Sierpiński-triangle fractal crystals with the C3v point group

Self-similar fractals are of importance in both science and engineering. Metal-organic Sierpin′ ski triangles are particularly attractive for applications in gas separation, catalysis and sensing. Such fractals are constructed in this study by using 1208 V-shaped 4,400-dicyano-1,10：30,100-terphenyl molecules and Fe atoms on Au（1 1 1）, and studied in detail by low-temperature scanning tunneling microscopy. Density functional theory calculations are employed to rationalize the invisible Fe atoms in STM images. Monte Carlo simulations are performed to understand the formation mechanism of the surface-supported fractal crystals.