Modification of WS2 nanosheets with controllable layers via oxygen ion irradiation

Highlights: • The layer numbers of WS₂ nanosheets can be controlled with ion irradiation. • Controllable optical band gap achieved after ion irradiation. • Irradiation did not change the 2H-WS₂ phase structure of the WS₂ nanosheets. • Some properties can be conserved for potential applications after irradiation. As one kind of two-dimensional materials, WS₂ nanosheets have drawn much attention with different kinds of research methods. Yet ion irradiation method was barely used for WS₂ nanosheets. In this paper, the structure, composition and optical band gap (E_g) of the multilayer WS₂ films deposited by chemical vapor deposition (CVD) method on sapphire substrates before and after oxygen ion irradiation with different energy and fluences were studied. Precise tailored layer-structures and a controllable optical band gap of WS₂ nanosheets were achieved after oxygen ion irradiation. The results shows higher energy oxygen irradiation changed the shape from triangular shaped grains to irregular rectangle shape but did not change 2H-WS₂ phase structure. The intensity of $E_{2g}^1$ () and $A_{1g}$ () modes decreased and have small shifts after oxygen ion irradiation. The peak frequency difference between the $E_{2g}^1$ () and $A_{1g}$ () modes (Δω) decreased after oxygen ion irradiation, and this result indicates the number of layers decreased after oxygen ion irradiation. The E_g decreased with the increase of the energy and the fluence of oxygen ions. The number of layers, thickness and optical band gap changed after ion irradiation with different ion fluences and energies. The results proposed a new strategy for precise control of multilayer nanosheets and demonstrated the high applicability of ion irradiation in super-capacitors, field effect transistors and other applications.