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  • 1
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2651-2653 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A new atomic force microscope, which combines a microfabricated cantilever with an optical lever detection system, now makes it possible to measure the absolute force applied by a tip on a surface. This absolute force has been measured as a function of distance (=position of the surface) in air and water over a range of 600 nm. In the absolute force versus distance curves there are two transitions from touching the surface to a total release in air caused by van der Waals interaction and surface tension. One transition is due to lifting off the surface; the other is due to lifting out of an adsorbed layer on the surface. In water there is just one transition due to lifting off the surface. There is also a transition in air and water when the totally released tip is pulled down to touch the surface as the surface and tip are brought together. Based on the force versus distance curves, we propose a procedure to set the lowest possible imaging force. It can now be as low as 10−9 N or less in water and 10−7 N in air.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2491-2493 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have analyzed the structure of tilted superlattices on atomically stepped surfaces by using atomic force microscopy to detect ridges of GaAs formed by the selective oxidation and removal of intervening AlAs regions. Oxides were removed in a liquid cell of the atomic force microscope while scanning. We have demonstrated plan views which reveal the superlattice length and width uniformity, but the method is also in principle suited for cross-sectional samples.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Solar physics 108 (1987), S. 205-220 
    ISSN: 1573-093X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The global magnetic-field resonances previously found in a modal analysis of a 25 yr Mt Wilson-Kitt Peak data set of synoptic magnetic maps are also revealed when only the magnetic polarities are used, disregarding the magnitude of the flux. Thus the topological organization of the magnetic polarities alone suffices to bring out the correct modal structure, although the results are noisier as compared with the case when the magnetic fluxes are included. This result suggests that magnetic polarities indirectly inferred from Hα data may be used to study the resonances. Whereas synoptic magnetograph observations are not available before 1959, Hα observations date back to the last century, and could in principle be used to enhance the frequency resolution in the power spectra. Using zonal distributions of magnetic polarities inferred from Hα data by Makarov for the period 1941–1983, we have performed a power spectrum analysis of the rotationally symmetric spherical harmonic modes (m = 0), and compared the results with the corresponding analysis for the magnetic fields and polarities determined from real magnetograph data. The same parity selection rule that governs the 22 yr magnetic cycle in the magnetograph data is also revealed by the Hα data. The Hα results are however much noisier and do not show the pattern of resonant frequencies discovered in the magnetograph data for the modes of even parity. It is concluded that only real magnetograph data should be used to investigate the global resonances in the magnetic-field pattern.
    Type of Medium: Electronic Resource
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