bluuebunny/crossref_metadata_2025 huggingface dataset:
Model for a glow discharge in flowing nitrogen
Authors: Brunet H. , Rocca-Serra J.
Published: July 2002

A two-dimensional model of the positive column of a glow discharge in flowing nitrogen is presented. The model is applicable to a cylindrically symmetric and axially nonuniform weakly ionized discharge. Nitrogen ionization mainly results from associative ionization occurring in the collisions of metastable molecules in the a′1Σ−u and A3Σ+u electronic states. Gas heating explains the lowering of the electric field as the current increases or the flow velocity decreases. Under most conditions, vibrational deactivation results from superelastic collisions between excited molecules and electrons. Electric field, discharge voltage, vibrational and electronic populations, and gas temperature, are calculated as a function of pressure, flow velocity, diameter and length of the discharge, and current. Quantitative comparisons with available experimental data are made. Good agreement is observed for discharges at low pressures in gas flows with low Reynolds numbers.
Thermal transport measurements in six-beam, ultraviolet irradiation of spherical targets
Authors: Yaakobi B. , Barnouin O. , Delettrez J. , Goldman L. M. , Marjoribanks R. , McCrory R. L. , Richardson M. C. , Soures J. M.
Published: July 2002

Thermal transport, mass ablation rates, and preheat have been studied in spherical irradiation at λ=351 nm, using six of the 24 beams of the OMEGA spherical irradiation laser system at the Laboratory for Laser Energetics. Mass ablation rates are higher at 351-nm than at 1054-nm irradiation, even when compared at the same absorbed irradiance. Similar to the case of 1054-nm irradiation, very deep burnthrough was found at 351 nm. However, the shallow-gradient temperature profile at the heat front, characteristic of the experiments at 1054 nm, was not observed here, nor was the large difference between uniform and tight focus irradiation of spherical targets. Ablation pressures derived from charge-collector data rise from 10 to 100 Mbar for absorbed irradiance in the range of 4×1013 to 9×1014 W/cm2.
Nonlinear quasi-fracture behavior of polymers
Authors: Sun B. N. , Hsiao C. C.
Published: July 2002

This paper deals with the nonlinear quasi-fracture behavior of polymers. Using the finite element method, the quasi-fracture model composed of an isolated craze opening with a nonlinear boundary envelope forces represented by oriented fibril domains is analyzed in simply-stressed rectangular plate. The stress distribution, the displacement profile, as well as the yield or plastic or flow zone adjacent to the craze tips are obtained. It is found that the variation of the stress distribution near the craze tip is not as sharp as that for an elastic crack. The initial load required for yielding or flowing is greater for the quasifracture as compared with that for a classical fracture. Under the same load the yeild or flow zone is somewhat smaller as compared with that obtained on the basis of linear elastic-plastic fracture mechanics theory.
Conduction mechanism and flicker noise in ZnO varistors
Authors: Prudenziati M. , Masoero A. , Rietto A. M.
Published: July 2002

Measurements have been performed on the power spectral density Sv of the flicker noise in ZnO varistors as a function of temperature (from 110 to 370 K), bias voltage (from 10 to 90% of the varistor voltage), and frequency (from 0.1 Hz to 2 kHz). Capacitance-voltage (C-V) curves and current-voltage (I-V) characteristics as a function of temperature have also been measured. The picture resulting from these measurements is very self-consistent when the data are interpreted on the basis of a Schottky emission model and the flicker island models. In particular the temperature and frequency dependence of Sv have been found to provide direct experimental evidence for the thermally activated emission of electrons from localized states, distributed over a large spectrum of energy levels, at the ZnO grain boundaries. It is shown that both I-V, C-V curves and Sv data enable one to obtain reliable information on the intergranular barrier height, its dependence on temperature, and bias voltage. The degradation of I-V and noise characteristics observed in some samples under dc and temperature stress suggests that flicker noise can be used as a technique for the study of degradation effects.
Photoionization thresholds of rare-earth impurity ions. Eu2+:CaF2, Ce3+:YAG, and Sm2+:CaF2
Authors: Pedrini C. , Rogemond F. , McClure D. S.
Published: July 2002

The spectral dependence of the photoionization energy of Eu2+:CaF2, Ce3+:YAG, and Sm2+:CaF2 systems have been measured and thresholds experimentally determined and compared with theoretical values calculated from electrostatic models. It is shown that the excited state absorption transitions or the persistent hole burning observed by other authors occur above the threshold energy of photoionization of the impurities and that the states of the crystal which form the bottom of the conduction band may play an important role in the strong probability of these processes. A review of thresholds now known is also given.
Semiconductor analysis using organic-on-inorganic contact barriers. II. Application to InP-based compound semiconductors
Authors: Forrest S. R. , Kaplan M. L. , Schmidt P. H.
Published: July 2002

Organic-on-inorganic (OI) contact barrier devices have been applied to the study of InP and In0.53Ga0.47As surfaces. The characteristics of these devices differ from OI diodes fabricated using Si or Ge substrates in that the contact barriers for InP-based devices are relatively small (≤0.55 eV), and the diode characteristics are governed by a high density of states at the organic/inorganic interface. We present current-voltage and frequency-dependent admittance-voltage characteristics for OI diodes employing 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) and related compounds as the organic thin-film material. Analysis of characteristics using a theory presented previously [S. R. Forrest and P. H. Schmidt, J. Appl. Phys. 59, 513 (1986)] indicates that the surface state density is (i) independent of the organic material employed, and (ii) sensitive to the exposure of the surface to chemical treatment prior to the organic thin-film deposition. Using techniques derived previously, we determine the magnitude and energy distribution of the density of states at InP and In0.53Ga0.47As surfaces. It is found that the densities of states can vary between mid-1011 and 1015 cm−2 eV−1, depending on the surface treatment employed. Furthermore, some surface treatments result in an organic/In0.53Ga0.47As barrier height that is strongly dependent on applied voltage due to the presence of a high density of interface states.
Electron-beam poling of piezoelectric polymer electrets
Authors: Gross B. , Gerhard-Multhaupt R. , Berraissoul A. , Sessler G. M.
Published: July 2002

Irradiation with a monoenergetic electron beam is demonstrated as a poling technique for piezoelectric polymer electrets. Poling-current measurements during electron irradiation indicate a ferroelectric polarization of typically about 0.1 C/m2. The generated nonuniform polarization profiles are probed by means of laser-induced pressure pulses. It is found that the thickness of the unpoled sample volume is proportional to the 1.5th power of the electron energy used. The proposed method thus allows the fabrication of polymer electrets with a polarization zone of predetermined thickness for, e.g., application in flexure-mode devices.
Precise measurements of a magnetostriction coefficient of a thin soft-magnetic film deposited on a substrate
Authors: Tam A. C. , Schroeder H.
Published: July 2002

A novel magnetostriction measurement tool is developed for a thin soft-magnetic film on a nonmagnetostrictive substrate. The sensitivity is at least an order of magnitude better than prior art, and is adequate to measure a magnetostriction coefficient as small as 10−7–10−8 for a film as thin as 30 nm on a glass wafer of thickness 200 μm. To make a measurement, the sample wafer in the form of a rectangle is clamped near an edge, and a saturating rotating magnetic field of constant amplitude is applied in its plane; this rotating field causes the film to expand/contract in the direction of magnetization for a positive/negative magnetostriction coefficient and results in a periodic ‘‘warpage’’ of the sample at a frequency that is twice the rotation frequency of the field. A continuous helium-neon laser beam incident on the sample is used to sense this small periodic warpage. The reflected laser beam is detected by a position sensor; its output is normalized to the laser beam intensity to account for intensity fluctuation effects, and then fed to a phase-sensitive lock-in amplifier that is referenced to twice the field rotation frequency. This tool has been developed, characterized, optimized for noise reduction by suitable selection of frequencies and suspension techniques, and applied to measure the saturated magnetostriction coefficients of ultrathin soft-magnetic Permalloy-based films.
Nd-Fe-B die-upset and anisotropic bonded magnets (invited)
Authors: Nozawa Y. , Iwasaki K. , Tanigawa S. , Tokunaga M. , Harada H.
Published: July 2002

The hot working conditions were examined for Nd-Fe-B die-upset magnets. The Nd14Fe80B6 ternary composition has the best workability (die upsetting) from stress-strain curves for the initial stage of die upsetting at hot working temperature. The compression ratio defined as the inverse of reduction in height should be larger than 4 to have materials aligned. Alignment of c axis along the compressive stress direction is obtained, but grain coarsening occurs during die upsetting. Of several additional elements investigated, Ga is the best for enhancing the coercivity with a little sacrifice of remanence and no deterioration in hot workability. Typical magnetic properties for Nd14Fe79.25B6Ga0.75 die-upset magnets are Br =12.4 kG, iHc =19 kOe, and (BH)max =36 MGOe. The irreversible loss after exposure up to 160 °C is under 10% (Pc =2). The iHc of powder made by crushing the die-upset magnets is nearly independent of particle size. Decrease in iHc by pulverizing to several hundred micron is about 2 kOe. Anisotropic bonded magnets were developed using this powder. Best energy products of injection and compression molded magnets with Ga addition are 10 and 15 MGOe, respectively. The irreversible losses after exposure up to 120 °C is lower than 5% (Pc =2), which is enough thermal stability for polymer-bonded magnets.
Raman scattering determination of carrier distribution in GaP diodes
Authors: Nakashima S. , Yugami H. , Fujii A. , Hangyo M. , Yamanaka H.
Published: July 2002

Using a Raman microscope we have studied Raman scattering from plasmon-LO-phonon coupled modes in the cross section of GaP diodes. The line shape analysis of the coupled mode has provided the thermal-equilibrium carrier concentration and mobility. Their distribution is determined from the spatial variation of the spectra. The carrier distribution thus obtained is consistent with that estimated from capacitance measurements. The result demonstrates that the Raman microprobe is a powerful method for determining the distribution of the carrier concentration and mobility in semiconductor devices without electric measurements using electrodes.
A turbulent flow model for the rf inductively coupled plasma
Authors: El-Hage M. , Mostaghimi J. , Boulos M. I.
Published: July 2002

A mathematical representation is given for the turbulent fluid flow and energy transfer in an rf induction plasma. The flow and temperature fields are obtained through the solution of the two-dimensional rotationally symmetric turbulent Navier–Stokes equations along with the energy and the one-dimensional Maxwell’s equations for the electric and magnetic fields. The turbulent viscosity is determined using the standard k-ε model. Results are given for an argon plasma under atmospheric conditions. Different aspects of turbulent flows and their implications in rf plasmas are discussed. The results indicate the presence of both laminar and turbulent regimes in the same flow field. The effect of swirl in the plasma gas is to increase the overall turbulence level in the torch.
A parametric investigation of AlGaAs/GaAs modulation-doped quantum wires
Authors: Sherwin M. E. , Drummond T. J.
Published: July 2002

Poisson’s and Schrödinger’s equations have been simultaneously solved in cylindrical coordinates for the problem of a cylindrical modulation-doped quantum well, also referred to as a quantum wire. A transfer matrix method for the solution of Schrödinger’s equation has been implemented for cylindrical coordinates. For the case of a GaAs wire embedded in an AlGaAs host, a parametric investigation was undertaken to determine the effects of aluminum fraction, temperature, well radius, barrier doping, and spacer layer thickness upon the linear electron density within the quantum wire. Transferred electron densities in excess of 106 electrons per cm are easily achievable for a wide range of parameters.
Fabrication and properties of Nb/Al, Alox/Nb Josephson tunnel junctions with a double-oxide barrier
Authors: Houwman E. P. , Veldhuis D. , Flokstra J. , Rogalla H.
Published: July 2002

High-quality Nb/Al, Alox/Nb Josephson tunnel junctions using double-oxide layers as barriers have been fabricated. The critical current density is controlled by the thickness of the second Al layer. This layer has to be oxidized completely through in order to obtain high-quality junctions. Typically, gap voltages of 2.8–3.0 mV and Vm up to 70 mV at 4.2 K were obtained.
X-ray photoelectron spectroscopy of Nd2−xCexCuO4−y (x=0 and 0.15) thin films
Authors: Kohiki Shigemi , Kawai Jun , Hayashi Shigenori , Adachi Hideaki , Hatta Shin-ichiro , Setsune Kentaro , Wasa Kiyotaka
Published: July 2002

Electronic structure of Nd2−xCexCuO4−y (x=0 and 0.15) thin films was examined by x-ray photoelectron spectroscopy. The films were prepared by rf magnetron sputtering and successive annealing under reducing condition (reduction). The reduced films showed semiconducting and superconducting behaviors depending on the value x. The Cu, O, and Nd core-level spectra revealed that the doped electrons were predominantly in CuO2 plane of the Nd2CuO4 crystal. The Cu core-level spectra from x=0.15 films before and after the reduction suggested that the reduction added electrons to Cu4s-O2p extended conduction band, and strengthened Cu O bond covalency to screen the core hole state by mobile itinerant electrons.
A model for ac conduction in amorphous silicon nitrides
Authors: Shimakawa K. , Wakamatsu S.
Published: July 2002

The frequency-dependent conductivity of amorphous silicon nitride (a-Si1−xNx) films has been reported for the first time. The origin of the ac loss is discussed in terms of nitrogen-related two-level systems and electron transfer between Si dangling bond states.
Structure and orientation of films prepared by reactive sputtering of Ni, Fe, and NiFe in Ar/N2 mixtures
Authors: Takamori T. , Shih K. K. , Dove D. B. , Nywening R. W. , Re M. E.
Published: July 2002

Using controlled N2/Ar sputtering gas mixtures, rf-sputtered films were prepared from Fe, Ni, and Ni81Fe19 targets, and their structure and orientation were studied by x-ray diffraction. When no N2 was introduced during sputtering, all the films were oriented in the highest density planes; i.e., in (110), (111), and (111) for α-Fe, Ni, and γ-Ni81Fe19, respectively. With increasing N2 introduction, however, the orientation shifted to lower density planes, and eventually nitrides were formed. Multilayer films of metal and nitride were prepared with the Ni81Fe19 target by repetitive supply of N2 for short periods during sputtering. Strong orientation effects were observed depending on the number of layers grown. In addition, the x-ray diffraction of these films presented evidence of epitaxial growth of the nitrides (Ni,Fe)4N on the alloy layers.
Magnetic properties of the Y1−xGdxCo3B2 system
Authors: Ido H. , Yamauchi H. , Cheng S. F. , Sankar S. G. , Wallace W. E.
Published: July 2002

Magnetic properties of Y1−xGdxCo3B2 with x=0, 0.2, 0.4, 0.6, 0.8, and 1.0 have been studied in a wide temperature range from 4.2 to 1250 K. All compounds studied here have the CeCo3B2-type structure which is a derivative of the RCo5 type one. In this system, the Co atom is nonmagnetic down to 4.2 K and the Curie temperature decreases almost linearly with increasing composition x and is expected to vanish at around x=0 (YCo3B2). For the sample with x=0.2, a spin-glass freezing point has been found in addition to the usual ferromagnetic Curie temperature. Gd magnetic moments obtained from the saturation magnetizations at T=4.2 K are generally smaller than those obtained from the Curie–Weiss constants in the high-temperature paramagnetic region, which suggests a slight polarization of the Co atoms antiparallel to the Gd moment in the ferromagnetic region.
Effect of grain size and microstructure on magnetic properties of rapidly solidified Fe82.4Nd13.1B4.5 alloy
Authors: Manaf A. , Leonowicz M. , Davies H. A. , Buckley R. A.
Published: July 2002

The effect of grain size on the magnetic properties of a rapidly solidified low boron Fe-Nd-B alloy, both in directly quenched and in the overquenched and annealed conditions, has been studied. The magnetic properties in the as-quenched crystalline state and changes occurring on annealing of the overquenched ribbons are discussed in relation to the microstructure. High values of the remanent magnetization, above 0.9 T (9 kG), in combination with coercivities of 1100 kA m−1 (13.7 kOe), have been observed for the directly quenched, isotropic single-phase ribbons, for certain combinations of process conditions. The mean-grain size for these ribbons measured on the roll contact side was found in some cases to be <20 nm, representing an essentially nanocrystalline structure. The enhanced remanence is considered to result from intergranular magnetic exchange interactions between fine adjacent grains. The overquenched ribbons were aged at temperatures between 500 and 800 °C for various times and these exhibited grain sizes in the range of 40–55 nm. Their magnetic properties depend on the annealing temperature and are generally lower than for the directly quenched ribbons though Br is still slightly enhanced at 0.85 T (8.5 kG). Apart from the effect of larger grains, the lower magnetic properties of the overquenched and annealed ribbons result from a slightly different phase constitution. Indirect evidence of this is provided by initial magnetization and coercivity measurements, using a VSM, which indicate that, on devitrification of the overquenched amorphous phase, a small proportion of soft magnetic phase was always present but which was not observed in the optimal directly quenched samples. Details of the phase transformations are discussed.
Anomalous refractive index change and recovery of electro-optic coefficient r33 in proton-exchanged LiTaO3 optical waveguides after annealing
Authors: Yuhara Toshiya , Tada Kunio , Li Yu-Shan
Published: July 2002

An increase of surface refractive index and a recovery of the r33 electro-optic coefficient have been observed for proton-exchanged LiTaO3 optical waveguides after annealing. On the basis of the results of nuclear reaction analysis, x-ray rocking curve analysis, and infrared-absorption spectroscopy, a qualitative model to explain these phenomena is proposed. The evolutions of the index profile and the r33 coefficient after proton exchange and annealing are considered to be caused by the movement of protons in the crystal lattice and the interdiffusion of protons and Li ions. The condition required for the fabrication of waveguides with good electro-optic performance is also shown.
Role of point defects in the silicon diffusion in GaAs and Al0.3Ga0.7As and in the related superlattice disordering
Authors: Pavesi L. , Ky Nguyen Hong , Ganière J. D. , Reinhart F. K. , Baba-Ali N. , Harrison I. , Tuck B. , Henini M.
Published: July 2002

The mechanism of silicon diffusion in GaAs, Al0.3Ga0.7As, and the silicon diffusion-induced layer disordering of multiquantum wells have been studied by photoluminescence, secondary-ion-mass spectroscopy, and transmission electron microscopy across a corner of a wedge-shaped sample. The diffusion source was a grown in highly Si-doped layer. The main photoluminescence properties of point defects in GaAs and Al0.3Ga0.7As are reviewed to interpret the experimental data. The depth profile of the photoluminescence allows the spatial correlation between the luminescence spectra and the Si concentration profile obtained from secondary-ion-mass-spectroscopy measurements. On the basis of the photoluminescence results, the physical processes occurring during the Si diffusion are discussed. Frenkel defects (pairs of element-III vacancies and interstitials) are generated in the highly Si-doped region. The element-III interstitials rapidly diffuse towards the surface where they react with the element-III vacancies generated at the surface when annealing is performed in an external As pressure. This induces a supersaturation of element-III vacancies in the Si-doped region which drives the Si diffusion. Annealing in vacuum reduces the oversaturation of element-III vacancies and, hence, reduces the Si diffusion. A domination of the Si donor–element-III vacancy complex emission band was found in the spectra taken in the Si-diffused region. This gives evidence for the vacancy-assisted mechanism in the Si diffusion and in the impurity-induced disordering.
Diffraction from multilayer films with partially correlated interfacial roughness
Authors: Phang Y. H. , Kariotis R. , Savage D. E. , Lagally M. G.
Published: July 2002

The interfacial roughness in multilayer films is described by a model in which the parameters are directly related to those of microscopic growth processes. The height-height correlation function is extracted from this model. Stationary and nonstationary roughness are discussed. The diffuse intensity in diffraction from multilayer films that have various degrees of correlation in roughness between interfaces is calculated. The presence of perfect or partial interfacial roughness correlation can be distinguished unambiguously in the diffusely scattered intensity.
Modeling and experiment on plasma source ion implantation
Authors: Xia Zhongyi , Chan Chung
Published: July 2002

The critical plasma parameters for plasma source ion implantation (PSII) are the ion implantation current, the sheath expansion characteristic, the energy of the implanted ions, and the electric field intensity on the electrode surface. These quantities have been calculated for spherical electrodes using a fluid dynamic model. The results show that for the implantation time larger than ten ion plasma periods, both the ion current and the sheath expansion characteristic of the fluid dynamic model are consistent with that of the previous analytic models. But for implantation time less than ten ion plasma periods, the results are quite different. As the sphere radius gets smaller, the difference in the results becomes greater. In our experiments, the measured cathode current and the sheath expansion characteristic of the spherical cathode are shown to fit the fluid dynamic model better. The negative high voltage pulse employed in our experiments has a rising edge of less than 1 μs and a flat top approaching the theoretical model. The secondary electron emission coefficients for stainless steel and copper under PSII conditions have also been estimated using two different methods: retarding static electric field energy analyzer and the cathode current measurement. It is found that under PSII conditions, secondary electron emission coefficients are in general larger than the values taken under the condition of atomically clean surfaces in ultrahigh vacuum.
Phase evolution upon ion mixing and solid-state reaction and thermodynamic interpretation in the Ni-Nb system
Authors: Zhang Z. J. , Bai H. Y. , Qiu Q. L. , Yang T. , Tao K. , Liu B. X.
Published: July 2002

The amorphization of Ni-Nb multilayered alloy films by xenon ion irradiation at room temperature and by high-temperature solid-state reaction was studied. The composition range favoring amorphization was carefully determined to be 20–85 at. % Ni by energy-dispersive spectroscopy attached to the transmission electron microscope. A new metastable crystalline phase (MX) of hexagonal structure was formed in Ni75Nb25 and Ni70Nb30 multilayered films. Interestingly, in the Ni75Nb25 multilayered films, with increasing mixing dose an amorphous phase was first formed and then the MX-phase was observed, while in the Ni70Nb30 multilayered films the MX phase was formed at relatively low doses and turned amorphous upon further mixing or 400 °C annealing for 2 h. Besides, annealing of the as-deposited Ni70Nb30 multilayered films at 300 °C for half an hour also resulted in the formation of the MX phase. The thermal stability of the ion-mixed amorphous alloys was also studied by subsequent annealing. To give semiquantitative interpretation to all the above observations, the Gibbs free-energy diagram of the system, in which especially the free-energy curve of the MX phase is added, was constructed on the basis of the model of Nissen et al. [CALPHAD 7, 51 (1981)] and the method proposed by Alonso and Simozar [Solid State Commun. 46, 765 (1983)]. The explanation based on this diagram is in good agreement with our experimental results.
Scanning probe microscopy studies of electromigration in electroplated Au wires
Authors: Paniccia M. , Flinn P. , Reifenberger R.
Published: July 2002

Scanning probe studies of electromigration in 4-μm-wide by 1-μm-thick electroplated Au wires reveal changes in surface morphology. Features that develop on a submicrometer length scale were observed using current densities up to 7.5×106 A/cm2 and temperatures up to 280 °C for time intervals ranging from a few minutes up to a few days. Scanning probe images of the same area taken before, during, and after current stressing reveal substantial changes in surface morphology. Both hillock growth and void formation have been observed in situ. Changes in surface morphology caused by electromigration can be quantitatively described from the scanning probe images and new techniques for studying mass flow due to electromigration are now possible.
The electrical and electrochemical properties of gold-plated InP
Authors: Oskam G. , Bart L. , Vanmaekelbergh D. , Kelly J. J.
Published: July 2002

The electrical properties of InP/Au dry contacts and the influence of electrodeposited gold on the electrochemical properties of InP electrodes were studied. From current and impedance measurements on InP/Au dry contacts it is concluded that the chemical composition of an interfacial layer strongly influences the electrical characteristics. Furthermore, interface states are shown to play an important role. The interfacial layer and the interface states also determine to a large extent the electrochemical properties of the gold-plated electrodes.
Accurate determination of majority thermal-capture cross sections of deep impurities in p-n junctions
Authors: Palma A. , Jimenez-Tejada J. A. , Banqueri J. , Cartujo P. , Carceller J. E.
Published: July 2002

A new method for the direct determination of majority thermal-capture cross sections and concentration of deep levels in p-n junctions is proposed. The combined use of a capacitance technique and a numerical simulation (which reproduces the experimental details) provides accurate results through the fitting of experimental and numerical capture transients. The sensitivity of the method to these electrical magnitudes is also shown. This procedure is applicable not only to abrupt p+-n junctions, which have been quite thoroughly analyzed, but also to samples where a nonabrupt shallow-dopant profile together with a high concentration of deep levels makes them respond to a capture pulse in ways not reported until now. This method was used to analyze the two levels of platinum in silicon in nonabrupt p+-n junctions with a platinum concentration comparable to that of the shallow dopant.
Photoelectric study of β-FeSi2 on silicon: Optical threshold as a function of temperature
Authors: Lefki K. , Muret P.
Published: July 2002

Investigation of the photoelectric properties of several metal/β-FeSi2/Si heterostructures is presented. For thin silicide samples (200 Å), the photocurrent follows a Fowler’s law with a threshold Φ1 lower than the silicide band gap Eg. For thicker silicide samples (2500 Å), the behavior of the photocurrent is different because the optical absorption within the silicide can no longer be neglected: a maximum of the photocurrent is observed instead at Eg. The variations of Eg and Φ1 with temperature are compellingly similar and show the strong effect of the electron-phonon coupling. We suggest that the threshold Φ1 corresponds to transitions between a trap localized near the heterojunction and the silicide conduction band.
Millimeter wave amplification in a free electron laser with a focusing wiggler
Authors: Sakamoto K. , Kobayashi T. , Kawasaki S. , Kishimoto Y. , Musyoki S. , Watanabe A. , Takahashi M. , Ishizuka H. , Sato M. , Shiho M.
Published: July 2002

A mm wave amplifier experiment on a free electron laser was performed using an intense, mildly relativistic electron beam (0.7–0.9 MeV) with a combination of a focusing planar wiggler and a weak additional axial magnetic field in the so-called ‘‘group 1’’ region. A beam transport ratio of over 80%, through the whole wiggler length, was realized. In an amplification experiment, a spatial growth rate of 56 dB/m was obtained at a frequency of 45 GHz, and a power saturation was observed at a level of 6 MW, where the total gain was estimated to be 52 dB. It was shown that the off-axis component of the beam contributes considerably to the rf amplification in the focusing wiggler.
Positive identification of the ubiquitous triangular defect on the (100) faces of vapor-grown diamond
Authors: Everson M. P. , Tamor M. A. , Scholl D. , Stoner B. R. , Sahaida S. R. , Bade J. P.
Published: July 2002

Scanning tunneling microscopy and atomic force microscopy were used to index the faces and orientation of the sloping triangular defect which often appears on the {100} surfaces of chemical-vapor-deposited diamond. These features were confirmed to be 〈111〉 penetration twins which appear as sections of cubo-octahedra oriented with a 〈221〉′ direction parallel to the ‘‘parent’’ crystal’s {100} surface normal. Multiple twins of this type can give rise to the pentagonal structures usually attributed to simpler combinations of ordinary 〈111〉 twins. The ability to suppress this twin by proper choice of growth conditions is a major factor in controlling the morphology of vapor-grown diamond.
The polarized absorption spectroscopy as a novel method for determining the orientational order of poled nonlinear optical polymer films
Authors: Graf H. Michael , Zobel Oliver , East Anthony J. , Haarer Dietrich
Published: July 2002

A novel method for the determination of the order parameter A2 in anisotropic films with ∞ mm-symmetry, such as poled nonlinear optical polymer films, is presented. The order parameter A2 is believed to shed light on the understanding of the poling mechanism. Light with polarization parallel to the plane of incidence is used to study the absorption behavior of thin poled polymer films as a function of the angle of incidence. Moreover, the order parameter of unpoled samples can easily be determined. The results for the order parameter A2 obtained by polarized absorption spectroscopy are in good agreement with corresponding second-harmonic generation measurements.
Kinetics and mechanism of wet oxidation of GexSi1−x alloys
Authors: Park S.-G. , Liu W. S. , Nicolet M.-A.
Published: July 2002

The thermal oxidation of polycrystalline GexSi1−x (0.10≤x≤0.47) and pseudomorphic Ge0.2Si0.8 has been studied in wet ambient at 550 to 900 °C. A uniform GexSi1−xO2 oxide is observed by backscattering spectrometry for a high Ge content at low oxidation temperatures; a SiO2 oxide is obtained for a low Ge content at high temperatures; a GeySi1−yO2 oxide with reduced Ge content (y<x) is found in between. Ge piles up behind the oxide when SiO2 or GeySi1−yO2 form. The transition between these three types of oxides also depends on the crystallinity of the GeSi alloy. When a uniform GexSi1−xO2 oxide grows, its thickness is proportional to the square root of the oxidation duration, which indicates that the rate-limiting process is the diffusive transport across the oxide of, most probably, the oxidant. The rate increases with the Ge content in the alloys. The proportionality constant, B, for this process is B(T)=[(1.0±0.2)×1011 nm2/h]exp[(−1.1±0.2 eV)/kT] for Ge0.47Si0.53. It is proposed that, in general, the oxidation behavior is determined by the competition between the speed of the diffusive process in the unoxidized GeSi alloy and the velocity at which the oxidation front progresses. The controlling factors are the oxidation temperature, the composition, and the structure of the GexSi1−x alloy. A model is proposed that is based on these three factors. Analogies with this system exist where all three elements are solid.
Preparation and magnetic properties of BaM films with excellent crystallinity by Xe sputtering
Authors: Matsushita N. , Noma K. , Nakagawa S. , Naoe M.
Published: July 2002

M-type barium ferrite (BaFe12O19) films were deposited on a ZnO underlayer by sputtering with mixture of Ar, Xe, and O2 gases. PO2 and PAr+Xe were set at 0.01 and 0.09 Pa, respectively, where PXe was changed from 0.00 to 0.09 Pa. The dependencies of surface morphology, 〈D〉, Δθ50, Ms, and Hc⊥ and Hc∥ on PXe were investigated. Both BaM layers deposited at PXe and PAr of 0.09 Pa possessed smooth surface and exhibited Δθ50, Ms, Hc⊥, and Hc∥ of about 4°, 300 emu/cm3, 2.0 and 0.3 kOe, respectively. The BaM layer deposited at PXe of 0.04 Pa possessed a rough surface and exhibited Δθ50 and Hc∥ as large as about 9° and 0.6 kOe, respectively, and Ms as small as about 200 emu/cm3.
Fracture of metal-polymer line structures. I. Semiflexible polyimide
Authors: Chiu S. L. , Leu J. , Ho P. S.
Published: July 2002

The fracture characteristics of metal/polymer line structures formed by depositing Au/Cr lines on a semiflexible polyimide, pyromellitic dianhydride-oxydianiline (PMDA-ODA), substrate have been investigated using a stretch deformation technique. The delamination behavior, fracture morphology, fracture energy, and energy dissipation rate have been determined as a function of line width and thickness. The metal dimension was found to influence the crack formation mode and morphology. The experimental studies were supplemented by finite-element analysis to evaluate the stress distribution and deformation energetics of the line structure, which takes into account the plastic deformation of the metal and the polymer. Results from this analysis show that the observed fracture characteristics can be attributed to the edge and thickness effects induced by metal confinement. Essentially, the deformation behavior is determined by the mechanical environment induced by metal confinement at the interface. Plastic deformation of both metal and polymer plays an important role in controlling the stress distributions as well as the deformation energetics. The fracture energy of the metal-polyimide interface determined by an overall energy balance method was consistent with that obtained from energy dissipation rate. The average value is 25 J/m2 for the Au/Cr/PMDA-ODA line structure.
Equation of state of aluminum nitride and its shock response
Authors: Dandekar Dattatraya P. , Abbate A. , Frankel J.
Published: July 2002

Equation of state of aluminum nitride (AlN) is determined from the ultrasonic wave velocity measurements of longitudinal and shear modes to 0.7 GPa. The equation of state obtained from the ultrasonic data is used in conjunction with the shock Hugoniot data on AlN to estimate its strength under plane shock wave compression. Further, a better understanding of the existing shock Hugoniot data above its transition stress from wurtzite to rock salt structure is realized through a comparison with the static high-pressure investigations pertaining to this phase transition in AlN.
Magnetic properties of rare-earth compounds of the RCo10Mo2 type
Authors: Zeng D. C. , Tang N. , Zhao T. , Zhao Z. G. , Buschow K. H. J. , de Boer F. R.
Published: July 2002

The magnetic properties of the tetragonal ThMn12-type RCo10Mo2 compounds have been investigated by means of magnetic measurement and x-ray diffraction. It is found that the Co moment is roughly the same in all RCo10Mo2 compounds (0.9 μB/Co), excepting CeCo10Mo2 (0.7 μB/Co). It is also found that the Co sublattice displays easy c-axis magnetization. Nonaxial behavior at room temperature is observed only for SmCo10Mo2, whereas in ErCo10Mo2 a spin reorientation occurs from axial to planar magnetization upon cooling below Tsr=125 K. These results suggest that the A02 term, mainly responsible for the rare-earth-sublattice anisotropy has the same sign as in the R2Fe14B series (A02≳0). This is in contrast to other ThMn12-type compounds (RFe10V2, RFe11Ti) where it is generally assumed that A02<0. The intersublattice coupling of ErCo10Mo2 has been determined by means of the high-field free-powder method.
Raman spectroscopic analysis of the free carrier concentration in GaAs oval defects
Authors: Dobal P. S. , Bist H. D. , Mehta S. K. , Jain R. K.
Published: July 2002

The free carrier concentration at oval defects in silicon-doped GaAs grown by molecular beam epitaxy has been studied on the basis of longitudinal-optical (LO)-phonon plasmon coupled mode frequency through Raman spectroscopy. The carrier concentration at the oval defects was found to be lower as compared to the defect-free regions. The variations of surface depletion width with the concentration calculated from LO phonon intensities was also used to obtain the carrier concentration at the oval defects. Excellent agreement was found between the carrier concentrations obtained from these two methods.
Aspects of nucleation and growth of diamond films on ordered and disordered sp2 bonded carbon substrates
Authors: Hoffman A. , Fayer A. , Laikhtman A. , Brener R.
Published: July 2002

In the present work nucleation and growth of diamond by chemical vapor deposition (CVD) on highly oriented pyrolitic graphite (HOPG) and glassy carbon (GC) substrates have been investigated. These carbon substrates represent generic forms of well-characterized ordered and disordered sp2 bonded carbon materials. The nature of the precursor to diamond CVD is assessed by studying nucleation and growth on substrates abraded with hard powders whose debris may act as initial growth centers, e.g., diamond and c-BN, and hard powders onto which diamond CVD does not grow heteroepitaxially, e.g., alumina. Based on our experimental results it is concluded that the precursor to diamond nucleation may be debris left after the abrasion process and/or damage created preferentially on graphitic prism planes. A higher density of such damaged prism planes on GC than on HOPG resulted in a larger nucleation density on the former. Different morphologies of single particles deposited on HOPG and GC were found: well faceted on the former, and ball-like on the later as determined by scanning electron microscopy. This difference is explained on the basis of a larger concentration of active carbon species present at the GC surface as compared to the HOPG surface. The additional source of carbon is from etching of the GC and HOPG substrates which, under the diamond CVD conditions used in the present study, is twice higher for GC. The thermal stability of continuous films deposited on HOPG is better than those deposited on GC. The presence of different carbon phases in the deposited material was investigated by micro-Raman and scanning-Auger electron spectroscopies.
1.5 MeV ion-channel guided x-band free-electron laser amplifier
Authors: Takayama K. , Kishiro J. , Ebihara K. , Ozaki T. , Hiramatsu S. , Katoh H.
Published: July 2002

Experiments on the ion-channel guided x-band free-electron laser amplifier generated peak microwave power exceeding 100 MW at 9.4 GHz with a gain of 21 dB/m. Saturation in the evolution curve has been achieved and a frequency spread of 0.9% was observed. The amplified microwave was separated from the driving beam line and extracted without breakdown.
Molecular-beam-epitaxy growth of CdTe on InSb (110) monitored in situ by Raman spectroscopy
Authors: Drews D. , Sahm J. , Richter W. , Zahn D. R. T.
Published: July 2002

CdTe epitaxial layers were deposited on clean cleaved InSb(110) substrates by molecular-beam epitaxy at room temperature and elevated temperatures. The formation of interface and layer was investigated using Raman spectroscopy as a growth monitor, i.e., Raman spectra were taken on line without interruption of the deposition process. Fabry–Pérot interference of the incident as well as the scattered light within the heterostructure leads to a characteristic modulation of the substrate phonon scattering intensity. The modulation is calculated and serves as a measure for the layer thickness. For the deposition at elevated temperatures the true surface temperature is determined from the InSb TO phonon frequency shift. While at a substrate temperature of 150 °C the crystalline quality of the CdTe layer was improved compared to room-temperature growth, the deposition of CdTe at 300 °C resulted in the formation of a layer consisting of In2Te3 and liberated Sb. The effect of the laser radiation on the growth process at different temperatures is also discussed.
On the conductivity model for the electrorheological response of dielectric particles with a conducting film
Authors: Tang X. , Wu C. , Conrad H.
Published: July 2002

An analytical approach is given for the electric current and attractive force between spherical dielectric particles surrounded by a conducting film and situated in a nonpolar liquid. Good agreement occurs between the calculated values and those measured on humidified glass beads in silicone oil. Also, the model predicts a decrease from a quadratic electric field dependence of the force as the field strength is increased, in accord with the results for many electrorheological fluids. The effects of certain parameters which govern the conductivity of the host liquid and of the particles are considered.
Effects of inhomogeneity on conductivities of nonlinear composite media
Authors: Gu Guoqing , Yu K. W. , Wang Binghong
Published: July 2002

The effective response of a class of weakly nonlinear conducting composite media is investigated. We combine the previously developed perturbation expansion method for solving electrostatic boundary-value problems with the well-known Rayleigh method for treating periodic composite media to compute the effective conductivities. We derive general expressions for the effective nonlinear response functions and show that the results agree with the generalized Landau’s formula at low inclusion concentrations. Numerical calculations are also obtained for a square array of cylindrical inclusions suspended in a host medium in two dimensions. Possible applications and extensions of the method to more complicated problems are discussed.
Visible photoluminescence from helium-ion implanted carbon in silicon
Authors: Lockwood D. J. , Labbé H. J. , Siegele R. , Haugen H. K.
Published: July 2002

Silicon wafers implanted with 30 keV He ions at room temperature in a low pressure hydrocarbon atmosphere exhibited visible photoluminescence. The samples were characterized by Raman, infrared, transmission electron microscopy, and heavy ion elastic recoil detection analysis. Two different layers were distinguishable on top of the silicon, with the upper layer comprising mostly amorphous carbon, as confirmed on a similarly implanted Be sample. Green photoluminescence was found to arise from the thinner a-Si1−xCx:H interface layer. Such a buried intermixed layer could be incorporated into a stable visible light emitting device based on crystalline silicon.
Grain boundary diffusion effects on the sputter depth profiles of Co–Ag bilayers
Authors: Lee Y. S. , Choi I. S. , Lim K. Y. , Jeong K. , Whang C. N. , Choe H. S. , Lee Y. P.
Published: July 2002

We investigated the effects of surface roughness and grain boundary diffusion (GBD) at elevated temperatures on the Auger-electron-spectroscopy sputter depth profiles of Co–Ag bilayers and the GBD process of Ag atoms in Co. The Ag layer in the Ag/Co bilayer is transformed from a uniform layer to discrete islands by heat treatment. Enhanced mobility during sputtering at elevated temperatures makes Ag atoms migrate continually from islands to cover neighboring exposed Co, which reduces the size of Ag islands. On the other hand, the surface morphological modification of Co/Ag bilayer does not occur by heat treatment, and the depth profile at 340 °C resembles that from a uniformly intermixed film, which shows a drastic difference from that of Ag/Co. This is explained with a very thin and stable accumulation of Ag on the Co layer by GBD. A model of structural changes in Co/Ag subjected to ion sputtering at elevated temperatures is proposed on the basis of the results. The activation energy and pre-exponential factor for GBD of Ag in Co are found to be 0.46±0.06 eV and ∼1×10−8 cm2/s, respectively.
Proximity effects of negative charge groups contact-electrified on thin silicon oxide in air
Authors: Uchihashi Takayuki , Okusako Takahiro , Sugawara Yasuhiro , Yamanishi Yoshiki , Oasa Takahiko , Morita Seizo
Published: July 2002

We investigated proximity effects of negative charge groups contact-electrified on a thin silicon oxide in air with an initial separation (L) less than a few micrometers using a modified atomic force microscope. As a result, we found the following phenomena. Even for L∼2.0 μm, distributions of two negative charge groups approach each other with time after contact electrification, though this feature is contrary to the expected recession due to the Coulomb repulsive force. For less than L∼1.6 μm, each stable state joins in one negative charge group. These proximity effects seem to be induced by the interplay of the Coulomb repulsive force and the surface diffusion of charges.
Temperature scaling of the flux pinning force in Bi2Sr2Ca1Cu2O8+x thin films
Authors: Prischepa S. L. , Attanasio C. , Coccorese C. , Maritato L. , Pourtier F. , Salvato M. , Kushnir V. N.
Published: July 2002

The electrical transport properties of Bi2Sr2Ca1Cu2O8+x thin films have been measured in the temperature range from 20 to 50 K and in external magnetic fields up to 4 T. The dependence of the normalized pinning force f=Fp/Fp,max on the reduced magnetic field h=H/H* (H* is the irreversibility field) exhibits a scaling law behavior, indicating that a single pinning mechanism is present in the investigated temperature range. The Fp(H) curves were analyzed within the framework of the classical Anderson–Kim theory of flux creep, taking into consideration the nonlinear current dependence of the pinning energy U and its dependence on the temperature T, the magnetic field H, and the current density J. Under these assumptions a generalized formula for Fp was obtained which, assuming a suitable U(J) dependence, was able to explain the f(h) curve in the observed temperature range.