Photochemical Attachment of Reactive Cross-Linked Polymer Films to Si/SiO₂ Surfaces and Subsequent Polymer Brush Growth

Abstract

Thin films consisting of a mixture of acrylate/methacrylate monomers were photochemically attached to modified silicon wafer surfaces. Reactive functionality was embedded into the photopolymer film by adding alkoxyamine monomers (inimers) that facilitate polymer brush growth in subsequent polymerization reactions. We present a careful examination of each of the steps, from substrate preparation to silane coupling agent coating, photopolymer attachment, and polymer brush growth. Several 3-methacryloxypropyl silanes were evaluated as silane coupling reagents. The surface roughness of wafers increased from 0.2 to 0.6 nm after treatment with silane. Curing of a thin photopolymer film did not increase the surface roughness. Interestingly, brushes of d8 polystyrene grown from the photopolymer surface displayed half the roughness of the underlying polymer layer, displaying a smoothing effect. All photopolymer films attached to the wafers utilizing a silane layer had excellent adhesion. We studied the film surfaces by water contact angle measurements, atomic force microscopy, and IR and X-ray photoelectron spectroscopies.