Distinguishing Amorphous and Anisotropic Heat Transport in Sb₂S₃ via Thermal Conductivity Imaging

Thermal conductivity imaging at the microscale enables the identification of material heterogeneity arising from microstructural features and secondary phases. In this work, we use it to investigate the role of crystal quality and structural anisotropy in rotating lattice single (RLS) Sb₂S₃ crystals. Defect engineering, which alters the local chemistry and microstructure, is a primary method for optimizing semiconductor performance, and RLS crystals—formed via laser-induced crystallization—offer a novel way to locally engineer crystal orientation. Using frequency domain thermoreflectance, we resolve spatial variations in thermal conductivity (κ) across RLS and amorphous regions. Results show marked differences, with amorphous areas exhibiting κ as low as 0.6 Wm^-1K^-1, while RLS crystal lines display periodic κ variations ranging from 0.7 to 2.5 Wm^-1K^-1. Interestingly, these variations correspond to the change in local crystal orientation. Ab initio calculations corroborate the results and highlight how the anisotropy in κ closely ties to the bonding nature of Sb₂S₃. The crystal cross-plane direction (a axis) shows amorphous-like transport, whereas the in-plane directions (c and b axis) exhibit 2x and 4x larger conductivities, respectively. The strong in-plane anisotropy is attributed to the buckled structure of Sb₂S₃ along the c axis. These findings demonstrate the ability to control thermal transport via laser-induced crystallization and lattice rotation, with significant implications for advancing thermal management and optoelectronic applications where precise control over heat flow is essential