The Role of Alkali Metal in the Growth of Tungsten Disulfide through Chemical Vapor Deposition

GUAN-ZHEN WU^1*, Yu-Han Wang¹, Wei-Yen Woon¹

¹Department of physics, National central university, Taoyuan, Taiwan

* Presenter:GUAN-ZHEN WU, email:wuguanzhen0118@gmail.com

In recent years, transition metal dichalcogenides (TMDCs) received several attention since their atomically thin layered structure and unique characteristics. There is a transition from direct bandgap to indirect bandgap when the number of layer reduce from multilayers to monolayers. Chemical vapor deposition (CVD) is a way to grow high-quality TMDCs with astonishing optical and electronic properties. However, the grain size is usually limited in conventional CVD. The addition of alkali metal has been shown to greatly promote both growth rate and lateral growth. In this work, we explore the role of sodium chloride (NaCl) in the growth of tungsten disulfide (WS2). The nucleation density, grain size, coverage, and number of layers of the as-grown WS2 grown with different Na concentrations were observed and compared through optical microscopy. The optical properties and the lattice structure were studied through photoluminescence spectroscopy (PL) and Raman spectroscopy. The results show that alkali metal promotes both growth rate and grain size by lowering the reaction energy.

Keywords: Tungsten Disulfide, Chemical Vapor Deposition, Alkali Metal