Synthesis of Graphite/SiOC composites film on silicon substrate: Insights into chemical composition, structural, morphological, electrical and optoelectronic properties

Abstract

Graphite/SiOC composite (GSOC) thin films were synthesized on silicon substrates using an innovative “toast sandwich” method, where a silicon–graphite precursor mixture was deposited between two Si wafers and thermally treated at 350 °C to promote film adherence. The precursor solution was prepared directly from elemental silicon and graphite powders. A key challenge addressed in this work is the poor adhesion of polymer-derived SiOC on Si substrates—stemming from weak interfacial bonding strength and surface energy mismatch—which conventional deposition methods struggle to overcome. Our approach provides a simple and effective way to enhance film–substrate contact during thermal processing. The as-deposited GSOC films were further annealed at 1200 °C for 4 h, enabling compositional evolution and phase transformation. Structural, chemical, and functional properties were investigated using XRD, FTIR, XPS, AES, UPS, REELS, PL, and AFM. XRD confirmed the amorphous nature of the as-deposited film, while XPS and FTIR revealed the coexistence of Si–C and graphitic bonds. Annealing induced surface oxidation, leading to a transition from a carbon-rich (SiC-like) to an oxygen-rich (SiO₂-like) structure. REELS analysis indicated a bandgap widening from 8.1 eV (as-deposited) to 9.5 eV (annealed). UPS measurements showed a decrease in work function from 5.88 eV to 5.00 eV, and a shift in the Fermi level position from 3.72 eV to 5.56 eV (E_F–E_VBM). These changes reflect a transition from conductive to insulating behavior, as confirmed by Hall measurements showing a conductivity drop from 0.54 S/cm to 3.48 × 10⁻⁶ S/cm and carrier density reduction from 7.27 × 10¹⁷ to 2.64 × 10¹² cm⁻³. Photoluminescence analysis revealed SiC-like visible emission in the as-deposited film, while the annealed film demonstrated UV and violet emissions, suggesting potential use in advanced optoelectronic applications, particularly within the warm violet spectral range.