| Contact printing of two trichlorosilane inks, octadecyltrichlorosilane (OTS) and 7-octenyltrichlorosilane (OCT), on Si/SiO2 was investigated. Because these ink molecules are water sensitive, they can polymerize on the poly(dimethylsiloxane) (PDMS) stamp while being handled in air. Large siloxane polymers of OTS and OCT molecules formed on the stamp often deposit to the substrate, creating defects in these contact printed films. We were able to obtain relatively smooth films of OCT at sufficiently high concentrations of OCT; the quality of OTS films did not improve at high OTS concentrations. These observations are consistent with the following proposed mechanism for film deposition by contact printing: permeation of the ink molecules into the PDMS stamp, followed by diffusion-limited adsorption of the molecules to the Si substrate. Small molecules such as OCT monomers can diffuse in and out of the stamp easily, whereas polymers formed in the stamp are trapped in the PDMS matrix. Increasing the OCT concentration, therefore, increases the percentage of OCT monomers in the adsorbing species, resulting in films with fewer polymer defects. OTS molecules do not permeate into the stamp to the same extent as OCT, and a high concentration of polymerized OTS remains near the stamp surface. As a consequence, OTS films form by simultaneous adsorption of both OTS monomers and OTS polymers.; Two examples of Si patterning via microcontact printing (μCP) are given in this thesis. In both cases, Si substrates were patterned with OTS by MCP to protect the underlying substrate. The first example shows the use of an OTS template in orthogonal printing of OCT to activate OTS-free areas, followed by surface-initiated ring-opening metathesis polymerization (ROMP) of strained olefins to amplify the original pattern inscribed by μCP In the second example, an OTS template was used to selectively deposit a Pt(O) complex, which was used in Pt-assisted etching of Si(100) to produce porous silicon structures in the Pt-coated regions. |
