## 2 Materials and Methods  
We used one-sided polished Si(111) wafers (Wacker Chemie, Munich, Germany) with a diameter of 3 inches. The precursors for all processes were N\({}_{2}\) (99.999%), H\({}_{2}\) (99.999%), Ar (99.9999%), and CH\({}_{4}\) (99.9995%) (Linde Gas Bulgaria, Sofia, Bulgaria). The carbonization processes were performed via the CVD method in an Oxford Nanofab Plasmalab System 100 (Oxford instruments, Abingdon, UK) apparatus. All experiments at defined process parameters were conducted first with substrates with native oxide and then with substrates with removed native oxide, following the established protocols (e.g., [23; 24]). To verify the reproducibility of the CVD processes, the experiments were carried out at least two or three times with reproducible results. For the reduction of the native oxide in all experiments, the substrates were cleaned in Ar plasma at a temperature of 250 \({}^{\circ}\)C (Ar flow of 500 sccm, pressure of 3000 mTorr, power of 50 W, mid-frequency plasma at 13.56 MHz, and time of plasma etching of 10 min). Subsequently, all substrates were annealed in an H\({}_{2}\) atmosphere (flow of 500 sccm, pressure of 200 mTorr) at a temperature of 1150 \({}^{\circ}\)C for 5 min before the processes of the direct carbonization of the Si surface. All thermal processes were conducted in a vacuum of 200 mTorr (thermal annealing before the carbonization processes) or 300 mTorr (processes of heating, cooling, and carbonization). The heating process was carried out at a speed of about 600 \({}^{\circ}\)C/h with a break of 10 min at 250 \({}^{\circ}\)C for etching in Ar plasma in all cases. The carbonization processes were carried out by a thermally stimulated CVD process of methane (CH\({}_{4}\)) decomposition at about 1130-1140 \({}^{\circ}\)C and pressure of 300 mTorr in a gas mixture of H\({}_{2}\) (500 sccm) and CH\({}_{4}\) (10 sccm). The duration of the carbonization processes in the different experiments was 3, 5, 20, 60, and 90 min. After the carbonization, the reactor was allowed to cool naturally for about 15-18 h in a weak flow of Ar and H\({}_{2}\) gases. The experimental procedures for the carbonization processes are also presented graphically (Figure S1). The thickness of the films was measured with a TALYSTEP (Rank Taylor Hobson, Leicester, UK) profilometer and an atomic force microscopy (AFM), and the samples were scratched with an Ultra-High Strength Steel (UHSS) blade to access the thin film/substrate interface and to collect material for the TEM sample preparation. The AFM measurements were performed on the MFP-3D Origin (Oxford instruments, Asylum Research, Santa Barbara, United States Abingdon, UK) apparatus. The images were taken in a tapping mode. The measurements were carried out at steps of 20 \(\upmu\)m at scanning rates per line of 1.0 Hz and image resolution of 256 \(\times\) 256 points. Silicon probes with a cantilever length of 160 \(\upmu\)m and an Al reflective coating on the backside (AC160 TS-R3, Olympus, Hamburg, Germany) were used in the experiments. These probes had a nominal resonance frequency of the cantilever of 300 kHz and a typical force constant of 26 N/m. The nominal tip radius for these probes was 7 nm. Before the analysis, the images were flattened, and no further processing was performed. The image analysis was performed using Gwyddion 2.56. The ellipsometry measurements were performed using a Woollam M2000D (J.A. Woolam Co Inc., Lincoln, NE, USA) rotating compensator spectroscopic ellipsometer with a wavelength range from 193 to 1000 nm. The data acquisition and modeling software was CompleteEASE v.5.19 (J.A. Woollam Co., Inc.). SEM investigations were conducted using a LYRA TESCAN (SEM) (TESCAN GROUP a.s., Brno, Czech Republic) microscope in secondary electron image and backscattered electron image (SEI and BEI, respectively). Elemental analysis was performed by energy-dispersive X-ray analysis (EDX) at a Brucker QUANTAX 200 Spectrometer (Brucker Co., Elk Grove Village, IL, USA) unit.