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Review of Scientific Instruments

Issue 9 • Date Sep 1988

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Displaying Results 1 - 25 of 46
  • Variable‐temperature scanning tunneling microscope

    Page(s): 1897 - 1902
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    A thermally compensated tube scanner scanning tunneling microscope (STM) has been constructed and successfully tested. This design utilizes two concentric piezoelectric tubes, one for scanning and one for thermal compensation and inertial sample translation (over several mm), as well as fine adjustment of sample position while in tunneling range. This design eliminates the need for mechanical components such as springs, levers, gears, or stepper motors that are known to result in considerable vibration sensitivity, thermal drift, and low‐resonance frequencies. This new design demonstrates continuously variable‐temperature operation as well as atomic resolution without vibration isolation for the first time in a STM. Thermal drift of less than 1 Å/h and less than 10 Å/K have been determined. Also, the lowest mechanical resonance frequency of 21 kHz makes this new design suitable for high‐speed applications such as video rate scanning. View full abstract»

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  • Constant‐resolution tunneling spectroscopy

    Page(s): 1903 - 1905
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    An inelastic electron tunneling spectrometer is described which is capable of providing constant‐resolution spectra over the 0 to greater than 16 000‐cm-1 range. Constant‐resolution data acquisition is especially beneficial in the case of electronic transitions studied by tunneling spectroscopy. Data acquired as d2V/dI2, (d2V/dI2)/(dV/dI)2, and in constant‐resolution mode are compared. At intermediate and at high bias, either of the two latter data‐acquisition methods is superior to the first. At high bias voltage, constant‐resolution spectra are superior. View full abstract»

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  • Piezodriven scanner for cryogenic applications

    Page(s): 1906 - 1910
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    A scanning microscope stage has been developed for use at cryogenic temperatures. The stage uses a piezoelectric driving element and circular flexure hinges to achieve a slow scan travel of greater than 10 μm and a near‐resonance travel of 100 μm while immersed in liquid helium at 4.2 K. The scanner has been operated inside a pressure cell in a dilution refrigerator, where it dissipates less than 150 μW of heat at 100 mK. View full abstract»

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  • Multibeam receiver for millimeter‐wave radio astronomy

    Page(s): 1911 - 1919
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    An eight‐beam receiver system for millimeter‐wave radio astronomy is described. The receiver is designed to map spatially extended radio sources in both spectral line and continuum emission at a wavelength of 1.2 mm. This receiver is now in use on the 12‐m radio telescope on Kitt Peak in Arizona. View full abstract»

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  • Rapid electromechanical phase shifting in differential holography

    Page(s): 1920 - 1923
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    Procedures for the rapid and precise control by electromechanical means of the reference beam phase shift during differential holography are described. Phase shift is created with the use of a piezoelectric ceramic translator that is driven by a two‐step voltage pulse to minimize mechanical ringing. The resultant suppression of resonant vibration permits an order of magnitude reduction in the time interval between the exposures. The adjustment of the phase shift signal is assisted by use of feedback control arrangement to stabilize an interferometer. View full abstract»

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  • Conversion and amplification of photomultiplier anode current in multiple‐frequency phase fluorometry

    Page(s): 1924 - 1927
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    We have designed and built a low‐cost current–voltage converter with a bandwidth larger than 200 MHz and a fixed ac insertion gain of 20 dB for use in multiple‐frequency phase fluorometry (MFPF). We describe its application with the Hamamatsu R928 photomultiplier (PMT) and discuss problems of radio‐frequency (rf) interference, signal‐to‐noise ratio (S/N), PMT nonlinearity, and overall frequency bandwidth. The separation of ac and dc signal paths introduces the possibility of direct determination of relative modulation in two simultaneous measurements. We demonstrate that systematic errors such as PMT nonlinearity can be completely eliminated in MFPF by an appropriate experimental procedure and report an accuracy of our dual‐beam instrument of 5 ps. View full abstract»

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  • Critical assessment of fluorescence polarization measurements with a FACS IV cell sorter

    Page(s): 1928 - 1932
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    The usefulness and limitations of the Becton–Dickinson fluorescence‐activated cell sorter FACS IV for fluorescence polarization measurements were examined. A set of tests to determine the characteristics of the detection geometry, the optical properties of the beam splitter, and the capability to process fluorescence polarization data is presented. Recommendations are provided for correcting instrumental deficiencies. View full abstract»

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  • High‐performance GaAs polarized electron source for use in inverse photoemission spectroscopy

    Page(s): 1933 - 1940
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    The design and operating properties of a GaAs polarized electron source are presented. An electron optical system is described that passes more than 80% of the emitted electrons at 10 μA to the target under low‐energy (7–20 eV) parallel beam conditions. Laser excitation can give rise to abnormal energy distributions of the photoemitted electron beam. The existence of longitudinal modes gives a possible explanation for this behavior, which can be avoided using a mode stabilized light source. The overall performance of the polarized electron source is demonstrated by inverse photoemission spectra from Ni(110). View full abstract»

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  • Novel system for picosecond photoemission spectroscopy

    Page(s): 1941 - 1946
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    This article describes a laser‐based source and detection scheme for performing time‐resolved photoemission studies of materials. The pulsed laser source produces intense picosecond pulses of coherent radiation that are nearly continuously tunable from the near infrared to photon energies up to 13 eV. To achieve high sensitivity, a novel multianode time‐of‐flight spectrometer has been built that generates an angularly resolved intensity versus kinetic energy spectrum with better than 100‐meV resolution. The source and detector provide an opportunity to study the electronic dynamics of excited systems on a picosecond time scale. View full abstract»

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  • Resolution of time‐of‐flight mass spectrometers evaluated for secondary neutral mass spectrometry

    Page(s): 1947 - 1950
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    Mass resolution of a time‐of‐flight mass spectrometer with a two‐stage electrostatic reflector is calculated for secondary neutral mass spectrometry. The instrument parameters are optimized for energy and space focusing: correcting the flight time difference due to the energy width ΔE of sputtered particles and the spatial width Δs of an ionizing laser beam. The effect of Δs can be compensated by applying an acceleration field to the ionizing region, and the maximum resolution becomes about 1000 for ΔE=10 eV and Δs=1.0 mm. View full abstract»

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  • Improved LEED system using position‐sensitive detection

    Page(s): 1951 - 1953
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    An improved low‐energy electron diffraction (LEED) system using a two‐dimensional position‐sensitive detector is described. The system is capable of storing LEED patterns at a resolution of 256×256 channels with up to 216 counts per channel. The maximum electron count rate is 100 kHz. A new position computer with edge‐gating controls and a special event‐counting memory interfaced to a personal computer is used to record the LEED intensities. View full abstract»

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  • High‐resolution position‐sensitive detector

    Page(s): 1954 - 1956
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    This paper describes a position‐sensitive detector for particles or photons which has a spatial resolution of about 15 μm. The active area is about 1.3 mm in diameter. This represents an improvement of conventional position‐sensitive detection capability by about one order of magnitude and should be useful in spectrometry, spectroscopy, and atomic collision experiments. View full abstract»

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  • Absolute calibration of an atomic helium beam time‐of‐flight apparatus by flight path variation

    Page(s): 1957 - 1964
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    Virtually all inelastic helium atom scattering experiments utilize time‐of‐flight (TOF) analysis to energy analyze the scattered beam. To date, the demands upon the accuracy of these TOF measurements have not been particularly great (typically a few percent), and rather rudimentary calibration techniques have sufficed. For certain experiments, e.g., for time‐resolved measurements of specular scattering to determine surface‐bound states of helium or to observe surface‐step interference, this is no longer the case. We describe an in situ calibration technique based upon a variation of the TOF flight path that allows us to calibrate our path length and time origin to within a few millimeters and microseconds, respectively (≪2×10-3). A comparison with ‘‘zero flight time’’ laser timing measurements shows that finite drawout/transit times through the beam detector can introduce nonnegligible systematic errors into the laser calibration technique, even in the present favorable instance (light beam mass, drawout along the beam axis). We demonstrate the utility of surface diffraction as either a consistency check or to accurately determine unknown reciprocal lattice vectors. View full abstract»

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  • Beam depletion method for measuring velocity distributions of cluster beams

    Page(s): 1965 - 1970
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    A simple method to investigate the velocity distributions of cluster beams is presented. Following photon absorption, excited clusters are removed from the beam. This results in a reduced signal at the detector. Using time‐resolved detection, all the parameters of the velocity distribution can be extracted from the signal shape. The technique is demonstrated for a neutral sodium cluster beam. An analytical calculation of the signal shape is in excellent agreement with the data. View full abstract»

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  • Microjet burners for molecular‐beam sources and combustion studies

    Page(s): 1971 - 1979
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    A novel microjet burner is described in which combustion is stabilized by a hot wall. The scale is so small that the entire burner flow can be passed through a nozzle only 0.2 mm or less in diameter into an evacuated chamber to form a supersonic free jet with expansion so rapid that all collisional processes in the jet gas are frozen in a microsecond or less. This burner can be used to provide high‐temperature source gas for free jet expansion to produce intense beams of internally hot molecules. A more immediate use would seem to be in the analysis of combustion products and perhaps intermediates by various kinds of spectroscopies without some of the perturbation effects encountered in probe sampling of flames and other types of combustion devices. As an example of the latter application of this new tool, we present infrared emission spectra for jet gas obtained from the combustion of oxygen–hydrocarbon mixtures both fuel‐rich and fuel‐lean operation. In addition, we show results obtained by mass spectrometric analysis of the combustion products. View full abstract»

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  • Design and characterization of a 1200 °C entrained flow, gas/solid reactor

    Page(s): 1980 - 1984
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    The design and characterization of a 1200 °C flow reactor for studying noncatalytic, gas/solid reactions are presented. The reactor system is designed for high‐temperature, isothermal operation in a developing, laminar flow regime. The process gas is raised to the reaction temperature by flowing through a tubular preheat furnace fitted with sequential alumina honeycombs for increased convective and radiative surface area. The preheat furnace eliminates typical use of a flame burner to reach these high temperatures, thereby preventing the existence of combustion gases that may affect the reaction of interest. The reactive solid is introduced into the flow reactor by a water‐cooled injection probe. Reacted solids are collected by a stainless‐steel, water‐cooled probe capable of axial movement. Solids residence times can be varied between ∼50 and 250 ms, dependent upon process gas flow rate and collection probe height in the reactor. Sample results are presented for the calcium oxide/sulfur dioxide (CaO/SO2) reaction at varying times and temperatures. View full abstract»

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  • New lens for a low‐voltage scanning electron microscope

    Page(s): 1985 - 1989
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    This article introduces the idea of a ‘‘half ’’ pole‐piece to modify single pole‐piece lenses, enabling them to form an electron probe a few millimeters in front of the pole face. This modified single pole‐piece lens has relatively low spherical and chromatic aberration coefficients. If 2 mm is an acceptable working distance, then a 6‐Å radius probe can be made using 5‐kV electrons. View full abstract»

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  • Conceptual design and numerical simulation of a correlation diagnostic for measurement of magnetic fluctuations in plasmas

    Page(s): 1990 - 1997
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    It has been previously suggested that crossed‐sightline correlation of electron cylotron emission might be used to measure magnetic fluctuations in high‐temperature plasmas. Reported here are the results of a continuing project to determine under what conditions (if any) this measurement will be feasible. An initial conceptual design for the device hardware has been completed. Large portions of the numerical simulation are working, including ray‐tracing and emission/absorption packages. An initial discussion of data analysis for the experimental data is presented, and an analysis of the uncertainty in the line center (magnetic field) measurement in terms of the experimental uncertainties is given. View full abstract»

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  • Multipoint Thomson scattering measurements in a low‐density plasma

    Page(s): 1998 - 2001
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    A multipoint Thomson scattering apparatus has been constructed to measure electron temperature and density at several spatial locations in a low‐density toroidal plasma discharge. A multianode microchannel‐plate photomultiplier tube detector is used to provide the multipoint capability of this device. This detector, along with a simple and efficient optical collection system, allows for low‐density measurements. Critical for low‐density operation is a low stray light level from the laser, which has been achieved through careful design of the laser beam handling optics. The plasma parameters in which this device operates are in a regime where Langmuir probes are the usual diagnostic method. The design of this device is presented, along with electron temperature and density profiles of an electron cyclotron heated plasma in the Interchangeable Module Stellarator. Comparison is made with Langmuir probe measurements of similar discharges. Discrepancies between these methods are seen, and are attributed to plasma perturbations by the probe. View full abstract»

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  • Emissive probe measurement of electron temperature in high‐pressure plasmas (≥1 mTorr)

    Page(s): 2002 - 2007
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    A new method was investigated to determine the electron temperature with the emissive probe. The basis of the method is the use of a functional relationship between the floating potential and the heating voltage of the emissive probe. A new expression for the change of the floating potential was obtained as functions of the heating voltage and the electron temperature. This expression enabled us to determine the electron temperature from the measured floating potential. An experimental verification of the present method was made at relatively high pressures (above 1 mTorr). It was shown that the electron temperatures measured by the present method were consistent with those obtained by Langmuir characteristics and that the error in them did not exceed 10%. It was emphasized, further, that the method is very attractive because the circuit required is the same as that used in potential measurement. View full abstract»

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  • Beam density fluctuation diagnostic

    Page(s): 2008 - 2011
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    The conceptual design of a neutral particle analyzer that is optimized for spatially resolved fluctuation measurements is described. Estimates indicate that a pair of these analyzers could detect fluctuations in beam‐ion density associated with high β instabilities in the DIII–D tokamak. View full abstract»

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  • New UHV dilatometer for precise measurement of internal stresses in thin binary‐alloy films from 20 to 750 K

    Page(s): 2012 - 2017
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    We describe a new dilatometric device for internal stress measurements of thin binary‐alloy films, able to operate in ultrahigh vacuum in the temperature range 20–750 K. Using a three‐terminal capacitor method, the displacement of the free end of a thin cantilever substrate is monitored by the capacitance change. With a sensitivity of 1 nm for substrate displacements, the resolution for stress detection is 105 Pa in a 100‐nm‐thick film. Simultaneously with the stress measurement, the electrical resistivity of the film can be determined on the same substrate. The direct comparison of electrical and mechanical thin‐film properties gives the ability to obtain additional information on the growth process and on the thin‐film structure. Measurements of a crystalline Cu film and an amorphous Zr20 Co80 alloy film are shown. View full abstract»

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  • Optical interferometry for measuring instantaneous thickness of transparent solid and liquid films

    Page(s): 2018 - 2022
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    An optical‐interference method is proposed which enables measurements of instantaneous, uniform thickness of the order of 10 μm–1 mm of transparent (or weakly absorbing) solid materials or liquids. It uses a converging lens set by its focal length separated from the subject film. The lens turns parallel, monochromatic, coherent rays in an expanded laser beam into converging rays propagating as spherical waves toward the subject film. The rays reflected at the front and rear surfaces of the film pass again through the lens to be retransformed from the spherical waves into the plane waves, and form interference fringes on a screen. Knowing the number of fringes provided by the rays which are incident on the subject film at angles between two specified angles, we can readily calculate the thickness of the film. A prototype apparatus based on this method has been constructed and used successfully in measuring the thicknesses of both solid and liquid films. View full abstract»

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  • Direct pulse technique for spontaneous polarization dynamics and molecular reorientation processes in ferroelectric liquid crystals

    Page(s): 2023 - 2030
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    A method has been devised for studying the spontaneous polarization, dynamics of polarization reversal, and the molecular reorientation processes that occur in the bulk and surfaces of ferroelectric liquid crystals. These studies have been carried out by analyzing the current response to triangular‐ and square‐wave forms. The current response to a triangular wave yields the spontaneous polarization by conveniently subtracting the background contribution due to the conductive and capacitive currents. Molecular reorientation processes which take place within the bulk and the boundary surface layer can be studied by the appearance of polarization current peaks on the triangular‐wave response. The dynamics of polarization reversal between bistable states and of the polarization change between the zero‐field relaxed state and either of the saturation remanent polarization states have been studied by applying ‘‘symmetric’’ and ‘‘asymmetric’’ square waves. The technique can also be successfully applied to solid ferroelectrics for studying the spontaneous polarization and the domain dynamics during switching. View full abstract»

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  • Variable‐depth calorimetry of a layered material

    Page(s): 2031 - 2035
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    We have investigated the use of frequency variation in ac calorimetry in the measurement of thermal quantities within controllable distances of the sample heater and thermometer. This technique, useful in studies of heterogeneous samples where only a small part of the sample is of interest, e.g., surfaces, thin films, and interfaces, is applied to study the thermal properties of a test sample made from indium (In) sandwiched between layers of bulk gallium arsenide. We measure and analyze the frequency dependence of the thermal response of the sample, as well as the variation with frequency of the relative size of the anomaly observed at the In superconducting transition. The data are consistent with a model assuming a thermal diffusion‐limited sampling volume. View full abstract»

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Review of Scientific Instruments, published by the American Institute of Physics, is devoted to scientific instruments, apparatus, and techniques.

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Albert T. Macrander
Argonne National Laboratory