Electronic, Structural, and Electrochemical Modulation of Electrostatic Self-Assembled 1T-MoS₂Nanosheets via Topotactic Structural Conversion

Abstract

We studied the electronic, structural, and electrochemical modulation of electrostatic self-assembled thin films in which a nanoscale pair of single layer 1T-MoS2 nanosheets and charge-compensating polymers as a counterpart in the self-assembly process stacked up on the substrate after heating. Heating the self-assembled monolayer and multilayers of the 1T-MoS2 nanosheets at 300• C under vacuum triggered a yellow coloration and structural transformation, referred to as the 1T→2H transition, without a significant morphological change. In the topotactic conversion, an energy shift of the Mo 3d and S 2p core levels to a higher binding energy corresponds to the edge shift of the valence band, indicating the unique nature of this system as a MoS2 molecule. The single layer state, which is often modulated by stacking the metallic-like 1T-MoS2 nanosheets and the semiconductor 2H-MoS2 nanosheets, was retained in the multilayers due to the robust interlayer galleries filled by the polymers. Cyclic voltammograms of a Li-ion battery using the 1T-or 2H-MoS2 multilayer film electrodes provided useful information on the electrochemical reaction of the MoS2 slabs, especially at the early stage of electrochemical Li insertion. These self-assembled ultra-thin films, offering well-defined MoS2 nanosheet structures in terms of stacking order and crystal structure, will promote future applications of the single-layer 1T-and 2H-MoS2 nanosheets.