Using Graphene Liquid Cell Transmission Electron Microscopy to Study in Situ Nanocrystal Etching.

A Paul Alivisatos,Matthew R Hauwiller,Justin C Ondry

doi:10.3791/57665

Abstract

Graphene liquid cell electron microscopy provides the ability to observe nanoscale chemical transformations and dynamics as the reactions are occurring in liquid environments. This manuscript describes the process for making graphene liquid cells through the example of graphene liquid cell transmission electron microscopy (TEM) experiments of gold nanocrystal etching. The protocol for making graphene liquid cells involves coating gold, holey-carbon TEM grids with chemical vapor deposition graphene and then using those graphene-coated grids to encapsulate liquid between two graphene surfaces. These pockets of liquid, with the nanomaterial of interest, are imaged in the electron microscope to see the dynamics of the nanoscale process, in this case the oxidative etching of gold nanorods. By controlling the electron beam dose rate, which modulates the etching species in the liquid cell, the underlying mechanisms of how atoms are removed from nanocrystals to form different facets and shapes can be better understood. Graphene liquid cell TEM has the advantages of high spatial resolution, compatibility with traditional TEM holders, and low start-up costs for research groups. Current limitations include delicate sample preparation, lack of flow capability, and reliance on electron beam-generated radiolysis products to induce reactions. With further development and control, graphene liquid cell may become a ubiquitous technique in nanomaterials and biology, and is already being used to study mechanisms governing growth, etching, and self-assembly processes of nanomaterials in liquid on the single particle level.

Highlights

IntroductionSynthesizing nanocrystals[1] and assembling nanoparticles into larger structures[2,3] requires an understanding of the fundamental mechanisms governing how atoms and nanoparticles interact and bind together
Synthesizing nanocrystals[1] and assembling nanoparticles into larger structures[2,3] requires an understanding of the fundamental mechanisms governing how atoms and nanoparticles interact and bind together. Studies of these nanoscale processes would be performed in their native liquid environment with the corresponding spatial resolution necessary to observe the phenomena of interest, but these requirements pose challenges due to the nanometer length scale on which these systems operate
The aim of this article is to share the details of how graphene liquid cell transmission electron microscopy (TEM) experiments can be carried out (Figure 1), using an example experiment observing single particle etching of nanocrystals, and hopefully show that graphene liquid cell experiments are possible for almost any group with access to an electron microscope

Summary

Introduction

Synthesizing nanocrystals[1] and assembling nanoparticles into larger structures[2,3] requires an understanding of the fundamental mechanisms governing how atoms and nanoparticles interact and bind together. Studies of these nanoscale processes would be performed in their native liquid environment with the corresponding spatial resolution necessary to observe the phenomena of interest, but these requirements pose challenges due to the nanometer length scale on which these systems operate. The decreased scattering of these home-made liquid cells has enabled electron microscopy studies with greater spatial resolution including atomic resolution studies[19,20,21]

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Conclusion