The adsorption geometry and molecular self-assembly of graphene for 1,3,5-triphenylbenzene on Cu(111)

Electronic structures and adsorption geometry of 1,3,5-triphenylbenzene (TPB) on the Cu(111) surface, and followed by formation of graphene nano flakes (GNFs) upon annealing the sample were investigated by using angle resolved ultraviolet photoelectron spectroscopy (ARUPS) and density functional theory (DFT) calculations. The emission features d, e and f originated from TPB molecule at a coverage of 1.3 monolayer (ML) in UPS spectra are located at 4.65 eV, 6.76 eV and 8.57 eV below Fermi level, and the decrease of the work function upon increasing of TPB coverage on Cu(111) is attributed to the interfacial dipole formed between the adsorbate and the substrate. Formation of GNFs upon annealing of TPB overlayer on Cu(111) is approved by appearance of new features & h, i, j and k originating from GNFs, and located at 1.09, 4.97, 6.64, 9.23 and 11.23 eV below Fermi level. The ARUPS measurements and DFT calculations indicate that both TPB molecules and GNFs planes are nearly parallel to the Cu(111) substrate in the monolayer regime. Most importantly, the results show that, with decreasing of the coverage of TPB as precursor, the formation of GNFs, or graphitization temperature can be decreased down to 350 degrees C, indicating the crucial influence of intermolecular interaction on the dehydrogenation process.