Fabrication of chemical and topographic nanopatterns using functionalized block copolymer thin films

Abstract

Fabrication of Chemical Nanopatterns Using Functionalized Block Copolymers

The self-assembly of a block copolymer is one of the most promising ways for making nanometer-sized structures, such as spheres, cylinders, and lamellae in the thin film form. Consequently, block copolymer lithography has attracted much attention because it is easier than conventional lithography in the process of nanofabrication. Particularly, nanostructures of amphiphilic block copolymers are attractive because each block can be designed to be selectively responsive to different external stimuli. However, amphiphilic block copolymers tend to self-associate in aqueous solution and form micelles. It would be an excellent alternative for making thin film of amphiphilic block copolymer to utilize deprotection reaction during thermal annealing process simply by starting with protected block copolymer thin film. First, we demonstrate a novel method of dual patterning and sequential functionalization of block copolymers using a photocrosslinkable random copolymer film, poly(styrene-r-(tert-butyl acrylate)-r-(cinnamoyloxyethyl acrylate)). The tert-butyl esters of the block copolymer, polystyrene-block-poly(tert-butyl acrylate), coated on the patterned neutral brush were sequentially deprotected to give carboxylic acids using acid catalyst and heat treatment. The sequentially produced COOH-chemical patterns were used for the sequential patterning of gold, and silicon oxide nanoparticles as the potential applications. Secondly, the phase behavior of symmetric block copolymer thin films of intrinsic and deprotected polystyrene-b-poly(4-hydroxystyrene) (PS-b-PHOSt) was explored upon solvent annealing with acetone, a selective solvent for the PHOSt block. The thin film morphology of intrinsic PS-b-PHOSt shifts from stripe patterns to highly ordered nanoprotrusions as a function of increasing solvent annealing time. The same symmetric PS-b-PHOSt thin film formed by UV-induced deprotection of polys...