Exploitation of nanomaterials has the great potential to solve the most critical problems, e.g. energy shortage and climate change, which our mankind is currently facing. In this context, characterisation of energy related nanomaterials using a powerful technique --- transmission electron microscopy (TEM) plays an important role to learn the structure and chemistry on a nanometre and atomic level, and to understand mechanisms in nucleation and growth, in order to ultimately control their physical properties. In this presentation, two nanomaterial systems were characterised using advanced TEM techniques.
The first material system is a hybrid nanomaterial combining metal-oxide TiO2 and carbon-based nanomaterials including carbon nanotubes (CNTs) and single layer graphenes (SLGs)1-3. The synergetic functions of the nanocomposite exploiting the unique properties of each component allow for enhanced performance in many energy-related applications such as photocatalysis, solar energy and batteries. Through detailed (S)TEM characterisation, understanding of ALD nucleation and growth of TiO2 on CNTs and SLGs was gained. By tuning the ALD parameters e.g. temperature, number of cycles and post-deposition annealing, various morphologies of TiO2 films can be achieved on inert surfaces of CNTs and SLGs. Using atomic-scale imaging, the atomic structure of the nuclei was revealed and the information regarding the interface obtained. This study sheds light on atomic-scale engineering of nanocomposites based on metal oxides and carbon-based nanomaterials using ALD.
The second topic, which is our recent work, is an in situ TEM study on nucleation and growth of Au nanoparticles (NPs) in an aqueous solution4. Using liquid cell TEM (LC-TEM), a systematic study of the effect of electron dose rate, solute concentration, imaging mode (broad beam vs. scanning probe mode) and liquid cell setup (static vs. flow mode) on the growth mechanism and the ultimate morphology of Au nanoparticles (NPs) was performed in chloroauric acid (HAuCl4) solutions. In addition, as a proof-of-concept an Au nanostructure with a 3D faceted particle core and a dendritic shell can be produced in situ by simply tuning the electron dose in the 1 mM solution irradiated in a flow cell setup in the STEM mode. This work paves the way to study the growth of complex hetero-nanostructures composed of multiple elements in LC-TEM.