bluuebunny/crossref_metadata_2025 huggingface dataset:
Growth of giant magnetoresistance spin valves using indium as a surfactant
Authors: Egelhoff W. F. , Chen P. J. , Powell C. J. , Stiles M. D. , McMichael R. D.
Published: July 2002

We have investigated the use of In as a surfactant to achieve smoother interfaces in spin-valve multilayers of the general type: FeMn/Ni80Fe20/Co/Cu/Co/Ni80Fe20/glass. The coupling field is reduced from ∼0.8 to ∼0.3 mT, presumably by suppressing roughness at the Co/Cu/Co interfaces, when 0.5–1.0 nm In is deposited on the first Co film just prior to Cu deposition or on the Cu film just prior to deposition of the second Co film. The In has a strong tendency to float-out to the surface during deposition of the spin valve leaving the spin-valve layers largely intact. The exchange bias at the FeMn/Ni80Fe20 interface can be increased from 12 to 25 mT by the use of thicker In (1.4 nm).
N incorporation in InP and band gap bowing of InNxP1−x
Authors: Bi W. G. , Tu C. W.
Published: July 2002

The N incorporation behavior in InP grown by gas-source molecular beam epitaxy using a N radical beam source has been investigated. At a given growth temperature, the N composition in InNxP1−x is generally different from the N2 flow-rate fraction in the vapor phase, and as the N2 flow-rate fraction increases, it saturates after increasing to a certain point. This may be due to the small solubility of N in InP. Increasing the growth temperature will result in a loss of N incorporation into the InP as a result of the faster desorption of the N at high temperatures. Optical absorption measurements reveal that the band-gap energy of InNxP1−x decreases drastically, resulting in band-gap bowing.
Two-dimensional fluid model of an inductively coupled plasma with comparison to experimental spatial profiles
Authors: Bukowski J. D. , Graves D. B. , Vitello P.
Published: July 2002

A key need for the development and testing of models suitable for chemically active, low pressure plasmas is detailed comparisons between model predictions and experimental measurements. In this paper, a two-dimensional, axisymmetric fluid model of an inductively coupled plasma is described, and model predictions are compared to the experimental measurements of P. A. Miller, G. A. Hebner, K. E. Greenberg, P. D. Pochan, and B. P. Aragon [J. Res. Natl. Inst. Stand. Technol. 100, 427 (1995)] of electron density, electron temperature, and plasma potential. Comparisons between model predictions and experimental measurements were made in argon and chlorine discharges. Qualitative to semiquantitative agreement between the model predictions and experimental diagnostics was observed, suggesting that assumptions made in the model are reasonably accurate.
Formation of buried TiN in glass by ion implantation to reduce solar load
Authors: Was Gary S. , Rotberg Victor , Platts Dennis , Bomback John , Benoit Robert
Published: July 2002

Ti and N were implanted into soda lime glass to doses up to 4.5×1017 cm−2 to reduce solar load and infrared transmission. Analysis of the Ti+N implant distributions by Rutherford backscattering spectrometry and x-ray photoelectron spectroscopy (XPS) revealed profiles which closely followed each other as designed by the selection of implant energies. XPS, x-ray diffraction, and selected area electron diffraction in transmission electron microscopy also confirmed the existence of a crystalline B1-type, cubic TiN layer, 140 nm wide, at doses greater than 9×1016 cm−2. Optical measurements showed that the fraction of infrared radiation reflected was increased by almost a factor of 4 compared to an increase of 1.8 in the visible region. The percentage of the total solar energy rejected reached 80% at the highest dose, indicating that the buried TiN layer is highly effective in reducing solar energy transmission.
Characterization of the effect of growth conditions on a-SiC:H films
Authors: Rava P. , Crovini G. , Demichelis F. , Giorgis F. , Pirri C. F.
Published: July 2002

The effects of dissipated power and gas dwell time in SiH4+CH4 plasmas on the properties of a-SiC:H films deposited by plasma-enhanced chemical-vapor deposition have been investigated for different methane fractions in plasmas operating in the low-power regime. Optical, structural, and electrical characterizations have been performed in order to investigate the influence of dissipated power and molecule dwell time on the physical properties of a-SiC:H films. It was found that both the investigated deposition parameters can have a remarkable influence on carbon incorporation and on optical properties such as the energy gap. In particular an increase in the dissipated power or in the molecule dwell time leads to an increase in carbon incorporation and in energy gap. The electrical properties and defect density are still those of device quality films grown in standard deposition conditions and are not influenced by variations in dissipated power or gas dwell time. From these results some conclusions regarding the growth mechanisms are drawn.
Red shifting the intersubband response of quantum-well infrared photodetectors by thermal annealing
Authors: Malin J. I. , Liu P. , Sengupta D. K. , Fang W. C. , Chuang S. L. , Feng M. , Stillman G. E. , Hsieh K. C.
Published: July 2002

Selectively red shifting the photoresponse of intersubband GaAs/Al0.25Ga0.75As multiple-quantum-well (MQW) infrared photodetectors (QWIPs) by furnace and rapid thermal annealing is explored. Selective interdiffusion of the MQW is achieved by dielectric encapsulating (SiO2 or Si3N4) the surface. The high dark current of annealed QWIPs is attributed to dopant out-diffusion from the QWs into the barriers. Declining responsivities result from reduced carrier density in the QW and a red shift of the intersubband transition energy. In this work, the intersubband energy is determined by the Fourier synthesis model and compared with experimental results (further confirming the interdiffusion mechanism). Minimal dark current and responsivity degradation is observed for Si3N4-encapsulated QWIPs red shifted by 1 μm
Detection of stress concentrations around a defect by magnetic Barkhausen noise measurements
Authors: Mandal K. , Dufour D. , Sabet-Sharghi R. , Sijgers B. , Micke D. , Krause T. W. , Clapham L. , Atherton D. L.
Published: July 2002

The stress distribution around a 50% blind-hole pit in a steel pipe with a 9 mm wall has been studied using high-resolution magnetic Barkhausen noise (MBN) measurements. A magnetic disk read-head is used as the pick up coil in the MBN probe. The study shows a stress concentration factor of ∼2 at the defect edge perpendicular to the direction of applied stress and ∼−0.6 at the edge parallel to the same. The experimental results are consistent with the analytical solutions obtained by the Airy’s stress function approach.
Surface evolution on vicinal GaAs(001) surfaces in the transition range from two-dimensional to step-flow growth
Authors: Nörenberg H. , Däweritz L. , Schützendübe P. , Ploog K.
Published: July 2002

We have used a 90° double reflection high-energy electron diffraction (RHEED) setup to perform a comprehensive real-time study of the morphology of vicinal GaAs(001) surfaces during molecular beam epitaxy. The technique allows to record RHEED intensities simultaneously in the [1̄10] and [110] azimuths and thus enables a detailed study of anisotropy effects. Comparative measurements on surfaces with 2° misorientation towards (111)Ga (A surface) and towards (11̄1)As (B surface), respectively, show that independent on the step type and reconstruction anisotropy, recordings of the specular beam intensity in the azimuth perpendicular to the steps are clearly dominated by the evolution of the staircase order whereas intensity recordings in the azimuth parallel to the steps reveal the evolution of the step edge roughness. Measurements over a wide range of substrate temperatures give insight in the competition between kinetic processes and thermodynamic equilibrium on a length scale accessible to RHEED. For the A surface the transition between two-dimensional (2D) growth and step-flow growth occurs not only at higher temperature than on the B surface, but the disappearance of the intensity oscillations occurs also at different substrate temperatures in different azimuths. The ∼20 °C higher disappearance temperature in the [1̄10] azimuth is explained with a model based on previous scanning tunneling microscopy results which revealed an increasing elongation of the islands in [1̄10] direction with increasing substrate temperature. The B surface is more isotropic and hence no difference in the transition temperature in the two azimuths could be detected. During growth in the transition range between 2D and step-flow growth we observe increased terrace width fluctuations on the B surface, whereas the A surface becomes more uniformly stepped. This demonstrates that in the kinetically controlled regime the anisotropic barrier height for downward diffusion of adatoms over step edges plays an important role for the evolution of the surface morphology. At elevated temperature the barrier height allows downward jumps of the adatoms over B-type steps but not over A-type steps. At conditions close to the thermodynamic equilibrium a kinetic smoothing is observed on the A as well as on the B surface indicating another mechanism to be effective with a change of the energetics due to ordering of the steps in combination with a disordering of the reconstruction on the terraces. This surface is, however, metastable and recovers after growth interruption rapidly (at substrate temperatures >580 °C within less than 1s) to the equilibrium bunched surface.
High coercivity CoPtCr, CoPt films deposited at high power and high bias conditions for hard bias applications in magnetoresistive heads
Authors: Choe G. , Funada S. , Tsoukatos A. , Gupta S.
Published: July 2002

We report, for the first time, coercivity values greater than 2000 Oe with Mrt values of 3.0 memu/cm2 for Cr/CoPt12Cr13 and Cr/CoPt20 bilayer films deposited by dc magnetron sputtering at room temperature. CoPtCr films sputtered at a deposition rate of 98 Å/s and high bias voltage showed Hc of 1965 Oe with Mrt of 3 memu/cm2, while CoPt films sputtered at 99 Å/s and moderate substrate bias showed Hc of 2350 Oe with Mrt of 3 memu/cm2. X-ray diffraction studies indicated that Co(10.0) and (11.0) texture leading to in-plane orientation of c axis are promoted in the films sputtered at high deposition rate and bias conditions. Furthermore, the grain-to-grain epitaxy between the Cr underlayer and the Co alloy layer as well as the dense Co grains growing in a columnar shape without voids resulted in higher Hc and Mrt without degradation of coercive squareness. Plots of vs Mrt for films deposited under the optimum bias conditions offer a wide range of useful Hc and Mrt combinations for hard bias applications in magnetoresistive heads.
Systematic study of magnetic parameters of Ni–Zn ferrite synthesized by soft chemical approaches
Authors: Anil Kumar P. S. , Shrotri J. J. , Deshpande C. E. , Date S. K.
Published: July 2002

Active powders of Ni–Zn ferrite were synthesized by soft chemical approaches and were extensively characterized using x-ray diffraction, scanning electron micrographs, vibrating sample magnetometer, resistivity, and permeability/loss factor techniques. The variation in the sintering conditions established a useful microstructure–magnetic permeability correlation.
Analysis of eddy current loss in Mn–Zn ferrites for power supplies
Authors: Yamada S. , Otsuki E.
Published: July 2002

From the investigation regarding the dependence of power loss and electrical resistivity at a temperature at which crystalline anisotropic energy becomes zero, eddy current loss and residual loss could be obtained separately. The increase in residual loss as exciting magnetic flux density, Bm, follows Bm2 at 1 MHz and Bm3–4 at 100 kHz. This result shows that the residual loss arises from spin rotation inside the magnetic domain wall. The domain size was estimated to be in the region of 1–2 μm by applying the barlike domain-wall model to the eddy current loss obtained experimentally. The frequency of the spin rotation is estimated using the domain size, the thickness of the domain wall, and the exciting condition. The spin rotation inside the domain wall can reach the magnetic resonant frequency of Mn–Zn ferrites under the exciting condition of f>500 kHz and Bm>70  mT. This magnetic resonance occurring inside the domain wall is considered to generate the large residual loss.
Photothermal radiometry of infrared translucent materials
Authors: Paoloni S. , Walther H. G.
Published: July 2002

SiC layers on silicon have been investigated by photothermal radiometry to study the influence of infrared emission spectra on the photothermal signal behavior. This was done by placing different band pass filters in front of the infrared detector. Because of the small amplitude of the obtained infrared signal, background contributions must be eliminated. A technique to correct the data with respect to background is presented and experimentally tested.
Electronic effects of ion damage in hydrogenated amorphous silicon alloys
Authors: van Swaaij R. A. C. M. M. , Annis A. D. , Sealy B. J. , Shannon J. M.
Published: July 2002

Electronic properties of silicon rich amorphous silicon alloys were investigated using diode structures and thin films on Corning 7059 glass following the implantation of 1 MeV Ge+ ions with doses up to 2.4×1015 ions/cm2. Optical absorption measurements on hydrogenated amorphous silicon (a-Si:H) and amorphous silicon nitride (a-SiNx:H) showed that the optical band gap decreases with the implanted ion dose. The hydrogen concentration was not affected by the implantation and therefore the change in optical band gap was consistent with a broadening of the band tails as confirmed by dual beam photoconductivity measurements. Annealing studies showed that recovery of the band gap could be achieved at temperatures of ≈250 °C. This recovery was almost complete following low dose ion implantation, but a residual amount of damage remained which increased with the dose before saturating. Results of electrical measurements on metal-semiconductor barriers showed a correlation between optical and electrical behavior with ion dose. We propose a model in which the barrier height and the optical band gap vary in the same way with the ion dose.
Microstructural study of Mg-doped p-type GaN: Correlation between high-resolution electron microscopy and Raman spectroscopy
Authors: Tsen S.-C. Y. , Smith David J. , Tsen K. T. , Kim W. , Morkoç H.
Published: July 2002

A series of Mg-doped GaN films (∼1–1.3 μm) grown by reactive molecular beam epitaxy at substrate temperatures of 750 and 800 °C has been studied by high-resolution electron microscopy (HREM) and Raman spectroscopy. Stacking defects parallel to the substrate surface were observed in samples grown on sapphire substrates at 750 °C with AlN buffer layers (60–70 nm) at low Mg concentration. A transition region with mixed zinc-blende cubic (c) and wurtzite hexagonal (h) phases having the relative orientations of (111)c//(00.1)h and (11̄0)c//(10.0)h was observed for increased Mg concentration. The top surfaces of highly doped samples were rough and assumed a completely zinc-blende phase with some inclined stacking faults. Samples grown with a Mg cell temperature of 350 °C and high doping levels were highly disordered with many small crystals having inclined stacking faults, microtwins, and defective wurtzite and zinc-blende phases. Correlation between HREM and Raman scattering results points towards the presence of compressive lattice distortion along the growth direction which might be attributable to structural defects. The films grown at 800 °C had better quality with less observable defects and less yellow luminescence than samples grown at 750 °C.
Investigation of substrate-dependent nucleation of plasma-deposited microcrystalline silicon on glass and silicon substrates using atomic force microscopy
Authors: Smith L. L. , Srinivasan E. , Parsons G. N.
Published: July 2002

In order to define mechanisms for pulsed-gas plasma enhanced substrate-selective deposition of silicon, the initial stages of microcrystalline silicon (μc-Si) growth by plasma enhanced chemical vapor deposition on both c-Si and glass substrates were investigated by means of atomic force microscopy (AFM) and reflective high energy electron diffraction (RHEED). Differences in initial substrate morphology were reflected in significant differences in film surface morphology in the early stages of growth. AFM images and rms roughness measurements indicated that the initial growth on the c-Si substrate was three dimensional in character. On glass, the initial Si deposits were much more irregular in shape and the tallest features extended over wider areas than the initial deposits on c-Si. The character of the initial growth on glass was partly obscured by the roughness of the substrate, but the appearance of the initial Si deposits suggested a flatter and more two-dimensional character on glass than on c-Si. As the Si deposition progressed, the films on the different substrates developed similar morphology with increasing thickness. On the c-Si substrate, surface coverage was nearly complete at 50 Å. RHEED analysis of the films grown on c-Si revealed the presence of amorphous structure in the early stages of film growth, which began to transition to a randomly oriented μc-Si structure after 40–50 Å of growth. Observed differences in nucleation affirm and clarify proposed mechanisms and limitations for plasma enhanced selective μc-Si deposition.
The carrier contribution to the elastic constants in small-gap materials
Authors: Ghatak K. P. , Banerjee J. P. , Nag B.
Published: July 2002

We present a simple theoretical analysis of the carrier contribution to the second and third order elastic constants in nonparabolic materials on the basis of an electron dispersion law by taking into account various anisotropies of the energy band structure within the framework of k⋅p formalism. It is found that the carrier contributions to the elastic constants in n-Cd3As2, InSb, InAs, GaAs, Hg1−xCdxTe, and lattice matched In1−xGaxAsyP1−y increase with the increase of carrier degeneracy in different manners which, depend on the material parameters and band structure. A relationship between the said contributions and the thermoelectric power has been derived for materials obeying arbitrary dispersion laws in the presence of a classically large magnetic field. Our analysis is based on the derivation of a more generalized band structure of the materials which agrees well with the relationship suggested. It is also observed that the second and third order elastic constants increase with the decrease of alloy composition for ternary and quaternary compounds, respectively. The corresponding well-known results for degenerate wide-gap materials can be derived as special cases of our generalized analysis.
Optical measurements of oxidation behavior of silver nanometer particle within pores of silica host
Authors: Cai Weiping , Zhong Huicai , Zhang Lide
Published: July 2002

The oxidation behavior of silver (Ag) nanometer particles (about 3 nm in diameter) within pores of a silica host in ambient air (298 K) was investigated from optical absorption measurements. Thermodynamic analysis indicates that Ag nanoparticles can be oxidized in air at room temperature. Exposure to air results in a blueshift of the absorption edge with time, which is attributed to the surface oxidation of Ag nanoparticles. On this basis, we present a new method to investigate the oxidation process of Ag nanoparticles. Further experiments show that in air at room temperature oxidation occurs in surface layers of Ag particles in the form of a dense Ag2O film. Once the dense film is formed, further oxidation is restrained. A high relative humidity in the air results in fast surface oxidation. In air with a relative humidity 80% at room temperature, a dense film can be formed in 2 h. When the relative humidity is <30%, no measurable oxidation was found even after several months.
The grain size dependence of the mobility and lifetime in chemical vapor deposited diamond photoconductive switches
Authors: Yoneda Hitoki , Ueda Ken-ichi , Aikawa Yumi , Baba Kazuhiro , Shohata Nobuaki
Published: July 2002

The grain size dependence of the carrier lifetimes and collection distances of chemical vapor deposited (CVD) diamond films of 0.1–10 μm average grain size was measured. The estimated values of the mobilities and lifetimes indicated that the dominant recombination process had occurred inside the grains, not the grain boundaries. This finding was confirmed by measuring the electric field dependence of the lifetime and the collection distance. Under a high electric field, however, a major decrease in decay time is expected for smaller grain sizes, due to the increase in the number of carriers which reach the grain boundaries during their lifetime. Such a decrease was observed in a 0.8-μm grain size sample at E=105 V/cm. The data also showed that a 1-ps kV electrical pulse from a dc bias across a diamond film coated gap can be achieved with a CVD-deposited diamond photoconductive switch of sub-μm grain size.
Band discontinuities and local interface composition in BeTe/ZnSe heterostructures
Authors: Nagelstrasser M. , Dröge H. , Fischer F. , Litz T. , Waag A. , Landwehr G. , Steinrück H.-P.
Published: July 2002

Using photoelectron spectroscopy, we have investigated the band alignment at the interface of pseudomorphic BeTe/ZnSe(100) heterojunctions for different interface terminations. The heterostructures of high structural quality have been produced by molecular beam epitaxy; the interface termination was adjusted by variation of the growth parameters between the growth process of ZnSe and BeTe. The valence band offset for a Zn-rich BeTe/ZnSe interface is determined to be 1.26±0.15 eV, for the Se-rich BeTe/ZnSe interface a value of 0.46±0.15 eV is obtained. Our results show that the band alignment can be modified by the interface composition even for isovalent heterostructures.
Investigation of the magnetic properties of ErFe11Ti and ErFe11TiH in high magnetic field
Authors: Isnard O. , Guillot M.
Published: July 2002

Marked changes of the main structural and magnetic properties of the RFe11Ti phases are induced by hydrogen insertion. High field magnetization measurements are reported on magnetically oriented ErFe11Ti and ErFe11TiH samples under a field up to 240 kOe (24 T) in the 4.2–300 K temperature range. A raise of the Curie temperature and room temperature saturation magnetization upon hydrogen insertion is observed. The M(H) curves show a significant susceptibility is observed even at room temperature. The magnetic anisotropy constants are determined. Isofield magnetization curves reveal broad maxima in the 230 K range which reflect the fast decrease of the Er sublattice under high field.
Spin dynamics in S=1/2 chains and ladders from NMR and susceptibility measurements in Sr14−xNaxCu24O41
Authors: Carretta P. , Corti M. , Ghigna P. , Lascialfari A.
Published: July 2002

The authors report on NMR and susceptibility measurements in Sr14−xNaxCu24O41 for 0⩽x⩽2. The analysis of the susceptibility evidences that only a small fraction of Cu2+ spins are involved in the dimerization of Cu(1)O2 chains. The introduction of extra holes by Na+ doping is found to decrease the Cu(1)2+ uniform static susceptibility without affecting the amplitude of the dimerization gap. On the other hand, the amplitude of the spin gap in the Cu(2)2O3 two-leg-ladders and the resistivity are reduced by doping. The origin of the discrepancy in the amplitude of the gap estimated by means of nuclear spin-lattice relaxation and susceptibility measurements is briefly discussed.
Magnetic properties of CoFe2O4 thin films prepared by a sol-gel method
Authors: Lee Jae-Gwang , Park Jae Yun , Oh Young-Jei , Kim Chul Sung
Published: July 2002

Thin films with cobalt ferrite layers on thermally oxidized silicon wafers were fabricated by a sol-gel method. Magnetic and structural properties of the films were investigated with an x-ray diffractometer, a vibrating sample magnetometer and atomic force microscopy. The crystallization temperature for Co ferrite thin films was determined by using Mössbauer spectroscopy. Co ferrite films annealed at and above 450 °C have only a single phase spinel structure without any preferred crystallite orientation. Their rms surface roughness is less than 3 nm and the size of grains is about 30 nm for annealing temperatures greater than 650 °C. Films fired at and above 550 °C have moderate saturation magnetization and there is no significant difference of their magnetic properties for external fields applied parallel and perpendicular to their planes. The coercivity shows a strong dependence on the annealing temperature.
Exponential absorption edge and disorder in Column IV amorphous semiconductors
Authors: Zanatta A. R. , Mulato M. , Chambouleyron I.
Published: July 2002

We discuss the likely origin of the exponential absorption tail, or Urbach edge, of fourfold coordinated amorphous (a-)semiconductors. The present analysis is based on a compilation of a considerable amount of experimental data originating from a great variety of samples, alloys, and authors, and obtained with quite different spectroscopic techniques. An attempt is made to correlate the measured Urbach edge with the structural and optical properties of the samples. The present analysis indicates that the Urbach edge may not only reflect the shape of the joint density of states of the valence and conduction band tails, but may also have important contributions from short-range order potential fluctuations produced by charged defects or impurities.
Magnetically textured γ-Fe2O3 nanoparticles in a silica gel matrix: Optical and magneto-optical properties
Authors: Bentivegna F. , Nyvlt M. , Ferré J. , Jamet J. P. , Brun A. , Vis̆n̆ovsky S̆. , Urban R.
Published: July 2002

Optical and magneto-optical properties of maghemite superparamagnetic particles dispersed (f=0.28 vol % γ-Fe2O3) in a silica gel matrix have been studied at room temperature in the 1.5–3.7 eV spectral range. A permanent optical anisotropy can be induced when applying a magnetic field during the sol-gel freezing process. The permanent linear dichroism and birefringence in such in-plane magnetically textured samples are attentively studied. The spectral dispersion of Faraday effects in our textured samples is analyzed taking into account the in-plane optical anisotropy. Such a composite material is a promising candidate for future magneto-optical applications.
He-implantation induced defects in Si studied by slow positron annihilation spectroscopy
Authors: Brusa R. S. , Karwasz G. P. , Tiengo N. , Zecca A. , Corni F. , Calzolari G. , Nobili C.
Published: July 2002

Open volume defect profiles have been obtained by performing Doppler broadening measurements with a slow positron beam on p-type Si samples implanted near liquid nitrogen temperature with He ions at 20 keV and at 5×1015 and 2×1016 cm−2 fluence. The evolution of the defect profiles was studied as a function of isothermal annealing at 250 °C. The fraction of released He was measured by thermal programmed desorption. The defects could be identified as a coexistence of monovacancies stabilized by He-related defects and divacancies. The number of defects decreases for annealing time of a few minutes, then increases at longer annealing times. The mean depth of the defect profiles in the as-implanted samples was found to be very near the surface. After annealing, the mean depth increases to less than one half of the projected He range. This complex dynamics has been interpreted as due to passivation of vacancies by He during the implantation process and the first annealing step when no appreciable He is lost, and to subsequent depassivation during He desorption.
Effect of substrate absorption on the efficiency of laser patterning of indium tin oxide thin films
Authors: Yavas O. , Takai M.
Published: July 2002

Maskless laser patterning of indium tin oxide thin films for flat panel display applications was studied as a function of wavelength using different harmonics of a diode-pumped Q-switched Nd:YLF laser. Electrically isolating lines could be written at all wavelengths used. However, while lines written at the infrared and the visible wavelengths exhibited a ripplelike morphology due to incomplete material removal, ultraviolet laser irradiation produced residue-free etch lines with superior smoothness even at higher scan speeds. The threshold fluences for material removal at different wavelengths were found to correlate with the optical properties of the indium tin oxide film. In addition, numerical simulations of laser-induced temperature rise yielded peak surface temperatures well above the vaporization temperature of the indium tin oxide film, indicating that, at all wavelengths studied, material removal occurs via thermal vaporization. The calculations also revealed that the absorption of the ultraviolet laser light by the glass substrate is the key factor for the residue-free removal of the indium tin oxide film. Moreover, using a flashlamp-pumped Nd:yttrium-aluminum-garnet laser and a galvanometric scanning system, high process speeds in excess of 1 m/s could be achieved.
Photoreflectance mapping of InAlAs Schottky diode layer on InAlAs/InGaAs high electron mobility transistor wafers
Authors: Sugiyama H. , Yokoyama H. , Wada K.
Published: July 2002

The uniformity of surface layer characteristics of InAlAs Schottky diodes, the so-called level-shift diodes, on InAlAs/InGaAs high electron mobility transistors is noninvasively examined by photoreflectance (PR) spectroscopy, on-wafer mapping of PR signal intensity at a particular wavelength, and analyzed data. From the observed Franz–Keldysh oscillations, we have been able to evaluate the built-in dc electric fields in the i–n+, or so-called UN+, InAlAs Schottky diode layer. The on-wafer fluctuation of the electric fields in the diode layer, which is due to the fluctuation of the thickness of the diode layer, is clearly visualized by on-wafer mapping. Nonuniform composition of the InAlAs diode layers is also observed. The shape of the contour lines in the map of the PR signal intensity is related to the structure of the growth equipment. Our results suggest that photoreflectance mapping is quite effective for noninvasive screening of device epiwafers.
Diffusion of Cd in GaAs and its correlation with self-diffusion on the Ga sublattice
Authors: Bösker G. , Stolwijk N. A. , Mehrer H. , Södervall U. , Jäger W.
Published: July 2002

Cd diffusion into GaAs single crystals has been investigated in the temperature range 756–1201 °C. Penetration profiles measured by secondary ion mass spectroscopy and spreading-resistance profiling agree with each other and are numerically reproduced on the basis of the kick-out diffusion mechanism. A major involvement of vacancies via the dissociative mechanism can be excluded. This enables us to deduce from the Cd profiles effective Cd diffusivities (Dseff) as well as Ga diffusivities (DISD) mediated by doubly positively charged Ga self-interstitials (IGa2+). The Dseff values obtained from As-rich and As-poor ambients are mutually consistent. The same holds true for the DISD data. Reduced to 1 atm of As vapor pressure and electrically intrinsic conditions the Cd diffusion coefficient results as 1.76×104 exp(−4.80 eV/kB T) cm2 s−1 and the IGa2+-related self-diffusion coefficient as 3.5×104 exp(−5.74 eV/kB T) cm2 s−1. The present data provide strong evidence that in heavily p-doped GaAs atomic transport related to the Ga sublattice is governed by self-interstitials rather than vacancies.
Structural and electrical characterization of SrBi2Nb2O9 thin films deposited on YBa2Cu3O7−δ and Nb doped SrTiO3
Authors: Schwan Ch. , Haibach P. , Jakob G. , Martı́nez J. C. , Adrian H.
Published: July 2002

We have investigated the crystal structure and the ferroelectric properties of SrBi2Nb2O9 (SBN) thin films with YBa2Cu3O7−δ (YBCO) as the bottom and Au as the top electrode. Epitaxial heterostructures of YBCO and SBN were prepared by dc and rf sputtering, respectively, on SrTiO3 substrates. In a second layout we used a semiconducting Nb doped (0.05 wt % Nb) SrTiO3 (N-STO) substrate as the bottom electrode. The crystal structure of the films was characterized by x-ray diffraction. Since the SBN films exhibit a perfect c-axis oriented growth without the (115) phase the hysteresis loop measurements do not indicate ferroelectric behavior of the SBN films. The diode with a N-STO bottom electrode reveals, for a positive and negative applied voltage, a depletion and accumulation of the carrier density, respectively. The time dependent polarization and depolarization current can be described by a power law (Curie-von Schweidler). The conductivity as a function of applied voltage can be explained by the Schottky effect.
Reversible ultraviolet-induced photoluminescence degradation and enhancement in GaN films
Authors: Kim Bosang , Kuskovsky I. , Herman Irving P. , Li D. , Neumark G. F.
Published: July 2002

UV-induced modifications in undoped metalorganic chemical vapor deposition grown GaN on sapphire are observed from 9 to 160 K. The photoluminescence intensities of bound excitons (3.476, 3.482 eV), the yellow band (2.2 eV) and the blue band (2.9 eV) change with time when a fresh sample is irradiated by 325 nm (He–Cd laser). The free exciton peak at 3.488 eV is unchanged by laser irradiation. Initially the blue and donor-bound exciton emission degrade rapidly and the yellow luminescence increases, each at the same rate. Later, the yellow luminescence degrades and the donor-bound exciton emission increases very slowly, at the same rate. Mechanisms are proposed that may explain the luminescence pathways and defects involved.
Effect of microwave heating on BaTiO3:Nb ceramics with positive temperature coefficient of resistivity
Authors: Jida Shin’suke , Suemasu Takeshi , Miki Toshikatsu
Published: July 2002

The microwave heating technique is employed for obtaining high performance positive temperature coefficient of resistivity (PTCR) ceramics of Nb-doped BaTiO3 with a low resistivity at room temperature and a high resistivity jump above the Curie temperature. The grains of the BaTiO3:Nb ceramics prepared by microwave sintering are as large as 20–50 μm even when the Nb content exceeds 0.2 at. %, whereas such large grain size has never been obtained at this high content of Nb by ordinary sintering with an electric furnace. The large grains are also obtained by subjecting the heavily Nb-doped ceramics composed of fine grains to postheating with microwave after ordinary sintering. The room-temperature resistivity decreases down below 10 Ω cm and the PTCR character is obtained by postannealing in air. The mechanism of grain growth by microwave heating is discussed in terms of nonuniform temperature distribution of specimens during heating. The experimental data indicate that the microwave heating technique and the employment of a dopant that forms donor levels even at high doping levels will enable to develop high performance PTCR ceramics.
Nondestructive evaluation of metal contaminated silicon wafers using radiometric measurements
Authors: Kalli K. , Othonos A. , Christofides C. , Tardiff F.
Published: July 2002

We have performed nondestructive measurements on metal contaminated silicon wafers using photothermal radiometric measurements. Data were collected as a function of modulation frequency and time, showing clear distinctions between the different samples examined. The sensitivity of this technique to different forms of metallic contamination is examined. A qualitative and semiquantitative comparison is made between theory and experiment.
Aligned island formation using step-band networks on Si(111)
Authors: Homma Yoshikazu , Finnie Paul , Ogino Toshio , Noda Hideyuki , Urisu Tsuneo
Published: July 2002

We have achieved control of island formation using a patterned Si(111) surface with a periodic array of atomic-step bands and holes. Liquid metals, Au–Si or Ga, migrate on the patterned surface by annealing and form an island at a particular position in each pattern unit. The islands show highly uniform positions and narrow size distributions. To obtain such good uniformity, the diffusion length of surface atoms should be comparable with the pattern period. High mobility on step bands is also a necessary factor. Periodic arrays of Au islands are used as seeds for selective growth using a vapor-liquid-solid reaction.
Variability of effective parameters of random media
Authors: Keller Joseph B.
Published: July 2002

Effective parameters of a finite sample of a random medium are random variables. Their statistical properties are calculated for a medium consisting of a matrix of one material containing a small concentration of inclusions of other materials. The results are applied to a random resistor network in which the probability of a missing resistor is small.
Field emitters based on porous aluminum oxide templates
Authors: Davydov D. N. , Sattari P. A. , AlMawlawi D. , Osika A. , Haslett T. L. , Moskovits M.
Published: July 2002

The field-emission properties of cold cathodes produced using nano-porous anodic aluminum oxide (AAO) templates are reported. Several types of field emitters were fabricated: aligned copper nanowires grown halfway up the parallel nano-pores of the AAO; aligned multiwalled carbon nanotubes grown to the top of the pores; surfaces overgrown with random tangles of carbon nanotubes; and empty AAO templates. Significant field-emission currents (field enhancement values ∼ 1800) were obtained at threshold voltages as low as 80 V (corresponding to fields of 3–4 V/μm) on samples of nanotube tangles. Perfectly aligned carbon nanotubes were less efficient field emitters and had lower field enhancement values. These observations are explained in terms of the mean separation of active tips in the two sets of samples. Empty templates and metal nanowire arrays show lower field enhancements and higher threshold electric fields (40–70 V/μm). In these samples significant field-emission currents are produced at relatively low applied voltages of 110–300 V due to the small inter-electrode separations achieved on depositing a metal grid directly on the surface of the porous template.
Extreme precipitation strengthening in ion-implanted nickel
Authors: Knapp J. A. , Myers S. M. , Follstaedt D. M. , Petersen G. A.
Published: July 2002

Precipitation strengthening of nickel was investigated using ion-implantation alloying and nanoindentation testing for particle separations in the nanometer range and volume fractions extending above 10%. Ion implantation of either oxygen alone or oxygen plus aluminum at room temperature was shown to produce substantial strengthening in the ion-treated layer, with yield strengths near 5 GPa in both cases. After annealing to 550 °C the oxygen-alone layer loses much of the benefit, with its yield strength reduced to 1.2 GPa, but the dual ion-implanted layer retains a substantially enhanced yield strength of over 4 GPa. Examination by transmission electron microscopy showed very fine dispersions of 1–5 nm diameter NiO and γ-Al2O3 precipitates in the implanted layers before annealing. The heat treatment at 550 °C induced ripening of the NiO particles to sizes ranging from 7 to 20 nm, whereas the more stable γ-Al2O3 precipitates were little changed. The extreme strengthening we observe is in semiquantitative agreement with predictions based on the application of dispersion-hardening theory to these microstructures.
Analysis of torque in nested magnetic cylinders
Authors: Nı́ Mhı́ocháin T. R. , Weaire D. , McMurry S. M. , Coey J. M. D.
Published: July 2002

Rotatable nested cylindrical magnets may be used to generate variable magnetic fields. A mutual torque exists between the cylinders which is an important consideration in practical designs. We present a thorough investigation of this torque, combining experiment, computation, and theory. In the finite length case, in which the magnetization varies according to the prescription of Halbach, the torque is an end effect. It is proportional to sin α, where α is the angle defining the relative orientation of the cylinders. Practical designs use a discrete number N of permanent magnet segments to approximate the continuously varying magnetization of the ideal design. These introduce higher components sin(nα) to the angular dependence of torque, where the allowed values of n are restricted to n=(kN±1) according to the segmented magnet torque theorem.
Polarization and structural properties of high-energy electron irradiated poly(vinylidene fluoride-trifluoroethylene) copolymer films
Authors: Bharti Vivek , Xu H. S. , Shanthi G. , Zhang Q. M. , Liang Kuming
Published: July 2002

The effect of high-energy electron irradiation on structural and polarization properties of 50/50 mol % copolymer of poly(vinylidene fluoride-trifluoroethylene) was investigated for both mechanically stretched and unstretched films. Although stretching can significantly enhance the polarization and dielectric responses in unirradiated films, it was observed that this enhancement was not significant in irradiated films. In addition, the polarization in both types of films after irradiation can be described quite well by a logarithmic mixing law of composites, which consist of crystallites embedded in an amorphous matrix with nearly the same fitting parameters. On the other hand, the enhancement of the mechanical properties from stretching persists after the irradiation, and the elastic modulus along the stretching direction remains high after irradiation in comparison with unstretched films. It was found that the dielectric dispersion in both types of films after irradiation fits well to the Vogel–Fulcher law. It was also observed that the crystallinity decreases and the crosslinking coefficient increases continuously with dose. However, there was no direct one to one type relationship between the crystallinity and the crosslinking coefficient. Although stretching can reduce the rate of crosslinking, the reduction of crystallinity with dose for stretched and unstretched films does not show a marked difference.
Electrical and thermal properties of Tb0.3Dy0.7Fe2−x
Authors: Cook B. A. , Harringa J. L. , Hansen T.
Published: July 2002

Samples of Tb0.3Dy0.7Fe2−x where x=0.05–0.10 (TERFENOL-D) were characterized for electrical resistivity and thermal diffusivity between room temperature and the Curie temperature, which for this composition is 360 °C. Additionally, the thermal diffusivity of one of the samples was measured to 1000 °C. Measurements were performed on two different orientations of standard, production-grade, grain-oriented TERFENOL-D produced by a Bridgman growth technique at ETREMA Products, Inc. The orientations were parallel and normal to the 〈112〉 crystallographic direction. The electrical resistivity and thermal diffusivity both exhibited isotropic behavior over the temperature range studied. The electrical resistivity of all samples increased monotonically from 0.06 mΩ-cm at room temperature to 0.14 mΩ cm at 360 °C, consistent with behavior expected for normal metals. The thermal conductivity was found to decrease with temperature from 135 mW/cm °C at room temperature to 122 mW/cm °C at 360 °C. The thermal diffusivity was found to exhibit a sharp cusp in the vicinity of the Curie temperature, TC, increasing with temperature for T>TC. Application of the Wiedemann–Franz law indicates that over 86% of the heat is carried by electrons.
Photoinduced charge transfer in near-stoichiometric LiNbO3
Authors: Lee Myeongkyu , Takekawa Shunji , Furukawa Yasunori , Kitamura Kenji , Hatano Hideki
Published: July 2002

We have observed that near-stoichiometric LiNbO3 (nominally pure and Tb-doped) exhibits a strong and stable photoinduced absorption band extending from λ≈650 nm to the absorption edge when illuminated with ultraviolet light at 313 nm. It was found that crystals have both shallow electron traps close to the conduction band and deep traps located about 1.9 eV (λ≈650 nm) below it and that the deep-trapped charges give rise to this induced absorption band. The measured shallow-trap electron lifetime was about 4 s at room temperature both in nominally pure and Tb-doped crystals. The deep-trapped charges were thermally stable at room temperature and decayed in a near-exponential manner at high temperatures. The deep-trap decay time estimated at room temperature increased with increasing Tb concentration, being over 60 years in Tb 200 ppm doped crystal. These provide a favorable energy structure for effective two-color holographic recording at near-infrared ranges.
Thermally stable spin valve films with synthetic antiferromagnet pinned by NiMn for recording heads beyond 20 Gbit/in.2
Authors: Mao Sining , Mack Anthony , Singleton Eric , Chen Jian , Xue Song S. , Wang Hong , Gao Zheng , Li Jin , Murdock Ed
Published: July 2002

The thermal stability of spin valve films with synthetic antiferromagnet (SAF) pinned by antiferromagnetic IrMn, NiO, and NiMn layers were studied. The SAF layer enhances the thermal stability in general; however, the blocking temperature (and the blocking temperature distribution) of the antiferromagnet is still important for the magnetic rigidity of the pinned layer. Once the temperature reaches the blocking temperature the SAF layer can go into either the spin flip or flop state, depending upon the magnetic moment ratio of the reference layer and pinned layers. The GMR linear head response can be distorted for nonlinearity. The NiMn pinned SAF structure shows magnetic and thermal stability which makes it practical for the real products. A high GMR of 11% can be obtained in both bottom and top NiMn SAF spin valves by advanced processes. Recording heads were built using such stacks which demonstrated recording areal density of 20 Gbit/in.2 and beyond.
Diamagnetic levitation: Flying frogs and floating magnets (invited)
Authors: Simon M. D. , Geim A. K.
Published: July 2002

Contrary to our intuition, apparently nonmagnetic substances can be levitated in a magnetic field and can stabilize free levitation of a permanent magnet. Most substances are weakly diamagnetic and the tiny forces associated with this property make the two types of levitation possible. Living things mostly consist of diamagnetic molecules (such as water and proteins) and components (such as bones) and therefore can be levitated and can experience low gravity. In this way, frogs have been able to fly in the throat of a high field magnet. Stable levitation of one magnet by another with no energy input is usually prohibited by Earnshaw’s Theorem. However, the introduction of diamagnetic material at special locations can stabilize such levitation. A magnet can even be stably suspended between (diamagnetic) fingertips.
Analysis of power loss at high frequency for MnZn ferrites
Authors: Kawano T. , Fujita A. , Gotoh S.
Published: July 2002

Frequency dependence of power loss of MnZn ferrite was investigated in relation with the absolute complex permeability, μa(=μa−jμa″), in the frequency range 10 kHz–5 MHz and the temperature range 23–120 °C. Residual loss, Pr contributes more than half of the total power loss, Pc, at a frequency above 1 MHz and exhibits a close relationship with μa″. The specimen with grain size of 4 μm and ZnO content of 0 mol % indicates μa′ of 1280 and Pc of 140 kW/m3 at 1 MHz and 50 mT. In the second measurement at the remanent state after the dc magnetization of 400 A/m, these values, however, increased and then gradually recovered with time. This behavior is considered to be related to the diffusion of Fe2+ through cation vacancy.