Manipulation of epitaxial graphene towards novel properties and applications

The integration of epitaxial graphene on 4H-SiC with different metals may allow tunability of electronic and optical properties of graphene, enabling novel high-performance devices. Here we present a Raman spectroscopy study on epitaxial graphene decorated with electrodeposited Pb and Li adatoms and with magnetron sputtered 5nm-thick Ag nano-island films. We find that the presence of metals on the epitaxial graphene surface generates defects and induces n-type doping, which is evidenced by the observation of the defect related Raman modes (namely D, D′ and D+G) and systematic red-shift of the main characteristic modes of graphene. In-depth statistical analysis of the Raman data before and after metal deposition complemented by density functional theory (DFT) calculations allowed to link the interaction strength between the three selected metals and graphene with the metal-induced changes in the vibrational/electronic properties of graphene. Large-area uniform electron doping of epitaxial graphene and surface-enhanced Raman scattering (SERS) effect are reached by room temperature deposition of Ag nano-island films. Very promising results have been obtained from graphene subjected to electrochemical intercalation by Li, which can serve as prerequisites of the construction of Li batteries. The strong interaction between Li or Pb with graphene implies the possibility to exploit the epitaxial graphene as an efficient material for energy storage or for heavy metal sensing, while predominant van der Waals interaction between Ag and graphene favors the formation of extremely thin silver coatings towards two-dimensional metal systems. The present results give better understanding of the nature of epitaxial graphene response to metal deposition and can be useful to design high-performance energy storage devices, optical sensors and heavy metal detection systems.