bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress-density ratio slip-corrected Reynolds equation for ultra-thin film gas bearing lubrication
Authors: Ng Eddie Yin-Kwee , Liu Ningyu , Mao Xiaohai
Published: July 2002

The direct simulation Monte Carlo method is used to evaluate the improved slip boundary condition and slip-corrected Reynolds equation for gas lubrication in magnetic recording storage system. The study shows that in transition regime, the slip velocity is affected not only by shear stress, but also by density itself. In this ultra-thin film lubrication environment, the slip velocity has a linear relationship with the ratio of shear stress to density near the wall. This observation is particularly true when Knudsen number is around 1 or larger. Through this study, the authors have developed a new slip velocity model, named stress-density ratio model, particularly suitable to transition regime. Based on this novel model, a slip-corrected Reynolds equation is also derived and solved numerically. The stress-density ratio model is confirmed to offer a better applicability than the previous slip-flow models for modern computer magnetic storage device, where the Knudsen number of slider air bearing is in the range of unity or larger.
Mechanically reversible conductor–insulator transition in Mg2NiH4
Authors: Blomqvist Helen , Noréus Dag
Published: July 2002

An irreversible conductor-insulator transition has been observed when heating Mg2NiH4 in the temperature interval 110 to 570 K. The disappearance of the electric conductivity is concomitant with the appearance of stacking faults (or microtwinning) in the Mg2NiH4 structure, as observed by powder x-ray diffraction. However, the stacking faults are sensitive to applied mechanical pressure or grinding, and by compressing the hydride sample in a tablet press, Mg2NiH4 regains its electric conductivity as the observable amount of stacking faults is reduced. These phenomena are attributed to peculiarities connected with the stabilization of the electron-rich tetrahedral d10 [Ni(0)H4] complex by the lattice. Formally low-valent oxidation states usually demand good electron-accepting ligands with suitable π* or d orbitals to relieve the high electron density at the central atom. This is not possible when hydrogen is the only ligand, but the easily polarizable H− ion helps to distribute electron density by outward bonding to the lattice. This also stabilizes the [NiH4] complex. The present work shows that this stabilization mechanism is sensitive to disturbances in the lattice and that small disturbances can have profound effects on the electric conductivity of Mg2NiH4.
Spin hopping in a discontinuous La0.7Ca0.3MnO3 film
Authors: Ziese Michael
Published: July 2002

Magnetization and magnetotransport properties of a discontinuous La0.7Ca0.3MnO3 film on LaAlO3 are presented. The sample shows transport characteristics of a granular ferromagnet with an extraordinarily large magnetoresistance. The data are successfully interpreted within a model of spin-dependent tunneling between grains taking into account magnetic intergrain correlation effects.
Theoretical investigation of laser gain in AlGaInN quaternary quantum wells
Authors: Chow W. W. , Schneider H. C. , Fischer A. J. , Allerman A. A.
Published: July 2002

Microscopic calculations of laser gain spectra are presented for AlGaInN wurtzite quantum-well structures that are under compressive, zero and tensile strain. It is found that the optical nonlinearities induced by the combination of strain, quantum-confined Stark effect and many-body Coulomb interactions give rise to optical behavior that can differ significantly from that in conventional semiconductor lasers.
Three-terminal gated magnetoelectronic device
Authors: Zelakiewicz S. , Johnson Mark
Published: July 2002

In a Hybrid Hall device, magnetic fringe fields from the edge of a single, patterned ferromagnetic film generate a Hall voltage in a two-dimensional electron gas. By adding an electrostatic gate to this passive device and applying an electric field, we demonstrate the reduction of the carrier density by 50% and the consequent enhancement of the bistable output levels by 100%. This modulation of magnetoelectronic characteristics by using a gate voltage shows the possibility of creating an active spintronic device. The gated Hybrid Hall device may also be used as a nonvolatile memory cell with the unique attribute that isolation and storage are provided by a single device.
Specular spin-valve films with an FeCo nano-oxide layer by ion-assisted oxidation
Authors: Fukuzawa Hideaki , Koi Katsuhiko , Tomita Hiroshi , Fuke Hiromi Niu , Iwasaki Hitoshi , Sahashi Masashi
Published: July 2002

We compared the specular spin-valve films with an Fe50Co50 nano-oxide layer (NOL) and a Co90Fe10 NOL in a pinned layer, prepared by natural oxidation (NO) and ion-assisted oxidation (IAO). For the IAO, an Ar-ion beam was used for the energy-assist effect during the oxidation, resulting in thermally stable NOL formation. With small oxygen exposures during the oxidation for the Fe50Co50 NOL by IAO, good ferromagnetic coupling through the NOL and high specularity at the NOL interface were concurrently obtained. Moreover, twisted coupling through the NOL was observed for the Fe50Co50 NOL by IAO for higher oxygen exposures. On the other hand, the NO did not cause large magnetoresistance (MR) enhancement for either the Co90Fe10 or Fe50Co50 NOLs, and the Co90Fe10 NOL by IAO caused weak magnetic coupling through the NOL, resulting in a small MR ratio. The Fe50Co50 NOL for small oxygen exposures is a good candidate for a final specular spin-valve film head for 100-Giga-bit per square inch recording.
Organic electrical bistable devices and rewritable memory cells
Authors: Ma L. P. , Liu J. , Yang Y.
Published: July 2002

Electrical bistability is a phenomenon in which a device exhibits two states of different conductivities, at the same applied voltage. We report an organic electrical bistable device (OBD) comprising of a thin metal layer embedded within the organic material, as the active medium [L. P. Ma, J. Liu, and Y. Yang, US Patent Pending, (2001)]. The performance of this device makes it attractive for memory-cell type of applications. The two states of the OBD differ in their conductivity by several orders in magnitude and show remarkable stability, i.e., once the device reaches either state, it tends to remain in that state for a prolonged period of time. More importantly, the high and low conductivity states of an OBD can be precisely controlled by the application of a positive voltage pulse (to write) or a negative voltage pulse (to erase), respectively. One million writing-erasing cycles for the OBD have been tested in ambient conditions without significant device degradation. These discoveries pave the way for newer applications, such as low-cost, large-area, flexible, high-density, electrically addressable data storage devices.
Fluxon insertion into annular Josephson junctions
Authors: Ustinov Alexey V.
Published: July 2002

A technique of inserting magnetic fluxons into annular Josephson junctions is proposed and demonstrated experimentally. The method is based on local injection of current into one of the superconducting electrodes of the junction. The residual pinning of fluxons in the junction can be eliminated by choosing an appropriate injection current, which depends on the spacing between the injectors. The reported technique resolves the long-standing problem of a controlled preparation of fluxon states in annular Josephson junctions and can be used in various fluxon devices.
Temperature dependence of the domain wall depinning in magnetic hard-soft composites
Authors: Chui S. T. , Ma Yong-li
Published: July 2002

We study the temperature and composition dependence of the depinning field Hd in magnetic hard-soft nanocomposite by finite temperature Monte Carlo simulation for a model of the composites. As the amount of the soft magnetic material is increased, the depinning field increases, exhibits a maximum, and then decreases. As the temperature is increased, the position of this maximum increases. At the same time the overall magnitude of the depinning field decreases. We discuss the implication of our result on the energy product of nanocomposites of hard and soft magnets. The decrease of the switching field with temperature suggests that it is important to use a hard magnet component with a large anisotropy field.
Carbon nanotube electron emitters with a gated structure using backside exposure processes
Authors: Chung Deuk-Seok , Park S. H. , Lee H. W. , Choi J. H. , Cha S. N. , Kim J. W. , Jang J. E. , Min K. W. , Cho S. H. , Yoon M. J. , Lee J. S. , Lee C. K. , Yoo J. H. , Kim Jong-Min , Jung J. E. , Jin Y. W. , Park Y. J. , You J. B.
Published: July 2002

We have fabricated fully vacuum-sealed 5 in. diagonal carbon nanotube field-emission displays of a gated structure with reliable electron emission characteristics. Single-walled carbon nanotube tips were implemented into the gate structure using self-aligned backside exposure of photosensitive carbon nanotube paste. An onset gate electrode voltage for emission was about 60 V and the luminance as high as 510 cd/m2 was exhibited under an application of 100 V and 1.5 kV to gate electrode and anode, respectively.
A specular spin valve with discontinuous nano-oxide layers
Authors: Shen F. , Xu Q. Y. , Yu G. H. , Lai W. Y. , Zhang Z. , Lu Z. Q. , Pan G. , Al-Jibouri Abdul
Published: July 2002

Microstructures of the specular spin valve with two nano-oxide layers (NOL1 and NOL2) have been studied at the atomic level. When the NOLs are incorporated in a bottom-pinned spin valve, a significant enhancement in magnetoresistance ratio with greatly decreased sense-layer thickness is achieved. Cross-sectional high-resolution electron microscopy (HREM) studies show that the NOL1 introduced from oxidation of the original bottom-pinned CoFe layer is actually a mixture of oxides and ferromagnetic metals. No CoFe oxides but Ta2O5 is found over the oxidation-treated CoFe sense layer by HREM and x-ray photoelectron spectroscopy study. The Ta2O5 layer acting as the NOL2 can be interpreted as being formed through a solid-state oxidation reaction between the oxidized CoFe sense layer and the Ta capping layers.
Electronic structure symmetry of interfaces between pentacene and metals
Authors: Watkins N. J. , Yan Li , Gao Yongli
Published: July 2002

We examined the electronic structure of the interfaces formed between pentacene and various metals: Au, Ag, and Ca, using photoemission spectroscopy. For all interfaces, we observed the formation of an interface dipole that varied linearly with the measured metal work function. We observed that the behavior of the interfaces of Ca with pentacene was symmetric with respect to whether Ca was deposited on pentacene or vice versa. On the other hand, the interfaces of Au and Ag with pentacene were asymmetric. For both Au and Ag we saw indications that upon metal deposition, metal penetration resulted in a metallic surface with a work function significantly different from that of pure Au or Ag. This also resulted in different interface dipoles for these interfaces.
Basin boundaries and focal points in a map coming from Bairstow’s method
Authors: Gardini Laura , Bischi Gian-Italo , Fournier-Prunaret Daniele
Published: July 2002

This paper is devoted to the study of the global dynamical properties of a two-dimensional noninvertible map, with a denominator which can vanish, obtained by applying Bairstow’s method to a cubic polynomial. It is shown that the complicated structure of the basins of attraction of the fixed points is due to the existence of singularities such as sets of nondefinition, focal points, and prefocal curves, which are specific to maps with a vanishing denominator, and have been recently introduced in the literature. Some global bifurcations that change the qualitative structure of the basin boundaries, are explained in terms of contacts among these singularities. The techniques used in this paper put in evidence some new dynamic behaviors and bifurcations, which are peculiar of maps with denominator; hence they can be applied to the analysis of other classes of maps coming from iterative algorithms (based on Newton’s method, or others).
Mechanical damage induced luminescence band in GaAs
Authors: Swaminathan V. , Young M. S. , Caruso R.
Published: July 2002

In this paper we report the observation of a new luminescence band at ∼1.4 eV in the low temperature (10 K) spectrum from bulk GaAs crystals when they are subjected to surface damage by saw cutting, mechanical polishing, and scribing. The band is observed in all crystals, independent of the growth method, dopant, and conductivity type. The peak position of the 1.4-eV band shifts to lower energy with decreasing excitation intensity by as much as 7 meV per decade change in excitation power. The luminescence quenches thermally above ∼30 K with an activation energy of 33±7 meV. We suggest that this new luminescence is a donor-acceptor pair transition involving defects introduced by the surface damage. The mechanical damage, as monitored by the intensity of the luminescence band, is found to extend into the crystal by 10–20 μm depending on the severity of the damage, and it anneals out at ≳400 °C.
Formation of amorphous layers by ion implantation
Authors: Prussin S. , Margolese David I. , Tauber Richard N.
Published: July 2002

This study was directed toward exploring the relationship between the implant conditions and the depth and nature of the amorphous layers generated in silicon. Interest in amorphous layer morphology stems from its role in affecting crystal defects remaining after amorphous-to-crystalline transformation. High-dose implants of As, P, and B were used to generate buried and surface amorphous layers at slightly higher than room temperature. The amorphous layer depths were measured and the depth-fluence and depth-energy relationships were compared with Brice’s analysis. It was found that good fits were obtained for a threshold damage density of 2.5×1020 keV cm−3 for As and 1.0×1021 keV cm−3 for P. For B, the results could be described by a threshold damage density of 5.0×1021 keV cm−3 or greater. Lower weight ion implantations exhibit a greater tendency to generate buried amorphous layers as well as to generate amorphous layers which include a smaller fraction of the total implanted fluence than is found for heavier ion implantations. These two factors make it more likely for residual crystal defects to be associated with lower weight ion implant distributions.
Direct evidence for an order/disorder phase transition at x≂0.3 in single-crystal metastable (GaSb)(1−x)(Ge2)x alloys: High-resolution x-ray diffraction measurements
Authors: Shah S. I. , Kramer B. , Barnett S. A. , Greene J. E.
Published: July 2002

High-resolution triple-crystal x-ray diffractometry has been used to investigate long-range order in single-crystal (100)-oriented metastable (GaSb)(1−x)(Ge2)x alloys. Measurements of the integrated intensities of superstructure and fundamental reflections provide the first direct evidence of an order/disorder, zinc blende to diamond, structural transition in (III-V)(1−x)(IV2) x alloys. The transition in (GaSb)(1−x)(Ge2)x was found to occur at x≂0.3. The long-range order parameter S and the probability r that a Ga or Sb atom will occupy a site on its corresponding sublattice were determined as a function of composition from the normalized ratio of the integrated intensities of the (200) superstructure to the (400) fundamental reflections. S(x), which is unity for pure zinc blende structure GaSb, initially decreased slowly with increasing Ge concentration, but decreased ever more rapidly as x approached 0.3. S(x) was essentially zero for alloys with x>0.3, indicating a ‘‘disordered’’ diamond structure. Correspondingly, r decreased from 1 at x=0 to 0.5 at x≥0.3.
An interferometric investigation of the thermalization of copper atoms in a magnetron sputtering discharge
Authors: Ball L. T. , Falconer I. S. , McKenzie D. R. , Smelt J. M.
Published: July 2002

The average kinetic energy of the atoms sputtered from the copper cathode of a magnetron sputtering discharge has been deduced from the shapes of their Doppler-broadened emission lines, which were measured with a high-resolution scanning Fabry–Perot interferometer. At a fixed distance from the cathode the energy decreased with increasing sputtering gas pressure, as expected. The experimental points fell between the theoretical curves of Westwood [J. Vac. Sci. Technol. 15, 1 (1978)], and Meyer, Schuller, and Falco [J. Appl. Phys. 52, 5803 (1981)] lying somewhat closer to the former than to the latter.
Growth-induced anisotropy in bismuth: Rare-earth iron garnets
Authors: Fratello V. J. , Slusky S. E. G. , Brandle C. D. , Norelli M. P.
Published: July 2002

The bismuth-doped rare-earth iron garnets, (R3−x−yBixPby)Fe5O12 (Bi:RIG, R=Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y), were prepared under constant growth conditions to investigate the influence of ionic species on the bismuth-based growth-induced uniaxial anisotropy Kgu. The effect of ionic species on growth-induced anisotropy in Bi:RIG was not consistent with the ionic size model of site ordering. In particular, Bi:SmIG, Bi:EuIG, and Bi:TbIG displayed high growth-induced anisotropies, up to 331 000 erg/cm3 at room temperature for x≊0.5. The temperature dependence of these Kgu’s was somewhat higher than that of the well studied Bi:YIG. The site ordering of Bi can be modeled by assuming that small, low-oxygen-coordination BiO+3−2ww melt complexes have a strong site selectivity for small, high-oxygen coordination sites at the growth interface.
Internal friction in solids
Authors: Wert C. A.
Published: July 2002

Study of the damping of vibrations in solids has developed into an acoustical spectroscopy which can elucidate many geometrical, thermodynamic, and kinetic characteristics of solids. In a relatively brief 15 years, between 1935 and 1950, Clarence Zener contributed physical insight, analytical procedures, and suggestions for important topics which persist even today. This review traces development of ideas and techniques from that period to the present. It uses chiefly as examples the flow of heat across vibrating reeds (and the corollary Gorsky effect), the Snoek effect in interstitial alloys, and the Zener effect in substitutional alloys. Internal friction of molecular reorientation in polymeric solids is described. Finally, the joint use of internal friction and dielectric loss is demonstrated to provide additional insight into molecular configurations in solids which are both mechanical and electric dipoles.
Lattice-strained heterojunction InGaAs/GaAs bipolar structures: Recombination properties and device performance
Authors: Ramberg L. P. , Enquist P. M. , Chen Y.-K. , Najjar F. E. , Eastman L. F. , Fitzgerald E. A. , Kavanagh K. L.
Published: July 2002

Double-heterojunction NpN GaAs/InxGa1−xAs/GaAs bipolar transistor layers have been grown by molecular-beam epitaxy, and large-area devices have been processed and characterized. The indium mole fraction in the strained base layer, and thus the band offsets, has been varied with significant differences in current gains. From the gain versus indium-composition relation a valence-band offset of ΔEv =9.7 meV/% In is derived. We found that the highest base-In content yields the highest-gain devices despite the presence of interface misfit dislocations and dark-line defects.
Structure and recombination in InGaAs/GaAs heterostructures
Authors: Fitzgerald E. A. , Ast D. G. , Kirchner P. D. , Pettit G. D. , Woodall J. M.
Published: July 2002

The defect structure of lattice-mismatched 1-μm InxGa1−xAs (x≊0.12, misfit Δa/a≊8.5×10−3) epilayers on GaAs was studied with scanning cathodoluminescence (CL), transmission electron microscopy (TEM), high-voltage electron microscopy, and scanning electron microscopy. CL shows that nonradiative recombination lines exist in the GaAs buffer layer as far as 4000 Å from the interface. The density of these defects is independent of substrate dislocation density. Plan-view TEM analysis indicates that the majority of these dislocations in the buffer layer are sessile edge half-loops. Cross-sectional TEM shows that loops also extend into the InGaAs epilayer, but the majority of the loops are located on the buffer layer (substrate) side of the interface. A model is proposed to explain sessile edge dislocation formation in the buffer layer. A comparison of CL and high-voltage electron microscopy images from the same interface area reveals that the dark nonradiative recombination lines seen in scanning luminescence images in this high misfit system do not correspond to the normal, isolated misfit dislocation. The nonradiative recombination line spacing is 3 μm, whereas the interface dislocation spacing is 400–1000 Å. It is shown that the nonradiative recombination lines observed in CL of the interface correspond to specific groups of dislocations with different TEM contrast behavior. The dark nonradiative recombination lines also correlate with asymmetric surface ridges, suggesting that they introduce preferred nucleation sites, and that these effects are different for the two 〈110〉 directions.
Magnetic properties of gas atomized powders of Al74Mn20Si6
Authors: McHenry M. E. , Dunlap R. A. , Chatterjee R. , Chow A. , O’Handley R. C.
Published: July 2002

Rapidly quenched powders of Al74Mn20Si6 were prepared by the ultrasonic gas atomization technique. Particles ranged from less than 40 μm to greater than 150 μm. The smaller particles were found to be primarily of the icosahedral phase. Larger powders showed an increasing proportion of the β-Al-MnSi phase. There was no evidence for the presence of α-AlMnSi commonly found in crystallized icosahedral AlMnSi alloys. Magnetic measurements showed the existence of a local Mn moment in all alloys. This moment was found to be 1.27 μB for the icosahedral phase and 0.63 μB for the β phase.
Raman scattering measurement of silicon-on-insulator substrates formed by high-dose oxygen-ion implantation
Authors: Takahashi Jun-ichi , Makino Takahiro
Published: July 2002

Raman scattering spectroscopy is applied to an evaluation of silicon-on-insulator substrates formed by high-dose oxygen-ion implantation. This implantation creates a superficial crystal silicon/buried oxide/substrate silicon structure. Two peaks are found in the Raman spectra of the substrates. Their intensity ratio varies with the exciting laser wavelength. One narrow peak at 521 cm−1 is assigned to optical phonons in the substrate silicon, and the other broader peak at lower frequency is assigned to the superficial silicon. With an increase in postimplantation annealing temperature, the Raman peak frequency of the superficial silicon increases and the linewidth becomes narrower, approaching the values of single-crystal silicon. One possible interpretation for the Raman peak downshift is that the oxygen-ion implantation causes structural deformations of the superficial silicon layer, mainly oxygen precipitation and defect generation.
Hole trapping in oxides grown by rapid thermal processing
Authors: Seager C. H. , Schubert W. K.
Published: July 2002

Thin, high-quality SiO2 films have been grown by rapid thermal oxidation techniques and subjected to a variety of post-oxidation annealing protocols. The hole trapping rates in these films have been measured by subjecting them to x rays and Fowler–Nordheim tunneling injection. The density of hole traps is seen to depend crucially on the temperature and oxygen content of the post-oxidation annealing environment. These results support recent suggestions that an oxygen deficient defect near the Si/SiO2 interface is the primary hole trap in MOS (metal-oxide-semiconductor) devices.
High-power conversion efficiency in a strained InGaAs/AlGaAs quantum well laser
Authors: Bour D. P. , Evans G. A. , Gilbert D. B.
Published: July 2002

A strained quantum well laser with a front-end power conversion efficiency exceeding 33% under continuous-wave operation is demonstrated. The laser structure, grown by atmospheric pressure organometallic vapor-phase epitaxy, consists of a 70-Å In0.2Ga0.8As quantum well active region with graded index separate confinement heterostructure. Lasing wavelength is 930 nm, and the front-end differential quantum efficiency is 58% for broad-area oxide stripe lasers with a high-reflection coating on the rear facet. Front-end, continuous power outputs greater than 1 W are available. Although these strained quantum well lasers have threshold currents as low as lattice-matched GaAs quantum well lasers, their internal quantum efficiencies appear to be reduced, thus limiting the maximum attainable conversion efficiency.
Lattice-mismatch-generated dislocation structures and their confinement using superlattices in heteroepitaxial GaAs/InP and InP/GaAs grown by chemical beam epitaxy
Authors: Chu S. N. G. , Tsang W. T. , Chiu T. H. , Macrander A. T.
Published: July 2002

We report a detailed transmission electron microscopy and x-ray double-crystal diffractometry study of the lattice-mismatch-induced defect structures in InP grown on (100) GaAs substrate and vice versa by chemical beam epitaxy. A rough estimate of the dislocation densities in GaAs on InP is 2×1010 cm−2 at the interface and 5×107 cm−2 at the surface of the epilayer. The corresponding values in InP on GaAs are slightly lower as expected for the compressive stress state for InP. The majority of the dislocations lie on the {111} slip planes with 1/2 [110]- and 1/2 [101]-type Burgers vectors. A cross-grid-type interfacial misfit dislocation array is not observed. Instead, a complicated dislocation structure near the interface, consisting of overlapping pyramidal dislocation tangles (PDT) similar to those observed previously in InGaAs on InP caused by interfacial misfit particles, is presented. The interfacial dislocations form a cellular structure in GaAs on InP and a random structure in InP on GaAs. A Moiré fringe spacing study of InP on GaAs indicates a localized change in composition at the interface, possibly due to As incorporation or GaAs/InP intermixing. The formation of PDT defects and the variation in composition at the interface suggest a breakdown of layer-by-layer growth in the initial stage of growth which results in island nucleation. A dislocation mechanism for the PDT formation is also proposed. All epilayers prepared by chemical beam epitaxy (CBE) without two-stage growth are specular. X-ray rocking curve linewidth measurement shows a general reduction in the linewidth with increasing growth temperature and is insensitive to the substrate misorientation. Fine surface morphology revealed by Nomarski interference microscopy shows no correlation with x-ray linewidth. Results on the reduction of dislocation by varying growth temperature, substrate misorientation angle, and using AlGaAs/GaAs superlattice barriers for dislocation propagation are presented and their effectiveness are discussed. A realistic scheme to achieve an unwarped wafer with low dislocation density is proposed.
Temperatures in the plume of a dc plasma torch
Authors: Scott D. A. , Kovitya P. , Haddad G. N.
Published: July 2002

A magnetohydrodynamic model of a plasma torch that describes the complete torch system from the gas injection, through the arc region, and out into the plasma plume is presented. It is a two-dimensional model but includes a swirl component of the flow and the K-ε model of turbulence and assumes local thermodynamic equilibrium. Temperatures in the plume of a plasma torch have been determined spectroscopically by measuring the emission from neutral argon atoms, and these temperatures have been compared with the predictions of the model.
Tungsten etching mechanisms in CF4/O2 reactive ion etching plasmas
Authors: Bestwick Tim D. , Oehrlein Gottlieb S.
Published: July 2002

I n situ x-ray photoelectron spectroscopy (XPS), etch rate measurements, and optical emission spectroscopy have been used to examine the etching characteristics of tungsten in CF4/O2 reactive ion etching plasmas. It is found that the etch rate maximum of tungsten occurs at a proportion of oxygen in excess of that required to produce the maximum gas phase fluorine atom concentration, and this cannot be explained by using an etch mechanism model similar to that developed for silicon. XPS results have been used to identify tungsten oxyfluoride (WOF4) on the etched surface, and a model for tungsten etching is proposed that involves tungsten oxyfluoride as an important etch product.
Scanning tunneling microscopy as a tool to study surface roughness of sputtered thin films
Authors: Schönenberger C. , Alvarado S. F. , Ortiz C.
Published: July 2002

A three-dimensional image of the surface roughness of four conducting iron-oxide Fe3O4 thin films was obtained using a scanning tunneling microscope. We obtain grain size and surface roughness of films deposited on Si(100) by reactive sputtering at different substrate temperatures. The apparent grain size lies between 10 and 50 nm, and depends on the substrate temperature and film thickness. We have also determined the scanning tunneling microscopy parameters (tip size and shape) to obtain ‘‘real’’ images (i.e., images without artifacts) of the films.
Effect of third-element additions on properties of Co-Cr-based films
Authors: Sagoi Masayuki , Inoue Tetsuo
Published: July 2002

The fundamental effects of adding several elements to the Co-Cr system on the properties of Co-Cr-based films were extensively investigated. Tantalum, molybdenum, vanadium, and rhenium were chosen as the additives. A large amount of each element was added to a Co–17-at. % Cr film. Ta addition improved the squareness and suppressed the in-plane coercive force without lowering the perpendicular coercive force for the films with perpendicular magnetization. All the additives were effective in suppressing the grain growth. The ternary alloy films were likely to have finer grains than Co-Cr films. Ta was found to be the most advantageous in a wide range of the content, from the total balance of squareness, coercive force, and grain size. The recording characteristics of Co-Cr-Ta films were also examined in comparison with those of Co-Cr films. The recording density and the signal-to-noise ratio of Co-Cr-Ta films were appreciably higher than those of Co-Cr films.
Theoretical and experimental characterization of positive-column plasmas in oxygen glow discharge
Authors: Ichikawa Yukimi , Wu Richard L. C. , Kaneda Teruo
Published: July 2002

Combined theoretical and experimental studies have been accomplished in order to elucidate the features of positive columns in oxygen glow discharges. The Langmuir probe technique was utilized to measure the plasma parameters such as electron temperature and electric field. A tandem mass spectrometer was used to measure relative concentrations of charged particles. These experimental results were found to be in good agreement with the present theoretical calculations based on a slightly ionized stationary plasma model.
Field-effect transistor structure based on strain-induced polarization charges
Authors: Kuech T. F. , Collins R. T. , Smith D. L. , Mailhiot C.
Published: July 2002

We suggest a new field-effect transistor structure based on strain-induced polarization charges. The structure utilizes the pseudomorphic growth of a barrier layer on a substrate oriented in a polar direction (i.e., 〈111〉, 〈211〉, ...). Polarization charges in the large band-gap material are generated by the piezoelectric effect. A two-dimensional electron gas, whose density can be modulated by an external bias, forms at the heterointerface to screen the polarization charges. Zero-bias densities of several times 1011 e/cm−2 and turn-off threshold voltages of 0.5 V can be achieved in the (Ga,In)As-(Al,In)As model system. Both normally-on and normally-off structures are possible.
Polarization mechanisms of morphotropic phase boundary lead barium niobate (PBN) compositions
Authors: Guo R. , Bhalla A. S. , Randall C. A. , Chang Z. P. , Cross L. E.
Published: July 2002

Investigations of the polarization mechanisms in tungsten bronze relaxor ferroelectrics, Pb1–xBaxNb2O6 (PBN[(1−x) %]), in particular, of the morphotropic phase boundary compositions have been carried out for both ceramics and bulk crystals by means of electrical, thermal, optical, and electron-microscopic methods. Relations of phase-transition behavior with compositional and polarizational fluctuations have been carefully studied. Instead of a sharp boundary composition, it is found that a rather wide composition range, 1−x≊0.63±0.03 in Pb1−xBaxNb2O6, corresponds to the orthorhombic and tetragonal morphotropic phase boundary. It is demonstrated with the help of optical conoscopic interference figures that for the near-morphotropic phase boundary single crystal PBN of tetragonal symmetry, the polarization vector can be switched orthogonally to an orthorhombic phase simply by the application of an electric field, which authenticates optically the 90° polarization rotation. A transmission electron microscope study in the temperature range from −180 °C to room temperature revealed the presence of incommensurate ferroelastic domains in the morphotropic phase boundary composition PBN crystals. In light of the above observed experimental data, the polarization mechanisms of the morphotropic phase-boundary compositions are discussed in terms of qualitative thermodynamics.
High-detectivity GaAs quantum well infrared detectors with peak responsivity at 8.2 μm
Authors: Janousek B. K. , Daugherty M. J. , Bloss W. L. , Rosenbluth M. L. , O’Loughlin M. J. , Kanter H. , De Luccia F. J. , Perry L. E.
Published: July 2002

GaAs quantum well infrared detectors with peak responsivity at 8.2 μm and significant response beyond 10 μm have been demonstrated with detectivities of 4×1011 cm (Hz)1/2 /W at 6 K; this detectivity is the highest reported for a quantum well detector. The detectors comprised 50 GaAs quantum wells of width 40 Å with an average Si doping density of 1×1018 cm−3 separated by 280-Å barriers of Al0.28Ga0.72As. In this design, the state to which electrons are excited by infrared absorption and from which they are subsequently collected lies in the continuum above the energy of the Al0.28Ga0.72As conduction-band minimum. The maximum detector responsivity was mesured to be 0.34 A/W. The device dark current density is 5.5×10−6 A/cm2 with the detector biased for maximum detectivity (3.5 V), and the dark current remains constant with increasing temperature up to 50 K. The detector noise current was observed to be a constant fraction (70%) of the shot noise down to noise currents of 10−14 A/(Hz)1/2. A theoretical model for the dark conduction process in a quantum well detector has been developed which successfully predicts the observed dark current noise.
Competing anisotropies and first-order magnetization processes
Authors: Bolzoni F. , Pirini M. F.
Published: July 2002

The analysis of the canting model theory up to the fourth order, including the in-plane contribution to the total anisotropy, is presented. The origin of the first-order magnetization process (FOMP) is well explained in terms of competing anisotropies. The fourth-order terms are essential for the presence of a FOMP; in fact, computer simulations, with only second-order terms, show regular magnetization curves, and the representation, in terms of equivalent single sublattice anisotropy constant K*i, explains the origin, from the competition, of the high-order terms, but they are not strong enough to produce FOMP transitions. An analysis of the effects of each parameter in the energy expression is given, in particular the behavior of the magnetization curves and the evolution of the easy cone are studied. An analytical expression for the anisotropy field and of the energy instability at zero field (origin of easy cone) has been derived. As an application of the model, an analysis of the magnetization curves, in hard direction of single crystals of PrCo5, Nd2Fe14B, and Pr2Fe14B is given; the good agreement with experimental results shows that the above model explains well the origin of the spin reorientation and of the FOMP transitions observed in these compounds.
Photochemical formation of silver metal films from silver salt of natural high molecular carboxylic acid
Authors: Yonezawa Yoshiro , Takami Akinori , Sato Tomoo , Yamamoto Katsuhiko , Sasanuma Takako , Ishida Hideyuki , Ishitani Akira
Published: July 2002

Thin films of silver salt of alginic acid, a typical high molecular carboxylic acid in nature, were photolyzed by 253.7 nm light. On irradiating with a 15-W sterilization lamp in air at relative humidity of more than 70%, the silver alginate films first became yellow-brown colored due to formation of photolytic colloidal silver particles. When irradiation was continued, the irradiated surface of the films finally changed into clear silver mirror. The morphology of these films was observed by means of a high-resolution scanning electron microscope. Colloidal silver particles (10–50 nm diam) formed by a short-time irradiation were sparsely distributed at the film surface. As a result of prolonged irradiation for ∼180 min, film surface was covered with aggregated colloidal silver. The x-ray diffraction study of the irradiated films revealed sharp diffraction lines, indicating that the colloidal silver was in a highly crystalline state. A preliminary observation of a microtomed cross section of the film showed that colloidal silver particles had a tendency to precipitate at the irradiated side of the film. These observations were consistent with more than a 108 -fold decrease of the sheet resistance and change in transmittance spectra of the films caused by photolysis. It has been proposed that silver atoms from the silver alginate migrate and coalesce to yield the colloidal silver. The colloidal silver particles further diffuse in the film and aggregate themselves at the irradiated surface, giving rise to silver metal films.
Stress distribution in an aluminum interconnect of very large scale integration
Authors: Niwa H. , Yagi H. , Tsuchikawa H. , Kato Masaharu
Published: July 2002

Thermal stress-induced void formation in aluminum interconnect has become a major reliability problem in the usage of very large scale integration circuits. The purpose of this work is to analytically evaluate stresses in the Al line. By applying Eshelby’s method in micromechanics, the stresses in the Al line were estimated analytically as a function of the aspect ratio of the Al line cross section. The yielding criteria in plasticity were applied to examine whether the calculated stresses can induce relaxation by plastic deformation. The analytically calculated results were compared with previous results of numerical calculation and experimental observation.
Excimer laser ablated lead zirconate titanate thin films
Authors: Roy D. , Krupanidhi S. B. , Dougherty J. P.
Published: July 2002

Lead zirconate titanate (PZT) thin films on platinum coated silicon were prepared by excimer laser ablation and were crystallized by subsequent annealing. Films deposited at various fluences and post-annealed showed slight variations in lead content which seemed to affect the orientation. The relatively lead rich films showed (110) orientation and the orientation changed to (111) as the Pb content decreased. Crystalline perovskite PZT films showed a dielectric constant of 800, a remnant polarization of 32 μC/cm2 and a coercive field of 130 kV/cm.
Grain growth kinetics and interfacial energies in nanocrystalline Ni-P alloys
Authors: Lu K. , Wei W. D. , Wang J. T.
Published: July 2002

Grain growth process in nanocrystalline Ni-P alloys was investigated by use of differential scanning calorimetry and x-ray diffraction. Two exothermal peaks which result from grain growth processes of Ni3P and Ni crystallites, respectively, have been detected upon heating the nanocrystalline samples at constant heating rates. Activation energies for the two processes of grain growth were calculated by means of the relationship of grain growth temperature and heating rate using the Kissinger equation. Average interfacial energies of Ni3P/Ni3P grain boundary and Ni3P/Ni boundary were determined from the heat released during grain growth.
Hot workability of melt-spun Nd-Fe-Co-B magnets
Authors: Yoshida Y. , Kasai Y. , Watanabe T. , Shibata S. , Panchanathan V. , Croat J. J.
Published: July 2002

Anisotropic Nd-Fe-B magnets are produced from melt-spun ribbons by hot working technique. The processing is facilitated by improved workability. In order to obtain a sound magnet, it is important to suppress the crack initiation and growth. An investigation was carried out to study the deformation mechanism of the alloy system and to improve workability by changes in alloy composition. Alloy ribbons with composition (Nd13.6−xRx) (Fe77.6−y Ty Co2.8)B6.0 [R=Ce, Dy; T=Al, Si, V, Cu, Ga, Zr, Nb, Mo, Sn; x= 0, 1, 2; y=0, 0.5, 1.0] were prepared by melt spinning and then hot pressed into fully dense compacts. These compacts were upset in a hot working simulator. Hot workability was evaluated by measuring the crack opening displacement on the surface at the half height of the upset specimen. The relationship between strain rate and flow stress was found to be expressed by the equation: ε̇ = Aσn exp( − Q/RT). Values of n and Q were obtained for quarternary composition (Nd-Fe-Co-B). The effects of strain and strain rate on magnetic properties were also studied for quarternary composition. Of the additive elements, cerium and silicon addition showed significant improvement in workability without loss of coercivity.
Hot workability of R-Fe-B alloys and their magnetic properties
Authors: Akioka K. , Kobayashi O. , Yamagami T. , Arai A. , Shimoda T.
Published: July 2002

The hot workability of R-Fe-B alloys and their magnetic properties were extensively investigated. Modified hot pressing employing a ring which constrains an alloy ingot enabled hot working without cracking at high strain rates up to ε̇ = 1 × 10−1/s. Excessive discharging of the liquid R-rich phase was controlled and the refinement of crystal grains occurred at high strain rate hot pressing. Through these effects the maximum Hci reached 18 kOe, and a (BH)max of 33.3 MGOe with a moderate Hci of 15 kOe was obtained in a composition of the Pr-Fe-B-Cu system. Post-heat treatment at 475–525 °C was effective for enhancing Hci. It was found that even in Nd-based alloys, a (BH)max of more than 30 MGOe was achieved by hot pressing at a high strain rate, because the change in composition during pressing is minimized.
First order magnetization process in (Nd,Pr)2Co14B compounds
Authors: Sun X. K. , Zhao Zhi-gang , Wang Qun , Zhong Xia-ping , Zhang Zhi-dong , Chuang Y. C.
Published: July 2002

High-field magnetization behavior of (Nd,Pr)2Co14B compounds at T=4.2 K has been studied through applying high fields up to 35 T. Taking the misalignment of grains in the samples into account, the anisotropy constants K1, K2, and K3 were determined by means of fitting the hard magnetization curves. Within the framework of the theory developed by Asti and Bolzoni, FOMP phenomena are predicted to occur in the whole system (0<x<1). Accompanying the transformation from easy cone (x=0) to easy axis (x≳0.2), the type of FOMP changes from P1C to P1. The critical field of the FOMP transition increases with increasing Pr content. Magnetic measurements show that a valence instability of the Pr ion may exist.
Magnetic properties and microstructures of CoNiCr and CoFeCr thin films
Authors: Tang L. , Thomas G. , Khan Mahbub R. , Duan S. L. , Heiman Neil
Published: July 2002

The large difference in coercivities between CoNiCr (800 Oe) and CoFeCr (200 Oe) thin films, which were deposited on Cr-coated NiP/Al substrates under the same conditions, is related to their differences in microstructures. The magnetic properties were measured with a vibrating sample magnetometer and the microstructures were studied by transmission electron microscopy. It is found that both the CoNiCr and the CoFeCr films are hcp in phase, and of similar grain sizes. However, the stacking fault density (fcc region) is higher in CoNiCr films than in CoFeCr films, which may account for the difference in their coercivities. The presence of stacking faults is related to composition effects on stacking fault energy and their generation to release residual stresses.
Surface-limited release of deuterium from tantalum
Authors: Wampler W. R.
Published: July 2002

The release of deuterium (D) from solution in tantalum (Ta) was examined. Nuclear reaction analysis was used to measure the concentration of D in solution during isothermal release of the D. The rate-controlling process for D release was molecular recombination at the surface. The release followed second-order kinetics, which shows that the recombination occurs from sites which have a binding energy for the D less than or equal to the energy of solution. Recombination therefore cannot be occurring from the more strongly bound low-coverage chemisorption sites. A model for the release rate which uses no free parameters is described. Experimentally determined recombination coefficients for Ta, Pd, and Fe spanning 18 orders of magnitude are in good agreement with the model.
Correlation between the photoreflectance response at E1 and carrier concentration in n- and p-GaAs
Authors: Badakhshan Ali , Glosser R. , Lambert S.
Published: July 2002

We investigated the photoreflectance (PR) response of metalorganic chemical vapor deposition-grown n- and p-type GaAs at the higher-energy transition E1(≊2.9 eV). The doping level range of interest was 2×1016–4×1018 cm−3 for Si:GaAs and 6×1016– 1×1019 cm−3 for Zn:GaAs. Both the position and the broadening parameter, Γ1, of the E1 transition within the doping concentration range were investigated. The evaluation of Γ1’s, based on the curve fitting of the PR response and the Kramers–Kronig analyzed data reveal a nearly linear relation between Γ1 and the logarithm of the carrier concentration. This observation has the potential application for contactless determination of carrier concentration in moderate and heavily doped nanoscale films. Secondary-ion mass spectroscopy measurements show that there is relatively large compensation in Si:GaAs samples, but it does not correlate with the broadening of the E1 structure.
Raman study of longitudinal optical phonon-plasmon coupling and disorder effects in heavily Be-doped GaAs
Authors: Mlayah A. , Carles R. , Landa G. , Bedel E. , Muñoz-Yagüe A.
Published: July 2002

Raman spectroscopy measurements have been performed on GaAs:Be samples with high crystalline quality and exceptional heavy doping level ranging from 1019 to 1.4×1021 cm−3. The recorded spectra show a structure we assigned to a coupled LO phonon-damped plasmon mode. A theoretical expression for the Raman scattering rate by this mode has been derived from a dielectric model and compared to the experimental data. Using a fitting procedure the doping level of the samples has been estimated in agreement with Hall measurements. Moreover, the study of the Raman intensity evolution of both unscreened-LO and coupled phonon-plasmon structures, provided a convenient and rapid method to determine the activated carrier density in p-doped polar semiconductors. Disorder effects due to the dopant impurities have been also observed and analyzed using a spatial correlation model description.