Impact of the electron beam on the thermal stability of gold nanorods studied by environmental transmission electron microscopy

Abstract

In-situ transmission electron microscopy experiments are of great interest to nanoscience and nanotechnology. However, it is known that the electron beam can have a significant impact on the structure of the sample which makes it important to carefully interpret in-situ data. In this work, we studied the thermal stability of CTAB-stabilized gold nanorods under different gaseous environments in an environmental transmission electron microscope and compared the outcome to ex-situ heating experiments. We observed a remarkable influence of the electron beam: While the nanorods were stable under inert conditions when exposed to the electron beam even at 400°C, the same nanorods reshaped at temperatures as low as 100°C under ex-situ conditions. We ascribe the stabilizing effect to the transformation of the CTAB bi-layer into a thin carbon layer under electron beam irradiation, preventing the nanorods from deforming. When exposed to an oxidizing environment in the environmental transmission electron microscope, this carbon layer was gradually removed and the gold atoms became mobile allowing for the deformation of the rod. This work highlights the importance of understanding the phenomena taking place under electron beam irradiation, which can greatly affect in-situ experiments and conclusions drawn from these. It stresses that in-situ electron microscopy data, taken on measuring the temperature dependence of nanoparticle properties, should be carefully assessed and accompanied by ex-situ experiments if possible.

3D characterization of heat-induced morphological changes of Au nanostars by fast in situ electron tomography

“…It is important to note that CTAB can be transformed by the electron beam into a protective amorphous carbon layer, which has been shown to prevent deformation of Au NRs upon in situ heating, even for heating at 400°C for one hour. 35 This again stresses the need for a fast acquisition procedure to perform such in situ experiments in 3D. Over the course of time of one conventional tomography experiment, we were able to perform ten fast tomographic acquisitions.…”

“…Dose reduction is crucial, since it was recently shown that even apparently beam-insensitive nanomaterials such as Au nanorods exhibit an altered thermal stability upon in situ heating, compared to ex situ experiments. 35 In what follows, we make use of this novel technique to study the heatinduced 3D morphological changes of highly anisotropic Au NSs. Aided by the drastic reduction in acquisition time of the fast tomography experiment, gradual changes can be examined, as opposed to earlier ex situ work in which electron tomography series could only be obtained before and after heating.…”

Thermal Stability of Gold/Palladium Octopods Studied in Situ in 3D: Understanding Design Rules for Thermally Stable Metal Nanoparticles

“…This effect can be most likely attributed to the electron beam induced transformation of the surrounding ligands into a protective carbon shell as observed for other Au NPs. 48 This carbon shell most likely hinders surface diffusion and could be the reason for the slowing down of the deformation of the pure Au octopods. This is supported by the observation that Au octopods, that were not irradiated by the electron beam, lost all prominent morphological features at 200 • C (Figure S14).…”

3D characterization of heat-induced morphological changes of Au nanostars by fast in-situ electron tomography

“…Dose reduction is crucial, Nanoscale Accepted Manuscript 6 since it was recently shown that even apparently beam-insensitive nanomaterials such as Au nanorods exhibit an altered thermal stability upon in-situ heating, compared to ex-situ experiments. 35 In what follows, we make use of this novel technique to study the heat-induced 3D morphological changes of highly anisotropic Au NSs. Aided by the drastic reduction in acquisition time of the fast tomography experiment, gradual changes can be examined, as opposed to earlier ex-situ work in which electron tomography series could only be obtained before and after heating 36 .…”