Ion flux-dependence of secondary charged particle emissions from non-metallic surfaces

We have measured the total secondary charged particle emission (SCPE) yields by H+ and H- impact from some non-metallic surfaces such as oxidized Be. It is found that the SCPE yields by H+ impact remarkably depend on the current (flux) of the incident ions, while those by H- ion impact are nearly constant. In particular, it is noted that when the current of the incident H+ ions exceeds a critical value, the SCPE changes from negative (electrons) to positive (ions).