bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo modeling of electrophotographic x-ray detectors
Authors: Sahyun M. R. V.
Published: February 2003

A Monte Carlo model for an electroradiographic detector is presented. It takes into consideration recombination as a loss factor inherent in the physics of the x-ray photon attenuation, but one whose importance decreases with increasing photon energy, owing to the increasing spatial dispersity of the hole-electron pairs, therewith. This treatment reasonably simulates both the applied field and the x-ray photon energy dependences observed experimentally for the apparent carrier pair production energy in amorphous Se and particulate, tetragonal PbO devices. An activation energy for free carrier generation in Se, despite the excess thermal energy with which the carriers are initially produced, is also required to make the model correspond with experiment in the Se case. Bonding theory suggests that this is an inevitable consequence of the disordered state of the amorphous radioconductor. Detective Quantum Efficiency estimates can be extracted from the Monte Carlo simulation. These data indicate that the primary loss factor in xeroradiographic detectors, from the standpoint of signal-to-noise ratio, is incomplete attenuation of the incident x-ray energy.
Depletion layer studies and carrier photogeneration in doped merocyanine photovoltaic cells
Authors: Chamberlain G. A.
Published: February 2003

The capacitance and photocurrent of Al/Cl2-doped merocyanine/Au thin film photovoltaic cells have been studied as a function of applied voltage bias. The capacitance data indicated that a Schottky barrier had formed between the Al and organic dye. The barrier width, built-in potential, and carrier concentration were 23 nm, 1.05 V, and 1018 cm−3, respectively. Photocurrent measurements at different excitation wavelengths strongly suggest that carrier photogeneration is a bulk phenomenon. Combining these observations with a study of the effects of doping with molecular chlorine, we propose that carriers are generated by electron transfer from a thermalized exciton to a dopant site. The dopant is thought to be adsorbed in the dye layer as the acceptor half of a weak charge transfer complex. A quantum yield of 11.2% at 632.8 nm based on light absorbed by a 30-nm thick merocyanine film was measured for the chlorine-doped cell.
Calculations of experimental implications of tensor properties of resistance fluctuations
Authors: Weissman M. B. , Black R. D. , Snow W. M.
Published: February 2003

A method of determining the dependence of several experimentally accessible parameters of resistance fluctuations on the tensor properties of the underlying resistivity fluctuations, is presented. Experimental work has already demonstrated the utility of this method in studying 1/f noise.
The dynamics of electron-hole collection in quantum well heterostructures
Authors: Tang J. Y. , Hess K. , Holonyak N. , Coleman J. J. , Dapkus P. D.
Published: February 2003

The dynamics of carrier collection in quantum-well heterostructures are studied by photoemission experiments and Monte Carlo simulations. It is shown that carrier scattering decreases rapidly for well sizes Lz ≲100 Å. The collection mechanism depends sensitively on details of the band structure. The energy distribution function of the carriers after collection exhibits significant structure with respect to multiples of the phonon energy. This feature is also reflected by the experimental results.
The effect of strain upon the velocity of sound and the velocity of free retraction for natural rubber
Authors: Gent A. N. , Marteny P.
Published: February 2003

Measurements have been made of the velocity of sound and the velocity of free retraction for stretched strips of vulcanized natural rubber. Both of these velocities are found to increase markedly with increasing strain, in agreement with earlier work. The velocity of sound is shown to be related to the appropriate modulus of elasticity, defined by the slope of the curve relating true stress to tensile strain. Values obtained range from about 50 to about 800 m/s. The effects of prior stretching and of stress relaxation on the velocity of sound are shown to arise from corresponding changes in the modulus of elasticity at a given strain. The velocity of free retraction is shown to be directly related to the velocity of sound in the stretched strip and to the imposed tensile strain, increasing from zero up to about 100 m/s at high strains.
Stability of bubbles in a closed volume of liquid-gas solution
Authors: Ward C. A. , Tikuisis P. , Venter R. D.
Published: February 2003

The conditions are examined under which a single bubble and a number of bubbles are in equilibrium within a closed volume of liquid that is maintained at constant temperature and pressure. It is predicted that depending on the amount of gas present in the volume, there may be no equilibrium state for the bubble or bubbles, one equilibrium size, or two possible equilibrium sizes. In the latter case, it is also predicted that the equilibrium state corresponding to the larger bubble size is a stable equilibrium state. This is in contrast to the case of an unbounded volume of liquid where there is the possibility of only one equilibrium state for a bubble, and this state is unstable. The predicted stability for a bubble in a closed volume was examined experimentally, and agreement was found between the measurement and the prediction. A striking result is the reduction in the stable equilibrium size with the number of bubbles present. In particular, micron-sized bubbles can be shown to be in stable equilibrium under the constraint of a closed volume, and for reasonable conditions of liquid temperature and pressure.
Measurement of the tandem mirror experiment x-ray spectrum
Authors: Burginyon G. , Snyder H. D. , Stoering J. P. , Toor A. , Poulsen P. , Anderson C.
Published: February 2003

We measured x-ray spectrum at the Tandem Mirror Experiment (TMX) facility as a function of time using a new x-ray spectrometer with medium energy resolution that measures as well as identifies x rays in intense and varied particle and radiation backgrounds. The x-ray spectrum was deconvoluted from single-channel energy responses recorded one at a time for each shot. The data for each channel were normalized to the total x-ray energy, which was measured separately for each shot. After a few milliseconds during which conditions within the plasma pulse stabilized, the spectrum consisted of a broad peak with a typical median energy of 0.66±0.04 keV, which can be interpreted as predominantly line emission. Resolution studies indicate that neonlike titanium may be a better interpretation than heliumlike oxygen; however, no quantitative model has been compared.
Scaling of ion expansion energy with laser flux in moderate-Z plasmas produced by lasers
Authors: Gupta P. D. , Goel S. K. , Uppal J. S.
Published: February 2003

Ion expansion energy measurements in plasmas created by focusing 1-GW, 5-nsec Nd:glass laser on plane solid targets of polythene, carbon, and aluminum are reported. It is observed that the scaling of ion expansion energy with laser flux Φ varies between Φ0.28 and Φ0.66 for polythene, Φ0.28 and Φ0.70 for carbon, and Φ0.51 and Φ0.44 for aluminum in the flux range 5×1010–5×1012 W/cm2 of our experiment. The scaling is either much slower or faster than a scaling of Φ4/9 expected from a self-regulating model for plasmas created in the low flux range. It is shown that this behavior, as well as results of experiments on similar plasmas reported by other authors, can be explained when radiation losses and the energy spent in ionization are also considered in the self-regulating model.
Dependence of striation spacing in linear laser sparks on gas pressure and luminosity
Authors: Schmieder Robert W.
Published: February 2003

The variation of spacing between separate plasma regions in linear sparks produced by a laser spike train on initial gas pressure and the correlation between the spacing and plasma luminosity have been investigated for several gases in the range 20–760 Torr. Fourier analysis of the quasiperiodic images reveals details of these sparks not readily seen in the photographic and diode-array images.
Vibrationally excited diatomic molecules as charge injectors during corona charging of polymer films
Authors: Haridoss S. , Perlman M. M. , Carlone C.
Published: February 2003

Neutral species in corona discharges have been identified spectroscopically as vibrationally excited states of nitric oxide, electronically excited states of nitrogen which can lead to ground state vibrational metastables by collisions, and perhaps oxygen. These molecules act as energy carriers to the polymer surface, and are effective injectors of negative charge in virgin and etched low density polyethylene, high density polyethylene, polypropylene, and even in polytetrafluoroethylene. Charge injection could not be detected in positively charged samples. Removal of the injecting energy by blowing air tangential to the face of the sample results in reduced negative charge decay. Blowing for times of the order of milliseconds can deexcite these metastables by increased collisions, or can physically blow them away, or both. A previous suggestion that photons of energy ?6 eV, resulting from excited molecules were the charge injectors has been disproved.
The existence of an electron shock structure in the electrical breakdown of nitrogen
Authors: Jurenka H.
Published: February 2003

Experimental evidence is presented to show the existence of a regularly repeating structure in the luminous core that appears during the final stage in the electrical breakdown of N2 at atmospheric pressure. A simple analysis identifies this pattern as an electron shock structure in the inviscid core of an underexpanded jet originating at the cathode spot. The results support the concept of wave propagation through the collision-dominated electrons.
Anode surface temperature and spot formation model for the vacuum arc
Authors: Jolly D. C.
Published: February 2003

A simplified model is developed to calculate the temperature rise of the anode surface in vacuum arcs. The model predicts the threshold current for anode melting as a function of the properties of the arc and electrode materials. The calculated and measured currents agree well for six anode materials. In five of these cases an anode spot formed at the time calculated for melting to occur. It is concluded that for the geometry analyzed, anode spot formation is closely linked to anode melting and possibly to magnetic deformation of the molten surface. This lends support to the conjecture of Lafferty that localized heating of the anode can trigger spot formation.
A new method of electric field measurements in corona discharge using Pockels device
Authors: Hidaka Kunihiko , Fujita Hiroyuki
Published: February 2003

The investigations of the dc electric field distorted by space charges have been made by means of the optical method using a Pockels device. The Pockels device was rotated to eliminate field disturbances caused by surface charges accumulated on it. The present method has the advantage of directly measuring the electric field in a dc corona discharge. The method was successfully applied to the measurement of the electric-field distribution in a needle-to-plane gap of 10 cm with a positive dc corona. The field distortion was clearly observed in a wide range of applied voltages between 30 and 98% of the breakdown voltage 52 kV. It was found that the electric field inside the corona streamers was 3.5 kV/cm, while 14 kV/cm near the tip of the streamers. Furthermore, the experimental results were theoretically confirmed at the relatively low voltage.
Performance of a seven-segment iridium oxide electrochromic display
Authors: Shay J. L. , Schiavone L. M. , Epworth R. W. , Taylor D. W.
Published: February 2003

We describe the electrical and optical performance of a prototype seven-segment iridium oxide electrochromic display. The response time is ∼0.4 s for a 2.5-cm digit and varies as the square of the digit dimensions. It is shown that driver electronics can be implemented very simply for electrochromics.
A fast algorithm for inhomogeneous slab scattering problems from the integral equation approach
Authors: Su Ching-Chuan , Chen Chun-Hsiung
Published: February 2003

A wave-propagation problem in the presence of an inhomogeneous dielectric slab is treated by integral equations. The problem is first formulated in the Fredholm integral equation, and then in the Volterra equation after some transformations. A fast algorithm is then derived to numerically compute the Volterra integral equation efficiently for both the exterior- and interior-excited cases. Finally, this algorithm is applied to find out the eigenvalues and eigenfunctions of dielectric slabs with both homogeneous and parabolic profiles.
A pinch effect for intense, magnetized, non-neutral electron beams
Authors: Adler R. J. , Miller R. B.
Published: February 2003

An intense, magnetized, non-neutral electron beam has been observed to pinch as it impinges on a witness foil. A simple theoretical model of the effect is presented and compared with the experiment. These results are of particular importance for beams used to produce gamma rays and when beam parameters are measured using a grounded probe.
The effect of thickness on the acousto-electro-optical study of a nematic liquid crystal
Authors: Hakemi H.
Published: February 2003

Acousto-optical effects in nematic liquid-crystal thin films were studied in the presence of an ac electric field applied parallel to the direction of molecular alignment. According to the dielectric properties of the nematic material, the electric field induced an additional realignment torque to the molecules. At large thicknesses (≊100 μm) the results were as expected. At small thickness range (≲20 μm), the acoustic and electric crossed-field relation showed a different linear slope at higher optical-transmission and field-intensity regions, suggesting an additional contribution due to the effect of the surface-nematic energy in the overall mechanism of interactions.
Identification of AsGa antisites in plastically deformed GaAs
Authors: Weber E. R. , Ennen H. , Kaufmann U. , Windscheif J. , Schneider J. , Wosinski T.
Published: February 2003

AsGa antisite defects formed during plastic deformation of GaAs are identified by electron paramagnetic resonance (EPR) measurements. From photo-EPR results it can be concluded that the two levels of this double donor are located near Ec −0.75 eV and Ev +0.5 eV. These values are coincident with the Fermi level pinning energies at Schottky barriers. The upper level can be related to the ’’main electron trap’’ EL2 in GaAs. Photoluminescence experiments before and after thermal annealing suggest that AsGa defects reduce the near band edge luminescence efficiency. A dislocation climb model is presented which is able to explain AsGa formation during dislocation movement. The production of AsGa antisites during dislocation motion under injection conditions in light emitting devices may thus be connected with degradation of the light output.
Fast current measurements for avalanche studies
Authors: Verhaart H. F. A. , van der Laan P. C. T.
Published: February 2003

The electrical method is often used to study avalanches in gases. In this paper a substantial improvement of the time resolution of the measuring system is reported. To release the primary electrons within a very short time a transversely excited atmospheric pressure N2 laser with a pulse width of 0.6 ns is used. Secondly the high-frequency response of the entire circuit is analyzed. As one of the results of this analysis a subdivided cathode is used consisting of a central measuring electrode surrounded by a grounded electrode. The diameter of the circular measuring electrode determines a maximum gap distance for reliable measurements, which can be calculated from a theory of Shockley and Ramo. As an example of the high-frequency response of our experimental setup avalanches in nitrogen are shown and analyzed. Avalanche measurements in air clearly show a dependence on the humidity, presumably caused by rapid detachment and conversion processes.
A method for measuring the change of ultrasound velocity in a liquid
Authors: Toda Kohji , Urabe Heijiro
Published: February 2003

A method for measuring the change of sound velocity from a reference state in a liquid is described. Two interdigitial transducers on a piezoelectric substrate are in contact with the liquid, and are used as an input and an output transducer for constructing a liquid delay device. The phase difference between an input and a delayed output signal is detected as a dc voltage via a phase comparating circuit. The temperature dependence of the sound velocity in water, measured by the present method, agrees well with the published data. The influence of hydrostatic pressure on the sound velocity in water is given.
Spectral characteristics of single-mode injection lasers: The power-gain curve from weak stimulation to full output
Authors: Sommers H. S.
Published: February 2003

Experimental study of the mode powering in an assortment of single-mode lasers covering samples of most of the contemporary structures reveals a common property: the functional dependence on gain of the power in the strong mode. The high-power asymptote is a linear function of the gain, while the low-power asymptote of the light-emitting diode (LED) state is linear in the reciprocal of the departure of the gain from its threshold value. The entire dependence is expressed by a universal dimensionless function of the gain, which is independent of laser structure, and which describes both asymptotes, provides a reasonable connecting link, and gives an experimental fiduciary of threshold. The fiduciary is the current at the sharp maximum in the logarithmic derivative of mode power with respect to junction voltage. Exerimental study reveals that this fiduciary corresponds closely to the conventional extrapolated threshold, with the inflection point in the junction resistance, and with the peak in noise. The universal function yields the dependence of power in the dominant mode on junction voltage given by the steady-state solution of North’s P* theory. It is not consistent with the gain clamping at threshold that is described by familiar hole-burning theories of injection lasers, which limit the lasing region to far too small a range of gain. The same function is found to describe a published measurement of the transition of threshold of an He-Ne laser.
Electromagnetic decay into two surface plasma waves in a semi-infinite plasma
Authors: Yasumoto K. , Noguchi T.
Published: February 2003

The parametric decay instability of two high-frequency surface plasma waves, which arises when an intense electromagnetic plane wave is incident on a semi-infinite, unmagnetized plasma from a vacuum, is investigated on the basis of the hydrodynamic equations for warm electrons. It is shown that the instability occurs only if the incident wave is of the transverse magnetic type. The growth rate for the instability and the threshold amplitude of the incident wave are determined. In contrast to the usual ’’two-plasmons decay instability’’ in an infinite, unmagnetized plasma, the present ’’surface-decay instability’’ is possible even if the incident pump field is spatially homogeneous.
Infrared emission and recombination from a dense sodium plasma produced by resonant optical pumping
Authors: Kumar J. , Silfvast W. T. , Wood O. R.
Published: February 2003

The results of an experimental investigation of the infrared recombination emission from a dense sodium plasma produced by resonant optical pumping are reported. Possible explanations for the important experimental features of the infrared emission are discussed. The temporal behavior of the decay of the infrared emission indicates that the primary electron loss mechanism of the plasma is three-body collisional recombination.
Voltage breakdown between closely spaced electrodes over polymeric insulator surfaces in air
Authors: Gray Eoin W. , Harrington Daniel J.
Published: February 2003

Voltage breakdowns of some narrow gap electrodes [2–10 mil (0.05–0.25 mm)] on polymeric insulator surfaces (epoxy-glass and triazine) have been examined over the pressure range from atmospheric pressure to 127 Torr and are shown to be an air breakdown modified by the presence of the insulator. Breakdown values as a function of the number of the breakdown and discharge energy level were also examined. In the worst case the breakdown voltage was observed to decrease by approximately 1300 V after about five successive breakdowns. The breakdown voltage between narrowly spaced metallic contacts on dielectric surfaces has been assumed to exhibit a Gaussian distribution. Non-Gaussian, bimodal distributions have been observed in the present work. These bimodal distributions, found on fine line epoxy-glass and triazine printed wiring boards, and attempts for explanation in terms of the flashover discharge initiating mechanisms, including the effects of ultraviolet radiation and a negative-ion flux on breakdown, are described. Negative ions appear to reduce the standard deviation but do not reduce the breakdown voltage. Ultraviolet radiation reduces both the standard deviation and the breakdown voltage. Increasing the conductor overlap distance (line length) reduced the breakdown voltage.
Pressure enhancement by conically convergent shocks in composite cylinders and its application to shock recovery experiments
Authors: Syono Yasuhiko , Goto Tsuneaki , Sato Toshiyuki
Published: February 2003

Pressure enhancement due to conically convergent shocks is experimentally demonstrated in the composite cylinder assembly made of materials with different shock velocities and shock impedances. The formation of the Mach configuration leads to a remarkable energy accumulation in the central part of the composite cylinder. The shock pressure achieved in the 2024 Al-copper assembly is 122.5 GPa with an impact velocity of 2.1 km/s of copper flyer, which is about 2.4 times greater than that expected from the standard shock condition. The application of the technique to recovery experiments for shock-loaded materials in the megabar range is proved to be successful.
Ion optical properties of an electron-beam-guiding ion source
Authors: Kishi Tohru , Takagi Toshinori
Published: February 2003

Ion optical properties of an electron-beam-guiding ion source have been studied by numerical calculation of the ion beam trajectories in the gun region and by experiments. It was found that the ions drifting toward the anode aperture could be focused as a small spot on the emitting end of the pipe cathode of outside diameter 1 mm and inside diameter 0.6 mm. For the gun configuration used, the best focus condition was obtained at Vg =−23 V, Va =2 kV, and Ip =2 mA when a bismuth block target was used as a source material, where Vg, Va, and Ip were the bias voltages of the beam-forming electrode and anode, and the total electron beam current. The maximum ion beam current density and normalized brightness were of the order of 2.7 μA/cm2 and 9.1×1010 A/m2 rad2.
The effects of electron retention and spin pair bonding on crystal cohesion in insulator oxides and halides
Authors: Van Uitert L. G.
Published: February 2003

Ionization for salts in aqueous solution tends to equal formal valence (e.g., thorium can exist in solution as Th4+). However, as shown using lattice energy and melting point data, ionization in oxide or halide crystals does not exceed the number of s state electrons per metal atom (e.g., thorium in ThO2 has a formal valence of 4 and yet exhibits a cation ionization level of 1.9). Low values of ionization may be associated with internal coupling, electron transfer between metal atoms, and/or electron pairing between atoms that can form anions. The latter is likely to occur when the cations are small. When atoms that can form anions share electrons, they exhibit a reduced ‘‘demand’’ for charge from the metal atoms present. This results in a weaker bond and in the melting point decreasing logarithmically (rather than increasing) as bond length decreases.
Radiation from a dipole in the presence of a grounded gyromagnetic slab
Authors: Tsalamengas John L. , Uzunoglu Nikolaos K.
Published: February 2003

Radiation from dipoles in the presence of a grounded gyromagnetic slab is considered. The Green’s function for an arbitrarily oriented elementary dipole source is derived first, assuming that the static magnetic field applied to the gyromagnetic slab is either vertical or parallel to the slab surface. A plane-wave Fourier representation is employed to expand the field in and out of the slab. Several symmetry relations are exploited to reduce the complexity of the solution. Radiation properties of the grounded slab, such as the surface wave launching and the far-field behavior, are then investigated. It is shown that the far-field amplitude and phase can be controlled by varying the external static magnetic field. Numerical results are presented for several cases.
Effective propagation constants for coherent electromagnetic wave propagation in media embedded with dielectric scatters
Authors: Tsang L. , Kong J. A.
Published: February 2003

In studying the multiple scattering of electromagnetic waves by random distributions of scatterers with appreciable fractional volume, the approach of quasicrystalline approximation together with the hole correction approximation has been a common method. In this paper, it is shown that such an approach will give rise to negative attenuation rate indicating a growth of the coherent wave in space which is a nonphysical solution. The result of the Percus–Yevick equation is a better representation of the pair distribution function for appreciable concentration. We use it together with the quasicrystalline approximation to study multiple scattering of electromagnetic waves by discrete spherical scatters. Waterman’s T matrix formalism is used in formulating the multiple scattering problem. Closed from solutions are obtained for the effective propagation constants in the low frequency limit and agree with Twersky’s results. Effective propagation constants at higher frequencies are calculated by numerical methods.
Electron drift in a linear magnetic wiggler with an axial guide field
Authors: Pasour J. A. , Mako F. , Roberson C. W.
Published: February 2003

Electron trajectories through a linear magnetic wiggler in an axial guide field are calculated numerically. Off-axis electrons are shown to drift in a direction perpendicular to the wiggler field because of the wiggler gradient. Effects of self-fields and initial conditions are analyzed, and the results compared to those obtained with a helical wiggler. An empirical analytic expression for the linear wiggler drift is presented, and means of stabilizing the drift are discussed.
Scattering of a Gaussian beam by a homogeneous dielectric cylinder
Authors: Kozaki Shogo
Published: February 2003

The scattering of a Gaussian beam considering amplitude and phase distribution by a homogeneous dielectric cylinder is analyzed. A simpler expression is successfully obtained by using a new method. The spatial pictures in the amplitude and phase of the total Gaussian beam near the cylinder are both theoretically and experimentally clarified. The scattering patterns are also presented.
Calculated threshold current of GaAs quantum well lasers
Authors: Dutta N. K.
Published: February 2003

A model calculation of the threshold current of a laser in a quantum well structure is presented. The band-to-band radiative recombination rate is calculated using a constant density of states and the k-selection rule. This calculation shows that the threshold current of a GaAs single quantum well laser has low-temperature sensitivity (T0∼330 K for T>300 K). The calculated threshold current of a 200-Å-wide GaAs single quantum well laser is ∼550 A/cm2. The results of the calculation are compared with experimental results.
Mode stabilized terrace InGaAsP lasers on semi-insulating InP
Authors: Chen T. R. , Yu K. L. , Koren U. , Hasson A. , Margalit S. , Yariv A.
Published: February 2003

Mode stabilized terrace InGaAsP lasers have been fabricated on semi-insulating InP substrates. The fabrication involves a selective, single-step liquid phase epitaxial growth process, and a lateral Zn diffusion. Two versions of the terrace lasers are fabricated, and threshold currents as low as 35 mA and 50 mA respectively are obtained. The lasers operate with a stable single lateral mode. High power performance is observed. These lasers are suitable for monolithic integration with other optoelectronic devices.
Reflection and transmission coefficients for nonlinear media: Self-induced transmission, amplified reflection, phase conjugation, third harmonic generation, second harmonic generation
Authors: Band Yehuda B.
Published: February 2003

We propose a method using invariant imbedding of integral equations for determining the reflection and transmission coefficients for Helmholtz wave equations which are nonlinear because of nonlinear polarization terms. The present method generalizes previous treatments by (a) properly including reflection and refraction at dielectric interfaces, (b) allowing solution for spacially inhomogeneous and/or absorptive nonlinear media, and (c) bypassing the adiabatic (or slowly varying envelope) approximation. Propagation equations for the reflection and transmission coefficients of the nonlinear phenomena enumerated in the title are presented for various geometries.
Performance of a plasma-filled, series-field-coil ion beam diode
Authors: Mendel C. W. , Mills G. S.
Published: February 2003

An ion diode having many characteristics desirable for ion beam fusion is described. These features include bunching, excellent impedance match to the pulser, self-magnetic insulation of electrons, and selectable ion species. The diode accomplishes this by employing a series magnetic field coil and an initial plasma fill. The series field coil is configured in such a way as to give uniform electron loss and ion current density over the entire anode. Data are presented to show experimental agreement with the model.
Magnetization reversal in thin magnetic films with perpendicular anisotropy
Authors: Mansuripur Masud
Published: February 2003

A one-dimensional theory of magnetization reversal in thin, perpendicularly anisotropic magnetic films is presented. It is postulated that the presence of a defective point creates an infinitely deep, infinitely narrow potential well which inhibits the rotation of local magnetization. The interval D between neighboring defects, the saturation magnetization Ms, the anisotropy constant Ku, and the exchange energy constant A are assumed to be finite and uniform across the film. Starting with an initial state where the film is uniformly magnetized to saturation in the easy direction, we show that a discontinuous change of state occurs when the reverse external field H reaches a critical value Hc. The domains thus nucleated at the critical field expand to cover the entire area of the film as H increases beyond Hc. Using the normalized values of H and D, defined, respectively, as h = H/(2Ku/Ms) and d = D/(4A/Ku)1/2, we show that the critical field hc is a function only of d and that its value decreases significantly as d increases.
Dynamic properties of charged walls in ion implanted garnets
Authors: Kryder M. H. , Argyle B. E.
Published: February 2003

The dynamic behavior of the charged wall in the ion implanted layer of contiguous disk bubble devices is determined for the first time without the disturbing influence of a bubble domain being coupled to the charged wall. The charged wall was stabilized next to a nonimplanted region by an applied in-plane field Hx and was oscillated along ŷ by an rf field hy  sin ωt. Oscillations in Faraday magneto-optic contrast signals proportional to the wall oscillations were detected with a high-speed photomultiplier (PMT) when a focused laser beam was obliquely incident on the region of the charged wall. The drive frequency ω was provided by an rf tracking generator which was phase locked to a spectrum analyzer set to detect the fundamental amplitude response of the PMT signals. Our measurements were made on the doped yttrium iron garnet (YIG) layers Gd, Tm, Ga:YIG and Eu, Tm, Ga: YIG typically used for driving 5- and 1-μm bubbles, respectively. The charged wall amplitude rolloff with frequency interpreted in terms of an overdamped linear oscillator reveals a relaxation frequency near 10 MHz when Hx = 30 Oe, for example, in contrast to ∼0.5 MHz when the bubble is attached. The linear mobility of the charged wall μcw = 6600 cm/sec Oe determined in Gd, Tm, Ga: YIG from the relaxation frequency contrasts with an effective mobility μeff = 250 cm/sec Oe when the bubble is attached. These results confirm our earlier assumption [B. E. Argyle, et al., IEEE Trans. MAG-14, 593 (1978)] that the damping which affects the upper limiting frequency of operation in this contiguous disc material comes mainly from the bubble domain and almost none (i.e., ≲5%) from the charged wall. In addition, no velocity saturation effects are observed in the isolated charged wall at least up to 12.8 MHz. The maximum velocity 28 000 cm/sec inferred from the maximum harmonic amplitude at this frequency is at least 25 times the saturation velocity of an isolated bubble, e.g., 1100 cm/sec, in the nonimplanted film. A simple theoretical model taking into account restoring torques on the wall magnetization due to in-plane anisotropy and wall demagnetization predicts velocity saturation will occur at yet several times larger velocity than the maximum response we can observe in the present experiment.
Luminescence of NaCl:Tl and NaCl:In at high pressure
Authors: Littman J. E. , Drickamer H. G.
Published: February 2003

The effects of pressure up to 40 kbar and temperatures down to 100 °K on the intensity and lifetime of NaCa:Tl+ and NaCl:In has been studied. A kinetic model describing these luminescent properties has been proposed. The 3Tlu level is in thermal equilibrium with 3Alu. Both 3Tlu and 3Alu have nonradiative pathways to the ground state 1Alg. In addition 3Tlu is radiatively coupled to the ground state. Increasing pressure increases the radiative rate from 3Tlu to 1Alg and has no effect on the equilibrium between 3Tlu and 3Alu. The back feeding rate from 3Alu to 3Tlu is temperature sensitive for NaCl:Tl but not for NaCl:In.
Excitonic luminescence and edge emission in AgGaS2 crystals
Authors: Aicardi J. P. , Leyris J. P. , Poure A.
Published: February 2003

The low temperature cathodoluminescence spectra of AgGaS2 are investigated in this work. In the purest single crystals (sample A1) at 4.2 K, the luminescence spectra are dominated by free excitons, by exciton bound to impurities, and by an edge emission peaked at 2.590 eV. Our study shows the presence of an acceptor level at 110 meV which should be responsible of the bound exciton at 2.689 eV as well as of the edge emission. In other samples, we only observe the free exciton at 2.700 eV and a green broad emission band at 2.470 eV.
A Mössbauer study of the ferrimagnetic Fe1−xCrxBO3 system
Authors: Ruckman M. W. , Levy R. A. , Chennette R.
Published: February 2003

Mössbauer effect measurements were made on solid solution Fe1−xCrxBO3, with 0⩽x⩽0.60, at room and at liquid nitrogen temperatures and on Fe0.50Cr0.50BO3 at temperatures from 82.5 to 150 K. The hyperfine field strength at Fe3+ sites decreases with increased Cr content. The isomer shift increases appreciably in samples containing Cr at low concentrations. The Mössbauer linewidth increases with increasing Cr content and exhibits a shoulder at 0.40⩽x⩽0.60. The data suggest that the presence of Cr3+ ions disrupts the magnetic superexchange interaction. Variations in the isomer shift, magnetic hyperfine splitting and linewidth as a function of increasing temperature in samples of Fe0.50Cr0.50BO3 suggest that a significant antiferromagnetic component is present in samples with Cr concentrations 0.40⩽x⩽0.60.
The growth of polycrystalline silicon on molybdenum, tantalum, tungsten, and their disilicides
Authors: Campisi G. J. , Bevolo A. J. , Shanks H. R. , Schmidt F. A.
Published: February 2003

Silicon was electron beam vaporized in an ultralow pressure system on substrates of molybdenum, tantalum, and tungsten between 550–850 °C. Polycrystalline silicon was grown on the molybdenum and tungsten substrates at 550 °C with grains measuring ∼0.3 μm in cross section and having a {110} orientation. This orientation was attributed to the deposition technique and substrate temperature. At 670 °C silicon reacted with the tantalum substrates to form a thin interfacial layer of TaSi2 but grew with a {110} and {111} orientation. At this same sample temperature {111} and {110} polycrystalline silicon was detected on molybdenum and tungsten. By increasing the substrate temperature to 750 °C, silicon reacted with the metals to produce ’’columnar’’ structures composed of {110}, {111}, {100}, {311}, or {331} silicon crystallites that grew on a layer of the respective metal disilicide. Phosphorus coevaporated with the silicon retarded the rate of the silicide growth at 670 and 750 °C. Only the refractory metal disilicides MoSi2, TaSi2, and WSi2 were obtained at 850 °C by reaction of the vapor deposited silicon with the substrate metal.
Semiconductors for high-voltage, vertical channel field-effect transistors
Authors: Baliga B. J.
Published: February 2003

The influence of material parameters upon the characteristics of vertical channel power field effect transistors is examined. It is demonstrated that for devices with the same breakdown voltage and device structure, the on-resistance is inversely proportional to the third power of the energy band gap and inversely proportional to the mobility. In addition the frequency response of these devices increases in proportion to the mobility and the energy band gap. Calculated device parameters for III–V semiconductor compounds, as well as their alloys, have been compared to those of a silicon device with the same breakdown voltage. It is found that devices fabricated from GaAs, InP, and GaP are expected to have a current handling capability which is a factor of 12.7, 5, and 1.85 better than that of the silicon device with the same breakdown voltage. In addition, the current handling capability of devices fabricated from the alloy semiconductors GaAlAs, GaAsP, and InGaP are even superior to those of a GaAs device with the same breakdown voltage.
Charge collection scanning electron microscopy
Authors: Leamy H. J.
Published: February 2003

This review encompasses the application of the scanning electron microscope to the study and characterization of semiconductor materials and devices by the Electron Beam Induced Conductivity (EBIC) method. In this technique, the charge carriers generated by the electron beam of the microscope are collected by an electric field within the material and sensed as a current in an external circuit. When employed as the video signal of the SEM, this collected current image reveals inhomogeneities in the electrical properties of the material. The technique has been used to determine carrier lifetime, diffusion length, defect energy levels, and surface recombination velocities. Charge collection images reveal the location of p-n junctions, recombination sites such as dislocations and precipitates, and the presence of doping level inhomogeneities. Both the theoretical foundation and the practical aspects of these effects are discussed in a tutorial fashion in this review.
Electron channeling patterns in the scanning electron microscope
Authors: Joy David C. , Newbury Dale E. , Davidson David L.
Published: February 2003

This article provides a comprehensive review of the theory, practice, and application of electron channeling patterns in the scanning electron microscope. An atlas of indexed channeling maps for the bcc, fcc, diamond cubic, and hcp systems is included with a bibliography of 240 references containing all known published work on electron channeling for crystallographic studies in the SEM.
Reply to ‘‘Comment on ‘Anisotropic suspension display’ ’’
Authors: Beni G. , Craighead H. G. , Hackwood S.
Published: February 2003

We point out that, in the paper proposing Anisotropic Suspension Display, the electric fields were not estimated to be three orders of magnitude lower than required. We also point out that the angle-of-view problem is minor.
Laser-induced damage to transparent conducting SnO2 films at 1062 nm
Authors: Subhash N. , Sathianandan K.
Published: February 2003

Transparent conducting SnO2 films prepared by chemical vapor deposition were damage tested at 1062 nm using an electro-optically (EO) Q-switched Nd:glass laser emitting 15-ns pulses. The damage threshold energy densities for films of thickness 151.0 and 140.9 nm were found to be 18.2±1.3 and 15.9±1.1 J/cm2, respectively. These films find application in large aperture Pockels cells and other EO modulators for pulse shaping and gating purposes in high power laser amplifiers.
Stability analysis of Kamimura-Dawson diffusion in a collisionless plasma
Authors: Berryman James G.
Published: February 2003

It has been predicted theoretically and observed experimentally that the cross-field particle diffusion coefficient is inversely proportional to density for a highly collisionless plasma in the presence of a sheared magnetic field. The asymptotic solution of the corresponding one-dimensional model equation nt=[ln(n/n0)]xx on 0≤x≤1 with n(0,t)=n(1,t)=n0 is shown to have the form ln(n/n0)=ε21/2 sin πx+ε2ψ2(x)+ε 3ψ3(x)+0(ε4) where ε=A exp(−π2t/n0), ψ2 and ψ3 are known functions, and the amplitude A alone is dependent on the initial data. The asymptotic behavior of the particle distribution can therefore be predicted from knowledge of the distribution at some earlier time.
On the analysis of small-angle scattering with elliptical azimuthal symmetry
Authors: Hall Peter L. , Mildner D. F. R.
Published: February 2003

Inhomogeneities which have azimuthal symmetry around some unique axis exhibit small-angle neutron scattering with elliptical symmetry. It is not necessary that these inhomogeneities have an ellipsoidal shape. The model of Debye et al. has been generalized to incorporate an anisotropic correlation length having this symmetry. A method is given for fitting two-dimensional intensity data to this model. This is illustrated by data taken for sections of slate and shale rock cut normal to the direction of the bedding planes, and which exhibit both large- and small-pore anisotropies.
Electrochemical enhancement of contrast ratio in fluorescent liquid crystal cells
Authors: Sarna R. K. , Sengupta S. K. , Labes M. M.
Published: February 2003

Europium chelates in cholesteric or nematic phases show a brilliant red (612 nm) fluorescence which can be quenched electrochemically. Either cathodic or anodic quenching can occur depending on total electrolyte concentration, the latter process involving oxidation of the ligand. By combining the electrochemical effect with a field induced cholesteric–nematic transition, enhanced contrast ratios can be achieved for electro-optic display.
Halogen lamp recrystallization of silicon on insulating substrates
Authors: Vu D. P. , Haond M. , Bensahel D. , Dupuy M.
Published: February 2003

Growth of large-area single-crystal silicon on an insulator is achieved by a zone melting technique using halogen lamps. The single-crystal, typically 3–4 mm by several centimeters, is composed of subgrains showing no internal defects, with boundaries parallel to the scan direction. The crystallographic orientation is (001) along the normal to the film plane and (100) along the scan direction.
Measurement of photoacoustic transient heat exchange
Authors: Lambert David K.
Published: February 2003

A thin film thermoelectric device was used to study gas-solid transient heat transfer under conditions identical to those used for photoacoustic measurements. Although the species and pressure dependence agreed qualitatively with conventional theory, quantitatively our measured heat exchange is about a factor of two larger. We attribute the discrepancy to the neglect gas viscosity.
Production of intense light ion beams on a multiterawatt generator
Authors: Maenchen J. W. , Young F. C. , Stringfield R. , Stephanakis S. J. , Mosher D. , Goldstein Shyke A. , Genuario R. D. , Cooperstein G.
Published: February 2003

The operation of a pinch-reflex diode as an intense pulsed ion-beam source has been scaled up to the multiterawatt PITHON generator. Ion beams with currents of 1 MA at 1.8 MeV have been extracted in a 130 kJ, 100-ns pulse. The corresponding ion production efficiency is 60%. Power losses were observed in interfacing the coaxial diode to the biconic vacuum feed of the generator. By using smaller area diodes, the average current density at the anode source was increased to 20 kA/cm2. Proton and deuteron beams were studied in both planar and spherical diode geometries. The ion beam is focused predominantly by self-magnetic fields for planar diodes and predominantly by electrode shaping for spherical diodes. Current densities exceeding 150 kA/cm2 were achieved with spherical diodes. The spatial evolution of the anode and cathode plasmas was studied by laser holographic interferometry. As the peak of the power pulse is approached, plasmas were observed to expand from the electrodes in fairly uniform profiles with steep density gradients and to accelerate across the vacuum gap. After peak power, anode plasma fluctuations and a high-velocity (30 cm/μs) axial plume develop; the latter expands radially coincident with collapse of the power pulse.
Determination of effective surface recombination velocity and minority-carrier lifetime in high-efficiency Si solar cells
Authors: Rose B. H. , Weaver H. T.
Published: February 2003

A mathematical analysis for minority-carrier diffusion in a solar cell base is used to extract bulk lifetime τ and effective back-surface recombination velocity S from measurements of asymptotic decay times of short-circuit current and open-circuit voltage. Since the decay times depend individually on both S and τ, it is necessary to use both current and voltage data for unique results. Experimental measurements of current and voltage transients are presented from variable base resistivity cells, γ-irradiated cells, and cells with intentionally damaged back-surface field regions. Lifetimes determined in these experiments are compared with conventional techniques. The results show that these conventional techniques yield lifetimes in serious error for cells whose diffusion lengths approach base thickness.
Interaction between chromium oxide and chromium silicide
Authors: Cros A. , Pollak R. A. , Tu K. N.
Published: February 2003

We have used x-ray induced photoemission spectroscopy and Rutherford backscattering spectroscopy to study the chemical reaction between Cr2O3 and CrSi2. We observed that upon annealing a Cr film on a Si substrate at 550 °C to form CrSi2, the native chromium surface oxide will decompose while a film of SiO2 will form when the CrSi2 growth front reaches the Cr2O3.
Electromigration transport mobility associated with pulsed direct current in fine-grained evaporated Al-0.5%Cu thin films
Authors: English A. T. , Kinsbron E.
Published: February 2003

Pulsed-current induced electromigration mass transport velocities have been measured in Al-0.5%Cu evaporated thin films using the Blech–Kinsbron edge-displacement technique. The objective was to clarify the dependence of electromigration on pulsed duty cycle (fraction of time that current is on). In the frequency range 0.01–105 Hz, we observe a rate of mass transport per unit of on time which is essentially constant, regardless of duty cycle, so long as the current density is not so high as to produce significant Joule heating on each pulse. Past studies, conducted using current density j at and above 4×106 A/cm2, were difficult to interpret due to the presence of thermal transients as well as the general elevation of temperature above ambient.