Non-Aqueous Electrodeposition of 2-D Layered MoS2 from a Tailored Single Source Precursor

Abstract

2-D layered transition metal dichalcogenide (TMDC) materials have been intensively investigated in the past few years because of their remarkable properties such as semiconductivity, strong spin splitting, tunable band gaps etc.1, that make them ideal candidates for optoelectronic and electronics applications2-3. The flagship of TMDCs is MoS2 due to its unique electronic, optical and other features, including size-dependent band gap4. A number of techniques have been recently established for obtaining ultra-thin MoS2 films, however, improved processing methods for scalable production of the films are highly desirable. At present, the TMDCs are typically deposited by vapour deposition methods such as magnetron sputtering5 and chemical vapour deposition (CVD)6. However, these techniques are expensive and mostly involve constraining deposition conditions such as high temperature and high vacuum. On the other hand, electrodeposition, being a low cost alternative technique, has a number of key advantages that make it an interesting materials deposition process. First, electrodeposition is a ‘bottom-up’ growth technique where conformal deposition occurs via atom by atom growth over the exposed electrode surface. Secondly, electrodeposition is, in general, a low temperature technique that is mostly performed in ambient conditions and it is very efficient in use of materials. The deposition only occurs in areas defined by the electrical contact and is under direct electrical control during the growth. Thanks to these advantages, electrodeposition finds use in key high tech areas such as deposition of magnetic read-write heads and the copper interconnects in microprocessor chips7. Water is the most commonly employed solvent in electrodeposition, however, its narrow potential window induces limitations in depositing metals/compounds requiring large negative overpotentials, and also the water reduction and H2 evolution reactions introduce additional complexity to the experiments. Here, we employ an electrolyte system based on tetrabutylammonium tetrathiomolybdate as a single source precursor for MoS2, with compatible tetrabutylammonium halide supporting electrolyte and trimethylammonium chloride as proton source in a weakly coordinating, non-aqueous solvent, which provides the ability to deposit 2-D TMDC films with desired structures and properties. In the present study, we report on the electrodeposition of 2-D MoS2 films from dichloromethane. The electrodeposited MoS2 films were characterized by variety of methods including Scanning Electron Microscopy (SEM), Raman spectroscopy and X-ray diffraction. A detailed investigation on the electrochemical growth mechanism of MoS2 has been conducted using Electrochemical Quartz Crystal Microbalance (EQCM). The influence of various growth parameters on the structure and composition of the thin films will also be discussed. This work was funded by EPSRC grant reference EP/P025137/1. [1] Nature Chemistry, 2013. 5: 263. [2] Chemical Society Reviews, 2015. 44(21): 7715-7736. [3] Chemical Society Reviews, 2015. 44(9): 2664-2680. [4] Chemical Society Reviews, 2018. 47(16): 6101-6127. [5] Nanoscale, 2015. 7(6): 2497-2503. [6] Chemical Society Reviews, 2015. 44(9): 2744-2756. [7] IBM Journal of Research and Development, 1998. 42(5): 567-574.