bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-dependent phenomena at low temperature in magnetic digital compact cassette tape
Authors: Zhang X. X. , Tejada J.
Published: July 2002

In this paper we report on the low-temperature magnetic relaxation of CrO2 particles of digital compact cassette tapes. The observed temperature dependence of the magnetic viscosity, S≡∂M/∂ ln t, shows three different regimes below room temperature. The most remarkable is that for T≤5 K, S(T) remains constant, suggesting the occurrence of macroscopic quantum tunneling of magnetization.
Macroscopic quantum tunneling in antiferromagnetic horse-spleen ferritin particles (abstract)
Authors: Tejada J. , Zhang X. X.
Published: July 2002

In this paper we report a comprehensive study of the low temperature magnetic relaxation of nanometer-scale antiferromagnetic horse-spleen ferritin particles. First we report on the static magnetic characterization of the sample at low and high field in the temperature interval between 4 and 300 K. Secondly, we present experimental results on the magnetic relaxation of the remanent magnetization Mr(t) associated with the uncompensated surface spins on such small particles. The magnetic viscosity S≡1/Mr[dM/d ln(t)] is proportional to temperatures above 3 K. At lower temperatures, the viscosity is independent of temperature, providing evidence to quantum tunneling of the Néel vector.
An ultrasonic study of the Néel transition in dilute Cr-Al alloy single crystals
Authors: Alberts H. L.
Published: July 2002

Measurements are reported of the temperature variation of the sound velocity and ultrasonic attenuation coefficient of Cr-Al alloy single crystals containing 1.2, 1.9, and 2.6 at % Al. The results close to the Néel temperature are not satisfied by existing theories for the critical behavior of itinerant electron antiferromagnets.
Efficient Preisach demagnetization algorithm and its experimental testing
Authors: Adly A. A. , Zhao Y. J.
Published: July 2002

The topic of demagnetization has always been considered important to the area of magnetics in general. Whether it is required to characterize the initial permeability of a premagnetized sample or to erase, nondestructively, previously recorded data on disks or tapes, demagnetization processes are indispensable. Theoretically, demagnetization can be achieved by applying infinite ac field cycles with slowly decaying amplitudes. In practice, however, only a finite subset of this sequence may be applied. As a result, achieving the demagnetized state, or even a zero residual magnetization state, becomes uncertain. The purpose of this paper is to present an efficient Preisach-type demagnetization algorithm that can lead to a zero residual magnetization state within few field cycles. While this state might not fully match the demagnetized state, it can be regarded as a good approximation especially for data erasure applications. The algorithm has been experimentally tested and compared to particular demagnetization techniques employing finite ac field cycles with decaying amplitudes. Some sample results of this experimental testing are reported in the paper.
Perturbative approximation scheme for isolated impurity bonds in the two-dimensional spin-1/2 Heisenberg antiferromagnet
Authors: Schlottmann P.
Published: July 2002

An isolated impurity bond of coupling−K replacing a link J in the spin-1/2 Heisenberg antiferromagnet on a square lattice is considered. A simple perturbative approximation scheme is deviced, in which the two-site cluster formed by the spins linked by the impurity bond is embedded into the linearized spin wave approximation for the antiferromagnet. The resolvent for the local states of the cluster is calculated in three successive levels of approximation. The ground state wave function, the magnetization at the impurity link, and the transverse correlation across the impurity link as a function of the coupling K are discussed.
Electronic transport processes and the transition from double to single barrier tunnel junctions
Authors: Kirk E. C. G. , Blamire M. G.
Published: July 2002

Nb/AlOx/Al/AlOx/Nb devices have been fabricated with Al interlayer thicknesses which range from a few nm to zero. Low temperature measurements of the current versus voltage characteristics show the coexistence of both a direct tunneling channel via a double thickness barrier, and a two stage process via the interlayer. Despite a considerably higher specific conductance, we show that the latter dominates the low voltage electrical properties only when a continuous interlayer exists, and that for discontinuous layers the low voltage conductance is controlled by Coulomb blockade.
A novel appproach to secondary defect reduction in separation by implantation of oxygen material
Authors: Ellingboe S. L. , Ridgway M. C.
Published: July 2002

The effect of a preanneal Si implant after the initial O implant in the fabrication of separation by implantation of oxygen (SIMOX) material has been examined. In addition to studying the effect of the Si dose and implant temperature on the residual disorder, the Si implant energy was varied in order to elucidate the mechanism of secondary defect reduction in SIMOX material. Initial experiments showed that a low implant temperature (150 °C) and a moderate dose (5×1016 cm−2) of 4.2 MeV Si ions were the most successful in reducing the volume fraction of polycrystalline Si at the front Si/SiO2 interface. A systematic study of low-, medium-, and high-energy Si implantation with ion ranges less than, equal to, and greater than the initial O implant has been performed. The Si range and defect production per ion were shown to be most important in determining the final defect structure in SIMOX material formed by MeV O implantation in Si. Low- and medium-energy Si-implanted SIMOX material has a more homogeneous buried SiO2 layer and a less defected Si overlayer than virgin SIMOX (O-implanted Si which has not received a preanneal Si implant). The high-energy Si implant slightly reduced the defect density in the Si overlayer and planarized the back Si/SiO2 interface for SIMOX material formed at an implantation temperature of 300 °C but did not homogenize the buried SiO2 layer.
Self-diffusion in indium antimonide
Authors: Rastogi Anjali , Reddy K. V.
Published: July 2002

In the present paper indium and antimony self-diffusion was studied in the temperature range 400–500 °C in single crystals of indium antimonide. The crystals were grown by the Bridgman technique. The radioactive tracer diffusion method was employed using In114m and Sb125 isotopes. Anodic oxidation technique was developed and used for serial sectioning. The penetration profiles were fitted to the error function solution of diffusion equations. For indium self-diffusion, the activation energy and pre-exponential factor were found to be 1.45 eV and 6.0×10−7 cm2/s, respectively, while for antimony diffusion the activation energy was obtained as 1.91 eV with a pre-exponential factor of 5.35×10−4 cm2/s. The results were compared with the earlier experimental studies and theoretical calculations. The migration enthalpies of indium and antimony atoms are estimated to be 0.66 and 0.70 eV, respectively. The corresponding formation enthalpies are 0.79 eV for In vacancy and 1.21 eV for Sb vacancy formation.
Copper silicide precipitation influenced by the strain of a Ge0.02Si0.98 heteroepitaxial layer
Authors: Kissinger G. , Morgenstern G. , Richter H.
Published: July 2002

Copper silicide precipitates in silicon by forming elliptical colonies in {110} planes. In strained Ge0.02Si0.98 heteroepitaxial layers on (001) silicon substrates the colonies prefer {110} planes intersecting the surface under an angle of 45° with zero strain and avoid {110} planes perpendicular to the surface with maximum compressive strain. For the first time copper silicide precipitate colonies lying in (001) surrounded by Lomer dislocations have been observed and studied in detail. They are due to the maximum tensile strain in the [001] direction. The ordering of colonies increases as long as no relaxation via misfit dislocations occurs. The depth of the defect zone containing copper silicide precipitate colonies in the substrate wafer increases with the thickness of a thermal oxide layer on its surface. After annealing in nitrogen the copper silicide precipitate zone remains constant. The morphology of the copper precipitate colonies is first of all determined by the stress of the studied layer system and only to a less extent by the available silicon self-interstitials. Copper silicide precipitate colonies grow below a relaxing heteroepitaxial layer in a patterned arrangement that corresponds to the arrangement of the misfit dislocations. The elastic strain of the heteroepitaxial layer strongly influences the accumulation of copper impurities in the silicon substrate. The smaller the distance between the misfit dislocations becomes, the smaller is the depth of the defect zone containing copper silicide precipitate colonies.
Vapor phase epitaxy of InP with halide transport on earth and under microgravity
Authors: Kimura T. , Nishimura T. , Murotani T. , Ono H.
Published: July 2002

Vapor phase epitaxial growth of InP with halide as the transport agent has been carried out in closed ampoules on earth and under microgravity. On earth, a large variation in the thickness of the InP grown layer has been observed with the change of the disposition of ampoules against a gravity field. A microgravity experiment has been conducted on board the Technologische Experimente Unter Schwerelosigkeit rocket for a period of approximately 6 min. The growth of the S-doped InP layer was confirmed.
The fluorescence of a dye sensitized ferroelectric polymer in an external electric field
Authors: Verkhovskaya K. A. , Fridkin V. M. , Bune A. V. , Tatikolov A. S. , Legrand J. F.
Published: July 2002

The influence of an external electric field on the fluorescence of the ferroelectric vinylidene fluoride-trifluoroethylene copolymer P(VDF-TrFE) doped by rhodamine is revealed. The fluorescence also shows anomalies in the region of the ferroelectric phase transition in P(VDF-TrFE). These phenomena are explained by the influence of polarization on the radiationless electron transitions in the dye molecules.
Scanning tunneling microscopy characterization of the morphology of Fe/C multilayers grown on silicon substrates
Authors: Vázquez L. , Vara J. M. , Ziegler E.
Published: July 2002

Fe/C multilayers have been deposited by rf sputtering on two silicon substrates with a significant difference in surface quality. Scanning tunneling microscopy (STM) shows a roughness replication process: the smoother the substrate, the smoother the final surface. Both samples present a Gaussian height distribution. The fractal analysis of the STM data shows that, for dimensions larger than the grain size, the surface can be described as a self-affine fractal with a fractal dimension of 2.6±0.1, which agrees with the prediction of ballistic deposition models without restructuring. For dimensions lower than the grain size, the fractal dimension is close to the Euclidean value 2.
Energies for atomic emissions from defect sites on the Si surfaces: The effects of halogen adsorbates
Authors: Khoo G. S. , Ong C. K. , Itoh Noriaki , Kanasaki Jyun’ich
Published: July 2002

A study was made of the energies for ejection of Si atoms and SiCl molecules from defect sites on Si (100) and (110) surfaces, including adatoms, kinks, and vacancies, with and without interaction with Cl adsorbates. It is found that the energies for emitting a Si atom from defect sites are smaller than those for the perfect site and almost proportional to the coordination number for the Si (110) surface. It is also found that the interaction of Cl with defects reduces the energy for the ejection of a Si atom and a SiCl molecule, depending on the adsorption site.
Resonant structure in the conductivity of two-dimensional heterojunction systems: A memory function approach
Authors: Hasbun J. E.
Published: July 2002

The resonant structure in the conductivity of a two-dimensional system such as a GaAs/AlGaAs heterojunction is investigated using a memory function approach. In a one-subband model the memory function obtains the expected dependence of the plasmon resonance on the electron concentration. A nonanalytic behavior is, however, obtained when a two-subband model is employed within the random phase approximation. In particular, a negative lifetime is found at low frequencies that is attributed to its inability to handle the full electron-electron interaction tensor. It is found that if certain matrix elements are discarded, the resulting memory function does become analytic. The result thus obtained for the electron lifetime agrees with experiment. In addition, the memory function calculated conductivity for the two-subband case shows a richer structure than the one-subband conductivity above.
Two-dimensional versus three-dimensional excitons in wide GaAs quantum wells
Authors: Kusano Jun-ichi , Bauer Gerrit E. W. , Aoyagi Yoshinobu
Published: July 2002

Excitons confined in high-quality GaAs/Al0.19Ga0.81As double heterostructures have been studied experimentally and theoretically with emphasis on phenomena associated with the transition from a two-dimensional exciton in a quantum well to a three-dimensional exciton in a thin film. Exciton luminescence and reflectance spectra are obtained for GaAs film widths between 750 and 5200 Å. Exciton polariton luminescence is observed for the 5200 Å sample. Highly resolved exciton peaks are obtained in the free-exciton luminescence spectra for both the 990 and 2010 Å samples. Magneto-exciton spectra of the 990 Å sample reveal an enhanced spin splitting of the ground-level exciton. Experimental results of both the 750 and the 990 Å samples are qualitatively explained by an effective-mass theory which considers mixing of a large number of quasi-two-dimensional excitons. The large spin-splitting of the 990 Å sample is a distinctive feature of a wide quantum well which can be explained by the well width dependence of exciton mixing. The comparison between the discrete luminescence spectrum of the 2010 Å sample and the reflectance spectrum with an exciton polariton interference pattern is presented. The quantization of the spatial dispersion contributes to the luminescence phenomena of the quasi-three-dimensional exciton which means that the exciton coherence length must be larger than 4020 Å.
Nanocrystalline Nd12Fe80B6Nb1Ga1 melt-spun ribbon with textured surface
Authors: Kim Y. B. , Kim C. S. , Kim D. H. , Lee K. H. , Kim T. K.
Published: July 2002

In Nd-Fe-B melt-spun ribbon, Ga addition is found to be effective for the orientation of c axis of 2-14-1 grains normal to the ribbon plane even at high wheel surface velocity. A Nd12Fe80B6Nb1Ga1 melt-spun ribbon quenched with optimum wheel surface velocity was found to have textured structure on the free-side surface. Furthermore, this melt-spun ribbon was composed of fine grains of about 30 nm in size which is believed to be enough to provoke intergrain exchange interaction. The remanence and energy product of the field aligned powder of this melt-spun ribbon was about 7% and 20% higher than those of the not-aligned powder, respectively.
Third-order nonlinear optical properties in Langmuir–Blodgett films of 4-docosylamino-4-nitroazobenzene
Authors: Fujiwara I. , Ishibashi T. , Asai N.
Published: July 2002

The third-order nonlinear optical properties of 4-docosylamino-4-nitroazobenzene (DANAB) Langmuir–Blodgett (LB) films were investigated. The orientation of the DANAB molecules in the LB film is designed to be aligned virtually perpendicular to the substrate by mixing DANAB and fatty acid, which has the effect of preventing the cascading effect. It was found that DANAB film, mixed with a fatty acid, form H aggregates. The frequency dispersion was measured using the third harmonic generation method with the optical parametric oscillator. It is indicated that the third-order nonlinear optical susceptibility [χ(3)] is enhanced because of the resonance and molecular aggregation effects. The value of the χ(3) under the resonant condition of 3.1×10−12 esu and that under the nonresonant condition of 1.5×10−12 esu were obtained.
Exchange interaction constants in CdCoSe diluted magnetic semiconductors
Authors: Stankiewicz Jolanta , Palacio Fernando , Campo Javier
Published: July 2002

The photoconductivity of diluted magnetic semiconductors Cd1−xCoxSe (0.011≤x≤0.041) has been measured at temperature of 1.6 K and in a magnetic field up to 6 T. The photocurrent spectra show two peaks near the band-gap energy. They shift towards lower energies as the magnetic field intensity is increased. We interpret these lines in terms of free-exciton (exciton A and B) dissociation. The large values of the observed shift arise from exchange interactions. A comparision of this shift with magnetization measurements done on the same samples allows us to estimate the exchange integrals for the CdCoSe system.
Low-temperature synchrotron-radiation-excited etching of silicon dioxide with sulfur hexafluoride adsorption
Authors: Ogawa Taro , Mochiji Kozo , Ochiai Isao , Yamamoto Seiji , Tanaka Kenichiro
Published: July 2002

Ultralarge-scale integration circuits now require innovative microfabrication processes in order to achieve gigabit-scale integration. One approach is to use soft x rays, because they can give excellent spatial resolution by their short wavelength and high-reaction selectivity by core-electron excitation. Synchrotron-radiation (SR) -excited etching of SiO2 and Si is studied from the viewpoints of pattern replicability and analysis of etching selectivity between two layers. Deep-submicron patterns of SiO2 are formed by cooling the specimen with liquid N2 and adsorbing SF6 reaction gas during SR irradiation. Photon-stimulated desorption ions from SF6-adsorbed SiO2 and Si surfaces are first investigated. As a result, ion species such as SiF+n and SO+n, which are etching products from the surface, are obtained only from SiO2, and this selective etching of SiO2 is also investigated by x-ray photoelectron spectroscopy. In this selective etching mechanism, constraint of Si-etching by passivation of photofragment S+ ions is most likely. The higher selectivity of this reaction can be used not only for bulk SiO2 etching, but also for Si-surface cleaning by eliminating native oxide.
Spraying of zirconium-diboride powder by an electrical column explosion technique and its mechanism
Authors: Tamura Hideki , Nagahama Mutsuhisa , Tanabe Yasuhiro , Sawaoka Akira B.
Published: July 2002

An electrical column explosion technique was proposed for the spraying of zirconium-diboride powder. For the study on its spraying mechanism and the feasibility of high-density coating, the explosion of a column specimen composed of an alumina tube containing the powder was examined under argon gas of 0.1 MPa with time-resolved measurements of the heating process of an exploding column, behavior of a discharge channel, and spraying of ZrB2 powder through column explosion. From these measurements, there is convincing evidence that the column explosion was started with electrical discharge of argon gas among ZrB2 particles inside the tube, and with sequential temperature increase of the particles to the melting point. Electrical discharge and rapid heating inside the column specimen during a few tens of μs were expected to initiate microcracks due to shocklike intense stress in the tube, and further to cause fracture of the column. In fact, another gas breakdown was induced outside the column, and it was followed by the formation of a cylindrical shock wave and an electrical discharge channel, and by their radial expansion. The fracture of the column was found at a later period of electrical discharge, and it caused the dispersion of lots of small fragments. Consequently, ZrB2 powder was ejected symmetrically. ZrB2-coated substrates were analyzed with a scanning electron microscope and an energy-dispersive x-ray spectroscope. It was confirmed that the coating resulted from the deposition through impacts of fine molten particles on the substrate. The substrate was covered completely with ZrB2 deposition through spraying only a few times. No pore was found under observation of several μm in size in the deposition layer and the layer-substrate interface. Hence, the ZrB2 spraying experiments presented have revealed the high feasibility of high-density coating of conductive refractory ceramics powder with this column explosion technique.
Effect of Cr addition on magnetization of Cu-Co alloy. II
Authors: Kondo Shin-ichiro , Hasaka Masayuki , Morimura Takao , Yamamoto Takeshi , Yamamoto Kazuhiro
Published: July 2002

The magnetic behavior of Cu97.7Co2Cr0.3 and Cu97Co2Cr1 alloys was examined in order to investigate the effect of Cr addition to the magnetization of the alloy and prove the presence of Cr atoms in the magnetic clusters. The magnetization of the Cu-Co-Cr alloys is strongly influenced by the amount of Cr added to Cu-Co-Cr alloys. Further, the results indicate there are Cr atoms in the magnetic clusters. The magnetic moment of the cluster was calculated from the experimental data. The results illustrate that the value of the magnetic moment is dependent on the Cr concentration in the noted alloys and this supports the presence of Cr atoms in the magnetic cluster.
Transient thermoelectric effect in bismuth single crystals
Authors: Sasaki M. , Tai G. X. , Inoue M. , Bidadi H.
Published: July 2002

The photo-induced transient thermoelectric effect (TTE) has been measured for bismuth single crystals along nearly the X and Y axes over the temperature range 6–300 K and time range 50 ns–2 ms. The decay curves of the TTE voltages are characterized by multiple relaxation processes for thermal diffusions of photogenerated electrons and holes. From the analysis of the relaxation times, we have evaluated the carrier mobilities and their effective masses of each carrier pocket at the L and T points based on the existing band model; in particular, we have found an additional hole pocket at the L point lying below the Fermi energy. This TTE technique is shown to be useful for understanding electronic properties of a multicarrier system.
Preparation and optical properties of sol-gel derived ZnSe crystallites doped in glass films
Authors: Li Guangming , Nogami Masayuki
Published: July 2002

Borosilicate glass films nominally containing up to 40 wt% ZnSe semiconductor crystallites have been successfully prepared on silica glass substrates by the sol-gel process. The influence of heat treatment on optical absorption, emission, and excitation properties was studied. On heating the films at temperatures from 500 to 750 °C in a hydrogen atmosphere, small ZnSe crystallites with an energy gap varying from 2.93 to 2.63 eV are formed, giving a strong emission with a peak ranging from 540 to 630 nm that is attributed to Se-vacancy defects of the crystallites. The redshift of the emission peak, with respect to the energy gap, is independent of particle size, remaining at around 0.65 eV. The size of the crystallites is estimated to range from 2.8 to 9.5 nm.
Solid-phase epitaxial regrowth of Sb-implanted Si1−xGex strained layers: Kinetics and electrical properties
Authors: Atzmon Z. , Eizenberg M. , Shacham-Diamand Y. , Mayer J. W. , Schäffler F.
Published: July 2002

Kinetics and electrical properties of solid-phase epitaxial regrown (SPEG) layers of Sb-implanted strained Si1−xGex alloys are reported. Two sets of Si1−xGex epilayers with compositions of x=0.08 and 0.18, molecular beam epitaxy grown on Si(100) substrates, were implanted at room temperature with Sb+ ions at an energy of 200 and 100 keV, respectively, and doses of 1014 and 1015 ions/cm2. A set of Si(100) samples was also implanted as a reference. The samples were annealed at temperatures of 525, 550, and 575 °C for durations between 5 s and 10 min. For the higher-dose Sb-implanted Si0.92Ge0.08 layer (1015 cm−2) ion backscattering measurements in the channeling mode show a decrease in the regrowth rate compared to Sb-implanted Si(100). The activation energy of the SPEG process for the Si0.92Ge0.08 alloy was 2.9±0.2 eV, higher than the value of 2.4±0.2 eV obtained for pure Si. For the alloy with 18% Ge the SPEG rate for the 1015 cm−2 dose was much smaller compared to the sample with 8% Ge. For the lower-dose implantation (1014 cm−2) the regrowth rates for Si0.92Ge0.08 and pure Si were very close, and the activation energies were 2.8±0.2 and 2.7±0.2, respectively. It was also found that the SPEG rate in a rapid thermal annealing was significantly higher than that for a sample heated in a conventional furnace.
Concentration profiles of As in a Ga rich solution during electroepitaxy of GaAs using a computer simulation technique
Authors: Qhalid Fareed R. S. , Dhanasekaran R. , Ramasamy P.
Published: July 2002

Concentration profiles of As in front of a GaAs crystal interface growing in a Ga rich solution have been determined during the electroepitaxial growth of GaAs layers using a computer simulation technique. The effect due to Peltier heating or cooling and electromigration during growth have been incorporated to simulate the concentration profiles. The growth velocity in the absence and presence of convection, due to Peltier effect and electromigration, are calculated under different conditions. It is observed that there is a transition in the movement of arsenic atoms towards the GaAs crystal interface from smooth and orderly to turbulent and wavy as the intensity of electric field increases during the electroepitaxial growth of GaAs.
Strain-induced electrically active stoichiometric defects in InAsyP1−y deposited onto (100) InP by gas-source molecular beam epitaxy
Authors: Kruzelecky R. V. , Qiu C. , Thompson D. A.
Published: July 2002

InAsyP1−y epilayers were deposited by gas-source molecular beam epitaxy onto (100) InP, systematically varying the As fraction from 0.15 to 0.75, corresponding to a lattice mismatch of 0.5%–2.4%. Thin (≊190 Å), largely strained InAsyP1−y films exhibit a smooth, planar morphology and good photoluminescence characteristics even for strains exceeding 2%. In thicker films, depending on the growth parameters, capacitance-voltage depth profiling indicates a strain and thickness dependent formation of electrically active defects that results in a net ionized donor concentration with a peak value as high as 2×1019 cm−3 after about 500 Å of growth. Corresponding photoluminescence measurements suggest that these defects are associated with a shallow level about 10 meV below the conduction band edge of the InAsyP1−y. As the thickness further increases, the net residual donor concentration reduces to <3×1015 cm−3 near the top surface of 1.2-μm-thick epilayers with y≤0.6.
New features of injection phenomena in graded semiconductor structures with intervalley crossover
Authors: Peka H. P. , Pulemyotov D. A. , Radzivilyuk V. A.
Published: July 2002

An effect of injected charge carrier accumulation (depletion) at the intervalley crossover of a graded semiconductor has been reported. We proved that an abrupt change in electron mobility in the vicinity of the intervalley crossover was primarily responsible for this effect, whereas a change in the quasielectric field had only a slight effect on the injected carrier coordinate distribution. Photoconductivity spectra were found to be a convenient way of investigating the charge carrier profile in graded structures. The experimental spectra of the diode structures based on a graded AlxGa1−xAs alloy compound have been found in satisfactory agreement with theoretical predictions.
Reactive-ion-beam-sputtered WNx films on silicon: Growth mode and electrical properties
Authors: Eizenberg M. , Meyer F. , Benhocine A. , Bouchier D.
Published: July 2002

WN films were deposited on clean Si(100) substrates via reactive-ion-beam sputtering a W target by a nitrogen ion beam in an UHV system. The energy of the incident ions varied in the range of 0.250 to 3 keV. The growth mode dependence of the films on the nitrogen ion energy was studied by in situ Auger electron spectroscopy measured as a function of coverage. Nitridation of the Si at the first stage of deposition has been found. This nitridation was more pronounced for the lower N beam energies, and minimal for the 2 keV beam. A similar trend was observed for the bulk film composition. In a complementary way, the dependence of electrical properties of the WN/Si junctions on the nitrogen energy has been studied. A higher barrier height on p-type Si than on n-type Si was found, unlike the expectation for regular metallization of W and its compounds on Si. The electrical characteristics can be attributed to the deposition technique. For the low-energy beams, the formation of the interfacial layer was probably dominating, while at higher energies radiation damage and possibly also N implantation played a more important role.
Thermal conduction behavior in polycrystalline (Sr1−x,K2x)Zr4(PO4)6 ceramic
Authors: Liu Dean-Mo , Chen Chien-Jen , Lin Li-Jiaun
Published: July 2002

Single-phase (Sr1−x,K2x)Zr4(PO4)6 ceramic (with x=0.0–0.8) demonstrated values of thermal conductivity decrease with increasing potassium content to a minimum value at x=0.5, which suggests a maximum content of lattice defect, i.e., oxygen vacancy, at this composition. The thermal conductivity of the ceramic then increased with further increase of potassium. The thermal conduction in (Sr1−x,K2x)Zr4(PO4)6 ceramic (at x=0.5) appears to exhibit a strongly lattice-defect dependence with a calculated phonon mean free path of approximately 3.04 Å, rather than a phonon-phonon dependence as observed in a number of dielectric materials. A linear relationship of the thermal conductivity in terms of porosity with temperature up to 600 °C has been correlated and can be simply expressed as K=K0 (1−p) regardless of the influence of emissivity factor.
Krypton excimer emission from discharge excited rare gas clusters
Authors: Masters M. F. , Tucker J. E. , Wexler B. L. , Searles S. K.
Published: July 2002

We report the time-resolved observation of krypton second continuum excimer emission near 146 nm from a pulsed-discharge excited gas jet. The excimer emission reaches a peak intensity several millimeters from the nozzle and lasts up to several microseconds after the termination of the discharge. We report the temporal behavior of the excimer emission as a function of gas pressure, discharge energy, and position within the cathode-anode gap. The temporal and spatial characteristics of the excimer emission during the discharge are due to cluster excitation in the jet expansion region and is from a combination of the A 3∑+u and the B 1Σ+u states. A kinetic mechanism involving metastable atoms and clusters is described to explain the observed afterglow emission.
Direct measurement of CAs in group III+C coimplanted GaAs
Authors: Madok J. H. , Haegel N. M. , Moll A. , Haller E. E. , Yu K. M.
Published: July 2002

The effect of In and Ga coimplanted with C into GaAs on the concentration of CAs has been investigated by local vibrational mode spectroscopy, Rutherford backscattering, particle-induced x-ray emission, and Hall effect. The dose of the C was fixed at 5×1014 cm−2, 27 keV, while the doses of either In, 185 keV, or Ga, 160 keV, ranged from 5×1013 to 5×1015 cm−2. Based on the Hall-effect and local vibrational mode data, 99% of the C, when implanted alone and annealed, is not located as isolated, substitutional atoms on either sublattice, but in an inactive complex. The coimplanted group-III species acts to increase both the concentration of CAs ([CAs]) and the sheet hole concentration. For coimplant doses of 5×1013 and 5×1014 cm−2, these values are in good agreement. Increasing the dose of the group-III coimplanted ion to 5×1015 cm−2 results in a hole concentration that is 45% less than the [CAs] and the coimplanted ions begin to occupy nonsubstitutional sites. The reduction in the concentration of holes due to CAs at the highest dose of coimplanted ion appears to be caused by a compensating defect which limits the maximum sheet hole concentration obtainable by the coimplantation technique in GaAs.
Characterization of the initial stages of hydrogen-radical-assisted chemical-vapor deposition of amorphous silicon from disilane on cleaved and sputter-roughed graphite surfaces
Authors: Kawasaki Mitsuo , Suzuki Hideo
Published: July 2002

Thin hydrogenated amorphous silicon (a-Si:H) films were deposited on as-cleaved and sputter-roughed surfaces of highly oriented pyrolytic graphite (HOPG) from disilane by hydrogen-radical-assisted chemical-vapor deposition, which utilized a filament-assisted thermal decomposition of hydrogen. The initial stages of film growth were studied by x-ray photoelectron spectroscopy (XPS). The XPS data taken for films deposited on the cleaved HOPG surface exhibited such features correlative with a layer-by-layer type of growth. The corresponding film structures, as inferred from the hydrogen-induced Si 2p binding-energy shift and the resistivity against aerial oxidation, are such that even submonolayer films deposited at room temperature can achieve a highly cross-linked amorphous network in which the monohydride configurations predominate. Construction of an extended amorphous network was strongly disturbed on the sputter-roughed HOPG surface for films less than a few atomic layers. The corresponding initial-stage film structures thus present good contrast to those on the cleaved surface. Si2H5 radicals are likely species to contribute to the unique low-temperature growth of a-Si:H from disilane.
Effective Young’s modulus and Poisson’s ratio for the particulate composite
Authors: Barta Štefan
Published: July 2002

Relations for effective Young’s modulus and for effective Poisson’s ratio of the multicomponent particulate composite in the framework of the average field approximation are derived. In the case of a binary system, the existence of the percolation phase transition is shown and relations for effective parameters of a percolating system are analyzed in detail.
Substrate photoluminescence: An aid in the evaluation of pulsed laser evaporation and epitaxial growth of Cd1−xMnxTe epilayers on (111)GaAs
Authors: Keeler W. J. , Harrison D. A. , Dubowski J. J.
Published: July 2002

Photoluminescence (PL) emitted from (111)Cd1−xMnxTe/(111)GaAs:Si heterojunctions produced using pulsed laser evaporation and epitaxy (PLEE) has been studied at 11.5 K. The heterojunctions show PL from the substrate E0 and E0+Δ0 gap regions as well as from the epilayer. The substrate E0+Δ0 signal is particularly sensitive to the epilayer growth temperature and is strongest for samples grown on substrates held at Tg=290 °C. The heterojunction PL also includes a component produced by Si dopant atoms in the substrate that undergo clustering changes as the growth temperature is raised. Through comparison with annealing studies of the substrate, it is argued that the PLEE ablated material possesses sufficient kinetic energy to increase the effective temperature above Tg at the growth surface.
II-VI compound thin-film deposition by resonant laser sputtering
Authors: Liu Z. , Gelinas M. P. , Coombe R. D.
Published: July 2002

Time-resolved laser-induced fluorescence measurements indicate that Zn atoms excited to the 4 3PJ metastable state react rapidly with group-VI molecules O2, CS2, and H2S. Rate constants for these processes are presented. Based on these data, a method for deposition of thin films of the ZnO or ZnS products of these reactions is demonstrated, wherein the Zn atoms are both sputtered from a target and excited to the 4 3PJ state by near-resonant radiation from a pulsed XeCl laser.
Interfacial characteristics of AlGaAs after in situ electron cyclotron resonance plasma etching and molecular beam epitaxial regrowth
Authors: Hong M. , Mannaerts J. P. , Grober L. , Chu S. N. G. , Luftman H. S. , Choquette K. D. , Freund R. S.
Published: July 2002

Regrown/processed AlGaAs interfaces using secondary ion mass spectrometry, cross section transmission electron microscopy (TEM), and reflection high energy electron diffraction have been characterized. Two sets of samples, GaAs/Al0.4Ga0.6As (with GaAs on top) and Al0.4Ga0.6As/GaAs (with Al0.4Ga0.6As on top), are used as starting materials. For the GaAs/Al0.4Ga0.6As samples that are first exposed to atmosphere, the experiment is performed in an integrated processing system where etching and regrowth chambers are linked together by ultrahigh vacuum transfer modules. The etching process includes electron cyclotron resonance (ECR) hydrogen plasma cleaning of GaAs native oxides, ECR SiCl4 plasma anisotropic deep etching into Al0.4Ga0.6As, and an optional, brief Cl2 chemical etching. Regrowth is carried out using solid-source molecular beam epitaxy (MBE). Despite the in situ processing, significant amounts of C, Si, and O impurities at the 10, 5, and 50×1012 cm−2 levels exist at the interfaces. However, the impurity level is one order of magnitude smaller than that in air-exposed, ECR plasma etched and MBE regrown Al0.4Ga0.6As/GaAs of the set 2 samples. As revealed using TEM, isolated small particles (presumably correlated to aluminium oxides) exist at the regrown/processed interface of the set 1 samples, but no other defects such as dislocation are seen. Impurities and defects are mainly caused by the high reactivity of AlGaAs during ECR plasma etching.
Periodicity of crossover currents in a Rutherford-type cable subjected to a time-dependent magnetic field
Authors: Akhmetov A. A. , Devred A. , Ogitsu T.
Published: July 2002

The behavior of Rutherford-type cables under a time-dependent magnetic field is studied. Existing models are extended describing the currents flowing through the resistive contacts at the crossovers between the cable strands by considering crossover current distributions that are not uniform along the cable axis. The generalized system of equations is applied to a few cases of practical interest and shows that, if not uniform, the crossover current distribution is periodic, with a period equal to the cable pitch length.
Growth, structural, and electrophysical investigations of Pb1−xGdxTe thin layers
Authors: Zlatanov Zahari , Maksimov Maksim
Published: July 2002

Epitaxial films of Pb1−xGdxTe were deposited on cleaved (111) BaF2, (100) KBr, or (100) KCl substrates by the electron-beam evaporation method. X-ray data, electron microscopy, and Auger-electron spectroscopy show that only part of the gadolinium from the source material (polycrystalline ingots with x=0.0, x=0.01, x=0.02, x=0.04) is incorporated in the film’s lattice. Hall-effect and conductivity measurements have established that the Gd atoms act as weak donors. The Hall coefficient RH was found to be practically temperature independent in the range 77–300 K which indicated that Gd did not produce an impurity level in the energy gap. Decrease in the Hall mobility with alloying was observed. A discussion of the carrier scattering mechanisms is presented.
Growth of bismuth silicate films on Si and its dielectric properties
Authors: Kim Jong Hee , Tsurumi Takaaki , Kamiya Toshio , Daimon Masaki
Published: July 2002

Crystalline bismuth silicate films were grown on a Si substrate by metalorganic chemical vapor deposition. A 100 nm SiO2 layer on Si was changed to bismuth silicate film by the reaction with a Bi and O2 gas mixture. A deposition of less than 30 min formed a single-crystalline phase, having a certain crystallographic relation with (100)Si substrate. The capacitance of the specimen has increased fivefold over that of the original specimen. The crystallinity of deposited films was increased markedly by heat treatment. At the same time, the capacitance of the specimen increased. However, the oxidation of the Si substrate and the formation of a Bi-rich surface caused a drastic decrease in the capacitance of the specimen.
The effect of high-Z atomic radiators on the x-ray emission rate from a laser-produced nitrogen plasma
Authors: Filbert P. C. , Kohler D. A. , Walton R. A.
Published: July 2002

The effect of a small admixture of high-Z atomic radiators on the radiation rate of a laser-produced nitrogen plasma has been experimentally studied for application to a nitrogen recombination soft x-ray laser. The experiments used a miniature supersonic gas jet as a laser target that is capable of producing an on-axis density of 1×1019 atoms/cm3. Nitrogen gas was seeded with 1%, 2%, and 5% (by number) of Ar, Kr, and Xe and irradiated with 31 J, 3 ns full width at half maximum pulses of 1054 nm light. The time-dependent intensity of x rays between 114 and 140 Å was measured from these plasmas and it was found that the e−1 decay time decreased with increasing Z and with the concentration of the high-Z radiator. Several time-integrated N VII spectral lines relevant to a nitrogen soft x-ray laser are plotted against the measured e−1 decay time and it was found that the N VII line at 133.8 Å is observed to be unusually bright as compared to the N VII 4-2 and 2-1 transitions, suggesting that enhanced recombination effects are possibly being seen. In addition, theoretical calculations of the N VII first- and second-excited state population dynamics are presented that predict a population inversion in recombining nitrogen, indicating a small signal gain of 4.4 cm−1. It is concluded that a low-Z soft x-ray laser is feasible using a laser-heated gas jet target and that possible gain enhancement might be possible by adding high-Z radiators to increase the cooling rate of the plasma.
Strain effect in the critical current densities of superconducting Nb3Ge tapes
Authors: Nakagawa Y. , Umeda M.
Published: July 2002

The dependence of the critical current density in chemical-vapor-deposited Nb3Ge tapes on tensile strain was investigated in magnetic fields up to 14 T perpendicular to the tape plane. The pinning force density Fp was found to be well represented by the strain scaling relation, Fp=c[Hc2(ε)]0.93h0.46(1−h)2.4, where Hc2(ε) is the upper critical field dependent on the applied strain ε and h is the reduced magnetic field H/Hc2(ε). For the Nb3Ge tapes studied, Hc2(ε) was found to be expressed by the form Hc2(ε)=Hc2(εm)[1−1550‖ε0‖1.92], where εm is the applied strain corresponding to zero intrinsic strain and ε0 is an intrinsic strain expressed by ε−εm. From the strain scaling relation, the values of the maximum upper critical field corresponding to the zero intrinsic strain, Hc2(εm), were calculated as 27.2 T for the Nb3Ge tape with 10.6-μm-thick Nb3Ge layers and a critical temperature Tc (midpoint) of 19.6 K, and 24.8 T for the Nb3Ge tape with 1.3-μm-thick Nb3Ge layers and Tc of 18.3 K. For these same tapes, the critical fields at the zero applied strain, Hc2(0), were 25.7 and 22.8 T, respectively.
Quantum corrections to the conductivity and quantum Hall effect in GaAs-GaAlAs multiple quantum well structures
Authors: Kulbachinskii V. A. , Kytin V. G. , Kadushkin V. I. , Shangina E. L. , de Visser A.
Published: July 2002

The magnetotransport properties of GaAs-GaAlAs multiple quantum well structures, with widths of the quantum wells Lw=33–66 Å, have been investigated over a wide temperature and field range. The variation of the electron mobility with Lw (and temperature) can be accounted for by interface roughness scattering. A negative magnetoresistance was observed. An analysis within the theory of weak localization allowed us to evaluate the relaxation time of the phase of the electronic wave function and its temperature dependence τφ(T). Measurements in high-magnetic fields (up to 40 T) at T=4.2 K revealed pronounced Shubnikov-de Haas oscillations and the quantum Hall effect.
Regular and periodic peaks in device current, capacitance, and intersubband photocurrent from a multiple-double-well
Authors: Li Jianmeng , Liu H. C. , Buchanan M. , Wasilewski Z. R. , Simmons J. G.
Published: July 2002

Extremely regular periodic peaks in device current, capacitance, and intersubband photocurrent are observed in a multiple-quantum-well structure in which the period is a coupled double well. Hysteresis is displayed in all the measurements with respect to the scan direction of the applied voltage. A phenomenological model is used to explain the observed results. The complexity of charge transport in such a system where high- and low-field domains are formed is also discussed.
Microstructural dependence of vacancy diffusion in ordered alloys
Authors: Lindsey T. F. , Fultz B.
Published: July 2002

The dependence of the vacancy diffusional correlation factor on microstructure was investigated by Monte Carlo simulations (MCS). The MCS used activated state rate theory to model the vacancy diffusion. We varied the temperature, size of ordered domains, and the state of order within the domains. Correlations in the vacancy movement were found to vary widely, and numerical values are presented. Two different results were obtained, one for ordering in a homogeneous alloy and another for ordering in an alloy having domains. However, given the existence of domains, the vacancy correlation factor was observed to be independent of domain size. Oscillations in the correlation function were observed, and were attributed to pair trapping of the vacancy.
Epitaxial growth in large-lattice-mismatch systems
Authors: Zheleva Tsvetanka , Jagannadham K. , Narayan J.
Published: July 2002

Epitaxial growth in the TiN/Si and TiN/GaAs metal-semiconductor systems with a large lattice mismatch was investigated. The orientation relationships have been found to be 〈001〉TiN∥〈001〉Si for TiN growth on Si(001) and [001]TiN∥[110]GaAs and [11̄0]TiN∥[1̄10]GaAs for TiN growth on GaAs(001). The epitaxial growth is characterized by domain epitaxial orientation relationships with m lattice constants of epilayer matching with n of the substrate and with a small residual domain mismatch present in the epilayer. This residual mismatch is responsible for a coherent strain energy. The magnitude of compression of Ti—N bond in the first atomic layer, contributing to the chemical free energy during the initial stages of growth, is found to be a very important factor in determining the orientation relationship. This result was used to explain the differences in the orientation relationships between TiN/Si and TiN/GaAs systems. The various energy terms associated with the domain epitaxial growth are evaluated to illustrate that the domain epitaxial growth is energetically favorable compared to the lattice-mismatched epitaxial growth. The results of this analysis illustrate that the observed variations in the epitaxial growth are consistent with the minimum energy configurations associated with the domain epitaxial growth.
Influence of microstructure on the resistivity of Al-Cu-Si thin-film interconnects
Authors: Kim Choongun , Selitser S. I. , Morris J. W.
Published: July 2002

The rate of resistivity decay in Al-2Cu-1Si thin-film conductors was studied as a function of temperature and grain size distribution. The decay kinetics were assumed to be governed by the rate of precipitate reconfiguration to grain boundaries. This assumption was confirmed by transmission electron microscopy (TEM) observations of the microstructure during resistance decay, and by studies of lines of two different widths. The results can be explained qualitatively from the microstructure of the lines. In particular, increasing the mean grain size slows the rate of resistivity decay, and establishing a bimodal distribution with a significant population of relatively large grains has the same effect. A simple model was developed to treat these effects quantitatively. The model assumes a cylindrical grain geometry and a uniform initial distribution of Cu and ignores the effect of intragranular precipitation. The model yields reasonable values for the activation energy for Cu diffusion in thin films, and predicts the correct dependence of the decay rate on grain size and grain distribution; however, it appears to overestimate the value of the preexponential factor D0.