Probing a New Form of Surface Chemistry: Interactions with Point Defects Edmund G. Seebauer, Department of Chemical & Biomolecular Engineering, University of Illinois at Urbana-Champaign In the same way that gases react with surfaces from above, point defects within a solid can react from below. Such defects include vacancies and interstitial atoms. Little attention has been paid to this form of surface chemistry, even though the rates govern many aspects of important phenomena such as solid-state diffusion, photostimulated power production and catalysis in semiconductors, solid electrolyte sensors, and metal oxide catalysis. To better understand such chemistry, we employ measurements of solid-state diffusion in semiconductors. Saturating dangling bonds at the surface or at solid-solid interfaces controllably interferes with both the annihilation and generation of defects. For silicon, we have learned: Control of surface chemical state can affect pn junction formation in transistors for integrated circuits, by means we can now quantify with considerable precision. Solid-solid interfaces modified by low-energy ion implantation can accomplish similar purposes. We have definitively observed an electrostatic contribution to the behavior in addition to dangling bond exchange. We have observed related effects in oxide semiconductors such as titanium dioxide for catalysis. Annihilation Generation Bonding orbitals Adsorbate atoms Interstitials Bonding orbitals Vacancy Lattice atoms Absorbate Interstitial