High resolution observation of a noble-metal/ZnO-QDs/rGO ternary system through an ultra-thin SiNx window using in situ liquid cell scanning electron microscopy†

In situ liquid cell electron microscopy technology has high temporal and spatial resolution, enabling real-time observation of physical and chemical processes in liquid environments. However, the common in situ liquid cell scanning electron microscopy (LC-SEM) technology has faced limitations due to the relatively large thickness of the SiN_x window, resulting in unsatisfactory resolution and limiting the broad adoption of the LC-SEM technology. This article represents one novel approach of utilizing ultra-thin SiN_x windows for LC-SEM observation of the distribution and dynamic changes of gold (Au) nanoparticles/zinc oxide quantum dots (ZnO QDs)/reduced graphene oxide (rGO) ternary composites in liquid. The results demonstrate a single/near-single dispersed distribution of ZnO QDs on the surface of the rGO, with Au nanoparticles and ZnO clusters mainly concentrated on the rGO folds. The composite structure demonstrates relative stability, attributed to electrostatic forces. Using Au nanoparticles and ZnO QDs as hierarchical reference markers, a high LC-SEM image resolution of ∼4 nm is obtained, which allows the observation and motion analysis of the Au nanoparticles, rGO nanosheets, and ZnO QDs in the liquid cell. Such LC-SEM technology shows good repeatability on the noble-metal/ZnO-QDs/rGO ternary composite samples, with good potential for future QD composite material research studies.