Influence of Initial Film Properties in UVO-Mediated Patterning of an Elastomeric Film Using a TEM Grid

Ultraviolet irradiation of a cross-linked polydimethylsiloxane (PDMS) Sylgard 184 film in the presence of atmospheric oxygen (UVO) through a bare transmission electron microscope (TEM) sample holding grid is a rather simple and widely utilized technique for creating micropatterned surfaces. The surface oxidation of a Sylgard 184 film due to UVO exposure is associated with densification and the formation of a silica-like surface layer, which under a TEM grid happens only over the exposed areas of the film, resulting in a physicochemical pattern. It is known that the depth (<b><i>h</i>_<i>D</i></b>) of the features depends on the duration of UVO exposure (<b><i>t</i>_<i>E</i></b>). In this article, we show for the first time that <b><i>h</i>_<i>D</i></b> also depends on the initial film thickness (<b><i>h</i>_<i>F</i></b>) and the cross-linker percentage (<b><i>C</i>_<i>L</i></b>, ratio of part A to part B) in a Sylgard 184 thin film. We show that for a specific <b><i>t</i>_<i>E</i></b>, <b><i>h</i>_<i>D</i></b> progressively decreases with the reduction in <b><i>h</i>_<i>F</i></b>. On the other hand, <b><i>h</i>_<i>D</i></b> shows a nonmonotonic dependence with <b><i>C</i>_<i>L</i></b>, resulting in patterns with maximum depth for <b><i>C</i>_<i>L</i></b> ≈ 10.0%. We attribute this observation to the combined effect of resistance against the penetration of the propagation front by the rigid substrate as well as stress relaxation within the exposed parts of the film below the propagating front in films with higher <b><i>C</i>_<i>L</i></b> values leading to the variation of <b><i>h</i>_<i>D</i></b>. The observation reported here would allow the potential fabrication of polymer films with physicochemical patterns with feature height on demand by a one-step, facile technique.