# Study on the Absorbing Properties of V-Doped MoS2
## 3 Result and Discussion  
### The Phase Structure and Microstructure of VMS and VMSA Materials  
Figure 2a presents the XRD patterns of both the unannealed VMS and annealed VMSA samples. Both samples exhibit distinct diffraction peaks, these peaks are consistent with the reference card PDF # 37-1492 (MoS\({}_{2}\)). There are obvious diffraction peaks near the diffraction angles of about 14.33\({}^{\circ}\), 33.02\({}^{\circ}\), 39.67\({}^{\circ}\), and 58.04\({}^{\circ}\), which correspond to the (002), (100), (103), and (110) crystal planes. This result means that V mainly exists in MoS\({}_{2}\) in the form of doping. Then, it can be found that VMS and VMSA both exhibit similar characteristic peaks, indicating that annealing treatment did not destroy the crystal structure of MoS\({}_{2}\). Moreover, the lattice microstrain of VMS and VMSA can be calculated using the following formula [15]:  
\[\beta_{hkl}=\beta_{s}+\beta_{D} \tag{1}\]  
\[\beta_{hkl}=\frac{k\lambda}{D\cos\theta}+4\varepsilon\tan\theta \tag{2}\]  
\[\beta_{s}=4\epsilon\tan\theta \tag{3}\]  
In this equation, \(\beta_{hkl}\) is the semi-peak width, and \(\beta_{s}\) and \(\beta_{D}\) are the semi-peak width caused by the microscopic morphology and the semi-peak width caused by the grain size, respectively. The values of D, \(\lambda\), \(\varepsilon\), and \(\theta\) are grain size, wavelength, strain constant, and peak position, respectively, with k being a constant of 0.89. As shown in Figure 2b, VMSA displays a greater microstrain than VMS, which may be attributed to the increased disorder within the MoS\({}_{2}\) crystal caused by the doping of V. To further confirm our results, the XPS was adopted. In Figure 2c, the peaks at 228.0 eV (3\(d_{5/2}\)) and 231.2 eV (3\(d_{3/2}\)) correspond to Mo\({}^{4+}\) and no corresponding oxidation state of Mo\({}^{6+}\) is found [16]. These peaks located at 514.8 and 522.1 eV are attributed to V 2\(p_{3/2}\) and V 2\(p_{1/2}\), indicating the V\({}^{4+}\) chemical state of VMS (Figure 2d) [17]. The two peaks at 512.5 and 520.2 eV can be assigned to V\({}^{2+}\), which can be attributed to the slight oxidation of V [18]. It is worth noting that the characteristic peak of V\({}^{4+}\) is significantly enhanced while that of V\({}^{2+}\) is weakened after annealing treatment, indicating that more V element has been doped into the MoS\({}_{2}\) crystal structure. Furthermore, the characteristic peaks of V\({}^{4+}\) show a noticeable shift after annealing treatment, which proves the significant regulatory effect of V doping on the electronic structure of MoS\({}_{2}\)[16]. For the S 2\(p\), the two peaks at 161.1 and 162.4 eV are corresponding to S 2\(p_{3/2}\) and S 2\(p_{1/2}\) of S\({}^{2-}\), respectively [19]. Overall, the XRD and XPS results effectively demonstrate that annealing treatment effectively improves V doping in the MoS\({}_{2}\) crystal structure, which has a significant modulation on the energy band and electrical structure of MoS\({}_{2}\).  
Morphology is another important factor that affects the electrical structure and microwave absorption properties of materials. Figure 2f-i display SEM images of VMS and  
Figure 1: Flowchart of preparation experiment.  
VMSA at 1.00 \(\upmu\)m and 3.00 \(\upmu\)m scales, the figure reveals that the two groups of samples have a similar flower-like structure, indicating that annealing treatment did not alter their original morphology. As previously reported works, such flower-like structures are beneficial for promoting multiple reflections/scatterings of EM waves, thereby enhancing the EM wave absorption performance of the samples [20; 21; 22]. However, in this work, the effect of morphology on VMS and VMSA is the same, so it is not the primary factor influencing their performance changes.