Self-assembled Nanostructures On Graphite By External Stimul Investigation With STM Technique

The construction and regulation of surface nanostructures can be combined with prior art to enable fabrication of devices on unreachable scales by current technology.This thesis mainly explores the assembly and regulation of nanostructures at the graphite interface by means of scanning tunneling microscopy(STM)technology..The main contents are as follows:(1)The self-assembly of two kinds of bowlene molecules of Cora-5COOH and Cora-5Py on the graphite surface was studied by STM technique.The effects of the concentration of host molecules(1,3,5-Tris(10-carboxydecyloxy)benzene,TCDB)and guest molecules on the self-assembled structure of the binary host-guest system were studied.The STM image shows that the TCDB presents a square cavity structure.When the guest molecule Cora-5COOH is introduced,the self-assembly structure is disordered.While TCDB can form a stable host-guest assembly structure with Cora-5Py.The self-assembly structure of TCDB/Cora-5Py changes with the concentration of the guest molecule.According to the results of density functional theory,TCDB/Cora-5Py is a thermodynamically stable state.It was found that the size effect between host and guest and concentration-dependent effect played the critical role.This work will help to advance our understanding of the dynamic process of self-assembly of host and guest molecules.(2)The self-assembly of two azobenzene-containing macrocyclic molecules on the graphite surface was studied by STM technique,in which LC-1 contains two azobenzene groups and LC-2 contains three azobenzene groups,respectively.When the host template TCDB is introduced,both LC-1 and LC-2 can enter the cavities formed by the TCDB,forming a regular linear lattice structure,in which the LC-1 molecules are in the(t,t)configuration,LC-2 molecules are in the(t,t,t)configuration.After irradiation with UV light,it was observed that LC-1 was converted to the(c,c)configuration and LC-2 was converted to the(t,t,c)configuration.This shows that the host-guest effect and the illumination effect have important significance in the photoisomerization process of photoisomers containing azobenzene.This work provides an easy way to study the photoisomerization of macrocyclic compounds containing azobenzene groups.This may be beneficial for the fabrication of nanostructures and the development of photosensitive nanodevices.(3)Self-assembled structure of both N2S4-OR(1)and N2Se4-OR(2)without sphenanthrene fused pyrrole ring,and both N2S4-OR(3)and N2Se4-OR(4)with phenanthrene fused pyrrole ring were studied in different solvents such as heptanoic acid and octylbenzene by STM technique.The assembly structure of N2S4-OR(1),N2Se4-OR(2)in different solvents were not significantly different.So there is no solvent dependency.N2S4-OR(3),N2Se4-OR(4)clearly showed different self-assembled structures in octylbenzene and heptanoic acid solvents.Understanding the effects of solvents on current systems will allow us to control the molecular ordering of two-dimensional physical adsorption monolayers,which is important for the design and manufacture of porphyrin-based devices.