ABSTRACT
In this final lecture of the programme I shall endeavour, as I was asked, to look forward to the imaging techniques which might become coupled with microscopy in the future. A review of the titles preceding this presentation might indicate that all has already been said. Nevertheless, starting from the viewpoint that this years spectroscopy is next years microscopy, there are points to be made.
Experimental techniques can be grouped, conveniently, in terms of their resolution in each of four modes: depth, chemical state, microstructural, and position; the latter being of most importance for techniques having any claim to be the basis of a microscopy. Metal oxidation, if a significant commercial problem, presents a thick film for analysis and it could be felt that depth resolution is of lesser interest. However, as examples in the literature have already shown, depth resolution is important in the analysis of spalling interfaces, of thin barrier layers, or of grain boundaries revealed in fracture cross-sections. The established techniques of AES (SAM), SIMS and EPMA between them supply all that is needed for the identification of elements present in the above situations. They serve chemical state determination and structure less well however.
Of the techniques available for chemical state resolution, photoelectron spectroscopy may be most appropriate. It is, for example, able to reveal the difference between mixed oxides, e.g., spinel, and single oxides; between valence states; and between cations associated with different anions (chlorides and oxides). Developments in imaging XPS will be reviewed and future possibilities outlined. In addition the basis of chemical state recognition by means of Auger spectroscopy will be outlined and an indication given of the situations in which high (energy) resolution would give worthwhile information in Auger images.
Whilst great advances in the preparation of cross-sections for TEM have been made it still remains that structural information associated with the SEM would be a great advantage. Techniques capable of giving structural information in the reflected mode are not common and it may be that the direct use of the STM on cross-sections will make this need redundant. However, the observation of EXAFS-like structure in the Auger spectrum is exciting and could assist in the study of grain boundary structure.
