Tailoring Self-assembled Nanostructures At Interface By External Stimuli Investigation With Stm Technique

ABSTRACT:Enormous research efforts are currently devoted to molecular nanodevices, and functionalized organic molecules are promising building blocks for nanoscale structures. Realization of this charming idea properly relies on controlling self-assembled adlayer at solid/liquid interface. In addition, attributed to the unique high-spatial resolution at the molecular level, scanning probe microscope (SPM) has a great advantage in the research of nanostructures at solid/liquid interface.In this thesis, we fabricated some interesting binary organic nanostructures by designing molecular structures and introducing external stimuli. Scanning tunneling microscopy (STM) was taken as the main research means, combined with density functional theory (DFT) simulations, to study the adsorption of molecules on surfaces, to reveal the driving forces and possible issues affecting molecular self-assembly. The main conclusions are as follows:(1) Based on in situ Schiff-base reaction at the solid/liquid interface, two kinds of chiral self-assembled structures have been directly formed and confirmed by means of high-resolution STM technique. The achiral5,5’-(2,5-bis (octyloxy)-1,4-phenylene) bis (thiophene-2-carbaldehyde)(PT2) molecules formed chiral lamellar adlayers. However, upon the addition of5-aminoisophthalic acid (5A-acid) or dimethyl5-aminoisophthalate (5A-ate), the chiral lamellar structure was transformed into the chiral "flower" or "worm" architectures, respectively. It was turned out that the transformations of structures resulting from the occurrence of the condensation reaction on the surface at room temperature. What’s more, the intermolecular hydrogen bonds played a very important role in the construction of these two amazing chiral structures. The research provides a new method to construct two-dimensional (2D) chiral self-assembled systems, which will be potentially applied to the fabrication of functional films and nanodevices.(2) The adsorption and assembling behaviors of phthalocyanine (H2Pc) molecules were studied. It was shown that triphenylene-2,6,10-tricarboxylic acid (H3TTCA) self-assembled "chicken wire" structures served as a template for the ordering of H2PC molecules in five new one-dimensional (1D) nanoarrays. These five kinds of nanoarrays could be precisely turned into2H2Pc@H3TTCA nanoarrays by adjusting the substrate temperature. High-resolution STM images, as well as DFT calculations, revealed that the preferential adsorption of the2H2Pc@H3TTCA nanoarrays in the rearrangement of the H3TTCA supramolecular networks. The result is quite important for helping us gain insight into dynamic procedures of self-assembly and control molecular pattern formation on the surface.