Preparation And STM Investigation Of Supramolecular SAMs Directed By Lateral Hydrogen Bonds And Metal-organic Coordination Bonds

For nanotechnology to find wide practical use, we need to develop methods for controlled mass fabrication of nanosystems and nanodevices. Supramolecular self-assembly provides such a basic"bottom-up"technique to create SAMs with a controlled and repeatable manner. These functional surfaces fabricated by supramolecular SAMs have potential applications in fields of sensors, molecular recognition and nanoelectronics. In this paper, we systematically investigated a series of supramolecular SAMs directed by lateral non-covalent bonds with different strength. A new kind of method has been developed for fabrication of supramolecular SAMs with high thermal stability at air/substrate interface. The role of the adsorbate-substrate interactions has been discussed in the supramolecular SAMs directed by weak and strong lateral molecule-molecule interactions. Our research contents and main conclusions are:1) The self-assembled monolayers (SAMs) of alkanols (1-CNH2N+1OH) with varying carbon chain length (N=10-30) at the interfaces between alkanol solutions (or liquids) and the Au (111) surfaces have been systematically studied by means of scanning tunneling microscopy (STM). The carbon skeletons were found to lie flat on the surfaces. The odd-even effect known in the alkane SAMs also appears in the alkanol SAMs. Thus the odd N alkanols adopt the perpendicular lamellar structures owing to the favorable interactions of the methyl terminals as in the case of the odd alkanes. The herringbone-like structures were found dominant in the alkanol SAMs for even N<18, whereas the tilted structures and herringbone-like structures coexist in the SAMs of long chain alkanols for even N>18. In contrast to alkanes on the Au (111) surfaces, where no SAMs on the unreconstructed gold substrate were observable, alkanols can form SAMs on either the reconstructed or the unreconstructed gold surfaces.2) A new method was established for construction of CA·M SAMs with high thermal stability at air/substrate interface. The CA·M SAMs with long range and uniform structures were successfully constructed on reconstructed Au(111) and Au(100) surfaces. In addition to the self-assembly of CA·M, the self-assembly of melamine molecules and cyanuric acid molecules have been investigated in Au(111) surfaces. The structural model of the SAMs of melamine molecules, cyanuric acid molecules and CA·M complex were established based on the high resolution STM images. Combined with density functional theoretical (DFT) calculations, the role of the adsorbate-adsorbate and the adsorbate-substrate interactions were discussed. Our results suggest that the substrates are able to adjust the final structures of the CA·M SAMs even when the strength of the adsorbate-adsorbate interactions is three times larger than that of the adsorbate-substrate interactions.3) A simple one-step procedure has been developed for the preparation of the SAMs of metal-organic coordination polymers (MOCPs). The MOCPs of DHBQ-Cu system and Bpy-Cu system were directly synthesized on the preheated Au (111) surfaces from aqueous solutions. Incommensurate structures were found in the SAMs of MOCPs, which suggest that the adsorbate-adsorbate interactions dominate the self-assembly of MOCPs on Au (111) surfaces.