(421a) Evaluating and Improving the Stability of Organic Monolayer Coatings

Their small size, low cost, and ease of manufacture make MEMS devices attractive candidates for future therapeutic and diagnostic applications. However, the negative charge of the native silicon oxide surface makes such devices particularly prone to non-specific protein adsorption and biofouling. In order to realize the potential of such devices, reliable and stable surface modification methodologies must be developed to address these problems. As a starting point, this work will investigate the thermal and aqueous phase stability of various monolayers on silicon surfaces. Monolayers of chlorosilanes, methoxysilanes, and alkenes of various lengths will be applied to silicon surfaces, and the film properties will be assessed by atomic force microscopy and contact angle analysis before and after thermal and aqueous phase exposure. For methoxysilane films, thermal annealing and annealing in controlled humidity will be investigated to determine if either offers advantages in film properties and thermal and aqueous immersion stability. Furthermore, those molecules that are oxidatively bound to the silicon surface will also be deposited onto a seed layer, and the properties of these films will be compared to films in which no seed layer was used. Also, a secondary surface treatment by trimethylchlorosilane will be employed, and its effect on thermal and aqueous immersion stability will be evaluated. Lastly, unsaturated pendant groups will be studied for their ability to form cross-linked surface networks, and the effect of cross-linking on thermal and aqueous immersion stability will be determined.