Introduction

The papers in this and two further issues are a selection, after careful refereeing, from the many submitted for publication in theJournaZ of Microscopy by invited speakers and contributors alike at ‘MICRO 82’. A feature of the conference was the increased importance attached to applications of the high resolution approach as well as to new techniques generally, and this is reflected in the papers chosen for this issue. While in past years the challenge for those seeking atomic level resolution has been for the engineer and microscopist, increasingly it is up to the material scientist both to interpret the images which can now be obtained and to make appropriate applications of this exciting technique. This is emphasized by the fact that it is apparent that the full interpretation of a through focal series of images, taken at high resolution in a matter of minutes, can involve computational analysis requiring several man-months and not a little theoretical development of both scattering and transfer theory. I t is ‘rare’ (the ‘scientific’ euphemism for never) that an image of a defect in a material can be visualized directly in terms of the projected potential. There has been both a marked and rapid development of our appreciation of the problems involved. This is demonstrated by a comparison of not only the levels of resolution attained but also of the depth of interpretation in the papers in this issue by comparison with those in a previous special issue (Vol. 119, Pt 1) arising from a specialist High Resolution meeting held only 3 years ago. But is there a danger that the mastery of a difficult technique has become a goal in itself? Do we, for example, really need electron microscopes capable of zero free transfer down to spacings in the 0.13-0.18 nm range for the direct interpretation of images of real materials ? In fact at defects in materials with such spacings ‘resolutions’ markedly better than this would be needed for direct interpretation even if the specimen could be realistically treated, as is practically never the case, as a weak phase object. Alternatively should we now be concentrating still more heavily on improving our interpretive ability for images of thicker material for which, as was amply demonstrated at the meeting, we can already obtain micrographs which are close to the quality required for full and hopefully unique structural interpretation ? This latter approach would require both an improved understanding of inelastic scattering, a more careful devotion to the independent determination of the relevant variables, and the parallel application of less direct techniques. After all the problems of interest to the materials scientist are generally attacked only in specimens of 50 nm or more in thickness. Clearly, as is usually the case, advances on all the above fronts are still required. That they will be worthwhile is amply demonstrated by both the quality and the increasing breadth of application of the papers in this issue.