Construction of Two Dimensional Chiral Networks

Transcription

1 Supporting Information Construction of Two Dimensional Chiral Networks through Atomic Bromine on Surfaces Jianchen Lu, De-Liang Bao, Huanli Dong, Kai Qian, Shuai Zhang, Jie Liu, Yanfang Zhang, Xiao Lin *, Shi-Xuan Du *, Wenping Hu, Hong-Jun Gao Institute of Physics & University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing , P. R. China Institute of Chemistry, Chinese Academy of Sciences, Beijing , P. R. China *To whom correspondence should be addressed. S1

2 1. Methods Experimental details. Experiments were performed by using an ultrahigh vacuum low-temperature scanning tunneling microscopy (LT-STM) system (Omicron) with a base pressure better than mbar. The atomically clean Ag(111) and Cu(111) (MaTecK) surfaces were obtained by cycles of argonion sputtering and annealing to 720 K and 750 K, respectively. First, the bromine atoms were introduced by thermal decomposition of HBr gas molecules through a hot filament with a deposition rate of about 0.25 monolayer per hour, while the sample surface faced toward the filament at a distance of 5 mm. Then the DPA or DcC 6 PA molecules were thermally deposited onto Ag(111) or Cu(111) surfaces by a Knudsen cell (Kentax) after thermal purification, while the Ag and Cu substrates were held at room temperature. After deposition, the samples were transferred to the LT-STM operating at 4.2 K. All the STM images were acquired in the constant-current mode by using an electrochemically etched tungsten tip, and all given voltages are applied to the sample with respect to the tip. Nanotec Electronica WSxM software 1 was used to process the STM images shown here. Molecules synthesis. 2,6-diphenylanthracene (DPA) is synthesized through three convenient steps with yields over 85%. For more detailed synthesis information and characterizations, see the previously published paper. 2 2,6-di(4-cyclohexylphenyl)anthracene (DcC 6 PA) is synthesized as following: a 100 ml flask, 474 mg (1 mmol) 2,6-Diyl bis(trifluoromethanesulfonate)-anthracene, 450 mg (2.2 mmol) (4- cyclohexylphenyl) boronic acid and Pd(PPh 3 ) 4 63 mg (0.05 mmol) were added under argon. Then 2 ml ethanol, 8 ml toluene and 2mL 2M K 2 CO 3 aqueous solution were added. The whole system was heated to 90 and kept overnight. Then the whole system was filtered, the filtrate was washed with triethylamine, dichloromethane, water and ethanol successively. DcC 6 PA was obtained as a greenish yellow solid in a yield of 83% (410 mg). And the product was further purified by train-sublimation. MS (EI): m/z 494 (M + ). Elemental analysis calculated for DcC 6 PA: C 92.26, H Found: C 91.96, H Calculation details. Density functional theory (DFT) based first principles calculations were performed in a plane-wave formulation with the projector augmented wave method (PAW) as implemented in the Vienna ab initio simulation package (VASP) code. 3,4 The Perdew Burke Ernzerhof (PBE) 5 parametrization of the generalized gradient approximation (GGA) 6 was used. The cutoff energy for the plane waves was 400 ev. For the model, three-layer/two-layer atomic slabs were used to simulate the Ag(111)/Cu(111) substrate, with molecules and Br atoms adsorbed on one side. The vacuum layer is 15 Å between neighboring slabs. In relaxation, atoms in the bottom layer of the substrate were fixed and all the other atoms were relaxed until the atomic forces were less than 0.02 ev/å. The Brillouin zone was sampled with only the Γ-point in all calculations. A dispersion correction of total energy (DFT-D2 method) 7 was used to incorporate the long-range van der Waals interaction. S2

3 2. STM images of Br atoms on Ag(111) surfaces Before deposition of the molecules, there are sub-monolayer of bromine atoms on the surface. After deposition of the molecules, the bromine atoms coordinate with molecules without forming any islands. The ratios of bromine atoms to DPA molecules on Ag(111) surface can be different in different structures shown in Fig. 1,2 in the main text. We have summarized them in Table S1. Figure S1. Large scale (A) and zoom-in (B) STM images of bromine atoms on Ag(111) surface. The deposition parameters are filament current of 1.45 A, HBr pressure of mbar and deposition time of 90 min. The Br atoms are clearly identified as chains structures on Ag(111) surface. Scanning parameters: (A) V s = 1.0 V, I t = 0.8 na; (B) V s = 0.1 V, I t = 0.1 na. S3

4 3. Height difference of DPA layer and Br atomic layer on Ag(111) The lower panel of Fig. S2 shows the side view of optimized atomic configuration of Br-mediated selfassembled structure of DPA molecules on Ag(111) along the blue arrow in the upper panel. Obviously, all Br atoms are under the DPA layer and have the same height. The height difference between the DPA layer and the bromine layer is ~ 0.63 Å, while the distance between the bromine layer and the top layer of the Ag substrate is ~ 2.38 Å. Figure S2. Top view and side view (along the blue arrow) of optimized configurations of Br-DPA network on Ag(111). S4

5 4. Schematic structural models for structure II, III, and IV, and the density for bromine atoms at fcc sites and/or hcp sites in each structure We have drawn schematic structural models for structure II, III, and IV (shown in Fig. S3(A), (B) and (C)) to identify the sort of hcp, fcc adsorption sites for bromine atoms in the all four structures of Br-DPA on Ag(111). For structure I, II, III and IV, the ratio for bromine atoms at fcc sites to those at hcp sites is 1:0, 5:4, 1:1 and 0:1, respectively. We plot the density of bromine atoms on hcp sites and/or fcc sites as a function of molecular self-assembly density, as shown in Fig. S3(D). The ratio for bromine atoms on fcc and/or hcp sites seems irregular to the density of molecules. It can be understood by the fact that the adsorption energies of bromine atoms on hcp sites and fcc sites on Ag(111) surface are quite similar (E adhcp = 3.09 ev, E ad-fcc = 3.10 ev). Therefore, the distribution of these two types of bromine atoms would depend on the self-assembly structures of molecules. Figure S3. (A), (B) and (C) Schematic structural models for structure II, III, and IV, respectively. (D) The plot of the density of bromine atoms on hcp and/or fcc sites as a function of the density of molecules. The four grey ellipse represent four structures. Each one contains two types of bromine atoms. S5

6 5. Control of selective formation of four kinds of networks For the Br-DPA networks on Ag(111) surface, we obtain four large-scale structures (structures I, II, III, IV). It is worth exploring the relationship of different structures and the ratio between the number of Br atoms and the number of DPA molecules. Table S1 shows the density of Br atoms and DPA molecules as well as the ratio of them for the above mentioned four atomic 2D Br-DPA networks. Obviously, the ratio is 3, 5, 4, and 1 for structures I, II, III, and IV, respectively. When excessive bromine atoms were deposited on the surfaces, only structure I and some bromine chain structures (Fig. S1) were observed. Otherwise, coexistence of two structures on one sample may be achieved. For instance, Fig. 2(C) shows structure IV and structure III (lower right corner). To obtain a large-area, uniformly structured network, precise control of the ratio of Br atoms to DPA molecules and removal of defects by post-annealing are needed. Furthermore, greater Br atom intensity means more hydrogen bonds can form between Br atoms and molecules, that is, a more stable structure. Obviously the ranking of structural stability is structure I > structure II > structure III > structure IV. In this way, we can modulate the structural changes from metastable structure to stable structure by post-annealing or by depositing extra bromine atoms; that is to say, we can selectively control the formation of different 2D Br-DPA networks. Table S1. Density of Br atoms and DPA molecules for four 2D Br-DPA networks on Ag(111) surface. S6

7 6. STM topography of Br-DPA networks on Cu(111) surface Figure S4(A) is a large-scale self-assembled structure of Br-DPA on Cu(111) surface. The top right and bottom left show the L-chiral domain, whereas the middle is R-chiral domain. Figure S4(B) is a zoom-in image from the dashed yellow frame in (A). The position of domain boundary is clearly identified and marked by two arrows. Molecular models of L-DPA and R-DPA are overlaid to highlight the two chiral domains. More importantly, it is obvious that the Br atoms still exist in the domain boundary and reside in the junctions of three DPA molecules and at the kink sites of DPA molecules, which meets the requirement of maximizing the number of hydrogen bonds. Figure S4. (A) Large-area STM image of atomic bromine mediated self-assembled periodic hydrogen bond networks on Cu(111) surface containing two chiral domains. (B) Close-up STM image of (A). The green dashed arrows indicates the boundary between two chiral domains. Scanning parameters: (A) V s = 0.1 V, I t = 3.0 na; (B) V s = 0.1 V, I t = 3.0 na. S7

8 7. Self-assembly data on the pristine DPA and DcC 6 PA networks on Ag(111) surface We obtained the self-assembly data of the pristine DPA and DcC 6 PA on Ag(111) surface. Figure S5(A) shows a large-scale self-assembled structure of DPA with L-chiral. Figure S5(B) is a zoom-in image overlaid with a molecular model and a unit cell. The L-DPA molecules are clearly identified. Figure S5(C) is the DFT optimized adsorption configuration of DPA on Ag(111). Figure S5(D) is a simulated STM image based on the calculated molecular structure in (C) which is consistent with the experimental observation STM image in (B). We also obtained a large-scale STM image for R-DPA (Fig. S5(E)) and highly-resolved image (Fig. S5(F)). For the pristine DcC 6 PA on Ag(111) surface, we present the related STM images in Fig. S6(A) (L- DcC 6 PA) and 6(B) (R-DcC 6 PA). Several proposed DcC 6 PA molecular packing structures are superimposed to the STM images. Obviously, self-assembly structures of the pristine DPA and DcC6PA molecules on the Ag(111) are guided and dominated by the van der Waals interactions between molecules and between molecules and substrate. Figure S5. Large area (A) and atomic-resolved (B) STM images of pristine L-chiral DPA molecules (L- DPA) on Ag(111). Some molecular modes and a unit cell have been superimposed on the STM image. (C) Top view and side view of DFT optimized adsorption configuration of DPA on Ag(111). (D) Simulated S8

9 STM image based on the model in (C). (E) and ( F) Large scale and high resolution STM images of selfassembled R-chiral DPA molecules (R-DPA) on Ag(111), respectively. Scanning parameters: (A) V s = 1.0 V, I t = 0.03 na; (B) V s = 3.0 V, I t = 0.03 na; (E) V s = 3.0 V, I t = 0.03 na; (F) V s = 2.5 V, I t = 0.03 na Figure S6. STM images of L-DcC 6 PA (A) and R-DcC 6 PA (B) on Ag(111) overlaid with related molecular models. Scanning parameters: (A) V s = 2.0 V, I t = 0.05 na; (B) V s = 0.5 V, I t = 0.1 na. S9

10 References (1) Horcas, I.; Fernandez, R.; Gomez-Rodriguez, J. M.; Colchero, J.; Gomez-Herrero, J.; Baro, A. M. WSXM: a Software for Scanning Probe Microscopy and a Tool for Nanotechnology. Rev. Sci. Instrum. 2007, 78, (2) Liu, J.; Zhang, H.; Dong, H.; Meng, L.; Jiang, L.; Jiang, L.; Wang, Y.; Yu, J.; Sun, Y.; Hu, W.; Heeger, A. J. High Mobility Emissive Organic Semiconductor. Nat. Commun. 2015, 6, (3) Kresse, G.; Furthmuller, J. Efficient Iterative Schemes for Ab Initio Total-Energy Calculations Using a Plane-Wave Basis Set. Phys. Rev. B 1996, 54, (4) Kresse, G.; Joubert, D. From Ultrasoft Pseudopotentials to the Projector Augmented-Wave Method. Phys. Rev. B 1999, 59, (5) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, (6) Perdew, J. P.; Chevary, J. A.; Vosko, S. H.; Jackson, K. A.; Pederson, M. R.; Singh, D. J.; Fiolhais, C. Atoms, Molecules, Solids, and Surfaces: Applications of the Generalized Gradient Approximation for Exchange and Correlation. Phys. Rev. B 1992, 46, (7) Wu, X.; Vargas, M. C.; Nayak, S.; Lotrich, V.; Scoles, G. Towards Extending the Applicability of Density Functional Theory to Weakly Bound Systems. J. Chem. Phys. 2001, 115, S10