In Situ Ion Etching in a Scanning Electron Microscope

Abstract

A facility for in-situ ion etching in a scanning electron microscope has been developed and successfully applied to a variety of materials. Two forms of the saddle field ion source, namely the cylindrical and spherical source, have been used and a comparison between these has been made in terms of etching rates, uniformity of etching, contamination and rise in temperature of the specimen during ion bombardment. Artefacts produced during etching, including structures not previously reported in the literature, have been studied and in particular cone formation has been followed during its growth. It has been shown that some of these artefacts can be avoided by rotation of the specimen but this often results in a loss of the desired structural features. The ion etching technique has been shown to give valuable structural information on various metals, alloys and sinters and is in general superior to chemical etching. Insulating materials such as plastics, ceramics, glass and resins have been successfully etched but in some cases artefacts are produced due to thermal degradation. Furthermore, some of these materials do not provide much useful information as there is only a small variation in the sputtering yield of the constituent elements. In contrast to a number of other workers, it is concluded that ion etching of soft biological tissues, such as the rat duodenum, can be of considerable value. This arises from the selective intake of the heavy fixation elements by different parts of the tissue, thus producing a large variation in the sputtering yield. A detailed study of hard biological materials, such as dental tissues and restorative materials, has also been shown to yield valuable structural information. A study of specific problems, such as the reprecipitation of calcium phosphate during demineralisation of teeth and the decay of amalgam restorations has proved the value of the technique in areas where structural information is not of major interest.