Photo-oxidation Dynamics in GaSe Flakes Probed through Temporal Evolution of Raman Spectroscopy

The effect of native defect density on structure evolution during oxidation has not been systematically studied for two-dimensional (2D) materials. Photo-oxidation provides a way to fasten oxidation in 2D materials. The oxidation dynamics in atomically layered GaSe is systemically studied here through the temporal evolution of Raman spectroscopy. Two stages of oxidation processes are observed under above-gap laser irradiation in ambient conditions. First, the Raman intensity in GaSe flakes linearly decreases with the square root of oxidation time, and the slope shows a linear dependence on the square root of laser power. This stage is associated with photo-oxidation-induced structural damage with the formation of randomly distributed oxidation products, i.e., Ga2Se3, Ga2O3, and crystalline and amorphous selenium. A model is proposed to interpret the oxidation kinetics in GaSe flakes in terms of illumination time, laser power, and native defect density. Second, continuous change in slope is observed, which is due to the oxidative products merging to form a large oxidation lump. The evolution of defect density in GaSe flakes in terms of laser power, oxidation time, and native defect density during oxidation shines new light on the understanding of the stabilities of 2D materials in ambient environments.