V. K. Zworykin, G. A. Morton, E. G. Ramberg, I. Hillier and A. W. Vance,
Electron Optics and the Electron Microscope. John Wiley and sons. New York, 1945, p. 766.

V. K. Zworykin, G. A. Morton, E. G. Ramberg, I. Hillier and A. W. Vance.
Electron Optics and the Electron Microscope.

The book under review is constructed in a very distinctive way. Its entire content is divided into two large parts: practical and theoretical. The first part is intended for a far less prepared reader than the second, and contains a qualitative treatment of almost all the basic questions of electron optics. The second part is presented with extensive use of mathematical apparatus and contains a more detailed analysis of the theoretical questions connected with the calculation of electron-optical systems.

Let us turn to a brief account of the contents of the individual chapters of the book. The first chapter gives a popular exposition of the basic principles of electron optics. Here not only the main characteristics of electron lenses and optical systems are considered, but also a qualitative survey is given of the shortcomings of electron images.

The second chapter briefly describes all the applications of electron optics, or rather even of corpuscular optics in the general sense of the word (apart from the electron microscope). Here electron guns, electron-optical image converters, cathode-ray tubes, multistage photocells, mass spectrographs, and accelerating particles are described.

In the third chapter, also cursorily, a survey is given of all types of electron microscopes, with somewhat greater attention devoted to the electrostatic microscope. Evidently, the authors deliberately allowed this disproportion so that in the subsequent exposition the main attention could be given to the electromagnetic type of microscope.

The fourth chapter gives a qualitative, but detailed, exposition of questions connected with the action of individual elements of electron optics with high resolving power. Here, successively, beginning with the source of electrons and ending with the projection lens, all the main parameters of the individual elements of the system are analyzed. In addition, the role of the thickness of the object and the influence of external fields on the quality of the image are analyzed.

The fifth chapter is devoted to the designs of magnetic electron microscopes, with attention drawn to especially important details of the designs.

The sixth chapter begins with the question of the joint accounting for diffraction and spherical aberration. Then an analysis is given of chromatic aberration caused by the initial distribution of electron velocities, and, finally, the very important question of tolerances for fluctuations of the supply voltage is considered.

The seventh chapter describes power-supply circuits for electron microscopes. It must be said that the construction of rational power-supply circuits is a task perhaps no less serious than the construction of the microscope itself. The latter is especially true for electromagnetic microscopes, where very high stability of the supply voltage is required.

The eighth chapter is devoted to manipulation with the electron microscope itself. The technique of working with an electron microscope is still quite complex. The preparation of objects for investigation generally requires skill—in electron microscopy this is an especially delicate and complicated matter. In addition, the adjustment of electron microscopes, especially of the types described in the book under review, is also far from simple. In the same chapter the stereoscopic method in electron microscopy is described and, finally, the use of the electron microscope as an electronograph. In this connection, excellent diffraction patterns are obtained.

The last chapter of the first part—the ninth—briefly describes the results of the application of electron microscopes in the most varied fields of science and technology. Many striking microphotographs are presented here, but after reading this chapter one is left with the impression that the possibilities of electron microscopy have not yet been exploited at all seriously. This impression obviously corresponds to the actual state of affairs. Too little time has yet passed since the electron microscope appeared as an instrument genuinely convenient for laboratory work.

Regarding the first part of the book, one may make remarks chiefly connected with a certain already existing obsolescence of the material. Electron microscopy is developing so rapidly that in the three years that have passed since the writing of the book, new designs and new methods have already appeared. Electron microscopes of the new design are simpler and more convenient to use than those described in the book. The replica method has undergone wide development and improvement and has become one of the basic methods (the use of polystyrene). An important event was the development of the shadow method, which uses oblique metal deposition (see UFN, vol. XXXVI, issue 3). Finally, as a result of careful investigation of diffraction effects, it has been possible to determine the role of field asymmetry in image formation and to obtain a practical resolving power coinciding with the theoretical one. Before these results, the practical resolving power of the electron microscope was considerably below the theoretical.

On the other hand, the material of the book is, of course, more recent than Ardenne’s book Supermicroscope, which appeared in 1940.

The second part of the book, as we have already indicated, is intended for a more qualified reader. This part begins with chapter ten—the theoretical foundations of electron optics. Here there are even Lorentz transformations and a discussion of the question of the dualism of particle and wave. The expediency and effectiveness of such a very cursory presentation of these questions in the present book arouse serious doubts. The remaining content of the chapter is a variational formulation of the fundamental laws of electron optics and the question of the intensity of electron beams.

The next chapter gives a brief exposition of questions connected with determining the configuration of electric fields formed when electrodes of various shapes are used. In this connection, not only the theoretical side of the question is presented, but also an account is given of the method of the electrolytic bath.

The twelfth chapter is naturally devoted to methods for determining electron trajectories in specified fields. Here an idea is given of the calc—

Bibliography

...lenses, and of graphical methods for determining trajectories. In addition, apparatus is described for the automatic plotting of trajectories and, finally, an elegant rubber-membrane method.

Chapter thirteen contains a detailed exposition of the Gaussian dioptrics of electrostatic lenses.

Chapter fourteen gives a detailed treatment of all questions concerning configurations of magnetic fields, and describes methods for determining these configurations. Chapter fifteen analyzes, in lucid form, the motion of electrons in magnetic fields and under the simultaneous action of electric and magnetic fields. Chapter sixteen gives a sufficiently complete account of all types of aberrations of electron lenses, including the influence of space charge and external fields. Chapter seventeen examines all methods for correcting electron lenses. Lens correction, as the authors rightly point out, is the central problem of electron optics. There is continuous progress in this direction, and therefore the material of the chapter is already somewhat out of date.

A separate chapter is devoted to the very current question of the optics of fast particles, when relativistic corrections begin to make themselves felt. The question of accelerators is presented very briefly and incompletely, which is characteristic of the treatment in the book of any question of electron optics not directly connected with electron microscopy.

The last chapter is very interesting: the formation of the image in the electron microscope, although it does not make use of all the data available in the literature on this question (for example, Glaser’s work). In this chapter, for the first time, questions connected with the passage of electron beams through an object are set forth fairly systematically and fully. At the end of the book there are two small appendices. One appendix is devoted to fluctuations in power-supply circuits; the other contains several tables and graphs of the dependence of the mean free path of the electron on pressure.

The bibliography is given at the end of each chapter, and it is convenient that the title of each article is given. The bibliography is carried up to 1944.

In giving the book an overall assessment, one must again return to the question of the composition of the book. It seems to us that combining in one book two parts intended for two completely different levels of readers is not very successful. The less qualified reader receives four hundred pages of text almost inaccessible to him. The specialist receives three hundred and fifty pages of a semi-popular exposition of all the basic questions of electron optics. We have already indicated above a certain obsolescence of the book. The value of the book lies in the fact that it was written by a group of workers of a major laboratory (RCA) in the field of electron optics and to a certain extent summarizes the experience of this laboratory.

— V. Fabrikant