Martensite-like phase transformation of ligand-capped SnS tetrahedrons from π phase to α phase and its impact on H₂ evolution performance

π-Tin sulfide (SnS) is an emerging semiconductor of interest with attractive properties for applications in solar energy conversion and non-linear optics. However, its intrinsic metastability raises concerns and requires further investigation. Here, we report a newly discovered martensite-like phase transition in ligand-capped π-SnS tetrahedrons by a post-annealing treatment. By adjusting the annealing temperature, we found that the desorption of surface ligands initiated the rearrangement of surface atoms, thus triggering a chain phase transformation from π phase to α phase through the displacement of adjacent atoms. Large amounts of boundaries and stacking faults were present in this process, as shown from high-resolution transmission electron microscopy combined with selected area electron diffraction. Furthermore, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy showed that the initiation temperature for phase transition relies on surface ligands. Hexamethyldisilazane (HMDS)-capped tetrahedrons show higher stability against a temperature of 500 °C than oleylamine (OLA)-capped tetrahedrons due to the stronger interaction between HMDS ligands with SnS surface atoms. The mechanism involved in the ligand-affected structure evolution of π-SnS tetrahedrons and the corresponding H2 generation performance is discussed in detail.