Interface Charge Density Research Articles

Boron-doped diamond MOSFETs operating at temperatures up to 400°C

The boron-doped diamond (B-diamond) metal-oxide–semiconductor field–effect transistors (MOSFETs) are fabricated and characterized at operating temperatures up to 400°C. The SiO2 serves as the gate oxide insulator, while the Ti/Pt bilayer is employed as the gate contact metal. As the operating temperature rises from room temperature (RT) to 400°C, the absolute drain current maximum for the B-diamond MOSFET increases from 3.9 μA mm−1 to 177.4 μA mm−1. Conversely, the on-resistance decreases significantly from 1469.8 kΩ mm to 16.5 kΩ mm. The on/off ratio for the MOSFET at RT is 1.9 × 105, which increases to over 5.0 × 106 at temperatures exceeding 100°C. The threshold voltage exhibits a decreasing trend, though it deviates from this trend at 300°C. The subthreshold voltage and extrinsic transconductance maximum show increasing trends from 113 mV dec−1 to 299 mV dec−1 and from 0.9 μS mm−1 to 23.1 μS mm−1, respectively. The interfacial trapped charge density is found to be stable in the range of 8.0 × 1011–2.3 × 1012 eV−1 cm−2.

Degradation Properties of Organic Light‐Emitting Diodes with Modified Interface Charge Density via Dipolar Doping Studied by Displacement Current Measurement

Degradation Properties of Organic Light‐Emitting Diodes with Modified Interface Charge Density via Dipolar Doping Studied by Displacement Current Measurement

Performance analysis based on biomolecule position and pH-sensing mechanism for vertical TFET

Abstract In this study, the impact of the diffusion mechanism of a biomolecule in the nanocavity ( T b i o ) region on the electrical characteristics of a split-gate, step-channel electrolyte-insulated semiconductor vertical TFET (SGSC-EIS-VTFET) pH biosensor was investigated. The impact of the transport sensing mechanism, that is, diffusion-limited process and rapid mixing process of biomolecules in the nanocavity sensing area, on the pH of the analyte was also examined. Physics-based modelling was used to determine the interface charge density at the oxide-silicon interface of the proposed vertical TFET pH biosensor. We also considered the effect of pH values on the proposed device performance, like drain current (I ds), transconductance (gm), current sensitivity (SID), and voltage sensitivity (SV) after the inclusion of electrolyte medium. Here, the maximum SV ∼ 145 mH pH−1 for T b i o = 6 nm, which is higher than the Nernstian limit (59.2 mV pH−1), and SID has been enhanced by 10 times per pH variation. This study indicated that the diffusion of biomolecules significantly impacts the performance parameters of the proposed structure because of the realistic dominance of the sensing mechanism and the conjugation of analyte on the sensing area.

Enhancing electrostatic spray-painting efficiency with modified high-voltage conductors: A numerical study on pulsed electric fields

This study presents a numerical simulation of electrostatic spraying using a rotary bell sprayer equipped with a high-voltage control ring conductor. The effects of the electric field generated by constant and pulsed voltages at various frequencies applied to the electrostatic rotary bell sprayer (ERBS) with the control ring are explored. Using the OpenFOAM computational fluid dynamics framework, the simulations employ a three-dimensional Eulerian-Lagrangian method. The implemented algorithm models fully turbulent airflow using a Large Eddy Simulation (LES) approach, along with detailed modeling of spray dynamics, electric fields, and droplet tracking. The primary objective is to investigate the influence of different voltage application modes on the spraying process, with a focus on optimizing droplet consistency and control. The impacts of constant and pulsed voltages on spray plume formation, droplet volumes, and critical spraying stages are examined. Through in-depth analysis of electric field distributions, interface charge densities, and velocity fields, the complex interactions governing pulsed and constant voltage spraying processes are elucidated. The results show that pulsed voltage applied to the control ring shapes the spray plume and alters droplet behavior, though with limited effectiveness. In contrast, applying a pulsed voltage of −40 kVrms to the sprayer’s body cup at frequencies of 800 Hz and 1600 Hz significantly improves spray characteristics, resulting in a modified torus shape and a narrower size range of larger droplets compared to constant voltage condition of −40 kV. This leads to a more uniform droplet size distribution, consistent paint film, and minimal overspray. Consequently, transfer efficiency (TE) increases by 6% at 800 Hz and 4.8% at 1600 Hz compared to constant voltage. This indicates that 800 Hz is the optimal frequency for applying pulsed fields, due to its notable effectiveness in improving deposition efficiency and minimizing material waste.

Electrodeposition for Metal Recovery from Spent Batteries: Strategies for Improving Selectivity

Selective recovery of critical metals such as cobalt and nickel at a molecular level is crucial for the sustainable recycling of Li-ion batteries. However, the similarity in reduction potentials between these metals presents a significant challenge for achieving selectivity during electrodeposition, particularly for elements like cobalt and nickel (with E°Co = −0.277 V and E°Ni = −0.250 V vs SHE). In this presentation, we introduce a key strategy aimed at controlling selectivity toward either cobalt or nickel during potential-dependent electrodeposition. Initially, manipulating the electrolyte composition to introduce an excess of chloride ions enables precise control over speciation, leading to the distinct formation of anionic cobalt chloride complexes (CoCl42-) while keeping nickel predominantly in its cationic form ([Ni(H2O)5Cl]+) within an aqueous electrolyte. This forms the basis for potential-dependent selectivity. Additionally, regulating the interfacial charge density through electrode functionalization further fine-tunes selectivity by controlling the diffusion coefficient of the target ions. Moreover, we demonstrate the effectiveness of temperature-dependent control in achieving selectivity, resulting in a Ni/Co ratio exceeding 100. Unlike traditional selective electrodeposition methods, where the extended enrichment of one metal on the solid surface adversely impacts dynamic selectivity due to concentration change in the bulk electrolyte, our innovative approach guarantees high-purity and high-recovery metal extraction even during prolonged electrodeposition. This study presents a hopeful prospect for selective electrodeposition as a proficient separation method in battery recycling procedures.

Enhancing Interfacial Capacitance Using Anionic Amphiphiles in Ionic Liquid Electrolyte Blends

The acceleration of climate change due to carbon emissions has generated an imminent need to transition towards renewable energy sources. However, the intermittent nature of renewable sources like wind or solar energy necessitates breakthroughs in energy storage devices that can rapidly charge and discharge. This demand creates a new role for high power density supercapacitors. While supercapacitors can quickly discharge electricity, they are limited by low energy densities. This limitation in energy density has generated research interest into charge storage mechanisms at interfaces and new types of supercapacitor electrolytes. An ideal supercapacitor electrolyte has a wide electrochemical stability window and high capacitance to maximize the energy density. Ionic liquids (ILs) show potential for this role with their wide electrochemical stability windows, nonflammability, and nonvolatility. Problematically, strong ion correlations present in ILs result in low capacitances. I will discuss our work aimed at tuning ionic correlations in binary IL blends to provide pathways towards higher energy density capacitive interfaces. We show how the addition of surface-active amphiphilic anions weakens these correlations increasing the interfacial charge density and capacitance of these IL blends. Notably, we find that mixing surface-active amphiphilic anions with nonamphiphilic ILs doubles the capacitance at negative surfaces. We hypothesize that polarity-dictated anion-anion van der Waals interactions serve to weaken IL cation-anion interactions and ultimately drive molecular assembly at negative surfaces, increasing capacitance. I will also present our complementary investigations of non-amphiphilic binary IL mixtures and provide spectroscopic insight into bulk ion correlations within these systems. Our study ultimately paves the path towards fundamental investigations into the chemical nature of additives in ionic liquid blends to boost performance within next-generation supercapacitors.

Reinforced interfacial coupling effect of NiO/Ni2P by Fe doping for boosting water splitting

Nickel-based catalysts are suitable for water splitting to generate hydrogen. However, the low conductivity and weak stability have always been urgent issues to be addressed in nickel-based catalysts. Fe-doped nickel oxide/nickel phosphide (Fe-NiO/Ni2P) was prepared as a bifunctional electrocatalyst by doping metal and constructing heterogeneous interface. The introduction of Fe contributed to the reinforced interfacial coupling effect of NiO/Ni2P to promote charge transfer and accelerate reaction kinetics. The heterojunction regulated the interfacial charge density between NiO and Ni2P to improve the electronic environment of Ni2+ and enhance conductivity. The O-Fe-P bond at the heterogeneous interface induced the directional transfer of electrons and ensured the structure stability. The synergistic effect of Fe doping and heterogeneous interface increased the adsorption energy of *O and coordinated the adsorption energy of *H, advancing the catalytic performance. Fe-NiO/Ni2P exhibited the overpotential of 242 mV and 141 mV at 10 mA cm−2 for oxygen and hydrogen evolution, respectively.

Engineering of charge density at the anode/electrolyte interface for long-life Zn anode in aqueous zinc ion battery.

The aqueous zinc ion battery emerges as the promising candidate applied in large-scale energy storage system. However, Zn anode suffers from the issues including Zn dendrite, Hydrogen evolution reaction and corrosion. These challenges are primarily derived from the instability of anode/electrolyte interface, which is associated with the interfacial charge density distribution. In this context, the recent advancements concentrating on the strategies and mechanism to regulate charge density at the Zn anode/electrolyte interface are summarized. Different characterization techniques for charge density distribution have been analysed, which can be applied to assess the interfacial zinc ion transport. Additionally, the charge density regulations at the Zn anode/electrolyte interface are discussed, elucidating their roles in modulating electrostatic interactions, electric field, structure of solvated zinc ion and electric double layer, respectively. Finally, the perspectives and challenges on the further research are provided to establish the stable anode/electrolyte interface by focusing on charge density modifications, which is expected to facilitate the development of aqueous zinc ion battery.

Strengthened ozone adsorption through positive electric field-induced charge migration on various TiO2 crystal surfaces: A mechanistic and theoretical study

This study investigates the enhancement of ozone adsorption on diverse TiO2 crystal interfaces through an innovative electrochemical modulation approach. The research focuses on the effects of applied electric field strength and reaction sites on ozone interfacial adsorption energies for Ti/Anatase TiO2 (0 0 1) and Ti/Rutile TiO2 (1 1 0) interfaces. The findings reveal that positive electric fields significantly enhance ozone adsorption on both interfaces, with adsorption energies increasing by up to 18% for Ti/Anatase TiO2 (0 0 1) and 15% for Ti/Rutile TiO2 (1 1 0). Notably, double water molecule sites (≡(H2O)2) play a crucial role in this enhancement process. The study demonstrates that the applied electric field alters the charge distribution at the TiO2 catalytic interface, thereby increasing interfacial charge density and promoting charge migration to ozone. Furthermore, this process leads to enhanced overlap and hybridization between ≡(H2O)2 sites and the s and p orbitals of ozone molecules, resulting in the formation of chemical bonds with lower Fermi levels. These comprehensive results demonstrate the broad applicability of the electrochemical interfacial ozone adsorption enhancement method across different crystal types and surfaces. Consequently, this study provides essential data to support the advancement of greener and more energy-efficient heterogeneous catalytic ozonation processes, potentially contributing to significant improvements in ozone-based water treatment technologies.

Degradation mechanism of SiC diodes under thermal and irradiation stress

Abstract Silicon carbide (SiC)-based diodes are widely used due to their high temperature resistance. In this paper, breakdown voltage of 4H-SiC JBS diodes and capacitance-voltage of 4H-SiC MOS capacitors with identical interfacial structure were both measured at high temperature to study their interfacial properties. By analyzing the variation of interfacial properties, the correlation between thermal stress and failure mode of 4H-SiC JBS diodes was further established to reveal their degradation mechanism. During initial high temperature storage, interfacial negative effective charge density of 4H-SiC JBS diodes may increase, leading to the decrease of breakdown voltage. As storage time increases, interfacial charge density began reducing, resulting in the increase of breakdown voltage. Avalanche luminescence verifies that the variation of interfacial charge density under thermal stress led to the degradation of 4H-SiC JBS diodes and further affected their breakdown voltage. Finally, degradation mechanism of SiC-JBS, SiC-SBD and SiC-PIN diodes under irradiation stress was investigated. After irradiation, forward current of some SiC diodes increased at a small forward voltage. However, the reverse characteristics deteriorated obviously and even failed.

Improved electrical performance for SiO2/β-Ga2O3 (001) MIS capacitor by post-deposition annealing

In this study, we have fabricated a high-performance SiO2/β-Ga2O3 (001) MIS capacitor and investigated the effect of low-temperature post-deposition annealing (PDA) on its electrical properties. The SiO2/β-Ga2O3 (001) MIS capacitor exhibits improved gate leakage current and breakdown electrical field after the PDA treatment. The high-frequency capacitance-voltage hysteresis curves reveal that the fixed charge density, as well as the fast and deep near-interfacial trapped charge densities, decreases with the PDA process. We achieved an interfacial trapped charge density as low as 1.6 × 1011 cm−2 eV−1 at an energy of 0.6 eV below the conduction band of β-Ga2O3 (001) through 400 °C annealing.

Electrostatic Surface Charging by Water Dewetting.

Water dewetting generates static electricity. We reviewed historical experiments of this phenomenon, and we studied the charging of polymer slides and metal electrode supported polymer films withdrawn vertically from a pool of aqueous solutions. For pure water, charging was negative and surface charge densities increased with the speed of dewetting, which we explain by the thermally activated entrainment of nanometer-sized water droplets or clusters charged by unbalanced adsorbed electric double-layer ions. Surface charge densities increased for reduced polymer film thickness following a power law, which we explain by reduced discharge of the entrained water volumes. At low salinity c ≲ 10 μM, charging was proportional to electrokinetic interfacial charge densities: the negative charging was increased for alkaline solutions and for most salts at μM concentrations and the charge polarity was inversed to positive for a cationic surfactant, a salt with a highly positively charged cation, and for a strong acid at approximately pH 4. Charging was reduced again for c ≳ 100 μM, especially at high dewetting speeds and for chaotropic ions, which we explain by the entrainment of larger and more discharged droplets. We determined adsorption energies of the charged water clusters on the dewetted surface from thermally stimulated discharge of the charged polymer slides and we show that the surface charge distribution, imaged by charged toner powders and measured microscopically by Kelvin probe force microscopy, is a record of the dewetting process that provides spatial and kinetic information about the three-phase contact line motion.

Ultralow-Power DST-TFET pH Sensor Exceeding the Nernst Limit with Influence of Temperature on Sensitivity.

In this paper, a dual-source T-channel TFET (DST-TFET)-based pH sensor demonstrating the pH change in the electrolyte has been studied. The proposed device exceeds the Nernst limit of 59 mV/pH by ∼5 folds. The simulation is performed on an ATLAS TCAD tool (SILVACO) and pH is determined by calculating the interface charge density (Δσ) using appropriate physics models. The voltage sensitivities, using various oxides (SiO2, HfO2, Al2O3) with a maximum achieved sensitivity (SV) of 297.66 mV/pH ∼5× Nernst limit, have been calculated. Moreover, this high value of SV is achieved at an ultralow operating voltage of 0.1 V. The results have been validated by proper calibration of models with the experimental data. It is evident from the results that DST-TFET performs well at ultralow power compared to several previously reported devices. Furthermore, the temperature study has been implemented in the proposed sensor to investigate the IDS-VGS characteristics and sensing performance of the device. The pH sensitivity and voltage sensitivity decreased with increase in temperature. The proposed pH sensor with such high sensitivity is an exclusive choice for pH-sensing applications.

SiC whisker toughened WC-Al2O3-ZrO2 binderless cemented carbides via fast-hot-pressed sintering and DFT calculations

Binderless cemented carbide has garnered attention for its exceptional hardness and suitability in extreme service conditions. The absence of a metal binder, however, leads to inadequate fracture toughness, which limits its broader application. This study explores the influence of SiC whisker on the microstructure and mechanical properties of WC-Al2O3-ZrO2 binderless cemented carbide, utilizing a combination of experimental method and Density Functional Theory (DFT) calculations. The inclusion of 1 wt% SiC whisker resulted in a notable increase in fracture toughness, reaching an impressive toughness of 16.4 ± 0.5 MPa⋅m1/2, while maintaining a high Vickers hardness of 19.4 GPa. DFT calculations provided insights into the interface energy, cohesive energy, and charge density differences at the WC/SiC interface. This work also presents two models depicting the behavior of whiskers during fracture, based on the observed microstructure and computational findings. Overall, the present work offers significant insights and practical guidance for advancing binderless cemented carbide technologies.

Investigation of Interlayer Dielectric in BaTiO3/III‐Nitride Transistors

In this study, the impact of varying the thickness of the Al2O3 interlayer dielectric on the electrical characteristics of BaTiO3/III‐nitride transistors is investigated. In the findings, it is revealed that a minimum thickness of 8 nm for the Al2O3 layer is crucial to maintain high device performance and protect against sputtering‐induced damage during BaTiO3 deposition. The fabricated BaTiO3/Al2O3/AlGaN/GaN high electron mobility transistors exhibit exceptional electrical properties, including a maximum current density of 700 mA mm−1, an on‐resistance of 5 Ω mm, an ION/IOFF ratio of 107, a subthreshold slope of 119 mV dec−1, and significantly reduced gate leakage current. The devices with the optimal 8 nm Al2O3 thickness demonstrates excellent agreement between theoretical and experimental values for effective mobility, achieving a value of 1188 cm2 V−1·s at a 2D electron gas density of 1013 cm−2. Furthermore, in the study, it is confirmed that increasing the Al2O3 thickness also improves the quality of interface charge density, as evidenced by the results obtained from capacitance–voltage measurements. In these findings, the critical role of controlling the Al2O3 thickness in optimizing the electrical characteristics and overall performance of BaTiO3/III‐nitride transistors are highlighted.

Reduction in density of interface traps determined by C-V analysis in III-nitride-based MOSHFET structure

An in situ metal-organic chemical vapor phase epitaxy is used to grow a complete AlGaN/GaN metal oxide semiconductor heterojunction field effect transistor (MOSHFET) structure, gated by a gallium oxide (Ga2O3) layer; we observed reduction in the interfacial trap density compared to its version wherein the Ga2O3 was grown ex situ, after breaking the vacuum, all else being the same. A remarkable decrease in the interfacial charge density for in situ MOSHFET structures in the range of 70%–88% for 10–30 nm oxide layer thickness and improvements in other electrical parameters required for high-performing devices were observed.

CoP Quantum Dots Embedded in Carbon Polyhedra through Co─P─C Bonding Enabling High‐Energy Lithium‐Ion Capacitors

AbstractPhosphides with high theoretical capacity are considered ideal anode materials for lithium‐ion capacitors (LICs), but poor electronic conductivity as well as unsatisfied cyclic stability limits the performance of the phosphides. Here a covalently bonded CoP@C heterostructure is reported, which consists of 5 nm CoP quantum dots (QDs) like pomegranate seeds pinned in carbon polyhedron through interfacial Co─P─C bonding. The ultrafine size of CoP QDs provides more reactive sites and a shorten electrons/ions diffusion path, boosting the specific capacity. The Co─P─C bond induces the energy band variation of CoP and increases the interfacial charge density, bringing about fast kinetics. Besides, the Co─P─C bond introduces a robust pining effect among CoP QDs and carbon polyhedra, greatly improving the structure stability of 5 nm CoP QDs. The CoP@C heterostructure electrode exhibits high capacity (nearly 1000 mAh g−1) and superior cycling stability. It is worth noting that a prototyped LIC full‐cell of YP80//CoP@C presents an impressive high energy density of 172 Wh kg−1 and a power density of 10.8 kW kg−1. Moreover, the LIC possesses an ultra‐long life, retaining 80% after 20,000 cycles. This study offers an effective design for phosphides achieving fast kinetics and superior structure stability through an interfacial bonding approach.

First-principles comparative study on diamond/carbide combinations: Interfacial adhesion and bonding nature

Joining diamond and metal is vital to expand their application scope in electronic and military industries. A metallic carbide layer will be inevitably introduced on diamond to ensure strength and wettability, its tight interfacial adhesion with diamond needs to be satisfied in priority. Here, the bonding characteristics of diamond(001)/carbide(001) interfaces were comparatively studied through first-principles calculations, wherein six experimentally possible carbides MxCy (TiC, Cr3C2, V8C7, Mo2C, ZrC, and WC) were employed. By evaluating the thermal stability, activity, and mechanical properties of bulk MxCy, as well as the corresponding interface energy and adhesion work, three outstanding interface structures (with Cr, W, and Ti) were yielded. Further analysis of electronic structures showed the interfacial bonding originated from M–C bonds and stronger CC covalent bonds. Besides, bonding strength was found to be significantly related to interfacial charge density and orbital hybridization. Overall, Cr might be the preferable carbide former with high interfacial stability and strength. This study provided atomic insights into the tailoring of diamond/carbide combination with superior interfacial compatibility to develop high-performance diamond devices.

Modulation of electrical properties of sputtered Ta2O5 films by variation of RF power and substrate temperature

Dielectric thin films are important building blocks of microelectronic devices, and hence, research on the development of high-k dielectric thin films has drawn tremendous research interest. In this research, thin films of tantalum oxide (Ta2O5), a high-k dielectric material, are deposited on the Si substrate by the radio frequency (RF) magnetron sputtering technique. During the deposition of Ta2O5 thin film, the sputtering parameters such as sputtering power and substrate temperature were systematically varied, and post-deposition structural, morphological, and electrical properties of sputtered Ta2O5 films are studied by x-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscope, capacitance–voltage (C-V) and current–voltage (I-V) measurement techniques. The annealed Ta2O5 thin film at the temperature of 900 °C for 1 h possesses polycrystalline nature with β—phase orthorhombic crystal structure. The film deposited at 150 W and substrate temperature at room temperature has shown comparatively lower surface roughness, which depicts the energy, and mobility of adatoms greatly influenced by RF power and substrate temperature. With the increase in sputtering power, the oxide charge density (Qox) is found to increase. On the other hand, Qox is found to decrease with the increase in substrate temperature. The film deposited at RF power of 150 W and substrate temperature of 300 °C is found to be of high dielectric constant, low oxide and interface charge density, and lower leakage current.

Temperature-dependent differential capacitance of an ionic liquid-graphene-based supercapacitor.

One of the critical factors affecting the performance of supercapacitors is thermal management. The design of supercapacitors that operate across a broad temperature range and at high charge/discharge rates necessitates understanding the correlation of the molecular characteristics of the device (such as interfacial structure and inter-ionic and ion-electrode interactions) with its macroscopic properties. In this study, we use molecular dynamics (MD) simulations to investigate the influence of Joule heating on the structure and dynamics of the ionic liquid (IL)/graphite-based supercapacitors. The temperature-dependent electrical double layer (EDL) and differential capacitance-potential (CD-V) curves of two different ([Bmim][BF4] and [Bmim][PF6]) IL-graphene pairs were studied under various thermal gradients. For the [Bmim][BF4] system, the differential capacitance curves transition from 'U' to bell shape under an applied thermal gradient (∇T) in the range from 3.3 K nm-1 to 16.7 K nm-1. Whereas in [Bmim][PF6], we find a positive dependence of differential capacitance with ∇T with a U-shaped CD-V curve. We examine changes in the EDL structure and screening potential (ϕ(z)) as a function of ∇T and correlate them with the trends observed in the CD-V curve. The identified correlation between the interfacial charge density and differential capacitance with thermal gradient would be helpful for the molecular design of the IL-electrode interface in supercapacitors or other chemical engineering applications.