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

Abstract

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.

Revealing the origin of PL evolution of InSe flake induced by laser irradiation

“…We designed the developed technique to avoid the effects of heat caused by prolonged exposure to laser irradiation on a sample previously reported. 15,16,20 We sequentially measured the Raman/PL spectrum of InSe akes by increasing the number of measurements. The time gap between each measurement was 3 s. For each measurement the acquisition time for the Raman/PL spectrum was 3 s, and twice accumulated.…”

“…It is known that the in situ Raman spectroscopy is also a powerful tool to monitor the degradation process. 20,29 Fig. S4a and b † show the stacked Raman spectra with increasing measurements under the irradiation of 0.2 mW and 2 mW in air, respectively.…”

“…On the other hand, long-time laser irradiation may result in heat accumulation on the surface of materials, thus the practical experimental results will suffer an inuence from the distinct heat dissipation especially for the materials with bad environment stability. In order to avoid the inuence from long-time irradiation adopted in previous reports, 15,16,20 we developed a modied laser treated technique that the photo-ablating and PL measurement can be simultaneously achieved by repeating measurements at the same point.…”

Photocatalytic Oxidation in Few‐Layer Tellurene for Loss‐Invariant Integrated Photonic Resonance Trimming

“…A focused or waveguide‐confined beam provides localized and deterministic control of the refractive index. [ 18 ] The micro‐Raman spectroscopies revealed the laser‐induced atomic structure transition pathways along t ‐Te, glass TeO 2 , crystalline γ ‐TeO 2 , β ‐TeO 2 , to α ‐TeO 2 . [ 20–22 ] The photo‐oxidation experiments are only carried out in bulk Te with visible top excitation.…”

“…[16] The research on the oxidation process in 2D materials has been focused on improving their ambient stability or tailoring the material's electronic properties. [17,18] The chiral chain atomic structure in 2D Te is stable and naturally protects the chalcogen from oxidation in ambient conditions. While the reports on baking-induced oxidation of trigonal Te (t-Te, a bulk form of chiral chain structure) or 2D Te are not found, laser-induced oxidation in t-Te has been observed by many groups.…”