INVESTIGATION OF ELECTRON-INDUCED DAMAGING OF MOLECULAR OVERLAYERS BYIMAGING STATIC SECONDARY-ION MASS-SPECTROSCOPY

We applied time of flight-secondary ion mass spectroscopy (SIMS) imagi ng under static conditions to investigate the interaction of electrons with a covalently bonded silane self-assembled layer of pentaflourphe nyldimethylchlorosilane on Si and a physisorbed Langmuir-Blodgett film of a phospholipide dipalmitoylphosphatidylcholine on Au. Well defined surface areas of the respective layer system were irradiated with ele ctron beams of different energies (0.5-25 keV) and different fluences (up to 3 X 10(14) electrons/cm(2)). The prebombarded surface areas wer e analyzed by imaging static SIMS, providing characteristic secondary ion intensities as a function of electron energies and fluences. From these results energy dependent electron induced damage cross sections sigma(e)(E) could be determined. We found a strong energy dependence o f sigma(e)(E), very similar to that well known for electron induced se condary electron yields. For both investigated layers we found very si milar damage cross sections sigma(e) of about 10(-15) cm(2) for 1 keV electrons. This is in contrast to the strong influence of the binding energy between the molecular overlayer and the substrate, onion induce d damage cross sections ai. Our results demonstrate the general capabi lities of imaging static SIMS to investigate quantitatively damaging e ffects in molecular overlayers and surfaces. (C) 1998 American Vacuum Society. [S0734-2101(98)03906-2].