Secondary ion emission from polymethacrylate LB-layers under 0.5-11 keV atomic and molecular primary ion bombardment

Secondary ion yields Y(X-i(q)) increase considerably when changing from ato mic to molecular primary ions, whereas the parallel increase in the corresp onding damage cross sections sigma(X-i(q)) is much smaller. This results in a net increase of ion formation efficiencies E(X-i(q)) = Y/sigma. For a mo re detailed understanding of the complex sputtering and ion formation proce sses, in particular for molecular primary ion bombardment, the secondary io n emission of well-defined polymethacrylate LB mono- and multilayers on Ag was investigated. For characteristic secondary ions X-i(q) emitted from the se overlayers Y(X-i(q)) and sigma(x(i)(q)) for 11 keV Ne+, Ar+, X-e+, O-2(), SF5+, C7H7+, C10N8+, C6F6+ and C10F8+ bombardment were determined and co mpared. The influence of primary ion energy was investigated in the energy range between 0.5 and 10 keV for Xe+ and SF5+ bombardment. For multilayers we found yield increases up to nearly a factor of 1000, whe n changing from Ne+ to SF5+ bombardment. We found a more pronounced yield a nd efficiency enhancement for multi than for monolayer coverages, a saturat ion of Y, sigma and E enhancement for primary ions made of more than 6 heav y constituents at constant primary ion energy, no chemical effect on the se condary ion yields under static SIMS conditions (SF5+ / C7H7+ e.g.), and a pronounced decrease in secondary ion yields and secondary ion formation eff iciencies for SF: primary ions with impact energies below 2 keV. (C) 2000 E lsevier Science B.V. All rights reserved.