UV Raman spectroscopy of segregated carbon in silicon oxycarbides

Abstract

Polymer-derived silicon oxycarbides exhibiting ≤1 and 10 vol.% of segregated carbon finely dispersed within a glassy Si_xO_yC_z matrix have been investigated by UV Raman spectroscopy using a laser excitation of 4.8 eV (λ = 256.7 nm). Carbon exists as amorphous sp²–sp³ bonded component in SiOC/C (≤1 vol.%) pyrolyzed at 1100°C in H₂, including C–C single bonds, polymeric chains and small polycyclic aromatic hydrocarbons (PAHs). The formation of nanocrystalline carbon at T > 1400°C is seen in the Raman spectra of SiOC/C (≤1 vol.%) and SiOC/C (10 vol.%) by the appearance of the G band of graphite. Tempering at 1600°C increases the degree of order within the carbon phase. However, the slight narrowing of the G peak with processing temperature (by about 5%) indicates still not well-crystallized carbon: the Raman results can be best explained by turbostratic carbon (with a lateral size L_a of ≈2 nm) and do not support the model description in literature as a network of single layer graphene.