Introduction

Scanning techniques for obtaining topographical information about an object are now widely used in science and technology. Usually, a two-dimensional image is constructed from the signal generated by the scanning process, and this information is restricted to a region close to the sample surface. [5.1]. Here a well focused electron beam is scanned over the surface of the specimen and a response signal such as the emitted secondary electrons or the back-scattered electrons are recorded as a function of the coordinate point (x, y) of the beam focus on the sample surface. We emphasize that this technique essentially yields only information about the composition (atomic, chemical, or metallurgical microstructure) and the geometry of the specimen.

Some time ago, low-temperature scanning electron microscopy (LTSEM) was introduced [5.2] which by now has matured into an important new diagnostic tool. LTSEM extends the temperature of scanning electron microscopy to the regime of liquid helium and liquid nitrogen by providing the necessary sample cooling. However, more importantly, LTSEM yields information on the local electronic function and not just the local structure with high spatial resolution. In this way it has provided important input for the understanding of the physics of superconducting electronic circuits and devices. Of course, LTSEM is equally important for the evaluation and analysis of low Tc and high Tc superconductors. The principle of LTSEM utilizes the electron beam as a local heat source on the one hand, and the sensitive response of superconductors to small temperature changes on the other hand [5.2].