Sexithiophene Adlayer Growth on Vicinal Gold Surfaces

Abstract

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.

Molecular chains and carpets of sexithiophenes onAu(111)

“…2͑a͔͒ we infer that 6T molecules are residing at the bottom of the edge, which nicely confirms the previously proposed notion that 6T layers on Au͑111͒ terraces start to grow from the bottom of step edges. 27 A similar behavior was reported by Chizhov et al 36 for Cu-phthalocyanine on Au͑111͒, by Glöckler et al 37 for perylene-3,4,9,10-tetracarboxylic-3,4,9,10-dianhydride and N,N'-dimethylperylene-3,4,9,10-bis͑dicarboximide͒ on Ag͑111͒, and by Xiao et al 38 for C 60 on Au͑11 12 12͒, where the molecules formed chains sitting next to step edges, in that last specific case on fcc sites.…”

Commensurate surface structures and concertedcis-trans-isomerization within ordered monolayers ofα-sexithiophene on Ag(001)

“…4all molecules are of bent shape and two pairs of molecules arrange in a plait-like structure ͑PL͒. The observation of an ordered domain of bent 6T molecules is in contrast to any known 3D crystal structure and to all reports for thin films so far 1,6,10,13,17,21,25. Both molecules in a pair are bent to the same direction, and the pairs are arranged into parallel rows.…”

“…In contrast to these expectations, up to now ordered struc- tures of 6T have been observed exclusively in all-trans configuration on metal substrates. 1,6,10,13,17,21,22,25 Consequently, if the molecules do not remain in the all-trans state after sublimation, they must change back to the all-trans configuration during or after adsorption.…”

“…This orthogonal row ͑OR͒ structure has similarities with the diagonal ͑DR͒ structure discussed above and is also similar to molecular rows of 6T and end capped 6T which have been found on other substrates. 10,17,21 The rows follow the ͓110͔ and ͓110͔ directions. Along the rows a regular moiré pattern with a periodicity of four molecules is clearly visible in Fig.…”

“…1,3,[5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] While on many oxide surfaces, with a weak molecule-substrate interaction, -conjugated molecules are found to adsorb in an upright standing configuration, 3,23,24 on metal substrates, such as Cu, Ag or Au, molecules in the first layer have been found to be flat lying. 1,6,10,13,17,25 On Ag͑110͒ and Ag͑111͒ 6T seems to adsorb into commensurate structures with the molecular axis parallel to the high-symmetry ͓001͔ and ͓110͔ direction, respectively, based on near-edge absorption fine structure ͑NEXAFS͒ and reflection high-energy electron diffration ͑RHEED͒ results. 16 Here we study the adsorption of 6T on the unreconstructed Ag͑001͒-͑1 ϫ 1͒ surface using scanning tunneling microscopy ͑STM͒ and low-energy electron diffraction ͑LEED͒.…”