Molecular engineering in symmetric end-substituted oligothiophene derivatives: analysis of condensed-phase photoemission spectra using semiempirical Hartree-Fock calculations.

The electronic structures of two series of end-capped thiophene oligomers, one set containing the electron-deficient dimesitylboryl end-cap and one containing the electron-rich triaryl amine end-cap, have been modeled using semiempirical quantum chemical calculations and the results used to assign features in the photoemission spectra of the materials in the condensed phase. For the thiophene oligomers end-capped with the electron-deficient dimesitylboryl moieties, the energy of the occupied frontier orbitals is largely governed by pi-type orbitals of the thiophene repeat units in the oligothiophene main chain. Conversely, in oligomers end-capped with electron-rich triarylamine moieties, the occupied frontier orbital energies are largely governed by orbital states of heavily mixed character associated with thiophene pi-type systems and the low-lying nitrogen lone pairs of end capping groups.

Fiber optic light collection system for scanning-tunneling-microscope-induced light emission.

We report a compact light collection scheme suitable for retrofitting a scanning tunneling microscope (STM) for STM-induced light emission experiments. The approach uses a pair of optical fibers with large core diameters and high numerical apertures to maximize light collection efficiency and to moderate the mechanical precision required for alignment. Bench tests indicate that efficiency reduction is almost entirely due to reflective losses at the fiber ends, while losses due to fiber misalignment have virtually been eliminated. Photon-map imaging with nanometer features is demonstrated on a stepped Au(111) surface with signal rates exceeding 10(4) counts/s.

Sexithiophene adlayer growth on vicinal gold surfaces.

We have investigated the initial stages of vacuum-deposited sexithiophene (alpha-6T) adlayer formation on Au(111) vicinal surfaces at room temperature. The in situ scanning tunneling microscopy (STM) and photoemission spectroscopy (PES) reveal a step edge-driven growth of alpha-6T on the Au(111) vicinal surfaces that first leads to the formation of an ordered monolayer, comprising two phases with the molecular major axes aligned along the step edges. The monolayer formation is then followed by the appearance of a single-phase 2D superstructure at a two-monolayer coverage. The results highlight the potential of using vicinal metal surfaces as templates for generating organized organic nanostructures over macroscopic areas for applications in organic electronics and moletronics.