Selective growth of I-phase copper molybdenum sulphide two-dimensional nanostructures and evaluation of their optical and pseudocapacitive properties
摘要
Copper molybdenum sulphide (CMS), a ternary transition metal dichalcogenide (TMD), is interesting because of its two-dimensional (2D) nanostructure. Unlike the well-investigated binary layered molybdenum disulphide (MoS2) counterpart, there is scope to explore phase, morphological, stoichiometric, and defect-related electronic properties with respect of its technological potential. In this study, off-stoichiometric CMS (Cu2MoS4) colloidal nanostructures (6.4–12.4 nm) were grown under variable conditions of temperature (190–300 °C) and time (5–30 min). The nanostructures crystallize in the body centred tetragonal structure of the I-phase (I-CMS) and display a correlation of particle size, thickness, layering, and composition with growth conditions. Growth temperature influences their layer stacking, whilst growth time influences their lateral dimension. The off-stoichiometric nanostructures are copper and molybdenum-rich rendering shallow-lying acceptor states of copper adatoms and donor states of vacancies of sulphur. These, along with surface trapping states, are likely implicated in tunable UV–visible absorption with indirect bandgaps (2.6–2.8 eV), as well as broad visible photoluminescence which tails into the NIR region involving fast radiative recombination of lifetimes (0.29–3.35 ns). Additionally, electrodes of the I-CMS nanostructures display slightly variable pseudocapacitance of charge-storage, primarily via sodium ion intercalation with a good specific capacitance of ~ 86 F g−1 at 5 mV s−1 scan rate. Importantly, this is the first study involving the growth of Cu2MoS4 via colloidal hot injection as a facile route for phase selectivity, composition, morphology, and electronic properties for applications such as photovoltaics, optoelectronics, and pseudocapacitive electrodes for energy storage devices.