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Nanoscale Metal-molecule contacts

Several differently substituted 1,4-bis(phenylethynyl)benzene molecules have been analyzed regarding their suitability as nano-electrical devices. Since the molecules have the same fully conjugated backbone and only differ in their side groups it has been possible to study the influence of such side groups. First, the contact stability of the molecules was investigated by molecular dynamics simulations. Not only the energetically optimized contact geometries, but also energetically less favorable contract geometries remained contacted. In the next step, the density-functional-based tight-binding method was employed to analyze the density of states as well as the charge transport properties of both molecules. This investigation showed that the side group effect reduces the energy gap between the highest occupied and the lowest unoccupied molecular orbital. However, the charge transport was lowered by the influence of the side group. Furthermore, the molecular density of states gets significantly changed if the molecule is contacted by metallic leads.