Resolution limit due to thermal effects in 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. The 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, one can reduce the thermal healing length considerably below its low-frequency limit because of the thermal skin effect. It appears that, depending upon the sample parameters, a spatial resolution limit of less than1 µm can be obtained.