bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo simulation of a complex fluid confined to a pore with nanoscopically rough walls
Authors: Porcheron Fabien , Schoen Martin , Fuchs Alain H.
Published: July 2002

Understanding the properties of fluid films of nanometer scale thickness confined between two solid substrates is of fundamental interest as well as of practical importance for engineering applications such as lubrication, adhesion, and friction. We address here the question of the effect of the wall corrugation on the confined fluid structure. We report configurational bias grand canonical Monte Carlo simulations for model butane confined between planar and nonplanar walls. Furrowed walls have been used to model surface roughness effects on the nanometer length scale, while the confining walls remain smooth on the atomic scale. It is shown that the fluid confined between planar walls exhibits a damped oscillatory solvation pressure profile. A transition from an oscillatory to a nonoscillatory behavior is observed when the characteristic length of the furrow reaches the typical dimensions of a butane molecule. It is inferred from these simulations that disrupted oscillatory forces observed in the experiments may reflect the coupling between molecular and nanoscopic roughness length scales.
Different designs and limits of longitudinal magnetic recording media
Authors: Girt Er. , Richter H. J. , Munteanu Mariana , Yen Ed , Harkness Samuel D. , Brockie Richard M.
Published: July 2002

Combining antiferromagnetically coupled (AFC) and laminated media (LM), we were able to incorporate the stability of AFC media with the signal-to-noise ratio (SNR) of LM. This improvement is directly related to the decrease of the demagnetization field which is calculated to be up to 50% of the LM case for some configurations of AFC+LM that were experimentally realized. The stabilization layer also increases the magnetic energy barrier of the recording layers in the AFC+LM structure, which further improves the stability of this media. An improvement of ∼1 dB in SNR was observed in AFC+LM in comparison to single layer media.
Evaluation of the fundamental properties of quantum dot infrared detectors
Authors: Phillips Jamie
Published: July 2002

The physical properties of detectors based on intraband optical absorption in quantum dots is described and examined in the interest of providing a competitive alternative infrared (IR) detector technology. These quantum dot detectors are an extension of quantum well infrared photodetectors and are expected to have a large performance advantage. A model is developed for quantum dot infrared photodetectors based on fundamental performance limitations enabling a direct comparison between IR materials technologies. A comparison is made among HgCdTe, quantum well, and quantum dot IR detectors, where quantum dots are expected to have the potential to outperform quantum wells by several orders of magnitude and compete with HgCdTe. In this analysis, quantum dots are expected to possess the fundamental ability to achieve the highest IR detector performance if quantum dot arrays with high size uniformity and optimal bandstructure may be achieved.
Nuclear magnetic resonance study of the crystallization kinetics in soft magnetic nanocrystalline materials
Authors: Barbatti C. F. , Sinnecker E. H. C. P. , Sarthour R. S. , Guimarães A. P.
Published: July 2002

We used the nuclear magnetic resonance technique to study the evolution of the structural and magnetic properties of Fe-based melt-spun ribbons of Fe73.5Cu1Nb3Si13.5B9, Fe73.5Cu1Nb3Si18.5B4, and Fe86Zr7Cu1B6, as-cast and annealed at 500, 540, and 430 °C, respectively. Experiments were carried out at 4.2 K and zero-applied magnetic field, and in a controlled radio-frequency (rf) field. This type of measurement allows us to observe B and Nb sites, and makes it possible to distinguish signals associated with regions of different magnetic hardnesses. The results exhibit a high dependence of the spectra on rf power. For Fe–Si-based alloys, we observe well-defined Nb93 resonance signals from three distinct sites according to the concentration of Fe atoms in their neighborhood. In the Fe73.5Cu1Nb3Si18.5B4 spectra we also observe a peak around 34 MHz, connected to the B11 resonance in different Fe–B compounds, which remains as the rf power decreases, suggesting that the signals come from atoms inside a soft magnetic region. As for the Fe–Zr alloy, we also observe a peak around 36 MHz, identified as the B11 resonance, and a broad line around 62 MHz.
Monte Carlo simulation of the magnetization of a ferromagnet with antiphase boundaries
Authors: Berger L. , Labaye Y. , Crisan O. , Greneche J. M. , Coey J. M. D.
Published: July 2002

The magnetic properties of a ferromagnetic cylinder containing an antiphase boundary with antiferromagnetic interactions are studied using atomic Monte Carlo simulation. The approach to saturation shows a reduced magnetization compared with the completely ferromagnetic sample, even in huge applied fields. The magnetization profiles are studied as a function of the number of ferromagnetic planes in the cylinder with 80 atoms per plane and also as function of the ratio of the bulk-to-antiphase exchange coupling. Hysteresis appears after removing the applied field for relatively low antiphase boundary densities. It is shown that the antiferromagnetic coupling across the antiphase boundary leads to a progressive rotation of spins as the two half “domain walls” at the boundary with opposite chirality narrow with increasing applied field.
Unstable van der Waals driven line rupture in Marangoni driven thin viscous films
Authors: Warner M. R. E. , Craster R. V. , Matar O. K.
Published: July 2002

An intriguing, dramatic and, at present, not fully understood instability often accompanies surfactant driven flows on thin films. This paper investigates a candidate mechanism that could create and drive this instability, van der Waals rupture, via numerical simulations coupled with analytical techniques. The spreading process itself is modelled with a pair of coupled evolution equations for the fluid film thickness and surfactant concentration that are derived in the lubrication approximation. These equations are then linearized about a base state that corresponds to the one-dimensional rupturing solution, and equations for the evolution of the transverse disturbances are derived. These linearized equations are investigated in several ways: numerical simulations where the perturbations are driven by the time evolving base state, or where the base state is frozen at a time tf close to the rupture event. The quasistatic initial value problem is also investigated as an eigenvalue problem, where the eigenvalue represents the quasistatic growth rate. We also take advantage of recent similarity scalings and results deduced for rupture, in the absence of surfactant, to motivate some of our numerical investigations. Additionally, we investigate the fully nonlinear equations including the transverse components. Perhaps interestingly, three-dimensional reconstructions of the film profile using the most dangerous mode from linear theory, as well as profiles from direct numerical simulations of the full nonlinear governing equations, that is, including interactions in the transverse direction, assume the form of finger-like patterns.
Quantum studies of Eley–Rideal reactions between H atoms on a graphite surface
Authors: Sha Xianwei , Jackson Bret , Lemoine Didier
Published: July 2002

Results from electronic structure studies and quantum scattering calculations are presented for the reaction of gas-phase H atoms with H atoms adsorbed onto a graphite surface to form H2(g). H can chemisorb on graphite directly over a carbon atom, with the carbon puckering out of the surface plane by several tenths of an Å. Using an ab initio approach based on the density functional theory, and treating the graphite substrate as a slab, we compute the potential energy surface for this reaction, for three cases. In the first case the adsorbed H is initially in the chemisorbed state and the lattice is held fixed in the puckered position during the reaction. In the second case the adsorbed H is initially in the chemisorbed state, but the lattice is allowed to fully relax for each configuration of the two H atoms. In the third case the H initially on the surface is in the physisorbed state. We use a fully quantum mechanical scattering approach to compute reaction cross sections and product H2 translational, rotational, and vibrational state distributions for each case.
Computer simulation of the phase behavior of a model membrane protein: Annexin V
Authors: Bates Martin A. , Noro Massimo G. , Frenkel Daan
Published: July 2002

The bulk thermodynamic properties of membrane proteins originate from a complex combination of molecular interactions. We propose a simple model based on the pair interactions between a model membrane protein, annexin V. The experimental observations of a honeycomb (p6) and a triangular (p3) phase are successfully reproduced with Monte Carlo computer simulations. Grand canonical simulations and a newly developed “strip”-move constant pressure technique reveal the stability of a dilute fluid phase and a dense solid phase, not observed with the current experimental technology. While this model is extremely simple in that it relies only on hard-body and short-range directional interactions, it nevertheless captures the essential physics of the interactions between the protein molecules and reproduces the phase behavior observed in experiments.
Influence of iron–silicon interaction on the growth of carbon nanotubes produced by chemical vapor deposition
Authors: de los Arcos T. , Vonau F. , Garnier M. G. , Thommen V. , Boyen H.-G. , Oelhafen P. , Düggelin M. , Mathis D. , Guggenheim R.
Published: July 2002

Carbon nanotubes are often grown by chemical vapor deposition on silicon substrates covered with an iron catalyst. Photoemission and scanning electron microscopy studies presented here reveal how the iron silicide interface phase formed at elevated temperatures influences the catalytic efficiency of the iron. Moreover, we will show how the deposition of a thin layer of dense titanium nitride between the silicon substrate and the iron catalyst effectively prevents the formation of the silicide phase and consequently improves the carbon nanotubes growth.
Adsorption of α-pyridone on Cu(110)
Authors: Frankel D. J. , Chen Q. , Richardson N. V.
Published: July 2002

α-pyridone was absorbed onto a Cu(110) surface at room temperature under UHV conditions. This caused the (1×1) LEED pattern to fade suggesting adsorption into a disordered structure. Upon annealing to 590 K, an (8×2)gg LEED pattern with glide planes along both 〈110〉 and 〈001〉 directions was observed, which indicates the formation of a well-ordered monolayer. Following low-temperature (150 K) adsorption, temperature programmed desorption revealed the existence of a multilayer with a desorption temperature of 310 K, followed by desorption of the monolayer only above 850 K. High-resolution electron-energy loss spectroscopy showed that, initially in the monolayer at room temperature, the molecules have an upright geometry. However, annealing leaves only the out-of-plane CH bending mode at about 804 cm−1 which suggests that the molecule exclusively lies flat on the surface when the (8×2)gg periodicity is formed. Scanning tunneling microscopy reveals molecular resolution images of well-ordered monolayers. The experimental results are consistent with a model in which molecular dimers, held together by H-bonding, are the basic unit of the two-dimensional array.
Nematic textures in F-actin
Authors: Das P. , Roy J. , Chakrabarti N. , Basu S. , Das U.
Published: July 2002

Actin filaments, which are protein polymers occurring abundantly and ubiquitously in muscle and nonmuscle cells, are known to align in a shear flow, and with an external magnetic field. They form a nematic liquid crystal of the athermal type at a low concentration. Typical defects and textures of the nematic actin liquid crystal are described in this work. The generation of well-aligned nematic single crystals has been reported, in the vicinity of an air–water interface, with the actin filaments spontaneously aligning normal to the interface. Away from the air-water interface nematic single crystal domains are due to the alignment of the actin filaments parallel to the glass surface. The twist-bend nature of the disclination line of integral strength (m=1) has been attributed to the relative magnitudes of the anisotropic curvature elastic constants, which reflect the filaments’ semirigidity.
A vapor barrier Couette shear cell for small angle neutron scattering measurements
Authors: Porcar L. , Hamilton W. A. , Butler P. D. , Warr G. G.
Published: July 2002

We describe the design and operation of a temperature controlled Couette shear cell for small angle neutron scattering (SANS) studies of complex fluids under flow. This design incorporates a vapor barrier, which prevents sample evaporation to relatively high shear rates. This cell enables the investigation of systems which are highly sensitive to evaporation. Over the duration of a Couette SANS measurement composition phase transitions due to evaporation can be misinterpreted as true shear-induced transformations. We give a brief report of recent experiments performed on one such system: bicontinuous L3 sponge phases for which the surfactant membrane constituents are Cetylpyridinium chloride and hexanol. These clearly demonstrate the limitations of previous designs and the utility of the vapor barrier in measurements of a predicted shear induced sponge to lamellar phase transition. Using this cell we also describe and test a simple and effective way to put SANS data taken in the tangential Couette configuration on an absolute scale.
Measurement of the global structure of interchange modes driven by energetic electrons trapped in a magnetic dipole
Authors: Levitt B. , Maslovsky D. , Mauel M. E.
Published: July 2002

Measurements of the radial, azimuthal, and field-aligned mode structures of interchange instabilities excited by energetic electrons confined by a magnetic dipole are presented. The mode structures are determined using a correlation analysis of movable high-impedance floating potential probes located at various positions within the plasma. The hot electron population, produced by electron cyclotron resonance heating, becomes unstable to hot electron interchange (HEI) instabilities which saturate nonlinearly with a complex and time-varying frequency spectrum. Although the mode frequencies vary dramatically, it is found that the mode structures do not evolve significantly in time, being determined by the azimuthal mode numbers. These measurements are compared to a self-consistent nonlinear particle simulation of the HEI mode in dipole geometry. Upon appropriate adjustment of the boundary conditions, the simulation reproduces the measured radial and azimuthal structures at large amplitudes.
Complex dynamics in a simple model of pulsations for super-asymptotic giant branch stars
Authors: Munteanu Andreea , Garcı́a-Berro Enrique , José Jordi , Petrisor Emilia
Published: July 2002

When intermediate mass stars reach their last stages of evolution they show pronounced oscillations. This phenomenon happens when these stars reach the so-called asymptotic giant branch (AGB), which is a region of the Hertzsprung–Russell diagram located at about the same region of effective temperatures but at larger luminosities than those of regular giant stars. The period of these oscillations depends on the mass of the star. There is growing evidence that these oscillations are highly correlated with mass loss and that, as the mass loss increases, the pulsations become more chaotic. In this paper we study a simple oscillator which accounts for the observed properties of this kind of stars. This oscillator was first proposed and studied in Icke et al. [Astron. Astrophys. 258, 341 (1992)] and we extend their study to the region of more massive and luminous stars —the region of super-AGB stars. The oscillator consists of a periodic nonlinear perturbation of a linear Hamiltonian system. The formalism of dynamical systems theory has been used to explore the associated Poincaré map for the range of parameters typical of those stars. We have studied and characterized the dynamical behavior of the oscillator as the parameters of the model are varied, leading us to explore a sequence of local and global bifurcations. Among these, a tripling bifurcation is remarkable, which allows us to show that the Poincaré map is a nontwist area preserving map. Meandering curves, hierarchical-islands traps and sticky orbits also show up. We discuss the implications of the stickiness phenomenon in the evolution and stability of the super-AGB stars.
Electrical cutting and nicking of carbon nanotubes using an atomic force microscope
Authors: Park Ji-Yong , Yaish Yuval , Brink Markus , Rosenblatt Sami , McEuen Paul L.
Published: July 2002

An atomic force microscope (AFM) has been used to modify the electrical properties of carbon nanotube devices. By applying voltage pulses from a metal-coated AFM tip, electrical breaks (“cuts”) or tunneling barriers (“nicks”) can be created at any point along a tube. These methods are applied to make single tube devices by cutting uninteresting nanotubes or create small quantum dots with large charging energies by placing two tunneling barriers 50 nm apart along a nanotube.
Propagating fronts, chaos and multistability in a cell replication model
Authors: Crabb Rebecca , Mackey Michael C. , Rey Alejandro D.
Published: July 2002

Numerical solutions to a model equation that describes cell population dynamics are presented and analyzed. A distinctive feature of the model equation (a hyperbolic partial differential equation) is the presence of delayed arguments in the time (t) and maturation (x) variables due to the nonzero length of the cell cycle. This transport like equation balances a linear convection with a nonlinear, nonlocal, and delayed reaction term. The linear convection term acts to impress the value of u(t,x=0) on the entire population while the death term acts to drive the population to extinction. The rich phenomenology of solution behaviour presented here arises from the nonlinear, nonlocal birth term. The existence of this kinetic nonlinearity accounts for the existence and propagation of soliton-like or front solutions, while the increasing effect of nonlocality and temporal delays acts to produce a fine periodic structure on the trailing part of the front. This nonlinear, nonlocal, and delayed kinetic term is also shown to be responsible for the existence of a Hopf bifurcation and subsequent period doublings to apparent ‘‘chaos’’ along the characteristics of this hyperbolic partial differential equation. In the time maturation plane, the combined effects of nonlinearity, nonlocality, and delays leads to solution behaviour exhibiting spatial chaos for certain parameter values. Although analytic results are not available for the system we have studied, consistency and validation of the numerical results was achieved by using different numerical methods. A general conclusion of this work, of interest for the understanding of any biological system modeled by a hyperbolic delayed partial differential equation, is that increasing the spatio-temporal delays will often lead to spatial complexity and irregular wave propagation.
Spiral breakup as a model of ventricular fibrillation
Authors: Panfilov Alexandre V.
Published: July 2002

The phenomenon of spiral breakup in a 2D and a 3D excitable medium is described. Differences between breakup in two dimensions and in three dimensions are discussed. Spiral breakup in an anatomical model of the ventricles of the heart is also studied. The patterns of excitation in the heart are presented at different wavelengths together with their electrocardiograms. Finally it is suggested that the phenomenon of spiral breakup is a possible mechanism of the ventricular fibrillation (VF).
Hyperchaotic qualities of the ball motion in a ball milling device
Authors: Caravati C. , Delogu F. , Cocco G. , Rustici M.
Published: July 2002

Ball collisions in milling devices are governed by complex dynamics ruled by impredictable impulsive forces. In this paper, nonlinear dynamics techniques are employed to analyze the time series describing the trajectory of a milling ball in an empty container obtained from a numerical model. The attractor underlying the system dynamics was reconstructed by the time delay method. In order to characterize the system dynamics the calculation of the spectrum of Lyapunov exponents was performed. Six Lyapunov exponents, divided into two terns with opposite sign, were obtained. The detection of the positive tern demonstrates the occurrence of the hyperchaotic qualities of the ball motion. A fractal Lyapunov dimension, equal to 5.62, was also obtained confirming the strange features of the attractor.
From scattering singularities to the partition of a horseshoe
Authors: Lipp C. , Jung C.
Published: July 2002

In a chaotic scattering system there are two different approaches to construct a symbolic dynamics. One comes from the branching tree obtained from a scattering function. The other comes from a Markov partition based on the line of primary homoclinic tangencies in the Poincaré map taken in the interaction region. In general the two results only coincide for a complete horseshoe. We show how to make a different choice for the partition in the internal Poincaré section based on scattering behavior and not on homoclinic tangencies. Then the corresponding symbolic dynamics coincides also for the incomplete case with the one obtained naturally from the scattering functions. The scattering based partition lines of the horseshoe are constructed by an iterative procedure.
Nonlinear calculation of a temperature profile produced in a two-layer structure by a scanning cw elliptical laser or electron beam
Authors: Yamada Masayoshi , Nambu Katsumi , Yamamoto Keiichi
Published: July 2002

We present the algorithm to relate the nonlinear heat equation including temperature-dependent parameters to the Green’s function solution of the linear heat equation for a two-layer structure. Also derived is the linear solution for an elliptical beam. For silicon-on-silicon dioxide, the actual temperature profile based on the present algorithm is numerically calculated and compared with the linear calculation.
Determination of the effective radiative lifetime of the 6 3P1 atomic mercury level in low-pressure mercury discharges
Authors: van de Weijer P. , Cremers R. M. M.
Published: July 2002

Experiments are described in which low-pressure mercury, mercury-argon, and mercury-krypton discharges were irradiated with a dye laser pulse at 405 nm, thus exciting mercury atoms from the metastable 6 3P0 level to the 7 3S1 level. The 7 3S1 level decays radiatively to the 6 3P levels. By recording the time dependence of the 6 3P1 level density at the 254-nm fluorescence signal, the effective radiative lifetime of this level was determined. These measurements were performed for a wide range of mercury vapor densities. From the effective radiative lifetime and the 6 3P1 level density, the 254-nm output can be calculated. Reasonable agreement is found for two discharges of which the 254-nm output had been measured directly.
Aging effects on amorphous Tb–transition-metal films prepared by diode and magnetron sputtering
Authors: Hong M. , Bacon D. D. , van Dover R. B. , Gyorgy E. M. , Dillon J. F. , Albiston S. D.
Published: July 2002

We have studied and compared the aging characteristics of the amorphous Tb(FeCo) films from both dc getter diode and magnetron sputtering. No protecting layer such as SiO2 or Al2O3 was put on the films. Fresh films of 1.0-μm thickness from diode sputtering showed a perpendicular anisotropy and well-behaved magnetic properties using a vibrating sample magnetometer and an automatic torque magnetometer. We noticed a decrease in perpendicular anisotropy when the films were exposed to the air. However, this aging phenomenon was not observed in films of the same thickness prepared by magnetron sputtering even after seven months’ exposure to the air. The reasons for the difference are due to two distinct reaction mechanisms: bulk reaction in diode-sputtered films and surface reaction in magnetron-sputtered films. A variation of the microstructure is believed to attribute to this. The surface reaction was studied in thinner magnetron-sputtered films of 10 and 25 nm, where the surface-to-bulk ratio is larger. A decrease in perpendicular anisotropy with aging was observed in these thinner films.
Magnetic properties of MnAlGe and related compounds
Authors: Kamimura T. , Ido H. , Shirakawa K.
Published: July 2002

MnAlGe is a ferromagnet with a unique crystal structure including two-dimensional arrays of Mn atoms in it. In order to find the magnetic properties characteristic of this structure, magnetic and electric measurements were made for Mn0.9M0.1AlGe (M:Mn, Cr, Fe) and MnGaGe. It has been found that the susceptibility above the Curie temperature (TC) does not obey the Curie–Weiss law over the very wide temperature range. Obtained susceptibility vs temperature curves are well expressed by a formula χg=C/(T−θa)γ with a composition dependent parameter γ ranging from about 1.3 to 1.5. In MnAlGe the formula with γ=1.49 holds in the whole temperature range from just above TC (=503 K) to Tt (=853 K, a temperature of solid-state transition). The Curie temperature of Mn1−xMxAlGe(x≤0.2) varies monotonically when they are plotted against the averaged number of d electrons per transition-metal atom. The temperature dependencies of saturation magnetization and electric resistivity were also measured for these specimens.
Effective electrical conductivity of two-phase disordered composite media
Authors: Torquato S.
Published: July 2002

Perturbation expansions of the effective electrical conductivity σe of any two-phase isotropic composite medium of arbitrary dimensionality d (where d=2,3) are derived. It is shown that certain Padé approximants of a particular series representation of σe yield known rigorous bounds on the conductivity of the composite. The relationships between the conductivities of certain models that are exactly realized by some of these bounds and the perturbation expansions are discussed. A new expression for the conductivity of a broad class of three-dimensional dispersions of inclusions is derived. The formula for σe, which depends upon, among other quantities, a certain three-point probability function of the composite medium, is shown to accurately predict σe of both periodic and random arrays of impenetrable spheres, for a wide range of phase conductivities and inclusion volume fractions.
Effect of doping concentration on the performance of large-grain polycrystalline silicon solar cell
Authors: Dimitriadis C. A.
Published: July 2002

A theoretical study of the influence of the doping concentration on the efficiency of large-grain polycrystalline silicon solar cells is presented. For grain-boundary states density between 1011 and 1013 cm−2, we find the maximum efficiency for typical semi-infinite solar cells to occur at doping concentration in the range between 1 and 4×1016 cm−3.
Mechanisms of exchange anisotropy (invited)
Authors: Malozemoff A. P.
Published: July 2002

Exchange anisotropy refers to a group of phenomena which appear in ferromagnetic-antiferromagnetic sandwiches, particularly to a field offset in the hysteresis loop. After a brief review of experiment and earlier theory, a new theory is described involving a random field at the interface which causes the antiferromagnet to break up into domains, whose size is inversely proportional to the exchange field offset. The theory is extended by considering the temperature dependence and also the topological properties of the domains, in particular nonzero winding numbers which increase the size of the domains and give them added stability. The metastability of such structures provides an explanation of the magnetic ‘‘training’’ effect observed in multiple cycles of the hysteresis loop.
Optical observation of evanescent surface magnons in thin magnetic films
Authors: Srinivasan G. , Emtage P. R. , Booth J. G. , Patton C. E.
Published: July 2002

A new type of nonpropagating surface-wave-like magnon has been detected in yttrium iron garnet films (YIG) in a magnetostatic wave (MSW) device structure using Brillouin light scattering. The measurements were carried out on a YIG film stripline device operated at 2–4 GHz. With an applied magnetic field parallel to the stripline, magnon signals were observed at fields above the surface wave band edge. Theory shows that highly localized, evanescent surface modes can exist at such fields, but only when a ground plane is present; the bandwidth in field or frequency is inversely proportional to the separation between the film and the ground plane. The observed evanescent wave band limits are in good agreement with the theoretical values.
Electrical transport, optical properties, and structure of TiN films synthesized by low-energy ion assisted deposition
Authors: Savvides N. , Window B.
Published: July 2002

Thin films of TiN, covering a narrow range around stoichiometric composition, were synthesized by low-energy ion assisted growth at deposition temperatures TD=100, 300, 500, and 700 °C. The deposition apparatus consisted of an unbalanced dc magnetron sputter source which allowed high rate deposition from a titanium target with simultaneous bombardment of the growing film by a beam of mixed Ar+ and N+2 ion species at an ion-to-condensing atom arrival rate ratio of five. For each deposition temperature, films were prepared at various ion energies in the range Ei =2–100 eV. The presence of reactive N+2 ions

and the effects of ion bombardment facilitate increased incorporation of nitrogen and decrease the overall defect density in the structure of TiN. Electrical transport properties of films were investigated by measurements of the temperature dependence of resistivity ρ(T) in the range T=4–300 K, and superconducting transition temperature Tc. These measurements were complemented by measurement of optical reflectance, x-ray diffraction, and scanning electron microscopy investigations to determine the structure and composition of films. Collectively the film properties have a strong dependence on ion energy and deposition temperature. Films deposited at optimum conditions (TD =500 °C and Ei =30–50 eV) possess a high degree of crystalline perfection with a strong (200) texture and a high optical reflectance (82% at λ=800 nm). These properties correlate with the following optimum electrical properties: room-temperature resistivity ρ300∼26 μΩ cm, resistivity ratio RR=2.13, temperature coefficient of resistivity TCR=2.43×10−3 K−1, and Tc =5.35 K. These results represent the best results yet reported for microcrystalline TiN films. The temperature dependence of resistivity has a normal-metal behavior and it obeys Matthiessen’s rule. The phonon contribution to resistivity at room temperature, ρthermal, is about 14 μΩ cm and is in agreement with that of single-crystal TiN. As the disorder in the structure of TiN increases, TCR is found to decrease and zero TCR is predicted for limiting values of resistivity ρ300=300–400 μΩ cm.
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u measurement of ion-beam-induced deposition of gold
Authors: Dubner A. D. , Wagner A.
Published: July 2002

An experimental system for measuring ion-beam-induced deposition yield is described. Gold films were deposited on quartz-crystal microbalances (QCM) by decomposing dimethyl gold hexafluoroacetylacetonate molecules (C7H7F6O2Au) with a 5-keV argon-ion beam. The QCMs provide an in situ measurement of the deposition rate as a function of ion dose, dose rate, gas pressure, and substrate temperature. The deposition yield, or mass deposited per incident ion, is shown to increase with increasing pressure and decreasing temperature. The yield is independent of the ion dose rate, which implies that the deposition process is not due to macroscopic heating. The deposition yield is shown to depend on the sputter yield of the substrate. The density of the deposited films was determined to be about 10 g/cm3, which is about half the density of bulk gold (19.3 g/cm3). The difference in density is due to carbon contamination in the deposited films.
Time resolved x-ray diffraction study of laser annealing in silicon at grazing incidence
Authors: Buschert J. R. , Tischler J. Z. , Mills D. M. , Zhao Q. , Colella R.
Published: July 2002

The loss of crystallinity at the surface of a silicon single crystal exposed to intense pulsed laser irradiation has been observed by means of a grazing incidence diffraction technique. The Bragg peak is shown to disappear during melting, and gradually reappear during subsequent stages of recrystallization.
Measurements of carbon thin films using x-ray reflectivity
Authors: Toney Michael F. , Brennan Sean
Published: July 2002

We report x-ray reflectivity measurements on ultrathin (∼250 Å) amorphous carbon films and show that for film thicknesses of a few hundred angstroms this is an extremely effective, accurate, and nondestructive technique for measuring the thickness, density, and microscopic surface roughness. These properties are difficult to accurately measure using other methods. However, since they affect the functional performance of these films and are dependent on preparation conditions, their determination is particularly important.
Continuous steering of MSSW waves in YIG double layers
Authors: Sun Kunquan , Vittoria Carmine
Published: July 2002

In this paper we report on the calculations for the magnetostatic wave propagation characteristics in single-crystal double layers of yttrium iron garnet with arbitrary direction of magnetization. The induced uniaxial magnetic anisotropy field is assumed to be different in the two layers, and hence the magnetization in one layer is aligned at an angle with respect to the magnetization direction in the other layer. The magnetostatic surface wave propagations with the greatest bandwidths and the maximum energy deliveries in each layer can be strongly affected by the application of an applied magnetic field and the magnetostatic coupling between the two layers.
Improved flash x-ray uniformity at 19 MeV using a compound-lens diode
Authors: Sanford T. W. L. , Halbleib J. A. , McAtee W. H. , Mikkelson K. A. , Mock R. C. , Poukey J. W.
Published: July 2002

Significantly improved spatial uniformity of bremsstrahlung radiation, relative to a planar-anode diode, is obtained on the HERMES III accelerator when a compound-lens diode is used to control the 19-MeV, 700-kA electron beam. The compound-lens diode uses a conical anode to control the beam electrostatically, followed by a gas cell with externally applied current to control the beam magnetically. Variation of the external current enables average doses at the target to be varied by a factor of 3 without breaking the vacuum system of the accelerator to change diode hardware.
Induced anisotropies in NiCo obliquely deposited films and their effect on magnetic domains
Authors: Aitlamine H. , Abelmann L. , Puchalska I. B.
Published: July 2002

Oblique and in-plane anisotropies in obliquely evaporated NiCo thin films were investigated in order to understand their origin. All the compositions studied clearly show the effect of columnar grain morphology coupled with some intrinsic factors such as magnetostriction and crystallinity. Energy calculations are undertaken to explain the effect of these anisotropies on domain structures and the existence of strong and weak stripe domains depending on the composition and incidence angle.
A quick thermoelectric technique for typing HgCdTe at liquid nitrogen temperature
Authors: Chen M. C.
Published: July 2002

A simple and quick technique based on thermoelectric effect of semiconductors has been developed for screening the conductivity type of narrow band-gap HgCdTe materials. This technique generates a temperature gradient across the sample by partly dipping it in liquid nitrogen. The induced Seebeck voltage is then measured by loading two spring contact probes to two separate points on the sample below and above the liquid nitrogen level. It was found, as expected by the theory, that the thermoelectric measurements on p-type HgCdTe are much less influenced by the inverted surface effects than Hall measurements.
Effects of substrate temperature on chemical structure of amorphous carbon films
Authors: Cho N. H. , Veirs D. K. , Ager J. W. , Rubin M. D. , Hopper C. B. , Bogy D. B.
Published: July 2002

Amorphous carbon thin films were prepared at 30, 200, and 450 °C by magnetron sputtering of a graphite target. The surface structure and chemical bonding (sp2/sp3) of the carbon films were characterized by scanning tunneling microscopy (STM) and Raman spectroscopy. STM images show that graphite microcrystallites of 20–40 Å in size are present at the surfaces of all the films and the number of the microcrystallites increases with increasing substrate temperature. The microcrystallites often contain structural defects. Raman measurements show that increasing the substrate temperature results in an increase in the sp2-bonded fraction of carbon atoms and a decrease in the microstructural defects. These results indicate that the microstructural changes are correlated with changes in the chemical bonding ratio (sp3/sp3) and no diamond microcrystallites are present in the amorphous carbon. A three-dimensional atomic structure of the graphite microcrystallites is discussed in terms of turbostratic graphite.
Coupled edge-guided magnetostatic waves
Authors: Hyben P. , McKinstry K. D. , Kabos P.
Published: July 2002

The magnetostatic dispersion relations for a device consisting of two ferrite slabs of thickness d, separated by an air gap of width w, and placed between parallel ground planes is derived. In particular, edge waves and the influence of structure parameters on the pinning conditions of coupled magnetostatic waves to the edge of the ferrite slab are investigated. The obtained theoretical results have been confirmed experimentally.
Vanadium: From cluster to semi-infinite crystal
Authors: Dreyssé H. , Dorantes-Davila J. , Vega A. , Balbas L. C. , Bouarab S. , Nait-Laziz H. , Demangeat C.
Published: July 2002

Antiferromagnetic coupling between nearest neighbor vanadium atoms is discussed in the case of free-standing cluster and slabs, steps at the surface of V and V islands on Ag(001). In the self-consistent tight-binding derivation of the unrestricted approximation of the Hubbard–Hamiltonian, we have investigated the onset of magnetism in terms of the exchange integral J. For each topological arrangement of the V clusters [free-standing or as overlayer on Ag(001)], various possible magnetic states are considered and transition from nonmagnetic to magnetic order is characterized. The (001) surface is shown to present magnetism for a value of J lower than those for the other crystallographic faces.
Approach to study the relation between optical energy gap and hydrogen concentration in hydrogenated amorphous silicon thin films
Authors: Zhu Furong , Singh Jai
Published: July 2002

Using experimental plasmon loss energy of a-Si the number of valence electrons per unit volume in amorphous silicon thin films is determined. The characteristics of hydrogen incorporation in silicon network is studied by a quantitative model assuming that the structure of a good quality a-Si:H thin film dominantly consists of Si–H and Si–Si bonds only. Using the concept of Penn gap and bond polarizability, we have derived an expression for the optical energy gap as a function of hydrogen concentration for a-Si:H thin films. The calculated results, thus, obtained agree very well with the experimental results.
The effect of annealing and crystallization on the magnetoelastic properties of Fe-Si-B amorphous wire
Authors: Atkinson D. , Squire P. T. , Gibbs M. R. J. , Atalay S. , Lord D. G.
Published: July 2002

The effect of furnace annealing on the magnetic and magnetoelastic properties of amorphous wire of composition Fe77.5Si7.5B15 has been investigated. The field dependence of Young’s modulus and magnetization combined with x-ray analysis and scanning electron microscopy have been used to monitor the effects of annealing. The results indicate that progressive annealing leads first to relief of the radial casting stress with a corresponding reduction in angle between the average easy direction and the wire axis. Further annealing leads to surface crystallization for which it is suggested that the moments take up a circumferential orientation. Annealing still further leads to crystallization of the bulk material which greatly increases the anisotropy and greatly reduces the ΔE effect.
Formation of 250-μm-diameter diamond crystals by combustion flame method: Effects of preformation of molybdenum oxide on the substrate
Authors: Abe Toshimi , Suemitsu Maki , Miyamoto Nobuo , Sato Noriyoshi
Published: July 2002

Combustion flame method using acetylene and oxygen has recently proved itself to be a powerful tool to obtain qualified diamond microcrystals with excellent easiness of the performance. Analysis on the spatial variation of the morphology of the deposited film by this method indicates that both the carbon-bearing radicals from the inner flame and the molybdenum oxide formed by the outer flame are the essence of the growth. The latter aspect has therefore been more definitely incorporated into the process by forming an oxide film prior to the deposition. This preoxidation, together with the simultaneous application of a magnetic field proposed recently by the authors, has led to a drastic suppression of the graphite formation and an excellent increase of the deposited area and of the microcrystal diameter of the diamond. Especially, crystals as large as 250 μm have been successfully grown.
Incongruent transfer in laser deposition of FeSiGaRu thin films
Authors: van de Riet E. , Kools J. C. S. , Dieleman J.
Published: July 2002

The laser ablation and deposition of FeSiGaRu is studied. The deposited thin films are analyzed with Auger electron spectroscopy and Rutherford backscattering spectrometry. It is found that the gallium and ruthenium content of the thin films is strongly dependent on the laser fluence. At high laser fluences (6 J/cm2) the thin films are depleted of gallium due to preferential sputtering of the gallium atoms from the thin film. Near the threshold fluence (1.9 J/cm2) the films contain an excess of gallium due to preferential evaporation of gallium from the target. The latter conclusions are based on time-of-flight studies of ablated atoms and ions and on measurements of the atoms that are sputtered from the substrate by the incoming flux.
Upconversion dynamics of Er3+:YAlO3
Authors: Simkin D. J. , Koningstein J. A. , Myslinski P. , Boothroyd S. A. , Chrostowski J.
Published: July 2002

The dynamics of the green (2H11/12, 4S3/2) and red (4F9/2) upconversion emission excited by 15 ns pulses from an Er:fibre laser at 1500 nm are presented and analyzed. The upconversion process is found to fit a kinetic model, which includes both cross relaxation and energy transfer.
Effect of the chemical nature of transition-metal substrates on chemical-vapor deposition of diamond
Authors: Chen X. , Narayan J.
Published: July 2002

Chemical-vapor deposition of diamond on transition-metal substrates of Cu, Ni, Fe, and their alloys NiAl, Ni3Al, FeSi2, and FeSi has been investigated. It is shown that diamond grows easily on Cu with a very small amount of graphite, while on Ni and Fe there is rapid growth of the graphite layer before diamond deposition. The formation of graphite is attributed to the decomposition of carbon-containing precursors due to the strong catalytic reactivity of Ni and Fe substrates with carbon. The deactivation of these substrates by forming NiAl and FeSi2 results in the suppression of graphite and formation of high-quality diamond. However, for Ni3Al and FeSi substrates which are not completely deactivated, deposition of graphite still takes place. A mechanism based on the electronic structure of substrate atoms, particularly on the 3d shell structure of Cu, Ni, and Fe is proposed to understand the above behavior. Requirements for the stabilization of sp3 bonding of carbon on different substrates are discussed.
BP at megabar pressures and its equation of state to 110 GPa
Authors: Xia Hui , Xia Qing , Ruoff Arthur L.
Published: July 2002

Energy-dispersive x-ray-diffraction studies were carried out on the III-V compound BP to megabar pressures using diamond-anvil techniques and a high-energy synchrotron x-ray source. The BP sample remained stable in its zinc-blende phase to at least 110 GPa, the upper pressure limit of this experiment. The equation-of-state and Birch coefficients of BP were obtained from this experiment. The measured bulk modulus of BP is slightly lower than the value obtained in recent theoretical calculations based on the total energy pseudopotential method within the local-density approximation.
An alternate route to giant magnetoresistance in MBE-grown Co–Cu superlattices (invited)
Authors: Clarke Roy , Barlett Darryl , Tsui Frank , Chen Baoxing , Uher Ctirad
Published: July 2002

Co–Cu superlattices grown by MBE in the (111) orientation show weak or nonexistent interlayer exchange coupling, yet several groups have observed large high-field magnetoresistance signals in excess of 30%. In the present work, we address some of the questions relating to GMR and the interlayer coupling by studying samples with atomically abrupt interfaces, as probed by real-time RHEED techniques, HRTEM, and spin-echo NMR. We propose that the lowered dimensionality of the structure leads to an enhancement of the scattering of conduction electrons from paramagnetic interfaces obeying a Langevin-like saturation at very high fields, well beyond the switching field of the Co layers. Scaling between the GMR and thermopower measurements suggests that a spin-dependent density of states at the Co–Cu interfaces is responsible for the observed magnetotransport behavior in these samples, rather than antiferromagnetically coupled Co layers.
Magnetic properties of Y(Fe,Co)10Mo2 alloys
Authors: Xu Xie , Tucker Roy , Shaheen S. A.
Published: July 2002

The structural and magnetic properties of YFe10−xCoxMo2 alloys (0≤x≤10) have been investigated by means of x-ray diffraction, thermomagnetic analysis, and magnetometry techniques. All the alloys exhibited the tetragonal ThMn12 structure and were almost single phase materials. With the increase of Co content x, Tc increases initially, reaching a maximum at x∼6, followed by a decrease at higher x values. X-ray diffraction analyses on magnetically aligned samples indicate that YFe10Mo2 exhibits an axial easy direction of magnetization (EDM) at room temperature, and the addition of Co initially causes the EDM to deviate gradually from the c axis with increasing x (x≤4). On further increase of Co content (x≥5), the EDM of the YFe10−xCoxMo2 compounds tends to become axial again, reaching a complete uniaxial behavior for the terminal compound YCo10Mo2.