Effect of Al2O3 capping layer on the crystallization behavior of optical Sb2S3 films

Nanoscale Sb2S3 utilizes the reversible crystalline-amorphous phase transition and is widely used in phase-change memory and near-infrared optoelectronic devices. However, a critical bottleneck persists as its high oxidation susceptibility degrades photoelectrochemical performance. Herein, the crystallization mechanism and oxidation protection pathway of Sb2S3 thin films are clarified by interface engineering. Based on scanning transmission electron microscopy, upon annealing at 300 °C, uncapped Sb2S3 precipitates “pearl chain-like” Sb2O3 along Sb2S3 polygonal domains. The oxidized structure is formed by the permeation and diffusion of environmental oxygen. In contrast, the Al2O3/Sb2S3 heterojunction film annealed at the same temperature exhibits only a single crystalline phase of Sb2S3, confirming the heterointerface as an efficient strategy for blocking oxidation while ensuring the structural integrity and performance stability. Furthermore, the Al2O3/Sb2S3 thin film annealed at 350 °C undergoes a structural transition to a biphasic coexistence structure, where elemental Sb is dispersedly embedded atop the Sb2S3 matrix. This phenomenon originates from a thermal diffusion-dominated crystallization mechanism. These findings provide a universal “heterointerface construction” strategy for oxidation protection of nanoscale phase-change thin films, offering critical guidance for optimizing Sb2S3 device structures and extending their service life.