Structural and electrical characterization of graphene after ion irradiation

Graphene is a recently discovered material consisting of a two-dimensional sheet of Carbon atoms arranged in an hexagonal pattern. It is a zero-gap semimetal whose electrical properties can be tuned by controlled induction of defects such as vacancies. In his work, graphene flakes were produced with the standard method of mechanical exfoliation. Afterward, we have used light optical microscopy (LOM), atomic force microscopy (AFM), Raman spectroscopy and in-situ electrical measurements to investigate the changes in structural and electrical properties after defect introduction by ion irradiation. The ion bombardment was performed with two different systems, a focused ion beam at the Microstructure laboratory and an ion accelerator at the Tandem laboratory, both at Uppsala University. The main goal of the work was to develop and test a contacting scheme for the graphene flakes that would allow us to perform in-situ I-V measurements during defect insertion. In this respect, the project was a success. The different characterization techniques yielded different types of information. LOM is useful as a first screening to identify the graphene candidates; Raman spectroscopy can provide information on both the flake thickness (mono-layer or multi-layer) and on the defect density, although the latter only qualitatively. The AFM analysis did not give significant results as it could not unambiguously discern any sign of ion impact neither on the graphene flakes nor on the substrate.