Physikalisches Institut

Imaging techniques at low temperatures




At our institute we have low-temperature scanning electron microscopy (LTSEM) and low-temperature scanning laser microscopy (LTSLM) available. These techniques allow the spatially resolved analysis of various physical properties of samples at low temperature (down to approx. 2 K).

The basic principle of both techniques is based on the local heating of a sample by a focused electron or laser beam. This leads e.g. to changes in the sample resistance, which can be detected as a global change of voltage drop across the sample. By scanning across the entire sample and simultaneous recording of the beam-induced change of resistance as a function of the beam spot position on the sample surface, one obtains an image of the corresponding physical properties. Depending on the physical quantity which is detected and on the mode of operation one can e.g. image spatial variations in the critical temperature of superconductors or the spatial distribution of current or magnetic field.

The spatial resolution of both techniques is approximately 1µm; here the scanning laser microscope offers the advantage of operation also in high magnetic field.

More details on both techniques: