Gaochen Gu

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.

Influence of Relativistic Effects on Assembled Structures of V-Shaped Bispyridine Molecules on M(111) Surfaces Where M = Cu, Ag, Au

The self-assembly behavior of a V-shaped bispyridine, 1,3-bi(4-pyridyl)benzene (BPyB), was studied by scanning tunneling microscopy on the (111) surfaces of Cu, Ag, and Au. BPyB molecules coordinately bonded with active Cu adatoms on Cu(111) in the form of complete polygonal rings at low coverages. On Ag(111), BPyB molecules aggregated into two-dimensional islands by relatively weak intermolecular hydrogen bonds. The coexistence of hydrogen bonds and coordination interaction was observed on the BPyB-covered Au(111) substrate. Density functional theory calculations of the metal-molecule binding energy and Monte Carlo simulations were performed to help understand the forming mechanism of molecular superstructures on the surfaces. In particular, the comprehensive orbital composition analysis interprets the observed metal-organic complexes and reveals the importance of relativistic effects for the extraordinary activity of gold adatoms. The relativistic effects cause the energy stability of the Au 6s atomic orbital and decrease the energy separation between the Au 6s and 5d orbitals. The enhanced sd hybridization strengthens the N-Au-N bond in BPyB-Au-BPyB complexes.

One-dimensional molecular chains formed by Sierpiński triangles on Au(111)

One-dimensional molecular chains with Sierpinski triangles as building blocks were prepared on Au(111) and studied by low-temperature scanning tunneling microscopy. Fractal Sierpinski triangles were stabilized by the coordination interaction between 1,3-bi(4-pyridyl) benzene (BPyB) and Co atoms. At low coverages, Sierpinski triangles of high orders were observed. At high coverages, Sierpinski triangles formed two types of one-dimensional molecular chains. The high coverages and matching between molecular size and surface lattices are attributed to the formation of molecular chains.