acquire many insights in interesting topics such as interparticle interactions and colloidal self-assembly. [1][2][3] Liquid-cell (scanning) transmission electron microscopy [4,5] (LC(S)TEM) has recently emerged as a powerful tool to observe dynamic processes of nanoparticles (NPs) in liquid with nanometer spatial resolution. However, the electron beam significantly influenced the observed phenomena in many cases. So far, strongly slowed down diffusion of NPs was observed in LC(S)TEM studies. Possible explanations for this phenomenon, apart from trivial difficulties such as the imaging system not being fast enough to image free Brownian motion, include hydrodynamic slowing down near the window's surface, [10,16] a highly viscous ordered liquid layer near the windows, [10,15] and strong (sometimes beam-induced) interactions with the liquid-cell windows. [6,10,15,16,18] Observing 3D Brownian motion in the electron microscope that is not significantly altered by the electron beam and/or the presence of the windows would open the way for many experiments, including studies on colloidal self-assembly of NP dispersions. [30] The objective of this work is to find conditions and identify key experimental parameters for which 3D Brownian motion is observable in LC(S)TEM.In this study, we combine a low dose scanning transmission electron microscopy (STEM) technique with viscous liquid media having a high dielectric constant to observe bulk diffusion of gold NPs and titania particles in LC(S)TEM. The significantly faster diffusion of particles in comparison to many previous liquid-cell electron microscopy studies that we report on in this work underlines the importance of choosing a suitable electron microscopy imaging technique, electron dose rate and solvent in order to study dynamic processes in LC(S)TEM without artefacts. Results and DiscussionFor this work, we studied two different systems. One with bigger particles in a less viscous solvent and one with smaller particles in a more viscous solvent. The bigger particles serve as a first check whether free diffusion is at all possible within the In theory, liquid-cell (scanning) transmission electron microscopy (LC(S)TEM) is the ideal method to measure 3D diffusion of nanoparticles (NPs) on a single particle level, beyond the capabilities of optical methods. However, particle diffusion experiments have been especially hard to explain in LC(S) TEM as the observed motion thus far has been slower than theoretical predictions by 3-8 orders of magnitude due to electron beam effects. Here, direct experimental evidence of undamped diffusion for two systems is shown; charge-neutral 77 nm gold nanoparticles in glycerol and negatively charged 350 nm titania particles in glycerol carbonate. The high viscosities of the used media and a low electron dose rate allow observation of Brownian motion that is not significantly altered by the electron beam. The resulting diffusion coefficient agrees excellently with a theoretical value assuming free diffusion. It is confirmed that the par...
The recent development of liquid cell (scanning) transmission electron microscopy (LC-(S)TEM) has opened the unique possibility of studying the chemical behavior of nanomaterials down to the nanoscale in a liquid environment. Here, we show that the chemically induced etching of three different types of silica-based silica nanoparticles can be reliably studied at the single particle level using LC-(S)TEM with a negligible effect of the electron beam, and we demonstrate this method by successfully monitoring the formation of silica-based heterogeneous yolk–shell nanostructures. By scrutinizing the influence of electron beam irradiation, we show that the cumulative electron dose on the imaging area plays a crucial role in the observed damage and needs to be considered during experimental design. Monte-Carlo simulations of the electron trajectories during LC-(S)TEM experiments allowed us to relate the cumulative electron dose to the deposited energy on the particles, which was found to significantly alter the silica network under imaging conditions of nanoparticles. We used these optimized LC-(S)TEM imaging conditions to systematically characterize the wet etching of silica and metal(oxide)–silica core–shell nanoparticles with cores of gold and iron oxide, which are representative of many other core–silica–shell systems. The LC-(S)TEM method reliably reproduced the etching patterns of Stöber, water-in-oil reverse microemulsion (WORM), and amino acid-catalyzed silica particles that were reported before in the literature. Furthermore, we directly visualized the formation of yolk–shell structures from the wet etching of Au@Stöber silica and Fe 3 O 4 @WORM silica core–shell nanospheres.
In this work, an industrially scalable method for a precisely controlled deposition of subnanosized metallic particles (e.g., platinum) on reduced graphene oxide has been developed. Partially reduced graphene oxide, a band gap engineered form of graphene, has been utilized for two purposes: the reduction of the metallic particles and a support layer. For the partial reduction, graphene oxide has been treated with a highly concentrated sodium hydroxide solution and the reduction process has been continued (and monitored) until obtaining a stable product. The chemical stability and band gap modulation process of the partially reduced graphene oxide have been discussed comprehensively. We have shown that the graphene oxide which also exhibits semiconducting properties is not a suitable choice as a photocatalyst material mainly because of its chemical instability and considerable photocorrosion. An innovative reactor with large-scale production capacity for pulsed UV illumination and continuous treatment of the reaction suspensions has been designed. A simple flow control in this reactor enables us to have precise control of the number of photoexcited electrons and consequently of the photodeposition of the subnanosized Pt particles.
Graphene-containing fibrous structures with a high level of affinity towards a polymer matrix solution have been proved to be promising for high performance macroscopic nanocomposite reinforcement purposes.
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