Synthesis Of Silicon-based And Carbon-based Molecules And Their Single-molecule Conductance Studies

The development of microelectronics is in an important period of theoretical and technological innovation.Advances in science and technology have driven the demand for semiconductor devices with higher integration,but the miniaturization of siliconbased semiconductor integrated circuits faces huge challenges in both process technology and physical principles.The advent of single-molecule electronics research holds promise for solving existing problems intrinsic to traditional silicon-based semiconductors,providing us the opportunity to miniaturize electronic devices using bottom-up construction methods.The research objectives of this thesis are to explore the basic principles and regulations of the electron transmission of nanoscale molecular wires from a precise chemical synthesis approach.The inspiration for the choice of molecular skeletons comes from two research area of “traditional silicon-based semiconductor materials” and “emerging carbon-based semiconductor materials”.Based on the above considerations,a series of silicon-based and carbon-based molecules with specific structures were designed and synthesized in this thesis.Their charge transport properties were explored through single-molecule conductance technology,aiming to provide experimental reference and theoretical support for the construction of functional molecular devices.Converting silicon-based or carbon-based molecules into functional molecular electronic devices and making them active components in circuits will bridge the gap between the two different fields of the established technology in the semiconductor industry and single molecule electronics and provide new ideas for the development of chips in the post-Moore era.The main research content is divided into the following two parts:(1)Silicon is the core material used in the traditional semiconductor industry.In this thesis,a series of silane molecules with special structures were designed and synthesized: sila-adamantane,bicyclo[2.2.0]hexasilane,mono-anchored bicyclo[2.2.2 ]octasilane and C-Si series.Facing the challenges of harsh reaction conditions and low yields in the synthesis of sila-adamantane and C-Si series,a safer and more efficient synthesis scheme was proposed.The successful preparation of silaadamantane realized the transformation of the bulk silicon lattice structure to molecular silicon compound.For the mono-anchored bicyclo[2.2.2]octasilane,its superior insulating properties were demonstrated through the EGa In technology measurement.The scanning tunneling microscope-based break junction(STM-BJ)measurement of C-Si series shows the molecular junction is stable and efficient electronic pathways can be formed.For the different types of C-C bonds in the “doped” molecular framework,the conductance difference is not significant.The research on the electrical conductivity of silicon electronic materials has important guiding significance for the miniaturization of devices.(2)Carbon materials have excellent mechanical,electrical and chemical properties,and are expected to be the next generation electronic materials.In this thesis,a series of carbon-based molecules with fused-ring aromatic hydrocarbons as molecular skeleton were designed,they are phenanthrene series(two-dimensional rigid structure),anthracene series(three-dimensional rigid structure)and helicene series(threedimensional elastic structure),and their synthetic characterizations and corresponding conductance measurement were carried out.For the phenanthrene series,by changing the positions of the dithiomethyl anchoring groups,the conductance difference is as high as 20 times,which means the conductance can be effectively regulated.Density Functional Theory(DFT)calculations elucidate the regio and steric effects of the anchoring group on its electronic properties,this provides a new strategy for tuning the conductance of graphene nanoribbons at the single-molecule level.Aiming at the purification problems of the anthracene series molecules,taking advantage of the property of silver ions to easily form silver ion-? bond complexes with aromatic compounds,the anthracene series was innovatively purified by silver nitrate-modified silica column,and a new scheme was proposed for the separation and purification of polycyclic aromatic hydrocarbons.Conducting conductance test on the anthracene series molecules,it is found that the conductance values of the four molecules are almost the same,indicating that the conductivity of the molecules cannot be significantly changed by changing the degree of overlap between the electron clouds in the skeleton.For the helicene series,due to the spring-like non-planar structure of the helicene molecule,its electron transport will reflect the difference “through-bond” and“through-space” coupling.Based on the corresponding Power Spectral Density(PSD)measurements,we found that the [4]helicene mainly rely on “through-bond”conductance,while [5]helicene is dominated by “through-space” conductance.This provides a guiding significance for the conductance research of three-dimensional structure molecules.In summary,through the study of the electron transport properties of silicon-based and carbon-based molecules at the nanoscale,this thesis has brought inspiration to the development of the miniaturization of traditional silicon-based electronic devices.The findings of this thesis provide new ideas for understanding electron transport at the nanoscale and a new avenue for developing functional single-molecule devices.