Current–Voltage Characteristics of the Aziridine-Based Nano-Molecular Wires: a Light-Driven Molecular Switch

Using nonequilibrium Green＇s function formalism combined first-principles density functional theory, we analyze the transport properties of a 4,4-dimethyl-6-（4-nitrophenyl）-2-phenyl-3,5-diaza-bicyclo[3.1.0]hex-2-ene molecular optical switch. The title molecule can convert between closed and open forms by visible or ultraviolet irradiation. The I-V characteristics, differential conductance, on-off ratio, electronic transmission coefficients, spatial distribution of molecular projected self-consistent Hamiltonian orbitals, HOMO-LUMO gaps, effect of electrode materials Y（111）（Y =Au, Ag and Pt） on electronic transport and different molecular geometries corresponding to the closed and open forms through the molecular device are discussed in detail. Based on the results, as soon as possible the open form translates to the closed form, and there is a switch from the ON state to the OFF state（low resistance switches to high resistance）. Theoretical results show that the donor/acceptor substituent plays an important role in the electronic transport of molecular devices. The switching performance can be improved to some extent through suitable donor and acceptor substituents.

Single-chain and monolayered conjugated polymers for molecular electronics

Exploring the charge transport properties and electronic functions of molecules is of primary interest in the area of molecular electronics.Conjugated polymers（CPs） represent an attractive class of molecular candidates,benefiting from their outstanding optoelectronic properties.However,they have been less studied compared with the small-molecule family,mainly due to the difficulties in incorporating CPs into molecular junctions.In this review,we present a summary on how to fabricate CP-based singlechain and monolayered junctions,then discuss the transport behaviors of CPs in different junction architectures and finally introduce the potential applications of CPs in molecular-scale electronic devices.Although the research on CP-based molecular electronics is still at the initial stage,it is widely accepted that（1） CP chains are able to mediate long-range charge transport if their molecular electronic structures are properly designed,which makes them potential molecular wires,and（2） the intrinsic optoelectronic properties of CPs and the possibility of incorporating desirable functionalities by synthetic strategies imply the potential of employing tailor-made polymeric components as alternatives to small molecules for future molecular-scale electronics.

First-principle studies of Ⅰ-Ⅴ properties of a molecular wire

The elastic scattering Green function method has been developed to describe the I-V characteristics of molecular wires. The molecular electronic structure and the interaction between the molecule and the gold surface are two key factors for the charge transport properties of molecular wires in the formulas. An ab initio calculation at the hybrid density functional theory level is carried out to obtain the electronic structure of 4-4′-dimercaptodibenzene molecule. The frontier orbit theory and the perturbation theory are employed to determine the constant of the interaction energy between molecule and surface quantitatively. The numerical results show that the bonding between the sulfur atom and the gold atoms corresponds mainly to the covalent bond. Some molecular orbits are extended over molecule and gold cluster that certainly give channels for the charge transport, other molecular orbits are localized and the charge transport can take place by tunnel mechanism. At zero bias region, there exists a current gap. With the increasing bias, the conductance of the wire takes a shape of plateaus.

Effect of Chirality on the Electronic Transport Properties of the Thioxanthene-Based Molecular Switch

Based on the nonequilibrium Green function method and density functional theory calculations, we theoretically investigate the effect of chirality on the electronic transport properties of thioxanthene-based molecular switch. The molecule comprises the switch which can exhibit different chiralities, that is, cis-form and trans-form by ultraviolet or visible irradiation. The results clearly reveal that the switching behaviors can be realized when the molecule converts between cis-form and trans-form. ~urthermore, the on-off ratio can be modulated by the chirality of the carbon nanotube electrodes. The maximum on-off ratio can reach 109 at 0.4 V for the armchair junction, suggesting potential applications of this type of junctions in future design of functional molecular devices.

Electrically Driven Nonresonant Single Molecular Switches

Electrical switching of a single-molecule junction provides a practical module to perform sophisticated operations in electronic devices.However,designing an all-electrically-driven molecular switch is a great challenge.Here,we experimentally and theoretically investigated the charge transport characteristics of isoindigo(ISO)-molecules at the single-molecule level using the scanning tunneling microscope break junction technique.We find that the single-molecule junctions of ISO-molecules display bias voltage-driven switching characteristics.These switches are realtime,reversible,and nondestructive under low-bias voltages.Experimental results show that the mechanism of the switch is not the transition from nonresonant charge transport to resonant charge transport,but it is the shift of the frontier orbital energy levels of ISO-molecules and the change of the interfacial electronic coupling with bias voltage.Our results will advance the design of high-performance bias voltage-driven molecular switches.

Influence of InAs deposition thickness on the structural and optical properties of InAs quantum wires

The influence of InAs deposition thickness on the structural and optical properties of InAs/InA1As quantum wires （QWR） superlattices （SLS） was studied. The transmission electron microscopy （TEM） results show that with increasing the InAs deposited thickness, the size uniformity and spatial ordering of InAs QWR SLS was greatly improved, but threading dislocations initiated from InAs nanowires for the sample with 6 monolayers （MLs） InAs deposition. In addition, the zig-zag features along the extending direc- tion and lateral interlink of InAs nanowires were also observed. The InAs nanowires, especially for the first period, were laterally compact. These structural features may result in easy tunneling and coupling of charge carders between InAs nanowires and will hamper their device applications to some extent. Some suggestions are put forward for further improving the uniformity of the stacked InAs QWRs, and for suppressing the formation of the threading dislocations in InAs QWR SLS.

温稠密氢氘混合物热力学、光学和电子输运特性理论研究

温稠密状态下的氘氚混合物是惯性约束聚变必然要经历的中间物质状态.其在温稠密状态下的热力学特性和输运参数在聚变实验设计研究中起着重要作用.但由于氚具有放射性,实验中可以用氢氘混合物来模拟替代研究氘氚混合物.本文采用了密度泛函理论分子动力学模拟和基于自洽流体变分理论的化学模型,构建了氢氘混合物在0~200 GPa和300~10000 K宽范围状态方程和声速数据库.此外,结合Kubo–Greenwood公式计算得到了氢氘混合物电子电导率以及光学反射率和折射率,建立起混合物绝缘–金属化相变与实验上易探测的光学物理量反射率和折射率之间的联系,为从实验角度探索氢及其同位素的金属化提供了理论指导.

Silicon-Based Molecular Switch Junctions

In contrast to the static operations of conventional semiconductor devices,the dynamic conformational freedom in molecular devices opens up the possibility of using individual molecules as new types of devices such as a molecular conformational switch or for molecular data storage.Bistable molecules such as those having two stable cis and trans isomeric confi gurations could provide,once clamped between two electrodes,a switching phenomenon in the non-equilibrium current response.Here,we model molecular switch junctions formed at silicon contacts and demonstrate the potential of such tunable molecular switches in electrode/molecule/electrode confi gurations.Using the non-equilibrium Green function(NEGF)approach implemented with the density-functional-based tight-binding(DFTB)theory,a series of properties such as electron transmissions,current voltage characteristics in the different isomer conformations,and potential energy surfaces(PESs)as a function of the reaction coordinates along the trans to cis transition were calculated for two azobenzene-based model compounds.Furthermore,in order to investigate the stability of molecular switches under ambient conditions,molecular dynamics(MD)simulations at room temperature were performed and time-dependent fl uctuations of the conductance along the MD pathways were calculated.Our numerical results show that the transmission spectra of the cis isomers are more conductive than trans counterparts inside the bias window for both model compounds.The currentvoltage characteristics consequently show the same trends.Additionally,calculations of the time-dependent transmission fluctuations along the MD pathways have shown that the transmission in the cis isomers is always signifi cantly larger than that in their trans counterparts,showing that molecular switches can be expected to work as robust molecular switching components.

A first-principles study of dihydroazulene as a possible optical molecular switch

By applying nonequilibrium Green's function formalism combined with first-principles density functional theory, we investigate the electronic transport properties of the dihydroazulene optical molecular switch. Three kinds of adsorption sites including the hollow, bridge and top sites are studied. The two forms of this molecule, namely the open form and the closed form, can reversibly switch from each other upon photoexcitation. Their transmission spectra are remarkably distinctive. Theoretical results show that the current of the closed form is always significantly larger than that of the open form for all three adsorption sites, which promises this system as possibly one of the good candidates for optical switches due to its unique advantage, and which may have some potential applications in the future molecular circuit.

电场作用下分子导线的理论研究

利用从头计算法分别在HF/6-31G,HF/6-31G*,HF/6-31G**,HF/6-31+G,HF/6-31++G,HF/6-31+G*,HF/6-31+G**,HF/D95+*,B3LYP/6-31G*和B3LYP/6-31+G*水平上计算了5个单体的聚乙炔分子导线,从几何构型、SCF能量和分子轨道能级三个方面讨论了外电场对分子导线的影响,给出了聚乙炔分子导线性质与外电场变化的定量关系.

有机分子电子器件的研究进展

随着传统硅基电子器件的发展日趋受限,以原子和分子作为电子元器件的研究受到了越来越多的重视。概述了分子电子器件的概念和基本原理,详细介绍了分子导线、分子二极管、分子开关、分子存储器件和分子场效应晶体管的工作原理及最近的研究进展。具有π-共轭结构的有机分子体系是构造分子导线的理想单元;分子结的电子结构不对称性是分子具有整流特性的根本原因;轮烷和索烃是构造分子开关的理想单元之一;分子场效应晶体管的工作原理是量子隧穿,主要是金属-绝缘体-金属间的隧穿效应。最后阐述了目前分子电子器件研究中存在的主要问题。

电化学方法制备原子尺度间隙的Au隧道结过程研究

采用电化学方法制备了溶液中稳定的Au隧道结,对制备过程中量子线到隧道结的整个实验过程进行了研究.结果表明,由于存在机械应力,直接腐蚀Au丝很难精细控制电化学过程,导致无法直接制得隧道结.通过向溶液中加入氯金酸进一步电化学沉积/腐蚀成功地解决了此问题,但溶液中Au离子的自沉积作用导致所形成的隧道结不稳定.针对这一问题,对实验过程进行了改进,采用将腐蚀直接制得的电极对在盐酸溶液中定向电沉积的办法制备得到了溶液中稳定的Au隧道结.

分子线电子输运特性的第一性原理研究

从第一性原理出发 ,利用密度泛函理论研究了SH -C8H16-SH分子和金表面的相互作用 ,并利用分子前线轨道理论和微扰理论定量地确定了该相互作用能常数 ,然后 ,利用弹性散射格林函数方法研究了该分子与金表面形成的分子线的伏 安特性 .研究结果表明 ,当含有硫氢官能团的有机分子化学吸附于金表面时 ,硫原子将与金原子形成以共价键为主的混和键 ,此时 ,扩展的分子轨道使分子线的电导呈现出欧姆特性 ,而对于局域的分子轨道 ,电子的输运只能通过隧道效应来实现 .对分子线伏 安特性的计算结果显示 ,在零偏压附近 ,存在一个电流禁区 ,随着偏压的增加 ,分子线的电导呈现出平台特征 .

电场对分子线电子结构的影响

从第一性原理出发 ,利用密度泛函理论计算了分子 2 氨基 5 硝基 1,4 二乙炔基 4 苯硫醇基苯与金原子团形成的分子线的电子结构 ,从轨道、能级及吸附电子三个方面讨论了电场对分子线电子结构的影响。该工作将有利于未来纳米电子学器件的设计。

分子的电子结构对分子线电子输运性质的影响

分子通过硫氢官能团可以很强地吸附于金表面上 ,从而可作为连接体用于纳米电子学中的分子器件 .利用密度泛函理论计算了分子的电子结构 ,讨论了温度对分子结构的影响 ,并利用轨道的扩展情况讨论了分子电子结构对分子线电导的影响 .

分子电子学

作为纳米电子学的一个重要分支,分子电子学在近年来得到了巨大的发展,并成为国际上研究的热点。本文介绍了各种分子器件的制作技术及基本工作原理,回顾了近年来分子电子学的最新进展,展望了分子电子学的未来发展。

环双(对-苯基-对草快)对中性客体的分子识别和分子开关

用 AM1及 MNDO方法对环双 (对 -苯基 -对草快 )与中性客体的配合物进行理论研究 ,得到稳定化能和配合物相互转换的 ΔΔE值 ;以 AM1优化构型为基础 ,用 INDO/ SCI方法计算 4种配合物光谱 ,并用AM1方法计算主体与二苯醚衍生物在 H+存在下的势能曲线 ,探讨分子开关形成机理 .

基于PET过程的分子开关型荧光传感器研究进展

光诱导电子转移(PET)是一种重要的光物理过程,基于分子荧光发射强度对PET过程的依赖性以及对PET过程的物理结合调控、氧化还原调控和复杂结合调控,人们设计制备了一系列对分析物具有不同响应行为的开关型荧光传感器。与一般的荧光传感器相比较,这类荧光传感器具有响应快速、使用方便等特点。此外,多种逻辑门功能都可以通过开关型荧光分子的设计来实现,这就为分子器件、分子计算机乃至其它复杂分子机器的设计开发奠定了基础。介绍了基于PET过程的开关型荧光传感器研究现状,展望了此类研究的发展趋势。

用于识别金属离子的超分子荧光/磷光传感器

本文总结了近年来用于金属离子识别的超分子荧光 /磷光传感器的研究工作进展 ,着重介绍了光诱导电子转移及单体 -激基缔合物体系在金属离子识别中的应用。

基于Rotaxane单分子层的双稳态器件研究

利用微电子工艺制备了基于Rotaxane单分子层的双稳态分子电子器件,并对其电学特性进行了表征。研究发现,在Ti/Rotaxane/Au双稳态,器件具有可逆可重复的开关存储特性。将器件从初始的高阻态转变为低阻态的正向开关阈值电压为1.3 V,将低阻态转变为高阻态的负向开关阈值电压仅为-1.7 V。这种基于Rotaxane交叉结构的有机双稳态器件可望应用于非易失性分子存储器。