Temperature dependence of transport behavior of a short DNA molecule

DNA molecules may work as novel devices due to their interesting electronic transport properties. We here propose a theoretical method to deal with the temperature dependence of the transport behavior of a short DNA molecule, taking into account Coulomb interaction of electrons and the coupling between electrons and the two-level system in the DNA molecule. The nonlinear current-voltage curves are derived by using the Landauer formulae. We find that the voltage gap of the current-voltage curves is sensitive to the parameters of the two-level system. We also find that Coulomb blockade peaks can be controlled by varying the temperature, which relates to particular features of the DNA molecule.     

Negative Differential Resistance and Rectifying Effects of Diblock Co-Oligomer Molecule Devices Sandwiched between C_2N-h2D Electrodes

Based on nonequilibrium Green's function method in combination with density functional theory, we study the electronic transport properties of dipyrimidinyl-diphenyl molecules embedded in a carbon atomic chain sandwiched between zigzag graphene nanoribbon and different edge geometries C_2N-h2D electrodes. Compared with the graphene electrodes, the C_2N-h2D electrode can cause rectifying and negative differential resistance effects.For C_2N-h2D with zigzag edges, a more remarkable negative differential resistance phenomenon appears, whereas armchair-edged C_2N-h2D can give rise to much better rectifying behavior. These results suggest that this system can be potentially useful for designs of logic and memory devices.     

室温下吡啶溶液中的富勒稀荧光研究(英文)

室温下,在C6 0 -吡啶溶液中观察到了3 99nm到75 0nm范围内C6 0 丰富的荧光峰。C6 0 和吡啶之间的相互作用,破坏了C6 0 分子的高度对称性,从而放松了选择定则,使得荧光辐射率增强。这种相互作用也被C6 0 -吡啶溶液中C6 0 的电化学还原和表面增强拉曼散射证实。     

C60分子在Si（111）-7×7表面分子束外延生长的STM研究

在超高真空中采用分子束外延(molecular beam epitaxial)技术进行C₆₀分子在硅（111）-7×7表面的生长,并利用扫描隧道显微镜进行原位研究.室温下,相对于无层错半胞（unfaulted half unit cell）,C₆₀更易于吸附在有层错半胞（faulted half unit cell）.表面台阶处的电子悬挂键密度最高,通过控制温度和时间进行退火处理后,C₆₀分子会向着台阶的方向扩散并聚集.测量分子在不同吸附位 关键词： 60分子')" href="#">C₆₀分子 分子束外延 Si(111)-7×7 超高真空扫描隧道显微镜     

Analysis of Co-Tunneling Current in Fullerene Single-Electron Transistor

Single-electron transistors (SETs) are nano devices which can be used in low-power electronic systems. They operate based on coulomb blockade effect. This phenomenon controls single-electron tunneling and it switches the current in SET. On the other hand, co-tunneling process increases leakage current, so it reduces main current and reliability of SET. Due to co-tunneling phenomenon, main characteristics of fullerene SET with multiple islands are modelled in this research. Its performance is compared with silicon SET and consequently, research result reports that fullerene SET has lower leakage current and higher reliability than silicon counterpart. Based on the presented model, lower co-tunneling current is achieved by selection of fullerene as SET island material which leads to smaller value of the leakage current. Moreover, island length and the number of islands can affect on co-tunneling and then they tune the current flow in SET.     

C_(60)在室温有机溶剂中荧光的研究

本文在室温下对C60分别在吡啶、甲苯和乙腈中的荧光了研究,实验表明:C60在吡啶中的荧光由以440nm、570nm和700nm为中心的三个荧光带组成;C60在甲苯中的荧光由以430nm和700nm为中心的两个荧光带组成;C60在乙腈中的荧光由以570nm和700nm为中心的两个荧光带组成。经比较分析发现C60-有机溶剂体系700nm区域的荧光带的发射与溶剂的种类无关,而440nm和570nm区域的荧光带及其精细结构可以反映C60与溶剂分子的特殊相互作用。进一步提出C60-吡啶体系以570nm为中心的荧光带是由吡啶分子通过含孤对电子的N与C60形成的电荷转移络合物发出的。     

Transport in graphene nanostructures

Graphene nanostructures are promising candidates for future nanoelectronics and solid-state quantum information technology. In this review we provide an overview of a number of electron transport experiments on etched graphene nanostructures. We briefly revisit the electronic properties and the transport characteristics of bulk, i.e., two-dimensional graphene. The fabrication techniques for making graphene nanostructures such as nanoribbons, single electron transistors and quantum dots, mainly based on a dry etching ??paper-cutting?? technique are discussed in detail. The limitations of the current fabrication technology are discussed when we outline the quantum transport properties of the nanostructured devices. In particular we focus here on transport through graphene nanoribbons and constrictions, single electron transistors as well as on graphene quantum dots including double quantum dots. These quasi-one-dimensional (nanoribbons) and quasi-zero-dimensional (quantum dots) graphene nanostructures show a clear route of how to overcome the gapless nature of graphene allowing the confinement of individual carriers and their control by lateral graphene gates and charge detectors. In particular, we emphasize that graphene quantum dots and double quantum dots are very promising systems for spin-based solid state quantum computation, since they are believed to have exceptionally long spin coherence times due to weak spin-orbit coupling and weak hyperfine interaction in graphene.     

Transport properties of copper phthalocyanine based organic electronic devices

Ambipolar charge carrier transport in Copper phthalocyanine (CuPc) is studied experimentally in field-effect transistors and metal-insulator-semiconductor diodes at various temperatures. The electronic structure and the transport properties of CuPc attached to leads are calculated using density functional theory and scattering theory at the non-equilibrium Green’s function level. We discuss, in particular, the electronic structure of CuPc molecules attached to gold chains in different geometries to mimic the different experimental setups. The combined experimental and theoretical analysis explains the dependence of the mobility and the transmission coefficient on the charge carrier type (electrons or holes) and on the contact geometry. We demonstrate the correspondence between our experimental results on thick films and our theoretical studies of single molecule contacts. Preliminary results for fluorinated CuPc are discussed.     

Preferable Orientations of Interacting C_(60) Molecules inside Single Wall Boron Nitride Nanotubes

This work focuses on the preferable orientation analysis of the hybrid system where the Ceo molecules are encapsulated inside the boron nitride nanotubes by using the two-molecule model.The low-energy state can be acquired in the contour map,which provides the visual information of the systematical van der Waais interaction potential for the Ceo molecules adopting different orientations.Our results show that the C_(60) molecules exhibit the preferred pentagon and hexagon orientations with the tube's diameter smaller and larger than 13.55 A,respectively.The preferred two-bond orientation obtained in the single-molecule model is absent in this study,indicating that the intermolecular interaction of adjacent C_(60) molecules plays an important role in the orientational behaviors of this peapod structure.     

Effects of electron-vibration coupling in transport through single molecules

Using scanning tunneling spectroscopy, we study the transport of electrons through C(60)?molecules on different metal surfaces. When electrons tunnel through a molecule, they may excite molecular vibrations. A fingerprint of these processes is a characteristic sub-structure in the differential conductance spectra of the molecular junction reflecting the onset of vibrational excitation. Although the intensity of these processes is generally weak, they become more important as the resonant character of the transport mechanism increases. The detection of single vibrational levels crucially depends on the energy level alignment and lifetimes of excited states. In the limit of large current densities, resonant electron-vibration coupling leads to an energy accumulation in the molecule, which eventually leads to its decomposition. With our experiments on C(60)?we are able to depict a molecular scale picture of how electrons interact with the vibrational degrees of freedom of single molecules in different transport regimes. This understanding helps in the development of stable molecular devices, which may also carry a switchable functionality.     

Spectroscopic interrogation and charge transport properties of molecular transistors

ABSTRACT

Molecular transistors have been extensively investigated as the building blocks for the ultimate miniaturization of electronic devices. They are assembled from single molecules and molecular monolayers serving as a current-carrying channel in a conventional field-effect transistor configuration, in which gate electrodes have been electrically or electrochemically implemented in several types of test beds such as electromigration junctions, mechanically controllable break junctions, and devices with carbon-based electrodes. The energy level alignments of the component molecules incorporated into the transistor can be tuned using molecular orbital gating and it can ultimately control the flow of charge carriers. Herein, we review recent progress in studying spectroscopic characterization techniques and charge transport properties of molecular transistors.     

硅纳米结构晶体管中与杂质量子点相关的量子输运

在小于10 nm的沟道空间中,杂质数目和杂质波动范围变得十分有限,这对器件性能有很大的影响.局域纳米空间中的电离杂质还能够展现出量子点特性,为电荷输运提供两个分立的杂质能级.利用杂质原子作为量子输运构件的硅纳米结构晶体管有望成为未来量子计算电路的基本组成器件.本文结合安德森定域化理论和Hubbard带模型对单个、分立和耦合杂质原子系统中的量子输运特性进行了综述,系统介绍了提升杂质原子晶体管工作温度的方法.     

Quantification of Low Concentrations of DNA Using Single Molecule Detection and Velocity Measurement in a Microchannel

We present a novel method for quantifying low concentrations of DNA based on single molecule detection (SMD) for molecular counting and flow measurements inside a microchannel. A custom confocal fluorescence spectroscopic system is implemented to detect fluorescent bursts emitted from stained DNA molecules. Measurements are made one molecule at a time as they flow through a femtoliter-sized laser focal probe. Durations of single molecule fluorescent bursts, which are found to be strongly related to the molecular transit times through the detection region, are statistically analyzed to determine the in situ flow speed and subsequently the sample volume flowing through the focal probe. Therefore, the absolute concentration of a DNA sample can be quantified based on the single molecule fluorescent counts from the DNA molecules and the associated probe volume for a measured time course. To validate this method for quantifying low concentrations of biomolecules, we tested samples of pBR322 DNA ranging from 1 pM to 10 fM (∼3 ng/ml to 30 pg/ml). Besides molecular quantification, we also demonstrate this method to be a precise and non-invasive way for flow profiling within a microchannel.     

共轭聚合物单分子构象和能量转移特性研究

利用基于宽场显微光学系统的单分子散焦成像技术测量了不同构象poly[2,7-(9,9-dioctylfluorene)-alt-4,7-bis(thiophen-2-yl)benzo-2,1,3-thiadiazole](PFO-DBT)共轭聚合物单分子的光物理与动力学特性.通过分析共轭聚合物单分子的荧光轨迹和对应的发射偶极取向变化识别共轭聚合物单分子发光单元,发现延伸构象下的单分子呈现多发色团发光特性,而折叠构象下的单分子保持高效链间能量转移,呈现单个发色团发光特性.共轭聚合物单分子构象对能量转移效率的影响可用于研究基于共轭聚合物的光电器件和分子器件.     

对Cu(111)表面吸附的单个苉分子的分子轨道进行成像:一个实验与理论相结合的研究

结合扫描隧道显微学测量和密度泛函理论计算研究了直接吸附在Cu（111）表面的单个苉分子的电子结构性质.在低覆盖度下,苉分子表现出了单分散的吸附行为,利用dI/dV谱和图像可以辨别出吸附的单个苉分子在-1.2 V附近的最高占据态和1.6 V附近的最低未占据态.此外,还可以观测到苉分子未占据态的dI/dV信号对采谱位置具有很强的依赖性.第一性原理计算很好地模拟了这些实验结果,并且将它们归因于分子-衬底相互作用引起的苉分子不同分子轨道之间的混合态的能量和空间分布.该工作提供了吸附在金属衬底表面的苉分子的局域电子结构信息,将促进对单分子器件中电子输运性质对分子-金属电极耦合的依赖性的理解.     

A New Effect of Oxygen Plasma on Two-Dimensional Field-Effect Transistors:Plasma Induced Ion Gating and Synaptic Behavior

Plasma treatment is a powerful tool to tune the properties of two-dimensional materials. Previous studies have utilized various plasma treatments on two-dimensional materials. We find a new effect of plasma treatment. After controlled oxygen-plasma treatment on field-effect transistors based on two-dimensional SnSe_2, the capacitive coupling between the silicon back gate and the channel through the 300 nm SiO_2 dielectric can be dramatically enhanced by about two orders of magnitude(from 11 n F/cm~2 to 880 nF/cm~2), reaching good efficiency of ionliquid gating. At the same time, plasma treated devices show large hysteresis in the gate sweep demonstrating memory behavior. We reveal that this spontaneous ion gating and hysteresis are achieved with the assistance of a thin layer of water film automatically formed on the sample surface with water molecules from the ambient air, due to the change in hydrophilicity of the plasma treated samples. The water film acts as the ion liquid to couple the back gate and the channel. Thanks to the rich carrier dynamics in plasma-treated two-dimensional transistors, synaptic functions are realized to demonstrate short-and long-term memories in a single device. This work provides a new perspective on the effects of plasma treatment and a facile route for realizing neuromorphic devices.     

Influencing the angular emission of a single molecule

We present the first experimental proof for the influence of a nearby nanosized metal object on the angular photon emission by a single molecule. Using a novel angular sensitive detection scheme, we directly quantify the redirection of angular emission for different molecular dipole orientations as an object is scanned laterally over the molecule at different heights. An excellent agreement between experiments and 2D-numerical simulations is found for molecules oriented perpendicular to the sample, whereas, for parallel orientations, the observed behavior contradicts the calculated behavior.     

Dissociation of H_2 on Mg-coated B_(12)C_6N_6

The dissociation of H_2 molecule is the first step for chemical storage of hydrogen, and the energy barrier of the dissociation is the key factor to determine the kinetics of the regeneration of the storage material. In this paper, we investigate the hydrogen adsorption and dissociation on Mg-coated B_(12)C_6N_6. The B_(12)C_6N_6 is an electron deficient fullerene, and Mg atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The preferred binding sites for Mg atoms are the B_2C_2 tetragonal rings. The positive charge quantity on the Mg atom is 1.50 when a single Mg atom is coated on a B_2C_2 ring. The stable dissociation products are determined and the dissociation processes are traced. Strong orbital interaction between the hydrogen and the cluster occurs in the process of dissociation, and H_2 molecule can be easily dissociated. We present four dissociation paths, and the lowest energy barrier is only 0.11 eV, which means that the dissociation can take place at ambient temperature.     

Coupling single molecule magnets to ferromagnetic substrates

We investigate the interaction of TbPc(2) single molecule magnets (SMMs) with ferromagnetic Ni substrates. Using element-resolved x-ray magnetic circular dichroism, we show that TbPc(2) couples antiferromagnetically to Ni films through ligand-mediated superexchange. This coupling is strongly anisotropic and can be manipulated by doping the interface with electron acceptor or donor atoms. We observe that the relative orientation of the substrate and molecule anisotropy axes critically affects the SMM magnetic behavior. TbPc(2) complexes deposited on perpendicularly magnetized Ni films exhibit enhanced magnetic remanence compared to SMMs in the bulk. Contrary to paramagnetic molecules pinned to a ferromagnetic support layer, we find that TbPc(2) can be magnetized parallel or antiparallel to the substrate, opening the possibility to exploit SMMs in spin valve devices.     

带电荷C60分子的电子结构及其非线性光学性质

应用Su-Schrieffer-Heeget(SSH)模型研究带电荷C₆₀分子的结构和电子结构.分析所带电荷量对结构的影响,计算带不同电荷数时C₆₀分子的电子结构,进一步对三阶非线性光学极化率进行了研究.