Mass spectroscopic studies of the ArF-laser photoablation of polystyrene

Abstract

We have investigated the photoablation of polystyrene by ArF-laser radiation (193 nm) with respect to the chemical nature and energy distribution of ejected molecular species. A novel analytical technique combining photoionization by vacuum-ultraviolet laser radiation at 118.4 nm with time-of-flight mass spectrometry has been employed. At near threshold fluences above 15 mJ cm⁻² the main neutral photoablation product is the styrene monomer. Using direct time resolved detection the kinetic energy distribution of the product molecules has been determined, it peaks at about 0.7 eV. From the low fragmention-yield at near threshold fluences we can estimate that the mean internal energy of the monomers is less than 2 eV. This and the “narrow” time-of-flight distribution can be modeled by an adiabatic expansion of the ablated molecules.