外界作用对有机分子器件电输运性质的影响

发布时间：2018-03-30 20:37

本文选题：分子器件　切入点：负微分电导效应　出处：《山东师范大学》2017年硕士论文

【摘要】：随着科技的不断进步,微观器件越来越小型化,人们对微观世界的认识也越来越广泛,研究单个分子器件的功能特性也取得了不俗的成果,并且伴随着实验和理论的完善,出现了不同种类的分子器件,例如:分子导线、分子开关、分子传感器等等。其中分子传感器中的负微分电导(NDC)效应就是分子器件中的一个十分理想的功能特性,并且得到了越来越多的关注和研究。本文利用密度泛函理论(DFT)和非平衡格林函数(NEGF)方法研究了低偏压下以9,10-二氢蒽为核心的单硫醇化芳香基亚乙炔分子(简称为TADHA分子)器件的NDC效应以及影响其NDC效应的外界因素。在低偏压下取得较大的NDC效应是单分子器件的一个非常理想的功能特性。依据Perrin M.L.等人研究的TADHA分子,由于其是由两个共轭分支组成,所以TADHA分子是一个可以拉伸、压缩的非刚性分子。而且他们的实验研究结果显示该分子结在较低偏压状态下呈现出了优异的NDC效应。为了解释低偏压状态下呈现出的优异的NDC效应,我们在Perrin M.L.等人的实验基础上对TADHA分子结进行了拉伸和压缩计算,讨论了电极之间的距离改变对分子结的NDC效应的影响。结果显示在对分子结进行拉伸和压缩的过程中,存在着一个能量最低的电极距离,即平衡距离。在电极的平衡距离下由于外界偏压作用引起HOMO和HOMO-1能级的劈裂,使得分子结在较低偏压下产生了明显的负微分电导。随着电极距离的缩短,分子结的电流和负微分电导行为都随之变大;相反由平衡距离处开始拉伸两电极时,分子结的负微分电导慢慢变小直至最后消失,而当NDC效应消失后,分子结又呈现出了整流特性。考虑到一般分子器件的组装是在溶液环境中进行的,若分子结组装后干燥不彻底,仍然会存有部分水吸附在分子结附近,为此,我们就尝试研究了将单个或多个水分子吸附在TADHA功能分子上,拟探究H20的吸附是否会对较低偏压下的NDC效应产生影响。结果显示H2O的吸附作用对分子器件的电子传输特性和负微分电导效应存在不同程度的影响,具体表现在:单个或两个H20吸附对分子器件的负微分电导影响较小,随着吸附H20的数目的增加,对电输运的影响也越来越明显;并且H20吸附位置不同,其对分子器件的电输运性质影响也不同。除此之外,H20吸附还导致了分子结的对称性被破坏,所以分子结也出现了整流特性。并且H20的吸附位置不同,对电输运性质和NDC效应的影响也不同,具体表现在:吸附位置越靠近分子结的中间部分,对NDC效应影响越明显。除此之外,我们进一步研究了 F2的吸附效应对TADHA功能分子的NDC效应的影响。理论结果显示,F2的吸附抑制了 NDC效应的产生,并且导致低偏压下的电流、电导变小。但是同时,F2的吸附使得分子结不对称性增加,出现了较大的整流比,整流效果变强,而且F2的吸附位置越靠近TADHA分子中间位置,最大整流比越大,整流效果越明显。本论文一共有六个章节的内容:第一章是综述,对分子电子学领域的主要研究内容和研究现状进行了简单的介绍;第二章是本论文中的理论部分,主要包括DFT理论和NEGF方法;第三章主要讨论了电极距离的改变对TADHA分子结的负微分电导效应的影响,发现在适宜的电极距离下,两个电极之间的距离越小,NDC效应越明显;第四章讨论了 H20的吸附效应对TADHA分子结的电输运特性的影响,探究了不同数目的H20吸附在TADHA分子结的不同位置处时对负微分电导效应的影响;第五章讨论了气体小分子(具有强氧化性的F2)对低偏压下的负微分电导的影响,可以看出F2的吸附对分子结的负微分电导起到了抑制作用,不同吸附位置处的抑制作用也不相同;第六章对研究的工作做出了总结,并对接下来将要开展的工作进行了展望。
[Abstract]:With the continuous progress of science and technology, more and more micro device miniaturization, understanding of the microscopic world is more and more widely, functional properties of single molecule devices have also achieved good results, and with perfect theory and experiment, the different kinds of molecular devices, such as molecular wires, molecular switch, molecular the sensor and so on. The negative differential conductance sensor (NDC) molecules in an ideal function effect is in molecular devices, and get more and more attention and research. By using the density functional theory (DFT) and non equilibrium Green function (NEGF) method to study the single thiol 9,10- two hydrogen anthracene core under low bias of aryl ethynylene molecular (TADHA molecules) external factors NDC effect devices as well as the influence of the NDC effect. The larger NDC effect under low bias is single An ideal function sub device. On the basis of TADHA molecular Perrin M.L. et al, because it is composed of two conjugate branches, so the TADHA molecule is a non rigid molecule can stretch, compression. And experimental study on their results show that the molecular junction at low bias state show NDC effect is excellent. In order to explain the low bias condition showed excellent NDC effect in our experimental based on TADHA Perrin M.L. et al. Molecular junctions were tensile and compression calculation, discusses the distance between the electrodes change on NDC effect of molecular junctions. The results showed that the tensile and compression process in the molecular junction, there is a lowest energy electrode distance, namely the balance distance. In the distance between the electrodes due to external bias caused by HOMO and HOMO-1 energy level splitting, the molecular junction in The low bias has a negative differential conductance significantly. With the shorter distance of electrodes, current molecular junctions and negative differential conductance behavior increases; instead the balance begins at a distance stretching two electrode, negative differential conductance of the molecular junction slowly decreases until it finally disappeared, and when the NDC effect disappeared after the molecular node presents rectification characteristics. Considering the general assembly of molecular devices is carried out in solution in the environment, if the molecular junction after assembly will still not completely dry, water adsorption in the near molecular junction therefore, we try to study the adsorption of single or multiple functions of water molecules in the TADHA molecules. To explore H20 whether the adsorption will affect the NDC effect on the low bias. The results show that the electronic transmission characteristics of adsorption of H2O on molecular devices and negative differential conductance effect has different effect, the specific performance In: single or two H20 negative differential conductance effect on the adsorption of smaller molecular devices, with the increase in the number of H20 adsorption, the influence of electrical transport is becoming more and more obvious; and the H20 adsorption at different positions on the electrical transport properties of molecular devices have different effects. In addition, the adsorption of H20 to the symmetry of the molecular junction was destroyed, so molecular junctions also appeared different adsorption sites and rectifying properties. H20, the influence of electrical transport properties and NDC effect is different, specific performance in the middle part of the adsorption position near the molecular junction, the NDC effect more obvious influence. In addition, we further studied the effect of NDC F2 on the effect of adsorption effect of TADHA molecules. The theoretical results show that the adsorption of F2 inhibited the NDC effect, and lead to the current low bias, the conductance decreases. But at the same time, the adsorption of F2 molecules do not make The symmetry of the increase, there was greater than the effect of rectification, rectification and strong adsorption position of F2 is close to the middle position of the TADHA molecule, the maximum rectification ratio increases, the rectification effect is more obvious. This thesis consists of six chapters: the first chapter is the summary, makes a brief introduction to the field of molecular electronics. The main research contents and research status; the second chapter is the theoretical part of this paper, mainly including the DFT theory and NEGF method; the third chapter the effects of negative differential conductance effect of electrode distance changes on the TADHA molecular junction are discussed in this paper, found in the appropriate electrode distance, the distance between the two electrodes is smaller, NDC the effect is more obvious; the fourth chapter discusses the adsorption effect of H20 transport on the characteristics of TADHA molecular junction, explores a different number of H20 adsorption at different locations of the TADHA junction effect of negative differential conductance Ring; the fifth chapter discusses the small gas molecules (strong oxide F2) effect on the negative differential conductance under low bias voltage, it can be seen that F2 adsorption to the inhibition of negative differential conductance of molecular junctions, inhibition of different adsorption position is not the same; the sixth chapter of the research work made summary and the next work to be carried out are discussed.

【学位授予单位】：山东师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TN601

【参考文献】