Hexagonal Electrodes Research Articles

Two-dimensional-materials-based transistors using hexagonal boron nitride dielectrics and metal gate electrodes with high cohesive energy

Two-dimensional-materials-based transistors using hexagonal boron nitride dielectrics and metal gate electrodes with high cohesive energy

Flexible High-Temperature MoS2 Field-Effect Transistors and Logic Gates.

High-temperature-resistant integrated circuits with excellent flexibility, a high integration level (nanoscale transistors), and low power consumption are highly desired in many fields, including aerospace. Compared with conventional SiC high-temperature transistors, transistors based on two-dimensional (2D) MoS2 have advantages of superb flexibility, atomic scale, and ultralow power consumption. However, MoS2 cannot survive at high temperature and drastically degrades above 200 °C. Here, we report MoS2 field-effect transistors (FETs) with top/bottom hexagonal boron nitride (h-BN) encapsulation and graphene electrodes. With the protection of the h-BN/h-BN structure, the devices can survive at much higher temperature (≥500 °C in air) than those of the MoS2 devices ever reported, which provides us an opportunity to explore the electrical properties and working mechanism of MoS2 devices at high temperature. Unlike the relatively low-temperature situation, the on/off ratio and subthreshold swing of MoS2 FETs show drastic variation at elevated temperature due to the injection of thermal emission carriers. Compared with metal electrode, devices with a graphene electrode demonstrate superior performance at high temperature (∼1-order-larger current on/off ratio, 3-7 times smaller subthreshold swing, and 5-9 times smaller threshold voltage shift). We further realize that the flexible CMOS NOT gate based on the above technique, and demonstrate logic computing at 550 °C. This work may stimulate the fundamental research of properties of 2D materials at high temperature, and also creates conditions for next-generation flexible harsh-environment-resistant integrated circuits.

Leaf and hexagonal grid designs for lead-acid battery. An EIS analysis

This work explore the fabrication of two distinct metallic grid architectures of positive electrode, namely hexagonal and leaf shapes, within the aim of improving the economic and the qualitative electrical performance aspects of lead-acid batteries in the automotive industry. By following a well-established aging procedure, Electrochemical Impedance Spectroscopy has been employed for their characterization by using different grid-acidic electrolyte interface changes. Two particular, parameters were investigated in order to predict the evolution of batteries lifetime performance: the resonance frequency single parameter, and time-dependent analysis of Constant Phase Element at 75 % State of Charge. Single resonance frequency fluctuations have been monitored at each PEIS step, in which we plotted the imaginary part of the impedance as function of frequency. An performance of battery lifetime has resulted for leaf battery than for hexagonal model, by comparison of the exponential-like increment degradation curve vs cycle number at SoC = 100 %. By using the effect of Q1 linear decay in the equivalent Randle circuit at 75 % SoC, we obtained for both models a smooth trend of the linear decay slopes, in particular in the second part of their lifetime, in agreement with previous investigated cells, demonstrating that is a robust feature, present in all fabricated cells. A fitting linear regression analysis depending on cycle number was applied to both batteries, in order to highlight the degradation grade of these curves. Another linear fit calibration of the degradation speed was applied for the second sector of batteries lifetime, pointing out a positive correction for the Q1 linear decay with ∼30 % for leaf cell over the hexagonal model, but less than previous investigated rectangular models or the industrial type. This suggests that the current homogeneity on the rectangular models during the charge-discharge processes is better distributed in the lower and upper parts of the plates than for hexagonal or leaf electrodes, being spotted here by the effect of current uniformity on their Randle circuit. The homogeneity of the electric field is not ensured by the shape of individual sectors, rather by their size and orientation.

Study of the transport properties of cobalt atomic contact under mechanical strain in a nitrogen atmosphere

Achieving an efficient spin-filter effect and large magneto-resistance in molecular junctions is very important in spintronics. By employing the non-equilibrium Green's function formalism combined with the density functional theory, this study investigated the atomic structures and spin-resolved transport properties of molecular junctions consisting of nitrogen (N2) sandwiched between two cobalt (Co) electrodes with different crystal lattices as a function of stretching distance. In the case of face-centred cubic Co electrodes, our calculations showed that the transport properties depend strongly on the stretching process, which changes the contact between the N2 and Co electrodes. Specifically, the maximum spin polarization is due to the configuration of N2 molecules sitting in parallel with the protruding Co atoms. Furthermore, the Co dxz,yz orbitals interact with the N px,y orbitals, which contribute to the high transmission coefficient at the Fermi level for spin-down electrons. Meanwhile, the Co s-dz2 hybridization orbitals, which interact weakly with the N p orbitals, contribute to the small transmission coefficient at the Fermi level. This can also be verified by the molecular junction model adopting simple monatomic Co chain electrodes, which also show a perfect spin-filter effect and achieve an ideal magnetoresistance. In contrast, in the case of hexagonal Co electrodes, the spin-filter effect disappears. However, the effect appears again by adding one more Co atom to the central point contact. Our findings show that the spin-resolved electronic transport of molecular junctions depends on the stretching process and the nature of the electrodes, which can help in the future design of molecular devices based on the spin degree of freedom.

Thickness-controlled porous hexagonal NiO nanodiscs electrodes for use in supercapacitors: How nanodiscs thickness influences electrochemical performance

Two-dimensional (2D) nickel oxide (NiO) hexagonal nanodiscs were synthesized via a hydrothermal route, followed by successive calcination. The decisive roles of the [OH−]/[Ni2+] molar ratios, as well as the calcination temperatures, were found in controlling the nanodiscs morphology of the NiO nanostructures. The increase in the concentration of OH− ions in the precursor solution influenced the crystal growth that directed to the formation of the hexagonal nanodisc morphology with increased edge thickness and beyond certain limits transformation from the nanodiscs to complete 3D morphology. The nanodiscs grew with increasing exposed surface size with a high BET area and varied thicknesses from 4 to 20 nm. The increase in calcination temperature improved crystallinity by eliminating crystal defects and voids, while crystals grew along the (200) plane. However, a reduction in the BET area and pore volume occurred at higher calcination temperature because of the collapse in micro-mesopores. The electrochemical performances of NiO electrodes show dependence on the thickness of the nanodiscs, the calcination temperature, and the type of current collector used. A distinct electrochemical feature was observed for NiO nanodiscs over planar conductive carbon fiber paper and 3D porous Ni foam substrates. The hydrothermal approach reported here to produce thickness-controlled NiO nanodiscs with high intrinsic surface area has great potential for developing next-generation battery-type faradic electrodes in conjunction with carbon allotropes and other metal oxide materials for high power and energy density throughput.

Electrical Model for Complex Surface DBD Plasma Sources

Electrical models can play a crucial role in the characterization, design, and definition of optimal operating conditions of nonthermal plasma sources in a wide field of applications. Various electrical models are available from the literature, with most modeling the behavior of volume dielectric barrier discharge (DBD) plasma sources. Although electrical models for surface DBD plasma sources are presented from the plasma actuator community, these models are limited to simple and mostly linear surface DBD plasma sources. This study presents a new electrical model focusing on surface DBD plasma sources with complex electrode designs. The proposed model employs the ratio of the electrode surface into a discharging and nondischarging area to consider complex electrode designs, such as meshed and hexagonal electrodes. Microdischarges during plasma ignition phase have been modeled through the superposition of a discharge current to the displacement current. The proposed electrical model has been validated over a large range of operating conditions. It is shown that the simulated electrical characteristics using the developed model are in reasonable agreement with measurements.

Study on the Shape of Staggered Electrodes for 3-D Electrical Capacitance Tomography Sensors

A conventional electrical capacitance tomography (ECT) sensor consists of multiple rectangular electrodes in a single plane. To generate 3-D images, some researchers use an ECT sensor with multiplane rectangular electrodes and in-line arrangement of different electrode planes and measure the capacitance between the electrode pairs not only within the same plane but also between different planes. Because those electrode pairs in different planes are far away from each other, the measured capacitance signals between them are weak and, hence, are easily affected by noise, resulting in the obvious disturbance on the measured signals and, hence, low image quality. To address those problems, the 3-D ECT sensors with different arrangements and different shapes of electrodes are studied to investigate the effect of different arrangements and different shapes of electrodes on the measured capacitance signals and the image quality. Four 3-D ECT sensors are made with different arrangements or shapes of electrodes: rectangular electrodes are in line arrangement, whereas diamond, circular, and hexagon electrodes are staggered arrangement. The performance of the four 3-D ECT sensors is compared. The results show that 3-D ECT sensors with staggered electrodes can decrease the disturbance on the measured signals and improve the image quality of static models compared with that with conventional rectangular electrodes. Among the three 3-D ECT sensors with staggered electrodes, the 3-D ECT sensor with hexagonal electrodes has superior performance to the other two 3-D ECT sensors with diamond and circular electrodes. It was used to measure moving objects and a fluidized bed.

Electrochemotherapy in the treatment of cutaneous malignancy: Outcomes and subgroup analysis from the cumulative results from the pan-European International Network for Sharing Practice in Electrochemotherapy database for 2482 lesions in 987 patients (2008–2019)

BackgroundElectrochemotherapy (ECT) is a treatment for both primary and secondary cutaneous tumours. The international Network for sharing practices on ECT group investigates treatment outcomes after ECT using a common database with defined parameters. MethodsTwenty-eight centres across Europe prospectively uploaded data over an 11-year period. Response rates were investigated in relation to primary diagnosis, tumour size, choice of electrode type, route of bleomycin administration, electrical parameters recorded and previous irradiation in the treated field. ResultsNine hundred eighty-seven patients, with 2482 tumour lesions were included in analysis. The overall response (OR) rate was 85% (complete response [CR]: 70%, partial response rate: 15%, stable disease: 11%, and progressive disease: 2%). For different histologies, OR and CR rates for metastases of malignant melanoma were 82% and 64%, basal cell carcinoma were 96% and 85%, breast cancer metastases were 77% and 62%, squamous cell carcinoma were 80% and 63% as well as Kaposi's sarcoma were 98% and 91%, respectively. Variance was demonstrated across histotypes (p < 0.0001) and in accordance with size of lesion treated (dichotomised at diameter of 3 cm (p < 0.0001). Hexagonal electrodes were generally used for larger tumours, but for tumours up to 3 cm, linear array electrodes provided better tumour control than hexagonal electrodes (80%:74%, p < 0.003). For tumours more than 2 cm, intravenous administration was superior to intratumoural (IT) administration (p < 0.05). Current recorded varied across tumour histologies and size but did not influence response rate. In previously irradiated areas, responses were selectively lower for IT administration. ConclusionsThese cumulative data endorse efficiency of ECT across a broad range of histotypes. Analysis of 2482 lesions details subgroup analysis on treatment response informing future treatment choices.

Radiological findings of porcine liver after electrochemotherapy with bleomycin.

BackgroundRadiologic findings after electrochemotherapy of large hepatic blood vessels and healthy hepatic parenchyma have not yet been described.Materials and methodsWe performed a prospective animal model study with regulatory approval, including nine grower pigs. In each animal, four ultrasound-guided electroporated regions were created; in three regions, electrodes were inserted into the lumen of large hepatic vessels. Two types of electrodes were tested; variable linear- and fixed hexagonal-geometry electrodes. Ultrasonographic examinations were performed immediately and up to 20 minutes after the procedure. Dynamic computed tomography was performed before and at 60 to 90 minutes and one week after the procedure.ResultsRadiologic examinations of the treated areas showed intact vessel walls and patency; no hemorrhage or thrombi were noted. Ultrasonographic findings were dynamic and evolved from hyperechogenic microbubbles along electrode tracks to hypoechogenicity of treated parenchyma, diffusion of hyperechogenic microbubbles, and hypoechogenicity fading. Contrast-enhanced ultrasound showed decreased perfusion of the treated area. Dynamic computed tomography at 60 to 90 minutes after the procedure showed hypoenhancing areas. The total hypoenhancing area was smaller after treatment with fixed hexagonal electrodes than after treatment with variable linear geometry electrodes.ConclusionsRadiologic findings of porcine liver after electrochemotherapy with bleomycin did not show clinically significant damage to the liver, even if a hazardous treatment strategy, such as large vessel intraluminal electrode insertion, was employed, and thus further support safety and clinical use of electrochemotherapy for treatment of hepatic neoplasia.

Cell patterning via optimized dielectrophoretic force within hexagonal electrodes in vitro for skin tissue engineering

Tissue reconstruction through in vitro cell seeding is a popular method for tissue engineering. In this paper, we proposed a thin-layer structure consisting of multiple hexagons for the regeneration of skin tissue. Cells could be seeded and cultured within the structure via dielectrophoresis (DEP) actively. A thin layer of the structure was fabricated with biocompatible medical-grade stainless steel via precise laser cutting. The fabricated layers were stacked together to form a 3D electrode pair, which could be used to generate a 3D electric field. Thus, the suspended cells within the structure could be patterned via DEP manipulation. The input voltage was examined and optimized to ensure cell viability and patterning efficiency during the DEP manipulation process. As soon as we applied the optimized voltage, human foreskin fibroblast (HFF) cells could be attracted along the edge of the electrodes, forming hexagonal cellular patterns. After that, a single layer of the patterned cells was further cultured in an incubator for 7 days and observed under a microscope. The obtained images showed that the seeded cells could proliferate and fill in the hexagonal wells, which could be used for further skin tissue regeneration. As shown in the experimental results, this structure could be used for active cell seeding and proliferation for the development of skin tissue engineering.

Electrode Structure Effects on Electrostatic Spray System Efficiency for Bladeless Wind Power Generation

The liquid medium can be atomized into small droplets and then it moves towards the reverse direction of the electric field force under the wind action, which can increase overall electrical potential energy of the system and realize the conversion of wind energy to the electric energy. In this paper, multi injection needle mesh electrode is taken in the electrostatic wind power generation system as the research object. Based on the ANSYS simulation platform, electric field distribution and the influence of electric field intensity on spray effect at injection needle in different structure like quadrangular, rhombic, circular and hexagonal high pressure electrodes are studied. The results show that the voltage level of discharge terminal in circular electrode structure is significantly higher than that of the other electrode structures and voltage level is needed for multiple jets significantly lower than the other electrode structures.

Rapid synthesis of hexagonal mesoporous structured NiCo2O4 via rotary evaporation for high performance supercapacitors

In this study, hexagonal mesoporous structured NiCo2O4 with uniform size is successfully synthesized via a facile rotary evaporation. Hexagonal NiCo2O4 electrodes exhibit a high specific capacitance of 568.0 F g−1 at 1 A g−1, standout rate performance of 71.0% retention for current increases 16 times, and excellent cycling stability of 76.8% capacitance retention after 2000 cycles, which are attributed to interconnected mesoporous self-assembly architecture and larger specific surface area generated through the novel rotary evaporation. This strategy provides a new avenue to develop and broaden more mesoporous self-assembly functional materials.

Safety and feasibility of electrochemotherapy in patients with unresectable colorectal liver metastases: A pilot study

Background and objectivesElectrochemotherapy is a novel ablation technique combining chemotherapeutic agents with reversible cell membrane electroporation. Previous experiences have shown its efficacy for cutaneous tumors. Its application for deep-seated malignancies is under investigation. We performed a prospective, pilot study to evaluate the feasibility, safety, and efficacy of intraoperative electrochemotherapy for otherwise unresectable colorectal liver metastases. MethodsElectrochemotherapy with bleomycin was combined with open liver resection and performed with linear or hexagonal needle electrodes according to an individualized pretreatment plan. The primary endpoints were: feasibility, as ratio of completed to planned treatments; safety, and efficacy, as per response assessed at 30 days with MRI and according to RECIST. The secondary endpoint was overall and progression-free survival at month 6. ResultsA total of 9 colorectal liver metastases were treated in 5 patients with 20 electrode applications. No intraoperative complications were observed. At day 30, complete response was 55.5% and stable disease 45.5%. All (5) patients reached a 6 months overall survival, and 4 out of 5 patients had 6 months progression free survival. ConclusionsElectrochemotherapy is a feasible and safe adjunct to open surgery for treatment of unresectable colorectal liver metastases. Larger studies and longer follow-ups are favored to better define its role in the treatment of secondary liver malignancies.

Influence of Electrodes on Electric Field Distribution for Effective Electrochemotherapy

Electro oration is the application of electrical pulses for enhanced drug delivery. When used for delivering chemo drugs, it is called electrochemotherapy (ECT). For inoperable and chemo- and radio-resistant tumors, we need an alternative technique and ECT is a viable option as evidenced by the treatment of thousands of patients, effectively. The efficiency of the ECT depends on the voltage (electric field) magnitude, pulse duration, number of pulses, the drug molecule to be delivered and the electrode geometry and size. It is of practical interest to study the effect of material on the efficacy of the therapy. Towards this, in this research, we investigated the influence of electric field distribution due to different electrode materials. For this purpose, both platinum and surgical steel needle array electrodes were used. Surgical steel is the most commonly used material for electro chemotherapy applications. These needle electrodes are of both hexagonal and pentagonal configurations with a central electrode in each. ANSYS, the industry standard software that used finite element method is used to study the electric field distribution, of both healthy tissue and tumor tissue using these two electrode configurations and the two different materials. Both unipolar and bipolar voltages were studied. The results indicate that the electric field distribution, both in magnitude and pattern is similar for both electrodes, for both configurations and materials, which is desired from the clinical aspect. The electric field intensities for the hexagonal and pentagonal needle electrodes were 1280V/cm and 1180V/cm respectively in the case of tumor tissue (correlating well with the desired level of 1200V/cm). They were 835V/cm and 843V/cm for these electrodes in the case of healthy tissues. The values were same in the case of bipotential voltages too.

WSe₂ Light-Emitting Tunneling Transistors with Enhanced Brightness at Room Temperature.

Monolayers of molybdenum and tungsten dichalcogenides are direct bandgap semiconductors, which makes them promising for optoelectronic applications. In particular, van der Waals heterostructures consisting of monolayers of MoS2 sandwiched between atomically thin hexagonal boron nitride (hBN) and graphene electrodes allows one to obtain light emitting quantum wells (LEQWs) with low-temperature external quantum efficiency (EQE) of 1%. However, the EQE of MoS2- and MoSe2-based LEQWs shows behavior common for many other materials: it decreases fast from cryogenic conditions to room temperature, undermining their practical applications. Here we compare MoSe2 and WSe2 LEQWs. We show that the EQE of WSe2 devices grows with temperature, with room temperature EQE reaching 5%, which is 250× more than the previous best performance of MoS2 and MoSe2 quantum wells in ambient conditions. We attribute such different temperature dependences to the inverted sign of spin-orbit splitting of conduction band states in tungsten and molybdenum dichalcogenides, which makes the lowest-energy exciton in WSe2 dark.

Cathodically induced antimony for rechargeable Li-ion and Na-ion batteries: The influences of hexagonal and amorphous phase

Cathodic corrosion, a green electrochemical method, has been employed to obtain Sb nanomaterials utilized as anode material for lithium-ion batteries and sodium-ion batteries. Interestingly, two different corrosion mechanisms are found, coming from the impact of electrolyte, resulting in the formation of hexagonal and amorphous Sb in aqueous and organic solution, respectively. With the help of water-soluble carboxymethyl cellulose binder and the electrolyte additive fluoroethylene carbonate, both hexagonal and amorphous Sb electrodes exhibit good cycling stability when utilized as anode materials for lithium-ion batteries and sodium-ion batteries. Additionally, both the hexagonal and amorphous Sb electrodes show very good rate capability in lithium-ion batteries. Even at high current density (2000 mA g−1), the hexagonal and amorphous Sb give reversible capacities of 422 and 379 mA h g−1, respectively. Surprisingly, when used as anode materials for sodium-ion batteries, the hexagonal Sb electrode exhibits a good rate performance of 632, 625, 569, 515 and 426 mA h g−1 at a current density of 100, 200, 500, 1000, and 2000 mA g−1, respectively. However, limited rate performance is observed from the amorphous Sb electrode in case of sodium-ion battery due to the large impedance.

Ni2+ion assisted synthesis of hexagonal α-Fe2O3nanoplates as anode materials for lithium-ion batteries

Fe2O3 hexagonal nanoplates have been successfully synthesized via a molten salt procedure with the assistance of Ni2+ ions. The resulting Fe2O3 is characterized by X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). According to the microscopy observations, the morphology and size of the sample can be tailored by the foreign ions (Ni2+). Moreover, galvanostatic cell cycling is employed to evaluate the electrochemical performance of the obtained Fe2O3. The results show that the Fe2O3 hexagonal nanoplate electrodes have stable cycling performance with a reversible capacity of over 711 mA h g−1 after 100 cycles at a current density of 100 mA g−1. The sample with optimized structure shows the best rate performance with a high capacity of 418 mA h g−1 (40th cycle) even at a current density of 1000 mA g−1.

Structural, optical, photoluminescence, electrochemical, and photoelectrochemical properties of Fe doped ZnSe hexagonal nanorods

The present investigation describes that the iron (Fe) doped ZnSe hexagonal nanorods were successfully synthesized via chemical synthesis specifically galvanostatic mode of electrodeposition and addition of Fe in order to improve the PEC performance of ZnSe electrodes using a galvanostatic mode. These crystalline Fe doped ZnSe hexagonal nanorods electrodes are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and optical properties, such as UV–vis spectroscopy, photoluminescence spectroscopy, electrochemical impedance spectroscopy (EIS), Raman spectroscopy and photoelectrochemical properties. It is seen that at 5% Fe doped ZnSe hexagonal nanorods show the open circuit voltage (Voc) was 100mV, and short circuit current (Isc) was 110μA. The observed fill factor and efficiency were found to be 44% and 0.15%, respectively.

A prototype GEM-TPC for PANDA

The PANDA fixed-target experiment planned at the future international Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany, will investigate fundamental questions in non-perturbative QCD. It features a cooled antiproton beam with momenta from 1.5 to 15 GeV/c and will reach luminosities of up to 2⋅1032 cm−2 s−1 corresponding to a p̄p-annihilation rate of 2⋅107 s−1. One option for the central tracker of the target spectrometer was a cylindrical, ungated, continuously running TPC with GEM-based amplification stage surrounding the interaction point.To show the feasibility of such a detector, a prototype with a drift length of 727.8 mm and an inner (outer) radius of 52 mm (154 mm) was built. The pad plane of the detector has 10254 hexagonal pickup electrodes which are read out using 42 front-end cards, each equipped with four AFTER chips, originally developed for the T2K experiment.The prototype was installed and tested in the FOPI spectrometer at GSI (Darmstadt, Germany). The central drift chamber and the RPC-TOF system of FOPI give excellent reference for momentum and energy loss measurements with the TPC. A superconducting solenoid magnet creates a magnetic field of 0.6 T. Gas mixtures of Ar/CO2 (90/10) and Ne/CO2 (90/10) were used with different drift fields ranging from 150 to 350 V/cm. A 83mKr source was used for gain calibration.The GEM-TPC will significantly improve the vertex resolution and secondary-vertex detection of the FOPI spectrometer, where it was used in a three-week physics campaign with a π− beam in June 2011. A detailed overview of the detector hardware and electronics will be presented together with first results from the commissioning of the detector.

Development of piezoelectric MEMS deformable mirror

This paper reports on piezoelectric micro-electro-mechanical systems deformable mirrors with high-density actuator array for low-voltage and high-resolution retinal imaging with adaptive optics. The deformable mirror was composed of unimorph structure of lead zirconate titanate (PZT) thin film deposited on Pt-coated silicon on insulator substrate and a diaphragm of 10 mm in diameter formed by backside-etching the Si handle wafer. 61 hexagonal electrodes were laid out on the PZT thin film for the high-density actuator array. In order to reduce the dead space for the lead lines between the electrodes and connecting pads, a polyimide layer with through holes on the electrodes was patterned as an electrical insulator. To confirm the application feasibility of the fabricated DMs, displacement profiles of the actuators were measured by a laser Doppler vibrometer. Independent applications of voltages on individual actuators were confirmed.