Fig. 3: On-surface synthesis of the hydrogenated tetraazaundecacene 1 and the analog with edge-fused five-membered rings 2 by annealing the sample at 280 °C.
From: On-surface synthesis and characterization of nitrogen-substituted undecacenes
a Overview STM topography image of the surface after annealing, showing multiple linear uniform species (one highlighted by the white arrow) and species with laterally extending features near one or both (highlighted by green arrow) of the nitrogen sites. Vb = −0.2 V, It = 70 pA, scale bar: 2 nm. Δz denotes the relative height w.r.t. clean Au(111) surface. b, e Constant-height frequency-shift nc-AFM images of the two highlighted cases acquired with a CO-functionalized tip (z offset −25 pm below STM set point: 5 mV, 30 pA), scale bar: 1 nm. c, f Simulated nc-AFM images for 1 and 2 based on the DFT equilibrium geometry. d, g DFT equilibrium adsorption geometry of 1 and 2 on Au(111). h dI/dV spectrum acquired on 1 at the position indicated by the blue dot in the inset (inset shows an STM image with Vb = −0.4 V, It = 40 pA, scale bar: 1 nm). PIR and NIR stand for positive and negative ion resonance, respectively. Reference dI/dV spectrum taken on the bare Au(111) surface is depicted in pink. i Constant-height differential conductance (dI/dV) maps acquired at bias voltages 1.00, −0.45, −0.80, −1.20 V (first column; from top to bottom) together with the corresponding DFT-calculated LDOS maps (second column) and corresponding molecular orbital isosurfaces at isovalues ±0.01 a.u. (atomic units; third column). Scale bars: 1 nm. The experimental maps are assigned to molecular orbitals based on the matching with calculated maps.
