Systematic improvement of excitonic features in hydrothermally synthesized WS2 due to post-synthesis drying

Abstract

WS2 nanostructures were produced by mechanically exfoliating bulk WS2 powders synthesized through a solution-based hydrothermal route using WCl6 and thioacetamide (TAA) as reactants. An unoptimized post-synthesis recipe, which constitutes the last step, is the major hindrance in achieving a reproducible and scalable production strategy of layered bulk WS2 crystals. We have reported a comprehensive study on the crystal, morphological, and luminescence properties of WS2 material which have undergone post-synthesis treatment i.e. dried at mild temperature with varied dwelling times. The as-synthesized WS2 material which used to be in distorted 1T metallic phase, due to ionic intercalation released from the organic reactants, was found to evolve crystallographically into a stable 2H semiconducting phase with increased drying temperature and dwelling time. An in-depth optical analysis of the WS2 nanostructures through PL and PLE spectroscopy revealed substantial improvement in the intensity of A and B excitonic features for the sample dried at 80 °C for 24 h, indicating a reduction in the non-radiative defect centers in the sample under the post-synthesis conditions. We believe an effective post-synthesis treatment is needed for semiconducting 2H-WS2 synthesis through the solution route to improve its crystal (i.e. structural) and optical properties for potential electronic applications.