Investigation of $E_{2g}^{1}$ and $A_{1g}$ Raman Modes of Few-Layer MoS$_2$ on HfO$_2$ Substrate

The recent research work by Radisavljevic \textit{et al.}[1] shows that the mobilities of monolayer MoS$_{2}$ transistors can be improved by employing a thin layer of hafnium oxide as top-gate dielectric. Dielectric screening has been successfully demonstrated to suppress the Coulomb interactions of charged impurities on the substrate. Therefore, we develop an alternative method of building monolayer MoS$_{2}$ transistors on HfO$_{2}$ substrate. Owing to the low contrast of few-layer MoS$_{2}$ flakes on thin HfO$_{2}$ layer, which makes the realization of such device configuration difficult. By utilizing the thickness dependence of in-plane and out-of-plane Raman peaks of MoS$_{2}$ flakes, $E_{2g}^{1} $and$A_{1g} $, respectively, we establish an efficient approach to improve the identification of MoS$_{2}$ layers by Raman spectrum instead of AFM. Our investigation of Raman spectrum of few-layer MoS$_{2}$ on HfO$_{2}$ shows the significant difference from those on SiO$_{2}$. The substrate dependence of Raman spectrum as well as its further application will be discussed in this talk.\\[4pt] [1] Radisavljevic, \textit{et al., Nat. Nanotech}. \textbf{6}, 147 (2011)