IMAGING OF THE GRAIN STRUCTURE OF THIN HTS FILM BY A SINGLE-LAYER FLAT-COIL-OSCILLATOR TEST-METHOD (SFCO-TECHNIQUE)

An imaging technique has been created (using a focused He-Ne laser beam as a probing signal) capable of imaging the grain structure of HTS thin films with 2–3 μ spatial resolution. It is based on detection of an inductance change of a single-layer flat pick-up coil, placed at the face of the specimen. This leads to frequency changes of a stable tunnel diode oscillator. Test device enabled 2D-mapping of the grain structure of the bridge-shaped YBaCuO film. Basically, the method is capable of imaging fine peculiarities of normal-metallic to superconductive phase transition and 2D-current distribution, as well as may identify localized defects in thin HTS-materials with sub-μ spatial resolution, using non-bolometric response. However, the achieved 2–3 μ resolution of a bolometric nature (in a given device with ∼3 mm-size coil) is limited and depends on how narrow is possible to focus the probing beam, while the own spatial resolution of the tested flat-coil technique is better than 0.1 μ, and can be improved by 1–2 orders of the value by reducing pick-up coil size.