X‐ray microanalysis of wet biological specimens in the environmental scanning electron microscope. 1. Reduction of specimen distance under different atmospheric conditions

SUMMARY X‐ray microanalysis of non‐biological and biological specimens was carried out in the environmental scanning electron microscope (ESEM) under different conditions of specimen distance (the distance travelled by the electron probe within the specimen chamber) and chamber atmosphere. Using both water vapour and argon atmospheres, it was shown that reduction in specimen distance had no effect on atmospheric gas X‐ray signal in either case. Unlike water vapour, increased levels of argon (up to 10 torr) caused a marked depression of specimen P/B ratios, with a decrease in both characteristic and background (continuum) counts. These effects in argon were not altered by reduction in specimen distance. Specimen distance was important in relation to beam skirting and elemental analysis. With an extended assembly (short specimen distance), beam skirting in a water‐vapour atmosphere was much reduced – leading to enhanced element detectability in a discrete biological specimen (Anabaena cyclindrica).