The rapid development of halide perovskite synthesis offers the opportunity to fabricate high-quality perovskite nanocrystals (NCs), whose structural uniformity can lead to assembled supra-structures with improved device performance and novel collective properties. Light is known to significantly affect the structure and properties of halide perovskites and plays a crucial role in the growth and assembly of their crystals. Nevertheless, the light-induced growth mechanisms of perovskite NCs are not yet clearly understood. In this work, we performed a systematic study of the visible-light-induced template-free synthesis of CsPbBr3 nanowires (NWs) generated through self-assembly of cubic (in phase and close to cubic morphology) NCs. Using atomic-resolution electron microscopy, we visualized the cubic-to-orthorhombic phase transition in NCs and the interface between coalesced NCs. Remarkably, the images of the interface revealed the coexistence of CsBr and PbBr2 surface terminations in halide perovskites. Our results shed light on the mechanism underlying the observed anisotropic assembly of halide perovskites and elucidate the vital role of light illumination during this process. More importantly, as an elegant and promising green-chemistry approach, light-induced self-assembly represents a rational method for designing perovskites.

First-principles molecular dynamics simulation reveals the effects of electronic excitation in the amorphization of Ge-Sb-Te. The excitation makes the phase change an element-selective process, lowers the critical amorphization temperature considerably, for example, to below 700 K at a 9% excitation, and reduces the atomic diffusion coefficient with respect to that of melt by at least 1 order of magnitude. Noticeably, the resulting structure has fewer wrong bonds and significantly increased phase-change reversibility. Our results point to a new direction in manipulating ultrafast phase-change processes with improved controllability.