硅基和碳基分子的合成及其单分子电导研究

【作者】 陈艳；

【导师】 肖胜雄；

【作者基本信息】 上海师范大学 ， 环境科学与工程， 2022， 博士

【摘要】 微电子的发展正处于理论以及技术革新的重要时期,科技水平的进步促使人们对更高集成度的半导体器件的需求更加强烈,但是硅基半导体集成电路的缩微化面临着工艺技术和物理原理的挑战。单分子电子学为解决传统硅基半导体缩微化问题提供了新思路,有望指导科学家们通过“自下而上”的构建方法实现电子器件缩微化。本论文的研究目标是在精准化学合成的基础上,探索纳米级分子导线的电子传输规律及其调控机制,而选择何种基质材料的灵感来源于“硅基传统半导体材料”以及“碳基新兴半导体材料”两个方向。基于以上考虑,本论文设计合成了一系列具有特定结构的硅基和碳基分子,通过单分子电导测试技术探索其电荷传输特性,希望能为构筑功能性分子器件提供实验借鉴和理论支撑,以期在既定半导体工业技术和单分子电子学这两个不同的领域之间建立一个桥梁——将硅基分子或者碳基分子制备为功能性分子电子器件,使其成为电路中的有源元件,为后摩尔时代芯片的开发提供新思路。主要研究内容分为以下两个部分:(1)硅是传统半导体的核心材料,本论文第一部分设计并合成了一系列具有特定结构的硅烷分子:金刚硅烷、双环[2.2.0]己硅烷、单锚定基团修饰的双环[2.2.2]辛硅烷以及“掺杂”碳-硅烷。针对金刚硅烷以及“掺杂”碳-硅烷合成中存在的反应条件苛刻、产率低等挑战,提出了更加安全高效的合成方案,其中金刚硅烷的成功制备实现了单晶硅晶格结构向分子硅化合物的转化。通过镓铟共晶合金技术对单锚定基团修饰的双环[2.2.2]辛硅烷的自组装单层膜进行了测试,电导测试结果表明其具有优异的绝缘性能。采用扫描隧道显微镜裂结(Scanning Tunneling Microscope-based Break-Junction,STM-BJ)技术对“掺杂”碳-硅烷进行单分子电导测试,结果表明“掺杂”碳-硅烷能够与金电极形成稳定的分子结,构筑高效稳定的电子通路。同时还发现,“掺杂”碳-硅烷分子骨架中碳碳键类型的变化对其单分子电导的影响不明显。上述硅基分子的电导研究对硅基半导体器件的缩微化具有重要的借鉴意义。(2)碳材料具有优异的力学、电学和化学性能,有望成为下一代电子材料。本论文第二部分设计了一系列以稠环芳烃为分子骨架的碳基分子,分别是菲系列(二维刚性结构)、蒽系列(三维刚性结构)以及螺烯系列(三维弹性结构),并完成了其合成、表征以及相应的电导测试。对于菲系列分子,当改变二硫甲基锚定基团在菲分子骨架上的位置时,其电导差异可以高达20倍,实现了对其电导的有效调控。密度泛函理论(Density Functional Theory,DFT)计算结果阐明了锚定基团的区域效应和空间效应对其电子性质的影响,该研究为石墨烯纳米带在单分子水平上的电导结构调整提供了一种新的策略。针对蒽系列分子难以分离提纯的问题,本文利用银离子容易与芳香化合物形成银离子-π络合物的特性,使用硝酸银改性的硅胶柱对蒽系列分子进行了有效纯化,为稠环芳香化合物的纯化提供了简便可行的解决方案。对蒽系列中的四个分子进行电导测试,发现其电导值几乎相同,说明对于该类三维刚性分子,通过改变分子骨架中电子云之间的重叠程度,不足以显著地改变其电导性能。对于螺烯系列,由于螺烯分子具有弹簧状的非平面共轭结构,其电子传输会表现出“通过键”耦合和“通过空间”耦合的两种不同电子传输方式。结合功率谱密度测试(Power Spectral Density,PSD),分析发现四螺烯主要是以“通过键”方式进行电子传输,而七螺烯主要是以“通过空间”方式进行电子传输。上述碳基分子的电导研究对于开发基于三维立体分子的电子器件具有指导意义。综上所述,本论文通过对硅基和碳基分子在纳米尺度上的电子输运特性研究,为传统硅基电子器件缩微化的发展开辟了新思路,为纳米尺度下分子的电子传导研究提供了新的视角,并为功能性单分子器件的创制提供了新途径。更多还原

【Abstract】 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-π 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.更多还原