Atom Probe Field Ion Microscopy

This book is one of the series of `Monographs on the physics and chemistry of materials', published by the Clarendon Press. Its title is perhaps unduly restrictive inasmuch as the identification of single atoms in the field ion microscope (Atom probe FIM) is merely the end stage in a long chain of computer-assisted operations plus the equally important task of interpreting the projected image. The intellectual insights and experimental skills of the inventor, E W Mueller, were remarkable when he first introduced them in Germany in the 1930s, especially as it seemed that the method was unlikely to prove useful in practice. Fortunately, his later collaborators in the USA helped him greatly to improve the basic theory and the experimental handling of the FIM. After 50 years or so of effort worldwide, atom probe FIM eventually took its place as a specialized analytical technique. This was too late, however, for Mueller to qualify for the award of a Nobel Prize. The present multi-author volume forms a major resource in FIM, ambitiously covering the whole field and citing over 3000 references. The authors of this book (MKM at the Oak Ridge Laboratory and the other three in the Department of Materials at Oxford University) span between them the research period 1960 to the present day. During this time they have made major contributions to Atom Probe FIM. The unusually brief preface was not signed by M G Hetherington; he was killed in a tragic car crash and is the `Mark' to whom the book is dedicated. By some curious oversight, the preface does not disclose the purpose of the book and the readership to whom it is addressed. This seems to depute this non-trivial task to the reviewer. The preface fancifully likens the FIM to a spacecraft inspecting `the inner space of the world of atoms and molecules'. The FIM is in fact a simple electrostatic projection ion microscope in which, unusually, the specimen is also the source of ions (or electrons in the electrostatic version). It was in fact Mueller's genius to recognize that a heated wire tip tends to assume an atomically smooth spherical surface, retaining the underlying crystal structure at the atomic level. The electrons or ions emitted from the surface then form a highly magnified image of the surface atoms in their crystallographic positions. He also realized that the short De Broglie wavelength of ions would improve the resolution and permit magnifications of a million times at which individual atoms would be clearly revealed. He had found at an early stage that most tips could be shaped by a combination of heating and the application of a negative pulse with respect to the specimen. The latter makes possible the controlled removal of a layer of atoms, thereby revealing the atomic arrangement in three dimensions. A hole in the fluorescent screen allows an atom passing through to be identified in a spectrometer. With the advent of the computer and suitable detectors, the point of arrival of each atom can be recorded automatically together with its atomic number. The projected image can then be indexed and analysed. All this is copiously illustrated with tables, diagrams and images. The schematic arrangement of various FIM instruments explains clearly the underlying design principles. The book is an excellent resource for anyone entering the field. It is not possible to cover this vast subject in 500 or so pages. The method chosen here is to explain some point briefly and give a reference. However, the reference listed is often not to the person cited in the text, but to the author of a later review paper. A further annoying feature is that neither the title nor the last page number of the reference are given. How many readers, for example, will recognize that E W Mueller, Z. Tech. Phys. 17 (1936) 412 is not a one page Abstract but his complete 1936 Doctoral Dissertation? Nevertheless, this reviewer found that it was quite possible to enjoy this book even if one could not easily fathom the references. The remarkable developments set out in the book are of great general interest to all electron and ion microscopists as well as to postgraduate research students. In spite of the shortcomings mentioned above, the book can still be strongly recommended at all levels among those who feel curious about this non-obvious way of doing high resolution ion microscopy and analysis at the atomic level.