Control of Photoactivity over Polycrystalline Anatase TiO 2 Thin Films via Surface Potential
Ong, S. W. Daniel
Seebauer, Edmund G.
Date of Issue2015
Energy Research Institute @NTU
The utility of thin-film TiO2 for photocatalysis would be greatly improved if the spatial variation of the electronic band edges near the surface could be engineered a priori to control the current of photogenerated minority carriers. The present work demonstrates such a concept. In particular, remote oxygen plasma treatment of polycrystalline anatase TiO2 with specified majority carrier concentration is employed in the test case of methylene blue photodegradation. The photoreaction rate varies by up to 35% in concert with a 0.4 eV change in built-in surface potential measured by photoelectron spectroscopy. The correlation between these changes agrees quantitatively with a photodiode–photocurrent model. The plasma treatment affects concentration of charged native defects within the first few atomic layers of the surface, most likely by lowering the concentration of oxygen vacancies within surface crystallites. In tandem, the position in the deep bulk is controlled via engineering the defect concentration at grain boundaries, thus illustrating the coordinated use of multiple defect engineering practices in polycrystalline material to accomplish quantitative manipulation of band bending and corresponding photocurrent.
The Journal of Physical Chemistry C
© 2015 American Chemical Society. This paper was published in The Journal of Physical Chemistry C and is made available as an electronic reprint (preprint) with permission of American Chemical Society. The published version is available at: http://dx.doi.org/10.1021/acs.jpcc.5b09272. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.