One of the key challenges in chemistry is to break and form bonds selectively in complex organic molecules that possess a range of different functional groups. To do this at the single-molecule level not only provides an opportunity to create custom nanoscale devices, but offers opportunities for the in-depth study of how the molecular electronic structure changes in individual reactions. Here we use a scanning tunnelling microscope (STM) to induce a sequence of targeted bond dissociation and formation steps in single thiol-based π-conjugated molecules adsorbed on a NiAl(110) surface. Furthermore, the electronic resonances of the resulting species were measured by spatially resolved electronic spectroscopy at each reaction step. Specifically, the STM was used to cleave individual acetyl groups and to form Au-S bonds by manipulating single Au atoms. A detailed understanding of the Au-S bond and its non-local influence is fundamentally important for determining the electron transport in thiol-based molecular junction.
Adsorption behavior of iron–phthalocyanine (FePc) at low submonolayer coverage on a reconstructed Au(111) single crystalline surface was investigated by a combination of low temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. A site- and orientation-selective adsorption was found at different temperatures and molecular coverages by means of STM. Further DFT calculations demonstrate that the energy difference between different adsorption configurations leads to the selectivity, and thus the formation of one-dimensional molecular chains on the monatomic step edges in the fcc surface reconstruction domains. The exact adsorption site and configuration of the FePc molecule as well as the simulated STM images are obtained on the basis of DFT calculations, which is in good agreement with experimental observations.
The synthesis and structures of graphene on Ru(0001) and Pt(111), silicene on Ag(111) and Ir(111) and the honeycomb hafnium lattice on Ir(111) are reviewed. Epitaxy on a transition metal (TM) substrate is a pro-mising method to produce a variety of two dimensional (2D) atomic crystals which potentially can be used in next generation electronic devices. This method is particularly valuable in the case of producing 2D materials that do not exist in 3D forms, for instance, silicene. Based on the intensive investigations of epitaxial graphene on TM in recent years, it is known that the quality of graphene is affected by many factors, including the interaction between the 2D material overlayer and the substrate, the lattice mismatch, the nucleation density at the early stage of growth. It is found that these factors also apply to many other epitaxial 2D crystals on TM. The knowledge from the reviewed systems will shine light on the design and synthesis of new 2D crystals with novel properties.
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