## 4 Discussion  
Both the pressure and the microwave power applied during the growth of N-UNCD films, using the MPCVD growth process, are critical for the incorporation of N atoms in the N-UNCD film. The gas pressure and microwave power, applied during N-UNCD films growth, influence substantially the temperature of the substrate during film growth, which is critical for efficient N atoms incorporation into the films' grain boundaries, as shown by the data in Figures 4 and 5. The results show that a minimum pressure of 80 mbar is required at a power of 4500 W to obtain a relatively high electrical conductivity in the N-UNCD films. The temperature of the substrate during growth increased, directly proportional to the gas pressure and microwave power, which induce increase of the substrate surface temperature to a maximum value of -880 \({}^{\circ}\)C for the N-UNCD film grown at 100 mbar and 4500 W, correlated to N-UNCD films with the highest electrical conductivity. Thus, the data obtained in the R&D reported here, indicate that 100 mbar and 4500 W provide currently, the optimum parameters combination to produce N-UNCD films with the highest electrical conductivity, until now. The presence of N atoms, in the N-UNCD films was detected using XPS analysis. The XPS spectra showed that the N is peak intensity increases, correlating with an increase in electrical conductivity for up to 5 orders of magnitude, compared with the resistivity of insulating UNCD films, indicating that N atoms incorporation in the grain boundaries of UNCD films produces the electrically conductive of the N-UNCD films [5; 6]. The development of optimized corrosion resistant/electrically conductive N-UNCD films may provide a key application as Lithium (Li)-corrosion resistant coating on anodes and cathodes for Li-ion batteries (LIBs). The N-UNCD coating on the LIBs' electrodes would protect them from corrosion by Li ions, which are substantially responsible for the degradation of the specific energy after charge/discharge cycles of LIBs. In fact, preliminary experiments performed recently by [PERSON] and colleagues, demonstrated that LIBs with commercial natural graphite (NG)/copper anodes coated with unoptimized N-UNCD films, exhibit practically no degradation in specific energy after about 100 charge/discharge cycles [19; 20]. On the contrary, commercial LIBs with uncoated NG/Cu anodes exhibit substantial reduction in specific energy after the same 100 charge/discharge cycles [19; 20]. In addition, the same preliminary work demonstrated  
Figure 5: Electrical measurements for N-UNCD films grown at different total pressures at 4000 and 4500 W.  
that the N-UNCD coating can eliminate the uncontrollable development of the solid electrolyte interface dendritic layer (known as SEI layer) [19] at the anode/electrolyte interface. The SEI layer is largely responsible for the degradation in capacitive energy of LIBs [21] and also is the main contributor to anode overheating and potential subsequent explosive failure [21], as it occurred in a LIB powering a Samsung cell phone in a plane in 2016, resulting in a billion US dollar loss. Therefore, development of optimized N-UNCD coating may have a transformational positive impact in the development of a new generation of LIBs with \(\geq\)10 longer charge/discharge life and order of magnitude safer.