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

Modification of argon plasma-pretreated single-crystal silicon wafer surface via UV-induced graft polymerization with various functional monomers, such as acrylamide (AAm), N,N'-diamethylaminoethyl methacrylate (DMAEMA), and 2,2,2-trifluoroethyl acrylate (TFEA), was achieved. The modified Si(100) surfaces were characterized by X-ray photoelectron spectroscopy (XPS), imaging XPS, atomic force microscopy (AFM), and water contact angle measurements. The graft polymerization was affected by plasma pretreatment time and UV irradiation time. XPS results suggest that mild and brief plasma treatment is sufficient to cause surface oxidation and to generate sufficient peroxides and hydroxyl peroxides for the subsequent UV-induced graft polymerization in the presence of a vinyl monomer. Prolonged plasma treatment and the accompanying overoxidation of the silicon surface have an adverse effect on the graft polymerization. For all the cases investigated, the XPS results revealed 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 exhibited structural domains. Contact angle measurements further indicated that the silicon surface could be selectively made hydrophilic or hydrophobic through the proper choice of monomers used for graft polymerization.