Eventual Chemical Transformation of Metals and Chalcogens into Metal Chalcogenide Nanoplates through a Surface Nucleation-Detachment-Reorganization Mechanism

Abstract

Many studies have reported the synthesis of two-dimensional (2D) nanoplates and nanosheets of the layer-structured metal chalcogenides but also have reported various structures far from the 2D shape. In multicomponent compounds, the elemental concentrations keep changing during the reaction; hence, the reactions are considered to be nonstoichiometric from the nucleation and may include continuous changes in the structure and composition. The different shapes of the metal chalcogenides with the layered structure are attributed to the nonstoichiometric reactions. However, it has not been studied if such nonstoichiometric reactions eventually produce 2D nanoplates, and the mechanism involved in the transformation has not been understood. This study investigates a two-step chemical reaction as an extreme nonstoichiometric nucleation and growth. It reveals that the layer-structured metal chalcogenides (M2X3, M = Sb and Bi, X = Se and Te) with the R3̅m space group can be obtained by transforming premade pure chalcogen (Se, Te) thick nanorods or metal microparticles (Bi). By coupling our first-principles calculations with a shape-prediction thermodynamic model, we have also examined and rationalized the shape/aspect ratio of the M2X3 nanocrystals under different experimental growth conditions. The tendency of anisotropic growth to form the 2D shapes during the transformations are discussed on the basis of experimental results and theoretical calculations.