Thesis

The international community is engaged in developing the policy to reduce greenhouse gases (GHGs) emission, in particular carbon dioxide (CO2), in order to reduce the risks associated to the global warming. Consequently, it is very important to find low-cost processes to dissociate and then capture carbon dioxide (CO2), as well as to develop low power, high performance sensors suitable to monitor GHGs reductions.A common and existing method for sensing the concentration of gases is achieved by using semiconducting metal oxides surfaces (MOS) like SnO2, ZnO, and TiO2. Moreover, one route to achieve CO2 dissociation is plasma assisted catalytic decomposition. However, surface defects, and in particular oxygen vacancies and charged trapped therein, play an important role in the (photo)reactivity of MOS. The way optical properties of surfaces are modified by such defects is not completely understood, nor is the additional effect of the presence of the gas. In some models, the importance of charge transfer is also emphasized.

In this Ph.D. work, theoretical methods will be used to model the surface with defects and predict the optical properties. The objective is threefold: To apply the theoretical frameworks developed at LSI for the study of defects to predict the defect charge states in bulk; To study the effect of the surface on the defect stability; to study bulk and surface optical properties, and find out spectroscopic fingerprints of the molecular absorption and dissociation near to the surface. Materials/gas under considerations are oxides like titanium oxide, eventually deposited on a layer on gold, and carbon dioxide. The theoretical method will be the time dependent density functional perturbation theory method (TDDFPT) developed at LSI in collaboration with SISSA, Trieste (Italy).

Ref.: I. Timrov, N. Vast, R. Gebauer, S. Baroni, Computer Physics Communications 196, 460 (2015).