J-P Morniroli. Published by Societe Francaise des Microscopies. 2002 (English translation)
ISBN 2-901483-05-4
Reviewed by: John Spence, University of Arizona, USA
This is an excellent book! From an academic curiosity thirty years ago, the convergent-beam electron diffraction (CBED) method has recently become an indispensable tool in semiconductor materials defect analysis, and in nano-phase identification in materials science generally. The method, which is often provided as a "nanodiffraction" mode on modern electron microscopes, provides transmission electron diffraction patterns from sub-nanometer areas of thin crystalline films, using a highly convergent beam, so that Bragg spots appear as discs, and it is the contents of these disks, or "rocking curves" which are analyzed. As interest in the synthesis of finer-grained materials and individual nanostructures grows, techniques such as electron nanodiffraction have increased greatly in importance.
The method uses the brightest continuous particle source known to physics (the field-emission gun) to produce the largest number of scattered particles from the smallest volume possible by any analytical technique, and hence the largest amount of information from the smallest volume of matter. In one spectacular recent example, we have seen the transmission electron diffraction pattern published from a single, isolated, double-walled carbon nanotube, strung across a hole in a carbon film, using a variant of the CBED method (Science 300:1419, 2003).
CBED has traditionally been used to determine the space-group of TEM samples on a nanometer scale. It is also powerful for mapping out strain-fields in thin films, for accurate structure-factor measurement in simple crystals of known structure (to provide information on the charge state of ions and covalency), and for lattice parameter measurement with an accuracy not much lower than possible using X-ray diffraction, but again on a nanoscale. It also provides the most accurate method of high voltage measurement, while methods for measuring Debye-Waller factors have also been described.
The perfection of the small volume of crystal irradiated usually means that the CBED signal, particularly if elastically filtered, now provides the most accurately quantifiable information obtainable on a modern electron microscope. More recently the method has been developed for defect analysis using large-angle patterns (LACBED), and that is the main topic of this book. In this mode the electron source is conjugate to plane slightly above or below the sample, and is isolated by an aperture to prevent overlap of Bragg diffraction orders. (A very small aperture is found to have an energy-filtering effect).
The book benefits greatly from being written by someone who has taught this material expertly for some years, and is a rare example of a pedagogically sound text. Professor Morniroli, together with the Bristol group, have pioneered the field of defect analysis by CBED, and he is superbly qualified to write it. Early chapters cover the theory of electron diffraction and the electron-optics of the CBED mode. The book is distinguished by many clear diagrams. Elementary crystallography, Kossel patterns, the hybrid CBIM image mode, the LACBED mode, indexing patterns, Kikuchi lines, and multiple scattering effects are all described in detail.
The heart of the book is a description of the method of finding Burger's vectors from LACBED patterns, and this is demonstrated with many useful worked examples. In semiconductor materials analysis and elsewhere this method has now replaced TEM imaging, because it has several advantages (for anisotropic materials, accessibility of high orders, application to very small Burger's vectors, etc). Simple rules, based on two-beam theory, have been devised to aid the analysis by Cherns and Preston. In dense tangles of dislocations, however, the defocused probe of the LACBED mode may not be able to isolate a single dislocation. A section on fault vectors for planar faults also follows, together with a treatment of partial dislocations, grain boundaries and twins.
The high quality of the book is a direct result of the fact that it comes from a working research group with many students, whose practical experience is reflected in the many worked examples. The book is particularly strong on ray diagrams which clearly demonstrate conjugate planes, and effects of aberrations, for a TEM in its defocused diffraction modes.
Every researcher brings a different personal history to a subject, and my own was strongly influence by the many papers in the 1950's and 1960 by Lehmfuhl, Fujimoto, Goodman, Moodie and others who built on Mollenstedt's work to establish the CBED method and demonstrate its usefulness for space-group determination. Perhaps this work, in the middle of the last century (!), is now too old to be retrievable on the web, however I would recommend its inclusion in a future edition (together with Zuo's fine work on structure-factor refinement (eg. Nature 401, p.49 ) for the bibliography. Cowley's extensive work on coherent CBED from defects (eg Zhu and Cowley, A38 J. Appl. Cryst. 16, p. 171 (1983) for planar fault vectors) and the connection between, say, Tanaka's LACBED mode and in-line holography is unreferenced, as is an early demonstration of Burger's vector determination by CBED (Acta A38, p.55 (1982)).
These are minor quibbles - for anyone who has wondered why the defocused Bragg diffraction pattern in a TEM turns into a set of images (and how this effect might be used), this is the book to get. And it will provide a superb teaching text now for courses on electron diffraction around the world. Every TEM materials lab should have one.