Formation of Extended Covalently Bonded Ni Porphyrin Networks on the Au（lll） Surface

The growth and ordering of {5,10,15,20-tetrakis（4-bromophenyl）porphyrinato}nickel（II） （NiTBrPP） molecules on the Au（111） surface have been investigated using scanning tunnelling microscopy, X-ray absorption, core-level photoemission, and microbeam low-energy electron diffraction. When deposited onto the substrate at room temperature, the NiTBrPP forms a well-ordered close-packed molecular layer in which the molecules have a flat orientation with the porphyrin macrocycle plane lying parallel to the substrate. Annealing of the NiTBrPP layer on the Au（111） surface at 525 K leads to dissociation of bromine from the porphyrin followed by the formation of covalent bonds between the phenyl substituents of the porphyrin. This results in the formation of continuous covalently bonded porphyrin networks, which are stable up to 800 K and can be recovered after exposure to ambient conditions. By controlling the experimental conditions, a robust, extended porphyrin network can be prepared on the Au（111） surface that has many potential applications such as protective coatings, in sensing or as a host structure for molecules and clusters.

Effect of electron injection in copper-contacted graphene nanoribbons

For practical electronic device applications of graphene nanoribbons (GNRs), it is essential to have abrupt and well-defined contacts between the ribbon and the adjacent metal lead. By analogy with graphene, these contacts can induce electron or hole doping, which may significantly affect the I/V characteristics of the device. Cu is among the most popular metals of choice for contact materials. In this study, we investigate the effect of in situ intercalation of Cu on the electronic structure of atomically precise, spatially aligned armchair GNRs of width N = 7 (7-AGNRs) fabricated via a bottom-up method on the Au(788) surface. Scanning tunneling microscopy data reveal that the complete intercalation of about one monolayer of Cu under 7-AGNRs can be facilitated by gentle annealing of the sample at 80 °C. Angle-resolved photoemission spectroscopy (ARPES) data clearly reflect the one-dimensional character of the 7-AGNR band dispersion before and after intercalation. Moreover, ARPES and core-level photoemission results show that intercalation of Cu leads to significant electron injection into the nanoribbons, which causes a pronounced downshift of the valence and conduction bands of the GNR with respect to the Fermi energy (ΔE ~ 0.5 eV). As demonstrated by ARPES and X-ray absorption spectroscopy measurements, the effect of Cu intercalation is restricted to n-doping only, without considerable modification of the band structure of the GNRs. Post-annealing of the 7-AGNRs/Cu/Au(788) system at 200 °C activates the diffusion of Cu into Au and the formation of a Cu-rich surface Au layer. Alloying of intercalated Cu leads to the recovery of the initial position of GNR-related bands with respect to the Fermi energy (E F), thus, proving the tunability of the induced n-doping.