bluuebunny/crossref_metadata_2025 huggingface dataset:
A high power, tunable, arc-lamp pumped Nd-doped lanthanum-hexaluminate laser
Authors: Tin Padetha , Schearer L. D.
Published: July 2002

An LNA (Nd-doped lanthanum-hexaluminate) crystal has been pumped with a cw, krypton arc lamp in a commercial Nd:YAG cavity. The cw output power greater than 6 W is obtained in a 28-cm long, plane mirror cavity. The free-running wavelength is near 1083 nm and has a width of about 0.8 nm. Inserting a 0.25 mm thick, uncoated solid etalon in the cavity permits the laser output to be continuously tuned from 1082 to 1084 nm by tilting the etalon. The laser bandwidth is reduced to below 0.016 nm. Over 3 W are obtained at the helium resonance transition. The maximum power output is limited by severe thermal lensing effects in the LNA crystal. The single, arc-lamp pump is operated at less than 70% of its maximum rated current; thus, substantial increases in the power output can be expected if crystal quality can be improved.
Deconvolution of Gaussian filters and antidiffusion
Authors: Konstantopoulos C. , Mittag L. , Sandri G. , Beland R.
Published: July 2002

It is known that the diffusion of a density profile is obtained by convolving a Gaussian with the given density profile. This suggests that the time reversed process (antidiffusion) can be defined by an appropriate convolution inverse. We show that this is indeed the case and we develop a general method for calculating convolution inverses.
The ambipolar diffusion length measured by the surface photovoltage technique
Authors: van den Heuvel J. C. , Geerts M. J. , Metselaar J. W.
Published: July 2002

The surface photovoltage (SPV) technique is often used to determine the diffusion length in hydrogenated amorphous silicon (a-Si:H). The use of this technique for a-Si:H is disputed because it has been shown by computer simulations that the drift component is not negligible compared to the diffusion current in SPV measurements on a-Si:H. For crystalline semiconductors the SPV technique gives the minority-carrier diffusion length while the drift current is negligible. We found from the solution of the transport equations that the SPV technique can be used in the case of a-Si:H, but gives the ambipolar diffusion length which consists of the mobility and lifetime of both holes and electrons. However, the term diffusion length is misleading since the hole drift current and the hole diffusion current are of the same order of magnitude for a-Si:H. This result is in accordance with the results of the computer simulations mentioned earlier. The drift current assists the diffusion current and increases the measured diffusion length by a factor (2)1/2 compared to the situation with diffusion current alone.
Preparation of oriented high-T
c Tl-Ca-Ba-Cu-O thin films from co-condensed amorphous Ca-Ba-Cu alloys by post-deposition oxidation and Tl diffusion
Authors: Naugle D. G. , Wang P. S. , Shao X. Y. , Hermann A. M.
Published: July 2002

Single-phase Tl2Ca1Ba2Cu2O8 thin films with zero-resistance transition temperature up to 100 K have been prepared on single-crystal MgO substrates from codeposited Ca-Ba-Cu amorphous metallic alloy precursors. After thermal oxidation of the metallic alloy film, Tl from Tl2O3 was vapor deposited and diffused into the resulting mixed metal oxide during a rapid high-temperature anneal. The films prepared in this process are highly oriented with the c axis normal to the substrate.
Boron diffusivity in nonimplanted diamond single crystals measured by impedance spectroscopy
Authors: Narducci Dario , Cuomo Jerome J.
Published: July 2002

Boron diffusivity in single-crystal diamond has been investigated. To this aim, a novel method using impedance spectroscopy for the study of the atomic diffusivity in wide-gap semiconductor has been developed, along with a model for the analysis of the dielectric response function. The advantages of this procedure are discussed. Boron diffusivity in diamond has been determined to be 6.9×10−20 cm2 s−1 at 800 °C. A discussion of the results and a comparison with previous estimates are presented.
α-radiation-induced deep levels in low-doped n-type silicon
Authors: Zafar N. , Iqbal M. Zafar
Published: July 2002

Observations on deep levels introduced in silicon by α-particle irradiation are reported. Low-doped n-type samples are used and deep level transient spectroscopy is applied to detect the deep levels. Preliminary results provide evidence for some new defect states in addition to those previously reported. The study also reveals interesting metastability and room-temperature transformation effects associated with some of the deep levels introduced.
Nonlinear effect on surface charging by diatomic ion bombardment
Authors: Inoue K.
Published: July 2002

Surface charging by ion bombardment is investigated using a quasistable charging condition in which one can evaluate the degree of charging by an intensity of secondary ions. It is found that a nonlinear effect on the charging occurred under monoatomic and diatomic ion bombardments. Namely, O+2 -ion irradiation enhances the charging in comparison with O+-ion irradiation, although atomic dose and energy/atom are kept the same in both ion bombarbments. Since the results also show that the surface charging is suppressed when the energy of incident ions is higher, the nonlinear effect by diatomic ion irradiation is attributed not to an increase of energy density, but to a dense cascade in the overlapping region of cascades caused by two constituents of the incoming diatom.
ZnSe p-n junctions produced by metalorganic molecular-beam epitaxy
Authors: Migita M. , Taike A. , Yamamoto H.
Published: July 2002

The p-n junction in nitrogen-doped p-type ZnSe/undoped n-type ZnSe on n-type GaAs (100) is successfully produced by metalorganic molecular-beam epitaxy. p-type conduction of ZnSe is achieved as a consequence of high nitrogen doping (5×1018–1×1019 cm−3). The data points of C−2 (C: capacitance) against voltage of the p-n junction are approximated by a straight line and the diffusion potential estimated from the plots is about 2.4 eV. Electron-beam-induced current also directly demonstrates the formation of a ZnSe p–n junction. Furthermore, blue emission is observed from the 5-V foward-biased ZnSe p-n junction at 77 K.
Preparation, structure, and electric properties of plasma-polymerized titanium-containing organic thin films
Authors: Kagami Yoshiharu , Yamauchi Takeshi , Osada Yoshihito , Yoshizawa Isao
Published: July 2002

Polymeric thin films were prepared from gaseous titanium tetraisopropoxide by low-temperature plasma polymerization. The films exhibited n-type semiconductor properties and showed conductivities in the range between 10−8–102 s/cm. High photocurrent under irradiation of 30 mW/cm2 of visible light was observed which exceeded the value found for plasma-polymerized copper acetylacetonate thin films by nearly three orders of magnitude. From x-ray photoelectron spectroscopy analysis, it was found that the films largely consist of metallic and organic layers corresponding to TiOx(0<x<2) and (CH2)n, respectively. Transmission electron micrograph observations and electron diffraction measurements made it possible to conclude that the film has a specific texture consisting of amorphous metal layers with an average thickness of 15–25 nm inside a polymer matrix.
A Monte Carlo study for minority-electron transport in p-GaAs
Authors: Taniyama Hideaki , Tomizawa Masaaki , Furuta Tomofumi , Yoshii Akira
Published: July 2002

Minority-electron transport in p-GaAs with a wide range of acceptor doping concentration from 1017 to 1019 cm−3 is studied in detail. Using the Monte Carlo method in which electron-hole interactions are taken into account, electron transport properties in p-GaAs, such as drift velocity and electron temperature, are calculated. The calculated results show good agreement with the experimental ones. Furthermore, in order to make the features of minority-electron transport clear, the electron transport properties in n-GaAs, where electrons act as majority carriers, are also calculated. In comparison with majority-electron transport, drift velocity, and electron temperature for the minority electron are greatly reduced. Throughout the study, it is shown that the interaction with holes is essential for minority-electron transport in p-GaAs.
Effects of nonlinear dissipation on the supercurrent decay of a Josephson junction
Authors: Silvestrini Paolo
Published: July 2002

The thermal-induced escape out of the zero-voltage state of a Josephson junction is discussed removing the main assumption of the resistively shunted junction model. This model assumes that the junction dissipation is dominated by a linear ohmic shunt resistor. However, the presence of quasiparticles excitations produces dissipation in the junction through nonlinear mechanisms. As a consequence, the dynamical resistance is strongly voltage dependent. In the present work, we study the effect of this voltage-dependent dissipation on the supercurrent decay in connection with the general problem of a Brownian particle in a metastable state in the presence of a velocity-dependent friction coefficient. An analytical expression for the lifetime of the metastable state is obtained, providing an answer to the open question of what resistance dominates the junction damping. A comparison of the theory with experimental results is also presented.
Study of Co-Cr films for perpendicular magnetic recording using nuclear magnetic resonance
Authors: Yoshida Kazuetsu , Kakibayashi Hiroshi , Yasuoka Hiroshi
Published: July 2002

A 59Co nuclear magnetic resonance measurement and a transmission electron microscope observation are utilized to investigate the compositional distribution of Co-Cr films with and without heat treatment. The spin-echo spectra of evaporated films are found to be entirely different from those of Co-Cr alloy powders. The spectra of films comprise a very complicated hyperfine field distribution and the resonant frequencies are much higher than those of powder samples, implying the existence of various kinds of segregation regions typical of a film. Chrysanthemumlike patterns, which disappear with heat treatment, are also observed for chemically etched films. This disappearance is accompanied by the disappearance of the highest-frequency resonant line.
5.5 eV optical absorption, supralinearity, and sensitization of thermoluminescence in LiF TLD-100
Authors: McKeever S. W. S.
Published: July 2002

The concept of competition-during-heating as a mechanism for TL supralinearity and sensitization in TLD-100 is re-examined. It is demonstrated that with this model it is not necessary that the competing traps be removed by radiation in order for supralinearity to be obtained. Furthermore, the arguments for and against the proposal that the precursors to the 5.5 eV centers are the required competing centers are reviewed. It is shown that those experiments which are cited as arguments against this proposal have other interpretations different from those published so far. These new interpretations are consistent with the original view that the 5.5 eV centers’ precursors are indeed competitors to the main TL process. MgOH centers are also likely competitors in samples with substantial OH contents.
Computer simulation of actual and Kelvin-probe-measured potential profiles: Application to amorphous films
Authors: Arch J. K. , Fonash S. J.
Published: July 2002

We have employed a first-principles computer program to simulate actual potential profiles and potential profiles obtained experimentally from the Kelvin probe technique. Our results show that the Kelvin probe technique can be used as an in situ method for qualitatively characterizing amorphous films and structures during deposition. However, without additional information about the density and energy distribution of localized states in the bulk and at the free surface, we find that it is difficult to obtain, from the Kelvin probe measurement alone, an accurate quantitative measure of the actual spatial dependence of band bending in films and device structures. In addition, this computer analysis shows that interpretation of the profiles obtained from the Kelvin probe contact potential method can lead to misleading conclusions about the density of states in these amorphous materials. We also show that the barrier height of Schottky contacts or the built-in potential of junctions of differently doped layers can be obtained directly from Kelvin probe contact potential measurements only for films whose free-surface band bending is known from other experimental data. We see that this surface band bending can be significant even for small free-surface-state densities and is more pronounced in higher-quality films.
Investigation of the nonlinear behavior of a partially ionized, turbulent plasma in a magnetic field
Authors: Stafford Scott A. , Kot Mark , Roth J. Reece
Published: July 2002

In this paper, a number of the methods of nonlinear dynamics are applied to the study of electrostatic turbulence in a magnetized, steady-state, partially ionized plasma. Electrostatic potential fluctuations were obtained by using a capacitative probe. These signals were captured, digitized, and recorded with a LeCroy transient recorder system interfaced to an IBM-AT personal computer. A commercially available software program was used to calculate power spectra, to reconstruct and plot phase portraits, take Poincaré sections, compute correlation dimensions and Lyapunov exponents, and to perform other manipulations of the time series of electrostatic potential fluctuations obtained from the plasma. Evidence of low-dimensional chaos was sought, and trends were investigated which related the state of the turbulence to such plasma parameters as the anode voltage (rms electrostatic potential), background gas pressure (collisionality), and magnetic induction. These variables were found to have a significant effect on the nonlinear dynamics of the plasma.
Narrow Bloch walls and intrinsic characteristics of the pseudoternary Nd14Fe78−xMnxC8 systems
Authors: Xing F. , Ho W. W.
Published: July 2002

The lattice constants of Nd14Fe78−xMnxC8 compounds decrease with the increase of Mn context x and have a minimum at about x=14. The Curie temperature Tc decreases linearly and falls off below room temperature beyond x=14. The strong reduction of the saturation magnetization and Tc are attributed to the antiparallel alignment of the Mn and Fe atoms moments. The behavior of magnetization and magnetization reversal in the high-Mn-containing samples at low temperature can be interpreted by the narrow domain wall effect. The relationship of the intrinsic coercive force i Hc on temperature agrees well with the exponential formula of the narrow Bloch wall.
On the interactions of dislocation with planar free surfaces
Authors: Louat N. P. , Sadananda K.
Published: July 2002

Fourier synthesis is employed to obtain solutions to the coupled singular integrations which, according to the method of dislocation continua, represent equilibrium. The cases of screw and edge dislocations totally contained within parallel planar surfaces are considered first. An initial extension of the method to problems in three dimensions is then made and exemplified by the treatment of an edge dislocation which lies normal to a free surface.
Determination of proximity effect parameters in electron-beam lithography
Authors: Misaka Akio , Harafuji Kenji , Nomura Noboru
Published: July 2002

A new empirical method for determining proximity parameters in electron-beam lithography is introduced on the assumption that the proximity function is composed of two Gaussians. This method is based on the clearance of resist after development in the nonexposed square region surrounded by the latticed exposed one. Since there are many identical patterns arranged two dimensionally, statistically averaged data of proximity parameters is obtained without undertaking scanning electron microscopy for linewidth measurements. Theoretical considerations are combined with the experimental observations in order to calculate proximity parameters by the use of the design pattern.
Texture analysis of smooth i
n s
i
t
u laser ablated YBa2Cu3O7 thin films on (100) SrTiO3
Authors: Cillessen J. F. M. , de Leeuw D. M. , Kinneging A. J. , Zalm P. C. , Bongers P. F.
Published: July 2002

The texture of YBa2Cu3O7 thin films on (100) SrTiO3, grown by in situ laser ablation, was investigated by x-ray diffraction. The surface morphology is smooth with only 105 cm−2 particulates of about 0.1 μm in diameter. High-resolution x-ray diffraction shows that the c-axis of YBa2Cu3O7 is epitaxially aligned with the [001] direction of SrTiO3 irrespective of the misorientation. The {018} pole figure of YBa2Cu3O7 shows a fourfold symmetry which indicates that the films are ordered with respect to the substrate lattice. Moreover, the alignment in the {018} pole figure of the (220) reflections of SrTiO3 and the (018) reflections of YBa2Cu3O7 indicates that over the whole surface of the film the a- and b-axes of YBa2Cu3O7 are aligned along the [100] and [010] direction of SrTiO3. The epitaxial nature of the films, the low density of particulates, and the lack of interdiffusion as concluded from secondary ion mass spectrometry measurements, allows for the preparation of heteroepitaxial stacks containing high-Tc superconductors.
Mechanism of rapid thermal nitridation of thin oxides
Authors: Shih D. K. , Joshi A. B. , Kwong D. L.
Published: July 2002

The nitrogen/oxygen replacement reaction which occurs during rapid thermal nitridation (RTN) of oxides has been investigated by Auger electron spectroscopy and Fourier transform infrared spectroscopy techniques. Results have indicated that out-diffusion rate of nitridation by-products is responsible for the observed nitrogen profile in RTN oxides. Based on the results, an attempt has been made to describe the mechanism of the nitridation reaction. The proposed mechanism considers the diffusion of NHx species and nitridation by-products along with the structural modifications in SiO2 during RTN. Electrical measurements on metal-oxide-semiconductor capacitors were used to further support the proposed mechanism for the nitridation process.
Experimental study of optical waveguides with absorption induced by metallic electrodes
Authors: Djanta G. N. , Coutaz J. L.
Published: July 2002

We have experimentally studied the influence of metallic slabs deposited in the vicinity of an optical waveguide on its guided propagation properties. The observed induced optical absorption is well described by the theory of the azimuthal effective-index method recently proposed by Marcatili and Hardy [IEEE J. Quantum Electron. QE-24, 766 (1988)].
Boron ion implantation in p-type Hg0.8Cd0.2Te
Authors: Kumar R. , Dutt M. B. , Nath R. , Chander R. , Gupta S. C.
Published: July 2002

Differential Hall measurements at 77 K were done on 150-keV boron implanted p-type mercury-cadmium-telluride (HgCdTe). n+ layers formed as a result of implantation with various doses were very sharp and thicknesses of the n+ layers were found to depend on boron dose. The sheet carrier concentration tends to saturate above the dose 1×1013 cm−2.
A model for a continuous-wave iodine laser
Authors: Hwang In Heon , Tabibi Bagher M.
Published: July 2002

A model for a continuous-wave (CW) iodine laser has been developed and compared with the experimental results obtained from a solar-simulator-pumped CW iodine laser. The agreement between the calculated laser power output and the experimental results is generally good for various laser parameters even when the model includes only prominent rate coefficients. The flow velocity dependence of the output power shows that the CW iodine laser cannot be achieved with a flow velocity below 1 m/s for the present solar-simulator-pumped CW iodine laser system.
Poisoning studies of an osmium-coated dispenser cathode
Authors: Nexsen W. E. , Turner W. C.
Published: July 2002

The results of our studies on the reduction of the emission current from an osmium-alloy-coated dispenser cathode (derivative of the M cathode) due to exposure to various gases or vapors are reported. The primary interest of these studies is poisoning by chemical agents that might be encountered in the vacuum system of an induction linear accelerator. Of the constituents normally found in a tight unbaked vacuum chamber, the cathode is most sensitive to partial pressures of water vapor. Of the vapors studied which might be encountered in an induction accelerator, Freon was the most virulent poison.
Polarization currents in varistors
Authors: Modine F. A. , Major R. W. , Choi S. I. , Bergman L. B. , Silver M. N.
Published: July 2002

The time, voltage, and temperature dependencies of transient polarization currents are reported for two types of varistors (i.e., ZnO and a SiC composite). The current transients exhibit a power-law time response to a step change in voltage (i.e., I≊I0/tm, where m is slightly less than unity) that persists over a time scale exceeding 10−8–104 s. The polarization current increases linearly with low applied voltage, but at more than a linear rate for higher voltage. The temperature dependence of the polarization current in medium voltage ZnO varistors is described by an Arrhenius plot with a change of slope near 200 K, which suggests thermal activation energies of about 160 and 10 meV. The time dependence of the polarization currents is confirmed and extended to short times by the ac admittance measured as a function of frequency. Transient changes in the ac admittance accompany the transient polarization currents, and exhibit time and temperature dependencies that reveal their close relationship to the polarization currents. By comparing transient admittance data to predictions of the Mott–Schottky theory of a barrier, it is concluded that the theory gives an inadequate account of the ac conductance, even though the voltage dependence of the capacitance is predicted well. Theoretical explanations of the polarization currents that are based upon a distribution of exponential relaxation times are examined. A reasonable account of the polarization current is provided, but the origin of the distribution is uncertain. Possible origins are a distribution of thermal activation energies or electron hopping among randomly distributed donors.
Growth of epitaxial films of Bi2Sr2CaCu2O8+x onto SrTiO3 substrates from liquid KCl solution
Authors: Balestrino G. , Marinelli M. , Milani E. , Paoletti A. , Paroli P.
Published: July 2002

Epitaxial films of Bi2Sr2CaCu2O8+x have been grown from liquid KCl solution, onto (100)-oriented SrTiO3 substrates. The films show a resistance versus temperature behavior of ‘‘metallic’’ character down to the transition temperature. The residual resistance extrapolated at 0 K is 1/10 of resistance at room temperature. The onset of the superconducting transition is at 81 K, and zero resistance is obtained at 78 K.
An investigation of the microstructure of electroless Co-alloy film
Authors: Liu Zhihui , Yang Chen , He Yusheng , Chen Haoming
Published: July 2002

The existence of phosphorus in grain boundary will cause the c axis of α-Co to orient along the film normal. Furthermore, it has been found that the phosphorous segregation in the boundary is controlled by the MnSO4 concentration in the bath through its effect on chemical or electrochemical properties of complex ions in the bath.
Removal of native silicon oxide with low-energy argon ions
Authors: Salimian S. , Delfino M.
Published: July 2002

Electron cyclotron resonance argon plasmas have been used to clean native silicon oxide at low (≊100 eV) ion energies. In situ x-ray photoelectron spectroscopy (XPS) allowed us to evaluate the effectiveness of this process by studying the Si 2p and O 1s photoemission spectra. Results indicate complete and rapid removal of chemically bound oxygen to silicon and the presence of small levels of adsorbed or interstitially implanted oxygen. Implanted argon was detected by XPS; however, the concentration appears to be greatly reduced by operating under low substrate bias conditions.
Zinc selenide films and heterojunctions
Authors: Chu T. L. , Chu Shirley S. , Chen G. , Britt J. , Ferekides C. , Wu C. Q.
Published: July 2002

Polycrystalline films of zinc selenide (ZnSe) have been deposited on glass and ZnO:F/glass substrates at 400–500 °C by the reaction of diethylzinc (DEZn) and diethylselenium (DESe) in a hydrogen atmosphere. The DESe/DEZn molar ratio in the reaction mixture is an important factor affecting the deposition rate and dopant incorporation in deposited films. The deposited films have high lateral electrical resistivity and poor photoconductivity. The resistivity can be reduced and photoconductivity significantly improved by the incorporation of a group VI (Cl or Br) or a group III (Al) dopant, and the use of trimethylaluminum (TMAl) as a dopant is considerably more effective than the use of Cl or Br compounds. The structural, optical, and electrical properties of ZnSe films have been characterized. The use of ZnSe films as a heterojunction partner in II-VI thin-film solar cells has been explored. Zinc telluride and cadmium telluride films were deposited on ZnSe/ZnO:F/glass substrates, and the characteristics of ZnSe/ZnTe and ZnSe/CdTe junctions studied.
An improved approach to the Shockley–Read–Hall recombination in inhomogeneous fields of space-charge regions
Authors: Schenk A.
Published: July 2002

The rate formula of Shockley–Read–Hall (SRH) recombination is generalized for multiphonon transitions in an inhomogeneous electric field. A three-band model and Fermi statistics are used. The thermal generation and recombination at deep centers is tunnel assisted, if it occurs in the electric field of space-charge layers. Trap tunneling without phonon assistance turns out to be an exceptional case as well as the exclusive thermal multiphonon transition at zero field strength. Generally, every single recombination act is a combination of thermal capture and tunneling into the trap. A background of the order of an interband tunnel length contributes to the local rate. In the Boltzmann case the well known form of the SRH rate is derived, but with spatially variable lifetimes. Their position dependence directly reflects the shape of the electric field strength, if the traps are uniformly distributed. Depending on the external parameters, the calculation of the SRH current density leads to I-U characteristics, which exhibit interesting substructures in the case of certain discrete trap configurations. The theory is applied to a Hg0.8Cd0.2Te n+p junction and a GaAs surface potential.
The relationship between deposition conditions, the beta to alpha phase transformation, and stress relaxation in tantalum thin films
Authors: Clevenger L. A. , Mutscheller A. , Harper J. M. E. , Cabral C. , Barmak K.
Published: July 2002

We demonstrate that the high temperature polymorphic tantalum phase transition from the tetragonal beta phase to the cubic alpha phase causes a large decrease in the resistance of thin films and a complete stress relaxation in films that were intrinsically compressively stressed. 100 nm beta tantalum thin films with intrinsic stresses of 2.0×1010 dynes/cm2 (tensile) to −2.3×1010 dynes/cm2 (compressive) were deposited onto thermally oxidized (100) silicon wafers by evaporation or dc magnetron sputtering with argon. In situ stress and resistance at temperature were measured at 10 °C/min up to 850 °C in purified helium. Upon heating, the main stress mechanisms were elastic deformation at low temperature, plastic deformation at moderate temperatures and stress relief because of the beta-to-alpha phase transition at high temperatures. The temperature ranges over which the elastic and plastic deformation and the beta-to-alpha phase transition occurred varied with deposition pressure and substrate biasing. Incomplete compressive stress relaxation at high temperatures was observed if the film was initially deposited in the alpha phase or if the beta phase did not completely transform into alpha by 800 °C due to substrate biasing during the deposition. We conclude that the main stress relief mechanism for tantalum films with intrinsic compressive stresses to completely relax their stress is the beta-to-alpha phase transition, while for intrinsically tensile films, this transformation has a much smaller effect on the stress.
Dry etching of Ti in chlorine containing feeds
Authors: d’Agostino R. , Fracassi F. , Pacifico C.
Published: July 2002

The reactivity of titanium has been studied in a chlorine containing environment with and without plasma. It has been found that chlorine (atoms or molecules) is not able to remove the native surface oxide unless drastic conditions are realized. Once the oxide is removed, titanium does not appreciably react with molecular chlorine without plasma unless fluorine is present on its surface. Fluorine has a catalytic effect and makes the titanium surface more reactive towards chlorine. Plasma superimposition does not change the reaction pattern, it acts only by increasing the substrate temperature and supplying energy by means of low energy ion bombardment.
Mechanically driven alloying and grain size changes in nanocrystalline Fe-Cu powders
Authors: Eckert J. , Holzer J. C. , Krill C. E. , Johnson W. L.
Published: July 2002

Highly supersaturated nanocrystalline FexCu100−x alloys (10≤x≤95) have been prepared by mechanical alloying of elemental crystalline powders. The development of the microstructure is investigated by x-ray diffraction, differential scanning calorimetry, and transmission electron microscopy. The results are compared with data for ball-milled elemental Fe and Cu powders, samples prepared by inert gas condensation, and sputtered films. The deformation during milling reduces the grain size of the alloys to 6–20 nm. The final grain size of the powders depends on the composition of the material. Single-phase fcc alloys with x≤60 and single-phase bcc alloys with x≥80 are formed even though the Fe-Cu system exhibits vanishingly small solid solubilities under equilibrium conditions. For 60≤x≤80, fcc and bcc solid solutions coexist. The alloy formation is discussed with respect to the thermodynamic conditions of the material. The role of the large volume fraction of grain boundaries between the nanometer-sized crystals, as well as the influence of internal strains and stored enthalpies introduced by ball milling, is critically assessed.
Ion-induced secondary electron emission in SiH4 glow discharge, and temperature dependence of hydrogenated amorphous silicon deposition rate
Authors: Böhm Christian , Perrin Jérôme , Roca i Cabarrocas Pere
Published: July 2002

The ion-induced secondary electron emission coefficient γ from the a-Si:H film deposited from a SiH4 glow discharge is measured in situ using an electrostatic grid analyzer. At low SiH4 pressure and discharge power density, γ≊0.033±0.004 and the overall electrical power dissipation does not vary with the gas and wall temperature between 25 and 250 °C, when the SiH4 molecular density is kept constant. However, the a-Si:H film deposition rate does depend on the temperature, which reveals the effects of thermally activated gas phase of H and SiH2 radicals arising from SiH4 dissociation.
Device applications of interband tunneling structures with one, two, and three dimensions
Authors: Gilman J. M. A. , O’Neill A. G.
Published: July 2002

A systematic study of interband tunneling between states of one, two, and three dimensions (1D, 2D, 3D) is presented based on the theory of the Esaki tunnel diode, modified to take interdimensional tunneling into account. I-V characteristics are given for each of the nine possible combinations. Three systems are dealt with in greater depth: 2D-3D tunneling, where a comparison with experimental data is made, 2D-2D tunneling, where improvements over the conventional tunnel diode characteristic are seen, and 2D-1D tunneling where the prospect of a tristable device is discussed.
Spall strength of molybdenum single crystals
Authors: Kanel G. I. , Razorenov S. V. , Utkin A. V. , Fortov V. E. , Baumung K. , Karow H. U. , Rusch D. , Licht V.
Published: July 2002

Spall strength measurements for commerical grade molybdenum and molybdenum single crystals were made in a wide range of load durations (∼10−9 s – 10−6 s) and intensities (∼5 – 100 GPa). Resistance to fracture of pure single crystals was found to exceed two times the spall strength of polycrystalline molybdenum and to increase with shorter load duration. The value of the shock wave amplitude does not influence the spall strength of single crystals. The largest spall strength obtained under nanosecond load duration amounts to 30% of the ultimate theoretical strength.
Microwave dielectric resonance of a fluoride glass
Authors: Taijing Lu , Dai Yisheng , Ding X. Z. , Ong C. K. , Tan B. T. G.
Published: July 2002

The dielectric properties of a fluorozirconate glass are investigated in the frequency range from 0.5 to 13.5 GHz using a microwave vector network analyzer. A prominent dielectric resonance is observed around 7.0 GHz. The resonance may be due to a fundamental interunit vibrational mode of the basic structural ZrFn polyhedral units of the fluorozirconate glass.
Metal-oxide-semiconductor field-effect-transistor substrate current during Fowler–Nordheim tunneling stress and silicon dioxide reliability
Authors: Schuegraf Klaus F. , Hu Chenming
Published: July 2002

The origin of the substrate current of a metal-oxide-semiconductor field-effect transistor when the gate oxide undergoes Fowler–Nordheim stress is investigated. It is also shown that anode hole injection current predicts the breakdown of silicon dioxide between 25 and 130 Å and 2.4 and 12 V. While the measured substrate current is entirely due to anode hole injection for oxides thicker than 55 Å, tunneling by valence-band electrons contributes to the substrate current in thinner oxides. Valence-band electron tunneling current is shown to increase with oxide stressing similar to low-voltage gate oxide leakage; apparently, both are enhanced by trap-assisted tunneling. For oxides of thickness between 25 and 130 Å, the theory of anode hole injection directly verified for oxides thicker than 55 Å is able to model silicon dioxide breakdown accurately.
Nonlinear four-terminal microstructures: A hot-spot transistor?
Authors: Kulik I. O.
Published: July 2002

Four-terminal microcontacts between metallic electrodes develop nonlinear current-voltage dependencies both in the source and control channels as well as between the channels. Theory is presented of the nonlinearity caused by the reabsorption of nonequilibrium phonons emitted in the contact by injected electrons. Temperature of the lattice due to heating by the current is of the order T∼eV/4, which results in substantial increase of the resistance both in the bias direction and in the direction perpendicular to the bias. Performance characteristics of such a device at low temperature compared to the Debye temperature are quite promising for frequencies below 109 Hz.
Hydrogen dissociation on hot tantalum and tungsten filaments under diamond deposition conditions
Authors: Otsuka Toru , Ihara Manabu , Komiyama Hiroshi
Published: July 2002

The electric power consumed by hot tantalum and tungsten filaments used to dissociate hydrogen molecules into hydrogen radicals was measured at filament temperatures of 2000, 2300, and 2500 °C and hydrogen pressures from 0.5–100 Torr. The measured power consumption at pressures above 30 Torr was well represented by a model that assumed thermodynamic equilibrium between H2 and H near the filament. With decreasing pressure, however, the dissociation of H2 shifted from an equilibrium-controlled regime to a surface-reaction-rate controlled regime. The relationship between the power consumption and the pressure in the surface-reaction-rate controlled regime was correlated with the surface dissociation probability, which was determined to range from 0.18 to 0.94.
Diffuse x-ray scattering from misfit dislocations in SiGe epitaxial layers with graded Ge content
Authors: Holý V. , Li J. H. , Bauer G. , Schäffler F. , Herzog H.-J.
Published: July 2002

A theory has been developed describing x-ray diffuse scattering from misfit dislocations in epitaxial layers. This approach has been used for explaining the origins of diffuse x-ray scattering from SiGe layers with linearly graded Ge content. The distribution of the diffusely scattered intensity in reciprocal plane measured by triple-axis x-ray diffractometry has been compared with theoretical predictions and a good agreement has been achieved. It is demonstrated that the main part of the diffusely scattered intensity originates from random strains caused by misfit dislocations at the substrate–epilayer interface or in the relaxed part of the compositionally graded layers. The contribution of the threading dislocation segments to the diffuse scattering is rather small.
Surface modification mechanism of materials with scanning tunneling microscope
Authors: Kondo Seiichi , Heike Seiji , Lutwyche Mark , Wada Yasuo
Published: July 2002

The surface modification mechanism with scanning tunneling microscope (STM) is investigated. Experiments in both ultrahigh vacuum and air are reported, using several kinds of materials to understand the mechanism systematically. Threshold voltages (Vt’s), which are defined as the voltages above which modification is possible under the STM tip, have linear dependence on the binding energies of the materials. Thus, the STM surface modification mechanism is attributed to the local sublimation induced by tunneling electrons. For the modification in air, it is also ascribed to the chemical reaction induced by tunneling electrons with adsorbed water, and the Vt’s also fit on this line by taking the reaction energy into consideration. Therefore, the process is a direct consequence of the high flux of low-energy electrons incident on the surface from the STM tip.
Microstructural control of NdFeB cast ingots for achieving 50 MGOe sintered magnets
Authors: Scott D. W. , Ma B. M. , Liang Y. L. , Bounds C. O.
Published: July 2002

The combination of chemical composition and microstructure of cast alloy has been found to be critical to the performance of NdFeB sintered magnets. Maximizing the amount of Nd2Fe14B phase (or minimizing the amount of secondary phase) by reducing the Nd content more closely to the stoichiometric composition appears to be essential for obtaining high BHmax magnets. However, α-Fe precipitation has been found to increase with decreasing Nd content and severely hinders the development of high BHmax magnets. A two-step method, incorporating ingot casting and isothermal annealing, has been developed to minimize the amount of precipitated α-Fe in low Nd content alloys. This method provides a drastic improvement in the Br and BHmax of sintered magnets obtained. By decreasing the Nd content to 13 at. % in the cast alloy, incorporating better particle control during fine milling, and controlling grain growth during sintering; magnets with a Br of more than 14.5 kG and a BHmax of 50 MGOe have been consistently obtained. Furthermore, because of the reduction in the amount of Nd-rich grain boundary phase, a significant improvement in the corrosion resistance of magnets was also observed.
Application of standard and modified Judd–Ofelt theories to a praseodymium-doped fluorozirconate glass
Authors: Goldner P. , Auzel F.
Published: July 2002

A method which takes into account normalized oscillator strengths is detailed for the calculation of parameters in Judd–Ofelt theory (B. R. Judd, Phys. Rev. 127, 750 (1962), G. S. Ofelt, J. Chem. Phys. 37, 511 (1962)). In the case of a Pr3+-doped fluorozirconate glass, the Judd–Ofelt parameters obtained in this way do not depend strongly on the transitions included in the fit. Particularly, it is no longer necessary to exclude the 3H4→3P2 transition from the analysis. Two modified theories [F. Auzel, S. Hubert, and P. Delamoye, J. Lumin. 26, 251 (1982), and A. A. Kornienko, A. A. Kaminskii, and E. B. Dunina, Phys. Stat. Solidi. 157, 267 (1990)] are also considered but do not improve the calculated intensities when the energy of the 5d level is set to its experimentally determined value. Finally, in connection with 1.3 μ amplification, the 1.3 μ reabsorption (1G4→1D2) oscillator strength is computed from the various models as well as the 1.3 μ emission branching ratio (1G4→3H5/1G4→3H6). The best agreement with experiment is obtained with the standard Judd–Ofelt theory.
Electrical resistivity of single-crystal Al2O3 shock-compressed in the pressure range 91–220 GPa (0.91–2.20 Mbar)
Authors: Weir S. T. , Mitchell A. C. , Nellis W. J.
Published: July 2002

The electrical resistivity of single-crystal Al2O3 was measured at shock pressures in the range 91–220 GPa. Shock pressures were generated by impacts of hypervelocity projectiles accelerated with a two-stage light-gas gun. The resistivity varied from 170 to 20 Ω cm in the pressure range 91–180 GPa and then rapidly decreased to 0.2 Ω cm at 220 GPa.
Generalization of hysteresis modeling to anisotropic materials
Authors: Ramesh A. , Jiles D. C. , Bi Y.
Published: July 2002

An extension to the model of hysteresis has been presented earlier which included the effect of anisotropy in the modeling of the anhysteretic magnetization curves of uniaxially anisotropic single crystalline materials. Further exploration of this extension shown here considers different kinds of crystal anisotropy in materials. Theory considers that the differential susceptibility at any given field is determined by the displacement of the prevailing magnetization from the anhysteretic magnetization. Thus, it has been shown that the effect of anisotropy on magnetic hysteresis in materials can be incorporated into the model of hysteresis through the anisotropic anhysteretic. This extension is likely to be particularly useful in the case of hard magnetic materials which exhibit high anisotropy.
Synthesis of nanocrystalline diamond thin films from an Ar–CH4 microwave plasma
Authors: Zhou D. , McCauley T. G. , Qin L. C. , Krauss A. R. , Gruen D. M.
Published: July 2002

Nanocrystalline diamond thin films have been synthesized in an Ar–CH4 microwave discharge, without the addition of molecular hydrogen. X-ray diffraction, transmission electron microscopy, and electron energy loss spectroscopy characterizations show that the films consist of a pure crystalline diamond phase with very small grain sizes ranging from 3 to 20 nm. Atomic force microscopy analysis demonstrates that the surfaces of the nanocrystalline diamond films remain smooth independent of the film thicknesses. Furthermore, the reactant gas pressure, which strongly affects the concentration of C2 dimer in the Ar–CH4 plasma as well as the growth rate of the films, has been found to be a key parameter for the nanocrystalline diamond thin film depositions.
Surface photoabsorption transients and ordering in GaInP
Authors: Hsu T. C. , Stringfellow G. B. , Kim J. H. , Seong T. Y.
Published: July 2002

Heterostructures and quantum wells can be produced in GaInP without changing the solid composition by simply varying the order parameter. Since CuPt ordering reduces the band-gap energy, changes in the order parameter induced by changes in growth conditions result in heterostructures with band-gap energy discontinuities as large as 160 meV. The most convenient growth parameter to change is the flow rate of the P precursor. However, previous work has shown that under some conditions the change in order parameter is sluggish, giving rise to graded heterostructures. The cause of the slow change in order parameter is the topic of this article. CuPt ordering has been shown to be driven by the formation of [1̄10] P dimers, characteristic of the (2×4) surface reconstruction. Thus, this study of the transient in the degree of order induced by changing the flow rate of the P precursor has relied on the use of surface photoabsorption (SPA) to monitor the surface reconstruction during the period after the partial pressure of the P precursor was reduced. The SPA transient has then been correlated with the abruptness of the heterostructure interface, determined from the transmission electron microscopy images and the photoluminescence spectra, for organometallic vapor phase epitaxial (OMVPE) growth at temperatures of 620 and 670 °C using the P precursors phosphine (PH3) and tertiarybutylphosphine (TBP). For TBP at both 620 and 670 °C, the SPA reflectance transient is extremely short, with a time constant of less than 10 s, corresponding to the time response of the OMVPE growth system. Abrupt interfaces are produced using these conditions. For PH3, the SPA reflectance transient is abrupt at 670 °C; however, at 620 °C the SPA response is extremely sluggish, with a time constant of approximately 6.5 min. The effect is tentatively attributed to a surfactant effect due to H on the surface. Corresponding heterostructures were abrupt at 670 °C and graded at 620 °C.
Frequency dependence of photoresist ashing with dielectric barrier discharges in oxygen
Authors: Falkenstein Zoran
Published: July 2002

This article presents results of the frequency dependence on surface etching of a Novolak-type polymer (Shipley, SPR2) on Si wafers using dielectric barrier discharges in oxygen near atmospheric pressures and room temperature. The etching depth of the photoresist is measured by mechanical profilometry as a function of the applied sinusoidal frequency (1–40 kHz) at different oxygen pressures (250–750 mbar) and gap distances (1–20 mm), along with the energy density that is supplied to the sample surface and into the gas volume, respectively. This approach enables one to generate figures of merit for the etching rates, allowing comparison with conventional plasma surface treatments, as etching rate per power density coupled onto the sample surface (nm min−1 W−1 cm2), or coupled into the gas volume (nm min−1 W−1 cm3). For all gap spacings and gas pressures both power-density specific etch rates increase with increased applied frequencies, and show an optimal gap distance and gas pressure. The surface of the etched photoresist is characterized by scanning electron microscopy, showing decreasing material damage with increasing frequency. The results obtained in this work suggest dielectric barrier discharges at high frequencies (>10’s kHz) as an efficient, alternative plasma source for general surface processing, as they can provide nonthermal gas discharges near atmospheric pressures and thereby eliminate the need for costly vacuum systems without major damage of the plasma-treated surface.
Spin dynamics of strongly doped La1−xSrxMnO3
Authors: Vasiliu-Doloc L. , Lynn J. W. , Mukovskii Y. M. , Arsenov A. A. , Shulyatev D. A.
Published: July 2002

Cold neutron triple-axis measurements have been used to investigate the nature of the long-wavelength spin dynamics in strongly doped La1−xSrxMnO3 single crystals with x=0.2 and 0.3. Both systems behave like isotropic ferromagnets at low T, with a gapless (E0<0.02 meV) quadratic dispersion relation E=E0+Dq2. The values of the spin-wave stiffness constant D are large (DT=0=167 meV Å2 for x=0.2 and DT=0=176 meV Å2 for x=0.3), which directly shows that the electron transfer energy for the d band is large. D exhibits a power law behavior as a function of temperature, and appears to collapse as T→TC. Nevertheless, an anomalously strong quasielastic central component develops and dominates the fluctuation spectrum as T→TC. Bragg scattering indicates that the magnetization near TC exhibits power law behavior, with β≃0.30 for both systems, as expected for a three-dimensional ferromagnet.