Growth of covalently bonded Sierpiński 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.