Direct laser patterning of octadecylsiloxane monolayers on surface-oxidized silicon substrates: Indications for a photothermal excitation mechanism

A focused laser beam at a wavelength of 514 nm has been used to pattern octadecylsiloxane monolayers grown on distinct substrates which expose a silicon oxide surface. Patterning experiments on conventional silicon substrates with a native oxide layer result in a decomposition of the monolayer along well-confined lines. The line widths generally are well below the focal laser spot diameter of 2.5 ± 0.3 μm indicating a nonlinear dependence of the overall process on the laser intensity. Very similar results were obtained using thermally oxidized silicon substrates. In contrast, experiments to pattern coated quartz plates failed even if the laser power and hence the local irradiance at the surface was raised to much higher values. Altogether, these experiments strongly support a photothermal excitation mechanism, that is, a decomposition of the monolayer as a result of the laser induced local temperature rise.