Internal energy evaluation of sputtered molecule under size-selected argon cluster ion bombardment onto soft or hard sample

The effect of the hardness of samples on the secondary ion emission under large argon cluster (Ar n + ) bombardment was investigated by measuring the internal energy (IE) of benzylpyridinium (BPY) ion species. We prepared two samples of BPY films deposited on the Si substrate: Sample A is a thin film with a thickness of approximately 1 nm, and sample B is a thick film with a thickness of over 100 nm. The samples were irradiated with argon clusters at kinetic energy ( E ) of 5 keV and cluster size ( n ) between 500 and 3000, and TOF-SIMS spectra were measured. The dissociation ratio of backscattered Ar clusters in the spectra indicates that the thin film sample is hard and the thick film sample soft. The IE of the released molecular ions was estimated to be lower for the thick film with the same E / n conditions. This indicates that for the thick film, the kinetic energy of the cluster is dissipated into the bulk, resulting in soft desorption ionization of surface molecules.