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Tiny TEM

John Hren

Transmission Electron Microscopy: A Textbook for Materials Science. David B. Williams and C. Barry Carter. 729 pp. Plenum Press, 1996. $95.

Transmission Electron Microscopy offers us an excellent example of a textbook that has truly advanced teaching in a specialty. The authors are both active experimentalists and teachers, and they have organized the book and the topics to address the needs of students who are entering a new and somewhat abstract subject. They have not directed their efforts slavishly toward exactness, but have tried to promote better understanding of the underlying physics and mathematics through the use of descriptive example and analogy. As a consequence, some explanations are imprecise, and some critics will argue that they lack rigor. I believe the overall effect to be excellent, however, and the imprecisions are either corrected later or are at least acknowledged in the text.

The need for such a semiquantitative approach stems from the fact that most students have a cursory familiarity with optical microscopes and scanning electron microscopes where the images can often be interpreted intuitively. The world of transmission electron microscopy (TEM) is quite different, however. Almost no image can be intuitively understood. The concepts of image contrast are obscure and depend on the nature of the specimen and its preparation, as well as the precise operating conditions of the microscope. In short, black and white are not necessarily black and white! They can be inverted or merged into shades of gray. The microscopic image, the nature of the sample, its relationship to some bulk material from which it was removed, the physics of the microscope, and the details of electron-specimen interactions are all issues that must be addressed in parallel. In turn, such complexity is barely comprehensible to a student who lacks access to a microscope and a tutor, assuming that they are already well versed in the discipline. Thus by necessity this book is directed toward about one-half of the potential audience; that is, toward materials scientists (here taken to include all physical scientists) but not biologists or medical scientists. There is no easy way to cross this interpretational divide.

Operation of a TEM by one who lacks simultaneous expertise in both the discipline and the physics of electron microscopy not only produces results of decreasing usefulness, but can lead to totally misleading scientific conclusions. The scientist who thinks a sample may be analyzed intelligently by a TEM "operator" who is not expert in the underlying discipline is seriously misinformed. But this textbook will help teach the student of materials science the essential knowledge of electron microscopy each must master.

The last quarter of this book is devoted to analytical electron microscopy (AEM), a subfield that examines local chemical compositional analysis as deduced either from x rays generated by electrons or by the energy losses encountered by the electrons as they pass through the specimen. These procedures, which sprang into prominence in the late 1970s as the technology advanced, have now matured into precise analytical methods. The electron microscope has become an analytical machine that can simultaneously give details of microstructure (nanostructure), crystallography, composition and even local atomic bonding. Having worked with AEM since its early development, the authors present their approach to analyses with elegance and directness.

With all the evident praise from this reviewer, there remain a few shortcomings to the book. Problems are sorely needed, as are more worked examples. One hopes that both will be added in a subsequent edition. Simplification may aid comprehension, but it sometimes leads to errors, and there are some, but they are minor and correctable. Some of my students who used this text provided comments that will be forwarded to the authors. Both changes will make this a better text; however, it will be competing with itself because, in my view, it is already the best textbook for this audience available.—John J. Hren, Materials Science and Engineering, North Carolina State University

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