ERC Consolidator program NANO-INSITU

In 2015, M.A. van Huis was awarded an ERC-CoG grant entitled 'Nanoscale Chemical Reactions Studied with In-Situ Transmission Electron Microscopy'. 

Great successes have been achieved in nanoscience where the development of functional properties and the assembly of nanostructures into nanomaterials have become increasingly important. In general, both the tuning of the chemical and physical properties and the self-assembly of nanocrystals into 2D or 3D superstructures take place in a liquid environment. When analysing the structural properties of nanocrystals using Transmission Electron Microscopy (TEM), this liquid environment is contained between membranes to keep it in the high vacuum. The purpose of this research program is to devise methodologies which will turn real-time atomic resolution imaging and chemical analysis on nanoparticles in solution into reality.

This new in-situ technology will elucidate what really happens during chemical reactions, and will thereby enable the development of new nanomaterials for optoelectronics, lighting, and catalysis. Oriented attachment processes and self-assembly of nanoparticles, which are key to the large-scale production of 2D and 3D nanomaterials, can also be followed in the Liquid Cell. Furthermore, reduction, oxidation and hydration of nanoscale metal oxides such as magnesia, titania, and iron/cobalt oxides, that are of major importance for fields such as catalysis and geoscience. Our research group has extensive experience in in-situ TEM and recently has achieved significant successes in Liquid Cell studies. We are in an ideal position to develop this new technology and open up these new research areas, which will have a major impact on science, industry, and society.

WP1. Development of in-situ methodology for Liquid Cell TEM

Work package 1 dealt with the development of in-situ TEM technology for Liquid TEM, and was mainly owned by PhD student Tom Welling. Although the research is also much aided by technological developments conducted at the in-situ TEM holder producing companies such as Protochips, great challenges still need to be overcome to prevent charging effects from the electron beam, both on the thin SiN windows containing the thin fluid, and in the fluid itself. In order to study self-assembly, first of all nanoparticles in solution have to be able to self-diffuse in a Brownian manner. By choosing low-dose electron beam conditions, and a solvent with a high dielectric permittivity (glycerol carbonate), we have been the first to achieve self-diffusion rates of titania and gold nanoparticles in liquids that follow the theoretical expectation for Brownian motion. The mobilities found in our research are orders of magnitude higher than the mobilities reported by others in the literature. (T.A.J. Welling et al., Particle and Particle Systems Characterization 37 (2020) 2000003). This study featured on the cover of the journal:

Furthermore, so-called rattle particles were studied which consist of a moveable core inside a larger silica shell. The silica shell is porous so that the liquid within takes the same composition as the liquid around the shells. The mobility of the core nanoparticles inside the shell was manipulated by changing the ion concentration in the liquid, and by applying AC electric fields of different frequencies. This enables spectacular control over the motion of nanoparticles in liquid confinement.[T.A.J. Welling et al., ACS Nano 15 (2021) 11137-11149]

WP2. In-situ study of cation exchange reactions in heterogeneous nanocrystals

Work package 2 concerned the in-situ study of cation exchange reactions in heterogeneous nanocrystals. First, much time was invested in the synthesis of large PbSe nanocubes and CdS nanorods, which are very suitable to perform cation exchange on. Investigations of in-situ cation exchange in liquid were conducted, with much focus on mitigating the effect of secondary nucleation of metal nanoparticles from metal precursors. Also the wet chemical etching of silica nanoparticles was investigated, which required extensive research into low-dose imaging conditions, and which was published in a methods-type paper.[A. Grau-Carbonell, ACS Applied Nano Materials 4 (2021) 1136-1148]. This study featured on the supplementary cover of the journal:

WP3. In-situ study on self-assembly of nanoparticles and 2D materials

Work package 3 on the in-situ study on self-assembly of nanoparticles was owned by PhD student Dnyaneshwar Gavhane, who intensively investigated the assembly and transformations of 2D chalcogenide nanosystems. Already spectacular findings were recorded during in-situ TEM experiments, showing a successive transformation from orthorhombic CoSe₂ to cubic CoSe₂ to hexagonal CoSe to tetragonal CoSe (D.S. Gavhane et al., npj 2D Materials and Applications 5 (2021) 24). A collaboration with the AMOLF Institute (Amsterdam, The Netherlands) resulted in a paper which was published in Advanced Materials (B. Sciacca et al.). Furthermore, the in-situ horizontal or vertical growth of the 2D material WS₂ was deciphered in detail and published in the high-ranking journal Advanced Functional Materials D.S. Gavhane, et al., Adv. Funct. Mater. 32 (2022) 202106450). This paper also featured on the cover of the journal:

WP4. In-situ study on reduction, oxidation and hydration of metal oxide nanomaterials

Work package 4 on the in-situ study of reduction, oxidation, and hydration of metal oxides was mainly owned by PhD student Xiaodan Chen. She investigated the thermal evolution of various transition metal oxide nanoparticle systems. In particular, she monitored the heating-induced transformation of anatase TiO₂ nanorods to rock salt TiO nanoparticles (X.D. Chen et al., ACS Applied Nano Materials 5 (2022) 1600-1606), witnessed the spectacular transformation of Co₃O₄ nanoparticles to CoO (X.D. Chen et al., J. Mater. Chem. C 9 (2021) 5662-5675), and a massive temperature-induced delamination of MoO₃ nanocrystals into MoO₂ nanoflakes. 

Finally, a paper with density functional theory (DFT) calculations on the thermal stability of transition metal oxides (TMOs) was published in npj 2D Materials and Applications (H. van Gog et al. npj 2D Mater. Appl. 3 (2019) 18). Here a new structural 2D phase, called the so-called t-phase, was discovered for the compound MnO by means of ab initio molecular dynamics (AIMD) simulations.