STEM versus CTEM beam damage: paraffin single crystals

Abstract

IntroductionCurrently, the resolution of structural detail in conventional transmission electron microscopy (CTEM) of organic materials is limited by the electron beam damage suffered by the sample. It has recently been shown that the imaging modes now available in scanning transmission electron microscopy (STEM) provide the potential for improvements in resolution over CTEM methods. However, the effect of the sensitivity of an organic sample itself to beam damage has not been compared in STEM versus CTEM. In STEM each element of the sample area is briefly illuminated with a small diameter, high flux, scanning electron beam, whereas in CTEM the entire sample area is continuously illuminated with a large diameter, lower flux, static electron beam. Although it has been shown that the amount of sample damage in CTEM is independent of dose rate(2), the electron flux in STEM may range from 3 to 4 orders of magnitude greater than that in CTEM, with a possible influence on damage rate. Generally, the effects of beam size, high flux, and short dwell time of the scanning electron beam on sensitivity of the sample to damage in STEM are not known.