Rectification properties of carbon nanotube "Y-junctions"

Phonon-assisted nearly pure spin current in DNA molecular chains: a multifractal analysis

Motivated by the development of molecular spintronics, we studied the phonon-assisted spin transport along a DNA chain in the presence of environmental-induced dephasing using multifractal analysis. The results demonstrate that a nearly pure spin current is generated in the presence of the voltage gate. The pure spin current is enhanced by increasing thermal effects. The vibration modes due to the thermal phonon bath assist in generating the spin current, so the spin state is more delocalized in strong electron-phonon coupling. The phonon chirality can translate to the electron spin to create a nontrivial spin texture, including spin currents. The spin states become more extended by increasing the phonon temperature. On the other hand, the spin states are less localized in longer chains as the spin selectivity is higher in longer chains than in short ones. Therefore, we can engineer a molecular spintronic device by controlling phonon effects on the storage and transport of binary digits.

Asymmetric Wigner molecules in nanowire Y-junctions

The possibility of crystalline states of interacting electrons, known as Wigner crystals, has been intensively studied in each of the three dimensions. One-dimensional (1D) systems, however, can be interconnected forming two-dimensional (2D) lattices, being a three-terminal Y-junction (Y-J) the simplest one. Then, even when electrons in the individual branches of the Y are confined in 1D, as the Y-J is in 2D, one could expect significant differences in the crystalline state of the electron gas in a Y-J. With the recent report of fabrication of defect-free GaAs/AlGaAs Y-Js by epitaxial methods, the study of semiconductor Y-Js acquires a special relevance due to its eventual direct exploration. Here, by considering the collective electron interactions using a Yukawa-like effective potential, we explore a two-electron distribution in nanowire Y-Js by modulating its electron density via a screening parameter. We find that the electrons changes from a quasi-continuous to a Wigner molecule-like distribution when the electron density decreases in the Y-J. In bold contrast to the strict 1D case, where equidistant distributions of equal density are obtained in the Wigner regime, in the Y-J equidistant distributions of asymmetric density are induced. We also explore the effect of an external electric field acting along the Y-axis on the asymmetric distributions.

Gate potential-controlled current switching in graphene Y-junctions

In this work we investigate the ballistic transport of electrons through three-terminal graphene-based devices. The system consists of a Y-shaped junction formed by three armchair-edged graphene nanoribbons with a rectangular gate potential applied to one of the output branches, whereby current control can be established by the controlling of the refractive index in graphene p-n junctions. Transport properties are obtained by using the Landauer-Büttiker formalism and the tight-binding model within the nearest-neighbor approximation, which allows the calculation of the conductance as function of the Fermi energy, the applied potential, and the system size, as well as the current density. The results demonstrate that the applied electric field can tune the current transmission between the input and two output leads and, consequently, the proposed system acts as a current switch.

Carbon Nanotube Assembly and Integration for Applications

Carbon nanotubes (CNTs) have attracted significant interest due to their unique combination of properties including high mechanical strength, large aspect ratios, high surface area, distinct optical characteristics, high thermal and electrical conductivity, which make them suitable for a wide range of applications in areas from electronics (transistors, energy production and storage) to biotechnology (imaging, sensors, actuators and drug delivery) and other applications (displays, photonics, composites and multi-functional coatings/films). Controlled growth, assembly and integration of CNTs is essential for the practical realization of current and future nanotube applications. This review focuses on progress to date in the field of CNT assembly and integration for various applications. CNT synthesis based on arc-discharge, laser ablation and chemical vapor deposition (CVD) including details of tip-growth and base-growth models are first introduced. Advances in CNT structural control (chirality, diameter and junctions) using methods such as catalyst conditioning, cloning, seed-, and template-based growth are then explored in detail, followed by post-growth CNT purification techniques using selective surface chemistry, gel chromatography and density gradient centrifugation. Various assembly and integration techniques for multiple CNTs based on catalyst patterning, forest growth and composites are considered along with their alignment/placement onto different substrates using photolithography, transfer printing and different solution-based techniques such as inkjet printing, dielectrophoresis (DEP) and spin coating. Finally, some of the challenges in current and emerging applications of CNTs in fields such as energy storage, transistors, tissue engineering, drug delivery, electronic cryptographic keys and sensors are considered.

The formation and stability of junctions in single-wall carbon nanotubes

The structure and stability of molecular junctions, which connect two single-wall carbon nanotubes (SWCNTs) of different diameters and chiral angles, (n ₁, m ₁)-(n ₂, m ₂), are systematically investigated by density functional tight binding calculations. More than 100 junctions, which connect well-aligned SWCNTs, were constructed and calculated. For a highly stable junction between two chiral (n ₁, m ₁) and (n ₂, m ₂) SWCNTs with opposite handedness, the number of pentagon-heptagon (5/7) pairs required to build the junction can be denoted as ∣∣n ₂ - n ₁∣ - ∣m ₂ - m ₁∣∣+min{∣n ₂ - n ₁∣, ∣m ₂ - m ₁∣} with (n ₂, m ₂) rotating π/3 angle or not. While for a junction connected by two zigzag, armchair or two chiral SWCNTs with the same handedness, the number of 5/7 pairs is equal to ∣n ₁ - n ₂∣ + ∣m ₁ - m ₂∣. Similar to the formation energies of grain boundaries in graphene, the curve of the formation energies vs. chiral angle difference present an 'M' shape indicating the preference of ∼30 degree junctions. Moreover, the formation energies of the zigzag-type and armchair-type junctions with zero misorientation angles are largely sensitive to the diameter difference of two sub-SWCNTs.

Coherent transport in Y-junction graphene waveguide

We performed a series of theoretical transport studies on Y-branch electron waveguides which are embedded in mid-size armchair graphene nanoribbons. Non-equilibrium Green's function with different approximations of tight-binding Hamiltonian has been employed. Using the first nearest hopping approximation, we observed very pronounced conductance quantization, the structure of which depends on geometrical design and shows a spacing of 4e ²/h, indicating the existence of valley degree of freedom. Moreover, by incorporating the third nearest approximation, we observed seminal plateaus deviated from multiples of 4e ²/h conductance, suggesting the lift of valley degeneracy. Finally, Quasi-one dimensional band structure calculations have been performed to study the availability of energy channels and the role of the major geometrical parameters on the transport.

In situ nanojoining of Y- and T-shaped silver nanowires structures using femtosecond laser radiation

We report the in situ joining of spatially separated silver nanowires without additional filler material by controlled irradiation with femtosecond laser pulses. Nanojoining under these conditions arises from highly localized heat generation in the vicinity of the gap between adjacent silver nanowires. Melting, followed by the flow of silver into the gap, is optimized by adjusting the direction of laser polarization relative to gap geometry. Our results show that melting of silver occurs on both nanowires in the vicinity of the gap between the two components. Successful formation of a joint is found to be a function of the angle between the long axis of the nanowires and the gap distance. Finite element simulations show that the strong localized electric field generated by optical excitation determines the location and the morphology of the resulting bond. Light coupling and the resulting emission properties of these Y-shaped nanowire structures have been simulated and are compared to similar structures where the gap remains open. It is suggested that joined Y-shaped couplers will have a higher switching ratio between emitted nanowire ends than those occurring in open-gap structures. Nanojoining induced by localized heating under strong field excitation may enable the production of robust branched metal nanowire structures for optical applications.

Transport investigation of branched graphene nanoflakes

We present a theoretical study of current-voltage characteristics of different junctions of graphene nanoribbons. We considered isolated Y- and T-junctions of graphene nanoribbons (GNRs) with various geometry parameters and a graphene Y-junction in the graphane sheet. Our ab initio calculations based on the nonequilibrium Green's functions formalism displayed the influence of the geometry parameters of different ribbons on the I-V curves e.g. the shifting of zero voltage regions. We showed that not only the shape of the structure, but also the arrangement of electrodes attached to the structure will lead to changes in the transport properties.

ELECTRONIC STRUCTURE OF THE FINITE-SIZED SINGLE-WALLED CARBON NANOTUBES

The effects of tubule length and terminal capping on the geometrical and electronic properties of finite-sized zig-zag (9, 0) single-walled carbon nanotubes (SWNT), which length varying from 2 up to 12 unit cells (~50 Å), were investigated using molecular mechanics, semi-empirical methods (AM1 and EHMO) and density functional theory (B3LYP). AM1 method indicates how the nanotube ends are capped affects strongly the tubule geometric parameters. Although these effects seem to decrease exponentially as the tube gets longer, the converging values for C–C bond length in the open- and closed-end structures are slightly different. It was learned that combination of low-level methods like AM1 and EHMO (which tend to overestimate and underestimate the HOMO–LUMO energy gap, respectively) together with high-level method such as DFT is efficient to estimate band gap for finite-sized nanostructures. The HOMO–LUMO energy gaps obtained from semi-empirical and DFT methods decrease as the tubule length increases. Terminal capping also affects strongly the electronic structure of finite-sized nanotube. Thus, closing the terminal ends by fullerene hemisphere broadens the energy gap of the hydrogen-saturated open-end nanotube. Although the open-end SWNT has much lower AM1 HOMO–LUMO energy gap than the closed-end SWNT, these orbitals unfortunately are localized near the capping hydrogen, thereby do not provide conducting channels for electrons. By comparing only the delocalized frontier orbitals, both structures yield closer energy gap. Analysis of the energy gap based on EHMO, AM1 and DFT results suggests that both open- and closed-end finite-sized SWNT are semiconductor, in agreement with recent scanning tunneling experiment. It was found that the slight accumulated negative charges are likely to locate at the nanotube's fullerene tips.

Joining carbon nanotubes

To fully exploit the exceptional electronic and mechanical properties of carbon nanotubes in real-world applications, it is desirable to create carbon nanotube networks in which separate, multiple nanotubes are joined so that as many as possible of the properties of single nanotubes are conserved. In this review we summarize the progress made towards this goal, covering techniques including electron and ion beam irradiation, Joule heating and spark plasma sintering.

Thermal conduction and rectification in few-layer graphene Y junctions

By using molecular dynamics simulations, we have studied heat flux in graphene Y junctions with lengths of 16.7 nm. It is found that the heat flux runs preferentially from the branches to the stem, which demonstrates an obvious thermal rectification effect in these asymmetric graphene ribbons. More interesting, compared to single-layer graphene Y junctions, a larger rectification ratio can be achieved in double-layer structures, due to the presence of layer-layer interactions. Combined with the availability of high quality few-layer graphene materials, our results shed light on heat conduction in graphene nanoribbons and may open up few-layer graphene applications in thermal management of nano electronics.

Molecular dynamics simulations of thermal transport in porous nanotube network structures

Carbon nanotube based 3D nanostructures have shown a lot of promise towards designing next generation of multi-functional systems, such as nano-electronic devices. Motivated by their recent successful experimental synthesis as well as characterization, and realizing that thermal dissipation is an important concern in proposed devices because of ever-increasing power density, we have investigated the phononic thermal transport behavior in 3D porous nanotube network structures using reverse non-equilibrium molecular dynamics simulations. Based on our study, the length scale associated with the distance between nanotube junctions emerges as the most dominating parameter that governs phonon scattering (hence the characteristic mean free path) and the heat flow in these nanostructures at molecular length scales. However, because of their spatial inhomogeneity, we show that the aerial density of carbon nanotubes (normal to heat flow) is also of critical importance in determining their system-level thermal conductivity. Based on our findings, we postulate that both parameters should be considered while designing nano-devices where thermal management is relevant.

Morphology controlled surface-assisted self-assembled microtube junctions and dendrites of metal free porphyrin-based semiconductor

Solution-vapor annealing of drop-cast thin films of meso-5,10,15,20-tetra-n-decylporphyrin H(2)T(C(10)H(21))(4)P deposited on SiO(2) substrate and quartz leads to the formation of well-defined self-assemblies. Their self-assembling properties in n-hexane vapor and chloroform vapor were comparatively investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD) technique, and IR and UV-vis spectroscopy. Intermolecular pi-pi interaction in cooperation with the van der Waals interaction of metal free porphyrin and solvent-solute interaction leads to the formation of microleaves and microtube dendrites in n-hexane vapor and chloroform vapor, respectively. Electronic absorption spectroscopic data on the self-assembled microstructures reveal the J-aggregate nature in both the microleaves and microtube dendrites. However, the difference in the shift of the Soret and Q bands for the two kinds of aggregates relative to corresponding solution absorption bands indicates the dependence of the solvent-porphyrin molecular interaction during the annealing self-assembly process, which counterbalances the intermolecular interactions, particularly the hydrophobic interaction between side chains. IR and XRD results clearly reveal the higher molecular ordering nature of microtube dendrites than that of microleaves, further confirming the effect of the solvent on tuning the intermolecular interaction and in turn the molecular packing mode in aggregates of porphryin compounds. The present results appear to represent the first example of orderly micrometer-sized tube junctions and dendrites of porphyrin prepared through a self-assembly process, providing an effective and new method toward the synthesis of complicated nanotubular structures. In addition, micrometer-sized leaves and tube dendrites were revealed to show good semiconductor features. Highly reproducible and sensitive gas response characteristics have also been observed in these microstructures.

Selective generation of single-walled carbon nanotubes with metallic, semiconducting and other unique electronic properties

As-synthesized single-walled carbon nanotubes (SWNTs) are mixtures of semiconducting and metallic species and separation of the two is of crucial importance for many applications. In this article, the methods employed for the enrichment of semiconducting and metallic SWNTs are presented, along with possible procedures to prepare either of the species selectively. Equally important are the methods for chirality selection. The discovery of metal-semiconductor transitions in SWNTs induced by interaction with electron donor and acceptor molecules is not only of academic interest, but may also find applications. Synthesis of Y-junction SWNTs with unique electronic properties at the junction is yet to be fully accomplished.

Molecular dynamics study of damage production in single-walled carbon nanotubes irradiated by various ion species

The irradiation-induced damage production in single-walled carbon nanotubes (CNTs) by several types of ions is investigated using the molecular dynamics method with analytical potentials. We found that, in the incident energy range 25-1000 eV, the bonding action or the chemical effect of the ions could significantly enhance their damage capabilities to CNTs relative to that of non-bonding ions, and the dependence of damage yield on the ion mass is no longer monotonic. This is contrary to the previous viewpoint that the chemical aspect of the interaction is of no importance to the ion-induced defect production mechanism in CNTs. The bonding interaction of ions with CNTs also increases their implantation probabilities into CNTs. The chemical erosion effect of incident ions remarkably intensifies the sideward recoil from CNTs under irradiation while the downward recoil is still governed by the physical collision effect.

Probing electrical transport in individual carbon nanotubes and junctions

The electrical transport properties of individual carbon nanotubes (CNTs) and multi-terminal junctions of CNTs are investigated with a quadraprobe scanning tunneling microscope. The CNTs used in this study are made of stacked herringbone-type conical graphite sheets with a cone angle of ∼20° to the tube axis, and the CNT junctions have no catalytic particles in the junction areas. The CNTs have a significantly higher resistivity than conventional CNTs with concentric walls. The straight CNTs display linear current-voltage (I-V) characteristics, indicating diffusive transport rather than ballistic transport. The structural deformation in CNTs with bends substantially increases the resistivity in comparison with that for the straight segments on the same CNTs, and the I-V curve departs slightly from linearity in curved segments. The junction area of the CNT junctions behaves like an ohmic-type scattering center with linear I-V characteristics. In addition, a gating effect has not been observed, in contrast to the case for conventional multi-walled CNT junctions. These unusual transport properties can be attributed to the enhanced inter-layer interaction in the herringbone-type CNTs.

Magnetoresistance of nanoscale molecular devices based on Aharonov-Bohm interferometry

Control of conductance in molecular junctions is of key importance in the growing field of molecular electronics. The current in these junctions is often controlled by an electric gate designed to shift conductance peaks into the low bias regime. Magnetic fields, on the other hand, have rarely been used due to the small magnetic flux captured by molecular conductors (an exception is the Kondo effect in single-molecule transistors). This is in contrast to a related field, electronic transport through mesoscopic devices, where considerable activity with magnetic fields has led to a rich description of transport. The scarcity of experimental activity is due to the belief that significant magnetic response is obtained only when the magnetic flux is of the order of the quantum flux, while attaining such a flux for molecular and nanoscale devices requires unrealistic magnetic fields. Here we review recent theoretical work regarding the essential physical requirements necessary for the construction of nanometer-scale magnetoresistance devices based on an Aharonov-Bohm molecular interferometer. We show that control of the conductance properties using small fractions of a magnetic flux can be achieved by carefully adjusting the lifetime of the conducting electrons through a pre-selected single state that is well separated from other states due to quantum confinement effects. Using a simple analytical model and more elaborate atomistic calculations we demonstrate that magnetic fields which give rise to a magnetic flux comparable to 10(-3) of the quantum flux can be used to switch a class of different molecular and nanometer rings, ranging from quantum corrals, carbon nanotubes and even a molecular ring composed of polyconjugated aromatic materials. The unique characteristics of the magnetic field as a gate is further discussed and demonstrated in two different directions. First, a three-terminal molecular router devices that can function as a parallel logic gate, processing two logic operations simultaneously, is presented. Second, the role of inelastic effects arising from electron-phonon couplings on the magnetoresistance properties is analyzed. We show that a remarkable difference between electric and magnetic gating is also revealed when inelastic effects become significant. The inelastic broadening of response curves to electric gates is replaced by a narrowing of magnetoconductance peaks, thereby enhancing the sensitivity of the device.

Electron transport properties of ordered networks using carbon nanotubes

The electronic transport properties of ordered networks using carbon nanotubes as building blocks (ON-CNTs) are investigated within the framework of a multiterminal Landauer-Buttiker formalism using an s,p(x),p(y),p(z) parameterization of the tight-binding Hamiltonian for carbon. The networks exhibit electron pathway selectiveness, which is shown to depend on the atomic structure of the network nodes imposed by the specific architecture of the network and the distribution of its defects (non-hexagonal rings). This work represents the first understandings towards leading current through well-defined trajectories along an organic nanocircuit.

Preparation of quadrate crystalline Cu(TCNQ) microtubes and assembly of a novel copatterned structure

Crystalline microtubes of functional Cu(TCNQ) were prepared using a facile method of dissolution. XRD, SAED, and EDX characterization showed that they belonged to phase I of Cu(TCNQ), which is important in nanoelectronics and nanodevices. Furthermore, a novel micrometer and nanometer structure co-patterned morphology was assembled, which may have potential applicaton in building nanoscale electrodes or patterning other nanosize functional materials.

Dilute anionic surfactant solution route to polyaniline rectangular sub-microtubes as a novel nanostructure

A facile and low-cost approach has been developed for tailoring polyaniline rectangular sub-microtubes as a novel nanostructure of a conducting polymer in dilute sodium dodecyl sulfate (SDS) solution by the oxidation polymerization of aniline at room temperature. It was found that the size and uniformity of polyaniline rectangular sub-microtubes could be appropriately adjusted by tuning the concentration of aniline and the molar ratio of oxidant to aniline, respectively. The morphological evolution of rectangular sub-microtubes under different reaction times has been followed, and a possible formation mechanism has also been discussed in this report. The directing role of other anionic surfactants with -SO3(-) as the hydrophilic group for constructing polyaniline rectangular sub-microtubes has been investigated in detail.

A Magnetism-Assisted Chemical Vapor Deposition Method To Produce Branched or Iron-Encapsulated Carbon Nanotubes

A magnetism-assisted chemical vapor deposition method was developed to synthesize branched or iron-encapsulated carbon nanotubes. In the process, the external magnetic field can promote the coalescence or division of the catalyst particles, causing the formation of branched or encapsulated nanostructures. This finding will extend the understanding of the chemical vapor deposition method in a magnetic field and promote the applications of branched or encapsulated nanostructures.

Covalent 2D and 3D networks from 1D nanostructures: designing new materials

We show extensive theoretical studies related to the generation and characterization of 2D and 3D ordered networks using 1D units that are connected covalently. We experimentally created multi-terminal junctions containing 1D carbon blocks in order to study the most common morphologies and branched structures that could be used in the theoretical design of network models. We found that the mechanical and electronic characteristics of ordered networks based on carbon nanotubes (ON-CNTs) are dominated by their specific super-architecture (hexagonal, cubic, square, and diamond-type). We show that charges follow specific paths through the nodes of the multi-terminal systems, which could result in complex integrated nanoelectronic circuits. The 3D architectures reveal their ability to support extremely high unidirectional stress when their mechanical properties are studied. In addition, these networks are shown to perform better than standard carbon aerogels because of their low mass densities, continuous porosities, and high surface areas.

Current rectification by asymmetric molecules: An ab initio study

Current rectification effect in an asymmetric molecule HCOO-C6H4-(CH2)n sandwiched between two aluminum electrodes has been studied using an ab initio nonequilibrium Green's function method. The conductance of the system decreases exponentially with the increasing number n of CH2. The phenomenon of current rectification is observed such that a very small current appears at negative bias and a sharp negative differential resistance at a critical positive bias when n>or=2. The rectification effect arises from the asymmetric structure of the molecule and the molecule-electrode couplings. A significant rectification ratio of approximately 38 can be achieved when n=5.

Step-shaped bismuth nanowires with metal-semiconductor junction characteristics

Uniform and step-shaped Bi nanowire (NW) arrays have been synthesized by electrochemical deposition inside the uniform and step-shaped nanochannels of an anodic aluminium oxide template. These Bi NWs are highly oriented and single crystalline. The current-voltage characteristics of the parallel uniform Bi nanowires show that the contacts between Bi NWs and gold film do not make significant contributions to the I-V characteristics of the step-shaped Bi NWs. The diameters of the thick segment and the thin segment of the step-shaped Bi NWs are about 70 and 40 nm, respectively. Their current-voltage characteristics show conventional metal-semiconductor junction behaviour. The approach can be exploited to produce one-dimensional metal-semiconductor junctions using step-shaped NWs consisting of other semi-metals without any external doping, which may find various applications in nanotechnology.

A new method to synthesize complicated multi-branched carbon nanotubes with controlled architecture and composition

Here we develop a simple method by using flow fluctuation to synthesize arrays of multi-branched carbon nanotubes (CNTs) that are far more complex than those previously reported. The architectures and compositions can be well controlled, thus avoiding any template or additive. A branching mechanism of fluctuation-promoted coalescence of catalyst particles is proposed. This finding will provide a hopeful approach to the goal of CNT-based integrated circuits and be valuable for applying branched junctions in nanoelectronics and producing branched junctions of other materials.

Surface reconstructions and stability of X-shaped carbon nanotube junction

A complete surface reconstruction takes place after a local connection between two crossed tubes is established, leading to the creation of an extended X-shaped junction constituted by topological defects with smooth negative curvature. Molecular-dynamics simulations show that the surface reconstructions occur through (1) generalized Stone-Wales transformation and (2) the movement of sp and sp3 atoms and their transformation to sp2 atoms by bond rearrangement. Based on both the principle of energy minimization and a generalized Euler's rule, it is demonstrated that the most stable structure for X junctions contains only 12 heptagons. The annealing temperature influences the topological structure and stability of junctions.

Novel electrical switching behaviour and logic in carbon nanotube Y-junctions

Carbon-nanotube-based electronics offers significant potential as a nanoscale alternative to silicon-based devices for molecular electronics technologies. Here, we show evidence for a dramatic electrical switching behaviour in a Y-junction carbon-nanotube morphology. We observe an abrupt modulation of the current from an on- to an off-state, presumably mediated by defects and the topology of the junction. The mutual interaction of the electron currents in the three branches of the Y-junction is shown to be the basis for a potentially new logic device. This is the first time that such switching and logic functionalities have been experimentally demonstrated in Y-junction nanotubes without the need for an external gate. A class of nanoelectronic architecture and functionality, which extends well beyond conventional field-effect transistor technologies, is now possible.

Shape and complexity at the atomic scale: the case of layered nanomaterials

In nature there are numerous layered compounds, some of which could be curved so as to form fascinating nanoshapes with novel properties. Graphite is at present the main example of a very flexible layered structure, which is able to form cylinders (nanotubes) and cages (fullerenes), but there are others. While fullerenes possess positive curvature due to pentagonal rings of carbon, there are other structures which could include heptagonal or higher membered rings. In fact, fullerenes and nanotubes could display negative curvature, thus forming nanomaterials possessing unexpected electronic and mechanical properties. The effect of curvature in other nano-architectures, such as in boron nitride and metal dichalcogenides, is also discussed in this account. Electron irradiation is a tool able to increase the structural complexity of layered materials. In this context, we describe the coalescence of carbon nanotubes and C(60) molecules. The latter results now open up an alternative approach to producing and manipulating novel nanomaterials in the twenty-first century.

Electronic transport in Z-junction carbon nanotubes

In this paper, the electronic transport in different Z-shape carbon nanotubes containing double knee junction structures on the same tube is studied. One consists of (5,5)-(9,0)-(5,5) double knee nano-metal-metal-metal junctions and another consists (6,6)-(10,0)-(6,6) double knee nano-metal-semiconductor-metal junctions. With the nearest-neighbor pi-orbital tight-binding model, quantum conductances of these double knee junctions are calculated using the Landauer formula. The interesting conductance curves are provided to exhibit a potential application in the arena of molecular electronics.

Carbon nanotube "T Junctions": formation pathways and conductivity

Using tight-binding molecular dynamics we simulate the formation of single wall carbon nanotube T junctions via the fusing of two nanotubes. We propose energetically efficient pathways for this process in which all atoms maintain their sp(2) arrangements throughout. Recent experimental advances have greatly increased the plausibility of synthesizing T junctions as proposed in the simulations. We further report I-V characteristics of the formed junctions.

Capacitive-coupling-enhanced switching gain in an electron y-branch switch

We have fabricated electron Y-branch switches (YBS) on modulation doped GaAs/AlGaAs heterostructures. The Y branch consists of a one-dimensional source, which is split along the branching section into two one-dimensional drains. In addition to source drain voltages, external electric fields can be applied via gates along the branches. In the nonlinear transport regime sweeps of the side-gate voltages lead to a voltage difference between the drain reservoirs with gain. This switching gain increases superlinearly with the bias voltage applied between the source and the drains of the YBS. We explain the bias voltage enhanced switching by a capacitive coupling of the branches.