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Review of Scientific Instruments

Issue 8 • Date Aug 2001

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Displaying Results 1 - 25 of 56
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • Collisions of ions with surfaces at chemically relevant energies: Instrumentation and phenomena

    Page(s): 3149 - 3179
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    An overview of gaseous ion/surface collisions is presented, with special emphasis on the behavior of polyatomic projectile ions at hyperthermal collision energies (1–100 eV) and the instrumentation needed for such studies. The inelastic and reactive processes occurring during ion/surface collisions are described in terms of several archetypes, viz., elastic and quasielastic scattering, chemical sputtering leading to release of surface material, inelastic scattering leading to surface-induced dissociation (SID) of the projectile, ion/surface reactions, and soft landing. Parameters that are important in ion/surface interactions are discussed, including the interaction time, the conversion of translational to internal energy, the translational energies of the scattered ions, the effects of scattering angle, and the influence of the nature of the surface. Different types of tandem mass spectrometers, built specifically to study ion/surface collision phenomena, are discussed and the advantages and disadvantages of the individual designs are compared. The role of SID as a technique in bioanalytical mass spectrometry is illustrated and this inelastic collision experiment is compared and contrasted with gas-phase collision-induced dissociation, the standard method of tandem mass spectrometry. Special emphasis is placed on reactive scattering including the use of ion/surface reactions for surface chemical analysis and for surface chemical modification. © 2001 American Institute of Physics. View full abstract»

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  • Effect of strain on temperature measurements using the fluorescence intensity ratio technique (with Nd3+- and Yb3+-doped silica fibers)

    Page(s): 3180 - 3185
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    The effect of strain upon the fluorescence intensity ratio technique of optical fiber based temperature sensing has been investigated using a series of different Yb3+- and Nd3+-doped optical fibers. Measurements were conducted with each of the doped fibers for temperatures between approximately 10 and 140 °C and for strain values between 50 and 2100 με. Results suggest that the strain-temperature cross sensitivity for the fluorescence intensity ratio method is minimal, with an applied strain of 1000 με inducing temperature errors of less than 0.4 °C. © 2001 American Institute of Physics. View full abstract»

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  • Fiber optic sensor for dual measurement of temperature and strain using a combined fluorescence lifetime decay and fiber Bragg grating technique

    Page(s): 3186 - 3190
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    A fiber optic sensor device has been developed incorporating a short length of erbium doped fiber fused in close proximity to a single-fiber Bragg grating, to measure both the fluorescent lifetime decay and the wavelength shift in these respective elements, for temperature and strain determination. Calibration results obtained from this simple, low cost, intrinsic sensor scheme show standard deviation errors of 20.4 μϵ and 1.2 °C over strain and temperature ranges of 22–1860 μϵ and 25–120 °C, respectively. © 2001 American Institute of Physics. View full abstract»

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  • First operation of circular dichroism measurements with periodic photon-helicity switching by a variably polarizing undulator at BL23SU at SPring-8

    Page(s): 3191 - 3197
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    This article presents the first operation of the magnetic circular dichroism (MCD) measurement system with periodic photon-helicity switching. The measurements were performed at the newly constructed soft x-ray beamline—BL23SU— at the third-generation synchrotron radiation facility, SPring-8. The monochromator control system was synchronized to the movement of the magnetic row (phase shift) of an APPLE-2 (Sasaki) type variably polarizing undulator. The periodic phase shift of the undulator provided the switching of helicity polarizing soft x rays up to 0.1 Hz. The closed-orbit distortion of the storage ring was controlled to avoid optical axis disturbances at this beamline as well as at other beamlines. The circular dichroism spectra with helicity switching by APPLE-2 show the possibility of high-sensitivity MCD measurements. This method promotes precise MCD measurements and can be a powerful technique to study magnetism as well as dichroism. © 2001 American Institute of Physics. View full abstract»

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  • Portable long trace profiler: Concept and solution

    Page(s): 3198 - 3204
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    Since the early development of the penta-prism long trace profiler (LTP) and the in situ LTP, and following the completion of the first in situ distortion profile measurements at Sincrotrone Trieste (ELETTRA) in Italy in 1995, a concept was developed for a compact, portable LTP with the following characteristics: easily installed on synchrotron radiation beam lines, easily carried to different laboratories around the world for measurements and calibration, convenient for use in evaluating the LTP as an in-process tool in the optical workshop, and convenient for use in temporarily installation as required by other special applications. The initial design of a compact LTP optical head was made at ELETTRA in 1995. Since 1997 further efforts to reduce the optical head size and weight, and to improve measurement stability have been made at Brookhaven National Laboratory. This article introduces the following solutions and accomplishments for the portable LTP: (1) a new design for a compact and very stable optical head, (2) the use of a small detector connected to a laptop computer directly via an enhanced parallel port, and there is no extra frame grabber interface and control box, (3) a customized small mechanical slide that uses a compact motor with a connector-sized motor controller, and (4) the use of a laptop computer system. These solutions make the portable LTP able to be packed into two laptop-size cases: one for the computer and one for the rest of the system.© 2001 American Institute of Physics. View full abstract»

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  • Atomic streak camera operating in the extreme ultraviolet

    Page(s): 3205 - 3207
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    We present a new type of streak camera to measure the temporal shape of pulses in the extreme ultraviolet (XUV) region: A cloud of noble gas atoms is used as a photocathode. The first results at 57 nm show a time resolution of 10 ps. Modifications to improve the time resolution are discussed. Using a noble gas as a photocathode has the potential to decrease the temporal resolution of the streak camera in the XUV to less than 0.5 ps. © 2001 American Institute of Physics. View full abstract»

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  • Phase noise transfer in resonant optical cavities

    Page(s): 3208 - 3214
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    We study theoretically and experimentally the field circulating in a resonant optical cavity when the phase of the incident field and the length of the cavity exhibit fluctuations about their mean values. With a simple model we derive transfer functions which relate the spectral density of phase noise of both the input field and the cavity length to that of the circulating field. In agreement with the standard steady state result, we find that phase noise in the incident field is low pass filtered by the cavity. Cavity length fluctuations are found to be high pass filtered in their transfer to the circulating field. These results are used to present a control loop model of the cavity-laser system. We verify the model experimentally with a Pound–Drever–Hall discriminator and apply it to a discussion of the stability of a frequency reference at 532 nm. © 2001 American Institute of Physics. View full abstract»

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  • Hyper-Rayleigh scattering in the Fourier domain for higher precision: Correcting for multiphoton fluorescence with demodulation and phase data

    Page(s): 3215 - 3220
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    An improved experimental technique for the suppression of the multiphoton fluorescence contribution in hyper-Rayleigh scattering experiments for the determination of the first hyperpolarizability of molecules in solution is presented. This improvement allows for a better correction for the fluorescence artifact, so as to eliminate any overestimation for the value of the first hyperpolarizability. The measurement of the demodulation only of the fluorescence as a function of modulation frequency [Olbrechts etal, Rev. Sci. Instrum. 69, 2233 (1998)] is now complemented by the measurement of the phase lag between the intermediate scattering and the time-delayed fluorescence. From the simultaneous data reduction of demodulation and phase shift toward the hyperpolarizability, fluorescence contribution, and fluorescence lifetime, an improvement in precision of 1 order of magnitude is demonstrated. This level of precision has been used to show the relative impact of f-orbital filling and ligands on the molecular second-order nonlinear optical response of lanthanide complexes containing a hemicyanine chromophore. © 2001 American Institute of Physics. View full abstract»

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  • Generation of circularly polarized light by superposition of coherent transition radiation in the millimeter wavelength region

    Page(s): 3221 - 3224
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    Circularly polarized light was generated in the millimeter wavelength region from superposition of forward transition radiation (TR) and backward TR emitted from two metallic screens placed along a trajectory of a short-bunch beam of electrons of 42 MeV. The degree of the circular polarization was analyzed to be 97% of the polarized radiation at λ=2.25 mm, using a Soleil’s compensator and a wire-grid polarizer. The geometry of the metallic screens was discussed from the point of the phase difference between the forward TR and the backward TR. © 2001 American Institute of Physics. View full abstract»

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  • Optical signal coupling in microchannel plate detectors with a subnanosecond performance

    Page(s): 3225 - 3229
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    For an application in high-performance mass spectrometry we adapted our recent design of a fast microchannel plate detector such that the signal output when registering a single particle is realized via optical impulses which are then forwarded to the data acquisition system. The charge impulse collected at the anode of the detector is converted to a light impulse using a vertical cavity surface emitting laser diode. Such an assembly has the advantage that the electrical circuitry at the anode is very small and thus high signal quality is achieved even in the gigahertz frequency range. Furthermore, such a detector can easily be operated at high electric potentials without the need for capacitive signal coupling. © 2001 American Institute of Physics. View full abstract»

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  • High speed laser shadowgraphy for electromagnetically driven cylindrical implosions

    Page(s): 3230 - 3236
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    A laser shadowgraphy system for high-speed imaging of a convergent cylindrical shockwave generated by an electromagnetically driven solid density liner implosion in Lucite is described. The laser shadowgraphy system utilizes an advanced high-energy, long-pulse, frequency-doubled Nd:YAG laser for target illumination and a fast framing camera for multiple frame imaging of the shockwave as it radially converges and transits the Lucite. The time window resolution is 10 ns as determined by the fastest exposure time capable with the camera. Two on-axis symmetric implosions and two off-axis asymmetric implosion experiments were fielded at the Air Force Research Laboratory’s Shiva Star 4.2 MJ capacitor bank z-pinch facility. For each experimental shot, the shadowgraphy system captured several frames of shadowgraph images as the shockwave moved through the Lucite. Analysis of the shockwave shadowgraph image shapes is done by fitting each shadowgraph image to a generic elliptical fit function and plotting the resultant two-dimensional image fits for comparison. For the on-axis symmetric implosion shots, a radial trajectory plot is extracted and a radial shock velocity is calculated. The Lucite shock speed is seen to increase monotonically from an initial velocity of 7.9 mm/μs to a near final velocity of 13.4 mm/μs as convergence effects dominate the shock speed calculated at small radii. © 2001 American Institute of Physics. View full abstract»

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  • Compensation of beam deflection due to the magnetic field using beam steering by aperture displacement technique in the multibeamlet negative ion source

    Page(s): 3237 - 3244
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    A beam steering technique using aperture displacement was examined to correct the negative ion beam deflection due to the magnetic field for electron suppression in a large-area multibeamlet H- source. The total deflection angle was estimated, including the effect of the deflection by the electron suppression magnetic field and the beam steering by the aperture displacement, both by linear optics theory and by three-dimensional beam trajectory simulation. Two methods were compared; one used the displacement both of the grounded grid (GG) apertures and of the exit part of the extraction grid (EG exit) apertures, and the other used the displacement only of the EG exit. The beam steering experiments were performed using a large-area multibeamlet H- source with both displacement methods, and the results were compared with the theoretical estimations. As a result, both methods were effective to correct the beam deflection. In particular, the displacement of only the EG exit with a simplified displacement structure achieved a large steering angle by a small displacement. The steering angle in the experiment was a few mrad smaller than the estimations. Based on these results, the aperture displacement of the EG exit was applied to the 1/5 segment of a H- source in the Large-Helical-Device neutral beam injector, where the GG apertures are displaced only focusing of the large-area multibeamlet. In this case, 1.0 mm of the displacement is concluded to be proper to sufficiently compensate the beam deflection at 180 keV, from extrapolation of the beam energy characteristics at 100–140 kev. © 2001 American Institute of Physics. View full abstract»

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  • A magnifying lens for velocity map imaging of electrons and ions

    Page(s): 3245 - 3248
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    We have designed and implemented an electrostatic lens that magnifies the images of an existing velocity map imaging apparatus up to a factor of 20. The lens can be used to vary the magnification while keeping the field strength in the interaction region constant. For the region of interest where magnification is required (low energy ions or electrons, in a high external field) the lens does not add any observable aberrations to the imaging. We have characterized the performance of the lens using the imaging of slow photoelectrons. © 2001 American Institute of Physics. View full abstract»

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  • Magnetic probe construction using thick-film technology

    Page(s): 3249 - 3259
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    Thick-film technology has been successfully adapted for the design and fabrication of magnetic probes of a new type suitable for use in the simultaneous ultrahigh vacuum and high temperature environment of a nuclear fusion device. The maximum usable temperature is expected to be around 900 °C. This new probe has a specific sensitivity (coupling area per unit volume) an order of magnitude higher than a conventional coil. The new probe in one implementation is capable of simultaneously measuring magnetic field in three orthogonal directions about a single spatial point and in two frequency ranges. Low frequency coils have a measured coupling area of 296–323 cm2, and a frequency response of about 300 kHz. High frequency coils have a design coupling area of 12–15 cm2. © 2001 American Institute of Physics. View full abstract»

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  • New diagnostic method for monitoring plasma reactor walls: Multiple total internal reflection Fourier transform infrared surface probe

    Page(s): 3260 - 3269
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    Films and adsorbates that deposit on reactor walls during plasma etching and deposition affect the discharge properties such as the charged particle and reactive radical concentrations. A systematic study of this plasma–wall interaction is made difficult by a lack of diagnostic methods that enable one to monitor the chemical nature of the reactor wall surface. A new diagnostic technique based on multiple total internal reflection Fourier transform infrared (MTIR-FTIR) spectroscopy was developed to monitor films and adsorbates on plasma etching and deposition reactor walls with monolayer sensitivity. Applications of this MTIR-FTIR probe are demonstrated. Specifically, we use this probe to (i) detect etch products and films that deposit on the reactor walls during Cl2 plasma etching of Si, (ii) determine the efficacy of a SF6 plasma to clean films deposited on reactor walls during Cl2/O2 etching of Si, and (iii) monitor wafer-to-wafer etching reproducibility. © 2001 American Institute of Physics. View full abstract»

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  • Compact collimated vacuum ultraviolet diagnostics for localized impurity measurements in fusion boundary plasmas

    Page(s): 3270 - 3276
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    Compact vacuum ultraviolet diagnostics for impurity emission measurements in boundary plasmas of nuclear fusion plasma devices are described. The instruments are designed for monitoring intensities of resonant impurity lines between 300 and 2000 Å. The intensities are used to infer basic yet important plasma parameters, such as density of impurity charge states, radiated power, or electron temperature and density estimates. All utilized components and materials satisfy ultrahigh vacuum and high bake-out temperature requirements, enabling the instruments to qualify for vacuum port or in-vessel placement, in close proximity to emitting plasmas. The instruments have high spatial (Δl≤1 cm) and temporal (Δτ≤100 μs) resolution. The spectral resolution is Δλ≤20 Å. Planar diffraction gratings at near-normal incidence are used for dispersion of incident radiation, collimated by high precision mechanical stacked grid collimators. Highly localized field of view, adequate throughput, and compactness distinguish these diagnostics from conventional slit instruments. A prototype monochromator for λ=1550 Å has been built, evaluated, radiometrically calibrated, and used on the CDX-U spherical torus for monitoring C IV emission in ohmic and high harmonic fast wave heated plasmas with Te(0)≤100 eV. An attractive mechanical collimator based Wadsworth mount spectrometer concept is presented and its application to impurity content and transport measurements in tokamaks is discussed. © 2001 American Institute of Physics. View full abstract»

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  • A Linux cluster for between-pulse magnetic equilibrium reconstructions and other processor bound analyses

    Page(s): 3277 - 3280
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    A 12-processor Linux PC cluster has been installed to perform between-pulse magnetic equilibrium reconstructions during tokamak operations using the EFIT code written in FORTRAN. The MPICH package implementing message passing interface is employed by EFIT for data distribution and communication. The new system calculates equilibria eight times faster than the previous system yielding a complete equilibrium time history on a 25 ms time scale 4 min after the pulse ends. A graphical interface is provided for users to control the time resolution and the type of EFITs. The next analysis to benefit from the cluster is CERQUICK written in IDL for ion temperature profile analysis. The plan is to expand the cluster so that a full profile analysis (Te, Ti, ne, Vr, Zeff) can be made available between pulses, which lays the ground work for Kinetic EFIT and/or ONETWO power balance analyses. © 2001 American Institute of Physics. View full abstract»

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  • Closed-cycle refrigerator-cooled scanning SQUID microscope for room-temperature samples

    Page(s): 3281 - 3290
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    We have designed, built, and operated a scanning superconducting quantum interference device (SQUID) microscope that uses a closed-cycle refrigerator to cool a YBa2Cu3O7 (YBCO) dc SQUID to 77 K. The SQUID is mounted in custom vacuum housing that has a thin sapphire window that maintains thermal isolation of the SQUID while allowing samples to be imaged in air at room temperature. Samples are mounted on an x–y scanning table and can be brought to within about 60 μm of the SQUID for magnetic field imaging. The SQUID has an effective pick-up area of 1.2×10-9m2 and a level of flux noise of 10.5 μΦ0/Hz1/2 in the white noise region (above 500 Hz). We describe the performance of the system and present images of a variety of samples. © 2001 American Institute of Physics. View full abstract»

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  • A novel imaging x-ray microscope based on a spherical crystal

    Page(s): 3291 - 3303
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    A novel, compact, large field, and spectrally tunable imaging x-ray microscope is presented. It is based on the use of an isotropic point x-ray source and a spherically curved crystal. The x-ray beam intensity is modulated by the object attenuation, then monochromatized and enlarged using a spherical crystal and, finally, imaged using a detector downstream from the crystal. We demonstrate by ray tracing simulations that this system allows microscopy studies with high spatial resolution, high magnification ratios, and large field of view. Microscopes using this model can be easily built using different x-ray sources, like conventional x-ray tube generators, x rays emitted by laser-generated plasmas or x-pinch plasmas, and also synchrotron radiation when used in combination with other condenser optics. Preliminary experiments are presented to demonstrate the feasibility of the proposed setup. High resolution (∼4 μm) monochromatic (δλ/λ∼10-5–10-3) images over a large field of view (few mm2) were recorded in the spectral range 8–14 Å using a laser-generated plasma source and a spherical mica crystal. Compared to x-ray crystal imagers used in relation with plasma sources, the new configuration produces high quality stigmatic images working at many different Bragg angles, thus improving the spectral tunability and allowing a more flexible design. © 2001 American Institute of Physics. View full abstract»

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  • Quantitative comparison of three calibration techniques for the lateral force microscope

    Page(s): 3304 - 3312
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    The quantitative use of atomic force microscopes in lateral mode for friction measurements has been limited by uncertainty about reliable calibration techniques. This article describes a comparison of three methods that have been proposed for the calibration of the lateral sensitivity of atomic force microscopes: (a) one based on movement of the photodiode assembly, (b) one based on the slope of the friction-loop while the contacting surfaces are in static contact, and (c) one based on a comparison of the lateral force signal on a surface with changing slopes of known orientation. All three methods gave comparable results thereby confirming their robust nature, and also confirming the validity of atomic force microscope methods for lateral force measurement. However, (b) indicated that for the commercial instrument used here, the lateral signal sensitivity is load dependent. A simple extension to (a) revealed the nature of this dependence: a misalignment of the four-quadrant photodiode detection system with respect to the alignment of the reflected beam path resulting in a coupling of the normal and lateral signals. The result is that the lateral signal does not scale directly with friction, requiring that for friction versus applied load studies, lateral signal calibration be performed across the full range of applied loads of interest. To a greater or lesser extent, this shortcoming will be evident in a wide range of commercial instruments. All three methods studied here have special advantages: (a) provides the most complete information about the detector response, (b) provides a calibration method when friction characteristics of colloid probes of a wide range of possible materials are of interest, and (c) has the advantage of also providing information about the state of the tip geometry. © 2001 American Institute of Physics. View full abstract»

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  • A system for performing simultaneous in situ atomic force microscopy/optical microscopy measurements on electrode materials for lithium-ion batteries

    Page(s): 3313 - 3319
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    An atomic force microscope (AFM) equipped with an optical charge coupled device camera has been placed in an Ar filled glovebox for the purpose of studying the change in morphology of electrode materials as they react with lithium. In order to minimize noise induced by vibration, the AFM is mounted on granite blocks suspended from the ceiling of the glovebox by a combination of flexible rubber cords and metal springs. The AFM, which is equipped with an environmental chamber surrounding the sample, is then enclosed in a specially constructed draft shield that allows the circulation of Ar gas by the purification system during imaging. A special electrochemical cell was constructed to hold the working electrode under study. Repeated imaging with little drift is possible while electrodes are reacted with lithium for periods of many days. Examples of measurements made by this device will be given for the case of lithium alloying with sputter-deposited Si–Sn thin films. The optical and AFM images obtained as a function of lithium content in the films are assembled into time-lapsed “movies” showing the evolution of the morphology of the sample along with the corresponding electrochemistry. These movies are available for download through the Electronic Physics Auxiliary Publication Service (EPAPS). © 2001 American Institute of Physics. View full abstract»

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  • High performance feedback for fast scanning atomic force microscopes

    Page(s): 3320 - 3327
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    We identify the dynamics of an atomic force microscope (AFM) in order to design a feedback controller that enables faster image acquisition at reduced imaging error compared to the now generally employed proportional integral differential (PID) controllers. First, a force model for the tip–sample interaction in an AFM is used to show that the dynamic behavior of the cantilever working in contact mode can be neglected for control purposes due to the relatively small oscillation amplitude of the cantilever in response to a defined topography step. Consequently, the dynamic behavior of the AFM system can be reduced to the behavior of the piezoelectric scanner making the design of a model based controller for the AFM possible. Second, a black box identification of the scanner of a commercial AFM (Nanoscope IIIa, Digital Instruments) is performed using subspace methods. Identification yields a mathematical model of the scanner which allows us to design a new controller utilizing H theory. Finally, this controller is implemented on an existing AFM and operated in contact mode. We demonstrate that such an H-controlled AFM system, while scanning at rates five times faster than conventional PID-controlled systems, operates with reduced measurement error and allows scanning at lower forces. © 2001 American Institute of Physics. View full abstract»

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  • Application of a one-port dielectric resonator for measurement of the intermodulation in high temperature superconducting films

    Page(s): 3328 - 3331
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    A technique for characterization of intermodulation performance of unpatterned high TC superconducting (HTS) films, based on the application of the resonator with a single coupling probe is proposed. It allows us to sufficiently increase the sensitivity in comparison with the conventional method based on the resonator with two coupling probes. The measurements of the power at mixed frequency as a function of input power are performed for epitaxial HTS films of various surface resistance and thickness. From the experimental data an intermodulation coefficient α is determined, which provides the film intermodulation properties independently on the measuring system. © 2001 American Institute of Physics. View full abstract»

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  • Selected error sources in resistance measurements on superconductors

    Page(s): 3332 - 3339
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    In order to investigate the causes that produce some of the unwanted effects observed in the resistance versus temperature profiles, a variety of sources of error for resistance measurements in superconductors, using a standard four-probe configuration, have been studied. A piece of superconducting Y1Ba2Cu3O7-x ceramic material has been used as the test sample, and the resulting effects in both accuracy and precision in its temperature dependent resistance are reported here. Studied measurement error sources include thermal emf’s, temperature sweep rates, Faraday currents, electrical-contact failures at the sample’s surface, thermal contractions at mechanically attached instrumental wires, external electromagnetic fields, and slow sampling rates during data acquisition. Details of the experimental setup and its measurement error function are also given. © 2001 American Institute of Physics. View full abstract»

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Aims & Scope

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

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Editor
Albert T. Macrander
Argonne National Laboratory