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Register a new userSupramolecular Chemistry Based on 4-Acetylbiphenyl on Au(111)
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On a gold surface, supramolecules composed of 4-acetylbiphenyl molecules show structural directionality, reproducibility and robustness to external perturbations. We investigate the assembly of those molecules on the Au(111) surface and analyze how the observed supramolecular structures are the result of weak long-range dispersive forces stabilizing the 4-acetylbiphenyl molecules together. Metallic adatoms serve as stabilizing agents. Our analysis suggests new ways of creating complex molecular nano-objects that can eventually be used as devices or as seeds for extended hierarchical structures.
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We report on a theoretical study of adsorption of 4-Acetylbiphenyl molecule and its diffusion properties in the main directions of the Au(111) surface. Structural changes of the molecule, which are induced by adsorption lead to stronger conjugation of the $pi$-system. The molecule is adsorbed in a flat configuration on the surface with roughly the same binding energy along the [110] and [112] directions, in good agreement with experiments. Furthermore, the diffusion barriers imply an important directionality of the molecule-surface interactions. This is somewhat surprising because our calculations show that the prevailing interaction is the long-range molecule-surface van der Waals interaction. Despite of its weakness, the van der Waals interaction discriminates the preferential adsorption sites as well as imposes a molecular geometry that needs to be considered when rationalizing the diffusion barriers.
We present a detailed theoretical investigation on the magnetic properties of small single-layered Fe, Co and Ni clusters deposited on Ir(111), Pt(111) and Au(111). For this a fully relativistic {em ab-initio} scheme based on density functional theory has been used. We analyse the element, size and geometry specific variations of the atomic magnetic moments and their mutual exchange interactions as well as the magnetic anisotropy energy in these systems. Our results show that the atomic spin magnetic moments in the Fe and Co clusters decrease almost linearly with coordination on all three substrates, while the corresponding orbital magnetic moments appear to be much more sensitive to the local atomic environment. The isotropic exchange interaction among the cluster atoms is always very strong for Fe and Co exceeding the values for bulk bcc Fe and hcp Co, whereas the anisotropic Dzyaloshinski-Moriya interaction is in general one or two orders of magnitude smaller when compared to the isotropic one. For the magnetic properties of Ni clusters the magnetic properties can show quite a different behaviour and we find in this case a strong tendency towards noncollinear magnetism.
Surface alloying is a straightforward route to control and modify the structure and electronic properties of surfaces. Here, We present a systematical study on the structural and electronic properties of three novel rare earth-based intermetallic compounds, namely ReAu2 (Re = Tb, Ho, and Er), on Au(111) via directly depositing rare-earth metals onto the hot Au(111) surface. Scanning tunneling microscopy/spectroscopy measurements reveal the very similar atomic structures and electronic properties, e.g. electronic states, and surface work functions, for all these intermetallic compound systems due to the physical and chemical similarities between these rare earth elements. Further, these electronic properties are periodically modulated by the moire structures caused by the lattice mismatches between ReAu2 and Au(111). These periodically modulated surfaces could serve as templates for the self-assembly of nanostructures. Besides, these two-dimensional rare earth-based intermetallic compounds provide platforms to investigate the rare earth related catalysis, magnetisms, etc., in the lower dimensions.
The spin structure of the valence and conduction bands at the $overline{text{K}}$ and $overline{text{K}}$ valleys of single-layer WS$_2$ on Au(111) is determined by spin- and angle-resolved photoemission and inverse photoemission. The bands confining the direct band gap of 1.98 eV are out-of-plane spin polarized with spin-dependent energy splittings of 417 meV in the valence band and 16 meV in the conduction band. The sequence of the spin-split bands is the same in the valence and in the conduction bands and opposite at the $overline{text{K}}$ and the $overline{text{K}}$ high-symmetry points. The first observation explains dark excitons discussed in optical experiments, the latter points to coupled spin and valley physics in electron transport. The experimentally observed band dispersions are discussed along with band structure calculations for a freestanding single layer and for a single layer on Au(111).
We present a complete characterisation at the nanoscale of the growth and structure of single-layer tungsten disulfide (WS$_2$) epitaxially grown on Au(111). Following the growth process in real time with fast x-ray photoelectron spectroscopy, we obtain a singly-oriented layer by choosing the proper W evaporation rate and substrate temperature during the growth. Information about the morphology, size and layer stacking of the WS$_2$ layer were achieved by employing x-ray photoelectron diffraction and low-energy electron microscopy. The strong spin splitting in the valence band of WS$_2$ coupled with the single-orientation character of the layer make this material the ideal candidate for the exploitation of the spin and valley degrees of freedom.
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