Examination of superconducting micro-circuits by low-temperature-scanning-electron-microscopy

By scanning a thin-film superconductor with the electron beam in a scanning electron microscope equipped with a low-temperature stage, a two-dimensional voltage image of spatial structures in the sample configuration can be generated. The spatial resolution of this technique has been investigated by monitoring the voltage response of a current-biased superconducting microbridge as a function of the distance between the microbridge and the point of the electron-beam focus. Our results indicate that the electron irradiation can be treated as a local heating effect and that the spatial resolution is dominated by the thermal healing length. By modulating the beam at high frequencies, the thermal healing length is reduced considerably below its low-frequency limit because of the thermal skin effect. It appears that, depending upon the sample parameters, a spatial resolution limit less than 1 μm can be obtained for frequencies of the beam modulation in the range 10 - 1000 MHz.