The surface of an azoaromatic polymer film is optically altered to produce local highly efficient diffraction gratings. The gratings obtained are stable but can be erased by heating the polymer above its glass transition temperature and no permanent damage of the film is observed. Multiple gratings can be simultaneously written and gratings can be overwritten. Atomic force microscopy was used to investigate the gratings produced on the surfaces. Possible mechanisms responsible for the surface alteration are discussed.
The role of oxygen and other impurities on the crystallization characteristics of Ni-Zr glasses near the composition NiZr2, as well as for FeZr2, CoZr2, and NiHf2, has been investigated. For NiZr2 glasses with 1 at. % oxygen, the first crystallization product is the metastable E93 structure with a =1.227 nm instead of the equilibrium C16 structure. A similar effect is found for samples containing ≳3 at. % B. For FeZr2, CoZr2, and NiHf2 the first crystallization product is also E93 structure, even with very small levels of oxygen (≤0.2 at. %). The formation of the E93 structure is always accompanied by an increase in the electrical resistivity, an increase which transmission electron microscopy shows is intrinsic to the phase and unrelated to crystallite size. For Ni36.5Zr63.5 and Ni42Zr58 the crystallization is also accompanied by an increase in electrical resistance and the evolution of a crystal structure similar to the E93 structure in the size of the unit cell and packing fraction but with a different space group. We propose that the formation of these structures is triggered by atomic size nuclei of ZrO2, (or ZrB2) quenched in from the melt.
We have developed a low temperature magnetic force microscope capable of operation down to 6 K in vacuum by using piezoresistive cantilevers. We use the non-contact frequency modulation technique to detect the magnetic force gradient between an iron-coated tip and the sample. We demonstrate the operation of this new instrument by obtaining images of magnetic domains in VHS tape at room temperature, 77 and 6 K. This microscope is ideally suited for the characterization of thin films of high temperature superconductors.
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