1,938 research outputs found

    Scanning microSQUID Force Microscope

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    A novel scanning probe technique is presented: Scanning microSQUID Force microscopy (SSFM). The instrument features independent topographic and magnetic imaging. The SSFM operates in a dilution refrigerator in cryogenic vacuum. Sample and probe can be cooled to 0.45 K. The probe consists of a microSQUID placed at the edge of a silicon chip attached to a quartz tuning fork. A topographic vertical resolution of 0.02 micrometer is demonstrated and magnetic flux as weak as 10−3Φ010^{-3} \Phi_{0} is resolved with a 1 micrometer diameter microSQUID loop.Comment: submitted to Review of Scientific Instrument

    Direct observation of vortices in an array of holes at low temperature: temperature dependance and first visualization of localized superconductivity

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    A scanning micro superconducting quantum interference device (microSQUID) microscope is used to directly image vortices in a superconducting Al thin film. We observe the temperature dependence of the vortex distribution in a regular defect (hole) array patterned into the Al film. The first direct observation of the localized superconducting state around the holes is shown as well as the effect of the hole size on nucleation of the superconducting state

    The Emission Microscope: A Valuable Tool for Investigating the Fundamentals of the Scanning Electron Microscope

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    In scanning microscopy in transmission (STEM) and reflection (SEM) the spreading of the spatial distributions of the forward-and backscattered electrons, respectively, deteriorates contrast and resolution. We therefore investigate this spreading by measuring quantitatively the corresponding distributions of secondaries released by these reemerging electrons. In order to carry out this experiment we visualize these distributions by using the surface of the specimen as the source of an emission microscope. The spreading of transmitted beams of 19.5 keV in thin films of Al and Ge 0 .2-2 μm in thickness is reported here as well as the spatial distributions of secondaries released by backscattered electrons from bulk Si-, Ge-, Ag- and Au-specimens for 20-70 keV energy of the primary probe. By evaluating these distributions we calculated an upper limit of the contrast available in SEM micrographs obtained in the secondary mode. The formation of edge brightening, flaring due to charging and the top bottom effect is demonstrated by means of emission microscopical micrographs

    Factoring and Fourier Transformation with a Mach-Zehnder Interferometer

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    The scheme of Clauser and Dowling (Phys. Rev. A 53, 4587 (1996)) for factoring NN by means of an N-slit interference experiment is translated into an experiment with a single Mach-Zehnder interferometer. With dispersive phase shifters the ratio of the coherence length to wavelength limits the numbers that can be factored. A conservative estimate permits N≈107N \approx 10^7. It is furthermore shown, that sine and cosine Fourier coefficients of a real periodic function can be obtained with such an interferometer.Comment: 5 pages, 2 postscript figures; to appear in Phys.Rev.A, Nov. 1997; Figures contained only in replaced versio

    A Few Steps Towards a More Quantitative Understanding of Contrast in the Scanning Electron Microscope

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    The interaction volume of the electron beam with the specimen in a scanning electron microscope (SEM) is a highly complex function of the surface structure of the specimen, its chemical composition and the energy of the scanning electron beam.· The video signals formed by secondary electrons (SE) or backscattered electrons (BSE) reflect this complexity insofar as they may contain not only information of the interior of the pixel which has just been scanned and its neighborhood, but may depend on surface details hundreds of microns apart from the impinging point of the electron beam. This leads to artifacts in scanning electron micrographs, e.g., edge brightening. The knowledge of the spatial distribution of the current density of the BSE and SE released by the impinging beam are the key for a more quantitative understanding of contrasts in scanning electron micrographs. In a first step, our emission microscopic method to visualize these distributions has been improved by substituting a photographic registration method by a charged couple device (CCD) densitometer. The resolution of our present densitometer (256 grey levels) is not sufficient to record the full dynamic range of the SE current density distributions. However, this will be possible in the near future with a state of the art CCD-camera and a 14 bit image processing system

    Measurement of the Current-Phase Relation in Josephson Junctions Rhombi Chains

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    We present low temperature transport measurements in one dimensional Josephson junctions rhombi chains. We have measured the current phase relation of a chain of 8 rhombi. The junctions are either in the classical phase regime with the Josephson energy much larger than the charging energy, EJ≫ECE_{J}\gg E_{C}, or in the quantum phase regime where EJ/EC≈2E_{J}/E_{C}\approx 2. In the strong Josephson coupling regime (EJ≫EC≫kBTE_{J}\gg E_{C} \gg k_{B}T) we observe a sawtooth-like supercurrent as a function of the phase difference over the chain. The period of the supercurrent oscillations changes abruptly from one flux quantum Φ0\Phi_{0} to half the flux quantum Φ0/2\Phi_{0}/2 as the rhombi are tuned in the vicinity of full frustration. The main observed features can be understood from the complex energy ground state of the chain. For EJ/EC≈2E_{J}/E_{C}\approx 2 we do observe a dramatic suppression and rounding of the switching current dependence which we found to be consistent with the model developed by Matveev et al.(Phys. Rev. Lett. {\bf 89}, 096802(2002)) for long Josephson junctions chains.Comment: to appear in Phys. Rev.

    Backscattered Electrons and Their Influence on Contrast in the Scanning Electron Microscope

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    The backscattered electron (BSE) induced secondaries (SE2) emerge from an area that is usually many orders of magnitude larger than the area in which the impinging primary probe releases secondary electrons (SE1). These SE2 secondary electrons form a) an undesired background signal in high resolution scanning micrographs and b) are responsible for the well known proximity effect in electron beam lithography. In this paper we focus our attention on the first topic exclusively: we discuss the complex influence of the SE2 on contrast in SEM micrographs (neglecting the components SE3 and SE4). We do this on the basis of our emission-microscopic measurements of the spatial distributions of SE1 and SE2 emerging from flat bulk specimens. By integrating these distributions in two dimensions we calculate the total number of SE1 and SE2 electrons and deduce the signal to backgroud ratio SE1/(SE1+SE2), i.e., the maximum contrast in one pixel ( single pixel contrast ) and the contrast of two adjacent pixels 1 and 2 according to its usual definition C= (I1 -I2)/(I1 +I2). We calculate the enhanced secondary emission factor for backscattered electrons from our total numbers of SE1 and SE2 for Si, Ge and Ag to Si=2.58, Ge=1.46, Ag=1,23
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