Interfacial Polarization Control Engineering and Ferroelectric PZT/Graphene Heterostructure Integrated Application

Integration and miniaturization are the inevitable trends in the development of electronic devices. PZT and graphene are typical ferroelectric and carbon-based materials, respectively, which have been widely used in various fields. Achieving high-quality PZT/graphene heterogeneous integration and systematically studying its electrical properties is of great significance. In this work, we reported the characterization of a PZT film based on the sol-gel method. Additionally, the thickness of the PZT film was pushed to the limit size (~100 nm) by optimizing the process. The test results, including the remnant and leakage current, show that the PZT film is a reliable and suitable platform for further graphene-integrated applications. The non-destructive regulation of the electrical properties of graphene has been studied based on a domain-polarized substrate and strain-polarized substrate. The domain structures in the PZT film exhibit different geometric structures with ~0.3 V surface potential. The I-V output curves of graphene integrated on the surface of the PZT film exhibited obvious rectification characteristics because of p/n-doping tuned by an interfacial polarized electric field. In contrast, a ~100 nm thick PZT film makes it easy to acquire a larger strain gradient for flexural potential. The tested results also show a rectification phenomenon, which is similar to domain polarization substrate regulation. Considering the difficulty of measuring the flexural potential, the work might provide a new approach to assessing the flexural polarized regulation effect. A thinner ferroelectric film/graphene heterojunction and the polarized regulation of graphene will provide a platform for promoting low-dimension film-integrated applications.

Drain-Induced Multifunctional Ambipolar Electronics Based on Junctionless MoS2

Applying a drain bias to a strongly gate-coupled semiconductor influences the carrier density of the channel. However, practical applications of this drain-bias-induced effect in the advancement of switching electronics have remained elusive due to the limited capabilities of its current modulation known to date. Here, we show strategies to largely control the current by utilizing drain-bias-induced carrier type switching in an ambipolar molybdenum disulfide (MoS2) field-effect transistor with Pt bottom contacts. Our CMOS-compatible device architecture, incorporating a partially gate-coupled p-n junction, achieves multifunctionality. The ambipolar MoS2 device operates as an ambipolar transistor (on/off ratios exceeding 107 for both NMOS and PMOS), a rectifier (rectification ratio of ∼3 × 106), a reversible negative breakdown diode with an adjustable breakdown voltage (on/off ratio exceeding 109 with a maximum current as high as 10-4 A), and a photodetector. Finally, we demonstrate a complementary inverter (gain of ∼24 at Vdd = 1.5 V), which is highly facile to fabricate without the need for complex heterostructures and doping processes. Our study provides strategies to achieve high-performance ambipolar MoS2 devices and to effectively utilize drain bias for electrical switching.

Thermal rectification through the topological states of asymmetrical length armchair graphene nanoribbons heterostructures with vacancies

We present a theoretical investigation of electron heat current in asymmetrical length armchair graphene nanoribbon (AGNR) heterostructures with vacancies, focusing on the topological states (TSs). In particular, we examine the 9-7-9 AGNR heterostructures where the TSs are well-isolated from the conduction and valence subbands. This isolation effectively mitigates thermal noise of subbands arising from temperature fluctuations during charge transport. Moreover, when the TSs exhibit an orbital off-set, intriguing electron heat rectification phenomena are observed, primarily attributed to inter-TS electron Coulomb interactions. To enhance the heat rectification ratio (ηQ), we manipulate the coupling strengths between the heat sources and the TSs by introducing asymmetrical lengths in the 9-AGNRs. This approach offers control over the rectification properties, enabling significant enhancements. Additionally, we introduce vacancies strategically positioned between the heat sources and the TSs to suppress phonon heat current. This arrangement effectively reduces the overall phonon heat current, while leaving the TSs unaffected. Our findings provide valuable insights into the behavior of electron heat current in AGNR heterostructures, highlighting the role of topological states, inter-TS electron Coulomb interactions, and the impact of structural modifications such as asymmetrical lengths and vacancy positioning. These results pave the way for the design and optimization of graphene-based devices with improved thermal management and efficient control of electron heat transport.

Tuning and Coupling Irreversible Electroosmotic Water Flow in Ionic Diodes: Methylation of an Intrinsically Microporous Polyamine (PIM-EA-TB)

Molecularly rigid polymers with internal charges (positive charges induced by amine methylation) allow electroosmotic water flow to be tuned by adjusting the charge density (the degree of methylation). Here, a microporous polyamine (PIM-EA-TB) is methylated to give a molecularly rigid anion conductor. The electroosmotic drag coefficient (the number of water molecules transported per anion) is shown to increase with a lower degree of methylation. Net water transport (without charge flow) in a coupled anionic diode circuit is demonstrated based on combining low and high electroosmotic drag coefficient materials. The AC-electricity-driven net process offers water transport (or transport of other neutral species, e.g., drugs) with net zero ion transport and without driver electrode side reactions.

Myosin waves and a mechanical asymmetry guide the oscillatory migration of Drosophila cardiac progenitors

Heart development begins with the formation of a tube as cardiac progenitors migrate from opposite sides of the embryo. Abnormal cardiac progenitor movements cause congenital heart defects. However, the mechanisms of cell migration during early heart development remain poorly understood. Using quantitative microscopy, we found that in Drosophila embryos, cardiac progenitors (cardioblasts) migrated through a sequence of forward and backward steps. Cardioblast steps were associated with oscillatory non-muscle myosin II waves that induced periodic shape changes and were necessary for timely heart tube formation. Mathematical modeling predicted that forward cardioblast migration required a stiff boundary at the trailing edge. Consistent with this, we found a supracellular actin cable at the trailing edge of the cardioblasts that limited the amplitude of the backward steps, thus biasing the direction of cell movement. Our results indicate that periodic shape changes coupled with a polarized actin cable produce asymmetrical forces that promote cardioblast migration.

Characteristics of Synaptic Function of Mesoporous Silica-Titania and Mesoporous Titania Lateral Electrode Devices

In this paper, we have fabricated non-volatile memory resistive switching (RS) devices and analyzed analog memristive characteristics using lateral electrodes with mesoporous silica-titania (meso-ST) and mesoporous titania (meso-T) layers. For the planar-type device having two parallel electrodes, current-voltage (I-V) curves and pulse-driven current changes could reveal successful long-term potentiation (LTP) along with long-term depression (LTD), respectively, by the RS active mesoporous two layers for 20~100 μm length. Through mechanism characterization using chemical analysis, non-filamental memristive behavior unlike the conventional metal electroforming was identified. Additionally, high performance of the synaptic operations could be also accomplished such that a high current of 10^-6 Amp level could occur despite a wide electrode spacing and short pulse spike biases under ambient condition with moderate humidity (RH 30~50%). Moreover, it was confirmed that rectifying characteristics were observed during the I-V measurement, which was a representative feature of dual functionality of selection diode and the analog RS device for both meso-ST and meso-T devices. The memristive and synaptic functions along with the rectification property could facilitate a chance of potential implementation of the meso-ST and meso-T devices to neuromorphic electronics platform.

Morphology around Nanopores Fabricated by Laser-Assisted Dielectric Breakdown and Its Impact on Ion and DNA Transport and Sensing

Laser-assisted controlled dielectric breakdown (LaCBD) has emerged as an alternative to conventional CBD-based nanopore fabrication due to its localization capability, facilitated by the photothermal-induced thinning down in the hot spot. Here, we reported the potential impact of the laser on forming debris around the nanopore region in LaCBD. The debris was clearly observable by scanning electron microscopy (SEM) and photoluminescence (PL) spectroscopy. We found that debris formation is a unique phenomenon in LaCBD that is not observable in the conventional CBD approach. We also found that the LaCBD-induced debris is more evident when the laser power and voltage stress are higher. Moreover, the debris is asymmetrically distributed on the top and bottom sides of the membrane. We also found unexpected rectified ionic and molecular transport in those LaCBD nanopores with debris. Based on these observations, we developed and validated a model describing the debris formation kinetics in LaCBD by considering the generation, diffusion, drift, and gravity in viscous mediums. These findings indicate that while laser aids in nanopore localization, precautions should be taken due to the potential formation of debris and rectification of molecular transport. This study provides valuable insights into the kinetics of LaCBD and the characteristics of the LaCBD nanopore.

Enhanced functional detection of synaptic calcium-permeable AMPA receptors using intracellular NASPM

Calcium-permeable AMPA-type glutamate receptors (CP-AMPARs) contribute to many forms of synaptic plasticity and pathology. They can be distinguished from GluA2-containing calcium-impermeable AMPARs by the inward rectification of their currents, which reflects voltage-dependent channel block by intracellular spermine. However, the efficacy of this weakly permeant blocker is differentially altered by the presence of AMPAR auxiliary subunits - including transmembrane AMPAR regulatory proteins, cornichons, and GSG1L - which are widely expressed in neurons and glia. This complicates the interpretation of rectification as a measure of CP-AMPAR expression. Here, we show that the inclusion of the spider toxin analog 1-naphthylacetyl spermine (NASPM) in the intracellular solution results in a complete block of GluA1-mediated outward currents irrespective of the type of associated auxiliary subunit. In neurons from GluA2-knockout mice expressing only CP-AMPARs, intracellular NASPM, unlike spermine, completely blocks outward synaptic currents. Thus, our results identify a functional measure of CP-AMPARs, that is unaffected by their auxiliary subunit content.

Designing Nanofluidic Diode from a Hybrid-Bilayer Covalent Organic Framework: Molecular Simulation Investigation

Nanofluidic diodes are potentially useful in many important applications such as sensing, electronics, and energy conversion. However, the manufacturing of controllable nanopores for nanofluidic diodes is technically challenging. Herein, a nanofluidic diode is designed from a highly programmatic covalent organic framework (COF). Through molecular simulation, remarkable diode behavior is observed in a hybrid-bilayer COF but not in its constituent single-layer COFs. The rectification effect of ion current in the hybrid-bilayer COF is attributed to an asymmetric electrostatic potential across the COF nanopore. Furthermore, a synergistic effect of counterion is unraveled in the hybrid-bilayer COF, and the presence of counterion is found to reduce the entry barrier and facilitate ion transport. The performance of the hybrid-bilayer COF as a nanofluidic diode is comprehensively investigated by varying salt concentration, layer number, interlayer spacing, and slipping. This proof-of-concept simulation study demonstrates the feasibility of the hybrid-bilayer COF as a nanofluidic diode and the finding may stimulate the development of new nanofluidic platforms.

A Pseudocapacitor Diode Based on Ion-Selective Surface Redox Effect

Supercapacitor diode (CAPode) is a novel device that integrates ion diode functionality into a conventional electrical double-layer capacitor and is expected to have great applications in emerging fields such as signal propagation, microcircuit rectification, logic operations, and neuromorphology. Here, a brand new pseudocapacitor diode is reported that has both high charge storage (50.2 C g^-1 at 20 mV s^-1 ) and high rectification (the rectification ratio of 0.79 at 200 mV s^-1 ) properties, which is realized by the ion-selective surface redox reaction of spinel ZnCo₂ O₄ in aqueous alkaline electrolyte. Furthermore, an application of the integrated device is demonstrated in the logic gate of circuit system to realize the logic operations of "AND" and "OR". This work not only expands the types of CAPodes, but also provides a train of thought for constructing high-performance capacitive ionic diodes.

Highly Tunable Lateral Homojunction Formed in Two-Dimensional Layered CuInP2S6 via In-Plane Ionic Migration

As basic building blocks for next-generation information technologies devices, high-quality p-n junctions based on van der Waals (vdW) materials have attracted widespread interest. Compared to traditional two-dimensional (2D) heterojunction diodes, the emerging homojunctions are more attractive owing to their intrinsic advantages, such as continuous band alignments and smaller carrier trapping. Here, utilizing the long-range migration of Cu+ ions under an in-plane electric field, a lateral p-n homojunction was constructed in the 2D layered copper indium thiophosphate (CIPS). The symmetric Au/CIPS/Au devices demonstrate an electric-field-driven resistance switching (RS) accompanied by a rectification behavior without any gate control. Moreover, such rectification behavior can be continuously modulated by poling voltage. We deduce that the reversable rectifying RS behavior is governed by the effective lateral build-in potential and the change of the interfacial barrier during the poling process. Furthermore, the CIPS p-n homojuction is evidenced by the photovoltaic effect, with the spectral response extending up to the visible region due to the better photogenerated carrier separation efficiency. Therefore, this work provides a facile route to fabricate homojunctions through electric-field-driven ionic migration.

Gating with Charge Inversion to Control Ionic Transport in Nanopores

Multivalent ions modify the properties of the solid/liquid interfaces, and in some cases, they can even invert the polarity of surface charge, having large consequences for separation processes based on charge. The so-called charge inversion is observed as a switch from negative surface charge in monovalent salts, e.g., KCl, to effective positive surface charge in multivalent salts that is possible through a strong accumulation and correlation of the multivalent ions at the surface. It is not known yet, however, whether the density of the positive charge induced by charge inversion depends on the pore opening diameter, especially in extreme nanoconfinement. Here, we probe how the effective surface charge induced by charge inversion is influenced by the pore opening diameter using a series of nanopores with an opening between 4 and 25 nm placed in contact with trivalent chromium ions in tris(ethylenediamine)chromium(III) sulfate at different concentrations. Our results suggest that the effective positive charge density can indeed be modified by nanoconfinement to the extent that is dependent on the pore diameter, salt concentration, and applied voltage. In addition, the correlated ions can increase the transmembrane current in nanopores with an opening diameter down to 10 nm and cause a significant blockage of the current for narrower pores. The results provide guidelines to control ionic transport at the nanoscale with multivalent ions and demonstrate that in the same experimental conditions, differently sized pores in the same porous material can feature different surface charge density and possibly ion selectivity.

Triplin: Functional Probing of Its Structure and the Dynamics of the Voltage-Gating Process

Gram-negative bacteria have a large variety of channel-forming proteins in their outer membrane, generally referred to as porins. Some display weak voltage dependence. A similar trimeric channel former, named Triplin, displays very steep voltage dependence, rivaling that responsible for the electrical excitability of mammals, and high inter-subunit cooperativity. We report detailed insights into the molecular basis for these very unusual properties explored at the single-molecule level. By using chemical modification to reduce the charge on the voltage sensors, they were shown to be positively charged structures. Trypsin cleavage of the sensor eliminates voltage gating by cleaving the sensor. From asymmetrical addition of these reagents, the positively charged voltage sensors translocate across the membrane and are, thus, responsible energetically for the steep voltage dependence. A mechanism underlying the cooperativity was also identified. Theoretical calculations indicate that the charge on the voltage sensor can explain the rectification of the current flowing through the open pores if it is located near the pore mouth in the open state. All results support the hypothesis that one of the three subunits is oriented in a direction opposite to that of the other two. These properties make Triplin perhaps the most complex pore-forming molecular machine described to date.

Multifunctionality of Li2 SrNb2 O7 : Memristivity, Tunable Rectification, Ferroelasticity, and Ferroelectricity

Layered Li₂ SrNb₂ O₇ , an inorganic oxide in its bulk single-crystalline form, is experimentally demonstrated to exhibit multiple structural facets such as ferroelasticity, ferroelectricity, and antiferroelectricity. The transition from a room temperature (RT) centrosymmetric structure to a low-temperature out-of-plane ferroelectric and in-plane antiferroelectric structure and the low-temperature (LT) ferroelectric domain configuration are unveiled in TEM, piezoresponse force microscopy, and polarization loop studies. Li₂ SrNb₂ O₇  also exhibits highly tunable ferroelasticity and excellent Li⁺ in-plane conduction, which leads to a giant in-plane memristor behavior and an in-plane electronic conductivity increase by three orders of magnitude by electric poling at room RT). The accumulation of Li⁺ vacancies at the crystal-electrode interface is visualized using in situ optical microscopy. The Li-ionic biased state shows a clear in-plane rectification effect combined with a significant relaxation upon time at RT. Relaxation can be fully suppressed at LTs such as 200 K, and utilizing an electric field cooling, a stable rectification can be achieved at 200 K. The results shed light on the selective control of multifunctionalities such as ferroelasticity, ferroelectricity, and ionic-migration-mediated effects (a memristor effect and rectification) in a single-phase bulk material utilizing, for example, different directions, temperatures, frequencies, and magnitudes of electric field.

Nucleobase-Bonded Graphene Nanoribbon Junctions: Electron Transport from First Principles

Carbon and hydrogen bonding constitute the backbone of life; in the form of graphene, possibly functionalized by DNA nucleobases, these hold promise for the programmable assembly of graphene-based nanoelectronic devices. It is still unknown how hydrogen-bonded junctions inherent in such devices will perform as electron transport media. Here, we design nucleobase-bonded graphene nanoribbons and quantify their quantum transport characteristics using first-principles calculations. Pronounced rectifying behavior and negative differential resistance are found, as well as high conductance of certain structures, with the guanine-cytosine junction in general being superior to the adenine-thymine junction. The identified sensitivity of the conductance to atomic details of the interfaces offers initial hints and guidance for experimental realization. The dependence of current on electrostatic gate doping, with an on/off ratio of ∼10², shows the potential of the junction as a field effect transistor.

Atomic-Scale Rectification and Inelastic Electron Tunneling Spectromicroscopy

The phenomenon of rectification describes the emergence of a DC current from the application of an oscillating voltage. Although the origin of this effect has been associated with the nonlinearity in the current-voltage I(V) relation, a rigorous understanding of the microscopic mechanisms for this phenomenon remains challenging. Here, we show the close connection between rectification and inelastic electron tunneling spectroscopy and microscopy for single molecules with a scanning tunneling microscope. While both techniques are based on nonlinear features in the I(V) curve, comprehensive line shape analyses reveal notable differences that highlight the two complementary techniques of nonlinear conductivity spectromicroscopy for probing nanoscale systems.

Unsupervised Domain Adaptive Corner Detection in Vehicle Plate Images

Rectification of vehicle plate images helps to improve the accuracy of license-plate recognition (LPR). It is a perspective-transformation process to project images as if taken from the front geometrically. To obtain the projection matrix, we require the (x, y) coordinates of four corner positions of plates in images. In this paper, we consider the problem of unsupervised domain adaptation for corner detection in plate images. We trained a model with plate images of one country, the source domain, and applied a domain adaptation scheme so that the model is able to work well on the plates of a different country, the target domain. For this study, we created a dataset of 22,096 Korea plate images with corner labels, which are source domain, and 6762 Philippines, which are target domain. To address this problem, we propose a heatmap-based corner-detection model, which outperforms existing scalar-regression methods, and an image classifier for mixed image of source and target images for domain adaptation. The proposed approach achieves better accuracy, which is 19.1% improvement if compared with baseline discriminator-based domain adaptation scheme.

An extracellular scaffolding complex confers unusual rectification upon an ionotropic acetylcholine receptor in C. elegans

Biophysical properties of ligand-gated receptors can be profoundly modified by auxiliary subunits or by the lipid microenvironment of the membrane. Hence, it is sometimes challenging to relate the properties of receptors reconstituted in heterologous expression systems to those of their native counterparts. Here we show that the properties of Caenorhabditis elegans levamisole-sensitive acetylcholine receptors (L-AChRs), the ionotropic acetylcholine receptors targeted by the cholinergic anthelmintic levamisole at neuromuscular junctions, can be profoundly modified by their clustering machinery. We uncovered that L-AChRs exhibit a strong outward rectification in vivo, which was not previously described in heterologous systems. This unusual feature for an ionotropic AChR is abolished by disrupting the interaction of the receptors with the extracellular complex required for their synaptic clustering. When recorded at -60 mV, levamisole-induced currents are similar in the wild type and in L-AChR-clustering-defective mutants, while they are halved in these mutants at more depolarized physiological membrane potentials. Consequently, levamisole causes a strong muscle depolarization in the wild type, which leads to complete inactivation of the voltage-gated calcium channels and to an irreversible flaccid paralysis. In mutants defective for L-AChR clustering, the levamisole-induced depolarization is weaker, allowing voltage-gated calcium channels to remain partially active, which eventually leads to adaptation and survival of the worms. This explains why historical screens for C. elegans mutants resistant to levamisole identified the components of the L-AChR clustering machinery, in addition to proteins required for receptor biosynthesis or efficacy. This work further emphasizes the importance of pursuing ligand-gated channel characterization in their native environment.

Li-Ion Intercalation, Rectification, and Solid Electrolyte Interphase in Molecular Tunnel Junctions

This paper describes Li-ion intercalation into a pyrenyl-terminated self-assembled monolayer (SAM) on gold, inspired by the graphite anode in a Li-ion battery, and its effect on tunneling performance in a molecular junction incorporating the SAM. As the concentration of the Li-ion precursor ([LiPF₆]) increased from 0 to 10^-2 M, the rectification ratio increased to ∼10². Further experiments revealed that the intercalation-induced changes in the orientation of PYR group and in the HOMO energy level account for the enhanced rectification. Treatment with high concentrations of LiPF₆ (from 10^-2 to 10⁰ M) yielded a considerable solid electrolyte interphase (SEI), mainly composed of LiF, on the surface of the SAM, resulting in the disappearance of rectification. This was attributed to renormalization of the HOMO level back to that of the intact SAM, caused by the SEI layer. Our work demonstrates the interplay among Li-ion intercalation, SEI, and tunneling in the molecular junction, benefiting the research of molecular electronics as well as SAM-based batteries.

Asymmetric Chemical Functionalization of Top-Contact Electrodes: Tuning the Charge Injection for High-Performance MoS2 Field-Effect Transistors and Schottky Diodes

The fabrication of high-performance (opto-)electronic devices based on 2D channel materials requires the optimization of the charge injection at electrode-semiconductor interfaces. While chemical functionalization with chemisorbed self-assembled monolayers has been extensively exploited to adjust the work function of metallic electrodes in bottom-contact devices, such a strategy has not been demonstrated for the top-contact configuration, despite the latter being known to offer enhanced charge-injection characteristics. Here, a novel contact engineering method is developed to functionalize gold electrodes in top-contact field-effect transistors (FETs) via the transfer of chemically pre-modified electrodes. The source and drain Au electrodes of the molybdenum disulfide (MoS₂ ) FETs are functionalized with thiolated molecules possessing different dipole moments. While the modification of the electrodes with electron-donating molecules yields a marked improvement of device performance, the asymmetric functionalization of the source and drain electrodes with different molecules with opposed dipole moment enables the fabrication of a high-performance Schottky diode with a rectification ratio of ≈10³ . This unprecedented strategy to tune the charge injection in top-contact MoS₂ FETs is of general applicability for the fabrication of high-performance (opto-)electronic devices, in which asymmetric charge injection is required, enabling tailoring of the device characteristics on demand.

Intrinsic Sources and Functional Impacts of Asymmetry at Electrical Synapses

Electrical synapses couple inhibitory neurons across the brain, underlying a variety of functions that are modifiable by activity. Despite recent advances, many functions and contributions of electrical synapses within neural circuitry remain underappreciated. Among these are the sources and impacts of electrical synapse asymmetry. Using multi-compartmental models of neurons coupled through dendritic electrical synapses, we investigated intrinsic factors that contribute to effective synaptic asymmetry and that result in modulation of spike timing and synchrony between coupled cells. We show that electrical synapse location along a dendrite, input resistance, internal dendritic resistance, or directional conduction of the electrical synapse itself each alter asymmetry as measured by coupling between cell somas. Conversely, we note that asymmetrical gap junction (GJ) conductance can be masked by each of these properties. Furthermore, we show that asymmetry modulates spike timing and latency of coupled cells by up to tens of milliseconds, depending on direction of conduction or dendritic location of the electrical synapse. Coordination of rhythmic activity between two cells also depends on asymmetry. These simulations illustrate that causes of asymmetry are diverse, may not be apparent in somatic measurements of electrical coupling, influence dendritic processing, and produce a variety of outcomes on spiking and synchrony of coupled cells. Our findings highlight aspects of electrical synapses that should always be included in experimental demonstrations of coupling, and when assembling simulated networks containing electrical synapses.

Geometric Tailoring of Macroscale Ti3C2Tx MXene Lamellar Membrane for Logic Gate Circuits

Constructing nanofluidic diode nanochannels with an asymmetric structure for logic gate circuits has attracted extensive research interests. Currently, the preparation of a geometrically asymmetric nanochannel relies on cost-effective material-processing methods and has been hard to scale up, limiting the development of nanofluidic research. Herein, we introduce the idea of geometric tailoring to cut the MXene lamellar membrane in different shapes and investigate the ion transport behavior systematically. The ion rectification can be regulated by adjusting geometric factors such as the asymmetric ratio and height of the trapezoidal membrane. On the basis of the above-mentioned research on rectification characteristics, we further optimized the trapezoidal membrane into a triangular membrane on the macroscopic level and successfully applied it to logic circuits, realizing the logic operations of "AND" and "OR". It is worth mentioning that the shape of a macrocut triangular membrane is exactly the same as the symbol of an electronic diode, and the conduction and cutoff directions of the ionic current are also exactly the same as those of electronic diodes. Our finding provides a facile and general strategy for fabricating a macroscale geometric asymmetry nanochannel-based two-dimensional lamellar membrane and shows the potential applications in complex highly integrated ionic circuits.

Bio-inspired Track-Etched Polymeric Nanochannels: Steady-State Biosensors for Detection of Analytes

Bio-inspired polymeric nanochannel (also referred as nanopore)-based biosensors have attracted considerable attention on account of their controllable channel size and shape, multi-functional surface chemistry, unique ionic transport properties, and good robustness for applications. There are already very informative reviews on the latest developments in solid-state artificial nanochannel-based biosensors, however, which concentrated on the resistive-pulse sensing-based sensors for practical applications. The steady-state sensing-based nanochannel biosensors, in principle, have significant advantages over their counterparts in term of high sensitivity, fast response, target analytes with no size limit, and extensive suitable range. Furthermore, among the diverse materials, nanochannels based on polymeric materials perform outstandingly, due to flexible fabrication and wide application. This compressive Review summarizes the recent advances in bio-inspired polymeric nanochannels as sensing platforms for detection of important analytes in living organisms, to meet the high demand for high-performance biosensors for analysis of target analytes, and the potential for development of smart sensing devices. In the future, research efforts can be focused on transport mechanisms in the field of steady-state or resistive-pulse nanochannel-based sensors and on developing precisely size-controlled, robust, miniature and reusable, multi-functional, and high-throughput biosensors for practical applications. Future efforts should aim at a deeper understanding of the principles at the molecular level and incorporating these diverse pore architectures into homogeneous and defect-free multi-channel membrane systems. With the rapid advancement of nanoscience and biotechnology, we believe that many more achievements in nanochannel-based biosensors could be achieved in the near future, serving people in a better way.

A Deep Learning Based Approach for Localization and Recognition of Pakistani Vehicle License Plates

License plate localization is the process of finding the license plate area and drawing a bounding box around it, while recognition is the process of identifying the text within the bounding box. The current state-of-the-art license plate localization and recognition approaches require license plates of standard size, style, fonts, and colors. Unfortunately, in Pakistan, license plates are non-standard and vary in terms of the characteristics mentioned above. This paper presents a deep-learning-based approach to localize and recognize Pakistani license plates with non-uniform and non-standardized sizes, fonts, and styles. We developed a new Pakistani license plate dataset (PLPD) to train and evaluate the proposed model. We conducted extensive experiments to compare the accuracy of the proposed approach with existing techniques. The results show that the proposed method outperformed the other methods to localize and recognize non-standard license plates.

"Ion Pool" Structural Ion Storage Device: A New Strategy to Collect Ions by Nanoconfinement Effects

Ion storage structure widely exists in organisms, which is used to harvesting energy in environment and converting it into ion concentration gradient to maintain complex life activities. The construction of ion storage structures relies on isolating the biological body fluids by biofilm systems, which can also be regarded as local ions confinement. Mimicking this ions storage process, an "ion pool" structural ion storage device is proposed in this research by artificial ion nanochannels, which can transform the electric power into ion concentration gradient. It is consisted of micrometer-sized ions reservoir and nanosized ions filters. Ions can be isolated within the "pool" and performed ultrahigh ions enrichment or depletion behavior deviated from bulk. Through numerical simulation by Poisson-Nernst-Planck equations, "ion pool" structural device achieves nearly 20 000 rectification ratio with low surface charge. An "ion pool" structural ions storage device is also constructed with block copolymer and polyethylene terephthalate composite membranes, a super high rectification ratio of 3184.0 is achieved from the experiment, which is the highest reported so far. The ion storage efficiency of the device reaches 14.90%, which is an order of magnitude better than non-"ion pool" structural nanofluid devices.

Construction of Supercapacitor-Based Ionic Diodes with Adjustable Bias Directions by Using Poly(ionic liquid) Electrolytes

The newly emerging supercapacitor-diode (CAPode), integrating the characteristics of a diode into an electrical-double-layer capacitor, can be employed to extend conventional supercapacitors to new technological applications and may play a crucial role in grid stabilization, signal propagation, and logic operations. However, the reported CAPodes have only been able to realize charge storage in the positive-bias direction. Here, bias-direction-adjustable CAPodes realized by using a polycation-based ionic liquid (IL) or a polyanion-based IL as electrolyte in an asymmetric carbon-based supercapacitor architecture are proposed. The resulting CAPodes exhibit charge-storage function at only the positive- or negative-bias direction with a high rectification ratio (≈80% for rectification ratio II, RR_II ) and an outstanding cycling life (4500 cycles), representing a crucial breakthrough for designing high-performance capacitive ionic diodes.

Analysis of Parameters of a Rectified Tank on the Basis of In-Situ Tests

The vertical deflection of building structures is a common problem. However, the rectification of objects is rarely carried out due to the lack of information about the parameters of objects requiring rectification. The subject of the analysis are parameters of rectified water tank 950 m³ in volume, which were investigated due to the stiffness and number of supports built into the structure. During in-situ testing, the stiffnesses of supports were determined. The model of the rectified structure was then defined and it was shown that its parameters can be described by means of three matrices: stiffness, displacement forms of the elevated object and displacement forms of supports. Absolute values of elements of the stiffness matrix increased as the stiffness and number of supports increased. At the same time, values of elements of the matrix of displacement forms of the elevated object increased. The conducted energy analysis demonstrated that the amount of energy required for the vertical displacement of the structure decreased with an increasing stiffness and number of supports. This means that placing a greater number of supports under rectified structures and ensuring more rigid supports is beneficial to the rectification. Results of the conducted analyses were confirmed during in-situ tests.

Inverted Ion Current Rectification-Based Chemical Delivery Probes for Stimulation of Neurons

Ion current rectification (ICR), diodelike behavior in surface-charged nanopores, shows promise in the design of delivery probes for manipulation of neural networks as it can solve diffusive leakages that might be critical in clinical and research applications. However, it has not been achieved because ICR has restrictions in nanosized dimension and low electrolyte concentration, and rectification direction is inappropriate for delivery. Herein, we present a polyelectrolyte gel-filled (PGF) micropipette harnessing inverted ICR as a delivery probe, which quantitatively transports glutamate to stimulate primary cultured neurons with high efficiency while minimizing leakages. Since the gel works as an ensemble of numerous surface-charged nanopores, the current is rectified in the micro-opening and physiological environment. By extending the charge-selective region using the gel, inverted ICR is generated, which drives outward deliveries of major charge carriers. This study will help in exploring new aspects of ICR and broaden its applications for advanced chemical delivery.

Bipolar Nanochannels: A Systematic Approach to Asymmetric Problems

Nanofluidic diodes are capable of rectifying the electrical current by several orders of magnitude. In the current state of affairs, determining the rectification factor is not possible as it depends on many system parameters. In this work, we systematically scan the effects of geometry and excess counterion concentrations (i.e., surface charge effects). We show that the current-voltage response varies between the two extreme behaviors of unipolar and bipolar responses. The exact behavior depends on the geometry and surface charge properties of the system. Here, we have gone beyond the typical setup that only considers the dynamics within the nanochannel itself and we have included the effects of the adjoining microchannels. Systems that include both nanochannels and microchannels exhibit the classical signatures of concentration polarization, such as ionic depletion and enrichment. Here, where we have scanned a wide range of parameters, we show that bipolar and semi-bipolar systems exhibit a wider range of phenomena that are intrinsically more complicated. Our system characterization is for both, the much more investigated case of steady state and the less investigated, but equally interesting, time-transient case. For example, it is common to characterize the system by its steady-state result (current-voltage response, rectification factor, and transport number). Here, we demonstrate that the time-transient behavior of the fluxes can also be used to characterize the system, and that the time-dependent rectification factors and transport numbers are meaningful. The systematic approach taken in this work, and the results presented herein, can be used to further elucidate the complicated behavior of the current-voltage response of nanofluidic diodes and to rationalize experimental results. The insights of this work can be used to enhance and improve the design of all nanofluidic diodes.

Electrografting of Carbon Surfaces with Aliphatic Chains and its Effect on the Rectification of Ferrocene as Redox Probe in Solution

The mediated oxidation of acetate and octanoate ions in acetonitrile was used to covalently modify carbon surfaces with films bearing saturated aliphatic chains of different length. Film thickness increases proportionally with the length of the aliphatic chain within the carboxylate precursor. The thickest film was obtained from octanoate oxidation and rectification occurs when ferrocene is used as redox probe in acetonitrile solution. This effect increases with the bulky and hydrophobic nature of the supporting electrolyte cations; n-Hx₄ N⁺ >n-Bu₄ N⁺ >Me₄ N⁺ . The combination of the bulky and hydrophobic properties of the supporting electrolyte ions as well as the hydrophobic properties of the electrografted films is the basis of rectification of ferrocene in cyclic voltammetry experiments. This phenomenon was simulated through a CEC mechanism in solution, where the mass transport inside the film channels was emulated through single chemical equilibria.

Non-linear Conductance, Rectification, and Mechanosensitive Channel Formation of Lipid Membranes

There is mounting evidence that lipid bilayers display conductive properties. However, when interpreting the electrical response of biological membranes to voltage changes, they are commonly considered as inert insulators. Lipid bilayers under voltage-clamp conditions display current traces with discrete conduction-steps, which are indistinguishable from those attributed to the presence of protein channels. In current-voltage (I-V) plots they may also display outward rectification, i.e., voltage-gating. Surprisingly, this has even been observed in chemically symmetric lipid bilayers. Here, we investigate this phenomenon using a theoretical framework that models the electrostrictive effect of voltage on lipid membranes in the presence of a spontaneous polarization, which can be recognized by a voltage offset in electrical measurements. It can arise from an asymmetry of the membrane, for example from a non-zero spontaneous curvature of the membrane. This curvature can be caused by voltage via the flexoelectric effect, or by hydrostatic pressure differences across the membrane. Here, we describe I-V relations for lipid membranes formed at the tip of patch pipettes situated close to an aqueous surface. We measured at different depths relative to air/water surface, resulting in different pressure gradients across the membrane. Both linear and non-linear I-V profiles were observed. Non-linear conduction consistently takes the form of outward rectified currents. We explain the conductance properties by two mechanisms: One leak current with constant conductance without pores, and a second process that is due to voltage-gated pore opening correlating with the appearance of channel-like conduction steps. In some instances, these non-linear I-V relations display a voltage regime in which dI/dV is negative. This has also been previously observed in the presence of sodium channels. Experiments at different depths reveal channel formation that depends on pressure gradients. Therefore, we find that the channels in the lipid membrane are both voltage-gated and mechanosensitive. We also report measurements on black lipid membranes that also display rectification. In contrast to the patch experiments they are always symmetric and do not display a voltage offset.

Tunable Nanopore Arrays as the Basis for Ionic Circuits

There has been considerable interest in preparing ionic circuits capable of manipulating ionic and molecular transport in a solution. This direction of research is inspired by biological systems where multiple pores with different functionalities embedded in a cell membrane transmit external signals and underlie all physiological processes. In this manuscript, we describe the modeling of ion transport through small arrays of nanopores consisting of 3, 6, and 9 nanopores and an integrated gate electrode placed on the membrane surface next to one pore opening. We show that by tuning the gate voltage and strategically placing nanopores with nonlinear current-voltage characteristics, the local signal at the gate affects ionic transport through all nanopores in the array. Conditions were identified when the same gate voltage induced opposite rectification properties of neighboring nanopores. We also demonstrate that an ionic diode embedded in a nanopore array can modulate transport properties of neighboring pores even without a gate voltage. The results are explained by the role of concentration polarization and overlapping depletion zones on one side of the membrane. The modeling presented here is intended to become an inspiration to future experiments to create nanopore arrays that can transduce signals in space and time.

2D-MoS2/BMN Ceramic Hybrid Structure Flexible TFTs with Tunable Device Properties

Two-dimensional (2D) layered semiconductor materials have emerged as prospective channel materials in flexible thin-film field effect transistors (TFTs) recently because of their unique electrical and mechanical characteristics. Meanwhile, high-quality ceramics, with outstanding dielectric property and fabrication process compatible with low-cost flexible substrates, have become one of the best candidates of gate dielectric layers in flexible TFTs. In this work, 2D MoS₂ and dielectric ceramic Bi₂MgNb₂O₉ (BMN) were utilized to fabricate flexible TFTs on low-cost polyethylene terephthalate substrates. The MoS₂/BMN hybrid structure exhibited good quality by Raman, X-ray photoelectron spectroscopy, and atomic force microscopy characterizations. In addition, the flexible MoS₂/BMN TFTs indicated good performances with a small gate voltage. More importantly, with the modulation of gate voltage, the flexible TFTs surprisingly exhibited three different device types, that is, multilayer MoS₂/BMN n-type TFT (device type 1), homojunction MoS₂/BMN TFT (device type 2), and thick MoS₂/BMN p-type TFT (device type 3). In particular, with different bias conditions, the homojunction TFT showed bipolarity of transfer characteristics and forward/backward rectifications of output characteristics similar to p-n/n-n junctions. The high dielectric constant and high quality of the BMN ceramic layer enabled the gate to effectively modulate these different structures of MoS₂ channels. The operation mechanisms of these three types of flexible TFTs were investigated. Additionally, the flexible MoS₂/BMN TFTs showed good flexibility and performance stability with external strains. The results prove the great potential of integration of 2D materials, high-quality dielectric ceramics, and low-cost plastic substrates for high-performance flexible TFTs and further applications of flexible electronics.

Optimized rectification of fiber orientation density function

PURPOSE

To demonstrate an optimized rectification strategy for fiber orientation density functions (fODFs).

THEORY AND METHODS

In white matter, fODFs can be estimated with diffusion MRI. However, because of signal noise, imaging artifacts and other factors, experimentally determined fODFs may take on unphysical negative values in some directions. Here, we show how to rectify such fODFs to eliminate all negative values while minimizing the mean square difference between the original and rectified fODFs. The method is demonstrated for a mathematical model and for fODFs estimated from experimental human data using both constrained spherical deconvolution and fiber ball imaging. Comparison with an alternative nonoptimized rectification approach is also provided.

RESULTS

For the mathematical model, it is found that the optimized rectification procedure removes negative fODF values while at the same time reducing the mean square error. Relative to the alternative rectification approach, the optimized fODFs are substantially more accurate. For the experimental data, the optimized fODFs have a lower average fractional anisotropy axonal and often fewer small peaks than the original, unrectified fODFs. The calculation of optimized fODFs is straightforward where the main step is the finding of the root to an equation in one variable, as may be efficiently accomplished with the bisection method.

CONCLUSION

Unphysical negative fODF values can be easily eliminated in a manner that minimizes the mean square difference between the original and rectified fODFs. Optimized fODF rectification may be useful in applications for which negative values are problematic.

Quantitative 3D Reconstruction from Scanning Electron Microscope Images Based on Affine Camera Models

Scanning electron microscopes (SEMs) are versatile imaging devices for the micro- and nanoscale that find application in various disciplines such as the characterization of biological, mineral or mechanical specimen. Even though the specimen’s two-dimensional (2D) properties are provided by the acquired images, detailed morphological characterizations require knowledge about the three-dimensional (3D) surface structure. To overcome this limitation, a reconstruction routine is presented that allows the quantitative depth reconstruction from SEM image sequences. Based on the SEM’s imaging properties that can be well described by an affine camera, the proposed algorithms rely on the use of affine epipolar geometry, self-calibration via factorization and triangulation from dense correspondences. To yield the highest robustness and accuracy, different sub-models of the affine camera are applied to the SEM images and the obtained results are directly compared to confocal laser scanning microscope (CLSM) measurements to identify the ideal parametrization and underlying algorithms. To solve the rectification problem for stereo-pair images of an affine camera so that dense matching algorithms can be applied, existing approaches are adapted and extended to further enhance the yielded results. The evaluations of this study allow to specify the applicability of the affine camera models to SEM images and what accuracies can be expected for reconstruction routines based on self-calibration and dense matching algorithms.

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)₆^4-] caused significant ICR inversion. The ICR inversion mechanism is evidenced to result from the adsorption of Fe(CN)₆^4--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)₆^4- 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.

High-Performance p-BP/n-PdSe2 Near-Infrared Photodiodes with a Fast and Gate-Tunable Photoresponse

Van der Waals heterostructures composed of transition-metal dichalcogenide (TMD) materials have become a remarkable compact system that could offer an innovative architecture for advanced engineering in high-performance energy-harvesting and optoelectronic devices. Here, we report a novel van der Waals (vdW) TMD heterojunction photodiode composed of black phosphorus (p-BP) and palladium diselenide (n-PdSe₂), which establish a high and tunable rectification and photoresponsivity. A high rectification up to ≈7.1 × 10⁵ is achieved, which is successfully tuned by employing the back-gate voltage to the heterostructure devices. Besides, the device significantly shows the high and gate-controlled photoresponsivity of R = 9.6 × 10⁵, 4.53 × 10⁵ and 1.63 × 10⁵ A W^-1 under the influence of light of different wavelengths (λ = 532, 1064, and 1310 nm) in visible and near-infrared regions, respectively, because of interlayer optical transition and low Schottky. The device also demonstrates extraordinary values of detectivity (D = 5.8 × 10¹³ Jones) and external quantum efficiency (EQE ≈ 9.4 × 10⁶), which are an order of magnitude higher than the currently reported values. The effective enhancement of photovoltaic characteristics in visible and infrared regions of this TMD heterostructure-based system has a huge potential in the field of optoelectronics to realize high-performance infrared photodetectors.

Rectification of Mobile Leidenfrost Droplets by Planar Ratchets

The self-transportation of mobile Leidenfrost droplets with well-defined direction and velocity on millimetric ratchets is one of the most representative and spectacular phenomena in droplet dynamics. Despite extensive progress in the ability to control the spatiotemporal propagation of droplets, it remains elusive how the individual ratchet units, as well as the interactions within their arrays, are translated into the collective droplet dynamics. Here, simple planar ratchets characterized by uniform height normal to the surface are designed. It is revealed that on planar ratchets, the transport dynamics of Leidenfrost droplets is dependent not only on individual units, but also on the elegant coordination within their arrays dictated by their topography. The design of planar ratchets enriches the fundamental understanding of how the surface topography is translated into dynamic and collective droplet transport behaviors, and also imparts higher applicability in microelectromechanical system based fluidic devices.

Scalable Electronic Ratchet with Over 10% Rectification Efficiency

Electronic ratchets use a periodic potential with broken inversion symmetry to rectify undirected (electromagnetic, EM) forces and can in principle be a complement to conventional diode-based designs. Unfortunately, ratchet devices reported to date have low or undetermined power conversion efficiencies, hampering applicability. Combining experiments and numerical modeling, field-effect transistor-based ratchets are investigated in which the driving signal is coupled into the accumulation layer via interdigitated finger electrodes that are capacitively coupled to the field effect transistor channel region. The output current-voltage curves of these ratchets can have a fill factor >> 0.25 which is highly favorable for the power output. Experimentally, a maximum power conversion efficiency well over 10% at 5 MHz, which is the highest reported value for an electronic ratchet, is determined. Device simulations indicate this number can be increased further by increasing the device asymmetry. A scaling analysis shows that the frequency range of optimal performance can be scaled to the THz regime, and possibly beyond, while adhering to technologically realistic parameters. Concomitantly, the power output density increases from ≈4 W m-2 to ≈1 MW m-2. Hence, this type of ratchet device can rectify high-frequency EM fields at reasonable efficiencies, potentially paving the way for actual use as energy harvester.

The Removal of Subterranean Stormwater Drain Sumps as Mosquito Breeding Sites in Darwin, Australia

The Northern Territory Top End Health Service, Medical Entomology Section and the City of Darwin council carry out a joint Mosquito Engineering Program targeting the rectification of mosquito breeding sites in the City of Darwin, Northern Territory, Australia. In 2005, an investigation into potential subterranean stormwater breeding sites in the City of Darwin commenced, specifically targeting roadside stormwater side entry pits. There were 79 side entry pits randomly investigated for mosquito breeding in the Darwin suburbs of Nightcliff and Rapid Creek, with 69.6% of the pits containing water holding sumps, and 45.6% of those water holding sumps breeding endemic mosquitoes. Culex quinquefasciatus was the most common mosquito collected, accounting for 73% of all mosquito identifications, with the potential vector mosquito Aedes notoscriptus also recovered from a small number of sumps. The sumps were also considered potential dry season maintenance breeding sites for important exotic Aedes mosquitoes such as Aedes aegypti and Aedes albopictus, which are potential vectors of dengue, chickungunya and Zika virus. Overall, 1229 side entry pits were inspected in ten Darwin suburbs from 2005 to 2008, with 180 water holding sumps identified and rectified by concrete filling.

[Detection and Rectification of Radiation Emission from Medical Laser Equipment]

By introducing the unqualified cases of radiation emission test of medical laser equipment, this paper analyses the causes of the problems and the corrective measures adopted, and analyses the effectiveness of the corrective measures. It is proposed that the design rules and rules related to radiation emission should be mastered from the input stage of product design and development, and the radiation emission problem should be considered and solved as soon as possible.

Putative interaction site for membrane phospholipids controls activation of TRPA1 channel at physiological membrane potentials

The transient receptor potential ankyrin 1 (TRPA1) channel is a polymodal sensor of environmental irritant compounds, endogenous proalgesic agents, and cold. Upon activation, TRPA1 channels increase cellular calcium levels via direct permeation and trigger signaling pathways that hydrolyze phosphatidylinositol-4,5-bisphosphate (PIP₂ ) in the inner membrane leaflet. Our objective was to determine the extent to which a putative PIP₂ -interaction site (Y1006-Q1031) is involved in TRPA1 regulation. The interactions of two specific peptides (L992-N1008 and T1003-P1034) with model lipid membranes were characterized by biophysical approaches to obtain information about affinity, peptide secondary structure, and peptide effect in the lipid organization. The results indicate that the two peptides interact with lipid membranes only if PIP₂ is present and their affinities depend on the presence of calcium. Using whole-cell electrophysiology, we demonstrate that mutation at F1020 produced channels with faster activation kinetics and with a rightward shifted voltage-dependent activation curve by altering the allosteric constant that couples voltage sensing to pore opening. We assert that the presence of PIP₂ is essential for the interaction of the two peptide sequences with the lipid membrane. The putative phosphoinositide-interacting domain comprising the highly conserved F1020 contributes to the stabilization of the TRPA1 channel gate.

Atomic-Scale Fluidic Diodes Based on Triangular Nanopores in Bilayer Hexagonal Boron Nitride

Nanofluidic diodes based on nanochannels have been studied theoretically and experimentally for applications such as biosensors and logic gates. However, when analyzing attoliter-scale samples or enabling high-density integration of lab-on-a-chip devices, it is beneficial to miniaturize the size of a nanofluidic channel. Using molecular dynamics simulations, we investigate conductance of nanopores in bilayer hexagonal boron nitride (h-BN). Remarkably, we found that triangular nanopores possess excellent rectifications of ionic currents while hexagonal ones do not. It is worth highlighting that the pore length is only about 0.7 nm, which is about the atomic limit for a bipolar diode. We determined scaling relations between ionic currents I and pore sizes L for small nanopores, that are I ∼ L¹ in a forward biasing voltage and I ∼ L² in a reverse biasing voltage. Simulation results qualitatively agree with analytical ones derived from the one-dimensional Poisson-Nerst-Planck equations.

Molecularly Controlled Stark Effect Induces Significant Rectification in Polycyclic-Aromatic-Hydrocarbon-Terminated n-Alkanethiolates

The variation of the electronic structure of individual molecules as a function of the applied bias matters for the performance of molecular and organic electronic devices. Understanding the structure-electric-field relationship, however, remains a challenge because of the lack of in-operando spectroscopic technique and complexity arising from the ill-defined on-surface structure of molecules and organic-electrode interfaces within devices. We report that a reliable and reproducible molecular diode can be achieved by control of the conjugation length in polycyclic-aromatic-hydrocarbon (PAH)-terminated n-alkanethiolate (denoted as SC₁₁PAH), incorporated into liquid-metal-based large-area tunnel junctions in the form of a self-assembled monolayer. By taking advantage of the structural simplicity and tunability of SC₁₁PAH and the high-yielding feature of the junction technique, we demonstrate that the increase in the conjugation length of the PAH terminal group leads to a significant rectification ratio up to ∼1.7 × 10² at ±740 mV. Further study suggests that the Stark shift of the molecular energy resonance of the PAH breaks the symmetry of the energy topography across the junction and induces rectification in a temperature-independent charge-transport regime.

Solution-Processed Ion-Free Organic Ratchets with Asymmetric Contacts

Ion-free organic ratchets with asymmetric injecting contacts (AICs) are fabricated using solution-processable organic semiconductors. Scanning Kelvin probe microscopy analysis reveals that the rectifying function is achieved via the "charge pump" mechanism. Electrical characterizations show that the device can readily operate under industrial standard radio frequency and its high-frequency performance may be enhanced through further material/device engineering. The built-in asymmetric feature exempts the devices from the complicated material design, device processing, and performance decay associated with the use of ion/semiconductor blends in ionic-organic ratchets. Thus, the AIC ratchets can deliver a persisting ratchet effect and have excellent material compatibility toward organic semiconductors.

High-Performance Two-Dimensional Schottky Diodes Utilizing Chemical Vapour Deposition-Grown Graphene-MoS2 Heterojunctions

Heterostructures based on two-dimensional (2D) materials have attracted enormous interest as they display unique functionalities and have potential to be applied in next-generation electronics. In this report, we fabricated three types of heterostructures based on chemical vapor deposition-grown graphene and MoS₂. A significant rectification was observed in the Au-MoS₂-Gr heterojunction, with a rectification ratio over 2 × 10⁴. The rectifying behavior is reproducible among nearly all 44 devices and is attributed to an asymmetrical Schottky barrier at Au-MoS₂ and MoS₂-graphene contacts. This rectification can be tuned by external gating and laser illumination, which have different impact on the rectifying ratio. This modulation of the Schottky barrier is evidenced by output characteristics of two symmetrical heterostructures: Au-MoS₂-Au and Gr-MoS₂-Gr field-effect transistors. The effective heights of MoS₂-graphene and MoS₂-Au Schottky barriers and their response to back-gate voltage and laser irradiation were extracted from output characteristics of Au-MoS₂-Au and Gr-MoS₂-Gr field-effect transistors. The tuned Schottky barriers could be explained by the Fermi level change of graphene and MoS₂. These results contributed to our understanding of 2D heterostructures and have potential applications in novel electronics and optoelectronics.

A thermodynamic description for physiological transmembrane transport

A general formulation for both passive and active transmembrane transport is derived from basic thermodynamical principles. The derivation takes into account the energy required for the motion of molecules across membranes and includes the possibility of modeling asymmetric flow. Transmembrane currents can then be described by the general model in the case of electrogenic flow. As it is desirable in new models, it is possible to derive other well-known expressions for transmembrane currents as particular cases of the general formulation. For instance, the conductance-based formulation for current turns out to be a linear approximation of the general formula for current. Also, under suitable assumptions, other formulas for current based on electrodiffusion, like the constant field approximation by Goldman, can be recovered from the general formulation. The applicability of the general formulations is illustrated first with fits to existing data, and after, with models of transmembrane potential dynamics for pacemaking cardiocytes and neurons. The general formulations presented here provide a common ground for the biophysical study of physiological phenomena that depend on transmembrane transport.

Directional coupling of oligodendrocyte connexin-47 and astrocyte connexin-43 gap junctions

Intercellular communication via gap junction channels between oligodendrocytes and between astrocytes as well as between these cell types is essential to maintain the integrity of myelin in the central nervous system. Oligodendrocyte gap junction connexin-47 (Cx47) is a key element in this crosstalk and indeed, mutations in human Cx47 cause severe myelin disorders. However, the permeation properties of channels of Cx47 alone and in heterotypic combination with astrocyte Cx43 remain unclear. We show here that Cx47 contains three extra residues at 5' amino-terminus that play a critical role in the channel pore structure and account for relative low ionic conductivity, cationic permselectivity and voltage-gating properties of oligodendrocyte-oligodendrocyte Cx47 channels. Regarding oligodendrocyte-astrocyte coupling, heterotypic channels formed by Cx47 with Cx43 exhibit ionic and chemical rectification, which creates a directional diffusion barrier for the movement of ions and larger negatively charged molecules from cells expressing Cx47 to those with Cx43. The restrictive permeability of Cx47 channels and the diffusion barrier of Cx47-Cx43 channels was abolished by a mutation associated with leukodystrophy, the Cx47P90S, suggesting a novel pathogenic mechanism underlying myelin disorders that involves alterations in the panglial permeation.

Synaptic Transfer between Rod and Cone Pathways Mediated by AII Amacrine Cells in the Mouse Retina

To understand computation in a neural circuit requires a complete synaptic connectivity map and a thorough grasp of the information-processing tasks performed by the circuit. Here, we dissect a microcircuit in the mouse retina in which scotopic visual information (i.e., single photon events, luminance, contrast) is encoded by rod bipolar cells (RBCs) and distributed to parallel ON and OFF cone bipolar cell (CBC) circuits via the AII amacrine cell, an inhibitory interneuron. Serial block-face electron microscopy (SBEM) reconstructions indicate that AIIs preferentially connect to one OFF CBC subtype (CBC2); paired whole-cell patch-clamp recordings demonstrate that, depending on the level of network activation, AIIs transmit distinct components of synaptic input from single RBCs to downstream ON and OFF CBCs. These findings highlight specific synaptic and circuit-level features that allow intermediate neurons (e.g., AIIs) within a microcircuit to filter and propagate information to downstream neurons.

Distinguishing Interface Magnetoresistance and Bulk Magnetoresistance through Rectification of Schottky Heterojunctions

High performance of many spintronic devices strongly depends on the spin-polarized electrical transport, especially the magnetoresistance (MR) in magnetic heterojunctions. However, it has been a great challenge to distinguish the bulk MR and interface MR by transport measurements because the bulk resistance and interface resistance formed a series circuit in magnetic heterojunctions. Here, a unique interface-sensitive rectification MR method is proposed to distinguish the interface MR and bulk MR of nonmagnetic In/GeO _x/n-Ge and magnetic Co/GeO _x/n-Ge diode-like heterojunctions. It is demonstrated that the low-field "butterfly" hysteresis loop observed only in the conventional MR curve originates from the anisotropic MR of ferromagnetic bulk Co layer, whereas the orbit-related large nonsaturating positive MR contains contributions from both the Schottky interface and bulk Ge substrate. This rectification MR method could be extended to magnetic heterojunctions with asymmetric potential barriers to realize a deeper understanding of the fundamental interface-related functionalities.