# Formation of Micro- and Nano-Trenches on Epitaxial Graphene
## 3 Results and Discussions
As shown in the lower part of Figure 4a, elemental analysis (EDS) is conducted to prove Ag particles which is measured from the red point marked in Figure 4a. Figure 4b shows the Raman spectra detected from each site, and a big difference can be distinguished. On region (B\({}_{1}\)) covered by Ag films without any sliding, it exhibits the classical Raman peaks of EG located at \(\sim\)1350 cm\({}^{-1}\), \(\sim\)1590 cm\({}^{-1}\) and \(\sim\)2700 cm\({}^{-1}\). The enhanced intensity around 1200 cm\({}^{-1}\) to 1800 cm\({}^{-1}\) represents the surface enhanced Raman spectra (SERS) by Ag particles, which is commonly observed [39; 40; 41]. There are big difference inside trench (A\({}_{1}\)) and on Ag trench head (C\({}_{1}\)). Raman peaks of graphene nearly disappears inside trench, only showing fairly weak Raman peaks of SiC substrate. The Raman peak on Ag trench head exhibits a typical structure of diamond-like carbon (DLC), which means amorphous carbon (\(\alpha\)-C) is merged into Ag particle [42; 43]. The difference of Raman spectra rightly demonstrates that graphene sheets can be damaged during the sliding of Ag particles. Carbon atoms can transform to amorphous carbon and merge into Ag particles. Figure 4c,d display the similar phenomenon on In/EG system. As shown in Figure 4c, inside trench, In particles without sliding and the trench head are also marked by A\({}_{2}\), B\({}_{2}\) and C\({}_{2}\), respectively. As shown in the lower part of Figure 4c, EDS analysis measured from the red point marked in Figure 4c can prove In particles on EG sheets. As shown in Figure 4d, normal Raman feature of EG is observed on the region of In particles without sliding. The Raman spectra of A2 and B2 do not differ strongly between each other. The peaks located at 1550 and 1700 cm\({}^{-1}\) in A2 and B2 are related to the SiC substrate. Different from Ag particles, there is no enhanced intensity observed in In/SiC system due to special metals for SERS detection. hence, the graphene peaks are weak, and the 1350 cm\({}^{-1}\) peak is very close to the noise threshold, it is not clearly visible in either A2 and B2 spectrum. But, the graphene peaks in A2 spectrum is much weaker than that in B2 one, which also indicates the damage influence of sliding In particles to EG sheets. Therefore, the sliding behavior of metal particles on EG is only motivated by high vacuum annealing resembles the catalytic etching effect, by which EG can be easily patterned. It is also found that the EG layer tends to be etched by the metal particles in the process of long time annealing in UHV, and nano-trenches are formed. Figure 5a,b displays the macro-morphology of EG, on which all the metals have been evaporated. Meanwhile, there exist a narrow channel originating from the edge of pits. It is deduced that EG has been scratched and broken by the sliding metal particles even during long term annealing (more than 24 h). The etching always happens at the high energy sites of edges and defective points. Figure 5c shows an enlarged image of one etched channel, and Figure 5d shows the atomic structure of the etched channel zoomed in from the green square in Figure 5b. As exhibited by the height profiles in Figure 5e,f acquired from the  
Figure 3: (**a**) The morphology of EG under optical microscopy. (**b**) Raman mapping of 2D-band measured from the dashed black rectangle region in (**a**). green lines in Figure 5c,d, the depth of the channel is about 0.5 nm, consistent with the interlayer distance of graphene. Meanwhile, the edge region is higher than the flat EG, indicating the edge structure caused by the broken of EG sheet. As shown in Figure 5d, there exist interference scattering patterns along the channel [44], meaning that a broken of continuity of EG layer and new edge has been formed. The profile heights and the atomically resolved structures prove that only the top EG layer has been etched.