Direct fabrication of two-dimensional ReS₂ on SiO₂/Si substrate by a wide-temperature-range atomic layer deposition

The building of high-quality, especially thickness-controllable ReS₂, is the crux of researching it and developing its wider application. In this work, ultrathin (1-5 layers) ReS₂ with controllable thickness and improved quality is obtained on SiO₂/Si substrates, using wide-temperature-range (WTR) atomic layer deposition (ALD). First, a WTR ALD system for building thin films and in situ annealing is constructed. ReS₂ of precise thicknesses can be achieved by regulating the number of ALD cycles, controlling the reaction temperature and plasma treatment. In particular, a method of in situ H₂S annealing is used to reduce S defects, which improves the quality of ReS₂. After annealing, the atomic ratio of S/Re in ReS₂ increases from 1.74 to 1.92, considering the presence of Re-O bond at the SiO₂-ReS₂ interface, which indicates that the S defects in ReS₂ films are completely eliminated at annealing temperature of 850 °C and 900 °C. In particular, at an annealing temperature of 900 °C, ReS₂ recrystallizes to form about 120 nm triangular grains, and its frictional force is reduced by 27.5% compared with the as-grown ReS₂.