| Popis: |
Graphene, despite its many remarkable material properties, is fundamentally limited for many photonic and microelectronic applications due to its semi-metallic nature. Chemical functionalisation of graphene affords one route toward opening an energy gap, potentially extending its utility to these areas. Graphene oxide strongly absorbs in the ultraviolet range and reduction by various chemical treatments has been demonstrated to shift the absorption peak toward the visible spectrum. Photoluminescence emission has also been observed across the spectrum from ultraviolet to infrared, further suggesting the possibility of tuning optical properties. However, such methods produce highly defective graphene oxide, with hydroxyl, carboxyl, and carbonyl moieties being left behind in addition to the desirable epoxy functional groups. Considerable damage to the graphene sub-lattice is also caused. More recently, chemical deposition of atomic oxygen on graphene has been shown to form epoxy functional groups on graphene without causing this damage. Ab initio and hybrid density functional theory and time-dependent density theory studies of graphene oxide and reduced graphene oxide are carried out to investigate its structural, electronic, and optical properties. Patterned removal of oxygen to form graphene quantum dots embedded in the graphene oxide lattice is shown to permit tuning of the energy gap and optical absorption from ultraviolet through to infrared wavelengths, with long calculated radiative relaxation times. A simple relationship between the predicted gap and size of the most symmetric quantum dot structures, which are also the most thermodynamically stable, is demonstrated. |
