Application of atomic and molecular primary ions for TOF–SIMS analysis of additive containing polymer surfaces

The influence of primary ion mass and composition on secondary ion emission of the additive Irganox 1010 (m=1176 u) in polyethylene was investigated. O+, Ar+, Xe+, O2+, CO2+, SF5+, C7H7+, C10H8+, C6F6+, and C10F8+ with a total energy of 11 keV were used as primary ions under static secondary ion mass spectrometry (SIMS) conditions. Positive and negative molecular secondary ions characterizing the additive were determined and their yields were evaluated. For all characteristic secondary ions we found a strong yield enhancement with increasing mass for atomic primary ions and increasing number of constituents for molecular primary ions. This yield enhancement is saturated once the molecular primary ion is made of more than six heavy atoms. In addition this yield increase depends on the mass and structure of the considered secondary ion. We did not find any evidence for an influence of the chemical composition of the applied molecular primary ions on the secondary ion emission when static SIMS conditions were met. The improved imaging capabilities of molecular primary ions was demonstrated by comparing focused Ar+ and SF5+ primary ion beams when mapping characteristic secondary ion emission from a structured additive containing polypropylene surface.