Functionalized Graphene as Superlattice and Gas Sensor

Sammanfattning: Graphene, an atomic-thin carbon sheet with carbon atoms tightly packed honeycomb-like lattice, has attracted enormous interest due to its unique chemical and physical properties. However, the intrinsic zero bandgap characteristic of graphene has so far prevented graphene from building effective electronic and optoelectronic devices. To address this concern, different functionalization methods have been proposed to modify the electronic properties of graphene. This thesis focuses on different graphene surface functionalizations and their applications in gas detections and superlattices.First of all, the surface cleanness of graphene plays a crucial role in the performance of graphene devices. To achieve a controlled removal of polymer residues on graphene surface, a facile solvent based method has been proposed, which can drastically improve the charge carrier mobility of graphene devices by a factor of 3, indicating a potential ballistic transport of graphene under ambient condition. In addition, an electron beam induced fluorination cycle is proposed to eliminate the airborne hydrocarbon contamination related to aging effects on the graphene surface. Subsequent spectroscopic analysis confirms the long-term preservation of graphene using such technique. A similar technique, ion beam induced covalent functionalization has been used to locally fluorinate graphene, which could enhance the sensitivity of NH3 sensing as compared to a pristine graphene gas sensor by a factor of 8. The use of non-covalent, π-π stacking interactions for the functionalization of graphene opens a pathway to bind the functionalizing groups from nearly unlimited variety of p conjugated molecules. Here, we demonstrate that the use of BP2T molecules functionalizing graphene leads to an enhanced sensitivity to NH3 by a factor of 3 comparing with that of pristine graphene. This particle beam induced functionalization technique can be used for the fabrication of graphene superlattices. Here, a direct nanostructuring technique by employing electron beam induced etching with different precursor gases has been proposed to achieve localized structuring of graphene/hBN structures. Suspended fluorinated graphene can be obtained by using this dual-beam process, suggesting the capability of printing antidot superlattices where graphene would be suspended in a controllable way. When functionalizing a graphene bilayer by electron beam activated fluorination, a new type of moiré superlattice with rectangular periodicity can be formed due to the crystalline mismatch between the topmost fluorographene and underneath pristine graphene. Recently, rotational moiré superlattices of graphene were shown to be superconducting. We believe that this unique structure has the potential to equally reveal novel properties of 2D materials.