Static SIMS Investigation of Ag-Supported Amino Acids

Abstract

The static mode of secondary-ion mass-spectroscopy (static SIMS) was used to investigate Ag-supported amino acids, the amount of amino acids on the Ag surface being systematically controlled. It is shown in this report that a mono-molecular layer (full coverage θ=1) is produced at a surface concentration of about 5×10 14 molecule/cm 2 . The possibility of the quantitative detection of amino acids with static SIMS for θ<1 is also demonstrated. The fact that the ratio (M-COOH) + /(M+H) + from a mixture of two amino acids remains constant as the mixture ratio varies indicates that these ions are formed from amino acids in the same bonding state on the surface. The absolute probability of formation of these ions is, however, strongly affected by the presence of another amino acid coexisting on the surface. The secondary (M+H) + and (M-COOH) + ion intensities are used to calculate the absolute ion yields for 15 amino acids and most of these yields are found to be larger than 10 -19 .