Hydrated Specimen Stability in the Electroscan ESEM: Specimen Surface Temperature Variations and the Limitations of Specimen Cooling

Abstract

Chamber temperature and pressure are the two principal factors in preserving hydrated specimens in a high vapour pressure or environmental SEM; in this study the Electroscan ESEM. Hydrated specimen stability, is achieved by operating at or near water saturated conditions in the specimen chamber.The ambient chamber temperature (in the ESEM) has been measured and found to be ∼29°C, ∼7°C higher than the laboratory environment. Water saturation at this temperature requires a chamber pressure of ∼30t and poor image resolution results from the high degree of primary beam scattering under these conditions. A low cost Peltier effect cooling stage has been constructed to provide cooling of specimens to ∼5°C. At this temperature water saturated conditions are achievable in the chamber at ∼5t with resultant good image resolution.Usage has shown that stability of sensitive hydrated specimens still remains difficult. This is due to the cooling and measurement of specimen temperature through the stage at the base of the specimen, rather than at the surface.