# Room-Temperature Formation of Hard BC\({}_{\rm x}\) Films by Low Power Magnetron Sputtering
## 3 Results and Discussion
### Film Structure, Composition, and Bonding Types
The main peak of the A50 film spectrum can contain the contribution of B-O deformation vibrations that appeared at 1280 cm\({}^{-1}\), which correlated with the EDX data on oxygen presence. Also, the FTIR spectrum of this sample contains a weak peak at 2554 cm\({}^{-1}\) which corresponds to stretching vibrations of the B-H bond. The carbon-rich B75 and B100 samples prepared at  
Figure 3: B, C, and O elemental composition of boron carbide films versus RF power at B4C target. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Atomic Concentration, at.\%**} \\ \cline{2-4}  & **B** & **C** & **O** \\ \hline A150 & 66 & 30 & 4 \\ B75 & 51 & 44 & 5 \\ B100 & 27 & 68 & 5 \\ \hline \hline \end{tabular} Note: The absolute uncertainty of all values is \(\pm\) 5%.  
\end{table} 
Table 3: Elemental composition of dual-target sputtered samples of series B.  
dual magnetron sputtering (Figure 4b) also contain the broad absorption bands centered at 1230 and 1215 cm\({}^{-1}\), respectively. The Raman analysis of all the deposited BC\({}_{\rm x}\) thin films revealed no vibrational modes corresponding to boron carbide (Figure 5) [58; 59]. The Raman spectra of the carbon-rich samples of series B contain two broad bands corresponding to D and G modes of the amorphous carbon phase [60; 61]. Whereas the G band is associated with the E\({}_{\rm 2g}\) in-plane graphite Raman active mode, the D band is a breathing mode of the A\({}_{\rm 1g}\) symmetry of the sixfold ring. Moreover, these bands were shifted to the left; this shift can be observed for BC\({}_{\rm x}\) films due to amorphization and a decrease in the size of carbon particles [12]. It should be noted that the low intensity and broadening of the D and G bands indicate a strong carbon disordering. Thus, the carbon-rich samples contain carbon clusters. As noted above, according to the B-C phase diagram, solubility of carbon in B\({}_{\rm 4}\)C does not exceed 20 at.%. Therefore, carbon at higher concentrations should be expected to separate into an additional phase. On the other hand, there is information that this limitation is removed in amorphous boron carbide [62]. Despite the excess of carbon content compared with the permissible but not much higher (C = 25-30 at.%), the Raman spectra of the samples of series A did not show any peaks except for the Si substrate. The analysis of B1s, C1s, N1s, and O1s the XPS spectra decomposed into components provides more detailed information on the chemical structure of the samples. The XPS spectra of the deposited films were recorded in order to reveal the effect of the power supplied to the RF magnetron using dual-target sputtering. It should be noted that XPS  
Figure 4: FTIR spectra of samples of (**a**) series A and (**b**) series B.  
Figure 5: Raman spectra of boron carbide films. allows for the analysis of only \(\sim\)9 nm of the film surface. XPS measurements were carried out without preliminary surface chemical etching or Ar\({}^{+}\) sputtering to avoid preferential sputtering of B or C atoms. Therefore, the composition of the surface and the bulk material can be significantly different. Figure 6 shows the core level spectra of the B1s, C1s, and O1s of the A50, A150, and B75 films. The large width of XPS lines indicates a nonuniform chemical environment of boron and carbon atoms in the films. These peaks have complex structures and are superpositions of several components with different contributions. The spectra of A150 and B75 show identical components with various intensities. Peaks in the region of 188.6-189.6 eV can be attributed to boron bonded to carbon in BC\({}_{x}\). According to the literature data, the binding energies of B\({}_{4}\)C and BC\({}_{3,4}\) compounds are 188.4 eV and 189.5 eV, respectively [63]. For the A150 sample, the maximum amount of boron in the film was found, and an increase in the component with E\({}_{\text{b}}\) = 188.6 eV was observed. As the sputtering power is reduced, such a component is practically not observable in the XPS spectra.