About the secondary electron emission from solid hydrogens: H2, HD, D2 and T2

Reported by Sørensen and Schou [H. Sørensen, J. Schou, J. Appl. Phys. 53 (1982) 5230], the electron-induced secondary electron emission yield curves, δ = f(E0), of condensed hydrogen and deuterium show a significant isotopic effect with a yield for D2 at about ∼1.5 times larger than that for H2 and very low values (δ < 0.1 at E0 = 3 keV) in contrast to the very large yields (δ > 50 at E0 = 3 keV) reported, elsewhere, for condensed rare gases. Combined to the use of a recent model, physical considerations on the interaction of secondary electrons with zero point fluctuations permit to suggest a coherent explanation for these facts. The values of SE attenuation for three isotopes are deduced (∼4 nm for H2; ∼5.6 nm for D2; ∼4.9 nm for HD) and the electron-induced secondary electron emission yield curves, δ = f(E0), initially limited to an investigated energy range, 0.5 keV < E0 < 3 keV, are extrapolated down to their maximum values ranging from δmax ∼ 0.95 at Emax0 ∼ 145 eV, for H2 to δmax ∼ 1.13 at Emax0 ∼ 175 eV for D2. From the estimate of the attenuation length of secondary electrons, the same extrapolation procedure is also applied to solid tritium. Some consequences on charging of thick films and of small clusters are deduced. Showing also an isotopic effect, the expected evolution of X-ray-induced secondary electron emission yields, δX = f(hν), of condensed H2, HD, D2 and T2 are finally estimated.