O/N替代掺杂对zigzag型硼氮窄纳米带能带及输运特性的影响

用第一性原理非平衡格林函数方法研究了O原子掺杂zigzag型硼氮窄纳米带(z-BNNNRs)的能带结构和电子输运特性.研究结果表明:O原子对N原子的替代掺杂使z-BNNNRs的能带结构出现明显变化,体系由半导体转变为金属;O掺杂明显地改变了z-BNNNRs体系的导电性能,在一定的偏压范围内产生明显的负微分电阻(NDR)现象,边缘掺杂比中间掺杂产生更大的负微分电导,进一步的输运性质计算给出的透射谱也印证了这一点.随着掺杂浓度的增加,负微分电导的极值也随之增大.     

量化方法研究分子结BEMP和TEMP的电子输运特性

通过结合杂化密度泛函和前线轨道理论与弹性散射格林函数方法研究了BE- MP(benzene-1,4-di-ethynyl-4-mercaptophenyl)和TEMP(thiophene-2,5-di-ethynyl-4- mercaptophenyl)两分子结的输运性质。基于杂化密度泛函方法计算两扩展分子电子结构的基础上,计算了两分子的输运性质．计算结果显示:电流增加来源于电极和分子轨道的共振;电导曲线呈现出平台特征．在此基础上从扩展分子A(Au-BEMP-Au)中间的苯环的旋转而引起电流减小的角度解释了负微分电阻现象．     

分子旋转对分子器件电子输运性质的影响

利用基于非平衡格林函数和密度泛函理论相结合的第一性原理计算方法,研究了一种可旋转分子跨接在金电极上的电子输运性质。计算结果表明:分子中的转子与定子间的旋转角度可以有效调控分子器件的电子输运性质。当夹角从30°变化到150°,分子器件的导电性呈现出增强、减弱的震荡变化。此外,当夹角变化到90°,分子器件的电流电压曲线打破其他角度呈现的线性变化特性,其电流值在2.4 V以后随着电压的增大而减小,表现出强烈的负微分电阻效应。     

超细钛金属线的电子性质

使用第一性原理方法计算研究了一系列无限长、 超细的钛金属线的结合能和电子性质, 并得到了这些超细金属线的电导. 结果表明, 超细钛金属线单位原子的结合能比体材料的结合能低得多, 而且与金属线截面半径的倒数在所计算的纳米范围内成线性反比关系. 钛金属线的电子结构性质表现出渐进的尺寸演化和明显的结构关联, 当金属线直径大于1 nm时表现出类似体材料的电子结构, 这与Ti团簇的电子结构性质相似. 对电导的计算发现, 金属线的电导随着线尺寸的变粗而增大, 电导通道的数目由金属线的结构对称性和粗细所决定.     

碱金属原子掺杂BDC60分子中整流特性第一性原理研究

利用第一性密度泛函理论和非平衡格林函数相结合的方法,研究了碱金属原子掺杂对BDC60 分子电子输运性质的影响. 计算结果表明,在极低偏压下碱金属掺杂的BDC60分子能够表现出非常优良的整流性能,同时也展示出显著的负微分电阻行为. 根据透射谱和前线分子轨道及其空间分布随外加偏压的变化等方面的分析,系统地讨论了整流以及负微分电阻行为产生的内在机理. 我们的研究有助于BDC60 分子在未来低偏压整流和负微分电阻分子器件中的应用.     

碱金属原子掺杂BDC60分子中整流特性第一性原理研究

利用第一性密度泛函理论和非平衡格林函数相结合的方法,研究了碱金属原子掺杂对BDC60分子电子输运性质的影响.计算结果表明,在极低偏压下碱金属掺杂的BDC60分子能够表现出非常优良的整流性能,同时也展示出显著的负微分电阻行为.根据透射谱和前线分子轨道及其空间分布随外加偏压的变化等方面的分析,系统地讨论了整流以及负微分电阻行为产生的内在机理.我们的研究有助于BDC60分子在未来低偏压整流和负微分电阻分子器件中的应用.     

氯化1-乙基-3-甲基烷基咪唑分子结构及其氢键作用能的密度泛函研究

采用量子化学密度范函方法计算研究了氯化1-乙基-3-甲基咪唑盐（[EMIM]C1）正负离子间相互作用的平衡构型和Cl^-离子从不同方位与咪唑阳离子的结合能．计算发现Cl^-可在咪唑环平面上结合形成离子键，其结合能为．368．97kJ／mol，还可与环上的三个H原子形成氢键，其氢键键长和结合能分别为0．2000nm／-378．03kJ／mol、0．2339nm／-344，69kJ／mol和0．2301nm／-346，01kJ／mol．结合能包括氢键作用能和正负离子的静电作用能，后者为主要贡献．从理论上展示了该离子液体的氢键结构．     

铜-真空-铜金属隧道结转变电压的理论研究

利用非平衡格林函数与密度泛函理论相结合方法研究了电极表面具有原子级突起的铜-真空-铜隧道结的转变电压.计算结果表明,铜电极真空隧道结的转变电压主要决定于电极表面尖端铜原子4p轨道的局域态密度,因而对电极取向和表面局域原子构型非常敏感.对于电极取向沿(111)方向的铜电极真空隧道结,当电极表面原子级突起取为铜吸附原子和金字塔型铜纳米粒子两种构型时,转变电压的计算值分别约为1.40和2.40 V.当电极取向沿(100)方向时,电极表面原子级突起分别为铜吸附原子和金字塔型铜纳米粒子两种构型的铜电极真空隧道结,其转变电压的差异更为显著.具体而言,电极表面有一金字塔型铜纳米粒子的铜电极真空隧道结的转变电压值减小至1.70 V,而电极表面原子级突起为铜吸附原子的铜电极真空隧道结却因铜吸附原子4p轨道的局域态密度过于扩展,即使在偏压超过1.80 V时仍然没有出现转变电压.这些结果表明转变电压谱可用作分析金属电极真空隧道结电子输运特性的有力工具.     

含氮-空位缺陷锯齿状石墨烯纳米条带中负微分电阻和自旋过滤效应

采用第一性原理和非平衡格林函数方法,系统研究了含氮空位缺陷锯齿状石墨烯纳米条带的自旋极化输运特性．理论计算结果表明边界非对称的这类石墨纳米条带的基态具有铁磁性,由其构建的分子结中负微分电阻效应具有鲁棒性,是电极局域的态密度及依赖偏压的散射区-电极耦合作用结果．此外,在特定偏压区域还观察到几乎完美的自旋过滤效应．     

PbTiO3纳米晶电子结构及铁电性理论研究

采用密度泛函方法,以镶嵌势能的团簇模型对PbTiO₃纳米晶电子结构进行了量子化学计算研究,得到簇模型中键长、键级及净电荷之间的变化规律.布居分析和态密度计算结果表明,O原子的2p轨道、Ti原子的3d轨道、Pb原子的6s轨道和6p轨道之间的相互作用是四方相PbTiO₃纳米晶体出现铁电性的重要原因,并计算得到不同晶粒PbTiO₃纳米晶的偶极矩和自发极化强度.     

Redox-driven conductance switching via filament formation and dissolution in carbon/molecule/TiO2/Ag molecular electronic junctions

Carbon/molecule/TiO2/Au molecular electronic junctions show robust conductance switching, in which a metastable high conductance state may be induced by a voltage pulse which results in redox reactions in the molecular and TiO2 layers. When Ag is substituted for Au as the "top contact", dramatically different current/voltage curves and switching behavior result. When the carbon substrate is biased negative, an apparent breakdown occurs, leading to a high conductance state which is stable for at least several hours. Upon scanning to positive bias, the conductance returns to a low state, and the cycle may be repeated hundreds of times. Similar effects are observed when Cu is substituted for Au and for three different molecular layers as well as "control" junctions of the type carbon/TiO2/Ag/Au. The polarity of the "switching" is reversed when the Ag layer is between the carbon and molecular layers, and the conductance change is suppressed at low temperature. Pulse experiments show very erratic transitions between high and low conductivity states, particularly near the switching threshold. The results are consistent with a switching mechanism based on Ag or Cu oxidation, transport of their ions through the TiO2, and reduction at the carbon to form a metal filament.     

The Diversity of Electron‐Transport Behaviors of Molecular Junctions: Correlation with the Electron‐Transport Pathway

We report the electron‐transport behaviors of a number of molecular junctions composed of π‐conjugated molecular wires. From calculations performed by using density functional theory (DFT) combined with the non‐equilibrium Green’s function (NEGF) method, we found that the length–conductivity relations are diverse, depending on the particular molecular structures. The results reveal that the conductance–length dependence follows an exponential law for many conjugated molecules with a single channel, such as oligothiophene, oligopyrrole and oligophenylene. Therefore, a quantitative relation between the energy gap (E_g)_∞ of the molecular wire and the attenuation factor β can be defined. However, when the molecular wires have multichannels, the decay of conductance does not follow the exponential relation. For example, the conductance of porphyrin‐based oligomers and fused thiophene decays almost linearly. The diversity of electron‐transport behaviors of molecular junctions is directly dominated by the electron‐transport pathway.     

一种双锂盐梳状聚合物电解质的制备及电化学性能

将聚乙二醇单甲醚(MPEG)接枝在聚(异丁烯-alt-马来酸酐)(PIAMA)上合成梳状锂单离子导体PIAMA-g-MPEG, 并与双(三氟甲基磺酰)亚胺锂(LiTFSI)复合制成双锂盐梳状聚合物电解质薄膜. 用核磁共振波谱 (¹H NMR)、 热重分析(TG)、 扫描电子显微镜(SEM)、 电化学阻抗(EIS)和电池充放电测试等方法对聚合物基体和电解质的物化性质和电化学性能进行了研究.结果表明, 设计的双锂盐梳状聚合物电解质能够有效解离并传输锂离子, 70 ℃下离子迁移数(t_Li⁺)为0.32, 离子电导率(σ)为1.5×10^-4 S/cm, 电化学稳定窗口为0~4.9 V (vs. Li/Li⁺). 组装Li|PIAMA-g-MPEG|Li电池并进行70 ℃恒电流充放电电压极化测试, 结果表明, 电解质与金属锂负极兼容性较好, 能够有效抑制锂枝晶的生长.组装LiFePO₄|PIAMA-g-MPEG|Li电池进行70 ℃长循环及倍率性能测试, 电解质表现出了优异的高温性能.     

苯并[1,2-b:4,5-b']二噻吩和二噻吩邻苯二甲酰亚胺的平面型交替共聚物的合成及其光伏性能

通过Stille聚合反应合成了含有苯并[1,2-b:4,5-b']二噻吩和二噻吩邻苯二甲酰亚胺的D-A结构平面共聚物PBDTPhBT.该聚合物热稳定性和在常见有机溶剂中的溶解性良好、在380～580nm范围内有强吸收.分子模拟计算的结果表明,聚合物主链具有较好的平面型.PBDTPhBT的光学带隙为2.10eV、用电化学方法测量的HOMO能级为5.23eV.以聚合物PBDTPhBT为给体、PC70BM为受体(给受体重量比为1:1)、Ca/Al为负极制备了本体异质结聚合物太阳能电池.在AM1.5,100mWcm2光照条件下器件的开路电压和短路电流分别为0.79V和5.63mAcm2,能量转换效率达到了1.76%.     

Effect of bond-length alternation in molecular wires

Current-voltage (I-V) characteristics for metal-molecule-metal junctions formed from three classes of molecules measured with a simple crossed-wire molecular electronics test-bed are reported. Junction conductance as a function of molecular structure is consistent with I-V characteristics calculated from extended Hückel theory coupled with a Green's function approach, and can be understood on the basis of bond-length alternation.     

Interpretation of stochastic events in single-molecule measurements of conductance and transition voltage spectroscopy

The first simultaneous measurements of transition voltage (V(t)) spectroscopy (TVS) and conductance (G) histograms (Guo et al., J. Am. Chem. Soc. 2011, 133, 19189) form a great case for studying stochastic effects, which are ubiquitous in molecular junctions. Here an interpretation of those data is proposed that emphasizes the different physical content of V(t) and G and reveals that fluctuations in the molecular orbital alignment have a significantly larger impact on G than initially claimed. The present study demonstrates the usefulness of corroborating statistical information on different transport properties and gives support to TVS as a valuable investigative tool.     

Strong effects of molecular structure on electron transport in carbon/molecule/copper electronic junctions

Carbon/molecule/copper molecular electronic junctions were fabricated by metal deposition of copper onto films of various thicknesses of fluorene (FL), biphenyl (BP), and nitrobiphenyl (NBP) covalently bonded to flat, graphitic carbon. A "crossed-wire" junction configuration provided high device yield and good junction reproducibility. Current/voltage characteristics were investigated for 69 junctions with various molecular structures and thicknesses and at several temperatures. The current/voltage curves for all cases studied were nearly symmetric, scan rate independent, repeatable at least thousands of cycles and exhibited negligible hysteresis. Junction conductance was strongly dependent on the dihedral angle between phenyl rings and on the nature of the molecule/copper "contact". Junctions made with NBP showed a decrease in conductivity of a factor of 1300 when the molecular layer thickness increased from 1.6 to 4.5 nm. The slope of ln(i) vs layer thickness for both BP and NBP was weakly dependent on applied voltage and ranged from 0.16 to 0.24 A(-1). These attenuation factors are similar to those observed for similar molecular layers on modified electrodes used to study electrochemical kinetics. All junctions studied showed weak temperature dependence in the range of approximately 325 to 214 K, implying activation barriers in the range of 0.06 to 0.15 eV. The carbon/molecule/copper junction structure provides a robust, reproducible platform for investigations of the dependence of electron transport in molecular junctions on both molecular structure and temperature. Furthermore, the results indicate that junction conductance is a strong function of molecular structure, rather than some artifact resulting from junction fabrication.     

Quantum Chemical Investigations on Electron Transport Characteristics of Porphyrin and Metal-porphyrin

IntroductionRecently, great advances have been made in theresearch of molecular electronics[1,2]. Molecular de-vices based on single molecule[3—5]or molecular clus-ters[6—8], negative differential resistance[9], electro-static current switching[10—12],…     

超分子配合物[Mn(phen)_2(NO_3)]NO_3·4H_2O的合成与晶体结构

制备了超分子配合物[Mn(phen)2(NO3)]NO3.4H2O,利用元素分析仪、红外光谱仪、X射线单晶衍射仪分析了其组成和结构,并测定了其摩尔电导率.结果表明,合成的配合物晶体属三斜晶系,空间群P-1,晶胞参数分别为:a=0.791 38(19)nm,b=1.023 9(2)nm,c=1.647 3(4)nm,α=105.414(4)°,β=103.295(3)°,γ=90.127(4)°,V=1.249 4(5)nm3,Z=2.就配合物晶体结构而言,有机基团和结晶水通过氢键和π-π堆积作用扩展为二维超分子体系,其中结晶水通过氢键作用形成四核簇.