# Epitaxial Graphene on 4H-SiC (0001) as a Versatile Platform for Materials Growth: Mini-Review
## 3 Deposition of Noble Metals on Epitaxial Graphene/4H-SiC by dc Magnetron Sputtering
Copyright 2021 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany. Figure 7: (Top view and side view) The optimized geometrical structures of gold (**a**) and silver (**b**) adatoms adsorbed onto monolayer epitaxial graphene. Blue, brown, and whitish balls designate Si, C, and H atoms, respectively. Yellow and gray colors correspond to gold and silver, respectively. This figure has been adapted with permission from [49]. Copyright 2021 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, Germany. Further increase in the nominal thickness of Ag initially led to the appearance of elongated islands (Figure 9b), followed by the formation of an interconnected network (Figure 9c,d) and a continuous silver layer at a thickness of 30 nm (Figure 9e). Careful analysis of defect-related Raman modes of epitaxial graphene after silver deposition enabled the estimation of the density of generated defects and elucidate their nature [47]. It was revealed that the \(D/G\) intensity ratio is very sensitive to alternation of the silver thickness (Figure 10a-d), demonstrating obvious enhancement with increasing of Ag-layer thickness. Figure 10: SEM images of MLG-supported silver films of different thickness: (a) 2 nm, (b) 5 nm, (c) 10 nm, (d) 15 nm, and (e) 30 nm, (f) Mutual correlation between D/G amplitude ratio on D’/G amplitude ratio for epitaxial graphene after deposition of Ag films with different thicknesses, respectively [47]. Copyright 2019 Elsevier B.V., Amsterdam, Netherlands. Figure 9: SEM images of MLG-supported silver films of different thickness: (a) 2 nm, (b) 5 nm, (c) 10 nm, (d) 15 nm, and (e) 30 nm, respectively [47]. Copyright 2019 Elsevier B.V., Amsterdam, Netherlands. Such behaviour implies two important consequences: (i) reduction in domain size in graphene (Figure 10e) and (ii) increase in density of defects up to 9.5 \(\times\) 10\({}^{11}\) cm\({}^{-2}\) for 15 nm-Ag-decorated epitaxial graphene. The peculiar dependences of \(D/G\) amplitude ratio on \(D^{\prime}/G\) amplitude ratio (Figure 10f) for all considered films suggest that the boundary-related defects are preferential defects in the MLG decorated with 2-10 nm Ag films while \(sp^{3}\)-type defects dominate in the case of 15 nm-Ag-covered MLG. It was also shown that the magnetron-sputtered 2 nm- and 5 nm-Ag layers donate electrons to epitaxial graphene, giving rise to a large area uniform \(n\)-doping of epitaxial graphene (0.95-1.36 \(\times\) 10\({}^{13}\) cm\({}^{-2}\)) [48], which is manifested by huge red-shift of 2\(D\) peak and a very narrow spread of experimental data points in 2\(D\)-\(G\) space. Concomitantly, the deposition of thicker Ag films (10 and 15 nm) caused large strain and doping fluctuations. Deposition of Metals (Copper, Lead, Mercury, Lithium) on Epitaxial Graphene/4H-SiC by Electrolating  
In addition to the dc magnetron sputtering technique, we also employed electrochemical deposition to investigate the early nucleation stages of several selected metals (lead, copper, and mercury) on epitaxial graphene [50; 51; 52]. Pb and Hg have been of interest related to toxic metal detection, while Cu attracts a lot of attention as a promising catalyst. A Three-electrode electrochemical cell made of epitaxial graphene as a working electrode, platinum wire as a counter electrode, and an underlying base for the silver-silver chloride reference electrode was designed to perform electrochemical tests. The fundamental mechanism behind this method is a reduction in metal ions at specific potential from different electrolyte solutions on the surface of the epitaxial graphene. The technological maturity of this technique and its simplicity makes it possible to grow ultrathin metal layers under room-temperature conditions quickly, the latter being a big advantage from a practical point of view. Recently, the important role of graphene in minimizing lattice strain and providing conditions for reversible electrodeposition of high-quality metal plates parallel to the electrode has been reported [53]. This is another example suggesting the usability of this method.