2, U.S. Naval Research Laboratory, Washington, District of Columbia, United States
3, U.S. Naval Research Laboratory, Washington, District of Columbia, United States
The use of in situ liquid cell transmission electron microscopy (LCTEM) provides a powerful tool to directly observe nanoparticles (NPs) suspended in solution, but care must be taken to understand and control how electron beam illumination affects not just the NPs, but also their local environment, which can then in turn affect the NPs. In this report, we present direct visualization of the dynamics of oleic-acid-capped PbTe NPs using LCTEM equipped with a high speed camera (Protochips Poseidon P500 wet cell holder in a JEOL JEM2200FS operating at 200kV and a Gatan OneView with a full resolution 4000 x 4000 pixel images acquired at 25 fps which is binnable to 50 and 100 fps). We observe electron dose rate dependent etching and dissolution of PbTe NPs in toluene; ranging from no perceivable effect on the particles with lower dose rates (30 e-/Å2/sec) to full dissolution with higher dose rates (150 e-/Å2/sec). In addition, the dissolution effects are also observed to depend on local NP concentration. Despite suspension in an organic solvent (toluene) which produces very few chemically-active species under electron (beta particle) radiation, the radiolysis of the water adsorbed on the LCTEM SiNx membrane during PbTe NPs loading results in multiple radiolytically-produced species. These radicals include several oxidizing species which cause etching of NPs. This behavior is initiated only after a threshold electron dose rate is received. This report provides direct evidence for the dissolution of PbTe NPs in organic solvents due to the radiolysis of adsorbed water. To prevent this dissolution, rigorous protocols to preserve anhydrous conditions, different capping agents, and sub-threshold dose rate imaging can be used. The authors acknowledge funding from the Office of Naval Research (Naval Research Laboratory Basic Research Program). This research was performed while N.B. and D.L.W. held National Research Council Research Associate Awards at the U.S. Naval Research Laboratory.