Synthesis and characterization of MoSe2 nanoscrolls via pulsed laser ablation in deep eutectic solvents†

Abstract

There is ongoing interest in the rapid, reproducible production of 2-dimensional (2-D) transition metal dichalcogenides (TMD), such as molybdenum-based TMD (MoX₂), where X is a chalcogen atom such as sulphur (S), selenium (Se) or tellurium (Te), driven by their unique optical and electronic properties. Once fabricated into an atomically thin layer structure, these materials have a direct-indirect bandgap transition, strong spin–orbit coupling, and favourable electronic and mechanical strain-dependent properties which are attractive for electronics. Pulsed laser ablation in liquid (PLAL) is an economic, green alternative for synthesis of TMD. It has been shown that in the case of MoX₂, the chemical processes during the plasma phase of the ablation can yield the formation of multispecies, including MoO_x quantum dots when oxygen-containing solvents are used. Here, we introduce the formation of MoSe₂ nanoscrolls with low oxygen content synthesized via pulsed laser ablation in deep eutectic solvents (PLADES). Our results suggest that the synthesis produces a stable colloidal solution of large 2-D structures with tuneable surface charge by replacing the deep eutectic solvent (DES) with DI water. Nuclear Magnetic Resonance (NMR) results suggest that irradiating the solvent at near infrared NIR energy does not affect its chemical composition. NMR also proves that serial washing can completely remove solvent from the nanostructures. Raman shifts suggest the formation of large, thin MoSe₂ nanosheets aided by the solvent confinement resulting from van der Waal forces and hydrogen bonds interactions between MoSe₂ and urea. Binding energies measured by X-ray photoelectron spectroscopy (XPS) confirm MoSe₂-DES preference to form 1T-MoSe₂versus molybdenum oxides and 2H MoSe₂ in DI-water. Raman and XPS findings were validated by transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Results of this work validate the use of PLADES for the synthesis of stable, crystalline, low-surface-oxygen-content colloidal MoSe₂ nanoscrolls in scalable quantities.