3 - Microanalysis by scanning transmission electron microscopy

Summary

Introduction

The electron–specimen interaction not only provides information about the atomic structure of the materials, but also gives clues about other physical properties of the materials. The science of extracting this valuable information from smaller and smaller volumes of specimens is called microanalysis and is a very fruitful development of modern electron microscopy. Playing a pivotal role in this science is the scanning transmission electron microscope (STEM) which was introduced mainly to provide point-by-point analysis at high spatial resolution. The advantage of scanning is that it enables each pixel to be associated with a data set which might be a diffraction pattern, an X-ray emission spectrum, or an electron energy loss spectrum. The advantage of transmission is that it prevents the beam broadening which degrades the resolution of images formed by scanning a bulk sample. In this chapter, we will review the physical principles of the various imaging and analytical techniques available in the STEM, and assess their usefulness in connection with the research into high-temperature superconductors (HTSC). In many ways, there is a large overlap between the requirement of HTSC research and other branches of the material sciences. Thus we hope that our review can also serve as a brief introduction to STEM for researchers both inside and outside the HTSC community. For specific examples of the application of the STEM in HTSC, we will refer readers to other chapters in this book and the original papers.

Electron optics of STEM

There are currently two variants of STEM, depending on whether it is specifically designed for scanning microscopy operation or adopted from conventional transmission electron microscopy work.