Supramolecular structures of anilino-nitro-azobenzene at different local coverage: (a) At a low coverage of 0.09 molecules/nm2 steps are decorated and supramolecular structures grow from these step edges. Two single molecules are marked by circles. Tunneling parameters: 0.31 nA, 275 mV. (b) At a medium coverage of 0.14 molecules/nm2 supramolecular structures form within the fcc domains of the Au(111) herringbone reconstruction. The circle marks a single molecule. Tunneling parameters: 91 pA, −539 mV. (c) At a large coverage of 0.23 molecules/nm2 the molecular structures deconstruct the surface. Tunneling parameters: 38 pA, 500 mV. (d) At a low coverage of 0.08 molecules/nm2 the same star-shaped structures as in (c) form in widened fcc domains. Tunneling parameters: 38 pA, 500 mV. (e) and (f) The zoom-in into a single trans- and a single cis*-isomer within a supramolecular structure is superimposed with ball-and-stick models from Ref. 15. (g) The high-resolution image of star-shaped structure on a fcc domain of the reconstructed surface is superimposed with ball-and-stick models. The thick lines indicate hydrogen bonds. Tunneling parameters: −219 mV, 110 pA.
Unoccupied orbitals of molecules within star-shaped structures: (a) and (b) The star-shaped structure is imaged differently at two different voltages: (a) 0.5 V, 16 pA, (b) 1.6 V, 16 pA, (c) dI/dV spectrum acquired above nitro group with modulation parameters of Vmod = 10 mV and νmod = 956.4 Hz. The average of ≈10 spectra is shown. (inset) LUMO of anilino-nitro-azobenzene as calculated semi-empirically using the parametric method 3 parameterization of MNDO for the Hamiltonian (Ref. 23) (d) and (e) A different star-shaped structure is imaged below and above the LUMO: (d) 0.344 V, 100 pA and (e) 2.4 V, 100 pA. At the lines, the line scans shown in (f) are recorded.
The dI/dV maps of a star-shaped structure are recorded at indicated voltages in the positive voltage range with modulation parameters: Vmod = 30 mV and νmod = 961 Hz at a current of 24 pA. The arrows at 1.3 V point to the nitro groups that broaden. The line scans are averages of line scans across the nitro groups as indicated in the map at 1.7 V in five different directions in order to reduce the influence of the artefacts.
Occupied orbitals of molecules within star-shaped structures: (a) The dI/dV spectrum is recorded with modulation parameters of Vmod = 10 mV and νmod = 956.4 Hz. (inset) The HOMO is calculated semi-empirically using the parametric method 3 parameterization of MNDO for the Hamiltonian Ref. 23. (b) and (c) The star-shaped structure are imaged differently at two different voltages of (b) −0.5 V, 40 pA and (c) −1.8 V, 40 pA. At the line scans shown in (d) are recorded. The arrows mark some of the anilino groups that appear brighter at higher voltage.
The dI/dV maps of a star-shaped structure are recorded at the indicated voltages in the negative voltage range with modulation parameters of Vmod = 50 mV and νmod = 961 Hz at a current of 110 pA. The sharp lines in the maps are an artefact of the measurement and should be disregarded. The line scans are averages of the line scans across the molecule as indicated in the map at −1.3 V in four different directions in order to reduce the influence of artefacts. The STM image in the lower right corner shows the surface region, on which the dI/dV maps were taken, 0.11 nA, −219 mV. The bright region on the lower right is a surface step.
(a) The dI/dV spectra in negative voltage range differ for differently bound isomers. Spectra are recorded with the manipulation parameters of Vmod = 10 mV and νmod = 956.4 Hz. (b) The STM images show the type of structures, on which the spectra were recorded. Color code corresponds to the color of the spectra. All spectra are the average of several spectra that were not necessarily measured on the same molecule, but always on the same spot of molecules in the same bonding type and with the same tip on the different structures. Tunneling parameters: 539 mV, 91 pA. (c) The dI/dV spectra in the positive voltage range for isomers bounded by four hydrogen bonds.
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