bluuebunny/crossref_metadata_2025 huggingface dataset:
Steady state oxygen surface content in oxygen sputtered silicon at impact energy of 5 keV per atom
Authors: Serrano J. J. , Blanco J. M. , Guzmán B. , De Witte H. , Vandervorst W.
Published: July 2002

A method is presented for the calculation of the oxygen surface concentration in steady state when sputtering silicon and silicon oxides with oxygen ions. The case of sputtering with 5 keV oxygen atoms as a function of incidence angle has been studied. Measurements of erosion rates under the mentioned sputtering conditions, including oxygen and noble gases as primary ions, with and without oxygen flooding, are the input data. The dependence of the component sputtering yield of silicon on the oxygen surface concentration is also obtained, as well as the preferential sputtering ratio. These quantities, from the point of view of the calculation work frame, depend on the degree of oxygen supersaturation (oxygen atomic fraction >2/3) at the surface in normal incidence. The possibility of supersaturation is a result of our assumptions and its level can be estimated within a narrow range.
A combined crossed-beam, ab initio, and Rice–Ramsperger–Kassel– Marcus investigation of the reaction of carbon atoms C(3Pj) with benzene, C6H6(X 1A1g) and d6-benzene, C6D6(X 1A1g)
Authors: Hahndorf I. , Lee Y. T. , Kaiser R. I. , Vereecken L. , Peeters J. , Bettinger H. F. , Schreiner P. R. , Schleyer P. v. R. , Allen W. D. , Schaefer H. F.
Published: July 2002

The reactions of atomic carbon, C(3Pj), with benzene, C6H6(X 1A1g), and with d6-benzene, C6D6(X 1A1g) were investigated at twelve collision energies between 8.8 and 52.5 kJ mol−1 using the crossed molecular beams technique. Forward-convolution fitting of the data, high-level electronic structure calculations, and Rice–Ramsperger–Kassel–Marcus (RRKM) investigations on the singlet and triplet C7H6/C7D6 potential energy hyperface suggest that at low collision energies the chemical reaction dynamics are indirect and dominated by large impact parameters. As the collision energy increases, smaller impact parameters become more important, and the chemical dynamics is increasingly direct. At all collision energies, the reaction proceeds on the triplet surface via a barrierless addition of the carbon atom to form a bicyclic intermediate followed by ring opening of the initial collision complex to a seven-membered ring intermediate (cycloheptatrienylidene). The latter decomposes without exit barrier to the thermodynamically less stable 1,2-didehydrocycloheptatrienyl radical, C7H5(X 2B1)+H, and its deuterated C7D5(X 2B1)+D counterpart. The formation of a C7D6 adduct is observed as a second channel. The barrierless route for the destruction of benzene can help to model important pathways for the synthesis of higher polycyclic aromatic hydrocarbon derivatives in the interstellar medium, in outflows of dying carbon stars, in hydrocarbon-rich planetary atmospheres, as well as in oxygen-poor combustion flames.
Vibrational coherence and nonadiabatic dynamics in the condensed phase
Authors: Gonzalez C. R. , Fernandez-Alberti S. , Echave J. , Chergui M.
Published: July 2002

The ultrafast nonradiative relaxation processes after photon excitation at 266 nm of Hg2 trapped in a cryogenic argon matrix are studied by molecular dynamics with quantum transitions. Fourteen electronic surfaces and their corresponding couplings are included in the simulations. The couplings between electronic states are modeled using a diatomics-in-molecules treatment of the mixing of the different states of Hg2 induced by the Ar atoms. While the initially excited electronic state is the D1u state, we observe that after 10 ps of dynamics most of the electronic population (90%) is in the A0g± states. The majority of nonadiabatic jumps take place in the first 2 ps of the dynamics and at large Hg–Hg nuclear distances close to the Franck–Condon region of excitation. These results confirm predictions from previous experimental steady-state spectroscopic studies. Finally, we also demonstrate the conservation of vibrational coherence of the Hg2 stretching mode during the first few picoseconds, despite several nonadiabatic crossing events during this time.
Anomalous isotopic predissociation in the F 3Πu(v=1) state of O2
Authors: Lewis B. R. , Gibson S. T. , England J. P. , Stark G. , West J. B.
Published: July 2002

Using a tunable, narrow-bandwidth vacuum-ultraviolet source based on third-harmonic generation from excimer-pumped dye-laser radiation, the F 3Πu←X 3Σg−(1,0) photoabsorption cross sections of O216 and O218 have been recorded in high resolution. Rotational analyses have been performed and the resultant F(v=1) term values fitted to the Π3 Hamiltonian of Brown and Merer [J. Mol. Spectrosc. 74, 488 (1979)]. A large rotationless isotope effect is observed in the F(v=1) predissociation, wherein the Lorentzian linewidth component for O218 is a factor of ∼50 smaller than the corresponding O216 linewidth. This effect, a consequence of the nonadiabatic rotationless predissociation mechanism, is described using a coupled-channel treatment of the strongly Rydberg-valence-mixed Πu3 states. Significant J, e/f-parity, and sublevel dependencies observed in the isotopic F(v=1) rotational widths are found to derive from an indirect predissociation mechanism involving an accidental degeneracy with the E 3Σu−(v=3) level, itself strongly predissociated by Σu−3 Rydberg-valence interactions, together with L-uncoupling (rotational) interactions between the Rydberg components of the F and E states. Transitions into the E(v=3) level are observed directly for the first time, specifically in the O218 spectrum.
Sensitivity-enhanced nuclear quadrupole correlation spectroscopy: Application of single transition operators in nuclear quadrupole resonance of half-integer nucleus
Authors: Wang Jia-Hsing , Liao Ming-Yuan
Published: July 2002

Single transition operators are adapted to simplify the density matrix theory for the spin dynamics calculation of quadrupole nuclei with more than one spin transition in zero field. We employ the formalism on the spin I=5/2 system with axial symmetry to obtain the responses of multiple pulses for nuclear quadrupole resonance regardless the spin relaxation. The theoretical calculation for pulse response is illustrated from one-pulse to multipulse and one-dimension to multidimension explicitly. Subsequently sensitivity-enhanced nuclear quadrupole correlation spectroscopy (SENQCOSY) is proposed and demonstrated. Experimental results are compared with conventional nuclear quadrupole correlation spectroscopy (NQCOSY) for Sb121 (I=5/2) in SbCl3 system. The maximum sensitivity is enhanced by a factor of 2.66, which are in good agreement with theoretical prediction.
Analysis of collector-emitter offset voltage of InGaP/GaAs composite collector double heterojunction bipolar transistor
Authors: Lew K. L. , Yoon S. F.
Published: July 2002

The Ebers–Moll-like terminal current expressions of a composite collector double heterojunction bipolar transistor (DHBT), which takes the recombination effect into account, have been formulated and an expression for collector-emitter offset voltage [VCE(offset)] has been derived. Factors affecting the VCE(offset) of a composite collector DHBT are investigated and good agreement between the calculated and reported experimental results is shown. Analytical results showed that the transmission coefficient of the base-collector (B-C) junction does not have a considerable effect on the VCE(offset), provided that the B-C junction is of good quality. Thus, despite its asymmetric structure, the VCE(offset) of an optimally designed composite collector DHBT could be as low as that of a conventional DHBT. Hence a composite collector DHBT with low saturation voltage and negligible VCE(offset) is possible if the two conditions: (i) good quality B-C junction, (ii) base transport factor, α≈1, are fulfilled.
Control of stress and plasma-induced heating during dc magnetron sputtering of permalloy films for microelectromechanical systems
Authors: Min Seungook , Bain James A. , Greve David W.
Published: July 2002

Low stress (<25 MPa), magnetically soft films of permalloy (Ni80Fe20) were deposited for microelectromechanical system based data storage application without significant plasma-induced substrate heating. Optimization of film properties was performed using a designed experiment, response surface methodology. In this study, the formation of an undesirable magnetic stripe domain structure formation degraded the magnetic properties of permalloy film. The relationship between the results of the factorial experiment are explained based on Murayama’s stripe domain theory.
Surface nitrogen concentration dependence of the nitrogen incorporation in reactively sputtered FeXN films
Authors: Zou Pei , Bain James A.
Published: July 2002

N incorporation is critical to soft magnetic properties of the FeXN film. Previous work showed experimentally that the N concentration is linearly proportional to the ratio of the N to Fe atomic fluxes arriving at the surface of the film (flux ratio rule). Recently it was shown that under certain conditions, N incorporation is more efficient than the flux ratio rule would suggest. In this work a simple analytic model based on steady-state N and Fe transport fluxes during the reactive sputtering process is used to understand these two observed phenomena. It is shown that the N concentration in the film depends on the amount of N on the surface of the growing film. In a surface N-depleted state, the flux ratio rule is followed, while in a surface-N rich state, the N incorporation in the film increases with deposition rates even when the ratio of incoming N to Fe fluxes is kept constant. Experimental data from sputtered FeAlN films can be reproduced reasonably well with the current analysis.
The Lund–Regge surface and its motion’s evolution equation
Authors: Chen Chunli , Li Yishen
Published: July 2002

The system of evolution equations for general motion of surfaces in orthogonal coordinates is analyzed to reduce the number of variables as well as equations. The explicit expression of the Lund–Regge surface is obtained. When the surface corresponds to the Lund–Regge equation, we prove that some components of velocity satisfy the linearizations of the Lund–Regge equation. The soliton solution is derived and one special case of the Lund–Regge surface is studied.
Design of powder aligning systems for the compression molding of radially anisotropic permanent magnet rings
Authors: Kinsey D. J. , Lillywhite S. J. , Jewell G. W. , Ede J. D. , Williams A. J. , Howe D. , Harris I. R.
Published: July 2002

The article describes the design of powder aligning fixtures for the compression molding of radially anisotropic NdFeB magnet rings. The implications of the high fields required are discussed, with particular reference to the limitations imposed on the aspect ratio of the magnets that can be satisfactorily aligned. Features for enhancing the magnitude of the aligning field in the mold cavity, e.g., a magnetic shunt to shield the inner core and tapering of the upper plate are discussed. These issues are illustrated by means of a design study on a powder aligning fixture for a NdFeB magnet ring with an outer diameter of 26 mm and a wall thickness of 3 mm. Extensive finite element analysis is employed to investigate the role of various features, and to optimize the geometry. The findings of the design study are validated by comparison with measurements on a prototype fixture.
Irreducible modules of finite dimensional quantum algebras of type A at roots of unity
Authors: Nakashima Toshiki
Published: July 2002

Properly specializing the parameters contained in the maximal cyclic representation of the nonrestricted A-type quantum algebra at roots of unity, we find the unique primitive vector in it. In this case, the representation is no longer irreducible. We show that the submodule generated by the primitive vector is the unique irreducible submodule and can be identified with an irreducible highest weight module of the finite dimensional A-type quantum algebra, which is defined as the subalgebra of the restricted quantum algebra at roots of unity.
Equivalence of diffusive conduction and giant ambipolar diffusion
Authors: Yairi Micah B. , Miller David A. B.
Published: July 2002

Two high speed diffusion mechanisms in semiconductor heterostructures, diffusive conduction, and giant ambipolar diffusion, are compared and shown to be nearly equivalent descriptions of the same physical process. Fundamental limits of this process are discussed.
Generalized sine-Gordon/massive Thirring models and soliton/particle correspondences
Authors: Acosta José , Blas Harold
Published: July 2002

We consider a real Lagrangian off-critical submodel describing the soliton sector of the so-called conformal affine sl(3)(1) Toda model coupled to matter fields. The theory is treated as a constrained system in the context of Faddeev–Jackiw and the symplectic schemes. We exhibit the parent Lagrangian nature of the model from which generalizations of the sine-Gordon (GSG) or the massive Thirring (GMT) models are derivable. The dual description of the model is further emphasized by providing the relationships between bilinears of GMT spinors and relevant expressions of the GSG fields. In this way we exhibit the strong/weak coupling phases and the (generalized) soliton/particle correspondences of the model. The sl(n)(1) case is also outlined.
Electron transfer in voltage tunable two-color infrared photodetectors
Authors: Majumdar Amlan , Choi K. K. , Rokhinson L. P. , Reno J. L. , Tsui D. C.
Published: July 2002

Two-color quantum-well infrared photodetectors (QWIPs) that are based on electron transfer between coupled QWs suffer from the presence of the shorter wavelength peak at all bias voltages. We investigate this problem in such detectors with 50 or 200 Å AlGaAs barriers between the QW pair. We deduce the absorption coefficient α and photoconductive gain g of the detectors with 50 Å barriers using corrugated QWIPs with different corrugation periods. We find that α has a number of small peaks in its spectrum but its value remains almost constant between 0.1 and 0.2 μm−1 in the 6–12 μm range for most experimental conditions. The wavelength dependence of g, which always has a pronounced peak at the shorter detection wavelength, determines the responsivity line shape. These results are attributed to insufficient electron transfer between the coupled QWs and to low tunneling probability of the longer wavelength photoelectrons. A comparison of measured responsivity and calculated absorption spectrum of the detectors with 200 Å barriers indicates that there is significant electron transfer between the coupled wells. Despite efficient electron transfer, these detectors have a shorter wavelength detection peak at all bias voltages because of significant short wavelength absorption in both the QWs.
Determination of Tc, vortex creation and vortex imaging of a superconducting Nb film using low-temperature magnetic force microscopy
Authors: Roseman M. , Grütter P.
Published: July 2002

Using a custom built low temperature magnetic force microscope, we have used the repulsive Meissner interaction between the magnetic tip and the sample to determine the critical temperature of a superconducting Nb film. Vortex creation by the tip stray field has been observed, in which two vortices have been nucleated, both simultaneously and in succession. We have also imaged vortices as a function of applied magnetic field, and have observed the expected linear dependence between vortex density and field strength.
Optical second harmonic intensity images of a silver grating surface
Authors: Sano H. , Kume M. , Nakagawa H. , Mizutani G.
Published: July 2002

We have obtained optical second harmonic (SH) intensity images of a silver grating surface. A stripe pattern was seen in the SH intensity image when the incident light polarization is perpendicular to the lines of the grooves of the grating. We have found that the strongest SH radiation comes from the bottoms of the grooves. On the other hand, the strong linear reflection comes from the slope of the grooves. We suggest that the enhancement of the electric field at the bottoms of the grooves has led to the observed strong SH radiation.
A parabolic approximation method with application to global wave propagation
Authors: Palmer David R.
Published: July 2002

Motivated by the difficulty in using the splitting matrix method to obtain parabolic approximations to complicated wave equations, we have developed an alternative method. It is three dimensional, does not a priori assume a preferred direction or path of propagation in the horizontal, determines spreading factors, and results in equations that are energy conserving. It is an extension of previous work by several authors relating parabolic equations to the horizontal ray acoustics approximation. Unlike previous work it applies the horizontal ray acoustics approximation to the propagator rather than to the Green’s function or the homogenous field. The propagator is related to the Green’s function by an integral over the famous “fifth parameter” of Fock and Feynman. Methods for evaluating this integral are equivalent to narrow-angle approximations and their wide-angle improvements. When this new method is applied to simple problems it gives the standard results. In this paper it is described by applying it to a problem of current interest—the development of a parabolic approximation for modeling global underwater and atmospheric acoustic propagation. The oceanic or atmospheric waveguide is on an Earth that is modeled as an arbitrary convex solid of revolution. The method results in a parabolic equation that is energy conserving and has a spreading factor that describes field intensification for antipodal propagation. Significantly, it does not have the singularities in its range-sliced version possessed by many parabolic equations developed for global propagation. We then discuss two extensions of the method; first to propagation along refracted geodesics and second to a description involving discrete, local, normal modes.
Measurements of germanium K-shell ionization cross sections and tin L-shell x-ray production cross sections by electron impact
Authors: Tang Changhuan , An Zhu , Luo Zhengming , Liu Mantian
Published: July 2002

This article reports experimental measurements of germanium K-shell ionization cross sections and tin L-shell x-ray production cross sections by electron impact. In order to avoid the difficulty of preparing thin and uniform self-supporting targets, thin targets with thick substrates are used in the experiments. Since electrons reflected by the substrate can induce additional ionization of target atoms, we developed a method to correct the measured x-ray intensities and eliminated the influence of the substrate on measured data. Our measured cross sections are in good agreement with previous measurements. The present results are also compared with the predictions of theories and semiempirical and empirical formulas. It is found that the K-shell ionization cross sections of Ge at energies from near threshold to 40 keV can be reasonably described by the semiempirical formula of Green and Cosslett. Experimental absolute L-shell x-ray production cross sections of Sn are presented. It seems that, so far, none of the available theories can adequately interpret our L-shell results at low energies.
Gamma-ray-irradiation effects on the leakage current and reliability of sputtered TiO2 gate oxide in metal–oxide–semiconductor capacitors
Authors: Wang Ching-Wu , Chen Shih-Fang , Chen Guan-Ting
Published: July 2002

The leakage current and reliability characteristics of γ-ray-irradiated sputtered titanium dioxide (TiO2) thin films have been systematically investigated. Analytical results revealed that the inferior polycrystallinity and the larger leakage current of the anatase structure of unirradiated TiO2 thin film could be effectively improved by raising the irradiation dose at low γ-ray doses [≦10 kGy(TiO2)]. However, any higher dose [>10 kGy(TiO2)] causes undesirable deterioration of the film crystallinity, yielding an increased leakage current. The optimal dose of γ-rays [10 kGy(TiO2) in this work] not only provides a proper energy transfer to the TiO2 film, but also reduces the oxygen deficiency and/or Si-diffusion contamination, resulting in a superior crystallinity, and thus causing the reduced leakage current. The excellent agreement between the E model (thermochemical-breakdown model) and the time-dependent-dielectric-breakdown data suggested strongly that the best long-term reliability of metal–oxide–semiconductor capacitors with the TiO2 gate oxide treated by 10 kGy(TiO2) of γ rays was due to the superior crystallinity and the smaller hole trap density at the TiO2/Si interface, resulting in an increased activation energy, thus reducing the occurrence of breakdown.
Thickness dependent phase transformations in implanted iron layers
Authors: Jagielski J. , Kopcewicz M. , Gawlik G. , Matz W. , Thomé L.
Published: July 2002

This article shows that phase transformations in implanted iron may strongly depend on the sample thickness. The effect essentially relies on the lower impurity concentration required for the formation of a given phase in thin films as compared with thick layers or bulk samples. The phase transformation in thin films is also more complete. In this work, the total transformation of pure iron into iron nitrides was observed upon nitrogen implantation of thin iron layers, whereas about 20% of Fe atoms remained in the crystalline α-Fe phase in nitrogen-implanted bulk samples.
Revised finite-difference time-domain algorithm in a nonorthogonal coordinate system and its application to the computation of the band structure of a photonic crystal
Authors: Wu Liang , He Sailing
Published: July 2002

A discretization grid and its associated time-stepping formulas for a finite-difference time-domain method in a nonorthogonal coordinate system are introduced to simulate electromagnetic wave propagation and scattering. The method is applied to compute the band structure of a photonic crystal with a skew lattice. Unlike the conventional finite-difference time-domain method in a nonorthogonal coordinate system, the present method can treat discontinuities in the material parameters appropriately and thus does not have any problem of numerical instability.
Using sequences of pulses to control coherence in an open quantum computing system
Authors: Qiao Bi , Ruda Harry E. , Chang J. F.
Published: July 2002

A method for quantum control of coherence in an open quantum computing system is presented. The approach was applied to finding a suitable control sequence for maintaining coherence in a silicon-based nuclear spin quantum computing system, subject to Bose-type environmental noise, and under the Born–Markovian and rotating wave approximations. It is shown that the evolution operator remains decoherence free while the three control pulses are being applied.
On the electronic structure of Cm(H2O)n3+ (n=1,2,4,6) by all-electron Dirac–Hartree–Fock calculations
Authors: Mochizuki Yuji , Tatewaki Hiroshi
Published: July 2002

Dirac–Hartree–Fock (DHF) calculations were performed to investigate the hydration of the trivalent Cm ion with a 5f7 configuration on the models of Cm(H2O)n3+ (n=1,2,4,6). The curium–oxygen distances and stabilization energies were evaluated. The DHF wave functions were analyzed by the Mulliken populations and spinor projections. Hydration was found to be characterized by the coordinate bond. An increase in the number of water molecules caused an increase in the curium–oxygen distance and a reduction of the stabilization energy per water molecule. The fluorescence transition energy was also estimated using the complete open-shell configuration interaction (COSCI) method. Redshifts due to hydration were obtained and were in accord with observations of the nephelauxetic effect. The isovalent gadolinium ion Gd3+ was also studied for comparison.
Investigation of amorphization and crystallization processes in ion-implanted garnet by transmission electron microscopy
Authors: Yoshiie T. , Bauer C. L. , Kryder M. H.
Published: July 2002

Amorphization produced by ion implantation and subsequent crystallization produced by thermal processing have been investigated in films of (SmYGdTm)3Ga0.4Fe4.6O12 garnet by transmission electron microscopy, incorporating a special cross-sectioning technique. These films were produced by liquid-phase epitaxy on {111} garnet substrates and subsequently implanted with ions of deuterium at 60 keV and doses ranging from 0.50 to 4.5×1016 D+2/cm2 and ions of oxygen at 110 keV and doses ranging from 0.95 to 8.6×1014 O+/cm2. The amorphization process evolves in four separate stages: (1) an implanted (crystalline) band, delineated by the implantion strain profile, forms at doses of about 0.50×1016 D+2/cm2/ and 0.95 O+/cm2, (2) isolated amorphous regions of about 10 nm in diameter form at doses of about 1.0×1016 D+2/cm2 and 1.9×1014 O+/cm2, (3) the amorphous regions merge to form a continuous band below the implanted surface at doses of about 3.0×1016 D+2/cm2 and 5.7×1014 O+/cm2, and (4) this band expands to the implanted surface at larger doses. Amorphization is caused by implantation with oxygen, but prior implantation with deuterium sensitizes the lattice by increasing the strain. The crystallization process evolves in three separate stages: (1) small crystallites, about 10 nm in size, form throughout the entire amorphous band after annealing for 10 min at 350 °C, (2) larger crystallites nucleate and grow from the implanted surface and amorphous/crystalline interface after annealing for 10 min at 450 °C, and (3) these crystallites grow in size until they merge to form a continuous polycrystalline layer. Some epitaxial regrowth of the monocrystalline into the amorphous region is also observed. Details of these processes are interpreted in terms of atomic displacement mechanisms and compared with corresponding changes of certain magnetic properties.
Low-noise properties of unbiased even-harmonic Josephson mixers
Authors: Fujisawa K. , Kita S. , Ohmae Y. , Yamaguchi A.
Published: July 2002

Noise properties of Josephson harmonic mixers were investigated both by simulation studies and by experiments. It was clarified that the unbiased mixing operation peculiar to even-harmonic Josephson mixers has a lower noise temperature than the biased operation. A minimum noise temperature of 121 K was obained for an unbiased second-harmonic Josephson mixer at 70 GHz. The cause of this low-noise property of the unbiased mixing was attributed mainly to the nonexistence of noise down-conversions by the odd-harmonics of LO and the Josephson oscillation.
Electron channeling radiation from diamonds with and without platelets
Authors: Park H. , Kephart J. O. , Klein R. K. , Pantell R. H. , Berman B. L. , Datz S. , Swent R. L.
Published: July 2002

Channeling-radiation spectra produced by planar-channeled, 30.5-MeV electrons in Type-Ia and Type-IIa natural diamonds have been measured and are compared with previous results for 54.5-MeV electrons. Because of the presence of platelets precipitated along the (100) planes in the Type-Ia diamond, the energies of the (100) spectral peaks are shifted downward relative to those for the Type-IIa diamond. We have developed a model to explain this effect.
Collective ion acceleration and relativistic electron-beam propagation
Authors: Smith John R. , Doggett Wesley O. , Armstrong Carter M.
Published: July 2002

Experimental results on the collective acceleration of ions using a relativistic electron beam (0.5 MeV, 30 kA, 60 ns) are presented. A gas cloud consisting of either H2, He, or N2 gas was used as the ion source. Ion species, charge state, and energy were measured. Ions were accelerated as derived from the hydrogen and helium gas sources but not from the nitrogen gas source. In almost all shots significant numbers of hydrogen and carbon impurity ions were accelerated. The electron beam exhibited asymmetric propagation characteristics in the region immediately downstream from the anode.
Organometallic vapor phase epitaxial growth of AlGaInP
Authors: Yuan J. S. , Hsu C. C. , Cohen R. M. , Stringfellow G. B.
Published: July 2002

AlxGayIn1−x−yP with x+y=0.51, lattice matched to the GaAs substrate, has been grown by organometallic vapor phase epitaxy. The simple, horizontal, IR heated system operates at atmospheric pressure using the reactants TMAl, TMGa, TMIn, PH3, and H2. Alloys giving room temperature, band edge photoluminescence (PL) have been grown in the temperature range 625–780 °C. Emission wavelengths as short as 5820 Å (2.13 eV) are reported. High growth temperatures are found to give layers with the best surface morphology and PL intensity. The use of high temperatures is especially important for high Al content alloys. PL at x=0.2 is obtained only for temperatures above 740 °C.
Nitrogen implantation of metals
Authors: Anttila A. , Keinonen J. , Uhrmacher M. , Vahvaselkä S.
Published: July 2002

Sixteen metals implanted to saturation with 300-keV N2+ ions have been studied using nuclear resonance broadening and Rutherford backscattering techniques to profile the implanted concentration. Blisters due to the implanted nitrogen were observed in Mg, Al, Ti, V, Cr, Nb, Mo, Ta, W, and AISI 304 steel but not in Cu, Zr, Ag, Hf, and Au. The nominal saturation concentration at maximum varied from 50 to 60 at. % for all cases except for Cu, Ag, and Au, where it was 20 at. %. The surface hardness was generally increased by a factor between 1.2 and 2.3. However, no increase was observed for Mo, Ag, and Au. The mononitride formation in Ti, Zr, and Hf was verified by x-ray diffraction. The formation of blisters and diffusion in the preparation of nitrides is discussed.
Weak-field magnetoresistance of indium-doped PbTe between 4.2 and 300 K
Authors: Abbundi R. J. , Allgaier R. S. , Houston Bland , Martinez Antonio , Davis John L.
Published: July 2002

Rotational weak-field magnetoresistance (WFMR) measurements were performed between 4.2 and 300 K on thin films of (111)-oriented n-type PbTe deposited on BaF2 and doped with approximately 0.1 and 0.25 at. % In. Due to substrate-induced strain, the 0.1% In-doped sample showed a significant departure from cubic symmetry at 4.2 K corresponding to a transfer of carriers into the valley along the strain axis in the PbTe multivalley conduction band. This in-plane stretching of the film was found to persist even up to 300 K. The 0.25% In-doped film was strained to a lesser extent at 4.2 K and by room temperature had changed from a tensile strain to a compressive strain. Such a change is attributed to the opposing effects of film-substrate lattice mismatch and the difference in their thermal expansion coefficients. The WFMR for the in-plane configuration of both films displayed an unusual skewness below 300 K which is normally not allowed in (111)-oriented films, whether cubic or trigonally distorted.
Lateral reaction of polycrystalline silicon film with overlapping aluminum film
Authors: Arai Hitoshi , Kohda Shigeto , Kitano Yoshitaka
Published: July 2002

Remarkable substitution reaction between aluminum and polycrystalline silicon, which occurs below the eutectic temperature (577 °C), has been studied. This reaction proceeds laterally in the polycrystalline silicon film, and the reaction product contains aluminum. In order to elucidate the cause of the rapid reaction, the influences of aluminum volume, substrate materials, and polycrystalline silicon grain size on the reaction rate were investigated. Results indicate that the reaction proceeds preferentially along polycrystalline silicon grain boundaries on SiO2 substrate and depends on silicon solubility and diffusivity in aluminum.
Effect of illumination and magnetic fields on the electron transport properties of Pb0.75Sn0.25Te doped with indium
Authors: Martinez Antonio , Abbundi R. J. , Houston Bland , Davis John L. , Allgaier R. S.
Published: July 2002

Electrical transport measurements between 300 and 1.5 K were made on two Pb0.75Sn0.25Te films doped approximately 0.5 at. % indium. The Hall mobility, Hall coefficient, and resistivity display an unusual temperature dependence relative to those of undoped PbSnTe which suggest a phase transition at approximately 18 K. These samples also exhibit high photosensitivity below 21 K where slowly relaxing and persistent photoconductivity was observed. Time constants for the photoconductive relaxation were found for temperatures between 8 and 19 K. The application of a magnetic field during sample cooldown had a large effect on the zero-field resistivity of the sample at 4.2 K.
Magnetic properties of Sm-Ti-Fe and Sm-Co based films
Authors: Cadieu F. J. , Cheung T. D. , Wickramasekara L.
Published: July 2002

High energy product Sm-Co based films have been synthesized by selectively thermalized rf sputtering in an in-plane magnetic field of 2.5 kOe. The films are made premagnetized and in most cases fields to 20 kOe do not increase the available moment. For those SmCo5 films that are directly crystallized onto heated substrates, a maximum coercive force of 23 kOe and BHmax=18 MG Oe is obtained. For those SmCo5 films that are sputtered first amorphous and then crystallized, coercive forces in the range of 22 kOe are observed. Samples of Sm2(CoFeZr)17 have been directly crystallized with a coercive force of 7 kOe and BHmax=21 MG Oe, and crystallized from an amorphous state with coercivities of 16–20 kOe. As previously reported for certain SmCo5 films all of these films exhibit flat-topped hysteresis loops. Further measurements on a new (Sm+Ti)Fe5 phase we previously reported have been made. High-field measurements to 90 kOe made on a 5 at. % Ti (Ti:Fe=1:19) sample gave an inplane coercive force of 10 kOe with an energy product of 12 MG Oe at −100 °C. Curie temperatures of 5, 10, and 15 at. % Ti samples are 608, 630, and 670 K, respectively.
Electron beam decomposition of CdCl2
Authors: Green Mino , Aidinis C. J. , Fakolujo O. A.
Published: July 2002

The e-beam stimulated reaction, CdCl2 (s)→Cd(s)+2 Cl(g), has been studied in cadmium chloride thin films between 303 and 483 K using 2-keV electrons. The dose required to make 90-nm-deep holes at 483 K is 3×10−3 C cm−2. Extrapolated dosing levels of ∼6×10−5 C cm−2 are expected. The use of CdCl2 as a positive-type electron resist in a new scheme is proposed. A working model, useful for considering the e-beam stimulated decomposition energetics and mechanism, is briefly discussed.
Schottky-barrier profiling techniques in semiconductors: Gate current and parasitic resistance effects
Authors: Look D. C.
Published: July 2002

The theory for obtaining mobility and carrier concentration profiles by the Hall-effect, magnetoresistance, and capacitance-conductance methods is developed in the relaxation-time approximation. This theory is then applied to semiconductors in which a Schottky barrier is used to control a depletion region. Particular emphasis is given to field-effect transistor structures which are ideally suited for geometric magnetoresistance measurements. A unique feature of the present model is the correction for finite gate (Schottky-barrier) current, which can be very important under forward-gate-bias conditions. The ability to use forward-bias makes the near-surface region more accessible. Also, parasitic resistance effects are treated. We apply these results to GaAs conducting layers formed by direct implantation of 4×1012/cm2, 100-keV Si ions into Cr-doped GaAs.
Effect of order-disorder transition on magnetic properties of high silicon-iron single crystals
Authors: Arai K. I. , Ohmori K. , Miura H. , Tsuya N.
Published: July 2002

Using high silicon-iron single crystals containing around 6.5 wt. % silicon, the quenching temperature dependence of the saturation magnetization, the magnetocrystalline anisotropy constant, and the magnetostriction constants were measured at room temperature. The saturation magnetization and the anisotropy constant of the crystals with 4.9–6.0 wt. % silicon quenched into oil from 1100 °C showed decreases of up to 12 and 80%, respectively, compared to crystals cooled slowly from 1100 °C, while the saturation magnetostriction constants λ100 and λ111 increased for quenched crystals. The decreases in the saturation magnetizations and the anisotropy constants and the increases in the saturation magnetostriction constants for the quenched crystals were correlated with decreases in an order parameter calculated from x-ray measurements.
Palladium silicide formation under the influence of nitrogen and oxygen impurities
Authors: Ho K. T. , Lien C.-D. , Nicolet M-A.
Published: July 2002

The effect of impurities on the growth of the Pd2Si layer upon thermal annealing of a Pd film on 〈100〉 and amorphous Si substrates is investigated. Nitrogen and oxygen impurities are introduced into either Pd or Si which are subsequently annealed to form Pd2Si. The complementary techniques of Rutherford backscattering spectrometry, and 15N(p,α)12C or 18O(p,α)15N nuclear reaction, are used to investigate the behavior of nitrogen or oxygen and the alterations each creates during silicide formation. Both nitrogen and oxygen retard the silicide growth rate if initially present in Si. When they are initially in Pd, there is no significant retardation; instead, an interesting ‘‘snow-plowing’’ effect of N or O by the reaction interface of Pd2Si is observed. By using N implanted into Si as a marker, Pd and Si appear to trade roles as the moving species, when the silicide front reaches the nitrogen-rich region.
Theory for small-angle scattering from quasi-random layered structures
Authors: Herman R. M.
Published: July 2002

A theory for small-angle scattering from quasi-random layered structures—for example, x-ray scattering from oriented polymer samples—is proposed. Being truly three dimensional, it utilizes refractive index correlation functions separable along local principal coherence axes within the sample. Realistic variations in directions parallel to the local mean lamellar plane, as well as in the inequivalent direction perpendicular to it, can be taken into account. When the incident waves propagate at nonzero angles with respect to local mean lamellar planes, diffraction into larger angles parallel to the overall mean lamellar plane is increased, while diffraction into the larger scattering angles in the direction perpendicular to this plane is attenuated. A continuous-domain model is proposed for describing these effects.
Investigation of deep levels in PbI2 by photoinduced current transient spectroscopy
Authors: Zielinger J. P. , Pohoryles B. , Balland J. C. , Gross J. G. , Coret A.
Published: July 2002

Deep levels in PbI2 have been investigated by photoinduced current transient spectroscopy for the first time. By separating the signal processing from the data acquisition it was possible to analyze the transient using different methods, in particular a four-gate treatment which allows to clear the detrapping current of uncontrolled changes of the recombination lifetime of thermally released carriers. Three hole traps located at 0.30, 0.47, and 0.66 eV have been detected and the corresponding thermal capture cross sections evaluated. In addition a photomemory effect has been evidenced. The main features of the excited state of the crystal are increased photosensitivity, neutralization of hole traps, and residual conductivity. It is believed that macroscopic recombination barriers acting as minority carrier traps under optical excitation are responsible for this phenomenon. The presence of these extended defects is probably related to the layered structure of PbI2. An energy model is proposed on the basis of which the observed logarithmic time dependence of the photosensitization at room temperature can be predicted. The model allows also to give a plausible interpretation for all the characteristic features of the photomemory effect and for various results previously reported by other authors.
On the perpendicular recording process
Authors: Lopez O. , Clark D. A.
Published: July 2002

An analytical model of the recording process is used to examine the factors that influence the recorded magnetization. If the ‘‘switching’’ occurs at the top of the medium, the magnetizaton is influenced mostly by the head-medium separation. If the ‘‘switching’’ occurs at the middle of the medium, the magnetization is influenced by the head-medium separation, the slope loop of the M-H at M=0, and the medium thickness. The magnetization is asymmetrical in both cases and the asymmetry translates into asymmetrical readback waveforms.
Magnetization processes in a thin-film recording head
Authors: Soohoo R. F.
Published: July 2002

The switching dynamics of a Ni-Fe thin-film head during the writing process have been studied in some detail. It was found that magnetization changes, via both domain wall motion and magnetization rotation, were executed in such a way as to avoid pole formation at the domain boundaries. Unlike the case of the reading process studied previously, it was found that the switching speed and frequency response of the head could be increased by increasing the write field. However, the field required to saturate the head in the hard direction has been observed to be as much as one order of magnitude larger than the anisotropy field of 1 or 2 Oe. Means of maximizing the write field for a given driving ampere-turns are discussed in the context of the head geometry.
Conduction of flux at high frequencies in Permalloy strips by small-angle rotations
Authors: Mallary M. L.
Published: July 2002

Data presented here on the permeability of Permalloy strips at high frequency indicates that flux is conducted by small-angle rotations without significant inhibition due to coupled domain wall motion. A new theory is proposed which postulates the existence of small angular variations of magnetization within transversely oriented domains in order to allow for flux conduction by rotation without the need for domain wall motion. Results from a computer simulation of this mechanism are presented.
Bit shift with ring heads on CoCr and CoCr/NiFe perpendicular recording media
Authors: Whisler J. W. , Hoinville J. R. , Stubbs D. P. , Moe C. D. , Skorjanec J.
Published: July 2002

Bit shift is a type of distortion of the stored information in a digital magnetic recording system, which, if too large, will result in data loss. This paper compares the bit shift performance of sputtered CoCr (0.5 μm) and sputtered CoCr/NiFe (0.25 μm/0.5 μm) perpendicular magnetic recording media when Mn-Zn ferrite ring heads (gap length = 0.375 μm, track width =37 μm) in contact with the media are used for reading and writing. Bit shift was measured as a function of bit density using zero-crossing, peak, maximum slope, and maximum curvature bit detection schemes. On single-layer media using zero-crossing detection, bit shift becomes severe (20%) at about half the D50 (the density at which the output is half of its maximum value), but using maximum slope detection bit shift does not become severe until about 80% of the D50. These results agree with previous reports (Saito et al., Intermag 1984). On dual-layer media using either zero-crossing or maximum slope detection the bit shift did not become severe until the D50 was reached. CoNi longitudinal media bit shift performance was similar to that of the perpendicular media.
Three-dimensional analysis of a slot motor solving directly for flux density
Authors: Hoole S. Ratnajeevan H. , Cendes Z. J. , Hoburg J. F.
Published: July 2002

The slot motor is used in high-power devices to open a circuit when the current exceeds a limiting value. It is critical for the proper functioning of the device, to predict exactly the force produced by the current. In this paper, the three-dimensional magnetostatic field within the motor is analyzed by solving directly for magnetic flux density and the results are used to predict the forces generated. The results are then verified experimentally. This paper also introduces the concept of the fictitious vector potential for the graphical display of three-dimensional magnetic fields.
Direct vector solution of three-dimensional magnetic field problems
Authors: Hoole S. Ratnajeevan H. , Cendes Z. J.
Published: July 2002

A new finite-element formulation of magnetic field problems is presented in which the vector field is solved for directly. Unlike solutions obtained by using scalar and vector potentials, a continuous solution in terms of the magnetic field intensity vector is obtained. The formulation is based on a matrix representation of the curl and divergence operators and provides a least-squares solution of the overdetermined system of equations. The procedure is used to solve both two- and three-dimensional problems in magnetic recording and in electric machine design.
Anisotropic ferromagnetic resonance linewidth in nickel at low temperatures
Authors: Rudd J. M. , Myrtle K. , Cochran J. F. , Heinrich B.
Published: July 2002

We have measured the ferromagnetic resonance linewidth ΔH at 24 GHz in (110) nickel disks at 4 K and from 60 K to room temperature. Samples had a nominal purity of 99.99% and a residual resisitivy ratio of 40. The applied field was in the plane of the sample and measurements were made with the field along each of the three principal axes [100], [110], and [111]. We find ΔH[110] >ΔH[111] and ΔH[100] for temperatures below 200 K. At 4 K we found ΔH[100] =1600±50 Oe, ΔH[111] =1800±50 Oe, and ΔH110] =2000±50 Oe.
Inelastic magnetic x-ray scattering (invited)
Authors: Platzman P. M. , Tzoar N.
Published: July 2002

Using the theory of magnetic x-ray scattering we will discuss the possibilities for employing inelastic scattering to probe the magnetic properties of condensed matter systems. In particular, we will show how the interference between the nonmagnetic (Compton) and magnetic scattering arising from the use of circularly polarized x-rays is absolutely essential in such experiments. The very beautiful preliminary experiments by Sakai and Ono on Fe which use circularly polarized Mössbauer γ rays will be discussed. They already show the sensitivity of the technique to the ‘‘magnetic form factor.’’ In addition we will consider the physics of a unique quarter wave plate employed in obtaining circularly polarized x rays, and discuss the implications of this advance for doing such experiments on existing synchrotron x-ray sources.
Applied field response of the spin glass state in amorphous NdFe2
Authors: Spano M. L. , Alperin H. A. , Rhyne J. J. , Pickart S. J. , Hasanain S. , Andrauskas D.
Published: July 2002

The magnetic correlations and the response of the spin system to an applied field have been studied in sputtered amorphous NdFe2 using high-resolution small angle neutron scattering (SANS) techniques. In zero field the line shape of the scattering is Lorentzian down to a spin freezing temperature of approximately 330 K. Below this temperature the line shape becomes increasingly non-Lorentzian and has been analyzed using a Lorentzian plus Lorentzian-squared cross section appropriate for a random anisotropy field system. The correlation length shows a broad maximum of 170 Å near 285 K (below Tc) and then decreases to a constant value of ≊80 Å for T< 100 K. SANS data taken in applied fields up to 18 kOe at 83 K produced constant intensity contours which are elliptically distorted with the Q∥H direction being the major axis. The overall intensity and the calculated spin correlation length both drop abruptly with increased field. This behavior is consistent with the field driving the dominant part of the spin system into an infinite cluster with the residual smaller spin clusters exhibiting a super-paramagnetic type response.
Dynamics of a concentrated spin glass: a-FeB2
Authors: Moorjani K. , Poehler T. O. , Satkiewicz F. G. , Manheimer M. A. , Webb D. J. , Bhagat S. M.
Published: July 2002

Electron spin resonance (ESR) measurements on a-FeB2 over wide ranges of frequency and temperature are reported. The resonance fields and intensities show anomalies at temperatures that are an order of magnitude higher than the spin-glass transition temperature. The results cannot be described in terms of existing theories and suggest that new macroscopic variables are needed for adequate description of ESR in spin glasses.