Fast-ion-induced sputtering of polymers

Abstract

Energetic ions in the electronic stopping regime (fast ions) impacting a solid can induce the ejection of intact large organic molecules into the gas-phase. This phenomenon, called electronic sputtering, has been employed in the Time-of-Flight (TOF) mass spectrometry of molecular solids, such as polymers, peptides and proteins. In this paper, results on the electronic sputtering of polymers are briefly reviewed with some comparison with data on sputtering by low-energy (keV) particles. Most of the information derived so far from fast-ion sputtering of polymers originates from low-mass fragment species. Fingerprint fragment ions present in the TOF spectra can be used for material identification and structural analysis of pristine and irradiated polymers. Besides that, studies of the properties of such ions (e.g. velocity distributions, effective ejection cross sections, etc.) can give information on the early physics and chemistry of ion tracks which are difficult to access by means of other experimental techniques. An important dimension in the fast-ion-induced sputtering of polymers is the synthesis and ejection of new and complex molecules. A remarkable example is the emission of large-mass pure carbon clusters from halogenated polymers in response to a single MeV ion impact. The applicability of fast-ion-induced sputtering in the determination of molecular weight distribution of polymers is also discussed in connection with recent results of crater formation by MeV ion impacts on polymer surfaces.