Thesis title: Synthesis, functionalization and characterization of two-dimensional materials
To meet the demands of ambition, innovation and development of the technology of electronic devices manufacturing, two-dimensional (2D) materials, which have the potential to replace the conventional Si-based materials, must be synthesized with high quality and performance using well-engineered, controlled, and reproducible synthetic methods. New strategies for altering their electrical and chemical structures should also be developed. Therefore, it is important to understand the chemical composition and electrical structures of these materials. This thesis presents an electron spectroscopic study of 2D materials, mainly by using X-ray photoemission spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). The 2D materials under investigation include free-standing nanoporous graphene (NPG), NPG functionalized with atomic hydrogen (H) and deuterium (D), potassium-doped NPG, ternary boron carbon nitride (B-C-N) layer on Ti substrates, and a preliminary study of MoS2 layer growth on Si and quartz substrates. For the first time to our knowledge, H-(D-) functionalization of free standing graphene samples was achieved with high quality, high H(D) coverage and low defects using four different clean and non-destructive irradiation techniques, typically Kaufman ion source, electron beam induced thermal energy ion source, hot ribbon and cracking capillary gun. The H-(D-) coverage was estimated by bringing to light the sp3-like modified bond in the C 1s core-level line-shape. The quality was verified by the C 1s line-shape and the very low D peak in Raman spectroscopy. Furthermore, the band gap opening was verified by the valence band (VB) spectral density measured by UPS. K doping of NPG was
performed in UHV with clean and controlled conditions, as verified and monitored by XPS. XPS of B-C-N on Ti substrate revealed the homogeneity through the stoichiometric ratio and the bonding scheme between the constituent elements, showing that B-C-N layers are formed by h-BN and C rich nanodomains with high doping levels of C and of B and N, respectively. Preliminary chemical vapour deposition (CVD) growths of MoS2 monolayer on Si and quartz substrates were investigated by optical spectroscopy and Raman spectroscopy, showing a homogeneous nanocrystalline MoS2 monolayer. In conclusion, these results may introduce a valuable reference, and hopefully, this can support the perspective of manufacturing of highly efficient energy storage, electronic and optoelectronic devices.