Carrier Mechanism Research Articles

Osmoporation is a versatile technique to encapsulate fisetin using the probiotic bacteria Lactobacillus acidophilus.

The objective of this study was to evaluate the performance of Lactobacillus acidophilus cells as a novel encapsulating carrier for fisetin via osmoporation. Initially, the effects of osmotic pressure and initial fisetin concentration on the performance of the osmoporation process were evaluated. The best results were achieved when 15MPa was applied, while the maximum loading capacity was reached when fisetin concentration of 2.0mg·mL-1 was used. For these conditions, the cell viability, encapsulation efficiency (EE), and encapsulated fisetin content (EF) were 72%, 28%, and 0.990mg, respectively. Further, the encapsulation was confirmed by Fourier transform-infrared (FT-IR), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analysis. DSC thermograms revealed an increase of 40°C in the melting point of fisetin after encapsulation. In addition, the enhancement of fisetin bioaccessibility by osmoporated biocapsules is shown for the first time in the literature. When the fisetin biocapsules were subjected to in vitro gastrointestinal digestion, 99.6% of the encapsulated content were retained through the gastric stage and 45.5% were released during the intestinal stage, despite no active cells were detected during simulated digestion. These results suggest that alive cells are required for an effective osmoporation-assisted encapsulation process; however, osmoporated biocapsules can efficiently protect and preserve labile compounds, independently of their activity. Overall, this study demonstrated that osmoporation using probiotic L. acidophilus is a simple, versatile, and efficient technique to encapsulate and deliver lipophilic fisetin for food applications. KEY POINTS : •Fisetin is efficiently encapsulated into L. acidophilus via osmoporation. •Fisetin bioaccessibility is improved by osmoporation into L. acidophilus. •Release mechanisms of osmoporation carriers are independent of the cell activity.

Recombination in gapless HgTe/CdHgTe quantum well heterostructure

Three recombination mechanisms of nonequilibrium carriers in gapless undoped quantum well in HgTe/CdHgTe heterostructure are considered. Dependencies of ensemble-average probability of recombination (inverse of recombination time) on concentration of nonequilibrium carriers for recombination with emission of optical phonons, recombination with emission of two-dimensional plasmons, and radiative recombination have been calculated. Key words: gapless HgTe quantum well, recombination mechanisms of nonequilibrium carriers.

Recombination in gapless HgTe/CdHgTe quantum well heterostructure

Three recombination mechanisms of nonequilibrium carriers in gapless undoped quantum well in HgTe/CdHgTe heterostructure are considered. Dependencies of ensemble-average probability of recombination (inverse of recombination time) on concentration of nonequilibrium carriers for recombination with emission of optical phonons, recombination with emission of two-dimensional plasmons, and radiative recombination have been calculated. Key words: gapless HgTe quantum well, recombination mechanisms of nonequilibrium carriers.

Controlling transmembrane ion transport via photo-regulated carrier mobility.

Stimuli-responsive transmembrane ion carriers allow for targeted and controllable transport activity, with potential applications as therapeutics for channelopathies and cancer, and in fundamental studies into ion transport phenomena. These applications require OFF–ON activation from a fully inactive state which does not exhibit background activity, but this remains challenging to achieve with synthetic transport systems. Here we introduce a novel mechanism for photo-gating mobile ion carriers, which involves modulating the mobility of the carriers within the lipid bilayer membrane. By appending a membrane-targeting anchor to the carrier using a photo-cleavable linker, the carrier's ion transport activity is fully switched off by suppressing its ability to shuttle between the two aqueous-membrane interfaces of the bilayer. The system can be reactivated rapidly in situ within the membrane by photo-triggered cleavage of the anchor to release the mobile ion carrier. This approach does not involve direct functionalization of the ion binding site of the carrier, and so does not require the de novo design of novel ion binding motifs to implement the photo-caging of activity. This work demonstrates that controlling the mobility of artificial transport systems enables precise control over activity, opening up new avenues for spatio-temporally targeted ionophores.

Dielectric and electrical properties of Ca-modified BFN perovskite

The present work reports fabrication of Ca-modified Ba(Fe1/2Nb1/2)O3 perovskite by solid state route at optimized temperature of 1250 °C through repeated firing method. X-ray diffraction profile reveals formation of the perovskite in single phase having monoclinic crystal structure. Detailed dielectric behavior is examined within frequency 100 Hz−5 MHz and temperature 25–300 °C. The perovskite has high dielectric constant and low loss value at room temperature that makes it suitable for designing energy storage appliances. Non-destructive impedance spectroscopy technique suggests the occurrence of non-Debye type relaxation and negative temperature coefficient of resistance property in the compound. Conductivity study suggests that hopping mechanism of charge carriers is responsible for the conduction process.

Electrical and magnetic properties of intercalated compounds in the Gd-=SUB=-x-=/SUB=-NbSe-=SUB=-2-=/SUB=- system (0≤ x≤0.33)

The electrical and magnetic properties were measured on polycrystalline samples of niobium diselenide intercalated with gadolinium atoms. The dependences of the electrical resistance on temperature point to a predominantly phonon scattering mechanism for charge carriers, while the concentration dependences are determined by increasing scattering by interstitial atoms. The magnetic properties of GdxNbSe2 (0≤ x≤0.33) were studied in the temperature range of 2-350 K and in the range of magnetic fields up to 70 kOe. Based on the results of studies of magnetic susceptibility and magnetization, the possibility of the existence of antiferromagnetic interactions in the studied compounds and the phenomenon of spin reorientation in a magnetic field are shown. The observed decrease in the effective magnetic moment of gadolinium ions with an increase with their concentration is discussed in terms of a possible intramolecular exchange. Keywords: niobium diselenide, gadolinium, intercalation, electrical resistance, magnetization, effective magnetic moment.

Электрические и магнитные свойства интеркалированных соединений в системе Gd-=SUB=-x-=/SUB=-NbSe-=SUB=-2-=/SUB=- (0 ≤ x≤0.33)

The electrical and magnetic properties were measured on polycrystalline samples of niobium diselenide intercalated with gadolinium atoms. The dependences of the electrical resistance on temperature point to a predominantly phonon scattering mechanism for charge carriers, while the concentration dependences are determined by increasing scattering by interstitial atoms. The magnetic properties of GdxNbSe2 (0≤x≤0.33) were studied in the temperature range of 2–350 K and in the range of magnetic fields up to 70 kOe. Based on the results of studies of magnetic susceptibility and magnetization, the possibility of the existence of antiferromagnetic interactions in the studied compounds and the phenomenon of spin reorientation in a magnetic field are shown. The observed decrease in the effective magnetic moment of gadolinium ions with an increase with their concentration is discussed in terms of a possible intramolecular exchange.

Plasmon-catalysed decarboxylation of dicarboxybipyridine ligands in Ru(II) complexes chemisorbed on Ag nanoparticles: conditions, proposed mechanism and role of Ag(0) adsorption sites.

Plasmon-catalyzed decarboxylation reactions of Ru(II) bis(2,2'-bipyridine)(4,4'-dicarboxy-bipyridine) denoted as Ru(bpy)2(dcbpy) and Ru(II) tris(4,4'-dicarboxy-bipyridine) denoted as Ru(dcbpy)3 complexes in hydrosol systems with Ag nanoparticles (NPs) conditioned by the presence of Ag(0) adsorption sites on Ag NP surfaces have been revealed by surface-enhanced (resonance) Raman scattering (SERRS and/or SERS) spectral probing and monitoring further supported by factor analysis. Interpretation of the experimental results was based on an identification of specific marker bands of the Ru-dcbpy and of the Ru-bpy units. Furthermore, by a series of specifically targeted SERRS and/or SERS experiments complemented by UV/vis spectral measurements and TEM imaging of deposited Ag NPs, plasmon catalysis by charge carriers, namely hot electrons (e-) and hot holes (h+), has been established as the most probable mechanism of decarboxylation reactions undergone by the carboxylate-chemisorbed Ru-dcbpy units of the complexes. The presence of Ag(0) adsorption sites on Ag NP surfaces as the necessary condition of the reaction progress is in full accord with the charge carrier mechanism of plasmon catalysis. In particular, the neutral Ag(0) sites create the interface required for the transport of hot e- to H+ co-reactants complementing thus the C-C bond breaking and CO2 formation caused by hot h+.

Anion Recognition through Multivalent C-H Hydrogen Bonds: Anion-Induced Foldamer Formation and Transport across Phospholipid Membranes.

A series of triazole-cyanostilbene receptors were designed and synthesized. The receptor binds with the anions through various CH···anion hydrogen bonding interactions, where strong binding was observed for SO42- anions followed by Cl-, Br-, NO3-, and I-, calculated from the 1H NMR titration experiment. The NOESY NMR experiment of the receptor confirmed the formation of anion-induced folded conformation. The CH···anion hydrogen bonding interaction-mediated anion recognition and foldamer formation were further confirmed from geometry optimization studies of the anion-bound complex. The receptor transports Cl- anions efficiently compared to SO42- anions across the lipid bilayer membrane via a mobile carrier mechanism.

Insight into the multiple roles of nitrogen doped carbon quantum dots in an ultrathin 2D-0D-2D all-solid-state Z scheme heterostructure and its performance in tetracycline degradation under LED illumination

The rational design of an all-solid-state Z scheme composite through a single-step hydrothermal treatment by combining ultrathin defect engineered graphitic carbon nitride nanosheets (DCN), tungsten oxide hydrate nanoplates (W), and nitrogen doped carbon quantum dots (NCQDs) has been reported. For the first time, this study demonstrates that NCQD could successfully exfoliate g-C3N4 to produce few-layered thick g-C3N4 nanosheets, besides playing the role of an electron mediator in the composite. The 10%W/1%NCQD/DCN composite exhibited the highest photocatalytic tetracycline degradation efficiency under an 18 W LED illumination. It illustrated a 31.5, 7.7, and 5.2-times higher apparent degradation rate constant (0.044 min−1) than W, bulk g-C3N4, and DCN, respectively. Further, the composite exhibited an outstanding efficacy toward the degradation of various real water matrices. The composite demonstrated high stability and reusability. Furthermore, a plausible all-solid-state Z scheme charge carrier mechanism is proposed based on the results of the radical scavenging experiments.

Effect of Transition Mechanism of Photon-Induced Carriers on Time Jitter of GaAs Photoconductive Semiconductor Switches

To investigate the effect of photon-induced carrier transition mechanism on switch stability, the time jitters of 2-mm-gap gallium arsenide photoconductive semiconductor switches (GaAs PCSSs) are compared when triggered by lasers of two different wavelengths, i.e., 1064 and 532 nm. The time jitter model is proposed to clarify the synergy of the multiple adjustable macroparameters of trigger conditions. The carrier valley occupation rates with respect to bias electric field are simulated, where the influence of the microprocedures, i.e., carrier generation, carrier intervalley transition, and carrier transportation, is considered. Our experimental results illustrate that the time jitter of the GaAs PCSS exhibits a nonmonotonous behavior and obtains a local minimum at ~3 kV/cm for 1064 nm; however, it shows a monotonous decrease to a constant value at about 3 kV/cm for 532 nm. Our analysis indicates that the discrepancy in GaAs PCSS time jitter is attributed to the difference in the relative fluctuation of the carrier velocity affected by the carrier valley occupation rate. This article is of great significance in optimizing the stability of GaAs PCSS and pulse power system by adjusting the macroparameters in the time jitter model.

Conditions for the identical distribution of free carriers in thin films

The condition of the same distribution of free carriers in thin films is necessary for comparing the mobility and analyzing the scattering mechanisms of carriers near semiconductor film/insulator interfaces. In thin film/insulator systems with different design parameters, it is difficult to ensure the same distribution of free carriers due to physical phenomenon such as the coupling effect. In this study, TCAD simulations of thin-film transistors, which have been used to monitor Si film properties, were applied to find parameters that allow tuning the potential distribution and, accordingly, the distribution of free carriers in films. It was found that such parameters are the film regime, the density of induced carriers, the gate voltage or threshold voltage of transistors. The conditions for the selection of parameters were found that ensure the same distribution of free carriers in thin-film structures for the cases of different thicknesses of films and the surrounding dielectrics. It was shown that the proposed approach can be used for a comparative analysis of the mobility in thin films and makes it possible to eliminate errors associated with different distributions of carriers in the films due to the coupling effect.

Crack propagation and attrition mechanism of oxygen carriers in chemical looping process

Chemical looping combustion (CLC) is one of the most promising CO2 capture technologies, where oxygen carriers (OCs) circulate between a fuel reactor and an air reactor and is mainly responsible for providing lattice oxygen and heat to the fuel reactor. The lifetime of OC is an important parameter that has a great effect on CLC’s economic performance. Attrition is one of the most crucial reasons that shortens OC’s lifetime. In this study, attrition behavior of an iron-based OC in relatively long-period experiments was carried out in a fluidized bed reactor, and cold attrition experiment (CAE), hot attrition experiment (HAE) and reactive attrition experiment (RAE) were tested to quantify the contribution of mechanical stress, thermal stress and chemical stress to OC’s attrition. Morphology of cracks, surface elements distribution and crystal phase of OC in different stages during cyclic reactions were studied in detail, and the attrition mechanism of OC is therefore proposed. For COs produced by powder mixing and sintering, results show that the contribution of chemical stress to the attrition of OC is a dynamic increase process, and it completely dominates the attrition after the 40th cycle. The attrition rate of OC under different conditions follows RAE > HAE > CAE and attrition type in CAE and HAE mainly follows surface abrasion, while the attrition in RAE is a mixed attrition mechanism dominated by bulk fracture. Analysis indicates crack propagation and the Fe-rich effect caused by the continuous oxidation–reduction reaction together lead to comminution of OC.

The mystery and promise of multivalent metal-ion batteries

Despite mounting interest and extensive research efforts in developing multivalent (MV) metal-ion battery chemistries (Zn2+, Mg2+, Ca2+, Al3+, etc.), the commercial prospects for these energy storage systems are still obfuscated by fundamental scientific questions and engineering challenges. In particular, the charge storage mechanism(s) of the positive electrode and the implications on achievable electrode and full cell-level performance remain intensely debated topics in the field. In this minireview, we highlight some of the recent progress and uncertainty in elucidating capacity contributions and accompanying mechanisms for different charge carriers (H+, MV-ion, structural ion, anion, and charged solvates/complexes). We then present cell balancing and increasing metal anode utilization as major remaining challenges and propose design strategies and future directions for realizing practical MV metal-ion batteries.

Multiferroic oxide BFCNT/BFCO heterojunction black silicon photovoltaic devices

Multiferroics are being studied increasingly in applications of photovoltaic devices for the carrier separation driven by polarization and magnetization. In this work, textured black silicon photovoltaic devices are fabricated with Bi6Fe1.6Co0.2Ni0.2Ti3O18/Bi2FeCrO6 (BFCNT/BFCO) multiferroic heterojunction as an absorber and graphene as an anode. The structural and optical analyses showed that the bandgap of Aurivillius-typed BFCNT and double perovskite BFCO are 1.62 ± 0.04 eV and 1.74 ± 0.04 eV respectively, meeting the requirements for the active layer in solar cells. Under the simulated AM 1.5 G illumination, the black silicon photovoltaic devices delivered a photoconversion efficiency (η) of 3.9% with open-circuit voltage (Voc), short-circuit current density (Jsc), and fill factor (FF) of 0.75 V, 10.8 mA cm−2, and 48.3%, respectively. Analyses of modulation of an applied electric and magnetic field on the photovoltaic properties revealed that both polarization and magnetization of multiferroics play an important role in tuning the built-in electric field and the transport mechanisms of charge carriers, thus providing a new idea for the design of future high-performance multiferroic oxide photovoltaic devices.

The Facile Synthesis of Cu2O-Cu hybrid cubes as efficient visible-light-driven photocatalysts for water remediation processes

It is considered that the photocatalyst materials will play a vital role in order to solve challenging problems in the century we live in, such as global warming, clean energy demands, and environmental pollution. The well-defined hybrid Cu2O-Cu architecture cubes are synthesized in a one-step procedure without using a template and surfactants via an aqueous solution-phase synthesis route at low temperatures. The hybrid Cu2O-Cu architecture cubes are synthesized through the reduction of D(+)- glucose in an alkaline solution, while the pristine cuprous oxide cubes are synthesized by using l-ascorbic acid as a reductant. Compared to pristine Cu2O cubes, the heterostructure Cu2O-Cu architecture exhibits superior photocatalytic performance also against both dyes and herbicide due to the enhanced separation and impressive transfer mechanism of charge carriers in the presence of copper. The low cost, abundance, and nontoxic nature of Cu2O make it a promising visible-driven material for advanced oxidation processes.

Internal migration networks and mortality in home communities: Evidence from Italy during the Covid-19 pandemic

Do internal migration networks benefit or harm their home communities in case of a communicable disease? Looking at the spread of Covid in Italy and using pre-determined province-to-province migration, excess mortality and mobile phone tracking data, we document that provinces with a greater share of migrants in outbreak areas show greater compliance with self-isolation measures (information mechanism), but also a greater population inflow from outbreak areas (carrier mechanism). For a subset of localities, the net effect on mortality is negative. However, for the average locality, the effect is positive and large, suggesting that the role of migrants as information providers is trumped by their role as virus carriers. The effect is quantitatively important and could be incorporated in epidemiological models forecasting the spread of communicable diseases.

Regeneration mechanism of CuO-CaSO4 based oxygen carriers

CuO-CaSO4 based materials are widely used in chemical looping technology. Although the reduction process is essential, the regeneration process of the oxygen carrier is also vital. The regeneration capacity determines the lifetime of the oxygen carrier. The exploration of the regeneration mechanism of oxygen carriers is an indispensable part of its applicability in industry. Recently, just a few reports were dealing with the regeneration of CuO-CaSO4 oxygen carriers. In the present work, the regeneration mechanism of the CuO-CaSO4 oxygen carriers was analyzed by thermodynamic, and kinetic analysis. It was observed that the high temperature is not beneficial to the occurrence of these reactions at 923 K. The CuO-CaSO4 oxygen carrier could be regenerated entirely. The regeneration process was described in two steps, with the 3D symmetry diffusion module. The first step was when CaS, Cu2S, Cu reacts with oxygen to produce CaSO4, Cu2O, CuSO4, and some CuO. The second step is the oxidation of Cu2O to generate CuO. After analysis, the regeneration kinetic function of the oxygen carrier compound of CuO-CaSO4 has been achieved. This work indicates that the CuO-CaSO4 based oxygen carrier is a recommended oxygen carrier in the chemical looping process, which lays a foundation for the practical industrial application of the oxygen carriers.

Investigation of Photoexcitation Energy Impact on Electron Mobility in Single Crystalline CdTe.

The exceptional electronic properties of cadmium telluride (CdTe) allow the material to be used in a wide range of high energy radiation detection applications. Understanding the mechanisms of local carrier scattering is of fundamental importance to understand the charge transport in the material. Here, we investigate the effect of photoexcitation on electron transport properties in chlorine doped single crystalline cadmium telluride (SC-CdTe:Cl). For this purpose time of flight measurements were performed on SC-CdTe:Cl in order to study the electron drift mobility in the low injection regime. Measurements were made at the temperature intervals of 80 to 300 K, for an applied electric field between 270 and 1600 V/cm and for wavelengths of 532, 355 and 213 nm. We have found that the electron drift mobility was affected by the excitation energy for temperatures below 200 K. In addition, the measurements revealed that it is possible to determine impurity and shallow trap concentration by this method. The method proves to be extremely sensitive in measuring very low impurity levels and in identifying dominant scattering mechanisms.

Tuning of electrical conduction properties of natural fibers and TiO2 based flexible paper composite sheets by electrodeposition of metallic nanolayers

In an era of modern smart technology, flexible electrodes are of great interest for different energy conversion as well as energy storage applications like solar cells, all solid-state batteries, and supercapacitors. Flexible metal oxide-based paper electrodes are advantageous in comparison to conventional electrodes due to their economical synthesis, biocompatibility, and environment-friendly characteristics. However, the electrical conductivity of paper electrodes is limited because of the insulating nature of natural fibers employed as a binder for the flexible matrix of metal oxides. The current study is an attempt to tune the electrical properties of lignocelluloses (natural fibers) and titanium dioxide (TiO2) based paper electrodes by facile electrodeposition technique. The crystalline parts (e.g., TiO2, Ag, and Au) of the prepared composite sheets were characterized by XRD analysis while the surface morphology was studied by SEM. FTIR was used to characterize the organic matter in LC fibers by identifying various molecular stretching and vibrational modes of C, H, and O-containing molecules. Electric permittivity was measured as a function of electric field frequency at room temperature which revealed the value of 23. 5 (at 1 kHz) for the sample LC/TiO2/Ag 9000s indicating the best charge storing capability of the sample. Impedance analysis was employed to identify various charge carrier mechanisms active in the sheets. It was found through impedance analysis that there is an active diffusion-controlled impedance mechanism of Au-coated samples causing an increased conductivity via the ionic diffusion. This diffusion-controlled conduction was modeled by the Warburg element. The enhanced conductivity due to ionic diffusion makes these samples more useful as electrodes. Cyclic voltammetry (CV) measurements of the electrodeposited samples established the increase in conductive properties and efficient kinetics of LC/TiO2 paper sheets. The current study suggests that Ag and Au-coated paper electrodes can be potential candidates for energy conversion and storage applications.