bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulsed laser-induced amorphization of silicon films
Authors: Sameshima T. , Usui S.
Published: July 2002

The reversible transition from crystalline to amorphous silicon was observed on films deposited on quartz substrates through laser-induced melting using a 30-ns pulsed XeCl excimer laser. A 20-nm-thick silicon film was completely melted and then amorphized. The melt duration exceeded 70 ns when the film was amorphized. The transition from liquid to the amorphous state would occur homogeneously throughout the film because the temperature gradient in molten silicon could be reduced to 1.0×105 K/cm (0.2 K/20 nm) at 70 ns after initiation of melt. The laser-amorphized film had a large mid-gap density of states of 5.3×1019 cm−3 eV−1. The density of states was remarkably reduced using a hydrogen plasma treatment at 250 °C for only 1 min. Thin-film transistors fabricated in a laser-amorphized film showed good characteristics with a carrier mobility of 0.6 cm2/V s after hydrogenation.
Optical emission diagnostics of H2+CH4 50-Hz–13.56-MHz plasmas for chemical vapor deposition
Authors: Shimozuma Mitsuo , Tochitani Gen , Tagashira Hiroaki
Published: July 2002

The emission spectra of H2+CH4 plasmas excited at 50 Hz–13.56 MHz were measured. The emission intensity ratios of Hα/H*2 (3Σg →3Σu) from H2+CH4 plasma at 50 Hz and 13.56 MHz were about 0.7 and 0.05, respectively. The electron temperature was obtained from the two-line radiance ratio method using the Balmer lines (Hα and Hβ), and rapidly decreased with an increase above 200 kHz. The electron temperature for H2+CH4 plasma is 16 000 K at 1 kHz and 8200 K at 13.56 MHz. The plasma-maintaining voltages for H2 and H2+CH4 mixtures were also measured. The maintaining voltages were constant below 200 kHz, and rapidly decreased between 200 kHz and 13.56 MHz. The position dependence of emission intensity was also measured for Hα, Hβ, and H*2 at 50 Hz and 13.56 MHz. The results are interpreted in terms of the electron distribution in the plasma.
A transform for the reduction in spatial frequency content of the optical reflectance of layered media
Authors: Swart Pieter L. , Lacquet Beatrys M.
Published: July 2002

The frequency components in the Fourier spectrum of the optical reflectance of layered media contain information regarding the optical thickness of the various layers. For multiple layers on a substrate, the vast number of spectral components complicates the analysis. By applying a simple bilinear transform to the optical reflectance pattern, the number of frequency components is drastically reduced. In this communication the mathematical analysis pertaining to this special transform is presented. Explicit expressions for a two- and three-layer structure are given. The power of the transform is illustrated by application to an idealized silicon-on-insulator structure, and it is demonstrated how the transformed reflectance is used for estimating layer thickness.
Propagating normal domains in large composite superconductors
Authors: Kupferman Raz , Mints R. G. , Ben-Jacob E.
Published: July 2002

We study the nucleation and propagation of the normal zone in large composite superconductors, considering the relatively long time of current redistribution in the stabilizer. We propose a model treating the composite as an effective electrical circuit, which yields two diffusion equations for the electric current and temperature distributions along the conductor. Numerical simulations are performed to study the dynamics of propagating normal domains in cryostable conductors. We derive an analytical solution for the margins of existence and velocity of propagation of the domain. The effect of the boiling crisis on the dynamics of the normal zone is also studied.
Magnetic properties of high-quality melt-spun Nd-Fe-Co-B-C ribbons and their bonded magnets
Authors: Yamamoto Hiroshi , Yamaguchi Takehito
Published: July 2002

Melt-spun ribbons of Nd-Fe-Co-B-C system alloys were prepared by the single roller rapid-quenching method. The effects of composition, substrate surface velocity, and heat treatment on the magnetic properties were studied. A maximum energy product of 140.5 kJ/m3 was obtained for Nd11Fe72Co8(B0.5C0.5)9 alloy ribbon prepared at a substrate surface velocity of 17.1 m/s. The amorphous Nd11Fe72Co8(B0.5C0.5)9 ribbons prepared at a substrate surface velocity of 20.7 m/s were crystallized by heat treatment, and the optimum annealing condition was found to be at 600 °C for 30 min. Then the value of (BH)max was 138.5 kJ/m3. The value of (BH)max for a Nd11Fe72Co8(B0.5C0.5)9 bonded magnet prepared by using the ribbons heated at 600 °C was 90.4 kJ/m3.
Pulverizing anisotropic rapidly solidified Nd-Fe-B materials for bonded magnets
Authors: Doser M. , Panchanathan V. , Mishra R. K.
Published: July 2002

The high (BH)max potential of Nd-Fe-B materials make them excellent candidates for bonded magnets. We have previously shown that anisotropic bonded magnets can be made from hot deformed rapidly solidified materials. The purpose of this paper is to show how hot deformed materials can be pulverized into desired particle size ranges by using specific hydrogen decrepitation (HD) cycles. Specific temperatures for hydriding and desorbing cycles to achieve desired particle size ranges and magnetic values are given. The data shows that there are optimum times and temperatures to achieve the desired magnetic properties. TEM and SEM photomicrographs of mechanically and HD pulverized materials are shown. TEM studies show that stacking faults generated during HD are relieved after desorption. With proper control of HD and desorption, bonded magnets have been produced having (BH)max values as high as 18.9 MGOe.
Magnetoelastic anisotropy in amorphous wires due to quenching
Authors: Velázquez J. , Vázquez M. , Hernando A. , Savage H. T. , Wun-Fogle M.
Published: July 2002

Amorphous wires are prepared by the in-water quenching technique. This procedure gives rise to local magnetoelastic anisotropies arising from the coupling between frozen-in internal stresses and magnetostriction. Azimuthal and axial components of internal stresses have been experimentally confirmed by the asymmetry of the Matteucci effect at different applied torques for the Fe77.5Si7.5B15 amorphous wire. According to classical theory of elasticity, internal stresses produced by the thermal gradient inside the wire during the quenching have been calculated. The nonzero values of azimuthal and axial stresses have been derived in addition to the well accepted radial stresses. This explains the present experimental results. Remanence and its dependence on tensile and torsional stresses has been also calculated.
Magnetic properties of ZrCo5.1−xFex alloys
Authors: Burzo E. , Grössinger R. , Hundegger P. , Kirchmayr H. R. , Krewenka R. , Mayerhofer O. , Lemaire R.
Published: July 2002

The results of magnetic measurements performed on ZrCo5.1−xFex alloys in the temperature range 4.2–900 K and fields up to 7 T are reported. The presence of solid solutions is evidenced in the composition range x<0.9. The Curie temperature and the saturation magnetization increase nearly linearly when cobalt is substituted by iron. In addition, the anisotropy field decreases and shows an unusual temperature dependence, with a maximum at T≂300 K.
Magnetic and structural characterization of sputtered FeN multilayer films
Authors: Russak Michael A. , Jahnes Christopher V. , Klokholm Erik , Lee Jo-Won , Re Mark E. , Webb Bucknell C.
Published: July 2002

The magnetic and structural properties of ferromagnetic FeN thin films, FeN/FeN (ferromagnetic/paramagnetic), and FeN/SiO2 multilayers deposited in a rotational dc magnetron sputter system were investigated. Monolithic films containing ≂2 at. % N2 had 4πMs values ≂25 kG. The Fe16N2 phase has been identified by electron microdiffraction in these films. Saturation magnetostriction (λs) has been related to N2 content and can be varied from −3×10−6 to 5×10−6 in a range of compositions where 4πMs is ≳22 kG. Lamination reduced easy and hard axis coercivity to <1 Oe and produced single domain configurations in yoke-shaped structures. Lorentz microscopy indicated that the ferromagnetic FeN layers in the FeN/FeN films were exchanged coupled while those in the FeN/SiO2 films were magnetostatically coupled.
Faraday rotation in diluted magnetic semiconductor superlattices (invited)
Authors: Kohl M. , Awschalom D. D.
Published: July 2002

The Faraday effect is considerably enhanced in diluted magnetic semiconductor systems and can therefore be used as a sensitive tool to perform magnetic spectroscopy. We investigate the Faraday rotation of CdTe/CdMnTe superlattice systems with different barrier-layer thicknesses, which allow the study of dimensionality-dependent effects. By optically exciting the charge carriers and tuning the excitation wavelength we observe a step-like behavior at the absorption edge reflecting the electronic density of states and a strong excitonic resonance, which is much more strongly pronounced than in conventional spectroscopy like absorption or photoluminescence excitation. Temperature-dependent Faraday rotation measurements allow the observation of the phase transition from a paramagnetic state to a spin-glass state of the Mn2+ spins. With decreasing barrier thickness LB we observe a strong deviation of the expected strength of the spin-exchange interaction below LB = 4 nm indicating a dimensional crossover to a two-dimensional spin system.
Magnetic, magneto-optic, and transport properties of Tb-doped EuS films
Authors: Gambino R. J. , Ruf R. R. , McGuire T. R. , Fumagalli P.
Published: July 2002

Films of EuS have been doped with up to 34-at. % Tb by coevaporation. From lattice constant measurements we conclude that the films are defect rocksalt structure solid solutions with the general formula Eu1−xTbxS1−y⧠y, where ⧠ represents a vacancy. The magnetic properties change drastically between undoped films and the Tb substituted samples. The Curie point increases from 20 to about 135 K and the coercivity increases from 60 Oe to about 4 kOe in the x=0.34 sample. Our measurements indicate an increase in RKKY exchange because of the higher carrier concentration caused by Tb doping. The increased carrier density causes a decrease in resistivity of at least two orders of magnitude to about 10−3 Ω cm, the same order of magnitude as reported for bulk solid solutions of EuS-GdS. The peaks in the magneto-optic Kerr spectrum of EuS at about 2 eV are decreased in amplitude, broadened and shifted in energy with Tb doping.
High frequency permeability of nanocrystalline Fe–Cu–Nb–Si–B single and multilayer films
Authors: Kataoka N. , Shima T. , Fujimori H.
Published: July 2002

Structure and magnetic properties of Fe–Cu–Nb–Si–B alloy single and multilayer films produced by rf sputtering have been investigated. The 1-μm-thick single films are of an amorphous phase in the as-sputter-deposited state and are crystallized into a mainly bcc phase with fine grains of nanometer size, as are melt-quenched ribbons with the same composition. The crystallization behavior and the Curie temperature of these single films are also similar to those of the ribbons. The crystallization-induced bcc phase possesses a high saturation magnetization of 1.3 T and good soft magnetic properties. For improving permeability at high frequency, an attempt has been made to multilayer the Fe–Cu–Nb–Si–B alloy with nonmagnetic materials such as SiO2. It has been found that Fe75.6Cu0.8Nb1.9Si13.2B8.5(500 nm)/SiO2(5 nm) multilayer films annealed at 500 °C for 1 h also consist of bcc fine crystallites and exhibit permeability as high as 7000 at 1 MHz and low coercivity of about 0.08 Oe.
Microstructural and magnetic characterization of rapidly solidified and annealed Pt–Co–B alloys
Authors: Qiu N. , Teubert J. A. , Overfelt R. A. , Wittig J. E.
Published: July 2002

Significant increases in intrinsic coercivity (Hic) of Pt–Co alloys have been obtained by the addition of boron and the application of rapid solidification processing. After rapid solidification by double anvil splat quenching with subsequent annealing at 650 °C for 30 min, an alloy of Pt42Co45B13 (at. %) exhibits an Hic as high as 14 kOe. Transmission electron microscopy and Lorentz microscopy were used to interpret the magnetic data. Annealing of the Pt–Co–B influences the L10 superlattice structure and grain size of the matrix, the crystal structure and size of Co-boride precipitate, and the distribution of magnetic domain walls. A microstructural analysis shows that the maximum Hic occurs when Co borides, having the Co3B structure, are within the single magnetic domain size. The magnetic hardening mechanism in Pt–Co–B is believed to be a combination of inhibited magnetic domain nucleation and difficult reverse magnetic domain growth caused by the interaction of the magnetically anisotropic Co borides with the L10 Pt–Co matrix.
First principle evaluation of hybridization and exchange effects for magnetic ordering in correlated-electron uranium systems
Authors: Sheng Q. G. , Cooper Bernard R.
Published: July 2002

Cerium and light actinide compounds show widely varied f-electron phenomena. The f-electron behavior in these systems ranges from well-localized to heavy-fermion-like or itinerant. Over a period of time we have been developing techniques to evaluate the fundamental interactions for correlated f-electron systems, such as band-f hybridization and band-f exchange, and trying to understand their properties and trends in the evolution of the properties between different isostructural cerium and light actinide compounds on the basis of absolute first principle calculations. Previous calculations are successful in explaining a variety of f-electron properties in cerium monopnictides and monochalcogenides. When going from localized f-electron cerium systems to more itinerant f-electron uranium systems, the hybridization between f- and non-f-conduction electrons is strongly enhanced by the self banding of the f states. We develop a scheme to evaluate the hybridization from the starting point that the f states are viewed as bands. We apply this scheme to uranium monopnictides and monochalcogenides to calculate their magnetic ordering.
Structure and magnetic properties of RFe11TiNx (R=Y, Sm, and Dy)
Authors: Liao L. X. , Altounian Z. , Ryan D. H.
Published: July 2002

Single phase alloys of composition RFe11Ti with R=Y, Sm, and Dy were prepared by induction melting. The samples were nitrided by thermal cycling to 770 K, at a heating rate of 10 K/min, under an atmosphere of nitrogen in a thermopiezic analyzer (TPA). For YFe11TiN the x-ray diffraction (XRD) patterns give a=0.8611 nm and c=0.4802 nm for the tetragonal structure, space group I4/mmm. This represents a 3% volume expansion of the nitrogen-free unit cell. The amount of absorbed nitrogen corresponds to one nitrogen atom per formula unit indicating that RFe11TiN is a true nitrogen compound with the nitrogen atoms occupying the 2b site in the structure. The expansion of the unit cell is accompanied by a dramatic increase in the Curie temperature for all compounds.
Reorientation phase transition behavior in metastable epitaxial cobalt-copper alloys
Authors: Kief M. T. , Mankey G. J. , Willis R. F.
Published: July 2002

We report experimental results on the ferromagnetic critical behavior of cobalt and metastable cobalt-copper alloy two-dimensional layers CuxCo1−x epitaxially grown on Cu(001). Copper alloying reduces the magnitude of the cobalt magnetic moment and introduces a magnetization component normal to the film. Reorientation of the magnetization back into the plane occurs via a second-order phase transition at a temperature which is lower than the film Curie temperature. We discuss these results in light of the recent predictions of Pescia and Pokrovsky.
The role of orbital polarization and correlation effects in the magneto-optic behavior of CeSb and CeTe
Authors: Lim S. P. , Cooper Bernard R.
Published: July 2002

CeSb and CeTe show giant magneto-optic Kerr rotations and also have extremely unusual magnetic ordering properties. CeSb shows peculiar and extraordinarily anisotropic antiferromagnetic behavior; while CeTe shows an ordered moment and TN only 15% that of CeSb, indicative of incipient heavy-fermion behavior. This has been understood in an absolute theory of orbitally driven correlated f-electron magnetism. We seek to understand the giant magneto-optic properties including the role, if any, of explicit correlation effects not captured by an exchange-correlation potential. To this end we have performed full potential linearized muffin-tin orbital polarized band calculations for the optical conductivity tensor, first only spin polarized (orbital polarization only via spin-orbit coupling) and second with explicit orbital polarization. As expected, for CeSb and CeTe the spin-polarized calculation gave the diagonal, ordinary optical, conductivity in good agreement with experiment; but the off-diagonal, magneto-optic, behavior was in poor agreement; and the ordered moment was much different from experiment. For the spin-and-orbitally polarized calculation, the ordered moment agreed reasonably well with experiment for CeSb but very poorly for CeTe. However, the magneto-optic behavior remained distinctly different from experiment for both materials. Thus as anticipated, explicit correlation effects associated with differing discrete f-configuration energies appear to be a central aspect of giant magneto-optic behavior.
Flux creep after thermal neutron irradiation of uranium-doped oriented compacts of YBa2Cu3Ox
Authors: Luborsky F. E. , Arendt R. H. , Fleischer R. L. , Hart H. R. , Lay K. W. , Tkaczyk J. E. , Orsini D. A.
Published: July 2002

Fission fragment damage was introduced by thermal neutron irradiation into aligned, sintered powder samples of YBa2Cu3Ox with uranium additions of 0.08 wt % UO2. This resulted in an increase in the intragranular critical current and a decrease in flux creep. Flux creep of the magnetization M exhibited simple log time dependence and was characterized by absolute and normalized slopes as functions of magnetic field and temperature. Before irradiation, the slopes were strongly field dependent and showed peaks as a function of temperature. After irradiation the slopes were much less field dependent and the peaks were suppressed. Both the magnitude and the field dependence of the creep were improved. Apparent pinning potentials at 0.8 T increased by a factor of about 2 on irradiation, for temperatures from 10 to 35 K. These increases in the apparent pinning potentials are attributed to the damage caused by the travel of the fission fragments through the crystal.
Vortex-flux rotation in polycrystalline YBa2Cu3O7 at 77 K
Authors: Liu Liwen , Kouvel J. S. , Brun T. O.
Published: July 2002

Magnetization-vector measurements at 77 K on a field-cooled sample rotated by angle θ relative to fixed field H reveal that MP, the penetrating vortex-flux component of the magnetization, undergoes some extraordinary changes at H≊30 Oe. As θ is raised above 180°, MP decreases in size to a very small minimum while its direction shifts rapidly, and these changes repeat as θ is then lowered below 180°. This behavior, which evolves systematically with H, was observed earlier for the same sample at 4.2 K but at much higher H (∼800 Oe) and is readily ascribed to a broad distribution in strength of the vortex pinning forces. Due to this distribution, the vortex lines bifurcate into two groups, one of which rotates rigidly with the sample while the other is held by H and turns frictionally relative to the sample.
Direct ion beam deposition of carbon films on silicon in the ion energy range of 15–500 eV
Authors: Lau W. M. , Bello I. , Feng X. , Huang L. J. , Fuguang Qin , Zhenyu Yao , Zhizhang Ren , Lee S.-T.
Published: July 2002

Direct ion beam deposition of carbon films on silicon in the ion energy range of 15–500 eV and temperature range of 25–800 °C has been studied. The work was carried out using mass-separated C+ and CH+3 ions under ultrahigh vacuum. The films were characterized with x-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and transmission electron diffraction analysis. In the initial stage of the deposition, carbon implanted into silicon induced the formation of silicon carbide, even at room temperature. Further carbon ion bombardment then led to the formation of a carbon film. The film properties were sensitive to the deposition temperature but not to the ion energy. Films deposited at room temperature consisted mainly of amorphous carbon. Deposition at a higher temperature, or post-deposition annealing, led to the formation of microcrystalline graphite. A deposition temperature above 800 °C favored the formation of microcrystalline graphite with a preferred orientation in the (0001) direction. No evidence of diamond formation in these films was observed.
Three-dimensional dark spatial solitary waves
Authors: Chen Yijiang
Published: July 2002

Three-dimensional dark spatial solitary waves of TM type are found to exist in the self defocusing nonlinear medium of the Kerr-law type over the range of the wave effective index neff from 0.82n0 to n0 of the linear refractive index of the medium. This contrasts with TE type which exists over all possible values of neff ranging from 0 to n0. The field profile shape of TM waves is also shown to vary with the wave effective index, whereas that of TE waves is independent of neff.
Direct current screening effect on dip occurrence in nematic electro-optical modulation
Authors: Sugimura Akihiko
Published: July 2002

The screening effect of dc voltage in a nematic liquid-crystal cell having polyimide alignment layers is studied experimentally and theoretically. The transmitted intensity of light passing through a liquid-crystal sample exhibits a dip arising from dc screening effects, which are never observed with ac voltage application. The dc screening effect is produced by two kinds of ionic charges in the boundary layer. One is adsorbed on the orientation film and the other compensates the adsorbed charges. The two kinds of charge model account quantitatively for the observed dip in transmission making its origin clear, and explain well the ionic conduction processes accompanying the application of dc voltage to a liquid-crystal sample.
O2(1Δ) generation in a bubble column reactor for chemically pumped iodine lasers: Experiment and modeling
Authors: Aharon O. , Elior A. , Herskowitz M. , Lebiush E. , Rosenwaks S.
Published: July 2002

O2(1Δ)is generated in a bubble column reactor by the reaction between chlorine diluted in inert gas and a basic hydrogen peroxide solution. It is fed to an oxygen-iodine laser system designed to operate under supersonic conditions. The O2(1Δ) yield is measured as a function of the time elapsed from the onset of bubbling, type of diluent, and molar flow rate of chlorine and diluent. The yield when the chlorine is diluted with helium is significantly higher than when diluted with argon. This is explained as a consequence of the shorter residence time of the mixtures with helium where the molecular weight is smaller. A model that accounts for realistic physical and chemical processes in this system is presented. The model is divided into two stages which together describe the processes that occur between the reactor inlet and the measuring point of the O2(1Δ) (before the supersonic nozzles). The first stage describes the processes occurring in the solution. It employs the film model for a fast reaction regime to describe the chlorine absorption, rather than film models where the instantaneous reaction regime is assumed and models assuming instantaneous absorption at the sparger outlet. The second stage describes the processes occurring in the gas phase above the solution. A good agreement between the model predictions and O2(1Δ) yield data from this and other studies is obtained. In particular, the model accounts for the optimal clear liquid height in the reactor. Since the process of chlorine absorption and O2(1Δ) production in the film is common to other types of reactor, the model can be used as a basis for analyzing the performance of those reactors as well.
The dynamics and stability of thin liquid films during spin coating. II. Films with unit-order and large Peclet numbers
Authors: Reisfeld B. , Bankoff S. G. , Davis S. H.
Published: July 2002

A thin liquid film drains radially off the surface of a horizontal, rotating substrate. Evaporation of solvent from the film increases the fluid viscosity and reduces the radial outflow. Governing equations are developed for the shape of the film interface as a function of space and time, as well as the axisymmetric solvent-concentration distribution, for both unit order and large Peclet numbers. The numerical solution of these equations elucidates how a spinning film with either a corrugated or a flat free surface evolves over time in the presence of a time-varying concentration (and viscosity) field. A correlation for the final film thickness in terms of the physical variables of the system is deduced from the governing equations, the result of which shows good agreement to published experimental results.
Identification of infrared absorption peaks of amorphous silicon carbon hydrogen alloy prepared using ethylene
Authors: Chen Jhy-Hong , Sah Wen-Jyh , Lee Si-Chen
Published: July 2002

Amorphous silicon-carbon hydrogen alloy was prepared by radio frequency glow discharge decomposition of silane-ethylene mixture. The infrared absorption spectra were measured at various stages of thermal annealing. By observing the change of relative intensities between these peaks the molecular bonding responsible for the absorption peaks could be assigned. For example, in addition to the CH3 radical commonly found in films prepared by silane-methane mixture, other carbon hydrogen radicals such as CH2 and C2H5 were also unambiguously identified. At same gas phase flow ratio (Xg = 0.8), the CHx contents of ethylene-based film is about 6.6 times larger than that of the methane-based film. Hence, to grow a-SiC:H with a larger optical gap, the ethylene will be a good choice as the deposition source.
Calculated electron and hole steady-state drift velocities in lattice matched GaInP and AlGaInP
Authors: Brennan Kevin F. , Chiang P.-K.
Published: July 2002

We present calculations based on an ensemble Monte Carlo program of the steady-state electron and hole drift velocities in bulk Ga0.52In0.48P and Al0.26Ga0.26In0.48P as well as present a list of material parameters for these substances which are of use in the modeling of semiconductor devices made from these material types. The calculations are made including a realistic treatment of both the conduction and valence energy bands based on the k*p method. All of the principal phonon scattering agents are included in our simulation as well.
Energy shift of (100)Si/SiO2 interface traps resulting from avalanche hole injection
Authors: Vishnubhotla Lakshmanna , Ma T. P.
Published: July 2002

Influence of avalanche injected holes on Si/SiO2 interface traps is reported. The major effect of avalanche hole injection is to shift the energy distribution of the interface traps (Dit) toward the conduction-band edge. In addition, in x-ray irradiated samples where a double-peak Dit distribution had been formed, the energy distance between the two peaks decreases with increasing injected hole fluence. When the trapped holes are neutralized by electron injection, however, the Dit distribution recovers to its initial energy position prior to avalanche hole injection. If we assume the interface traps correspond to the Pb centers in the electron spin resonance literature, then the energy shift of Dit due to avalanche injected holes may arise from the local structural change of the Pb dangling bond defect−a shift toward conduction band is consistent with a more planar configuration of the tetrahedral structure of the Si dangling bond defect.
Lithographic processing of YBa2Cu3O7 thin films: Impact on electrical contacts
Authors: Fagerberg R. , Vassenden F. , Gong Z. H. , Grepstad J. K.
Published: July 2002

Silver contact pads to c-axis-oriented thin films of YBa2Cu3O7 (YBCO) were defined using three different techniques: (1) deposition through stencil masks; (2) liftoff; and (3) Ar plasma etching of in situ deposited Ag. A specific contact resistance of ρc(77 K) = 1 × 10−7 Ω cm2 was found for the in situ deposited contacts. Contacts defined with stencil masks and liftoff showed a ρc(77 K) ∼ 10−5 and ∼ 10−2 Ω cm2, respectively. Core-level photoelectron spectroscopy measurements indicate that the resist and acetone applied to the YBCO thin film during patterning do not introduce surface impurity phases in addition to those formed upon air exposure. Distinct chemical shifts originating from process-induced surface impurity phases were observed in photoelectron spectra taken on films prepared for contact definition by liftoff, i.e., exposed to the lithographic developer and deionized water. These findings correlate with the measured increase in contact resistance. Cross-sectional transmission electron microscopy images of an in situ deposited Ag contact unveil a 20–30-Å-thick interface layer, in which the 12 Å periodicity along the YBCO c axis vanishes. The presence of this layer could explain the absence of Josephson effects in YBCO/noble-metal/low-Tc superconductor junctions where the currents are forced to flow perpendicular to the a-b planes.
Evaluation of diffusion length and surface recombination velocity in semiconductor devices by the method of moments
Authors: Cavallini A. , Fraboni B. , Cavalcoli D.
Published: July 2002

The diffusion length and surface recombination velocity of the minority carriers are determined from electron beam induced current (EBIC) profiles on a semiconductor containing a barrier perpendicular to the scanned surface. The evaluation of both the parameters has been obtained by the procedure called ‘‘of the first moments,’’ due to Donolato [C. Donolato, Appl. Phys. Lett. 43, 120 (1983)], which is based on the calculation of the first moment about the origin of two induced current profiles. This analysis, based on an exact integral property of the EBIC scans, allows evaluation of the diffusion length and the surface recombination without fitting the experimental profiles. In addition, it is easy to handle and can also be readily applied to real devices.
Induced electrostatic confinement of the electron gas in tensile strained InGaAs/InGaAsP quantum well lasers
Authors: Barrau J. , Amand T. , Brousseau M. , Simes R. J. , Goldstein L.
Published: July 2002

A new mechanism, injection induced electrostatic confinement of the electron gas, is proposed to explain the origin of the laser effect in tensile strained GaInAs/GaInAsP quantum well lasers.
Ellipsometric measurements of the CoSi2 formation from very thin cobalt films on silicon
Authors: Ko Sen-Hou , Murarka Shyam P. , Sitaram A. R.
Published: July 2002

Thin CoSi2 films (<80 nm) were formed by rapid thermal annealing of Co films sputtered on a single-crystal Si substrate. The kinetics of the formation of CoSi2 from CoSi was followed by the use of ellipsometry. Mixed phases of CoSi and CoSi2 were created at temperatures of 600, 625, 650, and 675 °C. The ellipsometric response of these samples were simulated using a model of two layers of silicide on a silicon substrate. The refractive indices of CoSi and CoSi2 were measured separately and were found to be 3.2+i2.44 and 2.2+i1.34, respectively. The analyses of the data indicate that the phase transformation from CoSi to CoSi2 is diffusion controlled and the activation energy of the reaction in this temperature range is 1.78 eV.
Representation of tails of periodic and infinite-range signals: Towards a treatment for truncation
Authors: Vermeulen A. C. , Delhez R. , de Keijser Th. H. , Mittemeijer E. J.
Published: July 2002

Two types of signals are considered: infinite-range signals and periodic signals. Tails of infinite-range signals can be described with an asymptotic power series (having terms of the type x−n with n≥2). For tails of periodic signals an asymptotic series [having terms of the type sin−n(πx/p) with p=period and n≥2] is derived from the asymptotic power series for the infinite-range signals using Poisson summation. It is shown that for practical purposes the tails of a signal can be described quite satisfactorily with only a few terms of the series. On this basis nonmeasurable parts of tails of both symmetric and asymmetric signals can be estimated reliably and thus the effects of the unavoidable signal truncation can be counteracted.
Gain measurements of high-pressure ultraviolet-preionized self-sustained discharge pumped atomic xenon laser
Authors: Komatsu Katsuhiko , Kannari Fumihiko , Obara Minoru
Published: July 2002

To explore the laser kinetics of atomic xenon lasers pumped by an ultraviolet-preionized, self-sustained discharge, time-resolved small-signal gains are measured using a long-pulse probe laser. Faster electron mixing processes among excited xenon manifolds in the 6p state may affect the small-signal gain distribution among 1.73, 2.03, and 2.65 μm laser lines, which share the same upper laser level Xe(5d[3/2]1) at excitation rates in excess of 160 kW/cm3. When the excitation rate in a late part of the discharge is increased, absorption caused by repumping of the lower laser level is observed at 1.73 μm. The measured gains are discussed in conjunction with multiline laser oscillation performance obtained by the same laser device.
Molecular orientation of vacuum-deposited thin films of zincnaphthalocyanine
Authors: Yanagi Hisao , Kouzeki Takashi , Ashida Michio , Noguchi Toru , Manivannan Ayyakkannu , Hashimoto Kazuhito , Fujishima Akira
Published: July 2002

Zinc 2,3-naphthalocyanine (ZnNc) was vacuum evaporated onto glass, NaCl, and highly oriented pyrolytic graphite (HOPG) substrates, and the molecular orientation was investigated by x-ray-diffraction, Fourier-transform-infrared–reflection-absorption spectroscopy, electronic spectroscopy, transmission electron microscopy, and scanning electron microscopy observations. Three types of molecular orientations were assigned for the deposited thin films depending on the different substrates kept at 250 °C. ZnNc molecules deposited on glass formed columnar crystals taking N orientation, in which molecular planes oriented perpendicularly to the substrate surface. Unidirectional epitaxic growth was observed in the film deposited on NaCl. ZnNc molecules seemed to be stacked in parallel having P orientation, where the molecular planes were parallel to the NaCl(001) surface. The ZnNc square lattice made an angle of 45° to the NaCl[100] direction (4×4-type orientation). The film deposited on HOPG exhibited I orientation, in which ZnNc molecular planes were inclined to the HOPG basal plane. The tilting molecules stacked in the direction normal to the surface. These different orientations in ZnNc thin films resulted in significant electronic spectral change in the longer-wavelength region.
Investigation of Ni–P–B ultrafine amorphous alloy particles produced by chemical reduction
Authors: Shen Jianyi , Hu Zheng , Zhang Qinghong , Zhang Lifeng , Chen Yi
Published: July 2002

Ni–P–B ultrafine amorphous alloy particles have been prepared by chemical reaction of nickel chloride, sodium hypophosphite, and potassium borohydride in aqueous solution. Two samples prepared at different initial pH values (pH=5 and 9) have been characterized by different experimental methods. X-ray and electron diffraction indicated that both samples were amorphous in nature, and transmission electron microscopy gave average diameters of 50 and 30 nm for particles prepared at pH=5 and 9, respectively. X-ray photoelectron spectroscopy revealed that nickel and phosphorus existed exclusively in their elemental states, while boron existed mainly in its elemental state but with some trace of its oxide on the surface. The crystallization process of the amorphous samples was investigated by differential scanning calorimetry and by x-ray diffraction after annealing the samples at various temperatures. The results are correlated with the microstructure of the as-prepared samples. It is found that when the initial pH of the reaction mixture is adjusted to 9, the pH value can be maintained automatically throughout the reaction and the sample thus formed has a fairly homogeneous microstructure.
Order-disorder and dielectric relaxation in SrFeO3−x
Authors: Liu Donhang , Yao Xi , Cross L. E.
Published: July 2002

The frequency-domain dielectric spectra of ceramic SrFeO3−x have been measured over wide temperature (100–300 K) and frequency (5 Hz–13 MHz) range. The results have been related to the defect ordering in this compound. The loss peak behavior results from a relaxation process has been identified for the ‘‘disordered’’ sample, while the anomalous low-frequency dispersion have been observed in the ‘‘ordered’’ sample.
The role of dislocation-dislocation interactions in the relaxation of pseudomorphically strained semiconductors. I. Theory
Authors: Stiffler S. R. , Stanis C. L. , Goorsky M. S. , Chan K. K.
Published: July 2002

The role of dislocation-dislocation interactions on the relaxation behavior of biaxially stressed semiconductor thin films is considered by including interaction terms in an energy minimization. Both parallel and crossing interactions are considered and energies are calculated for orthogonal arrays of equally spaced 60° misfit dislocations, and it is shown that the parallel interactions can be either attractive or repulsive. The equilibrium misfit dislocation density is shown to be a function of the ‘‘cutoff’’ distance for dislocation interactions in these structures.
Gain measurements at 780.8 nm in a copper hollow anode cathode laser
Authors: Zhang Zhigang , Perry N. D. , Tobin R. C.
Published: July 2002

The results of a parametric study of a copper hollow anode cathode laser operating on the He-Cu+ infrared lines are reported. The discharge voltage, the small-signal unsaturated gain on the 780.8-nm transition, and the ground-state copper atom concentration each exhibit a universal dependence on the ratio J/p of the discharge current density to the total pressure of the helium-argon buffer gas mixture. The laser output power dependencies (780.8 and 782.5 nm) on J/p, while not resulting in universal curves, have common threshold values of J/p. The threshold value of J/p for the 782.5-nm line is approximately twice that for the 780.8-nm line.
Wigner trajectories in resonant-tunneling diodes under transverse magnetic field
Authors: Hsu Y. , Wu G. Y.
Published: July 2002

We generalize the Wigner formalism to include effects of an in-plane magnetic field and present theoretical study of effects of a transverse magnetic field on tunneling dynamics for resonant-tunneling diodes. We solve transport equation for the steady-state Wigner distribution function. Particle trajectories are determined in phase space as contour lines of the distribution function. From trajectories we estimate tunneling times. Discussions of magnetic field dependence and transverse momentum dependence of tunneling times are presented.
Optical properties of amorphous InSb
Authors: Adachi S. , Miyazaki T. , Hamadate S.
Published: July 2002

We have presented experimental results for the optical constants of amorphous InSb films prepared by rf plasma deposition. The measured data are analyzed on the basis of a simplified model of nondirect optical transitions between the valence and conduction bands. Introducing a phenomenological damping effect into the model, the calculated spectra become structureless, which are typically observed in tetrahedrally bonded amorphous semiconductors. Results are in reasonable agreement with the experimental data over the entire range of photon energy (0.3–5.3 eV).
Elevated-temperature 3-MeV Si and 150-keV Ge implants in InP:Fe
Authors: Rao Mulpuri V. , Nadella Ravi K. , Holland O. W.
Published: July 2002

Variable-fluence 3-MeV Si+ and 150-keV Ge+ implants were performed into InP:Fe at 200 °C. Lattice damage in the material is greatly reduced over comparable room-temperature (RT) implantations and is rather insensitive to fluence for Si+ implantation in the range of 8 × 1014–5 × 1015 cm−2, and no amorphization occurs. For 8 × 1014-cm−2 Si+ implantation at 200 °C, the dopant activation is 82% and carrier mobility is 1200 cm2/V s after 875 °C/10-s annealing, whereas for the RT implantation the corresponding values are 48% and 765 cm2/V s, respectively. The reasons for the improved mobility in the elevated-temperature implants were investigated using Rutherford-backscattering spectrometry. At a dose of 8 × 1014 cm−2, the aligned yield after annealing is close to that of a virgin sample, indicating a low concentration of residual damage in the 200 °C implant, whereas the lattice remained highly defective in the RT implanted sample. Elevated-temperature implantation of Si+ and Pi+ ions was also investigated. Coimplantation did yield an improvement in activation for an implanted fluence of 2 × 1015 cm−2 Si+, but resulted in an inferior lattice quality which degraded the carrier mobility compared to a Si+ (only) implant. For a 1 × 1014-cm−2 Ge+ implant, the maximum dopant activation is 50% (donor) and the material did not turn p type even after 925 °C annealing.
A possible mechanism for the recrystallization of InSb film on mica substrates
Authors: Isai Masaaki , Yasuda Shun-ichi , Ogita Masami , Tanaka Ikuo
Published: July 2002

The recrystallization of InSb films while growing through the melting–solidification process was investigated in detail. A great fluctuation of the film temperature was seen in some cases of the growing film, especially in the early stage of the evaporation process. This fluctuation of the film temperature gives rise to the melting–solidification process. In this work, two distinct types of temperature fluctuations were observed. It was found that the shape of the temperature fluctuation curves can be reasonably explained by the variation of deposition rate in such a way that a higher deposition rate at the early stage of evaporation yields higher temperature fluctuations. The deposition rate was also found to depend on the preheating time of source, hence the optimum deposition rate was easily obtained by varying this time. The optimum substrate temperature and preheating time for high quality InSb films were 260 °C and 180 s, respectively. The present method greatly improves the reproducibility of preparing high quality InSb thin film.
Control of vinylsilane plasma by changing the pressure: Correspondence with a quantum chemical prediction
Authors: Sato Kota , Uchiyama Akihiko , Iwabuchi Susumu , Hirano Tsuneo , Koinuma Hideomi
Published: July 2002

The pressure dependence of the chemical structure and the optical band gap of the films produced by the glow discharge decomposition of vinylsilane was studied on the basis of infrared and ultraviolet absorption spectroscopies. There was a significant structural difference between the films prepared at pressures below and above 0.08 Torr. The results are discussed in relation to the initial step of gas phase reactions predicted on the basis of an ab initio molecular orbital calculation. Good consistency between the experiment and the theoretical calculation was obtained by taking a pressure dependent transition in the excited state through which the decomposition of vinylsilane predominantly proceeded into account. That is, the contribution of the transition to the lowest triplet and singlet excited states becomes larger with the increase of pressure.
Growth kinetics of tungsten microstructures produced via the hydrogen reduction of tungsten hexafluoride on laser-heated substrates
Authors: Auvert G. , Pauleau Y. , Tonneau D.
Published: July 2002

Laser-assisted chemical vapor deposition of tungsten microstructures (dots, stripes, or films) has been accomplished via the H2 reduction of WF6 on polycrystalline silicon-coated quartz substrates irradiated with a focused cw argon-ion laser beam. Tungsten dots were grown on the substrates via a pyrolytic process occurring within the laser-heated zone of about 200 μm in diameter. The morphology and height of these dots were determined as functions of deposition parameters by profilometer measurements. The effects of WF6 and H2 partial pressures on the morphology and deposition rate of W dots were investigated at a laser-induced surface temperature ranging from 340 to 950 °C. The deposition rate of flat-topped dots was independent of the deposition temperature and proportional to the WF6 partial pressure. The deposition rate of W dots with a Gaussian profile was independent of the WF6 partial pressure. At low temperatures (340–670 °C) and high H2 partial pressures (50–700 Torr), the deposition rate of Gaussian W dots was proportional to the square root of the H2 partial pressure. At high temperatures (750–950 °C) and reduced H2 partial pressures (20–80 Torr), the deposition rate of these dots was proportional to the H2 partial pressure. This reaction order equal to 1 was interpreted on the basis of the Rideal model involving a direct reaction between H2 molecules and fluorinated adspecies on the W surface. The nature of the fluorinated adsorbed phase on the metal surface was discussed in terms of coordination number of W and F atoms. A new reaction mechanism for the H2 reduction of WF6 promoted by laser irradiation of the deposition zone or accomplished in a conventional furnace-type reactor is discussed and proposed.
Passivation induced deep levels in GaInAs PIN planar photodiodes
Authors: Ducroquet F. , Guillot G. , Renaud J. C. , Nouailhat A.
Published: July 2002

The damage induced by the passivation process has been evaluated and compared by admittance and deep level transient spectroscopies in GaInAs planar photodiodes passivated by a silicon nitride film. The comparison is based on three deposition techniques: the chemical vapor deposition (CVD), the plasma-enhanced CVD (PECVD), and the ultraviolet activated CVD (UVCVD). Two deep levels, with properties and concentration which are found to be strongly dependent on the passivation techniques, are observed: The first, located at Ec−0.35 eV is detected in PECVD and UVCVD passivated diodes and attributed to the GaInAs surface degradation resulting from the deposition process. The second, located at Ec−0.19 eV appears only on CVD diodes and could be related to the high-temperature treatment specific to this technique.
Li doping of GaAlAs
Authors: Zazoui M. , Feng S. L. , Bourgoin J. C. , Powell A. L. , Rockett P. I. , Grattepain C. , Friant A.
Published: July 2002

A series of unintentionally doped Ga1−xAlxAs epitaxial layers grown by molecular beam epitaxy, having various Al compositions (0.15, 0.18, and 0.29), have been Li diffused at 300 °C. Capacitance–voltage techniques show that the initial n-type doping concentrations (of the order of 1016 cm−3) increase after diffusion by typically a factor 5 to 10 demonstrating that isolated Li interstitials do exist and behave as donors. However, secondary-ion mass spectroscopy measurements show that the material contains 1019–1020 Li cm−3, which indicates that a large fraction of the Li impurities is not electrically active. Thus Li also produces defects as revealed by the fact that free electrons are frozen in the diffused layers below 77 K. Search for the existence of Li associated DX centers deep defects related to the donor impurities has been performed by deep level transient spectroscopy. Only the DX centers present before diffusion, i.e., associated with residual donor impurities, are detected in the layer of 0.29 Al fraction. This implies that either Li donors do not induce the existence of DX centers or electron emission from Li DX centers occurs below 77 K.