Simple Exfoliation of Bulk Gallium Selenide to Single/Few‐Layers by a Temperature‐Adjustment Bath‐Ultrasonic Treatment

2D layered materials, such as gallium selenide (GaSe), if exfoliated adjustably, exhibit several excellent properties, offering great potential for diverse uses. Herein, bulk GaSe is exfoliated by a novel temperature-adjustment bath-ultrasonic method. The obtained single to few layers of high-quality GaSe nanosheets are deposited on a silicon/silicon dioxide (Si/SiO2) wafer and characterized by different methods to demonstrate the bath-temperature non-monotonic effect on the quality of nanoflakes. The optimal bath-ultrasonic experimental scheme of GaSe nanosheet preparation is proposed. The adjustment of temperature shows effective control over the micromorphology of the exfoliated GaSe material, especially the thickness of the nanosheets. Through atomic force microscopy (AFM) characterization of all samples, it can be observed that the nanosheets exhibit a uniform thickness, which means that this novel temperature-adjustment exfoliation method is of general significance. It is found that the bath temperature of the ultrasonic process plays an important role in the synthesis of samples. A reasonable exfoliation mechanism of 2D ultrathin nanosheets is proposed and the energetics of the bath-ultrasonic process are discussed.