EDS and WDS Automation: Past Development and Future Technology

Abstract

Early Development Automation of electron probe analysis began to flourish in the early 1970s spurred on by advances in computer technology and the availability of operating systems and programming languages that the individual researcher could afford to dedicate to a single instrument. By the end of the decade, most researchers and vendors in the microanalysis field had adopted the PDP-11 minicomputer, and languages such as FOCAL, FORTRAN and BASIC that ran on these computers. A good summary of these early efforts was given by Hatfield. The first use of the energy dispersive detector on the electron probe in 1968 added the need to control the acquisition, display and processing of EDS spectra. As a result, the 70’s were also a time when much attention was focussed on development of software for on-line data reduction and analysis. These efforts produced a suite of programs to provide matrix corrections and spectral processing, and automation of WDS data collection. The culmination of these development efforts was first reported in 1977 with the analysis of a lunar whitlockite mineral by simultaneous EDS/WDS measurement. This analysis determined the concentration of 23 elements, 8 by EDS and took a total of 37 minutes for data collection and analysis. In this paper, the authors noted the complementary use of the EDS and WDS (WDS for trace elements and severe peak overlaps, EDS for other elements and rapid qualitative analysis) in their automated instrument, a convention that remains common on the electron probe even today. Toward the end of the decade the analytical accuracy and precision achieved by automated analysis of bulk samples approached the limits of the instrumentation, with the exception of analysis of light element concentrations.Two Decades of Improvements The explosive growth in digital electronics and microprocessors for data processing and control functions during the 80’s was rapidly applied to electron probe automation. Second and third generation automation systems included direct control of many microscope functions, beam position and imaging conditions. Motor positioning was more precise and far faster. As a result, the data collection and analysis of 23 elements reported in 1977 could be accomplished at least three times faster on a modern instrument.