bluuebunny/crossref_metadata_2025 huggingface dataset:
Microscopic characterization of low-field switching in ferroelectric triglycine sulfate
Authors: Aragó Carmen , Fernandez del Castillo J. R. , Noheda Beatriz , Gonzalo Julio A.
Published: July 2002

Low-field (<1 kV/cm) switching has been investigated for thin plates (0.06<d<0.15 cm) of triglycine sulfate by means of field pulses with a linear rise time. The dependence of the maximum current density, jm, with the field value Em at which this maximum occurs is jm≅B1(Em−Ecw1)3/2, for 0.3<Em<0.5 kV/cm, and jm≅B2(Em−Ecw2), for 0.5<Em<1.0 kV/cm. This is satisfactorily explained taking into account the dominant role played by sidewise and forward domain wall motion, respectively.
Slow interfacial reamorphization of Ge films melted by ps laser pulses
Authors: Siegel J. , Solis J. , Afonso C. N.
Published: July 2002

Melting and rapid solidification is induced in 50-nm-thick amorphous Ge films on glass substrates by single laser pulses at 583 nm with a duration of 10 ps. The solidification process is followed by means of reflectivity measurements with ns time resolution both at the air/film (front) and the substrate/film (back) interfaces. Due to interference effects between the light reflected at the film–substrate and film–liquid interfaces, the back side reflectivity measurements turn out to be very sensitive to the melt depth induced by the laser pulse and their comparison to optical simulations enables the determination of the solidification dynamics. For low fluences, only a thin layer of the film is melted and solidification occurs interfacially leading to reamorphization of the molten material. The results provide a critical interface velocity for amorphization of ∼4 m/s, much slower than the one that has widely been reported for elementary semiconductors. For high fluences, the molten layer depth approaches the film thickness and the results are consistent with a bulk solidification process. In this case, recalescence effects upon solid phase nucleation become important and lead to the formation of crystallites distributed throughout the whole resolidified volume.
Modeling and basic data for streamer dynamics in N2 and O2 discharges
Authors: Kanzari Z. , Yousfi M. , Hamani A.
Published: July 2002

A second order hydrodynamics model of streamer dynamics is developed without using the classical restrictive approximations concerning the source term of the conservation equation of electron energy. The first three moments of the Boltzmann equation coupled to the Poisson equation for the space charge electric field are closed using the local energy approximation. The basic data needed for the present second order model for electrons and the first order model for ions are obtained from the solution of the steady state Boltzmann equation and the Monte Carlo simulation, respectively. The electron data associated with the source term of the electron energy conservation equation and which correspond to the different electron–molecule processes considered in our N2 and O2 discharges (ionization, attachment, excitation, elastic, and superelastic collisions) are explicitly given. Then, we give the results obtained with the present second order hydrodynamics model and concerning N2 and O2 gases at atmospheric pressure between parallel plate electrodes under overvoltage conditions. Comparisons are also performed with the results obtained from the classical first order model generally used in the literature.
Model for the recombination velocity of silicon interstitials at nonoxidizing interfaces
Authors: Tsamis C. , Tsoukalas D.
Published: July 2002

In this work we propose a model for the time dependence of the surface recombination velocity of silicon interstitials at nonoxidizing (inert) Si/SiO2 interfaces. The model takes into account the experimentally observed diffusion of silicon interstitials through a thermal oxide. Comparison with previously published experimental results from various sources as well as from new experiments, which we present here, demonstrate that the proposed model can accurately simulate one-dimensional as well as two-dimensional experiments. Analysis of the experimental data permits the estimation of the segregation coefficient of silicon interstitials at the silicon–oxide interface.
Optogalvanic transients in the 1s2,4→2p1,3 excitations of radio frequency neon plasma
Authors: Yao Xuan , Kumar D. , McGlynn S. P.
Published: July 2002

The optogalvanic effects (OGE) induced by pulsed laser excitation of Ne 1s2,4→2p1,3 transitions in a low power, ∼30 MHz radio frequency Ne discharge at ∼5 Torr are described. The polarity (sign) of the OGE signal is controlled by perturbations of the 1sj populations. The steady state 1s4 population is ∼101 times larger than the 1s2 population and the OGE signals for 1s4→2p1,3 excitations are correspondingly stronger than those for 1s2→2p1,3 excitations. The plasma temperature is found to be ∼1000 K. The excitations 1s2,4→2p3 are more efficient at signal production than the 1s2,4→2p1 excitations, which is contrary to prediction. The OGE signals are consequences of: (1) perturbation and reequilibration of the metastable 1s3 and 1s5 populations; (2) radiatively trapped 1s2→1S0 photons; and (3) collisionally induced 1s2, 1s4↔1s3, 1s5 energy transfer. The OGE signal components, both the ionization and photoacoustic constituents, are temporally coincident only when the immediate causative agents are trapped photons. When otherwise produced, the photoacoustic part is delayed relative to the ionization component by the time required for the acoustic wave to travel from the locus of excitation to the sensitive region(s) of the plasma.
Spontaneous lifetime control of quantum dot emitters in apertured microcavities
Authors: Graham L. A. , Huffaker D. L. , Csutak S. M. , Deng Q. , Deppe D. G.
Published: July 2002

Data are presented on modified spontaneous emission rates in quantum dot microcavity arrays. Three-dimensional optical confinement is achieved using apertured microcavities with square aperture sizes varied from 5 to 1 μm on a side. A maximum measured increase in the on-resonance spontaneous emission rate over that off resonance is ∼50%, and we identify this enhancement with apertured modes of the microcavity. Oscillations in the spontaneous emission rate versus wavelength correspond to spectral resonances in the higher order aperture modes.
Structural changes induced by nitrogen in the a-Ge:H network
Authors: Campomanes R. R. , Comedi D. , Chambouleyron I.
Published: July 2002

The structural modifications induced by the incorporation of nitrogen (2 at.%<CN<6 at. %, CN=N concentration) in radio frequency-sputtered hydrogenated amorphous germanium (a-Ge:H) has been studied by infrared spectroscopy. At all N concentrations there is a substantial increase of the density of voids, as indicated by the strength of the absorption band associated with the surface-like stretching vibration of the Ge–H dipole. As CN increases, the peak position of this mode shifts to smaller values. These effects are also detected through the analysis of the wagging vibration modes of the Ge–H dipole. Comparison of the present results with similar data for H-free a:GeN indicates that the presence of H in the reaction hinders the incorporation of the NGe3 skeletal group, characteristic of β-Ge3N4. The overall data indicate that almost all N incorporates in N–H and N–H2 configurations, which are responsible for the formation of a large quantity of small-size voids.
Dynamic FE simulation of μMAG standard problem No. 2 (invited)
Authors: Streibl B. , Schrefl T. , Fidler J.
Published: July 2002

μMAG standard problem No. 2 was studied using a three-dimensional finite element simulation based on the solution of the Gilbert equation. Asymptotic boundary conditions were imposed in order to compute the demagnetizing fields and a Gilbert-damping parameter (α=1.0) was used to drive the system towards equilibrium. The coercivities observed for the thin elongated platelet on which standard problem No. 2 is based show a slight dependence on its size. The width of the particle was varied from 1 to 30 times the exchange length while keeping the aspect ratio of 5:1:0.1 unchanged. An external field is applied parallel to the [111] direction, giving values of the coercive field ranging from −0.056 to −0.04 in units of the saturation magnetization Ms. With the external field applied parallel to the long axis of the particle a strong dependence of the coercivity on its size is found which can be attributed to different reversal mechanisms.
Two-plane focusing of high-space-charge sheet electron beams using periodically cusped magnetic fields
Authors: Basten M. A. , Booske J. H.
Published: July 2002

Numerical and theoretical analyses show that stable, two-plane focusing of finite width, elliptical cross section, sheet electron beams with high space charge (low voltage, high current density) can be accomplished using periodically cusped-magnetic (PCM) fields. Magnetic field strength requirements for focusing high-space-charge sheet beams are within technological capabilities of modern permanent magnet technology. Both an offset-pole PCM stack and a PCM stack combined with a periodic quadrupole magnet (PQM) edge array are shown to be effective for two-plane sheet beam confinement. The PCM-PQM hybrid configuration offers inherent advantages for independent adjustment of confinement fields to achieve beam matching (minimum ripple) in both transverse dimensions. The offset-pole configuration offers the advantage of open-side access for applications such as vacuum electronic microwave devices. It is also shown that PCM-focused sheet beam envelope stability obeys criteria equivalent to that previously identified for round-cross-section electron beams in periodic permanent magnet focusing.
Magnetic field effect on the transport process of paramagnetic or diamagnetic substances in the aqueous solution
Authors: Mogi Kunio , Sakihama Tatsuya , Hirota Noriyuki , Kitazawa Koichi
Published: July 2002

The influence of magnetic field on the mixing process of two aqueous solutions with different concentration of ions was examined. The two cells, containing solutions of MnCl2, CuSO4⋅5H2O and MgSO4⋅7H2O and separated by a porous membrane, were placed at various positions in a horizontal bore of a superconducting magnet of maximum field 8 T. Significant suppression and enhancement effects were observed in the former two solutions, whereas no effects were found in the MgSO4⋅7H2O solution. The magnetic field effects observed were discussed in terms of bulk solution flow induced by the gravity which was prevented or enhanced by the magnetic field gradient.
Investigation of the magnetic properties of SmFe10Mo2 and SmFe10Mo2H in high magnetic field
Authors: Isnard O. , Guillot M.
Published: July 2002

We have investigated the magnetic properties of the ferromagnetic compounds SmFe10Mo2 and SmFe10Mo2H; these compounds are potential candidates for high performance permanent magnets. High field magnetization measurements have been performed up to 24 T on both SmFe10Mo2 and SmFe10Mo2H compounds. The isothermal magnetization curves have been recorded at 4.2 and 300 K on powder samples. At room temperature both compounds exhibit a uniaxial behavior, with the easy magnetization direction along the tetragonal axis. Anisotropy parameters K1, and K2 have been extracted from a fitting of the magnetization curve. The insertion of hydrogen is found to increase the K1 parameter. The Curie temperature and the saturation magnetization are also presented for SmFe10Mo2 and SmFe10Mo2H, and the major changes upon hydrogenation are discussed. If the external field is applied perpendicular to the alignment direction of the powder, anomalous magnetization behaviors are observed in both compounds especially at low temperature. The shape of this anomaly is modified by the hydrogen insertion.
[
OH
(X)]
measurements by resonant absorption spectroscopy in a pulsed dielectric barrier discharge
Authors: Hibert C. , Gaurand I. , Motret O. , Pouvesle J. M.
Published: July 2002

Good understanding of the different phases of the plasma-chemistry involved is essential for the development of nonthermal plasma technologies for pollution control. These techniques are often based on the dissociation of parent gases to produce radicals that, in turn, decompose the toxic compounds. Our research concerns OH radical production in a pulsed dielectric barrier discharge (DBD). OH[A 2Σ+–X 2Π(0,0)] emission in argon-water vapor gas mixtures has been studied. Particular attention has been paid to the influence of water vapor partial pressure on the lifetime and intensity of emitted fluorescence in order to develop a pulsed DBD ultraviolet light source for spectroscopic investigation. This source was used to perform OH(X 2Π) time-resolved average absolute density measurements in other DBD discharges based on resonant absorption spectroscopy. This diagnostic has been validated in argon and air-water vapor mixtures. The temporal behavior of the density OH(X 2Π) radicals after a pulse discharge has been studied in argon and air with and without 500 ppm of trichloroethylene. This simple and inexpensive tool, compared to more sophisticated laser absorption or laser-induced fluorescence measurements for plasma investigation, is very useful for characterizing the OH radical potential for pollutant oxidation.
Carbon and lithium spectra from a vacuum spark
Authors: Podder N. K. , Clothiaux E. J.
Published: July 2002

Carbon and lithium spectra are obtained from vacuum spark discharges using a grazing-incidence flat-field spectrometer. Hydrogen and helium-like lines are identified in the carbon spectrum, where only the hydrogen-like lines are found in the lithium spectrum. The absence of the helium intercombination line in the carbon plasma indicates that the electron density is greater than 1×1019 cm−3. The electron density is found to be 2.8–4.4×1020 cm−3 for carbon and 7.3–10.2×1018 cm−3 for lithium plasma using the method of Stark width analysis for hydrogen-like carbon and lithium lines of the Lyman β and Lyman δ of each element. This method was developed and implemented earlier by E. V. Aglitskii, P. S. Antsiferov, I. M. Gaisinskii, E. A. Oks, and A. M. Panin (Institute of Spectroscopy Preprint #13, Troitzk, Moskow region, USSR, 1985). The Lyman β and Lyman δ lines are chosen for our analysis because these two lines do not have the central Stark components. A pinhole picture is obtained for the carbon plasma, and the pinch diameter is measured to be 100 μm from the equal density profile scan of the pinhole photograph. The optical depth and the escape factor are incorporated into the intensity calculation of the lines using an effective plasma size of 50 μm. In this calculation, the intensity ratio of the Lyman α to the helium-like γ line (1s4p→1s2) yields an electron temperature of about 90–95 eV for the carbon plasma. No temperature for the lithium was possible due to the unavailability of the helium-like lines.
Hydrogenation and annealing effects on the trapping times of the minority carriers in In-doped CdTe epitaxial layers grown on p-CdTe (211) substrates
Authors: Yuldashev Sh. U. , Bolotin I. L. , Hou Y. B. , Leem J. H. , Jeon H. C. , Kang T. W. , Kim T. W.
Published: July 2002

Photoconductivity (PC) measurements on as-grown, annealed, hydrogenated, and hydrogenated and annealed In-doped CdTe epitaxial films grown on p-CdTe (211) substrates by molecular beam epitaxy have been performed in order to investigate the behavior of the trapping times of minority carriers in In-doped CdTe films due to annealing and hydrogenation. The results of the PC decay curve showed a slow component with a time constant of a few milliseconds and this behavior was related to the existence of deep trap levels corresponding to minority carriers. The activation energies of the traps, as determined from the temperature dependence of the PC decay times, were (Ev+0.35) and (Ev+0.43) eV for the as-grown and hydrogenated In-doped CdTe epilayers, respectively. The trapping times of the minority carriers were significantly reduced by the hydrogenation treatment.
Anisotropic electrical conduction and reduction in dangling-bond density for polycrystalline Si films prepared by catalytic chemical vapor deposition
Authors: Niikura Chisato , Masuda Atsushi , Matsumura Hideki
Published: July 2002

Polycrystalline Si (poly-Si) films with high crystalline fraction and low dangling-bond density were prepared by catalytic chemical vapor deposition (Cat-CVD), often called hot-wire CVD. Directional anisotropy in electrical conduction, probably due to structural anisotropy, was observed for Cat-CVD poly-Si films. A novel method to separately characterize both crystalline and amorphous phases in poly-Si films using anisotropic electrical conduction was proposed. On the basis of results obtained by the proposed method and electron spin resonance measurements, reduction in dangling-bond density for Cat-CVD poly-Si films was achieved using the condition to make the quality of the included amorphous phase high. The properties of Cat-CVD poly-Si films are found to be promising in solar-cell applications.
Pulsed laser deposition of ZnO nanocluster films by Cu-vapor laser
Authors: Dinh L. N. , Schildbach M. A. , Balooch M. , McLean W.
Published: July 2002

The dependence of stoichiometry, grain size, cathodoluminescence colors, adhesion, and surface morphology of zinc oxide films, deposited by a Cu-vapor laser at room temperature, as a function of oxygen ambient pressure during synthesis were investigated. Auger electron spectroscopy showed that ZnO films with a Zn/O ratio close to 1 were obtained at oxygen pressures >10−1 Torr. X-ray diffraction revealed that pulsed laser deposited zinc oxide films were composed mainly of nanocrystals, the average grain size of which grew from 5 to 17.5 nm as the oxygen pressure was increased from 10−5 to 1 Torr. The surface morphology of the films, as determined by secondary electron microscopy, also exhibited increasing roughness as the grain size increased. Films grown in an oxygen pressure >1.5×10−1 Torr glowed blue under electron bombardment, while slightly substoichiometric films glowed white under similar excitation. Films deposited in an oxygen background pressure up to 1.5×10−1 Torr exhibited good adhesion to substrates. Deposition rate on the order of 4.6 nm/s was obtained.
Effect of a magnetic field on the plasma plume from Hall thrusters
Authors: Keidar Michael , Boyd Iain D.
Published: July 2002

An axial profile of the quasineutral plasma jet exhaust from a Hall thruster is studied. The plasma jet expansion is modeled using the sourceless steady-state hydrodynamic equations. It is considered that the plasma jet has a conical shape with a half angle of about 40°. The magnetic field surrounding the Hall thruster exit is included in the calculation. It is found that a magnetic field may significantly affect the axial profile of the plasma potential. For instance, in the case of zero magnetic field, the plasma potential is about −10 V at 1 m from the thruster exit, while in the case of a 0.1 T magnetic field, the plasma has a potential of about +25 V. Results predicted by the model are found to be in good agreement with experimental data for three different Hall thruster designs.
Angular dependence of exchange anisotropy in Ni81Fe19/CrMnPtx bilayers
Authors: Xi Haiwen , White Robert M.
Published: July 2002

We have investigated the unidirectional exchange anisotropy between a ferromagnetic (FM) Ni81Fe19 film and a disordered antiferromagnetic (AF) CrMnPtx (x=3, 6, or 9) film. The angular dependence of the exchange coupling in these FM/AF bilayers has been measured. We show that the complex angular dependence of this exchange coupling can be understood by a simple Stoner–Wohlfarth model involving only a uniaxial anisotropy and a unidirectional exchange coupling. Numerical results are in excellent agreement with the experimental data.
Effects of fluorine–oxygen substitution on the dielectric and electromechanical properties of lead zirconate titanate ceramics
Authors: Guiffard B. , Audigier D. , Lebrun L. , Troccaz M. , Pleska E.
Published: July 2002

In this study, a fluorine–oxygen substitution in lead zirconate titanate (PZT) ceramics with a nominal composition of Pb0.89(Ba, Sr)0.11(Zr0.52Ti0.48)O3 (PZT) doped with 1% MgO is proposed. The evolution of four dielectric and electromechanical coefficients—εr, tgδ, d33, and Qm—with increasing fluorine concentration showed that (MgO and F)-doped PZT ceramics are harder than only MgO-doped PZT (0 at. % F). The influence of the F–O substitution on the temperature dependence of the frequency constant N33 and the stress dependence of the piezoelectric coefficient d33 was investigated. A hysteretic free response of N33 and the lowest stress dependence of d33 were obtained for the (MgO and 4 at. % F)-doped PZT specimen. This material also exhibits the highest Qm in the (MgO and F)-doped PZT family and seems to be stoichiometric and without oxygen vacancies. For comparison, both the temperature and stress dependences of two commercial PZT ceramics are shown. The study of the influence of the Zr/Ti ratio on the temperature dependence of N33 revealed that fluorine stabilizes the rhombohedral phase/tetragonal phase interface. Both types of stability, versus temperature and uniaxial mechanical stress, may be linked to the domain wall configuration stabilization by Mg2+–F− dipoles which are less mobile than Mg2+–VO ones.
Dimension scaling of low frequency noise in the drain current of polycrystalline silicon thin-film transistors
Authors: Angelis C. T. , Dimitriadis C. A. , Farmakis F. V. , Brini J. , Kamarinos G. , Miyasaka M.
Published: July 2002

Experimental results of low frequency noise in polycrystalline silicon thin-film transistors (polysilicon TFTs) with varying gate dimensions (constant gate width W and varying gate length L) are presented. The power spectral density of the drain current fluctuations SI was found to depend linearly on the inverse of the effective gate area Ag,eff which is related to the gate area W×L and the number of grains present within the transistor channel. This result implies localization of the low frequency noise sources on the gate oxide-polysilicon interface and on the grain boundaries. The 1/Ag,eff scaling law must be taken into account for correct estimation of trap densities in polysilicon TFTs.
Space-charge recombination currents and their influence on the dc current gain of AlGaAs/GaAs Pnp heterojunction bipolar transistors
Authors: Ekbote S. , Cahay M. , Roenker K. , Kumar T.
Published: July 2002

The effects of Shockley–Read–Hall, Auger, radiative, and intrinsic surface base recombination processes in the emitter-base space-charge region on the current gain of Pnp AlGaAs/GaAs heterojunction bipolar transistors are analyzed. At low forward emitter-base bias, the current gain of a typical Pnp AlGaAs/GaAs heterojunction bipolar transistor is shown to be reduced substantially below its value calculated while neglecting recombination currents in the emitter-base space-charge region. Excellent agreement between theory and experiment is found for the current gain variation versus collector current density for a Pnp device recently reported by Slater et al. [IEEE Electron Device Lett. 15, 91 (1994)].
Dynamic studies of polymerization in liquid crystal-polymer mixtures
Authors: Fuh Andy Y.-G. , Tsai M.-S. , Fan Y.-H. , Lee C.-R. , Lo K.-Y.
Published: July 2002

This work studied the dynamic behavior of polymerization in films of liquid crystal (LC)-polymer mixtures by using the pump-probe technique. Chopped Ar+ laser pulses were used as pump beams, and probed by a cw He—Ne laser. The experimental results indicated that the transmission of the probe beam was modulated in response to the chopping frequency of the pump beam. The modulation was such that transmission during the on-time of the pump beam was initially smaller than, then equal to, and finally larger than that in the off-time. Analyzing the transparency difference between the films with and without the Ar+ laser pulse allows us to recognize the three stages of polymerization process, initiation, propagation, and termination. Moreover, both the LC content in the sample and the chopping on/off ratio of the pump beam significantly affected the turning point occurred and the modulation amplitude of the probe beam. A model is proposed to explain these observed results.
Optical properties of the quaternary alloy system Culn(SxSe1−x)2 investigated by spectroscopic ellipsometry
Authors: Zeaiter Khalil , Llinarès Claude
Published: July 2002

Experimental results for the pseudodielectric function 〈ε〉 of CuIn(SxSe1−x)2 alloy system are reported. The investigation has been performed on the full composition range using crystals cut from ingots of 10 mm diameter and 40 mm length. The ingots were grown using the classical Bridgman method. Ellipsometric measurements were performed at room temperature in the range 1.5–5.5 eV. The energies of critical points have been determined from the imaginary part of the dielectric function. The transition energies (E1, E2, E3, and E4) are found to shift linearly to higher energies as the sulfur content increases. The copper d level is found to be dominant in the ranges 2.5–3.5 eV for CuInSe2 and 2.8–4 eV for CuInS2.
GaInAsSb/InP heterojunction band offset: Measurement by absorption spectroscopy
Authors: Chang J. R. , Su Y. K. , Lu Y. T.
Published: July 2002

We report the study of unstrained Ga0.64In0.36As0.84Sb0.16/InP multiple-quantum-well structures by room-temperature absorption spectroscopy. In the absorption spectra, strong and well-resolved exciton peaks were observed. By comparing these transition energies with a theoretical calculation, we estimated the valence-band offset ratio to be 0.7±0.05 for the Ga0.64In0.36As0.84Sb0.16/InP heterojunction.
Electrical processes in nonpolar liquids based on initial transient response and recovery
Authors: Richley Edward A. , Mikkelsen James C.
Published: July 2002

Experimental and theoretical results for neutral barium petronate solutions in isopar L are reported. The experimental techniques are novel in that they include the use of ac conductivity measurements during transient depletion and recovery. Use is made of a one-dimensional numerical model to extract actual ion mobilities. Deviations from a one-dimensional theoretical model are shown to be due to a fluid instability which grows in the highly stressed space charge regions near the electrodes. This instability is examined theoretically and is shown quantitatively to have a predictable electrohydrodynamic origin. Furthermore, suspended particles are used to confirm the existence of unstable motion, and also to unambiguously determine the polarity of ions associated with each mobility. Under subsequent zero bias, recovery of the solutions from nearly complete depletion is shown to originate at the solid surfaces of the test cell.
Local responsivity in quantum well infrared photodetectors
Authors: Ershov M.
Published: July 2002

This article presents a theoretical and computational study of physical effects in quantum well infrared photodetectors (QWIPs) under localized excitation. The steady-state photoresponse involves the formation of the dipole layer near the photoexcited QW. The nonequilibrium (fast transient) responsivity is associated with the photoexcitation and sweep out of carriers from the QW region. Both steady-state and nonequilibrium local responsivities depend on coordinate across the QWIP, and decrease from emitter to collector. The nonequilibrium responsivity decreases to zero over a distance equal to the drift length near the collector. The proposed analytical models of the steady-state and nonequilibrium responsivities are in excellent agreement with the results of numerical simulation.
Electron stimulated oxidation of Al(111) in H2O vapor: Dipole orientation effects in the Al2O3 thin film
Authors: Popova I. , Zhukov V. , Yates J. T. , Chen J. G.
Published: July 2002

The electron stimulated oxidation of Al(111) using H2O(g) as a source of oxygen has been investigated at 300 K using near edge x-ray absorption fine structure (NEXAFS) and Auger electron spectroscopy. Irradiation with electrons (100 eV, 50 μA/cm2) produced thick Al2O3 film layers (up to 15 Å), compared to the films grown thermally (4 Å) by the same water exposure. A preferential normal orientation of the O–Al bonds was found for the films grown by the electron assisted process, causing the O K-edge NEXAFS spectra to depend on the incident angle of the polarized x-ray beam. In contrast, little polarization of the O–Al bonds was found for the case of Al2O3 films grown by thermal oxidation in H2O(g).
Spatial and angle distribution of internal stresses in nano- and microstructured chemical vapor deposited diamond as revealed by Brillouin spectroscopy
Authors: Krüger J. K. , Embs J. P. , Lukas S. , Hartmann U. , Brierley C. J. , Beck C. M. , Jiménez R. , Alnot P. , Durand O.
Published: July 2002

The use of a new Brillouin spectroscopic technique evidences the existence of internal stresses in white plasma assisted chemical vapor deposited diamond and allows a first assessment concerning their magnitude. The evaluation of the internal stresses is based on the pressure coefficients related to the longitudinal and transverse elastic constants.
Unpinning of the Au/GaAs interfacial Fermi level by means of ultrathin undoped silicon interlayer inclusion
Authors: Ivanco J. , Kobayashi H. , Almeida J. , Margaritondo G.
Published: July 2002

We present a photoemission spectroscopy study of As-rich n-GaAs(001) surface modified by the deposition of an undoped silicon overlayer with thickness quite narrowly covering the interval from ∼4 to 25 Å. We observed a nonmonotonic relation between the surface band bending and Si overlayer thickness with the lowest surface potential at about 10-Å-thick silicon overlayer. The valence band spectra inspection reveals the double leading edge incidental to alignment of the valence band edges of GaAs and Si overlayer with the offset of 0.29 eV and various theoretical models of semiconductor–semiconductor interfaces are discussed. Based on the influence of the silicon layer on both band bending and Schottky barrier height, it is concluded that the Schottky barrier height of Au/Si/GaAs structure evolves towards the Schottky limit for an ideal (par definition free of interface states) Au/GaAs junction as the silicon interlayer thickness reaches about 10 Å.
Superstructure ordering in lanthanum-doped lead magnesium niobate
Authors: Fanning D. M. , Robinson I. K. , Jung S. T. , Colla E. V. , Viehland D. D. , Payne D. A.
Published: July 2002

Superstructure reflections of lead magnesium niobate (PMN), Pb(Mg1/3Nb2/3)O3, were measured with synchrotron radiation x-ray diffraction. Our data conclusively demonstrate that the (h+12,k+12,l+12)-type reflections are the result of chemical ordering between the Mg and Nb ions in domains of 50 Å. Structure factor analysis of these peaks reveals an oxygen displacement within the ordered regions of 0.044(3) Å along a 〈100〉 direction towards the Nb ion. Single crystals of La-doped PMN (La–PMN) exhibit much larger chemically ordered regions (up to 900 Å for 10% La–PMN). Structural analysis of the La–PMN suggests that as the ordered region increases in size, the ordering changes from complete Nb:Mg ordering and approaches Nb:(Mg2/3Nb1/3) ordering. Although anticipated from electrostatic energy arguments, our conclusions are based on a clear trend in the bond length of the mixed site as a function of La doping.
Cherenkov waveguide laser driven by an electron bunch
Authors: Oganesyan S. G.
Published: July 2002

This article presents the theory of a Cherenkov waveguide laser driven by an electron bunch. The concepts of a long bunch and a short bunch have been introduced. As it is shown the long bunches of a Gaussian form produce electromagnetic pulses, which have exp[exp(−τ2)] type shape. These pulse lengths are directly proportional to the bunch ones. In the case of the short bunches (of a Gaussian shape as well), we have discovered a saturation effect. Namely, all electromagnetic pulses have the same length and nearly rectangular shape. Analysis showed that the pulse length depends only on the waveguide length and on the detuning of the phase velocity and the energy flux velocity of an amplified wave. The case when an electron beam comprises Nb identical bunches is considered as well. It is shown that such a device has (1) a regime when all bunches operate coherently and (2) a regime when they operate independently. The obtained results are illustrated by a numerical example.
Ion channeling studies on mixed phases formed in metalorganic chemical vapor deposition grown Mg-doped GaN on Al2O3(0001)
Authors: Sundaravel B. , Luo E. Z. , Xu J. B. , Wilson I. H. , Fong W. K. , Wang L. S. , Surya C.
Published: July 2002

Rutherford backscattering spectrometry and ion channeling were used to determine the relative quantities of wurtzite and zinc-blende phases in metalorganic chemical vapor deposition grown Mg-doped GaN(0001) on an Al2O3(0001) substrate with a GaN buffer layer. Offnormal axial channeling scans were used. High-resolution x-ray diffraction measurements also confirmed the presence of mixed phases. The in-plane orientation was found to be GaN[11̄0]‖GaN[112̄0]‖Al2O3[112̄0]. The effects of rapid thermal annealing on the relative phase content, thickness and crystalline quality of the GaN epilayer were also studied.
Temperature-dependent transport properties of InAs films grown on lattice-mismatched GaP
Authors: Gopal V. , Souw Victor , Chen E.-H. , Kvam E. P. , McElfresh M. , Woodall J. M.
Published: July 2002

Hall effect and electrical resistivity measurements were carried out on undoped InAs thin films grown by molecular-beam epitaxy directly on (001) GaP substrates. The large lattice mismatch between these two compounds results in a high density array of misfit dislocations at the heterointerface and threading dislocations in the InAs epilayer. The threading dislocation density varies with epilayer thickness, with the largest proportion being present near the heterointerface. This leads to variation of both the carrier concentration and electron mobility with thickness. Consequently, a multilayer analysis was used to interpret the transport data. This analysis yields a temperature-independent carrier concentration, which indicates degenerate donor levels in this narrow band-gap material. Room temperature mobilities in excess of 10 000 cm2/V s were obtained for thick InAs layers despite dislocation densities of 1010 cm−2. The relative insensitivity of the mobility to temperature suggests that temperature-independent scattering dominates over ionized impurity/defect and phonon scattering.
Optical storage effect due to photopolymerization of mesogenic twin molecules
Authors: Hoischen A. , Kitzerow H.-S. , Kürschner K. , Strohriegl P.
Published: July 2002

The photopolymerization of diacrylate mixtures containing a nematic twin compound and a chiral dopant leads to perfectly stable, highly crosslinked cholesteric networks. The Bragg reflection spectra of the respective monomer and polymer mixtures were measured and the influences of the chemical structure, the temperature and the concentration of chiral dopant on the reflection wavelength was studied. Subsequent UV exposures of different parts of the sample at different temperatures are suitable to generate colored patterns. Deposition of several cholesteric films with different Bragg wavelengths results in additive color mixing.
Stress, resistance, and phase transitions in NiCr(60 wt %) thin films
Authors: Brückner W. , Pitschke W. , Thomas J. , Leitner G.
Published: July 2002

The evolution in both stress and resistance has been investigated on sputtered NiCr(60 wt %) resistive films during annealing (temperature cycles to maximum 700 °C). Aiming at the correlation of stress, resistance, and microstructure, samples from measurements to various maximum temperatures were analyzed by x-ray diffraction and transmission electron microscopy including microanalysis. A series of metastable phases was found with increasing temperature: the as-deposited amorphous phase a, the supersaturated body-centered-cubic (bcc) solid solution αss(Cr) (400 °C), and the tetragonal σ phase (500 °C). This was followed by the equilibrium two-phase alloy bcc α(Cr) plus face-centered-cubic γ(Ni) (600 °C). The phase transitions, characterized by differential scanning calorimetry, were found to be exothermic. The transition a→αss(Cr) results in a distinct tensile-stress component due to material densification. The resistivity is sharply decreasing and the temperature coefficient of resistance is changing from negative to positive values during the a→αss(Cr) transition.
Transmission electron microscopy study of hydrogen-induced degradation in strontium bismuth tantalate thin films
Authors: Poonawala N. , Dravid V. P. , Auciello O. , Im J. , Krauss A. R.
Published: July 2002

The fabrication of nonvolatile ferroelectric random access memories based on SrBi2Ta2O9 (SBT) or other ferroelectric capacitors require exposure of these capacitors to processing gases mixtures including hydrogen. This results in a strong degradation of the capacitor electrical properties, mainly due to the interaction of hydrogen with the ferroelectric layer. Using surface analysis methods, we previously determined that the hydrogen-induced degradation of SBT capacitors might be partially due to the degradation of the near surface region of the SBT layer. It was also demonstrated that oxygen annealing after the hydrogen exposure results in the recovery of the degraded SBT surface layer and the electrical properties of the capacitor. We have now performed detailed cross sectional transmission electron microscopy studies of virgin, hydrogen, and oxygen annealed SBT/Pt/TiO2/SiO2/Si heterostructures. These studies combined microstructural imaging with a nanoscale compositional analysis of the SBT layer as a function of depth from the free surface of the film and across grain boundaries. High resolution energy dispersive x-ray spectroscopy revealed that hydrogen annealed SBT layers have a deficiency of Bi up to a depth of ∼30 nm underneath the free surface, and that there is accumulation of Bi at the grain boundaries of pristine, hydrogen, and oxygen-recovery annealed SBT layers. This suggests that the diffusion of Bi is largely controlled by grain boundaries and they play a critical role in controlling the electrical properties of SBT capacitors.
Characterization of arsenic dose loss at the Si/SiO2 interface
Authors: Kasnavi Reza , Sun Yun , Mo Renee , Pianetta Piero , Griffin Peter B. , Plummer James D.
Published: July 2002

Careful sample preparation and secondary ion mass spectroscopy have been used to characterize arsenic dose loss to the silicon–oxide interface. Using high resolution x-ray photoelectron spectroscopy for microprofiling, we have directly observed the pileup of arsenic at the silicon dioxide–silicon interface. At least half of the pileup is shown to be on the silicon side of the interface in the first monolayer of silicon. Monolayer chemical oxidation and etching are successfully used to profile this pileup in silicon. This pileup contains most of the arsenic dose loss that occurs during transient enhanced diffusion. This result is crucial to correctly model the dose loss and provides physical justification for using a trap/detrap model at the interface, which is necessary to account for the fact that the arsenic surface concentration remains constant during an anneal and the fact that the dose loss is partially reversible. Finally, we have found that normal etching of the oxide in dilute hydroflouric acid and subsequent rinsing in water and exposure to air causes a permanent loss in arsenic dose.
Electrical characterization, metallurgical investigation, and thermal stability studies of (Pd, Ti, Au)-based ohmic contacts
Authors: Chor E. F. , Zhang D. , Gong H. , Chong W. K. , Ong S. Y.
Published: July 2002

Although Pd/Ti/Pd/Au contacts are similar to their Pt/Ti/Pt/Au counterparts in providing low specific contact resistance, ρc, the former exhibits long-term thermal stability. Their projected mean times to 50% increase in ρc(μ50) at 150 °C to p+-GaAs (⩾3.43×1015 h) are higher than those of the latter by over five orders of magnitude. Contacts to p+-In0.53Ga0.47As are not as thermally stable, with a much lower albeit respectable μ50 at 150 °C of ⩾2.25×105 h. Contacts with an interfacial Pd layer provide ρc’s that are at least two times lower than those without, and the presence of an oxide layer (GaxTiyOz) at the Ti/GaAs interface is identified as a possible cause. Pd–Ga–As phases are formed at the Pd/GaAs interface, being As-rich (PdxGayAs) initially and convert to Ga-rich phases (PduGavAs) upon a high temperature anneal and the eventual composition depends on the evaporated interfacial Pd thickness and annealing conditions. This could probably explain the existence of an optimum interfacial Pd layer thickness of 100 Å for achieving the lowest ρc. The Ga-rich PduGavAs phases formed are inferred to cause the liberation of As atoms from the GaAs lattice, thus enabling them to diffuse out to the Ti and react to form TixAsy phases that bind the As from further out-diffusion. This has in turn led to the accumulation of As at the Pd/Ti interface.
The sputtering of radioactive recoil nuclides induced by fast neutron
Authors: Ye Bangjiao , Kasugai Yoshimi , Ikeda Yujiro , Fan Yangmei , Zhou Xianyi , Du Jiangfeng , Han Rongdian
Published: July 2002

The sputtering of radioactive recoil nuclides in nonelastic reactions induced by 14.9 MeV neutrons has been studied by both the theoretical calculation and the experimental measurement. The sputtering yields of recoil nuclides have been calculated for nonelastic neutron reaction based on the nuclear reaction dynamic and sputtering theory. Systematics of reduced sputtering yields depending on the mass number of recoil nuclides have been found for (n,2n), (n,p), (n,α) and (n,np) reactions. These systematics have also been demonstrated in the experimental measurement. Based on the differences of the calculating results and experimental ones, a universal revised calculating formula is presented for predicting the reduced sputtering yields induced by fast neutrons.
Diffusion of low-dose implanted aluminum in silicon in inert and dry O2 ambient
Authors: Ortiz Ch. , Mathiot D. , Dubois Ch. , Jérisian R.
Published: July 2002

Redistribution of a high-energy (3 MeV) low-dose (5×1013 cm−2) implanted aluminum profile in silicon under inert and dry O2 is investigated in the temperature range (900–1100 °C). The chemical profiles were measured by secondary ion mass spectroscopy and the effective diffusivities were extracted from the experimental data from fitting with calculated profiles obtained by numerical resolution of Fick’s law. It is found that the aluminum diffusion is significantly enhanced during thermal oxidation. The diffusivity enhancement decreases with the temperature. Comparison with boron data suggests that the mechanism of aluminum diffusion in silicon is similar to that of boron.
Disorder dependence of the magnetic moment of the half-metallic ferromagnet NiMnSb from first principles
Authors: Orgassa D. , Fujiwara H. , Schulthess T. C. , Butler W. H.
Published: July 2002

Using half-metallic ferromagnets in spin-dependent devices, like spin valves and ferromagnetic tunnel junctions, is expected to increase the device performance. However, using the half-metallic ferromagnet NiMnSb in such devices led to much less than ideal results. One of the possible sources for this behavior is atomic disorder. First-principles calculations of the influence of atomic disorder on the electronic structure of NiMnSb underline the sensitivity of half-metallic properties in NiMnSb to atomic disorder. In this article, we report on the disorder dependence of the total magnetic moment calculated by applying the layer Korringa–Kohn–Rostoker method in conjunction with the coherent potential approximation. We consider the following types of disorder: (1) intermixing of Ni and Mn, (2) partial occupancy of a normally vacant lattice site by Ni and Mn, and (3) partial occupancy of this site by Mn and Sb. In all cases the composition is kept stoichiometric. All three types of disorder decrease the moment monotonically with increasing disorder levels. For the experimentally seen disorder of 5% Mn and 5% Sb on the normally vacant lattice site, the total moment is decreased by 4.1%. The results suggest that precise measurement of the saturation magnetization of NiMnSb thin films can give information on the disorder.
Study of reversible and irreversible magnetization processes of coprecipitated cobalt ferrite
Authors: Medina-Boudri A. , Bueno-Baqués D. , Fuentes-Cobas L. , Miki-Yoshida M. , Matutes-Aquino J.
Published: July 2002

Cobalt ferrite was obtained by coprecipitation of iron and cobalt sulphates into acetone medium. The Co0.62+Fe0.43+[Co0.42+Fe1.63+]O4 cation distribution was obtained from Mössbauer spectroscopy at room temperature. Saturation magnetization of 74.1 emu/g and an intrinsic coercive field of 528 Oe were measured using a vibrating sample magnetometer. Using the moving Preisach model, separation of reversible (Mrev) and irreversible (Mirr) magnetization components was performed. The parameters η defined as η=(dMrev/dMirr)Hi and km the moving Preisach parameter expressed through the relation η=kmχrev, were evaluated in order to investigate the hysteretic behavior of Mrev. Additional characterization was done in order to investigate the elemental composition, structure, and morphology of the samples.
Precursors of fluorocarbon film growth studied by mass spectrometry
Authors: Teii Kungen , Hori Masaru , Goto Toshio , Ishii Nobuo
Published: July 2002

The precursor species of fluorocarbon film growth at the reactor wall irradiated by an electron cyclotron resonance C4F8 plasma have been studied by using a quadrupole mass spectrometer. The amount of polymeric neutral species [CmFn (m⩾2)] and absolute densities of CFx (x=1–3) radicals in the vicinity of the wall were measured by electron attachment and threshold ionization mass spectrometry, respectively. The trends in the film growth rate as a function of gas residence time, diluted hydrogen concentration, and microwave power were well accounted for by the competition between the incorporation of CFx radicals and positive ions and the removal by F and H atoms. The fluxes of CFx radicals and positive ions incident upon the wall were shown to be comparable with the net condensed carbon flux derived from the growth rate. In contrast, the trends in the amount of polymeric neutrals were not well correlated to the growth rate.
Fe K-edge x-ray magnetic circular dichroism study in R6Fe23 (R=Ho and Y) compounds near compensation temperature
Authors: Chaboy J. , Garcı́a L. M. , Bartolomé F. , Maruyama H. , Uemura S. , Kawamura N. , Markosayan A. S.
Published: July 2002

We present a x-ray magnetic circular dichroism (XMCD) study performed at the Fe K edge in R6Fe23 compounds exhibiting magnetic compensation (R=Ho and Y). The Fe K-edge XMCD signal has been identified as due to both Fe itself and rare-earth contributions. Following a simple two-sublattices model for the analysis of the dichroic signal the contribution of the rare-earth sublattice to total Fe K-edge XMCD signal has been extracted and proven to be directly correlated to the R magnetic moment.