ELEMENTAL MAPPING AND REDOX STATE DETERMINATION OF NANO- PARTICLES IN THE ENVIRONMENT USING HAADF-STEM, EF-TEM, STEM-EDX, EELS AND STEM-PEELS

摘要

Nano-size particles are common in geologic systems, and transmission electron microscopy is commonly used to investigate materials at this scale. However if the distribution of particles of interest is scattered or the concentrations are low (e.g., 10 to 100 ppm), analysis can be difficult. However, when the particle consists of relatively heavy elements, high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) can be useful for efficiently locating the nanoparticles, as the image contrast is strongly correlated with atomic number and sample thickness. Imaging using an annular dark field (ADF) detector is an incoherent process because thermal diffused scattered (TDS) electrons are the signal. The image contrast does not reverse by changing focus as it does in standard HRTEM imaging. The elemental mapping in nano-meter scale was generally carried out using energy filtered (EF-) TEM or STEM-energy dispersive X-ray spectrometry (EDX).