Strategies for size- and shape-controlled synthesis of nanocrystals have been explored to design functional nanomaterials for catalysis, energy storage, biomedical, optical and electronic applications. In situ liquid scanning transmission electron microscopy (STEM) has the unique ability to image evolving chemical processes within a liquid environment and at high spatial and temporal resolution. Herein, we report two strategies for the directed synthesis of metallic and bimetallic nanoscale architectures using in situ liquid STEM. In the first approach, we developed a direct write, template free method to fabricate self-supporting, hollow metallic nanostructures and we interpret the formation mechanisms based on direct observations of nucleation and growth. A liquid phase precursor solution containing reducible chemistries is encapsulated between electron transparent silicon nitride membranes. The electron beam that is generally used for imaging stimulates radiolysis; thereby, promoting the dissociation of water (H2O) molecules and the formation of complex radical species such as aqueous electrons (eaq-) and other reducing and oxidizing species. The highly reducing radiolysis generated species assist in the chemical reduction of metal ions from the precursor solution resulting in the formation of a metallic nanocrystal seed, which then acts as a catalyst generated H2 gas forming a metal encapsulated hollow nanobubble. In the second approach, we utilize a custom-built electron beam nanopositioning and scan generator system to precisely control the position and electron dose of focused electron beam in an aberration corrected STEM to fabricated metallic and bi-metallic nanostructured materials. These approaches enable fundamental electron beam interaction studies as well as open a new pathway for direct-write nanolithography from liquid phase solutions.
This research was supported by the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.