Although hexacene was first synthesized in 1939, the thin film properties, which are interesting for future applications and fundamental research, have never been investigated. Therefore, we synthesized hexacene by reduction of 6,15-hexacenequinone, evaporated hexacene, and grew films of variable thicknesses on Au(110). This allowed us to study the electronic properties and molecular orientations in the bulk as well as at the molecule–metal interface by X-ray absorption spectroscopy (XAS) and photoelectron spectroscopy. Valence band spectra of a multilayer hexacene film are compared to those of electronic states obtained from density functional theory calculations. C 1s core-level spectra show typical satellite structures of the extended aromatic π-system, similar to pentacene. XAS shows that anisotropy rises with decreasing film thickness and indicates that hexacene is almost flat lying on the Au(110) substrate. The different peak shapes of XAS spectra as a function of the film thickness, as well as changes in valence band spectra and C 1s satellite structures, indicate a strong electronic coupling of the molecular states with the states of the Au(110) substrate at the interface.

Interface properties of CoPc and CoPcF16 on Cu-intercalated graphene/Ni(111) were investigated by X-ray photoemission spectroscopy (XPS), ultraviolet photoemission spectroscopy (UPS), and X-ray absorption spectroscopy (XAS). We show that a charge transfer from graphene/Ni(111) to the Co ion of CoPc can be significantly reduced by Cu-intercalation of graphene, resulting in a partial decoupling of graphene from the Ni(111) substrate. This is not the case for CoPcF16 on Cu-intercalated graphene/Ni(111). Possible reasons and charge transfer channels are discussed. The comparison to CoPcF16 on the almost fully decoupled Au-intercalated graphene/Ni(111) suggests that the graphene-substrate coupling in the case of Cu-intercalation remains still significant.

Layered transition metal dichalcogenides (TMDCs), such as molybdenum disulfide (MoS2), are currently in the focus of interest due to their novel electronic properties. The adsorption of molecules is a promising way to tune the electronic structure of TMDCs. We study interface properties between MoS2 and differently fluorinated iron phthalocyanines (FePcF x , x = 0, 4, 16) using X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), angle-resolved photoelectron spectroscopy (ARPES), and X-ray absorption spectroscopy (XAS). A key parameter for the charge transfer is the ionization potential of FePcF x . A distinct electron transfer from a molecule to a substrate is observed for FePc and FePcF4. From energy-momentum ARPES maps, we suppose that the substrate and FePc-related states hybridize at the interface. This study demonstrates that a controlled tuning of the electronic structure of MoS2 by electron donors is possible, driven by the ionization potential difference between the substrate and the adsorbate.

The initial growth and interfacial electronic structure of perfluorinated iron phthalocyanine (FePcF 16 ) on Cu(111) has been studied using X-ray photoelectron spectroscopy (XPS) and polarization dependent X-ray absorption spectroscopy (XAS). The planar molecules are oriented preferred flat lying on the substrate surface during the growth of the first layers while the tilt angle is increased in thicker films. A clear interaction at the interface is observed, involving both the central metal ion and the macrocycle. At monolayer coverages, the Fe2p spectrum shows an interface signal at 707.1 eV, while the C-N component of the C1s spectrum is distinctly shifted with respect to the thicker films. In addition, the nitrogen atom is involved in the complex interaction (including charge transfer), best visible in the change of the shape in the π Ã resonance of N K edge spectra recorded from molecules at the interface.

The electronic structure of the central iron ion of perfluorinated iron phthalocyanine (FePcF 16 ) in thin films has been studied on Cu(111) and Ag(111) using polarization dependent X-ray absorption spectroscopy (XAS). The data are compared to FePc on Ag(111). Ligand field parameters have been computed, and multiplet calculations (CTM4XAS) were carried out to simulate XAS spectra. The planar molecules are preferentially oriented lying flat on the substrate surface during the growth of the 1−4 nm thick films. A clear polarization dependence of the Fe L edge absorption spectra is observed, arising from transitions into orbitals with in-plane and out-of-plane character. The shape of the spectra for three to four monolayers of FePcF 16 on Cu(111) is comparable to that of the thin films of FePc on Ag(111). However, a drastic change of the XAS peak shape is observed for thicker FePcF 16 films on both Ag(111) and Cu(111), although the molecular orientation is very similar to coverages consisting of a few monolayers. Since in both cases the film thickness is distinctly beyond the monolayer regime, interface interactions can be ruled out as a possible origin of this behavior. Rather, the different XAS peak shapes seem to indicate that the multiplicity may depend on the detailed arrangement of the FePcF 16 molecules. The large flexibility of the ground state of Fe could be of high interest for spintronic applications.