The development and applications of <italic>in situ</italic> liquid chamber TEM technologies

Abstract

Transmission electron microscopy (TEM), with the high spatial and temporal resolution, is widely used in nano material characterizations. Due to the vacuum compatibility issue, traditional TEM is mostly used for solid and dry samples. The progress of nano science involves a wide range of liquid environments, and the development of in situ liquid chamber TEM technologies has made it possible for real time dynamic analysis on samples in liquid environments, with nanometer scale imaging resolutions, and greatly expanded the application ranges of TEM. This field has now brought much attention internationally, and is currently growing with a very rapid speed. In this paper, we review the progress about in situ liquid chamber TEM that our group has participated in and/or carried out in the recent years. It includes the development of the in situ liquid chamber TEM experiment apparatus, and its applications in the fields of nano-material preparations and characterizations, electrochemical reaction processes, new energy materials and devices, and life sciences. At last, the future development trend of in situ liquid chamber TEM is prospected. Firstly, some in situ liquid chamber TEM experiment apparatuses have been developed. These in situ chambers are home-made, based on metal cages and O-ring seals, which allow silicon nitride window substrates to be quickly assembled together, with liquid samples sealed inside. Besides simple imaging, electrochemical and heating-cooling functions have been incorporated into the setups, allowing for more advanced analyses. Using these in situ TEM apparatus, several nano material and reaction systems have been monitored. A sliver particle aqueous solution sample has been characterized. The particles were observed to be about 5–18 nm, attached to the Si3N4 windows, and could not be able to move freely in the liquid. Fine structures within single particles could be clearly seen. Bubbles commonly exist in an in situ liquid chamber, which are important for effectively reducing the local liquid layer thickness and enhancing the imaging resolution. In Au particle aqueous solution sample, particle and particle cluster motions have been further observed. The results show that particles in a cluster gradually fused together with time. For Au/AgCl composite nanocube sample, more dramatic electron beam effect has been seen, and the nanocubes were transformed quickly into hollow structures. By means of a liquid phase electron beam induced deposition (LP-EBID) approach, Si and SiC x nano structures have been made with in situ liquid chamber TEM. Nano dots, nano lines and three-dimensional nano structures can be controllably made by adjusting the electron beam exposure conditions. Secondary electron effects are attributed to the nano structural growth mechanism. Choosing Ni/NiCl2 system, both electrochemical deposition and etching of the nickel nano films have been observed by applying electric biases of different polarities to the nickel electrodes in the in situ chamber. Instead of extensional growth on existing crystals, it is more commonly observed that new nickel nano particles grow out in front of the existing film first and then merge into the film. During electrochemical etching, holes form in the Ni films due to Rayleigh instability. The structures of E. coli cells in aqueous solutions have been studied. Most of the cells remaine intact under the electron beam irradiation, Pili motions have been observed in the TEM imaging. Fluorescent imaging data confirm that the cells can keep alive after long time electron bean irradiation during the experiment. In situ liquid chamber TEM has opened up a new way for conducting research in nano science, new energy materials and devices, life sciences, involving liquid environments. In the future, it is expected that advanced functions of the in situ liquid chamber TEM will be further developed, and the application scope will be further expanded.