Phonon Transport in Nanostructures

Recent experiments aiming to produce TiO2 nanostructures have been riddled with complications. It has been found that an undesired reaction occurs with the water used in the flaking process producing a sulphurous smell. This product suggests the production of TiOxS2−x in the layered crystal structure. This nanostructure has great potential benefits for the construction of semiconductor devices and novel electronic devices. In this investigation computational methods were used to preform first-principles Density Functional Theory (DFT) calculations of the layered crystal structures graphene and Molybdenum Disulphide, MoS2, as implemented with Quantum Espresso using the General Gradient Approximation (GGA). Unit crystal cells were built, and the DFT used to perform ab inito total energy calculations, bandstructure calculations, and to calculate the phonon frequencies at Γ and the K and M symmetry points. These were then used to ascertain the viability of the stability of a layered TiO2 crystal structure. It was found that for a two atom graphene nanostructure the total energy of the system is −22.731Ry. Moreover, the MoS2 layered nanostructure was found to have a total energy of −139.311Ry using a six basis atom unit cell. These values correspond to lattice constants of 2.54 Å and 3.16 Å for the two systems respectively.