MINIMIZING SAMPLE EVAPORATION IN THE ENVIRONMENTAL SCANNING ELECTRON-MICROSCOPE

The ElectroScan environmental scanning electron microscope (ESEM) enab les wet samples to be observed by eliminating air but allowing water v apour into the sample chamber. However, evaporation from, and condensa tion on, the sample may occur during the pumpdown sequence used to rea ch this state, which means that the sample may not be in its natural s tate when viewed if due care is not taken. In this paper, the pumping system of the ESEM is described mathematically and expressions are der ived for the evaporation and condensation. This treatment is then used to calculate the optimum pumpdown sequence. The importance of using t he optimized procedure is illustrated by micrographs of fat emulsions.