Wire Junctions Research Articles

Fabrication of a Printed Heater Using a Composite of Silver Nanowires and Neutral PEDOT:PSS

In this work, a low resistance heater based on a composite of silver nanowires (Ag NWs) and neutral poly (3,4-ethylenedioxythiophene) poly(styrene sulphonate) (PEDOT:PSS) is fabricated. Pure Ag NWs have poor substrate adhesion, poor environmental and thermal stability, and high surface roughness. Local hotspots at wire junctions also leads to uneven joule heating. These disadvantages are overcome by blending the NWs with PEDOT:PSS. Specifically, neutral PEDOT:PSS is used in this work as it is less hygroscopic and possess greater environmental stability compared to the conventionally used acidic PEDOT:PSS. The composite is synthesized as a stable printable dispersion and deposited on a flexible polyethylene terephthalate (PET) substrate using an extrusion-based direct write system. Film thickness was optimized to achieve low sheet resistance and good adhesion and it is laminated with polydimethylsiloxane (PDMS) for environmental protection. The heater shows uniform temperature distribution with a short response time and low operating voltage. Temperature distribution modelling was carried out using COMSOL and correlated well with the experimental data. The heater also exhibits good repeatability and cyclic thermal stability. A prototype device with temperature cut-off and feedback was also implemented using an Arduino controller.

Theoretical Study of Electronic and Thermal Transport Properties through a Single-Molecule Junction of Catechol

The study of molecular nanoelectronic devices has recently gained significant interest, especially their potential use as functional junctions of molecular wires. Aromatic systems with π-conjugated bonds within their chemical backbones, such as catechol, have attracted particular attention in this area. In this work, we focused on calculating and determining catechol’s electrical and thermal transport properties using the theoretical method of Green’s functions renormalized in a real space domain within a framework of tight-binding approximation to the first neighbors. Thus, we studied two theoretical models of catechol as a function of its geometry, obtaining striking variations in the profiles of electrical and thermal conductance, the Seebeck coefficient, and the figure of merit. The analyses of the results suggest the potential application of catechol as a likely conductive and thermoelectric molecule serving as a novel material to use in molecular electronic devices.

Scattering in quantum wires and junctions of quantum wires with edge states of quantum spin Hall insulators

An integral part of scattering theory calculations in continuum quantum systems involves identifying appropriate boundary conditions in addition to writing down the correct Hamiltonian. In the simplest problem of scattering in one dimensional lattice, scattering due to an on-site potential and scattering due to an unequal bond (in otherwise translationally invariant lattice) give different results for scattering amplitudes. While the scattering problems in the continuum and the lattice models can be mapped to one another for scattering due to on-site potential, the equivalent continuum model for scattering due to an unequal bond is missing. We introduce a new parameter c in the boundary condition of the continuum model that is equivalent to scattering due to an unequal bond on the lattice. Further, we study a junction between a normal metal quantum wire and a one dimensional edge of quantum spin Hall insulator (QSHI) in continuum using the parameter c. In the case of a junction between a normal metal quantum wire and the edge of QSHI, we identify the boundary condition that permits maximum transmission. Further, we solve the scattering problem between the junction of quantum wire and QSHI using a lattice model and map it to continuum model results. The problem of transport between four channels of spinful normal metal quantum wire and two channels of QSHI edge is not well-defined. We rectify this situation by formulating the scattering problem in terms of a junction of a semi-infinite normal metal quantum wire with an infinite edge of QSHI, gapping out one semi-infinite section of the QSHI edge by a Zeeman field and applying an appropriate boundary condition at the junction. We calculate the scattering amplitudes analytically.

Improvement of Electrical Properties of Silver Nanowires Transparent Conductive by Metal Oxide Nanoparticles Modification

At present, silver nanowire transparent conductive films (AgNWs-TCFs) still have problems such as high resistance of AgNWs network nodes, uneven distribution of resistance and poor electrical performance stability, which restrict their commercial application. Different from chemical modification, in this paper, a method of modifying AgNWs-TCFs with metal oxide nanoparticles (MONPs) is proposed, that is, ZnO, SnO2, Al2O3 and TiO2 etc., four transparent metal oxides are used as targets respectively in a magnetron sputtering process, modifying the silver nanowire network wire–wire junctions and silver nanowire in AgNWs-TCFs using active MONPs generated by magnetron sputtering. A series of AgNWs@MONPs for the AgNWs@ZnO-TCFs, AgNWs@SnO2-TCFs, AgNWs@Al2O3-TCFs and AgNWs@TiO2-TCFs were obtained. A significant decrease in the resistance of AgNWs-TCFs through the modification of MONPs was shown. Respectively, the reduction of resistance was 75.6%, 70.4%, 53.2% and 59.8% for AgNWs@ZnO-TCFs, AgNWs@SnO2-TCFs, AgNWs@Al2O3-TCFs and AgNWs@TiO2-TCFs. Correspondingly, its non-uniformity of resistance distribution was 12.5% (18.2% before), 10.0% (17.1% before), 10.1% (24.3% before) and 10.6% (13.4% before), respectively, which markedly improved the uniformity of electrical property. Respectively, their failure voltages reach 16, 16, 15 and 16 (V), so accordingly, the electrical stability is considerably enhanced. In addition, the uniformity of temperature distribution was also significantly optimized with its temperature non-uniformity of 10.4%, 8.7%, 10.3% and 9.6%, respectively. Contrast that with AgNWs@MONPs, and the failure voltages and temperature non-uniformity of AgNWs-TCFs are 12 V and 40.6%.

Conductance of electrostatic wire junctions in bilayer graphene

The conductance of electrostatic wire junctions in bilayer graphene, classified as trivial-trivial or trivial-topological regarding the confinement character on each junction side, is calculated. The topological side always corresponds to a kink-antikink system, as required for a proper connection with a trivial side. We report a conductance quench of the trivial-topological junction, with a conductance near quantization to $4{e}^{2}/h$, which is only half of the maximum value allowed by the Chern number of a kink-antikink system. The analysis allowed us to uncover the existence of a chiral edge mode in the trivial wire under quite general conditions. A double junction, trivial-topological-trivial, displays periodic Fano-like conductance resonances (dips or peaks) induced by the created topological loop.

Electro-thermo-mechanical characterization of microscale Ti-6Al-4V wires using an innovative experimental method

The deformation behavior of Ti-6Al-4V (at.%) wires under direct electric current was investigated. To minimize thermal effects due to Joule heating on plastic deformation, fine Ti-6Al-4V wires with 100 μm diameter were tested by developing and utilizing an innovative electro-thermo-mechanical tensile tester. The force-controlled tensile tester consists of an electronic balance, piezo actuator, optical camera, infrared thermometer, and electric power supply. To characterize the state of Joule heating in the fine wire, the temperatures at the wire and load frame junction were measured with a non-contact infrared thermometer and then a finite element analysis was conducted using the measured temperatures as boundary conditions. For validation of our experimental approach, we have carried out uniaxial tensile testing of Ti-6Al-4V wires under 0, 10, and 20 A/mm2 current densities, respectively, and the results were compared with previous reported values. In our specimen, the change of mechanical properties including the reduction of elastic modulus and strength and the increase of ductility and failure strain was observed with increasing the applied current. However, the level of change was not severe compared to other research. It could therefore be concluded that the thermal effect was minimized by using fine Ti-6Al-4V wires with a large surface-to-volume ratio. In the analysis of fracture surface, the transition from brittle to ductile fracture mode was clearly observed with increasing current density.

Electrical conductivity of random metallic nanowire networks: an analytical consideration along with computer simulation.

The current interest in the study of the 2D systems of randomly deposited metallic nanowires is inspired by a combination of their high electrical conductivity with excellent optical transparency. Metallic nanowire networks show great potential for use in numerous technological applications. Although there are models that describe the electrical conductivity of the random nanowire networks through wire resistance, junction resistance, and number density of nanowires, they are either not rigorously justified or contain fitting parameters. We have proposed a model for the electrical conductivity in random metallic nanowire networks. We have mimicked such random nanowire networks as random resistor networks (RRN) produced by the homogeneous, isotropic, and random deposition of conductive zero-width sticks onto an insulating substrate. We studied the electrical conductivity of these RRNs using a mean-field approximation. An analytical dependency of the electrical conductivity on the main physical parameters (the number density and electrical resistances of these wires and of the junctions between them) has been derived. Computer simulations have been performed to validate our theoretical predictions. We computed the electrical conductivity of the RRNs against the number density of the conductive fillers for the junction-resistance-dominated case and for the case where the wire resistance and the junction resistance were equal. The results of the computations were compared with this mean-field approximation. Our computations demonstrated that our analytical expression correctly predicts the electrical conductivity across a wide range of number densities.

A 1D:2D structured AgNW:MXene composite transparent electrode with high mechanical robustness for flexible photovoltaics

MXene nanosheets weld the wire–wire junctions of a AgNW network to improve the FTE performance, and flexible PSCs and OPVs based on AgNW:MXene FTE exhibit a champion PCE of 20.22% and 16.03%, respectively.

High-performance flexible UV photodetector based on self-supporting ZnO nano-networks fabricated by substrate-free chemical vapor deposition

Self-supporting ZnO nano-networks have been demonstrated by a substrate-free chemical vapor deposition process for the application as flexible ultraviolet (UV) photodetector. The device shows a responsivity of ∼300 mA W−1 over a wide wavelength range from 254 to 365 nm and a high UV/visible rejection ratio of more than 104. More interestingly, a short 90%–10% decay time of <0.12 s can be observed in the air atmosphere, and the current can fully recover to its original dark value within 1 s after switching off the light. The quick response speed should be associated with the wire–wire junction barriers and the adsorption/desorption process of oxygen molecules on the oxygen vacancies near the surface of the ZnO. In addition, the photocurrent, the dark current and the response speed of the ZnO nano-networks flexible UV photodetector nearly stay the same under different bending conditions, suggesting the excellent photoelectric stability and repeatability. Such a simple and cheap way for fabricating self-supporting ZnO-based devices has broad application prospects in the fields of flexible and wearable electronic devices.

Numerical study on the effects of experimental parameters on evaporation characteristic of a droplet

The simulation is used to research the effect of experimental parameters on evaporation characteristics of n-butanol-dodecane blends. These experimental parameters include droplet diameter, wire diameter, junction diameter, ambient temperature and n-butanol concentration. The equilibrium temperature (Tequ) slowly increases with time for the case with a thermocouple and it is nearly unchanged without a thermocouple. The change of droplet diameter at location 1# (D1#, location 1# is the beginning of droplet motion) has little impact on Tequ for the case without a thermocouple. With increasing D1#, the average evaporation rate (Kave) increases with a thermocouple and it is nearly constant without a thermocouple. Both Kave and Tequ firstly increase and then decrease with increasing wire diameter (Dwir) or junction diameter (Djun). From 600 to 800 K, Kave is the maximum when Dwir is 0.10 mm. The maximum is at Djun of 0.3 mm for 800 K and it is at 0.4 mm for 600 and 700 K. The change of Dwir or Djun has little effects on T2#, which is the droplet temperature at the location of 2# (location 2# is the end of droplet motion). Both T2# and Kave decrease with increasing n-butanol concentration. An obvious transition can be found for Kave when the mass fraction of n-butanol ranges from 12.5% to 25%. The normalized evaporation rate is reasonably predicted using a polynomial model.

Single-molecule junctions of multinuclear organometallic wires: long-range carrier transport brought about by metal-metal interaction.

Here, we report multinuclear organometallic molecular wires having (2,5-diethynylthiophene)diyl-Ru(dppe)2 repeating units. Despite the molecular dimensions of 2–4 nm the multinuclear wires show high conductance (up to 10−2 to 10−3G0) at the single-molecule level with small attenuation factors (β) as revealed by STM-break junction measurements. The high performance can be attributed to the efficient energy alignment between the Fermi level of the metal electrodes and the HOMO levels of the multinuclear molecular wires as revealed by DFT–NEGF calculations. Electrochemical and DFT studies reveal that the strong Ru–Ru interaction through the bridging ligands raises the HOMO levels to access the Fermi level, leading to high conductance and small β values.

Electrodeposition fabrication of Cu@Ni core shell nanowire network for highly stable transparent conductive films

Copper nanowire (CuNW) is one of the most promising candidates for next-generation transparent conductive film (TCF). However, practical applications of CuNW are still limited by several drawbacks, including loose wire to wire junctions, poor resistance against oxidation, chemical and thermal damage. To concurrently address these urgent issues, highly conductive and stable TCF is prepared based on Cu@Ni core-shell NW networks by electrodeposition. The coated Ni shell can weld stacked NWs tightly, which decreases the sheet resistance from 513 to 15.8 Ohm/sq (at a transmittance of 88%), as well as improves the mechanical stability (1.03-fold resistance increase after 2000 cyclic bending). The Cu@Ni NW TCF exhibits excellent antioxidation performance after storing in atmospheric environment for 168 h. The passivation Ni shell also improvs the chemical and thermal stability. The Cu@Ni NW network keeps intact after 450 s H2O2 corrosion and heating at 400 °C for 30 min. Moreover, a flexible transparent heater was fabricated based on these TCFs, which shows excellent uniform heating performance and high response speed.

Effect of tunneling on the electrical conductivity of nanowire-based films: Computer simulation within a core–shell model

We have studied the electrical conductivity of two-dimensional nanowire networks. An analytical evaluation of the contribution of tunneling to their electrical conductivity suggests that it is proportional to the square of the wire concentration. Using computer simulation, three kinds of resistance were taken into account, viz., (i) the resistance of the wires, (ii) the wire–wire junction resistance, and (iii) the tunnel resistance between wires. We found that the percolation threshold decreased due to tunneling. However, tunneling had a negligible effect on the electrical conductance of dense nanowire networks.

Emergent chirality in multilead Luttinger-liquid junctions out of equilibrium

We study charge transport through $N$-lead junctions ($N\geq 3$) of spinless Luttinger liquid wires with bias voltages applied to Fermi-liquid reservoirs. In particular, we consider a Y junction, which is a setup characteristic of the tunneling experiment. In this setup, the strength of electron-electron interactions in one of the arms ("tunneling tip") is different from that in the other two arms (which form together the "main wire"). For a generic single-particle $S$ matrix of the junction, we find that the bias voltage $V$ applied---even symmetrically---to the main wire generates a current proportional to $|V|$ in the tip wire. We identify two mechanisms of this nonequilibrium-induced "emergent chirality" in a setup characterized by the time-reversal and parity symmetric Hamiltonian of the junction. These are: (i) the emergence of an effective magnetic flux, which breaks time-reversal symmetry, and (ii) the emergence of parity-breaking asymmetry of the setup, both proportional to the interaction strength and the sign of the voltage. The current in the tip wire generated by mechanism (i) is reminiscent of the Hall current in the linear response of a system the Hamiltonian of which breaks time-reversal symmetry; however, in the absence of any magnetic field or a local magnetic moment. Similarly, mechanism (ii) can be thought of as an emergent "photogalvanic effect"; however, in the presence of inversion symmetry within the main wire. The nonequilibrium chirality implies a rectification of the current in the tip when the main wire is biased by $\it ac$ voltage.

Nanoparticle Linker‐Controlled Molecular Wire Devices Based on Double Molecular Monolayers

Highly conductive molecular wires are an important component for realizing molecular electronic devices and have to be explored in terms of interactions between molecules and electrodes in their molecular junctions. Here, new molecular wire junctions are reported to enhance charge transport through gold nanoparticle (AuNP)-linked double self-assembled monolayers (SAMs) of cobalt (II) bis-terpyridine molecules (e.g., Co(II)(tpyphS)2 ). Electrical characteristics of the double-SAM devices are explored in terms of the existence of AuNP. The AuNP linker in the Co(II)(tpyphS)2 -AuNP-Co(II)(tpyphS)2 junction acts as an electronic contact that is transparent to electrons. The weak temperature dependency of the AuNP-linked molecular junctions strongly indicates sequential tunneling conduction through the highest occupied molecular orbitals (HOMOs) of Co(II)(tpyphS)2 molecules. The electrochemical characteristics of the AuNP-Co(II)(tpyphS)2 SAMs reveal fast electron transfer through molecules linked by AuNP. Density functional theory calculations reveal that the molecular HOMO levels are dominantly affected by the formation of junctions. The intermolecular charge transport, controlled by the AuNP linker, can provide a rational design for molecular connection that achieves a reliable electrical connectivity of molecular electronic components for construction of molecular electronic circuits.

High-Resolution and Large-Area Patterning of Highly Conductive Silver Nanowire Electrodes by Reverse Offset Printing and Intense Pulsed Light Irradiation.

Conventional printing technologies such as inkjet, screen, and gravure printing have been used to fabricate patterns of silver nanowire (AgNW) transparent conducting electrodes (TCEs) for a variety of electronic devices. However, they have critical limitations in achieving micrometer-scale fine line width, uniform thickness, sharp line edge, and pattering of various shapes. Moreover, the optical and electrical properties of printed AgNW patterns do not satisfy the performance required by flexible integrated electronic devices. Here, we report a high-resolution and large-area patterning of highly conductive AgNW TCEs by reverse offset printing and intense pulsed light (IPL) irradiation for flexible integrated electronic devices. A conductive AgNW ink for reverse offset printing is prepared by carefully adjusting the composition of AgNW content, solvents, surface energy modifiers, and organic binders for the first time. High-quality and high-resolution AgNW micropatterns with various shapes and line widths are successfully achieved on a large-area plastic substrate (120 × 100 mm2) by optimizing the process parameters of reverse offset printing. The reverse offset printed AgNW micropatterns exhibit superior fine line widths (up to 6 μm) and excellent pattern quality such as sharp line edge, fine line spacing, effective wire junction connection, and smooth film roughness. They are post-processed with IPL irradiation, thereby realizing excellent optical, electrical, and mechanical properties. Furthermore, flexible OLEDs and heaters based on reverse offset printed AgNW micropatterns are successfully fabricated and characterized, demonstrating the potential use of the reverse offset printing for the conductive AgNW ink.

Pseudo-Biological Highly Performance Transparent Electrodes Based on Capillary Force-Welded Hybrid AgNW Network

Graphene/silver nanowire composite films have great potential as transparent conductive electrodes in the field of optoelectronic devices. So far, antioxidant and reducing the junction resistance are two major parameters in the silver nanowire electrode studies. In this paper, a pseudo-biological inspired structure for transparent electrodes was proposed by combining hybrid diameters silver nanowire network with the chemical vapor deposition-grown (CVD-grown) graphene as a passivation layer. Compared with the traditional structure, the silver nanowire network with this novel structure of human vascular tissue network greatly reduced the sheet resistance. An environmentally friendly liquid, deionized water, was selected for the generation of capillary forces at the liquid bridge, thereby improving the wire junction problem. After welding with the capillary force, the increase in the value of the figure of merit (FoM = σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> /σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</sub> ) acted a pivotal part in improving conductivity with excellent optical performance. In addition, graphene was chosen as an encapsulation layer to protecting silver nanowires from oxidation while improving electrical properties. Compared with the silver nanowire films with a diameter of 20 nm, the σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> /σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</sub> of the graphene/silver nanowire composite film increased by 69.6 % with a sheet resistance of 26.4 Ω/sq. More importantly, graphene is supposed to protect silver nanowires from oxidation and moisture, which makes the composite films promising as electrodes for underwater optoelectronic devices or a possible development in high humidity environments.

Highly reliable copper nanowire electrode with enhanced transmittance and robustness for organic light emitting diodes

Abstract A highly conductive and robust copper nanowire (CuNW) composite film is fabricated through a simple welding and reduction process. The nanowires are welded to a unit and reduced into pure metal copper without oxide layer on the surface by poly(ethylene glycol) (PEG). The electrical conductivity of the film significantly increases and the film's surface roughness decreases greatly since the wire junctions are well welded. When the polymethyl methacrylate (PMMA) is coated on the CuNWs as a protecting layer, the nanowires are tightly bonds to the substrate, and the transmittance of the film increases dramatically. The whole process can be accomplished within 10 min and the obtained film shows a low sheet resistance of 22 Ω/sq with a transmittance of 88%, which is among the top values to the best of our knowledge. This obtained CuNW/PMMA composite film can resist air, water and ethanol exposure without obviously conductivity deterioration. With this CuNW/PMMA composite film as anode for the organic light-emitting diode, the device shows better performance than that with ITO anode.

Thermoelectric voltage switching in gold atomic wire junctions

We explore the thermoelectric properties of gold atomic chains bridging gold electrodes by means of \textit{ab initio} and semi-empirical calculations, and heuristic reasoning. We predict the thermoelectric voltage induced by a temperature difference across such junctions to oscillate, repeatedly changing sign, as a function of the number of atoms $N$ making up the atomic chain. We also predict the amplitude of the oscillations to be proportional to $N$ for long atomic chains. Further we predict the thermoelectric voltage to change sign, in some cases, if the junction is stretched without changing $N$. Our predictions apply regardless of whether regular or irregular electrode grain boundaries are present and whether the electrodes are symmetric or asymmetric. Our findings may pave the way to the realization of new mechanically controllable voltage switches enabling direct conversion of heat into electricity in energy harvesting applications.

Functionalization of Silver Nanowire Transparent Electrodes with Self-Assembled 2-Dimensional Tectomer Nanosheets

Here, we describe the unusual self-assembly of amine-terminated oligoglycine peptides into extended two-dimensional sheets in the presence of silver nanowires. The resulting tectomer sheets are shown to have a strong affinity for the nanowires through a charge-transfer interaction as evidenced by X-ray photoelectron spectroscopy. We show that extended assemblies of metal–peptide hybrids offer additional augmentative functionalities; for instance, the tectomer sheets are hydrophobic in nature and act as a protective layer preventing oxidation and degradation of the nanowires when exposed to atmospheric conditions. Moreover, for silver nanowire percolating networks the presence of the peptide markedly increases the overall electrical conductivity through mechanical squeezing of wire–wire junctions in the network. The peptide–metal interface can be controlled by pH stimulus thus potentially offering new directions where silver nanowire assemblies are used for transparent electrodes ranging from antimicrobial...