PRELIMINARY EVALUATION OF AN SF5-BEAM FOR ANALYSIS OF ORGANIC THIN-FILMS BY SECONDARY-ION MASS-SPECTROMETRY( POLYATOMIC PRIMARY ION)

Organic vapor deposited thin films of pure biomolecules, polymer films and biomolecules dispersed in gelatin and biological tissue have been analyzed in a magnetic sector secondary ion mass spectrometer using a n SF5+ primary ion beam at keV impact energies, In comparison to Ar+ b ombardment under identical conditions, bombardment with SF5+ gives a 1 0 to 50 fold enhancement in the secondary ion yields for characteristi c molecular ions. The SF5+ primary ion beam can be focussed to a small spot allowing molecular ion images to be obtained at micrometer spati al resolution with enhanced sensitivity, More importantly, the decay i n molecular ion signal as a function of primary ion dose commonly obse rved in SIMS using monoatomic primary ions is either eliminated or gre atly reduced, allowing molecular depth profiles to be obtained of orga nic thin films. By continuing to sample intact molecules as sputtering proceeds into the sample, the total number of detected characteristic secondary ions is increased by as much as a factor of similar to 700 for SF5+ bombardment as compared to Ar+ bombardment under identical an alytical conditions, This effect is thought to be a result of the high erosion rate and the low penetration depth inherent in the use of a p olyatomic primary projectile. (C) 1998 John Wiley & Sons, Ltd, This pa per was produced under the auspices of the US Government and it is the refore not subject to copyright in the US.