Growth of covalently bonded Sierpinski triangles up to the second generation

Growth of covalently bonded Sierpinski triangles (CB-STs) on metal surfaces was investigated by scanning tunneling microscopy (STM). Three synthetic strategies (namely, dehydration condensation, cyclotrimerization coupling and Schiff-base reactions) were used to fabricate CB-STs. Second-generation CB-STs were obtained at the solid-vacuum interface utilizing the Schiff-base reaction between 4,4"-dialdehyde-1,1': 3',1"-terphenyl (TPDAL) and 1,3,5-tris(4-aminophenyl) benzene (TAPB) on Au(111). The CB-ST patterns persist at annealing temperatures as high as 500 K. Homotactic three-fold motifs, insufficient migration and irreversible covalent reaction are the main limitations for growing higher-generation STs. The present results provide new insights on the growth of STs on metal surfaces.National Natural Science Foundation of China [21522301, 21373020, 21403008, 61321001, 21433011, 61271050]; Ministry of Science and Technology [2014CB239302, 2013CB933404]; Research Fund for the Doctoral Program of Higher Education [20130001110029]SCI(E)ARTICLEsmhou@pku.edu.cn; yongfengwang@pku.edu.cn7166548-66552