“hydrophilic treatment” has been added to the Glossary of TEM Terms.

Hydrophilic treatment is a treatment method to improve the wettability of the surface of a substance to water. Hydrophilic treatment can be done by using chemicals or by irradiating high-energy plasma to change the surface molecules into a hydrophilic functional group. In the plasma hydrophilic treatment, nitrogen, rare gas or oxygen molecules are introduced between the electrodes, and a certain voltage is applied to the electrodes to generate plasma where these molecules separate into ions and electrons. The generated plasma reacts with the molecules of the substance surface to form functional groups, which activates the surface to water and improve the wettability of the surface.

Hydrophilic treatment in TEM specimen preparation is to improve the wettability of a carbon supporting film to water. In the hydrophilic treatment apparatus (DⅡ-29020HSD of JEOL) shown in Fig.(a), a plasma of oxygen molecules is generated by applying a voltage of a tens to a hundreds volts to a low vacuum in the chamber. The oxygen plasma cut the C-C bonds of the carbon supporting film to form C-O polar functional groups, which increases the wettability of the carbon film. As a result, a specimen solution or a staining solution is smoothly spread on the carbon film and dispersion of the specimen is improved (Fig.(b)).

The plasma used in hydrophilic treatment also has a cleaning effect of the organic contaminants of the supporting film surface and diamond knife surface. This cleaning also improves the wettability of the supporting film. The hydrophilic treatment apparatus (Fig. (a)) is also used sometimes to improve the wettability of diamond knifes used in ultramicrotomes.

Fig.(a) Hydrophilic treatment apparatus for electron microscopy, DⅡ-29020HSD

Fig. (b) Effect of hydrophilic treatment for the carbon supporting film on a grid

Related Term(s)