Depletion Region Research Articles

Triboelectric Charging Properties of the Functional Groups of Common Pharmaceutical Materials Using Density Functional Theory Calculations.

Triboelectrification is a ubiquitous and poorly understood phenomenon in powder processing, particularly for pharmaceutical powders. Charged particles can adhere to vessel walls, causing sheeting; they can also cause agglomeration, threatening the stability of powder formulations, and in extreme cases electrostatic discharges, which present a serious fire and explosion hazard. Triboelectrification is highly sensitive to environmental and material conditions, which makes it very difficult to compare experimental results from different publications. In this work, density functional theory (DFT) is used to investigate the charge transfer characteristics of several functional groups of paracetamol in order to better understand the mechanisms of charging at the nanoscale and the influence of the environmental and material properties on charge transfer. This is achieved by studying the structure and electronic properties at the molecule-substrate interface. Using this molecule-substrate approach, the charging contributions of individual functional groups are explored by examining the Hirschfeld charges, the charge density difference between the molecule and substrate, the density of states, and the location of the frontier orbitals (HOMO and LUMO) of a paracetamol molecule. Charge density difference calculations indicate a significant transfer of charge from the molecule to the surface. Observable regions of electron density enrichment and depletion are evident around the electron-donating and -withdrawing groups, respectively. The density of states for the paracetamol molecule evolves as it approaches the surface, and the band gap disappears upon contact with the substrate. Hirshfeld charge analysis reveals asymmetry in the charge redistribution around the molecule, highlighting the varying charging tendencies of different atoms.

High-temperature corrosion behavior of the FeCrAl laser cladding coatings in waste-to-energy superheaters: Influence of Al content

Enhancing the high-temperature corrosion resistance of superheaters in waste-to-energy plants (WTE) is key to improving the efficiency of WTE power generation. The present study employed laser cladding technology to fabricate Fe-13Cr-xAl coatings, and characterized the microstructure, phase structure, and Vickers hardness of the coatings using OM, SEM, XRD, and a Vickers hardness tester. The study investigated the influence of high-temperature corrosion resistance of the coatings under simulated WTE flue gas conditions. This study found that: Al and Cr both exist in the form of solid solution atoms in the laser cladding coatings. The Vickers hardness of the coatings gradually increased with increasing Al content. When the Al content exceeds 10 %, cracks begin to appear in the coatings, and the number and size of cracks increase with increasing Al content. The Fe-13Cr-7Al coatings exhibit the best high-temperature corrosion resistance under simulated WTE flue gas conditions, and it can achieve ∼73 % of the high-temperature corrosion resistance of the Inconel 625 alloy laser cladding coatings. During high-temperature corrosion, phase separation occurs near the grain boundaries, resulting in chromium depletion zones, which promote intergranular corrosion of the coatings. During the process of high temperature corrosion, the reactions between Al, Cl, and S exhibit the lowest Gibbs free energy. The continuous consumption of Al effectively protects the Fe and Cr in the substrate. Additionally, the formation of aluminum oxide in the coating hinders the inward diffusion of Cl2, thereby beneficially impeding the progress of corrosion. Excessive Al contents in the coatings introduced cracks that served as channels for molten salt to penetrate the matrix, thereby reducing the high-temperature corrosion resistance of the coatings.

Metastable precipitation and ion–extractant transport in liquid–liquid separations of trivalent elements

The extractant-assisted transport of metal ions from aqueous to organic environments by liquid-liquid extraction has been widely used to separate and recover critical elements on an industrial scale. While current efforts focus on designing better extractants and optimizing process conditions, the mechanism that underlies ionic transport remains poorly understood. Here, we report a nonequilibrium process in the bulk aqueous phase that influences interfacial ion transport: the formation of metastable ion-extractant precipitates away from the liquid-liquid interface, separated from it by a depletion region without precipitates. Although the precipitate is soluble in the organic phase, the depletion region separates the two and ions are sequestered in a long-lived metastable state. Since precipitation removes extractants from the aqueous phase, even extractants that are sparingly soluble in water will continue to be withdrawn from the organic phase to feed the aqueous precipitation process. Solute concentrations in both phases and the aqueous pH influence the temporal evolution of the process and ionic partitioning between the precipitate and organic phase. Aqueous ion-extractant precipitation during liquid-liquid extraction provides a reaction path that can influence the extraction kinetics, which plays an important role in designing advanced processes to separate rare earths and other minerals.

Self-powered α-GaOOH nanorod array/FTO photoelectrochemical photodetectors for solar-blind UV photodetection

We have grown α-GaOOH nanorod array/FTO structures with different precursor concentrations by hydrothermal processes without any seed layers. The optical bandgap is ∼5.1 eV, indicating their ability of solar-blind UV photodetection. Photoelectrochemical (PEC) properties of α-GaOOH nanorod array/FTO photodetectors as photoanodes show self-powered solar-blind UV photodetection. Due to the similar width of depletion regions of α-GaOOH nanorod array/FTO PEC photodetectors with changing the precursor concentrations, the peak responsivity is nearly the same. And they also show the similar response time (decay processes) ranging from 0.061s to 0.072s. Compared with the reported bare α-GaOOH nanorod arrays or heterojunctions, the maximum responsivity of 0.29 mA/W at 245 nm is comparable. However, fast collection speed without block of these seed layers between nanorod arrays and FTO results in faster response speed of 0.012 s in this work. Therefore, this article provides basic research in realizing high-performance self-powered α-GaOOH PEC photodetectors without seed layers.

The space-charge region at CsPbBr3 NC⊆Pb-MOF p-n junction by self-sacrificing MOFs to selective detect NH3·H2O or Fe3+

The rational design of p-n heterojunction is highly desirable to optimize electron distribution and photocarriers’ transfer pathway at space-charge region, which would influence the fluorescence detection. Herein, the inorganic perovskite CsPbBr3 nanocrystals (CPB NCs) have been encapsulated into Pb-centered MOFs via simple wet-chemical self-sacrifice to construct a “turn-off” sensor for the sensitive detection of NH3·H2O or Fe3+ in aqueous solution. The Mott-Schottky plots (M-S), ultraviolet photoelectron spectroscopy (UPS) and density functional theory (DFT) calculation have proved the formation of p-n junction between the derived CsPbBr3 and parent Pb-MOF. The CPB⊆Pb-MOF heterojunction has provided a strong platform to maintain high fluorescence performance and stability in aqueous solution as sensor. It is found that the static quenching process has affected the detection of Fe3+. More importantly, the occurrence of dynamic quenching with electron transfer is also verified by fluorescence lifetime, in-situ X-ray photoelectron spectroscopy (XPS) analysis. The phase transfer has taken major reason when being introduced by NH3·H2O. Fortunately, the 0.4CPB⊆Pb-MOF has exhibited best analytical performance for NH3·H2O or Fe3+. What’s more, it has been manufactured for the visual detection for NH3·H2O or Fe3+ in the real environmental water samples. Thereby, this perovskite based water detection system would broaden the application in point-to-point precise diagnostics.

Two‐Dimensional Characterization of Au/Ni/Thin Heavily‐Mg‐Doped p‐/n‐GaN Structure under Applied Voltage by Scanning Internal Photoemission Microscopy

The two‐dimensional characterization of the Au/Ni/thin p+‐GaN/n−‐GaN structure, which is a part of a junction barrier Schottky structure, is demonstrated by scanning internal photoemission microscopy (SIPM) method. In the SIPM photoyield image using a blue laser, small photocurrents based on the internal photoemission effect by electron injection across the metal/semiconductor interface (from Ni to GaN) are detected in the center of the electrode. On the periphery, large photocurrents in the opposite direction are detected. These currents are caused by the hole injection from Ni into p+‐GaN layer and the electrical field in the laterally extended depletion layer at the edge. By using a violet laser, large photocurrents based on the fundamental absorption generated in the depletion layer of the n−‐GaN layer are uniformly detected over the electrode. It is conformed that SIPM can be available for quasi‐three‐dimensional characterization of this structure.

Catalytic Activity and Electrochemical Stability of Ru1-xMxO2 (M = Zr, Nb, Ta): Computational and Experimental Study of the Oxygen Evolution Reaction.

We use computations and experiments to determine the effect of substituting zirconium, niobium, and tantalum within rutile RuO2 on the structure, oxygen evolution reaction (OER) mechanism and activity, and electrochemical stability. Calculated electronic structures altered by Zr, Nb, and Ta show surface regions of electron density depletion and accumulation, along with anisotropic lattice parameter shifts dependent on the substitution site, substituent, and concentration. Consistent with theory, X-ray photoelectron spectroscopy experiments show shifts in binding energies of O-2s, O-2p, and Ru-4d peaks due to the substituents. Experimentally, the substituted materials showed the presence of two phases with a majority phase that contains the metal substituent within the rutile phase and a second, smaller-percentage RuO2 phase. Our experimental analysis of OER activity shows Zr, Nb, and Ta substituents at 12.5 atom % induce lower activity relative to RuO2, which agrees with computing the average of all sites; however, Zr and Ta substitution at specific sites yields higher theoretical OER activity than RuO2, with Zr substitution suggesting an alternative OER mechanism. Metal dissolution predictions show the involvement of cooperative interactions among multiple surface sites and the electrolyte. Zr substitution at specific sites increases activation barriers for Ru dissolution, however, with Zr surface dissolution rates comparable to those of Ru. Experimental OER stability analysis shows lower Ru dissolution from synthesized RuO2 and Zr-substituted RuO2 compared to commercial RuO2 and comparable amounts of Zr and Ru dissolved from Zr-substituted RuO2, aligned with our calculations.

Normally-off GaON/p-GaN gate HEMTs with selective plasma oxidation: from structural characterization, performance improvement to physical mechanism

In this letter, a p-GaN gate high-electron-mobility transistor (HEMT) with a high threshold voltage and better gate reliability was demonstrated by using selective plasma oxidation (SPO) and an additional low-temperature annealing step before gate metal is evaporated. After the SPO, a gallium oxynitride (GaON) dielectric layer was formed on the surface of p-GaN under the gate metal, and was studied by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectrometry, high-resolution transmission electron microscopy and energy dispersion spectroscopy. In addition, the fabricated metal/GaON/p-GaN gate HEMT exhibited a large threshold voltage (V TH) improvement from 1.46 V to 2.47 V. Furthermore, the forward gate breakdown voltage (V GS,BD) increased from 7.55 V to 11.10 V, and the maximum forward gate operating voltage (V GS-max) significantly improved from 5.0 V to 7.80 V for a ten-year lifetime with a 63.2% failure rate. Kelvin probe force microscopy reveals that the surface potential increased after SPO, and the shift of valence band maximum obtained by XPS spectra was 0.7 eV lower than that of the p-GaN, which further improves the Schottky barrier height at the gate metal/GaON interfaces to holes, thereby improving V TH and reducing I GS of the device. As a barrier layer, GaON suppressed the injection of carrier into the depletion region under a high electric field and enhanced the reliability of the gate.

Tailoring of colloidal quantum dot layer thickness for highly efficient short-wavelength infrared photodiode

Colloidal quantum dots (CQDs) have emerged as promising materials for thin film photodiodes (TFPDs) in the short-wavelength infrared detection range, offering an alternative to III–V and HgCdTe-based TFPDs. However, optimizing the structure of CQD-based TFPDs remains a challenge, as it involves a delicate balance between reducing dark currents and enhancing carrier extraction efficiency. In this study, we explore the influence of varying the thickness of CQD layers to achieve a highly efficient photodiode. Our investigations reveal a continuous reduction in the dark current as the CQD layers become thicker, but we observe fluctuation in the external quantum efficiency (EQE). To shed light on this relationship between dark current density (Jdark) and EQE, we conduct capacitance measurements and employ optical simulations. From the capacitance measurements, they demonstrate an increased depletion width with varying CQD thickness, apart from layers exceeding 500 nm in thickness. Leveraging optical simulations, we propose an optimal thickness for CQD-based TFPDs and compare its EQE performance. The optimized CQD-based TFPD exhibits a Jdark of 4.1 μA/cm2 and EQE of 56.5%, and the highest specific detectivity, based on the assumption of shot noise dominance, is 1.78 × 1012 Jones at a wavelength of 1420 nm.

First evidence of a connection between cluster-scale diffuse radio emission in cool-core galaxy clusters and sloshing features

Radio observations of a few cool-core galaxy clusters have revealed the presence of diffuse emission on cluster scales, similar to what was found in merging clusters in the form of radio halos. These sources might suggest that a minor merger, while not sufficiently energetic to disrupt the cool core, could still trigger particle acceleration in the intracluster medium on scales of hundreds of kiloparsecs. We aim to verify the occurrence of cluster-scale diffuse radio emission in cool-core clusters and test the minor merger scenario. With the LOw Frequency ARray (LOFAR) at 144 MHz, we observed a sample of twelve cool-core galaxy clusters presenting some level of dynamical disturbances, according to X-ray data. We also performed a systematic search of cold fronts in these clusters, re-analysing archival Chandra observations. The clusters PSZ1G139.61+24, A1068 (new detection), MS 1455.0+2232, and RX J1720.1+2638 present diffuse radio emission on a cluster scale ($r $). This emission is characterised by a double component: a central mini-halo confined by cold fronts and diffuse emission on larger scales, whose radio power at 144 MHz is comparable to that of radio halos detected in merging systems with the same cluster mass. The cold fronts in A1068 are a new detection. We also found a candidate plasma depletion layer in this cluster. No sloshing features are found in the other eight clusters. Two of them present a mini-halo, with diffuse radio emission confined to the cluster core. We also found a new candidate mini-halo. Whereas, for the remaining five clusters, we did not detect halo-like emission. For clusters without cluster-scale halos, we derived upper limits to the radio halo power. We found that cluster-scale diffuse radio emission is not present in all cool-core clusters when observed at a low frequency, but it is correlated to the presence of cold fronts. The coexistence of cluster-scale diffuse radio emission and cold fronts in cool-core clusters requires a specific configuration of the merger and so it puts some constraints on the turbulence, which deserves to be investigated in the future with theoretical works.

Photoelectrochemical properties of anatase TiO2 nanostructures prepared by hydrothermal method: Effect of illumination and external bias on charge transport

A systematic study of photoelectrochemical properties in terms of carrier transport was conducted for TiO2 nanostructure films fabricated on Ti foil at different temperatures (130 °C–210 °C) through alkaline hydrothermal technique, along with the morphological, structural, and optical properties. For samples, the morphology transformed from nanosheets to nanowires, the phase converted from bi-phase of brookite and anatase to pure anatase along with the reduction in the amount of oxygen vacancies as temperature increases. Among them, the dark blue bi-phased TiO2 (brookite and anatase) prepared at 130 °C of hydrothermal treatment (TiO2-130) with nanosheets morphology displayed the optimum photoelectrochemical performance with the highest photocurrent density of 265 μA/cm2 at 1 V (vs. Ag/AgCl), largest carrier density of 1.809 × 1019cm−3 and narrowest space charge region of 11.73 nm. Besides, the large reduction in charge transfer resistance and the width of space charge region caused by simulated solar illumination facilitate the charge transport in photoelectrode especially the TiO2-130 with the largest reduction, indicating the great influence of illumination on carrier dynamics. Moreover, the external bias caused the reduction of resistance under irradiation, the increase in the resistance in the dark. Importantly, the TiO2-210 showed p-type conductivity under illumination inferred from the negative slope of Mott-Schottky plots, which is first observed and further confirm the influence of light on the charge transfer process.

Bio‐inspired Two‐dimensional Nanofluidic Ionic Transistor for Neuromorphic Signal Processing

AbstractVoltage‐gated ion channels prevalent in neurons play important roles in generating action potential and information transmission by responding to transmembrane potential. Fabricating bio‐inspired ionic transistors with ions as charge carriers will be crucial for realizing neuro‐inspired devices and brain‐liking computing. Here, we reported a two‐dimensional nanofluidic ionic transistor based on a MXene membrane with sub‐1 nm interlayer channels. By applying a gating voltage on the MXene nanofluidic, a transmembrane potential will be generated to active the ionic transistor, which is similar to the transmembrane potential of neuron cells and can be effectively regulated by changing membrane parameters, e.g., thickness, composition, and interlayer spacing. For the symmetric MXene nanofluidic, a high on/off ratio of ~2000 can be achieved by forming an ionic depletion or accumulation zone, contingent on the sign of the gating potential. An asymmetric PET/MXene‐composited nanofluidic transitioned the ionic transistor from ambipolar to unipolar, resulting in a more sensitive gate voltage characteristic with a low subthreshold swing of 560 mV/decade. Furthermore, ionic logic gate circuits, including the “NOT”, “NAND”, and “NOR” gate, were implemented for neuromorphic signal processing successfully, which provides a promising pathway towards highly parallel, low energy consumption, and ion‐based brain‐like computing.

Bio-inspired Two-dimensional Nanofluidic Ionic Transistor for Neuromorphic Signal Processing.

Voltage-gated ion channels prevalent in neurons play important roles in generating action potential and information transmission by responding to transmembrane potential. Fabricating bio-inspired ionic transistors with ions as charge carriers will be crucial for realizing neuro-inspired devices and brain-liking computing. Here, we reported a two-dimensional nanofluidic ionic transistor based on a MXene membrane with sub-1 nm interlayer channels. By applying a gating voltage on the MXene nanofluidic, a transmembrane potential will be generated to active the ionic transistor, which is similar to the transmembrane potential of neuron cells and can be effectively regulated by changing membrane parameters, e.g., thickness, composition, and interlayer spacing. For the symmetric MXene nanofluidic, a high on/off ratio of ~2000 can be achieved by forming an ionic depletion or accumulation zone, contingent on the sign of the gating potential. An asymmetric PET/MXene-composited nanofluidic transitioned the ionic transistor from ambipolar to unipolar, resulting in a more sensitive gate voltage characteristic with a low subthreshold swing of 560 mV/decade. Furthermore, ionic logic gate circuits, including the "NOT", "NAND", and "NOR" gate, were implemented for neuromorphic signal processing successfully, which provides a promising pathway towards highly parallel, low energy consumption, and ion-based brain-like computing.

Space charge region recombination in highly efficient silicon solar cells

The recombination rate in the space charge region (SCR) of a silicon-based barrier structure with a long Shockley–Reed–Hall lifetime is calculated theoretically by taking into account the concentration gradient of excess electron-hole pairs in the base region. Effects of the SCR lifetime and applied voltage on the structure ideality factor have been analyzed. The ideality factor is significantly reduced by the concentration gradient of electron-hole pairs. This mechanism provides an increase of the effective lifetime compared to the case when it is insignificant, which is realized at sufficiently low pair concentrations. The theoretical results have been shown to be in agreement with experimental data. A method of finding the experimental recombination rate in SCR in highly efficient silicon solar cells (SCs) has been proposed and implemented. It has been shown that at the high excess carrier concentration exceeding 1015 cm–3 the contribution to the SCR recombination velocity from the initial region of SCR that became neutral is significant. From a comparison of theory with experiment, the SCR lifetime and the ratio of the hole to the electron capture cross sections are determined for a number of silicon SCs. The effect of SCR recombination on the key characteristics of highly efficient silicon SCs, such as photoconversion efficiency and open-circuit voltage, has been evaluated. It has been shown that they depend not only on the charge carrier lifetime in SCR, but also on the ratio of hole to electron capture cross sections σp /σn. When σp /σn < 1, this effect is significantly strengthened, while in the opposite case σp /σn > 1 it is weakened. It has been ascertained that in a number of highly efficient silicon SCs, the distribution of the inverse lifetime in SCR is described by the Gaussian one. The effect described in the paper is also significant for silicon diodes with a thin base, p-i-n structures, and for silicon transistors with p-n junctions. In Appendix 2, the need to take into account the lifetime of non-radiative excitonic Auger recombination with participation of deep impurities in silicon is analyzed in detail. It has been shown, in particular, that considering it enables to reconcile the theoretical and experimental dependences for the effective lifetime in the silicon bulk.

Science in 2025-2027 and the SPQEO journal

Relevance of recent research is important for scientists and journals reporting research results. There are many sources of prognoses and one of them is the Report of European Commission "Looking into the R&I future priorities 2025-2027". It predicts the importance of the following areas for users: healthcare, energy, climate, sustainability and digitalization. The Ukrainian journal Semiconductor Physics, Quantum Electronics and Optoelectronics (SPQEO) actually focuses on these areas and contributes to the development of related knowledge. Monitoring of last SPQEO issues shows some interesting results: (i) the effect of local field amplification, which causes emergence of ponder motive forces acting on viruses until destruction of viral envelopes; (ii) the methods of malignant tumors treatment taking into account their genesis mechanisms and focusing on correction of definite pathogenesis components, while being nontoxic for other organs and tissues; and (iii) manipulation of the spectral characteristics of a “polycarbonate matrix – gold nanostructures – HTTH dye” system due to influence of gold nanostructures. SPQEO paid attention to the improvement of solar cells (SCs) by considering physical effects such as the effect of space charge region (SCR) recombination on the key characteristics of high-efficiency silicon solar cells, such as photovoltaic conversion efficiency and open-circuit voltage, is not only dependent on the charge-carrier lifetime in the SCR, but also on the ratio of hole-to-electron-capture cross section, σp/σn. Non- traditional SCs were also considered: SCs with perovskite thin films, SCs comprising CdS/CIGS heterojunctions, and vitamin B12-patterned silicon hybrids based SCs. Moreover, SPQEO also covers research results in the fields of quantum devices, diamond- like and oxide films, and light-emitting diodes.

Ethanolamine gas sensors based on NdFeO3 modified hexagonal pyramid shaped ZnO nanocrystals

It is well known that two metal oxides can form depletion layers at the interface by constructing heterojunctions due to the different Fermi energy levels of each metal oxide, which can improve the carrier mobility and provide significant advantages for gas sensing. In this work, NdFeO3 nanoparticles were grown on ZnO with hexagonal cone structure by secondary hydrothermal method to successfully construct n-ZnO/p-NdFeO3 heterojunctions, and the crystal structures, oxygen vacancies, microstructures, optical properties, and gas-sensing properties of the ZnO/NdFeO3 composites were investigated. The ZnO/NdFeO3 sensors showed good ethanolamine (EA) The response characteristics of the ZnO/NdFeO3 sensor to ethanolamine (EA) with a concentration of 100 ppm EA at 240 °C (Rg/Ra) is about 25, which improves the response by a factor of 1.6 and 1.32 compared with that of NdFeO3 and ZnO. Meanwhile, it has excellent selectivity, good cyclic reproducibility, and durable long-term stability with response/recovery times of 19 s/49 s. The improved EA sensing performance of NdFeO3-modified ZnO, in addition to its large specific surface area due to its unique rough inhomogeneous structure, is also related to the higher concentration of oxygen vacancies at the ZnO/NdFeO3 interface after the composite. In addition, the construction of ZnO/NdFeO3 heterostructure brings more efficient carrier migration, which is favorable to the surface reaction and diffusion of EA molecules, and lowers the ZnO operating temperature, thus reducing the energy consumption. The ZnO/NdFeO3 composite sensor based on n-p heterojunction provides a valuable strategy for the detection of volatile organic compounds.

Constructing mixed-dimensional lightweight magnetic cobalt-based composites heterostructures: An effective strategy to achieve boosted microwave absorption and self-anticorrosion

Subtle microstructure design and an appropriate multicomponent strategy are essential for advanced electromagnetic absorbing (EMA) materials with a wide effective absorption bandwidth (EAB) and intense absorption. However, sophisticated environments restrict the range of applications for EMA materials. Herein, three hollow spherical bifunctional CoSx/MnS/C nanocomposites with different crystal structures were constructed via cation exchange and subsequent vulcanization. The manganese sulfide and carbon generated during vulcanization exhibit a narrow band gap and enhanced conductivity, thereby facilitating conductive loss. The presence of cobalt sulfide facilitates the improvement of magnetic loss. More importantly, there is a potential difference between different phases at the heterogeneous interface, resulting in a region of space charge, which is conducive to interfacial polarization. The 3D hollow structure and heterogeneous dielectric/magnetic interfaces benefit the predominant EMA performance by forming perfect impedance matching, interface polarization, conduction loss, and magnetic loss effects. Specifically, an optimal reflection loss (RL) of –51.31 dB at 10.72 GHz and an effective EAB of 5.92 GHz at 2.1 mm can be achieved for Co1–xS/MnS/C nanocomposite. Moreover, the nanocomposites maintained promising self-anticorrosion properties in simulated seawater environments. Transition metal sulfides with superior self-anticorrosion properties provide a pathway to efficient wave-absorbing materials in complicated environments.

Suppression of dendrite formation via ultrasonic stimulation

This research introduces a chemistry-agnostic approach to achieve rapid and degradation-free battery charging via ultrasonic agitation. An ultrasonic device operating in the megahertz range was used to stimulate electrolyte flow from outside the cell. The acoustic streaming effect accelerates ion transport from the bulk electrolyte to the electrode surface and suppresses the formation of an ion depletion zone. An experimental setup was used to optically observe the formation of dendrites when the current imposed across two zinc electrodes exceeded the limiting current. Beyond this limit, diffusion alone cannot provide sufficient ions, resulting in an ion depletion zone. It was subsequently shown that dendrite formation was reduced by over 98% when 15x the limiting current was forced across the electrodes and acoustic stimulation was delivered. Furthermore, it was shown that compared to the scenario without ultrasonic stimulation, the steady state potential was also reduced by 29%, indicating much better ion exchange between the electrodes. These findings suggest that ultrasonic stimulation can be a tool for enhancing electrochemical processes such as battery charging and discharging.

Piezojunction effect in heterojunctions under external bias for ultrasensitive strain sensing

This paper investigates for the first time the piezojunction effect in heterojunctions under external bias for ultrasensitive strain sensing. As a proof of concept, we used sensing devices made of 3C-SiC/Si heterostructure with vertically aligned electrodes. Applying the beam bending method to characterize the sensing effect, the bending strain was introduced along the typical orientation [100] or [110] on (100) Si plane. Experimental results show a linear relationship between the relative change in the forward current and the applied strain from 0 to 500 ppm, decreasing under the tensile strain while increasing under the compressive strain. At the forward bias of 8 V, the obtained gauge factors (GFs) are 199.7 for [100] orientation and 173.1 for [110] orientation, which significantly enhance about 630 % and 540 % compared to the highest GF of n-type 3C-SiC in the literature. Interestingly, the GFs of the n+-3C-SiC/p-Si heterostructure are positive in contrast to the negative GFs of n-3C-SiC thin films. The results were explained by the strain modulation on the band split and electron mass shift along the out-of-plane direction as well as by the change in the barrier height, depletion region width, and carrier concentrations under the forward bias. The ultrasensitive piezojunction effect in the 3C-SiC/Si heterojunction demonstrated in this study can pave the way toward developing ultrasensitive mechanical sensors.

Electrical Characterization and Ammonia Gas Response of a p‐Si/n‐poly[benzimidazobenzophenanthroline] Thin‐Film Junction Diode

The electrical characterization and ammonia vapor (NH3) response of a p‐Si/n‐poly[benzimidazobenzophenanthroline] (n‐BBL) thin‐film junction diode are reported. The presence of a depletion layer at the n‐BBL/p‐Si interface is verified via capacitance–voltage measurements, and the built‐in potential is ≈1.8 V. Using the standard diode equation for data analysis, the turn‐on voltage, rectification ratio, and ideality parameter are found to be 2 V, 16, and 6, respectively. The diode is also tested in the presence of NH3 vapor where it retained its asymmetric J–V behavior with increased currents and an insignificant change in device parameters. NH3 is believed to interact with the adsorbed O2− species on the n‐BBL surface liberating electrons that enhance the diode current. The response time, recovery time, and sensitivity of the diode are 65 s, 121 s, and 52%, respectively. The removal of the gas restores the diode characteristics to their near original shape making it reusable. The diode is also electrically characterized as a function of temperature and is found to retain its rectifying behavior down to 150 K. The rectifying and gas‐sensing features make the diode multifunctional, which expands the range of applications of this ladder‐type conducting polymer.