Determination of experimental and theoretical kASi factors for a 200-kV analytical electron microscope.

The relative sensitivity of an analytical electron microscope and energy-dispersive x-ray detector to x-rays of various elements is investigated through an extensive kASi factor study. Elemental standards, primarily National Bureau of Standards multielement research glasses, were dry-ground into submicrometer-sized particles and analyzed at 200 kV accelerating potential. The effect of self-absorption of x-rays by the particle has been corrected for, allowing the experimental kASi factors from this study to approximate those that could be obtained from "infinitely thin" specimens. Whenever possible, elemental k-factors were determined by the analysis of many (up to a maximum of nine) different standard materials. Experimental kASi factors were calculated for a wide range of K alpha, L alpha, and M alpha x-ray lines. For comparison, theoretical kASi factors, employing a variety of ionization cross sections, were computed. Good agreement is obtained between several of the theoretical k-factor models and the experimental results. Mass volatilization of Na and K from the small glass particles during analysis is discussed, as are observations that the grinding and/or dispersing of standard materials in a liquid (such as ethanol) may promote leaching of certain elements from the particle matrix.