EMISSION OF SILICON CLUSTER IONS BY MOLECULAR ION-BOMBARDMENT

Silicon cluster ions (Si-n(+)) with n less than or equal to 8 emitted from a Si(100) surface under bombardment with 4 keV SF5+, SF+, F+, and Xe+ ions have been observed. It was shown that, in all cases, the rel ative cluster yields (Y) roughly exhibited a power-law dependence, Y(n ) proportional to n(-delta), where n is the number of atoms in the clu ster ion. The exponents delta of the power law were in the order of de lta(SF5+) < delta(SF+)< delta(Xe+)< delta(F+), which was the same orde r as that of the size of these ions. The results indicate that the siz e of the bombarded ions greatly affects the cluster-ion emission. For the SF5+ bombardments, the intensity of even-it clusters (Si-2(+), Si- 4(+), Si-6(+)) was greater than that of the adjacent cluster ions with odd-n, which is in good agreement with the calculated stability of si licon cluster ions in the gas phase. It is concluded that the silicon cluster ions are effectively produced by the polyatomic SF5+ bombardme nt through the formation of high-density collision cascades at their r adiated local area. (C) 1998 American Institute of Physics. [S0003-695 1(98)03019-8].