Chemical Functionalization of Water-etched Si(100)
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Chemical Functionalization of Water-etched Si(100) Carmen Say and K. T. Queeney Department of Chemistry, Smith College, Northampton, MA, 01063, U.S.A. ABSTRACT Etching of hydrogen-terminated Si(100) in deoxygenated water produces surfaces with a regular nanoscale topography. Surface infrared spectroscopy provides detailed information about this topography via interrogation of the silicon hydride species that populate this highly ordered surface. Here we investigate the feasibility of using siloxane chemistry to functionalize this surface while preserving the initial topography. The critical step in silanization to form high-quality organic layers is oxidative cleaning of the surface. By re-etching oxidized surfaces in hydrofluoric acid, we can repopulate surface hydride species and examine any apparent changes in topography that resulted from the oxidation step. We compare three different oxidation protocols and find that an SC-2 clean results in the least perturbation of the original topography. Preliminary results using both dynamic contact angle and atomic force microscopy suggest that the SC-2 oxidized surface can be functionalized with alkylsilane reagents to create a functionalized surface with regular, nanoscale topography, with all surface processing carried out under ambient conditions at or near room temperature. INTRODUCTION Surface topography, in conjunction with surface chemistry, places a critical role in the biomolecule-mediated attachment of microorganisms to solid substrates. Nanometer-scale topography has been shown to have a strong effect on cell-surface interactions, for instance in the proliferation of osteoblasts on particulate ceramics[1] and in the adhesion[2] and migration of epithelial cells.[3] A variety of approaches have been used in attempts to engineer synthetic surfaces to mimic naturally-occurring nanotopography.[4] Combining the effects of nanoscale topography in promoting cell attachment and growth with surface chemistry that can be designed to promote and/or inhibit certain types of attachment provides a unique opportunity to design surfaces for controlled cell culture. A challenge in many biomedical applications is the selective culture of e.g. pathogens of interest. For example, recent conflicting (and individually reliable) results about the underlying cause of cystic fibrosis induced lung infections seem to differ based on subtle differences in cell culture, differences that are critical to eliminate for identification of the actual in vivo mechanism of disease.[5] The ability to manipulate in a straightforward process both topography and surface chemistry on the relevant scales increase the potential selectivity of these surfaces and therefore their utility in such applications. Recent approaches to generating controlled nanoscale topographies have focused on methods that are neither as costly nor as limited in size range as conventional lithographic techniques. For example, a combination of masking using block copolymers and subsequent Si etching has been used
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