## 3 Results and Discussion  
Figure 1 shows the electrospray deposition process for synthesizing AZO TF and AZO-RGO NCTF. The precursor solution with or without GO is sprayed on the heated substrate, and the TF could be simply obtained on the SiO\({}_{2}\)/Si substrate. The TF samples are followed by the RTA process for crystallization of AZO as well as the reduction of GO. Figure 2a represents the XRD patterns of the AZO TF and AZO-RGO NCTF. The strong peaks at 56.13\({}^{\circ}\) could be indexed to Si(311) from the substrate. The main peaks of both samples are obtained from the wurtzite structure of ZnO (JCPDS card no. 36-1451), indicating that single phase ZnO was successfully prepared. Furthermore, no secondary phase is observed in the XRD pattern of the AZO-RGO NCTF, and the peak positions in the NCTF are not changed with the RGO incorporation due to the low RGO content. The XPS was carried out to investigate the chemical composition in the NCTF. The survey scan of XPS spectrum reveals that the NCTF has only Zn, O, C, and Si elements (Figure 2b). The Si peaks were originated from the substrate, and no Al signals were detected due to its low doping concentration. The C1s core level spectrum shows the chemical binding state of carbon atoms in RGO, and it was deconvoluted into sp\({}^{2}\) C centered at 284.5 eV, sp\({}^{3}\) C centered at 285.6 eV, and C-O centered at 286.6 eV [24; 25]. The ratio of sp\({}^{2}\) C/sp\({}^{3}\) C is sensitive to the degree of oxidation in RGO, and it decreases with the increasing oxidation level of RGO. It was reported that the ratio measured from the XPS spectrum of highly reduced graphene oxide (HRGO) was 2.15 [26]. In our case, the ratio of sp  
Figure 1: Schematic diagram of electrospray deposition used in this study. Figure 2: (**a**) XRD spectra of Al-doped ZnO thin film (AZO TF) and AZO-reduced graphene oxide (RGO) NCTF. (**b**) XPS wide scan and (**c**) C1s core level spectra of AZO-RGO nanocomposite thin film (NCTF). C/sp\({}^{3}\) C in the AZO-RGO NCTF was estimated to be 10.8, indicating that GO was effectively reduced during the RTA process. Figure 3 shows the SEM micrographs of the cross-section and plane view of samples. The cross-section SEM micrographs (Figure 3a,c) show the thickness of the samples was 200 nm. Furthermore, the plane-view SEM micrographs of the AZO TF and AZO-RGO NCTF (shown in Figure 3b,d) show that a dense TF was deposited on the SiO\({}_{2}\)/Si substrate. To obtain a detailed microstructure of the AZO TF and AZO-RGO NCTF, TEM analysis are conducted (Figure 4). Figure 4a,c show bright-field TEM analysis of the AZO TF and AZO-RGO NCTF, and the samples were comprised of primary nanograins (<10 nm), which indicates that the existence of RGO does not affect the grain size of the AZO-RGO NCTF. The selected area electron diffraction patterns obtained from Figure 4a,c (insets) revealed a set of distinct rings corresponding to hexagonal ZnO. Furthermore, Figure 4b shows a high-resolution TEM micrograph of the AZO TF, which shows an interplanar spacing of 0.28 nm corresponding to the lattice spacing of the ZnO plane. Figure 4d shows the high-resolution TEM image of AZO-RGO NCTF, and the red arrows indicate that RGO dispersed in the AZO-RGO NCTF, which shows the uniform dispersion of RGO without aggregation. The inset in Figure 4d shows the interlayer spacing of RGO (0.345 nm) obtained from the red rectangular box, which is slightly increased with that of graphite (0.335 nm) [27]. Beside the ratio of sp\({}^{2}\) C/sp\({}^{3}\) C in XPS spectrum, the interlayer spacing of RGO is also strongly dependent on its degree of oxidation [28; 29; 30]. It was reported that the interlayer spacing of HRGO, with a relative carbon to oxygen ration of 10, was 0.364 nm [29]. This means that the GO could be effectively reduced via the RTA process, which is consistent with the XPS result shown in Figure 2b. Figure 3: (**a**) Cross-sectional and (**b**) plane view SEM micrographs of AZO TF, (**c**) Cross-sectional and (**d**) plane view SEM micrographs of AZO-RGO NCTF.