Visualizing Gradual Aging of Lateral Heterostructured MoS₂-WS₂ Under Vacuum Conditions by Hyperspectral Phase...

Aging-related deterioration critically affects the performance of semiconducting devices that use two-dimensional transition-metal dichalcogenides (TMDs). Despite their significance, the long-term aging of TMDs under low-vacuum storage conditions remains poorly understood, particularly in lateral heterostructures, which are increasingly important for advanced electronic and optoelectronic applications. In this study, we systematically investigate the long-term aging of lateral heterostructured monolayer MoS₂-WS₂ stored under low-vacuum conditions for up to 40 months. Aging is initially observed at defect-prone sites in the outer WS₂ region and is progressively extended across the entire WS₂ domain, whereas the morphology of the inner MoS₂ domain is largely preserved. Conventional spectroscopic and microscopic analyses reveal the disappearance of WS₂ signatures but provide limited sensitivity for the identification of ultrathin and amorphous oxidation products. In contrast, hyperspectral phase microscopy (HPM) effectively tracks both morphological and compositional alterations, underscoring its exceptional sensitivity to changes in optical properties. By combining multiwavelength phase measurements with optical modeling, HPM measures the change in complex refractive indices during aging. These results highlight the utility of HPM as a robust, nondestructive platform for visualizing time-dependent optical and structural evolution in TMD heterostructures.