# Structural Modifications in Epitaxial Graphene on SiC Following 10 keV Nitrogen Ion Implantation
## 3 Results  
### Afm  
The pristine and nitrogen ion-implanted EG at \(1\times 10^{14}\) ions/cm\({}^{2}\) fluence is shown in Figure 1a,b which are Atomic Force Microscopy (AFM) phase images obtained at scan areas of 10 \(\upmu\)m \(\times\) 10 \(\upmu\)m. The pristine graphene is dominantly covered with monolayer graphene (ML) and bilayer (BL) graphene (darker areas) as depicted in Figure 1a. The thickness of graphene was obtained using optical reflectance mapping. Figure 1b shows changes in the surface morphology following ion implantation which resulted in fragmentation of the ML graphene shown by white arrows. Figure 1c is the phase image and Fig 1d is height image of the sample implanted at the highest fluence (\(1\times 10^{14}\) ions/cm\({}^{2}\)) showing presence of dot like structures (shown with black arrows) referred as \"nanostructures\". Their diameters are estimated from software Nanoscope III (V5.3) (Digital Instruments/Vecco Metrology group, Plainview, NY, USA) to be between 40-70 nm and the heights of around 0.8-1.2 nm. Figure 1: Atomic force microscopy (AFM) phase images of (**a**) pristine and (**b**) N\({}^{+}\) ion-implanted epitaxial graphene (EG) on SiC at \(1\times 10^{14}\) ions/cm\({}^{2}\) fluence over a scan area of 10 \(\upmu\)m \(\times\) 10 \(\upmu\)m with white arrows showing fragmentation of Monolayer (ML) graphene; (**c**) phase and (**d**) height image of N\({}^{+}\) ion-implanted EG on SiC at \(1\times 10^{14}\) ions/cm\({}^{2}\) fluence over scan area 2 \(\upmu\)m \(\times\) 2 \(\upmu\)m with black arrows showing presence of nanostructures. At the elastic impact of the energetic ions on the atoms of the material, i.e., in case of nuclear energy loss, the atoms of the material are dislocated from their initial sites in the lattice when the transmitted energy is higher than the displacement threshold energy. The minimum energy required for displacing a single C atom in graphene is 22.2 eV [28]. The minimum lattice displacement energy for the C atom is 20 eV and the Si atom is 35 eV in SiC [29]. In this case, the energy of the incident energetic ions (nitrogen ions) is much more than the energy required for displacing C atoms in graphene and Si and C atoms in the SiC lattice. This resulted in creation of C and Si Frenkel defects. Further, if the surface binding energy required by the atom to bind to the solid surface is lower than the incident energy of the ions, then the atom can be sputtered. In SiC, the surface binding energy was reported to be 7.4 eV for C and 4.7 eV for Si [30]. As the transferred energy is greater than the surface binding energy and the displacement threshold energy of Si and C atoms, it likely results in both displacement and sputtering of target atoms. We estimated the electronic energy loss (Se) and the nuclear energy loss (Sn) by the SRIM software for N\({}^{+}\) ion implantation in EG on SiC, and the results are tabulated in Table 1. It was found that in N\({}^{+}\) ion implantation, Sn dominates as compared to Se. The projected range for N\({}^{+}\) ion implantation is 10.4 nm along with a longitudinal straggling of 3 nm. This shows that most of the damages are generated due to the ion implantation are settled not in the graphene layer, but into the SiC substrate. In this work, defects in graphene are recognized as direct and indirect defects. Direct defects are referred to as defects that arise by the direct impact of the incident ions with C atoms of graphene. Indirect defects are the defects that are created by the impact of the substrate atoms on the C atom of graphene. During the process of collision of incident ions with the substrate atoms, the substrate atoms are sputtered. The sputtered substrate atoms further undergo collision with the C atom of graphene and remove the C atom from the graphene lattice. This process of defect generation in graphene is referred to as indirect defects [6].