bluuebunny/crossref_metadata_2025 huggingface dataset:
Interface imperfections in metal/Si multilayers
Authors: Windt D. L. , Hull R. , Waskiewicz W. K.
Published: July 2002

The structural and optical properties of Mo/Si and Ru/Si x-ray multilayers prepared by sputter deposition in argon have been examined using high-resolution transmission electron microscopy, optical profilometry, and x-ray and soft x-ray reflectance. We find that for Ru/Si, similar to previous results for Mo/Si, lower argon pressure during deposition results in smoother layers and higher reflectance. For low-pressure deposited multilayers, interfacial roughness is negligible compared to interfacial diffuseness; the presence of amorphous interlayer regions in both of these systems is the major cause of reduced reflectance.
Attractive-mode atomic force microscopy with optical detection in an orthogonal cantilever/sample configuration
Authors: Yang P. C. , Chen Y. , Vaez-Iravani M.
Published: July 2002

An attractive-mode atomic force microscope is described in which the cantilever is held orthogonally with respect to the sample. The technique utilizes a linear differential optical detection scheme for the cantilever vibrations. In this design, the cantilever end is not bent to form a tip. This geometry substantially reduces the possibility of spontaneous jump-to-contact of the tip onto the sample, allowing the tip/sample separation to be set essentially to any desired value. Relatively large- and small-scale results are presented on imaging a smear of red blood cells, demonstrating the resolution and sensitivity.
Generation of electron cyclotron resonance plasmas using a circular TE01 mode microwave
Authors: Hidaka R. , Hirotsu N. , Tanaka N. , Kawai Y.
Published: July 2002

An electron cyclotron resonance plasma using a circular TE01 mode microwave is generated to achieve larger diameters. It is shown that the input power of the circular TE01 mode is efficiently consumed to generate electron cyclotron resonance plasmas. The density and temperature of electrons is around 1012 cm−3 and 3–5 eV at 5 kW input power, respectively.
Temperature dependence of dc drift of Ti:LiNbO3 optical modulators with sputter deposited SiO2 buffer layer
Authors: Nagata Hirotoshi , Kiuchi Kazumasa
Published: July 2002

The temperature dependence of the dc drift of Mach–Zehnder external modulators is evaluated based on Ti diffused LiNbO3 with a sputter deposited SiO2 buffer layer. From Arrhenius’ plots of the results, activation energies of the drift rate between 25 and 80 °C were found to be about 1 eV. The activation energy seems to depend on the structural parameters of the SiO2 layer.
Electron-beam diodes using ferroelectric cathodes
Authors: Ivers J. D. , Schächter L. , Nation J. A. , Kerslick G. S. , Advani R.
Published: July 2002

A new high-current density electron source is described. The source consists of a polarized ferroelectric ceramic disk with silver electrodes coated on both faces. The front electrode consists of a periodic silver grid alternating with exposed ceramic. A rapid change in the polarization state of the ceramic results in the emission of a high-density electron cloud into a 1–10-mm accelerating diode gap. The anode potential is maintained by a charged transmission line. Some of the emitted electrons traverse the gap and an electron current flows. The emitted electron current has been measured as a function of the gap spacing and the anode potential. Current densities in excess of 70 A/cm2 have been measured. The current is found to vary linearly with the anode voltage for gaps ≤10 mm, and typically exceeds the Child–Langmuir current density by at least two orders of magnitude. The experimental data is compared with predictions from a model in which the electrons emitted from the ferroelectric reflex in the diode gap.
Co thickness dependence of the microstructure of Pt/Co multilayers
Authors: Li Z. G. , Carcia P. F. , Cheng Y.
Published: July 2002

We have studied with high resolution electron microscopy the microstructure of polycrystalline Pt/Co multilayers with between 13- and 18-Å-thick Pt and Co thicknesses up to 20 Å. For thin Co (∼4 Å), Pt/Co multilayers had (111)-fcc texture normal to the substrate and a coherent lattice with interplanar spacing of ∼2.2 Å, along the direction of chemical modulation. As the Co thickness increased, coherence was lost, and thicker Co layers had hcp structure with (002) texture, and the film surface roughness increased for less energetic deposition conditions. Coincident with a coherent structure (thin Co), Pt/Co multilayers have a large perpendicular magnetic anisotropy, important for their application in magnetic and magneto-optical devices.
Magnetic properties and read/write characteristics of Co-Cr-(Pt,Ta)/ (Cr-Ti,Cr) thin film media
Authors: Shiroishi Y. , Hosoe Y. , Ishikawa A. , Yahisa Y. , Sugita Y. , Suzuki H. , Ohno T. , Ohura M.
Published: July 2002

A Cr-Ti underlayer is found to enhance the in-plane coercive forces of Co-Cr-Pt and Co-Cr-Ta films; the maximum coercive force was 3.5 kOe for (CoCr0.15)0.84Pt0.16/CrTi0.2. The crystallites of Cr-Ti grow in a more highly oriented and uniform manner than ones of Cr, and their lattice spacings are closer to those of Co alloys than Cr, improving the epitaxial growth of Co-alloy crystallites with c-axis in-plane oriented components on the Cr-Ti underlayer. The crystalline anisotropy constant of Co-Cr-Pt with a high Pt concentration is found by torque measurement to be larger than that of Co-Cr-Ta. These can produce extremely high coercive forces in Co-Cr-Pt/Cr-Ti. The C/Co-Cr-Pt/Cr-Ti thin film media with high coercive forces show excellent read/write characteristics; the linear densities at 50% signal drop are very high, 175 and 101 kFCI, for the C/Co-Cr-Pt/Cr-Ti media at head-to-magnetic layer spacings of 0.01 and 0.07 μm.
Photoinduced magnetic behavior of the amorphous metallic spin glass material Fe3(GaTe3)2
Authors: Wu Biao , Ren Lianwei , O’Connor Charles J. , Jung Jin-Seung
Published: July 2002

A new ternary material Fe3(GaTe3)2 is prepared by using a rapid precipitation metathesis reaction between the Zintl material K3GaTe3 and FeCl2 in aqueous solution. The dc specific resistivity of this material is in the boundary expected for metallic conductors (ρ=4.36×10−3 Ω cm). The dc magnetic susceptibility of Fe3(GaTe3)2 is reported over 6–250 K temperature region and the material is characterized as a spin glass with a freezing temperature of about 22 K. Magnetization data are also reported as both thermal remanent magnetization and isothermal remanent magnetization as a function of magnetizing field. When cooled well below the spin glass freezing temperature, the spin glass material has been observed to exhibit photomagnetic effects consistent with a disruption of the spin glass state caused by UV radiation.
Improved microwave performance of Ag-doped Y1Ba2Cu3O7−δ thin film microstrip resonators
Authors: Pinto R. , Goyal Navdeep , Pai S. P. , Apte P. R. , Gupta L. C. , Vijayaraghavan R.
Published: July 2002

Microwave transmission properties of undoped and Ag-doped laser ablated thin film Y1Ba2Cu3O7−δ microstrip resonators have been studied both on <100≳ MgO and <100≳ LaAlO3 substrates at X-band frequencies. While the Q factor and microwave surface resistance, Rs, of undoped films showed better performance on LaAlO3 as compared to that on MgO, Ag-doped films on LaAlO3 showed far greater improvement as reflected not only by a decrease in Rs but also by a total absence of its microwave power dependence up to 13 dBm at 77 K. These results are explained as due to the influence of Ag in increasing the grain size and grain alignment and thus, significantly decreasing the density of grain boundary weak links which are known to affect the microwave transmission in high temperature superconductor films.
Structural properties of Co/Au superlattices investigated by high-resolution transmission electron microscopy
Authors: Mitwalsky A. , Spörl K. , Weller D.
Published: July 2002

Ion-beam-sputtered and electron-beam-evaporated Co/Au multilayers have been investigated with high-resolution transmission electron microscopy. The multilayers are found to exhibit a strong {111} texture and to contain Co predominantly in the cubic (fcc) phase. Misfit dislocations were directly observed and found to be located near the Co/Au interfaces. Structural features correlate with the magnetic anisotropy. Large crystalline units (vertical columns with ∼50 nm diameter reaching throughout the superlattice) are composed of small regions, a few nanometers in size (nanocrystallites), which are tilted towards each other by a few degrees. The microstructure of the large units remains unchanged for all investigated samples. The average size of the nanocrystallites and their mutual tilting angle vary systematically and are obviously correlated to the magnetic anisotropy. A high-crystalline quality (large nanocrystallites and small tilt angles) increases the value of the magnetic anisotropy constant Keffu. This behavior is unique for the presently investigated Co/Au multilayers independent of the fabrication technique. Moreover, these magnetostructural correlations may as well be valid for other magnetic/nonmagnetic metal superlattices.
Line shape analysis of higher order nonlinear processes in time-resolved degenerate four-wave mixing in GaAs
Authors: Wu Song
Published: July 2002

We theoretically calculate the line shapes of the third order, the cascaded third order, and the fifth order nonlinear processes in a femtosecond time-resolved four-wave mixing experiment. On the basis of the calculations, experimentally we distinguish the wavelength dependent contributions to the direct fifth order process and the cascaded third order process in bulk GaAs. Our results show that the cascaded process dominates at wavelengths near band gap resonance; however the direct process dominates away from resonance. The nonlinear susceptibilities χ(3) and χ(5) are also obtained.
Preparation of biaxially aligned cubic zirconia films on pyrex glass substrates using ion-beam assisted deposition
Authors: Sonnenberg N. , Longo A. S. , Cima M. J. , Chang B. P. , Ressler K. G. , McIntyre P. C. , Liu Y. P.
Published: July 2002

Yttria stabilized zirconia films were deposited using ion-assisted, electron beam deposition (IBAD) on pyrex glass substrates heated to 600 °C. Films deposited under these conditions without IBAD exhibit fiber texture such that preferred (100) orientation exists perpendicular to the substrate. The orientation of the films has been studied as a function of ion bombardment angle, deposition rate, ion current density, and ion beam energy. Films deposited with IBAD at bombardment angles of less than 63° display strong (100) preferred orientation perpendicular to the substrate. Films having ion to atom ratios of 0.05 exhibit (220) biaxial alignment in the plane of the film. Best results were achieved for films with deposition rates of 2.4 Å/s, beam energies of 75 eV and ion fluences of 18 μA/cm2. Increasing the beam energy to 300 eV increases the concentration of wire texture in these films. Films deposited at higher ion/atom ratios (0.11 and 0.25) produce films with alignments highly dependent on the angle of ion bombardment. Processing conditions have been shown, therefore, to effect absolute orientation, and not just the quality of the pre-existing orientation. The microstructures of the biaxially aligned films have been studied and this has allowed for a clarification of the growth mechanism of these films. A growth instability of the differing orientations during ion bombardment is shown to cause in-plane alignment rather than preferential etching of misoriented nuclei.
Surface and domain structures of ferroelectric crystals studied with scanning force microscopy
Authors: Lüthi R. , Haefke H. , Meyer K.-P. , Meyer E. , Howald L. , Güntherodt H.-J.
Published: July 2002

The understanding of the phenomena of ferroelectricity requires profound knowledge of the ferroelectric domain structure. In this paper we report on the progress of studying ferroelectric domains and domain walls with scanning force microscopy (SFM). Domains and domain walls of ferroelectric crystals of guanidinium aluminum sulfate hexahydrate (GASH) are imaged with SFM. Two sets of complementary results are obtained depending on the operation mode of the instrument. In the non-contact imaging mode (attractive force regime), domain walls are imaged. In the contact imaging mode (repulsive force regime) in addition to the domain wall structure, information about the polarity of the domains is obtained. In these latter images, the opposing contrast of the ferroelectric positive and negative domains is superimposed on the GASH cleavage structure. The imaging mechanism of the contact and noncontact modes are discussed. Corroborating scanning electron microscopy images are presented as well.
AFM structure and media noise of SmCo/Cr thin films and hard disks
Authors: Velu E. M. T. , Lambeth D. N. , Thornton J. T. , Russell P. E.
Published: July 2002

Longitudinal media for ultrahigh density recording require a high coercivity and a low medium noise. While the coercivity is controlled mainly by the chemical composition of the alloy, the medium noise is influenced significantly by the microstructure of the underlayer. We used atomic force microscopy (AFM) to study the microstructure of Cr underlayers and SmCo magnetic films. The AFM study shows that the Cr grains have elongated ‘‘rice’’-like granular features whereas the SmCo grains without an underlayer appear circular with nonuniform grain size. The Cr underlayer grows as well isolated columns with voids. When thin SmCo films (<20 nm) were deposited on the thin Cr (<35 nm) underlayers the SmCo grains were found to replicate the isolated, columnar structure of the underlayer. The intergranular exchange interaction and the recording media noise of SmCo/Cr thin films decreased with a decreasing thickness of the Cr underlayer. The medium noise of high coercivity SmCo/Cr hard disks prepared on thin Cr underlayers remained almost flat with no supralinear increase when tested up to 2760 fc/mm (70 kfci).
Effects of oxide addition on magnetic and structural properties of CoNiPt alloy films
Authors: Murayama A. , Kondoh S. , Miyamura M.
Published: July 2002

The effects of oxide addition on magnetic and structural properties of sputtered CoNiPt alloy films for high density longitudinal recording with a random c-axis orientation of hcp Co have been studied. It is found that the addition of SiO2 up to 4.2 at. % results in a significant increase in the in-plane coercivity from 1700 to 2400 Oe and a signal to media noise ratio with a slight decrease in coercive squareness from 0.90 to 0.87, while the perpendicular magnetic anisotropy is not significantly changed. X-ray diffraction shows that the c-axis orientation normal to the film plane does not change and the hcp lattice is strained due to the addition of SiO2. A marked decrease in the grain size is observed with the addition of 4.2-at. % SiO2, which causes the development of grain separation and therefore enhances the coercivity. The origin of the increase in coercivity with 2.1-at. % SiO2 is also discussed.
Optical and structural properties of MeV erbium-implanted LiNbO3
Authors: Fleuster M. , Buchal Ch. , Snoeks E. , Polman A.
Published: July 2002

LiNbO3 single crystals have been implanted with 2.0 or 3.5 MeV Er ions with fluences between 2.0×1014 and 7.5×1015 cm−2 and annealed at temperatures between 500 and 1060 °C in a wet oxygen atmosphere. Photoluminescence spectroscopy, Rutherford backscattering spectroscopy, and secondary-ion-mass spectrometry have been used to study the influence of the annealing treatment on the optical activity of the Er ions, the crystal structure of the implanted LiNbO3 layer, and the depth distribution of the Er ions, respectively. The as-implanted, amorphized LiNbO3 already emits the characteristic photoluminescence (PL) of Er3+ around 1.53 μm. Annealing for 1 min at 500 °C causes recrystallization of the amorphized layer by columnar solid-phase epitaxial regrowth from the substrate. The PL intensity increases by more than one order of magnitude on annealing at 500 °C and the PL lifetime rises from 1.65 to 2.85 ms. In contrast, much longer annealing times and a much higher temperature are necessary to remove the columns and restore the perfect lattice but do not further improve the optical properties. Up to an Er concentration of 0.12 at. % no concentration quenching effects are noticed. MeV implantation-doped samples show the same optical spectra as those doped during growth from the melt.
Ultraviolet spectroscopy of gaseous species in a hot filament diamond deposition system when C2H2 and H2 are the input gases
Authors: Toyoda H. , Childs M. A. , Menningen K. L. , Anderson L. W. , Lawler J. E.
Published: July 2002

The methyl radical density, acetylene mole fraction, filament properties, and diamond growth rate and film quality are measured in a hot filament chemical vapor deposition system when C2H2 and H2 are used as the input gases. The methyl radical density and acetylene mole fraction depend greatly on the degree of filament surface poisoning. This poisoning prevents diamond growth due to a lack of hydrogen atoms and/or methyl radicals. Understanding the large influence of the filament surface catalytic characteristics is important for developing a gas phase model of this system. The results obtained with C2H2 and H2 as the input gases are compared to those obtained with CH4 and H2 as the input gases. Under conditions when the filament surface is not poisoned, the methyl radical concentrations are similar when either C2H2 and H2 are the input gases or when CH4 and H2 are the input gases.
Effect of deposition parameters on the properties of In2O3/InP junctions
Authors: Korobov V. , Shapira Yoram , Ber B. , Faleev K. , Zushinskiy D.
Published: July 2002

Transparent conducting indium oxide films have been prepared by means of reactive evaporation of In onto p-type InP substrates at various deposition temperatures [in the range of 25 °C (RT)–330 °C] and under different oxygen pressures (in the range of 8×10−5 Torr up to 9×10−4 Torr). The chemical composition and structural properties of the films have been investigated using such analytical tools as Auger electron spectroscopy (AES), x-ray diffraction, and scanning electron microscopy (SEM). The combination of AES and SEM has proved to be extremely useful for interface analysis. The concentrations of oxidized and unoxidized (elemental) In in the tested samples have been investigated by deconvolution of the appropriate Auger MNN transitions using reference spectra of In2O3 and InP. The films were found to be polycrystalline at all deposition temperatures above RT under all the tested range of oxygen pressures. Nearly stoichiometric In2O3 films have been observed on all the investigated samples. Elemental In at the interfaces of films grown at low deposition temperatures has been noted. The effect of the oxygen pressure and deposition temperature on the films properties is discussed.
Generation of high-density O2 supermagnetron plasma over lower cathode by radio frequency power supply to upper cathode
Authors: Kinoshita Haruhisa
Published: July 2002

The density of supermagnetron plasma generated over a lower cathode, i.e., the wafer stage, was examined qualitatively by optical emission spectroscopy and compared to the results of Ar plasma measured by a similar method. Optical emission intensities (OEIs) of O (or Ar) atoms and O (or Ar) ions over the lower cathode were increased with each rf power. By increasing the upper cathode rf power (UPRF), a remarkable increase of OEI was observed at approximately 180° of the phase difference of two synchronous rf powers supplied to two cathodes, but there was a slight increase observed at approximately 0°. A lot of negative self-bias voltage was observed at about 180°, but there was little positive voltage observed at approximately 0°. The etch rate of the photoresist was increased with UPRF at 150° without increasing the self-bias voltage of the lower cathode. Highly uniform etching of ±5% was obtained in a 5-in.-diam photoresist wafer etching using a stationary magnetic field. 0.4 μm photoresist lines were etched vertically by using an upper cathode covered by a carbon plate.
Single crystalline GaSe/WSe2 heterointerfaces grown by van der Waals epitaxy. I. Growth conditions
Authors: Lang O. , Schlaf R. , Tomm Y. , Pettenkofer C. , Jaegermann W.
Published: July 2002

Epitaxial GaSe films have been prepared on WSe2 (0001) substrates with 14% lattice mismatch and characterized by photoelectron spectroscopy, electron diffraction, and ex situ by tunneling microscopy. The films grow in the Frank–van der Merve growth mode. The best films with perfect azimuthal orientation are formed after an annealing step at 720 K. The basic mechanisms of this van der Waals epitaxy are qualitatively discussed in terms of thermodynamic and kinetic parameters.
Electron-energy-loss spectroscopy of Fe thin films on GaAs(001)
Authors: Yuan J. , Gu E. , Gester M. , Bland J. A. C. , Brown L. M.
Published: July 2002

An electron-microscopy-based technique of electron-energy-loss spectroscopy (EELS) has been used to characterize electronic and magnetic properties of ultrathin Fe films grown on GaAs(100) surface, as a function of the film thickness. Large-area electron transparent membranes for microscopic analysis are prepared by ion-beam thinning or chemical etching from the substrate side, and the top surface of the ultrathin Fe film is protected by a thin Cr layer. Analysis of the Fe 2p, Cr 2p, and O 1s absorption spectra confirms that only the Cr layer is oxidized. The local magnetic moments of the ultrathin Fe films are deduced from the ‘‘white line’’ branching ratio in the Fe 2p absorption spectra. For Fe films as thin as 150 Å, the magnetic moment is not different from that found in bulk α-Fe. For a 70-Å Fe film, the local magnetic moment is enhanced although the average magnetization is reduced. As doping is suspected to be the cause for the departure from bulk α-Fe properties. In the case where the 50-Å film is polycrystalline and discontinuous, spatially resolved EELS has been used to distinguish small island clusters from large crystalline particles. The large particles are α-Fe crystallites and the islands are probably also heavily affected by As doping.
Characterization of polyester films used in capacitors. II. Effects of heat treatments on transient and steady-state charging currents in polyethylene terephthalate thin films
Authors: Thielen A. , Cerfontaine J. , Niezette J. , Feyder G. , Vanderschueren J.
Published: July 2002

The effects of various heat treatments performed before or after the vacuum deposition of aluminum electrodes on the charging currents flowing through polyethylene terephthalate (PET) thin films (6 and 12 μm) were studied. The amorphous phase of the PET films was characterized by the use of thermally stimulated current/relaxation map analysis spectrometry, allowing precise determination of thermodynamic and thermokinetic parameters. Density measurements were used to calculate the rate of crystallinity achieved after annealing. A correlation was found between the relaxation parameters of the α dipolar relaxation of PET, the rate of crystallinity, and the properties of the charging currents observed from room temperature to 200 °C. Strain-induced crystallization has been put forward to account for the experimental evidences.
A study of internal absorption in Zn(Cd)Se/ZnMgSSe semiconductor lasers
Authors: Kondo K. , Ukita M. , Yoshida H. , Kishita Y. , Okuyama H. , Ito S. , Ohata T. , Nakano K. , Ishibashi A.
Published: July 2002

Based on two different experiments and an optical field calculation, we show that the free-carrier absorption αfc in Zn(Cd)Se/ZnMgSSe semiconductor lasers is about 4 cm−1 and that it is smaller than that of GaAs/AlGaAs semiconductor lasers. We have measured the dependence of the L-I characteristics on the cavity length of double heterostructure (DH) lasers under photopumped operation and of single quantum well-separate confinement heterostructure (SQW-SCH) lasers under current-injected operation. For the DH laser, the total absorption coefficient αi and β×J0 product (β is a gain constant, and J0 is the nominal current density that makes the gain equal to zero) are estimated to be 4.2 cm−1 and 8.6×10 cm−1, respectively. For the SQW-SCH laser, αi, β, and J0 are estimated to be 21 cm−1, 4.23×10−3 cm×μm/A, and 1.9×10−3 A/(cm2×μm), respectively. By calculating the optical fields of these lasers, we have estimated that the absorption in a GaAs substrate is 16.53 cm−1 in the SQW-SCH laser and that it is negligible in the DH laser. We have shown that the large loss in the SQW-SCH laser is caused by both αfc and the absorption in the substrate and that αi in the DH laser is caused only by free carrier absorption.
Fabrication of magnetostrictive actuators using rare-earth (Tb,Sm)-Fe thin films (invited)
Authors: Honda T. , Arai K. I. , Yamaguchi M.
Published: July 2002

A new concept is proposed for the microactuation based upon magnetostriction. Magnetostrictive bimorph cantilever actuators and a traveling machine, composed of the magnetostrictive amorphous Tb-Fe and Sm-Fe thin films on a polyimide substrate, were fabricated. These actuators moved without power supply cables. The 3-mm-long cantilever actuator exhibited the large deflection above 100 μm in as low a magnetic field as 300 Oe and above 500 μm at resonant frequency in an alternating magnetic field of 300 Oe. Such unique characteristics suggest that magnetostriction is useful as the driving force of the microactuator.
Neutron-diffraction and Mössbauer effect study of the Tb2Fe17−xAlx solid solutions
Authors: Marasinghe G. K. , Mishra S. , Pringle O. A. , Long Gary J. , Hu Z. , Yelon W. B. , Grandjean F. , Middleton D. P. , Buschow K. H. J.
Published: July 2002

The magnetic properties of a series of Tb2Fe17−xAlx solid solutions, with nominal x compositions of 0, 2, 3, 4, 5, 6, 7, and 8, have been studied by neutron diffraction and Mössbauer spectroscopy. Neutron-diffraction data indicate that the compounds all crystallize with the Th2Zn17 structure and that the aluminum atoms are excluded from the 9d site and show a distinct preference for the 6c site only for an aluminum content greater than 6. The unit-cell volume increases by approximately 1% per aluminum atom substituted in the formula unit. The magnetic moment per formula unit, measured at 295 K, shows very little change for x less than or equal to 4, but decreases rapidly with increasing aluminum content for higher values of x. Mössbauer spectral results indicate that all the samples are ferromagnetically ordered at 85 K. However, at 295 K Tb2Fe9Al8 is paramagnetic and Tb2Fe10Al7 is either paramagnetic or has at most very small ferromagnetic moments. An analysis of the magnetic spectra with a basal magnetic model is successful for x values of 5 or less; however, at higher x values an axial model for the magnetization is required, indicating the presence of a spin reorientation with increasing aluminum content and decreasing temperature. The weighted average hyperfine field decreases approximately linearly by 21 kOe per substituted aluminum atom at 85 K and more rapidly at 295 K. As expected, the isomer shifts increase with increasing aluminum content as a result of interatomic charge transfer and intraatomic iron 4s-3d electronic redistribution.
O2 rf discharge structure in parallel plates reactor at 13.56 MHz for material processing
Authors: Shibata Mari , Nakano Nobuhiko , Makabe Toshiaki
Published: July 2002

The spatiotemporal structure of O2 rf discharges between parallel plates at 13.56 MHz is investigated by using the relaxation continuum model. The results for pressure of 0.5 Torr and the sustaining voltage of 75–200 sin ωt V are studied by considering the elementary particles, O+2, O+, O−2, O−, electrons, and O in O2. In these conditions, atomic oxygen, formed by the dissociative electron impact in O2 with density of ∼1014 cm−3, plays important role to the rf structure through the associative detachment process. That is, the expanding characteristics of the sheath width unique to the O2 rf discharge are realized with increasing the sustaining voltage. The validity of the numerical result is demonstrated with the spatiotemporal structure by the measurement by the spatiotemporally resolved optical emission spectroscopy. The flux of each particle to the electrode is also discussed.
Improving hydrostatic performance of 1-3 piezocomposites
Authors: Li L. , Sottos N. R.
Published: July 2002

Type 1-3 piezocomposites consist of aligned piezoelectric rods embedded in a passive polymer matrix and have better hydrostatic behavior than single-phase piezoelectric materials. The improved hydrostatic performance of 1-3 piezocomposites comes from two major effects: the axial stress amplification and the lateral stress reduction in the piezoelectric rods. An improved micromechanical model has been developed to predict the hydrostatic response of 1-3 piezocomposites and to examine the interaction between the piezoelectric rods and the polymer matrix. Effective hydrostatic piezoelectric constants for the composite are predicted and compared to those calculated using a generalized plane strain model. The influence of matrix stiffness, interlayer stiffness, rod aspect ratio, and rod volume fraction on the load transfer and the effective hydrostatic piezoelectric coefficient was investigated. The results obtained provide quantitative information on how various parameters affect the hydrostatic response of the composites.
Raman study of the network disorder in sputtered and glow discharge a-Si:H films
Authors: Morell G. , Katiyar R. S. , Weisz S. Z. , Jia H. , Shinar J. , Balberg I.
Published: July 2002

We have carried out a comprehensive study of the Raman spectra of a-Si:H films produced by the glow discharge (GD) and radio frequency sputtering (RFS) deposition techniques. The results show that the short-range disorder (bond-angle deviation), as measured by the width of the TO band (ΓTO), is larger in RFS than in GD a-Si:H films. The intermediate-range disorder (dihedral angle deviation), as measured by the ratio of the intensity of the TA band to that of the TO band (ITA/ITO), is generally larger in RFS than in GD a-Si:H films. However, while the ITA/ITO values of RFS films remain relatively close to those of GD films when the interior is probed, the near surface of RFS films shows much larger values evidencing the existence of a significant disorder gradient along the growth axis. Together, these results indicate that the network order and homogeneity of RFS amorphous silicon is lower than those of GD for substrate temperatures that produce the hydrogenated material. These structural differences are interpreted in terms of the differences between the two film growth processes and are believed to be the reason for the poorer transport properties of RFS a-Si:H films.
Positron annihilation in SiO2/Si structure at low temperature
Authors: Uedono A. , Moriya T. , Tanigawa S. , Kawano T. , Ohji Y.
Published: July 2002

Annihilation characteristics of positrons in SiO2/Si structure were studied by using a monoenergetic positron beam in the temperature range between 50 K and room temperature. In the SiO2 film, positrons formed positronium (Ps) and they annihilated from localized states in open spaces. Below 100 K, the Ps formation was found to be suppressed. This fact was attributed to the trapping of positrons by point defects in the SiO2 film at low temperature. The depth distribution of such traps was not homogeneous; its concentration in the central region of the SiO2 film was higher than that in the regions near the surface or the interface. The potential of monoenergetic positrons for the detection of the point defects provides unique information for depth distributions of hole traps in SiO2 films.
Deep level defects in alpha particle irradiated 6H silicon carbide
Authors: Rybicki George C.
Published: July 2002

A deep level transient spectroscopy study of native and radiation induced defects in metal organic chemical vapor deposition n on p 6H-SiC diodes has been conducted. Three majority carrier levels were found, at Ev+0.50, +0.55, and +0.69 eV, and three minority carrier deep levels were found, at Ec −0.38, −0.48, and −0.58 eV. These six levels were initially observed in the unirradiated materials. Their concentration increased 2 to 13-fold after irradiation to a fluence of 2×1011 cm−2 of 5.5 MeV alpha particles. In addition the carrier removal was monitored during irradiation, and a carrier removal rate of 7.8×104 cm−1 for 5.5 MeV alpha particles was measured. When compared with a similar study of alpha particle irradiation of InP, the results suggest that SiC has radiation resistance comparable to that of InP, another highly radiation resistant semiconductor.
Optimization of island size in single electron tunneling devices: Experiment and theory
Authors: Verbrugh S. M. , Benhamadi M. L. , Visscher E. H. , Mooij J. E.
Published: July 2002

We have investigated the influence of island size on the operation of single electron tunneling (SET) devices. The self-heating, self-capacitance, and charge noise have been determined for six SET transistors with island sizes varying from 0.17×0.17 μm2 to 5×5 μm2. The I–V characteristics of these devices can be well fit to a model where the heat flow from the device is limited by the electron-phonon coupling. The best fit to this model was obtained with an electron-phonon coupling parameter of Σ=0.3×109 W K−5 m−3. We have found a clear indication that the charge noise of our SET transistors, which are fabricated with the usual techniques, increases with increasing island size. These results have been used to estimate the thermal error of a single electron turnstile assuming that self-heating and charge noise in the turnstile are the same as in our SET transistors. The accuracy of the turnstile is dramatically reduced by the self-heating and the charge noise.
Electron beam propagation in linearly polarized undulators: The effect of the anharmonicity on the spatial and phase-space distributions
Authors: Dattoli G. , Ottaviani P. L.
Published: July 2002

The betatron part of the equations of motion of an electron beam, propagating in a linearly polarized undulator, can be derived from a quartic anharmonic oscillator Hamiltonian coupling the vertical and radial components. The relevant Liouville equation is solved, providing the evolution of the e-beam phase-space distribution, and analyze the variation, during the transport of quantities of physical interest. In particular, radial and vertical phase-space contour plots which exhibit distortions, due to nonlinear effects, and consequent emittance growth are discussed. The integration method employed is based on a symmetric split technique of the evolution operator associated to the Liouville equation under study. Previous results from a macroparticle simulation are used as benchmark. Finally, the split operator technique naturally leads to area preserving maps.
Scaling laws verification for capacitive rf-discharge Ar plasma using particle-in-cell simulations
Authors: Chung T. H. , Yoon H. S. , Lee J. K.
Published: July 2002

The characteristics of a 13.56 MHz capacitively coupled rf glow-discharge Ar plasma are studied by particle-in-cell simulation. The model simulates a planar plasma device which can be approximated using a one-dimensional plasma model. The model has proven to be useful to investigate the effect of varying control parameters such as neutral gas pressure, driver frequency, applied rf voltage on the characteristics of the discharge. A set of equations describing the dynamics of the system are presented and used to give analytic scaling laws. The simulation code is used to calculate the pressure dependence of plasma density, sheath width, peak position of the ionization event, and absorbed rf power. Scaling laws relating the control parameters to other operating functions such as average plasma potential, central electron density, absorbed rf power are examined and these functions are compared with simple analytical scaling formula.
Photoluminescence studies of relaxation processes in strained Si1−xGex/Si epilayers
Authors: Kveder V. V. , Steinman E. A. , Grimmeiss H. G.
Published: July 2002

The relaxation behavior of Si1−xGex/Si(001) strained layers has been studied during annealing in the temperature range 400–900 °C. Taking into account that the relaxation is mainly caused by nucleation and propagation of dislocations, the dislocation related luminescence has been used to characterize the relaxation process. It is shown that in highly stressed layers dislocations with nonequilibrium dissociation width are generated. Our data are in good agreement with previous transmission electron microscopy results.
Development and applications of a photoacoustic phase theory for multilayer materials: The phase difference approach
Authors: Jiang Eric Y. , Palmer Richard A. , Chao James L.
Published: July 2002

A quantitative photoacoustic (PA) phase theory for multilayer materials has been developed by using the surface temperature approach, and experimentally confirmed with the step-scan Fourier transform infrared PA phase data of multilayer polymer samples. This theory unifies several previous PA phase theories for specific cases and provides a clear picture of the relationship between the PA phase response of each layer and the thermal, optical, and geometric properties of a multilayer sample. Within the context of this model, it is shown how the PA phase difference is easily obtainable and instrument independent, and thus widely applicable to spectral depth profiling of multilayer materials. The theory can be readily applied to either qualitative discrimination of PA signals from different layers, or quantitative determination of the thermal diffusivities, optical absorption coefficients, or thickness of different layers.
Fast deposition of amorphous carbon films by an expanding cascaded arc plasma jet
Authors: Buuron A. J. M. , van de Sanden M. C. M. , van Ooij W. J. , Driessens R. M. A. , Schram D. C.
Published: July 2002

Using an expanding cascaded arc plasma jet, amorphous hydrogenated and fluorohydrogenated carbon films were deposited on silicon, glass, and steel substrates at high rates of tens of nanometers per second and on large areas of up to 100 cm2. The present work was aimed at depositing amorphous carbon films suited for optical and protective applications. Films deposited with the common argon/methane or argon/acetylene mixture tend to delaminate from the substrate when the film is thicker than about 1 μm. For this reason, also trials using other compounds like C7H8 (toluene), CF4, and H2, and mixtures of these, were carried out. Using toluene, several-μm-thick films with good adhesion to the substrate were deposited. With spectroscopic ellipsometry and infrared absorption spectroscopy optical parameters were obtained. Appropriate numerical models were developed for analyzing the data, taking into account interference fringes in the spectra due to multiple reflections in the thin film. The hydrogen and oxygen content in the films were determined with nuclear recoil techniques. Films deposited with the use of methane and acetylene are diamondlike with mainly sp3 bonding types, and a hydrogen content ranging from 36 to 26 at. % (with a low oxygen contamination of 1–2 at. %). Films deposited with the use of toluene are more polymerlike, with also sp1 and sp2 bonding types. These films have a high hydrogen content (35 at. %), and can be partially oxidized (up to 13 at. %).

In general, going from the polymerlike to the more diamondlike films, the refractive index increases from 1.3 to 2.2, and the band gap decreases from about 2 to 1 eV. By the admixture of hydrogen in the deposition plasma diamondlike films were produced with a larger band gap of 2.2 eV. The corrosion performance of the films was studied by storing them in a humidity cabinet. The corrosion resistance of films deposited with hydrocarbon/argon plasma mixtures appears to be limited. Thick films with a good corrosion resistance were produced by admixing a fluorine containing gas in the plasma. Analysis of the infrared absorption spectra showed that these films consist of amorphous fluorohydrogenated carbon. The presence of fluorine radicals in the plasma may lead to a chemically enhanced surface mobility, leading to a less porous film structure, and resulting in lower internal stresses. The growth rates and the corrosion performances of the films appear to be different for substrates of different types of steel. This may be attributed to different initial growth mechanisms, as a consequence of the difference in electrical and thermal conductivity of the two substrate types used here.
Particle size and interfacial effect on the specific heat of nanocrystalline Fe
Authors: Bai Hai Yang , Luo Jian Lin , Jin Duo , Sun Ji Rong
Published: July 2002

The specific heat of nanocrystalline iron with grain size of 40 nm has been measured in the low-temperature range from 1.8 to 26 K. The anomalous specific heat behavior of nanocrystalline iron is compared with that of the normal polycrystalline iron. It is found that the electronic specific heat coefficient γ obtained at low temperatures decreases by about 50%. A quadratic temperature-dependent term associated with surface modes in the heat capacity has been clearly observed. A large enhancement of the specific heat at higher temperatures is interpreted as the Einstein oscillator contribution due to weakly bound atoms at the interfaces of the nanocrystals.
Ellipsometric and thermoreflectance spectra of (AlxGa1−x)0.5In0.5P alloys
Authors: Ozaki Shunji , Adachi Sadao , Sato Masahiro , Ohtsuka Kouji
Published: July 2002

Spectroscopic-ellipsometry (SE) and thermoreflectance (TR) spectra of (AlxGa1−x)0.5In0.5P quaternary alloys are presented. Both measurements are carried out on the same samples in the 1–6 eV photon-energy range at room temperature. These spectra are analyzed based on a simple model of the interband transitions. The results are in satisfactory agreement with the experimental SE and TR data over the entire range of photon energies. The composition dependence of the interband critical-point and indirect-band-gap energies is also discussed.
Continuous decay of drift mobility in intrinsic a-Si:H and a-SiC:H upon light soaking investigated by the photomixing technique
Authors: Tang Yi , Braunstein R.
Published: July 2002

The photoconductivity, electron lifetime, and electron drift mobility in intrinsic hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon carbide (a-SiC:H) while light soaking were determined using a photomixing technique. In addition to the decay of the photoconductivity and electron lifetime, continuous decay of the electron drift mobility was found during the light soaking process, which reveals that the light-induced metastable defects of the Staebler–Wronski effect results in scattering as well as recombination of charge carriers. The drift mobility decreased by a factor of 2 for 20 h light soaking at 2.5 sun intensity. Experimental data were fitted to a stretched exponential law. Different stretched-exponential parameters for photoconductivity, lifetime, and drift mobility were obtained, which indicates the production of defects with different generation kinetics upon light soaking.
Effect of anisotropy dispersion on magnetization process in magnetoresistive sensor films
Authors: Shiiki Kazuo , Mitsui Yu , Hirata Yukinobu
Published: July 2002

The effect of anisotropy dispersion on the magnetization process in magnetoresistive sensor films is studied using micromagnetic calculation. It is assumed that the magnetization of the film is fixed at both ends to the track width direction, which corresponds to the average direction of the easy magnetization axis of the film. Magnetization distribution at different stages of the magnetization process is calculated by numerical integration of the Landau–Lifshitz–Gilbert equation. Our study shows that anisotropy dispersion causes buckling instead of coherent rotation of the magnetization. As dispersion increases, buckling becomes more pronounced. Furthermore, buckling does not completely disappear when the external magnetic field is weakened to a small value. The magnetization process is influenced by buckling, and this may lead to Barkhausen noise.
Microcavity effects in single-layer light-emitting devices based on poly(p-phenylene vinylene)
Authors: Cimrová Vera , Neher Dieter
Published: July 2002

The electroluminescence and photoluminescence light-emitting devices based on poly(p-phenylene vinylene) (PPV), with emitting layers of different thicknesses, were examined. It was shown that microcavity effects occur in thin PPV single-layer sandwich structures (ITO/PPV/Al, Au/PPV/Al) in both electroluminescent and photoluminescent emission. Microcavity effects were demonstrated for a range of different PPV layer thicknesses down to 40 nm. We have successfully prepared resonant-cavity single-layer light-emitting diodes with enhanced external quantum efficiencies of up to 0.1% photons/electron, with aluminum as the electron injecting and gold as the hole injecting electrode. Less pronounced microcavity effects were observed on devices with ITO as the hole injecting contact, due to the low reflectivity of the ITO-glass interface. These findings were confirmed by theoretical simulations based on an optical transfer matrix formalism.
Reduction of Co–Cr–Pt media noise by addition of Ti to Cr underlayer
Authors: Matsuda Y. , Yahisa Y. , Inagaki J. , Fujita E. , Ishikawa A. , Hosoe Y.
Published: July 2002

Effects of Ti addition to a Cr underlayer on the magnetic and crystallographic properties of Co–Cr–Pt media were investigated. C/Co–Cr20–Pt (Pt: 8 and 12 at. %)/Cr–Ti (Ti: 0–30 at. %) films were deposited on textured Ni–P/Al–Mg substrates by dc magnetron sputtering. In-plane Hc and S* increased as Ti was added to the Cr underlayer. The media noise at 167 kFCI decreased with an increase of the Ti content from 0 to 20 at. %. The normalized media noise of Co72Cr20Pt8/Cr75Ti25 media was 20% lower than that of Co68Cr20Pt12/Cr90Ti10 media where their coercivity and S* were almost the same. Further increase of the Ti caused the increase of the media noise. Transmission electron microscopy studies showed that average grain size of Cr–Ti films decreased from 30 to 20 nm with the increase of the Ti content from 0 to 20 at. %. The activation volume of Co68Cr20Pt12 films measured from the time dependences of remanence coercivity decreased by 30% as the Ti content increased from 0 to 20 at. %. The reduction of media noise is probably due to the decrease of the magnetic switching volume which is caused by the reduction of the grain size of Cr–Ti underlayers.
Co-Sm (1̄100)[0001]//Cr (1̄21̄ )[1̄01] epitaxy and its effects on magnetic properties of Co-Sm//Cr films
Authors: Liu Y. , Sellmyer D. J. , Robertson B. W.
Published: July 2002

It is well known that the Cr underlayer plays a critical role in generating large in-plane coercivity in Co-based magnetic thin films. In this paper we report in detail the Co-Sm (1̄ 100)[0001]//Cr (1̄ 21̄)[1̄ 01] epitaxy revealed by high resolution electron microscopy. The lattice mismatch between Co-Sm (1̄ 100) and Cr (1̄ 21̄) is less than 2%, suggesting an energetically favorable configuration. The high anisotropy observed in Co-Sm films is discussed by this epitaxial relation. © 1996 American Institute of Physics. [S0021-8979(96)15308-6]
Antiferromagnetic coupling in magnetic multilayers with a narrow gap semiconductor spacer
Authors: Shi Zhu-Pei , Klein Barry M.
Published: July 2002

Antiferromagnetic (AF) coupling has been observed in sputtered Fe/Si multilayers at room temperature, with thin spacers (<20 Å) which were claimed to be FeSi. To study the magnetic coupling in this system we extend the RKKY interaction approach to a temperature-dependent narrow gap semiconductor. The strong AF coupling at room temperature and weakly ferromagnetic (F) coupling at low temperatures observed in Fe/Si can be explained from this model.