中文摘要：

分形结构因其特殊的数学和美学意义受到科学家们长期以来的广泛关注。化学家更是试图利用共价键和配位键等来合成各类分子分形结构,但由于溶解性的限制,始终无法实现高级别、无缺陷的分子分形结构的构筑。最近我们采用超高真空表面制备方法,成功获得了基于卤键与配位键的谢尔宾斯基三角分形结构,并使用扫描隧道显微镜（STM）对其生长机制进行了研究。4,4′′′-二溴-1,1′：3′,1′′：4′′,1′′′-四联苯分子在Ag（111）表面通过自组装形成了一系列无缺陷卤键分形结构。由于卤键作用较弱,该结构只能稳定在液氮温度以下。在Au（111）表面共沉积4,4′′-二氰基-1,1′：3′,1′′-三联苯分子与铁原子可以制备出更稳定的配位分形结构。密度泛函理论计算揭示了分形结构的成像机制。蒙特卡洛计算表明,表面三节点的形成对谢尔宾斯基三角分形结构的生长具有重要意义。

英文摘要：

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 Sierpirnski 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 Sierpir~ski 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 Sierpirnski 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 stabilized through 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 Sierpirnski triangles.