Paper PS1-ThM1
Plasma Modification of Surface Traps in Mesoporous TiO₂

Thursday, October 18, 2007, 8:00 am, Room 606

Plasma surface modification can be effective in permanently modifying inorganic nanosurfaces. Particularly, mesoporous films formed from TiO₂ nanoparticles are interesting candidates for modification due to their important surface states needed for photovoltaic and photocatalytic applications. Plasma processing offers the opportunity of selectively modifying surface states to facilitate their investigation. Electron trap states in TiO₂-based devices, which are predominately located on TiO₂ particle surfaces,¹ can be detrimental in photovoltaic devices or beneficial in photocatalytic devices; consequently, controlling the quantity of these surface states by learning what causes and affects them will lead to more efficient devices. Here, low temperature inductively coupled plasmas are used to modify the surfaces of mesoporous TiO₂ films. Precursor gases such as O₂, H₂O, and H₂ have been used. Film surface states were primarily monitored by X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL). The binding energy of a second O1s peak in the XPS spectra increases for increasing O₂ plasma powers in the range of 75-225 Watts, and the modified films have at least a 6% increase in surface altering oxygen sites which persisted for more than 6 months. PL results suggest² a decreased density of surface traps in oxygenated films.

¹ N. Kopidakis, N. R. Neale, K. Zhu, J. van de Lagemaat,A. J. Frank, J Appl. Phys. Lett. 87, 202106.1 (2005).
² D. Zhang, J. A. Downing, F. J. Knorr, J. L. McHale, J. Phys. Chem. B 110, 21890 (2006).