## 3 Results and Discussion
### Structure and Morphology by Means of XRD, HRTEM, and Raman Analyses
#### 3.1.3 Raman Investigation  
In Figure 4a, the Raman spectra, recorded with the 514 nm laser line, of MoS\({}_{2}\)/TiO\({}_{2}\) n-sh obtained by ex situ (blue line) and in situ methods (red line) and of TiO\({}_{2}\) anatase nanosheet (n-sh) pretreated at 873 K (black line) are compared with that of bare MoS\({}_{2}\), used as a reference material (grey line). Considering the Raman spectrum of pure TiO\({}_{2}\) nanosheets (black line), the typical anatase TiO\({}_{2}\) fingerprint can be recognized. As a matter of fact, the four bands at 144, 396, 514, and 636 cm\({}^{-1}\) are ascribed to the E\({}_{\text{g}}\), B\({}_{\text{1g}}\), A\({}_{\text{1g}}\), and E\({}_{\text{g}}\) Raman active modes, respectively, of the anatase phase, as described in the literature [45; 46]. Moving to both the MoS\({}_{2}\)/TiO\({}_{2}\) n-sh obtained by the ex situ method (blue line), and by the in situ method (red line), it can be observed that the feature centered at 396 cm\({}^{-1}\), assigned to the TiO\({}_{2}\) anatase phase, is split into two components at 407 and 385 cm\({}^{-1}\) (blue line), and at 406 and 386 cm\({}^{-1}\), (red line), which can be ascribed to MoS\({}_{2}\) A\({}_{\text{1g}}\) and E\({}^{1}\)\({}_{\text{2g}}\) first-order Raman active modes, respectively (Figure 4b) [20]. The A\({}_{\text{1g}}\) mode is explained with a vibration along the stacking of MoS\({}_{2}\), while the E\({}^{1}\)\({}_{\text{2g}}\) mode is related to the lateral extension of the MoS\({}_{2}\) sheets. The asymmetry of both signals suggests the contribution of a variety of sites located on the MoS\({}_{2}\) boundaries characterized by slightly different nuclearity, together with the formation of small sulfide particles. Notice that on MoS\({}_{2}\)/TiO\({}_{2}\) n-sh obtained by the in situ method (Figure 4a, red line), a peak at about 227 cm\({}^{-1}\) has been observed, which has been assigned to LA phonons at the M point [47]. According to the authors, a relationship between the intensity ratio of the LA(M) peak and each of the first-order peaks has been found, which suggests a practical  
Figure 4: (a) Raman spectra, in the 800–100 cm\({}^{-1}\) range, of pure bulk MoS\({}_{2}\) used as a reference material (grey line), of MoS\({}_{2}\)/TiO\({}_{2}\) n-sh obtained by the ex situ method (blue line), of MoS\({}_{2}\)/TiO\({}_{2}\) n-sh obtained by the in situ method (red line), and of the TiO\({}_{2}\) anatase nanosheet (n-sh) pretreated at 873 K (black line). All spectra were recorded with the 514 nm laser line. (b) Enlarged views in the 425–365 cm\({}^{-1}\) range: the grey dashed lines in bulk MoS\({}_{2}\) spectrum indicate the positions of the E\({}^{1}\)\({}_{\text{2g}}\) and A\({}_{\text{1g}}\) peaks, respectively. Deconvolution of the Raman patterns are shown for ex situ (blue line) and in situ (red line) samples. route to quantify defects in single-layer MoS\({}_{2}\) using Raman spectroscopy, thus highlighting an analogy between the LA(M) peak in MoS\({}_{2}\) and the D peak in graphene. From Figure 4b, a difference of the frequency values between the A\({}_{\text{1g}}\) and E\({}^{\text{1}}\)\({}_{\text{2g}}\) modes of \(\cong\)20 cm\({}^{-1}\) for MoS\({}_{2}\)/TiO\({}_{2}\) n-sh obtained by in situ (red line), \(\cong\)22 cm\({}^{-1}\) for MoS\({}_{2}\)/TiO\({}_{2}\) n-sh obtained by ex situ (blue line), and \(\cong\)26 cm\({}^{-1}\) for the reference bare MoS\({}_{2}\) can be calculated. Reported in the literature as well, the difference of the frequency values between A\({}_{\text{1g}}\) and E\({}^{\text{1}}\)\({}_{\text{2g}}\) modes is indicative of the slab thickness [48]. This means that a relationship between the position of the A\({}_{\text{1g}}\) and E\({}^{\text{1}}\)\({}_{\text{2g}}\) vibrational modes and the number of layers in the MoS\({}_{2}\) particles has been established [41; 49]. Moreover, most of these studies focused on materials obtained by the ex situ method, via exfoliation and deposition on flat supports of bulk MoS\({}_{2}\).