bluuebunny/crossref_metadata_2025 huggingface dataset:
Drift mobility in hydrogenated amorphous silicon from photoconductivity decay
Authors: Moddel G. , Viktorovitch P.
Published: July 2002

We present the results of a study of the steady-state photoconductivity and its decay after the termination of illumination, as a function of temperature and intensity, in a-Si:H samples produced by rf sputtering and the plasma-enhanced chemical vapor deposition (PECVD) of silane. The electron drift mobility, deduced from the initial rate of decay of the photocurrent, appears activated, with activation energies in the range of 0.20–0.24 eV for the sputtered films and ∼0.1 eV less for the PECVD films. The activated behavior results from the interaction of photoconducting electrons with potential fluctuations, or a shoulder in the density of states below the extended state transport level. Inconsistencies in the interpretation of the drift mobility magnitudes are resolved by the proposition that a substantial fraction (>90%) of the photogenerated carries recombine very quickly only in films with a high hole μτ. In such films, only a small fraction of the photogenerated electrons contribute significantly to the steady-state photoconductivity measured in a coplanar gap configuration.
Influence of surface coatings on elasticity, residual stresses, and fracture properties of silicon microelements
Authors: Johansson Stefan , Ericson Fredric , Schweitz Jan-Åke
Published: July 2002

Microscale silicon cantilever beams of (100)〈100〉 and (100)〈110〉 orientations were magnetron sputtered with submicron layers of Al, Ti, or TiN, or thermally coated with SiO2. Theoretical expressions for the elastic deflection induced by residual stresses were derived, and utilized to deduce such stresses from observed deflections. A theory for the elastic stress distribution in coated beams exposed to external bending moments was utilized to deduce maximum stress levels at fracture in the coatings and in the substrates. The fracture tests were performed in situ in a scanning electron microscope by means of specially designed equipment. For uncoated beams, the average fracture stress was 6 GPa (maximum 13 GPa) for 〈100〉 beams, and 4 GPa (maximum 6 GPa) for 〈110〉 beams. Most coatings proved to have a strength-reducing effect, particularly the brittle, thin coatings of TiN, but also the Ti coatings (which displayed brittle fracture behavior). Ductile, thin coatings of Al were either neutral, or induced a small reinforcement. The influence of the thermal oxide was ambiguous: either a small strengthening or a small weakening effect. Five different types of fracture in coated silicon beams are discussed, and ‘‘reinforcement factors’’ associated with these fracture types are expressed in terms of fracture toughnesses. By comparing the experimental results with these expressions, it was possible to identify the probable types of fracture, and to explain why different strengthening or weakening effects occurred for different coatings.
Selective epitaxial growth in silicon on insulator: Planarity and mass flow
Authors: Williams D. A. , McMahon R. A. , Ahmed H. , Garry G. , Karapiperis L. , Dieumegard D.
Published: July 2002

Seeded zone-melt recrystallization using a dual electron beam system has been performed on silicon-on-insulator material, which was prepared with single-crystal silicon filling of the seed windows by selective epitaxial growth. The crystal quality has been assessed by a variety of microscopic techniques, and it is shown that single-crystal films 0.5–1.0 μm thick over 1.0 μm of isolating oxide may be prepared by this method. These films have considerably less lateral variation in thickness than standard material, in which the windows are not so filled. The filling method is suitable for both single- and multiple-layer silicon-on-insulator, and gives the advantages of excellent layer uniformity after recrystallization and improved planarity of the whole chip structure. Experiments using various amounts of seed window filling have shown that the lateral variations of silicon film thickness seen in unplanarized material are due to stress relief in the cap oxide when the silicon film is molten, rather than the effect previously postulated in which they were assumed to be due to the contraction of silicon on melting.
Transmission electron microscopy of strained InyGa1−yAs/GaAs multiquantum wells: The generation of misfit dislocations
Authors: Chang K. H. , Bhattacharya P. K. , Gibala R.
Published: July 2002

We have investigated the generation and propagation of misfit dislocations in strained InyGa1−yAs/GaAs multiquantum wells grown by molecular-beam epitaxy, with cross-sectional transmission electron microscopy. The samples are of excellent optical quality, with multiquantum wells having well widths of 100 Å, being characterized by excitonic linewidths and Stokes shifts of 1.5–2.5 and 1–2 meV, respectively. We have examined the growth of 2-μm-thick multiquantum-well samples grown either directly on GaAs, or with an intermediate composition buffer layer, and for the cases of small (y=0.07) and large (y=0.16) misfits. It is seen that for the case of quantum wells with small misfit, grown directly on GaAs, metastable growth can be achieved. This is confirmed by low-temperature absorption measurements and from transmission electron microscopy experiments performed both before and after post-growth thermal annealing. In the case of quantum wells with large misfits directly grown on GaAs, dislocations are generated within the first few periods, and high optical quality is retained in the subsequent free-standing quantum wells. In the case of quantum wells grown with an intermediate composition InxGa1−xAs buffer layer, dislocations are generated at the buffer-GaAs interface, and the freestanding multiquantum well is again of very high quality.
Effects of deuterium plasmas on silicon near-surface properties
Authors: Lindström J. L. , Oehrlein G. S. , Scilla G. J. , Yapsir A. S. , Corbett J. W.
Published: July 2002

The effects of reactive-ion etching and plasma etching (using deuterium) on the electrical properties of silicon have been studied employing capacitance-voltage measurements of Schottky diodes and secondary ion mass spectrometry. Both significant hydrogen penetration, which causes electrical deactivation of the boron dopant, and radiation damage result from the plasma exposure. A model is suggested to explain our results.
Minimum dc electric field requirements for removing powder layers from a conductive surface
Authors: Novick Vincent J. , Hummer Charles R. , Dunn Patrick F.
Published: July 2002

An electrostatic powder dispenser was constructed to dispense particles without the use of a carrier gas. This device consisted of two contoured, outer stainless-steel plates that were electrically grounded and a flat, inner copper grid that was electrified and contained a central powder reservoir. Experiments were performed to investigate the levitation of various powders from the reservoir in the presence of an applied dc electric field. Eleven materials including metals, oxides, and conductively coated oxides were studied under vacuum and atmospheric conditions. The electric field required to remove particles from the powder reservoir was found to be a function of particle density and size. An equation was developed that predicted the minimum voltage necessary to remove conductive particles larger than 10 μm in diameter from a conductive surface in a vacuum environment: E=[4.85(ρD)1/2 +0.362]×105 , where E is the field strength (V/m), ρ is the particle density (kg/m3 ), and D is the mass median particle diameter (m). For particles in this size range, gravitational and electrostatic forces appeared to dominate, whereas for particles with a mass median diameter less than 10 μm, adhesive forces appeared to dominate. This equation was also found to hold for the removal of glass beads in air. A semiquantitative model was developed that was consistent with experimental results. This model calculated the force and charge induced on the particles in an electric field while taking into account the neighboring particles.
Effect of beam self-rotation on a Čerenkov free-electron laser
Authors: Mishra G.
Published: July 2002

At large beam currents, the beam space charge produces a radial electric field causing E×B rotation of the beam. As the beam travels through a partially dielectric loaded waveguide, it emits coherent Čerenkov radiation at frequencies ω=βvb+l(ωα/γ0), where l is the azimuthal mode number, ωα is the angular frequency of rotation, and β is the propagation constant.
Spall due to short high-intensity impulses
Authors: Froeschner K. E. , Maiden D. E. , Chau H. H.
Published: July 2002

Spallation thresholds for (3)/(16) – (3)/(8) -in. 6061-T6, 5456, and 1100 aluminum and 6A14V titanium alloys were determined for impulses from 5 to 30 ktap with a pulse duration of 0.15 μs. These experiments show that for aluminum alloys the spall fracture stress is nearly a constant but varies between 16 and 20 kbar in different batches of material and shows suggestion of a weak dependence on strain rate with strain rates from 0.04 to 0.4 μs−1. The impulse threshold for spall was 7.5 ktap. For 6A14V titanium the spall fracture stress was 60 kbar and the impulse threshold was 15 ktap. The stress pulses were produced by impacting target samples with a 0.012-in. (0.305 mm) thick by 3-in. (76 mm) square Kapton impactor projectile at velocities ranging from 0.13 to 0.44 cm/μs. Data obtained include detailed records of the impactor and rear (spalled) surface velocity versus time measured with a dual-beam Fabry–Perot interferometer, as well as soft recovery of the target residual and spall fragments. From these we are able to determine the partitioning of impulse between the target residual and the spall fragment(s) and the critical spall fracture stress and strain rate. We have also made microphotographic inspections and measured the stress-strain properties of recovered target. The data show that the amount of impulse (momentum per unit area) absorbed by a structural wall by a short duration pulse is limited by the spall threshold. Increases in applied impulse above this spall threshold result in higher spall fragment velocities but no apparent increase in the impulse delivered to the residual structure. Spall is thus an effective damage limiting mechanism which must be considered when estimating the effectiveness of systems whose primary damage is structural collapse due to impulse generated by short duration pulses.
Composition and deposition temperature dependence of the structure of oxidized thin-film amorphous Tb-Fe
Authors: Hellman F. , Nakahara S. , Frankenthal R. P. , van Dover R. B. , Siconolfi D. J. , Gyorgy E. M.
Published: July 2002

The microstructure of oxidized amorphous Tb-Fe alloy thin films prepared by magnetron cosputtering has been studied as a function of alloy composition and the substrate temperature at which the films were grown. Transmission electron microscopy and Auger electron spectroscopy with ion-sputter depth profiling were used to characterize the films. The composition of the alloy has no dramatic effect on the oxidation rate; it does, however, effect the microstructure of the α-Fe2O3 layer that forms on the alloy. Oxidized alloys originally containing more than 27 at. % Tb show an extremely fine-grained structure, with grain sizes on the order of 30 Å. Alloys containing less Tb developed large (1–2 μm) [001]-oriented single-crystal α-Fe2O3 grains amongst the fine-grained α-Fe2O3. For alloys with less then 18 at. % Tb, only the large grains remain. Samples grown at deposition temperatures ranging from 85 K to 400 °C show a similar structure after oxidation.
Critical currents of sintered and melt-textured YBa2Cu3Ox
Authors: Alford N. McN. , Birchall J. D. , Clegg W. J. , Kendall K.
Published: July 2002

High critical-current densities, Jc, have been observed in single crystals and thin films of YBa2Cu3Ox. Jc in bulk materials is diappointingly low reaching a maximum in untextured material of about 103 A cm−2. The importance of raising Jc in bulk materials is paramount and most applications of bulk materials require high Jc in high magnetic fields. The work of Jin et al. in raising Jc to 17 000 A cm−2 in zero field represents a most important step in the development of bulk materials and gives real hope to bulk applications. In the communication we first describe the properties of untextured wire, and then we describe our process for melt texturing and the difficulties encountered.
The dependence of the Schottky emission coefficient on reverse bias
Authors: Mooney Jonathan Martin
Published: July 2002

The dependence of the Schottky emission coefficient on reverse bias has been measured on several PtSi Schottky diodes. The data as well as a model which fits the experimental results are presented. The model is based on the assumption that carriers are not emitted until they surmount the Schottky barrier and, further, that the probability of the carrier traveling from the metal-semiconductor interface to the Schottky barrier maximum within the semiconductor decays exponentially with distance.
Degradation of hydrogenated amorphous silicon films induced by irradiation of synchrotron radiation light
Authors: Saito Yoji , Inoue Katsushi , Yoshida Akira
Published: July 2002

Hydrogenated amorphous silicon films were rapidly degraded by the irradiation with vacuum ultraviolet light. Photoconductivity of the films decreases in inverse proportion to irradiation time of synchrotron radiation light. A direct bond-breaking model is proposed for the degradation mechanism.
High-quality homoepitaxial silicon films deposited by rapid thermal chemical vapor deposition
Authors: Green M. L. , Brasen D. , Luftman H. , Kannan V. C.
Published: July 2002

Homoepitaxial Si films have been deposited by rapid thermal chemical vapor deposition (RTCVD), a growth technique based on the combination of rapid thermal annealing lamps and a chemical vapor deposition chamber. The low thermal mass of the system allows the substrate to be heated and cooled rapidly, and to be held at temperature for short periods (seconds) of time, thereby allowing the growth of thin films. Si films have been grown epitaxially at temperatures between 600 and 900 °C. At 800 °C growth temperature, films with total C and O impurities less than 20 ppm, and defect densities less than 102 cm−2, have been grown. Finally, RTCVD and molecular-beam epitaxy have been compared with respect to the growth of Si-based structures.
Orientation dependence of twinning characteristics in Y-Ba-Cu-O superconducting thin films
Authors: Singh R. K. , Biunno N. , Narayan J.
Published: July 2002

The twinning characteristics of epitaxial and textured superconducting thin films grown on (100) SrTiO3 and (100) MgO substrates have been found to be dependent on the film orientation. Microstructural details of thin films deposited by the pulsed-laser evaporation technique followed by annealing in oxygen and helium atmospheres at 900 °C for short time intervals were examined using cross-section and planar transmission electron microscopy. The number density of twins in textured thin films having their c axis normal to the substrate were found to be significantly higher than those in textured films having their c axis parallel to the substrate. Calculations of stresses induced in thin films as a result of the tetragonal to orthorhombic phase transition indicated that large shear stresses and strain energies were introduced in films with their c axis perpendicular to the substrate, thereby resulting in a high number density of twins in this orientation.
Electrochemical and structural characterization of Ni-Fe thin films
Authors: Bornstein J. G. , Lee C. H. , Capuano L. A. , Stevenson D. A.
Published: July 2002

The results of an investigation of the relationship between potentiodynamic anodic polarization behavior, composition, and microstructure for both sputtered and electroplated Ni-Fe thin-film alloys is described. The presence of high-temperature phases established by sputter deposition correlate directly with the compositional dependence of the passive current density. These results correlate exceptionally well with previous studies on the corrosion of Ni-Fe films under simulated atmospheric conditions. Electroplated films of the permalloy composition show significantly different passive behavior, as compared to sputter deposited films. Possible explanations for this anomaly are discussed.
A phenomenological model of switching in metal-thin insulator-semiconductor-semiconductor devices: A development of the analogy with the thyristor
Authors: Choi W. K. , De Lima J. J. , Owen A. E. , Reynolds S.
Published: July 2002

The present understanding of the basic operational parameters of two- and three-terminal metal-thin insulator-semiconductor-semiconductor (MISS) switches is reviewed briefly. Although several different approaches have been tried, since the first descriptions of MISS devices in 1972, agreement between theory and experiment is at best semiquantitative. Even a parameter as basic as the (dc) static threshold voltage is not accurately predicted by current models. In the present paper a thyristor analogy is developed more fully and quantitatively, drawing upon well-established theories of instabilities in p-n-p-n structures. By making the justified assumption that in MISS devices inversion at the semiconductor-insulator interface forms only when the switching voltage is attained, it is possible to predict the threshold voltage and its temperature dependence in two-terminal structures. The effect of base current on the switching voltage of three-terminal devices can similarly be accounted for in a phenomenological way. Comparisons are made with published data from several sources and the thyristor model is shown to provide good agreement between experimental data and calculated parameters (values of the threshold voltage) for MISS devices with silicon oxide insulating layers.
Theoretical study of electron-beam-heated carbon plasma C+++ emission
Authors: Whetstone Shawn C. , Kammash Terry
Published: July 2002

The response of an electron beam heated carbon plasma is studied with particular attention given to Civ(C+++) line emission at 2530 Å which has shown promise in plasma lasing schemes. A theoretical model which follows the plasma’s hydrodynamics, ionization dynamics, and beam-plasma interactions is used to identify two distinct plasma responses which depend upon the heating rate. The response’s difference is caused by variation of radiated power with plasma temperature and density. The model’s predictions qualitatively agree with experimental observations at the University of Michigan.
Modeling the non-quasi-static metal-semiconductor space-charge-region capacitance
Authors: Liou J. J. , Malocha D. C.
Published: July 2002

A non-quasi-static (frequency-dependent) space-charge-region capacitance model for metal-semiconductor junctions is developed. The model includes free-carrier charge effects in the space-charge region and is not based on the quasi-static approximation that assumes infinite free-carrier velocity and thus zero delay time in the space-charge region. Comparison between the conventional quasi-static depletion model and the present model is included, and susceptances measured from a differential voltage technique for a NiSi2 -nSi diode and from a phase spectroscopy method for a Pd-nGaAs diode are used to assess the accuracy of the model.
Ferroelectric-like phase transition at about 320 K and crystal growth of tungsten-bronze-type Na13Nb35O94
Authors: Abrahams S. C. , Brandle C. D. , Berkstresser G. W. , O’Bryan H. M. , Bair H. E. , Gallagher P. K. , Drotning W. D.
Published: July 2002

The atomic coordinates of tungsten-bronze-type Na13Nb35O94, determined by Craig and Stephenson [J. Solid State Chem. 3, 89 (1971)], are characteristic of one-dimensional ferroelectric crystals. The transition temperature from the ferroelectric-like to the hypothetical paraelectric phase is predicted to be about 340 K, on the basis of these room-temperature atomic coordinates. Calorimetric and dilatometric measurements indicate a gradual transition that is complete on heating by about 320 K. Dielectric permittivity and loss measurements exhibit broad but minor anomalies at about 340 K over the frequency range 0.4–100 kHz. The dielectric loss at 10 kHz is very low, at 0.0035. The spontaneous polarization is predicted to be about 0.3 C m−2. Crystals with maximum dimensions of 2 cm in diameter by 5 cm in length along the c axis have been grown.
Inert gas reactive ion etching damage to GaAs using inverted heterojunctions
Authors: Knoedler C. M. , Osterling L. , Heiblum M.
Published: July 2002

Selectively doped inverted heterojunctions containing a two-dimensional electron gas were used as a sensitive vehicle for monitoring dry processing damage. We found that the electron sheet concentration, strongly dependent on the total number of carriers in the GaAs cap layer, and the mobilities were significantly depressed even for very short exposures to low-voltage helium plasmas. Argon, which caused less degradation than helium, was found to increase the sheet carrier concentration and hence the mobility after prolonged exposure. The damage mechanism responsible for the carrier loss in both cases is most likely the production of traps. The subsequent carrier increase seen for the argon case is probably attributable to the creation of a very thin donorlike damage layer on the surface of the GaAs cap layer.
A study of the separative performance of an underexpanded jet interacting with background gas mixtures
Authors: Qian Shao-Sheng , Muntz E. P.
Published: July 2002

The separating action of a rarefied, underexpanded jet on a mixture of background gases has been applied to the separation of gaseous isotopes. The technique is known as the jet membrane separation process. In this paper we examine in greater detail the separative performance of rarefied jets from orifices and short tubes. The situation where there is a significant leakage of the background species into the jet’s stagnation region is studied in detail, as this condition is of interest for applications. Based on the Muntz, Hamel, and Maguire (MHM) analysis [AIAA J. 8, 1651 (1970)], simple predictions of the background species’ number density distributions and elementary separation factors for an orifice and a short tube are developed and compared to experiment. An expression for the separative power per orifice or per tube is derived. Experiments on separative performance with upflow were done and the results compared to the predictions.
Critical current measurements in YBa2(Cu1−xFex)3O7−δ
Authors: Wördenweber R. , Sastry G. V. S. , Heinemann K. , Freyhardt H. C.
Published: July 2002

The influence of Fe substituted for Cu in YBa2Cu3O7−δ on the microstructure and the critical properties has been studied. In the concentration regime 0≤x≤0.05, the microstructure changes drastically from a twin structure for x≤0.01 to a microdomain structure for x≥0.02. The average spacing of the twin or domain boundaries varies from ∼90 nm for x=0 to ∼5 nm for x≥0.02, thus providing an ideal system to test the role of boundary pinning. Large intragranular pinning forces are observed for x≤0.01 followed by a sudden drop to values ∼20 times smaller for x≥0.02. However, although d/a0 (twin-spacing/flux-line lattice parameter) changes drastically from d/a0>1 for x=0 to d/a0<1 for x≥0.02, the same field dependence of Fp is observed for all Fe concentrations, i.e., Fp∼B2c2b(1−b)2. It is, therefore, concluded that the twin boundaries are not significantly contributing to the flux pinning and that the decrease in Fp for 0.01≤x≤0.02 is related to the decrease of the upper critical field Bc2, which is caused by a strong reduction of the electron density of states at the Fermi surface.
Magneto-optic circulator for optical fiber transmission
Authors: Yan Xuejin , Xiao Shangqing
Published: July 2002

We have developed a polarization-independent optical circulator for optical transmission systems whose overall dimensions are 25×18×18 mm3. The insertion losses and the isolations of the circulator are about 2.0–2.2 and 20–21 dB, respectively, at a 1.3-μm wavelength. The circulator consists of ‘‘polarization separators’’ on either side of a Faraday rotator and a λ/2 retardation plate. The polarization separator separates the incident beam into two polarized parallel beams with orthogonal linear polarizations. The separation of the two beams is 3.2 mm. The Faraday rotator consists of a yttrium-iron-garnet (YIG) crystal and Sm-Co permanent magnets. The size of the YIG block is 2.25 mm length×4.5 mm width×1.5 mm thick. The half-wave plate of the circulator is made of a white mica.
Characterization of refractory W, WNx, and WSix films on GaAs using thermoreflectance measurements
Authors: Uchitomi Naotaka , Nagaoka Masami , Toyoda Nobuyuki
Published: July 2002

Thermal-wave measurements have been carried out for characterizing refractory W, WNx, and WSix films on GaAs substrates. Thermal-wave signals from these films were measured as a function of annealing temperature up to 900 °C, together with four-point probe measurements and x-ray diffraction analysis. The thermal-wave signals indicated a good linear relation to electrical resistivity, as shown in the cases of W and WNx films formed by sputtering deposition. This relation was associated with the grain formation and growth of W and W2 N microcrystals as the annealing temperature increased. It was found that the thermal-wave measurement was a very sensitive method for detecting phase transformation and degradation at the metal-GaAs interface, which were shown in the case of WSix films formed by low-pressure chemical vapor deposition.
Scattering of Hermite–Gaussian beams from an irregular surface
Authors: Kojima Toshitaka
Published: July 2002

The scattering of two-dimensional Hermite–Gaussian beams of arbitrary order from a conducting irregular surface is analyzed by using the Kirchhoff or physical optics approximation and the plane-wave spectrum representation. Both coherent and incoherent components of the mean scattered power are derived. It is shown that, for the normal incidence of a fundamental beam, the decrease of the beam radius or spot size gives rise to the decrease of the ratio of the coherent component to the incoherent one in the backscattering. However, for the obliquely incident case, the ratio is increased by the decrease of the beam radius. For the first-order beam incidence, the deep dip appearing in the specular direction in the mean scattered power pattern rapidly disappears as the surface roughness is increased.
Low-temperature polycrystalline Si film growth on amorphous insulators by reactive ion beam deposition
Authors: Yamada Hiroshi , Torii Yasuhiro
Published: July 2002

Polycrystalline Si (polysilicon) film growth on amorphous insulators, such as borosilicate glass, fused quartz, silicon oxide films, and silicon nitride films, was investigated by using the reactive ion beam deposition (RIBD) method proposed recently. The RIBD method is based on the use of reactive ionized species produced from SiH4 electron-cyclotron-resonance plasma and controlled in the low-energy region of less than 500 eV. Polysilicon films can be grown at the low temperature of 250 °C. In the growth temperature range between 550 and 700 °C, polysilicon films with the strong Si(220)-preferred orientation parallel to the substrate surface can be obtained. X-ray diffraction intensity corresponding to Si(220) lattice planes was clearly dependent on ion energy, which presented a maximal level at 70–130 eV.
Surface microanalytical study on the tribological interface between the sputtered fluoropolymer film and a sliding ball
Authors: Sugimoto Iwao , Miyake Shojiro
Published: July 2002

The degradation mechanism of high-performance, lubricating sputtered fluoropolymer films rubbed with a stainless-steel ball is investigated using surface analytical methods such as micro-X-ray-photoelectron spectroscopy, micro-Auger-electron spectroscopy, micro-Fourier-transform-infrared spectroscopy, and laser Raman spectroscopy. The perfluorocarbon groups in the sputtered film are increased by introducing oxygen into the plasma. This technique lowers the friction coefficient of the lubricating characteristics. The film is decomposed into amorphous carbon and poorly fluorinated carbon, producing the C■C-rich wear particles. After the decomposed film is worn from the trace, abrasion between the film substrate metals and the sliding ball occurs, and the interface loses its lubricative characteristics owing to the adhesion of the fresh metals. These fresh metals react with the reactive carbon, which is a result of the mechanochemical decomposition of the film, and are oxidized in air.
Si-depth profiling with Rutherford backscattering in photoresist layers; a study on the effects of degradation
Authors: van IJzendoorn L. J. , Schellekens J. P. W.
Published: July 2002

The reaction of a silicon-containing vapor with a photoresist layer, as used in some dry developable lithographic processes, was studied with Rutherford backscattering spectrometry. Degradation of the polymer layer under ion beam irradiation was observed, but it was found that this had no influence on the shape of the Si-depth profile and the total areal density. The RBS measurements were also verified with secondary ion mass spectrometry measurements. To describe the degradation process that occurs in polymeric layers upon ion beam exposure, elastic recoil detection measurements were carried out on polystyrene layers. Only one dose-independent cross section for carbon and only one for hydrogen were needed to describe the degradation behavior.
Extreme-ultraviolet illumination effects on the PBFA-I magnetically insulated ion diode
Authors: Maenchen J. E. , Woodworth J. R. , Mehlhorn T. A. , Renk T. , Ruiz C. L. , Foltz B. W. , Jaramillo W. H. , Wenger D. F. , Reyes P. , Guidotti K.
Published: July 2002

We have examined the effect of illuminating the anode in the Applied-B ion diode in Sandia’s PBFA-I accelerator with 60–100 kW/cm2 of extreme-ultraviolet (XUV) photons a few hundred nanoseconds prior to the accelerator shot. We find that XUV illumination significantly shortens the turn-on time of the ion beam, especially under conditions in which the normal ‘‘flashover’’ ion-source mechanisms are suppressed. In addition to the anticipated XUV photodesorption and photoionization of the anode material, some of the improvement seen with XUV illumination may be due to photoejection of electrons from the power feeds and their subsequent interaction with the anode source. Also, XUV illumination of a fine polypropylene weave located at the virtual cathode radius can preform the virtual cathode, dramatically reducing the turn-on time of the ion beam in the diode.
On the behavior of interaction of a Pt-related center with radiation-induced defects and the trace platinum detection
Authors: Weng Y. M. , Ohta E. , Sakata M.
Published: July 2002

The interaction of platinum (Pt) with electron irradiation-induced defects has been observed. Platinum in silicon increases irradiation-induced defects remarkably, especially the A center, and lowers the annealing temperature to 220 °C for the A center and to 140 °C for the divacancy and E center. The level Ea (0.23) in the Pt-doped silicon is the Pt(−/0) level, an acceptor like the A center. A method is suggested for activating the platinum in silicon with low-energy electron irradiation and subsequent thermal annealing and detecting it by deep level transient spectroscopy (DLTS).
Computation of quantum mechanical transmission probability from plane interfaces using electronic band structures
Authors: Lee E. Y. , Schowalter L. J.
Published: July 2002

A method for computing the quantum mechanical transmission probability (QMTP) from plane interfaces is presented. The method uses the electronic band structure of the material and the independent-electron approximation, and consists of a proper reduction of the three-dimensional problem to a one-dimensional problem, using a generalized form of the WKB wave functions, and matching the wave functions at the interface to preserve the continuity of a generalized probability current and density. The method was used to compute the QMTP at the interface of a simple metal and the Si(100) and Si(111) surface for ballistic electrons traveling normal to the interface at the Schottky image barrier maximum. The result shows that the crystal orientation and the location of the band minimum affect the QMTP.
A high quantum efficiency GaInAs-InP photodetector-on-silicon substrate
Authors: Razeghi M. , Omnes F. , Blondeau R. , Maurel Ph. , Defour M. , Acher O. , Vassilakis E. , Mesquida G. , Fan J. C. C. , Salerno J. P.
Published: July 2002

We report the first Ga0.47In0.53As-InP photodetectors fabricated on silicon substrates, using the low-pressure metalorganic chemical vapor deposition growth technique. Quantum efficiencies of 0.34, 0.88, and 0.92, A/W at wavelengths of 0.8, 1.3, and 1.55 μm, respectively, have been obtained for the devices without antireflection coating. A reverse leakage current of 100 μA at −10 V bias was measured for 250-μm-diam diodes.
Abrupt heterointerfaces in Al0.35Ga0.65As/Al0.05Ga0.95As/Al0.35Ga0.65As quantum well structure grown by liquid-phase epitaxy
Authors: Chen Jiahn-Ann , Lee Jirhan-Huei , Lee Si-Chen , Lin Hao-Hsiung
Published: July 2002

The Al0.35Ga0.65As/Al0.05Ga0.95As/Al0.35Ga0.65As quantum well structure with a 70-Å-thick well has been successfully fabricated by liquid-phase epitaxy at 685 °C. The transmission electron microscope cross-section technique is applied to study the uniformity of the quantum well and the transition width at the heterojunction interface. An interesting phenomenon observed for the first time during liquid-phase epitaxy growth is that the interface of Al0.05Ga0.95As grown on Al0.35Ga0.65As is rather flat and sharp whereas the opposite growth sequence gives rise to a wavy interface. The transition width is less than 10 Å at the Al0.05Ga0.95As/Al0.35Ga0.65As interface but is about 30–50 Å at the inverted Al0.35Ga0.65As/Al0.05Ga0.95As interface. These values are much less than those reported in the literature. The peak energy of the photoluminescence spectrum reveals the quantum size effect.
Interaction between point defects and dislocation loops as the phenomenon able to reduce anomalous diffusion of phosphorus implanted in silicon
Authors: Servidori M. , Solmi S. , Zaumseil P. , Winter U. , Anderle M.
Published: July 2002

Phosphorus was implanted at doses below amorphization threshold in virgin silicon and in silicon containing interstitial dislocation loops. The loops were formed by high-dose Si+ implantation and 900 °C, 30 min annealing. Triple-crystal x-ray diffraction and junction depth measurements combined with secondary ion mass spectrometry were used for the analysis of implant defects and the determination of P distribution, respectively. Annealings were carried out in furnace in the range between 600 and 900 °C, and by electron beam at 1000 °C for 10 s. The results obtained show that the presence of loops strongly reduces the phosphorus anomalous diffusion. This phenomenon is the consequence of the absorption by the loops of the interstitial excess coming from dissolution of the clusters produced by the P implant. The influence of the loop position with respect to the P distribution on the extent of P diffusivity is analyzed and discussed.
Strained-layer superlattices for reduction of dislocation density in GaAs1−xPx on GaAs by organometallic vapor-phase epitaxy
Authors: Cao D. S. , Chen C. H. , Fry K. L. , Reihlen E. H. , Stringfellow G. B.
Published: July 2002

This paper presents results of organometallic vapor-phase-epitaxial growth of low dislocation density GaAs1−xPx on GaAs, utilizing a thin compositionally graded layer (2 μm) and a strained-layer superlattice (SLS) to reduce the dislocation density. The grown structure consists of three sections: (1) a 2-μm GaAs1−xPx graded layer with final phosphorus composition x1 on a GaAs substrate; (2) a GaAs1−yPy /GaAs1−y′Py′ SLS; and (3) a 1-μm GaAs1−xPx top layer with x=0.4. Three types of grading layers were investigated: sublinear, hyperlinear, and linear. The linear grading is found to give the lowest dislocation density. However, the 2-μm-thick linearly graded region is definitely too thin to release all the misfit strain. The residual strain produces dislocations after the SLS has been grown, resulting in dislocation generation in the constant composition layer. A novel method has been developed to eliminate this problem. The phosphorus composition at the end of the grading, x1, is made intentionally larger than both the average composition of the SLS and the top layer to prevent residual strain relief during the growth of the top layer. Using this ‘‘overshoot grading’’ method, the etch pit density in the top layer is reduced from 3×107/cm2 without the special structure to 6.5×105/cm2. The reduction of dislocation density by the SLS has been systematically studied with variation of the SLS parameters, including the thickness of each layer, the number of periods, and the composition change in the SLS. The results show that the SLS itself can reduce the dislocation density by about one order of magnitude. The combination of the SLS with overshoot grading yields the most effective elimination of dislocations. Using the optimum conditions, GaAs0.6P0.4 with good surface morphology, strong visible photoluminescence intensity, and a dislocation density of 6.5×105/cm2 has been obtained.
Chemical oxygen iodine laser of extremely high efficiency
Authors: Yoshida S. , Endo M. , Sawano T. , Amano S. , Fujii H. , Fujioka T.
Published: July 2002

We have developed a highly efficient chemical oxygen iodine laser with industrial uses in mind. A maximum overall efficiency of 40% has been achieved at a power level of 200 W. This efficiency makes the running cost of the iodine laser comparable to that of typical yttrium-aluminum-garnet lasers. The key issues for achieving high efficiency are discussed. Using the present system, we were successful in drilling a 1-mm-thick steel plate at a power level of 60 W, which we believe is the first demonstration of material processing by a chemical oxygen iodine laser.
Sorbed water and intrinsic stress in composite TiO2-SiO2 films
Authors: Sankur H. , Gunning W.
Published: July 2002

Water sorption and stress properties of mixed composition TiO2-SiO2 thin films, formed by reactive evaporative codeposition, were studied. These properties were observed to depend on the composition, and also on the reactive gas pressure and annealing conditions. Process conditions to produce water-free films were established. Detailed stress studies in vacuum and in ambient indicated that intrisic stress also depends on ambient conditions, with irreversible changes occurring during the initial exposure of the films to ambient. This induced opposite types of stress on TiO2- and SiO2-rich films. These observations can be explained in terms of the structural and compositional properties of the films.
Flexible carbonaceous and graphitized films by pyrolytic chemical-vapor-deposition method from hydrocarbons containing oxygen atoms
Authors: Fukuda M. , Mizogami S. , Matsuoka R. , Nogami K. , Yoshino K.
Published: July 2002

Carbonaceous films with high conductivity have been prepared by a pyrolytic chemical-vapor-deposition method using hydrocarbons containing oxygen atoms, phenols, carboxylic acids, etc. The films obtained are self-supporting and flexible. The electrical conductivities of the films depend on the pyrolyzing temperature but not remarkably on the kind of raw materials. The films are converted to high-quality graphitized films with conductivity of 1.6×104 S/cm by heating under an Ar atmosphere to 2800 °C. The electrical conductivity and thermoelectric power of the films are examined as a function of the heat-treatment temperatures. The excellent property of the films obtained in this study seems to arise from the effect of oxygen atoms in the process of condensed aromatic ring formation by pyrolysis.
Effects of compositional variations on the properties of superconducting (Bi,Pb)2Sr2Ca2Cu3Oδ
Authors: Green S. M. , Mei Yu , Manzi A. E. , Luo H. L. , Ramesh R. , Thomas G.
Published: July 2002

The results of a systematic study on compositional variations within the Bi2−xPbxSr2Ca2Cu3Oδ superconducting system are reported. It is found that a secondary phase (or phases), likely composed of Pb-Sr-Ca-Cu-O, forms when x exceeds 0.35, indicating that this is an upper limit on the amount of Pb which replaces Bi. Varying the Sr:Ca or Bi:Ca ratio has dramatic effects on the resistive and magnetic properties. It is suggested that there is a very limited range of solution among the alkaline-earth elements. Bi occupying Ca sites is probably deleterious for both Tc and the structural stability of the 2223 phase. Preliminary results on textured ceramic samples have yielded Jc (77 K) as high as 580 A/cm2 .
Study of charge-transfer interactions in polyvinylpyridine-halobenzoquinone complexes by x-ray photoelectron spectroscopy
Authors: Tan K. L. , Tan B. T. G. , Kang E. T. , Neoh K. G.
Published: July 2002

The charge-transfer (CT) interactions in electroactive polymeric complexes formed by nonconjugated polymers: poly-2-vinylpyridine, poly-4-vinylpyridine, and various halobenzoquinone electron acceptors such as: o-chloranil, p-chloranil, o-bromanil, and p-fluoranil have been investigated by means of x-ray photoelectron spectroscopy (XPS). In spite of the relatively high degree of CT interactions, the conductivity of the complexes remains low and in the range of 10−11–10−6 S cm−1. XPS core-level spectra for halogens, nitrogen, and oxygen allow the steric hindrance to CT interactions in the various complexes to be investigated and compared. In all the complexes, the presence of a halogen anion, a positively charged pyridinium nitrogen, and an oxygen anion is observed. This is indicative that CT interactions may have resulted in adducts arising from the formation of linkages between the polymers and the acceptors.
On the I-V characteristics of contacts made of Al/Ti:W films on amorphized (100)Si
Authors: Berger S. , Komem Y.
Published: July 2002

The effect of Ar ion implantation energy to amorphize the (100)Si substrate and heat treatments on the I-V characteristics was studied. It was found that the electrical resistance of the contacts increased as a result of increasing the ion implantation energy, the heat treatment temperature, and time. The I-V characteristics of the contacts are analyzed with a model of electrical conductivity in amorphous solids. Based on this model and the experimental results, the distance between two adjacent ionized defects that are active in the electrical conductivity, was calculated. The effect of ion implantation energy and the heat treatments on the I-V characteristics are correlated to the microstructural and compositional alterations in the amorphous Si region of the contacts.
Origin of the pulse response characteristics of zinc oxide varistors
Authors: Modine F. A. , Wheeler R. B. , Shim Youngjae , Cordaro James F.
Published: July 2002

Pulse response characteristics are reported for simple varistor materials in the ZnO-Bi2O3-MnO2 system. It is shown that small additions of Li2O or In2O3 can enhance or eliminate the materials inductive behavior, which is responsible for voltage overshoot and current undershoot. A possible connection of the inductive behavior with deep electron traps, which is suggested by the equal time constants at room temperature of the inductive current rise and the electron emission from the traps, is examined. Measurements of the pulse response characteristics at low temperature reveal a weak temperature dependence that fails to support such a connection. A phenomenological model is given that predicts the varistor pulse response characteristics. Both the experimental results and the model predictions are discussed in relation to theories that connect the inductive response to electron holes that become trapped at varistor barriers.
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u ac magnetic susceptibility of gadolinium thin films
Authors: Salas F. H. , Mirabal-García M.
Published: July 2002

We report measurements of the ac magnetic susceptibility on Gd(0001)/W(110) thin films grown in ultrahigh vacuum. The measurements were made by using a pickup coil, in which the geometry and the number of turns were optimized. We applied an alternating magnetic field of about 2 Grms at frequencies of 180 and 340 Hz. The growth mode and the deposition rate of the Gd films were determined by performing conventional Auger electron spectroscopy during film growth. In films with thickness larger than 10 nm our technique is sensitive up to 1016 atoms/Grms , which allowed us to study the critical behavior of the magnetic susceptibility as the Curie temperature is approached from above, T→T+C . A sharp maximum, which may be related to the Hopkinson effect, is observed at a temperature TH ≊289 K.
Hot-electron properties of GaAs planar-doped barrier diodes
Authors: Couch N. R. , Kearney M. J.
Published: July 2002

A study has been made of hot-electron effects in various designs of GaAs planar-doped barrier diodes under high bias. Monte Carlo simulations suggest that hot-electron intervalley transfer provides a fundamental limit to the resistance of these devices. From our results, we speculate on an upper cutoff frequency of 350 GHz for planar-doped barrier diodes.
Metalorganic chemical vapor deposition of superconducting YBa2Cu3O7−x in a high-speed rotating disk reactor
Authors: Noh D. W. , Gallois B. , Chern C. S. , Caracciolo R. , Kear B. H. , Zawadzki P. A. , Tompa G. S. , Norris P. E.
Published: July 2002

Metalorganic chemical vapor deposition (MOCVD) of YBa2Cu3O7−x films on (100) SrTiO3 was performed in a high-speed rotating disk reactor. Metal β-diketonates were used as source materials. Energy dispersive spectroscopy analysis showed as-grown and post-annealed samples to have a composition matching that of superconducting thin-film standards. X-ray data showed the annealed films to be highly oriented with the c axis perpendicular to the substrate. The best films exhibited an onset temperature of 90 K and zero resistance at 88 K. The width of the superconductive transition (<2 K) is the best value thus far reported for 123 films grown in a commercially available MOCVD system.
Elastic property measurements in fluid-filled porous materials
Authors: Jungman A. , Quentin G. , Adler L. , Xue Q.
Published: July 2002

The acoustical properties of fluid-filled sintered porous materials have been studied using ultrasonic wave irradiation and signal analysis in both time and frequency domains. The samples studied have a metallic frame with average grain sizes ranging from 18 up to 700 μm. They exhibit a high value of porosity (≂35%). The interest of this study is related to the fact that our samples have a rather similar porosity but grain sizes are different by a factor of more than 30. Experimental results of velocity and attenuation measurements are presented. Variation of the bulk velocities in the different samples is interpreted by considering a theoretical approach based on the poroelastic model, whereas attenuation mechanisms are explained by a simplified model of scattering related to the particle size.