# Room-Temperature Formation of Hard BC\({}_{\rm x}\) Films by Low Power Magnetron Sputtering
## 2 Materials and Methods
### Characterization Techniques  
Morphological examinations of film surfaces and elemental compositions were conducted by field-emission scanning electron microscope (FE-SEM) JEOL ISM 6700F equipped with an EX-23000 BU analyzer for elemental composition determination by X-ray energy dispersive spectroscopy (EDX). During the EDX measurement, the field emission electron gun (W) was operated at an energy of 3 keV (radius of the excitation volume \(\sim\)0.1 \(\mu\)m) and at a current of 1 nA according to the results of our previous study [44]. The X-ray detector EX 64165]NH has a resolution of 133 eV at the Mn K\({}_{\alpha}\) line (5.9 keV) at a count rate of 2000 cps (measuring time: 200 s) yielding a dead time loss of about 18%. The spectra were evaluated using the \"Analysis Station 3.30.06\" program from JEOL Engineering Co., Ltd. using ZAF correction (Z-atomic number, A-absorption, F-fluorescence). Structure investigations were carried out using a Shimadzu XRD-7000 diffractometer (CuK\({}_{\alpha}\) radiation, Ni filter, 20 range: 5-60\({}^{\circ}\), 20 step: 0.03\({}^{\circ}\), accumulation: 1 s). The examination of the types of chemical bonds and composition of the films was performed by Fourier transform infrared (FTIR), Raman, and X-ray photoelectron spectroscopy (XPS). \begin{table}
\begin{tabular}{c c c c} \hline
**Series** & **Sample** & **B\({}_{4}\)C Target Power, W** & **C Target Power, W** \\ \hline \multirow{6}{*}{A} & A50 & 50 & – \\  & A75 & 75 & – \\  & A100 & 100 & – \\  & A125 & 125 & – \\  & A150 & 150 & – \\  & B75 & 150 & 75 \\  & B100 & 150 & 100 \\ \hline \end{tabular}
\end{table} 
Table 2: Experimental conditions for magnetron sputtering of samples. The FTIR absorption spectra of the films were recorded using a SCIMITAR FTS 2000 spectrometer in the wavenumber range of 375-4000 cm\({}^{-1}\). The FTIR equipment has a Duraglow light source, KBr beam splitter, and DTGS Peltier cooling element as a detector. Thirty-two scans and an aperture equal to 4 at an achievable resolution of 2 cm\({}^{-1}\) were used during the measurements. In each case, the background spectrum of the Si substrate was subtracted from that of the sample. For the comparison of bonding density in all the FTIR spectra, the absorbance was normalized to the thickness of the appropriate film. Raman spectra were recorded on a LabRAM HR Evolution Horiba spectrometer equipped with a multichannel CCD detector cooled with liquid nitrogen. The spectra were excited by a 632.8 nm He-Ne laser line with a power of about 1 mW on the sample surface. The spectral resolution of the spectrometer was established in the range of 2.4-3.8 cm\({}^{-1}\). XPS spectra were recorded on a photoelectron spectrometer ES-300 (KRATOS Analytical) in the constant energy transmission mode of an energy analyzer of photoelectrons. The radiation energy of nonmonochromatic AlK\({}_{\alpha}\) of 1486.6 eV was used to excite the photoelectron spectra. An Au4f\({}_{7/2}\) gold binding energy of 84.0 eV was used as a primary standard for the calibration of electron energies. For the analysis of the chemical state of the elements, the regions of the core levels of the elements B1s, C1s, O1s, N1s, and Si2p were surveyed with a scan interval of 0.1 eV. The spectra were deconvoluted by approximating the experimental curves by the Gauss-Lorentz functions. The thickness and refractive index of the films were determined by ellipsometry (LEF-3M ellipsometer) at the wavelength of 632.8 nm. The measurements were carried out at seven angles. Optical transmittance of the films was measured using a scanning spectrophotometer UV-3101 PC Shimadzu in the range of 190-2500 nm with a resolution of 2 nm. The study of the mechanical properties (hardness and Young's modulus) of the films was performed by nanoindentation measurements (according to ISO 14577) with a scanning nano-hardness tester NanoScan-3D at several loads in the range from 1 to 70 mN, with at least 10 indents being made for each load to reduce the effect of the random error.