Ryu Group

Many molecular or material properties are affected by the charge state or charge density. When in contact, charge transfer may occur between any two unequal chemical entities because molecules and crystalline solids have varying affinity for an excess electron. Because of the high fraction of surface atoms, interfacial charge transfer are likely to significantly modify the electronic and possibly geometric structures of most 2D crystals. For example, the chemical reactivity and electrical conductivity of graphene, and the photoluminescence quantum yield of MoS2 can be greatly controlled by varying their charge density. We seek to unravel mechanisms for charge transfer processes induced by substrates and various charge dopants in order to establish chemical methods for controllable charge transfer or charge doping. Molecules may behave very differently exhibiting unique chemical properties and reactions in small nanoscopic space than in 3-dimensional free space. Molecular diffusion, for example, is known to be greatly affected by the size of the confined space and the chemical nature of the walls defining the space. In this regard, two-dimensional materials can also serve as a model system that provides two-dimensional confined space with van der Waals gap of ~0.3 nm. We are exploring diverse behaviors of molecules confined in the truly 2D space. We are also interested in chemical reactions and charge carrier behaviors of photoexcited 2D materials. For this purpose, photons can provide a specific amount of energy with high spatial and temporal resolution. Chemical reactions could be initiated by photo-exciting either the 2D crystals or adsorbed molecular species. Electron-hole pairs can also be created by photoirradiation. The ensuing charge transfer, migration, and chem