Direct Chemical Vapor Deposition Growth of Monolayer MoS₂ on TiO₂ Nanorods and Evidence for Doping-Induced Strong Photoluminescence Enhancement

Abstract

Herein, we demonstrate a simple technique to control the population of nonradiative trions and radiative neutral excitons in single-layer MoS2 to enhance its photoluminescence (PL) emission by forming a core–shell heterostructure (HS) of MoS2 on TiO2 nanorods (NRs). The monolayer MoS2 (1L-MoS2) shell is grown directly on a hydrothermally grown TiO2 NR core by chemical vapor deposition, and the HS shows a strong enhancement of PL intensity by about 2 orders of magnitude over the pristine 1L-MoS2 at room temperature. The enhancement of PL in the HS is attributed, first, to the p-doping in the MoS2 lattice through charge transfer from MoS2 to TiO2, and, second, to the radiative recombination of excitons which dominates over the nonradiative ones in the HS, as confirmed by the low-temperature PL analysis. The enhancement of PL because of the p-doping effect in the bare 1L-MoS2 has been confirmed by the oxygen plasma treatment causing the adsorption of oxygen molecules at the defect sites of MoS2, as revealed from the Raman and PL analyses. Our results provide a novel route to grow a core–shell HS of 1L-MoS2 and TiO2 NRs for the strong enhancement of excitonic PL emission, which is promising for future practical applications.