bluuebunny/crossref_metadata_2025 huggingface dataset:
3D computer simulation of the primary electron orbits in a magnetic multipole plasma source
Authors: Ohara Y. , Akiba M. , Horiike H. , Inami H. , Okumura Y. , Tanaka S.
Published: July 2002

Performance characteristics of the magnetic multipole plasma source depend strongly on the structure of the line-cusp magnetic fields and the behavior of the primary electrons. In order to design and improve the plasma source efficiently, we developed a computer code which can simulate primary electron orbits in the three-dimensional magnetic field generated in the source. Using this code, we compared the orbits of the primary electrons in the arc discharges with and without the mode-flip phenomenon. The result indicates that the trapping of the primary electrons in a local magnetic mirror fields causes the mode flip due to the reduction of the effective anode area. Trapping also degrades the spatial uniformity of the source plasma density, due to local arc discharge. The structure of the magnetic field can be optimized so that the primary electrons fill the center region of the source. The 3D simulation of the electron orbits turned out to be effective and useful in designing a multipole source.
The orientation of the magnetization of thin films as determined by the Hall effect
Authors: Stinson D. G. , Palumbo A. C. , Brandt B. , Berger M.
Published: July 2002

The Hall effect is a useful probe of the magnetization in thin metallic films since the signal is inversely proportional to the film thickness. Previously, the minimum in the coercivity, derived from the Hall hysteresis loop as a function of the angle of the applied field, has been used to determine the hard axis of magnetic thin films. A vibrating sample magnetometer can be used in this fashion if coherent rotation is the magnetization reversal mechanism. However, we show that even in the case of the Stoner–Wohlfarth model, the minimum of the Hall coercivity does not coincide with the hard axis. We propose an alternative method for determining the easy axis, which is independent of the magnetization reversal mechanism and does not require measuring the entire hysteresis loop. In addition, since for an arbitrary orientation of the applied field the measured Hall voltage will contain components due to magnetoresistance as well as the Hall effect, it is possible to extract a measure of the in-plane and perpendicular magnetization. Using this information, we derive a method of producing vector plots that show the magnitude and direction of the magnetization as a function of applied field for various applied-field orientations. Examples using CoCr and TbFe will be presented.
Spin waves in the triangular antiferromagnet CsMnBr3
Authors: Gaulin B. D. , Collins M. F. , Buyers W. J. L.
Published: July 2002

We report neutron scattering measurements of the spin-wave dispersion relations in the hexagonal triangular antiferromagnet CsMnBr3. The data in the easy plane are described satisfactorily in terms of a model with Heisenberg exchange parameter  J2=−0.0019 ±0.0002 meV between a magnetic atom and its six nearest neighbors and a single-ion anisotropy parameter D=0.014±0.002 meV. In a magnetic field of 3.7 T along a 〈100〉 direction the variation of the staggered magnetization, measured at (1/3 1/3 1), as a function of temperature shows two critical phase transitions separated by about 1.7 K. The triangular antiferromagnetic phase that occurs below 8.6 K in zero field is split by the field into two phases with transitions at 8.9 and 7.2 K. The intermediate phase below 8.9 K is of an unknown nature.
Chaos in magnetic garnet thin films
Authors: Wigen P. E. , Doetsch H. , Ming Y. , Baselgia L. , Waldner F.
Published: July 2002

Ferromagnetic resonance in thin magnetic garnet films has been studied at excitation frequencies of 10 GHz and from room temperature to 4.2 K. Powers sufficient to drive the magnetization to large precession angles have been studied. Second-order Suhl instabilities of the main resonance have been observed as an onset of auto-oscillations of the magnetization. These oscillations include regular and irregular oscillations, very noisy collective oscillations, as well as spiking. They have been observed in real time and by spectral analysis. In pure yttrium iron garnet (YIG) films the oscillations have been observed in the frequency range from 0.5 to 2 MHz at 300 and 4.2 K. In going from 300 to 4.2 K the threshold power level pth in YIG films is lowered by three orders of magnitude, while the frequency of the regular oscillations are nearly independent of temperature. If pth is connected to the intrinsic damping parameter γ, then γ is temperature dependent, which is in fair agreement with the large number of narrow resonance features observed in the films. Preliminary simulations using a model extending the S theory of Zakharov and Nakamura for large precession angles give time evolutions that are qualitatively similar to the experimental observations. Regular and weekly irregular oscillations are found for one spin-wave mode coupled to a linear resonance circuit, i.e., a phonon mode. More irregularity is found for two coupled spin-wave modes excited to large precession angles.
Spin-polarized 3He nuclear targets and metastable 4He atoms by optical pumping with a tunable, Nd:YAP laser
Authors: Bohler C. L. , Schearer L. D. , Leduc M. , Nacher P. J. , Zachorowski L. , Milner R. G. , McKeown R. D. , Woodward C. E.
Published: July 2002

Several Nd:YAP lasers were constructed which could be broadly tuned in the 1083-nm region which includes the helium 23S-23P transition, using a Lyot filter and thin, uncoated etalons within the laser cavity. 1 W of power could be extracted at 1083 nm through a 1% transmitting output coupler. This laser beam was used to optically pump metastable 4He and 3He 23S helium atoms in a weak discharge cell, spin polarizing the metastable ensemble. In a 3He cell the polarization is transferred to the nuclear spin system. A 3He target cell at 0.3 Torr was polarized to 52% in a few minutes. We describe the application of this system to the design of polarized targets for experiments in nuclear physics.
Optical properties and Stokes shifts in lamp-annealed InGaAs/GaAs strained layer superlattice
Authors: Kothiyal Govind P. , Bhattacharya Pallab
Published: July 2002

The effect of incoherent lamp annealing on the photoluminescence and optical absorption characteristics in InxGa1−xAs/GaAs(x=0.2 and 0.24) strained layer superlattices grown by molecular-beam epitaxy has been investigated. The annealing time and temperatures were varied from 5–25 s and 850–950 °C, respectively. It is seen that the main photoluminescence and absorption peaks a low temperatures (11.5 K) shift to higher energies with increase in annealing temperatures. We believe this is due to In-Ga atomic interdiffusion across the heterointerfaces and have estimated the magnitude of this interdiffusion by solving the appropriate Schrodinger equation for this region. The estimated interdiffusion constants D are ∼10−16–10−15 cm2/s for the above annealing conditions, which are about three orders of magnitude higher than those reported for long-term furnace annealed InxGa1−xAs/GaAs(x=0.13–0.15). Optimal rapid thermal annealing has a significant effect in improving the quality of the superlattices in terms of Stokes shift and absorption coefficients. Extremely small Stokes shift ∼1.1 meV was observed for In0.2Ga0.8As/GaAs superlattices annealed at 890 °C for 5 s.
Low-energy proton detection by Pd metal-insulator-semiconductor diodes
Authors: Hughes R. C. , Bastasz R.
Published: July 2002

It has been discovered that palladium-gated metal-insulator-silicon Schottky barrier diodes are very sensitive to fluxes of energetic protons in high vacuum. Data on the dosimetric response of the diodes to energetic protons are presented, along with data on the subsequent decay in the induced signal. A model for the response is developed, based on the response of similar structures to partial pressures of molecular hydrogen. The model involves adsorption sites at both the external Pd surface and the interface between Pd and SiO2, as well as known H absorption properties of bulk Pd. The sensitivity at 300 K of our diodes is about 109 protons (1011 cm−2). The inventory of protons stored in the bulk Pd, the surface, and at the interface indicates that the areal site density for the surface and interface is about 1015 cm−2.
New techniques for laser scattering in plasmas
Authors: Dangor A. E. , Dymoke-Bradshaw A. K. L. , Dyson A.
Published: July 2002

We report novel techniques for the scattering of laser light from plasmas to measure density and temperature. Subnanosecond laser pulses are used with fast optical streak cameras to monitor the dispersed scattered light. The spectra are recorded on photographic film. Time resolution down to 100 ps is obtained and stray light problems are eliminated so that the unshifted scattered light can be observed. The techniques have been used to measure densities in the range ne≊1016–1018 cm−3 and electron temperatures in the range Te≊5–35 eV with an accuracy of better than 10%. Laser pulses at 5265 Å with an energy of about 10 J are used and give little plasma heating.
Compensating vibrating reed magnetometer (invited)
Authors: Frey Th. , Jantz W. , Stibal R.
Published: July 2002

A new high-sensitivity magnetometer for susceptibility measurements in the temperature range 6–330 K has been developed. It uses the vibrating reed technique with amplitude sensing by piezoelements. The measurement is absolute because the magnetic moment of the sample is compensated by a loop current that is adjusted with a zero detection circuit. Dia-, para-, and ferromagnetic contributions can be evaluated simultaneously. The resolution for measuring magnetic moments is better than 10−7 emu, corresponding to a susceptibility of 10−11 cm3 at 10 kOe. Magnetic measurements of thin ferromagnetic films, diluted paramagnetic systems, and a superconducting material are presented to demonstrate the sensitivity and versatility of the system.
Surface magnetization of Co70V10B20 and Fe77Cr6B17 amorphous alloys
Authors: Woods J. P. , Ushioda A. , Fukuno A. , Sun S. W. , Henderson L. , O’Handley R. C.
Published: July 2002

Magnetization has been measured as a function of in-plane applied field and temperature by measuring the spin polarization of low-energy electrons (LEESPA) excited from the surface by an unpolarized electron beam (Ep=2 keV). These extremely surface sensitive data (probing <25 Å), taken on surfaces characterized by Auger electron spectroscopy, are compared with results obtained by magneto-optic Kerr effect (MOKE probing <250 Å) and bulk magnetometry. The LEESPA M-H loops show considerably lower remanence than MOKE indicating appreciable surface anisotropy. The LEESPA polarization approaches zero at approximately TC =170 °C for both the Co and Fe base alloys with less curvature than bulk magnetization does. The bulk TC’s are 20 °C higher than those measured by LEESPA.
The determination of heterojunction energy band discontinuities in the presence of interface states using capacitance-voltage techniques
Authors: Leu L. Y. , Forrest S. R.
Published: July 2002

Effects of trapped interface charge on the determination of heterojunction energy band discontinuity energies using capacitance-voltage (C-V) techniques are analyzed both theoretically and experimentally. We show that for shallow traps, whose charge occupancy is unchanged by variations in the applied voltage, the measured conduction band discontinuity energy (ΔEc) as determined by the depletion technique [Kroemer, Chien, Harris, and Edwall, Appl. Phys Lett. 36, 295 (1980)] is a function of trap density (σi). This error source in determining ΔEc is large for small values of ΔEc due to distortions of the conduction band induced by the trapped interface charge. In addition, the analysis used for determining σi and ΔEc via the depletion technique has been generalized to correct for the effects of both deep and shallow traps. We show that at low measurement frequency, the measured value of ΔEc is nearly independent of σi, and this value is near to the exact value of ΔEc measured in the absence of interface traps (i.e., for σi=0). However, at high measurement frequency (or low temperature), the measured ΔEc decreases with increasing σi or increasing trap energy depth from the conduction band minimum. These deviations from the actual value can be corrected by using the equations developed in this article. We apply these results to the understanding of In0.53Ga0.47As/InP heterojunctions. The computer-simulated apparent free carrier concentration profiles are used to fit experimental data at several temperatures. The best fit value of ΔEc (=0.22 eV) is in agreement with the value obtained via the emended equations. We explain the complex temperature dependence of these experimental profiles as due to donor traps near the heterojunction.
Localized energy pulse trains launched from an open, semi-infinite, circular waveguide
Authors: Shaarawi Amr M. , Besieris Ioannis M. , Ziolkowski Richard W.
Published: July 2002

A new decomposition of exact solutions to the scalar wave equation into bidirectional, backward and forward traveling plane waves is described. These elementary blocks constitute a natural basis for synthesizing Brittinghamlike solutions. Examples of such solutions, besides Brittingham’s original modes, are Ziolkowski’s electromagnetic directed energy pulse trains (EDEPTs) and Hillion’s spinor modes. A common feature of these solutions is the incorporation of certain parameters that can be tuned in order to achieve slow energy decay patterns. The aforementioned decomposition is used first to solve an initial boundary-value problem involving an infinite waveguide. This is followed by considering a semi-infinite waveguide excited by a localized initial pulse whose shape is related directly to parameters similar to those arising in Ziolkowski’s EDEPT solutions. The far fields outside the semi-infinite waveguide are computed using Kirchhoff’s integral formula with a time-retarded Green’s function. The resulting approximate solutions are causal, have finite energy, and exhibit a slow energy decay behavior.
Calcium fluoroaluminate glasses
Authors: Shelby James E. , Shaw Cathy M. , Spess Marie S.
Published: July 2002

Binary calcium aluminate glasses containing 59–70 mol % CaO have been formed, as have a series of glasses in which CaF2 replaces CaO. The transformation range viscosity and glass transformation temperature of the binary glasses decreases as the CaO concentration increases, whereas the thermal expansion coefficient, refractive index, and infrared cutoff wavelength increase. The substitution of CaF2 for CaO results in a decrease in the refractive index, viscosity, and glass transformation temperature, an increase in the thermal expansion coefficient and electrical conductivity, and no detectable change in the infrared cutoff wavelength. Magic angle spinning nuclear magnetic resonance indicates that the aluminum ions in these glasses are in tetrahedral coordination. These results will be discussed in terms of the structures of these glasses.
Characterization of ion-implanted and rapidly thermal annealed GaAs by Raman scattering and van der Pauw measurement
Authors: Yoshida Hiroshi , Katoda Takashi
Published: July 2002

The structures of microcrystalline or amorphous gallium arsenide (GaAs) introduced by 120-keV Si+- or P+-ion implantation with a dose of 1×1016 atoms/cm2 and the subsequent regrowth properties annealed by rapid thermal annealing in the range from 300 to 900 °C have been investigated by Raman scattering (RS) and by the van der Pauw measurement (sheet carrier concentration and sheet resistivity) [Phillips Res. Rep. 13, (1958)]. Raman spectra of the LO-phonon mode observed for 514.5- and 457.9-nm excitation of an Ar+ laser have been analyzed on the basis of a spatial correlation model [H. Richter et al., Solid State Commun. 39, 625 (1981); K. K. Tiong et al., Appl. Phys. Lett. 44, 122 (1984)]. The results show that the regrowth stages and the regrowth rates of the disordered GaAs in the annealing process depend on the excitation wavelength and annealing temperature, and the damaged layer regrows epitaxially toward the surface. Sheet carrier concentration was observed to increase steeply, and sheet resistivity decreased rapidly when the annealing temperature was raised from 600 to 700 °C. These results are consistent with the RS result of the 514.5-nm excitation in the same temperature range. The above results indicate that the implanted silicon atoms replace the GaAs lattice sites and the recrystallization of the microcrystalline GaAs substrate occurs in this temperature range. On the other hand, the sheet resistivities were observed to increase from about 5×104 to 5×106 (Ω/⧠), when the annealing temperature was raised from room temperature to 500 °C, contrary to the 600–700 °C case. From these facts, it is concluded that the regrowth process originates principally from the recrystallization of the ion-implantation-induced damaged GaAs substrate.
Magnetization steps in dilute magnetic semiconductors (invited)
Authors: Shapira Y.
Published: July 2002

At low temperatures the magnetization curve of a dilute magnetic semiconductor (DMS) exhibits an apparent saturation which is followed, at higher fields, by magnetization steps (MSTs). These MSTs are caused by crossings of energy levels for pairs of nearest-neighbor (NN) magnetic ions. The fields where the MSTs occur yield the NN exchange constant JNN. Examples of data obtained in both dc and pulsed magnetic fields are presented, and values of JNN for several II-VI DMSs containing Mn++ are given. The apparent (or technical) saturation value Ms, and the magnitude δM of each MST, indicate that the Mn++ ions are randomly distributed over the cation sites. A dramatic narrowing of the MSTs, and a fine structure, are observed in pulsed-field experiments on some DMSs. The fine structure in Cd1−xMnxS is attributed to two types of NNs (with different JNN) in the wurtzite structure of this material. The theory of the MSTs, including the effects of distant neighbors and of the Dzyaloshinski–Moriya interaction, is reviewed. Although thus far the predicted effects have been observed only in DMSs, they should also occur in many other dilute magnetic materials with antiferromagnetic interactions.
Formation and high-temperature stability of CoSix films on an SiO2 substrate
Authors: Morgan A. E. , Ritz K. N. , Broadbent E. K. , Bhansali A. S.
Published: July 2002

A thin α-Co layer with an amorphous Si underlayer has been sputter deposited onto a thermal SiO2 substrate, rapid thermal annealed in N2 at 700–1050 °C, and the phases formed examined using Auger electron spectroscopy, transmission electron microscopy, electron diffraction, and sheet resistance measurements. A CoSix film results where x is constant with depth and determined by the relative amounts of Co and Si deposited. With increasing x, phases identified are α- and β-Co containing dissolved Si, Co2Si, CoSi, and CoSi2. At high temperatures, the CoSi2 film agglomerates and thins the underlying oxide probably on account of excess Si in the silicide film. Furthermore, in an N2 atmosphere, the CoSi2 globules are converted into CoSi in accordance with the phase diagram.
e
−-beam deposition of ZrO2-Sc2O3 films
Authors: Qadri S. B. , Skelton E. F. , Harford M. , Lubitz P. , Aprigliano L.
Published: July 2002

A new method is presented of depositing zirconia-scandia films following evaporation of the oxide powders using an electron beam. The relative amount of Sc was increased in steps from 0 to 8 at. %. In the ‘‘as-deposited’’ state, all films were amorphous, but crystallized following post-deposition heat treatments. As the atomic percent of Sc was increased, the tetragonal phase of zirconia was stabilized. It appeared as a single phase for compositions with more than 5 at. % Sc.
Dopant incorporation in Si-implanted and thermally annealed GaAs
Authors: Wagner J. , Seelewind H. , Jantz W.
Published: July 2002

The incorporation of Si in ion-implanted and thermally annealed GaAs has been studied by local vibrational mode spectroscopy. Raman scattering and Fourier transform IR absorption have been used to analyze the Si site distribution both in the near surface region and averaged over the whole implanted layer, respectively. The samples implanted with doses of 5×1014 –1016 cm−2 were annealed with various techniques using different capping layers. The Si site distribution is found to depend strongly on the details of the annealing. In particular, capping with SiO2 leads to the formation of the so-called Si-X defect complex in addition to the incorporation of Si on both lattice sites and the formation of nearest-neighbor Si pairs.
Thermally stimulated studies of bismuth silicon oxide crystal
Authors: Takamori Takeshi , Just Dieter
Published: July 2002

Thermally stimulated current (TSC) of nominally undoped bismuth silicon oxide crystals was measured after UV excitation at liquid nitrogen temperature. The results were compared with the data in the literature, and the origins of some discrepancy discussed. The TSC measurement was very sensitive to the crystal lot; that is probably to the structural defects.
Hole transport in tri-p-tolylamine-doped bisphenol-A-polycarbonate
Authors: Borsenberger P. M.
Published: July 2002

Hole mobilities of binary solid solutions of tri-p-tolylamine and bisphenol-A-polycarbonate have been measured as functions of electric field and temperature for concentrations between 6% and 50% tri-p-tolylamine. The mobilities can be described by an exponential dependence on the square root of the electric field and a temperature-dependent activation energy. The results are discussed within the framework of a model involving hopping within a Gaussian distribution-of-states broadened by disorder.
Time-dependent collisional-radiative model for quantitative study of nonequilibrium plasma
Authors: Foord M. E. , Maron Y. , Sarid E.
Published: July 2002

In this paper fully time-dependent collisional-radiative (CR) calculations are used to study the highly dynamic nonequilibrium anode plasma in a magnetically insulated-diode experiment. The CR model for the C i–C iv atomic system is described in detail, including the radiative and collisional rates and the level structure of the system. The electron temperature is determined by comparing time-dependent line intensities for C ii and C iii ions to calculations of level-population ratios in which continuous particle injection from the anode surface into the plasma is taken into account. The electron temperature is approximately 7 eV. The time-dependent injected fluxes and the fluxes accelerated away from the plasma for C i, C ii, and C iii are determined by inverting the coupled CR rate equations. The calculated extracted flux near the end of the pulse is consistent with the measured carbon-ion current drawn from the plasma. Injection of excited particles is also investigated and is found to be important during the rise of the current pulse (≤50 ns). The importance of including multiple branching for ionization into excited final states is also shown. The time-dependent cooling rate due to inelastic electron-ion collisions and radiative processes is derived for general level-population distributions and is used to investigate the anode plasma. This work should also be relevant in the study of other pulsed-power nonequilibrium plasmas, such as recombining plasmas that have applications for UV and x-ray lasers.
Gas source molecular-beam epitaxy of Si and SiGe using Si2H6 and GeH4
Authors: Yamada A. , Tanda M. , Kato F. , Konagai M. , Takahashi K.
Published: July 2002

Gas source molecular-beam epitaxy (MBE) has been studied as a low-temperature Si and SiGe epitaxial method. Specular single-crystalline silicon films were successfully grown by the gas source Si MBE technique at a substrate temperature of about 650 °C. N-type doping was carried out using PH3 gas as a dopant and the maximum electron concentration of 2.9x1019cm−3 was obtained. Furthermore, p-type doping using B2H6 gas was carried out for the first time and the maximum hole concentration of 9.5×1017cm−3 was successfully achieved. The SiGe alloy layer was also grown by the gas source MBE technique using GeH4 as a Ge source gas. The Ge concentration of the sample could be precisely controlled by the molar fraction of Ge in supply and it was increased up to 0.30 with increasing the gas ratio of GeH4 to Si2H6.
A high-sensitivity alternating-gradient magnetometer for use in quantifying magnetic force microscopy
Authors: Gibson G. A. , Schultz S.
Published: July 2002

An extremely sensitive alternating gradient magnetometer (AGM) has been developed. This AGM has been designed as an aid in characterizing the response of magnetic force microscope tips to known magnetic fields and field gradients. It should also prove useful as a general purpose magnetometer for small samples. A sensitivity of ∼ 1.4 × 10−11 emu has been achieved. Minor improvements in vibration isolation should bring this number down to ∼ 10−12 emu. A sensitivity of ∼ 10−14 emu is theoretically possible. The capabilities of the AGM are illustrated with magnetization versus field data for an 8-μm Ni sphere.
A kinetic theory of ion collection by probe in flowing unmagnetized plasma
Authors: Chung Kyu-Sun
Published: July 2002

A one-dimensional kinetic model is developed for the flow of ions to a probe whose characteristic size is smaller than the ion gyroradius in drifting plasmas. Numerical solutions of the self-consistent plasma-sheath equations have been obtained for arbitrary external temperature and parallel plasma flow velocity. The ion current to the probe is obtained and the ratio of the upstream to downstream current is represented by the form R=exp[KUd], where Ud is the drift velocity in units of (Te/mi)0.5 and K is constant depending on the type of source in the sheath-transition region. Comparisons with other models are made.
A model for linewidth-dependent electromigration lifetime and its application to design rule scaling for narrow interconnects
Authors: Fu Kuan-Yu
Published: July 2002

Analytical formulae for linewidth-dependent electromigration lifetime, as represented by a log-normal distribution, are derived based on a linewidth-independent log-normal grain size distribution. This formulation can quantitatively explain the experimentally observed increase of both the Median-time-to-failure and standard deviation (σ) as the linewidth decreases to become comparable to or less than the median grain size. Comparison between the theoretical prediction and experimental data for three metallization systems all show reasonable agreement. Due to its analytical nature, the model can also be applied to define design rules versus linewidth for a given metallization technology down to the submicron linewidth. Conditions in limiting the process variations in order to optimize the scaling of design rules are discussed.
Photothermal electrostatics of the Pd-polyvinylidene fluoride photopyroelectric hydrogen gas sensor
Authors: Mandelis Andreas , Christofides Constantinos
Published: July 2002

A detailed photothermal electrostatic consideration of the Pd-pyroelectric junction H2 sensor is presented. Experimental evidence is in agreement with the fundamental features of the theory, which supports two possible mechanisms of ac-mode device operation: pyroelectric coefficient dependence on the hydrogenic dipole-induced charge density at the Pd-insulator polyvinylidene fluoride interface, and thermal-wave modulation of the hydrogen-concentration-dependent Pd work function. The dominant operating mechanism is found to depend on the experimental conditions. The concept of image dipole thermostatistical vibration and libration in the pyroelectric matrix is further successfully used to explain the temperature dependence of the photopyroelectric signal in support of the former above-mentioned mechanism.
The effect of shallow traps on the dark storage of photorefractive grating in Bi12SiO20
Authors: Tayebati Parviz
Published: July 2002

Dark decay of photorefractive gratings and persistent photocurrents in Bi12SiO20 are interpreted using a model of the photorefractive effect which includes shallow traps as well as deep traps. The model explains the grating spacing dependence of the coasting and initial decay rate quite well. The intensity dependence of the initial decay rate and coasting, however, suggest large optical absorption contradicting the results of direct measurements. It is suggested that the recombination of holes to the shallow traps as a possible explanation of the discrepancy. It is demonstrated, for the first time to our knowledge, that the photorefractive grating dark decay experiments can be used to determine the densities of ionized donors in dark (NA) in addition to the effective trap density (NE). We also report, for the first time to our knowledge, the observation of oscillatory dark decays of photorefractive grating in three Bi12SiO20 crystals and explain them in terms of the dynamics of coupled charge gratings.
Dislocations in mismatched layers of GaAsxP1−x in between GaP as observed by low-temperature cathodoluminescence: Part I. Grown on (001) oriented substrates.
Authors: Gustafsson A. , Pistol M.-E. , Gerling M. , Samuelson L. , Leys M. R. , Titze H.
Published: July 2002

The possibility of growing lattice-mismatched layers and quantum wells becomes more and more interesting for the fabrication of devices. For device performance it is necessary to control the formation of misfit dislocations within the mismatched layers. It is therefore essential to study the onset of misfit dislocations versus amount of mismatch and layer thickness. A preliminary cathodoluminescence (CL) investigation, performed on layers of GaAsxP1−x mismatched to GaP barriers, was presented [A. Gustafsson, J. Jönsson, M. Gerling, M. R. Leys, M.-E. Pistol, L. Samuelson, and H. Titze, Inst. Phys. Conf. Ser. No 100, 771 (1989)]. In this paper the critical thickness with respect to the composition, x, in GaAsxP1−x, is studied from a determination of the onset of the formation of dislocations as observed in the monochromatic CL images. The experimental values of the critical thickness are compared to theoretical predictions for the critical thickness, according to different theories. The best agreement is found with the mechanical equilibrium theory, which assumes that the barrier for the formation of dislocations is negligible.
Experimental investigation of a thin-film surface polariton polarizer
Authors: Sletten Mark A. , Seshadri S. R.
Published: July 2002

A new method of fabricating fiber optic surface polariton polarizers is described which produces devices with well-defined lengths and fiber core to flat spacings. The results of experiments investigating the length dependence of the extinction ratio are interpreted through the use of a new theoretical analysis. Successful investigations of the dependence of the extinction ratio on the fiber core to flat spacing should be possible with further fabrication modifications.
Vectorial magnetization of metal evaporated tapes
Authors: Richter H. J. , Hibst H.
Published: July 2002

Using a three-dimensional vector vibrating sample magnetometer the magnetization reversal behavior of obliquely evaporated Co-Ni-O layers (metal-evaporated tapes) is studied. It is found that the direction of preferred magnetization is tilted out of the film plane. In addition, the measurements show that the projection of the axis of preferred magnetization into the film plane does not coincide with the direction of tape motion in general. This is caused by the geometry of the evaporation process.
Direct measurement of the recombination rates in bulk InSb by time-resolved photoluminescence
Authors: Grober Robert D. , Drew H. Dennis , Burdge Geoffrey L. , Bennett Brian S.
Published: July 2002

Time-resolved photoluminescence has been used to study the decay of photoexcited carriers in bulk InSb at 2 K. The recombination occurs as a two step process exhibiting a fast and a slow decay. The fast decay, corresponding to band-to-band recombination, occurs with a time constant of the order of 60 nsec and is accompanied by time-resolved band gap renormalization. The slow process, identified in the band-to-acceptor photoluminescence, occurs with a time constant of 3.8 μsec. We show that this is in excellent agreement with the theoretical value of the band-to-acceptor radiative transition rate. These results help reconcile discrepancies that have long existed between conventional photoluminescence measurements and time-resolved photoconductivity measurements.
Dynamics of a 700-kA 19-MeV electron beam in a short gas cell
Authors: Sanford T. W. L. , Poukey J. W. , Mock R. C. , Welch D. R.
Published: July 2002

The transport of the Hermes III annular, 19-MeV, 700-kA, 25-ns, electron beam of radius ≲26 cm and current density ≳0.4 kA/cm2, through short gas cells filled with N2, is characterized as a function of injection parameters, cell length, and gas pressure. These measurements are compared with predictions of numerical and analytical models. The comparisons confirm the main features of the models and show that the early-time behavior of the beam and gas ionization determines the net current and associated magnetic fields for the entire pulse, particularly at low pressure. The net current is minimized for pressures near 3 Torr and is 4%–7% of the injected current at peak power. Owing to the radial distribution of the net current density, the mean beam trajectory is effectively ballistic at this pressure.
The influence of electrode areas on radio frequency glow discharge
Authors: Kasper W. , Böhm H. , Hirschauer B.
Published: July 2002

Argon, hydrogen, and germane plasmas were investigated in a variably configured radio frequency (rf) diode glow-discharge reactor system with a range of rf powers. Plasma parameters such as electron temperature, plasma density, plasma potential, and floating potential were determined and the internal distribution of voltages within the glow discharge was considered. An equivalent circuit for the discharge is presented and fundamental dependence between the voltage ratio and the electrode area ratio of squared power law compared with the usual fourth power law is measured and described. The main goal of this work was to obtain more information about the energy of ion bombardment on the growing film surface.
Surface analysis of PbTiO3 films prepared by the sol-gel method
Authors: Qu Bao-Dong , Wang Yu-Guo , Zhong Wei-Lie , Wang Ke-Ming , Wang Zhong-Lie
Published: July 2002

The surface of PbTiO3 films prepared by the sol-gel method was analyzed by the use of x-ray photoelectron spectra combined with secondary-ion mass spectra and infrared absorption spectra. The results suggested that traces of organic materials still existed at least in the surface layer of the films. The outmost surface was partly covered by adsorbed oxygen. The surface layer of the film deviated from stoichiometry because of the shortage of Ti; the thickness of it was estimated about 400 Å.
Acoustic field study in layered structures by means of x-ray diffraction
Authors: Zolotoyabko E. , Jacobsohn E. , Shechtman D. , Kantor B. , Salzman J.
Published: July 2002

A new approach for probing acoustic field in acousto-optical devices based on dynamical x-ray diffraction is demonstrated. The measurements were carried out on the ZnO-SiO2-Si system. The experimental results as well as the advantages of the method are discussed.
Thermal stability of NiSi2 on high-dose ion-implanted (001) Si
Authors: Chen W. J. , Chen L. J.
Published: July 2002

Thermal stability of polycrystalline NiSi2 on high-dose BF+2-, Si+-, B+-, F+-, As+-, and P+-implanted (001) Si has been studied by both cross-sectional and plan-view transmission electron microscopy as well as by sheet resistance measurements. The surface coverage and grain size of polycrystalline NiSi2 were found to be significantly influenced by the implantation species in silicon substrate. In Si+-, B+-, As+-, and P+-implanted samples, agglomeration of NiSi2 became very severe after 800 °C, 1-h annealing. The average grain sizes were larger than 0.5 μm. In contrast, almost full surface coverage was found in F+- and BF+2-implanted samples after 900 °C, 1-h annealing. The growth of laterally uniform NiSi2 and resistance to agglomeration at high temperatures in BF+2- and F+-implanted samples are attributed to the retardation of the growth of NiSi2 grains by the presence of fluorine bubbles at the grain boundaries. Sheet resistance data were found to correlate well with the morphological and microstructural observation.
Energy barriers for thermal reversal of interacting single domain particles
Authors: Chen Wenjie , Zhang Shufeng , Bertram H. Neal
Published: July 2002

An analytic solution to the energy barriers of two interacting single domain particles is presented. Identical volumes and uniaxial anisotropies are assumed with easy axes parallel to an external magnetic field. The locations and heights of the system energy barriers are analytically determined when the line joining the two particles is either parallel or perpendicular to the easy axes and the external field. The lowest energy barriers are saddle points of the energy surface and correspond to reversal modes under thermal agitation. When dipole coupling is not strong, the mode of thermal switching is asymmetric fanning or asymmetric coherent rotation, depending upon the bond angle, rather than symmetric fanning or coherent rotation that occurs at the nucleation field. An effective volume that describes the cooperative effect is calculated and good agreement with the numerical results using the Fokker–Planck equation is obtained. The energy barriers can be used to calculate the superparamagnetic relaxation time constants in the high barrier limit.
Electrical surface conductivity in quartz induced by ion implantation
Authors: Martin P. , Dufour M. , Ermolieff A. , Marthon S. , Pierre F. , Dupuy M.
Published: July 2002

Quartz was implanted with titanium ions at high doses (up to 3.3×1017 cm−2). At low energy (40 keV), a highly conductive layer was formed near the surface. The measured sheet resistance was less than 100 Ω/⧠. The implantation-induced changes in quartz were characterized using various methods such as cross-sectional transmission electron microscopy, Rutherford backscattering spectrometry, and x-ray photoelectron spectroscopy (XPS). As a result of ion implantation, SiO2 was dissociated. Metallic titanium and new chemical compounds between Si, O, and Ti were observed by XPS. However, no conductivity was observed with other metallic ions, such as Fe and Cu, which are known not to react chemically with SiO2. This suggests a correlation between the induced surface conductivity and the chemical reactivity of the implanted species with SiO2. The ion beam synthesis of such a near-surface conductive layer was then applied during the fabrication of miniaturized pressure sensors based on piezoelectric quartz. This technique is proposed to replace the more conventional approach, i.e., deposition of a thin metallic layer, and to resolve problems related to the hermetic seal made by field-assisted bonding between glass and quartz plate.
Electron energy distributions in electron cyclotron resonance discharges for materials processing
Authors: Weng Yilin , Kushner Mark J.
Published: July 2002

Electron cyclotron resonance (ECR) reactors are now being investigated for use in the plasma processing of semiconductors. The attractive feature of ECR excitation is that high plasma densities (1010–1012 cm−3) can be obtained at low pressures (0.1–a few mTorr). In this paper, we present results from a computer simulation of the electron kinetics in ECR reactors. The model is a multidimensional Monte Carlo simulation coupled with a fluid simulation with which the electron energy distribution (EED) may be calculated. We find that the electron temperature (Te =2/3〈ε〉) in Ar plasmas (0.1–10 mTorr, 100s W) is 10–20 eV in the ECR zone, falling to a few to 5 eV downstream of the ECR zone, in general agreement with experiments. The EED can be described as being multitemperature with a low energy component (5–10 eV) and a high energy tail extending to many 10s to 100s eV. Predicted ambipolar potentials are 10–30 V, increasing with decreasing pressure and increasing power deposition.
Kinetic model for hydrogen reactions in boron-doped silicon
Authors: Borenstein Jeffrey T. , Corbett James W. , Pearton Stephen J.
Published: July 2002

A comprehensive kinetic model for the in-diffusion of hydrogen atoms in boron-doped silicon during low-temperature plasma hydrogenation treatments is presented. The model accounts for several commonly observed features of secondary ion mass spectrometry profiles of hydrogenated p-type samples of varying resistivities. In high-resistivity material, the hydrogen profile is explained by invoking hydrogen dimer formation which, for short plasma exposure times, appears to follow steady-state kinetics. Hydrogen profiles in more heavily doped p-type samples, often assumed to be controlled by a single pairing reaction between H+ ions and dopant sites, are shown to be consistent with the trapping of several hydrogen atoms at each acceptor site.
Ellipsometry study on refractive index profiles of the SiO2/Si3N4/SiO2/Si structure
Authors: Chao Tien Sheng , Lee Chung Len , Lei Tan Fu
Published: July 2002

In this work, the refractive index profiles of SiO2/Si3N4/SiO2/silicon (ONO) structures were measured and analyzed by ellipsometry. The ONO structures were obtained by oxidizing the Si3N4/SiO2/silicon structure in a wet O2 ambient at the temperature range of 900–1050 °C for different lengths of time. It was found that for a nitride film thickness less than 250 Å, oxygen not only oxidized the surface, but diffused through the nitride and oxidized the inner surface of the nitride. This result was confirmed by the Auger analysis. The kinetics of the wet O2 oxidation of nitride at the above temperature range was linear for an oxidation time of 30–120 min. The activation energy was 2.24 eV.
High-temperature elastic constants of yttrium aluminum garnet
Authors: Stoddart P. R. , Ngoepe P. E. , Mjwara P. M. , Comins J. D. , Saunders G. A.
Published: July 2002

Elastic constants of yttrium aluminum garnet have been measured in the temperature range 300–1450 K using a combination of Brillouin scattering and refractive index measurements. Associated quantities such as the bulk modulus, anisotropy ratio, and thermo-optic coefficient have been determined.
Effects of post-diffusion annealing on Zn-diffused GaAs:Si
Authors: Ky Nguyen Hong , Ganière J. D. , Reinhart F. K. , Blanchard B. , Pfister J. C.
Published: July 2002

After Zn diffusion into Si-doped GaAs (n≊1.5×1018 cm−3), the Zn-diffused samples are annealed under different conditions: (i) in vacuum, (ii) in arsenic vapor, and (iii) with a Si3N4 mask capping the sample surface. The Zn concentration profiles obtained by secondary-ion-mass spectroscopy and the photoluminescence (PL) spectra taken at different depths below the sample surface are studied in detail. After annealing in vacuum, the steep (p+-n) Zn diffusion front advances into the bulk. We observe that the intensity ratio between the Si donor-gallium vacancy complex (SiGa-VGa) related emission band and the band-to-band (e-h) transition is enhanced in the region ahead of the Zn diffusion front. In contrast, Zn atoms diffuse deeper into the bulk of the samples annealed in arsenic vapor with or without capping layer. These samples show the kink-and-tail (p+-p-n) Zn concentration profiles with a decrease in the intensity ratio around the tail region. The analysis of the PL data suggest a supersaturation of gallium vacancies ahead of the diffusion front of the sample annealed in vacuum and an undersaturation of this defect around the tail region of the samples annealed in As vapor. Our results underline the important role of the nonequilibrium of the defect concentration during the postdiffusion annealing, which permits explanation of the anomalous double profile of Zn by the interstitial-substitutional mechanism.
Influence of frequency, pressure, and mixture ratio of electronegative gas on electrical characteristics of rf discharges in N2-SF6 mixtures
Authors: Kakuta Shigeru , Petrović Zoran Lj. , Tochikubo Fumiyoshi , Makabe Toshiaki
Published: July 2002

Electrical characteristics of rf discharges in SF6 and in its mixtures with N2 were experimentally investigated. In addition space- and time-resolved emission spectroscopy was used to gain a better understanding of kinetics of processes leading to various observed characteristics. A complicated dependence of minimum sustaining voltage on frequency was observed with a peak at 3 MHz. It was explained as the result of transition from the conditions where discharge is sustained by ionization in the bulk and the double-layer region to the conditions where secondary electron yield makes a large contribution. Another possible explanation is the one invoking transition from the conditions where at high-frequency double layer is formed by electron modulation to the condition where a double layer is formed by positive and negative ions. In voltage-current dependencies at 13 MHz two distinct regions were observed similar to the α to γ transitions observed for electropositive gases. Ionization by secondary electrons, however, is not supported by spatiotemporal emission measurements, thus explanation may be sought in different processes such as development of double layers and increased field in the bulk. The current-to-voltage phase is much smaller than in electropositive gases, thus the discharge appears more resistive. For a range of operating conditions the phase even becomes inductive due to negative ion inertia.
Transport and recombination in amorphous p-i-n-type solar cells studied by electrically detected magnetic resonance
Authors: Lips Klaus , Fuhs Walther
Published: July 2002

A detailed study of electrically detected magnetic resonance in p-i-n-type solar cells made from amorphous silicon is reported. It is found that the spectra depend sensitively on the applied voltage, and the intensity and photon energy of the light. The results support the present understanding of the mechanism of the device. It is shown that in general, the transport in the dark, and the charge collection under illumination, are controlled by recombination in the bulk of the i layer. Only when a high forward bias is applied and under illumination does recombination at the p-i interface play an important role. Degradation by both current and illumination results predominantly in an enhancement of the recombination rate in the i layer.
Proton implantation intermixing of GaAs/AlGaAs quantum wells
Authors: Redinbo Gregory F. , Craighead Harold G. , Hong J. Minghuang
Published: July 2002

We have investigated proton implantation enhanced intermixing of GaAs/AlGaAs quantum wells for H+ doses ranging from 5×1013 to 1×1016 ions/cm2. Implantation of 20 keV H+ followed by a high temperature rapid thermal anneal leads to enhanced diffusion of Al into the GaAs quantum well. Shifts of electron–heavy hole recombination energies due to compositional changes were observed using room temperature cathodoluminescence. Diffusion lengths of longer than 2 nm were calculated from energy shifts in a 5 nm well and were found to vary with both implanted dose and anneal time, as expected if the enhanced interdiffusion is caused by implantation introduced defects.
Epitaxial growth of CoSi2 on Si wafer using Co/Ta bilayer
Authors: Byun Jeong Soo , Kang Sug Bong , Kim Hyeong Joon , Kim Cha Yeon , Park Kyo Ho
Published: July 2002

A CoSi2 epitaxial layer was grown by thermal annealing of Co/Ta bilayer on a Si(100) wafer in the NH3 ambient. During thermal annealing an intermediate Ta layer between a Co layer and a Si wafer played two important roles for epitaxial growth of CoSi2. One was a reduction of a native oxide on a Si substrate, which resulted in an atomically clean Si surface. The other was a limitation of a flux of Co atoms to the Si surface, which made CoSi2 the most stable phase among several cobalt silicide ones. Both roles of the Ta layer made it possible to produce an epitaxial layer of CoSi2 with a coherent interface with a Si substrate, even at the early stage of thermal annealing.