Scanning Electron Microscopy: Physics of Image Formation and Microanalysis, Second Edition

Abstract

Scanning electron microscopy (SEM) is traditionally the Cinderella of electron microscopy, often seen as a playground for biologists and other disciplines remote from physics, and overshadowed by high resolution TEM, dominated by eminent scientists concerned with atomic structure and quantitative analysis. When Max Knoll in Berlin invented and constructed the first (crude) SEM in 1935 he did not bother to patent it. Some years later, von Borries and Ruska at Siemens und Halske Berlin, the first to realize high resolution electron microscopy in a commercial TEM, learned that Manfred von Ardenne in his private laboratory in Berlin had been given a contract by Siemens to develop an SEM. They immediately requested the management to cancel it as a waste of the Company's money, since the SEM `could never compete wth the TEM in image formation as the exposure time in serial scanning would be impossibly greater than in a comparable TEMimage'! This view changed only when field emission guns became available. Many other difficulties were also overcome by advances in desk-top computing. Today the SEM is the microscope of choice in many areas of science and technology.Reimer himself has always put forward the view that it is vital for all users of SEM to understand the physics of image formation, electron-specimen interaction and useful modes of instrument operation. This is best handled, according to Reimer, by a single author so as to ensure a consistent terminology and a uniform referencing system. It is clearly difficult to include all aspects of the subject. The art of the successful author is therefore to know what to omit, both in the text and the list of references, so that a reader can quickly locate his areas of interest and the relevant references. Reimer has honed this skill over a long career, having already published Transmission Electron Microscopy (Volume 36 of the Springer series on optical sciences) as well as the first edition (1985) of the present volume, which records the spectacular advances in SEM over the last few years; these include accelerating voltages down to 0.5 kV and computer control in operation and photography. Remarkably, theEverhart-Thornley detector, arising from an inspired suggestion by Sir Charles Oatley at Cambridge, still holds sway. Nevertheless, other specialized detectors are now also in use. This, together with the extensive use of computers to control the column and produce digital images, stored in a computer, has led to `instant' micrographs and archiving methods. The remarkable improvements in silicon-lithium energy-dispersivex-ray detectors with ultra-thin windows have greatly improved the analytical performance of the SEM, leading to the widespread use of SEM for rapid analytical chemical analysis.One of the curiosities of SEM is that some operators familiar with light microscope images imagine that the SEM image is much the same and can be interpreted fairly easily. This is not true and Reimer has gone to much trouble to seek out the most appropriate theoretical mechanisms for image interpretations in the SEM. The book can be read at many levels, depending on the reader's background and level of scientific curiosity. An attractive feature is that the book is not`dolled up' with striking micrographs that, in fact, teach very little. Instead, each well-thought-out diagram is packed with information, The micrographs themselves, often arranged in pairs, make telling points about items such as crystal orientation contrast in a back-scattered electron micrograph, for example.A word should perhaps be said about the seminal role of Peter Hawkes in `revising the Englishtext' as stated in the Preface. Reimer's English is `almost perfect but notquite', as Ellis Cosslett famously remarked about Jan Le Poole. It is a quirk of the English language that a sentence must `sound correct' even at the expense of the rules of grammar and syntax! Hawkes appears to have brought a fine linguistic polish to an already imposing text. In trawling through 447 pages of text I was able to find only one word that seemed to jar. Page 237 states `...darkroom work is unneeded when images are digitallyprocessed'.To conclude, this book is both linguistically and scientifically outstanding. It is an inspiring book for beginners and experienced SEM operators alike. The `filleted' list of references is especially useful. This volume makes an outstanding contribution to the deeper understanding of the SEM.T Mulvey