## 3 Results and Discussion  
### Microstructural Properties  
Figure 1 shows the XRD diffraction patterns of the VO\({}_{2}\)/glass film and VO\({}_{2}\)/Cu\({}_{50}\)Zr\({}_{50}\)/glass films. The generalized diffraction with the 20 ranging from 15\({}^{\circ}\) to 30\({}^{\circ}\) indicates the glass properties of the substrates. For the thin films, the peaks that were located at 27.80\({}^{\circ}\) are attributed to the VO\({}_{2}\) (011) peak (JCPDS No. 43-1051), which is the feature diffraction peak for M1-phase VO\({}_{2}\) thin films [29]. All of the VO\({}_{2}\) thin films are strongly oriented along the [011] direction, whether or not buffer layers were inserted on the glass substrate. The diffraction peak located at 31.47\({}^{\circ}\) belongs to the ZrO\({}_{2}\) (111) peak (JCPDS No. 65-1024), implying the monoclinic symmetry characteristics of the ZrO\({}_{2}\). The peak located at 42.42\({}^{\circ}\) is assigned to the Cu\({}_{2}\)O (200) peak (JCPDS No. 77-0199). The appearance of ZrO\({}_{2}\) and Cu\({}_{2}\)O may be due to the incorporation of Zr and Cu ions with oxygen during the VO\({}_{2}\) thin film growth. In addition, as the thickness of the buffer layer increases, the intensity of VO\({}_{2}\) (011) peaks (in units of counts per second (cps)) initially increases and then decreases, indicating that the crystal quality of VO\({}_{2}\) thin films initially improves and then worsens. The characteristic peaks of the VO\({}_{2}\) phase disappear in the 160 nm-thick VO\({}_{2}\)/Cu\({}_{50}\)Zr\({}_{50}\)/glass thin films, which clearly indicates that thicker buffer layers make VO\({}_{2}\) amorphous. Figure 1: X-ray diffraction (XRD) patterns of vanadium dioxide (VO\({}_{2}\)) films deposited on Cu\({}_{50}\)Zr\({}_{50}\) buffer layers with different thicknesses. Figure 2 shows the AFM micrographs of the surfaces of the VO\({}_{2}\)/glass film and VO\({}_{2}\)/Cu\({}_{50}\)Zr\({}_{50}\)/glass films. The surfaces of the VO\({}_{2}\)/Cu\({}_{50}\)Zr\({}_{50}\)/glass films are smoother and more uniform than the VO\({}_{2}\)/glass film. The measured roughnesses of the VO\({}_{2}\)/Cu\({}_{50}\)Zr\({}_{50}\)/glass films without a buffer layer, and with buffer layers with thicknesses of 40 nm, 80 nm, and 160 nm, are 2.86 nm, 1.32 nm, 1.51 nm, and 2.12 nm, respectively, indicating that the surface morphology of VO\({}_{2}\) films that are grown on glass substrates can be optimized effectively by embedding a Cu\({}_{50}\)Zr\({}_{50}\) buffer layer. What calls for special attention is a suitable thickness needs that the Cu\({}_{50}\)Zr\({}_{50}\) buffer layer need to select, since excess thickness of Cu\({}_{50}\)Zr\({}_{50}\) layers will generate rougher films. To further show the effects of the buffer layer thickness on the microstructures, the SEM images of the surface morphology of the VO\({}_{2}\)/Cu\({}_{50}\)Zr\({}_{50}\)/glass thin films with different buffer layer thicknesses are shown in Figure 3. The surfaces of all the films are found to be continuous and dense. The bright white segments that are visible on the surface of films are identified as amorphous metal V particles, according to the elemental analysis illustrated in the small red circles of Figure 3c,d by Energy-dispersive X-ray spectroscopy (EDS). After embedding an alloy buffer layer, the number of the amorphous metal V particles increases clearly, resulting in poor crystallinity of the VO\({}_{2}\) thin films on the thick buffer layer. By combining the above analysis, the following can be conjectured. When the buffer layer thickness is relatively thin (\(\sim\)40 nm), the incorporation of Zr atoms with O atoms during deposition forms monoclinic ZrO\({}_{2}\). The ZrO\({}_{2}\) interfacial layer serves as a template to improve the crystallinity of the upper VO\({}_{2}\) thin films. This result is highly consistent with the case of the VO\({}_{2}\)/Y-doped ZrO\({}_{2}\)/Si thin films [30], where the Y-doped ZrO\({}_{2}\) served as the buffer layer.