Influence of the irradiation wavelength on the ablation process of designed polymers

A photolabile triazene polymer was irradiated with a KrF (248 nm) and a XeCl (308 nm) excimer laser. The resulting ablation fragments were analyzed using time of flight mass spectroscopy (TOF-MS). The peak intensities of the main ablation fragments reveal a pronounced influence of the irradiation wavelength and fluence. After 248 nm irradiation the peak intensities of all polymer fragments reach maxima at high fluences whereas after 308 nm irradiation only the 168 amu peak intensity reaches a maximum. All other analyzed fragments (28, 35 and 76/77 amu) do not reveal a maximum. The time of arrival curves of the decomposition products at both irradiation wavelengths are composed of three distinctive components. Two quite sharp peaks are fitted by a Gaussian distribution, whereas a third broad peak is described by a decaying Maxwell-Boltzmann distribution. The first fast peak is attributed to the fragments produced during the laser pulse. The second peak was detected around 100 mus after the laser pulse. The peak is very sensitive to the alignment of the setup, but very insensitive to changes in the electrical fields, and was still pronounced after grounding the ionizer. Therefore the peak was assigned to excited neutral nitrogen molecules (metastable N-2). (C) 2002 Elsevier Science B.V. All rights reserved.