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.
Highlights
When scaled down to nanometer size, many materials exhibit properties quite different from those of a bulk phase
It is likely that part of the CTAB was still present as the Au NRs could still be dispersed in water after heating on a glass plate
For the NRs that were heated at 100°C only a small blue-shift from 812 nm to 805 nm occurred in agreement with a small decrease in aspect ratio to 3.1 as observed by Transmission electron microscopy (TEM)
Summary
When scaled down to nanometer size, many materials exhibit properties quite different from those of a bulk phase. Localized surface plasmon resonances (LSPRs) lie at the core of many applications as they lead to strong local electric field enhancements, especially at sharp corners and tips Due to their anisotropic shape, Au NRs exhibit a (degenerated) transverse and a longitudinal LSPR. Apart from well-known e-beam induced damages to the sample’s structure during regular TEM imaging [30], insitu TEM studies with or without heating under vacuum, gas-phase and liquid phase conditions, brought about additional challenges. It was recently shown, for example, that the electron beam leads to an increased dislocation activation during in-situ TEM experiments investigating tensile straining of aluminum and gold films [31]. Our research shows that an electron beam and the presence or absence of certain gasses can have a large impact on a sample during in-situ TEM experiments and calls for critical assessment of insitu TEM data and a need for comparison with ex-situ experiments before any conclusions about the sample structure and/or behavior can be drawn
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