## 3 Results and Discussion
Because the peak positions in the Raman spectra are correlated to the vibrational modes distinctive to a specific material, Raman spectroscopy is a powerful tool for identifying and characterizing the fingerprint of materials. The vibrational modes for the 211 MAX phases are theorized to be 24, but only four modes are Raman active and can be observed [52]. Of these four modes, \(\omega_{3}\) is infrared and Raman active, whereas the \(\omega_{4}\), \(\omega_{1}\), and \(\omega_{2}\) modes are only Raman active [52]. For the Ti\({}_{2}\)AlN MAX phase, the \(\omega_{3}\) and \(\omega_{4}\) modes are associated with the parallel and perpendicular vibrations of the Ti-Ti planes, whereas the \(\omega_{1}\) and \(\omega_{2}\) vibrational modes arise from the shear vibrations of the Ti-Al planes [10; 51; 53]. The representative Raman spectra of step annealed Ti\({}_{2}\)AlN are shown in Figure 2c, where all four Raman active modes are clearly observed at the peak positions of 149 cm\({}^{-1}\) (\(\omega_{1}\)), 229 cm\({}^{-1}\) (\(\omega_{2}\)), 234 cm\({}^{-1}\) (\(\omega_{3}\)), and 365 cm\({}^{-1}\) (\(\omega_{4}\)), providing strong evidence for the formation of the Ti\({}_{2}\)AlN MAX phase [10; 51; 54]. The step annealed Ti\({}_{2}\)AlN MAX phase was further etched by wet chemical etching to obtain multilayered Ti\({}_{2}\)N MXene sheets. In this particular method, the Al layer was removed by acid-salt treatment of the Ti\({}_{2}\)AlN MAX phase in a KF-HCl etchant solution [10; 26; 45; 55]. The effective formation and phase composition of multilayered Ti\({}_{2}\)N MXene sheets were analyzed using XRD, FE-SEM, and Raman spectroscopy respectively, and the corresponding results are demonstrated in Figure 3. The prominent peaks observed in the XRD pattern were consistent with previously reported results for Ti\({}_{2}\)N MXene, and they were indexed according to the JCPDS card no. 00-017-0386 of Ti\({}_{2}\)N, as shown in Figure 3a. Comparative analysis of the XRD patterns of the Ti\({}_{2}\)AlN MAX phase and Ti\({}_{2}\)N MXene shows that the sharp peak assigned to the (0 0 2) peak in the Ti\({}_{2}\)AlN MAX phase completely disappeared, and a broad curve was observed at that position. This observation may have resulted from the removal of the Al layer between two consecutive Ti\({}_{2}\)N MXene layers [26]. Similarly, the intense peak assigned to the (1 0 3) plane observed in the Ti\({}_{2}\)AlN MAX phase was completely absent in the XRD pattern of Ti\({}_{2}\)N MXene, which is significant evidence of the effective etching of the Al layer from the Ti\({}_{2}\)AlN MAX \begin{table}
\begin{tabular}{c c c} \hline \hline
**Ti\({}_{2}\)AlN** & **JCPDS-00-055-0434** & **As-Synthesized** \\ \hline Unit cell dimension (Å) & a = 2.989 & a = 2.995 \\  & c = 13.614 & c = 13.593 \\   Cell volume (Å)\({}^{3}\) & 105.33 & 105.63 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Crystallographic details on structural determination of as-synthesized Ti\({}_{2}\)AlN MAX phase. Figure 2: (a) XRD pattern, (b) FE-SEM image, and (c) Raman spectrum of as-synthesized Ti\({}_{2}\)AlN MAX phase. phase [10,26]. A new peak at approximately 54.4\({}^{\circ}\) marked with \"*\" in Figure 3a is observed, which is assigned to the XRD signal of the potassium fluoride (KF) residue [56], which was used along with HCl in the etchant. This may have remained in the exfoliated Ti\({}_{2}\)N MXene layers during the washing process. The formation of Ti\({}_{2}\)N MXene was further confirmed by FE-SEM. The FE-SEM image in Figure 3b shows the typical morphological characteristics of MXenes [55,57,58]. The etched Ti\({}_{2}\)N MXene showed visible delamination and increased space between the layers owing to the removal of the Al layer. In some areas, stacked layers appear instead of the delaminated and opened layers. This may be attributed to the intercalation of K\({}^{+}\) or water ions between the Ti\({}_{2}\)N layers during the etching process.