Effect of the film thickness on the fabrication of ordered TiO₂ thin film microstructures by transfer printing

This paper describes a transfer printing technique for directly patterning ordered TiO₂ thin films onto Si substrates. Two- or three-dimensional TiO₂ structures can be fabricated onto an Si substrate depending on the coating film thickness, which is controlled via the liquid phase deposition process parameters and attractive interaction forces between a poly(dimethylsiloxane) stamp and a polyelectrolyte layer during the transfer printing process. This additive transfer process is mediated by the presence of a thiol (SH)-terminated 3-mercaptopropyltrimethoxysilane self-assembled monolayer on the wafer surface. The transferred patterns are chemically bonded to the wafer surface, exhibiting strong adhesion. The attractive interaction forces between the stamp and the polyelectrolyte layer was weak enough to allow ready detachment of the patterns from the stamp during printing. Even the parts of a continuous TiO₂ film that are not in contact with the substrate effectively transfer to form a free-standing structure. With long and short deposition times, three-dimensional structures and ordered two-dimensional round-hole grid structures, respectively, are obtained after the removal of the stamps.