Surface, Interface, and Inorganic/Organic attachment

Surface and interface are one of the most important aspects for semiconductor physics. For organic-inorganic mixed systems, the attachments at the organic/inorganic interface is also extremely important. We have carried out ab initio calculations to study the atomic structures of such surface, interface, and inorganic/organic systems. In some cases, the total energy is used as the judge for choosing different atomic structures, and in other cases, ab initio molecular dynamics are used to determine the structure. The electronic structure at the surface and interface, the band alignment between the two sides of an interface, and electronic coupling crossing the interface are also important physics topics. We are also interested in finding the relationship between the surface structure and catalytical processes. The main tool to study these problems is the density functional theory (DFT) with codes like VASP, and PEtot. For organic systems, there is an issue of van der Waals interaction, which cannot be described by the current DFT functional. Some time an empirical vdW term is used on top of the DFT energy, although there are other more elaborated ways to include such interactions.

A few examples are given here for the systems studied in this group.

The CdS-Pt interface calculated using ab initio molecular dynamics (MD). The Schottkly barrier is then calculated based on the atomic structure. It agrees well with the experiment.

----------------------------------------------------------------------------

The CdSe polar surface (Cd terminated) passivation by te MPA organic ligands

----------------------------------------------------------------------------------------

The Ag2S_CdS interface (with partial cation exchange for the Cd with Ag), the Ag2S/CdS structure tend to form segmented bar code structure. This has a lot to do with the energy of Ag2S/CdS interfacial energy, which has been calculated using DFT.

--------------------------------------------------------------------------------------

The Cu2O_TiO2 interface calculated using DFT. 8 Cu2O lattice constants match 9 TiO2 lattice constants, as a result, a large supper lattice is needed for such study.

------------------------------------------------------------------------------------------------

Pd surface reconstruction after the surface absorption of CO molecules.

-----------------------------------------------------------------------------------------------------------------------------

P3HT laying on top of the ZnO nonpolar surface, and their wavefunction couplings.