First-principles study of the electronic transport properties of a C131 -based molecular junction

Using first-principles density functional theory and the non-equilibrium Green’s function formalism, we have studied the electronic transport properties of the dumbbell-like fullerene dimer C₁₃₁-based molecular junction. Our results show that the current-voltage curve displays an obvious negative differential resistance phenomenon in a certain bias voltage range. The negative differential resistance behavior can be understood in terms of the evolution of the transmission spectrum and the projected density of states with applied bias voltage. The present findings could be helpful for the application of the C₁₃₁ molecule in the field of single molecular devices or nanometer electronics.     

Negative differential resistance in the unsymmetrical C121-based molecular junction

Using first-principles density functional theory and non-equilibrium Green?s function formalism for quantum transport calculation, we have investigated the electronic transport properties of the unsymmetrical C₁₂₁-based molecular junction. Our results show that the current-voltage curve displays a negative differential resistance phenomenon in a certain bias voltage range. The mechanism for the negative differential resistance phenomenon is suggested. The present findings could be helpful for the application of the C₁₂₁ molecule in the field of single molecular devices or nanometer electronics.     

The dependence of electronic transport on compressive deformation of C60 molecule

The dependence of electronic transport on compressive deformation of C₆₀ molecule is studied theoretically in this work. Brenner's “second generation” empirical potential is used to describe the many-body short-range interatomic interactions for C₆₀ in the molecular dynamics simulations. Our results demonstrate that C₆₀ can be compressed up to a strain ε=0.31 before collapsing. Electronic transport under an applied bias is calculated by using a self-consistent field approach coupled with non-equilibrium Green's function (NEGF) formalism. The transmission probability, conductance gap, and conductance spectrum are found to be sensitive to the compression. The peak value of conductance decreases with the increase of strain until the C₆₀ is compressed up to a strain ε=0.31.     

Orientation effect on the electronic transport properties of C24 fullerene molecule

The transport properties of the cage-like molecule depend on its orientation between the electrodes, but the investigation on the mechanism has not been found. Using first-principle density-functional theory (DFT) and non-equilibrium Green’s function (NEGF) formalism for quantum transport calculation, we study the electronic transport properties of C₂₄ fullerene molecule with different orientations in Au–C₂₄–Au two-probe system. The effects of k-point sampling on the Brillouin zone are explored. Our results show that the negative differential resistance of C₂₄ molecule is found in such a system and can be tuned by the molecule's orientation in the two-probe system. We also proposed a mechanism for it. The I–V characteristic under bias voltage is determined. The present findings could be helpful for the application of the C₂₄ molecule in the field of single molecular devices or nanometer electronics.     

多晶样品SmxC60的电子输运性质研究

通过电阻和磁阻的测量，研究了多晶样品Sm_xC₆₀的电子输运性质．实验发现：Sm_xC₆₀的输运机制随ｘ的不同而发生变化．SmC₆₀的电阻率 温度关系可用涨落导致的隧道穿透模型解释，而Sm_2.75C₆₀的输运性质则可由弱局域化和电子-电子相互作用解释．Sm_2.75C₆₀的磁阻数据能用弱局域化和电子-电子相互作用模型很好地拟合，而SmC₆₀的磁阻数据则不能． 关键词：     

The spin-dependent electronic transport properties of M(dcdmp)2 (M = Cu,Au, Co,Ni) molecular devices based on zigzag graphene nanoribbon electrodes

The spin-dependent electronic transport properties of M(dcdmp)₂ (M = Cu, Au, Co, Ni; dcdmp = 2,3-dicyano-5,6-dimercaptopyrazyne) molecular devices based on zigzag graphene nanoribbon (ZGNR) electrodes were investigated by density functional theory combined nonequilibrium Green's function method (DFT-NEGF). Our results show that the spin-dependent transport properties of the M(dcdmp)₂ molecular devices can be controlled by the spin configurations of the ZGNR electrodes, and the central 3d-transition metal atom can introduce a larger magnetism than that of the nonferrous metal one. Moreover, the perfect spin filtering effect, negative differential resistance, rectifying effect and magnetic resistance phenomena can be observed in our proposed M(dcdmp)₂ molecular devices.     

First-principles electronic transport properties study of small carbon clusters: Cyclic C6

The transport properties of the six-atom carbon ring cluster C₆ sandwiched between Al(100) electrodes have been investigated by first-principles nonequilibrium Green's function technique. Our results demonstrate that the transport properties of monocyclic C₆ with D3h symmetry, with alternating bond angles, the most stable C₆ isomer, show metallic conductance. The charge transfer between the central molecule and the electrodes is very important for its transport properties. We also compare the equilibrium transmission spectra for C₆ in different isomers.     

Molecular control over Ag/p-Si diode by organic layer

Electrical transport properties of Ag metal-fluorescein sodium salt (FSS) organic layer-silicon junction have been investigated. The current-voltage (I-V) characteristics of the diode show rectifying behavior consistent with a potential barrier formed at the interface. The diode indicates a non-ideal I-V behavior with an ideality factor higher than unity. The ideality factor of the Ag/FSS/p-Si diode decreases with increasing temperature and the barrier height increases with increasing temperature. The barrier height (φ_b=0.98 eV) obtained from the capacitance-voltage (C-V) curve is higher than barrier height (φ_b=0.72 eV) derived from the I-V measurements. The barrier height of the Ag/FSS/p-Si Schottky diode at the room temperature is significantly larger than that of the Ag/p-Si Schottky diode. It is evaluated that the FSS organic layer controls electrical charge transport properties of Ag/p-Si diode by excluding effects of the SiO₂ residual oxides on the hybrid diode.     

碳链输运对基团吸附的敏感性分析

基于局域原子轨道的密度泛函理论和非平衡格林函数方法,研究了碳链输运特性对分别吸附7种常见官能团NO₂, CN, CHO, Br, C₆H₅, C₅H₄N和NH₂时的敏感性. 计算表明,电流对C₆H₅和CHO的吸附最为敏感,其次是对CN和C₅H₄N的吸附,在某些偏压下电流有大幅度的下降,其值 关键词： 碳链 输运特性 密度泛函理论 非平衡格林函数     

Transport properties and mechanism of C60 coupled to carbon nanotube electrode

By applying non-equilibrium Green's functions in combination with density-functional theory, we investigate electronic transport properties of C₆₀ coupled to carbon nanotubes and Li electrodes. The results show that electronic transport properties of CNT-C₆₀-CNT and Li-C₆₀-Li systems are completely different. Nonlinear I-V characteristic, varistor-type behavior and negative differential resistance (NDR) phenomenon are observed when electrodes are carbon nanotubes. We discuss the mechanism of I-V characteristics of CNT-C₆₀-CNT systems in details. Our results suggest conductance, energy level of Frontier molecular orbitals, energy gap between HOMO and LUMO, the coupling between molecular orbitals and electrodes are all playing critical roles in electronic transport properties.     

Rotational spectra of the deuterated carbon chain molecules: C3D, C4D, C3HD, and C4HD

The rotational spectra of the deuterated carbon chain molecules, C₃D, C₄D, C₃HD, and C₄HD, have been measured with the Fourier transform microwave (FTMW) spectrometer. The C₃D and C₄D radicals are produced by discharging the DCCD gas diluted in Ar. On the other hand, the gaseous mixture of HCCH, DCCD, and HCCD diluted in Ar is used for producing C₃HD and C₄HD. For C₃D, the molecular constants are determined from a joint least-squares analysis with the previously published millimeter- and submillimeter-wave data by considering the vibronic interaction between the ²Π ground state and the low-lying ²Σ vibronic state. The molecular constants of C₄D are determined by use of the conventional Hamiltonian of the ²Σ radical, while the effective rotational constant and centrifugal distortion constant are derived for C₃HD and C₄HD. In the present study, the hyperfine interaction constants of the deuterium nuclei in C₃D and C₄D are determined accurately. In particular, the nuclear quadrupole interaction constant, eQq, of the C₃D radical is found to be significantly smaller than those of C₂D and C₄D, indicating that C₃D has a floppy motion of the CCD bending mode due to the large Renner-Teller effect.     

EXTENDED SSH MODEL FOR C58B2 AND C58N2

The extended Su-Schrieffer-Heeger model is used to study the electronic energy levels and molecular structures for two kinds of isomers of C₅₈X₂(X=B, or N). In each case we obtain two sets of stable solutions. For C₅₈X₂ (1, 2), both sets of solutions are found to be reasonable, indicating two different phases. For C₅₈X₂(1, 60 ), only one set of solutions which satisfy the central inversion symmetry is physically reasonable.     

单硫醇分子结的几何结构和电输运性质:压力效应与末端基团效应

利用杂化密度泛函理论,研究了以甲基、醇基、羧基为末端基团的烷烃硫醇分子与金电极形成分子结的过程,得到了分子结的几何结构与外加压力的关系. 并在此基础上,利用弹性散射格林函数方法研究了烷烃硫醇分子的电输运性质. 研究结果表明,对于C₁₁S分子来说,当两电极距离大于2.1 nm时,该分子结断裂;对于C₁₁SOH和C₁₀SCOOH来说,相应的分子结断裂的电极距离基本相同(2.15 nm). 在相同的外加压力(4.0 nN)下,C_{11关键词： 压力 末端基团 烷烃硫醇分子 电输运性质}     

Molecular rectification of thiol-linked Au|PTCDI-[CH2]n|Au junctions

The electronic transport properties of the PTCDI-[CH₂]_n(0≤n≤6) molecular junctions with different molecular lengths are theoretically investigated via the first-principles density functional theory (DFT) and non-equilibrium Green's function (NEGF) method. Our results show that the transport properties depend on molecular lengths. The equilibrium conductance of the probed systems decreases exponentially with the increasing number n of the CH₂ unit. With n≥1, the rectifying effect has been found. In the n=6 case, a significant rectification ratio of 72.6 is achieved at the bias of ±2.1 V in our probed voltage range. The rectification effect arises from asymmetric molecular structures. Our results suggest these molecules have great potential application in the molecular-scale device.     

Ab initio study of transport properties of an all-carbon molecular switch based on C20 molecule

Choosing closed-ended armchair (5, 5) single-wall carbon nanotubes (CCNTs) as electrodes, we have investigated the electron transport properties across a carbon molecular junction consisting of a C₂₀ molecule sandwiched between two semi-infinite carbon nanotubes. It is shown that the Landauer conductance of this carbon hybrid system can be tuned within several orders of magnitude not only by varying the tube-C₂₀ distance, but more importantly by changing the orientation of the C₂₀ molecule and rotating the C₂₀ molecule or one of the tubes around the symmetry axis of the system at fixed distances. This fact could make this all-carbon molecular system a possible candidate for a nano-electronic switching device. Moreover, our study also reveals that molecular configuration selection and structural relaxation would play an important role in the design of such devices.      

Low temperature transport study of C60 thin film FETs

Low temperature transport in C₆₀ thin film field-effect transistors has been studied using several samples with various gate voltages. Nearest neighbor hopping and variable range hopping transport have been observed in the low temperature transport measurements. Analyzing the temperature dependence of the transport types, it was found that the electrical properties of the film can be improved by thermally agitated evaporation of C₆₀.     

Scanning tunneling microscopy of surface-adsorbed fullerenes: C60, C70, and C84

Scanning tunneling microscopy (STM) is used to characterize partial monolayers of C₆₀, C₇₀, and C₈₄ adsorbed on the Au(1 1 1) surface at room temperature and under ambient conditions. A high degree of structural polymorphism is observed for monolayers of each of these fullerenes. For C₆₀, three lattice packings are observed, including a previously unreported 7 × 7 R21.8° structure that is stabilized by adjacent surface step defects. For C₇₀, two lattice packings are observed, and analysis of molecular features in STM images allows molecular binding geometry to be determined. In one of the two observed lattice structures, C₇₀ molecules align their long axis along the surface normal, while in the other, molecules align parallel to the surface and along a gold lattice direction. The parallel geometry is also preferred for isolated and loosely packed molecules on the surface. C₈₄ exhibits a large number of lattice orientations and no long-range order, and likely binds incommensurately on Au(1 1 1). Time series of images of partial C₇₀ monolayers show progressive surface modification as a result of perturbation by the STM tip; this is in contrast to the behavior of C₆₀, where alterations in surface structure at room temperature are thermally driven.     

4,4′,4″-三(N-3-甲基苯基-N-苯基氨基)三苯胺掺杂MoOx作为空穴传输层对有机太阳电池性能的影响

通过采用4,4′,4″-三(N-3-甲基苯基-N-苯基氨基)三苯胺 (m-MTDATA)掺入MoO_x作为器件的空穴传输层来提高酞菁铜(CuPc)/C₆₀小分子 有机太阳电池的效率. 采用真空蒸镀的方法制备了一系列器件, 其中结构为铟锡氧化物 (ITO)/m-MTDATA:MoO_x(3:1)(30 nm)/CuPc(20 nm)/C₆₀(40 nm)/4,7-二苯 基-1,10-菲罗啉 (Bphen)(8 nm)/LiF(0.8 nm)/Al(100 nm)的器件, 在AM1.5 (100 mW/cm²)模拟太阳光的照射条件下, 开路电压V_oc=0.40 V, 短路电流J_sc=6.59 mA/cm², 填充因子为0.55, 光电转换效率达1.46%, 比没有空穴传输层的器件ITO/CuPc(20 nm)/C₆₀(40 nm)/Bphen(8 nm)/LiF(0.8 nm)/Al(100 nm) 光电转换效率提高了38%. 研究表明, 加入m-MTDATA:MoO_x(3:1)(30 nm)空穴传输层减小了有机层和ITO电极之间的接触电阻, 从而减小了整个器件的串联电阻, 提高了器件的光电转换效率.     

Iodine ion transport in solid electrolyte LiI(C3H5NO)2: a first-principles identification

The ion transport mechanism in solid electrolyte LiI(C₃H₅NO)₂ (J Am Chem Soc 127:6394, 2005) was investigated using first-principles molecular dynamics simulation. Both atomic and electronic structures and ion diffusion dynamics indicate that LiI(C₃H₅NO)₂ is a unique Iodine ion conductor. This conclusion is opposite to the common intuition that the diffusion should be more favorable for Li⁺ ions due to its lighter mass as compared to Iodine ions but agrees with the available experiments.     

C2和C2+,C2-的电子结构与势形共振

本文在独立电子近似的基础上,根据多重散射自洽场理论方法,计算了C₂和C₂⁺,C₂^-分子(离子)的电子结构,阐明了势形共振能量和上述分子(离子)电子数的关系,结果表明,随着电子数的减少,C原子2s-2p轨道杂化减弱,势形共振的能量将降低(如降低到阈值下,则势形共振消失)。 关键词：