【作者】 张艳；

【导师】 丁国辉；

【作者基本信息】 上海交通大学 ， 物理学， 2016， 硕士

【摘要】 分子电子学的出现,已经有40多年了。最近,随着实验技术的突破和理论方法的发展,科学家们真正获得了探索单分子结电导特性的机会。这使得分子电子装置将来有可能像硅材料一样,成为半导体领域主要器件的提供者。作为分子电子学的热门研究对象,DNA分子更是依据其良好的自组装能力,吸引了众多科研人员的目光。在这篇论文中,我们将研究DNA分子在电荷传输、交流响应和极化子迁移率等方面的特性。在第一章的绪论中,我们对分子电子学的发展历程进行了简要介绍,其中包括了重要的实验和理论介绍。针对本文主要的研究方向,我们还概述了DNA相关工作的最近进展,并且讨论了DNA分子的两种主要计算模型:一维模型和双链模型,并分析了它们各自的优缺点。在第二章中,我们首先推导了介观系统的含时、不含时电流以及传输系数的表达式。紧接着,我们选取利用Landauer公式,给出了DNA分子结的非平衡电流计算的相应公式。随后,我们对基于DNA序列（GC）N_GC和（GC）1（T A）N_{T A}（GC）3的伏安特性展开了详细的讨论。我们发现,通过门电压调节DNA最高占据分子轨道（HOMO）能级,DNA序列（GC）N_GC的电导率在低偏置电压处就开始快速增大。而对于DNA序列（GC）1（T A）N_{T A}（GC）3,实验中观测到的弱距离依赖电导表现也被我们所证实,我们对该实验现象提出一种新的解释,认为其导电机制并不是文献中提出的热辅助的电荷跳跃,而是TA碱基对中的离散量子阱态的隧穿效应。在第三章中,我们研究了光照下的DNA分子结的交流响应特性。首先,我们推导了DNA交流电导的实部和虚部公式。计算发现,在某些特殊频率处,DNA序列左右端交流电导的实部出现了电导抑制现象。我们把它归结为交流势引起的DNA中电子到电极费米能表面的激发,或者是DNA深层能级中电子到传输窗口中部分占据能级的激发。然而,对应的电导虚部曲线却十分的光滑,没有表现出明显的特征。基于DNA电荷传输的一维模型,我们在第四章中研究了电声耦合效应下的DNA分子中极化子迁移率。通过分析其温度依赖关系及不同长度和不同序列的迁移率,我们发现,尽管近似方法有所差异,但是我们的结果跟之前的三维晶体中的极化子迁移率定性吻合。在第五章中,我们给出了全文的总结和对未来工作的展望。更多还原

【Abstract】 As we known,scientists have studied the field of molecular electron-ics for more than 40 years.Recently,with the breakthrough of experi-mental techniques and the development of theoretical methods,scientists have actually obtained the chance to explore the conductance properties of single-molecule junctions.As the traditional silicon material,molecular electronic devices are likely to become one main candidate of components of the future semiconductor industry.As a research branch of molecular electronics,DNA molecules have frequently been brought to the center of hot topics.By now,DNA molecule has attracted a lot of attentions from worldwide researchers due to its good self-assembling ability.In this dissertation,we will study properties of charge transport,ac response and polaron mobility of DNA molecules.In the first chapter,we briefly cover the development history of molec-ular electronics,including the introduction of the corresponding important experiments and theories.With regard to the main topics of this dis-sertation,we also outline the recent advancements related to the DNA molecules,and discuss the pros and cons for two main transport computa-tional models of the DNA molecules:the one-dimensional model and the two-channel model.In the second chapter,we first derive the general expressions of time-dependent current,time-independent current and transmission coefficient in a mesoscopic system.Then,taking advantage of landauer formula,we obtain the transport current through DNA molecular junction with-in the non-equilibrium Green’s function approach.We make a detailed discussion about the I-V characteristics of DNA sequences（GC）N_GCand（GC）1（T A）N_{T A}（GC）3.We find that,by using a gate voltage to adjust the highest occupied molecular orbital（HOMO）in DNA,the conduc-tivity of sequence（GC）N_GCcan increase rapidly where the bias voltage is low.For DNA sequence（GC）1（T A）N_{T A}（GC）3,our work also shows the phenomenon of a weak distance dependent conductance,which is ob-served by a pioneering experiment.However,distinguished from thermal-ly induced hopping of charges explained by the experiment,the intrinsic physics mechanism of this phenomenon we propose is that discrete quan-tum well states in the T A base pairs dominate the quantum tunnelling process.In the third chapter,we study the ac response of the above mentioned DNA sequences（GC）N_GCand（GC）1（T A）N_{T A}（GC）3 under light illumina-tion.First,we derive formulas for the real and imaginary parts of the ac conductance of DNA molecule.By calculation,we find the suppression phenomenon in ac conductances’real parts of the left and right lead of DNA sequences at certain frequencies.In fact,the conductance suppres-sion can be attributed to the excitation of electrons in the DNA sequences to the Fermi surface of metal electrodes due to ac potential,or to the excitation of electrons in deep energy levels of DNA sequences to partially occupied energy levels in the transport window.Based on the one-dimensional model for electronic transport along D-NA,we investigate the polaron mobility in DNA molecule with the effect of electron-vibration coupling in the fourth chapter.By analyzing depen-dence of the DNA polaron mobility on temperature,lengths and sequences of DNA molecule,it is obvious that our results are qualitatively consis-tent with the previous polaron mobility of the three-dimensional organic crystal case in despite of two different approximation approaches.Finally,in the fifth chapter,we sum up the whole content of this dissertation and give some insights into the future works.更多还原