Supplementary Figure 1: Change of scanning tunneling microscopy (STM) tip state. a, STM tip transited from blurred (the top dark zone) to orbital

Transcription

1 Supplementary Figure 1: Change of scanning tunneling microscopy (STM) tip state. a, STM tip transited from blurred (the top dark zone) to orbital resolvable (the bright zone). b, Zoomedin tip-state changing point in a. The red arrow in b indicates the tip scanning direction. The yellow rectangles mark incomplete features of adsorbed molecules, indicating that pyridazine molecules undergo unstable precursor states before being chemically attached to the Ge(100) surface. Among these molecules, the rounded rectangles highlight an adsorbed molecule suddenly appearing and disappearing at the tip state change point. This suggests the change of the tip state from normal to orbital-resolving (marked by the red arrow) is related to molecules dropping from and reattaching to the tip apex, respectively. 1

2 Supplementary Figure 2: Theoretically predicted products and simulated scanning tunneling microscopy (STM) images of pyridazine adsorbed on Ge(100). a, Possible binding mechanisms, including N-dative (pyridazine binds to up- or down-ge dimer atom through a single N-Ge dative bond ), NN-dative (pyridazine binds to a Ge-Ge dimer through two N-Ge dative bonds), [4+2]-cycloaddition through two C=C bonds and [2+2]-cycloaddition through a single C=C bond. For NN-dative and the two cycloadditions, pyridazine may attach to two Ge atoms from the same dimer, the same dimer rows or neighboring dimer rows, as marked by the solid and dashed arcs. b to g, Stable adsorption structures after geometric optimization and their simulated STM images in the form of isosurface (h to m, bias -2.0 V, isovalue Å 3 ). Model names (based on their final binding configurations) and system energies (relative to the interaction-free system, in the unit of ev) are given below the figures respectively. The green hexagonal grids under isosurfaces highlight the dimer and the first sub-layer atoms. 2

3 Supplementary Figure 3: Simulated scanning tunneling microscopy (STM) images of two adsorption products of pyridazine on Ge(100) at different biases. a to d, Simulated STM images of NN-dative product (In Supplementary Fig. 2f). e to i, Simulated STM images of N-dative product (In Supplementary Fig. 2g). All lateral scale bars: 0.8 nm. Electron density is in the unit of e A 3. The real Fermi levels of semiconductor surfaces depend on doping and grounding, and they always fall in the band gaps. The calculated STM images based on Tersoff-Hamann approximation thus also depend on the real Fermi level. This Figure shows that simulated STM images at nominal biases in calculation (referred to the valence band maxima of each product as Fermi level in the calculation) well match the experimental figures at the same biases. When the simulated biases are too large (3d, 3h and 3i), the original nodal planes of the molecular features disappear. 3

4 L at 300K cm L 4.0L 2.0L 1.0L 0.5L Enery Loss(cm -1 ) Supplementary Figure 4: High resolution electron energy loss spectroscopy (HREELS) spectra of pyridazine adsorbed on Ge(100) with different coverages at liquid nitrogen temperature and 300 K. (1L 1Langmuir = 10 6 T orr s). The bottom left peak indicates the resolution of HREELS in the term of full width of half maximum of the elastic peak. This shows the energy loss peaks of pyridazine adsorbs on Ge(100) under different coverages and temperatures. The curves of 0.5 L (under liquid N 2 temperature,1l 1Langmuir = 10 6 T orr s) and 8 L (at 300 K) correspond to the chemisorption, which is the same state in our STM experiments. Compared to the physisorption curves (1.0, 2.0, 4.0, 8.0 L), five distinct peaks in the chemisorption curves are retained. As assigned in Supplementary Table 1, two peaks around 997 and 1595 cm 1 in all curves correspond to C=C stretching, indicating that the C=C bonds of pyridazine are not reacted upon adsorption. The peak at 2974 cm 1 suggests there is no sp 3 C-H, otherwise an extra peak would emerge below 2960 cm 1. Furthermore, the peak around 1376 cm 1 can be assigned to the sp 2 C-H scissoring mixed with CN stretching. The peak at 1440 cm 1 is related to sp 2 C-H scissoring. Except for the above five peaks, the feature around 1185 cm 1 only appears in physisorption states, and could be assigned to C=N and C=C stretching. This assignment is in agreement with the previous study, which reported this peak is enhanced for condensed pyridazine, but disappears in monomolecular IR spectrum. 1 In short, all five peaks in the chemisorbed states exist only on the condition that the aromaticity of pyridazine is retained. Hence the only possible binding manners should be N-Ge single and/or double dative bonding, supporting our STM interpretation and DFT calculation. 4

5 Supplementary Table 1: Vibrational frequencies (cm 1 ) and their assignments for physisorbed and chemisorbed pyridazine on the Ge(100) surface. Description of Vibration modes a Solid IR 1 HREELS spectra on Ge(100) Calculated peaks on Ge(100) Physisorption Chemisorption Physisorption Chemisorption ν(c 4 =C 5 )+δ(ch) s +ν(nn) ν(cn) s +ν(cc) s δ(ch) as +ν(cn) δ(ch) s +ν(cc)+ν(nn) ν(c 4 =C 5 )+δ(ch) s ν(ch) a ν, stretching; δ, bending; s, symmetric; as, asymmetric. 5

6 References [1] Breda, S., Reva, I. D., Lapinski, L., Nowak, M. J. & Fausto, R. Infrared spectra of pyrazine, pyrimidine and pyridazine in solid argon. J. Mol. Struct. 786, (2006). 6