bluuebunny/crossref_metadata_2025 huggingface dataset:
Production of high-energy photons from flash x-ray sources powered by stacked Blumlein generators
Authors: Coogan J. J. , Davanloo F. , Collins C. B.
Published: July 2002

Described here is the design and construction of a pulse-power generator capable of discharging at high repetition rates. It consists of eight triaxial Blumleins stacked in series at one end. These lines are charged in parallel and synchronously commuted with a single thyratron at the other end to produce an open circuit voltage across a stack of six times the charging voltage. An x-ray diode has been constructed and matched to this pulse-power source making possible the emission of an average bremsstrahlung exposure rate of 17 R/S from a sequence of 40-ns pulses. When operated at 60-kV charging voltage, direct spectral measurements show the output to be a true continuum, peaking at intensities in excess of 5×108 photons/keV/shot and containing useful intensities of photons having energies of 300 keV.
Silicon detector for low-energy electron spectroscopy
Authors: Daneshvar K. , Aitken R. G. , Singco G.
Published: July 2002

A novel silicon surface barrier detector has been constructed for low-energy electron spectroscopy. This detector consists of a high-resistance silicon wafer which is sandwiched between a rectifying barrier front and ohmic back contacts. The front electrode is a gold mesh metallization with an effective area of 8% of the detector surface. This electrode allows most of the electrons to reach the active region of the detector with the smallest possible degradation in their energy distribution due to electron straggling in the front electrode.
A metastable hydrogen atomic beam: Construction and characteristics
Authors: Biraben F. , Garreau J. C. , Julien L. , Allegrini M.
Published: July 2002

A detailed report on a thermal beam of 2S metastable hydrogen (deuterium) atoms is given. This beam is produced in two steps: molecular dissociation in a radiofrequency discharge and electronic bombardment. We have obtained a good collimation (beam spread ≂0.8°) and a very accurate shielding against electric parasitic fields so that quenching losses from the source region to the detection region are reduced to ≂2%. Velocity distribution in the beam has been thoroughly studied. We have recently used this beam to remeasure the fundamental physical constant R∞ (Rydberg constant) with a very high accuracy, limited only by the wavelength and frequency standard in the optical region. The characteristics of such a beam, although specifically designed for this measurement, can also be interesting for different types of experiments.
A controllable vibratory calciner for processing high-temperature superconductors and other ceramic powders
Authors: Spencer Nicholas D. , Beeckman Jean W. , Peders Thorvald S. , Cameron Craig P.
Published: July 2002

A novel vibratory calcination apparatus is described, that enables reactant powders to be heated at or above their sintering temperatures without excessive agglomeration. In addition, the vibration-induced fluidization leads to greatly improved gas-solid contact, which can significantly speed up reactions that are limited by the ingress or egress of gases. Unlike its gas-fluidized counterpart, the vibratory calciner does not lead to excessive loss of fines. Vibration is generated by means of a function generator-amplifier-loudspeaker voice coil system, which allows amplitude, frequency, and time dependence of frequency to be precisely controlled. The system has been used extensively in the laboratory for the calcination of high-temperature superconducting powders, where its use has led to greatly reduced calcination times and a much lower degree of agglomeration in the finished material.
Temperature control in small air-heated measuring cells
Authors: Iglesias María Celia López , Barón Máximo
Published: July 2002

Temperature control in a liquid sample contained in a Chatelain prism was achieved in a closed chamber through warm air circulation. A proportional electronic thermostat and two very small and thin thermistors allowed a control within ±0.1 °C.
Finite-element design of a guarded heating cylinder to measure thermal properties of materials
Authors: Nicolas J. , Martin F. , Andre Ph. , Rivez J.-F.
Published: July 2002

A device for the measurement of thermal properties of phase change materials and, in general, of medium thermal conductivity materials, is described. The measuring cell is a modified version of the guarded hot plate technique, here designed for about 8-cm-diam samples. A well-known difficulty arises in such a device: its limitation when the sample cross section becomes too small with respect to its thickness. A finite-element model is used to study the shape of isotherms in a thick sample (10 cm) for different configurations of the measuring device. This analysis has led to the selection of the optimum design. It shows that the instrument is able to handle samples with a diameter to thickness ratio of about 1 so far as the heat transfer coefficient remains beneath some limits (here 100 W/m2 K). The control system is also described and some typical results are presented.
Diagnostic system for determining the internal structure of a field reversed configuration
Authors: Slough J. T. , Milroy R. D.
Published: July 2002

A set of diagnostics has been developed to determine the structure and internal density profile of a field reversed configuration (FRC) in a nonperturbing manner. The primary diagnostic is a 50-channel tomographic array which uses bremsstrahlung radiation from the FRC in either the visible or near infrared. End-on imaging in both the visible and soft x-ray regions are used to improve inversion accuracy by providing additional information in the form of constraints. A five-channel interferometer will be used as a baseline check on the imaging diagnostic, and provide information on the basic symmetry of the FRC. Up to 80 BΘ probes, with the application of a diagnostic axial current, will be used to detect external changes in separatrix shape. Comparison of diagnostic signals with signals calculated from 3-D MHD simulations will provide for additional determination of internal mode activity.
Magnetic diagnostics in Alcator C-MOD
Authors: Granetz R. S. , Hutchinson I. H. , Gerolamo J. , Pina W. , Tsui C.
Published: July 2002

The full package of magnetics diagnostics for Alcator C-Mod is now installed inside the vacuum vessel. This consists of four poloidal arrays of pickup coils for measuring Bp, three Rogowski coils, a set of full flux loops, two diamagnetic loops with compensation coils, a small 2-D array of Mirnov coils to measure edge fluctuations, and some partial flux loops for detecting locked modes. All the coils have been absolutely calibrated to ±0.5% before installation, and an in situ calibration of this system will also be carried out. Internal mounting enables fast response despite the shielding effects of skin currents in the thick vessel wall. However, this complicates the design considerably due to constraints on physical size, vacuum compatibility, temperature extremes, protection from plasma damage, etc.
High throughput multilayer mirror based soft x-ray spectrometer for metallic impurity emission from tokamaks
Authors: Zwicker A. P. , Regan S. P. , Finkenthal M. , Moos H. W.
Published: July 2002

A near-normal incidence high throughput spectrometer with a flat multilayer mirror (MLM) as the dispersive element has been built and operated on the Texas Experimental Tokamak (TEXT). Using a Mo/B4C MLM that has a reflectivity of 20–30% and a bandpass of 4–9 Å (FWHM), the instrument has a wavelength range of 90–180 Å. The spectra obtained with this instrument have been compared to an artificial spectrum based upon a collisional-radiative model. From this comparison it is possible to identify the dominant titanium emission lines responsible for the broadband shape of the low-resolution experimental spectrum. This work is part of our continuing development of simple, near-normal incidence high throughput spectrometers for tokamak plasma diagnostics.
Simple raster generator for use with scanning tunneling microscopes
Authors: Maps J.
Published: July 2002

A simple, inexpensive circuit to generate a two-dimensional raster pattern for use in a scanning tunneling microscope is presented. The circuit is constructed from common analog and digital integrated circuits. Externally provided dc voltages and the use of analog multipliers allow for easily programmed scan ranges and the system is easily expanded for higher density images. Interfacing to personal computer-based data acquisition and video frame grabber boards is discussed.
A fully three-dimensional-movable, 10-m-long, remotely controllable probe drive for a plasma discharge device
Authors: Pfister H. , Gekelman W. , Bamber J. , Leneman D. , Lucky Z.
Published: July 2002

A unique, fully three-dimensional-movable, 10-m-long, remotely controllable probe drive, internal to a high vacuum system, is described. Details of its design and constructional considerations take into account the hostile environment of a magnetized plasma (p = 8 × 10−8 Torr, T=250 °C, and B=3000 G).
Analysis of large-area beam attacks on surfaces and testing of etching reactions
Authors: Janes J. , Bänziger U. , Huth Ch , Hoffmann P. , Neumann G. , Scheer H.-C. , Schneemann B. , Köhler U.
Published: July 2002

An apparatus has been constructed to analyze the particle flux of positive ions on surfaces from dry etching reactors. The particle flux can emerge from a great variety of reactive ion etching systems or from reactive ion beam etching sources. The particle beam passes through a small orifice with a diameter of 100 μm. A differentially pumped quadrupole mass spectrometer with a specially designed ion transfer optics performs the energy analysis of positive ions. The energy range can be varied between 0 and 500 eV with a resolution of 1%. The angular distribution measurements of the particle flux are carried out varying the inclination of the mass analyzer by ±20° with the vertex lying centrally in the sampling orifice. The angular resolution is about 1°. Rotation of the source on top of the apparatus and translation over ±10 cm in xy direction and 15 cm in z direction perpendicular to it is provided in order to assure fully local resolution. The electrical properties of the orifice-ion optics system is discussed with respect to their influence on ion trajectories. The purpose of the apparatus is to provide data on particle fluxes relevant for microelectronic processing.
The KSU-CRYEBIS: A unique ion source for low-energy highly charged ions
Authors: Stockli Martin P. , Ali R. M. , Cocke C. L. , Raphaelian M. L. A. , Richard P. , Tipping T. N.
Published: July 2002

The CRYogenic electron beam ion source at Kansas State University has been in operation since spring 1989. It produces up to Ar18+, Kr34+, and Xe44+ on a regular basis. Acceleration tubes and a beamline system were added during 1990. The ion source is mounted on a high voltage platform, which can be used to vary the ion energies between 2 and 200 kV per charge. The extraction-, analyzing-, and beamline systems were designed to accept a wide range of ion masses and charge states with the mass energy product (M⋅E/q2) stretching over four orders of magnitude. The system is used to study the low-energy highly charged ions interacting with electrons, atoms, thin foils, and surfaces.
Sources and methods of repetitively pulsed ion/plasma material treatment
Authors: Ryabchikov A. I. , Nasyrov R. A.
Published: July 2002

A brief review is presented on repetitively pulsed ‘‘Raduga 1–4’’ ion sources based on evaporation of the cathode material by vacuum arc. Their operation principles and functional possibilities are described. ‘‘Raduga-1,3’’ ion sources provide a formation of one component and multicomponent, not composition-controlled high intensity ion beams. Ion sources ‘‘Raduga-2,4’’ generate energy/composition-controlled multicomponent ion beams. Operation conditions of the sources providing a treatment of the details of complex shape as well as ion plasma treatment of the target are given. Features and prospects of the methods of repetitively pulsed multielement and high concentration implantation are discussed. The method of repetitively pulsed high concentration implantation is realized under ion/plasma operating conditions of the ion source ‘‘Raduga’’ and ion sputtering compensation of the target by plasma deposition.
Development of a dc, broad beam, Mevva ion source
Authors: Brown I. G. , Dickinson M. R. , Galvin J. E. , MacGill R. A.
Published: July 2002

We are developing an embodiment of metal vapor vacuum arc (Mevva) ion source which will operate dc and have a very large area beam. In preliminary testing, a dc titanium ion beam was formed with a current of approximately 0.6 A at an extraction voltage of 9 kV (about 18 keV ion energy, by virtue of the ion-charge state distribution) using an 18-cm-diameter set of multiaperture extraction grids. Separately, we have tested and formed a beam from a 50-cm-diameter (2000 cm2) set of grids using a pulsed plasma gun. This configuration appears to be very efficient in terms of plasma utilization, and we have formed beams with a diameter of 33 cm (FWHM) and ion current up to 7 A at an extraction voltage of 50 kV (about 100 keV mean ion energy) and up to 20 A peak at the current overshoot part of the beam pulse. Here we describe this part of our Mevva development program and summarize the results obtained to date.
Ultralow power low noise ultrahigh frequency magnetic resonance spectrometer
Authors: Andersen P. M. , Sullivan N. S. , Phelps L. W. , Legg J. B.
Published: July 2002

We describe a simple marginal oscillator that operates at ultralow power dissipation (≥20 μW at 750 MHz) for use in ultrasensitive low noise magnetic resonance detection at very low temperatures. We have operated the circuit down to 0.6 K with the sample maintained below 20 mK and in magnetic fields up to 4.0 T. The samples are maintained at mK temperatures by physically separating the sample from the rf coil.
A Bonse–Hart ultrasmall angle x-ray scattering instrument employing synchrotron and conventional x-ray sources
Authors: Chu Benjamin , Li Yingjie , Gao Tong
Published: July 2002

A Bonse–Hart ultrasmall angle x-ray scattering (USAXS) instrument employing both synchrotron and conventional x-ray sources was constructed. The instrument could be used to determine the structure of systems with inhomogeneity sizes on the order of ∼1000 nm. The characteristics of the instrument by using synchrotron and conventional x-ray sources were compared. The use of synchrotron radiation showed much improved features not only in scattered intensity, but also in angular resolution. The scattered intensity was increased by a factor of about 20. Therefore weaker scattering systems could be investigated. By using the synchrotron radiation, the deficiency of the Bonse–Hart camera could be compensated. An angular scan containing ∼30 data points in the scattering angle region smaller than ∼2 mrad with reasonable signal-to-noise ratio could be completed within 5–10 min for samples with reasonable scattering power. Therefore, kinetic studies could be possible if the half time of structural development in a system is of the order of hours. For static experiments, a conventional x-ray source could be used more conveniently to obtain a scattering curve with similar quality as that by means of synchrotron radiation partially because the channel-cut crystals were not optimized for the synchrotron beam divergence and partially because alignments could be accomplished at a more leisurely pace using the conventional x-ray source.
Absolute ultrasonic displacement amplitude measurements with a submersible electrostatic acoustic transducer
Authors: Yost William T. , Cantrell John H.
Published: July 2002

An experimental technique for absolute measurement of ultrasonic wave particle displacement amplitudes in liquids is reported. The technique is capable of measurements over a frequency range of two decades with a sensitivity less than one angstrom. The technique utilizes a previously reported submersible electrostatic acoustic transducer (ESAT) [Rev. Sci. Instrum. 50, 31 (1979)] featuring a conductive membrane stretched over a recessed electrode. An uncertainty analysis shows that the displacement amplitude of an ultrasonic plane wave incident on the ESAT can be experimentally determined to better than 2.3%–4%, depending on frequency, in the frequency range of 0.5–15 MHz. Membranes with lower and more uniform areal densities can improve the accuracy and extend the operation to higher frequencies.
Solid-state cesium ion gun for ion beam sputter deposition
Authors: Kim S. I. , Ahn Y. O. , Seidl M.
Published: July 2002

A compact cesium ion gun, suitable for ion beam sputter deposition in high vacuum environment, has been developed. The gun uses a solid-state cesium ion source described previously. This gun is compact, stable, and easy to use. It requires none of the differential pumping or associated hardware necessary in designs using cesium vapor and porous tungsten ionizers. The gun produces a cesium ion beam of 0.2 mA at 5 keV. A beam diameter of 0.2 cm is measured at a target which is 3 cm apart from the exit aperture of the accelerator electrode. The sputter deposition rate is of the order of 100 Å/min for several metal targets such as Au, Cu, Mo, W, and Ta, measured at 4 keV primary Cs+ ion beam energy and in a distance of 1.5 cm from the target. The lifetime of this gun is more than 20 C of cesium, which corresponds to 60 h of operation with an extraction current of 0.1 mA.
Measurement of beam properties and reproducibility on recent PBFA II target shots
Authors: Moats A. R. , Derzon M. S. , Johnson D. J. , Nelson W. E. , Pantuso J. G. , Ruiz C. L. , Wenger D. F.
Published: July 2002

Recent proton experiments on Particle Beam Fusion Accelerator II used a 2 μm gold foil cone to characterize the ion beam. Using the ion beam images obtained by viewing beam-induced characteristic line radiation emitted by such foils with time-integrated x-ray pinhole cameras, the beam centroid axial location and azimuthal symmetry have been analyzed for a recent series of target shots. Azimuthal symmetry on the target midplane on individual shots varied from 6% to 29%. Averaged over the entire series of shots, inferred intensities on the target midplane varied by 24% to 37% from quadrant to quadrant. The beam profiles and beam reproducibility are vital to the interpretation of the results of these target experiments.
Diamond deposition from fluorinated precursors using microwave-plasma chemical vapor deposition
Authors: Fox Ciaran A. , McMaster Mark C. , Hsu Wen L. , Kelly Michael A. , Hagstrom Stig B.
Published: July 2002

Diamond thin films were grown using fluorinated precursors by microwave plasma-assisted chemical vapor deposition. Using CH4/H2, CH3F/H2, and CF4/H2 gas mixtures, films were grown at surface temperatures in the range 600–900 °C at constant microwave power, carbon mole fraction, and pressure. Growth activation energies for the CH4/H2, CH3F/H2, and CF4/H2 mixtures were 12.6±1.8, 13.7±1.2, and 12.4±1.1 kcal/mole, respectively. Argon ion etching in conjunction with x-ray photoelectron spectroscopy indicated negligible fluorine incorporation into the films. These results are consistent with the hypothesis that diamond is grown from the same intermediates, namely methyl radicals and atomic hydrogen, for all of these mixtures.
MIT modular x-ray source systems for the study of plasma diagnostics
Authors: Coleman J. W. , Wenzel K. W. , Petrasso R. D. , Lo D. H. , Li C. K. , Lierzer J. R. , Wei T.
Published: July 2002

Two new x-ray source systems are now on line at our facility. Each provides an e-beam to 25 kV. Targets are interchangeable between machines, and four x-ray detectors may be used simultaneously with a target. The gridded e-gun of the RACEHORSE system gives a 0.5–1.0-cm pulsable spot on target. The nongridded e-gun of the SCORPION system provides a 0.3-mm or smaller dc microspot on target. RACEHORSE is being used to study and characterize type-II diamond photoconductors for use in diagnosing plasmas, while SCORPION is being used to develop a slitless spectrograph using photographic film. Source design details and some RACEHORSE results are presented.
A simple fast pulse gas valve using a dynamic pressure differential as the primary closing mechanism
Authors: Thomas J. C. , Hwang D. Q. , Horton R. D. , Rogers J. H. , Raman R.
Published: July 2002

In this article we describe a simple fast pulse gas valve developed for use in a plasma discharge experiment. The valve delivers 1017–1019 molecules per pulse varied by changing the voltage on the electromagnetic driver power supply. Valve pulse widths are observed to be less than 300 μs full width at half maximum with a rise time of less than 100 μs resulting in a maximum gas flow rate of ∼1022 molecules per second. An optical transmission technique was used to determine the mechanical opening and closing characteristics of the valve piston. A fast ionization gauge (FIG) was used for diagnosis of the temporal character of the gas pulse while the total gas throughput was determined by measuring the change in pressure per pulse in a small test chamber with a convectron tube gauge. Calibration of the FIG was accomplished by comparing the net change in pressure in a large chamber as measured by the FIG to the net change in pressure in a small test chamber as measured by the convectron tube gauge.
Time aberrations of uniform fields: An improved reflectron mass spectrometer for an atom-probe field-ion microscope
Authors: Scheinfein M. R. , Seidman D. N.
Published: July 2002

The mass resolution of the atom-probe field-ion microscope is limited by the time resolution of the ion-separating spectrometer. Time aberrations of uniform fields are investigated in general in order to characterize the optimal performance of high-transmission, high-mass resolution, multistage reflectron lenses. Correction of higher order time aberrations greatly improves the mass resolution. For an ion beam with an energy distributed uniformly about some nominal energy, E0±dE, mass resolutions (base width) of m/dm=848, 1344, 2151, 3571 can be achieved for single-, double-, triple- and quadruple-stage reflectron mass spectrometers when dE=0.1E0. A unique design example employing both second- and third-order time correction is given for an atom-probe field-ion microscope.
Symmetric differential capacitive pressure sensor
Authors: Peters Randall D.
Published: July 2002

Differential capacitive sensors are common to pressure gauges. Previous sensors of the bridge type have utilized only two variable (active) components, resulting in a half-bridge electrical equivalent circuit. There are numerous advantages of a symmetric full bridge, using four active components. The symmetry improves linearity and increases signal to noise ratio, especially when supported by electronics based on synchronous detection. Another advantage of symmetry is invariance to scaling, through immunity to stray capacitance. This feature is especially important in relationship to the current trend toward micro-electro-mechanical systems. A crude, inexpensive, macroscopic prototype of the present design was built with attention to high sensitivity. Constructed with a thin aluminized Mylar diaphragm, this device can readily resolve pressure changes smaller than 10−2 Pa.
Efficient compensation method for reducing ripple of Cockcroft–Walton generator in an ultrahigh-voltage electron microscope
Authors: Zhang Haibo , Takaoka Akio
Published: July 2002

To get ultrahigh stability of the dc high-voltage (HV) output, we propose a novel compensation method for reducing the periodic ripple included in the output of a Cockcroft–Walton (CW) generator circuit. A compensating signal is injected into the circuit via the ground end to compensate various ripple harmonics at the HV end. Considering the nonlinearity of a CW circuit, we first compose the signal with the linear superposition of harmonics minimizing individual ripple spectral components, and then reduce the deviation due to the nonlinearity through the fine adjustment on the synthesized signal. An experiment testing the method has been carried out in an ultrahigh-voltage electron microscope, compensating the ripple components from the fundamental to the ninth higher harmonics. Ripple has been decreased by above one order of magnitude, resulting in a percent ripple of less than 1×10−6.
Scanning tunneling microscope combined with scanning electron microscope for the study of grain boundaries
Authors: Thibado Paul M. , Liang Yong , Bonnell Dawn A.
Published: July 2002

An instrument that incorporates a scanning electron microscope (SEM) and a scanning tunneling microscope (STM) in an ultrahigh vacuum environment was designed to address the specific difficulties of imaging heterogeneous surfaces. A sample may be mounted in the STM for simultaneous STM and SEM imaging, or transferred to a manipulator where other surface analytical tools may be utilized. The STM is based on a viton-stainless-steel stack design and the SEM employs a 5 kV, electrostatic-lens electron gun. The sample mount is fixed, while the tip can be positioned in three orthogonal directions. Macroscopic positioning of the tip is accomplished using two orthogonal linear piezoelectric ‘‘inchworm’’ motors and a stepper motor, whereas microscopic positioning is accomplished with a piezoelectric tube scanner
Cooled video camera for optical investigations below 1 mK
Authors: Alles H. , Ruutu J. P. , Babkin A. V. , Hakonen P. J. , Manninen A. J. , Pekola J. P.
Published: July 2002

An optical imaging system for milliKelvin temperatures has been developed based on a regular B/W surveillance camera (25 frames/s), with its CCD sensor inside the 4-K vacuum can of our nuclear demagnetization cryostat. The heat leak to the nuclear stage, caused by the operation of the video camera, was reduced below 1 nW by careful rf shielding. The construction of the system and its limits of operation are discussed.
Signal processing in transceivers for nuclear magnetic resonance and imaging
Authors: Kasal Miroslav , Halámek Josef , Husek Vladimir , Villa Marco , Ruffina Umberto , Cofrancesco Pacifico
Published: July 2002

The relationships between signal processing schemes and expected performances of several types of NMR transceiver are discussed to show how emerging digital technologies may be used in future systems. We identify a transceiver architecture where accuracy of the analog signal processing functions is not critical, and top performances are obtained through real-time digital signal processing. Our receiver, comprising an oversampling analog-to-digital converter scheme, achieves a dynamic range of 12 bits at bandwidths above 1 MHz, and a dynamic range in excess of 16 bits at bandwidths <15 kHz. We give an outline of specifications and hardware design issues of the main parts of this transceiver and demonstrate experimentally the superior performances of our receiver.
A single-shot spectrograph for the soft x-ray region
Authors: Jasny J. , Teubner U. , Theobald W. , Wülker C. , Bergmann J. , Schäfer F. P.
Published: July 2002

A novel spectrograph comprised of a transmission grating, toroidal mirror, and microchannel plate detector is presented here. It is capable of detecting spectra in the wavelength range from 5 to 150 Å with a resolution of about 1.5 Å. Owing it to high efficiency, even an x-ray spectrum of a low-energy laser produced plasma, i.e., emission of the order of 10−10 J/sr, can be measured in a single shot.
Discharge characteristics of a 5 cm multipolar electron cyclotron resonance ion sourcea)
Authors: Srivastava A. K. , Sze F. C. , Asmussen J.
Published: July 2002

A compact 5-cm-diam multipolar electron cyclotron resonance (ECR) ion source is characterized. The source is experimentally studied with no grids using argon gas with 50–250 W of 2.45-GHz microwave input power. Using a microcoaxial probe it was confirmed that the exciting electromagnetic fields within the resonant cavity were indeed TE111, as expected from the critical cavity dimensions. Double Langmuir probe measurements indicate high densities of about (4–5)×1011/cm3 near the source, and 5 cm downstream from the source output the densities become very uniform with a value of about 5×1010/cm3 over a 10-cm diameter. Electron energy distribution functions (EEDF) were measured using a single Langmuir probe. Average electron energies were seen to be about 8–10 eV with an energy distribution function falling between a Maxwellian and a Druyvesteyn distribution. Ion energy distribution functions (IEDF) were measured with a multigrid energy analyzer. It was seen that the distribution functions were narrow and peaked [with a full width half maximum (FWHM) of about 5 eV] except under certain conditions. Above 200-W input power, and also below about 0.5 mTorr there is significant broadening of the ion distribution function. It is speculated that the former may be caused by gas heating, and the latter may be caused by the presence of Ar+2 ions. With its high current densities (≳10 mA/cm2) and low average ion energies (<40 eV), it is expected that this ion/plasma source will be very useful in many etching and deposition applications.
A frequency-agile hybrid spectral correlator for mm-wave radio interferometry
Authors: Torres Marc
Published: July 2002

A correlation spectrometer for the IRAM Plateau de Bure radio astronomy observatory is presented. It can process up to 960 MHz wide IF signals coming from the 4-antenna connected array. An IF processor selects the frequency window of interest, both in width and central frequency. A digital correlator produces channelized amplitude and phase information for the six pairs of antennas, which is later used for aperture synthesis mapping. Some original technical features are detailed. Some improvements suggested by observing results are discussed.
Fabrication of silicon-based optical components for an ultraclean accelerator mass spectrometry negative ion source
Authors: Kirchhoff J. F. , Marble D. K. , Weathers D. L. , McDaniel F. D. , Matteson S. , Anthony J. M. , Beavers R. L. , Bennett T. J.
Published: July 2002

An ultraclean accelerator mass spectrometry negative ion source for semiconductor material mass analysis has been built and is in operation at the University of North Texas’ Ion Beam Modification and Analysis Laboratory (IBMAL). The source is unique in that the active surfaces and apertures of the optical components in the ion source have been fabricated from high-purity single crystal silicon. This prevents both the 133Cs+ beam incident on the semiconductor samples and the negative ions from the sample surfaces from ‘‘seeing’’ and sputtering any metal surfaces (mostly stainless steel) in the beamline. The Cs+ beam can be rastered across the sample surface and the impact energy is adjustable to control depth-profiling rates. An ultraclean ion source of this type is necessary to prevent the injection of Fe and other beamline elements onto the sample or into the tandem accelerator, which is equivalent to putting an impurity signal into the mass analysis of the semiconductor sample. Suppression of these elements increases the sensitivity of the analysis to one part in 1012 for many masses. The fabrication and alignment of the optical components—einzel lenses, steerers, raster/scanners, and Faraday cups—in the negative ion source will be presented. Also, simulation trajectories are presented to show (1) the interaction of the incident Cs+ ion beam, the semiconductor sample, and holder (biased up to −30 kV), the extracted beam in the sample chamber, and associated potential field lines; and (2) the potential field lines of the octupole steerers.
Adaptation of particle-telescope technology for medium energy ion beam analysis
Authors: Arps James H. , Miklis Mark E. , Weller Robert A.
Published: July 2002

Medium energy (100–300 keV) time-of-flight spectrometry for surface analysis uses the correlated detection of an energetic ion and the secondary electrons emitted as it passes through a carbon foil. When microchannel plates are employed in this detection scheme, a typical mean efficiency of detection of less than 30% is achieved. When instead a surface barrier detector is used to detect the ion, providing simultaneous acquisition of velocity and energy information, certain advantages are realized over the two microchannel plate configuration in the characterization of low level constituents of surfaces. Specifically, energy-discriminated gating of the start pulse was observed to nearly eliminate count rate dependent background in a time-of-flight spectrum. Further reduction in background was obtained by the selective elimination of forward recoil species or backscatters from the substrate. Replacement of the stop microchannel plate by a surface barrier detector has resulted in improved detection efficiency for He, as well as provided a means for further study of the processes which affect time-of-flight spectrometer response, including multiple scattering and secondary electron emission in the start foil. In this publication, we describe the application of this particle telescope to the backscattering analysis of gold on silicon and the forward scattering measurement of hydrogen in a self-supporting carbon film.
An accelerator for alkali metal plasmas
Authors: Chakraborty A. K. , Kumar Ajai , Mattoo S. K.
Published: July 2002

A washer plasma gun for alkali-metal plasma is developed. This gun is suitable as a source for experiments on alkali-metal plasmas, plasma diagnostics, and in various applications such as ion-beam sputter deposition. The gun uses an injector of alkali-metal vapor based on the principles of laser ablation. Acceleration is performed by a large electrical field provided across eight washers. The gun is compact, stable, and easy to fabricate and use. The gun produces a neutral Li0 beam current of 1 A/cm2 and a Li+ ion current of 50 A/cm2 at its exit at 10 kV of capacitor bank voltage. With this intensity, it is possible to produce beams of neutral Li0 atoms of density 6×109 cm−3 and Li+ ions of density ∼1011 cm−3 at 1 m from the gun, moving with a velocity of ∼107 cm/s.
Electron cyclotron resonance multicharged ion source with elemental boron
Authors: Kato Y. , Ishii S.
Published: July 2002

Fundamental experiments have been carried out by using a two-stage electron cyclotron resonance (ECR) ion source (2.45 GHz) to produce multiply charged boron ions without gaseous feedstocks. A boron target, inserted into the ECR source, is heated and efficiently sputtered by dc bias. The B2+ ion current is successfully extracted under low microwave power (∼100 W). Dependence of extracted B+ ion current on dc bias voltage is similar to that of theoretical sputtering yield on incident ion energy.
Radio-frequency power combiner for cw and pulsed applications
Authors: Borg G. G. , Jahreis T.
Published: July 2002

We describe the design and operation of a circuit to combine the output signals of two high-power radio transmitters into a single load. A working unit is realized using a commonly available ferrite and cheap coaxial cables. Performance tests indicate satisfactory operation from 3 to 50 MHz with less than 1 dB total power loss while guaranteeing adequate isolation between the transmitters. The power combiner can also be constructed specifically to withstand high line voltages for short time periods thus making it suitable for high-power pulsed applications such as plasma formation and heating.
In situ testing and calibrating of z-piezo of an atomic force microscope
Authors: Fu Joseph
Published: July 2002

By scanning a slightly tilted, smooth surface with an atomic force microscope (AFM), it is possible to obtain hysteresis loops which contain information on the nonlinearity and hysteresis in the z axis of the AFM’s piezoelectric actuator. A 15% variation in vertical sensitivity was revealed by this PZT tube during vertical scans ranging in amplitude between 0.4 and 2.5 μm, which could result in a high level of uncertainty in a vertical measurement. Therefore a separate vertical measuring system or a correction scheme is required for a precise and accurate measurement.
Parallel, multichannel energy and angle resolving electrostatic electron analyzer
Authors: Downie Peter , Reynolds David J. , Powis Ivan
Published: July 2002

A new charged particle analyzer offering parallel and multichannel detection of a range of emitted energy and angle is described. Simultaneous multiplex detection of both these variables is achieved with the use of a two-dimensional position sensitive detector. The instrument is so arranged that angular information is recovered from the azimuthal coordinate, and energy from the radial coordinate of each detected particle. The instrument is based upon the original ‘Bessel Box’ design of Allen and co-workers and shares many of the favorable characteristics of that analyzer. General theoretical principles are considered and assessed, and then the actual performance of a specific device, fabricated for use in an angle resolved UV photoelectron-photoion coincidence experiment is reported. Simple in situ control of the operational mode of the instrument is described and demonstrated with the prototype, allowing convenient selection of the most effective compromise between resolution and bandwidth.
Performance of a solenoid-driven pulsed molecular-beam source
Authors: Abad L. , Bermejo D. , Herrero V. J. , Santos J. , Tanarro I.
Published: July 2002

The characteristics of a commonly used pulsed valve for the production of free jets and molecular beams are analyzed in detail. Special attention is paid to the formation of gas pulses providing a quasisteady flow during a certain time interval within the pulse duration, and to the estimation of a scaling parameter (effective diameter) for the description of the flow field. The adequacy of this effective diameter is checked by performing time-of-flight measurements on molecular beams of Ne, N2, and CH4, and stimulated Raman spectra on free jets of N2 and CH4.
A microwave-driven negative ion source
Authors: Wills J. S. C. , Schmeing H. , Diamond W. T. , Diserens J. , Imahori Y. , Taylor T.
Published: July 2002

A 2.45 GHz microwave-driven ion source, originally developed to generate a high-current 1H+ beam, has been adapted to serve as a universal negative-ion injector for the Tandem Accelerator Superconducting Cyclotron (TASCC) facility. Positive heavy ion currents from the source are converted into negative currents by means of a charge-exchange canal. So far, beams of 4He−, 16O−, and 18O− have been accelerated through the TASCC Tandem and 3He− and 209Bi− beams were accelerated through both the TASCC Tandem and cyclotron. A production version of the source has been designed, with emphasis on enhanced compactness and serviceability.
Fifty centimeter ion beam sourcea)
Authors: Hayes A. V. , Kanarov V. , Vidinsky B.
Published: July 2002

A 50-cm-diam ion source and its industrial applications are described. This is the largest commercial ion source presently available for ion beam etching and deposition over a full 20 in. diam. It has been used to generate beams of argon ions at 300–900 eV of ion energy and beam currents of 1–5 A with standard filament-type cathodes. Operation at even higher current levels is possible with high emissivity hollow cathodes. A presentation of general performance characteristics of the ion source is given and some of the special considerations required for reliable and cost-effective operation of large scale ion beam systems are discussed. To illustrate the application of this source, a brief description of a fully automatic production ion beam etching system developed around this ion source is given along with a description of the etch results. This system can simultaneously etch a batch of five 6-in.-diam wafers with etch rates of nickel–iron exceeding 500 A/min. The etch uniformity is excellent.
Improved apparatus for picosecond pump-and-probe optical measurements
Authors: Capinski William S. , Maris Humphrey J.
Published: July 2002

We present an improved method for making pump-and-probe optical measurements in the picosecond to nanosecond time range. In this type of measurement, a pump light pulse is used to excite the sample and the resulting changes in the optical properties are investigated by means of a probe pulse that is time-delayed relative to the pump pulse. In most measurements of this type, a mechanical stage is used to introduce the variable time delay of the probe pulse. As a result of imperfections in the stage motion, alignment problems, and divergence of the probe beam, it has been difficult to make accurate measurements when the time delay of the probe relative to the pump is in the range above a few hundred picoseconds. To overcome these difficulties, we have developed an apparatus that utilizes a single-mode optical fiber. In order to demonstrate the performance of this system, we present results of experiments in which the flow of heat from a thin film into a substrate has been measured.
The use of area detectors in Brillouin spectroscopy
Authors: Walton D. , Vanderwal J. J. , Xia H. , Zhao P.
Published: July 2002

The optical properties of area detectors used in conjunction with Fabry–Pérot interferometers are analyzed. A system using a charge-coupled device as a detector for Brillouin spectroscopy is described. With a 2 pass+2 pass tandem system the finesse ranges from 50 to 63. With a collection time of about 2.5 min, the intensity of the surface Rayleigh mode and the bulk acoustic modes of Si are comparable to those obtained by scanning for many hours.
High temperature scanning tunneling microscopy during molecular beam epitaxy
Authors: Voigtländer Bert , Zinner André , Weber Thomas
Published: July 2002

We have built and tested a system that is capable of simultaneous molecular beam deposition and scanning tunneling microscopy (STM) imaging at T=300–1000 K. The STM is based on the beetle-type design. Active compensation of thermal drift reduces the residual drift in the images to ∼2 Å/min at 850 K sample temperature. Measurements at varying sample temperatures are also feasible. Due to the open design of the STM, a molecular beam from a commercial microevaporator is aimed between tip and sample. With our system, simultaneous molecular beam epitaxy (MBE) and STM experiments during growth at high temperature are feasible. This method (MBSTM) provides the possibility to follow the MBE growth process with the STM in a real in situ way. The operation characteristics and performance of this instrument will be shown using examples of silicon homoepitaxy and Ge/Si heteroepitaxy.
The method of fluorescence decays simultaneous analysis
Authors: Apanasovich Vladimir V. , Novikov Eugene G.
Published: July 2002

A new method of high speed simultaneous deconvolution of multiple fluorescence decays with equal lifetimes and variable amplitudes is offered. The absence of need for initial guesses and comparably high accuracy make it suitable for obtaining initial conditions for other methods like iterative least squares. We discuss optimizations of the deconvolution procedure based on reductions of the matrix dimension. This establishes a higher processing speed and requires less computer memory. The properties and potential of this method were investigated through tests on simulated decay surfaces.
Mechanical oscillator tip-to-sample separation control for near-field optical microscopy
Authors: Decca R. S. , Drew H. D. , Empson K. L.
Published: July 2002

A nonoptical system for controlling the tip-to-sample separation in a near field scanning optical microscope is described. It consists of a tapered aluminum-coated fiber glued to a high-Q Si paddle mechanical oscillator. The paddle is driven at one of its resonances by a capacitively coupled electrode, and the amplitude of oscillation is detected through a second electrode. This resonant amplitude, which varies as the tip approaches the surface, is used as a feedback signal to control the separation between tip and sample. A separation stability better than 0.8 nm is achieved in the 0–200 nm range. We present a complete characterization of this system and demonstrate its capabilities with shear-force images of two samples.
High-sensitivity dielectric polarization noise measurements
Authors: Israeloff N. E. , Wang Xiangzhou
Published: July 2002

Techniques for measurement of low-level dielectric polarization noise spectra over a broad dynamic range are described. The method provides a powerful probe of 1/f noise and near-equilibrium dynamics in nonconducting materials of interest such as glass formers, liquid crystals, polymers, or ferroelectrics. Dielectric polarization noise was measured via voltage fluctuations in a capacitance cell filled with sample material. Measurements were carried out in the temperature range 80–400 K on glycerol and poly-vinyl-chloride near their respective glass transitions. To maximize the dynamic range and sensitivity and limit effects of stray capacitance an ultralow-noise junction field-effect transistor based preamplifier was operated adjacent to the sample in vacuum within the low-temperature cryostat. The technique offers potentially greater accuracy than susceptibility measurements in low-loss regimes, and may be useful in single-electron-transistor applications.
Suppression of interference effects in spectroscopy using an integrating sphere
Authors: Owen Geraint
Published: July 2002

Interference effects occur in the optical spectroscopy of thin film samples, and they can obliterate absorption spectra, especially if these are weak. A solution to this problem, originally proposed in 1976, is to place the sample inside an integrating sphere in the Edwards configuration so as to collect both reflected and transmitted light simultaneously. Surprisingly, the subsequent published literature on this technique is virtually nonexistent, despite its simplicity and effectiveness. This paper describes its use to measure absorption dips as weak as 2×10−4 in thin film samples.
“Hollow cathode” gun optics
Authors: Ciullo G. , Sharapa A. N. , Shemyakin A. V. , Tecchio L.
Published: July 2002

The generation of an electron beam by a hollow cathode gun in a cusp magnetic field is discussed. Such a gun is proposed for an electron cooling device without toroids. In a section with a homogeneous magnetic field, this beam experiences a disturbance region near the axis where the electron temperature becomes higher. The main purpose of the article is to define conditions for generating the beam so as to restrict the extent of this region as much as possible. It is shown that a state with a virtual cathode in the vicinity of the zero magnetic field point is the most suitable for this aim. The experimental and essential analytical results are presented.
Spin-resolved electron spectroscopy with highly polarized sources: Inverse photoemission from ferromagnets
Authors: Ciccacci F. , De Rossi S. , Pelucchi E. , Tagliaferri A.
Published: July 2002

We report on the use of recently developed spin-polarized electron sources with very high polarization for electron spectroscopy. In particular we present data of spin-resolved inverse photoemission from Fe(100) films excited by polarized electrons produced by a strained GaAsP negative electron affinity photocathode. This highly polarized source (beam polarization P=65%) allows a direct and almost complete decoupling of the majority and minority empty states in Fe(100), much better than the standard GaAs sources (P=20%–30%). The preparation and characterization of the strained photocathode is also discussed.
Modified Thomson spectrometer for the detection of low energy (<1 keV) high power ion beams
Authors: Lu Ming-fang , Liu Chi-zi , Yang Si-ze
Published: July 2002

By applying an after acceleration electric field, the detection and registration of the ion species and spectral distribution of low energy ion beams (<1 keV) have been achieved by the Thomson spectrometer with CR-39 nuclear track detector as detection plate. With the use of this modified spectrometer, the low energy and high energy density plasma ion beams generated by a coaxial plasma gun have been detected and investigated. The ion beams were mainly N+ ions and were distributed in the energy range from E∼0.12 to 0.4 keV.