Acta Phys. -Chim. Sin. ›› 2016, Vol. 32 ›› Issue (1): 195-200.doi: 10.3866/PKU.WHXB201511261

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Sierpiński Trangle Fractal Structures Investigated by STM

Gao-Chen GU,Na LI1,Xue ZHANG1,Shi-Min HOU1,*(),Yong-Feng WANG1,2,*(),Kai WU3,*()   

  1. 1 Key Laboratory for the Physics and Chemistry of Nanodevices, Department of Electronics, Peking University, Beijing 100871, P. R.China
    2 Beida Information Research (BIR), Tianjin 300457, P. R. China
    3 Beijing National Laboratory for Molecular Sciences, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, P. R. China
  • Received:2015-10-27 Published:2016-01-13
  • Contact: Shi-Min HOU,Yong-Feng WANG,Kai WU;;
  • Supported by:
    the National Natural Science Foundation of China(21522301, 21373020, 21403008, 61321001, 21433011, 21133001, 913000002);National Key Basic Research Program of China (973)(2014CB239302, 2013CB933404, 2011CB808702);Specialized ResearchFund for the Doctoral Program of Higher Education, China(20130001110029)


Self-similar fractals have been extensively investigated because of their importance in mathematics and aesthetics. Chemists have attempted to synthesize various molecular fractal structures through sophisticated design. But because of poor solubility, synthesis of defect-free fractals with large sizes in solution usually proves difficult. Recently, we reported the formation of extended and defect-free Sierpiński triangle fractals by halogen or coordination bonds on surfaces under ultrahigh vacuum conditions. Their growth mechanism has been systematically studied by scanning tunneling microscopy. Using 4, 4′′′-dibromo-1, 1′:3′, 1′′:4′′, 1′′′-quaterphenyl molecules, a series of Sierpiński triangles were successfully prepared on Ag(111) through self-assembly. A slow cooling rate is crucial for growing fractals of higher order. These fractals are only observed below liquid-nitrogen temperature because of the weak interactions in halogen bonds. More stable metal-organic Sierpiński triangles were fabricated by depositing 4, 4″-dicyano-1, 1′:3′, 1″-terphenyl molecules and Fe atoms on Au(111) and annealing at around 100 ℃ for 10 min. The fractals are stabilizedthrough coordination interaction between Fe atoms and N atoms in molecules. Density functional theory calculations revealed their imaging mechanism. Monte Carlo simulations displayed the formation process of surface-supported fractal structures. Three-fold nodes are believed to dominate the structure formation of Sierpiński triangles.

Key words: Fractal, Sierpiński triangles, Self-assembly, Surface science, Scanning tunneling microscopy


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