Electron microscopy of some inorganic crystals with novel morphologies

Abstract

This project concerns crystal growth of some inorganic crystals which have novel morphologies. In order to study their crystal growth routes and further reveal their crystal growth mechanism, intermediate samples were collected and analysed, including samples produced after reduced reaction time, with different concentration of reactant or at reduced reaction temperature. The analysis was mainly completed by scanning electron microscopy and high resolution transmission electron microscopy. Other complementary techniques are powder X-ray diffraction, energy dispersive X-ray spectroscopy, selected area electron diffraction, mass spectrometry, inductively coupled plasma - optical emission spectrometry and photoelectrochemical measurement.

Investigated inorganic crystals include hematite nanotubes and nanorings, silver dendrites and copper dendrites, and graphene-based metal oxides. Hematite nanotubes and nanorings can be fabricated through hydrolysis of ferric chloride in different concentrations of phosphate via hydrothermal reaction. Intermediate samples at a range of different times were collected and characterised. It was revealed that hematite nanocrystallites form from decomposition of β-FeOOH nanorods, and that the final morphology depends on the competition between aggregation of β-FeOOH nanorods and decomposition into hematite nanocrystallites. Silver dendrites and copper dendrites can be produced via replacement reaction at room temperature. When synthetic conditions were changed, dendrites of different morphologies can be synthesised. The crystal growth direction and growth mechanism were investigated. Metal oxides such as manganese oxide nanoparticles and nickel oxide hollow particles can form on electrochemically exfoliated graphene via hydrolysis and polymerisation process. It was found that polymerisation is a vital process in the formation of metal oxides on graphene since polymers have multiple interaction sites with the surface of graphene. The intermediate samples and growth process were studied in detail.