▎ 摘　　要

The temperature-induced phase transition of the n-C36H74 monolayer on the monolayer graphene grown on a Pt(111) surface is studied by X-ray absorption fine structure spectroscopy in the carbon near the K-edge (C K-NEXAFS). The C K-NEXAFS spectra of the n-C36H74 monolayer is separated from the spectra of the monolayer graphene by subtraction. The sigma(CC)* resonance predominantly observed in the normal incidence (NI) spectra is consistent with a chain axis lying flat on the graphene sheet at 120 K (crystalline phase) and 300 K (smectic phase). The sigma(CH)*/R resonance at 287.2 eV is characteristic of the monolayer, which is attributed to the sigma(CH)* orbitals distributed in an open space above the monolayer. The intensity ratio of the resonance for grazing incidence (GI) spectra with respect to that for normal incidence (NI) spectra decreases as a function of the temperature, which reflects the orientation change of the carbon plane with respect to the graphene sheet, from perpendicular (edge-on) to parallel (flat-on) orientation upon the crystalline smectic transition, and the expansion of the intermolecular spacings upon further transition to the fluid phase at 400 K.