Prolific cluster emission in sputtering of phenylalanine by argon-cluster ion bombardment

Large Ar-n(+) cluster ions (with n similar to 1500 Ar atoms per cluster) with a bombarding energy of 10 keV were used to investigate the sputter-induced emission of positive secondary ions from a phenylalanine specimen by orthogonal time-of-flight SIMS. An abundant flux of phenylalanine cluster ions (M-n+H)(+) with n <= 12 was observed. The yield of dimers relative to monomers is found to amount to 50 - 60% whereas that of turners and tetramers is roughly 10%. Tentatively, this prolific formation of these cluster species can then be ascribed to the concerted action of the large number of Ar atoms within their impact zone at the surface: these low-energy Ar species (with an average energy of only few eV) may effect the soft cleavage of the phenylalanine bonds in the solid and lead, eventually, to the intact emission of these phenylalanine moieties. (C) 2014 Elsevier B.V. All rights reserved.