Using In Situ Liquid TEM to Characterize the Size, Shape and Composition of Nanomaterials

composition of nanoparticles

Nanoparticle-based materials are frequently utilized in a variety of applications such as drug delivery, energy production, and catalysis. The shape, composition, and size of nanoparticles has a significant influence on their performance, so producing controllable manufacturing systems is crucial to the commercialization of the latest nanomaterials.

Powerful microscopes such as the transmission electron microscope (TEM) must be used in the characterization of nanoparticles.The TEM can resolve nanoscale characteristics and extract structural and chemical information through electron diffraction and x-ray (EDS) analysis, which is essential in understanding the properties of nanoparticles. The majority of nanoparticles are synthesized in liquid, and the high vacuum environment within the TEM makes the imaging of samples suspended in liquid more complex. To accurately comprehend the dynamic growth processes and natural behavior of nanoparticles in liquid, the use of emerging in situ methods, for example the Protochips Poseidon liquid cell, is fundamental.

Professor Wen-Wei Wu is a Distinguished Professor of Materials Science and Engineering at the National Chiao Tung University in Taiwan. His research concentrates on the characterization and growth of nanomaterials. His research group utilized the Poseidon liquid cell to envisage the growth dynamics of Au-Cu2O core-shell nanoparticles and to characterize the ensuing structure. The group engineered different Cu2O shapes in a controllable manner, and observed the growth process unfolding in real-time by tuning the surface functionalization of the initial Au nanoparticle.

Revealing the Dynamics of Core-Shell Nanoparticle Synthesis

Core shell nanoparticles have been employed in several applications, for example, solar cells and sensors. As with the majority of nanoparticles, the surface, or shell, composition and structure have a powerful influence on performance.Only in situ liquid TEM can show which factors affect how the shell is produced in real-time and at the nanoscale, and can offer guidance for controlled synthesis, even though several techniques are utilized before and after reaction to characterize particles in liquid.

The nanoparticles were grown through the combination of three solutions in the experiment. A solution of gold nanoparticles was flowed into the Poseidon cell first of all, which was followed by a combination of CuSO4/NaOH/H2O, and lastly ascorbic acid (a reducing agent).The researchers discovered that two kinds of core-shell structures were produced: multifaceted and cubic.The type of structure that formed was influenced by two factors: the dispersion of Au nanoparticles and the uniformity of citrate ligands on the seed Au nanoparticles. High resolution and dynamic imaging lasting several seconds enabled the quantitative determination of the shell growth rate over time (Figure 1) at 210 nm2/s.  

The growth of Au-Cu2O particles in liquid as a function of time. The yellow arrows indicate steric hindrance effects, and the red arrows indicate gold nanoparticles that lacked ligands.

Figure 1. The growth of Au-Cu2O particles in liquid as a function of time. The yellow arrows indicate steric hindrance effects, and the red arrows indicate gold nanoparticles that lacked ligands.

The impact of growth conditions on the structure of Au-Cu2O particles

Figure 2. The impact of growth conditions on the structure of Au-Cu2O particles

Additional ex-situ assessments of the Au/Cu2O interface showed that for the multi-faceted structure, the growth of Cu2O on Au is epitaxial. The shell and the core essentially have an equivalent crystalline orientation as displayed in Figure 3(a)-(e) below. For the cubic core-shell structure, the shell and core have mismatched crystalline orientations. The shell evolves independently from the gold core, and its facets are created on low-index planes to reduce surface energy as presented in Figure 3(f)-(j) below.

Core/shell interface structure for multi-faceted and cubic Au-Cu2O particles

Figure 3. Core/shell interface structure for multi-faceted and cubic Au-Cu2O particles

Conclusions

High-resolution and dynamic imaging employing the Poseidon Select liquid cell enabled the efficient characterization of the process of synthesis for Au/Cu2O core-shell nanoparticles in the TEM. The experimental parameters that determined the structure and rate of growth of the particles were revealed, and a model was produced to describe the growth. Crucial insight into the growth mechanisms and which factors influenced the resulting structure was gained by the researchers at NCTU. This empowered them to engineer and produce materials with significantly optimized performance, and more efficiently than ever before.

Liquid cell TEM is an effective tool for the rapid and precise characterization of the properties of nanomaterials, whether they are produced in-house or integrated within a process. There is no replacement for the precise measurement of the shape, composition, and size of nanomaterials in their native environment.

References

DOI: 10.1039/C9NR00972H
https://pubs.rsc.org/en/content/articlelanding/2019/nr/c9nr00972h#!divAbstract

This information has been sourced, reviewed and adapted from materials provided by Protochips.

For more information on this source, please visit Protochips.

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