Optically induced reversible wettability transition on single crystal lithium niobate surfaces

Abstract

Solid surfaces with controllable and reversible wettability are scientifically and technologically important. Here, we report on the reversible wettability transitions of single crystal (0001) lithium niobate (LiNbO3) surfaces by alternate ultraviolet (UV) and infrared (IR) light irradiation. The UV irradiation (170 mW/cm2) could markedly reduce the contact angle of LiNbO3 over 30 min from 55.3° to 10.7°. IR irradiation (200 mW/cm2) recovered the water contact angle from 10.7° to 55.1° over 1 h. First-principles calculations showed that under both O-poor and O-rich conditions, oxygen vacancies preferred to form at the Li-terminal (0001) surface rather than at the Nb-terminal surface and the O-terminal surface or in the bulk. We further show that this light induced wettability transition has a dependence on the light wavelength. The influences of relative humidity and oxygen concentration were also investigated.