Secondary electron emission from solid hydrogen and deuterium resulting from incidence of keV electrons and hydrogen ions

The secondary electron emission (SEE) coefficient delta was measured for solid hydrogen and deuterium resulting from the normal incidence of 0.5--3-keV electrons and 4--10-keV H+, H2+, H3+, and D3+ ions. The SEE coefficients for solid hydrogen are 60--70% of those for solid deuterium, and the coefficients are small, in contrast to what is expected for insulating materials. One explanation is that the secondary electrons lose energy inside the target material by exciting vibrational and rotational states of the molecules, so that the number of electrons that may escape as secondary electrons is rather small. The losses to molecular states will be largest for hydrogen, so that the SEE coefficients are smallest for solid hydrogen, as was observed. For the incidence of ions, the values of delta for the different molecular ions agree when the number of secondary electrons per incident atom is plotted versus the velocity or the stopping power of the incident particles. Measurements were also made for oblique incidence of H+ ions on solid deuterium for angles of incidence up to 75degree. A correction could be made for the emission of secondary ions by also measuring the current calorimetrically. At largest energies, the angular dependence corresponds to delta (theta) =delta (theta)(costheta)-1