Intrinsic thermal stability for scanning electron microscopy of thin-film superconductors

The criterion of intrinsic thermal stability (ITS) of thin-film superconductors predicts under which circumstances a thermal disturbance causes Joule heating. In the characterization method of low-temperature scanning electron microscopy (LTSEM), the absorption of the electron beam results in a well-controlled thermal disturbance. This work applies the ITS criterion to LTSEM of both high-Tc and low-Tc thin-film superconductors and predicts the conditions for which no voltage appears along the film. The analysis of the temperature field for high-Tc films differs from that for low-Tc films by the absence of the acoustic-mismatch thermal resistance between film and substrate at liquid-nitrogen temperature. The theoretical results for low-Tc films are in very good agreement with experimental data for LTSEM of lead films on sapphire substrates at 4.2 K.