relationship holding between these three activation energies further serves to explain the batch-to-batch variation observed in the LET dependence of TLD sensitivity and other phenomena that have been noted in respect to TLD sensitivity.
A study of secondary electron emission in insulators and semiconductors
Authors: Grais Khairi I. , Bastawros A. M.
Published: February 2003

The equation derived by G. F. Dionne [J. Appl. Phys. 44, 5361 (1973)], has been used as a basis for the present analysis. Escape probability has been determined for various insulators and semiconductors. The relative importance of the emission and production terms has been discussed in various energy gap-width regions. The role of electron affinity is also discussed. Values for the escape probabilities and the mean free paths of secondaries are given.
Near-threshold sputtering mechanisms from a computer simulation of argon- bombarded clean and oxygen-reacted copper single crystals
Authors: Webb R. P. , Harrison D. E.
Published: February 2003

Normal incidence argon-copper sputtering mechanisms have been investigated for ion energies just above threshold. Identical mechanisms operate in both the (111) and (001) surface orientations. Adsorption of an ordered oxygen overlay on the surface does not destroy the ejection processes. Although the mechanisms produce similar ejected atom energy distributions, the processes may be experimentally distinguishable through the angular emission spectrum of the ejected copper atoms.
Experimental investigation of magnetostatic surface wave amplification in GaAs-yttrium iron garnet layered structure
Authors: Yamada S. , Chang N. S. , Matsuo Y.
Published: February 2003

This paper describes the experimental results of the active interaction between drifting electron streams in n-GaAs and magnetostatic surface waves propagating on a relatively thin yttrium iron garnet (YIG) slab. A large relative gain of up to 17 dB is attained at a delay time of 0.15 μs by fine adjustment of this novel coupled system. This result corresponds to almost recovering the loading loss of the semiconductor in the whole delay time range observed. The effect of temperature on the amplifying characteristics is also studied by varying the repetition frequency in the pulse experiment.
Shear modulus gradients in adhesive interfaces as determined by means of ultrasonic Rayleigh waves (II)
Authors: Knollman G. C. , Hartog J. J.
Published: February 2003

Ultrasonic Rayleigh wave measurements made earlier on several different types of adhesives have led to the finding of a distinct gradient in shear modulus through the interfacial accommodation zone. As reported here, different preparations of substrate appear to have little effect on the nature and extent of the modulus gradient. However, cure time is found to play a significant role concerning the very existence of a gradient in shear modulus through the bondline region of an adhesive. The stated gradient may be attributable to residual stress in the interfacial zone.
Thermally stimulated currents in polyethylene irradiated by γ rays at low temperature
Authors: Lapke G. , Schmidt W. F. , Rabe J. G.
Published: February 2003

The influence of morphology and thermal history on the thermally stimulated current (TSC) of polyethylene samples irradiated with γ rays at low temperature has been studied. In low density polyethylene (LDPE) and high density polyethylene (HDPE), the TSC maximum occurs at about 50 and 110 °C, respectively, with further peaks observable at lower and higher temperatures. The amount of charge carriers detrapped increases by an order of magnitude when the crystallinity of LDPE changes from 42% to 55%. Annealing polyethylene samples at elevated temperature with subsequent slow cooling results in samples which produce TSC several times larger when compared with samples cooled from elevated temperatures with a high rate. The results are discussed in terms of one mechanism involving trapped ion pairs which undergo geminate recombination on detrapping causing only small TSC at low temperature. A second mechanism involves charges separated sufficiently to undergo volume recombination after detrapping causing the TSC maxima mentioned above. The traps of the latter mechanism are thought to be located mainly at the amorphous crystalline interface.
Geometrical effects in contact resistance measurements: Finite element modeling and experimental results
Authors: Natan M. , Purushothaman S. , Dobrowolski R.
Published: February 2003

We find experimentally and calculate by a numerical method the geometrical contribution to resistance due to current bending and constriction in 4-point contact resistance measurements in two configurations: 2I (cross stripes) and 2L. The geometrical effects in thin film couples increase in a 2I and decrease in a 2L with decreasing film thickness/width ratios, rendering the 2L configuration most suitable for interface resistance studies, particularly when the thickness to width ratios are less than 0.5. A set of scaling equations is provided, which enables the application of our results to predict geometrical contributions in these geometries for different materials and dimensions.
Raman spectra from Si and Sn implanted GaAs
Authors: Nakamura T. , Katoda T.
Published: February 2003

The variation of Raman spectra from Si and Sn implanted GaAs with various doses was studied. Si implanted GaAs showed one type of Raman spectra which indicates that the state is almost single crystalline with a high density of defects at a dose from 2×1012 to 1×1016 cm−2. Sn implanted GaAs showed, however, three types of Raman spectra corresponding to almost single-crystalline, amorphous, and mixed states depending on the ion doses. A model of the implanted region which includes partly crystalline and amorphous layers was proposed. The annealing behavior of the implanted region could be explained with the model.
Treatment of thermostimulated luminescence, phosphorescence, and photostimulated luminescence with a tunneling theory
Authors: Chang I. F. , Thioulouse P.
Published: February 2003

Based on a tunneling pair recombination concept, rigorous expressions of thermostimulated luminescence (TSL), phosphorescence (PP), and photostimulated luminescence (PSL) are derived. A novel method of examining the ratio of PSL and PP at fixed temperatures and fixed times is shown to be useful for the determination of energy levels of the trap which is involved in the tunneling. Application to the zinc-silicate phosphors gives reasonable results.
Luminescence study of a deep level in N-free GaP light-emitting diodes
Authors: Nishizawa J. , Jin C. C. , Suto K. , Koike M.
Published: February 2003

A 1.9-eV weak luminescence band observed at 77 K in nitrogen-free GaP light-emitting diodes grown by liquid phase epitaxy of Temperature Difference Method under Controlled Vapor Pressure in the vicinity of the optimum phosphorus vapor pressure has been studied. The relevant deep level has been found to act as a dominant nonradiative center at room temperature. The electroluminescence efficiency of the green emission band (555 nm at room temperature) and minority carrier lifetime are affected by this deep level. The centers which cause the 1.90-eV luminescence band are found to distribute in a p-type bulk region and also p-n interface region. It is proposed that the deep level is related to phosphorus vacancies.
Coupling of pulsed 0.35-μm laser radiation to titanium alloys
Authors: Rosen D. I. , Hastings D. E. , Weyl G. M.
Published: February 2003

An experimental and theoretical study has been performed on the response of a titanium alloy surface in vacuum to a XeF laser pulse (λ = 0.35 μm, pulse time = 1 μs). Thermal coupling measurements indicate an optical absorptance of 0.4–0.5. The onset of a measurable impulse is shown to result from bulk target vaporization for fluences ?5 J/cm2. The plasma formation threshold is obtained both theoretically and from experimental data, and good agreement is found. The theoretical model includes laser absorption in the target vapor through inverse bremsstrahlung and photoionization absorption, and collisional energy transfer between free electrons and bound electronic states of Ti.
Emission characteristics of single-crystal LaB6 electron gun
Authors: Takigawa T. , Sasaki I. , Meguro T. , Motoyama K.
Published: February 2003

Characteristics of electron beams emitted from an electron gun employing [100], [110], and [111] axial orientation LaB6 cathodes were investigated over a long period of time. Although the [100] cathode has high initial brightness, emission characteristics are unstable. This instability is caused by vaporization of the (100) plane, which has a low work function, on the cathode top. However, the [110] and [111] cathodes are stable, because the {100} surfaces are formed on the sloping surface of the cathode with time. Therefore, the [110] and [111] cathodes may be more suitable for many applications in spite of a lower initial brightness.
Electrical and structural properties of p-n junctions in cw laser annealed silicon
Authors: Maier M. , Bimberg D. , Fernholz G. , Baumgart H. , Phillipp F.
Published: February 2003

Depth profiles of the electrical quality of ion implanted and cw laser annealed p-n junctions in silicon are obtained for the first time by secondary ion mass spectroscopy. A comparison with the crystallographic properties of the surface and the junction as observed by Nomarski optical microscopy as well as cross-sectional and plan view transmission electron microscopy is made. Samples containing slip dislocations show better insulation and a lower reverse bias current across the p-n junction as comapred to samples with a perfect surface in agreement with current-voltage characteristics. Small dislocation loops located at the junction are found to degrade the junction quality.
On the cause of the flat-spot phenomenon observed in silicon solar cells at low temperatures and low intensities
Authors: Weizer V. G. , Broder J. D.
Published: February 2003

A model is presented that explains the ’’flat-spot’’ power-loss phenomenon observed in silicon solar cells operating under deep space (low temperature, low intensity) conditions. Evidence is presented suggesting that the effect is due to localized metallurgical interactions between the silicon substrate and the contact metallization. These reactions are shown to result in localized regions in which the PN junction is destroyed and replaced with a metal-semiconductor-like interface. The effects of thermal treatment, crystallographic orientation, junction depth, and metallization are presented along with a method of preventing the effect through the suppression of vacancy formation at the free surface of the contact metallization. Preliminary data indicating the effectiveness of a TiN diffusion barrier in preventing the effect are also given.
Calculation of sparking potentials in industrially important insulating electronegative gases
Authors: Govinda Raju G. R. , Hackam R.
Published: February 2003

A method for predicting the breakdown potentials in electronegative gases used for high-voltage insulation is proposed and described in detail. The method employs the Maxwellian electron-energy distribution function and the fundamental physical and data of the swarm properties of the gas, such as the ionization, attachment and momentum transfer cross sections, and the ionization and detachment energies. In some of the complex electronegative gases the fundamental data have not yet been reported due to either the inherent difficulty in measuring them or because their industrial importance became apparent only recently. Alternative approximate formulas for the relevant basic data of these gases are proposed, from which the breakdown voltage can be calculated without resorting to empirical methods. The approximations used are justified. The method is extended to calculate the breakdown voltage in a binary mixture of SF6 with CC2F2, C–C4F8, CBrCF2, and C4F6 for varying mixture ratios in the range 0–100† of the admixture. Reasonable agreement has been obtained with the measured values.
Stability of glow discharge
Authors: Wasserstrom E. , Crispin Y.
Published: February 2003

A macroscopic mathematical model is developed which describes the time-dependent behavior of the positive column of a weakly ionized electric discharge. This model is solved for the steady state, including the effects of Joule heating. These steady-state solutions are then perturbed and their stability with respect to the small disturbances is studied. Finally, comparisons are made to the experimental results of the stability of discharges in neon.
Enhanced photoemission from fluorine atoms in SF6 and CF4 arc discharge
Authors: Matsuzawa Hidenori , Suganomata Shinji
Published: February 2003

A new phenomenon, enhanced photoemission, during decaying arc discharges of SF6 at 3–40 Torr and of CF4 at 10–100 Torr has been studied spectrscopically. The enhanced photoemission, which consists mainly of the emission from fluorine atoms, corresponds to the occurence of an instability where negative ions seem to play an important role. The intensity of the photoemission oscillates at frequencies of the order of 105 Hz, and it is confirmed to be a wave. A relationship p×I = const. holds where p is the gas pressure and I the critical current under which the enhanced photoemission occurs.
Homogeneous electric field threshold switching phenomena in a multiplexible bistable liquid crystal display
Authors: Cheng Julian
Published: February 2003

An electrically addressed, thermally erased bistable nematic liquid crystal display with a potentially very large multiplexing capacity is described. A simple, uniform electric field geometry produces a nearly ideal electro-optic threshold response, with a very sharply defined threshold field and rapid saturation. The threshold is analytically shown to depend on the binding energy of disclination lines at a spatially finite surface orientational discontinuity. Moreover, the binding energy changes in time as the orientational discontinuity at the binding site is altered by the movement of a twist wall away from the junction. The nature and dynamics of this domain wall are described, as are the different distorted boundary layer configurations that arise in a uniform field geometry. The movement of this wall effectively reduces the binding energy of the disclinations, allowing switching to occur at lower fields. A dramatic voltage reduction is achieved with a short, low voltage pulse applied to prime the device prior to the onset of the switching pulse. This reduction makes 2:1 addressing possible at high speed (2 msec), using row and column voltage levels of approximately ±50 V. Similarly, 3:1 addressing is achieved with select and nonselect levels of 70 and 35 V, respectively. The high addressing speed results from the requirement of only a minimal amount of disclination movement, with the self-propelled annihilation of the detached loops carrying the switching process to completion thereafter.
Computer molecular dynamics simulation studies of grain-boundary structures. II. Migration, sliding, and annihilation in a two-dimensional solid
Authors: Bishop George H. , Harrison Ralph J. , Kwok Thomas , Yip Sidney
Published: February 2003

The dynamics of a high-angle tilt boundary in a triangular lattice with a truncated Lennard-Jones potential has been simulated by the method of computer molecular dynamics. Boundary migration was observed at various temperatures above a threshold, and was interpreted in terms of small steps involving coupled sliding and migration. In some cases, the simulation proceeded to the annihilation of a pair of boundaries with the attendant release of the boundary free energy and delocalization of the boundary free volume.
Dislocation-free zone model of fracture comparison with experiments
Authors: Ohr S. M. , Chang S.-J.
Published: February 2003

The dislocation-free zone (DFZ) model of fracture has been extended to study the relationship between the stress intensity factor, extent of plastic deformation, and crack tip geometry of an elastic-plastic crack as a function of applied stress. The results show that the stress intensity factor K decreases from the elastic value at first slowly, then goes rapidly to zero as the number of dislocations in the plastic zone increases. The crack with a zero stress intensity factor has its crack tip stress field completely relaxed by plastic deformation and hence is called a plastic crack. Between the elastic and plastic cracks, a wide range of elastic-plastic cracks having both a stress singularity and a plastic zone are possible. These elastic-plastic cracks with a DFZ are predicted if there is a critical stress intensity factor Kg required for the generation of dislocations at the crack tip. The expression for Kg is obtained from the crack tip dislocation nucleation model of Rice and Thomson. In most metals, the magnitude of Kg is less than the critical stress intensity factor for brittle fracture Kc. The values of K are determined from electron microscope fracture experiments for various metals and they are found to be in good agreement with the Kg predicted from the model. It is concluded that for most ductile and semibrittle metals, the mechanism of dislocation generation is more important than the fracture surface energy in determining the stress intensity factor at the crack tip.
Shear waves in soft gels with fixed rectangular boundaries
Authors: Ayant Y. , Durand M. , Geissler E. , Hecht A. M.
Published: February 2003

Soft gels contained in rigid rectangular cells are observed to give rise to low-frequency mechanical oscillations under zero displacement boundary conditions. The ratio of the bulk to shear modulus in such gels is very large, and the medium can be considered to be incompressible. We derive a modified form of the equation of motion for the shear waves, and solve, using a variational technique, for the fundamental modes in two two-dimensional cases, the infinite ribbon and the square. In three dimensions, long cells of square cross sections are investigated. Two types of waves arise: motion transverse to the cell axis and motion parallel to the axis. It is shown, both by a variational calculation and by Fourier decomposition, that the axial modes show a pronounced cellular structure, as in the case of the two-dimensional ribbon. The predicted fundamental frequency of the transverse waves is in good agreement with the experimental observations.
Quantum efficiency of internal photoeffects in narrow-gap semiconductor: A model
Authors: Scharoch Pawel , Szatkowski Jan , Pawlikowski Janusz M.
Published: February 2003

A phenomenological model of quantum efficiency of internal photoeffects is developed for narrow-gap semiconductors. Two competitive recombination mechanisms for electrons excited by photons with energies greater than double energy gap of semiconductor have been taken into consideration: (i) the dissipation of hot-electron energy by phonons in multiscattering processes, and (ii) Auger-type recombinations. The energy dependences of the impact ionization probability and the rate of electron energy losses are calculated and overlap integrals for semiconductors are evaluated using the explicit forms of wave functions for electrons and holes. Finally, the spectral characteristics of quantum efficiency have been calculated for two exemplary narrow-gap semiconductors: mixed CdxHg1−xTe crystals and InSb.
Defect production and lifetime control in electron and γ-irradiated silicon
Authors: Brotherton S. D. , Bradley P.
Published: February 2003

A study of the effect of 1- and 12-MeV electron and Co60 γ irradiation has been made on power p-i- n diodes and Schottky barrier diodes fabricated on the same starting material. A comparison of the results from these two types of structures illustrated the influence of device processing on the type of defects formed by subsequent irradiation. Detailed electrical characterization of the defects demonstrated good consistency between certain elements of the structural nature of the defect, inferred from these measurements, and those already obtained from electron spin resonance (ESR) measurements. Lifetime measurements on the p-i-n diodes indicated that both the A center and the divacancy were active recombination centers. Finally, data are presented on defect and lifetime annealing.
Deep levels in In0.53Ga0.47 As/InP heterostructures
Authors: Forrest S. R. , Kim O. K.
Published: February 2003

We report on deep levels in In0.53Ga0.47 As/InP heterostructure avalanche photodiodes grown by liquid-phase epitaxy. Two electron levels have been identified and studied using both admittance spectroscopy and a static capacitance-voltage technique. One level, found only in the InP layer, is acceptor-like with an activation energy of εtA = 0.20±0.02 eV and has a density in the bulk of the InP layer of NtA≊ 1015 cm−3. The density of the trap increases sharply at the In0.53Ga0.47 As/InP heterointerface to a value nearly ten times the background carrier concentration in this region. Filling of this trap at low temperatures reduces the conduction band discontinuity at the heterointerface from Δεc = 0.19 to 0.03 eV due to repulsion of the bands. The second trap, which is characteristic only of the In0.53Ga0.47 As, has an activation energy of εtB = 0.16±0.01 eV, and a density of between 3×1013 and 8×1013 cm−3.
Generation of a cold, intense relativistic electron beam using a magnetized foilless diode
Authors: Sheffield R. L. , Montgomery M. D. , Parker J. V. , Riepe K. B. , Singer S.
Published: February 2003

An annular electron beam with less than 30 mrad of angular velocity spread, a radius of 1 cm, and a current density exceeding 0.4 MA/cm2 has been generated with a magnetized foilless diode. The diode current loss is limited to less than a few percent by careful design of the tapered transition region connecting a self-magnetically insulated vacuum transmission line to the externally magnetized foilless diode. Details of the transition section design and operating characteristics of the electron beam generator are given.
Operating characteristics of a magnetically insulated reflex ion diode
Authors: Strobel George L.
Published: February 2003

Steady-state space charge limited-flow calculations have been carried out for an applied Bϑ magnetically insulated reflexing ion diode. Reflex ion energy spectra characteristic of a thin foil cathode and of a transparent mesh have been used. A one-dimensional calculation shows higher ion current densities with a mesh cathode, and that the emission electron current density increases with the applied Bϑ magnetic field. The ion current density is calculated to increase slightly with radius.
Saturation effects in three-level laser systems with constant loss
Authors: Reuven Yakir , Baer Michael
Published: February 2003

A quasi-steady-state analysis of a pulsed three-level laser system (homogeneously broadened) was extended to account for uniform losses along the cavity. It was found that in the low pumping rate limit such losses do not affect results previously obtained for systems without losses. In the high pumping rate limit the losses tend to reduce the spatial effects expressed by the correlation function, but the coefficient of the output radiation term, which is usually unity without losses, is decreased. Therefore, the output energy term in the spatially averaged rate equations, in the case where losses are incorporated, should be modified. The analytical results were confirmed by numerical solution of the exact (one-dimensional) space-time equations relevant to this system. Comparisons with other treatments were also carried out and the agreement obtained was satisfactory.
An iterative solution to Chandrasekhar X and Y equations for isotropic scattering
Authors: Caldwell J.
Published: February 2003

The X and Y functions of Chandrasekhar are defined in terms of two coupled integral equations whose solution for certain values of optical depth and albedo have already been found by means of iterative methods. This paper discusses the numerical difficulties of past iterative methods and describes an iterative approach which attempts to overcome some of these difficulties. This technique uses improved trial functions and is applied to the isotropic scattering case. Reasonable accuracy is achieved for certain cases at the expense of little computing time.
GeO2-ZnO-K2O glass as the cladding material of 940-cm−1 CO2 laser-light transmitting hollow-core waveguide
Authors: Hidaka T. , Kumada K. , Shimada J. , Morikawa T.
Published: February 2003

A hollow-core optical waveguide for 940-cm−1 CO2 laser light was fabricated with 80 mol % GeO2-10 mol % ZnO-10 mol % K2O glass functioning as the cladding, of which the refractive index nr is about 0.6 at 940 cm−1. The waveguide transmission loss is minimized at 940 cm−1 using the glass and is on the order of 0.1 dB/m for a 1-mm-i.d. hollow-core waveguide. Preliminary experiments of CO2 laser-light transmission for 0.6-mm-diam waveguides are also given. Measured loss, normalized to 1-mm-i.d. standard waveguide, is obtained to be 2 dB/m. The transmission mode observed is of the HE11-type only.
Analysis of thermal phase noise in fiber-optic sensors
Authors: Seiler Milton R. , Leach Eugene R.
Published: February 2003

An analysis is conducted of the thermally induced phase noise in a fiber-optic interferometer. This phase noise will represent the lower detection limit of fiber-optic sensors used for detecting low- level magnetic fields. The method herein uses a statistical approach to find the general form of the solution, and then relates this solution to the thermal properties of the fiber. Phase noise spectra are calculated over the region of 0.01–10 Hz. The spectral power density is found to vary as ω−7/2 over this spectral range. The analysis also shows that the major portion of the noise arises in the uncoated fiber. Noise may be reduced by using metallic coatings of low emissivity and, to some extent, by increasing the fiber diameter.
Radiative cooling with selectively infrared-emitting ammonia gas
Authors: Lushiku E. M. , Hjortsberg A. , Granqvist C. G.
Published: February 2003

Spectrophotometric measurements are reported for NH3 gas layers, and the potential use of this substance in radiative cooling devices is evaluated. The basic cooling parameters and the radiated power versus temperature drop are computed: the cooling power at near-ambient temperature can be exceptionally large. The radiative properties are discussed from the configuration of the NH3 molecule. Typically a 2-cm-thick NH3 gas slab can provide 26 Wm−2 useful cooling power at 15 °C below ambient temperature in a device with a moderate nonradiative loss (heat transfer coefficient of 1 Wm−2 K−1).
The influence of molecular nitrogen upon plasma channel formation by laser resonance saturation
Authors: Measures R. M. , Wong S. K. , Cardinal P. G.
Published: February 2003

Laser resonance saturation of alkali vapors represents a very attractive method of creating the extended plasma channels of interest in light ion beam fusion. We have undertaken a preliminary study of the influence of molecular nitrogen upon this laser ionization technique. Our results indicate that the electron cooling, resonance quenching, and the increase in the laser energy requirement are acceptable, providing that the alkali seeding exceeds 0.5%.
Optical constants and spectral selectivity of stainless steel and its oxides
Authors: Karlsson Björn , Ribbing Carl G.
Published: February 2003

Reflectance measurements on eleven grades of stainless steel have been performed. It is found that the metallurgical phase is a more important parameter for the reflectance behavior than the detailed content of the alloying elements. The optical constants for one austenitic and one ferritic grade have been calculated by the Kramers-Krönig analysis. For the extrapolation, a fitting procedure to the results from measurements with polarized light at 10° and 60° incidence was used. The austenitic steels have a higher reflectance than the ferritic and martensitic, but their integrated solar reflectance of 68% is considered too low for solar reflectors. Two of the natural oxides on stainless steel, Fe2O3 and Cr2O3, have been studied as separate films, and their optical constants determined by combined transmission and reflectance measurements. The metal and oxide results are combined in an evaluation of the optical selectivity that can be obtained with oxidized stainless steel surfaces. It is concluded that a ferritic steel base is to be preferred because of its lower reflectance. Assuming perfect boundary layers and using conventional interference calculations it is found that Fe2O3 gives better selectivity than Cr2O3 since both the first interference minimum and maximum will be lower in that case.
Effects of Cd-vapor and Te-vapor heat treatments on the luminescence of solution-grown CdTe:In
Authors: Norris C. B. , Zanio K. R.
Published: February 2003

We have employed cathodoluminescence at 80–300 K in the first comprehensive study of the effects of Cd-vapor or Te-vapor heat treatments on the luminescence of solution-grown CdTe:In. The broad 1.4-eV band present in as-grown material is weakened by Te firing and typically enhanced by Cd firing. These results do not support earlier connections between this luminescence and the VCd-InCd complexes predicted by defect chemistry calculations to be dominant in CdTe:In. Alternatives to straightforward interpretation are discussed for both experiments and defect modeling. The effects of the heat treatments on the injection-level dependence, frequency response, and temperature dependence of the 1.4-eV luminescence are described. This luminescence arises from localized transitions within compact complexes in our as-grown material, but different species of complexes or competing transition mechanisms are involved in heat-treated material. The edge emission, present in both as-grown and fired material, peaks near 1.57 eV at 80 K and thus is close to the band-gap energy of CdTe. However, frequency-response data reveal anomalous energy-storage processes which can slow the edge-emission kinetics to the microsecond regime following Cd firing. Another surprising result is the strong coupling in both kinetics and injection-level dependence between the edge emission and a sharp extrinsic band near 1.54 eV which is prominent in Te-fired CdTe.
Low energy Ar+ ion sputtering of liquid and solid indium
Authors: Hurst Barry L. , Cooper C.Burleigh
Published: February 2003

Liquid and solid indium targets were bombarded normally by Ar+ ions with energies (E0) ranging from 17 to 180 eV. The relative differential sputtering yields of the In were measured as a function of E0 and target temperature. At E0 = 107 eV, the relative yield of the liquid In was larger than that of the solid In by about 10%. The shapes of the yield versus E0 curves for the liquid and solid In were similar. The threshold of sputtering was about 17 eV for both liquid and solid. The effects of surface topography on sputtering yields seemed to be the same for the liquid and solid In. The higher yield of the liquid In is attributed to its lower binding energy.
Enhanced emission of positive cesium ions from zeolite
Authors: Matossian J. , Seidl M.
Published: February 2003

The thermionic emission of positive cesium ions from zeolite has been significantly increased in the pulsed regime due to the adsorption of electronegative gas atoms at the zeolite emitting surface. Extracted current densities are described by the Richardson equation, J0 = A(T)1/2  exp(−Φ0/KT). Adsorption of fluorine and chlorine rich gases lowers the Richardson work function Φ0 and the pre-exponential factor A. Specifically, fluorine adsorption reduces Φ0 to less than 0.1 eV and the pre-exponential factor by eight orders of magnitude. This results in over a 1000 fold increase of J0 at 800 °C. The changes are caused by a negative outward dipole layer at the emitting surface due to chemisorbed fluorine atoms. The coverage of these fluorine atoms obeys the Langmuir-Freundlich isotherm equation. Exposure of zeolite to oxygen results in an increase of up to an order of magnitude in A only. This is attributed to the production of additional active ion sites at the emitting surface.
Lateral seeding epitaxy by cw Ar laser irradiation and by high temperature chemical vapor deposition technique
Authors: Nagao S. , Kayano S. , Tsubouchi N. , Nishimura T. , Akasaka Y.
Published: February 2003

A single crystal Si film of [111] orientation has been obtained over patterned amorphous insulating layer stripes for lateral seeding recrystallization. High-temperature, vapor-phase-epitaxial (VPE) growth technique has been utilized to form single and polycrystalline Si films on (111) Si substrate with the insulator stripes. The single crystal film on the exposed Si substrate and polycrystalline film on insulator were recrystallized with a scanning cw Ar laser. Topographical features and crystalline perfection associated with the laser-induced recrystallization were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and TED (transmission electron diffraction). At high power laser irradiation, the resulting recrystallization of polycrystalline Si seeded by single crystal Si deposited on substrate has been observed.
Impurity and defect levels in beryllium-doped GaAs grown by molecular beam epitaxy
Authors: Bhattacharya P. K. , Bühlmann H.-J. , Ilegems M. , Staehli J. L.
Published: February 2003

Impurity and defect levels in Be-doped GaAs grown by molecular beam epitaxy have been studied by photoluminescence, Hall, and transient capacitance measurements. Epitaxial layers and n+-p diodes were grown at 602 °C using As4 molecular beams. The edge luminescence of our undoped and lightly Be-doped samples shows several defect-related transitions from 1.5049 to 1.5112 eV, in addition to the known donor- and acceptor-related excitonic transitions. Additional weak features occurring at energies from 50 to 100 meV below the band gap were also observed. Carbon was identified as the principal residual acceptor. Transitions involving Be were identified in the Be-doped layers and correlated with doping levels and binding energies from temperature-dependent Hall data. Deep level electron and hole traps with thermal activation energies ΔET ranging from 0.27 to 0.82 eV were detected in the GaAs layers. Trap concentrations were of the order of 1012–1014 cm−3 in layers with free-carrier concentrations ∼1016 cm−3. A hole trap with ΔET = 0.54 eV, consistently detected in our samples, is ascribed to Fe. A hole trap with ΔET = 0.90 eV which emerges after heat treatment may be related to As vacancies. The thermal capture cross section of the different traps have been estimated.
Background and temperature dependent current-voltage characteristics of HgCdTe photodiodes
Authors: Rosbeck J. P. , Starr R. E. , Price S. L. , Riley K. J.
Published: February 2003

The zero bias resistance-area products and current-voltage (I-V) characteristics as a function of temperature and infrared background radiation have been measured for HgCdTe photodiode samples with cutoff wavelengths near 9 μm at 80 K. A model is presented to account for the background and temperature dependence of the data. It is found that the reverse I-V curve shapes and magnitudes may be estimated as a function of both background and temperature by superposition of the total current from optical generation, thermal diffusion, and depletion region generation-recombination centers. The influence of background radiation was found to create an exceptionally linear reverse I-V characteristic that can be easily distinguished from other current generation mechanisms, and can be modeled by application of existing theory to HgCdTe photodiodes.
Pulse-laser-induced supersaturation of indium and antimony in germanium
Authors: Lawson E. M.
Published: February 2003

A pulsed ruby laser has been used to produce enhanced solubilities of indium and antimony in germanium. Lower limits for the solubilities have been obtained using Rutherford backscattering spectrometry and electrical measurements. The values obtained are ≳5.3×1020 cm−3 for indium and ≳6.2×1020 cm−3 for antimony.
Nuclear magnetic resonance in sedimentary rocks: Effect of proton desorption rate
Authors: Mendelson Kenneth S.
Published: February 2003

In a discussion of nuclear magnetic resonance of protons in the pore fluid of sedimentary rocks, Cohen and Mendelson assumed that the desorption rate of protons from the rock surface is much faster than the relaxation rate of the magnetization for protons on the surface. In the present paper it is shown that this assumption is not necessary and conditions are established under which the analysis of Cohen and Mendelson is valid.
Potential fluctuations in high-purity n-type III-V semiconductors
Authors: Fedders Peter A.
Published: February 2003

We investigate the effects of fluctuations in the Coulomb potential due to charged impurities in high-purity n-type III-V semiconductors at low temperatures. Assuming that charged donors and acceptors are randomly distributed at high temperatures, we conclude that the donors are selectively filled at low temperatures leaving nonrandom distributions of charged and filled donors. The potential fluctuations from these distributions can approximately account for a number of experimental observations on low-temperature high-purity GaAs including the apparent decrease of donor binding energy with increasing impurity concentration observed in Hall measurements, the sharpness and temperature dependence of the ls-2p transition along with the diffuse ls-conduction band edge observed in photoconductivity experiments, and the fact that experimentally observed photoconductivity line shapes are narrower than those previously predicted.
Diffraction studies of the high pressure phases of GaAs and GaP
Authors: Baublitz M. , Ruoff A. L.
Published: February 2003

High pressure structural phase transitions of GaAs and GaP have been studied by energy dispersive x-ray diffraction with the radiation from the Cornell High Energy Synchrotron Source. GaAs began to transform at 172±7 kbar to an orthorhombic structure possibly belonging to space group Fmmm. GaP transformed to a tetragonal β-Sn type phase at 215±8 kbar. Although pressure transmitting media were used to minimize shear stresses in the specimens, the high pressure diffraction results were interpreted as showing evidence for planar defects in the specimens.
Cr needle crystals with fcc structure plasma grown from Cr(CO)6
Authors: Okuyama F.
Published: February 2003

It is shown that needle crystals of Cr possessing a fcc structure are grown from Cr(CO)6 through a cathodic growth process. Electron diffraction studies revealed that the needles consisted of unoriented micro single crystals with a fcc lattice whose cell edge was ∼4.14 Å, and their composition was determined to be elementary Cr by Auger spectroscopy. It is hypothesized that the fcc structure of the Cr needles was attributable to their mode of growth in an extremely strong electric field.
Effects of Q-switched green laser beam scanning on silicon bipolar transistor electrical characteristics
Authors: Parker D. L. , Porter W. A. , Zhu Shan-ji , Lin Fa-yong
Published: February 2003

Silicon bipolar transistors were scanned by a Q-switched green (530-nm wavelength) laser beam and subsequently heat treated. Under fixed laser scanning conditions there is a laser power threshold (0.5 mW) above which the forward current gain begins to decrease and the reverse emitter-base junction leakage current begins to increase and another laser power threshold (0.8 mW) above which surface changes in the silicon and oxide are observable. The changes in electrical characteristics are stable for post scanning anneals up to 400 °C, yet are almost completely eliminated by 800 °C anneals. These effects are due to changes in the minority carrier lifetime and surface recombination rate by the laser scanning. Under proper scanning conditions current gain may be controlled without visible damage, without degradation of breakdown voltage, and without increased base-collector reverse leakage current.