Laser-assisted decomposition of alkylsiloxane monolayers at ambient conditions: rapid patterning below the diffraction limit

Abstract

Rapid patterning of octadecylsiloxane monolayers at ambient conditions is demonstrated using a focused laser beam at a wavelength of 514 nm. Surface-oxidized silicon substrates have been coated and subsequently processed at distinct laser powers over a wide range of writing speeds up to 25 mm/s. The method allows for a well-confined local decomposition of the monolayer with an unexpectedly high lateral resolution which is significantly below the diffraction limited laser spot diameter of the optical setup. In particular, at a 1/e² focal spot diameter of about 2.5 μm line widths close to 200 nm are reached. Complementary experiments at a spot diameter of about 1.2 μm yielded irregular lines with a minimum width close to 100 nm. The underlying highly superlinear dependence of the patterning process on the laser intensity is attributed to the interplay between the laser-induced local temperature rise and the thermally activated decomposition of the organic coating. A simple thermokinetic analysis of the data allows one to estimate effective kinetic parameters of the decomposition process and reproduce the experimentally observed functional dependence of the line width on the incident laser power and the writing speed.