Incubation and ablation behavior of poly(dimethylsiloxane) for 266 nm irradiation

Poly(dimethylsiloxane) (PDMS) has been irradiated with a frequency quadrupled Nd:YAG laser (266 nm) at a repetition rate of 1 Hz. The analysis of etch depth vs. pulse number data reveals a pronounced incubation behavior, i.e. ablation starts only after several pulses. The threshold of ablation (210 mJ cm-2) and the corresponding effective absorption coefficient (αeff=48900 cm-1), which is very different from the linear absorption coefficient (nearly zero), were determined. Incubation of polymers during ablation is normally related to changes of the chemical structure of the polymer. The incubation behavior of PDMS upon 266 nm irradiation was studied with UV-Vis spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, X-ray photoelectron spectroscopy (XPS) and Raman microscopy. The experimental data obtained with these techniques suggest that upon incubation O-H and Si-O groups are formed along with an increase in surface roughness. Ablation starts as soon as the absorption reaches a certain threshold. The ablation products consist of a silica-like material and carbon in the form of soot with some crystalline features