Fig. 2: Dehydrogenative polymerization of M1 on Au(111) surface.
From: Visualizing stepwise evolution of carbon hybridization from sp3 to sp2 and to sp
a Schematic representation of step (I) of M1, dehydrogenative homocoupling to form polymer 1A on Au(111). b Large-scale STM image (200 mV, 200 pA) showing self-assembled precursors M1 after room temperature (RT) deposition onto Au(111). c Zoom-in BR-STM image (2 mV, tip-sample distance offset Δz = 180 pm) of self-assembled precursors M1 on Au(111). d nc-AFM image (2 mV, Δz = 220 pm) corresponding to (c). The images of (c, d) are overlaid with the chemical structures of M1. e Large-scale STM image (200 mV, 100 pA) showing polymers 1A after annealing to 520 K for 20 min. The depressions on both sides of linkages are marked by white solid arrows. f–i Zoom-in STM image (200 mV, 100 pA) (f), BR-STM image (2 mV, Δz = 170 pm) (g), nc-AFM image (2 mV, Δz = 200 pm) (h) and Laplace-filtered image (i) of polymer 1A derived from the blue dashed box in (e). The images of (f-h) are overlaid with the proposed chemical structures of polymer 1A. Yellow arrows in (h, i) highlight as-formed L(C–C). White dotted circle indicates the brighter contrast of L(C–C) characterized by nc-AFM imaging. j DFT-calculated energy barriers for methylene dehydrogenation in prototype molecules of ethylbenzene (higher) and phenylacetonitrile (lower). IS: initial state. TS: transition state. FS: final state. k Top and side views (left and right panels, respectively) of charge-density difference between the adsorbed phenylacetonitrile molecule and Au(111) substrate. Purple: electron depletion; Green: electron accumulation. Isosurface: 4.6 × 10−3 e/Å3. DFT simulation functional: PBE + D3. Scale bars, 5 nm (b, e), 1 nm (c, d), 0.6 nm (f–i).
