Rectification Properties Research Articles

Improved rectification and transport properties of hybrid PEDOT:PSS/Ge/Si heterojunctions with Ge nanoclusters

The electrical characteristics and deep-level transient spectroscopy of a hybrid poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GeNCs/Si heterojunction with Ge nanoclusters grown by molecular beam epitaxy on a p-type Si(001) substrate are investigated. The heterostructure shows good rectifying J–V characteristics, the dark current exhibits an activation energies of 280 meV and 550 meV, while the reverse bias leakage current is suppressed due to the coating of Ge nanoclusters with PEDOT:PSS. We show that recombination via deep hole states close to grain boundaries can be partly suppressed by the PEDOT:PSS thin films, leading to a decrease in the saturation current and an improvement of the rectification without deterioration of forward current.

Camphor-Based CVD Bilayer Graphene/Si Heterostructures for Self-Powered and Broadband Photodetection.

This work demonstrates a self-powered and broadband photodetector using a heterojunction formed by camphor-based chemical vaper deposition (CVD) bilayer graphene on p-Si substrates. Here, graphene/p-Si heterostructures and graphene layers serve as ultra-shallow junctions for UV absorption and zero bandgap junction materials (<Si bandgap (1.1 eV)) for long-wave near-infrared (LWNIR) absorption, respectively. According to the Raman spectra and large-area (16 × 16 μm2) Raman mapping, a low-defect, >95% coverage bilayer and high-uniformity graphene were successfully obtained by camphor-based CVD processes. Furthermore, the carrier mobility of the camphor-based CVD bilayer graphene at room temperature is 1.8 × 103 cm2/V·s. Due to the incorporation of camphor-based CVD graphene, the graphene/p-Si Schottky junctions show a good rectification property (rectification ratio of ~110 at ± 2 V) and good performance as a self-powered (under zero bias) photodetector from UV to LWNIR. The photocurrent to dark current ratio (PDCR) value is up to 230 at 0 V under white light illumination, and the detectivity (D*) is 8 × 1012 cmHz1/2/W at 560 nm. Furthermore, the photodetector (PD) response/decay time (i.e., rise/fall time) is ~118/120 μs. These results support the camphor-based CVD bilayer graphene/Si Schottky PDs for use in self-powered and ultra-broadband light detection in the future.

Optoelectronic properties of Co/pentacene/Si MIS heterojunction photodiode

The Co/pentacene/n-Si/Al device with the Co/n-Si/Al device was fabricated and characterized by current-voltage measurements to understand the effect of the pentacene on electrical properties. The Co/pentacene/n-Si/Al device exhibited better rectification properties than reference device. The characteristic parameters such as barrier height, ideality factor, interface states density and series resistance values of the devices were calculated and discussed in details. Furthermore, I–V measurements of the Co/pentacene/n-Si/Al device were performed both in dark and under illumination conditions. The results revealed that the reverse current increased with increasing illumination intensity, and the device exhibited photodiode behaviors as well as good photocunducting characteristics. The C–V characteristics of the Co/pentacene/n-Si/Al were studied for various frequencies to determine the donor carrier concentration and fermi energy level. Experimental results highlights that the Co/pentacene/n-Si/Al device is a good candidate for optoelectronic device applications such as solar cells, photodiode, photodetector due to exhibiting good photoconducting characteristics.

The effects of temperature on the biophysical properties of optic nerve F-fibres

In multiple sclerosis, exacerbation of symptoms with rising body temperature is associated with impulse conduction failure. The mechanism is not fully understood. Remarkably, normal optic nerve axons also show temperature dependent effects, with a fall in excitability with warming. Here we show two properties of optic nerve axons, accommodation and inward rectification (Ih), respond to temperature changes in a manner consistent with a temperature dependent membrane potential. As we could find no evidence for the functional expression of KV7.2 in the axons, using the K+ channel blocker tetraethylammonium ions, we suggest this may explain the membrane potential lability. In order to understand how the axonal membrane potential may show temperature dependence, we have developed a hypothesis involving the electroneutral movement of Na+ ions across the axon membrane, that increases with increasing temperature with an appropriate Q10. Part, but probably not all, of the electroneutral Na+ movement is eliminated by removing extracellular Cl− or exposure to bumetanide, consistent with the involvement of the transporter NKCC1. Numerical simulation suggests a change in membrane potential of − 15–20 mV mimics altering temperature between room and physiological in the largest axons.

Molecular basis of junctional current rectification at an electrical synapse.

Rectifying electrical synapses (RESs) exist across animal species, but their rectification mechanism is largely unknown. We investigated why RESs between AVA premotor interneurons and A-type cholinergic motoneurons (A-MNs) in Caenorhabditis elegans escape circuit conduct junctional currents (I j) only in the antidromic direction. These RESs consist of UNC-7 innexin in AVA and UNC-9 innexin in A-MNs. UNC-7 has multiple isoforms differing in the length and sequence of the amino terminus. In a heterologous expression system, only one UNC-7 isoform, UNC-7b, can form heterotypic gap junctions (GJs) with UNC-9 that strongly favor I j in the UNC-9 to UNC-7 direction. Knockout of unc-7b alone almost eliminated the I j, whereas AVA-specific expression of UNC-7b substantially rescued the coupling defect of unc-7 mutant. Neutralizing charged residues in UNC-7b amino terminus abolished the rectification property of UNC-7b/UNC-9 GJs. Our results suggest that the rectification property results from electrostatic interactions between charged residues in UNC-7b amino terminus.

Thermal rectification in one-dimensional lattices with nonlinear system–reservoir coupling

In this work we study the thermal rectification properties of a one-dimensional, mass-graded oscillator lattice with nonlinear system–reservoir couplings. For the case of a harmonic oscillator chain the system presents no rectification at high temperatures and a very weak one for low temperatures as the asymmetric, nonlinear interaction with the thermal reservoirs is increased. The observed rectification rapidly degrades as either the thermal bias or mass asymmetry increase in magnitude. For an anharmonic oscillator Fermi–Pasta–Ulam lattice the rectification increases for the aforementioned conditions, and is maximized when only nonlinear system-reservoir interactions are considered. These latter ones correspond to the case of multiplicative noise affecting the boundaries of the lattice.

Characteristics of Current Transfer in PVA Films with Dispersed Multiwall Carbon Nanotubes on Silicon Substrates

Planar nanocomposite structures comprising poly(vinyl alcohol) films with dispersed multiwall carbon nanotubes (MWCNTs) deposited on silicon substrates and provided with aluminum contacts possess rectification properties and have asymmetric nonlinear current–voltage characteristics. Forward-biased nanocomposite structures exhibit a positive temperature coefficient of resistance (TCR) in a temperature interval of 270–350 K, whereas analogous PVA film structures without MWNTs have negative TCR values. Under reverse bias, the structures with MWNTs exhibit TCR with a sign changing from negative to positive. The observed behavior is explained in terms of the tunneling current transfer mechanism.

Effect of Anion Species on Ion Current Rectification Properties of Positively Charged Nanochannels.

Biological ion channels can realize delicate mass transport under complicated physiological conditions. Artificial nanochannels can achieve biomimetic ion current rectification (ICR), gating, and selectivity that are mostly performed in pure salt solutions. Synthetic nanochannels that can function under mixed ion systems are highly desirable, yet their performances are hard to be compared to those under pure systems. Seeking out the potential reasons by investigating the effect of mixed-system components on the ion-transport properties of the constructed nanochannels seems necessary and important. Herein, we report the effect of anions with different charges and sizes on the ICR properties of positively charged nanochannels. Among the investigated anions, the low-valent anions showed no impact on the ICR direction, while the high-valent component ferrocyanide [Fe(CN)64-] caused significant ICR inversion. The ICR inversion mechanism is evidenced to result from the adsorption of Fe(CN)64--induced surface charge reversal, which relates to solution concentration, pH conditions, and nanochannel sizes and applies to both aminated and quaternized nanochannels that are positively charged. Noticeably, Fe(CN)64- is found to interfere with the transport of protein molecules in the nanochannel. This work points out that the ion species from mixed systems would potentially impact the intrinsic ICR properties of the nanochannels. Replacing highly charged counterions with organic components would be promising in building up future nanochannel-based mass transport systems running under mixed systems.

Polyaniline for Improved Blue Energy Harvesting: Highly Rectifying Nanofluidic Diodes Operating in Hypersaline Conditions via One-Step Functionalization

Solid-state nanochannels have attracted substantial attention of the scientific community due to their remarkable control of ionic transport and the feasibility to regulate the iontronic output by different stimuli. Most of the developed nanodevices are subjected to complex modification methods or show functional responsiveness only in moderate-ionic-strength solutions. Within this project, we present a nanofluidic device with enhanced ionic current rectification properties attained by a simple one-step functionalization of single bullet-shaped polyethylene terephthalate (PET) nanochannels with polyaniline (PANI) that can work in high-ionic-strength solutions. The integration of PANI also introduces a broad pH sensitivity, which makes it possible to modulate the ionic transport behavior between anion-selective and cation-selective regimes depending on the pH range. Since PANI is an electrochemically active polymer, ionic transport also becomes dependent on the presence of redox stimuli in solution. We demonstrate that PANI-functionalized single-nanochannel membranes function as an efficient salinity gradient-based energy conversion device even in acidic concentrated salt solutions, opening the door to applications under a variety of novel operating conditions.

Screening Technologies for Inward Rectifier Potassium Channels: Discovery of New Blockers and Activators.

K+ channels play a critical role in maintaining the normal electrical activity of excitable cells by setting the cell resting membrane potential and by determining the shape and duration of the action potential. In nonexcitable cells, K+ channels establish electrochemical gradients necessary for maintaining salt and volume homeostasis of body fluids. Inward rectifier K+ (Kir) channels typically conduct larger inward currents than outward currents, resulting in an inwardly rectifying current versus voltage relationship. This property of inward rectification results from the voltage-dependent block of the channels by intracellular polyvalent cations and makes these channels uniquely designed for maintaining the resting potential near the K+ equilibrium potential (EK). The Kir family of channels consist of seven subfamilies of channels (Kir1.x through Kir7.x) that include the classic inward rectifier (Kir2.x) channel, the G-protein-gated inward rectifier K+ (GIRK) (Kir3.x), and the adenosine triphosphate (ATP)-sensitive (KATP) (Kir 6.x) channels as well as the renal Kir1.1 (ROMK), Kir4.1, and Kir7.1 channels. These channels not only function to regulate electrical/electrolyte transport activity, but also serve as effector molecules for G-protein-coupled receptors (GPCRs) and as molecular sensors for cell metabolism. Of significance, Kir channels represent promising pharmacological targets for treating a number of clinical conditions, including cardiac arrhythmias, anxiety, chronic pain, and hypertension. This review provides a brief background on the structure, function, and pharmacology of Kir channels and then focuses on describing and evaluating current high-throughput screening (HTS) technologies, such as membrane potential-sensitive fluorescent dye assays, ion flux measurements, and automated patch clamp systems used for Kir channel drug discovery.

High responsivity ZnO based p–n homojunction UV-photodetector with series Schottky barrier

In the present article, we proposed a p–n homojunction photodetector with a series Schottky barrier and a high value of responsivity in the ultraviolet region. The thin-film photodetector makes use of a junction between an RF-sputtered n-type ZnO nanostructure and a p-type copper doped ZnO (CZO) thin film derived through the spin coating process on an ITO coated glass substrate. Palladium metal contacts have been deposited to form the Schottky barrier in series with the p–n homojunction. The device has been simulated, fabricated, and tested only after ensuring the stability of the p-type CZO thin film. The measured I–V characteristics of the fabricated photodetector under illuminated and dark conditions showed excellent UV response and good rectification properties. The device exhibits a peak responsivity of 13.2 A W−1 for a reverse biasing voltage of 3 V. This value is much higher than the values reported by others for a ZnO based photodetector.

Thermoelectric and electron heat rectification properties of quantum dot superlattice nanowire arrays

Heat engines made of quantum dot (QD) superlattice nanowires (SLNWs) offer promising applications in energy harvesting due to the reduction in phonon thermal conductivity. In solid state electrical generators (refrigerators), one needs to generate (remove) a large amount of charge current (heat current). Consequently, a high QD SLNW density is required for realistic applications. This study theoretically investigated the properties of power factor and electron heat rectification for an SLNW array under the transition from a one-dimensional system to a two-dimensional system. The SLNW arrays show the functionality of heat diodes, which is mainly attributed to a transmission coefficient with a temperature-bias direction dependent characteristic.

Synthesis of ZnO nanorods on a silicon substrate via hydrothermal route for optoelectronic applications

In the present work, we have synthesized ZnO nanorods (ZnO NRs) by using hydrothermal technique. The morphological, structural and optical properties of ZnO NRs were investigated using x-ray diffraction (XRD), scanning electron microscope (SEM) and UV–Vis absorption. XRD pattern confirms the deposited film was highly oriented crystalline ZnO NRs along [002] direction. SEM shows the formation of submicron and NRs morphology. The optical absorption studies depict that the optical energy gap of the film was 3.5 eV. The fabricated n-ZnO NRs/p-Si heterojunction photodetector exhibits rectification properties with an ideality factor of 2.2. The highest responsivity and quantum efficiency of the photodetector were nearly 0.27 A/W and 89% at 350 nm, respectively, without using buffer layer.

Efficient metal ion sieving in rectifying subnanochannels enabled by metal-organic frameworks.

Biological ion channels have remarkable ion selectivity, permeability and rectification properties, but it is challenging to develop artificial analogues. Here, we report a metal-organic framework-based subnanochannel (MOFSNC) with heterogeneous structure and surface chemistry to achieve these properties. The asymmetrically structured MOFSNC can rapidly conduct K+, Na+ and Li+ in the subnanometre-to-nanometre channel direction, with conductivities up to three orders of magnitude higher than those of Ca2+ and Mg2+, equivalent to a mono/divalent ion selectivity of 103. Moreover, by varying the pH from 3 to 8 the ion selectivity can be tuned further by a factor of 102 to 104. Theoretical simulations indicate that ion-carboxyl interactions substantially reduce the energy barrier for monovalent cations to pass through the MOFSNC, and thus lead to ultrahigh ion selectivity. These findings suggest ways to develop ion selective devices for efficient ion separation, energy reservation and power generation.

Dendrimer-Au Nanoparticle Network Covered Alumina Membrane for Ion Rectification and Enhanced Bioanalysis.

Ion transport in an artificial asymmetric nanoporous membrane, which is similar to biological ion channels, can be used for biosensing. Here, a dendrimer-Au nanoparticle network (DAN) is in situ assembled on a nanoporous anodic aluminum oxide (AAO) surface, forming a DAN/AAO hybrid membrane. Benefiting from the high surface area and anion selectivity of DAN, the prepared DAN/AAO hybrid presents selective ion transport. Under a bias potential, a diode-like current–potential (I–V) response is observed. The obtained ionic current rectification (ICR) property can be tuned by the ion valence and pH value of the electrolyte. The rectified ionic current endows the as-prepared DAN/AAO hybrid with the ability of enhanced bioanalysis. Sensitive capture and detection of circulating tumor cells (CTCs) with a detection limit of 80 cells mL–1 as well as excellent reusability can be achieved.

Cover Feature: Effect of Electrolyte Ions on the Formation, Electroactivity, and Rectification Properties of Films Obtained by Electrografting (ChemElectroChem 4/2020)

Cover Feature: Effect of Electrolyte Ions on the Formation, Electroactivity, and Rectification Properties of Films Obtained by Electrografting (ChemElectroChem 4/2020)

Direct Activation of TRPC3 Channels by the Antimalarial Agent Artemisinin.

(1) Background: Members of the TRPC3/TRPC6/TRPC7 subfamily of canonical transient receptor potential (TRP) channels share an amino acid similarity of more than 80% and can form heteromeric channel complexes. They are directly gated by diacylglycerols in a protein kinase C-independent manner. To assess TRPC3 channel functions without concomitant protein kinase C activation, direct activators are highly desirable. (2) Methods: By screening 2000 bioactive compounds in a Ca2+ influx assay, we identified artemisinin as a TRPC3 activator. Validation and characterization of the hit was performed by applying fluorometric Ca2+ influx assays and electrophysiological patch-clamp experiments in heterologously or endogenously TRPC3-expressing cells. (3) Results: Artemisinin elicited Ca2+ entry through TRPC3 or heteromeric TRPC3:TRPC6 channels, but did not or only weakly activated TRPC6 and TRPC7. Electrophysiological recordings confirmed the reversible and repeatable TRPC3 activation by artemisinin that was inhibited by established TRPC3 channel blockers. Rectification properties and reversal potentials were similar to those observed after stimulation with a diacylglycerol mimic, indicating that artemisinin induces a similar active state as the physiological activator. In rat pheochromocytoma PC12 cells that endogenously express TRPC3, artemisinin induced a Ca2+ influx and TRPC3-like currents. (4) Conclusions: Our findings identify artemisinin as a new biologically active entity to activate recombinant or native TRPC3-bearing channel complexes in a membrane-confined fashion.

In situ synthesis of a MOFs/PAA hybrid with ultrahigh ionic current rectification.

In recent decades, the ionic current rectification (ICR) property of asymmetric nanochannels has been widely explored in applications of energy conversion, gas separation, water purification and bioanalysis/sensors. How to fabricate nanofluidic devices with a high ICR characteristic remains of critical importance to the development of nanofluidics. Herein, we fabricated an asymmetric MOFs/PAA hybrid via in situ synthesis of a zeolitic imidazole framework (ZIF-90) on porous anodic alumina (PAA) nanochannels. The introduction of asymmetric geometry and charge distribution provides the hybrid with ultrahigh ionic rectification, which can be easily measured using an electrochemical detector. This rectification mechanism is elucidated via finite element simulation, which proves that asymmetric geometry as well as the protonation and deprotonation under varied pH values dominates the ICR property. With the advantages of low cost and facile fabrication while supporting high ionic current rectification, the prepared MOFs/PAA hybrid can be considered as a significant paradigm in nanofluidic systems and has potential applications in the fields of new ionic devices and energy conversion systems.

Fabrication and SILAR cycle-dependent characterization of CdS/p-Si heterojunction photodetector

We report the fabrication CdS/p-Si heterojunction via a successive ionic layer adsorption and reaction (SILAR) technique with different CdS thickness controlled by SILAR cycles. A brief investigation has been carried out to study the nano-structural, photodetecting and optical characteristics of prepared CdS/p-Si heterojunction. Structural and morphological characterizations confirmed the formation of crystalline hexagonal CdS thin films with nano-sized grain particles that develops closed packed with SILAR cycles. Photoluminescence (PL) have been studied that emission peak at 472 nm associated with excitonic emission and a broad green emission peak positioned at 553 nm from the recombination of S−2 vacancy with valence band of CdS film. Current–voltage (I–V) and optoelectronic properties of prepared samples presented the rectification properties having the ideality factor more than unity, while the peaks of response have two peaks located at 450 and 800 nm with maximum responsivity at 6 SILAR cycles.

Fabrication of Bio‐Inspired 2D MOFs/PAA Hybrid Membrane for Asymmetric Ion Transport

AbstractBiological ion channels are known as membrane proteins which can turn on and off under environmental stimulus to regulate ion transport and energy conversion. Rapid progress made in biological ion channels provides inspiration for developing artificial nanochannels to mimic the structures and functions of ion transport systems and energy conversion in biological ion channels. Due to the advantages of abundant pore channels, metal–organic frameworks (MOFs) have become competitive materials to control the nanofluidic transport. Herein, a facile in situ synthesis method is developed to prepare hybrid nanochannels constructed by 2D MOFs and porous anodic aluminum (PAA). The introduction of asymmetries in the chemical composition and surface charge properties gives the hybrid outstanding ion current rectification properties and excellent ion selectivity. A power density of 1.6 W m−2 is achieved by integrating it into a salinity‐gradient‐driven device. With advantages of facile fabrication method and high ion selectivity, the prepared 2D MOFs/PAA hybrid membrane offers a promising candidate for power conversion and water desalination.