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Visualizing nanoscale assembly and fabrication in solution using in situ TEM
1  Department of Physics , National University of Singapore, 117551, Singapore
2  Centre for BioImaging Sciences, Department of Biological Sciences, National University of Singapore, 117557, Singapore
3  Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, 117546, Singapore

Abstract:

The assembly process of nanoparticles from individual atoms, and nanostructures from nanoparticles in solution is fundamental for materials engineering and “bottom-up” fabrication of functional nanodevices.

Using dynamic in situ TEM imaging [1-3] in liquids, I will describe how nanoparticles form in solution and how these nanoparticles interact with each other. First, I will discuss how phase separation of a solution containing Au ions into solute-rich and solute-poor phases leads to formation of Au nanocrystal through a pathway that does not follow classical nucleation theory (CNT). Namely, I will show that there are multiple steps that lead to formation of nuclei from which nanocrystals grow [4]. These steps are: 1) phase separation of liquid solution into solute-poor and solute-rich phases, from which 2) an amorphous nanoparticles which serve as a precursor for nuclei emerges. This is followed by 3) crystallization of amorphous nanoparticle into a crystalline nuclei.

Next, I will highlight the role of intermolecular forces between nanoparticles in solution and describe their role in the assembly of nanostructures from individual nanoparticle building blocks (bottom-up approach) [5]. Specifically, I will show how the balance between repulsive hydration force and attractive van der Waals (vdW) force results in a metastable nanoparticle-pair which promotes their subsequent attachment to each other [5]. I will also describe the dynamics of how capillary forces, interfaces and linker molecules aide in the assembly of nanoparticles [6-7].

Finally, I will conclude by describing our recent work where we track the nanoscale dynamics of wet-etch (top-down approach) processes to shape nanomaterials.

These findings highlight the role of solvent mediated physical and chemical forces in material synthesis and self-assembly of nanoparticles. Our observations also emphasize the importance of direct nanoscale observation in uncovering previously unknown intermediate states that are pivotal for synthesis and self-assembly.

 

References:

[1] M. J. Williamson, R. M. Tromp, P. M. Vereecken, R. Hull, F. M. Ross, Nature Materials 2 (2003), p. 532.

[2] H. Zheng, R. Smith, Y. Jun, C. Kisielowski, U. Dahmen, A. P. Alavisatos, Science 324 (2009), p. 1309.

[3] U. Mirsaidov, H. Zheng, D. Bhattacharya, Y. Casana, P. Matsudaira, Proc. Natl. Acad. Sci. U.S.A. 109 (2012), p. 7187.

[4] N. D. Loh, S. Sen, M. Bosman, S. F. Tan, J. Zhong, C. Nijhuis, P. Kral, P. Matsudaira, U. Mirsaidov, Nature Chemistry 9 (2017), p.77 .

[5] U. Anand, J. Lu, N. D Loh, Z. Aabdin,  U. Mirsaidov, Nano Lett. 16 (2016), p. 786.

[6] G. Lin, X Zhu, U. Anand, Q. Liu, J. Lu, Z. Aabdin, H. Su, U. Mirsaidov, Nano Lett. 16 (2016), p. 1092.

[7] G. Lin, S. W. Chee , S. Raj, P. Kral, and U. Mirsaidov, ACS Nano 10, p. 7443-7450 (2016).

 

Keywords: electron microscopy, in situ TEM, nanofabrication, nanoparticles, self-assembly
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