bluuebunny/crossref_metadata_2025 huggingface dataset:
Decay of secondary electron emission and charging of hydrogenated and hydrogen-free diamond film surfaces induced by low energy electrons
Authors: Hoffman A. , Laikhtman A. , Ustaze S. , Hamou M. Hadj , Hedhili M. N. , Guillotin J.-P. , Le Coat Y. , Azria R.
Published: July 2002

In this work, the decay of secondary-electron emission (SEE) intensity and charging of hydrogenated and hydrogen-free diamond film surfaces subjected to incident electron irradiation at energies between 5 and 20 eV are investigated. Electron emission curves as a function of incident electron energy were measured. For the hydrogenated films, it was found that the SEE intensity decays in intensity under continuous electron irradiation, albeit maintains a nearly constant onset. The decay in time of the SEE intensity was measured for various incident electron energies. From these measurements, the SEE intensity decay rate from the hydrogenated diamond surface was calculated as a function of incident electron energy and found to display a broad peak at ∼9 eV. The decay of the SEE intensity is explained as due to electron trapping in the near-surface region of the hydrogenated diamond films resulting in the formation of a depletion layer and upward surface band bending while overall charge neutrality is maintained. It is suggested that the mechanism of charge trapping is by resonant electron attachment of incident electrons into C–H (ads) bonds present within the near-surface region of the hydrogenated diamond films which displays a similar dependence on incident electron energy. Upward band bending results in a surface potential barrier to secondary electrons created within the solid. For the hydrogen-free diamond surface, decay in intensity and a positive shift in the onset of the SEE were observed for all incident electron energies and currents used. It was found that surface charging increases monotonically with incident electron energy. In this case, charging is associated with electron trapping into localized surface states of π* symmetry. These electronic states are associated with surface reconstruction resulting from hydrogen desorption.
Advantages of the “optical cavity substrate” for real time infrared spectroscopy of plasma–surface interactions
Authors: von Keudell A. , Abelson J. R.
Published: July 2002

Infrared reflectance spectroscopy can be used to analyze surface reactions during the plasma processing of thin films via the characteristic absorption modes of chemical bonds. However, infrared absorption is a relatively weak effect: to detect a submonolayer quantity of adsorbed or near-surface species in real time, the optical sensitivity must be enhanced in order to produce a measurable reflectance change. This article presents the use of a optically resonant dielectric stack, called an optical cavity substrate, to provide this sensitivity enhancement, and compares this approach quantitatively to other substrate/beam combinations. The optical cavity substrate provides several advantages: (i) a large signal enhancement for both bulk and surface vibrational modes, which is nearly independent of the film refractive index n and thickness up to ∼20 nm, (ii) a large signal enhancement for interfaces buried under thick films, and (iii) a relatively constant baseline signal, which simplifies the data analysis. To demonstrate the power of the optical cavity substrate, we analyze the growth of hydrogenated amorphous silicon in real time.
Space charge effects in polymer-based light-emitting diodes studied by means of a polarization sensitive electroreflectance technique
Authors: Michelotti F. , Bussi S. , Dominici L. , Bertolotti M. , Bao Z.
Published: July 2002

We used a single wavelength electro-optical reflection technique to study the creation of space charge distributions in a polymer light emitting diode, by monitoring the real third order nonlinear optical response of the electroluminescent layer. The diode is based on an aluminum/polymer/indium tin oxide stack, where the polymer is a derivative of poly(p-phenylene-vinylene) in which oxidiazole groups were grafted as side chains. The measured signal is strongly influenced by a space charge distribution and by screening in the organic layer. The space charge distribution is the superposition of a long lived contribution, close to indium tin oxide, due to charges trapped in deep levels, and of that of relatively mobile charges injected in the polymer film. In the frame of a model which takes into account Debye–Hückel screening, with screening length equal to 100 nm we estimated the carrier density of the long lived charge distribution to be 4.8×1023 m−3, for a uniform distribution in a 110-nm-thick layer. The influence of the injection of mobile charges on the electro-optic signal is an order of magnitude smaller than that of trapped charges. The real third order susceptibility of the polymer is estimated to be χ(3)=4×10−21 m2/V2.
Improvement of λ≈5 μm quantum cascade lasers by blocking barriers in the active regions
Authors: Yang Q. K. , Mann C. , Fuchs F. , Kiefer R. , Köhler K. , Rollbühler N. , Schneider H. , Wagner J.
Published: July 2002

We report the improvement of quantum cascade lasers emitting at λ∼5 μm by introducing AlAs blocking barriers together with strain-compensating InAs layers into the active regions. The blocking barriers are designed to selectively prevent electrons in the initial laser state from tunneling out of the active region, while maintaining the high tunneling probabilities of the electrons in the final laser states. Adopting blocking barriers, the maximum peak power per facet at 77 K (300 K) is increased from 285 (30 mW) to 900 mW (240 mW), and the maximum operation temperature in pulsed mode has been improved from 320 to 350 K with respect to a reference sample without blocking barriers.
Effect of hydrogen on adsorbed precursor diffusion kinetics during hydrogenated amorphous silicon deposition
Authors: Bray K. R. , Gupta A. , Parsons G. N.
Published: July 2002

Fractal analysis of the surface topography is used to study the effects of hydrogen dilution on the surface transport kinetics during the plasma deposition of hydrogenated amorphous silicon. Images obtained from atomic force microscopy are examined using dimensional fractal analysis, and surface diffusion lengths of growth precursors are estimated from the measured correlation lengths. The addition of small amounts of hydrogen (H2/SiH4 ratios <10/1) during deposition leads to a decrease in the diffusion length, but larger hydrogen dilutions result in increased diffusion length. Moreover, the measured surface diffusion activation barrier is reduced from 0.20 eV for deposition from pure SiH4 to 0.13 eV with high hydrogen dilution. Results are consistent with recent models for precursor surface transport during low-temperature deposition, and give insight into critical processes for low-temperature silicon crystallization.
Schwoebel-Ehrlich barrier: from two to three dimensions
Authors: Liu S. J. , Huang Hanchen , Woo C. H.
Published: July 2002

The Schwoebel-Ehrlich barrier—the additional barrier for an adatom to diffuse down a surface step—dictates the growth modes of thin films. The conventional concept of this barrier is two dimensional (2D), with the surface step being one monolayer. We propose the concept of a three-dimensional (3D) Schwoebel-Ehrlich barrier, and identify the 2D to 3D transition, taking aluminum as a prototype and using the molecular statics method. Our results show that: (1) substantial differences exist between the 2D and 3D barriers; (2) the transition completes in four monolayers; and (3) there is a major disparity in the 3D barriers between two facets; further, alteration of this disparity using surfactants can lead to the dominance of surface facet against thermodynamics.
High-current electron beam generation by a metal–ceramic cathode
Authors: Krasik Ya. E. , Dunaevsky A. , Gleizer J. Z. , Felsteiner J. , Kotov Yu. A. , Sokovnin S. Yu. , Balezin M. E.
Published: July 2002

We present results of the investigation of a metal–ceramic cathode suitable for technological applications. The cathode was tested in electron diodes powered by two different high-voltage generators (500 kV, 50 ns, 300 Ω, ⩽200 Hz and 300 kV, 250 ns, 84 Ω, ⩽5 Hz). The metal–ceramic cathode which was made in a form of a disk was composed of TiO2 ceramics with stainless steel spherical particles uniformly inserted inside. It was shown that already at relatively low accelerating fields (E⩽5 kV/cm) fast cathode plasma formation occurs as a result of surface flashover. This surface flashover is initiated in triple points located in micropores which were formed during the process of cathode preparation due to the different thermal expansion coefficients of the ceramic and the metal. Experimental data concerning the uniformity of the light emission from the cathode surface and inside the anode–cathode gap and divergence of the generated electron beams are presented. Also, it is shown that the uniformity of the generated electron beam depends strongly on the duration of the accelerating pulse.
Water absorption and interface reactivity of yttrium oxide gate dielectrics on silicon
Authors: Niu D. , Ashcraft R. W. , Parsons G. N.
Published: July 2002

High dielectric constant insulators deposited at low temperatures rapidly absorb water during exposure to the atmosphere, and the resulting OH leads to detrimental interface reactions. We report the effect of atmospheric exposure on ultrathin yttrium oxide, and details of silicon substrate reactions during postdeposition anneals. Infrared absorption analysis indicates significant absorption of water vapor during atmospheric exposure, even for very short times (<15 min). X-ray photoelectron spectroscopy demonstrates that after OH absorption, a thermally activated interface reaction proceeds with an activation energy of 0.33 eV, consistent with substrate reaction with OH present in the film. The OH absorption rate is reduced for annealed films or when capping layers are deposited in situ. Similar oxidation processes are expected to occur in other high-k materials of interest, where the rate of OH absorption will depend on the deposition process and material thermal history.
Measurement of piezoelectric coefficients of lead zirconate titanate thin films by strain-monitoring pneumatic loading method
Authors: Park Gun-Tae , Choi Jong-Jin , Ryu Jungho , Fan Huiqing , Kim Hyoun-Ee
Published: July 2002

A method to simultaneously measure the longitudinal (d33) and transverse (d31) piezoelectric coefficients of a lead zirconate titanate (PZT) thin film was developed. This system was based on the pneumatic loading method but was modified to monitor the radial strain when a pressurized gas was introduced into the chamber. The results of the bulk piezoelectric material measured by this system coincided with that measured by both the Berlincourt method and the resonance method. The effective d33 and the real d31 of the PZT thin film fabricated by the sol-gel multiple coating method, and poled at 300 kV/cm were 125 and −60 pC/N, respectively. The real d33 estimated upon considering the constraints by the silicon substrate was 180 pC/N.
Characterizing the dynamics of auditory perception
Authors: Ding Mingzhou , Tuller Betty , Kelso J. A. Scott
Published: July 2002

After listening to a sound that is presented repeatedly, subjects report hearing different transforms of the original sound. The frequency of reported transforms is a sensitive index of some speech disorders as well as cognitive flexibility in aging. In this paper, we propose and investigate quantitative measures that characterize the dynamics of this phenomenon, known as the verbal transformation effect. In particular, we show that the distribution of the dwell time, the time spent perceiving a string of a given phonemic form before switching to another form, obeys a power law for normal subjects with an exponent valued between 1 and 2. This result suggests that within this paradigm there is no characteristic time scale for the perceptual process. Additionally, we analyze the correlation properties of the transforms. We suggest that the complexity measures and techniques introduced here might be useful diagnostic tools for a number of speech and cognitive disorders.
Negative resistance of semiconductor heterojunction diodes owing to transmission resonance
Authors: Zohta Yasuhito
Published: July 2002

The influence of the quantum mechanical reflection on current-voltage characteristics is analyzed for small semiconductor heterojunction diodes including a potential barrier. It is shown that negative differential resistance can arise under conditions where the energy of electrons coming to the potential barrier can be controlled by an external field.
Blue light emission from ZnSe p-n junctions
Authors: Nishizawa Jun-ichi , Itoh Kazuomi , Okuno Yasuo , Sakurai Fumitoshi
Published: July 2002

Pure blue light emission has been obtained from ZnSe p-n junctions. ZnSe crystals are grown by the temperature difference solution growth method under controlled vapor pressure. A p-type ZnSe crystal can be grown from Se solution by doping with a group I element under controlled Zn pressure. The properties of p-type crystals have been measured by the van der Pauw method. A p-n junction has been made by the formation of the n-type layer by Ga diffusion into the p-type crystal. The fundamental properties of the p-n junctions are as follows: the value of n in the I-V characteristics ranges from 1.4 to 1.8 and the diffusion potential is between 2.5 and 2.7 eV. The emission spectrum from the p-n junction depends on the vapor pressure during growth and blue light emission is obtained with optimum pressure. The wavelength of the main emission peak is 460 nm at 77 °K and 480 nm at 300 °K. The brightness is 2 mcd at 2 mA.
Defect structures in rapidly degraded InGaAsP/InGaP double-heterostructure lasers
Authors: Ueda Osamu , Wakao Kiyohide , Yamaguchi Akio , Isozumi Shoji , Komiya Satoshi
Published: July 2002

Rapidly degraded InGaAsP/InGaP double-heterostructure lasers grown on (001)-oriented GaAs substrates by liquid phase epitaxy have been investigated by photoluminescence topography and transmission electron microscopy. 〈100〉-dark-line defects and 〈110〉-dark-line defects are observed in the degraded region. The 〈100〉-dark-line defects correspond to interstitial type dislocation dipoles caused by recombination enhanced dislocation climb. Their origins are threading dislocations, V-shaped dislocations, and dislocation networks. The 〈110〉-dark-line defects correspond to faulted dipoles extended from small faulted loops in the active layer, edge dipoles extended from threading dislocations, and glide dislocations. The velocities of the 〈100〉-dark-line defects are estimated by the operating time and the length of the dark lines, and are quite similar to those in rapidly degraded GaAlAs double-heterostructure lasers.
Solid phase regrowth of low temperature Be-implanted GaAs
Authors: Kwun Sook-Il , Lee M. H. , Liou L. L. , Spitzer W. G. , Dunlap H. L. , Vaidyanathan K. V.
Published: July 2002

Infrared reflection and transmission measurements were used to study the thermally induced regrowth of (100) oriented, Be-implanted GaAs samples. The samples used in this study were implanted at low temperature (−100 °C) with 250-keV Be ions to a fluence of 6×1015 cm−2. The samples were postannealed at temperatures ranging from 100 to 550 °C. Isochronal and isothermal annealing at a series of temperatures between 180 and 240 °C were performed. Infrared reflection spectra were analyzed by using a three or four layer dielectric model. Analysis of the annealing data suggests that an amorphous layer first anneals to a second metastable amorphous state and then becomes a damaged crystalline layer after annealing at 220 °C for 12 h. The observed regrowth is not by a simple epitaxial process. After annealing at 400 °C for 1 h, the damage in the layer is reduced sufficiently for the refractive index to recover almost to the preimplantation value. On annealing at 450 °C free carriers are observed. From the measured average regrowth rate for the amorphous layer at various anneal temperature, an effective activation energy is estimated to be about 1.45 eV. This compares with activation energies of 2.3 eV for Si and 2.0 eV for Ge.
The role of long-term lamp fluctuations in the random walk of frequency behavior of the rubidium frequency standard: A case study
Authors: Volk C. H. , Frueholz R. P.
Published: July 2002

A long-term frequency stability test has been performed on an EG&G prototype Rb atomic frequency standard. In addition to this test revealing excellent performance for a Rb atomic clock, some classic Rb clock behaviors were also observed; namely, long-term frequency drift, spontaneous frequency jumps, and random walk of frequency noise for long averaging times. By careful analyses of the complete test record, we have found that the spontaneous frequency jumps and the random walk of frequency noise can be attributed to the behavior of the clock’s discharge lamp. The long-term frequency drift, however, was found not to be primarily lamp related. Although results of only a single test on a single Rb clock are reported here, we believe that the results are applicable to the Rb clock technology as a whole.
Low-temperature photoluminescence properties of high-quality GaAs layers grown by molecular-beam epitaxy
Authors: Rao E. V. K. , Alexandre F. , Masson J. M. , Allovon M. , Goldstein L.
Published: July 2002

Low-temperature photoluminescence (PL) measurements have been performed on several molecular-beam epitaxial high-quality GaAs layers showing varied electrical characteristics (nominally undoped and intentionally doped n or p type). This work is carried out with a view to investigate the influence of the centers responsible for the defect–bound-exciton emissions (d,x) on the electrical properties of the layers. After a systematic study of the luminescence properties of the d,x emissions as a function of the electrical nature (doped n or p type), residual p doping level, PL excitation intensity, and sample temperature, we came to the following conclusion: In addition to the prominent residual carbon acceptors, at least a part of p conduction in nominally undoped p-type layers could come from the centers responsible for the d,x emission at 1.5109±0.0003 eV. This suggestion is tentatively ascertained by detecting an acceptor emission at ∼1.496±0.001 eV, shallower than the carbon acceptor about 3 meV. All these results in addition to those related to the detection of deeper acceptors in the spectral range 1.46–1.49 eV are presented and discussed.
Pressure dependence of the elastic moduli of single crystal MgF2 to 1 GPa
Authors: Vassiliou John K.
Published: July 2002

The six independent elastic constants of a single crystal of tetragonal MgF2 with rutile structure were measured ultrasonically at room temperature from ambient conditions to 10 kbar. The values at 1 bar and 10 kbar are (in 1011 dyn/cm2) C11: 14.081 (1 bar), 14.597 (10 kbar); C12: 9.003 (1 bar), 9.569 (10 kbar); C13: 6.417 (1 bar), 6.543 (10 kbar); C22: 20.490 (1 bar), 21.094 (10 kbar); C44: 5.664 (1 bar), 5.768 (10 kbar); C66: 9.560 (1 bar), 9.964 (10 kbar). CS=(C11−C12)/2 softens with pressure, while C44 shows a weak pressure dependence. Similar behavior has been observed in NiF2, ZnF2, TiO2, and in the distorted rutile crystal TeO2. The reported pressure induced transition from tetragonal MgF2 to distorted fluorite type observed at 250 kbar using x-ray scattering is not anticipated by the softening of CS which would lead to an orthorhombic distortion.
Application of pulse-echo ultrasonics to locate the solid/liquid interface during solidification and melting of steel and other metals
Authors: Parker R. L. , Manning J. R. , Peterson N. C.
Published: July 2002

The velocity of sound and the density have values that are sufficiently different for liquid as compared to solid phases of metals and alloys to permit the use of pulse-echo ultrasonic techniques to locate the solid/liquid interface during solidification and melting. Experimental results are presented for pulse-echo observation of the melting and freezing of pure iron, 304 stainless steel, and tin, using Bridgman-type furnaces with unidirectional heat flow, at frequencies from 1 to 5 MHz. For both iron and steel, rapid grain growth in the solid phase at high temperatures can strongly attenuate the sound waves and can also produce backscattered waves which obscure the identification of the solid/liquid echo. Additionally, in alloys the presence of a ‘‘mushy zone’’ rather than a sharp interface further reduces the reflected signal. These signal/noise problems were successfully overcome by the use of a transducer spatial scanning technique with computer signal averaging that permits the interface to be located even in concentrated alloys.
Effects of substrate crystallinity and dopant on the growth kinetics of platinum silicides
Authors: Takai H. , Psaras P. A. , Tu K. N.
Published: July 2002

The growth kinetics of platinum silicides have been studied on four substrate categories: single-crystal, amorphous, undoped polycrystalline, and phosphorus-doped (8×1020 at./cm3) polycrystalline silicon. The sequential growth of Pt2Si and PtSi were analyzed by Rutherford backscattering spectroscopy (RBS), Seeman–Bohlin x-ray diffraction, and cross-section transmission electron microscopy. Phosphorus depth profiles were measured by secondary ion mass spectroscopy (SIMS). Our results conclude that the activation energies for the growth of Pt2Si and PtSi are not affected by substrate crystallinity and doping of phosphorus. Analysis of the phosphorus profile by SIMS clearly showed that phosphorus atoms are segregated near the interface between PtSi and polycrystalline silicon, but not at the Pt2Si/polycrystalline silicon interface.
A comparison between thermal annealing and ion mixing of multilayered Ni-W films on Si. II
Authors: Pai C. S. , Lau S. S. , Poker D. B. , Hung L. S.
Published: July 2002

The reactions between bilayered Ni/W films and Si〈100〉 substrates induced by thermal annealing and ion mixing were investigated and compared. Samples were prepared by electron-beam sequential deposition of Ni and W onto the Si〈100〉 substrates and following by either furnace annealing (∼200–900 °C) or ion mixing (∼2×1015–4×1016 86Kr+ ions/cm2). The reactions were analyzed by Rutherford backscattering and x-ray diffraction (Read camera). Thermal annealing of both W/Ni/Si〈100〉 and Ni/W/Si〈100〉 samples led to the formation of Ni silicide next to the Si substrate and W silicide on the sample surface (layer reversal between Ni and W in the Ni/W/Si〈100〉 case). Ion mixing of W/Ni/Si〈100〉 samples led to the formation of Ni silicide with a thin layer of Ni-W-Si mixture located at the sample surface. For Ni/W/Si〈100〉 samples a ternary amorphous mixture of Ni-W-Si was obtained with ion mixing. These reactions were rationalized in terms of the mobilities of various atoms and the intermixings between layers.
Influence of P and As implantation of the formation of MoSi2
Authors: van Ommen A. H. , Wolters R. A. M.
Published: July 2002

Molybdenum disilicide films have been formed by a reaction of Mo with polycrystalline silicon. Implantation of phosphorus or arsenic prior to reaction has been shown to have a large effect on the silicidation process. The object of implantation was to enhance the silicide reaction by creating damage at the metal-silicon interface. This, then, results in silicide films with less surface roughness (and a lower electrical resistivity). Molecular P+2 ions were found to be more effective in creating damage than single P+ ions, due to the fact that for P+2 ions two simultaneous collision cascades occur which overlap. Apart from the beneficial effect of implantation damage, the introduction of phosphorus has a deleterious effect on the properties of the silicide films. This phenomenon is explained by the presence of a thin and nonuniform native oxide layer which hinders the silicide reaction. Without addition of phosphorus, new nuclei for the silicide reaction can be formed due to stress introduced by the formation of the silicide, which will act upon the oxide and cause it to break up at some weak spot. The effect of phosphorus is proposed to be that it renders the oxide more viscous which prevents this process from taking place. The x-ray diffraction spectra revealed that the orientation of the grains in the polycrystalline MoSi2 films is influenced by the method of preparation.
Dislocation motion in GaAs/AlxGa1−xAs structures
Authors: Kuesters K.-H. , De Cooman B. C. , Carter C. B.
Published: July 2002

Dislocations have been made to move through different compound semiconductor epilayer structures by deformation at 320 °C and have then been examined by transmission electron microscopy. The interaction between the dislocations and the GaAs/AlxGa1−xAs interface is shown to depend on the thickness of the AlxGa1−xAs layer. Dislocations are pinned at the interface and, for the MOCVD-grown material, within the AlxGa1−xAs layer. Dislocation dipoles, some of which are faulted dipoles, are then pulled out and lie preferentially along the heterojunction. It is emphasized that these dipoles, which may be important in device degradation, form as a result of dislocation glide and not dislocation climb.
Real time measurement of deposition initiation and rate in laser chemical vapor deposition
Authors: Allen S. D. , Jan R. Y. , Mazuk S. M. , Vernon S. D.
Published: July 2002

Laser chemical vapor deposition (LCVD) is a modification of conventional CVD using a laser heat source. Although the reactant systems used may be similar to conventional CVD, the film growth characteristics may differ in several ways. The changes in the optical properties of the film/substrate during deposition must be considered as the amount of laser energy absorbed determines the surface temperature and the maximum deposition rate. Also affecting the deposition rate is the diffusion of reactants to the reaction zone. Because of the small area heated in LCVD, higher surface temperatures can be accessed before diffusion and convection limit the deposition rate. For favorable reactant systems, very rapid deposition rates (greater than 100 μm/sec) and scan speeds for line deposition (greater than 10 cm/sec) can be achieved.
Configuration coordinate diagram for the E4 defect in electron-irradiated GaP
Authors: Huang Qisheng , Grimmeiss H. G. , Samuelson L.
Published: July 2002

The electronic properties of the defect E4 generated in GaP by 1-MeV electron irradiation have been studied. The defect exhibits very strong athermal annealing effects under e-h recombination conditions. By comparing thermal and optical data evidence is obtained for lattice relaxation when the charge state of the E4 defect is changed. A simple configuration coordinate diagram is presented which is in agreement with experimental data and which explains several important features of recombination-enhanced defects reactions and athermal annealing phenomena.
An analytical expression for the optical threshold in highly twisted nematic systems with nonzero tilt angles at the boundaries
Authors: Breddels P.A. , van Sprang H. A.
Published: July 2002

It has been shown recently that steep optical thresholds can occur in twisted nematic configurations with tilted boundary conditions. This is the case when the twist angle φ is between π and 2π. We have derived an analytical expression for this threshold, utilizing the results from a numerical evaluation of director patterns with a computer program. The consequences of the dependence of the threshold on the relevant physical parameters are discussed and the theory is compared with experimental data. Also we point out the differences with respect to the threshold equation for the conventional 90°-twisted nematic configuration.
Thermal stability of the Al/PdxW100−x/Si contact systems
Authors: Eizenberg M. , Thompson R. D. , Tu K. N.
Published: July 2002

Interactions of thin films of Al and Pd-W alloys (Pd80W20 and Pd20W80) deposited on Si and on SiO2 have been studied using Auger-electron spectroscopy, Rutherford backscattering spectrometry, x-ray diffraction, and forward current-voltage measurements of Schottky-barrier height. For the bilayer films deposited on the inert substrate of SiO2, Pd reacts with Al, forming Al-rich Al-Pd intermetallic compounds at 400 °C. Furthermore, in the Pd-rich alloys (Pd80W20) Al permeates through the whole alloy film readily at 500 °C, while in the W-rich Pd20W80 the integrity of the alloy film is preserved even following annealing at 600 °C. For the bilayer films deposited on single-crystal Si, the results of annealing show extraction of Pd to both sides of the alloy, forming Pd2Si at the Si side and Al-Pd intermetallic compounds at the Al side. In the case of the Pd-rich alloy (Al/Pd80W20/Si) contact deterioration due to Al penetration to the substrate interface is observed at 500 °C and possibly at 400 °C. In the case of the W-rich alloy (Al/Pd20W80/Si) the stability of the contact is preserved even following annealing at 550 °C for 30 min; the structure after the annealing is Al-Pd/Pd-W/Pd2Si/Si. The W-rich alloy is very promising for contact applications in Si devices due to the fact that both a shallow silicide contact and a built-in diffusion barrier are simultaneously obtained.
Chromite formation by shock-wave compression
Authors: Kleiman J. , Salansky N. M. , Glass I. I.
Published: July 2002

Chromite formation was observed in experiments with a flash-heating hemispherical-implosion system, when a cylindrical steel sample holder, with stainless-steel plug, containing a graphite/iron mixture was compressed by the implosion. The formation of chromite was observed and verified by x-ray diffraction, scanning electron microscopy, and chemical microanalysis. The diffusion rates of Cr from the plug to the sample were as high as 102–103 cm2 s and growth rates of chromite crystals were as high as 0.3–0.4 ms−1. The foregoing could be inferred from the observations of the recovered specimens. Possible ways of chromite formation and the causes for the unusually high diffusion and crystal-growth rates are discussed.
Observation of single-carrier space-charge-limited flow in nitrogen-doped α-silicon carbide. I. I-V characteristics and impedance
Authors: Tehrani S. , Kim J. S. , Hench L. L. , Van Vliet C. M. , Bosman G.
Published: July 2002

This paper first reviews the properties of silicon carbide, in which polytypism is a salient feature. If a highly compensated insulating polytype is sandwiched between low resistive polytypes, space-charge injection will occur. The theory of space-charge-limited current flow in the presence of traps is reviewed and a somewhat different version of the standard theory is presented, which shows more clearly the ohmic and space-charge-limiting regimes. Close analytical parametric forms for I and V are obtained. Experimental data on I-V characteristics and impedance are presented for 52–300 K. Except at the highest temperature, four regimes are clearly visible in the I-V curves. A quantitative comparison with the theory is made and various transport quantities for α-SiC are deduced.
Redistribution of dopant arsenic during silicide formation
Authors: Zheng L. R. , Hung L. S. , Mayer J. W.
Published: July 2002

A systematic study of arsenic redistribution in Ni, Cr, Ta silicide forming systems has been performed by implanting arsenic into metal layers or into single-crystal silicon substrates. During silicide formation arsenic accumulates near the interface region, incorporates in the silicide, or diffuses out of the silicide into the surrounding ambient. Differences in the dopant redistribution are related to the arsenic initial location relative to the moving species in silicide formation and the diffusivity of dopant atoms at the metal-silicon reaction temperature.
The role of activation energy distributions in diffusion related annealing in SiO2
Authors: Devine R. A. B.
Published: July 2002

Models for annealing processes in damaged, amorphous SiO2 are discussed. Using a series expansion approach, theories developed for diffusion-limited recombination are adapted to allow for a Gaussian distribution of activation energies. It is found that the effect of a distribution having deviation ΔE, and center EA can be accounted for by using an effective diffusion coefficient, D̃, such that in the series expansion any power (n) is defined by (D̃)n=Dn0 exp  1/2  (nΔE/kT)2 exp(−nEA/kT). This form is more complicated than that found previously for ‘‘pure’’ diffusion studies. The importance of the form of the distribution function for the activation energies is discussed in the context of the full diffusion-limited theory for annealing. It is argued that processes occurring at temperatures in excess of 500 °C are not due to diffusional recombination.
The thermionic emission and work function of U and UO2
Authors: McLean W. , Chen H.-L.
Published: July 2002

Thermionic emission measurements have been used to determine the work function (φ) of pure and oxidized uranium samples between 1100 and 1300 K; Auger electron spectroscopy (AES) was used to verify the cleanliness and compositions of the samples. It was found that impurities present in ppm amounts in the bulk U segregated to the surface upon heating and had an appreciable effect on the zero-field emission currents as well as the slopes of the Schottky curves obtained at various temperatures. A combination of ion-sputtering and ultrahigh vacuum (UHV) annealing at high temperatures was successful in reducing the total impurity level on the hot surfaces to 5%. At this low concentration of impurities, well-behaved Richardson line plots were obtained with A=135 A cm−2 K−2 and φ=3.54 eV for pure U and A=128 A cm−2 K−2 and φ=3.19 eV for UO2. The Schottky coefficients for clean U approached their ideal values at fields >400 V/cm.
Josephson 4 K-bit cache memory design for a prototype signal processor. III. Decoding, sensing, and timing
Authors: Henkels W. H. , Geppert L. M. , Kadlec J. , Epperlein P. W. , Beha H. , Chang W. H. , Jaeckel H.
Published: July 2002

Designs for peripheral and timing circuits for a Josephson cache memory chip, organized as 1 K × 4-bits, are described. The designs were carried out employing a 2.5-μm minimum-linewidth niobium edge-junction technology, in conjunction with the memory cell and driver array design described in the preceding companion paper. Significant changes in decoding, sensing, and timing, relating to widening operating margins over a predecessor all-Pb-alloy design are described in detail. The resultant nominal chip access time and power are, respectively, 970 ps and 10 mW.
Phase transformations in alloy and bilayer thin films of vanadium and silicon
Authors: Nava F. , Psaras P. A. , Takai H. , Tu K. N.
Published: July 2002

Phase transformations in coevaporated amorphous vanadium-silicon thin alloy films and bilayer vandium/silicon films have been studied as a function of heat treatment by in situ electrical resistivity measurement together with Rutherford backscattering spectrometry, Seeman–Bohlin glancing angle incidence x-ray diffraction, and scanning and transmission electron microscopy. In the as-deposited state the amorphous alloy films were silicon rich, having an atomic ratio of 1:3 for vanadium and silicon, respectively. Upon heat treatment a sharp decrease in resistivity occurs at approximately 250 °C, which has been determined to be a transformation from the amorphous to crystalline VSi2 phase. The kinetics of the transformation have been obtained by isothermal treatment over the temperature range of 184–220 °C. The transformation is described by a Johnson–Mehl–Avrami-type equation with an apparent activation energy of 1.30±0.06 eV. Subsequent heat treatment causes a gradual decrease in resistivity up to 850 °C. Upon cooling, a monotonic decrease in resistivity was observed. Heat treatment at high temperatures (900 °C) promotes the growth of nonuniformly distributed silicon grains. For the bilayer vanadium/silicon films, the sheet resistance increases gradually upon heat treatment up to 500 °C, then a sharp decrease is observed, which is due to the formation of VSi2. Further heat treatment at higher temperatures (850 °C) promotes a monotonical decrease in the resistance. The cooling behavior is similar to that of the crystallized alloy specimens except for having a slightly lower resistivity value. In a model for the two thin films connected electrically in parallel, the growth kinetics of VSi2 in the bilayer films has been found to be linear in time over the temperature range of 500–535 °C with an activation energy of 2.23±0.09 eV. The microstructure of films at various stages of annealing have been studied by x-ray diffraction and transmission electron microscopy. Correlation between the resistivity and microstructure is given and discussed. In situ resistivity of annealed films below room temperature has been measured. Crystalline VSi2 thin films do not become superconductive down to 2 K.
Monte Carlo simulations of hot-electron spectroscopy in planar-doped barrier transistors
Authors: Wang T. , Hess K. , Iafrate G. J.
Published: July 2002

We have developed a microscopic model to study the hot-electron-spectroscopy method which uses GaAs planar-doped barrier transistors. Our simulation is based on the Monte Carlo method and includes the effects of ionized impurity scattering, pair electron-electron scattering, long-range plasmon scattering, and coupled plasmon/phonon scattering. The nonparabolicity of the band structure and the Pauli exclusion principle are also taken into account in the highly doped base region. The numerical results show that the experimental method of Hayes will indeed reflect the overall momentum distribution of injected hot electrons if the planar-doped barriers are ‘‘ideal.’’ Ideal means that the self-consistent potential (due to conduction electrons and ionized impurities) is well described by the continuum approximation. We demonstrate that potential fluctuations arising from the discrete natue of the charges and reflection of electrons at the base-collector junction make it impossible to obtain the precise distribution function from the experiments.
Young modulus and internal friction of a fiber-reinforced composite
Authors: Ledbetter H. M. , Lei Ming , Austin M. W.
Published: July 2002

By a kilohertz-frequency resonance method we determined the Young modulus and internal friction of a uniaxially fiber-reinforced composite. The composite comprised glass fibers in an epoxy-resin matrix. We studied three fiber contents: 0, 41, and 49 vol %. The Young modulus fit a linear rule of mixture. The internal friction fit a classical free-damped-oscillator model where one assumes a linear rule of mixture for three quantities: mass, force constant, and mechanical-resistance constant.
Laser chemical vapor deposition of patterned Fe on silica glass: Observation and origins of periodic ripple structures
Authors: Jackman R. B. , Foord J. S. , Adams A. E. , Lloyd M. L.
Published: July 2002

Laser chemical vapor deposition of patterned iron deposits on silica glass has been carried out using an Ar ion laser-driven dissociation of iron pentacarbonyl vapor. The structure of the deposited films has been studied using optical, electron, and scanning Auger microscopic techniques. Extensive iron silicate formation is observed at the iron-glass interface and 50-μm periodic ripples are formed in the delineated deposits. The origin of the periodic structure is discussed with reference to the available analytical data and observations from related laser processing studies.
Hole-diffusion length and transport parameters of thin CdS films from a Schottky barrier
Authors: Ebothé Jean
Published: July 2002

The optoelectronic and transport properties of thin sprayed CdS films, having a thickness of less than 2 μm are reported. The use of two independent technics, surface photovoltage and photoelectrochemical measurements, led to a good agreement in the hole-diffusion length values. These range from 0.017 to 0.15 μm and behaved differently in two zones. A rapid increase of this parameter is observed below a film thickness of 0.4 μm. Above this thickness, the value obtained is constant. Specific space-charge widths are expected because of the respective measurement conditions. The hole-diffusion length decreases as carrier density increases. The hole lifetime shows a regular decrease as the thickness factor increases, while the hole-diffusion coefficient and mobility patterns are similar to that of the photocurrent.
Analysis of the tin diffusion step in Nb3Sn-Cu superconducting wire produced by the external tin process
Authors: Verhoeven J. D. , Heimes K. , Efron A.
Published: July 2002

Assuming volume diffusion is dominant, an analysis has been presented which allows one to analytically describe the three stages of the solid-state diffusion process for adding Sn in the external tin method for preparing Nb3Sn/Cu superconducting material. It is shown that one obtains a maximum intermetallic compound layer thickness in stage III which then decreases to zero thickness. Important practical questions in utilizing this process are the times required to complete stages I and II of the process, and this analysis predicts that the times required to complete stage I are on the order of days while stage II is completed in a matter of hours. The roles of grain-boundary diffusion and sample geometry are discussed and it is concluded that the analysis may be regarded as an upper bound for determining the times required to complete stages I and II of the solid state Sn diffusion process.
Magnetic field inside a long cylindrical deflection coil: A closed-form solution
Authors: Dasgupta Basab B.
Published: July 2002

We derive a closed-form expression for the magnetic field inside an (infinitely) long cylindrical deflection coil using the image current concept. The method of derivation is very general and can be applied to coils of arbitrary cross-sectional shape, unsymmetric coils, and coils nonconcentric with the core.
Silane thermometry in radio-frequency discharge plasma by coherent anti-Stokes Raman spectroscopy
Authors: Hata Nobuhiro , Matsuda Akihisa , Tanaka Kazunobu
Published: July 2002

The rotational temperature of silane molecules in a flowing gas as well as in a radio-frequency discharge plasma of silane has been determined by the analysis of its coherent anti-Stokes Raman spectra. The ν1 Q-band coherent anti-Stokes Raman spectra of silane have been measured under different conditions such as discharge off, discharge on, and electrode heating, and fitted to theoretically calculated curves for various rotational temperatures using a nonlinear least-squares method. The results have shown that discharge power as well as electrode heating increase the rotational temperature of SiH4.
Si-implanted n+-InP/p-InP junctions: Electrical characterization and noise
Authors: Conjeaud A. L. , Orsal B. , Dhouib A. , Alabedra R. , Gouskov L.
Published: July 2002

This paper describes the various types of reverse conduction in a n+, Si-implanted InP/p-InP junction and the behaviors of reverse I-V characteristics and noise in the different polarization ranges corresponding to generation-recombination, tunneling assisted by traps, and multiplication. An increase in the trap density and the reverse tunnel current with increasing dose of implanted ions was observed.
Measurement of intrinsic stress in silver films by using ellipsometry
Authors: Vijayakumar K. P. , Purushothaman C.
Published: July 2002

Annealing of silver films in the temperature range 30–300 °C is found to result in the minimization of stress in the films which, in turn, affects the hillock growth on the film surface. This variation in hillock growth is studied by using ellipsometry. It is found that the numerical value of the thermal stress in the film is approximately equal to that of the intrinsic stress when the hillock growth is retarded. The intrinsic stress in silver films is calculated by using this technique for different film thicknesses. The values of the film thicknesses are so selected that the difference between them is quite large. The results obtained in the present work are found to be in fairly good agreement with those obtained by earlier workers.
Steady-wave characteristics in shock-loaded steel specimens
Authors: Rosenberg Z. , Bless S. J.
Published: July 2002

The steady-wave features of the plastic shock wave in low carbon steel are explored with manganin stress gauges. We show that at the low stress range (20–45 kb) these waves are not steady and that the corresponding Bland numbers are much lower than unity, as expected for nonsteady waves.
Thermal domain drag effect in amorphous ferromagnetic materials. I. Theory
Authors: Jen S. U. , Berger L.
Published: July 2002

A steady, collective translation of domain walls has been detected through direct wall observations in metallic ferromagnets subjected to a constant temperature gradient. A 60-Hz ac external field HE is used to reduce the effect of pinning forces on the walls. Three driving mechanisms, Nernst–Ettinghausen mechanism, end-drive mechanism, and isothermal end-drive mechanism, are proposed. Three pinning mechanisms, bulk pinning, surface pinning, and end pinning are believed to be effective in these materials. The region in the (dT/dx,H0E) plane corresponding to static walls has a triangular shape. We have generalized the theory to include the three pinning wells, and the corresponding theoretical phase diagrams are shown. The saturation of phase boundary is also discussed.
Measurement of the silver freezing point with an optical fiber thermometer: Proof of concept
Authors: Dils R. R. , Geist J. , Reilly M. L.
Published: July 2002

Measurements were made at the gold and silver freezing points to demonstrate the accuracy of the new optical fiber thermometer (OFT). It is shown that the output signal from the OFT is related to the radiance from a blackbody source in a simple manner and that the temperature interval between the gold and silver freezing points, as determined with the OFT, is close to other recent results.
Analytic relationships for characterizing electrical properties and electron density profiles in gas discharge columns
Authors: Rogoff Gerald L. , Kussmaul Keith
Published: July 2002

A previous paper presented numerically determined values of a dimensionless quantity which is useful for characterizing gas discharge columns with electron production and loss rates linear and quadratic in electron density. That quantity, denoted by S, is useful for calculating voltage-current characteristics and for indicating the shape of the electron density distribution, i.e., its degree of diffuseness or constriction. (In terms of the electron density ne, S is the integral of −∇2ne/ne over the column cross section.) Crawford has presented an analytic approximation for a limited range of S for the case of a circular column cross section. In this note Crawford’s expression is compared with values obtained numerically, and it is found to be a very good approximation over its limited range of applicability. In addition, modified versions of Crawford’s expression are provided for use with all possible relative magnitudes and combinations of signs of the linear and quadratic rates. Analytic relationships between the maximum electron density and average electron density are also provided, both for direct use and to facilitate use of the expressions for S.
Ionized Mg doping in molecular-beam epitaxy of GaAs
Authors: Mannoh M. , Nomura Y. , Shinozaki K. , Mihara M. , Ishii M.
Published: July 2002

Using ionized Mg beams accelerated to energies from 130 to 500 eV, Mg doping was studied in molecular-beam epitaxy of GaAs. The incorporation coefficient of Mg increases by a factor of about 100 when compared with the use of neutral Mg beams. Hole concentrations as high as about 1×1019 cm−3 have been achieved. Photoluminescence measurements suggest that the damage due to Mg-ion bombardment is negligible when the ion accelerating voltage (Va) ≲130 V. For higher Va , the damage can be removed by postgrowth annealing.