Mid-infrared three-states nanoimaging of reconfigurable binary chalcogenide Sb2S3

Conventional ternary chalcogenide phase change materials (PCMs) have been widely used for near-infrared to mid-infrared applications but typically exhibit only two phases. In contrast, antimony sulfide (Sb 2 S 3 ) is a binary phase-change material that can take three states and consists of earth-abundant elements. Despite its potential as a new class of PCM, Sb 2 S 3 remains relatively underexplored. In the current work, we employ Raman spectroscopy and nano-FTIR to investigate phase transitions of Sb 2 S 3 induced by femtosecond-pulsed and continuous-wave lasers. In particular, nano-FTIR enables nanoscale characterization of reversible phase transitions and clear identification of the typically elusive intermediate state. By integrating nano-FTIR and Raman spectroscopy, we correlate morphological and chemical features with optical responses. Crucially, the nano-FTIR amplitude distributions under broadband excitation are governed not only by the magnitude of the dielectric constant but also by the sensing depths. This work advances the understanding and application of binary chalcogenide PCMs for mid-infrared photonic devices.