bluuebunny/crossref_metadata_2025 huggingface dataset:
Model for Si–SiO2 interface state formation during irradiation and during post-irradiation exposure to hydrogen environment
Authors: Mrstik B. J. , Rendell R. W.
Published: July 2002

When the oxide of a previously x-ray irradiated metal–oxide–semiconductor field-effect transistor is exposed to a hydrogen environment at room temperature the number of interface traps is observed to double, and the number of fixed oxide traps to decrease by a similar amount. From an analysis of this post-irradiation behavior we derive a model for the formation of interface states during and immediately after irradiation. In this model holes formed in the oxide during the irradiation split ≡SiH bonds in the oxide to form atomic hydrogen and ≡Si+. At room temperature the atomic hydrogen quickly dimerize to form H2. The H2 is then cracked by the ≡Si+ to form H+. Each H+ is transported to the interface, where it forms an interface state. This model also explains the results of a recent experiment which had seemed to indicate that no H+ was formed in the oxide as a result of irradiation.
Two-photon absorption in 4-butoxycarbonylmethylurethane polydiacetylene waveguides
Authors: Ehrlich J. E. , Valera J. D. , Darzi A. , Walker A. C.
Published: July 2002

The strong confinement of light in planar-optical waveguides has been used to measure the two-photon absorption coefficient, β, in 4-butoxycarbonylmethylurethane polydiacetylene (4BCMU) thin films. Prisms were used to couple the 30–60 ps pulses (up to 10 μJ) from a mode-locked YAG laser (λ=1.06 μm) into the thin-film waveguides. A simple analytical theory is compared with the experimental results to give a value of β≊4×10−3 cm/MW.
Epitaxial growth of α-Fe films on Si(111) substrates
Authors: Cheng Yang-Tse , Chen Yen-Lung , Karmarkar M. M. , Meng Wen-Jin
Published: July 2002

Epitaxial α-Fe films have been grown on HF cleaned Si(111) substrates at 30 °C by electron beam evaporation in an ultrahigh vacuum environment to a thickness of several thousands of Angstroms. Conventional θ−2θ x-ray diffraction shows that only the Fe(222) peak is present, indicating that the films are oriented with the Fe(111) plane parallel to the Si(111) plane. Transmission electron microscopy shows that the Fe[11̄0] direction is parallel to the Si[11̄0] direction in the plane of the substrate.
Magnetic multipole-based reactive ion etching reactor
Authors: Singh B. , Thomas III J. H. , Patel V.
Published: July 2002

The addition of a simple inexpensive magnetic multipole to a parallel plate triode results in a magnetic enhanced etch reactor configuration that has impressive low pressure characteristics. The multipole electrode which is in the form of a cylindrical multipolar bucket, open at both ends, is added to the powered electrode of the triode being employed as a plasma etching system. The multipole becomes, in effect, an extension of the ground shield, surrounding either electrode. The resulting electrode configuration produces an extremely uniform, dense plasma at pressures as low as 2–3×10−4 Torr. The effect of the magnetic enhancement (electron containment, uniformity profile modification, and low substrate bias) is particularly pronounced at lower pressures. Significant improvement over existing triode schemes is obtained using the grounded cylindrical multipolar bucket as an extension of the ground shield of the driven electrode (not the substrate electrode). This system is considerably simpler than dual frequency driven trielectrode systems since it uses 13.56 MHz excitation of both electrodes.
Laser-induced fluorescence of oxygen atoms in a plasma reactor
Authors: Hancock G. , Toogood M. J.
Published: July 2002

Two-photon laser-induced fluorescence (LIF) of ground-state oxygen atoms following excitation of the 2p3 3p1 3P–2p4 3P transition has been investigated in a rf parallel-plate plasma reactor. Stimulated emission on the 2p3 3p1 3P–2p3 3s1 3S transition is readily detected, and leads to marked nonlinearities in the LIF signal as a function of O-atom concentration. Absolute concentrations have been determined as a function of gas composition in CF4/O2 mixtures, and shown to depend on the measured wall loss rates. The method is used to indicate limitations in the use of optical emission as a diagnostic for O atoms.
Sub-μm linewidth input coils for low T
c integrated thin-film dc superconducting quantum interference devices
Authors: Ketchen M. B. , Stawiasz K. G. , Pearson D. J. , Brunner T. A. , Hu C.-K. , Jaso M. A. , Manny M. P. , Parsons A. A. , Stein K. J.
Published: July 2002

We have, for the first time, demonstrated integrated dc superconducting quantum interference devices (SQUIDs) with input coils of linewidth down to 0.5 μm. The SQUID inductance L consists of a single octagonal washer or two or four such washers configured in parallel. The input coil of inductance Li, which couples to L with a mutual inductance of Mi, consists of fine-line octagonal spiral(s) fabricated in close proximity to the washer(s). For a two-washer SQUID with twin 80-turn, 0.5 μm spirals, Li=2.5 μH, Mi=12.7 nH, L=109 pH, and the coupling constant k2=0.85. This entire device occupies an area of less than 0.2 mm2.
Semiconductor lasers on Si substrates using the technology of bonding by atomic rearrangement
Authors: Lo Y. H. , Bhat R. , Hwang D. M. , Chua C. , Lin C.-H.
Published: July 2002

We demonstrated InGaAs/GaAs strained quantum well lasers on silicon substrates. The epitaxial layers for lasers were first grown on a GaAs substrate and then bonded to a silicon substrate using the technology of bonding by atomic rearrangement. Covalently bonded III-V/Si heterointerface was confirmed by the cross-sectional transmission electron microscopy. The ridge waveguide lasers on Si substrates lasing at about 1 μm wavelength have a 12 mA threshold current and a 56% external quantum efficiency at room temperature, at pulsed condition. Both the threshold current and the external quantum efficiency are close to the values of lasers on GaAs substrates. The technology of bonding by atomic rearrangement will be useful for making optoelectronic integrated circuits on Si.
Optical functions of chemical vapor deposited thin-film silicon determined by spectroscopic ellipsometry
Authors: Jellison G. E. , Chisholm M. F. , Gorbatkin S. M.
Published: July 2002

The optical functions of several forms of thin-film silicon (amorphous Si, fine-grain polycrystalline Si, and large-grain polycrystalline Si) grown on oxidized Si have been determined using 2-channel spectroscopic polarization modulation ellipsometry from 240 to 840 nm (∼1.5–5.2 eV). It is shown that the standard technique for simulating the optical functions of polycrystalline silicon (an effective medium consisting of crystalline Si, amorphous Si, and voids) does not fit the ellipsometry data.
Microscopic-scale lateral inhomogeneities of the photoemission response of cleaved GaAs
Authors: Cerrina F. , Ray-Chaudhuri A. K. , Ng W. , Liang S. , Singh S. , Welnak J. T. , Wallace J. P. , Capasso C. , Underwood J. H. , Kortright J. B. , Perera R. C. C. , Margaritondo G.
Published: July 2002

Photoelectron energy distribution spectra taken for the first time on micrometer-sized areas of cleaved GaAs(110) reveal rigid shifts from location to location in the photoemission core level peak energies, indicating band-bending changes on a microscopic scale.
Photoconductivity in highly tetrahedral diamondlike amorphous carbon
Authors: Amaratunga G. A. J. , Veerasamy V. S. , Milne W. I. , Davis C. A. , Silva S. R. P. , MacKenzie H. S.
Published: July 2002

A photoconductive effect is observed in tetrahedral amorphous carbon (ta-C) or amorphous diamond films with a high proportion of sp3 bonding and a structure analogous to amorphous silicon. The spectral response is shown to peak at around 750–800 nm and extend into the near UV region. The maximum photoresponse coincides with the optical absorption edge. The quantum efficiency of 300 nm thick films with interdigitated electrodes is over 10% in the wavelength range 450–800 nm.
Self-limited layer-by-layer etching of Si by alternated chlorine adsorption and Ar+ ion irradiation
Authors: Matsuura Takashi , Murota Junichi , Sawada Yasuji , Ohmi Tadahiro
Published: July 2002

We report the observation of self-limited layer-by-layer etching of Si by alternated chlorine adsorption and low energy Ar+ ion irradiation using an ultraclean electron-cyclotron-resonance plasma apparatus. The etch rate per cycle increased with the chlorine supplying time and saturated to a constant value of about 1/2 atomic layer per cycle for Si(100) and 1/3 for Si(111), which was independent of the chlorine partial pressure in the range of 1.3–6.7 mPa. These results indicate that etching was determined by self-limited adsorption of chlorine. Moreover, the chlorine adsorption rate was found to be described by a Langmuir-type equation with an adsorption rate constant k=83 and 110 (Pa s)−1 for Si(100) and Si(111), respectively.
Si and N dangling bond creation in silicon nitride thin films
Authors: Warren W. L. , Robertson J. , Kanicki J.
Published: July 2002

We observe the simultaneous creation of paramagnetic Si and N dangling bonds when N-rich silicon nitride thin films are optically illuminated at low temperatures (110 K). Generally, only the Si dangling bond is observed if the illumination is performed at room temperature. In contrast, the N dangling bond is metastable, and has previously only been observed after a high temperature post-deposition anneal and followed by illumination. We propose that the low temperature illumination causes two processes: (1) Charge conversion of N3≡Si+ and N3≡Si− sites to give two N3≡Si⋅dangling bonds, and (2) charge transfer between Si2=N− and N3≡Si+ sites to form Si2=N⋅ and N3≡Si⋅dangling bonds.
Picosecond Raman studies of electric-field-induced nonequilibrium carrier distributions in GaAs-based p-i-n nanostructure semiconductors
Authors: Grann E. D. , Sheih S. J. , Chia C. , Tsen K. T. , Sankey O. F. , Guncer Selim E. , Ferry D. K. , Maracas G. , Droopad Ravi , Salvador A. , Botcharev A. , Morkoç H.
Published: July 2002

Electron transport in GaAs-based p-i-n nanostructure semiconductors under the application of an electric field has been studied by transient Raman spectroscopy on a picosecond time scale and at T≂80 K. For an injected carrier density of n≂2.2×1018 cm−3 and electric field intensity E=25 kV/cm, the drift velocity of electrons as high as Vd=2.5×107 cm/s was observed. These experimental results are in good agreement with Ensemble Monte Carlo calculations.
Electroabsorption in ultranarrow-barrier GaAs/AlGaAs multiple quantum well modulators
Authors: Goossen K. W. , Cunningham J. E. , Jan W. Y.
Published: July 2002

We measure electroabsorption in GaAs/AlGaAs multiple quantum well modulators with ultranarrow barriers so as to maximize the overall absorption coefficient by removing optically inert barrier material. Reduction <38 Å in the width of Al0.3Ga0.7As barriers results in resonant well coupling degrading performance. For AlAs barriers, resonant coupling is eliminated and we observe sharp excitons and the quantum confined Stark effect for barriers as narrow as 10 Å. However, optimum normally-on operation is obtained for 20–30 Å AlAs barriers, approximately 20% better than 38 Å Al0.3Ga0.7As barriers.
A thin atomic vapor as a nonlinear optical medium
Authors: Ai B. , Glassner D. S. , Knize R. J. , Partanen J. P.
Published: July 2002

We demonstrate efficient degenerate four-wave mixing in a 10 μm cell of cesium atomic vapor using resonant light. This thin atomic vapor can be utilized for processing high resolution images in a joint transform optical correlator. A figure of merit is presented showing that thin atomic vapors can perform optical correlation of images using fewer photons than other materials.
Density of amorphous Si
Authors: Custer J. S. , Thompson Michael O. , Jacobson D. C. , Poate J. M. , Roorda S. , Sinke W. C. , Spaepen F.
Published: July 2002

The density of amorphous Si has been measured. Multiple Si implants, at energies up to 8.0 MeV, were made through a contact mask to produce alternating amorphous/crystalline Si stripes with amorphous thicknesses up to ∼5.0 μm. For layers up to 3.4 μm (5 MeV), the amorphous Si is constrained laterally and deforms plastically. Above 5 MeV, plastic deformation of the surrounding crystal matrix is observed. Height differences between the amorphous and crystalline regions were measured for as-implanted, thermally relaxed, and partially recrystallized samples using a surface profilometer. Combined with ion channeling measurements of the layer thickness, amorphous Si was determined to be 1.8±0.1% less dense than crystalline Si (4.90×1022 atom/cm3 at 300 K). Both relaxed and unrelaxed amorphous Si show identical densities within experimental error (<0.1% density difference).
Deep level transient spectroscopy characterization of ferroelectric Pb(Zr,Ti)O3 thin films
Authors: Baude P. F. , Ye C. , Polla D. L.
Published: July 2002

Deep level transient spectroscopy (DLTS) has been used to investigate trap levels in sol-gel derived polycrystalline Pb(Zr0.54,Ti0.46)O3 thin films. Metal-ferroelectric-metal capacitor structures 2400 and 3000 Å in thickness were fabricated and characterized using a constant voltage DLTS system. Prominent peaks associated with a single trap level were observed in all samples studied. The activation energy was determined to be 267 meV from DLTS spectra Arrhenius plots. Infrared transmission characterization was performed on PbTiO3 thin films also prepared using sol-gel synthesis. A loss in the transmission at 270±12 meV was observed which we attribute to hole emission from the same trap detected using DLTS.
Single-walled carbon nanotubes produced at high yield by mixed catalysts
Authors: Seraphin Supapan , Zhou Dan
Published: July 2002

We report here on the high-density preparation of single-wall tubes in the presence of mixed catalysts of the types Fe/Ni and Co/Ni, in the soot as well as in the weblike deposits forming in the chamber. The yield is much higher than previously reported, and gram quantities can be obtained. Diameters cover the range from 0.9 to 3.1 nm, larger than previously reported, with the histogram showing only one peak at 1.7 nm. Evidence of an epitaxial action between C60 and single-walled nanotubes is presented. Results from the mixed catalysts Co/Cu, Ni/Mg, and Ni/Ti are also reported.
Rhodium- and iridium-related deep levels in In0.53Ga0.47As
Authors: Srocka B. , Scheffler H. , Bimberg D.
Published: July 2002

We investigated the doping of In0.53Ga0.47As with rhodium and iridium by liquid phase epitaxy and observed for the first time Rh- and Ir-related levels in InGaAs by means of deep level transient spectroscopy. Both dopants were found to produce near-midgap levels. The available data support an association of these levels with the transition metal (TM)2+/3+-single acceptor transitions caused by substitutionally incorporated TM ions on cation sites. The distribution coefficients determined from the trap concentrations in the layers are rather small, on the order of 1×10−6.
Possible phase locking of vertically stacked Josephson flux-flow oscillators
Authors: Ustinov A. V. , Kohlstedt H. , Heiden C.
Published: July 2002

A system of two vertically stacked Nb/Al-AlOx/Nb long Josephson junctions is studied experimentally. The magnetic coupling between the junctions is provided by their common electrode of the thickness d∼λL. The current-voltage characteristics of the stack displays resonant steps which are understood to be the phase-locked flux-flow resonances of the two junctions. These modes can be tuned by the magnetic field in a broad voltage range which corresponds to the Josephson frequencies between 150 and 600 GHz. Our observations suggest a possibility of application of the stacked long Josephson junctions as local oscillators for millimeter and submillimeter wave circuits.
Thermal conductivity of sputtered and evaporated SiO2 and TiO2 optical coatings
Authors: Cahill David G. , Allen Thomas H.
Published: July 2002

The thermal conductivity of SiO2 and TiO2 optical coatings are measured in the temperature range 80–400 K. For SiO2, the thermal conductivity of sputtered and evaporated films are 77% and 55% of the bulk value, respectively, independent of temperature. Similarly, the thermal conductivity of evaporated TiO2 is 63% of the conductivity of sputtered TiO2.
Repeatable electron emission from (Pb,La)(Zr,Ti)O3 ferroelectric cathodes using direct-current reset
Authors: Cavazos T. C. , Wilbanks W. L. , Fleddermann C. B. , Shiffler D. A.
Published: July 2002

The use of ferroelectric (Pb,La)(Zr,Ti)O3 as a cathode material is investigated. It has been suggested in the literature that by rapidly changing or reversing the spontaneous polarization in the ferroelectric, a large charge imbalance can be produced at the surface of the material. The field from this charge imbalance extracts bound carriers from the cathode. An approach to achieving this polarization change by using a negative bias field to preset the material prior to switching is discussed in this letter. This bias field can also be used to control the bound surface charge on the material. Emission currents on the order of 100 mA are observed and the emitted charge is on the order of 30 nC. Measurable emission occurs only when the material is driven into saturation.
Piezoelectric effects in (001)-oriented double barrier resonant tunneling structures
Authors: Cong L. , Albrecht J. D. , Nathan M. I. , Ruden P. P. , Smith D. L.
Published: July 2002

We show that piezoelectric effects can give rise to internal electric fields that modify the current–voltage characteristics of double barrier resonant tunneling devices, if suitable stresses are applied. Electric polarization fields in the direction perpendicular to the interfaces arise in heterostructures on (001)-oriented substrates under uniaxial stress parallel to the (110) or (11̄0) orientations. We measured current–voltage characteristics of (001)-oriented AlAs/GaAs/AlAs double barrier structures as a function of uniaxial external stress applied parallel to the (110) and the (11̄0) orientations. The substrate contact was grounded in all measurements. Under (110) stress, the resonance peaks shift to more positive voltages for both positive and negative bias. For (11̄0) stress, the peaks shift toward more negative voltages. We also calculated the current–voltage characteristics of resonant tunneling structures under uniaxial stress, taking into account stress effects on the band alignment and piezoelectric effects. We obtain satisfactory agreement between our calculations which contain no adjusted parameters and the measured data.
Effect of electron-electron interaction on hot ballistic electron beams
Authors: Schäpers Th. , Krüger M. , Appenzeller J. , Förster A. , Lengeler B. , Lüth H.
Published: July 2002

Electron-electron scattering of ballistic electrons in a two-dimensional electron gas was studied as a function of the electron excess energy above the Fermi energy and of temperature. At low temperatures of 1.4 K it is found that for excess energies of approximately 30% of the Fermi energy the electrons in a ballistic electron beam are already scattered significantly due to electron-electron interaction. A very good agreement between our experimental data and theory was found, when the measured data were compared with numerical calculations based on a theory of Giuliani and Quinn [Phys. Rev. B 26, 4421 (1982)], while the agreement was only poor for the analytical approximation of the electron-electron scattering rate.
Toroidally curved crystal for time-resolved x-ray spectroscopy
Authors: Hauer A. , Kilkenny J. D. , Landen O. L.
Published: July 2002

A toroidally bent crystal for producing a focused spectrum normal to the line of sight from a laser plasma is described. Experimental results using a pentaerythritol crystal are described which show a brightness gain of 50 over a flat crystal. Improvement in the resolution of dielectronic satellites to the heliumlike 1s2-1s3p, 1s2-1s4p, and 1s2-1s5p lines of silicon is demonstrated.
Detector development for γ-ray diagnostics of D-T fusion reactions
Authors: Moran Michael J.
Published: July 2002

The development of D-T fusion-energy sources requires intimate and precise measurement of fusion-burn conditions in reactor-development experiments. Some of the limitations inherent in presently available diagnostics based on massive particle emissions can be overcome by measuring fusion-generated high-energy γ rays. Although γ-ray intensities are low, γ rays offer diagnostic advantages of dispersion-free propagation and low intrinsic backgrounds. This paper describes two detector systems developed to study D-T fusion reactions by measuring the associated 16.7-MeV γ-ray emissions. The first system is a Compton-recoil spectrometer and features good energy resolution of the 16.7-MeV photons. This system uses a sector-magnet spectrometer to isolate electrons forward scattered by the high energy γ rays. The second system is a threshold Čerenkov detector and features a higher net sensitivity. A chamber filled with Co2 gas acts as a Čerenkov medium for electrons scattered by the 16.7-MeV photons. The gas pressure is adjusted so that electrons scattered by photons having energies less than 16.7 MeV do not have sufficient energy to generate Čerenkov light in the gas.
Hydraulic coupling for generating electrical power inside a high-voltage accelerator terminal
Authors: Sumbar Edmund , Vermeulen F. E. , Lawson R. P. W.
Published: July 2002

A hydraulic apparatus used to generate electrical power inside a 280-kV ion accelerator terminal is described. In this system, pressurized hydraulic oil flows through insulating hoses, transferring fluid power between ground and the high-voltage terminal. A maximum of 750 W was generated with the present equipment. Leakage current along the hydraulic-fluid lines was recorded as a function of time for an applied voltage of 280 kV. This current initially rose at an average rate of about 8 μA/min, reaching a maximum of about 760 μA within 2 h. Beyond 2 h, leakage current slowly decreased with time.
Amplification of subnanosecond light pulses by a synchronously fired Nd:YAG laser
Authors: Austin Robert H. , LeGrange Jane D.
Published: July 2002

We have used a simple dye laser driven by a Q-switched Nd:YAG laser as an amplifier for subnanosecond pulses from a nitrogen laser driven dye laser. Energy gains of up to 150 are observed, with final pulse energies of 200 μJ at 650 nm.
Pulsed-jet etch chamber for preparing silicon samples for transmission electron microscopy
Authors: Rivaud L. , Hawkins G.
Published: July 2002

An apparatus is described for wet chemical etching of silicon specimens for transmission electron microscopy. This etch chamber thins the central portion of a 3-mm disk to a specified thickness (1–50 μm) in a controlled and reproducible manner. The use of a pulsed jet in a sample chamber totally filled with etchant allows the etching process to be observed visually.
Static method to measure vapor pressure in the temperature range below 1100 K
Authors: Nishimura Jiro , Numata Takashi , Ogasawara Hiromitsu , Sakanoue Yoshio
Published: July 2002

In this paper, a static method of measuring vapor pressure with an optically flat glass-membrane pressure sensor in the temperature range below 1100 K is described. The furnace is designed so that the pressure can be measured contactlessly by the null method. A method of automatic pressure control using this sensor is described as well. The method is capable of controlling the pressure to the order of the sensitivity of the membrane.
In-reactor testing of ionic thermometers
Authors: Jakeš D. , Rosenkranz J. , Krett V. , Strnad M. , Kott J.
Published: July 2002

Ionic thermometers have been tested in a nuclear reactor with attention to the steepness of the ionic conductivity jump and the influence of a glass container on the accuracy of the temperature measurements. It was found that, at the neutron fluxes up to 1.5×1018 m−2 s−1 (thermal) and 3×1018 m−2 s−1 (fast) in a light water reactor, the change of conductivity jump slope is negligible or nil for an ionic thermometer filled by HgI2, i.e., at 256.0±0.2 °C. The need to use boron-free glass was confirmed. The impact on the accuracy of the temperature point indication in a nuclear reactor core is discussed, as well as obvious inertness of the melting process mechanism to the intense irradiation field.
Problems in the use of synchronously pumped picosecond laser systems for Raman spectroscopy
Authors: Everall N. , Howard J. , Hutchinson K. , Jackson R. W.
Published: July 2002

Emissions at wavelengths other than the main laser wavelength have been observed in Raman studies using a mode-locked and cavity-dumped picosecond laser system with a birefringent filter as a tuning element. These lead to very intense spurious features in the Raman spectra of solids. Operation of the standard laser system at low repetition rates leads to most of the laser power being carried in leakage light pulses.
Simple inexpensive high-voltage rectangular pulse generator
Authors: Grase F.
Published: July 2002

In this paper, we describe a simple high-voltage rectangular pulse generator for the gating of an image intensifier tube (type EMI 9912). This device, which uses a krytron, is able to furnish 4-kV pseudo-rectangular pulses with variable widths from 30 to 100 ns or more. The possible repetition rate is about 30 pps, the rise and fall time 5 ns, the total delay 100 ns, and the jitter less than 5 ns. The image intensifier tube is used for the study of luminous samples using the Raman effect.
Microcomputer-controlled Langmuir–Blodgett dipping trough
Authors: Van Ryswyk Hal , Eisenhart Joann M. , Blom Nils
Published: July 2002

An Apple II interfaced to a Langmuir–Blodgett trough and a microbalance maintains interactive control on film deposition.
Observation of electric field gradients near field-emission cathode arrays
Authors: Liang Y. , Bonnell D. A. , Goodhue W. D. , Rathman D. D. , Bozler C. O.
Published: July 2002

The variation of electric field gradient above arrays of field emission cathodes has been investigated using atomic force microscopy. The spatial distribution of electric field gradient was obtained as a function of bias and height. Results show a parabolic relationship between the sample bias and electric field gradient. Furthermore, the height dependence of the field gradient is found to follow a power law relationship. These new results demonstrate that force-gradient atomic force microscopy is capable of providing a direct visual presentation of the variation of field gradients above submicron-periodicity field emitter arrays.
Plasma calorimeter for absorption measurement of laser produced plasma
Authors: Uchida Shigeaki , Tanaka Masakazu , Sakawa Youichi , Nishimura Hiroaki , Yamanaka Tatsuhiko , Yamanaka Chiyoe
Published: July 2002

A new type of plasma calorimeter has been developed for laser light absorption and measurement of laser irradiated targets. The principle of this detector is the same as a bolometer; plasmas and x rays are absorbed by a thin glass plate which is transparent enough for laser light, and temperature rise of the absorber plate is detected by a faint increase of the resistance of a nickel resistance bulb. The structure and application example are described.
Instrument for differential ion flux vector measurements on Spacelab 2
Authors: Stone N. H. , Lewter B. J. , Chisholm W. L. , Wright K. H.
Published: July 2002

The differential ion flux probe (DIF probe) is a scientific instrument capable of deconvolving a multiplicity of ion streams, differing in flow direction and/or energy, and independently determining the flow direction, current density, temperature, and energy of each stream. The original instrument concept was developed for laboratory investigations in the area of plasma dynamics and was reported [N. H. Stone, Rev. Sci. Instrum. 48, 1458 (1977). Since then, the DIF probe has been redesigned and developed into a flight instrument to provide measurements of disturbed plasma flow conditions within the terrestrial ionosphere. It has flown on the STS-3 Space Shuttle mission, on sounding rockets, and recently on the Spacelab-2 mission as part of the plasma diagnostics package (PDP) experiment. Herein, we discuss the unique design and operational characteristics required for the flight model of the DIF probe.
Perpendicular ion energy analyzer for hot-ion plasmas
Authors: McCarrick M. J. , Ellis R. F. , Koepke M. , Majeski R. P.
Published: July 2002

A miniature analyzer probe is described for measuring the component of the ion energy distribution perpendicular to the confining magnetic field in a hot-ion plasma. The analyzer employs the magnetic field to exclude electrons due to their small gyroradii. Ions are selectively retarded by a positively biased collector. The limits on the operating regime of this analyzer are calculated. The device is used in the MIX 1 mirror machine where we measure an ion temperature of ∼100 eV and plasma density ≳1011 cm−3.
Corona excited supersonic expansion
Authors: Engelking P. C.
Published: July 2002

Stable operation of a corona excited supersonic expansion for the production of cold radicals or ions requires control of the geometry, chemistry, and electrical parameters. The nozzle must taper rapidly on the high-pressure side to a throat that opens up into a free expansion on the vacuum side. Optimum radical and ion production is obtained with only a few percent of precursor in an inert carrier gas. Capacitive loading must be kept to a minimum to prevent oscillation. It is shown that the finite response time of the plasma synthesizes an inductance that serves to decouple the negative resistance of the plasma from the rest of the circuit. Practically, oscillation is prevented if the circuit RC time constant is shorter than that which the plasma can follow.
A variable temperature ESE–ENDOR resonator for single-crystal studies
Authors: Reijerse E. J. , Klaassen A. A. K.
Published: July 2002

A microwave resonator is described for performing electron spin-echo (ESE) and electron spin-echo electron nuclear double resonance (ESE–ENDOR) measurements on single crystals. The ENDOR coil arrangement allows the crystal to be rotated about two independent axes. The system operates in a temperature range from 4 to 300 K using a helium flow cryostat.
Detector array for the measurement of the 14.7-MeV proton emission from TFTR
Authors: Strachan J. D.
Published: July 2002

The magnitude of the d(3He, p) α fusion emission is measured on the tokamak fusion test reactor (TFTR) by detection of the prompt losses of 14.7-MeV protons. This system consists of four detectors poloidally distributed along the bottom of TFTR. Each detector spatially resolves 14.7-MeV protons which are born above the detector and which grad B drift into the detector.
Design considerations for the construction of a reflecting symmetric multipass cell for use in laser molecular-beam experiments
Authors: Lethbridge P. G. , Stace A. J.
Published: July 2002

A theoretical discussion is presented of the design features that have been incorporated into a multipass cell appropriate for use in laser molecular-beam experiments. A detailed description of the cell in two dimensions is given, and this is later expanded to highlight the problems of alignment in three dimensions. A prototype cell, constructed using the guidelines presented here, has demonstrated that 31 passes through a molecular beam can be easily achieved. Computer simulations suggest that the optimum potential of the cell is ≊101 passes. The fact that the position of the emergent laser beam is clearly defined makes the cell particularly useful for the purposes of studying absorption spectra.
Pulsed EPR spectrometer
Authors: Quine Richard W. , Eaton Gareth R. , Eaton Sandra S.
Published: July 2002

A pulsed EPR spectrometer is described. This spectrometer is designed for the study of relaxation times of dilute solutions of samples in common solvents as a function of temperature both above and below room temperature. Resolution of pulse widths and spacings is 1 ns. Both continuous wave (cw) and pulsed electron spin-echo studies can be done on the same sample on the same spectrometer. Details of component choices and timing synchronization are provided. Phase alternation sequences for eliminating unwanted echoes are described. Examples of performance of the spectrometer are presented.
Magnetized double-plasma device for wave studies
Authors: Pierre T. , Leclert G. , Braun F.
Published: July 2002

The characteristics of the magnetized plasma obtained in a modified double-plasma device are presented. Primary ionizing electrons are produced by filament discharges in multipole devices located on either end of a magnetized plasma column. A very uniform magnetized plasma is produced in the column with a relatively small number of filaments by using coils to counterbalance the fringing field near the filaments. The obtained plasma is well suited for a large variety of wave experiments. The noise is maintained at a low level and the afterglow measurements reveal a very efficient confinement of the ionizing electrons, with a decay time of 0.2 ms.
Dye laser wavelength stabilization: An active control by interferometric fringe detection
Authors: Manohar K. G. , Dasgupta K. , Suri B. M. , Bhawalkar D. D.
Published: July 2002

An active wavelength stabilization and scanning system is described which reduces the dye laser wavelength fluctuation under feedback by detecting the changes in the fringe diameter of a temperature-stabilized Fabry–Perot interferometer with the help of two photodiodes. An estimate of the wavelength drift due to thermal effects is made. Short- and long-term fluctuations in the wavelength, monitored by recording iodine fluorescence are reported. The system response to a sudden external disturbance to the wavelength was studied.
Simple scheme for variable high-power laser beam attenuation
Authors: Bialkowski Stephen E.
Published: July 2002

A venetian style infrared attenuator placed prior to a pinhole spatial filter results in variable high-power laser attenuation. This attenuation scheme has a wide dynamic range, results in high-quality Gaussian beams, does not introduce beam walk-off error, and is independent of polarization.
Real-time, vibration-compensated CO2 interferometer operation on the DIII-D tokamak
Authors: Carlstrom T. N. , Ahlgren D. R. , Crosbie J.
Published: July 2002

A multichannel, two-color, quadrature heterodyne interferometer is used to measure the line density in the DIII-D tokamak. The unique feature of this real-time vibration-compensated interferometer is the combination of high speed (1 MHz), high resolution (2π/256), and wide range (±8193 fringes). Quadrature phase information from a CO2 laser (10.6 μm) and a He–Ne laser (0.63 μm) are digitized with high-speed (6 MHz) flash digitizers. Zero crossings of the signals are counted with digital circuitry yielding quarter fringe resolution with a 4-MHz bandwidth. Further fringe resolution of 1/256 is provided at 350 kHz by a PROM which uses the digital signals as input to a look-up table. Analog line density is presently available at 80 kHz with a system noise equivalent phase shift of ±2/256. Error monitoring is provided for low signal amplitude and exceeding the maximum fringe rate. In addition, a method to prevent coating of in-vessel mirrors due to plasma and vessel wall cleaning discharges has been developed.
Experimental apparatus for measuring noise in MOSFETs on silicon wafers
Authors: Comeau A. , Aubin M. , Orchard-Webb J. H.
Published: July 2002

We present an apparatus for measuring noise in MOSFETs on silicon wafers. The system can measure noise accurately down to 10 nV/Hz1/2 and has a useful bandwidth of 0.01 Hz to 30 kHz. The drain current, source voltage, gate voltage, and the temperature (77 to 400 K) are computer controlled. We have designed a chip with both N and P channel test transistors in a range of sizes and geometries. The chip also includes a diode for temperature measurement. The wafers are processed in a controlled industrial environment giving reproducible device characteristics. Schematics for an ADC-DAC high-performance card offering many programmable features are also presented. A very-low-noise preamplifier working at liquid-nitrogen temperature is also described. The system is not restricted to measuring MOS transistors; any passive or active device can be measured making only simple changes to the bias circuitry. We also present results obtained with a typical MOSFET.
Transmission characteristics of a triple quadrupole mass spectrometer with leaky dielectric end plates
Authors: Ketkar S. N. , Fite W. L.
Published: July 2002

The use of a rf-only quadrupole in tandem with a normal resolving quadrupole introduces artifacts in the mass spectra obtained using such an instrument. The reason for this is the presence of fringe fields in the region between the two quadrupoles. We report here the use of leaky dielectric material in between the two quadrupoles to avoid these artifacts.
High-sensitivity small size mirror mount
Authors: Damany H. , Laporte P.
Published: July 2002

A small size mirror mount is described, whose high sensitivity is obtained by the use of coaxial differential screws.
Technique for determination of the metastable fraction of multicharged ion beams
Authors: Snowdon K. J. , Havener C. C. , Meyer F. W. , Overbury S. , Zehner D. M. , Heiland W.
Published: July 2002

This article presents a simple method for absolute determination of the metastable content of a multicharged ion beam. The method takes advantage of the efficient neutralization of highly charged ions at metal surfaces. Filling of projectile inner shell vacant states occurs in part by Auger decay, leading to a characteristic projectile peak in the electron emission spectrum. The appearance of this peak is, therefore, a direct signature of either the existence of the corresponding vacancy in the incident projectile beam, or of a production process for this vacancy in the interaction. The role of the latter is determined by the use of Li-like projectiles, which have no metastable states. The method is calibrated by measuring the intensity of the ‘‘projectile peak’’ for a beam known to contain this vacancy. Using this method the metastable content of N5+, O6+, Ar8+, and Ar7+ beams from the ORNL electron cyclotron resonance ion source has been determined.
Chromatic time lag in picosecond-streak-camera objectives
Authors: Ihlemann J. , Helmbold A. , Staerk H.
Published: July 2002

Wavelength-dependent time lags due to group velocity dispersion (GVD)—much larger than estimated and documented thus far—have been determined experimentally for some widely used streak camera objectives. Correction procedures for signals delayed and broadened by group dispersion in streak camera objectives are briefly outlined.
Conceptual design and numerical simulation of a correlation diagnostic for measurement of magnetic fluctuations in plasmas
Authors: Thomas C. E. , Hanson G. R. , Gandy R. F. , Batchelor D. B. , Goldfinger R. C.
Published: July 2002

It has been previously suggested that crossed-sightline correlation of electron cylotron emission might be used to measure magnetic fluctuations in high-temperature plasmas. Reported here are the results of a continuing project to determine under what conditions (if any) this measurement will be feasible. An initial conceptual design for the device hardware has been completed. Large portions of the numerical simulation are working, including ray-tracing and emission/absorption packages. An initial discussion of data analysis for the experimental data is presented, and an analysis of the uncertainty in the line center (magnetic field) measurement in terms of the experimental uncertainties is given.
Proposed 2-MeV beam probe system for TEXT upgrade
Authors: Hickok R. L. , Schoch P. M.
Published: July 2002

Initial design studies of a heavy-ion beam probe that would be capable of accessing the full plasma cross section of Texas Experimental Tokamak upgrade showed that it would require a 2-MeV Tl+ beam. Such a beam probe would have an estimate sensitivity for measuring broadband potential fluctuations of 2 V rms, an accuracy for measuring potential profiles of ±40 V, and a resolution for measuring normalized broadband density fluctuations of 0.1%.
Resonance enhancement of optoacoustic signal for frequency stabilization of CO2 laser pump for CH3OH FIR laser
Authors: Fishback J. R. , Azar M. , Ventrice C. A. , Hutchinson D. P.
Published: July 2002

The resonance enhancement of an optoacoustic signal, generated in methyl alcohol vapor, is investigated with the objective of obtaining a reliable discriminator at reduced pump power levels. The 9P(36) pump line from a CO2 laser is used throughout the study. The optoacoustic signal strength and resonator Q are measured at the fundamental longitudinal resonant frequency for various resonator geometries and vapor pressures. Resonators of length ranging from 12 to 24 cm are examined for tubes of inner diameter 7.5, 9.5, and 10.6 mm. The maximum vapor pressure for which a reliable discriminator is obtained is found to be 1 Torr. Both the optacoustic signal strength and the resonator Q increase with increasing vapor pressure and decreasing resonator length. The highest Q is obtained for the 10.6-mm-i.d. tubes. Using a resonator of the length 14 cm and 10.6-mm i.d. at a vapor pressure of 1 Torr, it is found that a pump power as low as 0.4 W gives a reliable discriminator.
A precise calibration system for high-resolution visible-laser spectroscopy
Authors: Adam A. G. , Merer A. J. , Steunenberg D. M. , Gerry M. C. L. , Ozier I.
Published: July 2002

A method for calibrating high-resolution laser spectra in the visible is described. The system is based on an evacuated Fabry–Perot étalon whose cavity length is servolocked to a stabilized HeNe laser; the absolute order number of the fringe at the HeNe frequency is known and the free spectral range can be determined with high accuracy. For absolute-frequency measurements the order number of a transmission fringe is obtained from a commercial wavemeter (whose accuracy is sufficient to identify the fringe); the absolute frequency is then the HeNe frequency multiplied by the ratio of the ‘‘unknown’’ order number to the ‘‘lock-point’’ order number. The long-term frequency reproducibility of the system is better than 25 MHz. Small-frequency splittings such as molecular hyperfine intervals can be measured to ±1 MHz, while large-frequency intervals (of the order of 500 GHz) are consistent to better than 10 MHz.
Subpicosecond synchroscan operation of a Photochron IV streak camera
Authors: Finch A. , Sleat W. E. , Sibbett W.
Published: July 2002

The electronic drive circuitry employed in the operation of a synchroscan Photochron IV streak camera is described. The experimental performance of two synchronization systems, a passive configuration (whereby the deflection signal is derived directly from a mode-locked pulse source) and an active system (incorporating a tunnel-diode oscillator phase locked to the laser), have been compared. A semiquantitative assessment of phase noise in the deflection signal and its effects on achievable temporal resolution is detailed and tested experimentally. On the basis of this analysis it has been possible to optimize the streak circuitry and thereby demonstrate a limiting instrumental resolution of 930 fs.
Probing of the quantum dot size distribution in CdTe-doped glasses by photoluminescence excitation spectroscopy
Authors: de Oliveira C. R. M. , de Paula A. M. , Plentz Filho F. O. , Medeiros Neto J. A. , Barbosa L. C. , Alves O. L. , Menezes E. A. , Rios J. M. M. , Fragnito H. L. , Brito Cruz C. H. , Cesar C. L.
Published: July 2002

We studied confinement effects in CdTe quantum dots by means of photoluminescence excitation spectroscopy. We show that by changing the detection energy we can resolve the spectrum of quantum dots of different sizes inside their much broader size distribution in CdTe-doped glass. The spectra obtained show several well-resolved lines. There is excellent agreement between the photoluminescence excitation spectra peak energies and calculations of the confined energy transitions based on a modified multiband envelope function model.
A method to measure magnetic field perturbations in plasma devices
Authors: Jackson G. L. , DeGrassie J. S. , Schaffer M. J. , Taylor T. S. , Gentle K. W.
Published: July 2002

Magnetic field perturbations with specific spatial geometry can be detected in the presence of a large magnetic field ‘‘background’’ using printed circuit pickup coils which have the advantages of large effective area, near dc frequency response, precise geometry, thin profile, and low cost. The design and construction techniques to produce these coils are presented. A printed circuit coil has been used to detect the magnetic field from the perturbed plasma current distribution in the TEXT tokamak due to current in an external helical (m=7,n=3) winding. The measured sensitivity of this coil, ΔBcoil/Btotal, is ∼3×10−6.
Characterization of microchannel plates for plasma x-ray diagnostics in the 0.6–82-keV energy region
Authors: Yamaguchi N. , Cho T. , Kondoh T. , Hirata M. , Miyoshi S. , Aoki S. , Maezawa H. , Nomura M. , Satow Y.
Published: July 2002

Current response characteristics of microchannel plates (MCPs) x-ray detectors have been measured in a wide energy range from 0.6 to 82 keV using synchrotron radiation. In the current response curve with continuous photon energy, some discontinuities have been observed to correspond to absorption edges of elements which are the constituents of MCP glass and electrode materials (Si, Pb, Ba, and Fe). The dependence of the MCP response on the incident angle of x rays to the channel axis, θ, is also investigated. The characteristics change from the cot θ dependence for soft x rays (hν<4 keV) to the sec θ one for hard x rays (hν>60 keV). These results could provide guidelines on the design of x-ray diagnostic instruments using MCPs.
Triple resonance pulse transformer circuit
Authors: Bieniosek F. M.
Published: July 2002

A modified, resonant pulse transformer circuit, based on a generalization of the well-known double-resonance pulse transformer circuit, is described. This modified circuit allows complete energy transfer in the presence of non-negligible internal capacitance of realistic pulse transformers, and substantially reduces peak transformer voltage, compared to the double-resonance circuit. Conditions under which the internal capacitance significantly affects energy transfer, and sensitivity of overall efficiency to circuit component values are discussed.
Dynamic technique for measurement of the thermal conductivity and the specific heat: Application to silica aerogels
Authors: Bernasconi A. , Sleator T. , Posselt D. , Ott H. R.
Published: July 2002

We describe a dynamic technique for measuring both the thermal conductivity and the specific heat of poor thermal conductors in a single measurement. The technique is an extension of the widely applied thermal-relaxation technique. In the case of a sample having a thermal conductance comparable to the rate at which heat is removed from the sample, the observed temperature behavior of the specimen during its relaxation depends on both its thermal conductivity λ and specific heat Cp. This allows a determination of both thermal properties in a single measurement. In the present work this technique has been applied to the study of aerogels, which have a very low thermal conductivity at low temperatures (1.5<T<30K). Our results for samples with different mass densities are in agreement with previously published data obtained using other techniques and clearly confirm that the thermal properties in this class of materials are in magnitude and temperature dependence very different from classical disordered materials.