Measurements Of Current-voltage Characteristics Research Articles

Interpretation of field emission current–voltage data: Background theory and detailed simulation testing of a user-friendly webtool

In field electron emission (FE) studies, interpretation of measured current–voltage characteristics and extraction of emitter characterization parameters are usually carried out within the framework of “smooth planar metal-like emitter (SPME) methodology”, using a data-analysis plot. This methodology was originally introduced in the 1920s. Three main data-plot types now exist: Millikan–Lauritsen (ML) plots, Fowler–Nordheim (FN) plots, and Murphy–Good (MG) plots. ML plots were commonly used in early FE studies, but most modern analysis uses FN plots. MG plots are a recent introduction.Theoretically, it is now known that ML and FN plots are predicted to be slightly curved in SPME methodology, but a Murphy–Good plot will be very nearly straight. Hence (because 1956 Murphy–Good emission theory is “better physics” than 1928 Fowler–Nordheim emission theory as corrected in 1929), expectation is that parameter extraction using a MG plot will be more precise than extraction using either ML plots or FN plots.In technological FE studies, current–voltage characteristics are often converted into other forms. Thus, measured voltage may be converted to (apparent) macroscopic field, and/or current values may be converted to macroscopic current densities. Thus, four data-input forms can be found in the context of analysing FE current–voltage results.It is also the case that over-simplified models of measurement-system behaviour are very widely assumed, and the question of whether simple use of a data-analysis plot is a valid data-interpretation procedure for the particular system under investigation has often been neglected. Past published studies on field emitter materials development appear to contain a high incidence of spurious values for the emitter characterization parameter “characteristic field enhancement factor”. A procedure (the so-called “Orthodoxy Test”) was described in 2013 that allows a validity check on measurement-system behaviour, and found that around 40% of a small sample of results tested were spuriously high, but has had limited uptake so far.To assist with FE current–voltage data interpretation and validity checks, a simple user-friendly webtool has been under design by the lead author. The webtool needs as user input some system specification data and some “range-limits” data from any of the three forms of data-analysis plot, using any of the four data-input variations. The webtool then applies the Orthodoxy Test, and—if the Test is passed—calculates values of relevant emitter characterization parameters.The present study reports the following: (1) systematic tests of the webtool functionality, using simulated input data prepared using Extended Murphy–Good field electron emission theory; and (2) systematic comparisons of the three different data-plot types, again using simulated input data, in respect of the accuracy with which extracted characterization parameter values match the simulation input values. The paper is introduced by a thorough summary review of the theory on which modern SPME-based current–voltage data-analysis procedures are based. The need in principle to move on (in due course) to data-analysis procedures based on curved-emitter emission theory is noted.An important result is to confirm (by simulations) that, particularly in respect of the extraction of formal emission areas, the performance of the Murphy–Good plot is noticeably better than the performances of Fowler–Nordheim and Millikan–Lauritsen plots. This result is important for field electron emission science because it is now known that differences as between different theories of field electron emission often affect the formal emission area.

Improving the accuracy of temperature coefficient measurement of a PV module by accounting for the transient temperature difference between cell and backsheet

Accurate measurement of cell temperature inside a PV module is critical for the accurate measurement of Temperature Coefficients (TC) and Current-Voltage (I-V) characteristics corrected to Standard Test Conditions (STC). Estimating the cell temperature from the backsheet temperature while the module is heating or cooling is non-trivial because of the time-varying temperature difference between the cell and the backsheet. In this study, transient temperatures (for cell, EVA, front glass and backsheet) during heating and cooling are experimentally recorded for an inhouse laminated 4 cell multi c-Si PV coupon by inserting thermocouples during lamination. A One-Dimensional (1-D) transient simulation model using Finite Difference (FD) method is developed to observe the temperature profile along the thickness of the PV coupon. It is also used to obtain the temperature profiles for various layers for a full size 72-cell PV module as well as a glass-glass module with otherwise similar Bills of Materials. The maximum temperature difference observed between cell and backsheet was ∼ 2.35 ℃ for a glass-backsheet module and ∼ 5.3 ℃ for a glass-glass module which are heated to 75 ℃. Also, the transient temperature difference (TTD) showed an exponential decay profile after reaching the peak. The observed transient temperature difference led to ∼+7% error in the measurement of all the temperature coefficients of PV coupon or module if the backsheet temperature is used as a proxy for module / cell temperature. Accounting for this observed transient temperature difference between cell to backsheet leads to an improved accuracy of temperature coefficient measurements.

Evolution of WSe2 Flakes Synthesized by Thermally Assisted Conversion Method

We report the synthesis of tungsten diselenide (WSe2) flakes and continuous layers using an atmospheric pressure thermally assisted conversion (TAC) method, where the tungsten (W) layers were pre-deposited by a magnetron sputtering system onto fused silica substrates. Optical microscopy (OM) and atomic force microscopy (AFM) mapping predominantly revealed the formation of isolated flakes with different shapes, mainly concentrated near the substrate’s edges, which tended to form clusters and to further overlap to continuous layers, moving to the central part of the fused silica substrates. Raman spectroscopy and photoluminescence measurements confirmed the existence of atomically thin flakes and 2H-WSe2 continuous layers. The measured current–voltage characteristics indicated Ohmic behavior under dark conditions and photo illumination. Finally, the demonstrated resistor-like behavior suggested unlimited prospects for WSe2 integration into a variety of heterostructures.

Modeling the Short-Channel Effects in Coplanar Organic Thin-Film Transistors

We have developed models for three different short-channel effects [subthreshold-swing degradation, threshold-voltage roll-off, and drain-induced barrier lowering (DIBL)] in coplanar organic thin-film transistors (TFTs) and verified them against the measured current–voltage characteristics of TFTs having channel lengths as small as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.5 \mu \text{m}$ </tex-math></inline-formula> . To derive the models, the Schwarz–Christoffel transformation was applied to obtain a complex mapping function that links the coplanar device geometry to an equivalent geometry in a different coordinate system in order to solve Laplace’s equation of the 2-D potential problem. The solution to this potential problem serves as the basis for the definition of the short-channel models, which can be incorporated into any compact dc models for coplanar TFTs that use the TFTs’ threshold voltage and subthreshold swing as input parameters. To verify the model, the channel-length-dependent effects were extracted from technology computer-aided design (TCAD) simulations (transfer characteristics and surface-potential profile) and from measurements performed on organic p-channel TFTs fabricated using high-resolution stencil lithography.

Multi-Segment TFT Compact Model for THz Applications.

We present an update of the Rensselaer Polytechnic Institute (RPI) thin-film transistor (TFT) compact model. The updated model implemented in Simulation Program with Integrated Circuit Emphasis (SPICE) accounts for the gate voltage-dependent channel layer thickness, enables the accurate description of the direct current (DC) characteristics, and uses channel segmentation to allow for terahertz (THz) frequency simulations. The model introduces two subthreshold ideality factors to describe the control of the gate voltage on the channel layer and its effect on the drain-to-source current and the channel capacitance. The calculated field distribution in the channel is used to evaluate the channel segment parameters including the segment impedance, kinetic inductance, and gate-to-segment capacitances. Our approach reproduces the conventional RPI TFT model at low frequencies, fits the measured current–voltage characteristics with sufficient accuracy, and extends the RPI TFT model applications into the THz frequency range. Our calculations show that a single TFT or complementary TFTs could efficiently detect the sub-terahertz and terahertz radiation.

Electrophysical Properties of &lt;i&gt;N&lt;/i&gt;-Cuinse Based Heterostructures

By the method of thermal oxidation of n-type CuInSe2 crystals, n - n+ structures with a maximum absolute current photosensitivity of up to 10 mA / W were obtained at low rectification and no-load photovoltage. The used modes of thermal oxidation led to the formation of n-type layers on the surface of the n-CuInSe2 plates, the resistivity of which is 2-2.5 times higher concerning the initial substance. Measurements of the stationary current-voltage characteristics have shown that the structures obtained have a slight rectification K. All the structures obtained exhibit photosensitivity, which dominates when illuminated from the side of the layer in the spectral region of about 1 eV. The optimization of the process can reveal the technological possibilities of a significant improvement in the rectifying properties of isotypic structures based on CuInSe2.

Compact Model for Bipolar and Multilevel Resistive Switching in Metal-Oxide Memristors.

The article presents the results of the development and study of a combined circuitry (compact) model of thin metal oxide films based memristive elements, which makes it possible to simulate both bipolar switching processes and multilevel tuning of the memristor conductivity taking into account the statistical variability of parameters for both device-to-device and cycle-to-cycle switching. The equivalent circuit of the memristive element and the equation system of the proposed model are considered. The software implementation of the model in the MATLAB has been made. The results of modeling static current-voltage characteristics and transient processes during bipolar switching and multilevel turning of the conductivity of memristive elements are obtained. A good agreement between the simulation results and the measured current-voltage characteristics of memristors based on TiOx films (30 nm) and bilayer TiO2/Al2O3 structures (60 nm/5 nm) is demonstrated.

Electron Transport in Double-Barrier Semiconductor Heterostructures for Thermionic Cooling

We investigate electron transport in asymmetric double-barrier ($\mathrm{Al},\mathrm{Ga})\mathrm{As}/\mathrm{Ga}\mathrm{As}$ thermionic cooling heterostructures. Measurements of temperature-dependent current-voltage characteristics confirm that the dominant electron transport is a sequential process of resonant tunneling injection into and thermionic emission from the quantum-well (QW) cooling layer. The thermal activation energy of the current is found to be strongly dependent on the bias voltage. Furthermore, instead of showing a simple thermal activation behavior, the current exhibits rather complicated temperature and voltage dependence, particularly when the thermionic emission barrier is low. To establish a quantitative understanding, we develop an intuitive analytical model for sequential electron transport that explicitly takes into account scattering effects in the thermionic emission process from the two-dimensional QW states to the three-dimensional above-barrier states. The observed temperature-dependent sequential current is well explained by the present theory.

Effects of illumination on the electrical characteristics in organic thin-film transistors based on dinaphtho [2,3-b:2′,3′-f] thieno[3,2-b] thiophene (DNTT): Experiment and modeling

The electrical properties of dinaphtho [2,3-b:2′,3′-f]thieno[3,2-b]thiophene (DNTT) based organic thin film transistors (DNTT-TFTs) were investigated in detail under dark and various light illumination conditions with different channel lengths. We have exploited the experimental curves current–voltage of our TFT to extract electrical parameters such us mobility, threshold voltage, sub-threshold voltage and trapped density in dark and under illumination. By using an analytical model, we are able to reproduce very accurately the output and transfer characteristics with a joint analysis of the L = 100 µm and L = 500 µm electrical characteristics, the dependence of the contact resistance (Rc) upon the illumination conditions has been extracted. The used model gives a good agreement between the measured current–voltage characteristics of the DNTT-TFTs and those modeled in all measurement conditions (in dark and under illumination).

Study and Analysis of Simple and Precise of Contact Resistance Single-Transistor Extracting Method for Accurate Analytical Modeling of OTFTs Current-Voltage Characteristics: Application to Different Organic Semiconductors

Contact resistance (Rc) characterizes the interface of source-drain electrodes/organic semiconductors and controls the injection efficiency of carriers in organic thin-film transistors (OTFTs). This research paper presents and assesses two methods for extracting the value of the contact resistance from the measured current-voltage characteristics of OTFTs made with various p-type organic semiconductors as active layers. These two methods are the transition voltage method (TVM) and the transfer line method (TLM). The obtained Rc values by the TVM method are in fair agreement with those obtained by TLM, with a maximum percentage of difference around 10%, demonstrating the accuracy of the used transition-voltage method. An analytical model was employed to calculate output characteristics in the linear regime of OTFTs made with various organic semiconductors using the contact resistance values obtained by the transition voltage method. The calculated results are in reasonably good agreement with the experimental ones of each fabricated device, which affirms the ability of the used model to characterize the charge transport correctly in these types of devices. It can be concluded that the used TVM method is not only an easy and practical method, but also a precise way for extracting Rc in OTFTs produced using different organic semiconductor materials.

Investigation of electrolysis-related modification of graphene films in biosensors

In this work, the modification of the surface parameters of graphene chips after electrolysis treatment in a NaClO4 aqueous solution has been studied. Two electrolysis modes have been analysed. In the first one, a negative potential (-0.2 V) is applied to the graphene chips, while in the second one the potential is positive (0.8 V). Investigation using a number of techniques including atomic force microscopy, Kelvin probe force microscopy, Raman spectroscopy, measurements of current-voltage characteristics and low-frequency noise has shown that the electrolysis mode with application of a positive potential on graphene chips decreases the 1/f noise and allows one to obtain a uniform surface potential distribution while leaving the graphene structure undamaged. The results of this study help to understand the efficiency and reproducibility of the procedure for electrolysis treatment of graphene chips.

Influence of ceramic counter electrode on the properties of dye sensitized solar cell

Dye sensitized solar cells consisting of a sandwich structure have been a topic outspread in the science for above twenty years and they start a new development trend in obtaining energy from the sun. One the examined aspects of their application is building-integrated photovoltaics. Despite the fact that the higher efficiency of energy conversion was obtained with this type of substrate, glass, due to the cost of production and energy consumption, is disadvantageous in the case of production on an industrial scale. The article presents the possibility of replacing a classic glass substrate with an counter electrode based on a building ceramic tile material. A dye sensitized solar cell was built layer by layer on the tile. A method of atomization was used to deposit fluorine doped tin oxide. After that, a thin layer of platinum was printed. It does not require the use of high temperatures, complicated devices and high costs. Scanning electron microscope, atomic force microscope and Raman spectroscopy were used to evaluate the influence of the transparent conductive oxide layer on the photovoltaic properties of counter electrode tile. Electrical parameters of as prepared DSSCs with and without ceramic tile were characterized by measurements of current-voltage characteristics under standard AM 1.5 radiation. A dye sensitized solar cell integrated with building ceramic tile material was prepared successfully, which efficiency was over 4%.

Deterministic mechanisms of spiking in diffusive memristors

Diffusive memristors, which have been recently fabricated and measured, attract a significant interest being among the best candidates to mimic neuron activities and to implement novel computing paradigms. Such devices are capable of exhibiting a combination of dynamical, chaotic, and stochastic phenomena needed for efficient neuromorphic computational systems. However, understanding the contribution of deterministic and stochastic dynamics to the functional properties of a diffusive memristor is still an open problem. To study the deterministic mechanisms governing the dynamics of diffusive memristors, we analyze a model of a memristive circuit when the effects of the temperature noise are neglected. We reveal instabilities, which shape the current-voltage characteristic of the device and imply the onset of current self-oscillations. Finally, the results of modeling are compared with experimentally measured current-voltage characteristics.

Exploring the studies of charge transportation of an aromatic acid based Co(II)-Metallogel scaffold fabricated Schottky device

An efficient supramolecular metallogel of Cobalt(II) has been synthesized through the ultra-sonication technique. Cobalt(II)-salt (Cobalt acetate tetrahydrate), organic acid like terephthalic acid along with N,N-dimethyl formamide solvent are the key ingredients of the Co(II)-metallogel. The rheology-based experimental values of storage and loss modulus of the Co(II)-metallogel prove the mechanical efficiency of the metallogel-material. The chemical compositions are found through elemental investigations. The infrared spectral results help to realize the metallogel formation strategy. The electrical characteristics of the synthesized metallogel have been properly investigated. The semiconducting feature of the metallogel-material has been experimentally verified. The measured current-voltage characteristics of Cobalt(II)-metallogel (Co-TA) based thin film type metal-semiconductor (MS) junction-device shows a non-linear rectifying behaviour, representing a Schottky diode (SD) performance with promising electronic charge transport property.

Aerosol Deposition of Thin-Film Single- and Bi-layered Solid Electrolytes for Intermediate Temperature Planar Solid Oxide Fuel Cells

One of the main limiting factors determining an increase in the specific power and efficiency of solid oxide fuel cells (SOFCs) is the development of deposition technique for thin-film gas-tight electrolytes. Hence, the development of inexpensive and scalable technologies to form thin-film electrolytes is the key direction of SOFC improvement. Despite existence of well-developed techniques, such as chemical vapor/solution deposition (CVD/CSD), electrochemical deposition (ED), thermal spray (TS), physical vapor deposition (PVD), all of them have a trend in rising deposition temperatures or establishing high vacuum that causes an increase in cost. The aerosol deposition (AD) also known as vacuum kinetic spraying (VKS) is a technique for deposition of thin and thick, gas-tight and porous layers. The deposition occurs due to the impact of high-energy particles to substrate and their consequent fragmentation and consolidation, this phenomenon is called room temperature impact consolidation (RTIC). The AD method is distinguished by the ability to lower the formation temperatures of a gas-tight electrolyte layer down to room temperatures by using a high-energy aerosol jet under conditions of low vacuum (1 – 1000 Pa) and room temperature. In addition, the method is characterized by low equipment cost and easy scaling. The possibility to deposit gas-tight films and films with controlled porosity in a wild range of thickness makes it possible to create all functional SOFCs layers without intermediate sintering steps. In the present work, the aerosol deposition technique was used to deposit thin-film electrolytes for anode-supported SOFCs. Two types of anode-supported SOFCs were manufactured. Type-1: thin-film electrolyte with the composition 8 mol.% yttria-stabilized zirconia (8YSZ) deposited on a bilayered anode substrate (current-collecting and functional sublayers) using the AD method followed by the screen-printing of a composite cathode with the composition of (La0.8Sr0.2)0.95MnO3-δ (LSM) and zirconia co-stabilized with 10 mol.% of scandia and 1 mol.% of yttria (10Sc1YSZ). Type-2: bilayered thin electrolyte made of 8YSZ and 10 mol% gadolinia doped ceria (GDC) protective layer deposited on a bilayered anode substrate using the AD method, followed by the screen printing of an active cathode with the composition of (La0.80Sr0.20)0.95CoO3–δ (LSC). The high quality of electrolyte layers of both types of SOFCs was confirmed by scanning electron microscopy, as well as electrochemical measurements, including the measurements of current-voltage characteristics and impedance spectroscopy. At 800 °C the anode-supported cells with humidified hydrogen as a fuel, and air as an oxidant demonstrated the open-circuit voltage of more than 1.04 V for both types of SOFCs, as well as specific power of more than 420 mW/cm2 and 780 mW/cm2 for type-1 and type-2 of SOFCs, respectively. Based on the studies carried out, further steps were determined to improve the electrochemical parameters of the cells, as well as to scale up to deposition on substrates with an area of 100x100 mm2.This work was carried out with financial support from the Russian Scientific Foundation, grant no. 17-79-30071. Figure 1

Aerosol Deposition of Thin-Film Single- and Bi-layered Solid Electrolytes for Intermediate Temperature Planar Solid Oxide Fuel Cells

The aerosol deposition (AD) method is a technique for the formation of thin and thick, gas-tight, and porous layers by deposition of microscopic powder particles. In the present work, the AD was used to deposit thin-film electrolyte and protective buffer layers for planar anode-supported solid oxide fuel cells (SOFCs). The high quality of deposited layers was confirmed by scanning electron microscopy, as well as electrochemical measurements, including the measurements of current-voltage characteristics and impedance spectroscopy. At working temperature of 800°C the anode-supported cell with bi-layered electrolyte deposited by AD demonstrated the open-circuit voltage of more than 1.04 V, as well as specific power of more than 780 mW/cm2. The difficulties, advantages, and peculiarities associated with the formation of thin-film electrolyte and buffer layers of SOFCs by the AD method have been discussed.

АЛГОРИТМ І ПРОГРАМНЕ ЗАБЕЗПЕЧЕННЯ ДЛЯ ARDUINO-СИСТЕМИ ТЕСТУВАННЯ ФОТОЕЛЕКТРИЧНИХ МОДУЛІВ

В роботі представлено реалізацію програмного забезпечення та алгоритмів роботи для вимірювально-обчислювальної системи, що призначена для визначення в реальних умовах електричних характеристик фотоелектричних модулів методом змінного активного навантаження. Описано програмне забезпечення для пакета MATLAB, яке включає в себе користувацький інтерфейс та алгоритми управління процесом вимірювання вольт-амперних характеристик. Користувацький інтерфейс розроблений за допомогою пакета розширення MATLAB Support Package for Arduino Hardware.&#x0D; Це програмне забезпечення дозволяє проводити велику кількість вимірів у різних режимах з опціональним підключенням піранометра та заданням необхідної затримки між відліками, відображати ВАХ і потужнісну характеристику та основні параметри ФМ, зберігати дані та здійснювати менеджмент уже збережених даних, контролювати процес поточного виміру, проводити діагностику системи. Використання цієї системи актуально для тестування та діагностики поточного стану фотомодулів у польових умовах, визначення фактичних електричних параметрів фотомодулів. Слід зазначити, що ці параметри не надаються в повному обсязі виробниками, але вони суттєві для задач діагностики фотомодулів у складі фотоелектричних станцій, і перш за все – для оцінювання електричних втрат, обумовлених процесами деградації модулів. &#x0D; Вимірювальна схема вольт-амперних характеристик фотомодулів реалізована на базі мікроконтролерної плати Arduino Mega 2560, яка здійснює комутацію резисторів навантаження електронними реле, збір та передачу експериментальних даних на ПК через послідовний порт. Елементи схеми заміщення фотоелектричних модулів розраховуються за допомогою оригінального методу розв'язання системи нелінійних рівнянь за стійким ітераційним алгоритмом, який заснований на розкладанні нелінійних рівнянь за малими параметрами. Бібл. 7, рис. 4.

Structural, Morphological and Sensor Properties of the Fractal-Percolation Nanosystem ZnO/NiO

ZnO/NiO fractal-percolation nanosystems have been sensitized using a newly developed three-step technology. During the first stage, ionically sputtered Zn vapors have been deposited under near-equilibrium condensation conditions. In the second stage, Zn layers have been oxidized in air atmosphere, and during the final stage, a NiO layer has been deposited onto the ZnO surface using reactive magnetron sputtering. Gas sensor tests have been performed by measuring current–voltage characteristics of the fractal-percolation nanosystems in air containing methanol or methane. It has been shown that the shape of the I–V curve depends on the reactive gas nature, rendering the possibility to differentiate between different gases, which is an important step to increase sensor selectivity.

Improvement of ion conductivity and selectivity of heterogeneous membranes by sulfated zirconia modification

Inorganic-organic composites based on the foil and standard RALEX® cation-exchange heterogeneous membranes (Mega a.s., Czech Republic) were prepared by in situ modification with sulfated zirconia (S-ZrO2). The composite membranes were characterized by SEM, TGA, X-ray diffraction, and FTIR spectroscopy. The effect of S-ZrO2 doping on membrane transport properties was studied using measurements of water uptake, ion-exchange capacity, conductivity, cation diffusion, hydrogen permeability, current-voltage characteristics, and membrane specific permselectivity (Ca2+/Na+). The S-ZrO2 incorporation leads to an increase in conductivity and permselectivity of the composite membranes. The proton conductivity of the S-ZrO2-doped foil membrane (0.0316 S/cm at 30°С) is 4 times higher than that of the pristine membrane. The Ca2+/Na+ permselectivity of the standard RALEX® CM membrane doped by S-ZrO2 reaches 3.8 at low current densities. Moreover, the composite membranes retain their selectivity during the long-term tests (> 50 h continuous electrodialysis). The sulfated zirconia doping of heterogeneous membranes demonstrated an excellent separation efficiency that can be used in wastewater treatment, desalination, and related electromembrane separation processes as well as to reduce scaling of electrodialysis modules.

High signal-to-noise ratio differential conductance spectroscopy

The scanning tunneling microscope (STM) has enabled manipulation and interrogation of surfaces with atomic-scale resolution. Electronic information about a surface is obtained by combining the imaging capability of the STM with scanning tunneling spectroscopy, i.e., measurement of current-voltage (I/V) characteristics of the surface. We propose a change in the STM feedback loop that enables capturing a higher quality dI/dV image. A high frequency dither voltage is added to the bias voltage of the sample, and the fundamental frequency component of the resulting current is demodulated. The in-phase component of this signal is then plotted along with the X and Y position data, constructing the dI/dV image. We show that by incorporating notch filters in the STM feedback loop, we may utilize a high-amplitude dither voltage to significantly improve the quality of the obtained dI/dV image.