Graphitization of tincone via molecular layer deposition: investigating sulfur's role and structural impacts

This study investigated the synthesis of sp² carbons using molecular layer deposition (MLD) with tincone, which utilized tetrakis(dimethylamido)tin (TDMASn) as the metal precursor and 4-mercaptophenol (4MP) as the organic linker. Tincone films were deposited at 100 °C without impurities and then subjected to vacuum post-annealing in a tube furnace to induce graphitization. Compositional and structural analyses revealed significant changes as the annealing temperature increased, including the breakdown of the bonds between Sn, O, S, and C. This process led to the reduction of Sn, O, and S and the formation of sp² carbons. At 400 °C, the film thickness was reduced by 57.5%, and the refractive index increased from 1.8 to 1.97, as confirmed by the emergence of G-band and 2D-band peaks in the Raman spectra. X-ray photoelectron spectroscopy analysis indicated that the residual Sn content decreased to 0.75% at 600 °C. Interestingly, at temperatures above 400 °C, unique behavior was observed: increased C-S bonding disrupted the graphite structure due to the thiol (-SH) groups in 4MP. This disruption led to a reduction in C-C bonding and a decrease in the G-band peak in the Raman spectra. This study provides the first detailed investigation of the role of S in the graphitization of tincone, highlighting its impact on sp² carbon formation and emphasizing the importance of the careful selection of precursors and linkers in MLD processes.