Real-time high-resolution transmission electron microscopy observation of colloidal platinum nanocrystal growth using the graphene liquid cell

Abstract

Liquid phase transmission electron microscopy has solved many questions in biochemistry, materials science, environmental science, and catalysis due to the imaging capability down to nanoscale. Most of critical events, however, are still vague due to the lack of ability to study specimens in liquid with atomic resolution. We report a new and highly versatile approach to artificial layered materials synthesis which borrows concepts of molecular beam epitaxy, self-assembly, and graphite intercalation compounds. It readily yields stacks of graphene (or other two-dimensional sheets) separated by virtually any kind of “guest” species. The new material can be “sandwich like”, for which the guest species are relatively closely spaced and form a near-continuous inner layer of the sandwich, or “veil like”, where the guest species are widely separated, with each guest individually draped within a close-fitting, protective yet atomically thin graphene net or veil. The veils and sandwiches can be intermixed and used as a two-dimensional platform to control the movements and chemical interactions of guest species. We also report atomic resolution imaging of nanocrystals dynamics in Brownian-like liquid environments by using graphene liquid cell, a hermetically sealed enclosure by graphene membranes, and low-voltage aberration-corrected transmission electron microscopy. We demonstrate colloidal nanocrystal growth trajectories composed of sequential steps: correlated motion, oriented attachment, and faceting, with spatial resolution down to 0.14 nm and temporal resolution of 0.26 s. Our direct observation also provides colloidal nanocrystal diffusivity depending on their sizes down to sub-nanometre range. This ability of atom-resolved observation through liquid will provide explanations of ambiguous natural phenomena including liquid phase. Moreover, we propose three-dimensional observation of a platinum nanocrystal at atomic resolution using spontaneous nanocrystal rotation in liquid. We achieve spatial resolution down to 0.14 nm and temporal resolution of 30.5 ms.