Interaction of H and Li with epitaxial graphene on SiC: A comparative analysis by first principles study

Ever-growing energy consumption in the world fosters the development of innovative energy technologies for sustainable energy production and storage. In this view, monolayer epitaxial graphene grown on 4H-SiC (MLEG/SiC) may be considered as a potential component of energy-related systems. The current paper deals with modelling of adsorption, diffusion and intercalation of hydrogen and lithium using MLEG/SiC model encompassing 2 x 2 graphene on root 3 x root 3R30 degrees surface reconstructed nine-bilayer 4H-SiC. The obtained results demonstrate a strong and stable chemisorption of hydrogen on top site of epitaxial graphene with limited surface mobility, while lithiation process occurs via formation of LiC6 phase. The stages of hydrogen and lithium intercalation beneath graphene are studied in detail by performing potential energy scan. Energetic preferences for MLEG/SiC with intercalated hydrogen and lithium atoms versus MLEG/SiC with top-adsorbed H and Li are revealed. Li intercalant-induced complete decoupling of the buffer layer from the SiC substrate followed by the formation of bilayer graphene with inequivalent doping per layer is proposed as an explanation of experimentally observed Raman G peak splitting in electrochemically lithiated epitaxial graphene on 4H-SiC. This work provides deep insights into the nature of atomic-scale processes at epitaxial graphene, which is essential for improving performance of energy-related devices.Funding Agencies|Angpanneforeningens Forskningsstiftelse [16-541, 21-112]; VetenskapsradetSwedish Research Council [2018-04962]; Stiftelsen for Strategisk Forskning [RMA 15-0024]