Molecular orientation and lattice ordering of C60 molecules on the polar FeO/Pt(111) surface

Plastic Softening Induced by High-Frequency Vibrations Accompanying Uniaxial Tension in Aluminum

We have investigated the influences of high-frequency vibration (HFV) superimposed onto the monotonic uniaxial tension in single-crystal aluminum (Al) specimens by molecular dynamics simulations. It was found that HFV induces softening, i.e., reduction in peak stress. Similar to previous experimental results, the softening increases with the increasing HFV amplitude. Dependences on lattice orientation, tensile strain rate, and a preset notch are considered. Lattice orientation plays an important role in peak stress and plasticity. The evolution of the atomic structure reveals that dislocations have enough time to annihilate under a lower tensile strain rate, resulting in strong ups and downs in the strain–stress curves. Under a higher strain rate, newly appearing dislocations interact with previous ones before the latter annihilate, densifying the dislocation network. As a result, further dislocation motions and annihilations are considerably impeded, leading to a relatively smooth flow stage. Furthermore, by modifying the propagation direction of shear bands, a preset notch can strengthen the peak tensile stress under low-level amplitude HFVs.

Lattice-Directed Formation of Covalent and Organometallic Molecular Wires by Terminal Alkynes on Ag Surfaces

Surface reactions of 2,5-diethynyl-1,4-bis(phenylethynyl)benzene on Ag(111), Ag(110), and Ag(100) were systematically explored and scrutinized by scanning tunneling microscopy, molecular mechanics simulations, and density functional theory calculations. On Ag(111), Glaser coupling reaction became dominant, yielding one-dimensional molecular wires formed by covalent bonds. On Ag(110) and Ag(100), however, the terminal alkynes reacted with surface metal atoms, leading to one-dimensional organometallic nanostructures. Detailed experimental and theoretical analyses revealed that such a lattice dependence of the terminal alkyne reaction at surfaces originated from the matching degree between the periodicities of the produced molecular wires and the substrate lattice structures.

Two-level spatial modulation of vibronic conductance in conjugated oligophenylenes on boron nitride

Intramolecular current-induced vibronic excitations are reported in highly ordered monolayers of quaterphenylene dicarbonitriles at an electronically patterned boron nitride on copper platform (BN/Cu(111)). A first level of spatially modulated conductance at the nanometer-scale is induced by the substrate. Moreover, a second level of conductance variations at the molecular level is found. Low temperature scanning tunneling microscopy studies in conjunction with molecular dynamics calculations reveal collective amplification of the molecule's interphenylene torsion angles in the monolayer. Librational modes influencing these torsion angles are identified as initial excitations during vibronic conductance. Density functional theory is used to map phenylene breathing modes and other vibrational excitations that are suggested to be at the origin of the submolecular features during vibronic conductance.