Defect formation in a graphene overlayer on ruthenium under high pressure

Due to its highly corrugated moire structure and the nanometer modulation of its electronic properties, graphene deposited on ruthenium substrates (G-Ru for short) is a versatile playground for molecular deposition and chemical reactivity. Under local ultrahigh pressure conditions, one can expect an even richer behavior, reinforced by the likely appearance of defects. We have theoretically investigated the formation of such defects on G-Ru by using density functional theory methods. We show that defects can be produced in the high areas of the moire, either by generating reactive centers in graphene through the creation of vacancies or by modifying the relative carbon-ruthenium positions through conformational changes. The energetic cost to induce these defects is rather small, of the order of a few eV, so that defects are expected to appear when impacting a STM tip or applying high pressure by a diamond AFM tip in these regions. The different types of defects can be clearly distinguished from each other in our simulated STM images.