bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy loss of 24.8-MeV electrons by interacting with thick materials
Authors: Mikado Tomohisa , Tomimasu Takio
Published: February 2003

Energy spectra of 24.8-MeV electrons after emerging from C, Al, Cu, and Pb were measured at 0°, 5°, 15°, 30°, 60°, 120°, and 150°. The material thickness ranged from ∼1 to ∼3.6 g/cm2. Total energy spectra, defined as 2π ∫π0 f(E,θ)dE sin θdθ, were composed from these observed energy spectra. Average energy loss was calculated from the total energy spectrum for each material. By plotting the experimental data including the one obtained by Ziegler, an empirical equation estimating the average energy loss per unit path length was obtained. The most probable energy losses at 0° for C and Pb agree well with theoretical predictions, while those for Al and Cu are generally larger than calculated values by ∼6–7%. Discrepancy between the experimental and calculated values of the full width of f(E,0°) at half-maximum due to electron straggling becomes smaller as Z increases.
Design of rotationally symmetrical electrostatic mirror for time-of-flight mass spectrometry
Authors: Berger C.
Published: February 2003

In order to be able to use it in time-of-flight mass spectrometry, we have tried to find a mirror with as few spherical and chromatic aberrations as possible. We have studied the characteristics of the mirror with charged particles whose initial energy varies by ±1% around a central value and which go through an imaginary input pupil of radius 0.2 ρ (ρ being the radius of the three cylinders which go to make up the mirror). The best operating conditions are calculated for different source points on the axis, taking into account separate residual chromatic and spherical aberrations, and also in the case of simultaneous chromatic and spherical aberrations. The second part of the paper deals with flight time (internal mirror flight time and object-image flight time). The data enable us to establish that this convergent mirror plays an essential compensating role; it eliminates not only the initial energy spread effects, but also those of the ion bunch divergence. Consequently, all the above-mentioned particles have a flight time which is virtually constant.
Adverse shielding of the heating field and high ohmic loss introduced by electrostatic shields employed in radio-frequency heating of plasma
Authors: Faulconer D. W.
Published: February 2003

The electrostatic shields now commonly employed to shield antennas in the heating of plasma in the ion cyclotron frequency range are shown to reduce the specific radiation resistance of a long narrow antenna in the presence of plasma by a significant factor (on the order of 2/3 for a typical double-array shield) due to the effect of magnetic shielding of the magnetosonic polarization. An allied change in antenna specific inductance is also found. These effects are shown to diminish with increase in antenna width and should pose no major problem for the wide antennas projected for use in fusion experiments. In addition to the foregoing effects which are not ohmically dissipative in essence, electrostatic shields are also shown to introduce surprisingly high ohmic loss, this being of potential importance in shield design. The dependences of the above magnetic and ohmic phenomena on shield parameters are given and a shield design minimizing them is presented. Their repercussion on coupling efficiency and on the excitation voltage necessary for a given power flux from the antenna is discussed.
Intrinsic defects in ZnO varistors
Authors: Mahan G. D.
Published: February 2003

Theoretical calculations are presented for equilibrium concentrations of zinc and oxygen vacancies in ZnO. Results are presented at the sintering temperature, and also at room temperature. Theoretical calculations of reaction constants show that the intrinsic donor is the oxygen vacancy, rather than the zinc interstitial. The depletion of vacancies in the surface region, as the ZnO is cooled from the sintering temperature, is also calculated. Homojunction effects which are caused by such depletion are shown to be small.
Defects in Q-switched laser annealed silicon
Authors: Wang K. L. , Liu Y. S. , Possin G. E. , Karins J. , Corbett J.
Published: February 2003

This paper describes the characterization of residual defects using transient capacitance spectroscopy for ion-implanted Si annealed with a Q-switched Nd-glass laser. The deep-level defect levels observed in this study were similar to those obtained in low-fluence ion implanted samples. The spatial distributions of deep-level defect concentrations were obtained for conditions using different anneal energy densities. From the difference of the distribution profiles, it is concluded that the greater the annealing laser energy densities, the lower the defect concentration near the junction.The reduction of the defect concentration is partly due to the inward movement of the junction. Thus the defects detected are those which lie further down in the tail of the defect distribution profile and have a lower concentration. Other reasons for the reduction of the defect concentration can be due to thermal annealing as heat propagates into the substrate during laser radiation. The reduction of the defect concentration agrees with the improvement of the measured I–V characteristics. Annealing with multiple shots of laser radiation was performed and the annealing model was established. The junction movement was confirmed by an electron beam induced conductivity technique. The carrier diffusion length measured in the region, where a surface layer of 2–3 μm was etched, decreases as the annealing energy density increases. This may be explained by the fact that the native defects generated thermally in the melts at the surface diffuse into the bulk and subsequently are trapped by the impurities in Si.
Depth distributions of sulfur implanted into GaAs as a function of ion energy, ion fluence, and annealing temperature and encapsulation
Authors: Wilson R. G. , Jamba D. M. , Deline V. R. , Evans C. A. , Park Y. S.
Published: February 2003

Depth distributions are shown for sulfur implants into GaAs at energies from 40 to 600 keV and implant fluences from 4×1012 to 4×1016 cm−2. The four Pearson IV moments, including range and range straggle, are tabulated and plotted versus ion energy for these profiles. Redistributed sulfur profiles are shown for these same implants following annealing under three conditions. Annealed profiles are compared with electrical profiles from other work. Fractions of sulfur atoms in various locations are described. Annealed sulfur profiles are shown as a function of temperature for SiO2 and Si3N4 caps.
Kinetics of hopping of octahedral interstitials in arbitrary time dependent and inhomogeneous field: Body-centered cubic lattice
Authors: Oğurtani Tarik Ö. , Seeger Alfred K.
Published: February 2003

Atomic movements of interstitials (octahedral sites) species in an arbitrary time and space dependent field have been formulated in terms of a set of coupled linear differential equations for a body-centered cubic (bcc) lattice. The decoupled form of these equations has been solved exactly using the discrete Fourier k space transformation supplemented by a Laplace transform with respect to time. An explicit and compact expression for the Fourier transform of the partial concentration of interstitials is obtained for fields which have absolutely convergent norms in the time domain. Some special cases of general physical interest such as simple harmonic or static inhomogeneous fields are also treated. For the latter situations, a steady-state power dissipation and the thermodynamic equilibrium partition of defects over energetically distinguishable sites are uniquely determined, respectively. The inverse relaxation time spectrum of octahedral-interstitials which has three distinct branches, one acoustic and two optical in the first Brillouin zone, is also computed and presented along the [100], [110], and [111] directions of the cubic cell of a bcc structure.
rf-plasma deposited amorphous hydrogenated hard carbon thin films: Preparation, properties, and applications
Authors: Bubenzer A. , Dischler B. , Brandt G. , Koidl P.
Published: February 2003

The deposition of amorphous hydrogenated hard carbon (a–C:H) thin films from benzene vapor in a rf plasma is described. a–C:H was deposited on glass, quartz, Si, Ge, and GaAs. Negative self-bias VB and gas pressure P are shown to be the two significant parameters for an accurate control of the deposition process. The dependence of growth rate and deposition temperature on VB and P was determined; this gives an empirical relation for the average energy Ē of the ions forming the thin films. Refractive index (1.85–2.20 in the IR), optical gap (0.8–1.8 eV) and density (1.5–1.8 g/cm3) of a–C:H was measured. The optical gap varies linearly with the content of bonded hydrogen in the films. The density of a–C:H is proportional to the average ion energy Ē. We demonstrate the application of a–C:H as antireflective coating on Ge for 10.6 μm (reflection <0.2% at 10.6 μm) and as terminating layer of an optical multilayer stack.
Calculations of the time-dependent behavior of the reflex triode opening switch
Authors: Humphries S. , Fu Xi-Dong
Published: February 2003

A one-dimensional computer simulation was used to study time-dependent phenomena in the power gaps of reflex triodes used as high power opening switches. Constant gap voltage was assumed. It was found that current was carried by space-charge-limited electron flow through an enlarging cathode sheath. The sheath width was governed by erosion of the initial ion distribution through bipolar space-charge flow. The results suggest analytic formulae that may be applied to models of triode behavior with more complex driving circuits.
Carrier dependent parameters in a silicon optical waveguide
Authors: Willander M.
Published: February 2003

The infrared absorption (at λ=10.63 μm) of an electron-hole plasma, created in a thin silicon waveguide by intermittent electron beam bombardment, is measured experimentally and analyzed theoretically. In the absence of all external fields (except those of the probing laser beam) the imaginary dielectric constant is shown to be a linear function of the carrier concentration in the range 2×1022–2×1023 m−3 at room temperature. Furthermore, it is shown that the method can be used to study the possible carrier dependence of either the carrier lifetime or the surface recombination velocity.
Profile estimation of an implanted-diffused arsenic layer in silicon
Authors: Wang Way-Seen , Meng Huai-Ying
Published: February 2003

The nonlinear diffusion coefficient of a solid-state diffusion equation is approximated by a linear function of concentration, and then the resulting diffusion equation is solved exactly by the method of self-similar solution to obtain a simple expression for the profile estimation of an implanted-diffused arsenic layer in silicon. This expression is dependent only upon the total implant dose and the initial junction depth, but not the specific form of the initial profile. However, as the diffusion time is long enough, only the total implant dose is of significance. The approximate profile, junction depth, surface concentration, and sheet resistance agree quite well with those obtained by solving the nonlinear diffusion equation numerically or by carrying out the diffusion experimentally.
Effect of photoelectrochemical etching on charge collection efficiency in CdS: An electron beam induced current study
Authors: Hodes Gary , Cahen David , Leamy Harry J.
Published: February 2003

Parallel secondary electron and charge collection images of a CdS/Au Schottky barrier show that photoetching of the CdS improves the charge collection efficiency. This is explained in terms of preferential removal of (near) surface recombination centers by the photoetching. Evidence is given that lack of photoetching of specific areas of the surface is due to the fact that such areas are photoelectrochemically inactive, possibly because of poor electrical contact with underlying CdS, and combined photoetching and scanning electron microscopy investigation is suggested as a way to check semiconductors for inactive regions.
Thermally stimulated currents in polymers driven by temperature gradients
Authors: Sworakowski J. , Figueiredo M. T. , Ferreira G. F. Leal , Campos M.
Published: February 2003

Nonisothermal currents were measured in poly(methyl methacrylate) and poly- (tetrafluoroethylene) samples, not polarized with external fields before the measurements. The currents were attributed to thermally stimulated reorientation of dipoles driven by temperature gradients across the samples. Calculations, based on a model put forward in the paper, are shown to satisfactorily reproduce basic features of the experimental curves. It is suggested that the room temperature peak in poly (tetrafluoroethylene) is due to a pyroelectric effect and is associated with a reorientation of impurity dipoles during the phase transition.
Suppression of dielectric breakdown in MgO crystals at high temperatures by impurity doping
Authors: Tsang K. L. , Chen Y.
Published: February 2003

The effect of impurities and their concentrations on the dielectric breakdown of MgO crystals at 1473 K is studied using an electric field of 1500 V/cm. Crystals doped with H, Cu, Co, Fe, Ni, Cr, or V are used. The current behavior and the characteristic time for breakdown of each crystal are investigated. The presence of Cu, Co, or H suppresses the breakdown, but the presence of Fe, Ni, Cr, or V enhances it. The suppression or enhancement of the breakdown depends on the dopant concentration.
A study of the electrical and luminescence characteristics of a novel Si-based thin film electroluminescent device
Authors: Robbins D. J. , DiMaria D. J. , Falcony C. , Dong D. W.
Published: February 2003

The results of electrical and luminescence measurements on a new, low voltage, dc, thin film electroluminescent device structure are presented. The devices incorporate a two-phase Si-rich-SiO2/SiO2 electron injector layer which provides control of current, and an active luminescent ZnS:Mn layer in which light is generated by hot electron impact excitation of the Mn2+ activator in high electric field. Separation of the processes of current control and light generation into different layers permits the effects of space charge and the average field distributions to be determined. The electroluminescence intensity is simply proportional to the average power dissipated in the ZnS:Mn layer when the average field is in the range 0.6–1.2 MV cm−1, and when field distortion due to electron trapping in the SiO2 layer is small. When the field locally in the ZnS:Mn layer exceeds ∼1.7 MV cm−1, lattice ionization competes with impact excitation of Mn2+ and the quantum efficiency falls. A simplified model assumes that in a quasi-steady-state condition the majority of the device current is carried by electrons accumulated in the satellite (L, X) valleys in the conduction band of ZnS. The results are compared with previous studies, and their general significance as regards the limiting efficiency of high field electroluminescent devices using ZnS is discussed.
Zn incorporation in Ga1−xAlxAs grown by liquid phase epitaxy and its electrical properties
Authors: Vassilieff Georges , Saint-Cricq Béatrice
Published: February 2003

Zn doped Ga1−xAlxAs layers with different Al concentrations (x=0.2, 0.3, 0.6) have been grown by the conventional liquid phase epitaxy method (LPE). The Zn mole fraction in the liquid solution has been varied from 5×10−4 to 5×10−2 and the corresponding hole concentration in the solid has been studied using Hall measurements. The results are as follows: hole concentrations up to 1018 cm−3 are easily obtained for a high x of 0.6. The hole concentration in the solid varies according to the square root of the Zn mole fraction in liquid (XlZn), and varies as β exp(−α x) for a given XlZn. A global relation has been derived which totally defines Zn incorporation in Ga1−xAlxAs crystal. The acceptor activation energy has been calculated for different aluminum concentrations and has been found to vary between 15 meV for x=0 and 30 meV for x=0.6. These results have been compared with the results obtained from other dopants.
Wiggler-free free electron waveguide laser in a uniform axial magnetic field: Single particle treatment
Authors: Fruchtman A.
Published: February 2003

A wiggler-free free electron laser operating in a waveguide is analyzed by using a single particle treatment. The use of either a TE or a TM mode is shown to enhance the gain for a resonant frequency much higher than the cyclotron frequency. It is demonstrated that a source of a submillimeter radiation, based on this analysis, may have output power comparable to that of a wiggler-type free electron laser.
New class of gain guiding laser with a tapered-stripe structure
Authors: Mamine Takayoshi , Oda Tatsuji , Yoneyama Osamu
Published: February 2003

A new class of gain guiding laser with a tapered-stripe structure has been developed which exhibits a linear dependence of light output on cw current, a stable single-lobe far-field pattern along the junction at the power level of more than 10 mW, and an amount of astigmatism below 20 μm. It is also shown that a thin active layer thickness is desirable to achieve a stable lateral mode. The main feature of the tapered-stripe structure is that it offers an additional degree of freedom in controlling the beam spot size and the radius of curvature of the phase front separately, by varying the widths as well as the length of the tapered stripe.
Experimental study of the Scholte wave propagation on a plane surface partially immersed in a liquid
Authors: de Billy M. , Quentin G.
Published: February 2003

This study shows that as a pseudo-Rayleigh wave propagates on the surface of a semi-infinite elastic plane solid, partially immersed in a liquid, a new repartition of the energy appears at the liquid–solid interface. Two interface waves are generated: a generalized Rayleigh wave (or leaky Rayleigh wave) and a Scholte wave (or pseudo-Stoneley). We show that for values of the angle of immersion θi less than θi,m =θR/2+π/4 (where θR is the Rayleigh angle), the amplitude of the Scholte wave depends strongly on the wetting and on θi. In this angular region the leaky Rayleigh wave does not disturb the Scholte wave propagation. For θi>θi,m the experimental records present an oscillating behavior that we have attributed to the superposition of the pseudo-Stoneley wave and the generalized Rayleigh wave specularly reflected by the air–liquid interface.
Surface acoustic wave measurements using an impulsive converging beam
Authors: Yamanaka Kazushi
Published: February 2003

A method for velocity and attenuation measurement of leaky surface acoustic wave on small areas of a solid surface was developed. This technique uses an impulsive converging beam generated with an acoustic lens. Reflected waves from a sample consisted of the axial wave and the leaky surface wave separated in time domain. From the time interval between these waves, the velocity of the leaky surface wave is determined using an expression derived along with ray optics. Because time interval measurements do not require any mechanical scanning, they can be done without special attention paid for mechanical precision of the scanning system, enabling rapid and simple measurement. Since the impulsive wave has a broad frequency spectrum, spectroscopic analysis of leaky surface wave is also possible. Frequency dependent attenuation measurement of leaky surface acoustic waves on heat treated steels and velocity dispersion measurement of leaky surface wave on titanium nitride film on tool steel are demonstrated.
Thermal profiles and thermal stresses introduced on silicon during scanning line shaped beam annealing
Authors: Correra L. , Bentini G. G.
Published: February 2003

The evaluation of thermal profiles and introduction of defects due to thermal stesses induced on 〈100〉 silicon during the annealing carried out by the scanning of a line shaped e-beam source, has been performed. The computation of the temperature profiles along the sample for different beam scan speed and incident power has been used to evaluate the two-dimensional map of the thermal stresses induced over a 4×2 cm2 silicon sample 〈100〉 oriented. The computed stresses were then compared with the yield stress of the material at the actual annealing temperature. The topographic distribution of the thermal stresses shows quite a complicated trend changing drastically from compressive to tensile as a function of beam position along the sample; it can be concluded that the introduction of defects takes place mainly at the edge of the sample which is irradiated last. An experimental check of our computations has been performed by using a fast multiscanning electron beam along a line, joined to a mechanical translation of the sample through the scanned region. Pyrometric temperature measurements performed during the irradiation confirm our computed temperature profiles, whereas both sheet resistivity measurements and x-ray topography show that the introduction of defects actually takes place in the region of the sample and at the irradiation conditions foreseen by the present computation.
Time-dependent behavior of high-pressure mercury discharges
Authors: Stormberg H. P. , Schäfer R.
Published: February 2003

A numerical model has been developed for studying the time-dependent behavior of cylindrical high-pressure mercury discharges. The model makes it possible to calculate time-dependent plasma parameters such as temperature profiles, arc conductance, etc. for arbitrary supply voltage waveforms and frequencies. The model is based on an expansion of the heat flux potential into a series of Bessel functions of zero order. An analytical approximation for the local net emission has to be provided for the model. It has been evaluated as a function of lamp diameter, mercury pressure, axis temperature, and temperature profile by calculating the radiation transport in the mercury lines. The calculated wall temperature and luminous flux as well as the calculated time-dependent lamp voltage, current, and arc temperature profiles are compared with corresponding measurements.
Two-dimensional numerical simulation of an inductively driven imploding foil plasma
Authors: Kohn Brian J. , Roderick Norman F. , Beason Charles W.
Published: February 2003

A 1.9-MJ capacitor bank with intermediate inductive energy storage for pulse shortening has been used to implode a thin cylindrical sheath in a z-pinch geometry. Theoretical investigations of two-dimensional axisymmetric effects in the r-z plane, which lead to a thickening of the sheath, have been made using a two-dimensional magnetohydrodynamics code. The results of several calculations are presented which demonstrate how imperfections in the initial sheath geometry affect development of the acceleration-driven magnetohydrodynamic Rayleigh–Taylor instability.
The formation of double-valued sheaths in thermionic converters
Authors: Lundgren Lennart
Published: February 2003

A theory for the sheath in an ignited thermionic converter is presented. The theory includes the effect of the velocity spread of the particles but the charge-particle collisions are neglected. Conditions for the appearance of a virtual emitter are given. The theory is compared with a beam approximation theory and a hydrodynamic theory. All three theories give almost the same condition for the appearance of a virtual emitter in an ignited thermionic converter.
Two-temperature modeling of the free-burning, high-intensity arc
Authors: Hsu K. C. , Pfender E.
Published: February 2003

In this paper a two-temperature model (Te >Th) is applied to a free-burning, high-intensity, atmospheric pressure argon arc. With appropriate boundary conditions and nonequilibrium thermodynamic and transport properties, solutions of the conservation equations are obtained for the entire arc, except for the electrode sheath regions. Significant temperature discrepancies between electrons and heavy particles are found in the arc fringes. The elevated electron temperatures in the arc fringes lead to a rearrangement of the current density distribution which, in turn, has some effect on the temperature as well as on the velocity field in the arc core. Comparisons of the results of this study with spectrometric temperature measurements show better agreement than with results based on a one-temperature model.
High pressure measurements on photopumped low threshold AlxGa1−xAs quantum well lasers
Authors: Camras M. D. , Holonyak N. , Coleman J. J. , Drickamer H. G. , Burnham R. D. , Streifer W. , Scifres D. R. , Lindström C. , Paoli T. P.
Published: February 2003

Data are presented on the continuous (cw) 300 K photopumped laser operation of a low threshold Alx′Ga1−x′As–GaAs (x′∼0.30) single quantum well heterostructure (quantum well size Lz∼60 Å) subjected to high pressure (0–11 kbar) in a simple opposed anvil apparatus. Beyond ∼11 kbar where the central Alx′Ga1−x′As waveguide region undergoes a direct–indirect transition, and the waveguide confinement begins to weaken and deep levels tend to become important, the laser threshold increases rapidly and ‘‘quenches’’ cw 300 K operation. Pulsed 300 K photopumped laser operation of an undoped 121-period AlxGa1−xAs–GaAs (x∼0.5) superlattice in the pressure range from 0–11 kbar is shown for reference. The pressure coefficients of the quantum well heterostructure and the superlattice lasers are comparable (∼11 meV/kbar).
Wideband heterodyne detection in the far infrared with extrinsic Ge photoconductors
Authors: Dodel G. , Heppner J. , Holzhauer E. , Gornik E.
Published: February 2003

The heterodyne performance of Ge photoconductors doped with shallow impurities was investigated using optically pumped far infrared lasers. Two lasers operating on the 67-μm NH3 Raman line generated difference frequencies from 0–100 MHz. An additional frequency point at 1.155 GHz was produced with two methanol-isotope lasers at 118 μm. For three detectors with different doping levels IF bandwidths of 141, 63, and 8 MHz were measured using local oscillator powers of a few milliwatts. The detector gain and quantum efficiency were calculated from shot noise measurements. For impedance matched operation the calculated noise equivalent power (NEP) values are 2×10−18 W Hz−1 for the fastest detector and 6.5×10−19 W Hz−1 for the slowest detector.
The nonlinear generation of a steady magnetic field in a conducting sphere placed in an oscillatory magnetic field
Authors: Hugrass W. N.
Published: February 2003

It is shown that the nonlinear ‘‘Hall’’ force generated in a conducting sphere placed in an oscillatory (ac) magnetic field has a nonzero curl. It, therefore, drives a poloidal current which has a steady (dc) component and a second harmonic component. A general analytic expression for the dc toroidal magnetic field generated by the Hall current is obtained for the weakly nonlinear case: ωce/ν ≪1, where ωce =eB/m is the electron cyclotron frequency in the ac magnetic field and ν is the effective collision frequency. The dc magnetic field is evaluated numerically (using the general analytic formulae) for the special case where the applied ac magnetic field is uniform.
Field-assisted thermally stimulated current of mobile ions in a dielectric layer of a metal–oxide–semiconductor structure
Authors: Changhua Tan , Mingzhen Hsu , Yangyuan Wang
Published: February 2003

A field-assisted thermally stimulated ionic current method has been used to investigate the transient currents associated with mobile ions in dielectric layers of metal-oxide-semiconductor (MOS) structures. Assuming Poole–Frenkel effect, an interface trapping model has been used to analyze J–V curves. Using a ramp voltage, analytic expressions for normalized J–V curves are obtained. The single energy model and distributed energy model have been analyzed. The most probable trapping depth of mobile ions, attempt-to-escape frequency and trapping energy distribution of mobile ions may be determined from J–V curves. The experimental results are consistent with theoretical calculations.
Enhancement of growth rate due to tin doping in GaAs epilayer grown by low pressure metal-organic chemical vapor deposition
Authors: Chang C. Y. , Lee M. K. , Su Y. K. , Hsu W. C.
Published: February 2003

Tetraethyltin is used as an n-type dopant in homoepitaxially growing GaAs films from triethylgallium and arsine vapor in a low pressure system. The experimental data show that the growth rate can be enhanced by tin doping. It is found that the deep level transient spectroscopy concentration of the electron trap located at about 0.8 eV below the conduction band is suppressed by Sn doping. Gallium vacancy may be attributed to the trap. A growth model has been proposed, which can be substantiated by the experimental results.
Electrical conductivity measurements of some layered magnetic structures
Authors: Tigges C. P. , Drumheller John E. , Snively L. O.
Published: February 2003

The electrical conductivity for temperatures up to 416 K has been measured in several of the alkylammonium tetrahalidemetallate and the alkanediammonium tetrahalidemetallates where the halides were bromine and chlorine and the metal was copper or, in one case, cadmium. These salts are all good magnetic insulators at low temperature but behave as ionic, probably protonic, semiconductors as the temperature is increased. Room temperature conductivity for these samples is of order 10−12 Ω−1 cm−1 and varies as much as ten orders of magnitude over the measured temperature range. The possibility that the changes in activation energy are related to known structural phase transitions is discussed.
Impurity-to-band tunneling in semiconductors
Authors: Chaudhuri S. , Coon D. D. , Karunasiri R. P. G.
Published: February 2003

Rate formulas for impurity-to-band tunneling from shallow and deep impurity levels are discussed. For the case of deep levels involving carriers bound to neutral impurity centers, it is shown that there is no substantial difference between the results of Anderson and Hoffman and those of Chaudhuri, Coon, Derkits, and Banavar. On the other hand, a different field dependence is found for the case of deep levels associated with carriers bound to charged impurity centers.
50-Hz ac losses in inductive coils with mixed matrix fine filament NbTi composites at fields up to 1 T
Authors: Hlásnik I. , Seibt E. W.
Published: February 2003

Measurements of 50-Hz ac losses were performed using three characteristic NbTi coil samples with ultrafine filaments and a Cu–CuNi mixed matrix at fields up to 1 T and at 4.2 K. Critical current and quenching current densities were measured under dc and ac conditions as well as the losses with their hysteresis and eddy current loss proportions. To characterize the samples by their eddy current loss proportions the transverse resistivity of the matrix ρtrans was determined. The results for losses show that under 50-Hz ac loads alternating fields up to approximately 1 T are attained without quenching. The fact that the associated eddy current losses of about 105 W/m3 remain comparatively low at 0.5 T and 4.2 K opens up for such structured mixed matrix NbTi composites a novel field of application for superconducting generators and pulsed magnets with 50–60 Hz fed windings.
Modeling of thermally stimulated currents in polytetrafluoroethylene
Authors: Remke R. L. , von Seggern H.
Published: February 2003

A phenomenological model has been derived for thermally stimulated open-circuit current measured on negatively charged polytetrafluoroethylene electret film. The model is based on trap controlled release of negative charge carriers using approximations justified by thermally stimulated current and mean charge depth results. To describe the open-circuit current, a minimum of five traps was necessary including surface and bulk traps with activation energies of 1.3 (2), 1.4, 1.5, and 1.7 eV. In addition, attempt-to-escape frequencies were calculated and found in the range 1011–1013 s−1.
Magnetization reversal in cobalt–phosphorus films
Authors: Hughes Gordon F.
Published: February 2003

A brief review is given of preparation, structure, and magnetization reversal in Co–P thin films for digital recording. From this, a magnetization reversal theory is developed which correctly predicts a number of observed facts about Co–P. Among these are &mA0.1 (conventional theory predicts 0.64 and 0.51, respectively), avalanche and cluster reversal mechanisms, transverse ripple, and sawtooth structure in recorded bits. Limitations to high bit and track density recording are discussed. It is suggested that lower Mr/Ms remanent squareness values may alleviate these density limiting mechanisms.
Static properties of magnetic bubbles in garnet films with orthorhombic anisotropy
Authors: Breed D. J. , de Geus W.
Published: February 2003

The static properties of bubbles in (110) oriented garnet films of composition (Gd, Y)3 (Fe, Mn, Ga)5O12 have been studied. The anisotropy in these films is orthorhombic with the easy axis of magnetization perpendicular to the plane of the film and a secondary easy axis in the plane of the film. Two types of bubbles can be distinguished, A-type bubbles having no Bloch lines and B-type bubbles with Bloch lines. Magnetic fields parallel to the in-plane easy axis of magnetization have a strong influence on the diameter and on the collapse field. Whereas the properties of the B-type bubbles are independent of the sign of this in-plane field, the properties of the A-type bubbles do depend on the sign of this in-plane field. B-type bubbles easily change state and become A-type under influence of in-plane fields. At zero in-plane field the collapse fields of B-type bubbles are about 1 to 3% larger than the collapse fields of A-type bubbles. A theory is presented that takes into account the interaction between in-plane field and domain wall magnetization. In this way the experimental data obtained for the A-type bubbles are reproduced very well. The difference between the collapse fields of A- and B-type bubbles in zero in-plane field is explained by taking into account the influence of stray fields and Bloch lines on the domain wall energy.
Ferromagnetic resonance study of magnetic anisotropy and domain observations in implanted garnets misoriented from (111)
Authors: Niedoba H. , Nourtier C. , Puchalska I. B. , Gérard P.
Published: February 2003

The magnetic anisotropy of nonimplanted and implanted layers in garnet films misoriented from (111) has been studied by ferromagnetic resonance (FMR). The measured FMR field orientation dependence is consistent with a phenomenological model taking into account the growth-induced and stress-induced anisotropy contributions. The effective uniaxial anisotropy field H∇K, cubic magnetocrystalline anisotropy field H1, and anisotropy fields proportional to the crystallographic misorientation angle Δc:HδK and Hp (orthorhombic anisotropy field) are determined from the resonance field orientation dependence in two different planes. In the implanted layer only two stable equilibrium magnetizations exist. Charged wall motion is consistent with the easy and hard magnetization directions deduced from FMR.
Properties of ferrimagnetic echoes in yttrium iron garnet cylinders
Authors: Bucholtz F. , Webb D. C.
Published: February 2003

The first detailed study of the properties of ferrimagnetic echoes in cylinders of yttrium iron garnet has been performed. Data are presented showing the dependence of the echo on applied field Ha, pulse separation τ, signal pulse power Ps, and pump pulse power Pp. At a given frequency, echoes are found to occur in multiple, well-defined regions of the parameters τ and Ha. For low Ps and Pp, the echo power Pe increases linearly with increasing Ps but increases very rapidly with increasing Pp, following Pe∼P4.5p. Pe saturates at high power levels with the saturation level depending on both Ps and Pp. Additional experimental observations, which give further insight into the excitation and evolution of the echo, are also presented. Experimental results verify some of the qualitative predictions of various models previously proposed for the ferrimagnetic echo process but also point out some of the limitations of these models.
Determination of the nitrogen doping of liquid phase epitaxy GaP and GaxIn1−xP alloys by optical absorption and photoluminescence
Authors: Thierry-Mieg V. , Marbeuf A. , Chevallier J. , Mariette H. , Bugajski M. , Kazmierski K.
Published: February 2003

Optical absorption and photoluminescence have been used to determine the nitrogen concentration in liquid phase epitaxy GaP and GaxIn1−xP layers. Both methods give the same variation of nitrogen concentration. The same nitrogen maximum concentration of [N]=8×1017 cm−3 has been found in GaP and in Ga0.998In0.002 grown at 900 °C and PNH3>10−3 atm. In InGaxIn1−xP, it has been shown that the nitrogen concentration incorporated in the layer decreases as the indium amount increases for indium concentrations less than 5%, in samples prepared with identical growth conditions.
X-ray-induced luminescence in crystalline SiO2
Authors: Alonso P. J. , Halliburton L. E. , Kohnke E. E. , Bossoli R. B.
Published: February 2003

The x-ray-induced ‘‘blue’’ emission from commercially available, high-quality synthetic quartz has been studied between 80 and 300 K. Three overlapping bands, each having a different quenching temperature, have been experimentally resolved in the as-grown crystals. These bands peak at 440, 425, and 380 nm; their half-widths are 0.64, 0.75, and 0.92 eV; and they thermally quench in the 120–160, 170–210, and 220–270 K regions, respectively. An intense electron irradiation at room temperature or an electrodiffusion (sweep) in a hydrogen atmosphere eliminates the band at 380 nm. Our results suggest that the 380-nm band arises from recombination of an electron with a hole trapped adjacent to an alkali-compensated aluminum ion (i.e., an Al–M+ center). The origins of the bands at 440 and 425 nm remain unknown. As an application of these results, a screening test is described which could assist quality control during selection of quartz bars for use in precision frequency control devices.
TeOx thin films for an optical disc memory
Authors: Takenaga Mutsuo , Yamada Noboru , Nishiuchi Kenichi , Akahira Nobuo , Ohta Takeo , Nakamura Suguru , Yamashita Tadaoki
Published: February 2003

Tellurium suboxide thin films TeOx were found to change in refractive index and extinction coefficient on thermal or optical heating, with accompanying changes in the reflectivity and transmission. The preparation method and thermal or optical properties of the TeOx thin films were investigated to obtain a stable and highly sensitive optical disc memory. A two-source evaporation method using Te and TeO2 provided uniform and any desired composition. The properties of the film depended on the x value; increasing x to as large as x=1.2, which represents a Te-poor composition, produced an excellent humidity and heat stability, and decreasing x to 0.8 made the film more sensitive to a laser diode, but susceptible to humidity. The TeO1.1 thin film was found to sufficiently satisfy all requirements for practical disc applications. A reflective optical disc was prepared using the TeO1.1 thin film deposited on a polymethylmethacrylate substrate with grooves for optical tracking. This disc is capable of recording video signals at real time by laser diodes. It showed no reflectivity changes on recorded or unrecorded areas and no sensitivity change to laser light after long term storage in high humidity and temperature.
Simple method for preparing hydrogenated amorphous silicon films by chemical vapor deposition at atmospheric pressure
Authors: Ellis Frank B. , Gordon Roy G.
Published: February 2003

An inexpensive one-step method is presented for fabricating hydrogenated amorphous silicon (a-Si:H) films with good photovoltaic properties using chemical vapor deposition (CVD) from a mixture of polysilanes, SinH2n+2, in hydrogen at atmospheric pressure. This gas mixture is generated by a simple chemical reaction and used immediately in the CVD process. Thus, the highly flammable polysilanes need not be handled, distilled, stored, or transported. The conditions necessary for high (about 10%) hydrogen incorporation are explained. The method requires no expensive vacuum or electrical equipment and permits very high deposition rates (50–100 Å/s). It is shown that the growth rate of the film is determined by the gas-phase chemistry and not the surface chemistry. In addition a new, safe, and economical technique for phosphorus doping is described.
The influence of fusion temperature on the defect center concentration of GeO2 glass
Authors: Kordas G. , Weeks R. A. , Kinser D. L.
Published: February 2003

Paramagnetic resonance spectra of virgin glasses and γ-ray irradiated GeO2 glasses were studied with the electron spin resonance (ESR) method as a function of fusion temperatures. Fusions were made in air at temperatures between 1200 and 1650 °C and cooled at constant rate. In virgin glasses, only the E′ center was detected at concentrations of about 1015/g. After a γ-ray irradiation, a new resonance at the low-field side (lfs) of the E′1 center and a symmetric line with g=1.91 were observed. Measurements at various temperatures, power levels, and frequencies provide a basis for resolving the overlapping resonances. We labeled the paramagnetic center causing the lfs signal the H0 center. The g values of the H0 center are the basis for attributing this center to a hole located on a nonbridging oxygen. The g=1.91 resonance is attributed to Cr5+ or M5+0 impurities in the GeO2 glasses. At constant γ-ray dose, the H0 center concentration decreased and the E1 -center concentrations increased with increase of fusion temperature.
Characterization of polycrystalline electrodeposited CdSe photoelectrodes using photoluminescence spectroscopy
Authors: Silberstein R. P. , Tomkiewicz Micha
Published: February 2003

We have utilized both photoluminescence (PL) and Raman spectroscopy to nondestructively study the surface of polycrystalline electrodeposited CdSe photoelectrodes as a function of surface preparation and aging procedures. The excitation energy dependence of the PL efficiency at 77 K, which depends on surface band bending, is consistent with increased concentration of shallow levels in electrodeposited CdSe compared with single crystal material. No PL was observed for unannealed CdSe films; for annealed, unaged films the spectra at 77 K were qualitatively similar to those of single crystals in that spectral features could be identified with the A exciton at 1.815 eV and with a donor-acceptor-pair band at 1.70 eV exhibiting phonon replicas. The PL and Raman spectra of light-aged electrodes exhibit features which we identify with the formation of a surface layer of CdS and the presence of mixed compounds CdSxSe1−x, which are formed by chemical exchange with the polysulfide electrolyte during light-induced aging. The PL spectra at 4.2 K for the unaged and dark-aged electrodes exhibit sharp lines in the vicinity of 1.81 eV which we identify as due to bound-exciton recombination, but which differ in energy from those exhibited by the light-aged film.
Plasma enhanced metal-organic chemical vapor deposition of aluminum oxide dielectric film for device applications
Authors: Pande K. P. , Nair V. K. R. , Gutierrez D.
Published: February 2003

Low temperature (≤250 °C) deposition of aluminum oxide gate dielectric film using a new plasma enhanced metal-organic chemical vapor deposition technique is described. With this technique, the substrate was not directly exposed to the plasma which minimizes radiation damage to both the substrate and the film. A dc potential was used to generate the plasma and the deposition of the film was achieved at extremely low plasma power (≤2 W) using trimethylaluminum and nitrous oxide reactant sources. The dielectric films were found to have a resistivity of ∼1014 Ω cm, dielectric constant of 7.9±0.2, and breakdown field ≥106 V/cm. A linear dependence of the film growth rate upon TMAl concentration was observed, indicating that the growth process is mass transport limited. Metal–oxide–semiconductor device structures were fabricated both on n-Si and p-InP substrates and the interface properties were evaluated by capacitance–voltage and Auger measurements. Both the devices show sharp interface with a minimum density of states in the range of 8×1010–1011 cm−2 eV−1 for Si and 4×1011 cm−2 eV−1 for p-InP.
Excitation of striations in the positive column of a glow discharge
Authors: Sengupta D. , Sengupta S. N.
Published: February 2003

A new method of exciting striations in the positive column of a glow discharge, by introducing a stream of electrons in the Faraday dark space, is presented. The method is capable of exciting striations at the natural frequencies of self-excited striations under similar discharge conditions.
Local acoustoelasticity in poly(methyl methacrylate) by Brillouin scattering
Authors: Yap B. C. , Shichijyo Shiro , Takemura Tetuo , Matsushige Kazumi
Published: February 2003

The Brillouin scattering technique was used to study the local mechanical deformation of poly(methyl methacrylate) (PMMA). The extent of local stress concentration could be determined by measuring longitudinal hypersonic velocities in the close vicinity of a circular hole and a sharp single-edge-notch (SEN) in panel PMMA specimens under uniaxial tensile stress. Craze formation in PMMA is also briefly discussed in association with such a local deformation. Present studies demonstrate that the Brillouin scattering technique is a new and effective probe for such an investigation in transparent materials.
Pressure-induced phase transition of HgS
Authors: Huang T. , Ruoff A. L.
Published: February 2003

The high pressure phase transition of cinnabar (α-HgS) was studied by energy dispersive x-ray diffraction using a synchrotron x-ray source. The cinnabar crystal structure was found to transform to the sodium–chloride structure at about 130 kbar. The lattice parameter of the new phase was determined to be 5.070±0.005 A at 300 kbar. No further phase transition was observed up to 400 kbar.
A comparison of the uniaxial anisotropy in sputtered Co–Re and Co–Cr perpendicular recording media
Authors: Chen Tu , Charlan G. B. , Yamashita Tom
Published: February 2003

The effect of the presence of an intermetallic compound on the microstructure, crystalline anisotropic orientation, and perpendicular magnetic hysteretic properties was investigated based on CoRe and CoCr alloys. The results suggest that a phase segregation causes the formation of an intermetallic compound, Co3Cr, in the Co-rich CoCr alloy film. Consequently, it leads to the growth of isolated columnar particles because of the fact that the alloy composition lies within the two-phase region in the phase diagram. For homogeneous CoRe and CoCr alloys at high temperature, the resultant microstructures in a deposited film show equiaxial particles characterized by a large grain diameter. Magnetic hysteretic measurement on the film having various microstructure shows that high coercivity and good perpendicular anisotropy in the CoCr film is primarily due to the formation of isolated columnar particles in addition to the c-axis preferred orientation. Films having good c-axis preferred orientation but not the isolated columnar structure can not give good hysteretic properties for perpendicular recording media application. Also it was concluded in this work that in an isolated columnar structure film, the extent of c-axis dispersion (i.e., the value of Δθ50) affects the sharpness of the knee, but the Hc of the perpendicular hysteresis loop is not affected significantly.