Two Possible Configurations for Silver-C60-Silver Molecular Devices and Their Conductance Characteristics

Coherent electronic transport properties of silver-C60-silver molecular junctions in different configurations are studied using hybrid density function theory. The experimentally measured current flows of （760 molecules adsorbed on the silver surface are well reproduced by theoretical calculations. It is found that the current-voltage characteristics of the molecular junctions depend strongly on the configurations of the junctions. Transmission spectra combined with density of states can help us to understand in depth the transport properties. Different kinds of electrode construction are also discussed. With the help of the calculation, two possible configurations of silver-C60-silver molecular junctions are suggested.     

Electronic Transport in Molecular Junction Based on C20 Cages

Choosing closed-ended armchair （5, 5） single-wall carbon nanotubes （CCNTs） as electrodes, we investigate the electron transport properties across an all-carbon molecular junction consisting of C20 molecules suspended between two semi-infinite carbon nanotubes. It is shown that the conductances are quite sensitive to the number of C20 molecules between electrodes for both configuration CF1 and double-bonded models： the conductances of C20 dimers are markedly smaller than those of monomers. The physics is that incident electrons easily pass the C20 molecules and are predominantly scattered at the C20-C20 junctions. Moreover, we study the doping effect of such molecular junction by doping nitrogen atoms substitutionally. The bonding property of the molecular junction with configuration CF1 has been analysed by calculating the Mulliken atomic charges. Our results have revealed that the C atoms in N-doped junctions are more ionic than those in pure-carbon ones, leading to the fact that N-doped junctions have relatively large conductance.     

Physical model for the exotic ultraviolet photo-conductivity of ZnO nanowire films

Employing a simple and efficient method of electro-chemical anodization,ZnO nanowire films are fabricated on Zn foil,and an ultraviolet(UV)sensor prototype is formed for investigating the electronic transport through back-to-back double junctions.The UV(365 nm)responses of surface-contacted ZnO film are provided by I–V measurement,along with the current evolution process by on/off of UV illumination.In this paper,the back-to-back metal–seconductor–metal(M–S–M)model is used to explain the electronic transport of a ZnO nanowire film based structure.A thermionic-field electron emission mechanism is employed to fit and explain the as-observed UV sensitive electronic transport properties of ZnO film with surface-modulation by oxygen and water molecular coverage.     

INVESTIGATION OF PROPERTIES OF INFRARED ABSORPTION OF α-HELIX PROTEIN MOLECULES

The mechanism and properties of infrared absorption of α-helix protein molecules are studied by a theory of bio-energy transport established on the basis of molecular structure. From the vibrational energy-spectra of molecules obtained from this theory we know that the infrared lights with wavelengths of 2 μm −7 μm can be absorbed by α-helix protein molecules. This is basically consistent with experimental data of infrared absorption of collagen and hemoglobin and bivine serum albumen (BSA) proteins with α-helix structure. From these results we account further for the mechanism and properties of biological effect of infrared lights absorbed by the living systems, i.e., the energy of infrared lights is directly absorbed by the amide-Is in amino acid residues in the protein molecules, which results in vibration of amide-1 and change of conformation of proteins and transport of bio-energy from one place to other along the protein molecular chains in human beings and animals. This is a kind of non-thermally biological effect.     

Simulation of water potential for the electronic structureof serine

First-principles, all-electron, \textit{ab initio} calculations have been performed to construct an equivalent water potential for the electronic structure of serine (Ser) in solution. The calculation is composed of three steps. The first step is to search for the configuration of the Ser + NH₂O system with a minimum energy. The second step is to calculate the electronic structure of Ser with the water molecule potential via the self-consistent cluster-embedding method (SCCE), based on the result obtained in the first step. The last step is to calculate the electronic structure of Ser with the dipole potential after replacing the water molecules with dipoles. The results show that the occupied states of Ser are raised by about 0.017~Ry on average due to the effect of water. The water effect can be successfully simulated by using the dipole potential. The obtained equivalent potential can be applied directly to the electronic structure calculation of protein in solution by using the SCCE method.     

The equivalent potential of water molecules for electronic structure of lysine

In order to get more reliable electronic structures of proteins in aqueous solution, it is necessary to construct a potential of water molecules for protein’s electronic structure calculation. The lysine is a hydrophilic amino acid. It is positively charged (Lys+) in neutral water solution. The first-principles, all-electron, ab initio calcula-tions, based on the density functional theory, have been performed to construct such an equivalent potential of water molecules for lysine (Lys+). The process consists of three parts. First, the electronic structure of the cluster containing Lys+ and water molecules is calculated. By adjusting the positions of water molecules, the geometric structure of the cluster having minimum total energy is determined. Then, based on the structure, the electronic structure of Lys+ with the potential of water molecules is calculated using the self-consistent cluster-embedding (SCCE) method. Finally, the electronic structure of Lys+ with the potential of dipoles is calculated. The dipoles are adjusted so that the electronic structure of Lys+ with the potential of dipoles is close to that of water molecules. Thus the equivalent potential of water molecules for the electronic structure of lysine is obtained. The major effect of water molecules on lysine’s electronic structure is raising the occupied eigenvalues about 0.5032 eV, and broadening energy gap 89%. The effect of water molecules on the electronic structure of lysine can be simulated by dipoles potential.     

Current transport in ZnO/Si heterostructure grown by laser molecular beam epitaxy

The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a good rectifying behavior. The electrical properties of the heterojunction were investigated by means of temperature dependence current density-voltage measurements. The mechanism of the current transport was proposed based on the band structure of the heterojunction. When the applied bias V is lower than 0.15 V, the current follows the Ohmic behavior. When 0.15V 0.6 V), the space charge limited effect becomes the main transport mechanism. The current-voltage characteristic under illumination was also investigated. The photovoltage and the short circuit current density of the heterojunction aproached 270 mV and 2.10 mA/cm 2 , respectively.     

The study of a new n/p tunnel recombination junction and its application in a-Si：H/μc-Si：H tandem solar cells

This paper reports that a double N layer (a-Si:H/μc-Si:H) is used to substitute the single microcrystalline silicon n layer (n-μc-Si:H) in n/p tunnel recombination junction between subcells in a-Si:H/μc-Si:H tandem solar cells. The electrical transport and optical properties of these tunnel recombination junctions are investigated by current-voltage measurement and transmission measurement. The new n/p tunnel recombination junction shows a better ohmic contact. In addition, the n/p interface is exposed to the air to examine the effect of oxidation on the tunnel recombination junction performance. The open circuit voltage and FF of a-Si:H/μc-Si:H tandem solar cell are all improved and the current leakage of the subcells can be effectively prevented efficiently when the new n/p junction is implemented as tunnel recombination junction.     

Impact of coupling geometry on thermoelectric properties of oligophenyl-base transistor

Thermal and electron transport through organic molecules attached to three-dimensional gold electrodes in two different configurations, namely para and meta with thiol-terminated junctions is studied theoretically in the linear response regime using Green's function formalism. We used thiol-terminated(–SH bond) benzene units and found a positive thermopower because the highest occupied molecular orbital(HOMO) is near the Fermi energy level. We investigated the influence of molecular length and molecular junction geometry on the thermoelectric properties. Our results show that the thermoelectric properties are highly sensitive to the coupling geometry and the molecular length. In addition, we observed that the interference effects and increasing molecular length can increase the thermoelectric efficiency of device in a specific configuration.     

Resonance Transport of Graphene Nanoribbon T-Shaped Junctions

We investigate the transport properties of T-shaped junctions composed of armchair graphene nanoribbons of different widths. Three types of junction geometries are considered. The junction conductance strongly depends on the atomic features of the junction geometry. When the shoulders of the junction have zigzag type edges, sharp conductance resonances usually appear in the low energy region around the Dirac point, and a conductance gap emerges. When the shoulders of the junction have armchair type edges, the conductance resonance behavior is weakened significantly, and the metal-metal-metal junction structures show semimetallic behaviors. The contact resistance also changes notably due to the various interface geometries of the junction.     

OPE molecular junction as a hydrogen gas sensor

Oligo(phenylene ethynylene) (OPE) molecular junction has been suggested as a H₂ molecule sensor based on calculations using the first principles of density–functional theory and non-equilibrium Green's function. The electronic transport properties of the OPE molecule between two Au electrodes with or without adsorbed H₂ molecules are investigated. Results show that the adsorbed H₂ molecule significantly changes the characteristics of the current–voltage curve of the OPE molecular junction. The pure OPE molecular junction exhibits a significant negative differential resistance, but this kind of phenomenon will disappear or weaken after hydrogen molecules are adsorbed. The conductance of the junction also obviously decreases in the bias range of [−0.4, 0.4] V after adsorbing H₂ molecules. These effects can be used to design a H₂ molecule sensor.     

First-principles study of the electron transport through conjugated molecular wires with different carbon backbones

The nonequilibrium Green’s function approach in combination with density-functional theory is used to perform ab initio quantum-mechanical calculations of the electron transport properties of polyacetylene, polythiophene, poly(phenylene vinylene), poly(p-phenylene ethynylene), and poly(p-phenylene) molecules sandwiched between two gold electrodes. The results demonstrate that the conjugation path has a profound effect on the electron transport property of the molecular wires. Among the five molecular wires, polyacetylene is the most conductive one. The conductivities of the five molecular wires decrease with an order of polyacetylene > polythiophene > poly(phenylene vinylene) > poly(p-phenylene ethynylene) > poly(p-phenylene). The conductivities of polyacetylene and polythiophene are much higher than those of poly(phenylene vinylene), poly(p-phenylene ethynylene), and poly(p-phenylene). The difference of electron transport behaviors of these molecular wires are analyzed in terms of the electronic structures, the transmission spectra, and the spatial distributions of molecular orbitals.     

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}     

Effect of end groups on contact resistance of alkanethiol based metal-molecule-metal junctions using current sensing AFM

Tuning the charge transport through a metal-molecule-metal junction by changing the interface properties is widely studied and is of paramount importance for applications in molecular electronic devices. We used current sensing atomic force microscopy (CSAFM) as a tool to study the contact resistance of metal-molecule-metal (MmM) junctions formed by sandwiching self-assembled monolayers (SAMs) of alkanethiols with various end groups (-CH₃, -OH and -NH₂) between Au(1 1 1) substrates and Au coated AFM tips. The effect of interface chemistry on charge transport through such SAMs with varying end groups was studied in an inert, non-polar liquid (hexadecane) environment. We find that the contact resistances of these MmM junctions vary significantly based on the end group chemistry of the molecules.     

Ca掺杂的氧化铍纳米管吸附H2O和NH3的选择传感特

通过密度泛函计算, 借助NH₃和H₂O分子对未掺杂以及钙掺杂的BeO碳纳米管的结构和电传导性进行了研究. 结果发现,NH₃和H₂O分子可以吸附在纳米管侧壁的Be原子上,吸附能分别为约36.1和39.0 kcal/mol. 态密度分析显示BeO纳米管的电传导性在吸附后稍有变化. 对于NH₃和H₂O分子,纳米管表面的钙原子替换Be原子可使吸附能分别增加约7.4和14.7 kcal/mol. 与未掺杂纳米管不同的是,钙掺杂BeONT吸附NH₃和H₂O分子的电传导性更加敏感,且H₂O分子比NH₃分子更敏感.     

Structure and electronic properties of a heterojunction between a single wall carbon nanotube and a TiC cluster

Atomic structures and electronic properties of heterojunctions of Ti-TiC and TiC-single wall carbon nanotube, Ti₄₈-Ti₁₉C₂₆ and Ti₁₉C₂₄-C₃₀, are studied by the first principles calculation based on the density functional theory. At the junctions, these substrates are smoothly connected with each other and keep their original structures and electronic properties. The structures of the junctions obtained in the present work give a realistic model to ab initio study for electronic transport properties through the junction of a carbon nanotube and an electrode.     

Controlling spin off state by gas molecules adsorption on metal-phthalocyanine molecular junctions and its possibility of gas sensor

Employing Green's function (GF) technique in combination with spin-polarized density functional theory (DFT), we study the electronic structure and magnetic properties of metal phthalocyanine (MPc) (M?=?Mn, Fe, Co, Ni, Cu, Zn) with or without four different gas molecules (NO, CO, O₂ and NO₂) adsorbing on the M atom of MPc molecule. The corresponding stable adsorption structural configurations and transport properties of MPc molecular junctions are also investigated. Our results indicate that the magnetic moment of MPc for M?=?Mn, Fe and Co can be modified by the specific gas molecule adsorption, which is mainly ascribed to competitive relation of HOMO-LUMO Gap and Hund's rules. However, for M?=?Ni, Cu and Zn, it is difficult to detect gas molecule because the interaction of M atom and these gases is most of weak van der Waals interaction. Remarkably, the spin of MPc molecule can be switched to a magnetic off-state by specific gas absorption, giving rise to a potential application on controllable spintronic devices. In addition, CO, NO, O₂ and NO₂ gas molecules can be detected selectively by measuring spin filter efficiency of these MPc molecular junctions. On the basis of our results, MPc (M?=?Mn, Fe, Co) molecular junctions can be considered as a promising nanosensor device to detect individual gas molecules.     

分层掺B和吸附H2O碳纳米管的结构稳定性及电子场发射性能

运用基于第一性原理的密度泛函理论,系统研究了处于外电场中分层掺B并吸附不同数目H₂O碳纳米管体系的结构稳定性和电子场发射性能. 研究表明:第3层掺B并吸附5个H₂O的B₃CNT+5H₂O体系结构最稳定,管帽处Mulliken电荷最密集,尤其与单独掺B的B₃CNT和单独吸附H₂O的B₃CNT+5H₂O相比,其Fermi能级处态密度分别     

水分子对碳链的输运性质影响的第一性原理研究

用基于密度泛函理论的非平衡格林函数方法研究了水分子对7个碳原子组成的一维原子链的输运性质的影响.碳原子链放在具有有限截面的Al(100)电极中.研究发现，碳原子链上的水分子的数目和放置的位置的不同将对体系输运性质产生很大的影响.特别是，单个H₂O分子对碳链平衡电导的影响随其摆放位置的不同而出现奇偶振荡，例如，当位于奇数编号的碳原子上时，电导取极大值，当位于偶数编号的碳原子上时，取极小值.将两个H₂O分子置于不同的碳原子正上方时，在不同的位置平衡电导相差很大，在某些特殊的情况下原本受到抑止的第三个本征通道也有较大的贡献.此外，还研究了放置两个水分子时，体系的电流-电压(I-V)特性，随着水分子的数目和放置的位置不同，某些情况可能出现较大幅度的负微分电阻，而在另一些情况下却没有出现. 关键词： 平衡电导 透射谱 负微分电阻     

Mott insulator-superfluid phase transition in p-band triangle optical lattices with on-site rotation

In order to exploit the potential applications of graphene as gas sensors, the adsorptions of a series of small gas molecules (such as CO, O₂, NO₂ and H₂O) on pristine graphene (PG) and Si-doped graphene (SiG) have been investigated by ab initio calculations. Our results indicate that the electronic properties of PG are sensitive to O₂ and NO₂ molecules, but not changed much by the adsorption of CO and H₂O molecules. Compared with PG, SiG is much more reactive in the adsorption of CO, O₂, NO₂ and H₂O. The strong interactions between SiG and the adsorbed molecules induce dramatic changes to the electronic properties of SiG. Therefore, we suggest that SiG could be a good gas sensor for CO, O₂, NO₂ and H₂O.