Construction of moiré superlattice on the MoO2 (010) surfaces

Recently, the moire superlattice structure (MSS) has garnered increasing attention thanks to its extensive research potential in condensed matter physics. However, how to create MSSs on non-van der Waals crystal plates is still elusive. In the present study, we propose a new method to prepare MSSs on the MoO2 (010) surface by soaking MoO2 in sulfur vapour at high temperature. MoO2 is 2D non-layered materials and is prepared by annealing MoO3 with sulfur vapour at 500 °C. The torsional modulation between two stacked monolayers is periodic, which provides additional freedom to change the material properties. Under sulfur vapour, the surface atoms of MoO2 first change from monoclinic to tetragonal crystals, and the interlayer covalent bonds are broken at the same time. Then, the top layer and buffer layer atoms of MoO2 form the original MSS, and the top layer continue to rotate into different twisted angles. Our work provides some inspiration and reference to the preparation of MSSs on the surface of the other 2D non-van der Waals crystals. In addition, we further compared the wettability of MSS@MoO2 and ordinary MoO2 powder. The results show that the surface of MSS@MoO2 is strongly hydrophobic (approximately 140°), while that of ordinary MoO2 is superhydrophilic (4.3°). Our results suggest that MSSs may be a potential application to change the surface wettability of materials.