异构二芳基乙烯分子结低偏压电导机制的第一性原理研究

本文用结合密度泛函理论的非平衡格林函数方法研究了具有开环和闭环两种同分异构体的二芳基乙烯衍生物分子的结构-特性关系.该功能分子通过末端的吡啶基团连接到取向沿(111)方向的金电极.计算结果表明,异构体分子结的不同低偏压电导主要是由于它们具有不同的电子结构.两种构型分子结的低偏压导电都主要来自于电子隧穿最低未占据分子轨道(LUMO).由于具有扩展的单双键交替共辄结构,闭环构型分子具有更好的导电通道.通过计算分子结在平衡状态下的电子转移,可发现更多电子转移到闭环构型分子,导致了其LUMO能量更靠近费米能级,从而有利于低偏压下的导电性能.结果有助于理解二芳基乙烯分子及其衍生物分子的低偏压电导机制,也为设计更高性能的同类分子开关提供理论依据.

Inuence of Electron Donating Ability on Reverse Intersystem Crossing Rate for One Kind of Thermally Activated Delayed Fluorescence Molecules

First-principles calculations are applied for investigating influence of electron donating ability of donor groups in eight thermally activated delayed fluorescence(TADF)molecules on their geometrical structures and transition properties as well as reverse intersystem crossing(RISC)processes.Results show that the diphenylamine substitution in the donor part can slightly change the bond angle but decrease bond length between donor and acceptor unit except for the lowest triplet state(T1)of carbazole-xanthone molecule.As the electron donating ability of donor groups is increased,the overlap between the highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)is decreased.As the diphenylamine groups are added in donor part,the delocalization of HOMO is enlarged,which brings a decreased energy gap(ΔES1-T1)between the lowest singlet excited state(S1)and T1 state.Furthermore,with the calculated spin-orbit coupling coefficient(Hso),one finds that the larger value of<S1|Hso|T1>^2/ΔES1-T1^2 is,the faster the RISC is.The results show that all investigated molecules are promising candidates as TADF molecules.Overall,a wise molecular design strategy for TADF molecules,in which a smallΔES1-T1 can be achieved by enlarging the delocalization of frontier molecular orbitals with large separation between HOMO and LUMO,is proposed.

Theoretical design of single-molecule NOR and XNOR logic gates by using transition metal dibenzotetraaza[14]annulenes

The idea of replacing traditional silicon-based electronic components with the ones assembled by organic molecules to further scale down the electric circuits has been attracting extensive research focuses.Among the molecularly assembled components,the design of molecular logic gates with simple structure and high Boolean computing speed remains a great challenge.Here,by using the state-of-the-art nonequilibrium Green’s function theory in conjugation with first-principles method,the spin transport properties of single-molecule junctions comprised of two serially connected transition metal dibenzotetraaza[14]annulenes(TM(DBTAA),TM=Fe,Co)sandwiched between two single-walled carbon nanotube electrodes are theoretically investigated.The numerical results show a close dependence of the spin-resolved current-voltage characteristics on spin configurations between the left and right molecular kernels and the kind of TM atom in TM(DBTAA)molecule.By taking advantage of spin degree of freedom of electrons,NOR or XNOR Boolean logic gates can be realized in Fe(DBTAA)and Co(DBTAA)junctions depending on the definitions of input and output signals.This work proposes a new kind of molecular logic gates and hence is helpful for further miniaturization of the electric circuits.

Tuning the type of charge carriers in N-heterocyclic carbene-based molecular junctions through electrodes

Designing tunable molecular devices with different charge carriers in single-molecule junctions is crucial to the nextgeneration electronic technology.Recently,it has been demonstrated that the type of charge carriers depends on and can be tuned by controlling the molecular length and the number of interfacial covalent bonds.In this study,we show that the type of charge carriers can also be tuned by controlling the material and shape of electrodes.N-heterocyclic carbenes(NHCs)have attracted attention because of their ability to form strong,substitutional inert bonds in a variety of metals.Also,NHCs are more stable than the widely used thiol group.Therefore,we use electrodes to tune the type of charge carriers in a series of NHCs with different side groups.The ab initio calculations based on non-equilibrium Green’s formalism combined with density functional theory show that the dominant charge carrier switches from electrons to holes when gold electrodes are changed into platinum ones.The nature of the charge carriers can be identified by variations in the transport spectra at the Fermi level(EF),which are caused by the side groups.The projections of transport spectra onto the central molecules further validate our inferences.In addition,the transmission coefficient at EF is found to be dependent on the atomic interface structure.In particular,for the NHC without methyl or ethyl side groups,connecting a protruding atom on the electrode surface significantly enhances the transportability of both electrode materials.Overall,this study presents an effective approach to modifying transport properties,which has potential applications in designing functional molecular devices based on NHCs.

Effect of crystallographic orientations on transport properties of methylthiol-terminated permethyloligosilane molecular junction

The understanding of the influence of electrode characteristics on charge transport is essential in the field of molecular electronics.In this work,we investigate the electronic transport properties of molecular junctions comprising methylthiolterminated permethyloligosilanes and face-centered crystal Au/Ag electrodes with crystallographic orientations of(111)and(100),based on the ab initio quantum transport simulations.The calculations reveal that the molecular junction conductance is dominated by the electronic coupling between two interfacial metal–S bonding states,which can be tuned by varying the molecular length,metal material of the electrodes,and crystallographic orientation.As the permethyloligosilane backbone elongates,although theσconjugation increases,the decreasing of coupling induced by the increasing number of central Si atoms reduces the junction conductance.The molecular junction conductance of methylthiol-terminated permethyloligosilanes with Au electrodes is higher than that with Ag electrodes with a crystallographic orientation of(111).However,the conductance trend is reversed when the electrode crystallographic orientation varies from(111)to(100),which can be ascribed to the reversal of interfacial coupling between two metal–S interfacial states.These findings are conducive to elucidating the mechanism of molecular junctions and improving the transport properties of molecular devices by adjusting the electrode characteristics.

初探以工业工程之手法于连锁便利超商之应用--以统一、全家、莱尔富、OK便利商店为例之研究

工业工程（Industrial Engineering）俗称IE其目的在于运用有限的物力，场地与资金以达到最高产量与最低成本。台湾制造业上已有很大的成效，本研究在于探讨工业工程的专业与连锁便利商店的经营是否具有关联性。本文采用SPSS问卷分析中的次数分配、叙述性分析、信度分析以及因素分析，针对连锁便利商店中高阶主管（店经理、店长、副店长），来了解连锁便利超商在经营上是否运用了工业工程专业领域之知识；以及是否采用工业工程的相关专业来提升效率、降低成本、减少浪费，进而增加营收。透过深入分析本研究发现有七项工业工程的专业构（constructs）与连锁便利商店的营运具有密切的关联性。

Micro-structured lepidocrocite-type H_(1.07)Ti_(1.73)O_(4)as anode for lithium-ion batteries with an ultrahigh rate and long-term cycling performance

The lepidocrocite-type H_(1.07)Ti_(1.73)O_(4) microsized structures with a tap density of 0.88 g·cm^(-3) were prepared through the ion exchange method with K_(0.8)Li_(0.27)Ti_(1.73)O_(4) powder as the precursor,and they exhibited good rate performance and outstanding cycle stability as an anode material for lithium ion batteries(LIB).The ion exchange method provides favorable conditions for H_(1.07)Ti_(1.73)O_(4) as an anode electrode material for LIBs.X-ray photoelectron spectroscopy(XPS)result demonstrates the existence of defects in the nonstoichiometric H1.07Ti1.73O4,which have a beneficial effect on the LIB performance.The electrochemical performance test proves that the half-cell with microsized H_(1.07)Ti_(1.73)O_(4)as the anode electrode can maintain a specific capacity of 129.5 mAh·g^(-1) after 1100 cycles and 101 mAh·g^(-1)after 3000 long cycles at high current densities of 2.0 and 5.0 A·g^(-1),respectively.In addition,the small volume change rate of 3.6%in H_(1.07)Ti_(1.73)O_(4)during Li ion insertion was confirmed by real-time in situ transmission electron microscopy(TEM).The LiFePO_(4)||H_(1.07)Ti_(1.73)O_(4)full battery exhibits a longterm cycling stability with a specific capacity of73.8 mAh·g^(-1) at a current density of 500 mA·g^(-1) after 200 cycles.