Local characterization of HTS thin films by laser scanning microscopy

A high-resolution spatially resolved study of electrical inhomogeneties in high-Tc thin films by Laser Scanning Microscopy has been carried out. A laser beam was focused onto a submicrometer spot on the surface of a thin film microbridge that induced an increase in its local temperature. Bolometric or thermo-electric effects in the heated region resulted in a voltage change, δV, across the sample that has been measured as a function of the beam position (x,y). Direct measurements of the spatial distribution of the critical current density in the film has been performed from the δV(x,y) images of HTS microbridges. A system of weak links in the film is observed that may be attributed to the growth island boundaries. A spatial redistribution of the critical current as a function of temperature is observed in this system. It has been demonstrated that for some conditions, the electrical characteristics of the entire microbridge can be determined by only one weak link. The position of the weak links could be observed at room temperature using the thermo-electric response.