bluuebunny/crossref_metadata_2025 huggingface dataset:
Interference resonances in the permeability of laminated magnetic thin films
Authors: Webb Bucknell C. , Re Mark E. , Russak Michael A. , Jahnes Christopher V.
Published: July 2002

In high-frequency magnetic structures (like thin-film magnetic heads) which have been laminated to avoid eddy current loss, it is standard to assume that electromagnetic coupling across the dielectric separating the magnetic layers is small. We show that for macroscopic films with insulating interlayers, the laminated structure is better modeled by an anisotropic effective medium with a magnetic permeability of around 3000 but an insulating dielectric function perpendicular to the lamination plane, while still metallic parallel to the lamination plane. Electromagnetic waves can propagate parallel to the lamination direction but with 1/100 of the free-space wavelength. The electromagnetic (capacitive) coupling between the layers can lead to radically altered propagation of magnetic flux and generate novel permeance resonances caused by interference effects across the width of the film. A Fourier series solution constructed with a mean-field theory for the wave equation for laminated slab geometries predicts the permeance resonances observed experimentally.
A new portrayal of electron and hole traps in amorphous silicon nitride
Authors: Kamigaki Yoshiaki , Minami Shin-ichi , Kato Hisayuki
Published: July 2002

Trap centers in amorphous silicon nitride (a-SiNx) have been considered to be amphoteric. We found two signals of Si3 3/4 Si0 and N3 3/4 Si0 (Si dangling bonds with an unpaired electron) by an electron-spin-resonance method, and estimated the hole trap density to be larger than the electron trap density by about one decade, using the nonvolatile memory devices. As a result, we propose a new portrayal in which electron/hole traps are at the interface between Si clusters and a-SiNx bulk, and hole traps are at nitrogen vacancies in a-SiNx bulk.
Reconstruction of the charge collection probability in a semiconductor diode from collection efficiency measurements by the regularization method
Authors: Donolato C.
Published: July 2002

A new method is introduced to analyze the collection efficiency data that are obtained on a Schottky or p–n junction diode by irradiation with an electron beam with variable energy. The method aims at directly reconstructing the distribution φ(z) of the charge collection probability in the device, by inverting the integral transform that connects φ(z) to the measured collection efficiency profile. This inversion is generally an ill-posed problem, which, however, can be solved by the Tikhonov regularization method. This procedure is used to analyze published measurements obtained both on Si and GaAs diodes, and is shown to be particularly useful for characterizing nonideal devices.
Temperature feature of NdDyFeB magnets with ultrahigh coercivity
Authors: Gong Wei , Li Qingsheng , Yin Lin
Published: July 2002

The intrinsic coercivities Hc of Nd14DyxFe79−xB7 magnets, prepared by a powder metallurgical method, with an addition of Dy (x=2 at. %), reached 21 kOe. The intrinsic coercivity Hc was kept over 10 kOe when the heating temperature was 150 °C and the temperature coefficient α(Hc) = −0.35%/°C was in a temperature range of 16–150 °C. After aging at 120 °C for 400 h, the intrinsic coercivities Hc and magnetic energy products (BH)max of the magnets did not change as usual, remaining at Hc = 21 kOe and (BH)max = 30 MGOe. The NdFeB magnets with all kinds of the intrinsic coercivities were compared at various temperatures also. The experimental results show that high-temperature features of the NdFeB magnets were improved by increasing the intrinsic coercivity.
A high-sensitivity magnetoresistive magnetometer
Authors: Smith Neil , Jeffers Fred , Freeman Jay
Published: July 2002

A high-sensitivity, small-size, low-power-consumption, broad-bandwidth magnetometer has been built in which a magnetoresistive element is located adjacent to a gap between two thin-film flux concentrators. The concentrators magnify the sensed component of magnetic field 20-fold while simultaneously shielding orthogonal fields by more than a factor of 10. The sensor plus bias coil fit inside a 6-mm-diam probe. The intrinsic sensitivity is approximately 50 mV/(V Oe), and is flat from dc out to 50 MHz. With a sensitivity of 300 mV/Oe at 100 mW power, a 2-Hz slot signal-to-noise ratio (SNR) of 30 dB at dc, and a 200-Hz slot SNR of 40 dB at 1 MHz, has been measured when detecting a 1 gamma (10−5 Oe or 1 nT) signal field. With design enhancements and ac detection techniques to eliminate thermal drift and 1/f-type noise, detection of low-frequency magnetic fields of the order 1 mgamma could be achievable.
Photoelectron spectroscopy studies of chemical vapor deposition of Ta from a TaF5 precursor on Si and SiO2 substrates
Authors: Ugolini D. , Kowalczyk S. P. , McFeely F. R.
Published: July 2002

The increasing need for metallization of microelectronic structures involving deep trenches and high aspect ratio features has sparked considerable interest in chemical vapor deposition metallization schemes. In this work the results of photoemission investigations of the substrate-driven reduction of TaF5 to Ta metal on Si(111) and SiO2 substrates are reported. At moderate temperatures the reaction showed no selectivity between these two substrates, in contrast to the process with the similar molecule WF6. At 400 °C metallic Ta films could be grown on both Si and SiO2; however, x-ray photoelectron spectroscopy measurements show that the bonding of the film to Si(111) is dominated by fluorine atoms at the interface, whereas film growth on SiO2 tends to form an oxide interface with TaOF3 stoichiometry. Annealing of the deposited film to about 700 °C leads to Si diffusion to the surface which is accompanied by the release of fluorine from the film. The deposition of TaF5 on Si(111) at 250 °C results initially in a partly dissociative metallic deposition followed by a non-dissociative molecular chemisorption. Our experiments suggest the Si substrate to be reactive enough at the initial state of the deposition to break up theTaF5 molecule but that the process is quickly self-passivating.
Model of plasma immersion ion implantation for voltage pulses with finite rise and fall times
Authors: Stewart R. A. , Lieberman M. A.
Published: July 2002

In plasma immersion ion implantation, a target is immersed in a plasma and a series of negative, high-voltage pulses are applied to implant ions into the target. An approximate analytical model in one-dimensional planar geometry is developed to determine the time-varying implantation current, the total dose, and the energy distribution of the implanted ions for a voltage pulse with finite rise and fall times. Scaling rules are presented for the implanted current and energy distribution with respect to plasma density, peak applied voltage, and ion mass. Comparisons with numerical simulations are used to demonstrate that the accuracy of the model is well characterized by a single parameter: the ratio of the ion flight time to the pulse rise time.
A thermo-mechanical model for laser ablation
Authors: Zweig A. D.
Published: July 2002

A steady-state model for ablation of materials by strongly absorbed long-pulse lasers is developed. Material is removed by a combination of evaporation and ejection of liquid due to evaporation-induced pressure gradients at the bottom of the ablation crater. The relative strength of the two processes depends on the details of the liquid flow. An explicit expression for the drilling velocity is derived. The model explains experimental drilling-depth and recoil data. It is applicable to materials that melt and vaporize.
An investigation of hysteresis effects as a function of pumping speed, sputtering current, and O2/Ar ratio, in Ti-O2 reactive sputtering processes
Authors: Kusano Eiji
Published: July 2002

Understanding of mode transition and hysteresis behavior in reactive sputtering is necessary to widen its applications. The effects of physical pumping speed, sputtering current, and reactive/inert gas ratio on mode transitions and hysteresis in Ti-O2 dc reactive sputtering are examined. As O2 gas flow rate is increased or decreased, mode transition takes place as a consequence of the target poisoning or cleaning. The results obtained explain the important roles of pumping speed and sputtering current on hysteresis. Also, it is found that as pumping speed increases hysteresis width decreases. In addition, for smaller sputtering currents and constant pumping speed, hysteresis width shrinks. The change in transition points as a function of pumping speed and sputtering current are successfully explained by considering getter pumping capacity or getter pumping speed. Elimination of hysteresis is not investigated in this experiment. From the discussion it is suggested that hysteresis is a result of difference in sputtering yields from a poisoned target and from a metallic target, which provides a difference in gettering capacity.
Electron-paramagnetic-resonance signals and effects in marble induced by working
Authors: Maniatis Y. , Mandi V.
Published: July 2002

The effect of most usual kinds of mechanical treatment on marble, such as drilling, grinding, and polishing, has been systematically investigated with electron-paramagnetic-resonance (EPR) spectroscopy. Two different major effects have been observed: the decrease of Mn2+ and the creation of several kinds of lattice defects. Drilling can cause a drop in the intensity of Mn2+ by 50% and at the same time create a high concentration of lattice defects. The most characteristic is a defect, with a pair of peaks at g=2.0003 and 1.9997, created and filled with electrons simultaneously. The causes, nature, stability, and sensitivity to γ irradiation of the two effects have been investigated. For the filling of the above defects with the mechanical action a model has been proposed. This involves another, EPR-silent, defect that stores electrons by ionizing radiation during the geological age of marble and transfers a number of them by the mechanical treatment to the newly created defects. Another pair of defects (g=2.0069 and g=2.0059) has also been observed to be mechanically induced but not filled by the mechanical action. These are filled only by ionizing radiation. The reduction in the Mn2+ signal is caused by the pressure exerted on the grains during the mechanical treatment, destroying the crystal symmetry and probably causing jumping out of Mn2+ ions from their normal crystal symmetry sites. The decrease of the Mn2+ sextet with drilling causes great concern to provenance studies of ancient marble artifacts that are based on the intensity of the Mn2+ peaks. Finally, the polished surfaces of a number of ancient artifacts have been investigated for possible detection of absorbed radiation.
Electron heating by sheaths in radio frequency discharges
Authors: Wendt A. E. , Hitchon W. N. G.
Published: July 2002

The detailed interaction of individual electrons with oscillating radio frequency (rf) sheaths is considered in this reexamination of the sheath heating process. We develop an analytic expression for the energy delivered to the discharge through sheath heating and that lost due to electron escape to the electrode. Using a simple model of the time-dependent sheath electric field, we find that electron energy gain due to this process, averaged over an rf period is roughly proportional to the square of the maximum sheath speed and drops slightly with increasing electron temperature. Energy loss due to escaping electrons on the other hand, rises with temperature and ultimately outweighs gain when the average electron velocity exceeds the maximum sheath velocity. The requirement of a net power input to the plasma places upper bounds on bulk electron temperature and density attainable by plasmas to be maintained solely by this mechanism, independent of other aspects of container geometry. However, by increasing discharge frequency, power input can be increased for a fixed sheath voltage while reducing electron escape.
Observation and analysis of epitaxial growth of CoSi2 on (100) Si
Authors: Bulle-Lieuwma C. W. T. , van Ommen A. H. , Hornstra J. , Aussems C. N. A. M.
Published: July 2002

CoSi2 layers formed by the thermal reaction of vapor-deposited Co films on Si(100) substrates have been studied by transmission electron microscopy, and x-ray diffraction. It is shown that first a layer of CoSi is formed between Co and Si. Only thereafter is the formation of CoSi2 initiated at the Si/CoSi interface. In view of the similarity of the crystal structure and the small lattice mismatch between the Si and the CoSi2, epitaxy of aligned (100) CoSi2 is expected to occur. However, in addition to an aligned (100) orientation, CoSi2 occurs in a number of orientations, including a (110) preferential orientation. Many individual grains are composed of subgrains, slightly rotated with respect to each other and connected by small-angle boundaries. It is shown that the observations can be largely attributed to the geometrical lattice match between CoSi2 and Si. A computer program has been developed that searches systematically for a large number of possible geometrical matches. It allows us to calculate epitaxial relationships between CoSi2 and the Si(100) substrate. The probability of various fits is estimated on the basis of their strain energy and coincidence site density, showing good correspondence with the experimental observations.
Sheath structure around particles in low-pressure discharges
Authors: Daugherty J. E. , Porteous R. K. , Kilgore M. D. , Graves D. B.
Published: July 2002

Collisionless orbit theory is used to model isolated particles in low-pressure discharges with and without the presence of negative ions. The key results are as follows: (1) Debye–Hückel theory works well for approximating the potential profile around the particle, and (2) the size of the sheath around the particle is determined by a Debye length that results from linearizing the Poisson–Vlasov equation. These results are valid as long as the ratio of particle radius to Debye length is small and the ratio of Debye length to mean free path is small.
Modeling of time-dependent process changes and hysteresis in Ti-O2 reactive sputtering
Authors: Kusano E.
Published: July 2002

Understanding the mechanisms of reactive sputtering is thought to be crucial to obtain a better process control and widen applications of reactive sputtering. A model simulating reactive gas mass balance changes in reactive sputtering is described. The model is based on physical mechanisms involved in target and wall gettering behavior. This enables calculation of time-dependent condition changes that occur until the process reaches a steady state, without assuming how the process reaches a steady state. Another important feature of the model is that hysteresis curves are obtained as a result of the calculation of time-dependent target condition changes. This approach to obtain hysteresis curves is more similar to an actual reactive sputtering process. The proposed model clearly displays changes in target coverage, sputtered flux, and reactive gas partial pressure during compound-layer formation and sputter etching processes as a function of elapsed time. Effects of reactive gas flow rate, pumping speed, and sputtering current on compound-layer formation and sputter etching are also discussed. Hysteresis curves are yielded as a result of compound-layer formation and sputter etching calculations. The obtained curves are in accord with experimental results. Further, the dependence of hysteresis on pumping speed, sputtering current, and the difference of sputtering yields between metallic and compound-covered targets was investigated, resulting in showing a good agreement to that obtained experimentally. Mechanisms of hysteresis formation are also discussed on the basis of obtained results. It is concluded that hysteresis is formed because of the difference of gettering capacity before and after the target surface condition transition.
Transmission electron microscopy and transmission electron diffraction structural studies of heteroepitaxial InAsySb1−y molecular-beam epitaxial layers
Authors: Seong Tae-Yeon , Norman A. G. , Ferguson I. T. , Booker G. R.
Published: July 2002

Molecular-beam epitaxy InAsySb1−y layers were grown at temperatures ranging from 295 to 470 °C across the full composition range. Transmission electron microscopy and transmission electron diffraction (TED) examinations showed that for layers grown at and below 400 °C with nominal compositions 0.4<y<0.8, separation into two phases occurred resulting in a series of alternating plates approximately parallel to the layer surface. TED showed that the cubic lattices of the two phases were tetragonally distorted and their compositions were deduced to be typically InAs0.38Sb0.62 and InAs0.72Sb0.28. The plates were larger and more regular along the [1̄10] direction than the [110] direction. As the growth temperature increased from 295 to 400 °C, for layers of nominal composition InAs0.5Sb0.5, the plate length increased from 0.1 to 2.0 μm and the plate thickness from 10 to 50 nm. Crystallographic defects were present in the layers and their occurrence was different in the phase-separated and non-phase-separated layers. The plates formed spontaneously at the growing surface and were stable during subsequent annealing at 350 and 370 °C. It is suggested that they arise due to the presence of a miscibility gap at these growth temperatures. We have termed these spontaneously grown plate structures ‘‘natural’’ strained layer superlattices.
Perpendicular magnetic anisotropy and structures of epitaxial Co/Ag and Co/Au metallic superlattices
Authors: Kingetsu Toshiki , Sakai Katsura
Published: July 2002

The magnetic anisotropy and structures of Co/Ag and Co/Au metallic superlattices (SLs) grown by molecular-beam epitaxy were studied. In the Co/Ag SLs, the total magnetic anisotropy energy Keff was larger for the flatter Co/Ag interfaces and for the smaller strains of the Ag buffer layers. Particularly at 5 K, the perpendicular magnetic anisotropy was observed in the Co/Ag SLs with the nominal Co layer thickness t being 1 monolayer, and was strongly temperature dependent. The dependence of Keff⋅t on t was linear both at 5 and 300 K. The difference of the magnetic anisotropy in the Co/Ag and the Co/Au SLs was discussed in terms of structural characteristics. The origin of the perpendicular magnetic anisotropy was suggested to be the Néel-type surface anisotropy in the Co/Ag SLs and to be mainly the magnetoelastic anisotropy in the Co/Au SLs.
Effect of gas impurity and ion bombardment on stresses in sputter-deposited thin films: A molecular-dynamics approach
Authors: Fang C. C. , Jones F. , Prasad V.
Published: July 2002

Intrinsic stresses in sputter-deposited thin films are studied via a two-dimensional molecular-dynamics model. Two-body potential functions, periodic boundary conditions, and a generalized Langevin equation are applied to determine the microstructure of the film. The intrinsic stresses are then calculated using a stress method. 12 layers of substrate atoms are arranged in the (111) plane at the beginning of the film growth simulation. The molecular-dynamics simulations using the constant pressure and constant temperature ensemble are first carried out to obtain the zero stress state of the substrate. A thin film of Ni atoms is deposited in the presence of a background of argon and energetic ions in order to obtain a reasonable representation of the film structure. After the deposition process is completed, the film and the substrate are allowed to contract or expand in accordance with the elastic energies. It is found that the microstructure and intrinsic stresses of the film depend upon the incident energy of incoming particles, the ion bombardment, and the amount of trapped gas impurity. The model strongly suggests that the argon impurities trapped into the deposited film are the primary cause of the state of compressive stress. It also shows that in sputter-deposited films the magnitude of the compressive stress depends more strongly on the film structure than on the quantity of the argon gas trapped in the film. A tight packing of film atoms around argon atoms is likely to lead to higher compressive stresses in the film.
Positron annihilation in a metal-oxide semiconductor studied by using a pulsed monoenergetic positron beam
Authors: Uedono A. , Wei L. , Tanigawa S. , Suzuki R. , Ohgaki H. , Mikado T. , Ohji Y.
Published: July 2002

The positron annihilation in a metal-oxide semiconductor was studied by using a pulsed monoenergetic positron beam. Lifetime spectra of positrons were measured as a function of incident positron energy for a polycrystalline Si(100 nm)/SiO2(400 nm)/Si specimen. Applying a gate voltage between the polycrystalline Si film and the Si substrate, positrons implanted into the specimen were accumulated at the SiO2/Si interface. From the measurements, it was found that the annihilation probability of ortho-positronium (ortho-Ps) drastically decreased at the SiO2/Si interface. The observed inhibition of the Ps formation was attributed to an interaction between positrons and defects at the SiO2/Si interface.
Effects of operating conditions on the fast-decay component of the retained polarization in lead zirconate titanate thin films
Authors: Benedetto Joseph M. , Moore Randall A. , McLean F. Barry
Published: July 2002

The fast-decay component of the retained polarization in lead zirconate titanate ferroelectric capacitors was examined as a function of write/read voltage, number of cycles (fatigue), and temperature. The percentage of polarization loss within 1 s after the write pulse was found to be independent of the write/read voltage and only somewhat dependent upon the number of read/write cycles and temperature. A preliminary model is presented based on depolarizing fields within the ferroelectric due to nonswitching layers at the top and bottom interfaces.
The effect of chemical stresses on diffusion
Authors: Chu J. L. , Lee Sanboh
Published: July 2002

The effect of chemical stresses on diffusion has been investigated. A thin plate of isotropic material with boundary conditions of constant surface chemical potential and constant surface stresses is considered. If there is no rotation in the isotropic solid, the effective diffusivity arising from the chemical stresses is proportional to the concentration. The chemical stresses enhance the mass transfer because of increasing diffusivity. The initial surface concentration may differ from the final surface concentration for the constant surface chemical potential.
Investigation of the magnetization reversal mode for individual ellipsoidal single-domain particles of γ-Fe2O3
Authors: Salling C. , O’Barr R. , Schultz S. , McFadyen I. , Ozaki M.
Published: July 2002

We report measurements of the angular dependence of the switching field of individual ellipsoidal single-domain ferromagnetic particles. The measurements were carried out by Lorentz magnetometry on submicrometer γ-Fe2O3 particles and provide insights into the magnetization reversal for individual ellipsoidal particles of known morphology. The functional form of the switching field data indicates that the particles reverse by curling over a narrow range near 0 degrees and by coherent rotation at all larger angles. A value of 3±2×10−7 erg/cm for the exchange constant of the γ-Fe2O3 is obtained from these measurements. We suggest that the long desired goal of complete characterization of the magnetic properties of individual single-domain particles is now feasible.
Probing porous media with first and second sound. I. Dynamic permeability
Authors: Johnson David Linton , Hemmick Douglas L. , Kojima Haruo
Published: July 2002

The acoustic properties of first and second sound in He ii are used to probe the dynamic permeability k̃(ω), of porous media whose pores are large enough that the bulk properties of 4He are relevant. The measurements of phase velocity and attenuation, considered as functions of frequency and temperature, are in excellent agreement with the predictions based on a model k̃(ω) which involves four parameters: φ (porosity), α∞ (tortuosity), k0 (dc permeability), and Λ (dynamically connected pore size). The first three of these are measured by independent means; accurate values of Λ are extracted directly from the measurements in the high-frequency region of the data where the observed temperature and frequency dependences of the modes are precisely those predicted on theoretical grounds. It is shown empirically that Λ is in fact closely related to the dc permeability k0 for all known data sets, thus supporting an earlier conjecture based on theoretical ideas.
Optimum particle size distribution of an electrorheological fluid
Authors: Ota Motonori , Miyamoto Tetsuo
Published: July 2002

The optimum particle size distribution of an electrorheological fluid (ERF) is studied theoretically by the cubic particle chain model developed by the authors. For simplification purposes, the study is limited to a mixture that consists of two different particle sizes, i.e., small particles and large particles, but of the same permittivity. We adopt periodic boundary conditions with two chains in the unit cell. Static yield stress is calculated for three particle configurations. In the first configuration, each chain contains only one particle size, either small or large. The other configurations use chains which are constructed from small and large particles, arranged alternately. However, whereas the second requires particles of neighboring chains to be complementary, the third requires an alternating arrangement. The relative magnitude of the calculated yield stress in these the situations is τ2<τ3<τ1. In the first configuration calculated yield stress is independent of the particle size ratio. However in the second configuration, the yield stress increases as the size ratio approaches unity. From the results of these typical cases, we conclude that the ERF consisting of only the same particles gives the largest static yield stress. Also interactions among the chains as a description of the many-body effect is discussed.
Current-induced displacements of Bloch walls in Ni-Fe films of thickness 120–740 nm
Authors: Salhi E. , Berger L.
Published: July 2002

Rectangular current pulses of duration 0.14 μs, flowing across Bloch domain walls in Ni81Fe19 films, cause displacements Δx of these walls, observable by Kerr-contrast microscopy. In zero magnetic field, Δx reaches ≂14 μm/pulse at current densities ≂30% above the value jc where wall motion starts. This critical current density is jc≂1.2×1010 A/m2 for a film thickness w=263 nm. We have measured jc versus film thickness for w=120–740 nm, and find jc∝w−2.1. This suggests strongly that the observed wall motion is associated with an S-shaped distortion of the wall by the circumferential magnetic field of the current. This wall distortion is limited by the wall surface tension. The wall structure becomes that of the so-called asymmetric Néel wall. Through wall distortion, the current pulse pumps kinetic energy and momentum into the wall. This kinetic energy is then dissipated during ballistic wall motion happening largely after the end of the pulse. We also find jc to be independent of pulse duration.
Molecular-beam-epitaxial growth and magnetic properties of (111)Pt/Co/Ag, Pt/Co, and Ag/Co/Pt superlattices
Authors: Kingetsu Toshiki
Published: July 2002

The structural and the magnetic properties of (111)Pt/Co/Ag, Pt/Co, and Ag/Co/Pt superlattices (SLs) were studied. The samples were grown at 373 K on Ag buffer layers preformed on 7×7-(111)Si substrates by molecular-beam epitaxy. Reflection high-energy electron diffraction indicated that in-plane lattice constants of Co, Pt, and Ag layers changed continuously during layer growth in Pt/Co/Ag SLs with thin Co layers and Pt/Co SLs. The effective magnetic anisotropy energy Keff of a Pt/Co/Ag SL was similar to K̄eff, an average of Keff values of a Pt/Co and an Ag/Co SL with the same Co layer thicknesses. This suggests that the origins of perpendicular magnetic anisotropy in the Pt/Co system are different from those in the Au/Co system investigated earlier, in which the difference between the Au/Co and Au/Co/Ag SLs is small in Keff value.
Defect-based description of lithium diffusion into lithium niobate
Authors: Birnie Dunbar P. , Bordui Peter F.
Published: July 2002

A defect chemistry approach is used to analyze the observed concentration dependence of the lithium in-diffusion rate into lithium niobate. An ambipolar diffusion model is used where the lithium and niobium diffusion rates are coupled and therefore cause an internal electric field to develop during the diffusion process. Both lithium and niobium diffusion are found to proceed via simple vacancy mechanisms. The internal electric field forces the faster lithium diffusion to be reduced to a level consistent with the slower niobium diffusion process. This coupling gives a concentration dependence that matches the observed linear increase in interdiffusion rate as the total cation vacancy concentration decreases.
A highly oriented Al[111] texture developed on ultrathin metal underlayers
Authors: Kamijo Atsushi , Mitsuzuka Tsutomu
Published: July 2002

A highly oriented [111] texture is developed in ion beam sputtered Al films on metal underlayers of Ti, V, Cr, Co, Ni, Cu, or Y. The textured Al films show an extremely smooth surface. Deposition of highly textured Al films depends on the presence of this underlayer, the thickness of which must lie within a specific range that varies with the metal being used. We discuss here the mechanisms of texturing in terms of phenomenological surface-interface energy balance considerations. The great tolerance for high-power operations of Al films with a highly oriented [111] texture makes them particularly suitable for use as electrodes in surface acoustic wave devices.
Phase matched second harmonic generation using thin film ZnTe optical waveguides
Authors: Wagner H. P. , Wittmann S. , Schmitzer H. , Stanzl H.
Published: July 2002

Wide gap II-VI semiconductors have strong second order susceptibilities χ(2) and are therefore promising materials for efficient second harmonic generation. We have grown high quality single crystalline ZnSe/ZnTe/ZnSe/GaAs (001) waveguides by metalorganic-vapor-phase-epitaxy. Using end-fire coupling we observe a phase matched signal of the 1170.5 nm fundamental wave. The fundamental beam is generated by a tuneable KTP optical-parametric-oscillator pumped by a ps-Ti:sapphire laser system. Phase matching is achieved by coupling the TE0 fundamental mode with the TM2 second harmonic mode within the symmetric ZnTe waveguide.
Approximate cylindrical blast theory: Near-field solutions
Authors: Hutchens Gregory J.
Published: July 2002

A method for analyzing strong cylindrical blasts in cases where the source mass is not negligible is presented. Analytic expressions for the shock position as a function of time and shock speed and pressure as functions of position are derived. An approximation to classical Taylor–Sedov theory is extended to the near-field regime where the source mass is not negligible. Results from example calculations are compared to Taylor–Sedov theory as well as thermodynamic free expansion.
On the compensation mechanism in high-resistivity 6H–SiC doped with vanadium
Authors: Jenny J. R. , Skowronski M. , Mitchel W. C. , Hobgood H. M. , Glass R. C. , Augustine G. , Hopkins R. H.
Published: July 2002

A model is presented which describes the compensation mechanism resulting in semi-insulating 6H silicon carbide by vanadium doping. Undoped 6H–SiC crystals grown by physical vapor transport methods frequently contain between 1×1017 and 5×1018 cm−3 uncompensated boron acceptors. Upon addition of vanadium, the 3d1 electron of the vanadium donor compensates the holes of the boron centers. It is shown that when vanadium is present in concentrations greater than that of boron, the Fermi level is pinned to the vanadium donor level. From temperature dependent Hall effect measurements, this donor level has been determined to reside 1.35 eV below the conduction band minimum. Thermally stimulated current measurements on V-doped SiC crystals show that boron is the major compensating center for the vanadium impurity.
Microstructural analysis of YBa2Cu3Oy thin films deposited on SrTiO3 and LaAlO3 substrates by off-axis magnetron sputtering
Authors: García-González E. , Wagner G. , Reedyk M. , Habermeier H.-U.
Published: July 2002

The microstructural differences of YBa2Cu3O7−δ (YBCO) films prepared by in situ magnetron sputtering on (100)-SrTiO3 and (100)-LaAlO3 substrates have been investigated. A detailed analysis of the film orientation by means of Raman spectroscopy has been developed, showing that a certain amount of a-axis oriented grains always nucleate on the LaAlO3 surface, at the optimal deposition conditions for c-axis epitaxy. High-resolution electron microscopy has been used to show the epitactic nature of the YBCO films and has provided evidence for the orientational differences. A clear correlation between the degree of misorientation and the surface microstructure has been shown by atomic force microscopy and scanning tunneling microscopy, the bulk structure of these samples being reflected by their surface morphology.
Analytic model of power deposition in inductively coupled plasma sources
Authors: Vahedi V. , Lieberman M. A. , DiPeso G. , Rognlien T. D. , Hewett D.
Published: July 2002

A simple analytic model valid for all collisionality regimes is developed to describe the power deposition in a cylindrical inductively coupled plasma source with a planar coil. The heating is ohmic at high pressures and remains finite at low pressures. The low-pressure collisionless heating is due to kinetic nonlocal effects. The model is in good agreement with other calculations of collisionless heating. A diffusion model is then used to determine the plasma density profile and the electron temperature in terms of the gas pressure and the source geometry. The heating and diffusion models are used to determine the scaling of the inductive electric field with applied frequency and input power, and the results are compared with published experimental data to verify the scaling.
A numerical study of the dynamics and statistics of single electron systems
Authors: Fonseca L. R. C. , Korotkov A. N. , Likharev K. K. , Odintsov A. A.
Published: July 2002

We describe a new and efficient method for the numerical study of the dynamics and statistics of single electron systems presenting arbitrary combinations of small tunnel junctions, capacitances, and voltage sources. The method is based on numerical solution of a linear matrix equation for the vector of probabilities of various electric charge states of the system, with iterative refining of the operational set of states. The method is able to describe very small deviations from the ‘‘classical’’ behavior of a system, due to the finite speed of applied signals, thermal activation, and macroscopic quantum tunneling of charge (cotunneling). As an illustration, probability of dynamic and static errors in two single electron memory cells with 6 and 8 tunnel junctions have been calculated as a function of bias voltage, temperature, and switching speed.
Infrared reflectance of thick p-type porous SiC layers
Authors: MacMillan M. F. , Devaty R. P. , Choyke W. J. , Goldstein D. R. , Spanier J. E. , Kurtz A. D.
Published: July 2002

Thick p-type porous 6H SiC layers were fabricated by anodization of p-type 6H SiC bulk crystals in dilute HF. Striking differences are observed in the reststrahl region room-temperature reflectance of these porous layers compared to that of bulk 6H SiC crystals. Instead of the single broad band reflectance spectrum typically observed in bulk 6H SiC, a two-band reflectance spectrum is observed. Several effective medium models, based on different morphologies of the component materials, 6H SiC and air, are used to obtain the frequency-dependent dielectric function of porous SiC from which calculated reflectance spectra are generated. The best match between measured and calculated spectra is obtained for a Maxwell–Garnett model with SiC acting as the host material and air cavities acting as the inclusion material. The model reproduces the two reflectance band structure observed in the measured reflectance of the porous SiC layers. The differences in the reststrahl region reflectance spectra of the porous SiC layers, compared to bulk SiC, are associated with polarization effects introduced by the cavities combined with a mean field average of interactions among the cavities.
Optical and mechanical properties of plasma-beam-deposited amorphous hydrogenated carbon
Authors: Gielen J. W. A. M. , Kleuskens P. R. M. , van de Sanden M. C. M. , van Ijzendoorn L. J. , Schram D. C. , Dekempeneer E. H. A. , Meneve J.
Published: July 2002

Amorphous hydrogenated carbon films have been deposited on crystalline silicon and on glass from an expanding thermal plasma. Two deposition parameters have been varied: the electric current through the plasma source and the admixed acetylene flow. No energetic ion bombardment has been applied during deposition. Ex situ analysis of the films yields the infrared refractive index, hardness, Young’s modulus, optical band gap, bonded hydrogen content, and the total hydrogen and mass density. The infrared refractive index describes the film properties independent of which plasma deposition parameter (arc current or acetylene flow) has been varied. The hardness, Young’s modulus, sp2/sp3 ratio, and mass density increase with increasing refractive index. The optical band gap and hydrogen content of the films decrease with increasing refractive index. It is demonstrated that plasma-beam-deposited diamondlike a-C:H has similar properties as material deposited with conventional plasma-enhanced chemical-vapor-depositions techniques under energetic ion bombardment.
Optical properties of pulsed laser deposited bismuth films
Authors: de Sande J. C. G. , Missana T. , Afonso C. N.
Published: July 2002

Bismuth films are grown at room temperature onto Si substrates by pulsed laser deposition (PLD). Some films are deposited by dc sputtering (DCS) for comparison. PLD films are smooth and show micron-sized laminar grains as opposed to DCS films which are rough and show nanometer-sized columnar grains. The optical properties of the films have been studied by means of spectroscopic ellipsometry in the 300–800 nm wavelength interval over a period of six months. The results show that the refractive index of PLD Bi films is independent of the film thickness, thus providing reliable data of the optical constants of Bi films. In addition, it is shown that PLD films exhibit an improved stability to oxidation probably related to their favorable microstructural properties. The thickness dependence of the refractive index in DCS films is related to their surface roughness, the results being improved by pulsed laser melting of these films.
On the transient gas flow through catalytically active micromachined channels
Authors: Norberg P. , Ackelid U. , Lundström I. , Petersson L.-G.
Published: July 2002

Gas flow in long, narrow, very shallow, micromachined silicon dioxide–quartz glass channels was studied with the use of a mass spectrometric system. The channel bottom was partly covered with an evaporated, 10-Å-thick platinum film along its whole length, and the channel was inserted as the only leak between a gas mixing chamber and an ultrahigh vacuum mass spectrometer chamber. At a wide pressure range upstream of the channel (10–1000 Torr), the steady state flow through the channel was characterized as being close to molecular. At a pressure buildup of either H2 or O2 in the gas mixing chamber, the mass spectrometer response was delayed more than what can be explained by molecular diffusion. A total restriction of the diffusion due to adsorption on platinum is suggested. The assumption is in accord with different validation experiments. A model for the adsorption delay time is presented and discussed.
Free carrier absorption and lifetime mapping in 4H SiC epilayers
Authors: Galeckas A. , Grivickas V. , Linnros J. , Bleichner H. , Hallin C.
Published: July 2002

Results of carrier lifetime studies in low-doped epitaxial 4H SiC layers are reported. The free carrier absorption (FCA) technique was applied to extract carrier lifetime parameters and their spatial distribution in a wide photoexcitation range. The FCA magnitude is shown to scale linearly with the photoinjected carrier concentration, while the absorption cross section increases according to a λ4.4 law for near infrared wavelengths. High spatial resolution carrier lifetime mapping of large 4H SiC areas revealed features related to structural imperfections of epilayers. Finally, a density dependent fast lifetime component was observed at high injection levels and attributed to band-to-band Auger recombination.
Determination of the direct band-gap energy of InAlAs matched to InP by photoluminescence excitation spectroscopy
Authors: Roura P. , López-de Miguel M. , Cornet A. , Morante J. R.
Published: July 2002

A series of InxAl1−xAs samples (0.51<x<0.55) coherently grown on InP was studied in order to measure the band-gap energy of the lattice matched composition. As the substrate is opaque to the relevant photon energies, a method is developed to calculate the optical absorption coefficient from the photoluminescence excitation spectra. The effect of strain on the band-gap energy has been taken into account. For x=0.532, at 14 K we have obtained Eg0=1549±6 meV.
Scanning tunneling microscope study of the morphology of chemical vapor deposited copper films and its correlation with resistivity
Authors: Ramaswamy Geetha , Raychaudhuri A. K. , Goswami Jaydeb , Shivashankar S. A.
Published: July 2002

In this article we report the results of the scanning tunneling microscope study of the surface morphology of copper films grown by metalorganic chemical vapor deposition from the precursor Cu(tbaoac)2. Films ≈100 nm in thickness were grown by varying the reactor pressure. The images reveal the crucial role of the reactor pressure and growth rate on the morphology and grain growth of the films. Films grown at a low growth rate have a smooth surface with small well connected grains of ≈10–40 nm diameter with relatively lower resistivity, while films grown at higher growth rates have rougher surfaces and larger grain sizes of ≈10–100 nm diameter with poor connectivity that leads to higher resistivity. The correlation of the morphology with resistivity (ρ) and the temperature dependence of ρ in the range 300–4.2 K was investigated. Comparison with the ρ of pure bulk copper shows that these films have much higher resistivities. A large part of the high resistivity at room temperature arises from an enhanced temperature dependent part of ρ and is not due to an enhancement of the residual resistivity alone. The films exhibit deviations from Matthiessen’s rule. From a semi-quantitative analysis of the data using existing theories we could assign the large ρ as well as the temperature dependence of ρ to grain boundary scattering and surface scattering. However, for T>50 K we find that an extra temperature dependent ρ term which may be related to enhancement of electron-phonon interactions by the rough film surface is required.
Thermal power at a substrate during ZnO:Al thin film deposition in a planar magnetron sputtering system
Authors: Wendt R. , Ellmer K. , Wiesemann K.
Published: July 2002

In a balanced magnetron sputtering system the thermal power at a substrate has been determined from the temperature change of the substrate when the plasma is switched on. Using the temperature as a function of the potential of a probe, the calorimeter has been calibrated absolutely. A heat input equivalent of about 10 eV per electron has been determined for a dc discharge. The results for the total thermal power at the substrate are compared with values published by other groups for similar discharge systems. The contributions of different kinds of particles are discussed. For the dc discharge at a discharge power of 50 W and a pressure of 0.8 Pa, a thermal power of 15.6 mW cm−2 has been found which is mainly produced by particles other than the plasma ions. It can be concluded from the increase of the thermal power with decreasing pressure that bombardment by particles originating from the target is the main source of the substrate heating. In an rf discharge the ion energy is two times and the flux density is nearly three times higher than in a dc discharge. Here the dependence of the thermal power on pressure is only weak and mainly the plasma ions transport the power to the substrate.
Influence of Na and H2O on the surface properties of Cu(In,Ga)Se2 thin films
Authors: Heske C. , Richter G. , Chen Zhonghui , Fink R. , Umbach E. , Riedl W. , Karg F.
Published: July 2002

The influence of humidity on the electronic structure of Na-containing polycrystalline Cu(In,Ga)Se2 thin films on soda-lime glass substrates has been investigated by x-ray and UV photoemission as well as by Auger electron spectroscopy. Different interactions between coadsorbed Na, H2O, and the Cu(In,Ga)Se2 surface are revealed at low temperatures and upon annealing at room temperature. Both, reversible and irreversible interactions such as a H2O-induced reduction of the Na surface content and the formation of a Na–O–Cu(In,Ga)Se2 complex are observed. Our findings can be correlated with the influence of ambient conditions on Cu(In,Ga)Se2 solar cell adsorbers and demonstrate the importance of adequate encapsulation of Na-containing Cu(In,Ga)Se2-based thin-film solar cells.
Diffusion kinetics of the carburization and silicidation of Ti3SiC2
Authors: El-Raghy Tamer , Barsoum Michel W.
Published: July 2002

The ternary carbide Ti3SiC2 possesses a unique set of properties that could render it a material of considerable technological impact. The motivation for this work was to enhance the hardness and oxidation resistance of Ti3SiC2 by altering its surface chemistry. Reaction of Ti3SiC2 with single crystal Si wafers in the 1200–1350 °C temperature range resulted in the formation of a dense surface layer composed of a two phase mixture of TiSi2 and SiC. This layer grows in two distinct morphologies; an outer layer with fine (1–5 μm) SiC particles and an inner coarser (10–15 μm) one. The overall growth rates of the layers were parabolic. Comparison with previously published results supports the conclusion that diffusion of Si through TiSi2 is rate limiting. In the 1400–1600 °C temperature range, reaction of Ti3SiC2 with graphite foils resulted in the formation of a 15 vol. % porous surface layer of TiCx (where x>0.8). It is shown that the carburization kinetics are rate limited by the diffusion of C through TiCx. Both carburization and silicidation increased surface hardness, the latter also enhanced the oxidation resistance by about three orders of magnitude.
Bistable nematic azimuthal alignment induced by anchoring competition
Authors: Barberi R. , Bonvent J. J. , Giocondo M. , Iovane M. , Alexe-Ionescu A. L.
Published: July 2002

We present a novel method to obtain bistable azimuthal anchoring conditions for nematic liquid crystals. The fine control of the anchoring strengths of two independent planar surface anchoring attractors, perpendicular to each other, induces controlled surface transitions that give bistability. The independent anchoring sources are obtained by means of a composite surface made with a film of photopolymer on an anisotropic SiO layer. A phenomenological model, based on anchoring competition between the two orienting layers, is developed to describe the surface bistability.