## 3 Results and Discussion
### Comparison between Buffer Layers Grown on \(n\)-Type and SI 4H-SiC  
A comparison of the Raman spectra of buffer layers on \(n\)-type and SI 4H-SiC obtained at \(T_{\rm Ar}\) = 800 \({}^{\circ}\)C is presented in Figure 5a. The Raman spectrum of the buffer layer grown on n-type substrate displays D\({}_{\rm BL}\) (around 1330 cm\({}^{-1}\)) and G\({}_{\rm BL}\) (around 1580 cm\({}^{-1}\)) bands with similar intensities. The latter is slightly asymmetric due to a band at around 1530 cm\({}^{-1}\) (see also Figure 2). Such Raman spectrum is typical for carbon-rich graphitic clusters bonded to SiC [27] and can be associated with a large degree of disorder [47]. On the other hand, the buffer layer grown at the same conditions but on SI substrates exhibits blue shift of the D\({}_{\rm BL}\) and the G\({}_{\rm BL}\) bands, and the band at around 1530 cm\({}^{-1}\) becomes more pronounced. These are typical vibrational characteristics of a well-connected buffer layer domains [4]. Further information about disorder and the content of \(sp^{3}\) hybridization can be obtained from the histograms of the G\({}_{\rm BL}\) band position (Figure 6a,c) and the ratios of the D\({}_{\rm BL}\) and G\({}_{\rm BL}\) bands areas, \(A_{\rm D_{\rm BL}}/A_{\rm G_{\rm BL}}\), (Figure 6b,d). The G\({}_{\rm BL}\) band energy changes from 1583 cm\({}^{-1}\) to 1606 cm\({}^{-1}\) and the \(A_{\rm D_{\rm BL}}/A_{\rm G_{\rm BL}}\) changes from 2.0 to 1.3 comparing the buffer layers grown on \(n\)-type and SI substrates, respectively. A similar trend is also found for the case of \(T_{\rm Ar}\) = 1300 \({}^{\circ}\)C (Figure 6e,g). According to the amorphization trajectory presented for nano-crystalline graphite in Ref. [48], these changes can be associated with a significant reduction of the \(sp^{3}\) hybridization content for the case of the SI 4H-SiC. The \(A_{\rm D_{\rm BL}}/A_{\rm G_{\rm BL}}\) is further related to the degree of disorder introduced by the presence of \(sp^{3}\) defects, which is proportional to the average distance between the defects [47]. Accordingly, the density of defects in the buffer layer grown on the SI substrate is 46% lower and the crystallite size is 35% larger. Again, very similar trend is found for the buffer layer with \(T_{\rm Ar}\) = 1300 \({}^{\circ}\)C (Figure 6f,h). The observed differences between the two types of substrates could be understood considering the fact that electron concentration generally enhances thermal conductivity. Hence, temperature variations should occur slower for the SI substrates during the heating up, bringing the graphitization process closer to thermodynamic equilibrium and allowing the formation of a well-connected buffer layer with a lower density of defects. It is interesting to note that the vibrational features of the buffer layer formed underneath MLG, grown at \(T_{\rm gr}\) = 2000 \({}^{\circ}\)C for 0 s, (Figure 5b) become even finer and bear closer resemblance with the buffer vibrational density of states [42]. Note that the spectral features are identical for the buffer layers on conductive and SI substrates. This further highlights the important roles of the carbon-rich environment and the high temperature for the formation of high-quality buffer layer. Comparing the buffer layers grown on \(n\)-type substrates and different \(T_{\rm{Ar}}\), a moderate blue-shift of the G-like band position for \(T_{\rm{Ar}}\) = 1300 \({}^{\circ}\)C to 1593 cm\({}^{-1}\) with respect to the sample with \(T_{\rm{Ar}}\) = 800 \({}^{\circ}\)C (1583 cm\({}^{-1}\)) can be seen (Figure 6a,e). This can be explained by a reduced \(sp^{3}\) hybridization content as expected due to the higher temperature at which the reconstruction occurs. At the same time, the \(A_{\rm{D_{BL}}}/A_{\rm{G_{BL}}}\) increases from 2.0 to 2.7 (Figure 6b,f), which could be related to a reduced crystallite size with 30%. This finding is in accordance with our \(\mu\)-LEED results showing that the buffer layer with \(T_{\rm{Ar}}\) = 1300 \({}^{\circ}\)C has just begun to form.