Shedding light onto the nano- and micro-structures of B-containing SiOC glasses using high resolution TEM 3D imaging

The internal structure of nanostructured pyrolyzed SiBOC glasses has been analyzed using a combination of transmission electron microscopy techniques including high resolution imaging, EELS spectroscopy and 3D imaging. For the first time, we provide direct information on the 3D architecture within such complex glasses containing SiC nanograins, silica-rich and carbon nanodomains. Their sizes and relative 3D distribution have been precisely quantified. It was shown that the SiC nanocrystals and the silica-rich domains exhibit different types of connectivities with the graphitic carbon network. A direct evidence of the existence of “covalent” bridges between the edges of graphitic nanoplatelets and the SiC nanocrystals is provided. In addition, it was demonstrated that the silica rich domains are not covalently bonded to the graphitic platelets. As a consequence, this amorphous phase can be dissolved into HF and may generate a bimodal porosity, in strong relationship with the initial nanostructure of the SiBOC glass specimen.