bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental measurements and analysis of the loading and unloading response of longitudinal and lateral manganin gauges shocked to 90 kbar
Authors: Gupta Satish C. , Gupta Y. M.
Published: July 2002

Experimental results and analysis describing the response of manganin gauges oriented parallel and perpendicular to the shock front and embedded in an aluminum-oxide matrix are presented. Both loading and unloading data to 90 kbar were obtained. An analytic model for piezoresistance response coupled with the electromechanical constants, determined from independent quasistatic experiments, was used to calculate the gauge response. Good agreement was obtained between the experimental results and the analytic model calculations. The analytic model was also used to quantitatively analyze the residual resistance measurements. The results presented here can be used to analyze gauge data during unloading and multiple wave loading.
Range distribution of implanted cesium ions in silicon dioxide films
Authors: Fishbein Bruce J. , Plummer James D.
Published: July 2002

The distribution of ion-implanted cesium ions in thermally grown silicon dioxide has been examined over the implant energy range 50–145 keV using Rutherford backscattering spectrometry. The measured Cs concentration profiles were found to be closely approximated by positively skewed joined half-Gaussian distributions. The projected range and straggle of the Cs distributions were ∼25% greater than predictions based on the Linhard–Scharff–Schio/tt theory, and ∼10% greater than predictions made using the Monte Carlo method.
Bloch line influence on wall motion response in thin-film heads
Authors: Argyle B. E. , Petek B. , Re M. E. , Suits F. , Herman D. A.
Published: July 2002

We describe a new dynamic response behavior of domain walls in the permalloy of thin-film inductive heads. A laser magneto-optic microscope (LAMOM) which enhances the longitudinal Kerr effect, is used to image Bloch lines (BLs) within the 180° walls by aligning the optical plane of incidence perpendicular to these walls. BLs are visible due to the reversal in the Néel-type surface components of the wall magnetization at the BL position. Current pulses with fast transition times and ac currents within the frequency range of 1–10 MHz are applied to the integrated coil windings. Continuous excitation induces either a continuous flowing of the wall network or a temporary displacement. When individual pulses are applied, displacements of BLs are observed. Correlation of wall displacements with the BL displacements is demonstrated for some pulsed excitations.
Second-order Doppler shift in Mössbauer spectra of Fe-B and Fe-P amorphous alloys
Authors: Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: July 2002

The change of second-order Doppler shift with temperature in Mössbauer effect measurements was estimated by using the two-band model with two characteristic temperatures, θ1 and θ3, rather than the Debye model. The experimental results for Fe83B17, Fe80B20, and Fe80P20 amorphous alloys were in good agreement with the calculated ones. The isomer shift was also obtained and the bonding characteristics and s-electron density of the iron atoms in these substances were discussed.
An unstable resonator with a phase-unifying output coupler to extract a large uniphase beam of a filled-in circular pattern
Authors: Yasui Koji , Tanaka Masaaki , Yagi Shigenori
Published: July 2002

A novel unstable resonator to extract a large uniphase beam of a filled-in circular pattern has been investigated both theoretically and experimentally for the application to high-power lasers. The resonator consists of a phase-unifying partially reflecting output coupler and a concave total reflector. The extracted laser beams have been proved to be diffraction limited by the calculations for the Fresnel numbers N0=4.16, 12.5, and the magnification factors M=1.5, 2. Also, the calculations for N0=4.16 and M=1.5 have been verified by the experiment with a silent discharge-excited 1.5 kW cw CO2 laser.
Melting and solidification behavior of YBa2Cu3O7−x
Authors: McKittrick J. , Sasayama S. , McHenry M. E. , Kalonji G. , O’Handley R. C.
Published: July 2002

We have prepared the superconducting compound YBa2Cu3O7−x through a melt process. Solidification of this material at cooling rates <105 K/s yields BaCuO2 and a previously unreported metastable phase which indexes to a cubic pattern with a lattice constant of 0.701 nm. Faster solidification rates yield only the cubic phase and glassy materials. Annealing these materials in O2 gives rise to a single-phase material of the YBa2Cu3O7−x orthorhombic structure. The material has zero resistance at 91.6 K with a transition width of 1.4 K. The grain size of the materials after annealing averages 10 μm in length and 2–3 μm in width, and the grains are compositionally homogeneous. Twins are seen with spacings on the order of 20 nm. The irreversibility of the magnetization curve at low temperatures can be ascribed to strong flux pinning mechanisms.
Electron emission from glow-discharge cathode materials due to neon and argon ion bombardment
Authors: Szapiro B. , Rocca J. J.
Published: July 2002

We have measured the electron yields of 7 glow-discharge cathode materials under bombardment by neon and argon ions with energies between 1 and 20 keV. The surfaces of the samples were conditioned by operating the materials as cold cathodes in a high-voltage glow discharge before the electron yield measurement. The materials studied are oxidized magnesium, oxidized aluminum, a molybdenum-aluminum oxide sintered composite, molybdenum, stainless steel, copper, and graphite. The dependence of electron yield on ion velocity was found to be approximately linear for all materials and gases, with the slopes being strongly material dependent. The corresponding glow-discharge current intensities were observed to have a supralinear dependence on the electron yield. The results are relevant to the design and modeling of cold cathode high-voltage glow discharges.
Inclined pileup of edge dislocations near the crack tip
Authors: Dhondt Guido D. C. , Eringen A. Cemal
Published: July 2002

The formation of a plastic zone, in the form of a linear array of inclined edge dislocations in front of a mode-I crack in plane strain, is studied. The direction of the force field on an edge dislocation due to the crack load allows for the determination of the plastic zone as a function of the inclination angle. The dislocation distribution along the plastic zone is found from force equilibrium considerations. The results show the presence of a dislocation-free zone (DFZ) and a shrinking of the plastic zone size with greater angle of inclination. The latter angle does not seem to influence the DFZ size. The way in which we determined the stress field allows us to study the influence of defects on the plastic zone formation.
Effect of Al substitution on the magnetic properties of RCo5 (R=rare earth)
Authors: Ido H. , Konno K. , Cheng S. F. , Wallace W. E. , Sankar S. G.
Published: July 2002

Magnetic and structural characteristics of RCo5−xAlx have been established for R=Y, La, Ce, Pr, Nd, Sm, Gd, Dy, Er, and Tm. All systems have the CaCu5 structure. Al and Co are randomly distributed over the Co-sublattice sites. Al-substitution decreases μCo and Tc and significantly alters magnetic anisotropy. Analysis of the magnetic anisotropy data shows that the Sm anisotropy in SmCo4Al is only 32% of that in SmCo5. In terms of the point charge model this requires that Al carry a positive charge. This is consistent with inferences drawn from the decreased Co moment accompanying Al substitution, which implies electron transfer from Al to Co. At room temperature, RCo4Al systems are uniaxial for R=Y, La, Ce, Pr, Sm, and Er, whereas for R=Nd and Dy the magnetization is at an angle with respect to the unique c axis. PrCo4Al, NdCo4Al, DyCo4Al, and TmCo4Al exhibit changes in anisotropy at about 165, 295, 420, and 84 K, respectively.
Fluorine-doped tin dioxide thin films prepared by chemical vapor deposition
Authors: Maruyama Toshiro , Tabata Kenji
Published: July 2002

Transparent conductive tin dioxide thin films were prepared by a low-temperature atmospheric-pressure chemical vapor deposition method in air. The raw material was tin(II) trifluoroacetate. At a reaction temperature above 250 °C, polycrystalline thin films were obtained with a high deposition rate. This chemical vapor deposition method effectively incorporates F atoms into a crystalline structure and consequently maximizes the carrier concentration, yielding fluorine-doped SnO2 films of very low resistivity. For the 1260-nm-thick film deposited at 400 °C, the resistivity was 5.92×10−4 Ω cm, and the sheet resistance was 4.69 Ω/⧠. The deposition condition, structure, and characteristics of films were compared to the corresponding values in the chemical vapor depositions of SnO2 from tin(II) acetate.
Growth and characterization of (Ho,Tm,Er):YAG crystals for 2.09 μm laser
Authors: Shimony Y. , Kalisky Y. , Lotem H. , Goldbart Z. , Kagan J.
Published: July 2002

(Ho,Tm,Er):YAG single crystals of high optical quality suitable for 2.09-μm laser operation have been grown by the Czochralski method. Accurate crystal composition was obtained by new analytical technique. This technique enables the determination of the effective distribution coefficients for the yttrium as well as the other rare-earth ions incorporated into the garnet lattice. Lattice parameter and absorption spectra of the grown crystals are reported together, along with results of cw laser performances.
Theoretical model for deposition of superconducting thin films using pulsed laser evaporation technique
Authors: Singh R. K. , Holland O. W. , Narayan J.
Published: July 2002

We have theoretically and experimentally analyzed the laser-induced evaporation process for deposition of superconducting thin films from bulk targets. The spatial thickness variations have been found to be significantly different from a conventional thermal deposition process. Unlike a cos θ thickness variation expected from a thermal evaporation process, the laser evaporation process is characterized by a forward-directed deposit with a sharp variation in its thickness as a function of distance from the center of the deposit. We have studied in detail the interactions of nanosecond excimer laser pulses with bulk YBa2Cu3O7 targets leading to evaporation, plasma formation, and subsequent deposition of thin films. A theoretical model for simulating the pulsed laser evaporation (PLE) process has been developed. This model considers an anisotropic three-dimensional expansion of the laser-generated plasma, initially at high temperature and pressure. The forward-directed nature of laser deposition has been found to result from anisotropic expansion velocities of the plasma edges arising due to the density gradients in the gaseous plasma.

The physical process of the laser ablation technique for deposition of thin films can be classified into three separate interaction regimes: (i) interaction of the laser beam with the bulk target, (ii) plasma formation and initial isothermal expansion, and (iii) adiabatic expansion leading to deposition of thin films. The first two regimes occur during the time interval of the laser pulse, while the last regime initiates after the laser pulse terminates. Under PLE conditions, the evaporation of the target is assumed to be thermal in nature, while the plasma expansion dynamics is nonthermal as a result of interaction of the laser beam with the evaporated material. The expansion velocities of the plasma edges are related to the initial dimensions and temperature of the plasma, and the atomic weight of the respective species present in it. Preliminary calculations have been carried out on spatial thickness variations as a function of various parameters in PLE deposited thin films. The effects of the various beam and substrate parameters including energy density and substrate-target distance affecting the nature of deposition of superconducting thin films have been theoretically examined. Experimental results have been obtained from thin films deposited on silicon substrates by XeCl pulsed excimer laser (λ=308 nm, τ=45×10−9 s) irradiation. The spatial thickness and compositional variations in thin films have been determined using Rutherford backscattering technique and the results compared with the theoretical calculations.
Modeling inductively coupled plasmas: The coil current boundary condition
Authors: Yu Benjamin W. , Girshick Steven L.
Published: July 2002

In modeling inductively coupled plasmas, the boundary condition for the electromagnetic field equations can be treated by specifying either the current in the induction coil or the total power dissipated in the plasma. This paper presents a method for using the coil current boundary condition. An advantage of using the coil current boundary condition is that coil current, unlike plasma power dissipation, is easily measured; in this approach the plasma power dissipation is an outcome of the calculation. The results of sample calculations are presented, covering a range of coil currents from 59 to 110 A. The conditions of the calculations correspond to experimental argon plasmas at atmospheric pressure and at 3.0 MHz frequency. The calculated isotherms are in good qualitative agreement with photographs of the laboratory plasmas.
The high-frequency electric and magnetic fields of a solenoid
Authors: Harmon Gerald S.
Published: July 2002

General and simplified expressions for the electric and magnetic fields of a solenoid at frequencies up to 100 MHz are obtained from first principles for both an empty and a plasma-filled solenoid. For the empty solenoid, the field amplitudes usually differ only slightly from their low-frequency expressions, but there is a significant change in the phase of the fields with respect to the driving current in the solenoid, as the frequency increases. The expression found for the ratio of the longitudinal component of the electric field to the azimuthal component differs significantly from that which has previously been published. When the solenoid contains a moderately dense plasma, there is an even more pronounced change in both the amplitudes and phases.
Minimal ohmic contact resistance limits to n-type semiconductors
Authors: Kupka R. K. , Anderson W. A.
Published: July 2002

An exact general formula for the lower contact resistance limit is derived, giving the lowest possible ohmic contact resistance for nondegenerate and degenerate metal-semiconductor contacts. Calculations for nondegenerate semiconductors include the nonparabolic nature of the conduction-band electrons and full Fermi–Dirac statistics. A discussion of standard emission theories shows that they are not applicable in the ohmic contact limit because of ‘‘electron tail lowering’’ and the negligence of quantum-mechanical reflections due to occupied states on the opposite side of their derivation. Together with a proof that an abrupt n-n+ doping step is governed by thermionic emission, the ohmic contact resistance of a general ohmic contact is determined and it is shown that the n-n+ doping step is responsible for this limitation. Thus, the lowest possible contact resistance is determined by the bulk doping of the semiconductor for a large variety of different alloyed and nonalloyed contact structures and not by the surface doping concentration. The theory predicts a lowest possible contact resistance in the 1 × 10−8 Ω cm2 region for parabolic III-V semiconductors and of about 3 × 10−9 Ω cm2 for Si and Ge.
The variation of permeability with ferrite tile density
Authors: Hahn H. T.
Published: July 2002

The effectiveness of ferrites as specular radar absorbers may be related to the volumetric concentration of ferrite in the absorber. This relationship is indicated when the performances of ferrite composites are compared, and when the composites are compared with ferrite tiles. The density of a ferrite tile is dependent on both composition and the conditions of preparation. A series of samples with the composition Ni0.5Zn0.5Fe2O4 was prepared by seven different methods to yield ferrites with densities varying from 3.82 to 5.33 g/cm3. Micrographs are presented to illustrate the structural dissimilarities. The highest density was produced by hot isostatic pressing, a procedure that produced two regions of differing grain size. There was relatively little grain growth in the exterior region, but grains in the interior nearly doubled in size. The greatest effects of density on permeability were noted in the 100–200-MHz region. There, the real part of permeability (μ′) increased with density up to 5.1 g/cm3. The imaginary part (μ″) also increased with ferrite density. Since the microstructure greatly influences the magnetic loss, and the many processes used resulted in greatly varying microstructural differences, the increase of both μ′ and μ″ with density was conclusive. The presence of linewidth broadening as a result of energy absorption by various spin-wave modes was confirmed.
Pressure strengthening: A possible route to obtaining 9 Mbar and metallic diamonds
Authors: Ruoff Arthur L. , Luo Huan
Published: July 2002

With recent results by Ruoff et al. [Rev. Sci. Instrum. 61, 3830 (1990)] demonstrating pressures of 4.16 Mbar, greater than that at the center of the earth (3.61 Mbar), we thought it useful to approximately analyze the stresses in the diamond anvil, which we have done for two different stress distributions. We show that the yield strengths of perfect crystalline diamonds at the point where the shear stress in the diamond is a maximum is greatly enhanced by the presence of a large hydrostatic component of compressive stress, with the result that the onset of yielding occurs not at 3.2 Mbar (as it would if this effect were absent) but at 9.6 Mbar (pressure strengthening). The upper bound on the pressure which can ultimately be reached with diamond anvils will be determined by band overlap metallization, which is estimated by two methods to occur in the neighborhood of a sample pressure of 8–9 Mbar. Enormous tetragonal distortions (c/a≊0.75) are present in the diamond anvils when the pressure is 3.35 Mbar.
Time-resolved reflectivity as a probe of the dynamics of laser ablation of organic polymers
Authors: Paraskevopoulos George , Singleton Donald L. , Irwin Robert S. , Taylor Rod S.
Published: July 2002

The interaction of KrF excimer laser pulses with polyimide, poly(ethylene terephthalate), polystyrene, poly(methyl methacrylate), and polyethylene has been studied by time-resolved reflectivity. The width, fluence, and peak intensity of a KrF (248 nm) laser pulse reflected from the polymer surface was determined over a large range of incident laser fluences, 1–3000 mJ/cm2. The reflected pulse was truncated once the incident fluence exceeded a critical value (threshold), characteristic for each polymer. Above the threshold the pulse decayed exponentially with time constants ranging from 2 to 6 ns. For polyethylene, such a critical value appears to lie above the highest fluence available in the present experiments. The threshold fluences for pulse truncation are usually somewhat lower than the ablation thresholds measured photoacoustically. The mechanism of the process is discussed in terms of time-dependent absorption and scattering from particles emerging from the surface during ablation. Approximate calculations for ablation under our experimental conditions (ns wide excimer pulses) suggest that large particles are ejected initially which are continuously reduced in size during the laser pulse.
Autoresonance microwave accelerator
Authors: Shpitalnik R. , Cohen C. , Dothan F. , Friedland L.
Published: July 2002

A novel autoresonance acceleration scheme comprising a traveling electromagnetic wave and a magnetostatic field is discussed. A spatially tailored magnetostatic field keeps the electron in a constant phase and allows continuous acceleration. Numerical results are presented. Experimental results, showing acceleration from an initial value of 10 keV to energies of about 150 keV after 1.5 m by using a pulsed 50-kW peak power transmitter, are presented.
On the origin of spatial nonuniformities in the composition of pulsed-laser-deposited films
Authors: Saenger K. L.
Published: July 2002

A model is proposed for the origin of spatial nonuniformities in the composition of pulsed laser-deposited films derived from multicomponent targets. It is based on the idea that the forward peaking of each species in the plume depends on the species mass via the ratio of two mass-dependent velocities: the flow velocity, which characterizes the directed forward motion, and the mean random thermal velocity, which characterizes lateral motion. The on-axis enrichment of light-mass species observed in films deposited at moderate laser fluences (e.g., Cu in depositions of YBa2Cu3O7) is attributed to the dual effects of a mass-dependent collision rate and collision effectiveness. In weak expansions, these effects leave the lower mass species with a lower temperature, a higher flow velocity, and a relatively more forward-peaked distribution than their high-mass counterparts. The improved compositional uniformity observed for depositions at higher laser fluences is attributed to an incomplete transition to a stronger expansion regime in which all the species in the plume have the same flow velocity. In this regime, the high-mass species are relatively more forward peaked due to their lower mean thermal velocity which scales as (mass)−1/2.
Dynamics of laser sputtering at GaN, GaP, and GaAs surfaces
Authors: Namiki A. , Katoh K. , Yamashita Y. , Matsumoto Y. , Amano H. , Akasaki I.
Published: July 2002

Laser sputtering of GaAs, GaP, and GaN has been studied by measuring angle-resolved time-of-flight (TOF) distributions of emitted neutral particles. The observed mean translational energy and sputtering yield were found to show strong forward peaking depending on the laser power densities, thence on the desorption yield. This fact can be explained in terms of postdesorption collisions among desorbed particles as predicted theoretically [I. NoorBatcha, R. R. Lucchese, and Y. Zeiri, J. Chem. Phys. 86, 5816 (1987); 898, 5251 (1988), and Kelly and R. W. Dreyfus, Surf Sci. 198, 263 (1988); Nucl. Instr. Methods B 32, 341 (1988); J. Chem. Phys. 92, 5048 (1990)]. However, the observed velocity distributions of sputtered particles were found to be in contradiction with the so-called shifted Maxwellian, because the best-fitted center of mass velocities for Ga were always found to be negative. In addition, Kelly’s Mach number M, estimated from the energy spectra, was found to be significantly larger than those estimated from the yield spectra. It is suggested that energy transfer from the internal states of diatomic molecules to the translational motion of Ga may play an important role in the final TOF spectra.
Effect of crystallites on surface potential variations of Au and graphite
Authors: Camp J. B. , Darling T. W. , Brown Ronald E.
Published: July 2002

Surfaces made of the nonreactive materials Au and graphite exhibit low surface potential variations after a low-temperature ultrahigh vacuum bake. The variations (due to the finite size crystallites of these materials) may be reduced to a minimum by using Au surfaces of grain size less than 10 nm and graphite surfaces with highly aligned c-axis orientation. Procedures where this may be accomplished are described. Application to the Los Alamos antiproton gravity experiment is presented.
Pyrolysis and laser ablation of plasma-polymerized fluorocarbon films: Effects of gold particles
Authors: Creasy William R. , Zimmerman Jeffrey A. , Jacob Wolfgang , Kay Eric
Published: July 2002

Plasma-polymerized fluorocarbon (PPFC) films were analyzed by thermogravimetric analysis (TGA), direct pyrolysis/mass spectrometry, and laser-ablation/electron-impact mass spectrometry. Fourier transform mass spectrometry was used to detect products. The films were made by plasma polymerizing tetrafluoroethylene in an argon plasma. Two types of films were studied: with and without fine gold particles incorporated in the PPFC films. TGA showed that gold-containing films decompose more rapidly and at lower temperature with increasing gold content. Pyrolysis products were determined as a function of temperature. The predominant positive product ions, using 20 eV electron-impact ionization, were C2F4+, CF3+ and a distribution of higher-mass unsaturated fluorocarbon species, CnFm+, up to at least n=14 and m≥n+1. The predominant negative ions, formed by electron attachment, were also unsaturated fluorocarbon ions which extended up to 1145 u in mass. These species are different from those observed from polytetrafluoroethylene pyrolysis. No dependence of the positive-ion mass spectral distributions of pyrolysis products on gold content of the films was observed. However, the negative-ion pyrograms had a dramatically different temperature dependence for films with and without gold. The results imply that the gold-containing films have regions of lower molecular weight, and a possible formation mechanism is suggested. Laser ablation formed low-mass neutral fluorocarbon species. Ablation of the gold-containing film under direct laser ionization conditions (higher laser power), produced a spectrum resembling the pyrolysis spectrum, suggesting that the gold particles affect the mechanism of the ablation.
Electrodeposition of thin yttria-stabilized zirconia layers using glow-discharge plasma
Authors: Ogumi Zempachi , Uchimoto Yoshiharu , Tsuji Yoichiro , Takehara Zen-ichiro
Published: July 2002

A novel process for preparation of thin yttria-stabilized zirconia (YSZ) layers was developed. This process differs from other vapor-phase deposition methods in that a dc bias circuit, separate from the plasma-generation circuit, is used for the electrodeposition process. The YSZ layer was electrodeposited from ZrCl4 and YCl3 on a nonporous calcia-stabilized zirconia substrate. Scanning electron microscopy, electron probe microanalysis, electron spectroscopy for chemical analysis, and x-ray-diffraction measurements confirmed the electrodeposition of a smooth, pinhole-free yttria-stabilized zirconia film of about 3 μm thickness.
Control of repetitive electrical discharges by means of an external electrode
Authors: Curzon F. L. , Cobb R. W. , Mikoshiba S.
Published: July 2002

It is shown that the amplitude of flattopped pulses needed to maintain repetitive interelectrode discharges in a discharge tube can be reduced by applying a similarly shaped voltage pulse of opposite polarity to an external metal sheet coplanar with the cathode of the discharge tube. An explanation of the effect, based on the relative timing and amplitude of the various voltage pulses applied to the discharge system, is advanced. It is also shown how the effect may be of significance in controlling gas discharge display panels.
Synthesis of YBa2Cu3O7−δ films from separate oxide targets
Authors: Hussey B. W. , Gupta A.
Published: July 2002

Synthesis of YBa2Cu3O7−δ (YBCO) has been achieved using laser ablation of separate oxide targets YBa2Ox and CuO, as well as Y2Cu2O5 and BaCuO2. Results obtained using two synchronized lasers to ablate from the two targets show that high quality epitaxial YBCO films can be obtained independent of the laser pulse delay settings. The facile formation of the YBCO phase, irrespective of the nature of the reacting precursors, points to its high thermodynamic stability under conditions used for in situ growth of films.
Multiparameter measurements of thin films using beam-profile reflectometry
Authors: Fanton J. T. , Opsal Jon , Willenborg D. L. , Kelso S. M. , Rosencwaig Allan
Published: July 2002

Beam-profile reflectometry is a new technique for measuring the thickness and optical constants of dielectric, semiconducting, and thin metal films. The technique consists of measuring the intensity profile of a highly focused beam reflected from the sample. By using a linearly polarized light source and a tightly focussed beam, the S- and P-polarization reflectivities of the film are simultaneously obtained over a wide range of angles. The focusing also provides a submicrometer spot, thus allowing these measurements to be performed in very small geometries. How the information present in the reflectivity profiles can reveal information about as many as three unknown film parameters simultaneously is described, and results from film samples for which the multiparameter fitting capability was essential to the success of the measurement are also presented.
Magnetism and transport properties of evaporated Co/Ag multilayers
Authors: Araki Satoru
Published: July 2002

We report the magnetic and transport properties of Co/Ag multilayers grown by electron-beam evaporation in an ultrahigh vacuum. The oscillation of the interlayer exchange energy is confirmed for a Co layer thickness of 6 Å with a period of 16 Å. It is shown that the Co spins are aligned antiferromagnetically for only several monolayers of Co. The magnetoresistance (MR) ratio is 20% at room temperature and 41% at 77 K for [Co(6Å)-Ag(25Å)]×40. The electron mean free path estimated by the free electron model is shortened from the ferromagnetic state to antiferromagnetic one. We confirm that enhanced MR properties could be achieved by realizing a single crystal structure.
Heat transfer in a microelectronics plasma reactor
Authors: Daviet J.-F. , Peccoud L. , Mondon F.
Published: July 2002

Plasma etching has became an indispensible technique for microelectronics device manufacturing. However, its application is often limited by the wafer temperature increase due to the ion bombardment, which may exceed the susceptor temperature by as much as 200 °C when the semiconductor wafer is loosely lying on the cooled susceptor. The aim of this study is to perform an accurate evaluation of heat transfer in an industrial etching reactor, and in particular to point out the critical role of the susceptor/substrate interface in this problem of damageable overheating. The required experimental precision, necessary to reach this goal, is based on in situ temperature monitoring via fluoroptometry, and on electrical characterization of the plasma to investigate the effective heating power dissipated on the substrate. It is thus shown that the only wafer heating source to be considered is the real electrical rf power dissipated in the plasma, and that the heated substrate evacuates the main part of this power to the cooled susceptor, via thermal conduction through the residual gas present in the interface between these two elements. A non-negligible part of energy can also be lost via thermal radiation. The thermal conduction through the interface is shown to be strongly dependent on the gas pressure, and the quasilinear rate obtained is evidence for the molecular regime of the gas molecules in this region. The type of gas also strongly affects the interface heat flow, and in a quite uncommon way: an effect of thermal conductance inversion between two different types of gases when the pressure decreases is observed. A criterion is proposed to evaluate a priori and in a qualitative point of view whether a given couple of gases may exhibit this effect, which consequences are very important from a technological point of view.
Electron spin resonance of copper vacancy in CuAlS2
Authors: Aksenov Igor , Nishikawa Nobuyuki , Sato Katsuaki
Published: July 2002

Optically excited electron spin resonance (ESR) spectra of CuAlS2 single crystals, grown by the chemical vapor transport technique, have been studied at 110–300 K. An isotropic photosensitive ESR signal, consisting of one line at g=2.019, has been observed. This signal has been attributed to a hole trapped on a copper vacancy with the activation energy, found from the thermal quenching of the ESR signal, being equal to 0.19 eV.
Investigation of the ablated flux characteristics during pulsed laser ablation deposition of multicomponent oxides
Authors: Lichtenwalner D. J. , Auciello O. , Dat R. , Kingon A. I.
Published: July 2002

The ablated flux characteristics of PbZr0.52Ti0.48O3 (PZT), La0.5Sr0.5CoO3 (LSC), and MgO ceramic targets have been studied as functions of the ablation time, the ablation energy, and the chamber gas pressure. The time dependence of the ablation rate shows an initial exponential decay, reaching a steady-state value at longer times. The energy dependence of the ablation rate (in vacuum) reveals a distinct ablation threshold energy for MgO ablation, while for PZT and LSC no ablation threshold is evident. The differences in the ablation characteristics of these materials are explained mainly by differences in their melting points, thermal conductivities, and absorption coefficients. Upon adding O2 gas, a visual change in the color and shape of the PZT ablation plume is evident. The color change indicates a gas phase reaction of the ablated species with the O2 gas, while the shape change implies a change in the angular distribution of the ablated species. We have measured a narrowing of the ablated flux distribution from a PZT target as O2 is added, from a cos40 θ distribution in a low pressure, up to a cos260 θ distribution in an O2 pressure of 300 mTorr. This narrowing, or focusing, of the ablation plume is observed with high laser energies and high pressures of O2 or noble gases. At low laser power, the deposition rate decreases and the plume broadens as the gas pressure is increased. The plume narrowing and plume broadening regimes are both controlled by gas scattering effects. The angular distribution of depositing species, and the ratio of deposition flux to O2 flux, are very different in each of these regimes.
Electrical conductivity of tellurium deficient cadmium telluride
Authors: Shamsuddin M. , Nasar A. , Tare V. B.
Published: July 2002

The electrical conductivity of polycrystalline cadmium telluride having an impurity content of less than 200 ppm was measured in the temperature range of 675–975 K and in the ambient tellurium pressure varying from 1.0×10−15 atm to 2.0×10−5 atm. The electrical conductivity of polycrystalline CdTe doped with monovalent as well as trivalent cations has also been determined under similar conditions. The conductivity was found to change from predominantly p to predominantly n type at a critical tellurium pressure depending upon the temperature. The electrical conductivity increased with the increase in ambient tellurium pressures reached a maximum, and then decreased with further increase in tellurium pressure. The results have been used to discuss the probable defect structure of CdTe particularly with reference to the variation in ambient tellurium pressure.
Combined electronic-nuclear magnetic ordering of the Ho3+ ions and magnetic stacking faults in HoBa2Cu3Ox (x=7.0,6.8,6.3)
Authors: Roessli B. , Fischer P. , Staub U. , Zolliker M. , Furrer A.
Published: July 2002

Magnetic ordering of HoBa2Cu3Ox (x=7.0,6.8,6.3) was investigated by means of neutron diffraction. Long-range antiferromagnetism is found for x=7.0 below TN=190 mK and for x=6.8 below TN=100 mK corresponding to propagation vector K=[0,1/2,1/2] with magnetic moment directions parallel to the a axis. The observed temperature dependence of the magnetic order parameter is in excellent agreement with mean-field calculations taking into account crystal field, exchange, and hyperfine interactions. No magnetic superlattice reflections were detected for x=6.3. A highly unusual ordering behavior is observed in HoBa2Cu3Ox (x=7.0,6.8) where the three-dimensional magnetic ordering is imperfect, due to finite correlation length ξc=29 and 129 Å, respectively, along the c axis.
Correlation between structural, optical, and electrical properties of GaAs grown on (001) Si
Authors: Alberts V. , Neethling J. H. , Leitch A. W.
Published: July 2002

In this study transmission electron microscopy (TEM), photoluminescence spectroscopy (PL), and electrochemical capacitance-voltage measurements were used to characterize undoped GaAs films, grown by organometallic vapor phase epitaxy on (001) Si substrates. TEM studies indicated that the high defect density (threading dislocations and microtwins), present close to the interfacial region, drops rapidly with distance away from the interface. PL studies also indicated an increase in PL intensity and significant narrowing of the full-width at half-maximum of the excitonic transition with an increase in layer thickness, indicating an improvement in the optical quality of the epilayers. Electrochemical capacitance-voltage measurements indicated a uniform carrier concentration (low to mid 1015 cm−3 range), which is among the lowest yet to be reported for GaAs/Si grown by organometallic vapor phase epitaxy.
Two-dimensional magnetic order in Pb2Sr2TbCu3O8
Authors: Wu S. Y. , Hsieh W. T. , Li W-H. , Lee K. C. , Lynn J. W. , Yang H. D.
Published: July 2002

Neutron diffraction techniques have been used to investigate the magnetic ordering of the Tb ions in polycrystalline Pb2Sr2TbCu3O8. Significant magnetic correlations are found to develop below ∼10 K, and these correlations are two dimensional in nature, representative of the strongly anisotropic magnetic interactions in these layered materials. The correlation length increases with decreasing temperature, and long-range order is observed to develop at TN≊5.5 K. However, the sawtooth Bragg profile for the scattering demonstrates that the long-range order is two dimensional, rather than three dimensional, with a spin configuration where nearest-neighbor spins are antiparallel. The scattering profile can be explained quantitatively by assuming long-range order within the ab plane, with no significant correlations along the c axis to the lowest temperatures measured (1.36 K). Our results suggest that the system is well described by a two-dimensional Ising model. The only other (pure) system where a crossover to three-dimensional behavior is not observed is DyBa2Cu4O8.
Carrier transport in polycrystalline silicon films deposited by a layer-by-layer technique
Authors: He Deyan , Okada Naoto , Fortmann Charles M. , Shimizu Isamu
Published: July 2002

The transport processes in phosphorus-doped polycrystalline silicon thin films are examined by standard six-electrode Hall effect and conductivity measurements over a wide temperature range, 100–400 K. These films were deposited by a novel layer-by-layer technique at very low substrate temperatures (300–360 °C) using fluorinated precursors, SiFmHn (m+n≤3). The analysis indicated that the grain boundaries are the major barriers to carrier transport. The grain boundary carrier transport is controlled by thermionic emission at high temperatures, whereas at low temperatures, it is dominated by a tunneling process through the barriers. The electrical properties of these films were found to vary as a function of the film thickness. It appears that the grain boundary defects are passivated to a large degree by this novel deposition technique and that the grain boundary barriers are consequently smaller than those in films prepared by other growth schemes.
Selective incorporation of dye molecules on poly(methyl methacrylate) surface fabricated by laser irradiation
Authors: Uchida Tatsuya , Shimo Nobuo , Sugimura Hiroyuki , Masuhara Hiroshi
Published: July 2002

Dye molecules were selectively incorporated on the laser fabricated surface of poly(methyl methacrylate) by soaking the irradiated sample in an aqueous solution of dye molecules. The selectivity depended on the laser fluence. Dye molecules were observed only on the area irradiated at a laser fluence of 40 mJ cm−2 pulse−1, while at 570 mJ cm−2 pulse−1, dye molecules were not introduced on the ablated surface but were observed on the nonirradiated part hidden with a mesh mask. The spatial resolution of the simultaneous fabrication and chemical modification was a few micrometers. Multistep incorporation of dye molecules was also demonstrated. A metastable molecular species of a propagating radical was detected in the irradiated sample by ESR. X-ray photoelectron spectroscopy of the surface fabricated at 40 mJ cm−2 pulse−1 revealed the existence of oxygen-containing components. Contact angle measurements showed that the surface fabricated at low laser fluence was more hydrophilic than that at high fluence. Morphological changes of the surface were also considered to be responsible for the incorporation of the dye molecules. Among the various kinds of dye molecules, only the cationic molecules were incorporated, probably because of the interaction with polar chemical species on the fabricated surface. On the basis of these results, the incorporation mechanism was discussed.
Structure and composition of interfacial silicon oxide layer in chemical vapor deposited Y2O3-SiO2 bilayer dielectrics for metal-insulator-semiconductor devices
Authors: Sharma R. N. , Rastogi A. C.
Published: July 2002

A silicon oxide layer is formed at the interface of low pressure chemical vapor deposited Y2O3 film on Si after an annealing in O2 at 580 °C for 45 min. It shows a graded composition varying from SiO2 to SiOx (x∼1) which depends on the thickness of Y2O3 film as revealed by infrared and Auger electron spectroscopic studies. With 52-nm-thick Y2O3 film, a more ordered coesite-like (c-) SiO2 forms at the interface whose structure changes gradually to an amorphous (a-) SiO2, SiO2−x near the Si interface. With thicker Y2O3 film (∼110 nm) the formation of a-SiO2 is characterized by SiO4 linkage having short range order with larger size rings. The composition of silicon oxide changes gradually to SiOx with 1<x<2 near the Si interface. In thinner Y2O3 film (∼30 nm), in addition to c-SiO2 and a-SiO2, quasi-SiO2 with unlinked SiO4 tetrahedra are also observed. The interfacial growth of silicon oxide is due to the oxidation of Si by quasi atomic oxygen which migrates from its entrapped position in the Y2O3 film towards the Si-silicon oxide interface. This silicon oxide shows high intrinsic positive charges ∼4×1012 cm−2 and large density ∼1.0×1012 cm−2 eV−1 of interface states in comparison to thermally grown SiO2 on bare Si. According to this investigation, to use Y2O3/SiO2 bilayer dielectric as a metal-insulator-semiconductor capacitor in high density memory storage devices, the structure and composition optimization of SiO2 layer is very important.
Epitaxial growth of RbTiOPO4 films on KTiOPO4 substrates by excimer laser ablation technique
Authors: Liu Z. G. , Liu J. M. , Ming N. B. , Wang J. Y. , Liu Y. G. , Jiang M. H.
Published: July 2002

Transparent single-phase rubidium titanyl phosphate (RTP) films having excellent crystalline properties have been deposited by excimer laser ablation method on (001)- and (010)-oriented potassium titanyl phosphate (KTP) substrates, respectively. X-ray θ-2θ scans and pole figures showed that the laser-ablated RTP films grew epitaxially on, and had exactly the same orientations of, the underlying KTP substrates. X-ray photoelectron spectroscopy analysis revealed that the RTP films prepared with this method are nearly stoichiometric. It appears to be possible to use these films as waveguides having sharp waveguide/substrate interfaces.
Susceptibility of ErBa2Cu3O6 single crystal: A dipolar antiferromagnet
Authors: Abulafia Y. , Barak J. , Peng J. L.
Published: July 2002

The susceptibility of an ErBa2Cu3O6 single crystal was measured at 2 K<T<100 K. The low-temperature (T<10 K) data yield g∥=5.39 and g⊥=7.45. The shapes of the susceptibility curves are well explained by the dipolar fields, calculated for the Er3+ ions in the layered structure of the sample, and by a small contribution of exchange fields. Extending the calculations to the antiferromagnetic state of ErBa2Cu3O6 shows that this material is well described as a two-dimensional dipolar antiferromagnet. The dipolar field calculations are also applied to DyBa2Cu3O6 and GdBa2Cu3O6 and are shown to be compatible with the magnetic structure of these materials.
Magneto-optical properties of Ba-ferrite particulate media
Authors: Kishimoto M. , Sakurai Y. , Ajima T.
Published: July 2002

Magneto-optical properties of Ba-ferrite particulate media were investigated. Faraday rotation and reflectivity were measured for different thicknesses of the magnetic layer, and compared with the predictions of a simple analytical model. The magneto-optical output of the media measured using a laser showed a maximum at a particular thickness. The dependence of the magneto-optical output on thickness is explained on the basis of equations approximating the Faraday rotation and the reflectivity.
Interface alloying and magnetic properties of Fe/Rh multilayers
Authors: Hanisch K. , Keune W. , Brand R. A. , Binek C. , Kleemann W.
Published: July 2002

Rh(20 Å)/57Fe(tFe) multilayers with Fe thicknesses tFe of 2, 5, 10, and 15 Å prepared by alternate evaporation in UHV have been investigated by x-ray diffraction (XRD), Mössbauer spectroscopy, and SQUID magnetometry. First- and second-order superstructure Bragg peaks (but no higher-order peaks) in small-angle XRD patterns suggest some compositional modulation. Mössbauer spectra taken at 4.2 K are characterized by a distribution P(Bhf) of hyperfine fields Bhf. Peaks observed in the P(Bhf) curves near 17 and 35 T are assigned to an fcc-R_h_Fe interface alloy (∼7–24 at. % Fe) with spin-glasslike properties and to a disordered ferromagnetic bcc-F_e_Rh alloy (∼96 at. % Fe), respectively. The magnetic transition temperature of the fcc alloy was found to be 23 and 45 K for tFe=2 and 5 Å, respectively, and Bhf follows a T3/2 law. For tFe=2 Å, spin-glasslike behavior was observed by magnetometry.
Giant magnetoresistance peaks in CoNiCu/Cu multilayers grown by electrodeposition
Authors: Hua S. Z. , Lashmore D. S. , Salamanca-Riba L. , Schwarzacher W. , Swartzenruber L. J. , McMichael R. D. , Bennett L. H. , Hart R.
Published: July 2002

Giant magnetoresistance (GMR) of CoNiCu/Cu multilayers grown by electrodeposition was measured as a function of the copper layer thickness and effects of the order of 14% were obtained. The copper layer thickness ranged from 0.7 to 3.5 nm. Two peaks in the magnetoresistance were observed. One was centered at a copper thickness of ∼1.0 nm and the second was centered at ∼2.3 nm. Comparison of the field dependence of the magnetoresistance with the field dependence of the magnetization, as determined by vibrating-sample magnetometer, suggests that the saturation field for GMR and the magnetization are similar for the larger copper thicknesses, but are strikingly different near 1.0 nm copper thickness. This observation suggests that the GMR is affected by different factors depending on the thickness of the copper layer.
Frequency dependence of hysteresis curves in conducting magnetic materials
Authors: Jiles D. C.
Published: July 2002

An extension of the hysteresis model has been developed that takes into account the effects on the hysteresis curves of eddy currents in electrically conducting media. In the derivation presented it is assumed that the frequency of the applied field is low enough (or the thickness of the material medium small enough) that the skin effect can be ignored so that the magnetic field penetrates uniformly throughout the material. In this case, the dc hysteresis equation is extended by the addition of a classical eddy-current-loss term depending on (i) the rate of change of magnetization with time, (ii) the resistivity of the material, and (iii) the shape of the specimen; and on an anomalous (or excess) eddy-current-loss term which depends on (dB/dt)3/2. In the limit, as the frequency of the magnetic field tends to zero, the frequency-dependent hysteresis curve approaches the dc curve.