bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial and vectorial characterization of thermal relaxation using the spin-stand imaging technique
Authors: Tse C. , Mircea D. I. , Mayergoyz I. D. , Andrei P. , Krafft C.
Published: July 2002

The spatial and vectorial characterization of thermal relaxation of recorded magnetization patterns by using the spin-stand imaging technique [I. D. Mayergoyz et al., J. Appl. Phys. 87, 6824 (2000); 89, 6772 (2001)] is reported. In order to obtain such characterization, a recorded track is scanned at successive instants of time over periods of 70 hours. As a result, the spatial distributions of the read-back voltages (that constitute the “raw” images of the track) are consecutively collected. The images of the vectorial magnetization are then reconstructed and local magnetization relaxation rates are subsequently evaluated. It is demonstrated that the spatially inhomogeneous and vectorial nature of thermal relaxation of recorded patterns may result in temporal track broadening. It is found that this temporal track broadening is more pronounced for disks with higher coercivities.
The extraction of features from magnetic force microscopy images using neural network techniques
Authors: Jones H. V. , Chantrell R. W.
Published: July 2002

This paper describes a method of applying neural network techniques to analyze magnetic force microscopy (MFM) images of thin film media, and extract features such as vortices from the samples. The MFM images are pre-processed and applied to a self-organizing neural network (which organizes complex data into manageable groups), from which the locations and characteristics of various vortices can be observed. The results obtained illustrate that the majority of vortices present in the sample are detected (some of which are invisible to the human eye), and shows that a neural network approach is feasible to solve this type of problem.
Molecular equilibrium structures from experimental rotational constants and calculated vibration–rotation interaction constants
Authors: Pawłowski Filip , Jørgensen Poul , Olsen Jeppe , Hegelund Flemming , Helgaker Trygve , Gauss Jürgen , Bak Keld L. , Stanton John F.
Published: July 2002

A detailed study is carried out of the accuracy of molecular equilibrium geometries obtained from least-squares fits involving experimental rotational constants B0 and sums of ab initio vibration–rotation interaction constants αrB. The vibration–rotation interaction constants have been calculated for 18 single-configuration dominated molecules containing hydrogen and first-row atoms at various standard levels of ab initio theory. Comparisons with the experimental data and tests for the internal consistency of the calculations show that the equilibrium structures generated using Hartree–Fock vibration–rotation interaction constants have an accuracy similar to that obtained by a direct minimization of the CCSD(T) energy. The most accurate vibration–rotation interaction constants are those calculated at the CCSD(T)/cc-pVQZ level. The equilibrium bond distances determined from these interaction constants have relative errors of 0.02%–0.06%, surpassing the accuracy obtainable either by purely experimental techniques (except for the smallest systems such as diatomics) or by ab initio methods.
Lax–Phillips scattering theory of a relativistic quantum field theoretical Lee–Friedrichs model and Lee–Oehme–Yang–Wu phenomenology
Authors: Strauss Y. , Horwitz L. P.
Published: July 2002

The scattering theory of Lax and Phillips, originally developed for classical wave equations, has recently been extended to the description of the evolution of resonant states in the framework of quantum theory. The resulting evolution law of the unstable system is that of a semigroup, and the resonant state is a well-defined function in the Lax–Phillips Hilbert space. In this paper we apply this theory to a relativistically covariant quantum field theoretical form of the two (or more) channel relativistic quantum field theoretical form of the Lee model. We show that this theory provides a rigorous underlying basis for the Lee–Oehme–Yang–Wu construction.
Phases for dyadic orthonormal wavelets
Authors: Gu Qing , Han Deguang
Published: July 2002

We consider real-valued functions α(s) and wavelets ψ∈L2(R) such that eiα(s)|ψ̂(s)| is the Fourier transform of a wavelet. Such a function α(s) is called an attainable phase for the wavelet ψ. It is known that for all multiresolution analysis (MRA) wavelets, the phase function α(s)=12s is attainable, and any real function α(s) is attainable by any minimally-supported-frequency (MSF) wavelet. Besides this, very little is known in the literature about attainable phases for wavelets. We study the problem of determining functions which are attainable phases for some (non-MSF) wavelets. We prove that there exists a non-MSF wavelet for which there is no attainable “set-wise” linear phase. This answers a basic question about wavelet phases. Although we do not know whether for any irrational number a, as is attainable by some non-MSF wavelets, we show that there exist certain rational numbers a such that as is not attainable by any non-MSF wavelet. We also prove that there exists a large class of rational numbers a such that as is attainable by some non-MSF wavelets. We examine the relationship between different classes of wavelets admitting linear phases. In particular we present an example of a non-MSF wavelet which is not an MRA wavelet but admits linear phase 12s.
Det-Det correlations for quantum maps: Dual pair and saddle-point analyses
Authors: Nonnenmacher S. , Zirnbauer M. R.
Published: July 2002

An attempt is made to clarify the ballistic nonlinear sigma model formalism recently proposed for quantum chaotic systems, by looking at the spectral determinant Z(s)=Det(1−sU) for quantized maps U∈U(N), and studying the correlator ωU(s)=∫dθ|Z(eiθs)|2. By identifying U(N) as one member of a dual pair acting in the spinor representation of Spin(4N), the expansion of ωU(s) in powers of s2 is shown to be a decomposition into irreducible characters of U(N). In close analogy with the ballistic nonlinear sigma model, a coherent-state integral representation of ωU(s) is developed. For generic U this integral has (N2N) saddle points and the leading-order saddle-point approximation turns out to reproduce ωU(s) exactly, up to a constant factor. This miracle is explained by interpreting ωU(s) as a character of U(2N), and arguing that the leading-order saddle-point result corresponds to the Weyl character formula. Unfortunately, the Weyl decomposition behaves nonsmoothly in the semiclassical limit N→∞, and to make further progress some additional averaging needs to be introduced. Several schemes are investigated, including averaging over basis states and an “isotropic” average. The saddle-point approximation applied in conjunction with these schemes is demonstrated to give incorrect results in general, one notable exception being a semiclassical averaging scheme, for which all loop corrections vanish identically. As a side product of the dual pair decomposition with isotropic averaging, the crossover between the Poisson and CUE limits is obtained.
Determination of electron trap distribution in the gate–oxide region of the deep submicron metal–oxide–semiconductor structure from direct tunneling gate current
Authors: Chowdhury Murshed Mahmud , uz Zaman Saif , Haque A. , Khan M. Rezwan
Published: July 2002

The trap distribution inside the oxide layer of a metal–oxide–semiconductor device is studied via the direct tunneling gate current. Effects of traps are incorporated in the Schrödinger’s equation using an imaginary potential term. Different spatial distributions of traps have been considered to obtain a best fit between the simulated and the experimentally measured direct tunneling gate currents. Comparing our simulated current with experimental data, we have determined that the distribution of traps introduced during fabrication can be represented by a Gaussian function with its peak at the gate–electrode/oxide interface. This distribution is found to be independent of the gate–oxide thickness. Our results show that electric-field-induced traps, generated during tunneling, are proportional to the carrier density within the oxide layer and also to the traps introduced during fabrication.
Strain-induced anisotropic Ge diffusion in SiGe/Si superlattices
Authors: Lim Y. S. , Lee J. Y. , Kim H. S. , Moon D. W.
Published: July 2002

Anisotropic diffusion of Ge induced by nonuniform strain in SiGe/Si interfaces in the range of 700–850 °C is directly observed with medium-energy ion-scattering spectroscopy through its composition and strain profiles of atomic-layer depth resolution. For SiGe/Si interfaces with identical composition profiles but with different strain distributions, the anisotropic diffusion of Ge can be clearly correlated with the anisotropic relaxation of the nonuniform strain in the near-surface layer of several nm depth. The results suggest that atomic-scale strain control is critical to maintain abrupt SiGe/Si interfaces under thermal budget.
Ion-matrix sheaths related to targets with grooves
Authors: Demokan O.
Published: July 2002

In this work, the ion-matrix sheath near a target with a rectangular groove is studied analytically. A two-dimensional model with a single groove is adopted. The potential and electric-field profiles within the groove are analyzed to provide insight regarding the uniformity and efficiency of ion implantation on its walls. The deviation of the sheath edge from the planar geometry is also illustrated.
Quantizing Yang–Mills theory on a two-point space
Authors: Hüffel Helmuth
Published: July 2002

We perform the Batalin–Vilkovisky quantization of Yang–Mills theory on a two-point space, discussing the formulation of Connes–Lott as well as Connes’ real spectral triple approach. Despite the model’s apparent simplicity the gauge structure reveals infinite reducibility and the gauge fixing is afflicted with the Gribov problem.
The Bargmann transform and canonical transformations
Authors: Villegas-Blas Carlos
Published: July 2002

This paper concerns a relationship between the kernel of the Bargmann transform and the corresponding canonical transformation. We study this fact for a Bargmann transform introduced by Thomas and Wassell [J. Math. Phys. 36, 5480–5505 (1995)]—when the configuration space is the two-sphere S2 and for a Bargmann transform that we introduce for the three-sphere S3. It is shown that the kernel of the Bargmann transform is a power series in a function which is a generating function of the corresponding canonical transformation (a classical analog of the Bargmann transform). We show in each case that our canonical transformation is a composition of two other canonical transformations involving the complex null quadric in C3 or C4. We also describe quantizations of those two other canonical transformations by dealing with spaces of holomorphic functions on the aforementioned null quadrics. Some of these quantizations have been studied by Bargmann and Todorov [J. Math. Phys. 18, 1141–1148 (1977)] and the other quantizations are related to the work of Guillemin [Integ. Eq. Operator Theory 7, 145–205 (1984)]. Since suitable infinite linear combinations of powers of the generating functions are coherent states for L2(S2) or L2(S3), we show finally that the studied Bargmann transforms are actually coherent states transforms.
On quasicrystal Lie algebras
Authors: Mazorchuk Volodymyr
Published: July 2002

We realize the aperiodic Witt and Virasoro algebras as well as other quasicrystal Lie algebras as factor algebras of some subalgebras of the higher rank Virasoro algebras. This realization allows us to generalize the notion of quasicrystal Lie algebras. In the case when the constructed algebra admits a conjugation, we compute the Kac determinant for the Shapovalov form on the corresponding Verma modules. In the case of the aperiodic Virasoro algebra this proves the conjecture of R. Twarock.
Systematic corrections to the equivalent core model
Authors: Wohlfarth Mattias N. R. , Cederbaum Lorenz S.
Published: July 2002

The widely used equivalent core model (ECM) describes core hole states in systems with atomic charge Z by considering corresponding states with fully occupied core in systems with increased charge Z+1. When calculating energies of Z-core hole states, the valence energy of these states often has been assumed to equal the valence energy of the (Z+1) ground state. This approach misses several points: most importantly, the different spin symmetry of the corresponding states. The behavior of core hole states is governed by an effective 2×2 matrix Hamiltonian due to the two possible spin states of the core hole. A recently introduced diagonalization gives rise to a scalar core hole Hamiltonian. Both the ECM and the core hole Hamiltonian act in valence space. This allows establishment of a connection between these two approaches. By expressing the core hole Hamiltonian in the (Z+1) orbital basis, we systematically derive corrections to the ECM. Those corrections, including the one arising because of the different spin symmetry of the corresponding states, are presented in second order of Møller–Plesset perturbation theory (MP2). Hence, they can be implemented very easily so that ground-state calculations in a (Z+1) system may directly provide the core hole state energy in the original Z system.
Tuning of the magnetocaloric effect in La0.67Ca0.33MnO3−δ nanoparticles synthesized by sol–gel techniques
Authors: Hueso L. E. , Sande P. , Miguéns D. R. , Rivas J. , Rivadulla F. , López-Quintela M. A.
Published: July 2002

We report the effect of progressive reduction of the annealing temperature on the magnetocaloric effect (MCE) of La2/3Ca1/3MnO3−δ nanoparticles synthesized by the sol–gel technique. With this method, we are able to obtain particle diameters ranging form 60 to 500 nm. The peak in the MCE at the ferromagnetic to paramagnetic phase transition is strongly reduced as annealing temperature does, due to loss of the intrinsic first-order magnetic phase transition. This opens up a new way in which to tune the intrinsic properties of mixed-valence manganites, most of which are associated with the first-order character of the magnetic transition.
Epitaxial growth and electronic structure of LaTiOx films
Authors: Ohtomo A. , Muller D. A. , Grazul J. L. , Hwang H. Y.
Published: July 2002

LaTiO x films have been grown on (001) perovskite oxide substrates by pulsed-laser deposition. Both single-phase perovskite LaTiO3 and layered La2Ti2O7 films could be stabilized by varying the oxygen partial pressure and substrate temperature during growth. We have obtained a crystallographic and electronic phase diagram for LaTiOx films, demonstrating the ability to vary the titanium valence from 3+ to 4+ in thermodynamically unfavorable growth conditions by utilizing interface energies.
Do dynamical systems follow Benford’s law?
Authors: Tolle Charles R. , Budzien Joanne L. , LaViolette Randall A.
Published: July 2002

Data compiled from a variety of sources follow Benford’s law, which gives a monotonically decreasing distribution of the first digit (1 through 9). We examine the frequency of the first digit of the coordinates of the trajectories generated by some common dynamical systems. One-dimensional cellular automata fulfill the expectation that the frequency of the first digit is uniform. The molecular dynamics of fluids, on the other hand, provides trajectories that follow Benford’s law. Finally, three chaotic systems are considered: Lorenz, Hénon, and Rössler. The Lorenz system generates trajectories that follow Benford’s law. The Hénon system generates trajectories that resemble neither the uniform distribution nor Benford’s law. Finally, the Rössler system generates trajectories that follow the uniform distribution for some parameters choices, and Benford’s law for others.
Intelligent software: The OpenMol program
Authors: Diercksen Geerd H. F. , Hall George G.
Published: July 2002

The case is argued that the rigorous use of expert systems and abstract data types for quantum chemical calculations can lead to a more open, more flexible program, which is easier for a novice to use but also, through the possibility of rapid prototyping and symbolic manipulation, for an expert to exploit as an important working tool. The ideas behind this program are, however, quite general and apply equally to many other scientific areas where experience and different numerical techniques have to be combined in a flexible way to produce useful results.
Stepwise excitation of the Hg 61P1 level in the afterglow of a low-pressure Hg-Ar discharge
Authors: Wani Koichi
Published: July 2002

The excitation mechanism of mercury atoms in a low-pressure mercury-argon discharge was investigated, employing an afterglow method. The experimental results combined with theoretical calculations have proved that the dominant process to populate the Hg 61P1 level is the stepwise excitation via excited levels (63P−61P1) under conditions typical of fluorescent lamps (d=18.5–28.5 mm, I=0.3–0.5 A). When a Maxwell distribution of electron energy is assumed, the stepwise excitation is estimated to be about 73% of the total populating rate of the 61P1 level in the stationary state. This value is about twice that found in literature. In the afterglow, the percentage goes beyond 97% within 10 μs after the termination of the current. By considering a non-Maxwellian effect, the above partitions are estimated to decrease down to about 53% for the stationary state and to 93% for the afterglow. The stepwise excitation cross section was found to be in the order of 10−20–10−19 m2.
A new double-heterostructure optoelectronic switching device using molecular-beam epitaxy
Authors: Taylor G. W. , Simmons J. G. , Cho A. Y. , Mand R. S.
Published: July 2002

Two-terminal switching action is observed in a new optoelectronic device structure. The device has a high-impedance state without light emission and a low-impedance state characterized by strong spontaneous emission. The transition from either state to the other may be induced by the appropriate optical or electrical input. It is clear that with the appropriate optical cavity construction the switching device will operate as a laser in the on state rather than in the spontaneous mode reported here. In principle, the device offers large digital optical gain determined by its optical sensitivity and its maximum output power.
Generalized Norde plot including determination of the ideality factor
Authors: Bohlin K. E.
Published: July 2002

An extended Norde plot is described which makes it possible to determine the series resistance, barrier height, and ideality factor from one I-V measurement of a Schottky barrier diode. A theoretical derivation is performed followed with experimental data, which demonstrates the feasibility of the method.
Hole transport in a molecularly doped polymer: p-diethylaminobenzaldehyde-diphenyl hydrazone in polycarbonate
Authors: Schein L. B. , Rosenberg A. , Rice S. L.
Published: July 2002

Hole-drift-mobility measurements are presented for a molecularly doped polymer, p-diethylaminobenzaldehyde-diphenyl hydrazone in polycarbonate, over the widest temperature (213–373 K) and electric-field range (3.3–111 V/μm) yet reported. Use of these data and graphical techniques which we introduce allow us to unambiguously determine for the first time the functional form of the electric field and temperature dependence of the mobility. Consistent with results obtained by others, the observed field dependence cannot be accounted for by any known hopping model. The observed temperature dependence suggests that the activation energy may be temperature dependent.
Magnetic anisotropy and structure of magnetic recording media (invited)
Authors: Artman J. O.
Published: July 2002

The recording characteristics of magnetic media depend significantly on magnetic anisotropy. We have been pursuing an investigation of anisotropy in thin-film recording media involving coordinated TEM, SEM, x-ray and electron diffraction, x-ray fluorescence, TM, VSM examinations, and, in addition, ferromagnetic resonance (FMR). In CoCr films we have shown that the magnetic constituents often are stratified magnetically and correspondingly structurally. The magnetic deconvolution of such a composite specimen by FMR is relatively straightforward; it is difficult when quasistatic torque magnetometer or vibrating sample magnetometer techniques are employed. From FMR analysis, data are obtained on the effective magnetic anisotropy field components, on the γ factor (or equivalently the g value) and on the line breadth. If the value of 4πMs is available, the effective fields can be interpreted in terms of anisotropy energy components. By integrating over the FMR lines, information relating to the relative volumes of the constituents can be obtained. Many CoCr films are dual layer films in which a disordered ‘‘transition layer’’ intervenes between the substrate and the desired or ‘‘bulk’’ region. In such films the magnetocrystalline anisotropy of the disordered layer tends to average to zero, leaving the shape anisotropy dominant. We have performed annealing procedures with and without applied magnetic fields and have correlated the changed FMR spectra with ensuing changes in anisotropy and hence structure. We have begun an investigation of magnetoelastic effects in such films by FMR techniques.
Effect of manganese substitution in erbium-iron-manganese-boron: Spin reorientation, moment compensation, and structure
Authors: Fuerst C. D. , Meisner G. P. , Pinkerton F. E.
Published: July 2002

The importance of the Nd2Fe14B tetragonal phase to permanent magnet technology has led to the study of systems with rare-earth and transition-metal substitutions. We report on alloys formed by replacing iron with manganese in the Er2Fe14B system. Samples were characterized by x-ray diffraction, thermal analysis, and magnetization measurements. The 2-14-1 tetragonal lattice type forms for a large fraction of manganese substitution but not the entire range. The Curie temperature decreases rapidly from 560 K for Er2Fe14B to 20 K for alloys with high concentrations of manganese. The spin reorientation temperature also decreases, but not as rapidly. Compensation points were observed in the temperature dependence of the magnetization for intermediate manganese concentrations. The rapid decrease in the magnetization with Mn substitution indicates that, in addition to replacing a Fe moment, Mn lowers the average moment of the remaining Fe atoms. The linear response of the magnetization to the applied field arises from a noncollinear moment structure.
Segregated microstructure in sputtered Co-Cr film revealed by selective wet etching
Authors: Maeda Yasushi , Asahi Masayoshi
Published: July 2002

The segregated microstructure in a sputtered Co-18.1 at. % Cr film is examined. Thin foil samples are prepared for transmission electron microscopy using selective wet etching and ion-beam milling. The microstructure revealed by selective wet etching shows a definite striped pattern in each crystallite where the stripes run almost perpendicular to grain boundaries. Results of compositional analysis by an energy dispersive x-ray microanalyzer reveal that these stripes are caused by dissolution of the Co-rich ferromagnetic regions and that the remaining regions are Cr-rich and nonmagnetic. The results are explained by a new model for segregated microstructure formation. Ferromagnetic Co-rich regions are formed coherently in each single-phase hcp crystallite, with a wall-like structure perpendicular to the substrate plane. The observed microstructure suggests the existence of a magnetic unit far smaller than the crystallite diameter, which offers superior properties for high-density perpendicular magnetic recording.
Magneto-optical study of uranium additions to amorphous TbxFe1−x
Authors: Dillon J. F. , van Dover R. B. , Hong M. , Gyorgy E. M. , Albiston S. D.
Published: July 2002

Recent reports of huge magneto-optical Kerr rotations in certain crystalline metallic uranium compounds prompted a study of the magnetic and magneto-optical effects of uranium additions to a rare-earth transition metal amorphous alloy. Using variable composition samples, the polar Kerr effect at a small spot (e.g., 0.5 mm diam) was measured as field, temperature, and composition were varied. Points on the Curie line and the edges of the compensation region were determined from these observations. The compositions studied included (TbxFe1−x)1−yUy with 0.125≤x≤0.550 and y=0.0, 0.04, 0.07, 0.16. The addition of uranium to TbxFe1−x depresses the TC of Tb-rich material much more strongly than that of Tb-poor material. The compensation region does not shift at all with increasing y. It appears that uranium does not contribute to the magnetization of these amorphous alloys, nor does it significantly affect the magneto-optical effects.
Magnetic orientation of respirable asbestos fibers
Authors: Willey R. J.
Published: July 2002

Exposure to contaminated atmospheres is now strictly controlled and control limits have been delineated, giving maximum permissible concentrations of airborne fibers. These limits depend on the type of asbestos as well as concentration. Unfortunately, the current analytical technique cannot distinguish between different types of asbestos fibers or differentiate between asbestos and nonasbestos fibers of respirable size. In the current work orientations of amosite, chrysotile, and crocidolite have been measured as functions of magnetic field strength. Results show the family to have different orientation characteristics, and markedly different field strengths are required to align the various fibers. The results would indicate that a magnetic orientation technique can be used to distinguish between respirable asbestos and nonasbestos fibers and also to differentiate between the main types of asbestos fibers.
Simultaneous measurements of the electron and photon emission accompanying fracture of single-crystal MgO
Authors: Langford S. C. , Dickinson J. T. , Jensen L. C.
Published: July 2002

We investigate the simultaneous emission of electrons and photons during the deformation and fracture of two types of high-purity single-crystal MgO. These crystals exhibit significant differences in optical opacity due to differences in void and precipitate concentrations. Measurements of the emission of visible photons during deformation and prior to failure of the crystals are presented, along with the time dependencies of the photon and electron emission during and after fracture. Correlations with fracture strength and fractographic features are also discussed.
Oriented growth of niobium and molybdenum on GaAs crystals
Authors: Eizenberg M. , Segmüller Armin , Heiblum M. , Smith D. A.
Published: July 2002

Thin layers of Mo and Nb, 100–400 Å thick, were deposited onto clean (100) and (1̄1̄1̄)GaAs substrates under ultrahigh vacuum conditions in a molecular-beam epitaxy system, at slow rates and at relatively low temperatures. The microstructure of the films and the orientation relationship with the substrates were determined by in situ reflection high-energy electron diffraction, by transmission electron microscopy, and by grazing-incidence x-ray diffraction. In spite of the large lattice mismatch to GaAs (11% for Mo and 17% for Nb) and the low deposition temperatures(<400 °C), oriented deposits were obtained on both substrates for both metals. Although both metals are body-centered cubic with similar lattice parameters, and are both of similar chemical behavior, they grow differently on GaAs. Molybdenum grows epitaxially in the (111) orientation on both (100) and (1̄1̄1̄)GaAs substrates, whereas niobium grows with the (100) orientation on (100)GaAs, and with no simple orientation on (1̄1̄1̄)GaAs. In both cases, the orientational spread (deduced from the diffraction patterns) is smallest when the lattice planes parallel to the interface have the same symmetry in film and substrate.
Rapid isothermal processing
Authors: Singh R.
Published: July 2002

The physics and technology of a relatively new, short-time, thermal processing technique, namely rapid isothermal processing (RIP), based on incoherent sources of light for the fabrication of semiconductor devices and circuits, are reviewed in this paper. Low-cost, minimum overall thermal budget, low-power consumption, and high throughput are some of the attractive features of RIP. The discussion of RIP, in the context of other thermal processes, history, operating principles, different types of RIP systems, various applications of RIP using single processing steps, and novel applications of RIP, including in situ processing and multistep processing, is described in detail. Current trends are in the direction of RIP-dominated silicon integrated circuit fabrication technology that can lead to the development of the most advanced three-dimensional integrated circuits suitable for applications such as parallel processing and radiation hardening. RIP is not only a superior alternative to furnace processing, but it is also the only way to perform certain crucial steps in the processing of compound semiconductor devices such as high-mobility transistors, resonant tunneling devices, and high-efficiency solar cells. Development of more accurate temperature measurement techniques and theoretical studies of heat transfer and other fundamental processes are needed. Dedicated equipment designed for a specific task coupled with in situ processing capabilities will dominate the future direction of RIP.
Electromagnetic radiation from an AT-cut quartz plate under lateral-field excitation
Authors: Lee P. C. Y.
Published: July 2002

Equations of linear piezoelectricity (with the quasistatic approximation) for the quartz plate and Maxwell’s equations for the electromagnetic field in the surrounding vacuum are solved for the thickness-shear vibrations of rotated Y cut of quartz plate. For an AT-cut plate vibrating near the thickness-shear resonance excited by a uniform, lateral electric field of magnitude 1 V/m, the electromagnetic energy radiated from each face is about 0.13 μW/cm2. The radiated power is about 0.1 μW/cm2 if the plate is excited by a shearing face traction which produces a strain of 10−5. Present solution is compared in detail with Mindlin’s [Int. J. Solids Struct. 9, 697 (1972)] solution of equations of piezoelectromagnetism (without the quasistatic approximation) for the thickness-shear vibrations excited by shearing face traction. It is found that the percent difference in radiated powers computed from these two solutions, due to the quasistatic approximation, is in the order of β2(=v̂2/ĉ2), where v̂ is the velocity of the x1-thickness-shear wave, ĉ is the velocity of electromagnetic wave of E3 propagating in the x2 direction in quartz, and β≊10−5.
Passivation of interface defects in lattice-mismatched InGaAs/GaAs heterostructures with hydrogen
Authors: Gal M. , Tavendale A. , Johnson M. J. , Usher B. F.
Published: July 2002

We have found that in lattice-mismatched partially strained InGaAs/GaAs heterostructures, defect states caused by misfit dislocations can be neutralized by hydrogenation. This was concluded from the effect of hydrogen on the photoluminescence spectra of partially strained GaAs/In0.17Ga0.83As/GaAs quantum wells. Hydrogenation was also found to significantly increase the band-gap emission of structures with layer thicknesses well above the critical layer thickness for the given composition.
Enhancement of the negative ion flux to surfaces from radio-frequency processing discharges
Authors: Overzet L. J. , Beberman J. H. , Verdeyen J. T.
Published: July 2002

The relative flux of negative ions from rf discharges through CF4 and F2-He has been studied using mass spectrometry. The negative ion flux impinging on a surface in contact with a glow discharge is usually quite small because of the sheaths formed to contain the more mobile electrons. In the afterglow, however, these sheaths decay on the time scale of the electron density loss rate while negative ions can remain in the discharge region significantly longer. As a consequence, the negative ion flux to a surface in contact with the glow discharge can rise by a very large amount in the afterglow when the sheaths have diminished. It is shown here that the flux of the negative ions can be enhanced by factors of 50 to greater than 1000 by square wave amplitude modulating the rf discharge. This enhancement depends upon the dc self-bias voltage and the modulation frequency as well as the particular negative ion. Data are presented for both CF4 and F2-helium discharges, along with the correlation to simple models.
Effects of Cr underlayer thickness and texture on magnetic characteristics of CoCrTa media
Authors: Coughlin Tom , Pressesky Jason , Lee Sang , Heiman Neil , Fisher R. D. , Merchant Karen
Published: July 2002

For a longitudinal recording disk with a CoCrTa magnetic layer on a Cr underlayer, a thin Cr layer obscures the disk texture less than a thick Cr layer. This results in greater uniaxial in-plane anisotropy, Sr, S*, and lower Hc for the thin Cr disk, which has strong intergranular coupling along the disk texture lines. Thick Cr disks have higher in-plane coercivity but a stronger perpendicular anisotropy than thin Cr disks.
Comparison of infrared upconversion methods for photon-limited imaging
Authors: Watson Edward A. , Morris G. Michael
Published: July 2002

Infrared upconversion offers advantages over direct detection of thermal imagery, but has been of limited use because of low upconversion efficiencies and because of the complexity of the upconversion systems. Photon-limited imaging techniques can overcome the disadvantages of upconversion. The low-power levels required by photon-counting detectors make large upconversion efficiencies unnecessary. At the same time, photon-limited imaging offers advantages in speed of operation and ease of implementation. We investigate the application of photon-limited imaging to sum-frequency upconverters, infrared quantum counters in alkali-metal vapor, and a recently reported infrared phosphor. Upconversion efficiencies and noise effects associated with the different upconversion methods are derived. Two figures of merit are used to compare the upconversion methods. One figure of merit is the conventional noise equivalent differential temperature (NEΔT). The other is a criterion based on the statistics of photon-limited images applied to scene matching. We find that the sum-frequency upconverter and the phosphor require fewer detected photons than the infrared quantum counter to achieve the same values for the figures of merit. We also find that reliable scene matching can be performed with fewer detected photons than would be expected from the NEΔT figure of merit.
Mass spectroscopy study of products from exposure of cyclotrimethylene-trinitramine single crystals to KrF excimer laser radiation
Authors: Dickinson J. T. , Jensen L. C. , Doering D. L. , Yee R.
Published: July 2002

We report mass spectroscopic measurements of the charged particle, neutral, and excited neutral species emitted from the irradiation of single-crystal cyclotrimethylene-trinitramine (RDX) with 248-nm, 20-ns laser pulses. At laser fluences above 5 mJ/cm2 we observe RDX decomposition products of relatively small mass in both neutral and ionic states. With increasing fluence we see clear etching of the crystal, an increase in kinetic energy of the products, and the appearance of an intense, excited neutral species which we identify as NO in an energetic, long-lived electronic excited state. Evidence is also presented for a sustained decomposition reaction ignited by the laser pulse.
Conductance measurements on p-Si/SiO2 metal-oxide-semiconductor capacitors
Authors: Tayarani-Najaran M. H. , Sands David , Brunson Kevin M. , Thomas Clive B.
Published: July 2002

Conductance measurements have been performed on p-Si/SiO2 metal-oxide-semiconductor capacitors fabricated by thermal oxidation of the silicon in three different reactors under different conditions in three different commercial systems. In only one case (system 3) did we find the very broad conductance curves usually associated with p-Si/SiO2 junctions, the others from systems 1 and 2 exhibiting normal interface state response. However, in the sample from system 2, the response of bulk states inside the depletion region was found to distort the Gp/ω spectra, while the sample from system 1 showed no such response until annealing in H2/Ar gas at 500 °C reduced the interface state density to such a level that the bulk state responses were visible. We argue that the presence of bulk states probably explains the very broad Gp/ω curves observed by us, and further propose that some such mechanism accounts for the historical difficulties encountered with the conductance technique on p-Si/SiO2 capacitors.
Mixed-valence trinuclear manganese clusters: Influence of the electronic transfer on the magnetic properties
Authors: Gomez-Garcia C. J. , Coronado E. , Pourroy G.
Published: July 2002

The magnetic behavior of mixed-valence trinuclear clusters d4-d4-d5 is discussed on the basis of a model which takes into account valence delocalization and Heisenberg exchange. This model considers the competing effect between the electronic transfer and the localization of the extra electron due to an asymmetry of the triangular entity. The magnetic properties of the mixed-valence oxo-centered Mn(II)-Mn(III)-Mn(III) complexes formulated as Mn3O(O2CR)6L3 (R=Me, L=pyridine) are discussed on the basis of the developed model, supporting a significant intramolecular electron transfer. A comparison of these results to those previously reported by assuming a valence-trapped model is given.
Electrodeless high-pressure microwave discharges
Authors: Offermanns Stephan
Published: July 2002

A one-dimensional numerical model has been developed to describe a cylindrical high-pressure mercury plasma sustained by microwave energy within a cavity applicator by solving Maxwell’s equations together with the energy balance equation. The mercury line radiation has been taken into account for the energy balance by solving the radiation transfer equation for all significant wavelengths. An experimental microwave circuit for the frequency range of 2–4 GHz (S band) has been designed to guarantee stable discharge operation. Coupling efficiencies >99% into the microwave cavity can always be achieved with proper adjustments. Variation of discharge parameters leads to different types of temperature distributions including profiles with a local minimum in the axis. The temperature distributions predicted by the model are in good agreement with results from spectroscopic experiments.
Near-ultraviolet optical absorption in sputter-deposited cubic yttria
Authors: Kwok Chee-Kin , Aita Carolyn Rubin , Kolawa Elzbieta
Published: July 2002

Cubic yttria films were sputter deposited on unheated fused silica substrates. In situ optical spectrometry was used to monitor emission from six YI transitions in the discharge. A simple formalism was developed for estimating the ratio of yttrium arriving at the substrate in atomic form to yttrium bonded to oxygen in an unspecified molecular form. The optical absorption coefficient (α=∼103–105 cm−1) of the films was determined, post-deposition, over the energy range 5.0–6.2 eV. The results show that a large atomic yttrium flux to the substrate during deposition resulted in a ‘‘disordered’’ optical absorption edge. A large flux of yttrium bonded to oxygen resulted in an edge with two direct interband transitions separated by 0.66 eV, in good agreement with the bulk single crystal ε2 data and a recent theoretical energy band calculation for cubic yttria.
Heterogeneous processes in CF4/O2 plasmas probed using laser-induced fluorescence of CF2
Authors: Hansen S. G. , Luckman G. , Nieman George C. , Colson Steven D.
Published: July 2002

Laser-induced fluorescence of CF2 is used to monitor heterogeneous processes in ≊300 mTorr CF4/O2 plasmas. CF2 is rapidly removed at fluorinated copper and silver surfaces in 13.56-MHz rf discharges as judged by a distinct dip in its spatial distribution. These metals, when employed as etch masks, are known to accelerate plasma etching of silicon, and the present results suggest catalytic dehalogenation of CF2 is involved in this process. In contrast, aluminum and silicon dioxide exhibit negligible reactivity with CF2, which suggests that aluminum masks will not appreciably accelerate silicon etching and that ground state CF2 does not efficiently etch silicon dioxide. Measurement of CF2 decay in a pulsed discharge coupled with direct laser sputtering of metal into the gas phase indicates the interaction between CF2 and the active metals is purely heterogeneous. Aluminum does, however, exhibit homogeneous reactivity with CF2. Redistribution of active metal by plasma sputtering readily occurs; silicon etch rates may also be enhanced by the metal’s presence on the silicon surface. Polymers contribute CF2 to the plasma as they etch. The observation of an induction period suggests fluorination of the polymer surface is the first step in its degradation. Polymeric etch masks can therefore depress the silicon etch rate by removal of F atoms, the primary etchants.
Kinetics of photoresist etching in an electron cyclotron resonance plasma
Authors: Carl D. A. , Hess D. W. , Lieberman M. A.
Published: July 2002

An electron cyclotron resonance plasma processing system was used to etch hardbaked KTI-820 photoresist from single crystal silicon wafers, silicon dioxide films and patterned multilayer structures. Etch rates of 1500 nm/minute were observed at a substrate temperature below 373 K in a Pforward=750 W, 0.13-Pa ECR oxygen plasma with no applied substrate bias. The etch rate increased linearly with increasing power from Pforward=300–750 W. Etch rate was a complicated function of pressure and residence time, but a modified adsorption-reaction-ion-stimulated desorption rate expression could be used to fit the data. Etch rates decreased for increasing oxygen residence time at low operating pressures due to a combination of polymeric film formation of reaction products and reactant (atomic oxygen) depletion. Maximum etch rates were observed at approximately 0.13 Pa for all residence times. Multilayer photoresist structures were etched at various pressures as well as at a 45° angle to the incident plasma stream. Etch profiles for the variable angle runs indicated that the etch rate was strongly dependent on ion flux. Etch anisotropy increased with decreasing pressure, consistent with increased ion bombardment energy. The degree of anisotropy was, however, limited due to a non-normal component of ion energy, which has been interpreted previously as an ion temperature.
An extended ambipolar model: Formulation, analytical investigations, and application to photocurrent modeling
Authors: Ishaque A. N. , Howard J. W. , Becker M. , Block R. C.
Published: July 2002

An extended development of the ambipolar transport equation is presented with a thorough investigation of the commonly omitted terms and conventional approximations. An analytical technique of integrating the fully inclusive steady-state ambipolar equation is reported. This technique can yield closed form solutions for the frequently used recombination functions (Shockley–Read–Hall, band-to-band, and/or Auger models) that describe electron-hole recombination in indirect or direct band-gap semiconductors. The ensuing results are potentially applicable to many areas of current research. One such application is demonstrated by constructing a model for the photocurrent response of the reverse-biased silicon p-n junction in the presence of uniformly imposed external generation of excess carriers. The model is found to be in excellent agreement with numerical simulations. The extended ambipolar equation is shown to significantly improve the ability to model the current response due to excess carriers. Terms that are ignored or uncritically approximated in the conventional treatment of the ambipolar equation are found to have important consequences for modeling Dember-related second-order current response, as well as the asymptotic behavior of the photocurrent of a reverse-biased junction.
High-temperature superconducting vector switch
Authors: Chelluri B. , Barber J. , Clements N. , Johnson D. , Spyker R. , Sarkar A. K. , Kozlowoski G.
Published: July 2002

The feasibility of a high-temperature superconducting switch based on the principle of the superconducting vector switch (SVS) is discussed. This switch exploits the anisotropy in electrical conductivities of the high-temperature superconductors. Underlying the SVS mechanism is the ability to turn on/off large superconducting currents confined to the CuO2 planes that characterize these materials using lower currents flowing normal to the planes. The required conditions to optimize the switch and increase the gain are presented.
Micromagnetics of thin-film CoX media for longitudinal magnetic recording
Authors: Giles Roscoe C. , Mansuripur M.
Published: July 2002

We use large-scale computer simulations to model magnetization-reversal dynamics in thin films of sputtered CoX alloys (X=Cr, Pt, etc.). We use full Landau–Lifschitz–Gilbert dynamics to evolve very large (65,536-spin) systems for tens of thousands of time steps. Through such simulations, we are able to relate model micromagnetic parameters to complex phenomena observed experimentally. An important goal is to better understand the role of exchange coupling in the recording dynamics of these media. We present results on the microscopic magnetic states and structures found during reversal in a model CoX material.
Stress generation in thin Cu-Ti films in vacuum and hydrogen
Authors: Apblett C. , Ficalora P. J.
Published: July 2002

Thin bilayer films of copper metal on titanium were sputter deposited on oxidized silicon wafers and annealed in vacuum and hydrogen ambients. Annealing in vacuum caused the bilayers to fail in tension, while the hydrogen annealed films did not fail. This observation is explained as stress generated due to crystal lattice volume changes and thermal expansion coefficients.
Qualitative analysis of response caused by growing plane waves by underdetermined system theory
Authors: Sano Yukio
Published: July 2002

A qualitative analysis of the mechanical response of rate-dependent media caused by one-dimensional plane smooth- and continuous-wave fronts with the growing peaks of strain, particle velocity, and stress is performed by an underdetermined system of nonlinear partial differential equations. The response found by the analysis reveals that strain, particle velocity, and stress profiles in the smooth-wave front are not similar and that the front is composed of five partial waves having different properties. The property is represented by the set of strain rate, acceleration, and stress rate as in a previous study. The front of the wave front is necessarily a contraction wave in which strain, particle velocity, and stress increase with time. The second partial wave is another contraction wave. We call the wave a vice-contraction wave. The rear is assumed to be a rarefaction wave where they all decrease with time. Between these two partial waves there are two remaining partial waves. We call these waves mesorarefaction waves I and II. Wave II is a wave in which particle velocity and stress increase, notwithstanding the decrease in strain with time. It is followed by wave I in which the increase in stress with time occurs in spite of the decrease in strain and particle velocity. The continuous-wave front, which has discontinuous-movement velocities at the continuous, but nonsmooth, positions in the profiles of strain, particle velocity, and stress, is composed of five independent waves. These waves are a contraction wave, a vice-contraction wave, evolutional rarefaction waves II and I, and a rarefaction wave which possess the same properties as the corresponding partial waves in the smooth-wave front mentioned above. Both in the smooth-growing-wave front and in the continuous one the peak precedence is in the order of the strain, particle velocity, and stress peaks. The stress-strain path and stress-particle velocity path at a position in a rate-dependent medium which is passed by the continuous-wave front are schematically shown.