bluuebunny/crossref_metadata_2025 huggingface dataset:
Neon gas puff implosions on a high-current microsecond generator with and without a plasma opening switch
Authors: Deeney C. , LePell P. D. , Roth I. , Nash T. , Warren L. , Prasad R. R. , McDonald C. , Childers F. K. , Sincerny P. , Coulter M. C. , Whitney K. G.
Published: July 2002

Implosions of 2.5-cm-diam neon gas shells on a 1.2 μs quarter-period, 3 MA driver, FALCON, have produced no more than 7.6 kJ of kilovolt neon K-shell radiation. The incorporation of a plasma opening switch produces faster current pulses: up to 1.8 MA in 190 ns. With the higher rate of rise of current, neon gas puffs have produced up to 13.5 kJ of kilovolt K-shell radiation. Numerical calculations indicate that this increase in radiation is due to the achievement of a higher kinetic energy per ion at higher current levels. Spectroscopic measurements confirm that a significant fraction of the plasma is heated into the K-shell ionization states and that the faster current pulses increase this fraction up to 40%.
Resistivity and T
c measurements on YBa2(Cu1−xMx)3O7−δ films (M=Ni,Al)
Authors: Kim Jin-Tae , Xenikos Dimitrios G. , Thorns Ansgar , Lemberger Thomas R.
Published: July 2002

YBa2(Cu1−xMx)3O7−δ films (M=Ni and Al) with up to 11 at. % dopant are fabricated on (001) SrTiO3 substrates by codeposition of Y, BaF2, Cu, and M, and then post-annealing in moist oxygen. All films are 300 nm thick. They are highly oriented with the c axis perpendicular to the substrate, and their surfaces are as smooth as for undoped YBa2Cu3O7−δ films. Tc(x) decreases with x consistent with bulk ceramic samples. The resistivity is metallic and ranges from 100 μΩ cm to 2.5 mΩ cm at 100 K. The residual resistivity ρab(0) at T=0 K, extrapolated from ρab(T) above Tc is approximately proportional to x up to 7 at. % Al films and 11 at. % Ni.
Si:Sb blocked impurity band detectors for infrared astronomy
Authors: Huffman James E. , Crouse A. G. , Halleck B. L. , Downes T. V. , Herter Terry L.
Published: July 2002

We discuss the characteristics of impurity band conduction detectors prepared from epitaxial Si:Sb. These detectors are sensitive to infrared light at wavelengths between 2.5 and 40 μm and outperform the current state-of-the-art Ge:Be photoconductors for this wavelength range by a combination of a peak responsivity R=32 A/W, low noise equivalent power (NEP) =1.1×10−15 W/Hz1/2 (at a flux of 1012 ph/cm2 s), inherently low sensitivity to cosmic ray particles, and freedom from the anomalous behavior observed in photoconductors.
Second-harmonic generation and sum-frequency mixing of double-wavelength Nd:YALO3 laser to 413.7-nm violet coherent radiation in LiIO3 crystal
Authors: Shen H. Y. , Lin W. X. , Zeng R. R. , Zhou Y. P. , Yu G. F. , Huang C. H. , Zeng Z. D. , Zhang W. J.
Published: July 2002

A new method to get 413.7-nm violet coherent radiation by using second-harmonic generation and sum-frequency mixing of radiation from a 1341.4- and 1079.5-nm dual-wavelength Nd:YALO3 laser in a LiIO3 crystal is reported in this communication. First, the 670.7-nm red coherent radiation is obtained by second-harmonic generation of 1341.4-nm radiations in a LiIO3 crystal, and then the 670.7- and 1079.5-nm radiations are mixed again in a second LiIO3 crystal to get 413.7-nm radiation. The phase-matching angles are obtained for both nonlinear optical processes. The experimental results agree well with calculated results.
Electron spin resonance characterization and localization of a thermally generated donor inherent to the separation by implantation of oxygen process
Authors: Vanheusden K. , Stesmans A.
Published: July 2002

Defects in silicon-on-insulator structures, formed either by single or multiple-step implantation of oxygen, were monitored during the various processing steps using K-band electron spin resonance (ESR) at 4.3–30 K. While high temperature annealing at 1325 °C was observed to result in the entire removal of the initially observed implantation damage, both in the crystalline Si and the buried oxide, it also generated a new defect. The ionization state of part of these centers was observed to change into an ESR-active state upon γ irradiation to a dose of 1–10 Mrad (Si), caused by band bending resulting from γ-irradiation induced positive charging of the buried oxide. The signal is ascribed to a shallow effective mass donor in Si of axial symmetry and preferential alignment along [001], likely an oxygen-related heat-treatment donor. Controlled etch back of the structures affirmed the band bending hypothesis and revealed that the double donor defects reside in an interfacial Si layer of at least 600 Å thick at both sides of the buried oxide layer reaching a local volume density of about 1018 cm−3.
Modeling field dependence of giant magnetoresistance in ‘‘granular’’ and quasi-granular magnetic films
Authors: Parker M. R. , Barnard J. A. , Seale D. , Waknis A.
Published: July 2002

Giant magnetoresistance in granular alloy thin films prepared by co-sputtering as well as in quasi-granular disordered multilayers has been modeled with relative ease using a simple scattering concept appropriate to superparamagnetic films and involving the Langevin function. The model has been applied to both as-deposited and annealed samples with the result that approximate sizes of spin clusters may be determined.
Transistor and physical properties of polycrystalline silicon films prepared by infralow-pressure chemical vapor deposition
Authors: Miyasaka Mitsutoshi , Nakazawa Takashi , Itoh Wataru , Yudasaka Ichio , Ohshima Hiroyuki
Published: July 2002

The infralow-pressure chemical vapor deposition (ILPCVD) system has been developed to reduce the partial pressure of silane (PSiH4) to the sub-mTorr order by increasing the pumping speed, while aiming at the improvement of as-deposited polycrystalline silicon (poly-Si) film qualities. The films prepared by the system show better physical properties than ordinary low-pressure chemical vapor deposition (LPCVD) films at fixed temperature (600 °C), so that the low-temperature processed as-deposited poly-Si thin film transistors can be easily and significantly improved, having ON/OFF current ratios of more than 108. Physical analyses have confirmed that the films deposited at temperatures as low as 555 °C by the ILPCVD system are undoubtedly polycrystalline. The fabrication of poly-Si TFT’s through a low-temperature process confirms good semiconductive behavior of the films, even when deposited at 555 °C. The superiority of the ILPCVD over other LPCVD’s is explained by the deposition kinetics. The nature of LPCVD as-deposited polysilicon film is characterized by the competition between surface reaction rate and gas-phase mass-transfer rate. High-temperature or infralow-pressure deposition is controlled by gas-phase mass transfer of the reactant. The mass-transfer controlled deposition is found to be preferable to obtaining good polycrystalline silicon film, namely high crystallinity, 〈100〉 preferred orientation, large grains, and good semiconductive properties.
Radio frequency discharge modeling: Moment equations approach
Authors: Meyyappan M. , Govindan T. R.
Published: July 2002

A fluid model based on the three moments of the Boltzmann equation is presented to study rf discharges. With rate constants obtained from a zero-dimensional Boltzmann equation solver, the model is shown to reproduce excitation wave forms seen in experiments. Several other critical features previously reported by particle-in-cell simulations such as mechanisms of heating and relation between electron power deposition and ionization have also been reproduced. A parametric study for a 13.56-MHz argon discharge with varying rf bias and pressure has been used to derive scaling laws for the discharge.
Structural evolution of mechanical alloyed Fe-Al powders after consolidation and thermal ageing
Authors: Bonetti E. , Scipione G. , Valdre’ G. , Cocco G. , Frattini R. , Macrì P. P.
Published: July 2002

Elastic energy dissipation and dynamic Young’s modulus measurements coupled with x-ray and energy-dispersive analyses were employed to follow the structural transformation of bulk samples prepared by mechanical alloying Fe-Al powders mixed in the atomic ratio Fe/Al=3. The results show that it is possible to synthesize a nanocrystalline bulk Fe3Al intermetallic phase by properly combining mechanical treatments of the powders with suitable temperature thermal aging. Driving mechanisms and transformation paths leading to this stable phase, not otherwise observed in the simply thermally aged Fe-Al crystalline powders, are examined and discussed.
The measurement of irreversible magnetization and activation volumes
Authors: Cammarano R. , McCormick P. G. , Street R.
Published: July 2002

The phenomenological model of magnetization kinetics developed by Estrin et al. [J. Phys. 1, 4845 (1989)] yields a macroscopic magnetic equation of state or magnetic constitutive equation of functional form μ0H=f(Jirr,J̇irr), where, μ0H is the internal magnetic field, Jirr is the irreversible magnetic polarization and J̇irr its time derivative. In differential form the relation takes the form μ0 dH=(1/χirr)dJirr+Λd(ln J̇irr). The quantity Λ is related to the activation volume involved in the process of irreversible magnetization. To obtain Λ, three different experimental techniques are used. One involves the traversal of hysteresis loops at constant J̇irr, from which both χirr and Λ can be obtained most directly, using a modified version of a technique previously described. The second method involves traversing the hysteresis loop at constant μ0Ḣ, and subsequently separating the reversible and irreversible components of magnetization. In the third method, the parameter Λ is obtained from magnetic viscosity measurements, which is the technique most commonly used. Results are presented for all three experimental techniques for measurements performed on Alnico-type permanent magnets. The limitations of each method will be reviewed in relation to materials properties.
Simultaneous extraction of bulk lifetime and surface recombination velocities from free carrier absorption transients
Authors: Ling Z. G. , Ajmera P. K. , Kousik G. S.
Published: July 2002

Bulk lifetime and surface recombination velocities at both the front and the rear surfaces are important parameters that affect the performance of solar cells. In an earlier work [G. S. Kousik, Z. G. Ling and P. K. Ajmera, J. Appl. Phys. 72, 141 (1992)], a detailed theoretical analysis for a contactless nondestructive technique to obtain these parameters is presented. Here, the experimentally measured data using this new approach was presented. Moreover, the earlier analytical work has now been extended to also provide an estimate of the sensitivity of the extracted parameters to errors in experimental measurements. Results on measurements on single crystal silicon wafers are provided as an example.
Theoretical study of GaN growth: A Monte Carlo approach
Authors: Wang Kung , Singh Jasprit , Pavlidis Dimitris
Published: July 2002

An atomistic model consistent with a variety of experimental observations is developed for GaN growth by molecular-beam epitaxy. The model is used in Monte Carlo simulation to study the impact of substrate temperature, Ga flux, and V/III (group-V element to group-III element) ratio on growth rate and growth front quality. The growth rate increases with the V/III ratio reaching a saturation value which is determined by the Ga flux. The quality of the growth front improves by using a smaller Ga flux for a fixed temperature and V/III ratio or by reducing the V/III ratio at a given temperature. A consideration of the growth kinetics suggests that GaN grown surfaces are likely to be Ga stabilized. These theoretically estimated trends are evidenced by two-dimensional and three-dimensional growth front contours evaluated under various growth conditions.
Spatially and temporally resolved absolute O-atom concentrations in etching plasmas
Authors: Tserepi Angeliki D. , Miller Terry A.
Published: July 2002

The detection of atomic O by two-photon-allowed laser-induced fluorescence is implemented to obtain the spatial distribution and the temporal evolution of oxygen atoms in a 10 MHz parallel-plate rf discharge. Absolute concentrations are determined via a titration technique for intensities typically found in 20–100 W, 0.1–3 Torr O2 discharges, and are in the range 4–30×1014 atoms/cm3. The spatial O distribution after initial turn on of the discharge is rather uniform, indicative of a uniform production of O atoms throughout the interelectrode space. Furthermore, the decay of the O concentration reveals information about the reaction of O atoms with surface materials in the plasma environment, while the rise of the population indicates a time-dependent production rate. The dependence of the O-concentration rise and decay rates on discharge pressure, power, and gas composition is explored.
Ultrahigh frequency measurements of magnetic penetration length and surface impedance of YBa2Cu3O7−x microstriplines on Si and GaAs substrates
Authors: Rüders F. , Hollricher O. , Copetti C. A. , Förster A. , Buchal Ch. , Prusseit W. , Kinder H.
Published: July 2002

Superconducting microstriplines of YBa2Cu3O7−x have been deposited and patterned on substrates of silicon on sapphire and GaAs. In both substrates fast semiconducting photoswitches were fabricated and integrated into the microstriplines. Short lightpulses of 100 fs length generated electrical pulses in the semiconducting photoswitches. The electrical pulses were launched into the superconducting striplines, where they were detected by electro-optical sampling. This method permits the analysis of the frequency dependence of the YBa2Cu3O7−x surface impedance Zs(T,ν) and the magnetic penetration depth λ(T,ν) in the temperature regime 10≤T≤90 K and the frequency range 10 GHz≤ν≤600 GHz. The Zs and λ measurements showed that the electrical data of the YBa2Cu3O7−x were comparable to those of YBa2Cu3O7−x deposited on LaAlO3.
Electron injection polymer for polymer light-emitting diodes
Authors: Yang Y. , Pei Q.
Published: July 2002

We report the use of an oxadiazole-containing polymer, poly(phenylene-1,3,4-oxadiazole- phenylene-hexafluoroisopropylidene) (PPOPH), as the electron injection layer in polymer light-emitting diodes. By introducing a PPOPH layer between the cathode (aluminum) and the luminescent polymer (poly(2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene), the device performance was significantly improved; the quantum efficiency increased by a factor of 40, close to that of the same device using calcium as the cathode. By utilizing a porous polyaniline network electrode as the anode, the operating voltage was lowered by a factor of 2 with turn on at ∼5×105 V/cm.
Effect of ruthenium passivation on the optical and electrical properties of gallium antimonide
Authors: Dutta P. S. , Koteswara Rao K. S. R. , Bhat H. L. , Kumar Vikram
Published: July 2002

Improvements in optical and electrical properties were observed after ruthenium passivation of gallium antimonide surfaces. On passivation, luminescence efficiency increased up to 50 times and surface state density reduced by two orders of magnitude. Also, the reverse leakage current was found to decrease by a factor of 30–40 times. Increase in carrier mobility as a result of grain boundary passivation in polycrystalline GaSb was observed.
Thermodynamics and kinetics of the undercooled liquid and the glass transition of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 alloy
Authors: Busch R. , Kim Y. J. , Johnson W. L.
Published: July 2002

Differential scanning calorimetry (DSC) was used to determine the thermodynamic functions of the undercooled liquid and the amorphous phase with respect to the crystalline state of the Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glass forming alloy. The specific heat capacities of this alloy in the undercooled liquid, the amorphous state and the crystal were determined. The differences in enthalpy, ΔH, entropy, ΔS, and Gibbs free energy, ΔG, between crystal and the undercooled liquid were calculated using the measured specific heat capacity data as well as the heat of fusion. The results indicate that the Gibbs free energy difference between metastable undercooled liquid and crystalline solid, ΔG, stays small compared to conventional metallic glass forming alloys even for large undercoolings. Furthermore, the Kauzmann temperature, TK, where the entropy of the undercooled liquid equals to that of the crystal, was determined to be 560 K. The Kauzmann temperature is compared with the experimentally observed rate-dependent glass transition temperature, Tg. Both onset and end temperatures of the glass transition depend linearly on the logarithm of the heating rate based on the DSC experiments. Those characteristic temperatures for the kinetically observed glass transition become equal close to the Kauzmann temperature in this alloy, which suggests an underlying thermodynamic glass transition as a lower bound for the kinetically observed freezing process.
Reaction kinetics in synchrotron-radiation-excited Si epitaxy with disilane. I. Atomic layer epitaxy
Authors: Akazawa Housei , Utsumi Yuichi
Published: July 2002

We investigated the mechanism of silicon crystal growth mediated by a surface photochemical reaction. The growth process consists of reactive sticking of disilane (Si2H6) onto a partially hydrogen covered surface followed by the photon-stimulated desorption of hydrogen atoms and consequent regeneration of dangling bonds. The saturation coverage of Si admolecules resulting from self-limiting chemisorption of disilane was found to be 0.42 monolayer (ML), and the ejection of H+ and H+2 ions was observed by time-of-flight mass spectroscopy. Hydrogen removal by the purely electronic process differs from thermal desorption, however, in that not all of the hydrogen is removed. Analysis of film growth by repetition of the cycle of disilane exposure, evacuation, and synchrotron radiation irradiation showed that the onset temperature of thermal growth (350 °C) is the same as that of H2 desorption from the dihydride species. Below 350 °C a digital growth of 0.18 ML/cycle occurs over a wide range of gas exposure times, irradiation times, substrate temperatures, and the irradiation intensities. If the temperature is raised to facilitate thermal desorption of hydrogen atoms and migration of Si adatoms, the number of Si adatoms delivered in each cycle increases significantly. Photolytic, thermal, and photothermal effects result in growth rates of 0.4 ML/cycle at 430 °C and 1 ML/cycle 480 °C.
Photoinduced Ag migration in Ag–As–S glasses
Authors: Yoshida Norimitsu , Tanaka Keiji
Published: July 2002

The Ag content in Ag–As–S glasses can be spatially modified by illumination of visible light. Optical and thermal studies demonstrate that the Ag-content modification is caused by Ag+ ionic migration from the dark to the illuminated region in a sample. The migration can be reversed by changing the illuminated region. The magnitude of the Ag-content modification is maximal (∼7 at. %) at a composition of Ag25As25S50. The migration mechanism can be accounted for by assuming diffusion of photoexcited holes, and the composition dependence can be understood on the basis of the Owens’ thermodynamic model.
The effects of surface roughness on the angle-dependent total-reflection x-ray fluorescence of ultrathin films
Authors: Tsuji Kouichi , Yamada Takashi , Utaka Tadashi , Hirokawa Kichinosuke
Published: July 2002

We have experimentally investigated the effects that the surface roughness of the substrate has on the angle dependent-total-reflection x-ray fluorescence (AD-TXRF) profile of an ultrathin film. An optically flat Si wafer, a scratched Si wafer, and a grating were used as the substrates. The peak of the AD-TXRF curve of the ultrathin Au film on a rough substrate such as scratched Si, or grating was sharp in comparison with that of the optically flat Si. It is our hypothesis that the rough peaks play an important role in the AD-TXRF intensity measurement. Thus, a material with well-defined roughness should be used as the substrate for an AD-TXRF analysis, because the shape of the AD-TXRF curve of the ultrathin film is strongly dependent on the surface roughness of the substrate.
Surface photovoltage spectroscopy of InxAl1−xAs epilayers
Authors: Burstein L. , Shapira Yoram , Bennett B. R. , del Alamo J. A.
Published: July 2002

The surface and interface electronic structure of mismatched InxAl1−xAs epitaxial layers grown by molecular beam epitaxy on InP have been investigated using surface photovoltage spectroscopy. The crystalline structure of the epilayers was also examined by double-crystal x-ray diffraction. For coherently strained layers, only a few gap states are identified. Highly strained samples with inferior crystalline quality, as judged by a broadened x-ray diffraction peak and the absence of Pendellosung fringes, display a rich spectrum of states in the band gap. Some of the states are close to the surface while others are located in the vicinity of the InAlAs/InP heterointerfaces.
Photorefractive composites with high-band-gap second-order nonlinear optical chromophores
Authors: Burzynski Ryszard , Zhang Yue , Ghosal Saswati , Casstevens Martin K.
Published: July 2002

A series of photorefractive composite materials has been developed in which an inert polymer has been doped with second-order nonlinear optical chromophores, charge transporting agents, and photocharge generation sensitizers. The composites show high photoconductivity, large photorefractive responses, and optical transparency at many wavelengths. Photorefractivity has been demonstrated at wavelengths of 633, 514.5, and 488 nm, with net two-beam coupling gains.
Magnetoresistance values exceeding 21% in symmetric spin valves
Authors: Egelhoff W. F. , Ha T. , Misra R. D. K. , Kadmon Y. , Nir J. , Powell C. J. , Stiles M. D. , McMichael R. D. , Lin C.-L. , Sivertsen J. M. , Judy J. H. , Takano K. , Berkowitz A. E. , Anthony T. C. , Brug J. A.
Published: July 2002

We report values of the giant magnetoresistance (GMR) effect exceeding 21% in symmetric spin valves, the highest values ever reported for such structures. The key elements in this achievement are the use of a Co/Cu/Co/Cu/Co multilayer in which the center Co layer is substantially thicker than the outer Co layers and the use of the antiferromagnetic insulator NiO at the top and bottom to pin the adjacent Co layers magnetically. The relative Co layer thicknesses suggest that some specular scattering of conduction electrons may occur at the metal/insulator interfaces and may enhance the GMR.
Interface roughness scattering in AlAs/InGaAs resonant tunneling diodes with an InAs subwell
Authors: Roblin Patrick , Potter Robert C. , Fathimulla Ayub
Published: July 2002

We present simulation results on the current-voltage (I-V) characteristics of an InP-based AlAs/InGaAs resonant tunneling diode (RTD) with InAs subwell. Space-charge limited transport is accounted for using a self-consistent electrostatic potential calculated using the Hartree approximation. Three-dimensional scattering is simulated using the recently developed multiple sequential scattering theory. Interface roughness scattering is found to be dominant over polar phonon scattering in the devices studied. Of particular interest is interface-roughness (IR) scattering at the InGaAs/AlAs and InGaAs/InAs interfaces and its impact on the valley current. The existence of a critical terrace size that maximizes IR scattering is identified through simulation. The origin of the asymmetry commonly measured in the RTD I-V characteristic is discussed with respect to asymmetries in interface scattering. The use of the InAs subwell and associated interface roughness scattering to tune the peak current while keeping a nearly constant current peak-to-valley ratio is demonstrated.
Time-domain far fields
Authors: Yaghjian Arthur D. , Hansen Thorkild B.
Published: July 2002

The behavior of classical time-domain electromagnetic far fields is investigated with emphasis placed on those characteristics that are unique to the time domain. Necessary conditions are derived for the time-domain far fields to decay slower than 1/r and for the energy in a far-field pulse to decay slower than 1/r2. Time-domain near fields are expressed in terms of integrals over the time-domain far-field pattern. Analyticity with respect to angular variation of the time-domain far-field pattern is determined, and restrictions are derived on the time dependence of the electromagnetic far fields.
Study of high-field electron transport in semiconductors using balance equations for nonparabolic multivalley systems
Authors: Lei X. L. , Cao J. C. , Dong B.
Published: July 2002

Balance equations for high-field electron transport in nonparabolic multiband (multivalley) semiconductors are proposed based on the Heisenberg equations of motion for the total physical momentum, the total energy and the population of carriers in each energy band (each valley), and the statistical average with respect to an initial density matrix having a lattice wave-vector shift, an electron temperature, and a chemical potential for each energy band (each valley) as parameters. As an example, these equations are applied to the discussion of hot-electron transport in bulk Si, assuming Kane-type energy dispersion for six elliptical valleys. The theoretical results are in good agreement with experiments and with Monte Carlo simulations, over the entire range of the electric field up to 140 kV/cm.
Effect of ion energy on the optical and structural properties of SiO2 grown by plasma-enhanced chemical-vapor deposition
Authors: Durandet A. , McKenzie D. R.
Published: July 2002

The optical and structural properties of SiO2 films have been studied as a function of the energy of the ion bombardment applied during plasma-enhanced chemical-vapor deposition. The stress level, the degree of birefringence, and the type of microstructure on the surface and in the bulk showed systematic variations with energy. A theoretical model of the behavior of the stress developed in the layer during the deposition is compared to the experimental results. A second model developed to explain the birefringence enables the degree of columnar structure in the films to be estimated. The explanation for the variation of the refractive index with the ion energy requires the presence of a dense phase with refractive index greater than that of thermally grown SiO2. The volume fraction of the dense phase, and hence the film refractive index, is correlated with the magnitude of the compressive stress. Conditions of ion bombardment leading to optimum properties for our application were identified.
Annealing behavior of silver, copper, and silver–copper nanoclusters in a silica matrix synthesized by the sol-gel technique
Authors: De G. , Gusso M. , Tapfer L. , Catalano M. , Gonella F. , Mattei G. , Mazzoldi P. , Battaglin G.
Published: July 2002

Silver, copper, and mixed silver–copper nanocluster-doped silica thin layers were prepared by the sol-gel process. Samples were heat treated in different annealing atmospheres (air, argon, or 5%H2–95%N2) in the temperature range 500–1100 °C. Specimens were characterized by optical absorption spectroscopy, Rutherford backscattering spectrometry, x-ray diffraction, and transmission electron microscopy. Cluster growth and dissolution, as well as migration of metal atoms towards the sample surface, with a subsequent evaporation, were observed to occur at temperatures that depend on the annealing atmosphere. In the mixed silver–copper system, the formation of Ag–Cu phase-separated clusters was observed.
Simulation of radiation effects on three-dimensional computer optical memories
Authors: Moscovitch M. , Emfietzoglou D.
Published: July 2002

A model was developed to simulate the effects of heavy charged-particle (HCP) radiation on the information stored in three-dimensional computer optical memories. The model is based on (i) the HCP track radial dose distribution, (ii) the spatial and temporal distribution of temperature in the track, (iii) the matrix-specific radiation-induced changes that will affect the response, and (iv) the kinetics of transition of photochromic molecules from the colored to the colorless isomeric form (bit flip). It is shown that information stored in a volume of several nanometers radius around the particle’s track axis may be lost. The magnitude of the effect is dependent on the particle’s track structure.
Ion energy and angular distributions in inductively driven radio frequency discharges in chlorine
Authors: Woodworth J. R. , Riley M. E. , Miller P. A. , Hebner G. A. , Hamilton T. W.
Published: July 2002

In this article, we report values of ion energy and angular distributions measured at the grounded electrode of an inductively coupled discharge in chlorine gas. The inductive rf drive in our cell produced high plasma densities (1011/cm3 electron densities) and stable plasma potentials. As a result, ion energy distributions typically consisted of a single peak well separated from zero energy. Mean ion energy varied inversely with pressure, decreasing from 13 to 9 eV as the discharge pressure increased from 20 to 60 mTorr. Half-widths of the ion angular distributions in these experiments varied from 6° to 7.5°, corresponding to transverse energies from 0.13 to 0.21 eV. During the course of the experiment, ion energies gradually decreased, probably due to the buildup of contaminants on the chamber walls. Cell wall temperature also was an important variable, with ion fluxes to the lower electrode increasing and the ion angular distribution narrowing as the cell temperature increased.
Structural characterization of amorphous SiCxNy chemical vapor deposited coatings
Authors: Bendeddouche A. , Berjoan R. , Bêche E. , Merle-Mejean T. , Schamm S. , Serin V. , Taillades G. , Pradel A. , Hillel R.
Published: July 2002

Chemical bonding and local order around the different atoms of thick amorphous SiCxNy deposits [0.03⩽x/(x+y)⩽0.67] prepared with chemical vapor deposition at 1000–1200 °C using TMS–NH3–H2 have been investigated using x-ray photoelectron spectroscopy (XPS), Raman spectrometry, Fourier transform infrared spectrometry (FT-IR), electron energy loss spectroscopy (EELS) and Si29 magic-angle spinning nuclear magnetic resonance spectrometry (MAS-NMR). XPS analyses have shown that the main bonds are Si–C, Si–N, and C–C, and have suggested the existence of C–N bonds. According to Raman analyses and complementary FT-IR absorption of thin films, the coatings are nonhydrogenated. Si, C and N atomic chemical environments are more complicated than in a mixture of pure Si3N4–SiC phases. The examination of the Si KL2,3L2,3 line shapes recorded by XPS have allowed one to state the existence of Si(C4−nNn) units. Mixed coordination shells around silicon have been confirmed by EELS analyses. Additionally, FT-IR reflection analyses have proved that Si is both bonded with N and C. Indirect indication has been obtained owing to the Si29 MAS-NMR analyses of powders. Raman analyses have been conclusive to assume that C–C bonds correspond to a mixed sp3−sp2 carbon configuration linked with Si(C4−nNn) tetrahedra with 0⩽n⩽4.
Theoretical investigation of temperature induced phase transition in exchange coupled double layers
Authors: Sbiaa R. , Gall H. Le , Koshkina O. , Harfaoui M. El
Published: July 2002

In the present work the mean field theory is used to determine the magnetic properties of a GdCo “planar” layer under exchange interaction with a TbFeCo “perpendicular” layer. The magnetization distributions φ1 and φ2 in the planar and perpendicular layers are determined from a micromagnetic model using a variational method of the magnetic energies in the temperature range 0–500 K. φ2 presents small change with the temperature. On the other hand, φ1 and its mean value 〈φ1〉 are very sensitive to the temperature and the layer composition and thickness. A temperature induced phase transition with a magnetization reorientation from in-plane to a perpendicular direction can be induced in the planar layer in a temperature window ΔT which depends on its compensation temperature TCP1 and its thickness which has to be lower than a critical value.
Magnetotransport properties of NiFe–Ag granular alloys: Origin of the thermal behavior
Authors: Badia F. , Batlle X. , Labarta A. , Watson M. L. , Johnston A. B. , Chapman J. N.
Published: July 2002

The effect of the temperature and magnetic field on the giant magnetoresistivity (GMR) of two FeNi–Ag granular alloys of composition Fe11.4Ni6.4Ag82.2 and Fe7.6Ni16.4Ag76.0 is discussed. Both samples were prepared by rf magnetron sputtering. Parts of them were rapidly annealed at 600, 650, and 750 °C. All samples displayed giant magnetoresistivity which decays from its maximum value with a Tm behavior, with m≈0.8–0.9, suggesting that the decrease in the maximum magnetoresistivity is due to the reduction in the particle magnetization associated with the spin wave excitation, which is a different mechanism to the electron-magnon interaction responsible for the T dependence of GMR in magnetic multilayers. Magnetoresistivity ρM decreases with temperature sharing essentially the same temperature decrease as the square of the macroscopic magnetization M in the whole magnetic field range studied, which is due to the reduction in the particle magnetization and to superparamagnetic effects. The effect of the width of the particle size distribution and interparticle interactions on the linear relation ρM vs M2 are discussed. Care should be taken when representing ρM/ρ(T,H=0) vs (M/Ms)2 because the strong temperature-dependent slope shown in these plots is mainly due to the temperature dependence of both the resistivity ρ(T,H=0) and Ms, and it is not an intrinsic T dependence of GMR in granular alloys. Experimental results suggest that in granular materials, magnetoresistivity is dominated by magnetic moments at the surface of the particles, which also play a very important role in the demagnetization processes, and small magnetic particles.
Low-temperature admittance measurement in thin film amorphous silicon structures
Authors: Caputo D. , Forghieri U. , Palma F.
Published: July 2002

In this paper we analyze low-temperature admittance (capacitance and conductance) measurement as an effective tool for the characterization of amorphous silicon doped layers embedded in thin film structures. Temperature and frequency ranges of 20–250 K and 1–100 kHz, respectively, were used. Measurements were performed on p-i silver and p-i-n structures. Devices with different thicknesses, carbon, and boron content of the p-doped layer were examined. The evolution of the conductance of p-i-n solar cells under illumination was also investigated. Results show excellent sensitivity of the measurement to the states of the doped layer. This sensitivity is explained by using a finite difference simulation program, which proves that at low temperature the trapping process is spatially limited to the doped layers.
An exploratory study of the conduction mechanism of hydrogenated nanocrystalline silicon films
Authors: He Yuliang , Wei Yayi , Zheng Guozhen , Yu Minbin , Liu Min
Published: July 2002

By using the ultrahigh vacuum plasma enhanced chemical vapor deposition system to prepare nc-Si:H films with high conductivity, the experimental results show that the conductivity of nc-Si:H films increases with decreasing the mean grain size of films. Hence, there exists a small size effect on the conduction process. Based on the experimental data, we used the effective-medium theory to calculate the partial conductivity σc of crystallites and σi of the interface conductivity, respectively. Otherwise, we found that there existed two structure phase change point results from the effective-medium theory calculated for the materials of silicon films. The results suggest that the high conductivity of nc-Si:H films results mainly from the crystallites, and moreover, the interface region may serve as insulator layers. Thus, we may consider that the crystallites in nc-Si:H films act as quantum dots. In this paper, we present a heteroquantum dot tunneling model to discuss the transport process for the nc-Si:H films. Our calculated results agree very well with the experimental conductivity data for nc-Si:H films.
Cubic (In,Ga)N layers grown on GaAs(001) by dc plasma-assisted molecular beam epitaxy
Authors: Yang B. , Brandt O. , Jenichen B. , Müllhäuser J. , Ploog K. H.
Published: July 2002

Cubic (In,Ga)N layers with In contents up to 11% are grown on GaAs(001) by dc plasma-assisted molecular beam epitaxy. Comparatively high substrate temperatures are used to desorb In accumulated on the growth front by the massive In segregation in this material system. We report the observation of band-edge photoluminescence and the dependence of the emission energy on In composition for the (In,Ga)N layers.
Control of in-plane texture of body centered cubic metal thin films
Authors: Harper J. M. E. , Rodbell K. P. , Colgan E. G. , Hammond R. H.
Published: July 2002

We show that dramatically different in-plane textures can be produced in body centered cubic (bcc) metal thin films deposited on amorphous substrates under different deposition conditions. The crystallographic orientation distribution of polycrystalline bcc metal thin films on amorphous substrates often has a strong 〈110〉 fiber texture, indicating that {110} planes are parallel to the substrate plane. When deposition takes place under bombardment by energetic ions or atoms at an off-normal angle of incidence, the 〈110〉 fiber texture develops an in-plane texture, indicating nonrandom azimuthal orientations of the crystallites. Three orientations in Nb films have been observed under different deposition geometries, in which the energetic particle flux coincides with channeling directions in the bcc crystal structure. In-plane orientations in Mo films have also been obtained in magnetron sputtering systems with various configurations. These are described, and an example is given in which the in-plane orientation of Mo films deposited in two different in-line magnetron sputtering systems differs by a 90° rotation. In these two cases, there is a strong 〈110〉 fiber texture, but the in-plane 〈100〉 direction is oriented parallel to the scan direction in one system, and perpendicular to the scan direction in the other system. The conditions which produce such different in-plane textures in two apparently similar sputtering systems are discussed.
Electron-beam damaged high-temperature superconductor Josephson junctions
Authors: Pauza A. J. , Booij W. E. , Herrmann K. , Moore D. F. , Blamire M. G. , Rudman D. A. , Vale L. R.
Published: July 2002

Results are presented on the fabrication and characterization of high critical temperature Josephson junctions in thin films of YBa2Cu3O7−δ produced by the process of focused electron-beam irradiation using 350 keV electrons. The junctions so produced have uniform spatial current densities, can be described in terms of the resistive shunted junction model, and their current densities can be tailored for a given operating temperature. The physical properties of the damaged barrier can be described as a superconducting material of either reduced or zero critical temperature (Tc), which has a length of ∼15 nm. The Tc reduction is caused primarily by oxygen Frenkel defects in the Cu–O planes. The large beam currents used in the fabrication of the junctions mean that the extent of the barrier is limited by the incident electron-beam diameter, rather than by scattering within the film. The properties of the barrier can be calculated using a superconductor/normal/superconductor (SNS) junction model with no boundary resistance. From the SNS model, we can predict the scaling of the critical current–resistance (IcRn) product and gain insight into the factors controlling the junction properties, Tc, and reproducibility. From the measured IcRn scaling data, we can predict the IcRn product of a junction at a given operating temperature with a given current density. IcRn products of ∼2 mV can be achieved at 4.2 K. The reproducibility of several junctions in a number of samples can be characterized by the ratio of the maximum-to-minimum critical currents on the same substrate of less than 1.4. Stability over several months has been demonstrated at room and refrigerator temperatures (297 and 281 K) for junctions that have been initially over damaged and then annealed at temperatures ∼380 K. Junctions manufactured using conventional lithography (0.5 μm wide) and which are suitable for digital electronics (Ic=500 μA at 40 K) can achieve IcRn products of 650 μV at 40 K. The production of 100 of these stabilized junctions could be accomplished in ∼4 h of irradiation time. The IcRn scaling also indicates that junctions suitable for high sensitivity superconducting quantum interference devices (Ic∼100 μA) can be made with IcRn products of ∼120 μV at 77 K.
Theory of a high frequency magnetic tunable filter and phase shifter
Authors: Astalos R. J. , Camley R. E.
Published: July 2002

Microwave propagation in a layered dielectric/ferromagnet were explored in the past. Previous studies, however, made use of an approximation to the full permeability tensor in the ferromagnet. This approximation fails in a frequency range where the structure can act as a band pass filter. Here we seek to verify the behavior in the predicted band pass region using the full permeability tensor. We also explore the use of the layered structure in two devices: a tunable band pass filter and an adjustable phase shifter.
Measurements of negative ion density in high-density oxygen plasmas by probe-assisted laser photodetachment
Authors: Hayashi D. , Kadota K.
Published: July 2002

Probe-assisted laser photodetachment has been developed and applied to measure the negative ion density (n−) in high-density plasmas. Temporal variation of n− is obtained in high-density and low-pressure oxygen plasmas generated by helicon wave excitation. Negative ions are not observed in the active discharge phase and rapid increase of n− is seen only in the afterglow phase. This efficient production of negative ions is considered to be due to dissociative electron attachment to metastable molecular states, O2M(A3Σu+, A′3Δu, and c1Σu−), located at 4–5 eV above the ground state.
Chemical bonding and electronic structure in binary VNy and ternary T1−xVxNy nitrides
Authors: Sanjinés R. , Wiemer C. , Hones P. , Lévy F.
Published: July 2002

Core-level binding energies (BEs) and valence-band structures of VNy and Ti1−xVxNy films (0⩽x⩽1, 0.4⩽y⩽1.1), deposited by rf magnetron sputtering, have been investigated by x-ray photoemission spectroscopy. The core level BEs and valence-band spectra are discussed in relation to the microhardness (Knoop microindentation). The binding energy values and the shape of the core level peaks are representative of the chemical bonding between the elements, and are thus related to the microhardness. Comparison of the experimental spectra with various theoretical density of states calculations as a function of x and y shows evidence of the influence of nitrogen vacancies and of the vanadium content on the mechanical properties.
Solid state interdiffusions in epitaxial Fe/GaAs(001) heterostructures during ultrahigh vacuum annealings up to 450 °C
Authors: Lépine B. , Ababou S. , Guivarc’h A. , Jézéquel G. , Députier S. , Guérin R. , Filipe A. , Schuhl A. , Abel F. , Cohen C. , Rocher A. , Crestou J.
Published: July 2002

We have used a set of complementary experimental techniques to characterize an epitaxial structure (25 nm Fe)/GaAs(001) annealed at 450 °C under ultrahigh vacuum conditions. The solid state interdiffusion leads to the formation of an epitaxial reaction layer made of Fe2As patches embedded in a Ga rich Fe3Ga2−XAsX ternary phase. The epitaxial character of this layer explains how the usually reported epitaxial growth of Fe on GaAs performed in the temperature range of 175 to 225 °C is possible in spite of the species intermixing occurring at the interface. Moreover, the observed grains of Fe2As explain the decrease of magnetization at the interface in such contact, since Fe2As is an antiferromagnetic alloy.
Theoretical and experimental study of interband optical transitions in semiconducting iron disilicide
Authors: Filonov A. B. , Migas D. B. , Shaposhnikov V. L. , Borisenko V. E. , Henrion W. , Rebien M. , Stauss P. , Lange H. , Behr G.
Published: July 2002

The interband optical spectra of the semiconducting β phase of iron disilicide (β-FeSi2) were investigated in the energy range from 0.5 to 5.0 eV. The dielectric function and other optical functions were deduced from ellipsometric experiments and calculated within the local-density approximation by using the semirelativistic linear muffin-tin orbital method. Reasonable agreement between the calculated and measured data has been obtained.
Coercivity and exchange coupling in PrCo:Co nanocomposite films
Authors: Liu J. P. , Liu Y. , Sellmyer D. J.
Published: July 2002

Magnetic hysteresis and intergrain exchange coupling in nanostructured PrCo:Co composite films have been investigated. The composite thin films were made by multilayer sputtering and subsequent annealing. It is found that the coercivity mechanism is related to film morphology, especially the Co phase fraction. Evidence for the hard-soft-phase exchange coupling has been found and high energy products have been obtained.
Temperature dependence of ferromagnetic resonance as induced by NiO pinning layers
Authors: Lubitz P. , Krebs J. J. , Miller M. M. , Cheng Shufan
Published: July 2002

Ferromagnetic resonance (FMR) experiments have been conducted near 9.5 GHz on permalloy (Py) thin films which are components of spin valves and related structures. These so-called giant magnetoresistance structures often use antiferromagnetic NiO to achieve pinning of one magnetic layer. Magnetic anisotropies acting on these pinned layers were deduced by observing their resonances for fields perpendicular to and in the sample plane. We used data taken from 4 to 600 K to identify potential mechanisms of pinning, anisotropy, and linewidth. The anisotropic exchange pinning and an isotropic downward FMR shift vanish at a blocking temperature well below the bulk Neél temperature of NiO. The strong temperature dependencies of the isotropic shift and linewidth may reflect the presence of different spin pinning subsystems and the different time scales of the FMR and low frequency or static measurements.
A novel method for quantitative study of domain reversal behavior
Authors: Choe Sug-Bong , Shin Sung-Chul
Published: July 2002

A novel method to quantitatively analyze the domain reversal behavior has been adopted to understand the total-thickness-dependent domain reversal behavior in Co/Pd multilayers. The wall-motion speed and the nucleation rate were simultaneously determined by analyzing serial domain images observed using a real-time domain observation system. Using this method, sensitive decrement of the wall-motion speed with increasing total multilayer thickness has been found to be responsible for the contrasting reversal behavior in Co/Pd multilayers.
Exchange anisotropy in Ni82Fe18O{100}/Ni80Fe20 bilayers
Authors: Lai Chih-Huang , White Robert L. , Wang Connie P. , Anthony Thomas C.
Published: July 2002

Ni 0.82 Fe 0.18 O {100} epitaxial films, ranging in thickness from 70 to 1200 Å, were grown by solid-source metal-organic chemical vapor deposition. The exchange field for 45 Å Ni80Fe20 on Ni0.82Fe0.18O films reached 250 Oe at 200 Å Ni0.82Fe0.18O and then stayed almost constant with increasing thickness of Ni0.82Fe0.18O. Furthermore, the coercivity for those films is only 55 Oe. The high exchange field and the low coercivity are attributable to the high in-plane anisotropy of Ni0.82Fe0.18O{100} and the uncompensated spins in the interface of Ni0.82Fe0.18O/Ni80Fe20. The blocking temperature of these films is 180 °C, lower than that of NiO/Ni80Fe20 (∼220 °C). The reduction of the blocking temperature may result from local Fe–O–Fe or Fe–O–Ni bonding, which loses the superexchange interaction at a lower temperature than the blocking temperature of NiO.