## 5 Conclusions  
The experimental studies conducted allow some important conclusions to be drawn. It is obvious that regardless of how the silicon substrates are cleaned, a larger or smaller amount of native silicon oxide remains on their surface, depending on the treatment. Very often the thin film of mainly amorphous or nanocrystalline SiC (at short carbonization times 3-20 min) contains up to several mass percent impurities of C, O, Si-O, C=O, and Si-O-C. At long carbonization processes the thin films are mainly of crystalline SiC (3C-SiC or 39H-SiC) but also have impurities of C, O, Si-O, C=O, and Si-O-C. The crystal grain size determined by the Scherrer equation for the thin films obtained after carbonization for 60 and 90 min is about 7 nm and about 110 nm, respectively. Just below the thin film, in the volume of the Si substrates, as a result of the diffusion of C and O in the volume, a strongly enriched C and O region is formed, extending in depth from about 50 nm (at 3 min carbonization) to about 110-120 nm (at 90 min carbonization). In cases where the native oxide is not properly removed from the Si surface, the mixture is enriched with large amounts of Si-O/Si-O-C mixed phases of up to 25 mol% for substrates with non-removed native oxide. The significant diffusion of oxygen and carbon atoms into the bulk of the Si substrate makes the thin film/substrate interface indistinguishable and greatly complicates the determination of the thickness of the thin films by methods related to scratching the surface. However, the formation near the thin film/substrate interface in the Si- substrate, a region of highly enriched with C, O, Si-O, Si-O and Si-O-C species, is expected to compensate to some extent for the difference in the lattice parameters of SiC and Si as well as the difference in their thermal expansion coefficients and to suppress the formation of mechanical defects upon cooling of the samples. The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/app15137078/s1](https://www.mdpi.com/article/10.3390/app15137078/s1)]([https://www.mdpi.com/article/10.3390/app15137078/s1](https://www.mdpi.com/article/10.3390/app15137078/s1)). Figure S1: (a,b) Schematic representation of the experimental processes of carbonization of Si(111) substrates: (a) time distribution of the different gas flows, and (b) temperature regimes (blue trace) and the corresponding residual pressures in the reactor (red trace). Figure S2: (a-c) The XRD patterns obtained from samples C90 and O90, enlarged in the interval 20 = (30-31.5)\({}^{\circ}\), 20 = (35-40)\({}^{\circ}\) and 20 = (58-60)\({}^{\circ}\) (panels a, b and c, respectively). The reflections that can be ascribed to 36H-SiC [25] are indicated by the corresponding interplanar distances, while the reflections indicated by numbers should be related to 96R-SiC [26], as follows: 1 = d\({}_{(00-81)}\) and 2 = d\({}_{(00-80)}\). Strong reflections are associated with distances between crystal planes of 3.0217 A, 2.8328 A, 2.3244 A, and 1.5629 A, while the weak ones are associated with 2.9242 A and 2.5181 A, respectively. The reflection indicated by 3 is of unknown origin, but is very close to d\({}_{(015)}\)= 2.5636 A of 19H-SiC which possess trigonal symmetry (SG #156 P 3m1 and cell parameters a\({}_{0}\) = 3.0730 A, c\({}_{0}\) = 47.7530 A) [28]. (d) The XRD pattern obtained from sample C90, (@-20) scan, in the interval 20 = (35-76)\({}^{\circ}\) used for determination of the crystal grain size. The reflection used appears at 20 = 38.7\({}^{\circ}\) and corresponds to d\({}_{(00-39)}\) = 2.3244 A [25]. The estimated grain size is about 7 nm. (e) The XRD patterns in obtained from sample C60, (@-20) scan, in the interval 20 = (30-55)\({}^{\circ}\) used for determination of the crystal grain size. The pattern is indexed in cubic symmetry (SG #216 _F-43m_ and cell parameter a\({}_{0}\) = 3.3480 A [3] and the reflection used (at 20 = 35.8\({}^{\circ}\)) corresponds to d\({}_{(111)}\) = 2.5103 A. The estimated grain size is about 7 nm.