During the electron irradiation of synthetic diamond films, three successive regims are encountered as a function of the electron dose: (1) a reduction of the downward band bending of energy levels at the sample surface because an excess of secondary electrons leaves the sample; (2) the creation of an internal electric field in which secondary electrons drift to the surface, leading to an appreciable increase in the secondary emission and to a linear relation between the primary electron energy and the secondary electron field; and (3) the desorption of hydrogen terminating the carbon surface bonds. The secondary emission thus decreases to very low values. The rate of decrease of secondary emission is similar for C:H- and C:H:Ba-terminated diamond surfaces.

Diamond Relat. Mater.

Hopman, H. J., Verhoeven, J., Bachmann, P. K., Wilson, H., & Kroon, R. (1999). Secondary electron emission measurements on synthetic diamond films. Diamond Relat. Mater., 8, 1033–1038.