Nanoscale Imaging and Stabilization of Silica Nanospheres in Liquid Phase Transmission Electron Microscopy

Abstract

Liquid phase transmission electron microscopy (LP‐TEM) is a novel and highly promising technique for the in situ study of important nanoscale processes, in particular the synthesis and modification of various nanostructures in a liquid. Destabilization of the samples, including reduction, oxidation, or dissolution by interactions between electron beam, liquid, and sample, is still one of the main challenges of this technique. This work focuses on amorphous silica nanospheres and the phenomena behind their reshaping and dissolution in LP‐TEM. It is proposed that silica degradation is primarily the result of reducing radical formation in the liquid phase and the subsequent accelerated hydroxylation of the silica, while alterations in silica solid structure, pH, and oxidizing species formation had limited influence. Furthermore, the presence of water vapor instead of liquid water also results in degradation of silica. Most importantly however, it is shown that the addition of scavengers for reducing radicals significantly improved amorphous silica stability during LP‐TEM imaging. Devising such methods to overcome adverse effects in LP‐TEM is of the utmost importance for further development and implementation of this technique in studies of nanoscale processes in liquid.

Assessment of oxide nanoparticle stability in liquid phase transmission electron microscopy

“…Based on previous work [54,55] and this study, we can conclude that while the proposed formation of oxygen vacancies can still take place, especially at high electron beam dose rates [55], it is likely not a universal mechanism of oxide dissolution, nor the driving force. Oxide (and suboxide) hydration seems to be a key factor in determining their stability, but the exact mechanism of oxide dissolution in LP-TEM is clearly a very complex process and likely unique for each oxide.…”

“…Considering that the scanning is always in 1 direction, this could lead to directionality in electron beam induced effects. In fact, the previously mentioned selective etching that was observed for silica is a result of this effect [52,54]. The higher electron dose rates of the STEM probe, could also allow effects that only occur above a certain threshold of electron dose rate to take place easier in STEM than in TEM, such as nucleation [69].…”

“…For amorphous silica, it has recently been found that the mechanism likely involves the acceleration of silica hydroxylation and subsequent dissolution through the electron beam induced formation of reducing radicals capable of breaking the Si-O-Si bonds [54]. Suppressing the formation of these radicals by using a 1:1 acetic acid/sodium acetate buffer as radical scavenger, resulted in a more stable silica.…”

“…Although this effect is well-known for biological and carbonaceous samples [50], most LP-TEM studies so far have focused on metal nanoparticles, while the understanding of oxide degradation behavior is still limited. Recent investigations on iron (hydr)oxide [51] and silicon dioxide [52][53][54] have shown that oxide materials can also suffer from electron beam induced destabilization in a liquid environment. In addition, Lu et al [55] investigated dissolution behavior of several oxides in LP-TEM.…”

Controlling the Facet of ZnO during Wet Chemical Etching Its (0001¯) O‐Terminated Surface

“…can be produced in water by high energy electron beam irradiation and the etching mechanisms in LCTEM are very complicated. [ 14–17 ] ZnO is an amphoteric oxide which can be etched in deionized water (pH ≈ 6.7–6.9), ambient environment, H 2 O 2 , acid, and alkali solution. [ 18–22 ] Hence, most radicals (H 2 O 2 , H 3 O + , OH•, HO 2 •,etc.)…”