Environmental scanning electron microscope (ESEM)
This machine is designed to view a sample in its natural state, without the need for desiccation. Sample temperature and specimen chamber vapour pressure can both be controlled, allowing samples to be heated, cooled, wetted or dried.
Relative humidity (RH) can be controlled within the chamber by adjusting the temperature of the conventional stage (±20° C) along with the pressure. For example a relative humidity of 100% can be achieved by combination of low temperature (e.g. 4° C) and high water vapour pressure (e.g. 6.1 Torr). The advantage of using 100% RH is that the sample is not being dehydrated as it is being imaged. Water can also be condensed on the samples by going above 100% RH. Dynamic experiments can also be carried out on wet samples in real time, involving heating on a specialised hot-stage, anywhere up to 1500° C, cooling, wetting and drying. The samples can be imaged while these dynamic processes are occurring. Some examples of experiments that can be undertaken in the ESEM include the determination and imaging of melting dynamics for physical science materials; determination of crystallisation dynamics; and imaging of biological processes, for example pollen tube growth in real time through wetting of pollen.