bluuebunny/crossref_metadata_2025 huggingface dataset:
Real time spectroscopic ellipsometry characterization of the nucleation of diamond by filament-assisted chemical vapor deposition
Authors: Collins R. W. , Cong Yue , Nguyen H. V. , An Ilsin , Vedam K. , Badzian T. , Messier R.
Published: July 2002

The recently developed technique of real time spectroscopic ellipsometry (SE) has been applied to characterize the nucleation of diamond on c-Si by W filament-assisted chemical vapor deposition, leading to improved control over the process. Specifically, techniques are developed which minimize W contamination at the diamond/substrate interface; calibrations are performed which determine the temperature of the top ∼250 Å of the substrate under growth conditions; and alterations in gas flow conditions are implemented in response to diamond growth for a reduced induction time. With these procedures in place, real time SE provides the induction time, nucleation density, and mass thickness, and is in quantitative agreement with ex situ scanning electron microscopy.
Ballistic transport and solenoidal focusing of intense ion beams for inertial confinement fusion
Authors: Ottinger P. F. , Rose D. V. , Neri J. M. , Olson C. L.
Published: July 2002

Light-ion inertial confinement fusion requires beam transport over distances of a few meters for isolation of the diode hardware from the target explosion and for power compression by time-of-flight bunching. This paper evaluates ballistic transport of light-ion beams focused by a solenoidal lens. The ion beam is produced by an annular magnetically insulated diode and is extracted parallel to the axis by appropriate shaping of the anode surface. The beam propagates from the diode to the solenoidal lens in a field-free drift region. The lens alters the ion trajectories such that the beam ballistically focuses onto a target while propagating in a second field-free region between the lens and the target. Ion orbits are studied to determine the transport efficiency ηt (i.e., the fraction of the beam emitted from the diode which hits the target) under various conditions relevant to light-ion inertial confinement fusion. Analytic results are given for a sharp boundary, finite thickness solenoidal lens configuration, and numerical results are presented for a more realistic lens configuration. From the analytic results, it is found that ηt can be in the range of 75%–100% for parameter values that appear to be achievable. Numerical results show that using a more realistic magnetic-field profile for the lens yields similar values of ηt for small radius diodes but significantly reduced values of ηt for large radius diodes. This reduction results from the radial gradient in the focusing field at larger radius.
ZnGeP2 grown by the liquid encapsulated Czochralski method
Authors: Hobgood H. M. , Henningsen T. , Thomas R. N. , Hopkins R. H. , Ohmer M. C. , Mitchel W. C. , Fischer D. W. , Hegde S. M. , Hopkins F. K.
Published: July 2002

The growth of ZnGeP2 by the liquid encapsulated Czochralski method is reported for the first time herein. Large boules of ZnGeP2, with diameters up to 40 mm and weights up to 400 gm were grown by Czochralski pulling from B2O3 encapsulated melts under high pressure (20 atm Ar) using axial gradients ≤120 °C/cm. Boules pulled at ≤4 mm/h exhibited large (50×20×15 mm3) monocrystalline grains of α-phase ZnGeP2 with room temperature electrical properties of p-type conduction, carrier concentrations ranging from 1012 to 1016 cm−3, and mobilities of 20 cm2/V s or less. Optical samples exhibited broad IR transmission (0.7 to 12.5 μm), second harmonic generation at 4.7 μm with 7.2% conversion efficiency, a broad subband gap photoluminescence signature, and near band-edge absorption similar to that observed in Bridgman-grown ZnGeP2.
Constant current corona charging as a technique for poling organic nonlinear optical thin films and the effect of ambient gas
Authors: Dao Phat T. , Williams David J. , McKenna William P. , Goppert-Berarducci Kim
Published: July 2002

Poling, which involves the alignment of nonlinear optical (NLO) dipolar molecules in the direction of the applied electric field, was carried out using constant current charging, a recently developed corona charging technique. Using this technique, the sample surface voltage buildup, and hence the efficiency of the dipole alignment, can be monitored during the poling process. In addition, it will be shown that this capability also provides a way to detect the end point of the dipolar orientation. Corona charging of the organic NLO film used in this study, however, needs to be done in an inert atmosphere. Results from in situ IR spectroscopy measurement during corona charging of the NLO film, ultraviolet and visible absorption spectroscopy and electron scattering for chemical analysis of this film before and after poling, indicated that exposing it to corona discharge in air ambient caused oxidation of the polymer surface. Various types of nitrogen oxides and carboxylic acids were found to be the products of this oxidation reaction. Finally, we also obtained evidence showing that the surface charging process of the organic NLO film is affected by this newly grown oxidized layer.
Thermal stability of indium nitride single crystal films
Authors: Guo Qixin , Kato Osamu , Yoshida Akira
Published: July 2002

We examine the thermal stability of InN single crystal films. The films are not entirely stable and degrade at relatively low temperatures. No change on the surface of the film is found after heating the samples up to 500 °C in nitrogen atmosphere. However, if the films are heated above 550 °C, the surface undergoes a considerable change, owing to the decomposition and desorption of nitrogen.
Transient heating and melting transformations in argon-ion laser irradiation of polysilicon films
Authors: Xu Xianfan , Taylor Scott L. , Park Hee K. , Grigoropoulos Costas P.
Published: July 2002

Undoped, thin silicon films have been deposited at different temperatures on fused quartz substrates by low-pressure chemical vapor deposition. The heating of these films by continuous wave, argon-ion laser beam irradiation has been studied. In situ, normal incidence reflectivity measurements have been obtained at specified locations in the semiconductor films. Melting and recrystallization phenomena have been probed by transient measurements. The static film reflectivity at elevated temperatures, up to about 1400 K, has also been measured. The temperature field has been analyzed numerically, using a modified enthalpy model. Thin-film optics were used to calculate the argon-ion laser light absorption in the polysilicon layer and the transient reflectivity response to the probing laser light. The predicted and experimentally measured reflectivity histories have been compared. The initial stages of the phase change process have been captured by high-speed photography.
Growth and characterization of Bi12(Si1−xTix)O20 mixed crystals
Authors: Yeh T. S. , Hu L. J. , Tu S. L. , Yang S. J. , Hsu S. E. , Hsu Ken
Published: July 2002

Crystal growth of a sillenite structure with a composition of Bi12(Si1−xTix)O20 and the corresponding optical characteristics have been systematically examined. The incongruent melting materials Bi12TiO20(BTO) have been observed to form a solid solution with congruent melting materials Bi12SiO20(BSO) for the whole range of the x value. The cutoff wavelength increases and the optical activity decreases linearly with BTO content in the crystals. The photorefractive effect is modified significantly due to the addition of BTO. The diffraction efficiency (η) of the photorefractive grating increases first with BTO content for x≤0.33 and saturates for a larger amount of BTO addition. The response speed is, however, promoted markedly for x≥0.48.
In situ observation of Ba oxide layer at the interface between Y1Ba2Cu3O7−x film and MgO substrate
Authors: Kamei Masayuki , Aoki Yuji , Ogota Seiya , Usui Toshio , Morishita Tadataka
Published: July 2002

The very first stage of the growth of c-axis oriented Y1Ba2Cu3O7−x films prepared by coevaporation of metallic constituents on MgO(100) was examined in situ by new surface sensitive x-ray spectroscopy. Using reflection high-energy electron diffraction and total reflection-angle x-ray spectroscopy, the Ba oxide layer of Y1Ba2Cu3O7−x was found to grow at the interface between MgO(100). It was further observed that the coverage and the flatness of this Ba–oxide layer was higher than that of Y and Cu–oxide layers.
Ion-beam induced compaction in glassy carbon
Authors: McCulloch D. , Hoffman A. , Prawer S.
Published: July 2002

Cross-sectional transmission electron microscopy has been used to investigate the implanted layer in glassy carbon irradiated with 50 keV C ions to a dose of 5×1016 ions/cm2. It was found that in addition to the formation of an amorphous surface layer approximately 100 nm deep, the ion-beam modified layer was compacted from the unirradiated density of 1.5 to 2.4±0.2 g/cm3. Ion implantation was also found to increase the refractive index of glassy carbon from 1.8±0.1 to 2.4±0.1 which is also consistent with the proposition that an increase in the density of the implanted layer has occurred. The formation of a dense, amorphous carbon surface layer could explain the observed increase in wear resistance of glassy carbon following ion implantation.
Birefringence images of screw dislocations viewed end on in cubic crystals containing a long-range stress field
Authors: Ge Chuan-Zhen , Wang Hai-Wen , Ming Nai-Ben
Published: July 2002

The expression for the intensity distribution and computer-simulated images of screw dislocations with Burgers vector α〈111〉 or α/2〈111〉 viewed end on in cubic crystals subjected to a long-range uniaxial stress has been obtained by considering the anisotropy of both elastic and photoelastic properties of the material. The computer-simulated images of end-on screw dislocations show twofold symmetry with a pair of dark and bright petals which result from the effect of a long-range stress superimposed on that of the screw dislocations. The computer-simulated images are in good agreement with the experimental images observed in Ba(NO3)2 and Gd3Ga5O12 crystals. The principal stress of the long-range uniaxial stress field around the screw dislocation in the crystal wafer has been estimated, based on this theory.
Effect of surface passivation with SiN on the electrical properties of InP/InGaAs heterojunction bipolar transistors
Authors: Ouacha A. , Willander M. , Hammarlund B. , Logan R. A.
Published: July 2002

The effects of the SiN layer normally used to passivate and protect the exposed junction surfaces in InP/InGaAs heterojunction bipolar transistors have been studied and shown to degrade the transistor properties. These effects are ascribed primarily to surface damage associated with the high SiN deposition temperature (350 °C). A degradation of the emitter-base properties was observed through the nonideal behavior of the base current and the measured short minority-carrier lifetime in the base, extracted by using the base width modulation method. Degradation in the current gain and emitter injection efficiency was also observed. A clear recovery of the transistor was observed after removing the SiN passivation layer indicating that the high SiN deposition temperature results in a high-surface-state density which increases the surface recombination velocity and degrades the junction properties. It is concluded that a low-temperature deposition and good quality dielectric are necessary to exploit the excellent electrical properties of InP-based heterojunction bipolar transistors.
Sequential deposition of diamond from sputtered carbon and atomic hydrogen
Authors: Olson Darin S. , Kelly Michael A. , Kapoor Sanjiv , Hagstrom Stig B.
Published: July 2002

The growth of diamond thin films on a scratched silicon crystal surface by a chemical-vapor deposition technique is reported. The substrate was bombarded by sputtered carbon from a graphite target in a helium dc glow discharge, and subsequently exposed to atomic hydrogen generated by a hot tungsten filament. The resulting diamond films were characterized by Raman spectroscopy and scanning electron microscopy. Deposited film quality and growth rate were studied as functions of carbon and atomic hydrogen exposure. An increase in growth rate of diamond was observed with atomic hydrogen exposure. We also observe that only the first monolayer of carbon deposited with each exposure appears to be utilized. These observations suggest that the diamond growth is a surface reaction. Further, calculations based upon the carbon utilization in traditional hot filament reactors indicate that a gas-phase reaction process can account for neither the growth rate nor the saturation behavior observed. Based on this work it is proposed that the growth of diamond films is governed by surface reactions, and that the necessity of gas-phase precursors can be precluded.
Thermal emission rate of deep localized states in amorphous arsenic triselenide
Authors: Naito Hiroyoshi , Okuda Masahiro
Published: July 2002

Deep localized-state distribution in amorphous arsenic triselenide thin films has been measured with a modulated photocurrent technique. A peak in the deep localized-state distribution is found at 0.79 eV above the valence-band mobility edge. It is also found that the thermal emission rate of holes from the localized state at the peak is almost constant in the room-temperature range but exhibits thermally activated behavior below and above the room-temperature range. This anomalous temperature dependence of the thermal emission rate is interpreted on the basis of a thermally created defect.
Electromigration-induced void growth in bamboo structures
Authors: Kawanoue T. , Kaneko H. , Hasunuma M. , Miyauchi M.
Published: July 2002

A novel resistometric technique enables the investigation of single void nucleation and growth induced by electromigration (EM) for aluminum (Al) lines having a perfect bamboo structure in comparison with single-crystal Al lines. Fine tungsten (W) voltage probes were fabricated at every 4 μm along the Al line with grain sizes of 10 μm or more. Local electrical resistance changes have confirmed that a void nucleated only at the grain boundary and no damage appeared within the grains. The measured values of the local electrical resistance changes were converted to EM-induced void growth rates. The vacancy flux was deduced from the void growth rate under the assumption that a vacancy volume is equal to the atomic volume. It has been clarified that the vacancy fluxes for a bamboo-structured Al line were about one order magnitude smaller than the ideal vacancy fluxes in the Al lattice derived from the Nernst–Einstein relation. The vacancy fluxes for single-crystal Al lines were also quantified under an accelerated test at a high electric current density with a temperature gradient. These results suggest that the bamboo grain boundaries have a blocking effect on vacancy flow. This blocking produces vacancy supersaturation near the grain boundary, and the reduction in vacancy flux is well explained by the back-diffusion due to the corresponding concentration gradient.
Kinetics of the formation of C49 TiSi2 from Ti-Si multilayers as observed by in situ stress measurements
Authors: Jongste J. F. , Alkemade P. F. A. , Janssen G. C. A. M. , Radelaar S.
Published: July 2002

The formation of C49 TiSi2 from sputter-deposited amorphous Ti-Si multilayers on Si(100) substrates was studied during isochronal and isothermal heat treatment. The formation process was analyzed for multilayer periodicities (i.e., the thickness of one Ti and one Si layer) of 1, 5, and 12 nm, respectively, by in situ stress measurements and differential scanning calorimetry (DSC). A strong correlation between the evolution of the stress and the formation of the C49 TiSi2 phase was found. During heat treatment an abrupt change of the stress in the film was observed. DSC and x-ray diffraction experiments revealed that this change of the stress coincides with the formation process of the C49 TiSi2 phase. The transition temperature of the Ti-Si multilayer to the C49 TiSi2 phase shifts from ∼295 to ∼550 °C with increasing multilayer periodicity. From kinetic analysis of the experiments the activation energy of the C49 TiSi2 phase formation process was acquired. For the smallest periodicity of 1 nm an effective activation energy of 170±25 kJ/mol was found, for multilayers with 12 nm periodicity the activation energy was 280±40 kJ/mol. The difference in activation energy is explained by different rate-limiting steps during silicide formation as a function of the multilayer periodicity. DSC measurements revealed two processes during the formation of the C49 TiSi2 phase: mixing and crystallization. The enthalpy for mixing for Ti-Si multilayers with periodicities of 1 and 12 nm was −38 and −33 kJ/mol, respectively. The crystallization enthalpy was comparable for both periodicities: −5 kJ/mol.
Field emission from atomic size sources
Authors: Horch S. , Morin R.
Published: July 2002

The source area of electron field emission from ultrasharp 〈111〉-oriented tungsten tips terminated by a few (down to one single) atoms is confined to the very end of the tip, thus forming an atomic size electron source. The most remarkable emission property of such tips, the angular dispersion of the emitted electron beam, is measured both qualitatively and quantitatively for well-defined atomic arrangements at the tip apex and also for a wide range of applied electric fields and currents. It is shown that only pyramidally shaped tips emit electrons in sharp beams, with small opening angles down to less than 3°. The results suggest, in contrast to existing theories, that mesoscopic parameters, as the overall shape of the tip apex (on a scale of a few nanometers) and the associated patch field distribution, might play a crucial role in focusing the beam.
Photoconduction of synthetic pyrite FeS2 single crystals
Authors: Tsay Ming-Yih , Huang Ying-Sheng , Chen Yang-Fang
Published: July 2002

The photoconduction of synthetic pyrite FeS2 single crystals with low impurity concentration prepared by chemical vapor transport method is reported over a temperature range from 15 K to 300 K. The energy gap is determined from the photoconductive spectral response by the Moss rule. At room temperature the indirect energy gap is found to be 0.83±0.02 eV. According to the experimental evidence for a sharp antibonding p-like state above the Fermi level of FeS2 reported by Folkerts et al. [J. Phys. C 20, 4135 (1987)], the indirect gap is assigned as the transition between Fe 3d t2g and S 3p σ* states. The temperature variation of the indirect band gap shows a linear dependence between 100 K and 300 K with a negative temperature coefficience equal to 1.0±0.1 meV/K. A distinct feature at higher energy side of the spectrum is observed and attributed to the direct band-gap transition. At temperature lower than 60 K, a very sharp peak around 0.9 eV emerged below the absorption edge. This feature might be associated with the excess carriers induced by the photothermal ionization between the impurity levels and conduction band.
Magnetic properties and microstructures of the Nd-Fe-B system during the hydrogenation-decomposition-desorption-recombination process
Authors: Nakayama R. , Takeshita T.
Published: July 2002

The Nd-Fe-B and Nd-Fe-Co-B magnet powders with the high coercivity (≥10 kOe) were obtained by the hydrogenation-decomposition-desorption-recombination (HDDR) process at temperatures between 800 °C and 900 °C. We studied magnetic properties and microstructures of the Nd-Fe-B systems during the HDDR process. The NdH2 phase produced by decomposition of Nd2Fe14BHx with hydrogenation exists in the maze-like form of the size of 10−1 μm. It was found that the size of the NdH2 phase determines the size of the Nd2Fe14B phase formed by the recombination. NdH2, Fe, and Fe2B are more stable than Nd2Fe14B at temperatures from 800 °C to 900 °C. The magnet powders produced by the HDDR process are magnetically almost isotropic.
Influence of the alloying on the vibrational properties of amorphous silicon in the frequency range 200–450 cm−1: Raman studies
Authors: Tzolov M. B. , Tzenov N. V. , Dimova-Malinovska D. I.
Published: July 2002

Raman spectra of a large variety of amorphous silicon–carbon films prepared by magnetron sputtering at different technological conditions are studied. Great emphasis is given to the bands in the region 200–450 cm−1. The position of the well-defined dip between the bending mode band and the bands in the central region is used as a quantitative measure of the position of the bands in the central region. The relative carbon content in the films is estimated by infrared spectroscopy. It is shown that the changes in the central region of the Raman spectrum with the carbon atoms incorporation are due to the formation of a new bond type, but not due to increased disorder. It was found that the position of the above-defined dip could be used for comparison of the alloying atom content of nonhydrogenated amorphous silicon alloys. This is also applicable for hydrogenated samples having approximately one and the same hydrogen content.
Temperature dependence of the Γ8v-Γ6c gap of GaAs
Authors: Oelgart G. , Orschel B. , Proctor M. , Martin D. , Morier-Genoud F. , Reinhart F. K.
Published: July 2002

The photoluminescence (PL) peak positions of the ground state heavy and light-hole excitons on high-quality Molecular Beam Epitaxy grown GaAs/AlxGa1−xAs (x=0.3 and 1) multiquantum-well structures have been experimentally determined in the temperature range 4.2≤T≤340 K. Using these values and the well-known low-temperature energy of the GaAs Γ8V-Γ6C gap [EgΓ(GaAs,T=0 K)=1.5192 eV], we propose the temperature dependence to be EgΓ(GaAs,T)= 1.5192+5.16×10−5×T−1.99×10−6×T2 +2.60×10−9×T3 (EgΓ in eV). The nearly linear variation of EgΓ(GaAs,T) versus the temperature in the range 170 K≤T≤340 K can be approximated by a coefficient (dEgΓ/dT)=−4.4×10−4 eV/K, in excellent agreement with theoretical predictions.
X-ray diffraction characterization of ternary artificial superlattices
Authors: Goldfarb I. , Zolotoyabko E. , Shechtman D.
Published: July 2002

Thin films of alternating Au, Ag, and Cu wedge-shaped metal layers were made by magnetron sputtering in order to develop a method for investigation of a multicomponent systems. X-ray-diffraction patterns of all as-deposited samples revealed satellites in the vicinity of (111) reflections, evidence of composition-modulated artificial superlattice formation. The experimental spectra are well explained by the kinematical diffraction theory for imperfect superlattices. Computer simulations have demonstrated extremely high sensitivity to the fluctuations ΔH/H of the superlattice period H. As a result, a rapid and simple method of ΔH/H determination is proposed.
Enhancement of photosensitivity in chemically deposited CdSe thin films by air annealing
Authors: Nair M. T. S. , Nair P. K. , Zingaro Ralph A. , Meyers Edward A.
Published: July 2002

Improvement in photosensitivity, (σphoto−σdark)/σdark, of chemically deposited CdSe thin films on annealing in air is discussed. The as-prepared films of ∼0.5 μm thickness show photosensitivities of <10 under 600 W m−2 illumination. Upon annealing the films in air for 1 h each at various temperatures their photosensitivity increases depending on the temperature of annealing: ∼10 (200 °C), ∼102 (300 °C), ∼103 (400 °C), and ∼107 (450 °C). Air annealing at temperatures beyond 450 °C was found to cause degradation in the photosensitivity. The high photosensitivity is also accompanied by growth in photocurrent while maintaining a fast decay of ∼6 decades in <1 s after shutting off the illumination. Such a short decay time is unusual with chemically deposited photoconductive thin films. The results are explained on the basis of improvement in crystallinity and increase in chemisorption of oxygen upon annealing the films in air. X-ray-diffraction data and x-ray photoelectron spectroscopy depth profiling of the annealed films are presented in support of this explanation.
Doping of GaAs using SF6 plasma treatment
Authors: Cho Jaeshin , Saha Naresh C.
Published: July 2002

We propose a new method of making heavily doped n-type GaAs to a very shallow depth using sulfur hexafluoride (SF6) plasma treatment of the GaAs surface. Semi-insulating GaAs substrate implanted with Si was exposed to a sulfur containing SF6 plasma and capped with silicon nitride anneal cap. During a subsequent anneal step at an elevated temperature to electrically activate the implanted Si, the sulfur diffused into GaAs to a shallow depth of ∼600 Å resulting in further enhancement of net carrier concentration. With this technique the carrier concentration near the surface region was almost doubled compared to samples with Si implantation only. The enhanced carrier concentration improved the wafer-scale variation of ohmic contact resistance using AuGeNi contact metals from 0.089±0.073 to 0.049±0.017 Ω mm. The surface chemistry of SF6 plasma treated GaAs surface was characterized by x-ray photoelectron spectroscopy and Auger electron spectroscopy, and the results were compared with the carrier-concentration profiles and ohmic contact resistance.
Controlled p- and n-type doping of homo- and heteroepitaxially grown InSb
Authors: Thompson Philip E. , Davis John L. , Yang Ming-Jey , Simons David S. , Chi Peter H.
Published: July 2002

The p- and n-type doping, with Be and Si, respectively, of InSb grown on InSb and GaAs substrates using molecular-beam epitaxy was investigated. Using secondary-ion-mass spectrometry, an anomalous migration of Be toward the surface was observed for growth on InSb substrates when the substrate temperature exceeded 340 °C. This migration was not observed for Be-doped InSb layers grown on GaAs substrates. This redistribution of dopants was also not observed for Si-doped InSb layers. The doping efficiency of Be in InSb was approximately one-half that measured for Be in GaAs. For the doping efficiency of Si in InSb to reach that for Si in GaAs, the substrate temperature had to be maintained at ≤340 °C during growth. Using the low-temperature growth technique, Si delta-doped structures were grown which demonstrated two-dimensional electron gas behavior.
Interfacial anisotropy and magnetic transition of cobalt films on Cu(111)
Authors: Huang F. , Mankey G. J. , Willis R. F.
Published: July 2002

We measure the magnetic properties of ultrathin films of Co epitaxially grown on single crystal Cu(111) using surface magneto-optic Kerr effect. The magnetic behavior is compared with that of the same films, but covered by Cu overlayers to study the effects of film morphology on ferromagnetism. The uncapped films show mainly in-plane anisotropy, but a weak perpendicular magnetization is always present. Capping a 1.5 monolayer (ML) Co film with Cu significantly enhances perpendicular anisotropy with 1 ML of Cu overlayer eliminating the in-plane magnetization completely. The perpendicular magnetization reaches its maximum value with 3 ML of Cu overlayer, ∼5 times higher than the uncapped films, and then decreases as more Cu is deposited. Annealing can further increase the perpendicular magnetization with the in-plane component remaining weak. In sharp contrast, this perpendicular anisotropy enhancement by Cu overlayers is not seen for Co films on Cu(100). The temperature dependence of magnetization fits to the phenomenological power law M∼(1−T/TC)β with β=0.15±0.05 for the uncapped 1.5 ML Co film and shows a linear behavior after the film is covered by Cu overlayers.
High-field magnetization behavior in random anisotropy amorphous Co-Er alloys
Authors: Lassri H. , Driouch L. , Krishnan R.
Published: July 2002

Amorphous Co1−xErx ribbons with x=55 and 65 were prepared by the melt-spinning technique. Magnetization measurements were carried out in the temperature range 4–100 K under high magnetic fields up to 20 T. Even at 20 T the saturation is not fully attained. Assuming that Co has no moment in the alloy with x=65 the Er moment is found to be 7.0μB which indicates a speromagnetic spin structure. The Co moment in the alloy with x=55 is then found to be 0.1μB, which is negligibly small. By analyzing the approach to saturation using Chudnovsky’s theory we have extracted some fundamental parameters.
‘‘Loose spins’’ in Fe/Cu/Fe(001) structures
Authors: Heinrich B. , Celinski Z. , Liao L. X. , From M. , Cochran J. F.
Published: July 2002

Slonczewski recently proposed a model for the exchange coupling between ferromagnetic layers separated by a nonferromagnetic spacer based on the concept of ‘‘loose spins.’’ ‘‘Loose spins’’ contribute to the total exchange energy. We have studied the role of ‘‘loose spins’’ in bcc Fe/Cu/Fe(001) structures. bcc Fe/Cu/Fe(001) trilayers deposited at room temperature were investigated extensively in our previous studies. In our ‘‘loose spin’’ studies, the Fe was added inside the Cu interlayer. Several structures were atomically engineered in order to test the behavior of ‘‘loose spins:’’ One additional atomic layer of an (Fe+Cu) alloy were located in appropriate positions in a Cu spacer. The bilinear and biquadratic exchange coupling in the above structures was quantitatively studied with FMR in the temperature range 77–370 K and with MOKE at RT.
Preparation of Co-Zn ferrite films at low substrate temperature by plasma-free dc sputtering for magnetic recording media
Authors: Matsushita N. , Noma K. , Nakagawa S. , Naoe M.
Published: July 2002

Co-Zn ferrite films with small grains for magnetic recording media at ultrahigh density were deposited ‘‘plasma free’’ on a substrate by using the dc facing targets sputtering apparatus without subsequent annealing process. The films deposited at a substrate temperature Ts as low as 90 °C were composed of crystallites with excellent (111) orientation and exhibited a saturation magnetization 4πMs of 3.3 kG and an in-plane and perpendicular coercivity Hc∥ and Hc⊥ of 1.8 and 2.2 kOe, respectively. The films deposited at a Ts of 250 °C exhibited 4πMs of 4.8 kG and possessed almost the same Hc∥ and Hc⊥ of 1.5 kOe.
Low-temperature sputter deposition of high-coercivity Co-Cr films for perpendicular recording
Authors: Honda Naoki , Ouchi Kazuhiro , Iwasaki Shun-ichi
Published: July 2002

A low-temperature magnetron sputter-deposition method for Co-Cr medium has been developed. Films of 17 wt % Cr-Co were deposited to a thickness of 100–200 nm onto glass substrates over an extremely wide range of Ar gas pressures at room temperature. A high hcp c-axis orientation to the film normal (Δθ50<6°) could be obtained even at pressures over 50 Pa (375 mTorr) when the films were deposited onto a well-oriented c-axis Ti underlayer. Co-Cr films with a perpendicular coercivity as high as 1000 Oe with an anisotropy field of 5 kOe were obtained at extremely high Ar pressures; e.g., 70 Pa (525 mTorr). Scanning electron microscopy observations showed that the films had a fine columnar structure with distinct grain boundaries and the grain size was dramatically reduced with the introduction of the Ti underlayer. It was determined that the large anisotropy field for the Co-Cr films is attributed to crystalline anisotropy. The mechanism of magnetization reversal in the films is suggested to be rotational.
Friction and wear of ultrahigh-density magnetic tapes
Authors: Bhushan Bharat , Patton Steven T.
Published: July 2002

The objective of this study was to identify any differences in the friction and wear characteristics of particulate tapes produced with various magnetic particles and metal-evaporated (ME) tapes. Accelerated friction and wear experiments were conducted with a tape reciprocated in a shoeshine mode over an aluminum drum. We have found that barium ferrite and Co-γFe2O3 tapes exhibit the least damage to themselves and the mating drum. The ME tape exhibited the least durability among all tapes. The effect of tape roughness on friction was found to be dependent on the hardness of the mating material. Friction increased with an increase in the roughness during the tests with a soft aluminum drum due to severe plowing of the aluminum. However, friction decreased with an increase in the roughness with a hard ferrite surface which is consistent with the asperity contacts being elastic in nature (with no appreciable plowing contribution to the friction).
Magnetism of thin magnetic layers with strong anisotropy and quantum tunneling (abstract)
Authors: Perera P. , O’Shea M. J.
Published: July 2002

We report on the magnetic properties of Dy(t Å)/Mo(d Å), DyCo(t Å)/Mo(d Å), and Gd(t Å)/Mo(d Å) multilayers where d=180 Å and t ranges from 10 to 3000 Å. We find a decrease in Tc with decreasing t, with the most rapid decrease occurring for the Gd system where the anisotropy is the weakest. We have looked at the time dependence of magnetization in the anisotropic systems (Dy based). At long times (5×104 s) the magnetization shows a stretched exponential dependence on time as is found in other magnetically disordered systems. We have also looked at the rate of magnetic relaxation at short times (<1000 s) and find that it becomes independent of temperature below a temperature in the range 3–6 K depending on the magnetic layer thickness t. We shall consider the possibility of macroscopic quantum tunneling here and estimate the temperature, T*, below which a system is expected to cross over from thermally activated to quantum tunneling.1,2 We shall also compare our results to previous work on Dy/Cu.3
Photo-electron paramagnetic resonance investigation of the Cr3+ impurity and the (SCl)2− defect in synthetic FeS2 crystals
Authors: Yu Jiang-Tsu , Huang Ying-Sheng , Tsay Ming-Yih
Published: July 2002

The method of photo-electron paramagnetic resonance has been used to investigate the photosensitivities of the Cr3+, Ni2+, and (SCl)2− impurities and defects detected by electron paramagnetic resonance (EPR) in synthetic FeS2 crystals grown by the method of chemical vapor transport by using ICl3 as the transport agent. Cr3+ and (SCl)2− are photosensitive, but Ni2+ is not, to IR illumination with photon energy less than the band-gap energy. A decrease (photoquenching) in the EPR signal of Cr3+ and an increase (photoinduction) in the EPR signal of (SCl)2− were detected at low temperatures. At T≂110 K, the spectral response of the photoquenching of Cr3+ is the largest near λ=1425 nm−1 (0.87 eV), which can be correlated with the 0.90 eV photoconductivity peak and the 0.87 eV IR absorption peak observed at low temperatures in the same batches of crystals. After several cycles of on–off IR illumination, the equilibrium population of Cr3+ is less than that of the virgin state, indicating the presence of hole traps. The transient and equilibrium behaviors of the (SCl)2− defects are just the opposite, which indicates that a S2− defect behaves as a hole trap. A band model has been established to explain the observed photoquenching of Cr3+, the photoconductivity peak, and the IR absorption peak.
Effect of plasma etching, carbon concentration, and buffer layer on the properties of a-Si:H/a-Si1−xCx:H multilayers
Authors: Velasquez E. L. Z. , Fantini M. C. A. , Carreño M. N. P. , Pereyra I. , Takahashi H. , Landers R.
Published: July 2002

Small angle x-ray diffraction was used to diagnose the structural properties of a-Si:H/a-Si1−xCx:H multilayers deposited by rf glow discharge. Precise deposition rates were obtained from the experimental data. Two growth parameters were varied: the methane concentration in the gaseous mixture and the intermediary plasma etching time between consecutive depositions. Some samples had an additional buffer layer between the substrate and the heterostructure. The sharpest interfaces were obtained on samples with the intermediate buffer layer, plasma etching times of at least 2 min, and diamond-like a-Si1−xCx:H layers. Profiling by Auger electron spectroscopy and small angle x-ray diffraction results were used to estimate the interface thickness.
Au-Sn/W and Au-Sn/Cr metallized chemical vapor deposited diamond heat sinks for InP laser device applications
Authors: Katz A. , Baiocchi F. , Lane E. , Lee C. H. , Hall C. , Doting J. , Grijsbach C. , Harris K.
Published: July 2002

An attempt to apply a more stable metallurgical soldering system than the traditionally used Ti/Pt/Au-Sn reactive system was explored by replacing the barrier metals in between the chemical vapor deposited diamond (CVDD) submount and the Au-Sn solder with either W or Cr layers. In the case of the W layer a thin layer of Ti was added to improve the adhesion of Au-Sn solder to the W layer. The CVDD/W(100 nm)/Ti(10 nm)/Au-Sn(1.5–2.2 μm) system was heat treated at 350 °C for durations of 5 s–5 min, simulating a bonding cycle, and the metallurgical interactions were analyzed. Some diffusion of the Ti was observed, but the W layer remained intact. Thus, due to the absence of interaction between the Sn or Au and the W barrier layer, the Au:Sn ratio was kept uniform for long duration heating (≳2 min). The Au-Sn solder tends to ‘‘ball up’’ in local spots leading to the formation of local voids in the continuous solder layer over the W. In the case of the CVDD/Ti (100 nm)/Cr(200 nm)/AuSn(1.5–2.2 μm) structure a minimum interaction between the Au-Sn solder and the barrier was observed through a heating cycle at 350 °C for 5 min. This heat treatment, however, led to solder surface roughness in the order of about 5000 Å between bump peak and valley, but the Au:Sn composition remained in the eutectic ratio of 70:30 at. %. Both soldering metallurgical systems gave a potential good bonding of InP laser diodes to CVDD heat sinks.
Water vapor adsorption on YBa2Cu3O7−δ powder at 298 K
Authors: Ross K. A. , Westphal M. J.
Published: July 2002

Water vapor adsorption isotherms were determined by the gravimetric method for a YBa2Cu3O7−δ powder at 298 K. Adsorption energy released per unit area, adsorption site area, adsorbate fractional coverage, minimum pore radius, surface charge, surface potential, and adsorption bond energy were calculated to characterize the surface of the powder. The adsorbed water vapor may form an oriented chemisorbed layer.
Hydrodynamic compressibility of silicon carbide through shock compression of metal-ceramic mixtures
Authors: Grady D. E.
Published: July 2002

Shock-compression experiments were performed on 50% by volume ceramic-metal mixtures of silicon carbide and copper at pressures of 15–30 GPa. The objective of these experiments was to determine the hydrodynamic compressibility (dynamic pressure-volume response) of silicon carbide through shock measurements on the ceramic-metal composite and the application of analytic mixture theory. Compression states inferred for silicon carbide above 20 GPa appear consistent with hydrodynamic behavior and are in agreement with compression curves extrapolated from ultrasonic data. Dynamic strength or viscosity effects apparently complicate shock compression of the ceramic-metal composite at the lower shock pressures. Shock release experiments on the composites provide further high-pressure equation-of-state data for the ceramic-metal mixture.
Time-resolved photoluminescence of undoped InP
Authors: Keyes B. M. , Dunlavy D. J. , Ahrenkiel R. K. , Shaw G. , Summers G. P. , Tzafaras N. , Lentz C.
Published: July 2002

Energy and time-resolved photoluminescence data have been obtained for nominally undoped (n 4.5×1015 cm−3) bulk InP grown by the vertical-gradient freeze method. The data were taken as a function of temperature, from 80 to 290 K, and analyzed using a solution to the continuity equation. The resulting lifetime values range from 300 ns to 3.2 μs, and surface recombination velocities were fund to be on the order of 103 cm/s. The temperature dependence can be explained by assuming a radiatively limited recombination with a resulting B coefficient ≥5.9×10−11 cm3/s at 300 K.
Temperature dependence of Kerr rotation for Ni film
Authors: Di G.Q. , Uchiyama S.
Published: July 2002

We measured the temperature dependence of the Kerr rotation spectrum of a Ni polycrystalline film. We observed an increment of 35% for the polar Kerr rotation at 3.18 eV when the temperature was decreased from 300 to 84 K. This effect is much larger than the increment of 4% observed in the saturation magnetization over the same temperature range. The experimental data at low-temperature are in excellent agreement with published ab initio calculations, whereas the variation of the Kerr rotations with temperature may be attributed to the rearrangement of electrons in the 3d bands.
Structural and electrical properties of Si- and Se-implanted InP layers
Authors: Müller P. , Bachmann T. , Wendler E. , Wesch W.
Published: July 2002

Semi-insulating Fe-doped 〈100〉-InP wafers were implanted in a nonchanneling direction with 300 keV Si+ and 600 keV Se++ ions in the dose range of 1×1012–1×1016 cm−2. The implantation temperature was varied between room temperature and 425 K. The samples were capped and short time annealed by means of a graphite strip heater at 700–975 °C. The defect investigation of the as-implanted as well as of the annealed samples was performed with Rutherford backscattering spectrometry. A simple vacancy diffusion model is applied to describe the damage production, which yields critical implantation temperatures for amorphization. These temperatures are approximately 390 K for Si and 420 K for Se, for higher temperatures amorphization is not possible in InP. The electrical properties of the annealed layers are measured by the van der Pauw–Hall technique. The results are discussed with respect to the residual damage after annealing. Saturation values of the electrical activation were achieved at 3×1014 cm−2 for Si and 4×1014 cm−2 for Se, respectively.
Synthesis of β- and α-FeSi2 phases by Fe ion implantation into Si using metal vapor vacuum arc ion source
Authors: Liu B. X. , Zhu D. H. , Lu H. B. , Pan F. , Tao K.
Published: July 2002

High-current Fe ion implantation technique was employed to synthesize Fe-silicide layers on Si wafers, using a newly constructed metal vapor vacuum arc ion source. The Fe ions were extracted at a voltage of 40 kV with a varying ion current density from 65 to 152 μA/cm2 and a nominal ion dose varied from 3×1017 to 3×1018 Fe/cm2. At a fixed nominal dose of 4×1017 Fe/cm2, a semiconducting β-FeSi2 layer gradually grew on Si with increasing ion current density and a qualified β-FeSi2 layer with a relative sharp interface was obtained, when the ion current densities exceeded 115 μA/cm2. While implanting at a fixed ion current density of 152 μA/cm2 with varying ion dose, the β-FeSi2 phase began to form first at a nominal dose of 3×1017 Fe/cm2, and eventually transformed into a metallic α-FeSi2 phase when the nominal dose reached 3×1018 Fe/cm2. Further information of the formation of Fe disilicides was obtained by comparing the postannealing results of some of the implanted wafers with those observed immediately after implantation. The formation mechanism of the Fe disilicides is discussed in terms of the beam heating effect, which in turn resulted in a simultaneous thermal annealing during Fe ion implantation.
Low-temperature emission of Al0.48In0.52As under high pressures
Authors: Zhou H. P. , Sotomayor Torres C. M.
Published: July 2002

We investigated the low-temperature emission of Al0.48In0.52As under high pressures from 1 bar up to 92 kbar, paying special attention to the changes in luminescence mechanisms that occur concurrently with the crossover between the Γ- and the X-related states. By investigating the temperature and excitation power dependence of the photoluminescence together with the photoluminescence excitation, we demonstrate the low-temperature emission of Al0.48In0.52As is due to neutral donor-acceptor-pair (D0,A0) transitions with a relatively deep acceptor. This occurs in both the Γ- and the X-related states. We suggest the shallow donor ground states associated with the X and the Γ conduction bands seem to be tied quite rigidly to these conduction bands. Variations in the donor binding energies with the pressure and the Γ-X related state crossover seem to be minor. The linear pressure coefficients αΓ and αX of the (D0,A0) related to the Γ and the X levels in the conduction band are 7.9±0.1 and −2.9±0.1 meV/kbar, respectively. The Γ-X related state crossover occurs at ∼52.5±0.5 kbar at 2 K. The direct band gap EΓg and the indirect band gap Exg of Al0.48In0.52As are ∼1.61 and ∼2.17 eV at 1 bar and 2 K, respectively.
Growth kinetics of micrometer-size silicon lines produced by decomposition of silane using a laser direct-writing technique
Authors: Boughaba S. , Auvert G. , Pauleau Y.
Published: July 2002

Polycrystalline Gaussian shape silicon lines as small as 1 μm in width were deposited by pyrolysis of silane (SiH4) on polysilicon/silicon-dioxide/monosilicon substrates. As a heat source, a cw argon-ion laser operating in the 488–514 nm range was used. The growth kinetics and morphology of the silicon lines were investigated at various scanning speeds of the laser spot, laser beam powers, and reactant gas pressures. The scanning speed was varied between 1 and 100 μm/s and the SiH4 pressure was taken in the 5–250 mbar range. From the deposition kinetics, the vertical deposition rate of silicon was calculated. According to the SiH4 pressure and laser output power values, three successive kinetic regimes were observed. At low SiH4 pressures, the deposition rate of Si lines was proportional to the reactant gas pressure. At intermediate SiH4 pressures, the deposition rate was independent of the reactant gas pressure and complied with the Arrhenius law; the apparent activation energy was found to be 25 kcal mol−1. At relatively high SiH4 pressures, the deposition rate increased again with increasing SiH4 pressure. The structure of the deposited lines was analyzed through electron microdiffraction. The morphology of the deposited Si lines, investigated using an optical microscope and an atomic force microscope, was found to be very regular and uniform. The effect of the laser beam on the quality of the interfaces underlying the deposited lines was analyzed by means of a transmission electron microscope. On the basis of the experimental results, a reaction mechanism involving surface decomposition steps of ‘‘cold’’ SiH4 molecules is proposed and discussed in this article.
Rigorous derivation of multivalley hydrodynamic conservation equations in the single-electron-gas approximation
Authors: Jyegal J. , DeMassa T. A.
Published: July 2002

Multivalley hydrodynamic transport equations in the single-electron-gas approximation are rigorously derived for spherical and parabolic energy bands from the first three moments of the Boltzmann transport equation for describing macroscopic conservation of particles, momentum, and energy for electrons in a multiple-band semiconductor. Two different carrier temperature parameters appear in the set of multivalley macroscopic conservation equations. In the single-electron-gas approximation, it is shown that the electron temperature for macroscopic energy conservation generally differs from the electron temperature for macroscopic momentum conservation. Additionally, a new macroscopic transport parameter representing the thermal potential heat flux appears in the multivalley energy conservation equation. This parameter, however, vanishes when intervalley carrier transfer does not occur.
Novel variable gallium arsenide capacitors
Authors: Ashkinazi G. , Meyler B. , Nathan M. , Zolotarevski L. , Zolotarevski O.
Published: July 2002

The development of a new type of variable semiconductor capacitor is reported. Its essence is a monolithic (or hybrid) GaAs structure consisting of a reverse biased, high voltage, low reverse current Schottky diode connected in series (back-to-back) to a forward biased PiN diode. The PiN diode has an i layer with a net doping concentration (Nd-Na)i of less than 5×1011 cm−3 and a width of between 3 and 70 μm. The principle of operation is based mainly on control of the PiN diode diffusion capacitance by the reverse Schottky diode current. This current can be changed by structural design or by light. Experimental parameters of a light controlled capacitor include Cmax/Cmin ratios of 20 at ∼1 V and 4–5 at 35 V and a ΔC/ΔV slope of ∼2000 pF/V.