Exploration of Controlled Nitrogen Doping of TiO$_{2}$ Single Crystalline Thin Films

TiO$_{2}$ is a promising material for many photochemical applications, notably the direct conversion of solar energy into chemical (H$_{2})$ via photocatalytic splitting of water. One of the biggest challenges to incorporating TiO$_{2}$ into a practical device is developing accessible routes to reliably dope TiO$_{2}$ with impurities like C, N, or B that will extend the photoactivity of TiO$_{2}$ from the UV into the visible part of the solar spectrum. Fundamental studies of the doping and the resulting changes in photocatalytic properties require well-defined model systems, such as bulk-doped single crystalline TiO$_{2}$. We present results on in situ N-doping of single crystalline TiO$_{2}$ films during homoepitaxy on rutile TiO$_{2}$(110) using reactive magnetron sputtering. NO$_{2}$ is injected into the plasma to achieve bulk doping of the TiO$_{2}$ films. The doped film morphology and near-surface electronic structure is studied in situ by scanning tunneling microscopy, without any treatment that might affect the dopant distribution. Analytical transmission electron microscopy is used to map film structure, defects, and interfaces, and determine the doping profile.