Z-contrast scanning transmission electron microscopy of nanometer-scale coated particulate materials

Particulate materials with unique functional properties have been the focus of much attention in recent years. Of particular interest, due to their considerable scientific and technological importance, are particles coated with nanoparticles. These have greatly stimulated interest for their novel structure and properties. In these kinds of particulate materials, the interface structures between the support particle and the nanoparticle play a crucial role in controlling their properties. Consequently, imaging of the atomic structures at the interfaces can provide deep understanding of the relationship between the particulate and the corresponding properties. Z-contrast scanning transmission electron microscope (STEM) provides a new view of materials on the atomic scale, a direct image of atomic structure composition which can be interpreted without the need for any preconceived model structure. Therefore it is a powerful tool in the study of particulate materials. In this report, the authors present the structures of 18 micron diameter alumina particles coated with Ag nanoparticles. Particulates were prepared by a laser ablation technique, which involves laser ablation of the target material (Ag) onto a fluidized bed of core particles (alumina). The core alumina particles were fluidized inside the deposition system using a mechanical vibration method. For the STEM analysis, the particulates were lightly crushed in water using a pestle and mortar, then diluted in ethanol and deposited on a TEM grid coated with an amorphous carbon thin film