Electron Microprobes use wavelength-dispersive (WD) spectrometers that rely on curved diffractors and a Rowland circle geometry. With 5 WD spectrometers and a chamber designed around the unique requirements of the Rowland circle spectrometer geometry, a highly effective x-ray analytical system, with strong x-ray collection rates from Be to Pu is both feasible and commercially available.

Many scanning electron microscopes (SEM)s have a port that mechanically supports mounting a WD spectrometer onto the SEM. An individual Rowland circle WDS on an SEM is therefore possible and does provide the opportunity to bring WDS x-ray analysis to the SEM. While offering compatibility, the standard SEM is neither designed nor optimized for WDS analysis. The result is a sub-optimal WDS configuration with performance that seriously lags that on an electron microprobe.

The advent of a parallel beam WD geometry with a collimating optic that contains both a grazing incidence (low energy) and a polycapillary (mid to high energy) component has resulted in a WD spectrometer that is optimized for the broad range of SEM chamber designs available. The result is a dramatic improvement in WDS x-ray count rates across the broad spectrum of elements – Be to Pu – for virtually any SEM chamber geometry. Head to head comparisons between this type of spectrometer on a standard SEM and a Rowland circle WD spectrometer on a microprobe shows general parity in the results while showing general superiority to a Rowland circle WDS on an SEM.

 
This talk provides a technical discussion of the differences between Rowland circle and parallel beam WDS geometries, and compares the performance of each on the varying electron microscope platforms.