High Powerfactor in single and few-layer MoS2

The thermoelectric effect enables conversion between thermal and electrical energy, and provides one way to extract energy from waste heat. The efficiency of a thermoelectric device can be defined by a dimensionless figure of merit given by \textit{ZT}$=S^{2}\sigma {\rm T}/\kappa .$ In order to achieve efficient thermoelectric devices, $S^{2}\sigma $ needs to be kept high by optimizing the interplay between the $S^{\mathrm{\thinspace }}$and $\sigma $. The thin layered transition-metal dichalcogenide semiconductor MoS$_{\mathrm{2}}$ has attracted great interest because of two dimensional density of states and relatively high mobility, which could give a large $S^{\mathrm{\thinspace }}$and $\sigma $. Here we study on pristine exfoliated 1L-, 2L- and 3L MoS$_{\mathrm{2}}$ samples by simultaneous measurement of the Seebeck coefficient($S)$ and two probe electrical conductivity using nano-fabricated heater and thermometer. It firstly shows that atomic thin MoS2 which has a large effective band masses ($m\ast )$ as well as high mobilies ($\mu )$, increases the powerfactor $S^{2}\sigma .$to as high as $8.5\,mWm^{-1}K^{-2}$at room temperature$_{\mathrm{\thinspace }}$(twice as high as commercially used Bi$_{\mathrm{2}}$Te$_{\mathrm{3}})$. Further, we show for the first time that the confined two-dimensional density of states of the conduction band can be studied in monolayer MoS$_{\mathrm{2}}$ by measuring the gate-dependent Seebeck voltage.