Investigation of Nanostructured TiO2 Surface and Interface Electric Fields with Photoreflectance Spectroscopy

The electrical properties of buried solid-solid interfaces are essential to the optimization of devices such as dye-sensitized solar cells and photocatalysts. The degree of fixed charge buildup at these interfaces can be sample-dependent, influenced by only a small fraction of total surface sites, and challenging to quantify. This work describes the applicability of photoreflectance spectroscopy (PR) to the characterization of thin film nanostructured TiO2. The approach involves the synthesis of polycrystalline anatase TiO2 on quartz and Si(100) by atomic layer deposition with Ti(OCH(CH3)(2))(4) and H2O as precursors. PR reveals negligible band bending at the TiO2 free surface. A distinct spectral feature at 299.0 +/- 0.3 kJ/mol (3.10 +/- 0.0031 eV) is attributed to electronic states at the TiO2-Si interface. Temporal variations in the magnitude of this feature are discussed in the context of bulk carrier concentration, solid-solid interface chemical reactions, and charge exchange between interface and grain boundary states and the bulk bands. (C) 2012 American Institute of Chemical Engineers AIChE J, 59: 1049-1055, 2013