Quantitative Electron Diffraction from Thin Films

Abstract

The structure and morphology of a thin film is, apart from composition, probably its most significant feature. Again and again we find that electronic, chemical, mechanical, magnetic, optical, and superconducting properties depend on the arrangement of atoms and on disorder in this arrangement. As most thin films are created using some form of deposition technique in which atoms are brought together at a surface, it is at the surface that the first opportunity occurs for formation of a particular atomic structure and morphology. As deposition proceeds, a moving surface, the “growth front,” continues to serve as the template for structure formation. Various kinetic processes, such as atomic transport and the adsorption or desorption of atoms from already-formed structures, determine the final morphology of the film. Subsequent treatment can, of course, modify the structure and morphology, but clearly the initial events occurring at the surface influence, to a large measure, the final outcome.Techniques sensitive to surface structure and morphology are therefore an important component in the toolbox of methods for the quantitative analysis of the properties of thin films. Electron diffraction techniques have been, and continue to be, the most powerful and versatile of these. Even though electron diffraction is also useful for the structural analysis of the bulk, when one speaks of electron diffraction in the context of thin films, one almost invariably refers to surface-sensitive diffraction. Other methods, in particular scanning probe microscopy, have recently become popular. In many cases, such methods serve to re-emphasize the value of electron diffraction for quantitative structural analysis of thin films.