Applications of low-temperature scanning electron microscopy

Scanning electron microscopy performed on specimens cooled to the temperature of liquid helium yields interesting information on the spatial structures of various sample properties. In many applications of low-temperature scanning electron microscopy the perturbation of the sample due to the electron beam can simply be treated as a local heating effect. In this case the spatial resolution is limited by the thermal healing length of the particular geometric configuration. The spatial resolution can be improved considerably by means of high-frequency beam modulation and utilising the modulated signal. Irradiation with the electron beam results in two important sample responses. The electron-beam-induced local heating causes an electric resistance change yielding a two-dimensional voltage image. On the other hand, the region heated locally by the beam represents a phonon source. This provides the mechanism for obtaining a two dimensional phonon image. Recently, these principles have been applied in the following areas: hotspots in superconducting microbridges, spatial structures in superconducting tunnel junctions and phonon focusing in single crystals.