Electrophysical Characteristics Research Articles

Simulation of a Single-Electron Device Based on Endohedral Fullerene (KI)@C180

The progress of modern electronics largely depends on the possible emergence of previously unknown materials in electronic technology. The search for and combination of new materials with extraordinary properties used for the production of new small-sized electronic devices and the improvement of the properties of existing materials due to improved technology for their manufacture and processing, in general, will determine the progress of highly promising electronics. In order to solve the problematic tasks of the miniaturization of electronic components with an increase in the level of connection of integrated circuits, new forms of electronic devices are being created using nanomaterials with controlled electrophysical characteristics. One of the unique properties of fullerene structures is that they can enclose one or several atoms inside their carbon framework. Such structures are usually called endohedral fullerenes. The electronic characteristics of endohedral fullerenes significantly depend on the properties of the encapsulated atom, which makes it possible to control them by choosing the encapsulated atom required by the property. Within the framework of the density functional theory in combination with the method of the nonequilibrium Green’s functions, the features of electron transport in fullerene nanojunctions were considered, which demonstrate “core–shell” nanoobjects, the “core” of which is an alkali halide crystal—KI—and the “shell” of which is an endohedral fullerene C180 located between the gold electrodes (in the nanogap). The values of the total energy and the stability diagram of a single-electron transistor based on endohedral fullerene (KI)@C180 were determined. The dependence of the total energy of fullerene molecules on the charge state is presented. The ranges of the Coulomb blockade, as well as their areas associated with the central Coulomb diamond were calculated.

Microwave volt-impedance spectroscopy of semiconductor structure

Microwave voltage-impedance spectroscopy is used to study a semiconductor structure in the form of a doped n-GaAs film grown on a conducting n^+-GaAs substrate with a buffer sublayer. A system of concentric barrier contacts is formed on the structure surface. A technique has been developed for measuring complex impedance spectrum Z(f,U) of the sample as a function of DC bias voltage U. Spectra Z(f,U) were measured using a Cascade Microtech probe station in the frequency range 0.01-40 GHz with a lateral resolution of 15-30 μm at U=0-10 V. The main electrophysical characteristics of a semiconductor film were determined from the spectra: type, concentration and mobility of free charge carriers, electrical conductivity. An excess resistance was found in the range f=0.1-20 GHz. This effect is interpreted as the deep states (traps) recharging for two types of traps --- low-frequency l and high-frequency h with characteristic time tau_l=10-9 s, tau_h=4.2·10-11 s. A model description is proposed that explains the characteristic shape of the trap resistance spectrum, its dependence on the contact area and voltage U. Keywords: microwave band, near field, impedance, semiconductor, barier contact, deep states, electrophysical characteristics.

Микроволновая вольт-импедансная спектроскопия полупроводниковой структуры

Microwave voltage-impedance spectroscopy is used to study a semiconductor structure in the form of a doped n-GaAs film grown on a conducting n+-GaAs substrate with a buffer sublayer. A system of concentric barrier contacts is formed on the structure surface. A technique has been developed for measuring complex impedance spectrum Z(f,U) of the sample as a function of DC bias voltage U. Spectra Z(f,U) were measured using a Cascade Microtech probe station in the frequency range 0.01 – 40 GHz with a lateral resolution of 15 – 30 μm at U = 0 – 10 V. The main electrophysical characteristics of a semiconductor film were determined from the spectra: type, concentration and mobility of free charge carriers, electrical conductivity. An excess resistance was found in the range f = 0.1 – 20 GHz. This effect is interpreted as the deep states (traps) recharging for two types of traps – low-frequency l and high-frequency h with characteristic time τl = 10^(-9) s, τh = 4.2∙10^(-11) s. A model description is proposed that explains the characteristic shape of the trap resistance spectrum, its dependence on the contact area and voltage U.

Formation and Properties of Thermistor Chips Based on Semiconductor 3D Metal Oxide Films Obtained by RF-Magnetron Sputtering

The formation of oxide semiconductor films of the (Mn,Co,Cu)3O4 type by radio frequency magnetron sputtering is presented. The conditions of deposition and subsequent heat treatment make it possible to obtain films with electrophysical characteristics close to those of the bulk ceramic materials used as a target for magnetron sputtering. Two variants of thermistor geometry were implemented. In the first case, the working layer of oxide semiconductor was deposited directly on the dielectric substrate (planar geometry), and in the second case on the layer with high electrical conductivity (Ni or Al) forming the inner electrode (layered geometry). The lower limit of the nominal resistance of the planar thermistor while maintaining high temperature nonlinearity is ~ 10 kΩ. The layered structure with the inner electrode makes it possible to reduce the lower limit of resistance up to ~ 50 Ω without losing the temperature nonlinearity of the thermistor. In addition, heat treatment above 450 °C or current self-heating with sufficient power output leads to the appearance of a pronounced voltage nonlinearity, which increases the thermal constant B of thermistors from 2400-3400 to 5000-5500 K. The fields of application of oxide-film structures for the correction of linear resistors and the implementation of integration approaches in the construction of linearized sensors are discussed.

The conductivity and electrophysical characteristics of Janus-like TaSi2/Si nanoparticles

All applications of single nanoparticles as independent nano-objects are based not on their collective properties, but on their individual properties, which are currently insufficiently studied in the vast majority of cases. The same applies to single Janus-like TaSi2/i-Si nanoparticles, which are independent nano-objects with prominent individual properties. In this regard, a system of single Janus-like TaSi2/i-Si nano-particles with a seven percent weight content of the TaSi2 metal phase is investigated for the first time using atomic force microscopy methods, conductivity, static volt–ampere characteristics (VACs) and the spatial 3D structure of the electrostatics, namely: the thermal emissions and tunneling mechanisms responsible for current transfer through the close-contact area between TaSi2 and i-Si; the effect of a serial resistance of RS = 156 MΩ on the VACs, the barriers ϕbm ( f) = 0.578 eV and ϕbm (r) = 0.648 eV, large values of the ideality indices nf = 3.61 and nr = 5.07 for the VAC reverse and forward branches; the 3D distribution of the electrostatic potential of the surface 4.84 ⩽ Ф(x,y)⩽ 4.90 eV; the electrostatic field | E | = 1.76 × 106 V m−1, and the capacitive contrast ∂C(x, y)/∂z. The values of ϕbm , which are uncharacteristic for commonly used metal/Si Schottky contacts, and the abnormally large values of n and RS confirm the pronounced individual properties of these nanoparticles. The presence of a potential barrier in the close TaSi2/i-Si contact leads to the emergence of a space charge region with a sufficiently strong intrinsic electric field E. The latter contributes to the redistribution of electric charges and the appearance of an electric dipole moment in the particles, which increases the number of their degrees of freedom. All these individual features strongly influence the adhesion and transport properties of the particles and their interactions with electromagnetic radiation, which are of particular interest to specialists in the fields of semiconductor electronics, microwave engineering, nanomechanical systems, catalysis, and biomedicine.

Electrophysical Characteristics and Emission Spectra of Carbon Tetrafluoride Plasma

Electrophysical Characteristics and Emission Spectra of Carbon Tetrafluoride Plasma

Influence of Auxiliary Discharge on the Electrophysical Characteristics of Cesium Pulsed Radiation Sources

Influence of Auxiliary Discharge on the Electrophysical Characteristics of Cesium Pulsed Radiation Sources

Влияние наполнителя на деформацию полидиметилсилоксановых композитов под действием электрического поля

The study considers some aspects of the development of new stimuliresponsive materials capable to reversible deformation under an electric field due to the Maxwell pressure. To increase the response of the material to an external stimulus, an approach of polymer composites formation was chosen. Particles of various nature and shape were considered as fillers: powders of iron, montmorillonite and cellulose. Composite elastomeric materials based on polydimethylsiloxane with a low filler content of 5 wt% have been obtained. The morphology of the filler particles was confirmed by electron microscopy. Mechanical properties of the materials in uniaxial tests were studied. The Young’s modulus and constants for the 3-parameter Yeoh model in the range of deformations up to 800 % were determined. The electrophysical properties of the materials, as well as their response to an electric field at different strengths of 0.84 and 2.5 kV/mm have been studied. The effect of the filler nature on the conductivity and permittivity of composite materials was revealed. The data of mechanical and dielectric studies indicate that the filler concentration is below the percolation threshold for all composites. The composite with cellulose exhibits the greatest response to an external stimulus over the considered materials, which is determined by the balance of two factors: the value of Young’s modulus and the values of electrophysical characteristics. Directions for further research were determined and the prospects for the dielectric elastomers creation with predetermined properties were briefly discussed

Congenital Stationary Night Blindness: Clinical and Genetic Features.

Congenital stationary night blindness (CSNB) is an inherited retinal disease (IRD) that causes night blindness in childhood with heterogeneous genetic, electrophysical, and clinical characteristics. The development of sequencing technologies and gene therapy have increased the ease and urgency of diagnosing IRDs. This study describes seven Taiwanese patients from six unrelated families examined at a tertiary referral center, diagnosed with CSNB, and confirmed by genetic testing. Complete ophthalmic exams included best corrected visual acuity, retinal imaging, and an electroretinogram. The effects of identified novel variants were predicted using clinical details, protein prediction tools, and conservation scores. One patient had an autosomal dominant CSNB with a RHO variant; five patients had complete CSNB with variants in GRM6, TRPM1, and NYX; and one patient had incomplete CSNB with variants in CACNA1F. The patients had Riggs and Schubert-Bornschein types of CSNB with autosomal dominant, autosomal recessive, and X-linked inheritance patterns. This is the first report of CSNB patients in Taiwan with confirmed genetic testing, providing novel perspectives on molecular etiology and genotype-phenotype correlation of CSNB. Particularly, variants in TRPM1, NYX, and CACNA1F in our patient cohort have not previously been described, although their clinical significance needs further study. Additional study is needed for the genotype-phenotype correlation of different mutations causing CSNB. In addition to genetic etiology, the future of gene therapy for CSNB patients is reviewed and discussed.

Dual-modal in vivo assessment for electrophysical and hemodynamic characteristics of cerebral edema induced by lipopolysaccharide

The pathological features of cerebral edema are complicated. The intracranial pressure (ICP) is regarded as the most important indicator for monitoring cerebral edema. Recently, multi-parameter has been used to explore the types and pathogenesis of cerebral edema and design effective treatment strategies. This research focused on investigating the characteristic of the cerebral edema induced by lipopolysaccharide (LPS) in rats by using simultaneous electrophysical and hemodynamic parameters. The results showed that neurophysiologic parameters (firing rate (FR) and the power spectrum of local field potential (LFP power)) and hemodynamic parameters (relative concentration of oxygenated hemoglobin (ΔCHbO2), relative concentration of deoxyhemoglobin ΔCHbR) and relative cerebral blood flow (rCBF)) were linearly correlated, and the Pearson’s correlation coefficient was changed by pathological progression of cerebral edema induced by LPS. Furtherly, the treatment after two agents were observed successfully through these multi-parameters. Our findings revealed the relationship between neural activity and hemodynamic response during the progression of cerebral edema and provided a multi-parameter solution for cerebral edema functional monitoring and anti-edema drug efficacy evaluation.

Effect of voltage pulse duration on electrophysical and thermal characteristics of cold atmospheric plasma jet

The desirable properties of a cold atmospheric plasma jet (CAPJ) for medical applications are high efficiency of the treatment and low thermal effects. To meet these requirements, we propose to use the CAPJ generated with the positive pulsed (PP) voltage. In our experiments and fluid model simulations, it is shown that a change of the pulse duration allows us to control precisely the intensity of interaction of the plasma jet with the target and the heating of the contact zone. The helium CAPJ is formed with 13–30 kHz PP voltage frequencies with the pulse duration of 7–20 µs. The enhancement of plasma-target interaction is analyzed with the measured discharge current and calculated ionization rate near the target surface. The temperature measurements in the plasma-target active zone show that the heating by CAPJ excited with the PP voltage is generally less than in the case of AC voltage. The efficacy of treatment is tested on A549 cancer cells exposed to CAPJ ignited with the positively pulsed voltage with different pulse duration and with AC voltage.

Study of the electrophysical characteristics of plastic lubricants

Actively developing electric automobile transport assumes the creation of conductive lubricants. We pres­ent a setup designed to study the electrophysical properties of industrially produced and model plastic lubricants, as well as the samples of a similar consistency. The setup operates within the current frequency range from 0.1 to 1 kHz and includes a temperature-controlled measuring cell that allows changes in the sample thickness and temperature in the range from 20 to 120 °C. A method for determination of cur­rent-voltage characteristics with subsequent calculation of the specific electrical conductivity is proposed. The specific electrical conductivity of model plastic lubricants based on medical vaseline added with car­bon nanostructures (few-layer graphite fragments and their modified analogs) was studied using the de­veloped setup. Vaseline was used as a base model lubricant, since its rheological properties are similar to that of plastic lubricants and it does not contain any additional additives that can affect the measurement result. The electrically conductive properties of the dispersions of carbon nanostructures and their modi­fied analogs in vaseline were analyzed. It is shown that the introduction of carbon nanostructures into dielectric vaseline turns it into an electrically conductive material. The developed setup makes it possible to study the specific electrical conductivity of systems simulating plastic lubricants with a sufficient accuracy. The results obtained can be used to improve the methodology for studying the specific electrical conductivity of model and industrially produced plastic lubricants, including those with conductive additives.

Optical and Electrical Transport Properties of the ZnO:CdO Composite Film

In this work, zinc oxide films and composite ZnO:CdO films with cadmium oxide concentrations of 3 , 5 , 7 , 10 , and 12 were obtained by spin-coating on FTO. The films were annealed in the atmosphere under the same temperature conditions of 450°C. The morphology of ZnO:CdO composite films was studied by the SEM method and an electron-dispersion analysis of the concentration of the studied substance was carried out. The influence of the surface morphology of the composite film with an increase in the CdO concentration from 3 to 12 on the optical and electrotransport properties of the ZnO:CdO composite film was studied. The optical absorption spectra of composite films of zinc oxide and cadmium were measured. ATauc plot is presented to determine the band gap of a ZnO:CdO composite film. It has been established that an increase in the CdO concentration on the ZnO surface leads to a decrease in the optical band gap. The observed decrease in the optical band gap of the film with increasing CdO is due to the small band gap of CdO. The method of impedance spectroscopy was used to study the main electrophysical characteristics, in particular, the dynamics of charge carrier transfer in nanocomposite films based on ZnO:CdO. It has been established that the CdO layer on the ZnO surface contributes to a decrease in the resistance value of the composite film Rw, an increase in the charge recombination resistance parameter Rrec at the interface, and an increase in the efficiency of electron injection.

Electrophysical characteristics of power MOSFETs additionally implanted with nitrogen ions

The electrical characteristics of power MOSFETs additionally implanted with nitrogen ions have been studied. Ion implantation of nitrogen was carried out through a protective oxide of 23 nm thickness with energies of 20 and 40 keV and doses of 1 ⋅ 1013‒5 ⋅ 1014 cm–2. Rapid thermal annealing was carried out at temperature of 900 or 1000 °C for 15 s. It has been established that nitridisation of the gate dielectric makes it possible to reduce the noise of the gate leakage currents and their dispersion. In the direct order of heat treatment (first rapid thermal annealing, and then the removal of the protective oxide), for samples prepared with an additional operation of nitrogen ion implantation, there is an increase in the threshold voltage compared to control samples. The capacitance of the gate dielectric in the case of implantation of nitrogen ions in the direct order of heat treatment is less than for control samples. It has been established that in the direct order of rapid thermal annealing, the doses of nitrogen ion implantation do not cause significant changes in the maximum value of the current-voltage slope. At the same time, in all studied cases, there is a shift in the maximum value of the current-voltage slope towards higher gate voltages. In the reverse order of heat treatment (first the removal of the protective oxide, and then rapid thermal annealing), there are no significant differences in the value of the threshold voltage for the samples created with additional nitrogen implantation and the control ones. The maximum value of the current-voltage slope also does not experience significant changes. It is shown that in the voltage range from – 0.15 to 0 V, the drain current of nitrogen-implanted samples manufactured using the direct order of heat treatment is higher than for control samples, and the drain current of nitrogen-implanted samples obtained with the reverse order of heat treatment it is lower compared to control samples. Results are explained by a decrease in the density of surface states at the Si – SiO2 interface in MOS-structures created using an additional operation of nitrogen ion implantation in the direct order of heat treatment.

Численное моделирование низковольтных логических вентилей на базе полевых нанотранзисторов с переменным диаметром рабочей области

The issues of TCAD simulation of low-voltage logic gates made on SOI CMOS nanotransistors with cylindrical geometry with a fully enclosing gate with a variable diameter of the working area are discussed. Changing the geometry of the working area compared to the usual cylindrical shape improves the electrophysical characteristics and allows you to compensate for the limitations that arise as a result of scaling. Numerical studies of conical prototypes were carried out using mathematical simulation performed using the TCAD instrument technological simulation program based on the n- and p-type nanotransistor models developed by TCAD. The simulation results demonstrate improved electrostatic characteristics. The conical structure in the control voltage range from 0 to 0.6 V is characterized by a higher transistor current, a maximum Ion/Ioff current ratio, a low leakage current and a slope of the subthreshold characteristic close to the theoretical chapel. The dynamic characteristics of the developed physical models of the inverter and the chain of 11 inverters are numerically investigated for the optimized ratio of the diameters of the working area of 8.1/10 nm and the gate length of 25 nm. At control voltages of 0.6 V and a frequency of 25 GHz, the inverter model predicts a maximum switching delay of 1.5 ps, the limit level of active power of 0.21 μW, static 4.4 pW. The active power consumed by the circuit consisting of 11 inverters is 2.34 μW at control voltages of 0.6 V.

Peculiarities of the radiation defects generation and their isochronal annealing in monocrystalline n-Si+4at%Ge:P alloy

The effect of 60Co gamma–photon irradiation on the radiation defects generation and their isochronal annealing in monocrystalline n-Si+4at%Ge:P alloy  has been studied. Experimental bulk crystals were grown by Czochralski method in Ar atmosphere. Electrophysical characteristics were determined by the Hall effect measuring in a constant magnetic field at different stages of 20-minute isochronal annealing in 20-400°C temperature interval. It is established, that under the influence of compressive stresses localized near Ge atoms in the crystalline lattice of the experimental SiGe alloy decrease of the annealing temperature of radiation A-centers (VO) takes place. A change in dissociation temperature of radiation E-centers (PV) is revealed, stipulated by their directed migration in the stress field localized near dislocation.

Physical mechanisms of the influence of γ-ray surface treatment on the characteristics of close AuNi/n–n+-GaN Schottky contacts

The results obtained here suggest that low-dose 60Co γ-irradiation (Dγ ∼ 140 Gy) has a complex effect on close AuNi/n–n+-GaN{0001} Schottky contacts. This manifests in the disappearance of current steps in the initial section of the forward current–voltage curve, improvement in the average values of the ideality factor n, a decrease in the average values of the true Schottky barrier height ϕ bn in the middle section and an increase in series resistance R S and enhancement of the inhomogeneous metal–semiconductor contact series resistance effect in the final section. In all cases, the observed changes are sustainable. A combination of the Zur–McGill–Smith close Schottky contact defect model, the inhomogeneous contact model and the radiation-induced defect formation model provides an explanation for the physical mechanisms of changes observed in electrophysical and instrumental characteristics after γ-irradiation. Such mechanisms are associated with changes in the electrophysical nature of GaN structural defects (dislocations and interface states) and degradation of the homogeneity of contact conductivity. This paper shows that the low-temperature anomaly also manifests itself in close AuNi/n–n+-GaN Schottky contacts subjected to γ-irradiation.

Influence of physical aging of ferroelectric vinylidene fluoride copolymer films on their structural and electrophysical characteristics

AbstractGeneral problems of structural changes which occur at storage of two‐phase crystalline polymers with a metastable structure at room conditions are considered on the example of a vinylidene fluoride ‐ hexafluoropropylene copolymer. The physical aging occurs in flexible‐chain crystalline polymers (polyethylene, fluoropolymers under consideration, etc.), where, due to low glass transition temperatures, the liquid‐like dynamics of amorphous phase chains is realized at room temperature through cooperative micro‐Brownian motions with short relaxation times. Taking into account that covalent‐bound sections of the chains of the amorphous phase can enter the crystallites, the noted mobility may initiate changes in the size of the latter. Such a possibility is proved by the example of the noted copolymer. At low‐temperature crystallization of a vinylidene fluoride ‐ hexafluoropropylene copolymer from a solution the formed α‐phase crystals have little perfection. The size of the crystals increases when the films are stored in room conditions. Because of the crystal polymorphism, at the same time a certain fraction of γ‐phase crystals which are present in initial films undergo a polymorphic transformation γ → α. These processes lead to an increase in crystallinity. Moreover, during such processes additional structuring is observed, which is reduced to the displacement of various kinds of intra‐chain defects into the amorphous phase (and especially into the surface). Since the copolymers under study are ferroelectrics, they were studied by piezo force microscopy. It was found that despite the crystallization predominantly in nonpolar α‐phase, piezo force microscopy revealed a domain structure, which formation mechanism is discussed. The structural changes at physical aging of the films affect the character of the noted domain structure. Thus, it is suggested that the mechanism of the described structural changes is realized through the developed cooperative mobility of the chains in the amorphous phase, which characterizes the processes of rotational diffusion.

The Result of Successive Exposure to Reverse and Forward Bias on the Electrophysical Characteristics of ZnO:Al/i-ZnO/CdS/CuIn1 – xGax(S, Se)2/Mo Structure Solar Cells

The Result of Successive Exposure to Reverse and Forward Bias on the Electrophysical Characteristics of ZnO:Al/i-ZnO/CdS/CuIn1 – xGax(S, Se)2/Mo Structure Solar Cells

Radio-Absorbing Materials Based on Polymer Composites and Their Application to Solving the Problems of Electromagnetic Compatibility.

Recently, designers of electronic equipment have paid special attention to the issue of electromagnetic compatibility (EMC) of devices with their own components and assemblies. This is due to the high sensitivity of semiconductor microcircuits to electromagnetic interference. This interference can be caused either by natural phenomena, such as lightning strikes, or by technical processes, such as transients in circuits during fast periodic or random switching. Either way, interference implies a sudden change in voltage or current in a circuit, which is undesirable, whether it propagates along a cable or is transmitted as an electromagnetic wave. The purpose of this article is to review the works devoted to the development, creation, and investigation of modern polymeric nanocomposite materials used for shielding electromagnetic radiation and their effective application for solving problems of electromagnetic compatibility. Additionally, the approach to design EMI shielding complex media with predetermined parameters based on investigation of various properties of possible components is shown. In the review, all polymer composites are classified according to the type of filler. The issues of the interaction of a polymer with conductive fillers, the influence of the concentration of fillers and their location inside the matrix, and the structure of the nanocomposite on the mechanisms of electromagnetic interaction are considered. Particular attention is paid to a new generation of nanocomposite materials with widely adjustable electrical and magnetic properties. A wide class of modern filled polymeric materials with dielectric and magneto-dielectric losses is considered. These materials make it possible to create effective absorbers of electromagnetic waves that provide a low level of reflection coefficient in the microwave range. The model mechanisms for shielding electromagnetic radiation are considered in the paper. A detailed review of the electro-physical properties of polymer nanocomposites is provided. Multilayer electrodynamic media containing combinations of layers of filled polymer composite materials with nanoparticles of different compositions and manufactured using a single technology will make it possible to create electrodynamic media and coatings with the required electro-physical characteristics of absorption, transmission, and reflection. Within the framework of the two-layer coating model, the difference in the effects of the interaction of electromagnetic radiation with conductive layers located on a dielectric and metal substrate is demonstrated. It is shown that in order to achieve optimal (maximum) values of reflection and absorption of electromagnetic radiation in the appropriate frequency range, it is necessary to fit the appropriate layer thicknesses, specific conductivity, and permittivity. Such approach allows designers to create new shielding materials that can effectively vary the shielding, absorbing, and matching characteristics of coatings over a wide frequency band. In general, it can be said that the development of innovative polymer composite materials for shielding electronic devices from electromagnetic interference and excessive electromagnetic background is still an important task. Its solution will ensure the safe and uninterrupted operation of modern digital electronics and can be used for other applications.