UV laser-induced grating formation in PDMS thin films

Excimer laser (193 nm and 157 nm) induced ablation and structure formation in poly-dimethylsiloxane (PDMS) thin films is demonstrated. Ellipsometric measurements provide values of the optical constants of the films as well as their thicknesses, which are below 1 m. At fluences above 160 mJ/cm² two pulses of UV light induce gratings with at minimum 1-m periods and crossed gratings with 4-m periods. The structure heights are between 10 nm and 20 nm with ridge widths of several hundred nanometres. The ablation occurs after a single incubation pulse with a threshold that increases logarithmically with the ablation wavelength increasing from 157 nm to 1064 nm. At 193 nm the ablation rate for 2 J/cm² is 127 nm/pulse. PACS 79.20.La; 34.50.Dy; 68.55.Jk