Studying the Effect of Oxidation on the Thermolysis of (NH₄)₂WS₄ with In‐ and Ex‐Situ Electron Microscopy

Abstract

Thermolysis is a common technique in materials synthesis; however, oxidation of precursors used in these processes destroys the ability to generate end‐products with the desired composition and structure. Herein, the effects of oxidation on the thermolysis of (NH4)2WS4, a common precursor in the production of WS2 films, are studied utilizing electron microscopy. Specifically, in situ bright field, dark field, and secondary electron images were collected during heating of the aforementioned oxidized precursor from RT to 800 °C in 100 °C steps within a low kV scanning transmission electron microscope. These imaging results detail how the precursor transforms from its largely nondescript room temperature morphology to one having well formed 2D, 1D, and 0D nanostructures. Subsequent ex situ atomic level imaging shows that the 2D and 1D nanomaterials are composed of δ‐WO3 which has grown along its c‐axis, whereas the 0D nanoparticles are made solely of α‐W. Through the combination of both in and ex situ images, we have gained valuable insights into the structural and chemical changes that occur owing to the additional oxygen in the system, as well as the role that precursor density plays on the formation of these as formed nanomaterials.