Among the multitudinous methodologies to steer on-surface reactions, less attention has been paid to the effect of externally introduced halogen atoms. Herein, highly selective trans-dehydrogenation coupling at the specific meta-C−H site of two poly(p-phenylene) molecules, p-quaterphenyl (Ph 4 ) and p-quinquephenyl (Ph 5 ), is achieved on Cu(111) by externally introduced bromine atoms. Scanning tunneling microscopy/ spectroscopy experiments reveal that the formed molecular assembly structure at a stoichiometric ratio of 4:1 for Br to Ph 4 or 5:1 for Br to Ph 5 can efficiently promote the reactive collision probability to trigger the trans-coupling reaction at the meta-C−H site between two neighboring Ph 4 or Ph 5 molecules, leading to an increase in the coupling selectivity. Such Br atoms can also affect the electronic structure and adsorption stability of the reacting molecules. It is conceptually demonstrated that externally introduced halogen atoms, which can provide an adjustable halogen-to-precursor stoichiometry, can be employed to efficiently steer on-surface reactions.
The electronic properties of thin oxide films supported on metal substrates have been the fundamental issues for supported model catalysts. Scanning tunneling microscopy (STM) can be employed to acquire the local information with measured tunneling current versus tipsample distance (I−z) curves. In addition to the dipole moments of the thin film, charge transfer between the oxide film and metal substrate can also be determined. Here, the local work functions of the CeO 2 /Pt(111) and Cu 2 O/Cu(111) model systems are measured using the I−z spectroscopic mapping. The experimental results show that, unlike those for metal substrates, the work function measurements of the supported thin oxide layers via this methodology are strongly dependent on the applied bias voltages. However, only at low biases can highly reliable work functions be acquired. The work function change between one monolayer CeO 2 and bare Pt(111) substrate is −1.8 eV. Detailed analyses indicate that at higher bias voltages, the local work function measurement is severely perturbed by the electronic band structures of the thin oxide films. With the atomic resolution, local work functions of thin oxide layers supported by bulk metal substrates can be accurately determined by the STM I−z spectra, which is of great importance in explorations of surface electronic properties of thin oxide films.
The adsorption and assembly of sub-monolayered bowl-shaped corannulene (COR) on Cu(111) and Ag(111) are investigated by scanning tunneling microscopy (STM). Three COR configurations, namely, up, down, and tilted ones, are formed on Cu(111), as unraveled by high-resolution STM images. It is also experimentally revealed that monodispersed, hexagonal, and evenly spaced stripe patterns develop on both Cu(111) and Ag(111). A quantitative evaluation of the long-range intermolecular interaction on Cu(111) mediated by electrostatic repulsion and surface-state mediation is presented. At 0.05 monolayer (ML), the long-range monodispersed pattern is mainly induced by electrostatic interaction. At 0.24 and 0.47 ML, however, surface-state mediation plays a dominant role, and the electrostatic interaction is leveled due to the identical static environment for each molecule.
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