Paper SS-MoA7
Site-specific Chemistry in Aqueous Solutions Produces Atomically Flat Rutile (110)

Monday, October 28, 2013, 4:00 pm, Room 201 A

The high photocatalytic reactivity of nanocrystalline TiO₂ has attracted widespread interest for applications ranging from next-generation solar cells to self-cleaning surfaces; however, surface science investigations of these materials under technically relevant conditions have been hindered by a number of experimental difficulties. Moreover, the correlation between the chemical properties of clean TiO₂ surfaces produced in vacuum by repeated sputter-and-anneal cycles, the standard surface science technique, to those present in solution or in humid environments is unclear. We have used STM to investigate the atomic-scale reactivity of the most commonly studied TiO₂ polymorph, rutile, in pH-controlled aqueous solutions. Clean, atomically flat rutile (110) surfaces with well controlled step structures can be prepared using a simple aqueous solution. After mild heating (~150°C) to remove adsorbed water, STM reveals atomically flat surfaces of comparable quality to those produced using standard sputter-and-high-temperature-anneal cycles. The nature of the highly site-specific chemical reactions that produce these surfaces is revealed by kinetic simulations of pH-dependent changes in the etch morphology. A chemical mechanism for the production of atomically flat surfaces that is consistent with the inorganic chemistry of Ti(IV) compounds and the observed anisotropic reactivity is proposed.