Assembled liquid cell holder for in situ TEM
Image courtesy of Protochips


It is demonstrated that the redox reaction behaviors of Pd nanoparticles in HAuCl4solutions can be substantially modified by the introduction of hexadecyl trimethyl ammonium bromide (CTAB) agents through systematic liquid cell transmission electron microscopy (LCTEM) investigations. The gradual dissolution of Pd nanoparticles is observed when HAuCl4 solution is pumped into liquid flow cells, the etching characteristics of which are depended on both HAuCl4 concentrations and incident electron doses. In comparison, with the presence of CTAB agents, the dominated phenomenon appears to be the precipitation of Au species and incorporation onto the surface of Pd seeds. It is also observed that the rapid growth of Au on Pd seeds occurs by loading Pd and HAuCl4 solutions into static liquid cells. The resultant Au shells exhibit rather sparse structural configurations and are formed possibly by homogeneous nucleation/coalescence of Au species as well as monomer attachments. The observed Au‐shell growth instead of Pd dissolution is attributed to the presence of the residual regents, which may be also responsible for the initially already existing small Au adsorptions at the corner/edge sites of Pd seeds. The study provides a useful reference for the convenient fabrication of complex nanostructures and functional nanomaterials in a controllable way.

Impact Statement

It is a well documented phenomenon that the electron beam can induce both reductive and oxidative reactions in in-situ liquid phase experiments. Here, the redox effects of HAuClto either etch or precipitate onto palladium seed nanoparticles are studied using both flow and static liquid environments.  When HAuCl4 is flowed into a cell containing the palladium nanocube seed particles an oxidative etching process is observed, which is inhibited if the capping agent (CTAB) is added during the experiment.  In the presence of CTAB, characteristic growth phenomena is observed as gold is deposited onto the surface of the nanocube through beam induced reduction.  Interestingly, when the experiment was performed in a non-flow, static regime, the etching of the palladium nanoparticles by HAuCl4 was suppressed.