Study of ultraviolet-laser ablation products of several polymers using time-of-flight mass spectroscopy

Abstract

The material ejected into vacuum by 266-nm pulsed laser ablation of poly(α-methylstyrene) (PαMS), polycarbonate, poly(ethylene terephthalate), polybenzimidazole, and polyimide is examined using time-of-flight mass spectroscopy with both 193- and 248-nm ionization. PαMS is well behaved in that the primary ejected species are based on the monomer, and intact units ranging up to trimer are observed. The other four polymers show two distinct waves of material passing through the ionization zone: a fast wave (105–106 cm/s) consisting of small bare or nearly bare carbon clusters and a much slower one composed of mainly aromatic fragments in the 128±50 amu range. These species are all smaller than the corresponding monomers and tend to be fairly similar regardless of target material although the spectrum arising from each polymer is unique. It is speculated that the difference in behavior between PαMS and the others relates to the known favorable, thermally induced ‘‘unzipping’’ which occurs in PαMS; when this low energy decomposition channel is not open, the laser-induced temperature rise is greater, and more severe bond-breaking processes occur. This work supports our previous conclusion that polymer film formation by laser ablation proceeds by a fragmentation/repolymerization mechanism but does not generally identify the film-forming species. As part of establishing the range of molecules our ionization scheme is sensitive to, mass spectra of a number of different permanent organic vapors were taken using 193-, 248-, and 266-nm ionization. These results are also discussed.