Visualizing nanoscale assembly and fabrication in solution using in situ TEM

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).