Chemical modification of silicon (100) surface via UV-induced graft polymerization

Modification of argon plasma-pretreated single-crystal silicon wafer surfac e via UV-induced graft polymerization with various functional monomers, suc h as acrylamide (AAm), N,N'-diamethylaminoethyl methacrylate (DMAEMA), and 2,2,2-trifluoroethyl acrylate (TFEA), was achieved. The modified Si(100) su rfaces were characterized by X-ray photoelectron spectroscopy (XPS), imagin g XPS, atomic force microscopy (AFM), and water contact angle measurements. The graft polymerization was affected by plasma pretreatment time and UV i rradiation time. XPS results suggest that mild and brief plasma treatment i s sufficient to cause surface oxidation and to generate sufficient peroxide s and hydroxyl peroxides for the subsequent UV-induced graft polymerization in the presence of a vinyl monomer. Prolonged plasma treatment and the acc ompanying overoxidation of the silicon surface have an adverse effect on th e graft polymerization. For all the cases investigated, the XPS results rev ealed that the grafted polymers form a thin layer with a thickness of 5 nm or less on the silicon surface. The AAm and TFEA graft-polymerized surfaces were uniform in morphology. However the DMAEMA graft-polymerized surface e xhibited structural domains. Contact angle measurements further indicated t hat the silicon surface could be selectively made hydrophilic or hydrophobi c through the proper choice of monomers used for graft polymerization.