bluuebunny/crossref_metadata_2025 huggingface dataset:
Ordering effects on the electrical characteristics of Ga0.5In0.5P grown by metalorganic chemical vapor deposition
Authors: Lee M. K. , Horng R. H. , Haung L. C.
Published: July 2002

The relationship between electrical characteristics and structural ordering in undoped and Zn-doped Ga0.5In0.5P films grown by metalorganic chemical vapor deposition is investigated. The Schottky diode was used to examine the electrical properties of the undoped samples with ordered and disordered structures. With the same carrier concentration (∼1.5×1016 cm−3), the diode fabricated on the ordered film shows a degraded current-voltage characteristic. As the carrier concentration of Zn-doped Ga0.5In0.5P increases above 1.5×1018 cm−3, the energy gap of the ordered structure is larger than that of the disordered structure. It was found that the hole mobility of the ordered film is lower than that of the disordered film with the similar doping level. The behavior could be attributed to the existence of antiphase boundaries within the ordered structure. The antiphase boundaries can act as recombination centers and/or scattering centers and result in the extraordinary electrical properties of the ordered samples.
Dissociation of P-H, As-H, and Sb-H complexes in n-type Si
Authors: Pearton S. J. , Lopata J.
Published: July 2002

Reverse-bias annealing of P-H, As-H, and Sb-H pairs in hydrogenated Schottky diodes was used to establish the dissociation energies of these complexes. The annealing kinetics are found to be first order, with the dissociation frequencies thermally activated of the form ν=ν0e−ED/kT. The dissociation energies ED are found to be 1.20±0.05 eV for P-H, 1.12±0.05 eV for As-H, and 1.13±0.05 eV for Sb-H. The relative insensitivity of these values to the actual donor species is consistent with the currently accepted model in which the hydrogen passivates the electrical activity of the donor by attaching to one of the donors Si nearest neighbors at an antibonding interstitial site.
Nuclear magnetic resonance and infrared absorption studies of hydrogen incorporation in polycrystalline diamond
Authors: McNamara K. M. , Levy D. H. , Gleason K. K. , Robinson C. J.
Published: July 2002

Hydrogen incorporated into polycrystalline diamond was found to correlate with the optical absorption in the 8 to 10 μm wavelength IR region, where transparency is desired. In this first detailed study of diamond films by 1H NMR, average concentrations were found to be <0.25 at. % H. However, segregation produces regions of extremely high local hydrogen density as evidenced by a broad (50–70 kHz) Gaussian NMR component. The majority of this clustered hydrogen is rigidly held, while a fraction undergoes motional narrowing at room temperature, most likely due to methyl group rotation. Sites at grain boundaries are capable of accounting for a significant fraction of this hydrogen, as are defects and voids within the crystal or a heavily hydrogenated phase stable at the deposition temperature.
Electrical and structural properties of Ga0.51In0.49P/GaAs heterojunctions grown by metalorganic vapor-phase epitaxy
Authors: Paloura E. C. , Ginoudi A. , Kiriakidis G. , Frangis N. , Scholz F. , Moser M. , Christou A.
Published: July 2002

Undoped and Se-doped Ga0.51In0.49P/GaAs single heterojunctions grown by metalorganic vapor-phase epitaxy (MOVPE) are characterized with deep-level transient spectroscopy and transmission electron microscopy (TEM). The undoped MOVPE material, grown at 710 °C, is characterized by a deep electron trap with an activation energy that takes values in the range 700–900 meV. Se doping suppresses the formation of this trap when the doping level is higher than 5×1017 cm−3. Furthermore, Se doping suppresses the persistent photoconductivity that is observed in the undoped samples. Finally, analysis with cross-section TEM reveals that the samples undergo partial spinodal decomposition in a direction nearly vertical to the interface.
GaAs/AlAs quantum wells for electroabsorption modulators
Authors: Pezeshki B. , Lord S. M. , Boykin T. B. , Harris J. S.
Published: July 2002

We demonstrate both theoretically and experimentally that the quantum-confined Stark effect leads to larger absorption changes in GaAs/AlAs quantum wells compared to the more conventional GaAs/AlGaAs system due to the higher Γ confinement. The lower indirect valleys in AlAs do not degrade the performance and the exciton resonance is maintained at higher-energy shifts. The improvement in exciton oscillator strength is nearly 50% with a 70-meV shift. The greater exciton strength at high fields has important applications for optical modulators and switches that operate at the long-wavelength side of the zero-bias exciton.
Strontium titanate thin films by rapid thermal processing
Authors: Joshi P. C. , Krupanidhi S. B.
Published: July 2002

SrTiO3 thin films having perovskite structure were fabricated by sol-gel technique with a post-deposition rapid thermal annealing treatment at 550 °C for 60 s. The films exhibited good structural, dielectric, and insulating properties. The measured dielectric constant and loss factor at 100 kHz were 225 and 0.008, respectively. Unit area capacitance of 3.5 fF/μm2 and leakage current density of less than 10−8 A/cm2 were obtained for 500–800 nm thick films. A charge storage density of 18.3 fC/μm2 was obtained at an applied electric field of 100 kV/cm. The resistivity of these films was in the range of 1010–1013 Ω cm. The C-V measurements on films in metal-insulator-semiconductor (MIS) configuration indicated good Si/SrTiO3 interface characteristics.
Thermal imaging by ordered bundles of silver halide crystalline fibers
Authors: Paiss Idan , Katzir Abraham
Published: July 2002

Flexible bundles consisting of 70–2000 silver halide optical fibers were fabricated by extrusion of crystalline preforms. Such devices transmit in the mid-IR spectral region (4–20 μm), and are suitable for delivering thermal images of near room-temperature objects. Small diameter (1–3 mm) image guides of this type can thus map the temperature distribution of areas difficult to access by conventional devices. The fabrication of these guides, their optical properties, and their imaging capability are discussed.
Nonuniformities of native oxides on Si(001) surfaces formed during wet chemical cleaning
Authors: Aoyama T. , Yamazaki T. , Ito T.
Published: July 2002

We studied the uniformity of native oxide formed on Si(001) surfaces during wet chemical cleaning. Uniformity was determined by surface morphology at the initial stage of photoexcited fluorine etching. Since photoexcited fluorine etches Si 40 times faster than it etches Si oxide, it highlights Si native oxides on a Si surface making them observable by scanning tunneling microscopy or atomic force microscopy. Boiling in a HCl-H2O2-H2O (1:1:4) solution formed 30–70-nm islands of oxides. The regions between the islands were not oxidized. Boiling in NH4OH-H2O2-H2O (1:1.4:4) also formed oxide islands 30–70 nm in diameter, but the interisland regions were slightly oxidized. Boiling in a HNO3 solution resulted in a native oxide with pinholes at a density of 5×109 cm−2
Effects of thermal annealing on porous silicon photoluminescence dynamics
Authors: Ookubo Norio , Ono Haruhiko , Ochiai Yukinori , Mochizuki Yasunori , Matsui Shinji
Published: July 2002

Photoluminescence (PL) spectra and decay dynamics were studied for the spontaneously oxidized porous Si with subsequent various thermal annealing procedures. The PL decay was highly nonexponential and well described by the stretched-exponential function. The PL lifetime was shorter for the higher PL photon energy, but at the same photon energy it decreased by an order of magnitude by the thermal annealing in N2 gas, in parallel with the large PL intensity decrease. This PL quenching upon the annealing is presumably ascribable to both the structural changes and dangling bond formations in porous Si, as suggested by ESR measurements and the annealing experiments in H2 gas.
Random telegraph signals arising from fast interface states in metal-SiO2-Si transistors
Authors: Tsai Ming-Horn , Muto Hirotaka , Ma T. P.
Published: July 2002

Using fast sampling rates, we have been able to resolve random telegraph signals (RTSs) associated with trapping-detrapping of channel electrons by individual fast interface states in small metal-SiO2-Si transistors. Possible reasons why such fast RTSs have not been reported in the past are suggested. Some characteristics of the RTSs arising from fast interface states are presented and compared with those from the slow traps.
Traps in semi-insulating InP studied by thermally stimulated current spectroscopy
Authors: Fang Z.-Q. , Look D. C. , Zhao J. H.
Published: July 2002

Traps in Fe-doped semi-insulating InP samples have been studied by thermally stimulated current spectroscopy with IR (hν≤1.12 eV) excitation at 81 K. The possible involvement of native defects in determining the compensation mechanisms is suggested based on the observation of other than the usual 0.64 eV Fe-related activation energy for the dark current in one of the four samples supplied from different sources. A metastable behavior of traps in another sample was found and explained by a charge-controlled defect reaction model. Three out of the six traps observed are suggested to be electron traps and one among the other three traps is believed to be a hole trap.
Multichip module using multilayer YBa2Cu3O7−δ interconnects
Authors: Burns M. J. , Char K. , Cole B. F. , Ruby W. S. , Sachtjen S. A.
Published: July 2002

We report the first use of high temperature superconductors for multilayer interconnection of bare semiconductor die to form multichip modules. Ten die with a total of 160 pads were interconnected on a 3.4 cm2 substrate. The interconnections were a combination of YBa2Cu3O7−δ lines and vias on two wiring levels separated by an epitaxial insulating layer. Connection between the two YBa2Cu3O7−δ wiring layers was accomplished by the use of superconducting vias through the insulator. Two similar multilayer multichip module designs, with 30- and 10-μm-wide YBa2Cu3Oδ−7 lines, were constructed.
Measured and simulated electron energy distribution functions in a low-pressure radio frequency discharge in argon
Authors: Turner M. M. , Doyle R. A. , Hopkins M. B.
Published: July 2002

We report a combined experimental and computational study of a low-pressure radio frequency discharge in argon. We have determined the electron energy distribution function experimentally using a Langmuir probe system and by simulation using the particle in cell method. A close comparison of these data shows good agreement over pressures from 20 to 200 mTorr. This pressure range encompasses the putative transition from a stochastic to an ohmic electron heating mode [V. A. Godyak and R. B. Piejak, Phys. Rev. Lett. 65, 996 (1990)]. The simulation does show such a transition, and we agree with earlier estimates of the transition pressure.
Study of photoresponse of high-T
c Y-Ba-Cu-O superconducting ultrathin films using a picosecond laser pulse train
Authors: Shi L. , Huang G. L. , Lehane C. , Kim D. H. , Kwok H. S.
Published: July 2002

We have systematically studied the photoresponse of Y-Ba-Cu-O (YBCO) ultrathin films to a train of picosecond laser pulses. The onset and decay of nonequilibrium superconductivity due to different levels of optical excitation can be observed within the single pulse train. Thermal and nonthermal responses can be clearly identified. In addition, the superconducting film resistance was found to increase progressively with laser power above the onset threshold. The YBCO thin films were possibly excited into a nonequilibrium intermediate (resistive) state from the superconducting state. The laser intensity dependence indicated a nonthermal origin for these voltage pulses.
Optical reflectivity of 3C and 4H-SiC polytypes: Theory and experiment
Authors: Lambrecht W. R. L. , Segall B. , Suttrop W. , Yoganathan M. , Devaty R. P. , Choyke W. J. , Edmond J. A. , Powell J. A. , Alouani M.
Published: July 2002

Experimental and theoretical optical reflectivity in the range 4–10 eV are reported for the 3C and 4H polytypes of SiC. The calculations used the linear muffin-tin orbital method and the local density approximation. Good agreement in peak positions and line shape is obtained except for a nearly constant shift of ∼1.00 eV.
Improved strain analysis in semiconductor crystals by x-ray diffractometry enhanced with ultrasound
Authors: Zolotoyabko E. , Sander B. , Komem Y. , Kantor B.
Published: July 2002

A new method that combines double-crystal x-ray diffraction with high-frequency ultrasonic excitation is proposed in order to study small strains in semiconductor crystals. Ultrasound having a wavelength a little less than the x-ray extinction length affects the diffraction profile very near the Bragg position and, therefore, permits the detection of very small profile broadenings caused by lattice distortions. Experimental results obtained for fresh etched, boron-doped (001)Si samples, using (004)-reflection and Cu Kα radiation, have shown the presence of microstrains with the mean value of 〈Δd/d〉=5×10−6. Such small lattice distortion cannot be measured by standard double-crystal diffractometry without ultrasound.
Fabrication of Josephson junctions using an Al/Ta/Nb structure for x-ray detection
Authors: Morohashi Shin’ichi , Gotoh Kohtaroh , Komiya Satoshi
Published: July 2002

We fabricated Josephson junctions using an Al/Ta/Nb structure for x-ray detection. We selected a Ta layer to be the absorber of quasiparticles generated by incident x rays to the junction because of the long lifetime of quasiparticles and the absorption efficiency for x rays. A Nb layer served not only as a barrier for quasiparticle rejection, but also as a buffer layer for deposition of a body centered cubic Ta layer without heating during deposition. An Al layer acted as not only an overlayer for the formation of the AlOx barrier, but also as a layer for quasiparticle trapping. The Nb/AlOx-Al/Ta/Nb junction showed excellent current-voltage characteristics.
Gigahertz switching behavior of polarization-bistable InGaAsP/InP lasers under high-frequency current modulation
Authors: Klehr A. , Müller R , Voss M. , Bärwolff A.
Published: July 2002

The switching dynamics between TE- and TM-polarization states is studied in a strained ridge-waveguide InGaAsP/InP laser that exhibits TE/TM bistability. Using current modulation with frequencies between 50 and 500 MHz, three types of emission are distinguished. With increasing modulation amplitude, the laser runs through a region of TE emission, a range of stochastic switching between TE and TM modes, and a third region of regular polarization switching. The minimum modulation amplitude for regular switching rises strongly with frequency while the respective switching times decrease from about 700 ps at 50 MHz down to 250 ps around 500 MHz, corresponding to gigahertz mode switching.
Laser patterning of Y-Ba-Cu-O thin-film devices and circuits
Authors: Sobolewski Roman , Xiong W. , Kula W. , Gavaler J. R.
Published: July 2002

We report our studies on electrical properties of Y-Ba-Cu-O test devices and circuits fabricated using a laser-writing patterning technique. The patterning procedure is noninvasive, does not require a patterning mask, and does not contaminate nor damage the surface of patterned films. Our laser-written, oxygen-rich lines (typically 4–100 μm wide) possess excellent superconducting properties with zero resistivity at 89.5 K and critical current densities of above 2 MA/cm2 at 77 K. On the other hand, oxygen-poor regions are semiconducting and exhibit thermally activated transport, well described by a three-dimensional, variable-length hopping process. Their resistance below 100 K is above 10 MΩ/square. A number of test structures patterned by laser writing, such as a microbridge, coplanar transmission line, open-ended microwave resonator, photoconductive switch, and Y-Ba-Cu-O field-effect transistor, have been presented.
Small-signal modulation and temperature dependence of the tunneling injection laser
Authors: Davis L. , Sun H. C. , Yoon H. , Bhattacharya P. K.
Published: July 2002

Recently, we demonstrated a novel laser structure, called the tunneling injection laser, where the electrons are injected into the active lasing quantum well region via tunneling. High performance results for this device have now been demonstrated. A To of 160 K was found from temperature-dependent measurements (25–70 °C). High differential gain (5.5×10−16 cm2) and modulation bandwidth (12.5 GHz) have been attained relative to other single quantum well lasers.
Determination of the superconducting current path in Bi2223/Ag tapes
Authors: Cho J. H. , Maley M. P. , Willis J. O. , Coulter J. Y. , Bulaevskii L. N. , Haldar P. , Motowidlo L. R.
Published: July 2002

We have measured the anisotropic transport properties of Bi2223/Ag tapes with and without the silver sheath. The anisotropy ratio of the resistivity along the rolling plane to the resistivity perpendicular to the rolling plane (∼4–10) is orders of magnitude smaller than single-crystal anisotropy ratios. Results are consistent with current flow along crystallographic ab planes even for transport normal to the tape plane.
Structural properties and interfacial layer formation mechanisms of PbTiO3 thin films grown on p-Si substrates
Authors: Kim T. W. , Yoon Y. S. , Yom S. S. , Lee Jeong Yong
Published: July 2002

Ferroelectric PbTiO3 thin films were grown on Si(100) substrates by metalorganic chemical vapor deposition via thermal pyrolysis at relatively low temperature (∼500 °C) using Pb(tmhd)2, Ti(OC3H7)4, and N2O. Transmission electron microscopy results suggested that the grown PbTiO3 films were polycrystalline layers. Auger depth profiles indicated that the compositions of the as-grown films consisted of lead, titanium, and oxygen uniformly distributed throughout the films and that the films exhibited smooth interfaces. These results indicate that the growth of polycrystalline PbTiO3 layers instead of epitaxial films originated from the formation of an interfacial amorphous layer prior to the creation of the films. Further, a mechanism for the formation of an interfacial layer between the PbTiO3 thin films and the p-Si substrates is presented.
High-power diode-laser-pumped InAsSb/GaSb and GaInAsSb/GaSb lasers emitting from 3 to 4 μm
Authors: Le H. Q. , Turner G. W. , Eglash S. J. , Choi H. K. , Coppeta D. A.
Published: July 2002

Diode-array-pumped GaInAsSb/GaSb and InAsSb/GaSb double heterostructure lasers operated at 85 K yielded 95 mW average and 1.5 W peak power per facet at 3 μm, and 50 mW average and 0.8 W peak power facet at 4 μm. The highest operational temperature was 210 K for the 3-μm quaternary and 150 K for the 4-μm ternary.
Zero-dimensional states in macroscopic resonant tunneling devices
Authors: Sakai J. W. , Main P. C. , Beton P. H. , La Scala N. , Geim A. K. , Eaves L. , Henini M.
Published: July 2002

We demonstrate that it is possible to observe transport through individual tunneling channels due to zero-dimensional states in large area resonant tunneling devices (RTD). These localized states are found to be related to the presence of donor impurities in the vicinity of the quantum well but their binding energies are larger than that due to a single isolated hydrogenic donor. The states give rise to additional peaks in current voltage below the threshold for the main resonant peak. These peaks are visible in RTD with essentially any lateral dimension provided the current is measured with sufficient sensitivity.
Photoluminescence of Si/SiGe/Si quantum wells on separation by oxygen implantation substrate
Authors: Nayak D. K. , Usami N. , Fukatsu S. , Shiraki Y.
Published: July 2002

A study of the photoluminescence properties of Si/SiGe/Si quantum wells grown on separation by oxygen implantation (SIMOX) substrate by gas source molecular beam epitaxy is presented. Intense photoluminescence and carrier confinement in the quantum well are demonstrated. It is found that buried SiO2 isolates the top silicon on insulator from the back Si of SIMOX, and alters the photoluminescence properties of SIMOX compared to those of bulk Si. The SOI layer is found to be free of any strain. A SiO2/Si/SiO2 optical cavity is proposed by depositing SiO2 on SIMOX. A substantial enhancement of the photoluminescence intensity of SiGe quantum well is found, which is attributed to the optical confinement of incident beam in the cavity.
Electronic mobility gap structure and deep defects in amorphous silicon-germanium alloys
Authors: Unold Thomas , Cohen J. David , Fortmann Charles M.
Published: July 2002

Amorphous hydrogenated silicon-germanium alloys have been studied using a variety of junction-capacitance techniques to establish the dependence of the mobility gap electronic structure and the density of deep defects on the germanium content. The Urbach tail slope is observed to be nearly constant over the whole alloy range. The energy position of the dominant deep defect band near midgap is deduced and evidence for a shallower unoccupied defect band undergoing a large lattice relaxation is also observed. The total density of deep defects is found to increase exponentially with increasing germanium content and the details of this increase are shown to be consistent with a weak bond to dangling bond conversion model.
Generation of large, high density, homogeneous plasma by capillary discharge
Authors: Ehrlich Y. , Cohen C. , Zigler A. , Wark J. S.
Published: July 2002

Generation of 10-mm-long homogeneous plasmas with densities above 1020 cm−3 is reported. The plasma parameters are simply controlled by varying the discharge voltage. High homogeneity was achieved by using a long rectangular expansion channel made out of a high thermal conductivity alloy.
Nonlinear microwave impedance of superconductors and ac response of the critical state
Authors: Sridhar S.
Published: July 2002

The hysteretic ac response of the current-induced critical state of superconducting wires (strips of circular or rectangular cross-section) is expressed in a surface impedance formulation. The results for the rectangular strip are shown to be in good agreement with experimental results on the high power nonlinear response of superconducting microwave devices. The approach provides a proper framework to understand such nonlinear response.
Submicrometer fluorescence microprobe based on Bragg-Fresnel optics
Authors: Kuznetsov S. M. , Snigireva I. I. , Snigirev A. A. , Engström P. , Riekel C.
Published: July 2002

An x-ray fluorescence microprobe with linear Bragg-Fresnel lens was tested at the European Synchrotron Radiation Facility Microfocus beamline. A focal line with a width of 0.8 μm was observed using the knife-edge technique at a wavelength of 0.85 Å (14.6 eV). Wiener filtering with the Fast Fourier Transformation was applied to solve a convolution equation to evaluate the size of the probe from fluorescence data.
Experimental and theoretical results for a two-dimensional metal photonic band-gap cavity
Authors: Smith D. R. , Schultz S. , Kroll N. , Sigalas M. , Ho K. M. , Soukoulis C. M.
Published: July 2002

We demonstrate, by both microwave experiments and numerical simulation, that a two-dimensional lattice of metal cylinders can form a complete photonic band-gap (PBG) structure. The band structure exhibits a single broad PBG extending from zero frequency to a threshold frequency, above which all modes may propagate in some direction. A single cylinder removed from the lattice produces a defect mode localized about the defect site, with an energy density attenuation rate of 30 dB per lattice constant. The frequency dependence of the transmission through a finite thickness of this structure is also calculated in good agreement with the measurements. We suggest that the defect mode resonant cavity when formed by appropriate low loss metals may be advantageous for use in PBG high energy accelerator structures that we are evaluating.
Effects of gas flow ratio on silicon carbide thin film growth mode and polytype formation during gas-source molecular beam epitaxy
Authors: Tanaka Satoru , Kern R. Scott , Davis Robert F.
Published: July 2002

Silicon carbide thin films have been grown on vicinal 6H-SiC(0001) substrates by gas-source molecular beam epitaxy at 1050 °C. The effect of gas flow ratios (C2H4Si2H6=1,2,10) on the growth mode was examined via cross-sectional high resolution transmission electron microscopy and in situ reflection high energy electron diffraction. Step flow, step bunching, and the deposition of 6H-SiC occurred at the outset of the exposure of the (1×1) surface to the reactants using any flow ratio. Subsequent deposition resulted in step flow and continued growth of 6H films or formation and coalescence of 3C-SiC islands using the gas flow ratio of one of the ethylene-rich ratios, respectively. The (3×3) surface reconstruction observed using the former ratio is believed to enhance the diffusion lengths of the adatoms which, in turn, promotes step flow growth.
Experimental study of an In0.53Ga0.47As–InP resonant plasma waveguide modulator for medium-infrared light
Authors: Stiens J. , De Tandt C. , Ranson W. , Vounckx R. , Demeester P. , Moerman I.
Published: July 2002

We report on the first experimental study of a medium-infrared waveguide modulator based on the coupling between a dielectric grating coupler and an In0.53Ga0.47As–InP waveguide, operating near cut off, and containing a resonant semiconductor plasma. The prototype designed for demonstrating this novel effect was grown by metalorganic chemical vapor deposition. The experimental results show low power (225 mW), low voltage (15 V) operation for obtaining a modulation depth of 30%. The overall transmission efficiency is, however, rather low (0.5%) due to the wet chemical etching techniques used for defining the grating structure.
Dose-rate effects on radiation-induced bipolar junction transistor gain degradation
Authors: Wei A. , Kosier S. L. , Schrimpf R. D. , Fleetwood D. M. , Combs W. E.
Published: July 2002

Analysis of radiation damage in modern NPN bipolar transistors at various dose rates is performed with a recently introduced charge separation method and pisces simulations. The charge separation method is verified with measurements on metal-oxide-semiconductor capacitors. Gain degradation is more pronounced at lower dose rates. The charge separation technique reveals that depletion-region spreading and effective recombination velocity are both greater for devices irradiated at lower dose rates.
Thickness dependence of the coercive electric field of laser ablated niobium-doped lead-zirconium-titanate films
Authors: Björmander C. , Sreenivas K. , Duan M. , Grishin A. M. , Rao K. V.
Published: July 2002

Thickness dependence (over the range d=1.05 to 0.02 μm) of the coercive electric fields, Ec, of niobium-doped lead-zirconium-titanate (PNZT) films has been investigated in pulsed laser ablated c-axis-oriented PNZT/YBa2Cu3O7−x heterostructures deposited on LaAlO3 substrates. Our studies show that Ec has a d−2/3 dependence in good agreement with the domain nucleation model developed for ferroelectric single crystals by Kay and Dunn [Philos. Mag. 7, 2027 (1962)]. Reproducible structural properties as well as ferroelectric properties with rather high polarization which is independent of the film thickness have been obtained in these Nd:YAG pulsed laser ablated films.
Impact of the substrate on the low-frequency noise of silicon n+p junction diodes
Authors: Simoen E. , Bosman G. , Vanhellemont J. , Claeys C.
Published: July 2002

This letter describes the low-frequency noise characteristics in forward operation of near-ideal n+p junction diodes fabricated in different p-type silicon substrates. The highest noise is found typically in Czochralski substrates, while float-zone and epitaxial diodes yield a lower noise magnitude. The spectra are 1/fβ-like for low-frequency f and frequency independent for larger f, whereby the frequency exponent β changes from slightly below to slightly above 1 with increasing forward bias. The spectral density SI at constant frequency shows a Iν dependence, with ν close to 1.5 for near-ideal diodes. Furthermore, there exists a close relationship between the static diode characteristics (the ideality factor) and the low-frequency noise magnitude. The experimental observations are not in agreement with the Kleinpenning formulation for the diffusion noise in the quasineutral region of the diode, but suggest on the contrary a generation-recombination origin.
Microstructure of polycrystalline silicon films obtained by combined furnace and laser annealing
Authors: Carluccio R. , Stoemenos J. , Fortunato G. , Meakin D. B. , Bianconi M.
Published: July 2002

Amorphous Si films deposited by the low pressure chemical vapor deposition from disilane, and subsequently subjected to a combined furnace annealing at 600 °C/12 h and a sequential excimer laser annealing, results to polycrystalline silicon films with very large grains, low in-grain defect density, and smooth-free surface. Large but heavily defected grains are produced by the furnace annealing, the in-grain defects are mainly microtwins, which are eliminated by a combined liquid–solid state process induced by the laser annealing. The two-step annealing provides a very high quality polycrystalline material suitable for thin-film transistor application.
Oriented ferroelectric thin films of PbTiO3, (Pb,La)TiO3, and Pb(Zr,Ti)O3 by nebulized spray pyrolysis
Authors: Raju A. R. , Rao C. N. R.
Published: July 2002

Nebulized spray pyrolysis provides a good low-temperature chemical route for preparing thin films of PbTiO3, (Pb0.9,La0.1)TiO3 and Pb(Zr0.52,Ti0.48)O3. The films are a- or c- axis oriented, with spherical grains of ∼30 nm and give satisfactory P-E hysteresis loops.
Far-infrared imaging of tokamak plasma
Authors: Young P. E. , Luhmann N. C. , Taylor R. J. , Neikirk D. P. , Rutledge D. B.
Published: July 2002

A 20-channel interferometer has been developed which utilizes a linear, one-dimensional microbolometer array to obtain single-shot density profiles from the UCLA Microtor tokamak plasma. The interferometer has been used to study time-dependent phenomena in the plasma density profile. Observations of the sawtooth instability clearly show the growth of the m=0 mode from a localized oscillation (r=1 cm) on axis to an oscillation of the entire plasma. Also, measurements during the initial startup phase of the discharge show evidence of hollow density profiles. In addition, a simultaneous measurement of the poloidal magnetic field has been developed which provides 20 channels of polarimetry. Interferometry and polarimetry both use the same imaging system and the spatial resolution of both measurements has been tested using plastic and crystal-quartz test objects. The signal-to-noise ratio for the polarimeter has also proved adequate for the expected Faraday rotation angle (αmax=7°, Ip=70 kA, n=5×1013 cm−3).
Fast scanning heterodyne receiver for the measurement of the time evolution of the electron temperature profile on the Tokamak Fusion Test Reactor
Authors: Taylor G. , Efthimion P. C. , McCarthy M. , Fredd E. , Goldman M. A. , Kaufman D.
Published: July 2002

Two fast scanning heterodyne receivers, swept between 75–110 and 110–170 GHz in 2 ms every 4 ms, were developed to measure the electron cyclotron emission on the horizontal midplane of the Tokamak Fusion Test Reactor (TFTR) plasma. An absolute, in situ calibration technique enables the determination of the profile of the plasma electron temperature from the fundamental ordinary mode and second harmonic extraordinary mode cyclotron emission intensity, with an accuracy of better than 10%. Temperature measurements made with the scanning receivers agree well with data from laser TV Thomson scattering and x-ray pulse-height analysis measurements. The time evolution of the temperature profile during temperature sawteeth fluctuations is well documented when the period of the fluctuation (30–100 ms) is much longer than the instrument sweep repetition time.
Infrared camera and data-acquisition system in Doublet III (abstract)
Authors: Petrie T. W. , Scoville J. T.
Published: July 2002

Thermal imaging cameras sensitive to 3–5 μ radiation are routinely used to measure heat flow to the main limiter, to the vacuum vessel wall behind the main limiter, and to the divertor plate limiters. The cameras are equipped to provide either a standard television image with a time resolution of ∼16.7 ms or a surface temperature profile on one line of the image with a time resolution of ∼125 μs. In the former mode, we can determine both the location and the intensity of the heating on the main limiter during multi-megawatt neutral-beam injection into plasma; in the latter mode, we can measure heat pulses striking the limiter from plasma processes occurring on fast time scales (e.g., Hα spikes of ∼500-μs duration). Data is stored in both video image and digitized forms. In the latter, a ‘‘peak-sample-hold’’ circuit electronically records the maximum signal of each line sweep and stores this data in digitized form on magnetic tape. This facilitates later comparisons of infrared camera data with other diagnostic signals using plotting packages on the DEC-10.
1-m normal incidence UV spectrometer for plasma measurements (abstract)
Authors: Register D. F. , Jackson G. L. , Walker S. E.
Published: July 2002

An Acton Research VM 521-SG UV monochromator has been equipped with an intensified diode array detector for use as a mid-UV spectrometer. 600 and 2400 gr/mm gratings are used in a turret assembly for either low-resolution surveys or high-resolution Doppler ion studies. The detector is a CsI coated MCP with a P-11 output phosphor. The 1024 diode array is scanned at a 1-MHZ video rate allowing a complete spectra to be obtained in 1.0 ms. System performance and preliminary operation on the OHTE plasma will be presented.
Low-noise four-terminal ac resistance bridge
Authors: Narici L.
Published: July 2002

The results of a detailed noise calculation for a resistance bridge are presented. These results allow one to adapt the design of the bridge to any particular need, while maintaining optimized performance. A bridge has been built based on these results. The measured relative sensitivity of this bridge (2×10−5 with only 10 pW dissipated in the sensor) is ∼40% better than the best previous published results. With minor changes it is shown that this sensitivity can be improved by a factor of 3.
Analytical expressions for fusion spectra produced in ‘‘beam-target’’ fusion reactions
Authors: Heidbrink W. W.
Published: July 2002

For ‘‘beam-target’’ fusion reactions, collimated measurements of the energy spectrum of one of the reaction products can provide information on the degree of anisotropy of the reacting beam ions. Analytical expressions relating the fusion spectrum to the velocity distribution of the beam ions are given. Application of the expressions to measurements of the spectrum of 15-MeV protons produced by reactions between energetic 3He ions and relatively cold deuterons during ICRF heating in the PLT tokamak indicate that the velocity distribution of fast 3He ions is peaked perpendicular to the tokamak magnetic field.
Measurement of the magnetic field direction in a plasma by collective scattering with a CO2 laser
Authors: Holzhauer E. , Kasparek W.
Published: July 2002

The effect of strongly magnetized electrons on the spectrum of collective electron density fluctuations can be used to measure the magnetic field direction in a plasma with laser light scattering. The application of this method to measure the poloidal field in tokamaks is discussed. It is shown that noncircular beam cross sections will increase the angular resolution without loss in spatial resolution. In experiments to measure the ion temperature this technique results in an increase of scattered power received. The magnetic field direction was measured for the first time in a laboratory plasma using a pulsed CO2 laser and coherent detection.
Using the electronic top-loading analytical balance for surface tension measurements
Authors: Richlin Jack
Published: July 2002

An electronic top-loading analytical balance has been adapted to measure surface tension at liquid–gas interfaces. Because the zero position of the balance is automatically returned, the instrument is capable of good accuracy.
Pulsed nuclear-magnetic-resonance thermometer with a microprocessor for ultralow temperatures
Authors: Sawada Anju , Yano Hideo , Masuda Yoshika
Published: July 2002

A pulsed nuclear-magnetic-resonance (NMR) thermometer with platinum as a probe, which can operate at the NMR frequencies of 62.5, 125, 250, and 500 kHz, has been constructed. All of the various pulsed NMR sequences can be executed by commands from a microprocessor. The present system has excellent performance characteristics such as long-term stability, high resolution (16 bits), full automatic operation, and simplicity in electronic circuitry. It has been used at temperatures as low as 0.45 mK.
Gridded ionization chamber for detection of x-ray wave activity in tokamak plasmas
Authors: Goldman M. A. , Hill K. W. , Moshey E. A. , Sauthoff N. R. , von Goeler S.
Published: July 2002

In order to carry out x-ray observations of magnetohydrodynamic wave activity of the plasma during DD and DT (deuterium-beam-heated deuterium and tritium plasmas, respectively) operation of the Tokamak Fusion Test Reactor (TFTR), we will need detectors not susceptible to nuclear radiation damage. We have investigated the use of gridded ionization chambers as fast nondamageable x-ray detectors. A prototype chamber is described which was tested on the PDX tokamak. These tests and laboratory tests with a pulsed x-ray source suggest that the detector has sufficient sensitivity and speed for the required measurements.
Double tilt heating specimen holder for surface imaging by reflection electron microscopy using an EM 300 Philips microscope
Authors: Beauvillain J. , Claverie A. , Jouffrey B.
Published: July 2002

A new type of heating specimen holder which allows reflection electron microscopy (REM) imaging with incident and azimuthal angle control is described. A REM image is presented, from a bulk specimen whose surface was prepared in situ, and shows strong contrasts due to atomic steps.
Use of indium solder to patch leaks in silver-solder joints on cryostats
Authors: Holtz R. L. , Swenson C. A.
Published: July 2002

Indium metal as a solder can provide a convenient and effective, last resort, patching material for leaks which occur spontaneously in metallic low-temperature apparatus. Indium bonds well to many metals and, more importantly, remains ductile to 4 K. An indium patch therefore retains its integrity even where a leak has occurred due to the differential thermal expansions of construction materials.
Curved-tube flowmeters
Authors: Houtman H.
Published: July 2002

A new flowmeter design is presented which is suitable for accurately measuring flows ranging from ≂1 to ≂1000 cm3 s−1. It may be simply constructed from readily available parts and may be adapted to measure flow of any fluid for which a noncorrosive ball and transparent tube are available. Starting with standard Venturi meter theory, a formula is derived for the volume flowrate in terms of ball and tube dimensions, ball and fluid densities, and the angle at which the ball comes to rest in the tube. Actual examples of curved-tube flowmeters are given for particular cases of nitrogen at 0 – 42.4 cm3 s−1 and water at 0–11.4 cm3 s−1, constructed using bearing balls in standard Eastman Polyflo tubing. Using the formula as a guide, extension to lower and higher flowrates is straightforward.
Digital phase-sensitive detector using a Z80A single-board computer
Authors: DeRosa F.
Published: July 2002

A digital phase-sensitive detector was designed and built to circumvent the relatively slow, ∼1-ms response time of commercial lock-in amplifiers. A Z80A single-board computer with a suitably programmed EPROM and analog-to-digital and digital-to-analog converters is used. The response time, ∼40 μs, is primarily limited by the throughput of the analog-to-digital converter.
Electrostatic ion probe for tokamak-plasma-edge diagnostic
Authors: da Silva R. P. , Nascimento I. C. , da Cruz D. F. , Hershcovitch A.
Published: July 2002

An electrostatic probe for ion temperature and density measurements was built and tested in the scrape-off region of the TBR-1 small tokamak. The main parameters involved in the design and details of the construction of the probe are presented. The electron discrimination and the probe efficiency for ion detection were checked by measuring the probe current as a function of the collector retraction length for a constant voltage. The results for the ion temperature and density obtained from the characteristic curves are discussed and compared with previous measurements.
Feasibility of obtaining short electron-beam pulses from a Van de Graaff 3-MV accelerator using laser-photoelectron emission from a cold trioxide cathode
Authors: Luthjens L. H. , Hom M. L. , Vermeulen M. J. W.
Published: July 2002

Production of electron-beam pulses with a 700-ps FWHM duration, using laser-photoelectron emission from a cold trioxide cathode in a 3-MV Van de Graaff accelerator has been demonstrated. At 70-kW laser power (λ=337.2 nm) a current of about 1 mA has been measured which means a cathode quantum efficiency of 10−7. An electron transit time jitter of about 40 ps has been measured, to be attributed to voltage fluctuations on the accelerator tube electrodes resulting from the charging belt system. The results are discussed with respect to the feasibility to produce short pulses with a 1-nC total charge, taking into account the quantum efficiency of 10−4 measured in a test setup for the cold trioxide cathode. Larger quantum efficiency for the accelerator cathode and decrease of the transit time jitter are the main goals set for development of the Van de Graaff accelerator as a radiation source for very high time-resolution experiments in radiation chemistry and physics.
Faraday rotation in a multimode optical fiber in a fast rise-time, high magnetic field
Authors: Wessel F. J. , Wild N. C. , Fisher A. , Rahman H. U. , Ron A. , Felber F. S.
Published: July 2002

A magneto-optic Faraday rotation diagnostic was implemented on a Z-pinch driven flux-compression generator to measure line-averaged, megagauss, axial-magnetic fields up to 1.6 MG with rise times of 30 kG/ns. The axial-magnetic field rotated the plane of polarization of a 2-W argon laser beam in a 0.725-mm-diam, fused silica quartz fiber mounted coaxial with the Z pinch. The rapid rise time and the high radiation environment presented by the Z-pinch plasma caused a high-pressure impulse <100 kbar, to be coupled into the quartz-fiber probe disrupting the polarization-preserving properties of the fiber. The time scale for disruption was characteristic of a shock propagating radially through the fiber to its core. This paper will describe the response of the Faraday diagnostic under these conditions and present a simple model that describes the effects of fiber depolarization that is consistent with previous observations of stress-induced depolarization in optical fibers.
dc-ac hot-wire procedure for determining thermophysical properties under pressure
Authors: Nilsson O. , Sandberg O. , Bäckström G.
Published: July 2002

The paper describes a new hot-wire method for simultaneous determination of thermal conductivity and heat capacity per unit volume of electrically insulating liquids and solids under pressure. The method uses dc heating of the hot wire, whereas the temperature increase is recorded by an ac bridge circuit. The temperature data obtained are analyzed using the exact solution instead of the commonly used long time approximation. The procedure was tested on a number of alcohols and water and the accuracy was found to be 1.5%. New data on glycerol up to 1.5 GPa are presented. The appearance of an automagnetoresistance effect when Ni is employed as hot-wire probe is discussed.
Pressurized apparatus for measuring the cloud points of polymer solutions
Authors: Moradi-Araghi A. , Bruning D. D. , Doe P. H.
Published: July 2002

A cloud point cell designed to operate at pressures up to 200 psig and temperatures up to 400 °F (204 °C), has been used extensively for evaluating aqueous polymer solutions. This cell, coupled with a visible spectrometer equipped with fiber optics connected to its light source and detector, can be used for determining cloud points of solutions. The polymer solution sealed in a glass ampoule and placed under a nitrogen pressure of 120 psig can be heated up to 400 °F (204 °C). The advantage of this setup over the standard turbidometers is extension of temperature to beyond the boiling point of the solvent.
Computer control and data-acquisition system for the rf test facility
Authors: Stewart K. A. , Burris R. D. , Mankin J. B. , Thompson D. H.
Published: July 2002

The radio frequency test facility (RFTF) at Oak Ridge National Laboratory, used to test and evaluate high-power ion cyclotron resonance heating (ICRH) systems and components, is monitored and controlled by a multicomponent computer system. This data-acquisition and control system consists of three major hardware elements: (1) an Allen-Bradley PLC-3 programmable controller, (2) a VAX 11/780 computer, and (3) a CAMAC serial highway interface. Operating in LOCAL as well as REMOTE mode, the programmable logic controller (PLC) performs all the control functions of the test facility. The VAX computer acts as the operator’s interface to the test facility by providing color mimic panel displays and allowing input via a trackball device. The VAX also provides archiving of trend data acquired by the PLC. Communications between the PLC and the VAX are via the CAMAC serial highway. Details of the hardware, software, and the operation of the system are presented in this paper.
Experimental errors and artifacts for a time-domain lumped capacitor dielectric spectrometer
Authors: Eadline Douglas J. , Leidheiser Henry
Published: July 2002

An analysis of possible experimental errors and artifacts for a time-domain dielectric spectrometer (frequency range 107–109 Hz) is performed using mathematical models. The spectrometer requires an incident and reflected pulse to be referenced in time and aligned in amplitude. Effects due to time misreferencing and amplitude misalignment are studied using a simple Teflon dielectric model. The calculated spectra for misreferencing and misalignment errors for a Teflon model are compared to real spectrometer data. Time misreferencing errors greater than 40 ps produce large errors at high frequencies and the absolute time reference can vary by one-half the sampling interval. Amplitude misalignment can create both false and forced convergence at the end of the pulses. Most importantly, misreference and misalignment errors may generate pseudodielectric effects. Other general models dealing with artifacts due to the solid nature of the sample were developed to include contact resistance, contact inductance, and fringe capacitance. The inclusion of contact resistance produced loss behavior that moved to higher frequencies with lower resistances. When contact inductance is included, the ε′ values increase in the frequency range examined. Inclusion of fringe capacitance produced a slight rise in the ε′ values, proportional to the sample thickness. The time-domain lumped capacitor dielectric spectrometer becomes a viable tool in studies of dielectric materials at high frequencies when attention is given to possible experimental errors and artifacts.
Acceleration of laser-produced ions in a small Van de Graaff
Authors: Korschinek G. , Sellmair J.
Published: July 2002

The acceleration of heavy ions, produced in a laser-induced plasma, with a Van de Graaff has been demonstrated. In order to generate the ions, a prototype of a laser-ion source was constructed. Using a small Nd:YAG laser (flux≤6.5×108 W/cm2, pulsed), we were able to measure charge states of positive ions, Fen+, Tan+, Aun+ with n≤4. Currents up to 0.6 mA (during the pulse) could be observed.