The main initial source of information in the USA concerning the electron probe was a meeting at the Naval Research Laboratories in February 1958, followed in 1960 by a summer school at MIT organized by Prof. Norton and R. Ogilvie. Further visits to the USA and publications in English by the inventor of the instrument, R. Castaing, also contributed to the attention given here to the new technique. Since numerous research laboratories in the USA were keenly interested in the new device, the development of instruments and the contributions to its use were considerable. The relatively small number of active researchers in the field rendered personal connections and cooperation possible and attractive.

Before the availability of American-made commercial microprobes, many investigators built their own instruments. Most of them were not trained as instrument builders, and the usefulness of the resulting devices was somewhat limited. These improvisations in instrument construction ceased once commercial microprobe manufacturers entered the field. Yet, in the process, much was learned and the American investigators contributed significantly to the theory of microanalysis. We realized that, with the limited calculation facilities then available, the complex interactions leading to the x-ray signal had to be treated in simplified ways, and we described ‘approximations’ rather than ‘laws’ in our efforts to understand and quantitatively describe the physical facts. We also came to realize that even where the physical processes were well known, we often lacked the knowledge of the physical parameters required for quantitation and the effect of their uncertainties on the accuracy of the analytical results. Another area in which advances were needed, and soon achieved, was the application of the technique to a wide range of technical and scientific problems. The interaction between manufacturers and users greatly stimulated improvements in the instrument design.