bluuebunny/crossref_metadata_2025 huggingface dataset:
Power efficient double-resonance NMR probe for electromagnets
Authors: Moore Tony C. , Britt C. O. , Wade Charles G.
Published: July 2002

A NMR probe design of high efficiency is presented for a double-resonance spectrometer. The design uses easily constructed transmission line filters and a bridge box duplexing switch to reduce probe ringing. Circuits are used which allow independent tuning of the 100- and 25.1-MHz circuits in the probe. High strength rf fields are produced in the probe using low power transmitters, and good sensitivity is obtained on carbon.
Metallorganic vapor phase epitaxy reactor for i
n s
i
t
u optical investigations
Authors: Vaille M. , Favre R. , Monteil Y. , Bouix J. , Gibart P.
Published: July 2002

A metallorganic vapor phase epitaxy apparatus was built for in situ optical investigations of the gas phase. The quartz reactor lies on a support designed to move in a controlled, steady manner with respect to the optical path. The precision of the displacement is 0.01 mm. Temperature profiles above the substrate were established from the rotation spectra of H2 and N2 molecules.
Autonomous multichannel data-acquisition system
Authors: Kouroupetroglou G. T. , Caroubalos C. A. , Asimakopoulos D. N. , Vakasis N. T.
Published: July 2002

A flexible, general purpose, portable and autonomous data-acquisition system is presented. Data are stored on a nine-track IBM-format compatible digital magnetic tape recorder. The hardware allows data capture from 1 to 16 channels and with 12-bit resolution at speeds of up to 24 kHz, for relevant long time intervals. A special buffer has been also designed to support noninterleaved operation at the maximum transfer rates for both the analog-to-digital converter and the storage device.
Silicon resistor to measure temperature during rapid thermal annealing
Authors: Lim B. S. , Ma E. , Nicolet M-A. , Nathan (Natan) M.
Published: July 2002

A resistor composed of a piece of Si wafer and two thin silver wires attached to it, can reliably sense the temperature during rapid thermal annealing (RTA). As constant electric current passes through the Si piece, the resistivity change of Si with temperature produces a voltage signal that can be readily calibrated and converted to an actual temperature of the samples. An accuracy better than ±10 °C is achieved between 300° and 600 °C.
Raman scattering from LiF cluster-based nanophase film
Authors: Liu Fengqi , Han Min , Zhao Jijun , Chen Xiaoshuang , Wang Qun , Wang Guanghou
Published: July 2002

Raman scattering spectra are used to investigate LiF cluster-based nanophase films. The experiments confirm the existence of multi-order-like Raman scattering and surface phonon modes. Good agreement is achieved between the observed spectral lines and the calculated results if the Raman scattering lines are attributed to an appropriate linear combination of primary modes and surface optical modes. The fine structure observed in the case of the smaller cluster has reflected the intensity of the cluster-substrate interaction, which may result in the splitting of Raman peaks.
Equitemporal optics: a method to generate subpicosecond x-ray pulses (abstract)
Authors: Csonka P. L.
Published: July 2002

Certain classes of experiments would benefit from the availability of x-ray pulses of shorter time duration than what can be achieved today. These include accurate measurements of frequency and those of time resolution. One way to generate short x-ray pulses, is to utilize only part of an originally longer train of photons, and discard the rest. This approach is of little help if the phenomenon under study (such as synchrotron radiation pumped x-ray lasers) requires not only short pulses, but also high instantaneous photon intensity. When the time averaged photon intensity cannot be increased, the required threshold for the instantaneous intensity could nevertheless be reached (and the time resolution improved), if the time duration of individual photon pulses could be reduced without losing significant numbers of photons in the process. The term ‘‘equitemporal optics’’ denotes a collection of optical elements which can bring about a photon pulse length compression of this type. We demonstrate in general that practical equitemporal optics for x rays requires at least one optical element which is nonstationary. It is also shown that an equitemporal optics can be constructed for x rays by making use of only a single rotating mirror, while all other elements are stationary, provided that at least one of the stationary elements is a reflector. Furthermore, that reflector cannot be a single continuous mirror, but must contain more than one appropriately positioned discontinuous section. The number of sections must not be less than the time compression factor, ft, by which the original pulse length is to be reduced. Examples of appropriate reflectors are given. An equitemporal design of this type is presented which utilizes such a reflector together with a mirror rotating with a constant angular velocity. The time compression factor of this device is calculated.

It depends, among other things, on the emittance of the photon beam and the mirror speed of rotation. Limiting parameters and conditions will be discussed. Assuming the photon beam emittances produced by the PEP ring in Stanford, in conjunction with mirror speeds which can be achieved in practice, one can show that subpicosecond x-ray photon pulses can be generated in this manner. Alternatively, assuming the projected lower PEP emittances, one expects pulses of only a few femtoseconds duration. Concurrently, the same device will increase the instantaneous x-ray intensity by a factor in the range 102–104. The device may also be utilized to sharpen the leading (or trailing) edge of a photon pulse, without significantly altering the total pulse length.
Structural uniformity of multilayered tungsten-carbon Bragg reflectors prepared by rf magnetron sputtering
Authors: Takenaka Hisataka , Takaoka Hidetoshi , Ishii Yoshikazu , Hashizume Hiroo
Published: July 2002

Large area W-C multilayered films used as Bragg reflectors for SR in soft and hard x-ray regions are fabricated using alternate sputter deposition. The structure uniformity of these films is examined by our newly designed triple-axis diffractometer for large area x-ray diffraction topography using SR. The reflectivity of the films agrees well with the calculations which include film surface roughness and interfacial roughness. The diffraction topograph is almost the same as the image of the incident SR beam. The multilayered film examined is uniform in layer period within 2.6% over the whole 70×60-mm2 area of the multilayered film surface, and the layer period deviation across the substrate is within 0.1 nm.
Design and fabrication of condenser zone plates for a soft x-ray microscopy beamline in Hefei
Authors: Su Yong-gang , Hong Yi-lin , Fu Shao-jun , Tao Xiao-ming , Zhang Yun-wu
Published: July 2002

A synchrotron radiation soft x-ray beamline for scanning microscopy mainly, is being constructed in Hefei. It contains a linear monochromator consisting of a diaphragm of 7 μm diameter and one of three condenser zone plates (CZP). The three CZPs are for three overlapping wavelength ranges 1.97–2.78 nm (CZP23), 2.74–3.87 nm (CZP32), and 3.84–5.44 nm (CZP45), respectively. The processing steps for the condenser zone plate fabrication are summarized, especially the holographic exposure with a special optical system as a key step. Parameters of a prototype of CZP45 fabricated in Hefei are the following: D=2.9 mm, n=826, R1=0.05 mm, and ΔRn≊0.9 μm.
Soft x-ray source for BEPC synchcrotron radiation laboratory
Authors: Cui M. Q. , Xu W. X. , Liu L. B. , Heng H. G. , Tang E. S. , Sun Z. Y. , Qi L. R. , Xian D. C.
Published: July 2002

A set of fine-focusing soft x-ray sources has been manufactured to meet the requirements of research and development work at the BEPC Synchrotron Radiation Laboratory. The electrical and optical characteristics of the source as well as preliminary experiments on contact microscopy performed with the source are reported.
Interlock systems using programmable sequence controllers and a monitoring system of the Photon Factory beamlines
Authors: Satow Yoshinori , Ito Kenji , Kosuge Takashi
Published: July 2002

Fully utilizing programmable sequence controllers, interlock systems for the Photon Factory beamlines were newly designed and constructed for providing the reliable and versatile control logic that is required for beamline characteristics. The systems, accommodated with radiation safety and vacuum interlock logic as well as protection logic for various components against heat and radiation damage, are in operation on eight beamlines. A centralized monitoring system, to which all interlock systems for the beamlines are connected through optical fiber links, was constructed for simultaneously monitoring the operation status of the interlock systems. Individual operations of each interlock system are also controlled by the monitoring system. Log data collected by the monitoring system are summarized and analyzed in order to provide the necessary information for smooth and safe operation as well as for further improvements of the beamlines. The interlock and the monitoring systems are described along with operational remarks.
The study of interaction of electrons with an electromagnetic wave in an undulator
Authors: Amatuni A. Ts. , Petrossyan M. L. , Petrossyan B. V. , Ovsepyan A. S. , Harutunyan P. Ts. , Khachatryan L. V.
Published: July 2002

The results of an experimental investigation of electron beam spectral distribution after interaction with external electromagnetic waves in an undulator are given. The initial electron energy was 12 MeV, external electromagnetic wave power was 50 MW, the wavelength being 10 μm. A helical 20-cm-long undulator with a period length of 9.5 mm was used. The dependence of spectral distribution maximum change on undulator magnetic field strength was measured. The results are in good agreement with estimated findings taking into account the real parameters of the experimental setup. Electron energy maximum change was ±20 keV which is a result of electron acceleration or deceleration by the electromagnetic wave in the undulator.
Variable-period electrostatic and magnetostatic undulator designs for generating polarized soft x rays at PEP (abstract)
Authors: Tatchyn Roman
Published: July 2002

It can been shown that the generation of soft x rays on high energy storage rings such as PEP is most effectively performed with low-field, variable-period insertion devices, in contrast to the fixed-period devices represented by conventional transverse magnetostatic (TM) technology. Moreover, variable-period undulators of arbitrary field strength can be shown to be preferable to variable-gap devices under all circumstances where the generation of excessive superfluous power is undesirable, or where the available range of tuning with a single device must be maximized. In this article, basic arguments for these claims are presented, and an electrostatic implementation of a variable-period polarizing undulator is described. Some attractive properties of a recently designed, higher-field magnetostatic analog of the electrostatic device are also mentioned.
Design of a fast electron beam scanning system for compact synchrotron light sources
Authors: Moser H. O. , Lehr H.
Published: July 2002

The design of an electron beam scanning system for compact storage ring synchrotron light sources is described. The main features are a scan frequency of 100 Hz and an angular amplitude of ±5 mrad. Different configurations of scan dipoles permit confining the scan to one cell using four dipoles or to repeat the scan periodically along the whole circumference by means of two scan dipoles per cell. Combinations of these basic configurations are possible. The location of the nodes of the pivoting electron beam can be optimized with respect to the maximum scan angle by slightly unbalancing the field strength in different scan dipoles. The scan dipoles are H-shaped magnets made from laminated iron. Their gap width is 68 mm. They are powered by fast transistor-bridge supplies which are controlled by freely programmable function generators capable of realizing a triangular current waveform with a deviation of less than 0.1% except for a 1% neighborhood of the apex. Estimates of the influence of the scanning on both quantum and Coulomb lifetime indicate acceptable lifetime reductions provided the minimum distance between distorted closed orbit and aperture exceeds about six standard deviations of the spatial electron distribution.
Properties and applications of fast rotors in dynamical optics (abstract)
Authors: Csonka P. L.
Published: July 2002

The term ‘‘dynamical optics’’ is defined as a set of optical elements at least one of which is nonstationary as seen from the laboratory. Present technology allows the construction of fast rotating mirrors as components in dynamical optical systems. Calculations show that such systems can be used to achieve subpicosecond x-ray pulses and extremely high instantaneous intensities, and, alternatively they can be utilized to saturate the transverse coherence of x-ray beams thereby making possible to perform certain interference experiments. Some properties and additional applications of fast rotating mirrors are discussed: (1) The focusing properties of rotating mirrors can differ significantly from those of stationary reflectors, even though the mirrors are, of course, nonrelativistic. A small (diameter <1 mm) plane mirror when rotating can have a focal length fm down to a few meters. By changing the speed of rotation, the focal length can be altered continuously from its minimum value, fm, through infinity (when the mirror is at rest) to −fm (when it’s rotation is reversed). Thus, mirrors can be constructed which can be made to both focus and defocus with continuously and accurately variable focal length. (2) Rotating mirrors will induce a frequency change Δω in the reflected beam, allowing one in principle to tune across resonance lines, and also ‘‘active monochromatization’’ of x-rays, i.e., increasing the spectral intensity in a selected range, while decreasing it outside that range, all this without any change in the total photon beam intensity. This option is of interest when the total photon intensity cannot be increased beyond a certain limit, high resolution monochromatization is available, and large spectral density is called for in a chosen frequency range.

(3) The maximum speed whch a rotor can tolerate is determined by its shape as well as its mechanical properties, such as density, elasticity, and tensile strength. Because of their high intrinsic symmetry, spherical rotors are of interest both theoretically and experimentally, but higher speeds can be achieved by rotors specifically shaped for that purpose. A variety of examples will be given to illustrate the relationship between rotor speed and selected parameters.
Electron paramagnetic resonance study of luminescent stain etched porous silicon
Authors: Schoisswohl M. , Cantin J. L. , von Bardeleben H. J. , Amato G.
Published: July 2002

The defects and the morphology of stain etched porous Si of 60% to 70% porosity have been studied by electron paramagnetic resonance (EPR), scanning tunneling microscopy (STM), and Raman spectroscopy. The samples contain two pore phases with dimensions in the 1 and 10 nm range and present both visible and infrared photoluminescence. In as-prepared and aged samples two paramagnetic defects are detected: the Pb center at (111) Si/SiO2 interfaces and the silicon dangling bond (DB) center. The neutral Pb center concentration is ≊1×1018 cm−3, which is an order of magnitude higher than in comparable anodically etched porous Si. The angular variation of the Pb EPR spectrum proves the predominant monocrystalline character of the material. The neutral DB center concentration of ≤1×1017 cm−3 indicates in agreement with the Raman results only for a low fraction (≊1 vol %) of disordered Si. Our results demonstrate that highly luminescent porous silicon, retaining the crystallinity of the substrate, can be prepared by stain etching.
In situ fabrication of self-aligned InGaAs quantum dots on GaAs multiatomic steps by metalorganic chemical vapor deposition
Authors: Kitamura M. , Nishioka M. , Oshinowo J. , Arakawa Y.
Published: July 2002

Self-alignment of InGaAs quantum dots was achieved by growing the quantum dots on the multiatomic steps in metalorganic chemical vapor deposition. In this technique, first GaAs epilayer with multiatomic step structures along straight lines was grown on a vicinal GaAs substrate under appropriate growth conditions. Then, the InGaAs quantum dots were grown selectively on the multiatomic step edges using strain effects. This growth technique results in spontaneously aligned InGaAs quantum dots without any preprocessing technique prior to the growth.
Fabrication of all thin-film YBa2Cu3O7−δ /Pb Josephson tunnel junctions
Authors: Katz A. S. , Sun A. G. , Dynes R. C. , Char K.
Published: July 2002

All thin-film YBCO/Pb Josephson tunnel junctions have been fabricated. The junctions showed a well-defined Pb gap, Pb phonon structures, and very low leakage current. In addition, a higher bias spectroscopy revealed identical structures as have been seen in junctions made with single-crystal YBCO. A thin uniform Ag diffusion barrier at the junction interface lowers the junction resistance enough to study the Josephson effct in YBCO/Pb tunnel junctions. Both the temperature and the magnetic field dependencies of the magnitude of the Josephson current displayed conventional behavior. The junctions were very reproducible and uniform as indicated by the Ic(B) pattern.
Errors in the measurement of non-Gaussian noise spectra using rf spectrum analyzers
Authors: Anderson M. H. , Jones R. D. , Cooper J. , Smith S. J.
Published: July 2002

We discuss the nature of errors which may occur when the spectra of random signals not obeying Gaussian statistics are measured with typical rf spectrum analyzers. These errors depend on both the noise statistics and the process used to detect the random signal after it has been passed through a narrow bandpass filter within the spectrum analyzer. In general, for random signals not obeying Gaussian statistics, the output of the bandpass filter must be measured with a square law detector if the resulting measurement is to be strictly proportional to the power spectrum of the input signal. We compare measurements of the power spectra of non-Gaussian noise using a commerical spectrum analyzer with its resident envelope detector, with measurements by the same analyzer fitted with a square law detector. Differences of about 5% were observed.
A novel transient pulse viscometer for fluid viscosities at high pressures and elevated temperatures
Authors: Maini B. B. , Kokal S.
Published: July 2002

This article describes the design and principle of operation of a new capillary unsteady-state pulse viscometer for measuring the viscosities of fluids at high pressures and elevated temperatures. The asymptotic solution for the flow of a fluid in a capillary tube under a transient pressure gradient that decays at a rate proportional to the fluid flux in the tube is derived. The apparatus is relatively inexpensive to manufacture since it does not require a constant flow pump. Furthermore, it does not require large volumes of the fluid being measured and is comparatively faster than other conventional steady-state viscometers. The accuracy of the viscometer is comparable to or better than the commercial steady-state viscometers. The relevant flow equations are derived for calculating viscosity from measured differential pressure decay signals.
Efficiency of short heat exchangers for helium vapor cooling
Authors: Steffensrud D. , Bahls J. , Christenson E. , Fassnacht K. , Guckel E. , Harriman D. , Nahn S. , Vu P. , Zhang J.
Published: July 2002

We measured the heat transfer efficiency of short heat exchangers along the vent tube of a helium cryostat, and measured the temperature profile of the helium vapor along the vent tube. The results of our measurements show that the heat exchangers are in some cases considerably more efficient than indicated by simple model calculations. With a flow rate of 4.4×10−3 g/s, a heat-sink length of 7 cm is just long enough to sink 2.3 W at about 138 K with a few Kelvins temperature drop, while a 5 cm length is more than adequate to sink 0.5 W at 25 K.
Water vapor interference in the measurement of ozone in ambient air by ultraviolet absorption
Authors: Meyer C. P. , Elsworth C. M. , Galbally I. E.
Published: July 2002

Atmospheric observations show that ultraviolet absorption ozone monitors used for ambient measurements can, under some conditions, respond to variable water vapor concentrations with quantitative responses varying from instrument to instrument. A combined theoretical and experimental study shows that these monitors should not respond to water vapor. The source of the response appears to be the varying extinction of ultraviolet light by the windows of the optical cells. A change of 6-g H2O kg air−1 gives, at maximum, an extinction equivalent to 800 ppbv ozone. This changing extinction appears to be related to surface contaminants or surface structure on the cell windows. Instruments with such cell windows can give spurious ozone results in some measurement sequences.
A rotating spectrometer for separation/concentration of bioconvecting microorganisms
Authors: Noever David A.
Published: July 2002

The rotating spectrometer is discussed as a method to separate and concentrate microorganisms in free solution. Following focusing in a rotated frame, the separation is accomplished using different radial dependencies of concentrated algal and protozoan species. The focusing itself appears as concentric rings and arises from the coupling between swimming direction and Coriolis forces. A dense cut is taken at varying radii and extraction is replenished at an inlet. Unlike standard separation and concentrating techniques, the rotating method requires active organism participation and, in principle, can split different morphologies and swimming behaviors for the large class of organisms known to bioconvect.
Electrical field enhanced thermal quenching of a prominent thermally stimulated current peak in semi-insulating GaAs
Authors: Fang Z-Q. , Look D. C.
Published: July 2002

Detailed experimental results are presented for a ‘‘thermal quenching’’ of thermal stimulated current signals in the most prominent trap in undoped semi-insulating (SI) GaAs, T5 with an activation energy of 0.27–0.31 eV. A possible model for the thermal quenching of T5 is discussed, emphasizing the thermally stimulated nature of the quenching process, the effect of electric field and the formation of high-field domains. The thermal quenching of T5 can frequency be observed in SI GaAs grown by the vertical gradient freeze (VGF) technique, or by the liquid encapsulated Czochralski (LEC) technique under certain conditions.
Characterization and stabilization of an electron-cyclotron resonance plasma source using an automatic microwave tuner
Authors: Minomo S. , Kondo K. , Yoshizako Y. , Ishida Y. , Taniguchi M.
Published: July 2002

An automatic microwave stub tuner (AST) has been developed and used to characterize and stabilize an electron-cyclotron resonance (ECR) plasma source. The tuner provides a new method for measuring plasma impedance dynamically without disturbing the plasma. The Ar ECR plasmas were excited by a 2.45 GHz microwave (<800 W) in the presence of the static axial magnetic fields ranging from 875 to 2000 G, and the characteristics were investigated using a double probe and the AST. Results of these measurements indicated that the Ar ECR plasma had discrete stable modes where the plasma parameters and impedance varied continuously. For certain operating conditions, slight shifts of microwave power and/or magnetic-field strength brought about discontinuous mode transitions. In the transition regions, the drastic changes of plasma characteristics were observed, resulting in the instability of the plasma. It was quite effective for stabilizing the unstable plasmas to control the reflection coefficient of the microwave transmission line.
Infrared evidence for inhomogeneity in SiO2 films grown by plasma assisted oxidation of Si
Authors: Martinet C. , Devine R. A. B.
Published: July 2002

The longitudinal optic vibrational mode associated with the asymmetric stretch of the bridging oxygen atom has been studied in amorphous SiO2 grown by plasma assisted oxidation of Si. In films ≤70 nm thick the mode is observed displaced by −6 cm−1 with respect to the bulk value (1256 cm−1). Deconvolution of the spectra combined with chemical etchback of the films shows that they are inhomogeneous, the peak shift increasing to −12 cm−1 near the Si/SiO2 interface in films thicker than ∼20 nm.
An inexpensive optical multichannel analyzer built on an AT-compatible computer
Authors: Yip W. T. , Tse R. S.
Published: July 2002

An inexpensive optical multichannel analyzer (OMA) has been constructed on an AT-compatible computer. Both a linear charge-coupled device and a linear photodiode array can be used as the detector mounted at the exit of a number of polychromators. Circuits, software, and performance of the OMA are presented and discussed.
New experimental setup for photoelectron spectroscopy on cluster anions
Authors: Cha Chia-Yen , Ganteför G. , Eberhardt W.
Published: July 2002

We describe a new experimental setup for photoelectron spectroscopy on mass selected clusters. The recently developed pulsed arc cluster ion source (PACIS) for metal and semiconductor clusters is used as an anion source. The design of the PACIS is optimized for maximum intensity of cluster ion production and a minimum internal temperature of the particles. A simple modification allows vaporization of liquid and low melting point metals. The produced anions are mass selected via an inline time-of-flight setup with the option of using a reflectron for increased mass resolution. Photoelectron spectra of the mass selected cluster anions are collected in a ‘‘magnetic bottle’’ type electron spectrometer. First results on copper clusters are presented.
A cw electron nuclear double resonance resonator for single crystal studies
Authors: Willems J.-P. , Klaassen A. A. K. , Reijerse E. J. , Janssen G. E. , de Boer E.
Published: July 2002

The design of an electron nuclear double resonance (ENDOR) resonator suitable for single crystal studies is reported. An outline is given of the mechanical and electronic construction of the resonator. This paper will focus on the construction suitable for studies at 4.2 K, but the design can be easily adapted to a flow cryostat for variable temperature measurements. The rf-coil efficiency has been measured and is high and fairly constant over the frequency range from 0.3 to 20 MHz. Measurements on a test compound, show that the baseline stability is good over this frequency range. Even for low abundant nuclei as 13C, the signal to noise ratio is very good.
Interferometric measurements of the diameters of a single-crystal silicon sphere
Authors: Fujii K. , Tanaka M. , Nezu Y. , Nakayama K. , Masui R. , Zosi G.
Published: July 2002

A new interferometer has been developed for the accurate determination of the density of a silicon crystal, in which a single-crystal silicon sphere of nearly perfect geometry is placed in a Fabry–Perot etalon of accurately known plate distance, and the diameters are obtained by measuring the two gaps between the etalon and the adjacent surface of the sphere. A new method is used to measure the sum of the length of the two gaps by scanning the etalon against the sphere. Two wavelengths, 633 nm from a frequency-stabilized He–Ne laser and 441 nm from a free-running He–Cd laser, are used to determine the order of interference by applying the method of exact fractions. The diameter of about 94 mm has been measured with a resolution of 0.5 nm. Diameter measurements from uniformly distributed directions have shown that the mean diameter has been determined with a standard deviation of 8.6 nm, corresponding to 0.28 ppm in the volume determination. The total uncertainty of the volume is estimated to be 0.34 ppm. Effects of a thin oxide layer and impurities on the bulk density are discussed.
Automatic frequency control for solid-state sources in electron spin resonance
Authors: Pechan Michael J. , Xu Jiansheng , Johnson Lynn D.
Published: July 2002

A lock-in amplifier circuit has been designed and tested which serves as an automatic frequency control (AFC) for electron spin resonance (ESR) spectrometers employing solid-state microwave generators. Its implementation in a typical spectrometer is described and a detailed electronic schematic presented. Its performance is tested as a lock-in amplifier operating under open loop conditions, wherein operating with a 20-kHz reference, it yields an 81-dB improvement in signal to (9 kHz) noise ratio. This is consistent with expectations from computer simulations. When employed as an AFC in a typical X-band ESR system the capture and lock ranges are observed to be equivalent to those obtained from a commercial lock-in amplifier.
A very low-temperature specific heat calorimeter
Authors: Rapp R. E. , Siqueira M. L. , Viana R. J. , Norte L. C.
Published: July 2002

A specific heat calorimeter for the temperature range 0.07–1.3 K with a novel sample support of four commercial pencil leads is described. It is shown that this support substantially reduces the vibrational heat input to the sample assembly. The thermal shield of the calorimeter is vacuum tight to allow measurements with gas adsorbing samples. We estimate and derive expressions for the temperature dependence of the thermal conductances of the AuCu thermal link and of the pencil leads support.
Photovoltaic properties of a molecular semiconductor modulated by an exciton-dissociating film
Authors: Gregg Brian A.
Published: July 2002

A thin film containing an electron donor (tetraphenyl diamine) quenches the exciton fluorescence and substantially alters the photovoltaic properties of perylene bis(phenethylimide) cells. The film causes the open circuit photovoltage to shift positive by about 450 mV relative to cells without the film. In the case of silver back contacts, the presence of the film inverts the photovoltaic effect relative to that in the absence of the film, and causes the front electrode to become more photoactive than the back. These effects are interpreted as resulting from interfacial exciton dissociation rather than from junction formation.
Characteristics of a freely programmable ICCD detector for multichord particle influx measurements on the ASDEX-Upgrade tokamak
Authors: Kallenbach A. , Mayer H.-M.
Published: July 2002

The characteristics of a compact space and wavelength-resolving spectrometer-detector arrangement are described which is used to measure spectral line shapes simultaneously along several viewing chords. The system is based upon a freely programmable slow-scan charge-coupled device (CCD) camera gated by an image intensifier tube. Visible and near-UV light emitted near the plasma boundary is collected from up to 12 viewing chords and transmitted to the spectrograph by quartz fibers. Spectra can be recorded with a temporal resolution of 20 ms by means of multiple pixel binning during CCD readout. Integration of the spectral line profiles yield particle fluxes of various low-Z species for ohmically heated helium discharges. The calibration, sensitivity, and signal-to-noise ratio of the system are reconstructed considering each individual element, allowing an easy prediction of the performance of similar applications.
Accurate, inexpensive, thermal expansion microtranslator
Authors: Snyder James J.
Published: July 2002

We have developed an accurate, inexpensive translator utilizing the thermal expansion of an electrically heated wire. The resistance of the wire, measured in a Wheatstone bridge, provides a readout of the length of the wire based on its temperature coefficient of resistance.
Magnetic susceptibility of polychlorotrifluoroethylene (PCTFE)
Authors: Mari A. , Brossard L.
Published: July 2002

The magnetic susceptibility of polychlorotrifluoroethylene, commonly named as Kel’f, has been measured in a magnetic field of 2 T from 2 to 300 K. The susceptibility is diamagnetic above 3 K with a small Curie contribution at low temperature.
Simplified cascaded arc discharge source for production of a processing plasma
Authors: Okuno Yoshihiro , Yagura Shinya , Ishikura Hiroshi , Fujita Hiroharu
Published: July 2002

A simplified cascaded arc discharge source is proposed as one possibility for plasma processing. While decreasing the number of floating electrodes which constrict the arc channel, the plasma parameters remain almost unchanged. The device was found to produce very low electron temperature (∼0.5 eV) plasma, preventing damage on a substrate by high energy ions which might be accelerated in an ion sheath, with high density (∼1012 cm−3). This device is expected to be applied to new fields of plasma processing requiring low electron temperature.
A shielded, multichannel, extreme ultraviolet spectrograph for fusion plasma diagnostics
Authors: Parsignault D. R. , Krieger A. S. , Ramsey A. , Stratton B.
Published: July 2002

A high throughput, shielded, multichannel, extreme ultraviolet (XUV) spectrograph to be used for plasma diagnostics was built. The instrument uses seven hollow fibers to transport the radiation by multiple grazing incidence reflections from the tokamak port through the instrument’s shield to the spectrometer entrance slit. In this way, the ratio of background radiation streaming through the entrance slit to XUV flux is reduced by a factor of at least 2500. The seven hollow fibers provide seven channels corresponding to seven different lines of sight through the plasma. The spectrograph uses a toroidal mirror together with a plane, aberration-corrected grating to disperse radiation in the 50–200 Å region. Up to seven spectra are recorded simultaneously, at rates of 30–90 Hz, using a microchannel plate assembly optically coupled to a charge-coupled device camera. This will permit, during a single discharge, measurement of spatial emissivity profiles from various ionization states of an injected impurity, providing a better understanding of their time evolution and valuable information on cross-field ion transport.
Texture determination of the high temperature superconductors by emission Mössbauer spectroscopy
Authors: Chechersky Vladimir , Kopelev Nikolai , Tian Jing , Wei Yen , Nath Amar
Published: July 2002

A method using emission Mössbauer spectroscopy has been developed for determining the degree of texture of bulk samples of high temperature superconducting ceramics having axial type of texture. A special fitting procedure was used, which takes into account properties of the electric field gradient on the 57Co probe nucleus, based on expressions determining the probabilities of the quadrupole transitions assuming perfectly aligned crystallites [P. Boolchand et al., Phys. Rev. B 38, 11313 (1988)]. The deviation of the line intensity ratio of the measured spectrum from the value expected for 100% texture was taken into account by a reduction factor which is associated with the imperfectness of alignment [F. Hartmann-Boutron and V. Gross, Physica C 172, 267 (1990)]. This factor can be used as a precise measure of c-axis orientation regardless of the specific kind of orientation distribution of crystallites. The established correlation between the experimental value of the reduction factor and the characteristic parameters of different distribution functions permits us to compare the results of the texture determination by emission Mössbauer spectroscopy with those obtained from x-ray or neutron diffraction measurements. The high degree of reproducibility of the experimentally determined texture attests to use of this relatively simple, convenient, and accurate technique for texture characterization of the high temperature superconductor ceramics.
Measurement of superconducting characteristics of high T
c materials by the magnetic force sensing system
Authors: Ishigaki H. , Itoh M. , Endo H. , Hida A. , Yotsuya T. , Minemoto T.
Published: July 2002

A magnetic force sensing system using a highly sensitive force sensor was developed to measure the two-dimensional distribution of superconducting properties of high Tc materials. A probing tip made of a small piece of magnetized material was mounted on a cantilever scanned over superconducting surfaces. Magnetic properties of the superconductor generated force on the tip and the force was measured by an optical displacement sensor. Two kinds of YBCO superconductor were examined by the measuring system in order to compare their repulsive force and shielding characteristics. Two-dimensional distribution of repulsive force due to the Meissner effect of YBCO, which was fabricated by the melt powder melt growth (MPMG) process, showed evident nonuniformity which is attributed to the nonuniformity of chemical composition of the material. Although the MPMG materials are capable to be used as a magnetic shield, they have much larger residual flux than the materials fabricated by the solid phase reaction process.
Simple rough approach system for scanning tunneling microscope
Authors: Oliva A. I. , Rejón V. , Peña J. L.
Published: July 2002

A simple rough approach system for a scanning tunneling microscope (STM) is presented. The system uses a commercial low velocity washing machine timer motor working at 127 VAC, 60 Hz in a continuous rotation. The motor moves a differential screw system and is controlled by an electronic circuit to stop its rotation when a preset value of tunnel current is detected. This rough approach system is simpler and less expensive than a stepping motor and does not use high voltage amplifiers. This mechanism can be easily adapted to STMs with mechanical approach systems because it consists of only a few simple components.
Purely thermal wave based nonchemical photopyroelectric gas sensor: Application to hydrogen
Authors: Munidasa Mahendra , Mandelis Andreas
Published: July 2002

A commercially available polyvinylidene fluoride (PVDF) pyroelectric film with an optically generated thermal wave field has been introduced as the active device of a new nonchemical photopyroelectric gas sensor. The purely thermal wave based operating mechanism of this gas sensor is in contrast with a similar, surface chemically active Pd-coated device introduced earlier [A. Mandelis and C. Christofides, J. Appl. Phys. 70, 4496 (1991)]. The sensitivity to a particular gas at low flow rates (<500 ml min−1) is obtained through thermal boundary condition changes introduced by the gas at the film–gas interface, which depend on the thermophysical properties of the gas. The theoretical basis of this device is described. Photopyroelectric voltage amplitude and phase changes due to ambient hydrogen–air mixtures with respect to pure air, obtained through a lock-in amplifier, are also presented. It is shown that the data are in good agreement with the thermal wave theory. Sensitivity to other common gases used in industry and in environmental studies is also discussed.
Role of interface in ion mixing induced amorphization in the Ag–Mo system with very positive heat of formation
Authors: Jin O. , Zhang Z. J. , Liu B. X.
Published: July 2002

A free energy diagram of the Ag–Mo system with a very positive heat of formation of +57 kJ/mol was constructed, with special consideration to the interfacial free energy in the multilayered films for ion mixing. It was found that amorphization was possible to achieve within two separate composition ranges toward Ag and Mo ends, respectively, if 12 layers, or about 13% of the interfacial atoms were included in the films. Accordingly, ion mixing of the Ag–Mo multilayered films was conducted at liquid nitrogen temperature by 190 keV xenon ions and the formation of amorphous phases was in good agreement with the calculation. Besides, a new metastable fcc phase was formed and, more interestingly, it transformed into an amorphous state upon aging, which can also be interpreted by a related free energy calculation.
Elliptical reflector low-pass energy filter for a liquid metal ion source cluster deposition system
Authors: Anderson J. F. , Berry S. D.
Published: July 2002

We describe the design, construction, and implementation of a low-pass energy filter for use with a liquid metal ion source (LMIS) cluster deposition system. When combined with deceleration of cluster ions to a surface for landing, this filter provides bandpass energy selectivity for high resolution mass separation of clusters produced by the LMIS. We also present results of our initial testing, which shows the filter has an experimental relative energy resolution of less than 0.3%.
Temperature-dependent property measurements on multi-electroded thin-layer dielectrics
Authors: Tani Toshihiko , Xu Zhengkui , Moses Paul , Payne David A.
Published: July 2002

A measurement system was designed and assembled for the automatic collection of electrical data for thin-layer dielectrics as a function of temperature. The dielectrics were deposited on platinized silicon by sol-gel processing, and the dielectric thickness was 0.2–0.4 μm. Many (≳25) surface electrodes were formed by sputtering gold through a shadow mark, with a typical electrode size of 210×210 μm2. The measurement equipment was computer controlled, with three-axis digital stepping motors that could scan multi-electroded capacitors and collect statistically meaningful data. The temperature-dependent properties were measured between −100 and 300 °C as a function of frequency (100 Hz to 1 MHz) and applied field strength (0–50 MV/m). Data are reported for sol-gel-derived BaTiO3, PbZrO3, and (Pb,La)(Zr,Ti)O3 (i.e., PLZT) thin-layer capacitors. Capacitance values were typically 500–1000 pF, and the dielectric constant could be determined within a standard deviation of ±1.3%. Nanocrystalline BaTiO3 was found to have a dielectric constant of 210 at room temperature with no ferroelectric properties or dielectric anomalies between −80 and 200 °C. Antiferroelectric PbZrO3 had characteristic field-forced phase transformation behavior to the ferroelectric state with increasing bias. The field-induced polarization was approximately 300 mC/m2 and the coercive field was 22–28 MV/m. PLZT 8/65/35 had a dielectric constant of 556±7 at 25 °C, 100 KHz, and 50 mV.
Improved modeling of surface charge distributions in electret ionization chambers
Authors: MacDonald B. A. , Fallone B. G.
Published: July 2002

Additional considerations are discussed concerning the modeling of time-dependent surface charge distributions in electret ionization chambers during the charging and discharging of electrets with ionizing radiation. Estimates of position-dependent ion density in the charging chamber are made using (a) a single-scattering calculation of ionization due to recoil electrons and (b) an isotropic, inverse-square approximation of ionization density. These estimates are used in conjunction with a subroutine which solves Laplace’s equation for electric field and tracks charge carrier trajectories from the point of origin in the chamber to an electret surface where the charge becomes trapped. The results of improved measurements are also shown and compared with calculations.
A simple method for producing liquid or solid NMR samples containing dissolved gases at elevated pressures
Authors: Mazitov R. K. , Diehl P. , Garanin W. V. , Rotter G.
Published: July 2002

The method and apparatus for preparing liquid or solid NMR samples containing dissolved gas at elevated pressures up to 5 MPa is described. A minimal amount of gas under pressure (a few mm3), avoiding dangerous explosions, is stored in the samples. Any contact of the liquid with metal and contamination is avoided by using the frozen liquid as valves. The samples can be stored and studied by different spectroscopies, such as ESR, IR, or UV spectroscopy. Sample rotation in NMR spectroscopy and temperature variations are possible.
Vibrational spectroscopy of clusters using a ‘‘magnetic bottle’’ electron spectrometer
Authors: Handschuh H. , Ganteför G. , Eberhardt W.
Published: July 2002

The design of a high resolution ‘‘magnetic-bottle’’-type time-of-flight electron spectrometer suitable for the study of mass-separated metal and semiconductor cluster anions is described. A high collection efficiency is achieved by using magnetic fields to guide the photoelectrons, so that vibrationally resolved photoelectron spectra can be recorded at a low laser pulse energy (<10 μJ focused to 1 mm2) avoiding multiphoton processes. Spectra of clusters with a very low relative abundance, for example the products of chemical reactions involving clusters, can be recorded and an energy resolution of 6 meV (48 cm−1) achieved.
Emittance measurements at the ESRF
Authors: Tarazona E. , Elleaume P.
Published: July 2002

A new method of electron beam imaging is operating routinely at the ESRF. It uses the x-ray beam from an undulator. The white beam is monochromatized by a Si 400 Bragg reflection at 30 keV. The monochromatic beam is projected onto a fluorescent screen and imaged by a CCD camera. The emittance of the electron beam is deduced from the image size measured by the CCD camera and the independent knowledge of the beta function at the source point. This technique has measured emittances in the range of 0.2–20 nm rad with a precision of 20%. The principal limitation appears to be the single electron emission angular pattern which limits the minimum detectable emittance to 0.1 nm rad. This diagnostic has been routinely used for more than 1000 h. It is fully automated, resulting in a permanent display of the values of horizontal and vertical emittances without intervention by any operator.
Development of a fluorescent x-ray source for medical imaging
Authors: Toyofuku F. , Tokumori K. , Nishimura K. , Saito T. , Takeda T. , Itai Y. , Hyodo K. , Ando M. , Endo M. , Naito H. , Uyama C.
Published: July 2002

A fluorescent x-ray source for medical imaging, such as K-edge subtraction angiography and monochromatic x-ray CT, has been developed. Using a 6.5 GeV accumulation ring in Tsukuba, fluorescent x rays, which range from about 30 to 70 keV are generated by irradiating several target materials. Measurements have been made of output intensities and energy spectra for different target angles and extraction angles. The intensities of fluorescent x rays at a 30 mA beam current are on the order of 1–3×106 photons/mm2/s at 30 cm from the local spot where the incident beam is collimated to 1 mm2. A phantom which contains three different contrast media (iodine, barium, gadolinium) was used for the K-edge energy subtraction, and element selective CT images were obtained.
Computer simulation study of undulator radiation
Authors: Yagi K. , Yuri M. , Sugiyama S. , Onuki H.
Published: July 2002

Calculations of the radiation from a four-period polarizing undulator by use of the general radiation equation and numerical integration including the effects of electron-beam emittance, energy spread, and finite observation distance are presented. Accurate electron-beam profiles have been experimentally determined and modeled by the Monte Carlo method. Good agreement is found in spectral intensity between the measured and calculated spectra.