Investigation and development of a graphene electroburning platform for reliable single-molecule electrode fabrication

Molecular electronics has been considered a beyond-CMOS platform to pursue the scaling of electronic devices, by pushing it to the single-molecule level, and by using the paradigm in which individual molecules constitute the active components in electronic circuits, performing a variety of functions such as transistors and sensors. For many years, molecular electronics has traditionally advanced from materials such as gold electrode with nanogap formation methods such as electromigration and mechanical break junctions. Alternatively, graphene has opened a new possibility of acting as a stable electrode at room temperature for a long period of time and its unique electronic properties have been analyzed as a possible material to be the electrode for single-molecule electronics. Since atoms in graphene are stable at room temperature owing to their SP2 C-C covalent bonds, graphene can be a natural electrode for conjugated molecules, offering, at the same time, good orbital hybridization with the molecular channel and thus more natural support to transport in molecular devices. An established method for creating nanogaps in graphene is feedback-controlled electro-burning. This method can be an effective way to form nanogaps in single or few-layer graphene if certain prerequisites are met. This approach is related to the chemical reaction of carbon atoms of graphene with oxygen, and the process evolution is controllably performed using a feedback control system. In the first part of this work, a literature review is conducted on the graphene electroburning process, with a description of the main features and reasons for employing graphene as an electrode with its key characteristics. Additionally, the potential of graphene as an electrode is investigated through a study of its physical properties. Then, in its second part, the thesis focuses on the development of a feedback-controlled algorithm for the graphene electroburning-based nanogap formation. The algorithm is implemented in LabVIEW for an FPGA hardware platform. The system uses analog input voltage and analog output current modules with the FPGA-based controller and it is possible to achieve fast-speed feedback controlled algorithm with resolutions up to a few microseconds sampling rate. Then, using simulations in Synopsys' QuantumATK® software, the graphene electroburning process is analyzed in detail through the comparison of graphene nanoribbons with different atomic configurations and their properties such as current - voltage characteristics and transmission spectrum are reported to show the graphene as an electrode with different geometries and nanogap structures. The thesis findings are consistent with literature results from other groups, confirming the potential of electro-burned graphene electrodes as a reliable electrode for single-molecule electronics. Future works should focus on the testing and setup of the developed system on a real pre-patterned graphene sheet, addressing also higher sampling rates and time resolution.