An environmental scanning electron microscope can work at a higher chamber pressure compared to regular SEM being operated at low pressures (10^-5-10^-7 mbar). Wet mode SEM is a special case where water vapor is introduced into the microscope chamber at a pressure as high as 2000 Pa. Condensation of water can occur by adjusting the water vapor pressure and the sample holder temperature according to the phase diagram of water. The sample’s temperature can be controlled by a special cooling stage that operates in the range of -20°C-60°C. For instance, at a temperature of 5°C a vapor pressure of 780 Pa will assure 100% humidity that will follow by the formation of drops on the sample (Fig. 1). This imaging mode is great for studying hydrated samples without performing special sample preparation, for studying wetting phenomena in materials, for performing regulated dehydration of biological samples and for studying in-vitro recrystallization (Fig 2). The wet mode can be applied to life science and material science samples.

Environmental SEM allows monitoring of in vitro experiments. Micrographs in this figure show dissolution of kitchen salt with increased water vapor pressure (= increased humidity) and recrystallization of the crystals as the pressure goes down.

References

• Organization and Adhesive Properties of the Hyaluronan Pericellular Coat of Chondrocytes and Epithelial Cells. Miriam Cohen, Eugenia Klein, Benjamin Geiger, Lia Addadi. Volume 85, Issue 3, September 2003, Pages 1996-2005. https://doi.org/10.1016/S0006-3495(03)74627-X
• Diameter-dependent wetting of tungsten disulfide nanotubes. Ohad Goldbart, Sidney R. Cohen, Ifat Kaplan-Ashiri, Polina Glazyrina, H. Daniel Wagner, Andrey Enyashin and Reshef Tenne. PNAS November 29, 2016 113 (48) 13624-13629. https://doi.org/10.1073/pnas.1607202113