Experimental charge fractions of hydrogen scattered from insulators at 50–340 keV

Abstract

Ion bombardment of insulators induces accumulation of electric charges at and under the insulator surfaces. This paper deals with the effect of the accumulated electric charges on the charge fractions of scattered hydrogen. We have measured and compiled charge fractions of hydrogen, in the energy range (for the scattered particles) from 50 to 340 keV, scattered from polystyrene, polymethylmethacrylate, polycarbonate, polyethylene and silicon. In order to establish the effect of the charge accumulation, some samples have been cut from a thick (1 mm) sheet, while some others have been spin coated (∼250 nm) onto silicon wafers. Experimental measurements have been fitted with the equation f(0)= Aexp(− V 2/ V i V 0), where f(0) is the neutral fraction, V the velocity, V i the “Bohr velocity” for the electron of projectiles, A and V 0 the fitting parameters. Comparisons using the least-square fitting procedure have shown that the accumulation of electric charges on the thick polymer samples have decreased the values of the fitting parameter A which is more sensitive to the fractions at lower energies. On the other hand, an increase of the pressure in the vacuum chamber during the ion scattering has induced a general increase on the fitting parameter V 0 which impairs the global trend of the fractions with energy or velocity.