Negative differential resistance in polymer molecular devices modulated with molecular length

We study the electronic transport properties of polymer molecular devices by applying first-principles method. The results show that the electronic transport properties depend on molecular length. Negative differential resistance can be observed and can be modulated with molecular length.     

Low bias negative differential resistance with dual-peaks based on octacene molecular device

Based on non-equilibrium Green's function and density functional theory, a first-principles study of the transport properties of a molecular device is performed. This device is composed of two octacene molecules separated by a ethyl barrier, which are then linked to Ag leads through thiolates. The device shows low bias negative differential resistance effect with dual-peaks, which may be useful for designing molecular devices with low power-dissipation and multi-function in the future.     

A scheme for a topological insulator field effect transistor

We propose a scheme for a topological insulator field effect transistor. The idea is based on the gate voltage control of the Dirac fermions in a ferromagnetic topological insulator channel with perpendicular magnetization connecting to two metallic topological insulator leads. Our theoretical analysis shows that the proposed device displays a switching effect with high on/off current ratio and a negative differential conductance with a good peak to valley ratio.     

The electronic transport properties in C60 molecular devices with different contact distances

By applying non-equilibrium Green?s functions in combination with the density-functional theory, we investigate the transport behavior of molecular devices composed by metal electrode-C₆₀ molecule-metal electrode. Our results show that the electronic transport properties are affected obviously by the different contact distances between the electrodes, and the tunneling current decreases approximately exponentially at a certain bias with the increasing of contact distances. The negative differential resistance is observed and the peak-to-valley ratio can be tuned by different contact distances. The mechanisms of the contact distance effect and the negative differential resistance behavior are proposed.     

Spin-polarized transport properties of a pyridinium-based molecular spintronics device

By applying a first-principles approach based on non-equilibrium Green's functions combined with density functional theory, the transport properties of a pyridinium-based “radical-π-radical” molecular spintronics device are investigated. The obvious negative differential resistance (NDR) and spin current polarization (SCP) effect, and abnormal magnetoresistance (MR) are obtained. Orbital reconstruction is responsible for novel transport properties such as that the MR increases with bias and then decreases and that the NDR being present for both parallel and antiparallel magnetization configurations, which may have future applications in the field of molecular spintronics.     

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.     

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.     

SETMOS在蔡氏电路中的特性研究

利用拟合法简化了单电子晶体管与金属氧化物半导体混合结构器件SETMOS的负微分电阻特性方程,提出了由SETMOS设计多涡卷混沌电路的方法.理论上定性和定量地分析了负微分电阻特性对于多涡卷蔡氏电路平衡点的影响.经研究发现,多涡卷蔡氏电路混沌在非线性函数的各负斜率区中形成径向收缩、轴向拉伸的单向运动,而在各正斜率区中形成径向拉伸、轴向收缩的涡卷运动.这为进一步实现多涡卷电路及研究其复杂动力学行为提供了理论基础.     

SETMOS实现多涡卷蔡氏电路的研究

基于细胞神经网络结构,利用具有负微分电阻特性的单电子晶体管与金属氧化物半导体混合结构器件SETMOS实现了多涡卷蔡氏电路.对该电路系统的基本动力学特性(如相图、分岔图、Lyapunov指数、Poincaré映射和功率谱)进行了理论分析和数值仿真,并利用电路仿真实验验证了该三阶四涡卷蔡氏电路设计的正确性和可行性.研究结果表明,SETMOS的负微分电阻特性决定着多涡卷蔡氏电路的复杂动力学行为,而且所设计的电路结构简单易行.     

Tunneling through two single molecular magnets in series arrangement junction in parallel/antiparallel situations

We investigate the spin-dependent tunneling transport in a heterostructure with two single molecular magnets (SMMs). The tunneling magnetoresistance (TMR) and negative differential conductance due to the strong resonant tunneling in the junction are demonstrated by the master equation approach. At low bias voltage, the device presents low/high resistant states with the initial states of the single molecular magnets parallel/antiparallel. Strong Coulomb repulsive interaction suppresses the current greatly in antiparallel situation. At high voltage, the middle system containing two SMMs tends to be non-polarized, and acts like ordinary quantum dots.     

Controlling ionic current through a nanopore by tuning pH: a local equilibrium Monte Carlo study

ABSTRACT

The purpose of this work is to create a model of a nanofluidic transistor which is able to mimic the effects of pH on nanopore conductance. The pH of the electrolyte is an experimentally controllable parameter through which the charge pattern can be tuned: pH affects the ratio of the protonated/deprotonated forms of the functional groups anchored to the surface of the nanopore (for example, amino and carboxyl groups). Thus, the behaviour of the bipolar transistor changes as it becomes ion selective in acidic/basic environments. We relate the surface charge to pH and perform particle simulations (Local Equilibrium Monte Carlo) with different nanopore geometries (cylindrical and double conical). The simulations form a self consistent system with the Nernst–Planck equation with which we compute ionic flux. We discuss the mechanism behind pH-control of ionic current: formation of depletion zones.     

Transport behaviors and mechanisms in cuspidal blockade region for silicon single-hole transistor

The Si single-hole transistor displays the anomalously-extended cuspidal blockade region, which is elongated toward the 45°-tilted direction normal to gate vs. drain bias voltage regions in the Coulomb blockade diagram. This is attributed to the formation of an ultra small Si quantum dot (QD) into the gate-all-around (GAA) stack. Namely, the large one-electron-addition energy (= 447 meV) from the 2-nm-size Si QD enables the clear Coulomb-blockade events at room temperature, and the large voltage gain from the GAA stack allows the cuspidal extension of the blockade region through the renormalization of Coulomb-blockade energies at the adjacent bias points near the initial Coulomb-blockade state.     

Magnetic field control of current through model graphene nanosheets

We study magnetic field control of current through model graphene nanosheet junctions within the framework of the tight-binding approximation. Geometrical asymmetry in the coupling of graphene nanosheets to the contact leads emerges as one of the most important determining factors for the magnetic field control of current. The asymmetric connection split the otherwise degenerate energy levels of the structures leading to energy-resolved transmission peaks which the applied field modulates for a transmission maximum by narrowing the energy gap between the split energy levels. Also, the contact coupling strength plays a decisive role in controlling current in small structures, while its role is significantly less in large structures that have more closely-spaced energy levels. Model calculations on a graphene nanosheet junction with inter-site Coulomb interaction is found to sustain sensitivity to the applied magnetic field. Although several factors bear direct effect on the electron transport through molecular junctions, suitably constructed graphene nanosheet junctions would greatly enhance the prospects of current control under applied magnetic fields.     

Negative differential resistance in a carbon nanotube-based molecular junction

By applying non-equilibrium Green's function formalism combined with first-principles density functional theory, we have investigated the electronic transport properties of a carbon nanotube-based molecular junction with different terminations (H-, C- and N-). The results show that the different terminations at the carbon nanotube ends strongly affect the transport properties of the junction. The current through the N-terminated carbon nanotube junction is significant larger than that through the H- and C-terminated junctions at low biases. Moreover, negative differential resistance behaviors can be observed in the N-terminated carbon nanotube junction, whereas not in the other two cases.     

基于垂直晶体管结构的低电压并五苯光电探测器

并五苯(Pentacene)具有优良的场效应晶体管特性及在可见光区的高吸收系数, 被广泛应用于光敏(电)晶体管中. 垂直晶体管的沟道长度可做到纳米量级, 能有效提高器件的性能和工作频率, 同时降低能耗. 本文制备了一种基于垂直晶体管结构的低电压并五苯光电探测器ITO(S)/Pentacene/Al(G)/Pentacene/Au(D). 实验发现, 在工作电压低至-3 V时, 并五苯光电探测器ITO/Pentacene (80 nm)/Al(15 nm)/ Pentacene(80 nm)/Au 的阈值电压为-0.9 V, “开/关”电流比为10⁴, 表现出了良好的P型晶体管特性以及低电压调控性能. 在350-750 nm的不同波长单色光照射下, 器件的“明/暗”电流比和响应度随入射波长而变化; 在350 nm单色光照射下, 该光电探测器的“明/暗”电流比的最大值达到308, 其对应的响应度为219 mA·W^-1, 大于标准硅基探测器在350 nm 单色光照射下的探测率. 这为制备低电压下工作的高灵敏度全有机光电探测器提供了一种可行的方法.     

Detection of influenza A virus using carbon nanotubes field effect transistor based DNA sensor

The carbon nanotubes field effect transistor (CNTFET) based DNA sensor was developed, in this paper, for detection of influenza A virus DNA. Number of factors that influence the output signal and analytical results were investigated. The initial probe DNA, decides the available DNA strands on CNTs, was 10 µM. The hybridization time for defined single helix was 120 min. The hybridization temperature was set at 30 °C to get a net change in drain current of the DNA sensor without altering properties of any biological compounds. The response time of the DNA sensor was less than one minute with a high reproducibility. In addition, the DNA sensor has a wide linear detection range from 1 pM to 10 nM, and a very low detection limit of 1 pM. Finally, after 7-month storage in 7.4 pH buffer, the output signal of DNA sensor recovered 97%.     

Enhanced charge carrier injection in heterojunction organic field-effect transistor by inserting an MoO3 buffer layer

A top-contact organic field-effect transistor(OFET) is fabricated by adopting a pentacene/1,1’-bis(di-4tolylaminophenyl) cyclohexane(TAPC) heterojunction structure and inserting an MoO3 buffer layer between the TAPC organic semiconductor layer and the source/drain electrode.The performances of the heterojunction OFET,including output current,field-effect mobility,and threshed voltage,are all significantly improved by introducing the MoO3 thin buffer layer.The performance improvement of the modified heterojunction OFET is attributed to a better contact formed at the Au/TAPC interface due to the MoO3 thin buffer layer,thereby leading to a remarkable reduction of the contact resistance at the metal/organic interface.     

Polymer thin-film transistor based on a high dielectric constant gate insulator

In this paper full polymer thin-film transistors (PTFTs) based on Poly (acrylonitrile) (PAN) as the gate dielectric and poly (2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene-vinylene) (MEH-PPV) as the semiconductor layer were investigated by using different channel width/length ratios. Relatively high dielectric constant of the polymer dielectric layer (6.27) can remarkably reduce the threshold voltage of the transistors to below -3V. Hole field-effect mobility of MEH-PPV of the PTFTs was about 4.8×10^-4cm²/Vs, and on/off current ratio was larger than 10², which was comparable with that of transistors with widely used Poly (4-vinyl phenol) (PVP) or SiO₂ as gate dielectrics.     

Large negative differential resistance and rectifying performance modulated by contact sites in fused thiophene trimmer-based molecular devices

By applying density functional theory with non-equilibrium Green?s function formalism, we have carried out a theoretical study of the electron transport in fused thiophene trimmer-based molecular devices with ethylene connections at three different sites. The simulation results indicate that the electronic transport properties strongly depend on the contact sites. Negative differential resistance and rectifying behaviors occur simultaneously in the current–voltage curves when ethylene connects the fused thiophene trimer at one second-nearest site and one third-nearest site. A larger negative differential resistance occurs only when ethylene connects the fused thiophene trimer at two second-nearest sites.