Transmission electron microscopy study on clusters and nanostructured mesoporous materials

Clusters are entities of two to a few hundred thousand of atoms of the same or a different chemical kind packed together with an arbitrary morphology and internal structural ordering. “What is the morphology of a cluster, how will a cluster adapt itself to a substrate and will there be chemical ordering in bimetallic clusters?” are some questions that are tried to answer in this Ph.D. thesis. Therefore Au and different Au-Cu alloy clusters are studied with transmission electron microscopy (TEM).; The cluster-surface interaction of Au clusters deposited with low energy on MgO cubes and on amorphous carbon and its influence on the morphology of the Au cluster is investigated. Not only have the clusters different morphologies for the two different surfaces, also a dilation of the Au lattice is measured for the clusters deposited on the crystalline surface of MgO to perfectly accommodate the MgO lattice. Classical molecular dynamics (MD) is applied to model this behaviour. Good agreement is found between experimental images and simulated images using the model calculated by MD.; Au-Cu bimetallic alloy clusters are produced in a laser vaporisation source starting from Au-Cu alloy targets with different stoichiometric compositions. The overall chemical composition in the clusters is the same as the chemical composition of the target material; but the crystal structure of the Au-Cu alloy clusters differs from their known bulk crystal structure. No chemical ordering exists between Au and Cu atoms and the clusters are solid solutions. Monte Carlo (MC) simulations however predict Cu₃Au clusters ordered in the core but with a disordered mantle. The possible origins of the differences between experiment and Monte Carlo simulations are discussed.; In the second part of this Ph.D. thesis, transmission electron microscopy (TEM) on nanostructured mesoporous materials is discussed. Mesoporous materials, prepared with alkanes and trimethylbenzene as swelling agents, are studied. Two phases are found for these materials: a hexagonal phase, like MCM-41 and a face centered cubic phase. The defects in these textures are characterised and compared with the crystal defects in regular fcc crystals.; The structure and pore distribution of spherical MCM-41 particles are studied using scanning electron microscopy, X-ray diffraction and TEM. The results are compared with well known MCM-41 and point out the differences between the two materials. Where the MCM-41 material consists of unidimensional pores, hexagonally packed together, the spherical MCM-41 particles are found to have a spherically symmetric pore distribution, starting from the inner part of the particles to the surface.