bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical and magnetic microstructure of rapid thermally annealed thin film bismuth-doped garnets
Authors: Eppler W. R. , Cheong B. K. , Laughlin D. E. , Kryder M. H.
Published: July 2002

Bismuth-doped iron garnets are promising materials for blue light magneto-optic recording media. These materials have been deposited on glass substrates with bulk magnetic and magneto-optic properties suitable for magneto-optic recording. However, these films exhibit a very low carrier to noise ratio (CNR) when crystallized in conventional furnaces. The low CNR is due to the inability to write circular domains in these materials. Rapid thermal annealing (RTA) has been reported to produce films with a much finer grain size. We have confirmed by transmission electron microscopy that RTA does indeed reduce the grain size over an order of magnitude from films crystallized in a conventional furnace. Faraday microscopy has shown that films processed by RTA with smaller grain size (∼30 nm) support circular magnetic domains of much greater regularity than films crystallized in conventional furnaces. The improved regularity of static thermomagnetically written domains, in films crystallized by RTA, lends promise that the noise in these materials can be reduced.
Dependence of giant magnetoresistance on film thickness in heterogeneous Co-Ag alloys
Authors: Mitchell J. R. , Berkowitz A. E.
Published: July 2002

The dependence of magnetic properties on film thickness in as-deposited Co-Ag alloys is discussed. Films ranging in Co concentration from 0 to 100 vol % Co and thicknesses between 100 Å and 1 μm were deposited by sputtering onto Si(100) substrates. It was found that both magnetoresistance (MR, Δρ) and MR ratio (Δρ/ρ) increase with thickness. Resistivity (ρ) decreases with increasing thickness. The dependence of MR ratio on concentration of Co is not markedly different for 200 and 2000-Å-thick samples. Saturation magnetization is roughly constant for thicknesses greater than ∼200 Å, decreasing rapidly below this cutoff. However, most of both the thin (200 Å) and thick (2000 Å) films begin showing magnetic hysteresis between 10 and 100 K. The differences in transport and magnetization properties may be ascribed to differences in film growth for thin versus thick films.
The effects of film geometry on the properties of FeTaN films
Authors: Qiu Gan , Barnard J. A.
Published: July 2002

FeTaN single layer and FeTaN/SiO2 multilayer films were grown by high rate reactive dc magnetron sputtering. The film geometry (FeTaN layer thickness, SiO2 spacer thickness, and number of bilayer units) dependence of the structure, magnetic properties and high-frequency permeability characteristics were investigated.
Elemental composition and microstructure of reactively sputtered carbon nitride thin films
Authors: Kumar Sunil , Tansley T. L.
Published: July 2002

Thin films of carbon nitride have been grown on various substrates using low power radio frequency reactive sputtering of graphite in pure nitrogen plasma. A quantitative composition analysis using Rutherford backscattering spectrometry shows that the film contains about 51 at. % C, 44 at. % N, and 5 at. % O. The study of the microstructure of the films using cross-sectional scanning electron microscopy reveals highly oriented columnar structures.
Failure of three-dimensional random composites
Authors: Moukarzel C. , Duxbury P. M.
Published: July 2002

Using an optimized bond breaking algorithm, we simulated the failure of three-dimensional networks composed of two randomly interspersed components. We studied the strength and the number of bonds broken prior to the failure instability (the damage). When one phase is of low concentration, damage mostly occurs when the dilute phase is very weak and fails prematurely, although a limited ‘‘matrix damage’’ mechanism does exist. In contrast, when the composite is a 50/50 mixture and the two phases are macroscopically interpenetrating (both phases percolate), the ability to absorb damage is greatly enhanced. In the interpenetrating phase regime the strength of the composite is, in some cases, enhanced beyond that of the analogous particle reinforced composite. These features suggest that interpenetrating phase composites can have improved properties in comparison to conventional ‘‘particulate’’ composites. Analysis of the composite is neatly summarized in ‘‘damage maps’’ which give a quick indication of the regions in which the ability to absorb damage is enhanced. Using lattices of up to linear dimension L=40 we also study the finite-size-scaling laws for the average strength and damage of the networks.
Noise and photoconductive gain in AlGaAs/GaAs quantum well intersubband infrared photodetectors
Authors: Xing B. , Liu H. C. , Wilson P. H. , Buchanan M. , Wasilewski Z. R. , Simmons J. G.
Published: July 2002

We reevaluate the current model of noise gain and photoconductive gain for AlGaAs/GaAs quantum well infrared photodetectors. An experimental study is carried out on samples covering different types of intersubband transitions, i.e., bound-to-continuum, bound-to-quasibound, and bound- to-bound cases. A general difference between gains measured by dark current noise and by responsivity was found for all three cases, while agreement between them was found within some ranges of bias voltages for the bound-to-quasibound and bound-to-continuum samples. The thermal noise contribution to the total white noise is explicitly modeled and discussed.
Magnetic order and spin-flop transition in Co-Re multilayers
Authors: Tun Z. , Buyers W. J. L. , Swainson I. P. , Sutton M. , Cochrane R. W.
Published: July 2002

Polarized neutron reflectometry measurements were carried out on a thin-film Co-Re multilayer sample with Re thickness of 6 Å which is at the peak of the first oscillation of the magnetoresistance. Antiferromagnetic coupling between successive Co layers is observed at in-plane magnetic fields below 0.1 T. Towards the low field end of this regime, the axes of the antiferromagnetic domains are distributed relatively uniformly in the sample plane but at ∼0.1 T the moments flop perpendicular to the applied field. As the field is increased further, the Co moments are pulled into the field direction producing a partial ferromagnetic alignment. At 0.5 T, the highest field where the measurements have been made, the antiferromagnetic to ferromagnetic transition was found to be only ∼50% complete, indicating that the saturation field required for Co-Re system is much higher than that for Co-Cu multilayers of similar layer spacing.
Magnetostriction in TbDyFe thin films
Authors: Grundy P. J. , Lord D. G. , Williams P. I.
Published: July 2002

Magnetization and magnetostriction in amorphous binary TbFe and DyFe and amorphous and polycrystalline, ternary (TbxDy1−x)yFe100−y thin films have been investigated. The measurements reflect the compositional dependence of the easy direction of magnetization in the films. In plane magnetostrictions of over 300×10−6 were measured for some of the amorphous TbFe and TbDyFe films and values greater than 750×10−6 were obtained in polycrystalline TbDyFe films near to the Terfenol composition.
Effects of Ar-ion implantation and annealing on structural and magnetic properties of Co/Pd multilayers
Authors: Xiao John Q. , Liu K. , Chien C. L. , Schelp L. F. , Schmidt J. E.
Published: July 2002

The contrasting effects of ion implantation and thermal annealing on structural and magnetic properties of Co/Pd multilayers have been studied. Ion implantation causes local damage to the multilayers, resulting in enhanced magnetization due to the polarization of the neighboring Pd. Thermal annealing generates massive interdiffusion across the interfaces into the formation of Co-Pd alloys with a lower magnetization. Effects on coercivity and remanence have also been studied.
Anomalous interface magnetism in ultrathin Co films with in-plane anisotropy
Authors: Schumann F. O. , Buckley M. E. , Bland J. A. C.
Published: July 2002

Using the magneto-optical Kerr effect, we have observed a striking sensitivity of the magnetic properties of ultrathin Co/Cu(001) films to submonolayer coverages of Cu. In particular large nonmonotonic changes of the coercive field Hc, the height of the M-H loop (magneto-optical signal), and the ratio S of remanent and saturation magnetizations are observed. With increasing Cu thickness the coercivity first sharply decreases, reaching a minimum at around 0.2 monolayer (ML) followed by a gradual increase. In contrast, the magneto-optical signal is found to peak strongly at the same Cu overlayer thickness of 0.2 ML, decaying in magnitude with further Cu coverage.
Microstructure of the Cr underlayer and its effect on Sm-Co//Cr thin films
Authors: Liu Y. , Robertson B. W. , Shan Z. S. , Liou S. H. , Sellmyer D. J.
Published: July 2002

Sm-Co film is a potential candidate for the future high density recording media of 10 Gb/in2 which requires bit sizes of the order of 300 nm and grain sizes of about 10 nm. This article investigates the microstructure of the Cr underlayer in Sm-Co thin films and its effect on Sm-Co thin films prepared by the dc magnetron sputtering technique. The grain size of the Cr underlayer is found to be about 25 nm. Grains with small angle misorientation usually form local agglomerates. Studies by transmission electron microscopy (TEM) bright field images at different defocus settings and by high resolution electron microscopy indicate that a large proportion of the grain boundaries have gaps. The gap width (about 1–3 nm) varies from place to place. The Sm-Co films deposited on the Cr underlayer inherit similar gaps at positions adjacent to the grain boundary gaps of the Cr underlayer. Such gaps produce grain-like contrast of about 25 nm in TEM bright field images. However, such contrast becomes weak as the thickness of the film increases and disappears at a thickness of 96 nm, suggesting the gaps are sealed at places far from the Cr underlayer. The effect of the Cr underlayer on magnetic properties are discussed.
Anomalous depth distributions of bulk microdefects in heat-treated Czochralski silicon wafers due to nonequilibrium self-interstitials
Authors: Satoh Yuhki , Furuya Hisashi , Kadoi Mikio , Shimanuki Yasushi
Published: July 2002

Anomalous depth distributions of bulk microdefects (BMDs) are observed in Czochralski silicon wafers subjected to two-step annealing [(550–700 °C)×t1+(850–950 °C)×t2, where t1 and t2=1–100 h]. The number density of BMDs near the surface is smaller than that in the bulk when t1 is short, and is larger when t1 is long. The anomalous distribution extends deeper than 100 μm from wafer surfaces and cannot be explained by the behavior of interstitial oxygen atoms. Distributions are examined under various annealing conditions, such as annealing temperature, rate of temperature ramping, ambient atmosphere, and initial oxygen concentration. The anomalous distributions are found to be formed in the early stage of second-step annealing only when the annealing starts with a rapid temperature rise. A formation model of anomalous distributions is proposed based on the following assumptions: (1) self-interstitials exist in the thermal equilibrium state, (2) wafer surfaces are a permanent source and sink of self-interstitials, (3) growing oxygen precipitates produce self-interstitials, and (4) self-interstitial undersaturation enhances stable growth of precipitate nuclei, and supersaturation suppresses stable growth. The nonequilibrium self-interstitial concentration induced in the bulk after the rapid temperature rise is responsible for the anomalous distributions. All the experimental characteristics are reasonably explained by the model. The formation process of the anomalous distributions is detected by three-step annealing experiments. Basic properties of self-interstitials in silicon are extracted from experimental results combined with the model. The activation energy for migration is about 2.5 eV. The diffusion coefficient is about 10−6 cm2 s−1 at 900 °C. The thermal equilibrium concentration is estimated as about 1012 cm−3 at 1000 °C. These results are close to recent experimental estimates utilizing impurity diffusion in floating zone silicon.
Growth, structural, and optical properties of II-VI layers: (001) CdMnTe grown by molecular-beam epitaxy
Authors: Bodin C. , Cibert J. , Grieshaber W. , Si Dang Le , Marcenat F. , Wasiela A. , Jouneau P. H. , Feuillet G. , Hervé D. , Molva E.
Published: July 2002

The growth of CdMnTe by molecular-beam epitaxy is described, including an in situ calibration of alloy composition by reflection high-energy electron diffraction intensity oscillation, which takes advantage of the larger sticking coefficient of Mn with respect to Cd. Layers are studied by photoluminescence, x-ray diffraction, transmission electron microscopy, and cathodoluminescence imaging. Relaxation of the mismatch strain occurs through different mechanisms, depending on the sign and magnitude of the mismatch. Once identified the characteristic features of the cathodoluminescence images are used to determine the critical thickness of layers of uniform composition or of more elaborate heterostructures. A heuristic criterion for the relaxation of mismatch strain in heterostructures incorporating layers of continuously varying composition is checked.
Growth of β-SiC film by pyrolysis of polyimide Langmuir–Blodgett films on silicon
Authors: Yang Beifang , Cai Weili , He Pingsheng , Sheng Yongning , Jin Bangkun , Ruan Yaozhong , Hu Keliang , Huang Yunlan , Zhou Guien
Published: July 2002

The heteroepitaxial growth of β-SiC has been studied by pyrolysis of polyimide Langmuir–Blodgett films on silicon substrate in the temperature range 500–1000 °C in vacuum. Thin SiC films have been grown at temperatures above 700 °C. Both the onset temperature of the SiC formation and the growth rate of the SiC films were affected by the orientation of the silicon substrates. The growth rate of the SiC films increased with temperature and was controlled by the reaction of Si with C-containing reactants. By comparison with dip-coating polyimide films, it was found that the crystallinity of the SiC layers depended on the degree of order of the molecular arrangement in the polyimide films. Highly ordered superlattice structures of polyimide LB films favored the growth of single crystal SiC films.
Influence of the barrier thickness on the noise performance of AlAs/GaAs/AlAs double barrier resonant tunneling diodes
Authors: Ouacha A. , Willander M. , Brugger H. , Meiners U.
Published: July 2002

The noise characteristics of symmetrical double barrier resonant tunneling structures were measured in two samples with a fixed well width of 50 Å and barrier thicknesses of LB=8 monolayer and 10 ML, respectively. The measurement was done in the frequency range of 1 Hz–100 kHz and temperature range of 77–300 K. The noise due to the excess current in the valley region, observed in both devices, was associated with defect assisted tunneling which is a two-step process: generation-recombination noise due to the trapping and detrapping mechanism, and 1/f noise due to the scattering by phonons. The current dependence of 1/f noise contribution was investigated in the resonant tunneling and valley regions. The frequency exponent of the 1/f noise component was found to vary between 0.9–1.1 for double barrier resonant tunneling diode (DBRTD) with LB=8 ML and 1.1–1.2 for DBRTD with LB=10 ML. This noise investigation implies that there is a difference in the physics governing the transport between DBRTD with LB=8 ML and DBRTD with LB=10 ML.
A quantitative investigation of emission from low temperature laser-induced YBa2Cu3Ox plasma plumes
Authors: El-Astal A. H. , Ikram S. , Morrow T. , Graham W. G. , Walmsley D. G.
Published: July 2002

Quantitative emission spectroscopy has been used to study the plume formed following laser ablation of YBCO in an oxygen atmosphere. Excited state population distributions, determined from emission line intensity ratios, are used to investigate spatiotemporal variations in the local Boltzmann temperatures for both neutral and ionic species within the expanding plume. Temperatures, obtained from emission line intensity ratios of both Cu(I) and Y(I), decrease slowly and nonadiabatically in the range 1.0–0.5 eV during plume expansion. Higher initial Boltzmann temperatures of ∼3 eV are however obtained from the emission line intensity ratios of fast ions, which dominate the composition of the highly luminous expanding front of the plume. Quantitative comparison of emission intensities for the different neutral species present indicate that the neutral composition in the luminous region of the expanding plume is increasingly dominated by Cu(I) which has a faster expansion velocity and lower oxidation rate than Y(I) and Ba(I).
Wave-to-plasma power transfer in magnetically assisted high-frequency discharges in argon
Authors: Loureiro J.
Published: July 2002

A simplified discharge model for the prediction of the wave-to-plasma power transfer in high-frequency collisional argon plasmas in the presence of a static magnetic field is presented. The study is based on the solutions to the homogeneous electron Boltzmann equation for an oscillating electric field composed of a right- and left-hand-side rotating parts, moving around the magnetic-field lines. The mean absorbed power per electron to maintain the plasma is calculated for a container with nonconducting surfaces and the results are then compared with an experiment in the literature.
Determination of charge distribution volume in electron irradiated insulators by scanning electron microscope
Authors: Chen H. , Gong H. , Ong C. K.
Published: July 2002

The scanning electron microscope mirror image method is developed to measure the charge distribution volume in insulators. An electrostatic potential expression is derived by assuming the dipolar approximation and hemispheroid distribution. Dielectric samples with different relative permittivities are employed in charging experiments to justify our approach. The proposed method is employed to measure the radius of the charge distribution volume in polymethylmethacrylate samples irradiated by electron beams with energy ranging from 25 to 39 keV. Experimental results achieved are in good agreement with those obtained through the use of other experimental techniques and Monte Carlo simulation. The strength of the present method is in its ability to quantitatively give the total trapped charge and its distribution in the electron irradiated insulators in a single experiment.
Derivation and experimental verification of a particulate transport model for a glow discharge
Authors: Daugherty J. E. , Graves D. B.
Published: July 2002

The most important forces that influence the motion of particles in a glow discharge plasma are the electrostatic force, the ion drag force, the neutral drag force, thermophoresis, and gravity. In this article we present a transport model that predicts the distribution of particles in plasma reactors in terms of the fundamental forces that act on the particles. We compare the model predictions to experimental measurements of particle distributions in a rf parallel plate plasma reactor.
Stresses in Pt/Pb(Zr,Ti)O3/Pt thin-film stacks for integrated ferroelectric capacitors
Authors: Spierings G. A. C. M. , Dormans G. J. M. , Moors W. G. J. , Ulenaers M. J. E. , Larsen P. K.
Published: July 2002

A study of the stresses in a ferroelectric capacitor stack deposited on an oxidized silicon substrate is presented. The capacitor stack was prepared with sputtered Pt bottom and top electrodes and a ferroelectric film of composition PbZrxTi1−xO3 (PZT) with x≊0.5 which was deposited using a modified sol-gel technique. The stresses were determined by the changes in the radius of curvature of the wafer following the deposition steps, during and after annealing treatments, and after etching steps in which the top electrode, the PZT film, and the bottom electrode were successively removed. The largest stress effects are found in the Pt electrodes which are deposited under conditions giving an intrinsic compressive stress. An annealing treatment exceeding 500 °C changed the stress of the bottom electrode from ≊−750 MPa (compressive) to a large tensile stress (≊1 GPa). This stress is largely thermal and is caused by the differences in thermal-expansion coefficients of the Pt film and the Si substrate. The stress of the PZT film is numerically relatively small (below ≊200 Mpa) and it is found to be of both thermal and intrinsic origin. The deposition and annealing of the top electrode has a profound influence on the stress of the PZT film as well as on the electrical properties. The stress behavior of the as-deposited PZT film shows a poling direction mainly in the plane of the substrate. An annealing of the complete capacitor stack changes the poling direction of the ferroelectric film to be perpendicular to the substrate. This explains the observed electrical switching properties of as-prepared as well as annealed ferroelectric capacitors.
Spatial confinement and saturation of substitutional platinum by diffusion into ion-beam damaged silicon
Authors: Holm B. , Bonde Nielsen K.
Published: July 2002

The diffusion of platinum into lightly damaged regions of ion-implanted silicon has been investigated using deep-level transient spectroscopy and capacitance-voltage profiling. The samples consisted of PtSi/Si n-type Schottky diodes which had been implanted with O, F, or Cl to an intermediate depth between the zero-bias and reverse-bias depletion boundaries, and subsequently annealed at a temperature of 700 °C. The distribution of in-diffused Pt was obtained by monitoring the electron emission from the acceptor level (EC−ET=0.23 eV) previously assigned to Pt in a distorted substitutional configuration. The Pt was found to be distributed approximately congruous with the vacancy distribution generated during implantation. For a typical implantation dose (≊1011 cm−2) we recorded an enhanced accumulation of Pt by about two orders of magnitude as compared to diffusion into nonimplanted material. This apparent decoration of the primary damage profile occurs without the simultaneous introduction of other electrically active defects on a comparable scale. We infer that the residual damage present during annealing is sufficient to promote accumulation to saturation of substitutional Pt in the region of primary implantation damage. This rather remarkable property of guided in-diffusion, a kind of gettering phenomenon, may have potential applications in Si-device engineering.
Evidence for inelastic processes for N+3 and N+4 from ion energy distributions in He/N2 radio frequency glow discharges
Authors: Hwang Helen H. , Olthoff James K. , Van Brunt Richard J. , Radovanov Svetlana B. , Kushner Mark J.
Published: July 2002

The ion energy distributions (IEDs) striking surfaces in rf glow discharges are important in the context of plasma etching during the fabrication of microelectronics devices. In discharges sustained in molecular gases or multicomponent gas mixtures, the shape of the IED and the relative magnitudes of the ion fluxes are sensitive to ion–molecule collisions which occur in the presheath and sheath. Ions which collisionlessly traverse the sheaths or suffer only elastic collisions arrive at the substrate with a measurably different IED than do ions which undergo inelastic collisions. In this article we present measurements and results from parametric calculations of IEDs incident on the grounded electrode of a rf glow discharge sustained in a He/N2 gas mixture while using a Gaseous Electronics Conference Reference Cell (33.3 Pa, 13.56 MHz). We found that the shape of the IEDs for N+3 and N+4 provide evidence for inelastic ion–molecule reactions which have threshold energies of <10 eV.
Strain imaging of a Pb(Zr,Ti)O3 thin film
Authors: Takata Keiji
Published: July 2002

Strain-imaging observation of a lead-zirconate-titanate film using a tunneling acoustic microscope (TAM) is described. This method detects fine strains in the piezoelectric film generated by the tip voltage and, therefore, measures and images the piezoelectric properties of the sample. The strains are detected either as a surface displacement of the sample by the feedback loop to keep the tip-to-sample spacing constant, or as a vibration generated by an alternating current tip voltage by the acoustic transducer in the TAM. Microscopic properties of a 70-nm-thick Pb(Zr0.5Ti0.5)O3 film grown by sputtering were investigated, and ferroelectricity was observed by applying voltages to areas of a couple of tens of nanometers in diameter. Local polarization control and its related space charge effect induced by the tip voltage are also shown.
Audible acoustic wave emission in excimer laser interaction with materials
Authors: Lu Y. F. , Hong M. H. , Chua S. J. , Teo B. S. , Low T. S.
Published: July 2002

Audible acoustic wave generation during excimer laser interaction with materials has been investigated. It is found that the amplitudes of acoustic waves depend on laser fluence, pulse number, and substrate material characteristics and can be used to determine the nature of laser–material interactions. When laser fluence is below the ablation threshold of the materials, the amplitudes are reduced to zero at large pulse number due to the cleaning of contaminants on the substrate surface. As laser fluence becomes higher than the ablation threshold, the amplitudes of acoustic waves also reduce with increasing pulse number but to a constant level instead of zero due to laser ablation of substrate materials. Since the surface contamination can be completely removed by a few pulses at high laser fluence, the constant level is attributed to the material ablation. It is also found that the constant level increases with laser fluence. By establishing a relationship between the amplitudes and laser parameters, real-time monitoring of laser–solid interaction can be achieved. Fast Fourier transform analysis of the wave forms shows that there are several frequency components included in the acoustic waves with a peak around 10.9 kHz as the dominant one, which is related to laser material ablation. The monitoring of the acoustic wave emission can, therefore, be used to find the nature of laser–substrate interaction (i.e., surface cleaning or ablation), and to find the ablation threshold.
Properties of porous silicon layers studied by voltammetric oxidation
Authors: Guerrero-Lemus R. , Moreno J. D. , Martínez-Duart J. M. , Marcos M. L. , González-Velasco J. , Gómez P.
Published: July 2002

The existence of an outer cracked layer and an inner more structured porous layer has been observed in electrochemically obtained porous silicon when drying procedures are carried out. The changes in the charge transferred to the porous structure during voltammetric oxidation, the interference fringes obtained by Fourier-transform infrared spectroscopic measurements, and scanning electron microscopy micrographs confirm the existence of this double layer. Also, drying procedures and voltammetric oxidations drastically affect the intensity and wavelength of the peak maximum in the photoluminescence spectrum. The evolution of the luminescent properties is explained by the introduction of nonradiative recombination centers.
Inverse giant magnetoresistance (invited)
Authors: Renard J.-P. , Bruno P. , Mégy R. , Bartenlian B. , Beauvillain P. , Chappert C. , Dupas C. , Kolb E. , Mulloy M. , Prieur J. , Veillet P. , Vélu E.
Published: July 2002

Inverse giant magnetoresistance (GMR) is obtained in multilayers alternating two ferromagnetic layers F1 and F2 with different asymmetry of spin scattering, α1≳1 and α2<1. This is clearly demonstrated in the simple spin-valve system with perpendicular magnetization Fe1−xVx/Au/Co. With respect to Fe, the FeV alloys with x=0.18 and 0.29 exhibit an inversion of the spin scattering coefficients (αFe≳1, αFeV<1) due to the change of the densities of states at the Fermi level. The inverse MR of FeV/Au/Co is studied as a function of FeV layer thickness and temperature and compared to calculations based on the Camley–Barnas model. The data show that the inverse GMR is due to the bulk scattering within the FeV layer, which coexists with a substantial interface scattering favoring normal GMR.
The role of Ta and Pt in segregation within Co-Cr-Ta and Co-Cr-Pt thin film magnetic recording media
Authors: Kemner K. M. , Harris V. G. , Chakarian V. , Idzerda Y. U. , Elam W. T. , Kao C.-C. , Feng Y. C. , Laughlin D. E. , Woicik J. C.
Published: July 2002

Polarization dependent extended x-ray absorption fine structure (PD-EXAFS) and magnetic circular dichroism (MCD) measurements of CoCrTa and CoCrPt films, sputter deposited at varying substrate temperatures, were performed to investigate the average local structure and chemistry about the Ta, Pt, and Co atoms and the average magnetic moment of the Co and Cr atoms within these films. Results from the MCD measurements indicate the average net magnetic moment of the Cr atoms is opposite in direction and five percent in amplitude relative to the Co moments. Inspection of the Fourier transforms of the XAFS data from these samples shows an increase in structural disorder around the Ta and Pt atoms with increasing substrate deposition temperature. A further comparison between the Ta and Pt edge EXAFS results show that the temperature-dependent increase in structural disorder is greater around the Ta atoms in the CoCrTa system than it is around the Pt atoms in the CoCrPt system.
Seed layer induced (002) crystallographic texture in NiAl underlayers
Authors: Lee Li-Lien , Laughlin David E. , Lambeth David N.
Published: July 2002

The magnetic properties of Co alloy thin films are strongly dependent on their crystallographic texture and microstructure which in turn can be controlled by the texture of the underlayer. For Co alloy longitudinal recording media with Cr underlayers, it is desirable to have (002) textured Cr underlayers. Since NiAl has the B2 structure and has a lattice constant similar to that of Cr, NiAl has the potential to be an alternative underlayer to Cr. However, the (002) crystallographic texture of the NiAl films is difficult to obtain. It is found that the (002) texture in NiAl underlayers can be achieved by employing a seed layer of either (002) textured Cr or MgO. Because of the improved texture a significant increase of the in-plane coercivity in CoCrPt/NiAl films was obtained.
Study of the nitrogen diffusion mechanism in R2Fe17
Authors: Zhang Y. D. , Budnick J. I. , Hines W. A. , Yang D. P.
Published: July 2002

Previously, nuclear magnetic resonance experiments and diffusion calculations have indicated that the distribution of nitrogen atoms in a Y2Fe17Nx particle with intermediate N content is characterized by a nitrided region and an unnitrided region. In order to directly detect this two-region configuration, x-ray diffraction experiments have been carried out on systematically ground nitrogenated samples. Furthermore, x-ray diffraction and 89Y nuclear magnetic resonance on vacuum-annealed samples show that the two-region configuration is stable, and that the nitrogen atoms do not diffuse further into the particle. Thermal conductivity detection measurements indicate that only 5% of the inserted N atoms can be released by vacuum annealing at the nitrogenation temperature.
Origin of low frequency noise and 1/f fluctuations of tunneling current in scanning tunneling microscopes
Authors: Sugita Satoshi , Mera Yutaka , Maeda Koji
Published: July 2002

The generation mechanism of conspicuous low frequency noise (including 1/f fluctuations) observed in the tunneling current of scanning tunneling microscopes was studied experimentally by investigating combinations of Pt–Ir tips and Au films or crystalline graphite samples. For 1/f noise, the noise intensity at a fixed current increases with increasing bias voltage or increasing tip–sample distance z. The noise power varies from place to place in a sample surface of Au film. The spatial variation of the noise has a positive correlation with the magnitude of the tunneling barrier height φ measured by the z modulation method. The demodulated signal in the z modulation experiments also exhibits fluctuations with a 1/f spectrum of the relative magnitude nearly equal to that in the current noise. The above features are observed also in high vacuum (10−7 Pa), ruling out the possibility that the current noise is brought about by absorption/desorption of gas molecules in the ambient. Tips capable of imaging graphite surface in atomic resolution sometimes yield random telegraphic noise with a Lorentzian spectrum, which is well understood by considering that the sharp tips select a single relaxation process that happens to be located in the narrow current path. Nevertheless, the 1/f spectra were in many cases obtained even in the atomic-resolvable tips. The experimental results are discussed based on two models, the φ fluctuation model and the phonon density fluctuation model.
First principles determinations of magnetostriction in transition metals (invited)
Authors: Wu Ruqian , Freeman A. J.
Published: July 2002

The mechanism of magnetostriction in transition metal bulk (fcc Co) and thin films [Co/Pd(001) and Co/Cu(001)] is investigated using the ab initio full potential linearized augmented plane wave method. With the aid of the state tracking and torque approaches the magnetocrystalline anisotropy energy, the essential ingredient of the magnetostriction, is found to be a linear function of the interlayer distances. The calculated magnetostrictive coefficients and magnetoelastic coupling constants for bulk fcc Co agree very well with experiment. The calculated λ001 at the Co/Pd(001) interface is much larger in magnitude (+2.3×10−4) and differs in sign compared to that for Co/Cu(001)(−5.7×10−5). In these thin films, the hybridization between the Co- dxz,yz and the underlying substrate d states is found to play the key role.
Effect of base layers on the soft magnetic properties of FeTaN films
Authors: Inturi V. R. , Barnard J. A.
Published: July 2002

The effects of base layers with different crystal structures and well defined growth textures on the soft magnetic properties of FeTaN films have been studied. Broadly speaking, base layers with fcc or hcp crystal structures and having predominantly (111) and (0002) growth textures, respectively, significantly improve the soft magnetic properties of the subsequently deposited (110) textured bcc FeTaN films. Base layers with bcc crystal structures and (110) growth textures either degrade the soft magnetic properties or have little effect.
Temperature dependence of the band gap of Cd1−xZnxTe alloys of low zinc concentrations
Authors: Sánchez-Almazan F. G. , Navarro-Contreras H. , Ramírez-Flores G. , Vidal M. A. , Zelaya-Angel O. , Rodríguez M. E. , Baquero R.
Published: July 2002

The temperature dependence of the fundamental band-gap E0 of Cd1−xZnxTe alloys with zinc concentrations in the 0 to 0.3 range has been determined by modulated photoreflectance (PR). E0 is found to vary from 1.511 eV for x=0.00 to 1.667±0.008 eV for x=0.3, at room temperature and from 1.602 eV at x=0.00 to 1.762±0.004 eV for x=0.3 at 10 K. The measured broadening parameters Γ have values between 25 and 45 meV at room temperature and decrease monotonically to values around 5 meV or smaller at 10 K. The temperature dependence of the observed band gap energies is well described by the well known Varshni formula E(T)=E(0)−AT2/(T+Θ) for all samples studied. The PR temperature broadening is well understood assuming that it results from the scattering of the excitonic electron-hole pair responsible of the band-to-band transition PR signal off LO phonons.
An experimental study on the shear viscosity of solids
Authors: Kobayashi H. , Hiki Y. , Takahashi H.
Published: July 2002

Viscoelastic solids with high viscosity were experimentally studied with the intention of having them deformed under uniform shear stress. A kind of sandwich method was developed for applying a constant shear stress to a specimen, and its deformation was observed optically using heterodyne interferometry with a sensitivity of 10 nm in displacement measurement. Time-dependent deformation data were analyzed on the basis of a mechanical model of anelasticity plus viscosity. Viscosity in the range of 108–1014 Pa⋅s could be determined at temperatures of 20–200 °C. Through a simulation using the finite element method together with an experiment visualizing the deformation, the specimen deformation was shown to be of an almost uniform shear mode. Experiments were performed to determine the temperature dependence of viscosity for several kinds of glasses near their glass transition Tg, and the determined viscosity values were about 107 Pa⋅s at Tg. The viscosity values measured by a rotation disk viscometer were in good agreement with the present data. The viscosity of some glasses was also measured by the beam bending and penetration methods, and values of 109–1012 Pa⋅s at Tg were obtained. The large discrepancy between the two kinds of data was considered.
Magnetization of cadmium ferrite prepared by coprecipitation
Authors: Yokoyama M. , Sato T. , Ohta E. , Sato T.
Published: July 2002

We investigated the magnetization of the ultrafine cadmium ferrite particles formed during the coprecipitation method and discussed the origin of enhanced magnetization based on the magnetic properties. A transmission electron microscopy micrograph shows aggregation of fine particles having two kinds of shapes, fibrous and granular. X-ray diffraction patterns of the specimens prepared by the coprecipitation method are composed of peaks corresponding to CdFe2O4, Cd(OH)2, and α-FeO(OH). The pattern indicates that the peaks of CdFe2O4 are fairly broad, suggesting the formation of a very small crystallite, with an average size of ∼8 nm. The ultrafine CdFe2O4 particles exhibit ferromagnetic behavior and have a net magnetization of 89±5 emu/g at 6 K. These results suggest that there must be many ferromagnetic clusters consisting of Fe3+ ions at the B sites around Fe3+ ions at the A site by the A–B interactions. Thus, such a change in the distribution of Fe3+ ions in the ultrafine CdFe2O4 particles results in increasing magnetization with decreasing particle size.
Nanometer-scale heterogeneity in SiO2–GeO2 glass preforms and fibers prepared by vapor phase axial deposition method
Authors: Hosono Hideo , Kawamura Ken-ichi , Kawazoe Hiroshi , Nishii Junji
Published: July 2002

Nanometer-scale heterogeneity of Ge ions in SiO2:GeO2 (10–15 mol %) glass preforms prepared by vapor phase axial deposition method and in optical fibers drawn from the preform was found by transmission electron microscopic observation. Both preforms and fibers were comprised of 8–10 nm sized Ge-rich and Si-rich phases. Observation of Ge E′ centers in the as-prepared state and the formation of Ge E′ centers with light illumination with 5 eV-light may be understood by the occurrence of these heterogeneity.
Comment on ‘‘Krammer’s rate theory, broken symmetries, and magnetization reversal’’ [J. Appl. Phys. 76, 6310 (1994)]
Authors: Aharoni Amikam
Published: July 2002

In a series of papers, H. B. Braun [J. Appl. Phys. 76, 6310 (1994), and references therein] suggested a model for magnetization reversal in an infinite cylinder, but did not include the magnetostatic energy. It is shown here that the magnetostatic energy term of this one-dimensional soliton solution cannot be neglected, and cannot be normalized out. This argument invalidates all the theoretical conclusions from this model about superparamagnetism in an infinite circular cylinder, and about the reversal modes of elongated particles.
Carrier compensation and scattering mechanisms in p-GaSb
Authors: Dutta P. S. , Prasad V. , Bhat H. L. , Kumar Vikram
Published: July 2002

The hole transport properties of gallium antimonide with various degrees of tellurium compensation have been investigated in the temperature range of 4.2–300 K. For the undoped GaSb, the p-type conductivity arises from a doubly ionizable native defect VGa GaSb. In the Te compensated samples, apart from the Te-donor level and the VGaGaSb center, an acceptor level resulting from complexation of VGa GaSb with TeSb has been found. This acceptor level lies ∼70 meV above the valence band edge. The concentration of this center depends on the melt composition and the level of Te present in the melt during growth of crystals. Most interestingly, at very low level of Te concentration, an additional triple native acceptor (VGa GaSb VGa) has also been observed. With the increase in Te concentration, the mobility decreases and a shift in the mobility peak to higher temperature is observed. The low-temperature mobility is limited by ionized impurity scattering. At higher temperatures, the scattering mechanisms depend on Te concentration in the sample. In this regime, significant contributions from acoustic, nonpolar optical, and polar optical phonon scattering are observed for samples with low levels of Te. In contrast, the impurity scattering dominates even at room temperature for highly compensated crystals.
Preparation of hydrogenated amorphous germanium nitrogen alloys by plasma enhanced chemical vapor deposition
Authors: Xu Jun , Chen Kunji , Feng Duan , Miyazaki Seiichi , Hirose Masataka
Published: July 2002

A series of hydrogenated amorphous germanium nitrogen alloys have been prepared by using plasma enhanced chemical vapor deposition system. The structure, optical and electrical properties have been investigated and compared with the samples produced by reactive sputtering method. It is found that inclusion of nitrogen into a-Ge:H network increases the structural stability and induces the significant changes both in optical and electrical properties. Hydrogenated a-GeN films have also been fabricated by using nitridation and high hydrogen dilution technique. These unique features have been described in this article.
Non-contacting measurements of photocarrier lifetimes in bulk- and polycrystalline thin-film Si photoconductive devices by photothermal radiometry
Authors: Mandelis A. , Othonos A. , Christofides C. , Boussey-Said J.
Published: July 2002

Laser-induced and frequency-scanned infrared photothermal radiometry was applied to a crystalline-Si photoconductive device, and to polysilicon thin-film photoconductors deposited on oxidized Si substrates by an LPCVD method. A detailed theoretical model for the radiometric signal was developed and used to measure the free photoexcited carrier plasma recombination lifetime, electronic diffusivity and surface recombination velocity of these devices, with the simultaneous measurement of the bulk thermal diffusivity. A trade-off between detectivity/gain and frequency-response bandwidth was found via the lifetime dependence on the wafer background temperature rise induced by Joule-heating due to the applied bias. This effect was most serious with the bulk-Si device, but was limited by the high resistivity of the LPCVD thin-film devices. In the case of the bulk-Si device, the results of photothermal radiometry were compared with, and corroborated by, frequency-scanned photocurrent measurements. More sophisticated analysis was shown to be required for the interpretation of the polysilicon photoconductor frequency-responses, perhaps involving the fractal nature of carrier transport in these grain-structured devices.
Self-regulation of iron ion concentration in hydrated porous glasses
Authors: Choi C. , Haranczyk H. , Soga K. G. , Rumm R. J. , Pintar M. M.
Published: July 2002

The water proton spin-lattice relaxation rate was measured in Fe contaminated water filled porous glasses with pore diameters of 548 and 2917 Å at 0.65T at room temperature as a function of pore hydration. Two distinct regimes could be defined. A ‘‘wet’’ pores regime (0.6<V0/V<1) and a regime with water only within the pores (1<V0/V<4), where V0 is the pore volume and V the water volume. In both regimes, the proton relaxation rate varies linearly with V0/V. A small Fe ion concentration in porous silica glass water remains constant while the hydration of pores is changed by a factor of ≊4, which is a necessary assumption to model the observed proton spin-lattice relaxation rate. Such a constant small concentration premise agrees with the Langmuir isotherm, which for systems with large surface to volume ratios (S/V0), predicts a constant small volume concentration. In the two studied porous glasses with S/V0 of 9.2×106 and 42×106 m−1, the condition for large S/V0 was satisfied, while the Fe volume concentration which was ∼1 mM was small, as required. An analysis of the paramagnetically enhanced proton relaxation is presented.
Morphology and microstructure of epitaxial Cu(001) films grown by primary ion deposition on Si and Ge substrates
Authors: Karr Brian W. , Kim Y. W. , Petrov I. , Bergstrom D. B. , Cahill David G. , Greene J. E. , Madsen L. D. , Sundgren J.-E.
Published: July 2002

A low-energy, high-brightness, broad beam Cu ion source is used to study the effects of self-ion energy Ei on the deposition of epitaxial Cu films in ultrahigh vacuum. Atomically flat Ge(001) and Si(001) substrates are verified by in situ scanning tunneling microscopy (STM) prior to deposition of 300 nm Cu films with Ei ranging from 20 to 100 eV. Film microstructure, texture, and morphology are characterized using x-ray diffraction ω-rocking curves, pole figure analyses, and STM. Primary ion deposition produces significant improvements in both the surface morphology and mosaic spread of the films: At Ei>37 eV the surface roughness decreases by nearly a factor of 2 relative to evaporated Cu films, and at Ei≂35 eV the mosaic spread of Cu films grown on Si substrates is only ≂2°, nearly a factor of 2 smaller than that of evaporated Cu. During deposition with Ei≂25 eV on Ge substrates, the film coherently relaxes the 10% misfit strain by formation of a tilt boundary which is fourfold symmetric toward 〈111〉. The films have essentially bulk resistivity with ρ=1.9±0.1 μΩ cm at room temperature but the residual resistance at 10 K, ρ0, shows a broad maximum as a function of Ei, e.g., at Ei≂30 eV, ρ0=0.5 μΩ cm.
Low frequency noise in 4H silicon carbide
Authors: Levinshtein M. E. , Rumyantsev S. L. , Palmour J. W. , Slater D. B.
Published: July 2002

The bulk low frequency noise has been investigated in the 4H silicon carbide polytype. In the temperature range of 300–550 K the noise spectral density S is proportional to f−1.5, where f is the measurement frequency. A very low noise level has been observed for the bulk noise. At 300 K, the Hooge constant α is as small as (2–4)×10−6 at f=20 Hz and α⩽5×10−7 at f=1300 Hz. At T⩾600 K, the generation-recombination noise of a local level makes the main contribution into the total low frequency noise. The electron capture cross section σ of this level depends very strongly on temperature. In the temperature range of 620–700 K, the temperature dependence of σ can be expressed as σ∼exp(−E1/kT), with an activation energy E1 as high as 2.7 eV.
Electron mobility and subband population tuning by a phonon wall inserted in a semiconductor quantum well
Authors: Požela J. , Jucienė V. , Namajūnas A. , Požela K.
Published: July 2002

The electron-optical phonon scattering rate and electron subband population in a semiconductor quantum well (QW) containing a phonon wall (Ph-wall) is calculated. It is shown that the Ph-wall (a barrier of one–two AlAs monolayers) inserted into an AlAs/GaAs/AlAs QW changes radically the intra- and intersubband scattering rates. Electron subband energy spectra, phonon frequencies, electron and phonon wave functions and scattering rates are found to depend on the Ph-wall position in the QW. The largest decrease of the intrasubband electron-phonon scattering rate takes place when the Ph-wall is located at the QW center. The intersubband scattering rate increases resonantly when the intersubband energy separation is equal to the interface phonon energy. The Ph-wall increases the electron mobility in the QW except the areas where the resonance scattering takes place. The Ph-wall position in the QW causing the subband population inversion is determined in the case of optical excitation.