Molecular surface analysis by TOF-SIMS

Abstract

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) performs surface sensitive analysis of the elemental and molecular composition of solids. TOFSIMS is a relatively new embodiment of static secondary ion mass spectrometry (SSIMS) in which the dose of primary ions incident on the surface is typically less than 1012 ions/cm2. Since typical solid surfaces have an atomic density of 1015 atoms/cm2, this primary ion dose nominally removes less than 0.1% of a monolayer. Hence, SIMS analyses performed under these static conditions represent near surface analysis in which secondary ions are produced from the top few monolayers of the surface. The actual sampling depth is determined by the primary ion momentum, angle of incidence and chemistry of the surface. Since low dose primary ions cause minimal perturbation of the chemistry of the solid surface, SSIMS analyses often produce molecular or pseudo-molecular ions characteristic of the chemical composition of the surface. Thus, molecular ions or structurally significant fragment ions are often observed in SSIMS analyses of surfaces containing inorganic and organic residues, polymers surfaces, coatings, and biological materials such as tissues and membranes.