SEM and SAXS analyses for studying structural properties of porous materials and metal oxides

Abstract

Nanoscience is based on that materials show some unique properties that bulk materials do not have, such as quantum-size and surface effects, because of size. The properties such as melting point, fluorescence, electrical conductivity, magnetic permeability, and chemical reactivity change as a function of the size of the particle. The surface area per unit mass of a material and therefore reactivity will increase. So it is important to understand size, surface and structure of particles. In this thesis, the structural information of metal oxide and porous materials was studied by Scanning Electron Microscope (SEM) and Small Angle X-ray Scattering (SAXS) with 4 samples; aggregation free Au particles in ordered mesoporous carbon, silver alkanoic acid, ordered mesoporous silica and ceria nanoparticles. SEM is for analyzing morphology and surface of nanoparticles. Through the cross-sectioned particles, internal structure and its regularity also observed with Fourier transformed images. Because particles to observe are insulating materials, gentle beam mode of SEM was adopted to avoid electron accumulation without metal coating. SAXS is for describing spatial structure information and particle-particle interaction of materials. To understand particle-particle interaction, Guinier plot and radius of gyration (Rg) were examined from intensity profiles for different concentration of metal oxide nanoparticle dispersed into cyclohexane (0.1, 1, 2, 5, 10 wt %). For embodying low-resolution 3D model, ab-initio method was used through ATSAS program packages. Also numerical spatial values of ceria nanoparticles were calculated using NCNR SANS packages with IGOR PRO. From the results, we confirm that aggregation free Au particles in ordered mesoporous carbon, silver acetic acid as reference sample for in-situ SAXS experiments, partially ordered hexagonal pore arrangement region and 4×5×7 nm size parallelepiped shape ceria wrapped by decanoic acid..