# Structure and Electrical Properties of Carbon-Rich Polymer Derived Silicon Carbonitride (SiCN)
## 3 Results and Discussion  
### Investigation of the Carbon Phase  
Previous studies have shown that polysilazane-derived amorphous SiCN ceramics pyrolyzed at 900-1100 \({}^{\circ}\)C consist of mixed Si\({}_{x}\)C\({}_{y}\)N\({}_{x}\) bond and free carbon [35]. At a higher ceramization temperature (above \(\sim\)1350 \({}^{\circ}\)C), however, the microstructure evolves into crystalline nanodomains made up of SiC, Si\({}_{3}\)N\({}_{4}\) and C with the sp\({}^{2}\) hybridized carbon phase playing a major role in influencing the functional properties of the SiCN material [35, 36, 37]. The microstructural evolution of the sp\({}^{2}\) hybridized carbon phase in the prepared carbon-rich SiCN samples was investigated using Raman Spectroscopy. The primary signals of the Raman spectra showing the carbon phase are the D and G bands identified at \(\sim\)1350 cm\({}^{-1}\) and \(\sim\)1582 cm\({}^{-1}\), respectively, for the monoliths (see Figure 1a-c), but the secondary signals include prominent overtones and combination bands which are the 2D (or G'), 2D', T + D and D + G bands in the range of \(\sim\)2500-3250 cm\({}^{-1}\)[38,39]. A D' band (at \(\sim\)1500 cm\({}^{-1}\)) and T (\(\sim\)1200 cm\({}^{-1}\)) band which relate to amorphous carbon fractions and sp\({}^{2}\)-sp\({}^{3}\) C-C/C=C bonds respectively revealed in the monoliths are other two crucial bands that often stretch from the G and D band shoulders most especially shown in amorphous materials. The D' and T bands are prominent in the amorphous SiCN monolith samples produced at the pyrolysis temperature of 1100 \({}^{\circ}\)C. In the sample annealed at 1600 \({}^{\circ}\)C, a signal at ca. 820 cm\({}^{-1}\) was identified and assigned to \(\beta\)-SiC. In general, the peak position, width, intensities and overlapping Raman spectra give useful details on the structural evolution, defects and crystallite size of the graphitic carbon phase. The D band is a defect-prompted band that results due to a corresponding disorder (amorphization) from carbon nanostructure while the G band is formed by the internal stretching of highly ordered sp\({}^{2}\) hybridized carbon lattice [9,40,41]. At the temperature of 1100 \({}^{\circ}\)C, the D and G bands of the samples are seen to overlap which complicates separation of the profiles but at a temperature of \(\geq\)1400 \({}^{\circ}\)C, overlapping of the D and G bands has been greatly reduced (see Figure 1a-c). Moreover, Lorentzian fitting of the Raman bands was performed in order to extract information about the structural evolution of the carbon phase at elevated temperatures; and the rising intensities of the 2D band noticed in the prepared samples with an increase in temperature from 1100 \({}^{\circ}\)C to 1600 \({}^{\circ}\)C is an important indicator of the rising crystallinities of the graphitic nanostructure. The lateral size of sp\({}^{2}\) hybridized carbon, L\({}_{a}\), used to characterize the width of the graphitic crystallite of the samples along the a-axis, was determined using Equation (1) [42, 43, 44]. Where \(A_{D}\)/\(A_{G}\) is integrated intensities ratio of the D and G bands and \(\Lambda\) is the laser line wavelength (514 nm). \[\mathrm{L}_{a}=\left(2.4\times 10^{-10}\right)\ \Lambda_{L}^{4}\left(\frac{A_{D}}{A_{G }}\right)^{-1} \tag{1}\]The consistency of the integrated intensities ratio and its importance in the observation of the quantum Hall effect in graphitic materials for the design and fabrication of target electronic systems have been discussed in various studies [42, 43, 45]. The dependence of the lateral crystal size, L\({}_{a}\), of the graphitic nanostructure of the samples on the integrated intensities of the D and G bands, as well as its reliance on the thermal treatment, is presented in Figure 2a.