This article, dedicated to the memory of the late professor Raimond Castaing, will evoke the birth and the first developments of electron probe microanalysis in France.

The early days of the electron microprobe were characterized by the variety of designs emerging from different laboratories in Europe, the United States, and the USSR. Examples from Europe illustrate well the diverging trends in the evolutionary process at that time. Later, commercial pressures and a better understanding of user needs forced a rationalization on both sides of the Atlantic, to the point where only few variants have survived. These were memorable days, with scope for healthy rivalry and vigorous debate.

The history of electron probe analysis in the USA in its first two decades is reviewed, with reference to the personalities which were involved, the development of instrumentation and theory, and the technical problems and limitations of that era.

The development of the electron probe microanalyzer (EPMA) in Japan in the early 1960s, when Prof. R. Castaing visited Japan, is briefly outlined. In 1955, a review article was published by Prof. G. Shinoda in Oyobutsuri, the most popular journal in Japan, in which the EPMA was introduced. In 1957, a research group at the University of Tokyo started to develop an EPMA with a Grant-in-Aid for Developmental Research. Their research results led to the funding of a 2-year Grant-in-Aid for Cooperative Research Project (April 1960 to March 1962), which was chaired by Prof. Y. Sakaki. Prof. G. Shinoda who became the chairman of that project in April of 1962 led that group for another year until March of 1963. It was just after the start of the project that Prof. R. Castaing visited Japan in September of 1960 as a representative of the French Mission Culturelle. This visit gave a great push forward for the commercial development of EPMA instruments in Japan. The first three commercial EPMA instruments from Hitachi, JEOL, and Akashi Ltds. were installed in Tohoku, Osaka, and Waseda Universities in 1962, 1963, and 1964, respectively. Photographs of those first commercial EPMA systems, together with a brief description of the activities of the cooperative research projects, are presented.

Castaing’s successful implementation and application of the electron probe microanalyzer in 1950 stimulated a flurry of development activity around the world. The later versions of this instrument represented a truly international effort, with significant contributions by scientists from Europe, Asia, and North America. If the probe-forming system of the instrument was its heart, the X-ray wavelength spectrometer was its soul. This article reviews some of the history of spectrometer developments—lthrough the “golden years” of microprobe development, namely the dozen or so years following the publication of Castaing’s thesis, to the present. The basic physics of spectrometer and crystal design is reviewed. Early experimental devices, such as those developed by Castaing, Borovskii, Wittry, Duncumb, and Ogilvie are reported. Examples of commercial spectrometers such as those by ARL, MAC, Microspec, and Peak are described. Recent developments such as the combination of grazing-incidence optics with flat crystal spectrometers are noted, and the properties and uses of doubly curved crystals are discussed. Finally, the continued development of doubly curved crystal configurations, such as the “Wittry geometry” for scanning monochromators, and point-to-point focusing diffractors for producing small monochromatic X-ray probes to provide improved detection limits for microanalysis are considered.

This article will discuss the importance of Raimond Castaing’s thesis on the genesis of a nondestructive and truly quantitative microanalytical method that assisted the scientific community in moving forward in the development of microanalytical instruments. I will also share with you my recollection of the decades of improvement in the electron probe microanalyzer (EPMA), that has allowed us to reach our present level of instrument sophistication, and I will explore with you my thoughts on the future evolution of this technique. To conclude, I will present the current status of related microanalysis techniques developed under Castaing in Orsay in the 1960s, as Castaing’s interest in microanalysis was not limited to electron probe microanalysis alone.

As part of the Microbeam Analysis Society (MAS) symposium marking 50 years of electron microprobe analysis, this article reviews the important advances made over the decades to the automation of data collection and computerized analysis of data from the electron microprobe. Out of many innovations that contributed to the advance of microprobe automation, we have chosen to focus on a few developments that the authors feel represent the major trends in advancement of the “state of the art” of this instrumentation. After providing brief summaries of the three generations of advances in the hardware and software of automation systems, several key applications developments are described, followed by our prediction of which current developments may impact the future automation of the microprobe.

Quantitative X-ray microanalysis requires the use of many fundamental constants related to the interaction of the electron beam with the sample. The current state of our knowledge of such constants in the particular areas of electron stopping power, X-ray ionization cross-sections, X-ray fluorescence yield, and the electron backscattering yield, is examined. It is found that, in every case, the quality and quantity of data available is poor, and that there are major gaps remaining to be filled.

Errors in quantitative electron microprobe analysis arise from many sources including those associated with sampling, specimen preparation, instrument operation, data collection, and analysis. The relative magnitudes of some of these factors are assessed for a sample of NiAl used to demonstrate important concerns in the analysis of even a relatively simple system measured under standard operating conditions. The results presented are intended to serve more as a guideline for developing an analytical strategy than as a detailed error propagation model that includes all possible sources of variability and inaccuracy. The use of a variety of tools to assess errors is demonstrated. It is also shown that, as sample characteristics depart from those under which many of the quantitative methods were developed, errors can increase significantly.

The development of the electron microprobe by Raymond Castaing provided a great stimulus to materials science at a critical time in its history. For the first time, accurate elemental analysis could be performed with a spatial resolution of 1 µm, well within the dimensions of many microstructural features. The impact of the microprobe occurred across the entire spectrum of materials science and engineering. Contributions to the basic infrastructure of materials science included more accurate and efficient determination of phase diagrams and diffusion coefficients. The study of the microstructure of alloys was greatly enhanced by electron microprobe characterization of major, minor, and trace phases, including contamination. Finally, the electron microprobe has proven to be a critical tool for materials engineering, particularly to study failures, which often begin on a micro-scale and then propagate to the macro-scale with catastrophic results.

Examples of a few objects are presented, where the electron microprobe has proved that it can provide the conservator and the curator with information that will help in evaluating the authenticity of a particular art object. They will also obtain a better understanding of how an object was fabricated and what materials it was made from. The results of the analysis of paint samples, samples from metal artifacts, as well as specimens from marble sculptures, are described.

The impact of electron probe microanalysis on the study of geological and planetary materials has been tremendous. Electron microprobes evolved into routine analytical instruments in geological research laboratories as instrument capabilities improved and applications to geologic/planetary materials expanded. The contributions of electron probe microanalysis to the characterization of minerals, both terrestrial and extraterrestrial, and to other significant geological research, such as light element analysis, trace element analysis, and element mapping, is described.

A brief description is given of the events surrounding the development of biological X-ray microanalysis during the last 30 years, with particular emphasis on the contribution made by research workers in Cambridge, UK. There then follows a broad review of some applications of biological X-ray microanalysis. A more detailed consideration is given to the main thrust of current procedures and applications that are, for convenience, considered as four different kinds of samples. Thin frozen dried sections which are analyzed at ambient temperatures in a transmission electron microscope (TEM); semithin frozen dried sections which are analyzed at low temperature in a scanning transmission electron microscope (STEM); thick frozen hydrated sections which are analyzed at low temperature in a scanning electron microscope (SEM), and bulk samples which are analyzed at low temperature in the same type of instrument. A brief outline is given of the advantages and disadvantages of performing low-voltage, low-temperature X-ray microanalysis on frozen hydrated bulk biological material. The article concludes with a consideration of alternative approaches to in situ analysis using either high-energy beams or visible and near-visible photons.