bluuebunny/crossref_metadata_2025 huggingface dataset:
Charge-transfer-induced optical bistability in an asymmetric quantum-well structure
Authors: Seto M. , Helm M.
Published: July 2002

We present self-consistent calculations of the energy levels in an asymmetric coupled quantum-well structure coupled to a CO2 laser source which is nearly resonant with an intersubband transition. Solving Schrödinger’s and Poisson’s equations concurrently with a set of rate equations, it is shown that intrinsic optical bistability can be achieved. The bistability arises from charge transfer and a subsequent, self-consistent shift of the energy levels which feeds back to the absorption rate. Using realistic parameters, an on-off intensity ratio of 4:1 at switching powers of a few 100 kW/cm2 is predicted at about 10-μm wavelength.
Giant enhancement of luminescence intensity in Er-doped Si/SiO2 resonant cavities
Authors: Schubert E. F. , Vredenberg A. M. , Hunt N. E. J. , Wong Y. H. , Becker P. C. , Poate J. M. , Jacobson D. C. , Feldman L. C. , Zydzik G. J.
Published: July 2002

Si/SiO2 Fabry–Pérot microcavities with rare-earth-doped SiO2 active regions are realized for the first time. Cavity-quality factors exceeding Q=300 are achieved with structures consisting of two Si/SiO2 distributed Bragg reflectors and an Er-implanted (λ/2) SiO2 active region. The room-temperature photoluminescence intensity of the on-axis emission is 1–2 orders of magnitude higher for resonant cavity structures as compared to structures without a cavity.
Transverse electric and transverse magnetic polarization active intersubband transitions in narrow InGaAs quantum wells
Authors: Peng L. H. , Smet J. H. , Broekaert T. P. E. , Fonstad C. G.
Published: July 2002

Polarization-resolved infrared spectroscopy has been used to demonstrate the existence of transverse electric (TE) and transverse magnetic (TM) active intersubband transitions in lattice-matched, unstrained In0.53Ga0.47As/In0.52Al0.48As and strained In0.7Ga0.3As/AlAs quantum wells grown by molecular beam epitaxy on Fe-doped semi-insulating InP (001) substrates. It is shown that a previously reported intersubband absorption peak at 0.3 eV in a 4.0-nm wide, lattice-matched InGaAs/InAlAs quantum well can be resolved into two peaks active for TE and TM polarizations, respectively, with a 10 meV splitting between them. Bound to quasibound state transition at 0.59 eV (2.1 μm) for a narrow, 2.8-nm-wide InGaAs quantum well has also been observed. Group symmetry analyses considering D2d symmetry, tetragonal perturbation of local crystal and strain deformation potential, and interface roughness of the ternary quantum-well structure is proposed to explain the polarization selection rules, and the Stark splitting in the intersubband absorption.
Novel technique for preparing porous silicon
Authors: Hummel R. E. , Chang Sung-Sik
Published: July 2002

We have performed photoluminescence studies on porous, p-type as well as n-type silicon wafers which have been prepared in air or in a dry nitrogen atmosphere, utilizing a spark-erosion technique. This sample preparation, which does not involve aqueous solutions or fluorine contaminants, yields similar photoluminescence spectra as those obtained by anodic etching in HF or unbiased etching in various HF-containing reagents. The wavelength of the photoluminescence peaks are somewhat shifted into the blue region compared to porous silicon obtained by anodic etching. We have also taken photoluminescence spectra on amorphous silicon, SiO2, and oxidized, annealed porous silicon. Our results are interpreted in the light of the presently suggested theories.
Co/Ag multilayer film: Role of annealing on the magnetic properties
Authors: Schelp L. F. , Tosin G. , Carara M. , Baibich M. N. , Gomes A. A. , Schmidt J. E.
Published: July 2002

Co(15 Å)/Ag(60 Å) multilayers produced by electron beam deposition on a 50 Å chromium buffer layer over a Si(111) wafer have been studied by magnetoresistance, saturation magnetization, coercivity, and anisotropy. Annealing at various temperatures produces striking effects on the observed physical properties, such as an improvement on the value of the magnetoresistance associated to a ‘‘back-diffusion’’ process in the Co/Ag interfaces. This leads one to believe that interface roughness is indeed most important to understanding the connection between giant magnetoresistance and antiferromagnetic coupling, as well as the behavior of coercivity vs interface anisotropy in these materials.
Grazing-incidence x-ray diffraction characterization of Co-Pt magneto-optical thin films
Authors: Huang T. C. , Savoy R. , Farrow R. F. C. , Marks R. F.
Published: July 2002

The microstructures of epitaxial CoxPt1−x films (x≊0.25 and 0.5) and the orientation relationships with sapphire (0001) single-crystal substrates were determined by grazing-incidence x-ray diffraction. The epitaxial relationships between the CoPt3 film and its substrate are CoPt3[11̄0]∥Al2O3[303̄0] and CoPt3(111)∥Al2O3(0001). A significant amount of the ordered L12 phase was detected in CoPt3. The degree of long-range order in CoPt3 was 0.3, and the average domain size of the ordered phase was 80 Å. The CoPt film had two domains related by a 30° in-plane rotation. The epitaxial relationships between the CoPt film and its substrate were CoPt[100]∥Al2O3[303̄0] and CoPt(011)∥Al2O3(0001) for domain A and CoPt[100]∥Al2O3[112̄0] and CoPt(011)∥Al2O3(0001) for domain B. Domain A was found to be dominant and/or had a higher degree of long-range order than domain B.
Phosphorus diffusion in isoconcentration backgrounds under inert conditions in silicon
Authors: John Jay P. , Law Mark E.
Published: July 2002

The diffusivity of phosphorus in isoconcentration backgrounds under inert conditions in silicon is investigated. Phosphorus is implanted at low dose into silicon wafers that are constantly doped with arsenic and boron. These samples are annealed to remove any damage. Secondary ion mass spectroscopy (SIMS) measurements are taken of these as-implanted samples. The wafers are then diffused at both 900 and 1100 °C for 60 and 30 min, respectively. The wafer profiles are then measured using SIMS. The diffusivity of phosphorus is measured for five different dopant concentrations. The results show that a double-negative interstitial component of phosphorus is needed to adequately model the data. Also, the heavily doped boron sample shows a significantly retarded diffusivity at 1100 °C which suggests phosphorus-boron pairing or significant strain effects on diffusion.
High-power buried InGaAsP/GaAs (λ=0.8 μm) laser diodes
Authors: Garbuzov D. Z. , Antonishkis N. Ju. , Zhigulin S. N. , Il’inskaya N. D. , Kochergin A. V. , Lifshitz D. A. , Rafailov E. U. , Fuksman M. V.
Published: July 2002

Buried InGaAsP/GaAs (λ=0.78 μm) separate confinement-single quantum well laser diodes have been prepared and studied for the first time. It has been shown that a stable far field pattern can be observed even at 500 mW continuous wave (cw) output power for diodes with active region width of about 7 μm, and single zero-mode operation has been obtained up to 170 mW cw for diodes with a width of 3.8 μm. Mirror facet overheating for the diodes studied was an order of magnitude less than that for similar AlGaAs/GaAs diodes.
Monolithic integration of a vertical cavity surface emitting laser and a metal semiconductor field effect transistor
Authors: Yang Y. J. , Dziura T. G. , Bardin T. , Wang S. C. , Fernandez R. , Liao Andrew S. H.
Published: July 2002

Monolithic integration of a vertical cavity surface emitting laser (VCSEL) and a metal semiconductor field effect transistor (MESFET) is reported for the first time. The epitaxial layers for both GaAs VCSELs and MESFETs are grown on an n-type GaAs substrate by molecular-beam epitaxy (MBE) at the same time. The VCSELs with a 10 μm diam active region exhibit an average threshold current (Ith) of 6 mA and a continuous wave (cw) maximum power of 1.1 mW. The MESFETs with a 3 μm gate length have a transconductance of 50 mS/mm. The laser output is modulated by the gate voltage of the MESFETs and exhibits an optical/electrical conversion factor of 0.5 mW/V.
Selective etching of InP and InGaAsP over AlInAs using CH4/H2 reactive ion etching
Authors: Arnot H. E. G. , Glew R. W. , Schiavini G. , Rigby L. J. , Piccirillo A.
Published: July 2002

Selective etching of InP and InGaAsP over AlInAs was obtained using CH4/H2 reactive ion etching without the addition of a fluorine containing gas. By tuning the methane-to-hydrogen ratio, pressure, and power, sputter desorption of the reacted AlInAs etch products can be inhibited, thus enabling AlInAs to be used as an etch stop layer. The use of a fluorine free mixture enables dielectrics such as silicon dioxide or nitride to be used as the masking material.
Er3+ doping of CaF2 layers grown by molecular beam epitaxy
Authors: Daran E. , Bausa L. E. , Muñoz-Yagüe A. , Fontaine C.
Published: July 2002

Molecular beam epitaxy of CaF2 monocrystalline layers Er3+ doped up to a concentration of 5 wt % is demonstrated on CaF2 substrates. Separated effusion cells containing CaF2 and ErF3 were used. The photoluminescence spectra of the samples show emissions from centers of different symmetry identified by reference to published results obtained on CaF2:Er3+ bulk crystals. No influence of the substrate orientation—(100) or (111)—on the luminescence characteristics was observed.
Demonstration of Y1Ba2Cu3O7−δ and complementary metal-oxide-semiconductor device fabrication on the same sapphire substrate
Authors: Burns M. J. , de la Houssaye P. R. , Russell S. D. , Garcia G. A. , Clayton S. R. , Ruby W. S. , Lee L. P.
Published: July 2002

We report the first fabrication of active semiconductor and high-temperature superconducting devices on the same substrate. Test structures of complementary metal-oxide-semiconductor transistors were fabricated on the same sapphire substrate as test structures of Y1Ba2Cu3O7−δ flux-flow transistors, and separately, Y1Ba2Cu3O7−δ superconducting quantum interference devices utilizing both biepitaxial and step-edge Josephson junctions. Both semiconductor and superconductor devices were operated at 77 K. The cofabrication of devices using these disparate yet complementary electronic technologies on the same substrate opens the door for the fabrication of true semiconductive/superconductive hybrid integrated circuits capable of exploiting the best features of each of these technologies.
Nitrogen doping in AlGaP grown by metalorganic vapor phase epitaxy using ammonia
Authors: Adomi K. , Noto N. , Nakamura A. , Takenaka T.
Published: July 2002

Doping characteristics of nitrogen in AlGaP grown by metalorganic vapor phase epitaxy have been investigated using ammonia as the nitrogen source. It was found that nitrogen could be successfully incorporated into AlGaP up to as much as 1×1020/cm3 assisted by the gas phase parasitic reaction between trimethylaluminum and ammonia, while nitrogen incorporation into GaP was difficult. Nitrogen incorporation was found to be dependent on several factors such as ammonia concentration, Al composition, V/III ratio, and growth temperature. Exciton recombination bound to isoelectronic nitrogen in AlGaP was observed for the first time by photoluminescence measurement.
Highly oriented Hg-Ba-Ca-Cu-O superconducting thin films
Authors: Adachi Hideaki , Satoh Toshifumi , Setsune Kentaro
Published: July 2002

Hg-Ba-Ca-Cu-O thin films have been prepared on SrTiO3(100) substrates by rf-magnetron sputtering and subsequent annealing. The annealing treatment was carried out in a Hg-free atmosphere at the relatively low temperature of 650–700 °C. The films showed a highly oriented structure with the c axis of the Hg-1201 phase perpendicular to the substrates. The Hg-Ba-Ca-Cu-O films exhibited a sharp superconducting transition at around 85 K, and a resistivity anomaly at the higher temperature of 130 K was observed for some films.
Defect reduction by MeV ion implantation for shallow junction formation
Authors: Saito S. , Kumagai M. , Kondo T.
Published: July 2002

p-type shallow junction formation requires residual defects reduction for ion implantation to suppress boron-enhanced diffusion. We have demonstrated that MeV ion implantation is effective to reduce end-of-range defects for shallow junction formation. F+ preimplantation was carried out at 40 keV with a dose of 1×1015 cm−2. B+ ions were implanted at 10 keV with a dose of 5×1015 cm−2 in the F+-preimplanted samples, followed by 1 MeV F+, Si+, or 2 MeV As+ implantation at substrate temperatures of room temperature and 400 °C with doses ranging from 5×1014 to 5×1015 cm−2. Annealing was carried out by rapid thermal annealing at 1000–1100 °C for 10 s. F+ preimplantation induced shallower junction formation, however, much reduction of the junction depth was observed by 1 MeV F+ or Si+ implantation, because of end-of-range defects reduction for the suppression of boron-enhanced diffusion. About a 50% shallower junction depth was obtained by F+ preimplantation, followed by 1 MeV F+ or Si+ implantation, when this junction was compared with just B+-implanted samples.
Optical emission from the laser-induced plasma during excimer laser etching of diamondlike carbon films
Authors: Seth Jayshree , Padiyath R. , Babu S. V.
Published: July 2002

Optical emission from the laser-induced plasma plume produced during KrF (248 nm) excimer laser etching of diamondlike carbon films has been characterized. The emission spectrum in the visible and UV wavelength regions is dominated by the C2 Swan bands (d3Πg−a3Πu), CN violet bands (B2 Σ+−X2 Σ+), and a continuum emission in the 500–700 nm range. The emission intensities of the major bands are a strong function of film density. Higher emission intensities are observed during the etching of low-density films. The molecular vibrational temperatures for C2 and CN radicals, calculated from the emission intensities, are in the range of 10 000–20 000 K.
Band-gap engineering in periodic elastic composites
Authors: Kushwaha M. S. , Halevi P.
Published: July 2002

Periodic elastic composites can give rise to complete band gaps in which vibrations, sound, and phonons are forbidden. This is of interest for applications such as creation of vibrationless environment and improvements in transducers, as well as for pure physics related to localized vibrations and phonons. We present rudimentary ideas of the ‘‘band-gap engineering’’ necessary for designing suitable frequency gaps. This is illustrated by means of acoustic band structures, computed for periodic, binary composites of long, elastic cylinders that form a hexagonal lattice.
Solid-state reaction-mediated low-temperature bonding of GaAs and InP wafers to Si substrates
Authors: Ma Z. , Zhou G. L. , Morkoç H. , Allen L. H. , Hsieh K. C.
Published: July 2002

We report a low-temperature wafer bonding method for the realization of integration of GaAs- and InP-based optoelectronic devices with Si microelectronic devices. This method uses a Au-Ge eutectic alloy as the bonding material sandwiched between GaAs and Si wafers, and between InP and Si wafers. The bonding process was carried out at 280–300 °C by taking advantage of the low-temperature solid-state reactions occurring at GaAs/Au-Ge, InP/Au-Ge, and Si/Au-Ge interfaces. Both the simple mechanical test and standard thermal cycling test prove excellent structural integrity of the joined wafers. Structural analyses reveal only limited interfacial reactions as well as solid-phase epitaxial regrowth of GeSi alloys on the Si substrate.
Thermodynamic stability of GaAs sulfur passivation
Authors: Medvedev Yu. V.
Published: July 2002

The solid-state part of the Ga-As-S-O quaternary equilibrium phase diagram has been established from thermodynamic calculations. It is shown that GaS forms a chemically stable interface with GaAs, while As2S3 tends to react with GaAs and the reaction results in elemental As segregation at the GaAs/native sulfide interface. A recently developed chemical vapor deposition of GaS provides, hence, an ideal chemical passivation of GaAs.
Glancing angle x-ray diffraction: A different approach
Authors: Brussel B. A. van , Hosson J. Th. M. De
Published: July 2002

This letter describes a novel technique of diffracted beam glancing angle x-ray diffraction by which depth profiles of stresses and transformed phases in structures like implanted materials can be determined. An important feature is that this method may be applied successfully in a standard powder diffractometer. It is shown that, beside the well-known incident beam glancing angle method which usually requires rather sophisticated equipment with parallel beam optics combined with more intense x-ray sources, diffracted beam glancing angle x-ray diffraction can be applied as well.
Core-level photoemission and the structure of the Si/SiO2 interface: A reappraisal
Authors: Banaszak Holl Mark M. , Lee Sunghee , McFeely F. R.
Published: July 2002

Photoemission spectroscopy of spherosiloxane cluster derived Si/SiOx interfaces has allowed the direct assignment of observed spectral features to specific chemical moieties. The implications of these assignments for structural models of the Si/SiO2 interface are explored. Models specifically constructed to be consistent with photoemission data are shown to be incorrect after reanalysis of core-level shifts based on the recently synthesized model systems. A new model for the Si/SiO2 interface is proposed which is consistent with the current understanding of photoemission for Si/SiOx interfaces as well as with results from numerous other experiments.
Growth of KNbO3 thin films on MgO by pulsed laser deposition
Authors: Zaldo C. , Gill D. S. , Eason R. W. , Mendiola J. , Chandler P. J.
Published: July 2002

Crystalline and stoichiometric KNbO3 thin films have been grown on (100) oriented MgO substrates by pulsed laser deposition technique. Electron microprobe analysis and Rutherford backscattering spectroscopy of the films show a progressive loss of K with increasing substrate-target distance. To compensate for this K loss the ceramic KNbO3 targets were enriched with K2CO3 powder, pressed at room temperature, and sintered at 650 °C. For a substrate-target distance of 6 cm, targets with [K]/[Nb] molar ratio=2.85 yield stoichiometric KNbO3 films. A partial oxygen pressure of 2×10−2 mbar was optimum for growing transparent films. Films grown between 650 and 700 °C show the KNbO3 crystalline phase with its (110) axis preferentially oriented perpendicular to the surface of the substrate. At these temperatures KNbO3 diffusion into the MgO substrate is observed. Films grown from KNbO3 single crystal targets only contain a Mg4Nb2O9 crystalline layer.
Laser-induced deposition of alumina from condensed layers of organoaluminum compounds and water
Authors: Moore J. F. , Strongin D. R. , Comita P. B. , Ruckman M. W. , Strongin Myron
Published: July 2002

The photoassisted deposition of thin aluminum oxide films from layers of trimethylaluminum (TMA), dimethylaluminum hydride, and aluminum hexafluoroacetylacetonate condensed with water on a cold substrate has been investigated. Laser energies of 4.6 or 2.3 eV were used to drive the reactions which led to film growth. Experiments show that clean aluminum oxide films can be synthesized at 80 K by irradiating co-condensed TMA and H2O with 4.6 eV light. Techniques used to characterize the films include Auger electron spectroscopy and scanning electron microscopy.
Picosecond luminescence dynamics in CdS/CdSe Stark superlattices
Authors: Langbein W. , Hetterich M. , Grün M. , Klingshirn C. , Kalt H.
Published: July 2002

Screening of the intrinsic piezoelectric fields in hexagonal, strained layer CdS/CdSe type II superlattices by optically generated electron-hole pairs leads to a shift of the optical transitions of up to 400meV. After intense picosecond excitation, the transition energy follows a logarithmic law as a function of time. This temporal behavior is consistent with model calculations of the density dependent transition-matrix elements in the tilted bandstructure.
Bright red light-emitting organic electroluminescent devices having a europium complex as an emitter
Authors: Kido Junji , Hayase Hiromichi , Hongawa Kenichi , Nagai Katsutoshi , Okuyama Katsuro
Published: July 2002

Organic electroluminescent (EL) devices with a trivalent europium (Eu) complex as an emitter were fabricated. Triple-layer-type cells with a structure of glass substrate/indium-tin oxide/ triphenyldiamine derivative (TPD)/Eu complex: 1,3,4-oxadiazole derivative (PBD)/aluminum complex (Alq)/Mg:Ag exhibit bright red luminescence upon applying dc voltage. The EL spectrum consists of extremely sharp emission bands, which is a typical luminescence spectrum of the Eu complex. Luminance of 460 cd/m2 with an emission peak at 614 nm is achieved at a drive voltage of 16 V. This is the highest luminance so far obtained for the EL cells having a Eu complex as an emitter.
Selective removal of potassium from K4In4Sb6 via laser ablation/ionization
Authors: Panayotov Valentin , Hamar Kyle , Birdwhistell Teresa L. T. , Red Clarence , Dillon Jennifer , Dennison David , Barnes Anthony P. , Koplitz Brent
Published: July 2002

Results are reported on the Zintl phase material, K4In4Sb6, with respect to laser ablation and subsequent laser ionization/removal processes. A 308 nm laser pulse is used to ablate the Zintl compound, while a second laser ionizes ejected species within the extraction region of a time-of-flight mass spectrometer. With the second laser operating at 248 nm, selective ionization and removal of the potassium is clearly demonstrated. Such a strategy takes advantage of the different ionization potentials of K, In, and Sb, and implications for possible applications of this research to film growth are discussed.
Highly efficient light emission from ZnS1−xTex alloys
Authors: Sou I. K. , Wong K. S. , Yang Z. Y. , Wang H. , Wong G. K. L.
Published: July 2002

ZnS1−xTex (0≤x≤1) single-crystal alloy films were grown on GaAs and Si substrates by molecular beam epitaxy. Strong photoluminescence in the yellow to blue light region, with room-temperature external quantum efficiencies of 2%–4% at an unoptimized excitation wavelength of 365 nm, was observed. The enhancement of luminescence was attributed to the presence of Te isoelectronic hole traps in the films. Strong bowing of the band-gap energy as a function of composition x was also observed, with the minimum near x=0.7. The line width as well as the Stokes shift of the luminescence peak from the band edge were found to increase as Te composition decreases.
Use of InN for Ohmic contacts on GaAs/AlGaAs heterojunction bipolar transistors
Authors: Ren F. , Abernathy C. R. , Chu S. N. G. , Lothian J. R. , Pearton S. J.
Published: July 2002

Degenerately doped (n=5×1020 cm−3) InN grown by metalorganic molecular beam epitaxy is used for emitter Ohmic contacts on GaAs/AlGaAs heterojunction bipolar transistors (HBTs). Both abrupt InN/GaAs and graded GaAs/InGaAs/InN contact structures were investigated. Although, the contact resistivity of nonalloyed Ti/Pt/Au on InN was achieved as low as 1.8×10−7 Ω cm2, formation of a thin GaN layer at the interface of the InN/GaAs system limits nonalloyed TiPtAu metallization to contact resistivities of 10−4 Ω cm2. Whereas the graded structure, GaAs/InGaAs/InN material, system produces values of 5×10−7 Ω cm2 which resulted in the formation of conductive InN from nitridation of InAs instead of the GaN layer for the InN/GaAs system. The InN-based emitter contacts have superior surface morphologies to the more conventional InAs layers. The C-doped base (p=7×1019 cm−3) HBTs utilizing 2×5 μm2 InN-based emitter contacts is demonstrated with dc gains of 35.
X-ray tomography on plasmas with arbitrary cross sections and limited access
Authors: Decoste R.
Published: July 2002

An x-ray imaging system is described for 2D reconstructions of plasmas with viewing access limitations. A relatively small number of 72 detectors distributed over six fan arrays first provides partial views of the toroidal plasma in a poloidal plane. Next, the line-integrated data is deconvoluted using a computerized tomographic approach based on linear algebra and a least-squares fit. The arrangement and the number of detectors have been optimized to the point where significant reconstruction improvements are limited by available viewing access rather than by the number of lines of sight.
Fusion product measurements in tokamaks (invited; abstract)
Authors: Strachan J. D.
Published: July 2002

Diagnostic methods and the applications of fusion product measurements in tokamaks are reviewed with emphasis on results from PLT, PDX, and TFTR. Measurements have been made using the 2.5-MeV neutron from the d(d, n)3He reaction, the 3-MeV proton from the d(d, p)t reaction, both the 3.7-MeV alpha and the 14.7-MeV proton from the d(3He, p)α reaction, and the 14-MeV neutron from the d(t, n)α reaction. The common use of these measurements is the determination of the ion temperature from the magnitude of the d-d neutron emission. For tokamak plasmas, these results are usually in good agreement with the charge exchange ion temperature. Recently, the charged fusion products have been used for high-resolution spectroscopic purposes, and emission profile measurements. Pitch angle resolution of the escaping 3-MeV proton emission has been used to determine the poloidal magnetic field inside the tokamak. Major issues in this field include the expected tritium operation on TFTR where the neutron measurements will determine when tritium will be introduced into the TFTR vessel and provide a measurement of the fusion power multiplication value (Q). The TFTR Q∼1 experiments will also provide a chance to measure the confinement of 3.5-MeV alphas in a tokamak.
Magneto-optical ellipsometer
Authors: Nederpel P. Q. J. , Martens J. W. D.
Published: July 2002

A magneto-optical ellipsometer is described which uses polarization modulation and the longitudinal magneto-optical Kerr effect. The ellipsometer allows a full determination of the optical and magneto-optical constants of magnetic materials, as well as the registration of in-plane hysteresis loops. The latter application is illustrated on a Ni80Fe20 thin-film sample.
High-energy Nd:glass laser system for Thomson scattering diagnosis of high-temperature and low-density plasmas
Authors: Dooling J. C. , York T. M.
Published: July 2002

The determination of temperature of electron density of reactor-grade fusion plasmas (T>5 keV, Ne≥1013 cm−3) will require enhanced capability in Thomson scattering diagnostics. While improved detection systems will help, it is clear that the scattered population must be increased because of the excessive thermal broadening. The system described here has a Nd:glass oscillator followed by three stages of amplifier. At present, the system generates a 60 J single pulse with beam divergence less than 0.6 mR. This pulse can be used with a KDP-II frequency doubler to generate 30 J pulses of 1.06 and 0.53 μm.
Low-energy helium nozzle beam
Authors: Kern Klaus , David Rudolf , Comsa George
Published: July 2002

A high-intensity supersonic nozzle beam source is described, whose beam energy can be varied between 2 and 170 meV (helium). Experimental performance and time-of-flight measurements on cold helium beams are reported. Condensation in the free jet expansions of helium has been studied by mass spectrometric detection of He+2. A correlation between the maximum speed ratio and the onset of clustering is observed.
High-intensity flash x-ray apparatus for biomedical radiography
Authors: Sato E. , Isobe H. , Hoshino F.
Published: July 2002

The construction of a soft flash x-ray (FX) apparatus with a new type of FX tube for biomedical use is described. The FX apparatus may be used for condenser charging voltages of 50–90 kV and peak currents of 20–40 kA. The electric pulse width of the FX waveforms was almost constant and its value was about 0.3 μs. The effective focal spot varied according to the condenser charging voltage, the anode–cathode (A–C) distance, etc., ranging from 0.2–3.0 mm in diameter. We selected two combinations of electrodes: (a) for normal focusing and a high dose rate; (b) for fine focusing and a low dose rate. The FX intensity was determined by the condenser charging voltage and the A–C distance, while the FX quality (average spectrum distribution) was determined by the average voltage of the FX tube and insertion of metal filters. The average voltage of the FX tube varied according to the condenser charging voltage and the A–C gap impedance. Various clear FX images were obtained by controlling the FX intensity, quality, and the focal spot size. We used Fuji Computed Radiography (FCR) in conjunction with our FX radiography, and by controlling the FX quality and the focal spot size, we obtained some interesting biomedical radiograms.
TFTR diagnostic neutral beam
Authors: Schilling G. , Kozub T. A. , Medley S. S. , Young K. M.
Published: July 2002

A neutral beam has been designed and fabricated to aid in the measurement of ion temperatures of hot, dense tokamak fusion test reactor (TFTR) plasmas. The injected fast neutral atoms offer a twofold benefit: (1) Penetration to the plasma center considerably increases charge exchange neutralization of thermal plasma ions, leading to a localized enhancement of the thermal neutrals efflux into charge exchange neutral analyzers; and (2) charge exchange recombination of fully stripped intrinsic impurity ions, C or O, with fast neutrals allows Doppler broadening and shift measurements of the emitted light to determine both the impurity ion temperature and toroidal rotation with unbalanced beam heating. The design and construction of the beam and those features of the beam unique to its function as a diagnostic tool for TFTR will be presented.
Electron temperature and fluctuation correlation measurements using dual analyzers with a heavy ion beam probe
Authors: Michael J. D. , Saravia E. , Hickok R. L. , Jennings W. C.
Published: July 2002

A heavy ion beam probe has been operated with two separate electrostatic energy analyzers to allow simultaneous detection of 2+ and 3+ secondary ions coming from a singly charged probing beam. This configuration provides rapid, spatially resolved measurements of the electron temperature for Te ≤200 eV, and measurements of the correlation between density and space potential fluctuations from two separate locations in the plasma. The possibility of electron temperature fluctuations can also be investigated. Since the spatial location of the measurements can be varied, the correlation length in both the kr and kθ directions can be determined.
‘‘Tray’’ type calorimeter for the 15–300 K temperature range: Copper as a specific heat standard in this range
Authors: Martin Douglas L.
Published: July 2002

A calorimeter is described in which thermal contact with the sample is made via a grease film. Radiation shields built into the calorimeter minimize the effect of temperature gradients. Used in an adiabatic shield system the apparatus gives results of high precision and accuracy. The new design permits easy sample changing but there is a small specific heat anomaly owing to melting of the grease film. An all-metal water triple point cell can be installed in place of the sample to check the temperature measuring equipment. The adiabatic shield system used had four independently controlled elements. Experiment showed that a single controlled element is sufficient for discontinuous heating calorimetry. The apparatus could be run in both continuous and discontinuous heating modes. There was no significant difference in results. Measurements on pure copper are reported and the use of this material as a specific heat standard up to 300 K is discussed.
Novel two-dimensional position-sensitive detection system
Authors: Knibbeler C. L. C. M. , Hellings G. J. A. , Maaskamp H. J. , Ottevanger H. , Brongersma H. H.
Published: July 2002

A novel two-dimensional position-sensitive detection system has been designed, built, and tested. It has a relatively short processing time (900 ns) which enables countrates up to 105–106/s. The detector has a ring-shaped geometry. Both polar coordinates can be determined with an accuracy better than 1%. Although intended for use in an ion scattering spectrometer, the system can also be used for detection of other atomic particles or photons.
Performance of an automated rotating-detector ellipsometer
Authors: Nick David C. , Azzam R. M. A.
Published: July 2002

A computer-controlled rotating-detector ellipsometer (RODE) has been constructed using a windowless planar-diffused Si photodiode, a stepping motor, an operational amplifier, and a personal computer (PC) equipped with an A/D-D/A converter. The detector is mounted to the output shaft of the stepping motor at an optimum angle of incidence of ∼59° and is rotated through 360° about the incident beam as an axis. The detector output signal voltage is measured and stored in the PC at every 2° increment of the RODE angle θ. Fourier analysis of the recorded data provides a handedness-blind determination of the state of polarization of the incident light. A beam from a HeNe laser (λ=632.8 nm) is transmitted through the polarizing optics of an ellipsometer to provide the polarization states needed for calibration and testing. The calibration parameters mL and θr are determined by rotating the detector about a linearly polarized beam of light of zero reference azimuth. The RODE is subsequently tested and found to correctly measure the first two normalized Stokes parameters of a number of states with a residual rms error of ∼0.002. This limit on precision is dictated mainly by the 12-bit A/D converter. A small angular misalignment of the rotation axis of the detector with respect to the light-beam axis introduces odd harmonics in the detector signal; hence, its effect is readily isolated by appropriate data reduction. Thin-film coatings on the detector surface that significantly improve the performance of the RODE are proposed.
Small-scale electrochemical cleaning of molybdenum to improve spotwelding characteristics
Authors: Jones Mark E. , Koel Bruce E. , Weppner Richard T.
Published: July 2002

Electrochemical cleaning of molybdenum immediately prior to spotwelding has been found to improve adherence of both tungsten and tantalum to molybdenum. Normally electrochemical cleaning is accomplished by immersion in a large bath. We have had excellent results cleaning a small area under a single drop of cleaning solution immediately prior to spotwelding.
High speed signal averager for characterizing periodic signals in the time domain
Authors: Hair Dennis W. , Niertit Frank J. , Hodgson Donald F. , Amis Eric J.
Published: July 2002

A new data-acquisition and averaging system is described which rapidly digitizes and averages periodic signals of known frequency. Each acquisition channel has a programmable gain input amplifier, track and hold amplifier, 12 bit analog to digital converter, 4K by 32 bit memory buffer, and an arithmetic logic unit which adds the converter output directly to the contents of the current memory location. In the present implementation, two channels are used in parallel with a common sampling clock at rates up to 1.35 MHz. With real time ‘‘add to memory’’ capability, signal averaging can be continued to any desired degree in order to improve the signal-to-noise ratio and reject contributions from harmonics and asynchronous frequencies. This type of acquisition system is most suitable where a periodic signal of known frequency is applied to an experimental device and the system’s response, at the same frequency, must be accurately determined. The phase resolution of better than ±0.001° which this system provides, is particularly important for analysis of a ‘‘drive and response’’ experiment of this type.
Wide-band acousto-optic light modulator for frequency domain fluorometry and phosphorimetry
Authors: Piston David W. , Marriott Gerard , Radivoyevich Tomas , Clegg Robert M. , Jovin Thomas M. , Gratton Enrico
Published: July 2002

Multifrequency-phase and modulation fluorometry allows for accurate analysis of fluorescence decay in the frequency domain. Essential to these frequency domain methods is a high-frequency modulation of the light source. Techniques for generating wide-band modulation of light are currently limited to the use of Pockel’s cells and intrinsically modulated sources such as mode-locked lasers and synchrotron radiation. We present a method that employs two acousto-optic modulators in series for use with cw light sources. This modulator system gives two orders of magnitude more intensity output than the Pockel’s cell modulator and requires less than one-tenth of the rf driving power. In addition, the Pockel’s cell system is limited to modulation frequencies less than 250 MHz, whereas the particular implementation discussed here gives a quasicontinuous distribution of modulation frequencies from dc to 320 MHz. To obtain this range of frequencies, acoustic standing waves are set up simultaneously in each modulator, and the desired modulation frequency is achieved by choosing the proper combination of the two standing-wave frequencies. Light modulation is obtained at twice each of the individual standing-wave frequencies and at the sum and difference of twice the two acoustic frequencies. Data are presented to illustrate the use of this system for the measurement of phosphorescence as well as fluorescence decay.
Apparatus for codeposition and layered deposition of reactive metals and volatile organic compounds with control of stoichiometry and film thickness
Authors: Skowyra Joseph B. , Dye James L. , Pratt W. P.
Published: July 2002

An effective method is reported for the simultaneous or sequential physical vapor deposition of reactive alkali metals and volatile macrocyclic complexants which react to form thin stoichiometric films of alkalides and electrides. These thermally unstable and highly reactive films, typically between 300 and 1500 Å thick, are deposited under high vacuum onto a quartz substrate which can be cooled to as low as −130 °C. Quantitative optical absorption measurements are made on these films in situ. Acquisition of the optical data and control of sample deposition rates, oven temperatures, and film thicknesses are accomplished with a computer.
Four-channel x-ray spectrometer on a transmission grating with a combined system of detection
Authors: Alexandrov Yu. M. , Koshevoi M. O. , Murashova V. A. , Nikitina T. F. , Rupasov A. A. , Shikanov A. S. , Sklizkov G. V. , Yakimenko M. N. , Zakharenkov Yu. A. , Eidman K. , Sigel R. , Tsakiris G. D.
Published: July 2002

We have developed a new soft x-ray spectrometer covering the photon energy range of 50–500 eV. It employs a free-standing transmission grating coupled to a microchannel-plate detector (MCD). The performance of the device was tested by using radiation from a synchrotron with a continuous spectrum. The MCD shows a rather flat response over most of the useful spectral range, with an abrupt decrease in the sensitivity at the short-wavelength end. Its simplicity of operation makes the device attractive for such applications as the study of soft x-ray emission from laser-produced plasmas.
MAXIMUM: Status of the scanning photoelectron microscope (abstract)
Authors: Cerrina F. , Lai B. , Gong C. , Ray-Chaudhuri A. , Margaritondo G. , Green M. A. , Höchst H. , Cole R. , Crossley D. , Collier S. , Underwood J. , Brillson L. J. , Franciosi A. , DeLuca P. M. , Gould M. N.
Published: July 2002

The construction of the MAXIMUM scanning photoelectron microscope has been recently funded. A preliminary description has already been reported.1 We will present the final construction layout of the system, with particular attention dedicated to the optical components. Briefly, the system is based on a variable line spaced grating monochromator used to filter the radiation emitted by a 30 poles undulator installed at Aladdin. The radiation is then refocussed on a pinhole that is suitably demagnified by a Schwartzschild objective to a spot of less than 0.1 μm. The sample is located at the focus and mechanically rastered. The photoelectrons are energy analyzed by a commercial cylindrical mirror analyzer. The main characteristics of the system will be (1) high flux, (2) independent energy and spatial resolution, and (3) independent photon and electron energy resolution. All the components are fully decoupled thus allowing maximum flexibility. Detailed ray-tracing and flux estimates based on our new undulator modelling codes2 will be presented.
Optimization of a synchrotron based x-ray lithographic system
Authors: Bernieri E. , Balerna A.
Published: July 2002

Exposure time and mask contrast are two of the main parameters affecting the x-ray lithographic (XRL) process. In a synchrotron-based XRL system (SXRL), both parameters strongly depend on the source spectrum and beamline characteristics. Calculations have been done in order to optimize a SXRL system (source+beamline), taking also into account another important parameter like resolution. One of the main results is that a ‘‘cutoff’’ mirror, generally used in many beamlines, strongly increases exposure times without significantly improving contrast and resolution.
Lithography beamline design and exposure uniformity controlling and measuring
Authors: Qian Shinan , Jiang Dikui , Liu Zewen , Chen Qianhong , Kan Ya , Liu Wanpo
Published: July 2002

The lithography beamline design of Hefei National Synchrotron Radiation Laboratory is presented. A scanning mirror is used to cut off short wavelength radiation and to expand the vertical exposure dimension to 50 mm. A thin beryllium window is installed before the scanning mirror to prevent the longer wavelength radiation from going through. An exposure chamber with a vacuum of 5×10E−7 Torr is located at 7 m downstream from the source point. Because there is no window at the entrance of the chamber, a differential pumping system is used. The scanning mirror is driven by a stepping motor which oscillates through a 1° angle. The required driving speed curve is determined by a computer in order to obtain a uniform exposure area. An in situ moiré fringe grating system is used to measure the uniformity of the motor speed.
Modeling of undulator sources (abstract)
Authors: Chapman K. , Lai B. , Cerrina F. , Viccaro J.
Published: July 2002

We present a new code capable of realistically modeling the radiation from ideal undulator sources, including explicit electron emittance effects. The code has been developed as part of the SHADOW1 x-ray optics ray-tracing program, in order to predict the performances of undulator-based optical systems. The approach is based on a simplified field distribution that allows an efficient calculation of the electron trajectory and of the radiation field. We show explicitly that the undulator radiation pattern is shift-invariant with respect to the electron’s trajectory angles, so that the emittance effects can be included without recomputing the radiation distribution. Furthermore, the time consuming computation of the undulator emission patterns is decoupled from the Monte Carlo sampling of the wavefront, leading to a very fast code. This is achieved by computing the three-dimensional source probability distribution function and then using an inversion algorithm to generate a random variate according to the source distribution. The physical basis of the code and the algorithm used are discussed in detail and some results presented.
Performance of the cooling system for the soft x-ray double-crystal monochromator at the Photon Factory
Authors: Funabashi M. , Nomura M. , Kitajima Y. , Yokoyama T. , Ohta T. , Kuroda H.
Published: July 2002

A crystal cooling system was designed and tested successfully for the soft x-ray double-crystal monochromator in an ultrahigh-vacuum environment at the Photon Factory. The temperature rise at the surface of the InSb first crystal is reduced to less than 45 °C at an average stored current of 200 mA. With the help of a control software, the output beam can be fixed in a position for a wide energy range. In this paper, the heating effect on the double-crystal monochromator, and the design and performance of a water cooling system are described.
Injection, dynamic aperture, and beam instability of a small synchrotron radiation source in the hard-x-ray region
Authors: Okuda S. , Nakanishi T. , Itoga K. , Nakata S. , Yamamoto S. , Yamada T. , Iwamoto M.
Published: July 2002

A small synchrotron radiation source in the hard-x-ray region was conceptually designed and its injection scheme, dynamic aperture, and beam instabilities were studied. Synchrotron radiation with the critical wavelength of  0.1 nm is emitted from a pair of superconducting bending magnets. The storage ring has only one pair of quadrupole magnets to save its drift space. The decay time of the kicker magnet and the angle between the central orbit and the orbit of the injected beam were optimized by computer simulation. The reduction of the dynamic aperture due to the errors of the bending field is less than 20%. Considerations of possible instabilities showed that there is no critical instability up to the beam current of 200 mA when the beam is injected with higher energy than 650 MeV.
A spherical electrostatic spectrometer for surface Mössbauer studies
Authors: Stadnik Z. M. , Borsje H. R. , Swolfs A. E. M. , Leenders W. H. A. , Fuggle J. C.
Published: July 2002

The construction and operation of an ultrahigh-vacuum spherical electrostatic spectrometer for surface Mössbauer studies is reported. Data are presented which suggest that the recoil-free fraction at room temperature of very thin oxide layers on the surface of an iron foil is low.
VISAR analysis in the presence of large intensity changes: Application to the expanding ring
Authors: Gourdin W. H.
Published: July 2002

A method is described for adjusting recorded beam-intensity (offset) data to allow accurate recovery of weak fringes in a VISAR record. Extrema of the difference signal are used to determine the offset at intervals of π. A linear interpolation method is then employed to adjust the recorded beam-intensity data to pass through these points. Results from expanding ring experiments are used to demonstrate the technique.
Simple heating chamber for alloying contacts to Hall-effect samples
Authors: Schwartz B. D.
Published: July 2002

We describe a simple and efficient heating chamber which is useful for alloying metal-semiconductor contacts for Hall-effect measurements. Wafer sections up to 1 cm×1 cm can be heated to 750 °C within 2 min.
Spark gap monitoring circuit
Authors: Shikarkhane N. S.
Published: July 2002

I describe a circuit which gives reliable data of the firing sequence of a laser chain with the use of cheap plastic fiber-optic cables and counter circuits. This eliminates the need of an oscilloscope. The circuit is able to store data of up to 16 shots, and it can pinpoint a malfunctioning stage of a Marx bank from a large number of such units.
A design of large current ion gun employing liquid metal ion source
Authors: Mori Yuzo , Wang Hui , Endo Katsuyoshi , Yamauchi Kazuto , Ide Takashi
Published: July 2002

A lens system for a large current liquid metal ion source has been designed by a numerical computer simulation method. As a computed result, the lens system can focus an ion beam having an emission angle of 60° to a beam having a radius of 1.8 mm at 1 m from the ion source. Following the simulated result, the lens system was constructed and tested. When the total ion current extracted from the ion source was less than 10 μA, more than 95% of the total ion was focused to a beam with a radius of about 2 mm at 1 m from the ion source, which agreed well with the computer simulation result. When the total ion current became more than 10 μA, the minimum radius of the focused ion beam at 1 m from the ion source gradually increased with it. However, even if the total ion current was more than 50 μA, almost 80% of it could be obtained on a 1×1 cm2 target at 1 m from the ion source.