## 3 Results  
The N-UNCD films were characterized by X-ray diffraction (XRD), using a Rigaku diffractometer (Ultima III, Cu K\(\alpha\) radiation, 1.524 A), scanning electron microscopy (SEM, Zeiss- SUPRA-40) -Thornwood-New York, X-ray photoelectron spectroscopy (XPS-PHI 5000 Versa Probe II-ULVAC), and, Raman spectroscopy (Thermo Scientific-DXR, 532 nm wavelength LASER Beam). XRD, SEM, XPS, and Raman analysis were done to determine the films crystalline structure, morphology, film thickness, grain boundary structure, and to confirm the presence of N atoms, respectively. Four-point probe measurements were done to determine the electrical conductivity of the N-UNCD films grown through different conditions and correlate it with the characterized properties provided by the analytical techniques described above. Figure 1 shows the XRD analysis results from the series 3 N-UNCD films, wherein for all N-UNCD films the preferential orientation correspond to the diamond (111) planes. This measurement was performed in a 2 Theta configuration. The XRD diffractograms show only the peaks attributed to diamond at 43.9\({}^{\circ}\) (111), 75.4\({}^{\circ}\) (220) and 91.7\({}^{\circ}\) (331), indicating that the films are composed mostly by sp3 diamond-type bonded C atoms without any graphite phase, as determined using specific software [12]. Table 2 shows the calculated grain sizes of the N-UNCD films (using the Scherrer-Debye equation), resulting in estimated grain sizes of 7 to 9 nm for all cases, consistent with the N-UNCD grain sizes reported in prior work for N-UNCD films produced by MPCVD [4]. \begin{table}
\begin{tabular}{c c c} \hline
**Serie 1 (3000 W)** & **Serie 2 (4000 W)** & **Serie 3 (4500 W)** \\ \hline
70 mbar & 70 mbar & 70 mbar \\
80 mbar & 80 mbar & 80 mbar \\
90 mbar & 90 mbar & 90 mbar \\
100 mbar & 100 mbar & 100 mbar \\ \hline \end{tabular}
\end{table} 
Table 1: Experimental series and the corresponding growth parameters. Figure 2a-c show SEM micrographs (top view and cross section) of N-UNCD films grown at different total pressures, using the same microwave power, revealing smooth morphology composed of many agglomerates as is expected for N-UNCD films [1,4]. The SEM cross section images show film thicknesses of 550, 480, and 200 nm for the N-UNCD films grown at 80, 90, and 100 mbar with 4500 W power, respectively. This indicates that the growth rate decreases as the pressure increases. The N-UNCD films thickness decrease as a function of growth pressure could be due to a reduction in arrival of C2 dimers and CHx radicals-growth species, due to collision with other molecules and atoms in the plasma, and reduction in plasma area, which occurs as the \begin{table}
\begin{tabular}{c c c} \hline \hline
**Pressure (mbar)** & **FWHM (\(\mathbf{\theta}\))** & **Grain Size (nm)** \\ \hline
70 & 1.20 & 7 \\
80 & 1.23 & 7 \\
90 & 1.11 & 8 \\
100 & 0.93 & 9 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Grain sizes of N-UNCD films vs. film growth pressure. Figure 1: XRD diffractograms for N-UNCD films grown at different total pressures, keeping the microwave power constant at 4500 W.  
Figure 2: SEM top view and cross section images of N-UNCD films grown at: (**a**) 80 mbar and 4500 W, (**b**) 90 mbar and 4500 W, (**c**) 100 mbar and 4500 W.  
total pressure increases, resulting in the substrate not getting fully covered by the plasma at high pressures. Figure 3 show the XPS spectra, for: (a) N 1s peak observed from N-UNCD films grown at different total pressures, using the same microwave power; (b) N 1s peak and (c) C 1s peak for N-UNCD film grown at 100 mbar and 4500 W. Two peaks form the C 1s signal, as indicated by in situ XPS computer simulation, showing peaks at 284.4 and 285.5 eV. The peak at 285.5 eV is attributed to carbon atoms with the sp3 bonds of diamond [13], while the peak at 284.4 eV is due to Argon atoms incorporation in the diamond lattice as a byproduct of cleaning the sample of surface contaminants with Ar+ ion bombardment prior to XPS analysis [14].