Defects in semiconductors have been studied for many years, with a view toward controlling their behavior through various forms of defect engineering. In the Si-based microelectronics industry, numerous methods to characterize and control the behavior of defects have been developed, including novel techniques such as co-implantation, millisecond annealing, photostimulation and surface engineering. Closely related, yet unique defect engineering efforts have also been made for non-Si based microelectronic applications as well. The accumulated knowledge stemmed from microelectronics should also be able to be extended to metal oxide semiconductors, where promising applications (e.g., gas sensors and photocatalysts) are gaining increased interest. In particular, the use of surface engineering has been extended to titanium dioxide, opening up new possibilities of defect control. For further investigation of these effects, sulfur has been chosen as a surface controlling adsorbate, which can be used to manipulate the surface states. The successful deposition of the element through electrochemical means has been demonstrated on silicon and titanium dioxide substrates. In addition, experimental and computational studies on the behavior of the cation species in titanium dioxide using isotopic tracers have also been carried out, with an emphasis on the effect of surface states. It follows that the surface state can indeed influence the cation defect behaviors in a significant manner, which in turn affects the self-diffusion profiles.