Surface Molecular Assembly And Nanostructures Investigated With Scanning Tunneling Microscopy

The preparation of well-ordered monolayers,multilayers,or hetero-structures by molecular self-assembly plays a crucial role in the study of novel functional nanodevices.Scanning tunneling microscopy/spectroscopy(STM/STS)provide the possibily to explore both the self-assembled morphology and the electronic properties of adsorbates.In this paper,the STM/STS technologies were combined to study the self-assembled mono-and multilayer structures,co-assembled monolayers,and the electronic properties of de-coupled hetero-organic molecules.The main contents of this paper are as follows:1)Electronic decoupling of 3,4,9,10-perylene tetracarboxylic dianhydride(PTCDA)and fullerene(C60)molecules from supramolecular CA·M by STM/STSCyanuric acid and melamine(CA·M)supramolecular networks prepared by simple drop-casting in air conditions are utilized as a space interlayer to suppress the electronic interactions between the upper adsorbate and the metal substrate.The upper adsorbates of PTCDA and C60 were deposited under UHV on the CA·M networks by vapor deposition,forming organics/CA·M hetero-organic layers on Au(111).STM images reveal the morphology of urpper layers.For the sub-monolayer,PTCDA molecules adsorbed flatly on the CA·M network to form an ordered herringbone-like structure.In contrast,C60 molecules form multi-layer islands on CA·M.STS spectra obtained on the upper layers clearly reveal the molecular orbital characteristics.The energy gap between the highest occupied and the lowest unoccupied molecular orbitals is 3.6 eV for PTCDA,and 3.8 eV for the first layer C60 on CA·M.2)Preparation and characterization of self-assembled monolayers of organic diaryl ethylene molecules with different bonding groups on Au(111)In this work,the self-assembled structures of the bonding molecules DAE-TATA and DAE-SAC on Au(111)surface were studied by STM in air conditions.The STM results showed that the larger DAE-TATA bonding molecules are more loosely arranged and form a more uniform ordered structure which might be more suitable in the preparation of photovoltaic devices.This experiment provides one of the new materials for the preparation of optoelectronic devices in the future.3)Self-assembled structure of amorphous red phosphorus on Au(111)surfaceBoth theoretical calculations and previous experimental datas indicate that amorphous red phosphorus prefers a linear structure,but its most intuitive topography is still unclear.In this experiment,the geometric structure of amorphous red phosphorus was successfully observed on Au(111)surface by STM at the liquid-solid interface for the first time.The alignment of the linear structure was determined and it shed light on the studied in the red phosphorus system.4)Co-assembled structure of PTCDA molecules and graphene nanoribbons on Au(111)Thanks to the on-surface synthesis,it has been possible to prepare graphene nanoribbons(GNRs)with various widths in atomic precision.However,GNRs adsorb disorderly on the single-crystal surface.In this paper,the organic molecule PTCDA is utilized as co-adsorbate on the Au(111)with GNRs for the alignment of GNRs.Well aligned GNRs are observed on the Au(111)together with PTCDA,providing a promising method for the packing of GNRs.