bluuebunny/crossref_metadata_2025 huggingface dataset:
An experimental study of a metal-oxide-semiconductor photomultiplier
Authors: Lou L. F. , Tettemer G. L.
Published: July 2002

An investigation of the solid-state metal-oxide-semiconductor photomultiplier (MOSPM) has been performed. A semiquantitative description is given of the MOSPM and associated device physics. Experimental results are presented and interpreted, including the electrical response in the dark, the optical response, the dependence on applied voltage ramp rate, the dependence on light-pulse rise-time, and the effects of background light and optical intensity. An experimental comparison of the MOSPM with a GaAs photomultiplier tube (PMT) is also made. In terms of responsivity, the present MOSPM is equivalent to that for the PMT operated at 1300 V. However, the noise for the MOSPM under the present operating conditions is three orders of magnitude larger than that for the PMT. Methods for significantly reducing the noise are discussed. The MOSPM appears to have potential for utilization in the detection of low-intensity, fast-rise time light pulses.
Trap-dominated breakdown processes in an insulator bridged vacuum gap
Authors: Bommakanti R. G. , Sudarshan T. S.
Published: July 2002

Measurements of coordinated, time-resolved breakdown current and luminosity phenomena associated with a pulsed surface flashover event in an insulator bridged vacuum gap are presented. It was observed that the luminosity and current waveforms differ vastly in their temporal character. The luminosity profile has a sharp pulse with no counterpart in the current waveform. A significant afterglow activity is also observed after the cessation of the breakdown current. Further, the profiles of the luminosity and current waveforms changed with successive breakdowns. The rise times and decay times of the luminosity waveform, the time delay between the onset of the luminosity and current waveforms, and the rise time of the current waveform changed with successive breakdowns showing regular trends. The above modifications in the temporal profiles of luminosity with successive breakdowns are analyzed on the basis of carrier trapping and recombination processes within the localized levels of the forbidden gap associated with the insulator-vacuum interface. The experimental results reported here qualitatively support the surface flashover model based on carrier trapping for low mobility, large band-gap insulators. The analysis of the results is suggestive of a breakdown model in which hot-electron generation culminates in impact ionization-induced breakdown in the subsurface layers of the insulator.
Study of ultraviolet-laser ablation products of several polymers using time-of-flight mass spectroscopy
Authors: Hansen S. G.
Published: July 2002

The material ejected into vacuum by 266-nm pulsed laser ablation of poly(α-methylstyrene) (PαMS), polycarbonate, poly(ethylene terephthalate), polybenzimidazole, and polyimide is examined using time-of-flight mass spectroscopy with both 193- and 248-nm ionization. PαMS is well behaved in that the primary ejected species are based on the monomer, and intact units ranging up to trimer are observed. The other four polymers show two distinct waves of material passing through the ionization zone: a fast wave (105–106 cm/s) consisting of small bare or nearly bare carbon clusters and a much slower one composed of mainly aromatic fragments in the 128±50 amu range. These species are all smaller than the corresponding monomers and tend to be fairly similar regardless of target material although the spectrum arising from each polymer is unique. It is speculated that the difference in behavior between PαMS and the others relates to the known favorable, thermally induced ‘‘unzipping’’ which occurs in PαMS; when this low energy decomposition channel is not open, the laser-induced temperature rise is greater, and more severe bond-breaking processes occur. This work supports our previous conclusion that polymer film formation by laser ablation proceeds by a fragmentation/repolymerization mechanism but does not generally identify the film-forming species. As part of establishing the range of molecules our ionization scheme is sensitive to, mass spectra of a number of different permanent organic vapors were taken using 193-, 248-, and 266-nm ionization. These results are also discussed.
Resonant optical interactions in active dielectric films
Authors: Mendenhall S. N. , Stafsudd O. M. , Alexopoulos N. G.
Published: July 2002

An investigation of oblique plane-wave electromagnetic scattering in active dielectric films reveals the existence of anomalously large resonances that occur at discrete plane-wave angles of incidence. These resonances may be understood from a ‘‘leaky wave’’ phase matching condition whose predictions for the first three modes agree to within a few percent of those obtained from a rigorous treatment using Maxwell’s equations. Experiments using finite-diameter pump and probe laser beams verify the existence of these scattering resonances with enhancements of the scattered field intensities on the order of 100 observed in active dielectric films as thin as 6 μm. Saturation effects are discussed in the context of a very simple model whose predictions agree qualitatively with experimental measurements. Two novel laser oscillator configurations based upon resonant leaky waveguide interactions were tested and found to have very high-energy extraction efficiency (≥18%) with oscillation being easily achieved using active dielectric films as thin as 6 μm.
A study of Si implanted with oxygen using spectroscopic ellipsometry
Authors: McMarr P. J. , Mrstik B. J. , Barger M. S. , Bowden G. , Blanco J. R.
Published: July 2002

Si(100) wafers were implanted with O+ at an energy of 180 keV to a dose of 2.3×1018/cm2 in the separation by implanted oxygen process. Following implantation, one wafer was annealed at 1275 °C for 2 h. Spectroscopic ellipsometry measurements were then performed on these samples. Effective medium modeling of the measurements was used to nondestructively depth profile the samples. These results show that the superficial Si layer for the unannealed sample includes noncrystalline and crystalline components. In addition, the optical properties of the buried oxide for the unannealed sample were found to be different from those of bulk fused silica or thermal oxides of Si. The superficial Si layer for the annealed sample was crystalline Si, but the buried oxide consisted of a phase-separated mixture of noncrystalline SiO2 and crystalline Si. These results were further substantiated by selective chemical etch-back studies and additional spectroscopic ellipsometry measurements, and by other techniques, including Raman spectroscopy, infrared transmission measurements, sputter depth profiling using x-ray photoelectron spectroscopy, and Nomarski microscopy.
Temperature and relative density of atomic hydrogen in a multicusp H− volume source
Authors: Bruneteau A. M. , Hollos G. , Bacal M. , Bretagne J.
Published: July 2002

The Balmer β and γ line shapes have been analyzed to determine the relative density and the temperature of hydrogen atoms in magnetic multicusp plasma generators. Results for a 90-V, 4–40-mTorr, 1–18-A conventional multicusp plasma generator and a 50-V, 4-mTorr, 1–15-A hybrid multicusp plasma generator are presented. The relative number density of hydrogen atoms increased smoothly with pressure and discharge current but never exceeded 10%. The absolute atomic number density in a 90-V 10-A discharge varied in proportion with pressure. The atomic temperature (in the 0.1–0.4-eV range) decreased with pressure and slowly increased with the discharge current. The role of atoms in the processes determining the H− temperature and the H2 vibrational and rotational temperatures is discussed. The results confirm that in multicusp negative-ion sources collisional excitation of ground state atoms and molecules by energetic electrons is the dominant process in Balmer-β and -γ light emission.
The effect of deposition parameters on the wear properties of yttria-stabilized zirconia overcoats
Authors: Miller M. S. , Skelcher W. L. , Narayan P. B. , Swami G. T. , Crist J. , Peterson R. L. , Thomas R. R. , Erskine H. F.
Published: July 2002

Yttria-stabilized zirconia was rf-diode sputtered over a 250-nm chromium underlayer on textured aluminum-NiP 130-mm-diam substrates. Tribological properties of the overcoat were evaluated via contact start-stop (CSS) testing, as a function of oxygen partial pressure, substrate bias potential, and argon pressure. Depending on deposition conditions, a wide range of friction and wear properties was observed. Lower oxygen partial pressures (<0.01 Pa) produced the lowest average friction levels of 0.3–0.5 after 30 000 CSS. Use of high argon sputtering pressures (>1.6 Pa) produced overcoats which demonstrated definite wear and often crashed during contact stop-start testing. SEM and TEM photographs revealed that the overcoats with poor wear characteristics had significantly different grain sizes and higher void contents than overcoats with superior wear properties deposited at lower argon pressures. Application of a fluorocarbon surface lubricant reduced average friction levels after 30 000 CSS from 0.8 on an unlubed disk to 0.35.
Quadrupled nondestructive outputs from magnetoresistive memory cells using reversed word fields
Authors: Pohm A. V. , Comstock C. S. , Hurst A. T.
Published: July 2002

A new operating mode has been discovered in transverse magnetoresistive (MR) memory cells which increases the usable nondestructive sense output by more than a factor of 4 over the original mode described, which employed a unipolar word field. The new mode allows for increased cell density, decreased memory access time, and increased margins. This new operating mode was examined experimentally and analytically for experimental cells ranging in size from 1.5×5 μm to 1.8×18 μm. The MR material used in the cells consisted of two 150-Å-thick magnetic layers (65% Ni, 15% Fe, 20% Co) separated by a 50-Å-thick reacted tantalum layer to break the exchange. In the new operating mode, a word field of one polarity is used for writing (parallel to the edge magnetization) and a reversed polarity is used for reading. During the reading process, 120°–225° paired ‘‘walls’’ are formed at the edges. The energy in the walls is sufficient to restore the elements to their original states even if switching occurs (in a direction opposite to the normal rotation during writing). The operating margins are improved because while reading only one and not both the word field and the sense field are in a direction to cause normal switching.
Surface phonons in Cu/Ni superlattices
Authors: Mattson J. , Bhadra R. , Ketterson J. B. , Brodsky M. , Grimsditch M.
Published: July 2002

The modulation wavelength dependence of the surface-wave velocity in Cu/Ni superlattices has been investigated using Brillouin scattering. It is the first compositionally modulated system to be studied by this technique and the first for which elastic properties have been determined by both ‘‘macroscopic’’ methods and Brillouin scattering. Contrary to the enhancements previously reported in the biaxial modulus and in the Young’s modulus, the modulus associated with the surface-wave velocity shows no evidence of anomalous behavior.
Misfit strain relaxation in GexSi1−x/Si heterostructures: The structural stability of buried strained layers and strained-layer superlattices
Authors: Houghton D. C. , Perovic D. D. , Baribeau J.-M. , Weatherly G. C.
Published: July 2002

The critical thickness-strain relationships for buried strained layers and strained-layer superlattices (SLSs) are derived using an energy balance model. Relaxation of the entire heterostructure and individual strained layers by both 60° type a/2〈011〉 and pure edge dislocations is considered. GexSi1−x/Si heterostructures designed to investigate the stability regimes predicted by the model were grown by molecular-beam epitaxy. The extent of relaxation and the detailed dislocation structure were assessed in annealed structures by x-ray rocking curve analysis, transmission electron microscopy, and Nomarski microscopy of etched samples. Comparison of metastable as-grown and post-growth annealed microstructures revealed the evolution of misfit dislocation structure as equilibrium was approached on annealing in the temperature range 600–900 °C. The predominant relaxation mechanism for most GexSi1−x/Si heterostructures was by 60° a/2 〈011〉 misfit dislocations at the first strained-layer/substrate interface. However, for SLSs with strained layers exceeding their individual critical thickness, pairs of dislocations and prismatic loops on (011) planes were observed entrained within the GexSi1−x layers. The agreement between experimentally observed relaxation behavior and the critical thickness versus strain predictions of the energy balance model is remarkable. Superlattices and buried strained layers were found to be only slightly more stable than an uncapped strained layer of the equivalent strained-layer thickness. Interdiffusion was observed at annealing temperatures above 800 °C; annealing at 900 °C for 30 min was sufficient to eliminate the strain and composition modulation in a superlattice with a 55-nm period and x=0.25. The relative influence of the various strain relaxation mechanisms is discussed for the alloy range 0<x<1 and for geometries with strained-layer dimensions varying from 0.8 to ∼500 nm.
Structures and properties of chromium thin films prepared by anisotropic-emission-effect sputter deposition
Authors: Gotoh Yasuhito , Taga Yasunori
Published: July 2002

Chromium thin films were prepared by a sputter-deposition system in which substrates were arranged semicircularly against a chromium target. Structures and compositions of the films were investigated by x-ray diffractometer, x-ray photoelectron spectroscopy, electron probe microanalyzer, and scanning electron microscope. It was found that oxygen content in the films was highest at the opposite side of the target and was lowest at the position of 60° or 75° off with respect to the target normal. At the latter position, (110)-preferred orientation and enlargement of the bcc chromium lattice were observed. Although cracks were generated in the films deposited at the opposite side of the target, no cracks were generated in the films deposited at the oblique direction. These results on the chromium films could be explained in terms of the bombardment effect by the reflected argon atoms whose energy was a function of the scattering angle.
Liquid-phase epitaxy and characterization of Si1−xGex layers on Si substrates
Authors: Hansson P. O. , Werner J. H. , Tapfer L. , Tilly L. P. , Bauser E.
Published: July 2002

Liquid-phase epitaxy allows SiGe alloys of good quality to be grown on Si substrates. We deposit single crystalline, n-type Si1−xGex films with 0.7<x<1 from Bi solutions on (111)-oriented Si. The films are up to several μm thick and are uniform in thickness and in composition. The analysis by x-ray diffraction indicates good crystallinity and a dislocation density below 5×107 cm−2. Photoluminescence measurements show well-resolved peaks with the smallest linewidths reported so far for epitaxial SiGe. Hall-effect measurements yield electron concentrations around 1×1016 cm−3 and room-temperature electron mobilities of up to 340 cm2/V s.
Escape from quantum wells via polar optical phonon scattering
Authors: Liang Lie , Lent Craig S.
Published: July 2002

We calculate the rate for electrons confined in a quantum well to escape to unbound, current-carrying states by polar optical phonon scattering. We explicitly include the two-dimensional to three-dimensional nature of the transition and choose final state wave functions which are genuinely unbound. We find that the escape rate decreases dramatically as the well depth increases, even for electrons with more than enough energy to surmount the well walls. The real-space transfer rate is much smaller than either the bulk scattering rate or the confined bound-to-bound scattering rate. We explore this phenomenon and give a detailed explanation of the rate depression. We also show that the electron escape rates have a strong directional dependence in asymmetric wells. Electrons scatter out preferentially in the direction of the more abrupt interface.
Glow discharge simulation through solutions to the moments of the Boltzmann transport equation
Authors: Meyyappan M. , Kreskovsky J. P.
Published: July 2002

A self-consistent continuum model is presented for glow discharges based on the moments of the Boltzmann transport equation. The resultant set of governing equations consist of continuity and momentum equations for electrons and ions, an energy conservation equation for electrons and Poisson’s equation. An efficient numerical scheme to solve the set of coupled equations is presented. Results from case studies of dc discharges are used to illustrate the model. A parametric study varying the cathode voltage, gas pressure, and secondary electron emission coefficient predicts many of the well-known features of dc discharges.
Transient diffusion of ion-implanted B in Si: Dose, time, and matrix dependence of atomic and electrical profiles
Authors: Cowern N. E. B. , Janssen K. T. F. , Jos H. F. F.
Published: July 2002

The time evolution of B diffusion and electrical activation after ion implantation and annealing at 800 and 900 °C is studied using secondary-ion mass spectrometry and spreading-resistance profiling. The time evolution at 800 °C is observed in both crystalline and post-amorphized samples. Amorphized samples show near-normal concentration enhanced diffusion. Crystalline samples show anomalous transient diffusion, with a rapidly diffusing low-concentration region and a static peak region above a critical concentration Cenh=3.5×1018 cm−3. The peak region above Cenh is shown to be electrically inactive. The static, inactive B is released over a period of many hours, compared with the transient diffusion enhancement which relaxes to near-normal within 30 min. The time evolution of B diffusion at 900 °C is observed as a function of implantation dose. A critical concentration for transient diffusion, Cenh=8×1018 cm−2, independent of dose, is observed at this temperature. The transient diffusion enhancement in the diffusing part of the B profile increases with dose, up to a dose of ∼5×1014 cm−3, and saturates at higher doses. A comparison with published data shows that Cenh∼ni within a factor 2 over the temperature range 550–900 °C. We interpret our observations in terms of a nonequilibrium point-defect model of diffusion and intermediate defect formation.
Energy analysis of neutral atoms in broad oxygen ion beams by Doppler-shift measurements
Authors: Heinrich F. , Stoll H.-P. , Scheer H.-C. , Hoffmann P.
Published: July 2002

Optical emission spectroscopy has been established as a valuable method for the analysis of broad oxygen ion beams. The ion beams used for reactive ion-beam etching have been investigated in the energy range of 300–1500 eV. From survey spectra O+2 molecules and neutral O atoms are identified as main emitting species. Concerning the occurrence of emission lines the beam spectrum resembles that obtained from an O2 rf plasma. The intensity ratios however are strongly different within both spectra. Whereas electron impact is the main source for electronic excitation in ordinary etch plasmas, heavy particle collisions are suggested to play an important role in the investigated ion beams. Beam-induced emissions of atomic oxygen neutrals were recorded at high resolution of 0.1 Å. The O emission lines were found to be triple peaked. One peak at the unshifted wavelength and two Doppler-shifted peaks could be resolved. The absolute values of the wavelength shifts are well correlated to the energies of the initial ions extracted from the ion source by a grid optics. Besides slow atoms, atoms moving with the full beam energy as defined by the ion extraction conditions and with only half the beam energy are detected. The observed Doppler structure is attributed to charge exchange and dissociative collisions taking place in the gas phase.
Electron paramagnetic resonance and capacitance-voltage studies of ultraviolet irradiated Si-SiO2 interfaces
Authors: Brower K. L. , Schubert W. K. , Seager C. H.
Published: July 2002

Electron paramagnetic resonance and capacitance-voltage studies of hydrogen passivated Si-SiO2 interfaces indicate that UV irradiation of the interface does not result in the creation of new Pb centers or interface states providing no photocurrent is allowed to pass through the oxide. This is in contrast to the generally known fact that UV irradiation with photoinjection does form interface states.
Intensity-dependent upconversion efficiencies of Er3+ ions in heavy-metal fluoride glass
Authors: Yeh D. C. , Sibley W. A. , Schneider I. , Afzal R. S. , Aggarwal I.
Published: July 2002

The upconversion of infrared radiation to shorter wavelengths by Er3+ ions in heavy-metal fluoride glasses, some doped with Yb3+, has been studied over a wide intensity range and for various excitation wavelengths. The upconversion efficiency measured at room temperature varies linearly or quadratically with intensity and saturates at 100 W/cm2 or higher, depending on emission wavelength. For 4 mol % ErF3 in BaF2/ThF4, the 4I11/2 to 4I15/2 transition is over 10% efficient for 400 W/cm2 of absorbed 1.5-μm power, i.e., for 4I15/2 to 4I13/2 excitation. A rate equation model and Judd–Ofelt analysis of data for the glasses doped with just Er3+ provide an understanding of the upconversion process while yielding values for Er3+ energy-transfer rates and excited-state populations. These results could be used to develop glasses for lasing and as infrared optical detectors.
Stress relaxation of passivated aluminum line metallizations on silicon substrates
Authors: Korhonen M. A. , Black R. D. , Li Che-Yu
Published: July 2002

In the present study, the Eshelby theory of inclusions is applied to model the stresses arising after heat treatment at 400 °C in aluminum line metallizations, embedded in silicon/passivation matrix. The stresses obtained are about 200 MPa higher than the ones previously reported. Moreover, the stresses in the axial and width directions of the lines are shown to be on the same order, while the normal stress is smaller, especially in the lines of low thickness-to-width ratio. A modification of the familiar sin2 ψ method of x-ray stress measurement is presented to deal more accurately with the [111]-fiber texture present in the aluminum lines studied. The lateral and normal stresses in the aluminum metallizations after a heat treatment at 400 °C are measured in room temperature by x-ray diffraction from 4 h after the heat treatment at 400 °C up to 3 months. The experimental results are well in accord with predictions obtained from the Eshelby model. Particularly, the lateral stresses are found to be about equal, while the initial normal stress is smaller, but eventually becomes the largest stress component. Dislocation mechanisms to rationalize the present observations are discussed: at longer times, diffusion-controlled dislocation climb and void growth connected to it appear to be the most important mechanisms to relieve the stress, while during cooling dislocation glide is also significant.
Spectroscopic ellipsometry studies of YBa2Cu3O7−δ deposited on SrTiO3
Authors: Sengupta L. C. , Huang D. , Roughani B. , Aubel J. L. , Sundaram S. , Chang C. L.
Published: July 2002

The dielectric function ε=ε1−iε2 of the YBa2Cu3O7−δ high-Tc superconducting films grown on (100) SrTiO3 (c-axis oriented) and (110) SrTiO3 (ab-oriented) substrate was measured by spectroscopic polarization modulation ellipsometry (SPME) and changes in film orientation were studied by comparing films of various thicknesses. The films deposited on SrTiO3 (100) substrates demonstrated an isotropic ε1 that changed with film thickness. It is observed that the decrease in the metallic dielectric behavior associated with the increase in the thickness of the films grown on (100) SrTiO3 substrates is mainly due to a change in the orientation of the films. The films deposited on SrTiO3 (110) showed anisotropic dielectric behavior when the plane of polarization is parallel and perpendicular to the c-axis of the film. These studies show that for this high-temperature superconductor with anisotropic dielectric behavior, SPME is a highly sensitive technique capable of measuring small changes in the film orientation.
Growth and characterization of Fe-doped semi-insulating InP prepared by low-pressure organometallic vapor phase epitaxy with tertiarybutylphosphine
Authors: Huang Rong-Ting , Appelbaum Ami , Renner Daniel , Burke Wally , Zehr Stanley W.
Published: July 2002

Fe-doped semi-insulating InP epitaxial layers were grown by low-pressure organometallic vapor phase epitaxy with tertiarybutylphosphine (TBP), triethylindium (TEI) and iron pentacarbonyl [Fe(CO)5] as the reactant gases. The growth was performed by varying the growth rate, growth pressure and V/III ratio. The epitaxial layers were characterized by optical microscopy, secondary ion mass spectrometry, double crystal x-ray diffraction and current-voltage measurements. Semi-insulating InP epitaxial layers with specular surface morphology and low defect density were obtained at TBP partial pressure higher than 0.38 torr. A premature reaction between TEI and TBP was observed which presumably formed TEI:TBP adducts and/or polymers. As a result, the growth rate of Fe-doped semi-insulating InP layers grown at low pressure with TBP in our reactor decreased by 35% as the V/III ratio was increased from 15 to 46. Electrical measurements on these layers showed that the resistivity varied from 1.7×107 to 4×108 Ω cm as the V/III ratio was increased from 15 to 46. The resistivity of TBP-grown materials is comparable to that of PH3-grown materials over a measurement temperature range of 25–110 °C. Selective growth and surface planarization of Fe-doped InP grown with TBP and trimethylindium on patterned etched mesas were achieved.
The electromagnetic field of a horizontal electric dipole in the presence of a three-layered region
Authors: King Ronold W. P.
Published: July 2002

The electromagnetic field generated by a horizontal electric dipole in the air over the surface of a two-layered region is determined for continuous-wave excitation. The region of interest consists of a conductor coated with an electrically thin layer of dielectric under a half-space of air. Simple explicit formulas are derived for the field at all points in all three regions, including the surface wave. Typical applications are to microstrip circuits and antennas and to remote sensing from the arctic ice.
Magnetic anisotropy of sputtered media induced by textured substrate
Authors: Kawamoto Atsushi , Hikami Fuminori
Published: July 2002

Thin-film disks sputtered on the textured substrate can have a magnetization easy axis along the circumferential direction. The mechanism responsible for the induced magnetic anisotropy in CoCrTa films has been investigated. The in-plane anisotropic strain (εa) in CoCrTa films deposited on various thicknesses of Cr underlayer were calculated from the lattice constants of CoCrTa(101̄1) in circumferential and radial directions measured by x-ray diffraction. Both the in-plane magnetic anisotropy energy (Kθ) and the in-plane anisotropic strain in the compressive side ( − εa) were observed to increase with the decrease of the thickness of the Cr underlayer. The corresponding calculated magnetostriction constant λ was − 30 × 10−6. This value is consistent with the magnetostriction constant of CoCrTa films measured by three points bending method, thus suggesting that the magnetic anisotropy in CoCrTa films is induced by the anisotropic strain through the inverse magnetostrictive effect.
Characterization of magneto-optical recording media in terms of domain boundary jaggedness
Authors: Bernacki Bruce E. , Mansuripur M.
Published: July 2002

Noise in magneto-optical recording devices can be classified as system-related noise and media noise. Media noise is rooted in the magnetic and magneto-optical properties of the recording media. To investigate media noise and its relation to microstructure and micromagnetics of thin films, the jaggedness of magnetic domain boundaries is characterized using static domain observations in which the fractal dimension D is measured for the domain boundaries. Samples of TbFeCo deposited under similar conditions, but with slightly different compositions, exhibited different amounts of jaggedness, and hence, slightly different values of D, i.e., 1.05≤D≤1.20. Temperature dependent measurements performed on a TbFe sample showed increasing D with increasing temperature, 1.19≤D≤1.28 for 300 K ≤T≤360 K. Possible sources of jaggedness include structural/magnetic inhomogeneities as well as competition between domain-wall energy and demagnetization.
Measurements of the anomalous magnetoresistance effect in Co/Pt and Co/Pd multilayer films for magneto-optical data storage applications
Authors: Hajjar Roger A. , Mansuripur M. , Shieh H.-P. D.
Published: July 2002

The anomalous magnetoresistance effect in compositionally modulated TM/TM films (Co/Pt and Co/Pd) has been investigated. Results of measurements on samples at room temperature as a function of the strength of the applied magnetic field are reported. For each sample three different configurations are investigated in which the direction of the applied field is (i) perpendicular to the plane of the film, (ii) in the plane of the film and parallel to the direction of the electric current, (iii) in the plane of the film and perpendicular to the direction of the current. During these measurements the extraordinary Hall effect and the magneto-optical Kerr effect have also been monitored. This additional information, together with the magnetization measurement results obtained from a vibrating sample magnetometer, are used to analyze the data and to explain some of their interesting features.
Synchrotron radiation photoemission analysis for (NH4)2Sx-treated GaAs
Authors: Sugahara Hirohiko , Oshima Masaharu , Oigawa Haruhiro , Shigekawa Hidemi , Nannichi Yasuo
Published: July 2002

The chemistry of the (NH4)2Sx-treated n-GaAs (100) surfaces has been studied using synchrotron radiation photoemission spectroscopy. Ga 3d, As 3d, and S 2p photoemission spectra are measured before and after annealing in vacuum with a photon energy of about 210 eV, where S 2p core level spectra can be sensitively detected. It is found that Ga-S, As-S, and S-S bonds are formed on the as-treated GaAs surfaces, and that stable Ga-S bonds become dominant after annealing at 360 °C for 10 min in vacuum. The thickness of the surface sulfide layer is reduced from about 0.5 to 0.3 nm by annealing. The surface Fermi- level position of the as-treated surfaces is determined to be about 0.8 eV below the conduction band minimum, which is about 0.1 eV closer to the valence band maximum than that of the untreated surfaces. A Fermi-level shift of 0.3 eV toward a flat band condition is also observed after annealing. It is found that the Ga-S bonding plays an important role in passivating GaAs surfaces.
Annealing behavior of deep-level defects in semi-insulating gallium arsenide studied by photoluminescence, infrared absorption, and resistivity mapping
Authors: Müllenborn M. , Alt H. Ch. , Heberle A.
Published: July 2002

Deep-level defects in as-grown, ingot-annealed, and wafer-annealed samples of semi-insulating gallium arsenide have been investigated by spatially resolved measurements of room-temperature photoluminescence, infrared absorption, free-carrier lifetime, and resistivity. High-temperature ingot annealing mainly causes a homogenization of the EL2 distribution. Rapid cooling from a wafer annealing process at T>900 °C suppresses the formation of the previously lifetime-limiting recombination center. After wafer annealing the EL2 defect may be the dominant recombination center, while in as-grown and ingot-annealed material lifetime is limited by a different trap. There is experimental evidence that this trap is related to the 0.8-eV luminescence band and that its density is spatially anticorrelated to the EL2 distribution. Based on lifetime measurements and a correlation of EL2 and photoluminescence topographs, we developed a recombination model, which explains the relationship between defect densities, and photoluminescence. The effect of surface recombination is described by a numerical calculation.
Nonequilibrium response in attenuating smooth plane-wave fronts
Authors: Sano Y.
Published: July 2002

It has been clarified in an earlier work [Y. Sano, J. Appl. Phys. 65, 3857 (1989)] that the locations of attenuating peaks in smooth strain, particle velocity, and stress profiles in a smooth plane-wave front differ, that is, the order of peak precedence is stress, particle velocity, and strain. As a result of the precedence order, the wave front composed of elementary waves such as a contraction wave C, mesocontraction waves I and II, and a vice-rarefaction wave R was formed. That the process is degraded by another rarefaction wave Rb which first follows the wave R, and then outruns the waves R, II, and I in sequence, has also been proved. [Y. Sano, J. Appl. Phys. 67, 4072 (1990)]. After the completion of the degradation process, the wave front, i.e., the wave C, may attenuate little, but steepen. This paper extends the process under consideration to include the steepening process during which the wave C approaches a steady state. In addition to this extension, stationary phenomena in strain, particle velocity, and stress-time profiles are shown to be able to take place in the degradation process. It is one of the main purposes of this paper to show through the phenomena that the response caused by the wave fronts during the process will be unsteady and nonequilibrium. Furthermore, universal properties of the stress-particle velocity paths are clarified. The properties involve concavity or convexity of the path curves produced by the waves C, I, II, and R. Universal properties of the stress-strain paths such as concavity, convexity, or inflection of the path curves by the waves C, I, II, and R are also clarified. Through the behavior of the stress-particle velocity and stress-strain paths having the properties mentioned above, it is also shown that the response caused by the waves will be unsteady and nonequilibrium. The stationary phenomena, the universal properties, and the stress-particle velocity and stress-strain behaviors are compared with the previous experiments and computational data. Another main purpose of this paper is to confirm through comparison the occurrence of the elementary waves and the degradation process in the experiments.
Analysis of signals from superposed relaxation processes
Authors: Link Norbert , Bauer Siegfried , Ploss Bernd
Published: July 2002

System functions of many linear physical systems or autocorrelation functions of their output signals are often a sum of relaxator terms with different relaxation times and amplitudes. In the time domain a superposition of exponential decays e−γt is observed, while in the frequency domain a sum of relaxator terms of structure 1/(γ+iω) is measured. Thus, the response is either the Laplace transform of the system function or its Stieltjes transform, respectively. In both cases it is the task of an analyst to gain the relaxation times and weights from the measured signal. An exact reconstruction of the system function is limited by the noise, measuring time, and number of points measured. In this paper procedures for the approximate reconstruction of the system function are introduced. The equivalence of most of them is shown and their properties are discussed. An expression for the limit of resolution is derived for a given signal-to-noise ratio. The results are applicable to experimental data from various physical systems. For illustration the autocorrelation function of the light scattered from polymer solutions and the response of photoconductors are used.
A microstructural study of indium-indium oxide composite films
Authors: Kwon Chuhee , Kim Jaegyu , Lee Hu Jong , Jung Ho Chul , Park Chan Gyung
Published: July 2002

We have investigated the microstructure of indium-indium oxide composite films prepared by thermal vapor deposition in the oxygen atmosphere. The films show granular-amorphous structural phase transformation near the oxygen concentration of 2 × 10−4 Torr. Although the thermal evaporation generates films with indium grains much larger in size than the reactive sputter deposition, the film resistivity shows the characteristics of the homogeneous films as long as the thickness is larger than the grain size.
Intrinsic stress in hydrogenated amorphous carbon prepared by rf plasma decomposition of methane
Authors: Prince E. T.
Published: July 2002

An unconventional analytical/empirical approach was used to determine the intrinsic stress in thin films of hydrogenated amorphous carbon (a-C:H) from measurements at room temperature of total stress on glass. The a-C:H was deposited through the decomposition of methane in an rf plasma over a range of conditions defined by two parameters; namely, the self-bias voltage on the substrate support electrode, Vb, and the pressure of methane in the deposition chamber, P. The intrinsic stress was found to differ from the total stress at room temperature by a thermal stress introduced by the deposition process. Over the range of deposition conditions investigated, 400 ≤ Vb ≤ 1600 V and 1≤P≤16 mTorr, the intrinsic stress was compressive, high in level (varying only slightly between 1–3×1010 dynes/cm2) and proportional to a function of the deposition parameters, Vb−1/4P1/8. Over the same range of conditions, the thermal stress (at ∼20 °C) was tensile and proportional to Vb3/2P1/4. At the highest values of Vb and P investigated, 1600 V and 16 mTorr, respectively, the level of the thermal stress (∼0.8×1010 dynes/cm2) exceeded the level of the total stress (∼0.3×1010 dynes/cm2) by a significant margin. Implications are discussed.
Self-consistent modeling of surface wave produced discharges at low pressures
Authors: Sá A. B. , Ferreira C. M. , Pasquiers S. , Boisse-Laporte C. , Leprince P. , Marec J.
Published: July 2002

A self-consistent theory of a low-pressure gas discharge sustained by a surface wave (SW) is presented which provides a complete description of the plasma density (ne) and SW-field distribution both in the radial (r) and the axial (z) directions. The theory is based on a complete set of equations including Maxwell’s equations and the boundary conditions for the SW-field, the electron Boltzmann equation which yields local collisional and transport data versus the SW-electric field E, and the continuity and momentum transfer equations for the electrons and the ions. For given operating frequency, gas density, setup dimensions and total incident power Pi(0), the theory enables the determination of: (i) the SW-dispersion relation; (ii) ne(r,z) and E(r,z); (iii) Pi(z); and (iv) θ(z), the radially averaged mean absorbed power per electron. It is shown that Ē(z), the radially averaged field in the plasma, and θ(z) are practically constant along z, in spite of the fact that Pi(z) steadily decreases. Comparison with experiment is made for SW discharges in Ar operated at the frequencies of 433 MHz and 2.45 GHz.
Nonspecular x-ray scattering from multilayer structures
Authors: Kortright J. B.
Published: July 2002

Nonspecular x-ray (λ=0.154 nm) scattering from a 3.9-nm-period tungsten/carbon multilayer structure with scattering vectors near low-angle multilayer specular interference peaks is reported. Diffuse intensity results from kinematical small-angle scattering from in-plane structural inhomogeneities associated with the individual interfaces or layers having characteristic length scales much greater than the multilayer period. Modulations in this diffuse nonspecular intensity when the incident or observation angle is equal to the angle of the first-order multilayer Bragg peak result from standing-wave-enhanced scattering and other dynamical effects. The technique provides a sensitive measure of in-plane structural inhomogeneities of heterointerface systems.
The influence of ion flux on defect production in MeV proton-irradiated silicon
Authors: Hallén A. , Fenyö D. , Sundqvist B. U. R. , Johnson R. E. , Svensson B. G.
Published: July 2002

The production of stable vacancy-related point defects in silicon irradiated with 1.3 MeV protons has been studied as a function of ion flux (protons s−1 cm−2), while keeping the total fluence constant. Since the total fluence was very low (5 × 109 protons cm−2), no interference between neighboring ion tracks was expected. The defect concentrations have been measured by deep-level transient spectroscopy, and a decrease in the resulting defect density is found for increasing flux. This effect was unexpected and shows that there is an overlap between ion tracks, in spite of the low fluence. The behavior is attributed to the rapidly diffusing silicon interstitials, which overlap the vacancy distributions produced in adjacent ion tracks. When the ion flux is low, the distribution of vacancies from one ion becomes diluted and recombination with interstitials from ions impacting at a later time is rare. As the flux is increased the vacancy distribution from one ion will still be confined to a small volume when it is overlapped by interstitials from a later ion, leading to an increased recombination of vacancies and interstitials. Thus, within this low-fluence regime, the total concentration of stable vacancy-related defects decreases for a high flux. This result is supported by computer simulations of the defect generation kinetics.
Tantalum-based diffusion barriers in Si/Cu VLSI metallizations
Authors: Kolawa E. , Chen J. S. , Reid J. S. , Pokela P. J. , Nicolet M.-A.
Published: July 2002

We have studied sputter-deposited Ta, Ta36Si14, and Ta36Si14N50 thin films as diffusion barriers between Cu overlayers and Si substrates. Electrical measurements on Si n+p shallow junction diodes demonstrate that a 180-nm-thick Ta film is not an effective diffusion barrier. For the standard test of 30-min annealing in vacuum applied in the present study, the Ta barrier fails after annealing at 500 °C. An amorphous Ta74Si26 thin film improves the performance by raising the failure temperature of a 〈Si〉/Ta74Si26(100 nm)/Cu(500 nm) metallization to 650 °C. Unparalled results are obtained with an amorphous ternary Ta36Si14N50 thin film in the Si/Ta36Si14N50(120 nm)/Cu(500 nm) and in the Si/TiSi2(30 nm)/Ta36SiN50(80 nm)/Cu(500 nm) metallization that break down only after annealing at 900 °C. The failure is induced by a premature crystallization of the Ta36Si14N50 alloy (whose crystallization temperature exceeds 1000 °C) when in contact with copper.
Stress in polyimide films having a rodlike molecular skeleton formed on a silicon substrate
Authors: Nomura Hideshi , Eguchi Masuichi , Asano Masaya
Published: July 2002

Stress measurements of polyimide films deposited on silicon wafers were performed in situ during the curing and cooling cycles. The films were constructed from a single polyimide having a rodlike molecular skeleton. The stress in the film varied with film thickness. The stress before curing decreased with increasing film thickness. On the other hand, the stress after the thermal cycle increased with increasing film thickness, resulting from the increasing thermal coefficient of expansion. This phenomenon was thought to be caused by the decrease in the degree of the in-plane orientation of the polyimide molecular chain with decreasing stress before the curing process.
Thickness dependence of coercivity in Co-Ni thin films
Authors: Wan H. , Hadjipanayis G. C.
Published: July 2002

The magnetic properties and microstructure of sputtered Co80Ni20 thin films with a thickness in the range of 400–3800 Å have been studied using SQUID magnetometry, x-ray diffraction and transmission electron microscopy (TEM). Both the electron and x-ray diffraction results show that all the films have an hcp structure. As the film thickness decreases the grain size decreases and the c axis is inclined to the film plane. The intrinsic coercivity decreases as the thickness increases when the applied field is parallel to the film plane. The dependence of coercivity on the angle θ between the field direction and the normal to the film plane indicates that the coercivity is due to domain wall pinning. The domain wall structure and pinning force play a major role in the thickness dependence of coercivity for films with thickness D<1000 Å.
Ion energy distributions in radio-frequency discharges
Authors: Field D. , Klemperer D. F. , May P. W. , Song Y. P.
Published: July 2002

Using a theoretical description of potentials in radio-frequency (rf) discharges reported elsewhere [Song, Field, and Klemperer, J. Phys. D: Appl. Phys. 23, 673 (1990)] we derive the equations of motion for ions from the plasma region striking the cathode and anode in the absence of collisions in the sheath. We compute ion energy distributions (IEDs) which we find to be in excellent agreement with recent experimental data for Ar, Ar/H2 mixtures, O2, and CF4 parent gases. We also present a method of estimating IEDs which does not involve extensive computation, a development of particular value in the design of reactive ion etching processes.
Electron-beam-induced current images of sectioned p/n junctions in silicon: Influence of surface states at low acceleration voltages
Authors: Kuhnert Reinhard
Published: July 2002

On cross sections through semiconductor devices, the electron-beam-induced current (EBIC) mode of the scanning electron microscope yields two-dimensional information on the location of p/n junctions. High resolution can be achieved at low acceleration voltages. Specimens with independently determined doping profile are used to demonstrate that the charge collection is strongly influenced by charged surface states at the sectional plane. Different preparation sequences are described yielding different surface states. Therefore, junction delineation with the EBIC method is strongly affected by specimen preparation. For low-injection conditions, an analytical model is developed to describe charge-collection features at low acceleration voltages. The deviation of the maximum charge-collection signal from the junction position, which occurs as a consequence of the preparation-induced surface states, is well described by the model.
Photoacoustic frequency-domain depth profilometry of surface-layer inhomogeneities: Application to laser processed steels
Authors: Ma Tian-Chi , Munidasa Mahendra , Mandelis Andreas
Published: July 2002

An observed change in the photoacoustic signal frequency response of laser processed stainless-steel and carbon steel samples with respect to unprocessed reference samples is reported. A recently developed thermal wave theory for depth profiling of bulk inhomogeneities (where the surface thermal diffusivity is known and is the same as the homogeneous reference material) in condensed phases with arbitrary, continuously varying thermal diffusivity profiles [A. Mandelis, S. B. Peralta, and J. Thoen, J. Appl. Phys. 70, 1761 (1991)] has been modified to obtain quantitative thermal diffusivity profiles extending from the surface into the bulk. Profiles obtained using this method, which is, in principle, of nondestructive nature, are consistent with the profiles obtained from destructive methods such as cross-sectional optical metallographic examination and microhardness testing.