Donor Concentration Research Articles

Investigation of electrical and admittance analysis of Au/Thiophene/n-Si structure at room temperature

In this study, the Au/n-Si/Au–Sb and Au/Thiophene/n-Si/Au–Sb devices were fabricated at same conditions and electrical/dielectric properties were studied. The electrical measurements showed that the presence of the thiophene interface layer increased the rectification ratio (RR), approximately 2.5 times. Furthermore, the ideality factor (n) value increased from 1.6 to 2.2, the series resistance (Rs) decreased. The capacitance-voltage (C–V) curves indicated peaks for each frequency in accumulation region at about 0.2 V and the peak values decreased from 6.4 × 10−10 F to 4.3 × 10−11 F with increasing frequency. The conductance (G/ω) values decreased with increasing frequency. On the other hand, while the donor concentration (ND) is gradually decreased from 7.12 × 1014 cm−3 to 6.05 × 1014 cm−3 with increasing frequency, the zero-bias barrier height (ΦBo) increased from 0.330 eV to 0.627 eV. However, the Fermi energy (EF) has nearly not effected. The results showed that the thiophene can be used as effective interface material for interface engineering.

Frequency and temperature dependence of dielectric properties and capacitance–voltage in GO/TiO2/n-Si MOS device

Dielectric properties and capacitance–voltage of GO/TiO2/n-Si junction were investigated in frequency range 10–2 × 107 Hz and temperature (233–363 K). Reliance of $$\varepsilon^{\prime}$$ , $$\varepsilon^{\prime\prime}$$ , tanδ, Mʹ, Mʺ, impedance, and ac conductivity on frequency and temperature were studied. From results, it is found that $$\varepsilon^{\prime}$$ increases with increasing frequency at low-frequency region, while that it decreases at high frequencies. $$\varepsilon^{\prime\prime}$$ decreases with frequency (f) increment in the range 10–56 Hz and 1619–12195 Hz. It is observed the decrement of tanδ with increasing frequency in higher range 1,355,210–2 × 107 Hz. Real part of electric modulus (Mʹ) reduces with increment frequency. Conductivity rises with rising temperature. Moreover, activation energy (Ea) values decrease with increasing f then increase at higher f. Different parameters, such as carrier density, built-in potential, and barrier height, were derived from the reverse bias C−2–V curves. It is found that, built-in-voltage (Vbi), barrier height (φb), and Fermi energy (EF) increase with increasing temperature. Moreover, donor concentration (ND) and image force barrier lowering (∆φb) decrease with temperature increment. In addition, series resistance (Rs) decreases with temperature and frequency increment. In addition, this MOS structure GO/TiO2/n-Si works as a device, and by controlling the temperature, frequency, and voltage, the required properties from this device can be adjusted to make it suitable for any required applications; this is obvious from investigated dielectric properties.

Impact of SiO2 interfacial layer on the electrical characteristics of Al/Al2O3/SiO2/n-Si metal–oxide–semiconductor capacitors

The aim of this study is to reduce the oxide and interface-trap charges and also improve the stability at the oxide–semiconductor interface by growing a SiO2 interface layer on a Si wafer then depositing Al2O3 thin film. Effective oxide charges density (Nox), border trap charges density (Nbt), interface states density (Nit), diffusion potential (VD), donor concentration (ND), and barrier height $${(\varPhi }_{\mathrm{B}})$$ were calculated using the capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements at different annealing temperatures. The flat-band voltage (Vfb) changed with annealing temperature and the Vfb value for the 450 °C annealed sample was closest to the ideal Vfb. The sample also possessed a high dielectric constant. For these reasons, C–V and G/w–V values of this sample at different frequencies were obtained. Compared to previous studies, very low Nbtvalues (~ 109 eV−1 cm−2), low Nit values (~ 1010 eV−1 cm−2) and high $${\varPhi }_{\mathrm{B}}$$ values for the annealed samples were obtained due to the SiO2 interface layer.

Facile Method of Solvent-Flushing To Building Component Distribution within Photoactive Layers for High-Performance Organic Solar Cells.

Suitable donor and acceptor distribution in the blended photoactive layer benefits the charge transfer and exciton separation to boost the performance of organic solar cells (OSCs). Herein, we propose a universal solvent-flushing method for building component distribution in photoactive layers based on the different solubilities of the donor and acceptor in acetylacetone (Acac). The donor and acceptor concentration distribution through the photoactive layers is investigated by the time-of-flight secondary-ion mass spectroscopy, and the surface concentration changes are examined by contact angle measurements and atomic force microscopy tests. The charge-transfer properties of OSCs before and after Acac flushing are further investigated by the rectification ratio and light intensity-dependent Jsc and Voc measurements. For inverted OSCs based on PBDB-TF:IT-4F, the power conversion efficiency (PCE) enhances from 12.87 to 14.05%, and for a PBDB-TF:Y6-based device, the PCE also significantly increases from 15.40 to 16.51% because of greatly enhanced Jsc and FF, benefited from enhanced charge transport and suppressed charge recombination by solvent-flushing. Our findings suggest that solvent-flushing is a simply processed and easily controlled method to achieve vertical component distribution in photoactive layers to boost the performance of OSCs.

Controls of H2S, Fe2 +, and Mn2 + on Microbial NO3 --Reducing Processes in Sediments of an Eutrophic Lake.

Understanding the biogeochemical controls on the partitioning between nitrogen (N) removal through denitrification and anaerobic ammonium oxidation (anammox), and N recycling via dissimilatory nitrate (NO3–) reduction to ammonium (DNRA) is crucial for constraining lacustrine N budgets. Besides organic carbon, inorganic compounds may serve as electron donors for NO3– reduction, yet the significance of lithotrophic NO3– reduction in the environment is still poorly understood. Conducting incubation experiments with additions of 15N-labeled compounds and reduced inorganic substrates (H2S, Fe2+, Mn2+), we assessed the role of alternative electron donors in regulating the partitioning between the different NO3–-reducing processes in ferruginous surface sediments of Lake Lugano, Switzerland. In sediment slurry incubations without added inorganic substrates, denitrification and DNRA were the dominant NO3–-reducing pathways, with DNRA contributing between 31 and 46% to the total NO3– reduction. The contribution of anammox was less than 1%. Denitrification rates were stimulated by low to moderate additions of ferrous iron (Fe2+ ≤ 258 μM) but almost completely suppressed at higher levels (≥1300 μM). Conversely, DNRA was stimulated only at higher Fe2+ concentrations. Dissolved sulfide (H2S, i.e., sum of H2S, HS– and S2−) concentrations up to ∼80 μM, strongly stimulated denitrification, but did not affect DNRA significantly. At higher H2S levels (≥125 μM), both processes were inhibited. We were unable to find clear evidence for Mn2+-supported lithotrophic NO3– reduction. However, at high concentrations (∼500 μM), Mn2+ additions inhibited NO3– reduction, while it did not affect the balance between the two NO3– reduction pathways. Our results provide experimental evidence for chemolithotrophic denitrification or DNRA with Fe2+ and H2S in the Lake Lugano sediments, and demonstrate that all tested potential electron donors, despite the beneficial effect at low concentrations of some of them, can inhibit NO3– reduction at high concentration levels. Our findings thus imply that the concentration of inorganic electron donors in lake sediments can act as an important regulator of both benthic denitrification and DNRA rates, and suggest that they can exert an important control on the relative partitioning between microbial N removal and N retention in lakes.

Structure-Activity Relationships of Voltaglue Organic Blends.

Voltage-activated, one-pot adhesives are an emerging platform with many potential advantages, but require multicomponent grafting of electrochemical donors and acceptors for operation in organic environments. This formulation strategy reduces throughput efficiency, organic solubility, and requires additional purification of the grafted dendrimers. A more advanced strategy is proposed for setting up the donor-acceptor conductive network by exploiting a flexible blending design, providing faster throughput of structure-activity analyses with less synthetic investment. The blend method investigates the ampere-dependent storage modulus and gelation time as a function of both donor and acceptor concentration. This blend strategy allows a rapid evaluation of donor-acceptor parameters involved in voltage-activated adhesive formulations.

Interface confinement on the exciton recombination in thin CdS/ZnO shell/core nanowires

The modulation of exciton recombination is one of the core issues for the electronic/optoelectronic devices. Here, we investigate the exciton recombination and surface depletion of ZnO nanowires under various interface conditions in terms of continuum medium mechanics and bond relaxation method. We find that the enhancement of donor concentration, nanowire dimension and external temperature can modify the carrier recombination, surface barrier height and surface depletion depth. Moreover, coated a thin epitaxial layer on the nanowires is of great benefit to reduce the surface state for suppression of recombination rate. The related mechanism on the interface confinement has also been clarified. Our predictions agree well with the experimental measurements, which provide an effective guidance for the organization of electronic device design.

Differential Effects of Fatty Acid Saturation and Chain Length on NASH in Juvenile Iberian Pigs

Abstract Objectives Non-alcoholic fatty liver disease (NAFLD) represents the major cause of pediatric chronic liver pathology in the United States. The objective of this study was to compare the relative effect of inclusion of isocaloric amounts of saturated medium-chain fatty acids (hydrogenated coconut oil), saturated long-chain fatty acids (lard) and unsaturated long-chain fatty acids (olive oil) on endpoints of NAFLD and insulin resistance. Methods Thirty-eight 15-d-old Iberian pigs were fed 1 of 4 diets containing (g/kg body weight × d) 1) control (CON; n = 8): 0 g fructose, 10.5 g fat, and 187 kcal metabolizable energy (ME), 2) lard (LAR; n = 10): 21.6 g fructose, 17.1 g fat (100% lard) and 299 kcal ME, 3) hydrogenated coconut oil (COCO; n = 10): 21.6 g fructose, 16.9 g fat (42.5% lard and 57.5% coconut oil) and 299 kcal ME, and 4) olive oil (OLV, n = 10): 21.6 g fructose, 17.1 g fat (43.5% lard and 56.5% olive oil) and 299 kcal ME, for 9 consecutive weeks. Body weight was recorded every 3 d. Serum markers of liver injury and dyslipidemia were measured on d 60 at 2 h post feeding, with all other serum measures assessed on d 70. Liver tissue was collected on d 70 for histology, triacylglyceride (TG) quantification, and metabolomics analysis. Results Tissue histology indicated the presence of steatosis in LAR, COCO and OLV compared with CON (P ≤ 0.001), with a further increase in in non-alcoholic steatohepatitis (NASH) in OLV and COCO compared with LAR (P ≤ 0.01). Alanine and aspartate aminotransferases were higher in COCO and OLV (P ≤ 0.01) than CON. All treatment groups had lower liver concentrations of methyl donor's choline and betaine versus CON, while bile acids were differentially changed (P ≤ 0.05). COCO had higher levels of TGs with less carbons (Total carbons < 52) than all other groups (P ≤ 0.05). Several long-chain acylcarnitines involved in fat oxidation were higher in OLV versus all other groups (P ≤ 0.05). Conclusions Inclusion of fats enriched in medium-chain saturated and long-chain unsaturated fatty acids in a high-fructose high-fat diet increased liver injury, compared with fats with a long-chain saturated fatty acid profile. Further research is required to investigate the mechanisms causing this difference in physiological response to these dietary fat sources. Funding Sources ARI, AcornSeekers.

Characterization of the intestinal absorption of morroniside from Cornus officinalis Sieb. et Zucc via a Caco-2 cell monolayer model.

Morroniside is a biologically active polyphenol found in Cornus officinalis Sieb. et Zucc (CO) that exhibits a broad spectrum of pharmacological activities, such as protecting nerves, and preventing diabetic liver damage and renal damage. However, little data are available regarding the mechanism of its intestinal absorption. Here, an in vitro human intestinal epithelial cell model of cultured Caco-2 cells was applied to study the absorption and transport of morroniside. The effects of donor concentration, pH and inhibitors were investigated. The bidirectional permeability of morroniside from the apical (AP) to the basolateral (BL) side and in the reverse direction was studied. When administered at three tested concentrations (5, 25 and 100 μM), the apparent permeability coefficient (Papp) values in the AP-to-BL direction ranged from 1.59 × 10−6 to 2.66 × 10−6 cm/s. In the reverse direction, BL-to-AP, the value was ranged from 2.67 × 10−6 to 4.10 × 10−6 cm/s. The data indicated that morroniside transport was pH-dependent. The permeability of morroniside was affected by treatment with various inhibitors, such as multidrug resistance protein inhibitors MK571 and indomethacin, as well as the breast cancer resistance protein inhibitor apigenin. The mechanisms of the intestinal absorption of morroniside may involve multiple transport pathways, such as the passive diffusion and efflux protein-mediated active transport especially involving multidrug resistance protein 2 and breast cancer resistance protein. After the addition of CO, the Papp values in the AP-to-BL direction increased significantly, therefore, it can be assumed that some ingredients in the CO promote morroniside absorption in the small intestine.

Current-Induced Thermal Tunneling Electroluminescence in a Single Highly Compensated Semiconductor Microrod.

SummaryHere we demonstrate a novel and robust mechanism, termed as “current-induced Joule heating activated thermal tunneling excitation,” to achieve electroluminescence (EL) by the hot electron-hole-pair recombination in a single highly compensated semiconductor microrod. The radiative luminescence is electrically excited under ambient conditions. The current-induced Joule heating reduces the thermal tunneling excitation threshold of voltage down to 8 V and increases the EL efficiency ~4.4-fold at 723 K. We interpret this novel phenomenon by a thermal tunneling excitation model corrected by electric-induced Joule heating effect. The mechanism is confirmed via theoretical calculation and experimental demonstration, for the first time. The color-tunable EL emission is also achieved by regulation of donor concentration. This work opens up new opportunities for design of novel multi-color light-emitting devices by homogeneous defect-engineered semiconductors in future.

The role of doping molybdenum (Mo) and back-front side illumination in enhancing the charge separation of α-Fe2O3 nanorod photoanode for solar water splitting

Hematite (α-Fe2O3) has abundant reserves and an appropriate bandgap of ~2.1 eV for H2 production using water splitting. However, its potential application to solar water splitting is seriously limited by the extremely high charge recombination rate of the charge carriers. The present work investigates the photoelectrochemical (PEC) performance of molybdenum (Mo) doped α-Fe2O3 thin-film electrodes. The Mo-doped α-Fe2O3 samples were prepared by a hydrothermal method and then loaded with different Mo ratio to optimize the photocurrent density. The morphological characterization and crystal structure identified by FE-SEM, Raman, XRD, XPS and UV–vis analyses. Mo doping of α-Fe2O3, significantly enhanced the photocurrent density. The α-Fe2O3 film with optimized Mo-doped amount (10% Mo-doped α-Fe2O3) had a photocurrent density of 0.75 and 1.2 mA cm−2 in front and back-side illumination, respectively at 0.6 V versus Ag/AgCl under 100 mWcm−2 with an electrolyte of 1 M (pH = 12) aqueous NaOH solution, which are ~10 and 17 times higher than that of the pure α-Fe2O3 photoanode. The doping of Mo onto pure α-Fe2O3 increased the donor concentration 1.3-fold, reduced the width of the space charge layer (WSCL) 1.2-fold, and decreased the flat band potential (Vfb) 1.6-fold, which improved the photoelectrochemical efficiency.

Experimental and numerical study on photocatalytic activity of the ZnO nanorods/CuO composite film

The photocatalytic activity of the ZnO NRs/CuO composite film was investigated by using both experimental and numerical methods. The ZnO NRs/CuO composite film exhibits significantly enlarge absorption range to visible-light and suppress the recombination rate of the photogenerated electron-hole pairs, which can be well utilized as a photocatalyst. The ZnO NRs/CuO composite film also presents good stability, and reusability, and durability for photo-decomposition purpose. The optimal ZnO NRs/CuO composite film contains 1μ-thick of CuO film and 10 nm-thick of ZnO NRs film. The donor concentration in ZnO NRs film should be lower than 1016 cm−3. The short circuit current density of the optimal composite film is 25.8 mA/cm2 resulting in the calculated pseudo-order rate constant of 1.85 s−1. The enhancement in degradation efficiency of this composite film is attributed to the inner electric field and large effective surface area of ZnO NRs film.

Size Effect in Nanostructured SnO2/TiO2 Gas Sensors

Introduction Size effect in resistive-type responses to gases has been demonstrated for the first time in the case of SnO2 polycrystalline sensors [1]. Since then it is believed that the smallest the grain size, the higher change in the electrical resistivity of metal oxide nanomaterials can be expected upon interaction with oxidizing or reducing gases. This belief is based on the argument that the surface-to-volume ration increases with a decrease in the grain diameter and as a gas adsorption is a surface process this in consequence leads to an increased density of active sites available for gas-solid interaction [2-3].Therefore, the size reduction has been considered as a fundamental strategy for nanosensors, justifying an enormous effort towards application of nanotechnology in gas sensing devices.A closer look at this issue reveals that such simplified reasoning is not always true. Geometrical decrease in the grain size below 10 nm for SnO2 does not necessarily mean to be a good solution for other oxides such as TiO2. In fact, the most important is a comparison between the grain diameter d and the Debye length λD defined as: λD={(ε ε0φS)/(eND)}1/2 where ε and ε0 denote relative permittivity of the material and vacuum permittivity, respectively, φ S is the surface potential, e represents electron charge and ND stands for donor concentration.When the condition d << λD is fulfilled, the size effect should play a substantial role in gas sensing. Therefore, the aim of this work is to investigate the size effect in the electrical resistivity of SnO2/TiO2 upon interaction with oxidizing/reducing gases by intentional modification of λD by influencing: the electrical properties through donor concentration ND the structural properties through anatase to rutile ratio thus affecting relative permittivity, εmorphology through its impact on the surface potential, φ S Technology TiO2/SnO2 bi-layer nanoheterostructures have been synthesized in a two-step process: (i) magnetron sputtering, MS, followed by (ii) Langmuir-Blodgett, LB technique [4]. Mixed TiO2/SnO2 composites have been obtained by means of Flame Spray Synthesis, FSS [5], sol-gel [6] and by mechanical mixing of commercial Sigma-Aldrich nanopowders [7]. Experimental Methods Crystallographic structure of the nanocomposites was studied by X-ray diffraction in Bragg-Brentano geometry while that of thin films was determined by X-ray diffraction in grazing incidence GID geometry using Philips X’pert Pro diffractometer. Scanning electron microscopy SEM investigations were carried out with the use of FEI Nova Nano SEM 200 microscope. Transmission electron microscopy TEM was employed to study the morphology of the nanopowders. FEI Tecnai TF 20 X-TWIN microscope was used. Gas sensing properties were established by measuring resistive-type responses to hydrogen, and NO2 vs. time, within a temperature range of 200-400oC both in dc and ac mode. The experimental setup for sensor characterization was already described in [8]. Sensitivity of the sensors to the reducing gas was defined as R0/R while that to the oxidizing as R/R0, where R0 is the baseline resistance in the reference gas, i.e. in air. Results and Conclusions Nanopowders of TiO2 with different crystallite size, grown by FSS, demonstrate a size effect in the electrical conductivity (Fig.1a) which can be attributed to the activation energy decreasing with the particle size. No grain size effect in hydrogen sensing has been observed.Bi-layered heterostructures synthesized on special gas sensor substrates with precisely defined interdigital electrodes were tested towards NO2 detection over the low concentration range from 200 ppb to 20 ppm.High response to low concentration of NO2 (Fig. 1b) could be accounted for by two factors: particular morphology of SnO2 base layer with small, well-dispersed grains indicating possibility of a grain size effectwell-developed, rough surface of TiO2 overlayer grown by the LB technique. Acknowledgement National Science Center NCN, Poland project no. 2016/23/B/ST7/00894 is acknowledged.

Anisotropy of hydrogen plasma effects in bulk n-type β-Ga2O3

Bulk n-type β-Ga2O3 samples with orientation (−201) and (010) were exposed to a high density hydrogen plasma at 330 °C for 0.5 h. The effects were radically different for the two orientations. For the (−201) sample, H plasma exposure increased the net surface concentration of shallow donors from 2.7 × 1017 cm−3 to 2.6 × 1018 cm−3, with the shallow donors having an ionization energy close to 20 meV as deduced from the temperature dependence of the series resistance of Ni Schottky diodes. By sharp contrast, H plasma exposure of the (010) sample led to a strong decrease in the net shallow donor density from 3.2 × 1017 cm−3 to below 1015 cm−3 in the top 0.9 μm of the sample and to 3.2 × 1016 cm−3 near the edge of the space charge region at 0 V, with the total width of the region affected by plasma treatment being close to 1.1 μm. For both orientations, we observed a major decrease in the concentration of the dominant E2 traps near Ec-0.82 eV related to Fe acceptors. The deep trap spectra in hydrogenated samples were dominated by the E2* traps commonly ascribed to native defects in β-Ga2O3. The peak of these traps with a level near Ec-0.74 eV was masked in the starting samples by the peak of the E2 Fe acceptors present in high concentration, so that E2* only broadened the Fe peak on the low temperature side, but could be revealed by the modeling of the spectra. The concentration of the E2* center was not strongly affected in the hydrogen-treated samples with orientation (010), but in the (−201) samples, the concentration of the E2* peak was greatly enhanced. The results are discussed in conjunction with previous reports on hydrogen plasma treatment of β-Ga2O3 and on obtaining p-type conductivity in the surface layers of β-Ga2O3 crystals annealed in molecular hydrogen at high temperatures [Islam et al., Sci. Rep. 10, 6134 (2020)].

Precipitation of Molybdenum Oxides in Supersaturated Zinc Oxide Thin Films

Zinc oxide thin films saturated with molybdenum were prepared by RF magnetron sputtering process using zinc oxide and molybdenum targets for the co-sputtering. The sputtering power for zinc oxide was kept constant while that for molybdenum was varied from 0 watt to 35 watt. We found that the molybdenum-doped zinc oxide thin film change their color from transparent to grayish color as molybdenum sputtering power increases. The color change of the zinc oxide film suggests that the molybdenum changes its valance state as the molybdenum sputtering power was varied.A surprising finding about the study is the electrical conductivity increases and then decreases with molybdenum sputtering power. The increase of electrical conductivity should be attributed to the increase of donor concentration as more molybdenum atoms are incorporated. The decrease of conductivity, on the other hand, is not so well reported. Hall measurement study shows that the conductivity decrease is caused by decreased electron concentration. However, the electron mobility increases steadily with increased molybdenum sputtering power even though the electron concentration decreases. This is an indication that the electrical conduction no longer occurs through the molybdenum-doped ZnO grains.We propose that the conduction changes from grains to grain boundaries as molybdenum sputtering power increases. It means molybdenum is precipitated at the grain boundaries and forms conducting channels besides zinc oxide grains. The high mobility conduction channel is desired for devices using electron transport layers in their structures. The electrochemical solar cells are one of the devices that may benefit from the finding of molybdenum-doped oxide. We would like to present the valance change of molybdenum along with the conduction behavior, and would also like to predict the band alignment between zinc oxide and molybdenum oxide in the molybdenum-doped zinc oxide thin films. X-ray diffraction, UV-vis spectrophotometry, and x-ray photoelectron spectroscopy will be presented to show the conclusion that the electron mobility increase was attributed to the grain boundary conduction.

The Effect of Doping on Different FET Structures: MOSFET, TFET and FinFET

MOSFET have been scaled down over the past few years in order to give rise to high circuit density and increase the speed of circuit. But scaling of MOSFET leads to issues such as poor control gate over the current which depends on gate voltage. Many short channel effects (SCE) influence the circuit performance and leads to the indeterminist response of drain current. These effects can be decreased by gate excitation or by using multiple gates and by offering better control gate the device parameters. In Single gate MOSFET, gate electric field decreases but multigate MOSFET or FinFET provides better control over drain current. In this paper, different FET structures such as MOSFET, TFET and FINFET are designed at 22nm channel length and effect of doping had been evaluated and studied. To evaluate the performance donor concentration is kept constant and acceptor concentration is varied.

Deconvolution of temperature dependence of conductivity, its reduced activation energy, and Hall-effect data for analysing impurity conduction in n-ZnSe

ABSTRACT The temperature dependence of the reduced activation energy w = ε/kBT of the conductivity σ has been utilised for determining the impurity conduction mechanism in doped semiconductors in many studies. Herein, the formula for deconvoluting w when plural conduction mechanisms appear is used to confirm the analysis of the data of the Hall-effect measurements on Al-doped n-ZnSe samples. The analysis is performed on the basis of an impurity-Hubbard-band model which includes ε 2 conduction in the top Hubbard band as well as ε 3 and Efros-Shklovskii (ES) variable-range hopping (VRH) conduction processes in the bottom Hubbard band. As the result of the analysis, transitions among the three hopping conduction mechanisms of ε 2, ε 3, and ES VRH are clearly shown in the temperature dependence of w as well as in that of the Hall mobility, which are hardly noticed in the temperature dependence of σ. In addition, the power-law exponent of the prefactor of ES VRH conductivity is determined through the fit to the temperature dependence of w to show that it decreases from ∼ 1.5 to ∼ 0 with increasing net donor concentration.

Tracing the Full Bimolecular Photocycle of Iron(III)-Carbene Light Harvesters in Electron-Donating Solvents.

Photoinduced bimolecular charge transfer processes involving the iron(III) N-heterocyclic carbene (FeNHC) photosensitizer [Fe(phtmeimb)2]+ (phtmeimb = phenyltris(3-methyl-imidazolin-2-ylidene)borate) and triethylamine as well as N,N-dimethylaniline donors have been studied using optical spectroscopy. The full photocycle of charge separation and recombination down to ultrashort time scales was studied by investigating the excited-state dynamics up to high quencher concentrations. The unconventional doublet ligand-to-metal charge transfer (2LMCT) photoactive excited state exhibits donor-dependent charge separation rates of up to 1.25 ps–1 that exceed the rates found for typical ruthenium-based systems and are instead more similar to results reported for organic sensitizers. The ultrafast charge transfer probed at high electron donor concentrations outpaces the solvent dynamics and goes beyond the classical Marcus electron transfer regime. Poor photoproduct yields are explained by donor-independent, fast charge recombination with rates of ∼0.2 ps–1, thus inhibiting cage escape and photoproduct formation. This study thus shows that the ultimate bottlenecks for bimolecular photoredox processes involving these FeNHC photosensitizers can only be determined from the ultrafast dynamics of the full photocycle, which is of particular importance when the bimolecular charge transfer processes are not limited by the intrinsic excited-state lifetime of the photosensitizer.

Effect of hydrogen on semiconductor properties and pitting initiation of 2205 duplex stainless steel passivation film

PurposeThis paper aims to study the effect of current density of hydrogen charging on the semiconductor properties and pitting initiation of 2205 duplex stainless steel (DSS) passivation film.Design/methodology/approachIn this work, the 2205 DSS is pre-hydrogenated and passivated. Then, the passivation film is tested by electrochemical impedance method, Mott–Schottky curve method and dynamic potential scanning method. The influences of hydrogen on the properties of the passivation film and the corrosion behavior of the matrix were studied by analyzing the curves obtained in the electrochemical test. The surface of the passivation film after pre-hydrogenation and anodic polarization was observed by using the ultra-depth three-dimensional microscopy and the scanning electron microscope. The integrity, density and corrosion morphology of the passivation film were studied and discussed.FindingsWith the increase of the hydrogen current density, the growth of the passivation film is hindered, the concentrations of donor and acceptor in the film are increased, the conductivity of the passivation film increases. In the anodic polarization, the dimensional passive current density increases with the increase of the hydrogen current density, and the pitting potential is reversed, the more likely the sample is pitting. In general, hydrogen hinders the formation of the passive film on duplex stainless steel, which increases the concentration of point defects in the passive film. Finally, the passive film is easy to crack and pitting.Originality/valueThe performance of passive film is an important condition to influence the corrosion behavior of stainless steel. However, little research has been done on the effects of hydrogen on the electrochemistry and pitting sensitivity of 2205 DSS passivation films. The effect of hydrogen on semiconductor properties and pitting initiation of 2205 DSS passivation film is needed to be investigated.

The effects of W/Mo-co-doped BiVO4 photoanodes for improving photoelectrochemical water splitting performance

The poor electrical conductivity of bismuth vanadate (BVO) can be improved by metal-doping at optimum percentage. Previously, we improved the photoelectrochemical (PEC) properties of BVO photoanodes by optimizing the different atomic percentage of molybdenum (Mo). Here, we co-doped BVO simultaneously with tungsten/molybdenum (W/Mo) to enhance the water splitting properties of BVO photoanodes. At optimum co-doping percentages of 0.5 %W-2%Mo BiVO4 (0.5W-2Mo-BVO) the photocurrent density maximum was ∼ 0.97 mA cm−2 at 0.6 V vs. Ag/AgCl. The water splitting was performed under 100 mW. cm-2 irradiation and 0.6 V vs. Ag/AgCl applied voltage for 0.5W-2Mo-BVO. The H2 production was 19.5 μmol.cm-2 after 2 h at optimized W/Mo co-doping. W/Mo co-doping into BiVO4 greatly improved the electron mobility, as demonstrated by photocurrent, Mott-Schottky, electrochemical impedance, open circuit potential (ΔOCP) and incident photon conversion efficiencies (IPCE) measurements. As compared to pure BVO, 0.5W-2Mo-BVO showed ∼2700-fold increase in the donor concentration (ND) and greatly decreased (1/60) space charge layer thickness (WSCL), which induced efficient charge carrier mobility and enhanced the PEC performance.