## 3 Result and Discussion
### Structural Properties  
The structural analysis of CuO nanocoatings was evaluated from XRD spectra. Figure 5a-d shows the XRD patterns of CuO nanocoatings spin-coated on SS substrates at RS of 700, 800, 900, and 1000 rpm. The crystallographic orientations originated at 26 values of 32.6\({}^{\circ}\), 35.5\({}^{\circ}\), 38.6\({}^{\circ}\), 48.8\({}^{\circ}\), 53.5\({}^{\circ}\), and 58.2\({}^{\circ}\), respectively, corresponding to (110), (111), (111), (20\(\overline{2}\)), (020), and (202) planes of the monoclinic phase structure of CuO, and it is well-matched with the previous literature (according to the JCPDS card No. 80-1917) [44,45]. For all the obtained nanocoatings, characteristic of diffraction patterns at 20 values of 43.58\({}^{\circ}\) and 50.72\({}^{\circ}\) attributed to (111), and (200) planes of face centered cubic (fcc) of Chromium Iron Nickel (Cr0.19 Fe0.7 Ni0.11) (SS) substrate are observed (according to the JCPDS card No. 033-0397). The average crystalline size (D) of the coatings was calculated from [PERSON]'s formula, D = 0.9 \(\lambda\)/gcos\(\theta\), where \(\lambda\) is the wavelength, \(\beta\) is the full width at half maximum (FWHM) of the peak at the diffracting angle \(\theta\) by determining the width of (111) Bragg reflection [46] and found, respectively to be 76, 57, 44, and 36 nm at RS of 700, 800, 900, and 1000 rpm. The results are in agreement with the trend observed by SEM. As shown in Figure 5a-d, increasing RS results decrease in the intensity of the coatings, which confirms that the thickness, particle size, and crystallite size of the deposited coatings are decreased [39,47].  
Figure 4: AFM images of CuO nanocoatings (**a**) 700 rpm, (**b**) 800 rpm, (**c**) 900 rpm, and (**d**) 1000 rpm.  
The elemental composition of the green synthesized CuO nanocoatings deposited on SS substrates was analyzed by using the EDX technique. EDX of typical CuO nanocoatings with nanorod-like structures (as observed in SEM) are shown in Figure 6a-d. The EDX spectra reveal the presence of strong peaks attributing to Cu and O in the spectrum confirming the purity of CuO nanocoatings. The EDX spectra also show weak peaks of Fe and Cr originating from the SS substrate.  
The surface electronic states and elemental composition of CuO nanocoating on SS substrate were analyzed via X-ray photometry spectroscopy (XPS) and the results displayed in Figure 7 are associated with 700 rpm. The wider scan spectra of CuO nanocoating confirm the presence of Cu, O, C, Ca, N, and Na elements. The high resolution of XPS spectra of Cu2p shows two peaks of Cu 2p\({}_{1/2}\) and Cu 2p\({}_{3/2}\) at 953.15 and 933.72 eV binding energy, respectively, atypical characteristic peaks of Cu (II) for CuO. The binding energy of Cu2p\({}_{1/2}\) and Cu2p\({}_{3/2}\) are separated by 20 eV, essentially identical binding energies of Cu2p of Cu(II). The satellite peak at 944.13 eV confirms the presence of paramagnetic chemical states of Cu2+. From XPS spectra a peak with low intensity centered at 932.62 eV binding energy is associated to Cu1+. As demonstrated in Figure 7, the corresponding XPS spectra O in CuO reveals two-peaks, indicating that there are two-oxygen states. The peak at 529.30 eV binding energy corresponding to the metal-oxygen (M-O) lattice confirms the formation of CuO [48; 49; 50]. Among them, the C element might derive from impurities on the surface of samples.  
Figure 6: EDX spectra of CuO (**a**) 700 rpm, (**b**) 800 rpm, (**c**) 900 rpm, and (**d**) 1000 rpm.