Hydrogenated cove-edge aluminum nitride nanoribbons for ultrascaled resonant tunneling diode applications: a computational DFT study.

While synthesizing quasi-one-dimensional nanoribbons, there is a finite probability that edges have cove-edge defects. This paper focuses on the structural, electronic, and transport properties of cove-edge aluminum nitride nanoribbons (AlNNR) using density functional theory and the non-equilibrium Green's function (NEGF) method. The cove-edge AlNNRs are thermodynamically stable and exhibit metallic behavior. Interestingly, the calculated current-voltage characteristics of the cove-edge AlNNR-based nanodevices show negative differential resistance (NDR). The H-AlN-Cove nanodevice exhibits high peak-to-valley current ratio (PVCR) of the order of 107. The calculated PVCR of the H-AlN-Cove nanodevice is 106times higher than that of the silicene nanoribbon (SiNR) and graphene nanoribbon (GNR), and 104times higher than that of the phosphorene nanoribbon (PNR) and arsenene nanoribbons (ANR)-based devices respectively. The NDR feature with high PVCR provides a prospect for the cove-edge AlNNR in nanodevice applications.

Research on Electro-Optical Characteristics of Infrared Detectors with HgCdTe Operating at Room Temperature.

This paper presents a thorough analysis of the current-voltage characteristics of uncooled HgCdTe detectors optimized for different spectral ranges. HgCdTe heterostructures were grown by means of metal-organic chemical vapor deposition (MOCVD) on GaAs substrates. The obtained detector structures were measured using a Keysight B1500A semiconductor device analyser controlled via LabVIEW for automation. The experimental characteristics were compared with numerical calculations performed using the commercial platform SimuAPSYS (Crosslight). SimuAPSYS supports detector design and allows one to understand different mechanisms occurring in the analysed structures. The dark current density experimental data were compared with theoretical results at a temperature of 300 K for short, medium, and long wavelength infrared ranges. The dark current density of detectors optimized for different wavelengths was determined using various generation-recombination mechanisms. Proper matching between experimental and theoretical data was obtained by shifting the Shockley-Read-Hall carrier lifetime and the Auger-1 and Auger-7 recombination rates. Exemplary spectral responses were also discussed, giving a better insight into detector performance. The matching level was proven with a theoretical evaluation of the zero-bias dynamic resistance-area product (R0A) and the current responsivity of the designed detectors.

A Novel Extraction Procedure of Contact Characteristic Parameters from Current-Voltage Curves in CdZnTe and CdTe Detectors.

The estimation of the characteristic parameters of the electrical contacts in CdZnTe and CdTe detectors is related to the identification of the main transport mechanisms dominating the currents. These investigations are typically approached by modelling the current-voltage (I-V) curves with the interfacial layer-thermionic-diffusion (ITD) theory, which incorporates the thermionic emission, diffusion and interfacial layer theories into a single theory. The implementation of the ITD model in measured I-V curves is a critical procedure, requiring dedicated simplifications, several best fitting parameters and the identification of the voltage range where each transport mechanism dominates. In this work, we will present a novel method allowing through a simple procedure the estimation of some characteristic parameters of the metal-semiconductor interface in CdZnTe and CdTe detectors. The barrier height and the effects of the interfacial layer will be evaluated through the application of a new function related to the differentiation of the experimental I-V curves.

Effects of Charge Compensation on Colossal Permittivity and Electrical Properties of Grain Boundary of CaCu3Ti4O12 Ceramics Substituted by Al3+ and Ta5+/Nb5.

The effects of charge compensation on dielectric and electrical properties of CaCu3Ti4-x(Al1/2Ta1/4Nb1/4)xO12 ceramics (x = 0-0.05) prepared by a solid-state reaction method were studied based on the configuration of defect dipoles. A single phase of CaCu3Ti4O12 was observed in all ceramics with a slight change in lattice parameters. The mean grain size of CaCu3Ti4-x(Al1/2Ta1/4Nb1/4)xO12 ceramics was slightly smaller than that of the undoped ceramic. The dielectric loss tangent can be reduced by a factor of 13 (tanδ ~0.017), while the dielectric permittivity was higher than 104 over a wide frequency range. Impedance spectroscopy showed that the significant decrease in tanδ was attributed to the highly increased resistance of the grain boundary by two orders of magnitude. The DFT calculation showed that the preferential sites of Al and Nb/Ta were closed together in the Ti sites, forming self-charge compensation, and resulting in the enhanced potential barrier height at the grain boundary. Therefore, the improved dielectric properties of CaCu3Ti4-x(Al1/2Ta1/4Nb1/4)xO12 ceramics associated with the enhanced electrical properties of grain boundaries. In addition, the non-Ohmic properties were also improved. Characterization of the grain boundaries under a DC bias showed the reduction of potential barrier height at the grain boundary. The overall results indicated that the origin of the colossal dielectric properties was caused by the internal barrier layer capacitor structure, in which the Schottky barriers at the grain boundaries were formed.

Flexible Polymer-Organic Solar Cells Based on P3HT:PCBM Bulk Heterojunction Active Layer Constructed under Environmental Conditions.

In this study, some crucial parameters were determined of flexible polymer-organic solar cells prepared from an active layer blend of poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) mixed in 1:1 mass ratio and deposited from chlorobenzene solution by spin-coating on poly(ethylene terephthalate) (PET)/ITO substrates. Additionally, the positive effect of an electron transport layer (ETL) prepared from zinc oxide nanoparticles (ZnO np) on flexible photovoltaic elements' performance and stability was investigated. Test devices with above normal architecture and silver back electrodes deposed by magnetron sputtering were constructed under environmental conditions. They were characterized by current-voltage (I-V) measurements, quantum efficiency, impedance spectroscopy, surface morphology, and time-degradation experiments. The control over morphology of active layer thin film was achieved by post-deposition thermal treatment at temperatures of 110-120 °C, which led to optimization of device morphology and electrical parameters. The impedance spectroscopy results of flexible photovoltaic elements were fitted using two R||CPE circuits in series. Polymer-organic solar cells prepared on plastic substrates showed comparable current-voltage characteristics and structural properties but need further device stability improvement according to traditionally constructed cells on glass substrates.

Characteristics Comparison of Neon, Argon, and Krypton Ion Emissions from Gas Field Ionization Sources with a Single-Atom Tip.

A scanning ion beam instrument equipped with a gas field ionization source (GFIS) has been commercialized, but only helium and neon are currently available as GFISs. In this study, the characteristics of neon, argon, and krypton ion emissions from a single-atom tip are compared, specifically for faster fabrication by milling of a silicon sample. Although the boiling point of argon is about 87 K, our experiments on characterizing argon ion emission can be carried out at temperatures of about 50 K at an argon gas pressure lower than 0.1 Pa. Argon exhibits ion current characteristics, as a function of tip voltage, between those of neon and krypton. The value obtained by multiplying the ion emission current by the sputtering yield is suitable for a figure of merit (FOM) for faster fabrication. The FOM for argon is the highest among the three ion species. This value must be extensively evaluated from the viewpoint of practical nano-fabrication application. The instabilities of neon, argon, and krypton ion currents (3σ) become as low as 8% in 1 h, which is sufficient for fabrication applications. We conclude that an argon or krypton GFIS ion beam instrument will be a useful tool for nano-fabrication.

Current-Induced Concentration Polarization of Nanoporous Media: Role of Electroosmosis.

Current-induced concentration polarization of nanoporous media is explored theoretically by using approach of local thermodynamic equilibrium within nanopore cross-sections. The problem is solved in quadratures in terms of irreversible thermodynamics. The phenomenological coefficients are further specified by using capillary space-charge model for straight slit-like and cylindrical capillaries. This analysis reveals several novel features of current-induced concentration polarization related to the (electro)osmotic volume transfer. It confirms the previous finding that volume transfer can suppress the limiting-current phenomena but obtains more accurate criteria for this. In particular, it shows that the critical nanopore size and/or electrolyte concentration depend on the nanoporous-medium relative thickness. Under no-limiting-current conditions, the salt concentration at the interface between nanoporous medium and unstirred layer is a nonmonotone function of current density. This gives rise to unconventional current-voltage characteristics. Moreover, under certain conditions, the analysis predicts the existence of ranges of "prohibited" current densities where the problem does not have 1D stationary solution, which could give rise to a kind of "phase separation" with coexisting zones of different local current densities corresponding to the same voltage. Besides the advanced understanding of current-induced concentration polarization of nanoporous media, this analysis provides guidelines for the optimization of sample preconcentration systems in (bio)chemical microanalysis.

Membrane Position Dependency of the pKa and Conductivity of the Protein Ion Channel.

The dependency of current-voltage characteristics of the α-hemolysin channel on the channel position within the membrane was studied using Poisson-Nernst-Planck theory of ion conductivity with soft repulsion between mobile ions and protein atoms (SP-PNP). The presence of the membrane environment also influences the protonation state of the residues at the boundary of the water-lipid interface. In this work, we predict that Asp and Lys residues at the protein rim change their protonation state upon penetration to the lipid environment. Free energies of protein insertion in the membrane for different penetration depths were estimated using the Poisson-Boltzmann/solvent-accessible surface area (PB/SASA) model. The results show that rectification and reversal potentials are very sensitive to the relative position of channel in the membrane, which in turn contributes to alternative protonation states of lipid-penetrating ionizable groups. The prediction of channel position based on the matching of calculated rectification with experimentally determined rectification is in good agreement with recent neutron reflection experiments. Based on the results, we conclude that α-hemolysin membrane position is determined by a combination of factors and not only by the pattern of the surface hydrophobicity as is typically assumed.

Electrical and Physical Characteristics of WO3/Ag/WO3 Sandwich Structure Fabricated with Magnetic-Control Sputtering Metrology †.

In this work, three layers of transparent conductive films of WO3/Ag/WO3 (WAW) were deposited on a glass substrate by radio frequency (RF) magnetron sputtering. The thicknesses of WO3 (around 50~60 nm) and Ag (10~20 nm) films were mainly the changeable factors to achieve the optimal transparent conductivity attempting to replace the indium tin oxide (ITO) in cost consideration. The prepared films were cardinally subjected to physical and electrical characteristic analyses by means of X-ray diffraction analysis (XRD), field-emission scanning electron microscope (FE-SEM), and Keithley 4200 semiconductor parameter analyzer. The experimental results show as the thickness of the Ag layer increases from 10 nm to 20 nm, the resistance becomes smaller. While the thickness of the WO3 layer increases from 50 nm to 60 nm, its electrical resistance becomes larger.

Graphene Based Biosensor Model for Escherichia Coli Bacteria Detection.

As a new nanomaterial, graphene demonstrates great potential as an electrode for biomedical applications in sensing molecules and cells. Thus, development of biosensors based on graphene is gaining much interest due to its exceptional properties such as, large surface-to-volume ratio, high conductivity and high flexibility. In this work a liquid gated graphene field effect transistor based biosensor model is analytically developed for electrical detection of Escherichia Coli O157:H7 bacteria. The effect of graphene functionalization on the graphene conductance in the presence of E. coli is investigated. E. coli absorption effects on the graphene surface in the form of conductance variation are considered. Therefore the graphene conductance as a function of E. coli concentration which controls the current­voltage characteristics of biosensors is presented. According to the simulated results, the proposed sensor model can be applied as a powerful tool to predict the biosensor performance.

RNA-based detection of genetically modified plants via current-voltage characteristic measurement.

The widespread adoption of genetically modified (GM) crops has escalated concerns about their safety and ethical implications, underscoring the need for efficient GM crop detection methods. Conventional detection methods, such as polymerase chain reaction, can be costly, lab-bound, and time-consuming. To overcome these challenges, we have developed RapiSense, a cost-effective, portable, and sensitive biosensor platform. This sensor generates a measurable voltage shift (0.1-1 V) in the system's current-voltage characteristics, triggered by an increase in membrane's negative charge upon hybridization of DNA/RNA targets with a specific DNA probe. Probes designed to identify the herbicide resistance gene hygromycin phosphotransferase show a detection range from ∼1 nM to ∼10 µM and can discriminate between complementary, non-specific, and mismatched nucleotide targets. The incorporation of a small membrane sensor to detect fragmented RNA samples substantially improve the platform's sensitivity. In this study, RapiSense has been effectively used to detect specific DNA and fragmented RNA in transgenic variants of Arabidopsis, sweet potato, and rice, showcasing its potential for rapid, on-site GM crop screening.

Modeling the current-voltage characteristics of thin-film silicon solar cells based on photo-induced electron transfer processes.

Power conversion efficiency of p-i-n type macrocrystalline silicon (µc-Si:H) solar cells has been analyzed in terms of sequential processes of photo-induced electron transfer. The effect of the excitonic state on the charged carrier generation has been studied compared to a conventional scheme in which only charged carriers are taken into account for the operation of the solar cells. A numerical model has been developed to calculate current-voltage characteristics of solar cells on the basis of two types of charged carrier generation processes (exciton process and charged carrier process). The light trapping effect due to a textured back surface reflector (BSR) was embedded in the numerical model by using the effective medium theory in combination with the matrix method in the field of the electromagnetic theory of light. As an application of this modeling, it was found that the reported data of the power conversion efficiency were not explained by the conventional charged carrier process model and that the combined model of the charged carrier process with the exciton process well explains the performance of the p-i-n type µc-Si:H solar cells. In this way, the typical power conversion efficiencies were estimated to be 10.5% for the device (i-layer thickness: 1.8 µm) with the BSR (period: 600 nm; height: 250 nm) and 8.6% for the device with the flat reflector under the condition that the fractions of the exciton process and charged carrier process were 60% and 40%, respectively.

Computational Design of an Electro-Membrane Microfluidic-Diode System.

This study uses computational design to explore the performance of a novel electro-membrane microfluidic diode consisting of physically conjugated nanoporous and micro-perforated ion-exchange layers. Previously, such structures have been demonstrated to exhibit asymmetric electroosmosis, but the model was unrealistic in several important respects. This numerical study investigates two quantitative measures of performance (linear velocity of net flow and efficiency) as functions of such principal system parameters as perforation size and spacing, the thickness of the nanoporous layer and the zeta potential of the pore surface. All of these dependencies exhibit pronounced maxima, which is of interest for future practical applications. The calculated linear velocities of net flows are in the range of several tens of liters per square meter per hour at realistically applied voltages. The system performance somewhat declines when the perforation size is increased from 2 µm to 128 µm (with a parallel increase of the inter-perforation spacing) but remains quite decent even for the largest perforation size. Such perforations should be relatively easy to generate using inexpensive equipment.

A Portable Device for I-V and Arrhenius Plots to Characterize Chemoresistive Gas Sensors: Test on SnO2-Based Sensors.

Chemoresistive nanostructured gas sensors are employed in many diverse applications in the medical, industrial, environmental, etc. fields; therefore, it is crucial to have a device that is able to quickly calibrate and characterize them. To this aim, a portable, user-friendly device designed to easily calibrate a sensor in laboratory and/or on field is introduced here. The device comprises a small hermetically sealed chamber (containing the sensor socket and a temperature/humidity sensor), a pneumatic system, and a custom electronics controlled by a Raspberry Pi 4 developing board, running a custom software (Version 1.0) whose user interface is accessed via a multitouch-screen. This device automatically characterizes the sensor heater in order to precisely set the desired working temperature, it acquires and plots the sensor current-to-voltage and Arrhenius relationships on the touch screen, and it can record the sensor responses to different gases and environments. These tests were performed in dry air on two representative sensors based on widely used SnO2 material. The device demonstrated the independence of the Arrhenius plot from the film applied voltage and the linearity of the I-Vs, which resulted from the voltage step length (1-30 min) and temperature (200-550 °C).

Island-Type Graphene-Nanotube Hybrid Structures for Flexible and Stretchable Electronics: In Silico Study.

Using the self-consistent charge density functional tight-binding (SCC-DFTB) method, we study the behavior of graphene-carbon nanotube hybrid films with island topology under axial deformation. Hybrid films are formed by AB-stacked bilayer graphene and horizontally aligned chiral single-walled carbon nanotubes (SWCNTs) with chirality indices (12,6) and 1.2 nm in diameter. In hybrid films, bilayer graphene is located above the nanotube, forming the so-called "islands" of increased carbon density, which correspond to known experimental data on the synthesis of graphene-nanotube composites. Two types of axial deformation are considered: stretching and compression. It has been established that bilayer graphene-SWCNT (12,6) hybrid films are characterized by elastic deformation both in the case of axial stretching and axial compression. At the same time, the resistance of the atomic network of bilayer graphene-SWCNT (12,6) hybrid films to failure is higher in the case of axial compression. Within the framework of the Landauer-Buttiker formalism, the current-voltage characteristics of bilayer graphene-SWCNT (12,6) hybrid films are calculated. It is shown that the slope of the current-voltage characteristic and the maximum values of the current are sensitive to the topological features of the bilayer graphene in the composition of graphene-SWCNT (12,6) hybrid film. Based on the obtained results, the prospects for the use of island-type graphene-nanotube films in flexible and stretchable electronic devices are predicted.

Features of the Carrier Concentration Determination during Irradiation of Wide-Gap Semiconductors: The Case Study of Silicon Carbide.

In this paper, the features of radiation compensation of wide-gap semiconductors are discussed, considering the case study of silicon carbide. Two classical methods of concentration determination are compared and analyzed: capacitance-voltage (C-V) and current-voltage (I-V) characteristics. The dependence of the base resistance in high-voltage 4H-SiC Schottky diodes on the dose of irradiation by electrons and protons is experimentally traced in the range of eight orders of magnitude. It is demonstrated that the dependence of the carrier concentration on the irradiation dose can be determined unambiguously and reliably in a very wide range of compensation levels, based on the results of measuring the I-V characteristics. It is shown that the determination of the carrier removal rate using the I-V characteristics is more correct than using the C-V characteristics, especially in the case of high radiation doses.

Investigation of Transport Processes through Ion-Exchange Membranes Used in the Production of Amines from Their Salts Using Bipolar Electrodialysis.

The influence of the nature of amine solutions on the frequency spectrum of the electrochemical impedance of the bipolar membrane aMB-2m is investigated. Moreover, the effect of the circulation rate of solutions in the electrodialyzer chambers on the volt-ampere characteristics of the Ralex AMH and MA-40L anion-exchange membranes and the aMB-2m bipolar membrane has been investigated. The diffusion characteristics of various types of anion-exchange membranes in a system containing dimethylammonium sulfate ((DEA)2H2SO4), as well as the diffusion characteristics of the Ralex AMH membrane in systems with methylammonium sulfate, dimethylammonium sulfate, diethylammonium sulfate, and ethylenediammonium sulfate ((MA)2H2SO4, (DMA)2H2SO4, (DEA)2H2SO4, EDAH2SO4) have been studied. It is shown that diffusion permeability depends on the structure and composition of anion-exchange membranes, as well as on the nature of amines. The technical and economic characteristics of the electromembrane processes for the production of amines and sulfuric acid from amine salts are determined. It is shown that when using Ralex AMH anion-exchange membranes in an electrodialyzer together with bipolar aMB-2m membranes, higher concentrations of diethylamine and sulfuric acid are achieved, compared with the use of MA-40L anion-exchange membranes.

Spin-Coating and Aerosol Spray Pyrolysis Processed Zn1-xMgxO Films for UV Detector Applications.

A series of Zn1-xMgxO thin films with x ranging from 0 to 0.8 were prepared by spin coating and aerosol spray pyrolysis deposition on Si and quartz substrates. The morphology, composition, nano-crystalline structure, and optical and vibration properties of the prepared films were studied using scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD), and optical and Raman scattering spectroscopy. The optimum conditions of the thermal treatment of samples prepared by spin coating were determined from the point of view of film crystallinity. The content of crystalline phases in films and values of the optical band gap of these phases were determined as a function of the chemical composition. We developed heterostructure photodetectors based on the prepared films and demonstrated their operation in the injection photodiode mode at forward biases. A device design based on two Zn1-xMgxO thin films with different x values was proposed for extending the operational forward bias range and improving its responsivity, detectivity, and selectivity to UV radiation.

Application of fuzzy neural network model and current-voltage analysis of biologically active points for prediction post-surgery risks.

The work investigates neural network model for prediction of post-surgical treatment risks. The descriptors of the risk classifiers are formed on the basis of the analysis of the current-voltage characteristics of one, two and three biologically active points. The training and verification samples were formed by examining 120 patients with a diagnosis of benign prostatic hyperplasia. Of these, 62 patients were successfully operated on (class C1), 30 had various complications after surgery (class C2), 28 patients required additional treatment (class C3). The constructed classifiers showed a high quality of predicting critical conditions during surgical treatment.

Non-topographic current contrast in scanning field emission microscopy.

In scanning field emission microscopy (SFEM), a tip (the source) is approached to few (or a few tens of) nanometres distance from a surface (the collector) and biased to field-emit electrons. In a previous study (Zanin et al. 2016 Proc. R. Soc. A 472, 20160475. (doi:10.1098/rspa.2016.0475)), the field-emitted current was found to change by approximately 1% at a monatomic surface step (approx. 200 pm thick). Here we prepare surface domains of adjacent different materials that, in some instances, have a topographic contrast smaller than 15 pm. Nevertheless, we observe a contrast in the field-emitted current as high as 10%. This non-topographic collector material dependence is a yet unexplored degree of freedom calling for a new understanding of the quantum mechanical tunnelling barrier at the source site that takes into account the properties of the material at the collector site.