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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 685-694 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A CW electron spin resonance (ESR) spectrometer working at earth-field is described for the first time. The optimized sensitivity has allowed to reduce the size of the sample holder down to 100 mm3, a low value for such a low working frequency (1.845 MHz). At this frequency, only narrow ESR signals are significant (maximum sweep 125 μT or 100 A/m). The use of the Bloch configuration and the particular care to optimize the sensitivity lead to a design that partially compensates the lack of sensitivity due to low fields. Small material quantities are thus usable. Moreover, the spectrometer is low cost, portable, and easily reproducible with the announced performance. The main use of the spectrometer is to characterize materials for earth field magnetometry. For that purpose it has been necessary to define a figure of merit for magnetometry. Until this study, the only parameter discussed was the linewidth of the homogeneous ESR line (i.e., T2). The detailed discussion of the figure of merit, taking into account not only the material but the couple spectrometer material, considerably decreases the predominance of the linewidth and let emerge secondary factors such as packaging, susceptibility, ESR lineshape, T1 vs T2, etc. The figure of merit evaluated from the material parameters has been experimentally measured for different π radicals. Comparison with their performance in earth field magnetometry demonstrates the pertinence of the proposed figure of merit.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2016-03-05
    Description: A novel configuration of a deuterium z-pinch has been used to generate a nanosecond pulse of fast ions and neutrons. At a 3 MA current, the peak neutron yield of (3.6 ± 0.5) × 10 12 was emitted within 20 ns implying the production rate of 10 20 neutrons/s. High neutron yields resulted from the magnetization of MeV deuterons inside plasmas. Whereas deuterons were trapped in the radial direction, a lot of fast ions escaped the z-pinch along the z-axis. A large number of 〉25 MeV ions were emitted into a 250 mrad cone. The cut-off energy of broad energy spectra of hydrogen ions approached 40 MeV. The total number of 〉1 MeV and 〉25 MeV deuterons were 10 16 and 10 13 , respectively. Utilizing these ions offers a real possibility of various applications, including the increase of neutron yields or the production of short-lived isotopes in samples placed in ion paths. On the basis of our experiments with various samples, we concluded that a single shot would have been sufficient to obtain GBq positron activity of 13 N isotopes via the 12 C(d,n) 13 N reaction. Furthermore, the first z-pinch generated neutron radiograph produced by ≈20 ns pulses is presented in this paper.
    Print ISSN: 1070-664X
    Electronic ISSN: 1089-7674
    Topics: Physics
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  • 3
    Publication Date: 2014-12-12
    Description: The sheet resistance of thin film structures is commonly measured using a four-point-probe setup and involves the application of geometrical correction factors depending on the sample geometry and electrode pitch. The characterization of small thin film structures in the micrometer range requires probe tip diameters and spacings that are of similar size. An experimental realization with micro-manipulators is possible as tip distances in a range of a few micrometers can be achieved. However, such a setup requires an additional correction factor accounting for the finite probe tip contact area. Neglecting such a correction leads to an underestimation of the sheet resistance when the electrode pitch is comparable to the probe contact area diameter. Based on numerical simulation results, we develop a simplified method applying a new phenomenological correction scheme which takes into account the finite contact area size for small probe distances. This method can be applied directly without any additional numerical simulations and corrects the underestimation due to the probe tip size significantly.
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
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  • 4
    Publication Date: 2016-10-13
    Description: Structured metallic tips are increasingly important for optical spectroscopies such as tip-enhanced Raman spectroscopy, with plasmonic resonances frequently cited as a mechanism for electric field enhancement. We probe the local optical response of sharp and spherical-tipped atomic force microscopy (AFM) tips using a scanning hyperspectral imaging technique to identify the plasmonic behaviour. Localised surface plasmon resonances which radiatively couple with far-field light are found only for spherical AFM tips, with little response for sharp AFM tips, in agreement with numerical simulations of the near-field response. The precise tip geometry is thus crucial for plasmon-enhanced spectroscopies, and the typical sharp cones are not preferred.
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
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