Hydrogen profiles in the surface of reduced lead-silicate glasses

It is shown that the thermochemical reduction of alkali-lead-silicate glass does not lead to any significant incorporation of hydrogen in the surface, but greatly sensitizes the surface to the chemical and physical adsorption of water. The treatment creates a thin (25 nm) compositionally modified layer of silica-rich, perhaps microporous, glass at the surface where the hydrogen concentration due to adsorption is irreversible. A more uniform, in-depth hydrogen profile that extends thousands of angstroms into the treated surface is reversible. The time and temperature of thermochemical treatment influence the initial kinetics of the adsorption. These observations are of practical significance to the behavior of electron multiplier and microchannel plate devices that have been exposed to humid environments. It is demonstrated that vacuum annealing after heat treatment can be used to limit the rate and extent of water adsorption.