Schottky Plots Research Articles

Effect of sulfurization on physical and electrical properties of MoS2 films synthesized by electrodeposition route

Thin films of uniform molybdenum disulphide (MoS2) were produced on conducting glass (FTO) using the electrochemical route from aqueous solution (NH4)2MoS4 then subjected to annealing treatment under argon gas with and without sulfur. The influence of sulfurazation on the structural, morphological, optical, and electrical properties of samples was investigated. Scanning electron microscopy exhibits homogeneous surface of the samples. Furthermore, the sample exposed to sulfur treatment has narrower grains comparing with that annealed without sulfur. Energy dispersive x-ray spectroscopy (EDX) confirmed the existence of the MoS2 films with a 2.1 S/Mo atomic ratio for the samples heated with sulfur and a 1.76 atomic ratio for those annealed without sulfur. Our results showed that the type of conduction (n or p) have been found to be sensitive to the S/Mo ratio. In fact, an excess of sulfur anions induces a p-type conductivity while a lack of sulfur results an n-type conductivity. X-ray diffraction showed that with sulfuration, the (002) plan main peak is shifted to smaller angle. This is in direct relation to the stress due to the excess of sulfur. As a fact, sample with grater grain size (D) shows the lowest microstrain (ε) and dislocation density (δ). Moreover, the band gap energy values confirmed the results found in fact, referring to the UV–vis diffuse reflectivity spectra, the band gap energy value of the thin films with lack of sulfur was 1.76 eV and 1.66 eV for those annealed with sulfur. In addition, according to the Mott–Schottky plots we confirmed that the films treated without sulfur show n-type conductivity with a carrier density of 3.24 × 1022 cm−3 and a flat-band potential of −0.66V. However, the films annealed with sulfur showed a p-type semiconductor character with a 1.46 × 1022 cm−3 carrier density and a −0.24 V flat-band potential.

A study on preparation and corrosion behavior of nano rare earth oxide‐modified chromized coatings

AbstractThe corrosion resistance of carbon steel in a harsh environment was improved by preparing a chromized coating on the surface through the method of pack cementation. Nano rare earth‐oxides (NREOs), Y2O3, CeO2, and La2O3 were added to the pack and to further enhance the performance of the chromized coatings. Morphological results showed that NREO refined the microstructure of chromized coatings by retarding the growth of grains. The Mott–Schottky plots demonstrated that coating Cr–La2O3 displayed fewer defects than the other two composite coatings, which was beneficial to reduce the corrosion tendency. In addition, the potentiodynamic polarization and impedance spectroscopy analysis showed that the order of the corrosion rates of the achieved coatings was pure Cr > Cr–Y2O3 > Cr–CeO2 > Cr–La2O3, which revealed that the corrosion resistance increased accordingly.

Effect of aluminum Tripolyphosphate on pitting initiation on carbon steel in chloride contaminated concrete pore solution

Purpose Aluminum tripolyphosphate was used as a corrosion inhibitor in a simulated concrete pore solution. For studies of the inhibition mechanism of aluminum tripolyphosphate on the carbon steel, its influence on the pitting initiation on the carbon steel in a Cl− containing pore solution were investigated. Design/methodology/approach Potentiodynamic polarization curves, Mott–Schottky plots and potentiostatic polarization of the carbon steel in the pore solution with different content of aluminum tripolyphosphate were measured, as well as the optical micrographs of pitting on the carbon steel was observed. Findings The metastable pitting potential and the stable pitting potential increased, while the donor density and the flat band potential decreased with the concentration of aluminum tripolyphosphate in solution. Furthermore, the initiation of pitting was suppressed, as well as the transition from metastable to stable pitting was hindered by the aluminum tripolyphosphate. The scale parameter (a), in the extreme distribution of the maximum current peak, could be used to predict the transition from metastable to stable pitting. Originality/value The inhibition mechanism of aluminum tripolyphosphate on carbon steel in pore solution was revealed. It suppresses the initiation of pitting and hinders the transition from metastable to stable pitting. Furthermore, a parameter defined as the scale parameter (a) in the extreme distribution of the maximum current peak was introduced to predict the transition from metastable to stable pitting.

Enhanced Photoelectrochemical Activities of ZnO Nanorod Arrays After a Modification of ZnS or ZnIn2S4

Highly ordered ZnO nanorod arrays (NRAs) were prepared via a facile ion-exchange route for the photoelectrochemical (PEC) application. Then, ZnO NRAs were modified with ZnS and ZnIn2S4, respectively, through using a hydrothermal treatment method again. It was found that both the ZnS and ZnIn2S4 modifications were in favor of enhancing the PEC activity of ZnO NRAs, although there were no obvious enhancements in the visible-light absorption. Thus, the enhancement was attributed to both the efficient charge separation and excellent electrocatalytic activity of ZnIn2S4. The Mott–Schottky (M–S) plots of two samples were compared and analyzed for clarifying the intrinsic mechanism. A schematic band model has also been proposed for clarifying the charge transfer process in a heterojunction.

EFFECTS OF NITRITE ANIONS ON SURFACE PASSIVE FILM PROPERTIES FOR Q235 CARBON STEELS

In this paper, for Q235 carbon steels in NaNO2solutions with different concentrations of NO[Formula: see text], a passive film composed of mainly Fe2O3was formed on the Q235 surface, and the effects of NO[Formula: see text] concentrations on the properties of passive film were studied by electrochemical methods and microstructural analyses. The applications of electrochemical impedance spectroscopy (EIS), Mott–Schottky (MS) plot, scanning electron microscope (SEM) and X-ray photoelectron spectroscope (XPS) were carried out to characterize the resistance, defect, morphology and composition of passive film, respectively. The passive film resistance and defect, respectively, increased and decreased with the increase of NO[Formula: see text] concentration until the NO[Formula: see text] concentration was up to 0.01[Formula: see text]M, which was the critical NO[Formula: see text] concentration of stable passivation for the Q235 surface. The relation between the electrochemical behavior and the passive film was also discussed in detail.

Investigations on ITO/Ag-WO3/Ag heterojunction Schottky solar cell: Fabrication and characterization through I–V and C–V

This paper deals with the fabrication and characterization of heterojunction Schottky solar cell based on single layer solution processed Ag-WO3 nanoparticle. Various device parameters were investigated using current-voltage (I–V) characteristics, capacitance-voltage(C–V) characteristics and impedance spectroscopy (IS). Ag-WO3/Ag Schottky junction shows rectification with high ON/OFF ratio of 292:1 The photovoltaic characterization results show that the fabricated solar cell responds even to a very weak illumination (35 mW/cm2) of 500 W halogen lamp giving 0.344% efficiency with 78.76% fill factor, 0.132 V open circuit voltage and 1.3 mA short circuit current. Mott Schottky plots were found to be frequency dependent resulting in capacitance dispersion which affects various device parameters like built-in potential, acceptor concentration, depletion width and barrier height. A possible equivalent circuit of the device is also analyzed which indicates the presence of roughness in the deposited films.

Hydrothermal synthesis of 3D hierarchical flower‐like CuGaO 2 with high surface area for dye‐sensitised solar cell

CuGaO2 has been receiving much attention due to its potential as photocathode instead of NiO for p-type dye sensitised solar cells (p-DSSCs). The improvement in the photovoltaic performance of such devices also depends on the increase of the efficient dye loading by significant enhanced specific surface areas. This work reports for the first time the fabrication of the three-dimensional (3D) hierarchical flower-like CuGaO2 nanostructures in a high uniformity by a facile one-step hydrothermal synthesis. The growth mechanism and the effects of the reaction parameters (time and reducing agent) on the formation of the 3D hierarchical flower-like CuGaO2 nanostructures were investigated in detailed. It is significantly to note that the prepared 3D hierarchical flower-like CuGaO2 nanostructures exhibit the highest specific surface areas reported (60 m2/g with ethylene glycol). Due to the efficient dye loading by high specific surface areas, the performance of p-DSSCs based on delafossite CuGaO2 is enhanced. Thereby, based on the optical investigation, electrochemical impedance measurement and Mott–Schottky plots, the improved performance can be attributed to high loading of the dye molecules, the enhanced light-scattering and the reduced interface recombination.

On the material characteristics of a high carbon cast austenitic stainless steel after solution annealing followed by quenching in a CNT nanofluid

AbstractSolution annealing followed by quenching in carbon nanotubes (QCNT) nanofluid treatment was applied to generate very high interstitial carbon content,≈0.30 wt.%, in an austenitic stainless steel (ASS). The high interstitial carbon content leads to remarkable improvement in mechanical properties with essentially no loss of ductility, with no chromium carbides and/or martensite formation. To evaluate the localized corrosion tendency and passivity behavior, 3.5 wt.% NaCl and borate buffer solutions were used, respectively. Based on the electrochemical corrosion results, both high carbon and low carbon (0.030 wt.%) QCNT-treated ASS alloys show comparable passivity and localized corrosion performance. In addition, Mott–Schottky plots revealed that the anodic films on QCNT-treated samples exhibit similar semiconducting characters.

Electrochemical Characterization of CuSCN Hole-Extracting Thin Films for Perovskite Photovoltaics

CuSCN thin films (optimized previously for perovskite photovoltaics) are deposited on glass, F:SnO2 (FTO), Au, glass-like carbon (GC), and reduced graphene oxide (rGO). They exhibit capacitive charging in an electrochemical window from ca. −0.3 to 0.2 V vs Ag/AgCl. Outside this window, CuSCN film is prone to chemical and structural changes. Anodic breakdown (at ca. 0.5 V) causes restructuring into submicrometer particles and denuding of the substrate. The natural p-doping is demonstrated by both the Hall effect and Mott–Schottky plots from electrochemical impedance. The corresponding flatband potentials (in V vs Ag/AgCl) varied with the substrate type as follows: 0.12 V (CuSCN@FTO), 0.08 V (CuSCN@Au), −0.02 V (CuSCN@GC), and 0.00 V (CuSCN@rGO). The acceptor concentrations determined from electrochemical impedance spectroscopy are by orders of magnitude larger than those from electrical conductivity and the Hall effect, the latter being regarded correct. Raman spectra confirm that thiocyanate is the domina...

Functionalized conjugated polymer with plasmonic Au nanoalloy for photocatalytic hydrogen generation under visible-NIR

Abstract Gold based multimetallic nanoalloys decorated on conjugated polymer nanofibers have been prepared using a greener approach without using any reducing agent. The as-prepared nanohybrids exhibited superior catalytic activity for solar hydrogen production under visible light (λ > 420 nm) irradiation and near infrared light irradiation. The UV–Visible diffuse reflectance spectra displayed strong absorption in the visible region which significantly favours the photocatalytic performance. Furthermore, the efficient charge separation suggested by electrochemical impedance measurement and photocurrent response curves for Au50Pt24Pd26/PPy nanohybrids which exhibited significant enhancement in H2 generation rate compared to Au/PPy nanohybrids. The strong interface contact between Au nanoalloys and PPy nanofibers play an important role for the migration of electron during catalysis. The Mott–Schottky plot revealed that photo generated charge carrier concentration has been increased for Au50Pt24Pd26/PPy nanohybrids (7.93 × 1011cm−3) compare to pure PPy (1.43 × 1011 cm−3). The present study provides a new prospect for using conducting polymer based hybrid as photocatalysts for efficient solar hydrogen production.

The semiconductor properties of passive films and corrosion behavior of stainless steel reinforcing bars in simulated concrete pore solution

The vulnerability of concrete reinforcing steels to corrosion when depassivation occurs, typically in the presence of chloride, makes it important to understand the nature of the steels’ passive films. In Part I of the study, electrochemical techniques and Mott–Schottky analysis were used to investigate these films formed on five different grades of stainless steel and carbon steel reinforcing bars exposed to simulated concrete pore solution. The influence of the steel composition and surface finish on Mott–Schottky plots and the electronic properties are discussed in relation to the steels’ corrosion resistance. A p-type semiconductor behavior was observed in the stainless steel alloys in the cathodic potential regions and an n-type in the anodic potential regions. The n-type behavior is similar to that observed in the carbon steel. The electronic and electrochemical properties of the austenitic grades were superior to the duplex grades. The molybdenum-containing grades, 316LN and 2205, did not show the expected superior properties compared to molybdenum-free grades, 304L and 2304. Also, the replacement of nickel by manganese in the 24100 alloy was not found to be detrimental. The as-received bars showed electronic and electrochemical properties that are more realistic to field conditions than those of the polished cross-sections.

Conduction through plasma-treated polyimide: analysis of high-field conduction by hopping and Schottky theory

Plasma surface modification of polyimide (PI) films has been used to modify the material’s wetting and adhesion properties but has also been found to impact high-field electrical properties. Previous work by Meddeb et al. (Chem Phys Lett 649:111–114, 2016. https://doi.org/10.1016/j.cplett.2016.02.037 ) demonstrates a significant reduction in high-field leakage current at high temperatures because of O2 plasma treatment of PI. In this study, we investigate field-dependent current density [J(E)] data measured in our previous study by Meddeb et al. (2016) to identify the surface and bulk mechanisms responsible for high-field conduction behavior of O2 plasma-modified PI films. Specifically, we analyze the J(E) data using three conduction theories: Poole–Frenkel, Schottky, and Hopping. Poole–Frenkel and Schottky analyses are performed by the implementation of linear regression. Hopping analysis was performed using a rigorous statistical technique that incorporates nonlinear regression as well as a bootstrap statistical analysis of fit parameters. Analysis of J(E) data over the temperature range 25–175 °C indicates that 13-micron-thick untreated PI films are dominated by a hopping process at lower temperatures; however, transition to Schottky-dominated conduction occurs as temperature is increased. Films treated with O2 plasma show similar characteristics to the untreated set: Hopping dominated conduction at low temperatures with gradual transition to Schottky. However, the transition to Schottky conduction occurs at a higher temperature in plasma-treated films in comparison with the untreated control set. These results are verified by (1) extracting dielectric permittivity from Schottky plots as a function of temperature and (2) a statistical interpretation of confidence intervals calculated for hopping fit parameters used in low-temperature nonlinear regression. Outcomes from theoretical analysis of the data are used to provide further insight into how surface chemistry may be tailored to limit high-field leakage current in polyimides and insulating polymers in general.

Z-scheme Bi2WO6/CuBi2O4 heterojunction mediated by interfacial electric field for efficient visible-light photocatalytic degradation of tetracycline

In order for the removal of Tetracycline (TC) in wastewaters, an efficient binary Bi2WO6/CuBi2O4 Z-scheme heterojunction photocatalyst was synthesized by loading Bi2WO6 (BWO) nanoparticles on CuBi2O4 (CBO) nanorods via a solvothermal route. The obtained Bi2WO6/CuBi2O4 composite displays photocatalytic activity for TC degradation more than five times higher than that for pure CBO nanorods. The recycling experiment shows that over 91% of TC can be photo-degraded by the optimal Bi2WO6/CuBi2O4 photocatalyst within 60 min even after four cycles. Results of SEM, transient photocurrent response, EIS measurement prove that solvothermal process for BWO loading can introduce rough surface with high-density negative charge on CBO, contributing to effective photo-induced carrier transfer. XPS, Mott–Schottky plots and PL spectra reveal that the loading of BWO as well as interfacial charge redistribution can induce the formation of interfacial electric field for Z-scheme heterojunction, contributing to the high oxidation and reduction capabilities ability of Bi2WO6/CuBi2O4 composite. The study on photocatalytic mechanism discloses that hole (h+) and superoxide radical (O2−) are dominating reactive oxidation species (ROS) in the photodegradation process. This study has provided a novel route to fabricate Z-scheme photocatalysts for effective photocatalytic degradation processes.

An efficient wide range photodetector fabricated using a bilayer Bi2S3/SnS heterojunction thin film

This study presents a detailed optoelectronic investigation on the bilayer Bi2S3/SnS heterojunction photodetector. The Bi2S3 and SnS nanostructures were synthesized by an ultrasonication method and deposited in the form of thin films by a thermal evaporation system to fabricate the photodetectors. The performed optoelectrical measurements showed that the Bi2S3 and Bi2S3/SnS photodetectors are respectively n- and p-type electrical conductivity. This finding was further confirmed by current–voltage (I–V) analysis, Mott–Schottky plots and photoresponse measurements. According to the obtained gain and sensitivity values, the Bi2S3/SnS heterojunction provides a higher photon-to-electrical carrier conversion relative to the Bi2S3 photodetectord due to the enhanced photogeneration of electron–hole pairs and separation of the photoinduced charge carriers under the influence of the electric field build-in at the heterojunction’s interface. The heterojunction exhibited a remarkable photoresponse from 400 to 800 nm by giving the photocurrent gain (G), sensitivity (S), and external quantum efficiency (EQE) values of 8460%, 450% and 45%, respectively. The obtained results represent the Bi2S3/SnS heterojunction photodetector as a potential candidate for devising high-performance optoelectronic devices.

Photo-electrochemical properties of Sb2S3/TiO2 heterostructures integrally synthesis by hydrothermal method

TiO2 based heterostructures exhibits better photoelectrochemical performances than TiO2 photoanodes solely. However the fact that their synthesis necessitates more than one technique increases their cost. Finding simple and low cost methods to fabricate these heterostructures remain a challenge to many researchers. Trying to overcome this challenge, we propose, in this work, a facile and low cost strategy to sensitize TiO2 nanorod arrays with Sb2S3 nanoparticules, in order to improve the visible light absorbance and the photoelectrochemical performance of the Sb2S3/TiO2 related photoanodes. Such photoanodes were successfully prepared on an F: SnO2 conductive glass by a two-step process of hydrothermal method. Scanning electron microscopy indicated that the Sb2S3 nanoparticles were distributed homogeneously on the surface of TiO2 nanorods. Linear sweep voltammetry results indicated that the highest photocurrent density reached 0.97 mA cm−2 at an applied potential of 0 V vs Ag/AgCl. This performance is attributed to the appropriate relative energy band gap positions between the Sb2S3 and TiO2 in one hand and Sb2S3 and electrochemical potential of water oxidation on the other hand. Flat-band potential and free carrier concentration was determined by Mott–Schottky plots. Electrochemical impedance spectroscopy was employed and an equivalent circuit model is proposed.

Photocatalytic hydrogen generation using gold decorated BiFeO3 heterostructures as an efficient catalyst under visible light irradiation

Perovskites based oxides materials with a suitable energy level have been considered as efficient photocatalysts for solar hydrogen generation. Gold nanoparticles (Au NPs)-sensitized BiFeO3 (BFO) perovskite heterostructures was synthesized, characterized and tested for hydrogen generation under visible light (λ > 420 nm) irradiation. Au/BFO heterostructures was synthesized using a facile hydrothermal method followed by radiolysis without using any surfactant or strong reducing agent. The shape-dependent photocatalysis revealed that the BFO octahedron (BFO-Oct) exhibited higher hydrogen generation (1.4 mmol h–1 g–1) than the BFO nanosheets (BFO-Ns) (1.1 mmol h–1 g–1) and BFO cylindrical shaped (BFO-Cyl) (0.5 mmol h–1 g–1). After radiolytic construction of the Au/BFO heterostructure, more efficient hydrogen generation was obtained due to the photoinduced electron transfer. The photoresponse of the Au/BFO heterostructures was also assessed in terms of the photocurrent via photoelectrochemical (PEC) measurement which showed Au/BFO-Ns generated higher photocurrents than BFO-Ns by a factor of ∼3.8. The Nyquist plot demonstrated facile charge transfer of BFO-Ns after formation of heterojunction with Au NPs. The Mott–Schottky plot revealed that catalysts are n-type and photo generated charge carrier concentration has been increased for Au/BFO heterostructures (0.92 × 1017 cm−3) compared to pure BFO (0.47 × 1017 cm−3). On the basis of experimental results, the enhanced photocatalytic activities of Au/BFO heterostructures could be ascribed to the significant visible light absorption and the efficient charge carrier separation. This study offers a new route to design noble metal modified perovskites based heterostructure as photocatalysts for water splitting.

Study on DC Conductivity of PPy-ZnO Nanocomposites

In the present work, the nanocomposites of PPy-ZnO were prepared by chemical oxidative polymerization technique using an anhydrous ferric chloride (FeCl3) as an oxidizing agent. The prepared samples were characterized via XRD and SEM (Scanning electron microscope) to determine the crystal size and porosity, respectively. Using, screen printing technique, thick films of the samples were fabricated. At room temperature and stepwise increasing temperature, dc conductivity of the samples had been measured and it was found that sample PZ2 has smallest average crystalline size 99.40 nm. DC conductivity measurement showed nearly linear variation of ln(i) versus ln(V), exhibiting ohm’s law being obeyed on logarithmic scale. Maximum value of current density, 1.261 x10-5 A/m2 for PZ2 (70% PPy + 30%ZnO) sample was obtained from schottky plot, at 400 K. Thus PZ2 sample is best among the prepared samples and its activation energy recorded to be 0.1106 eV.

Characterization of cadmium sulfide buffer layers using electrolyte contacts

Electrolyte contacts were used to characterize cadmium sulfide (CdS) films grown by chemical bath deposition on fluorine-doped tin oxide glass (FTO). Capacitance measurements were made in a buffered electrolyte free of redox species, and cyclic sweep voltammetry was carried out using an electrolyte containing Fe(CN)64− ions. A theoretical model was developed to describe the influence of pinholes on Mott Schottky plots of CdS-coated FTO. The model allows estimation of the pinhole coverage by fitting the Mott Schottky plot over an extended voltage range. Cyclic voltammetry in a hexacyanoferrate(II) electrolyte also allows detection of pinholes, but quantitative estimation of pinhole coverage is complicated by the fact that diffusion of Fe(CN)64− to pinholes occurs by hemispherical diffusion, which can substantially enhance the current response. Comparison of the results of capacitance and voltammetry measurements provides insights into average pore size and number density. Results presented for CdS films grown using two different chemical bath compositions reveal substantial differences in pinhole numbers and doping density.

A multiphase BiVO4 with the potential of being an environmental photocatalyst

Novel Y3+ and Mo6+ dual-doped, multiphased BiVO4 nanoparticles (NPs) were synthesised using a modified hydrothermal method through a gradient doping method. Yttrium (III) was used as a phase-stabilising agent for the tetragonal phase, while Mo6+ was used to control the volume of the crystals. The NPs were characterised using SEM, TEM, PL, FTIR, XRD, and BET to determine crystal phase, morphology, and surface area. It was found that the introduction of the dopants and formation of the phase junction lead to diminished PL spectra indicative of reduced electron–hole recombination. The 10% (m–m) Y–Mo dual-doped multiphased BiVO4 NPs have the highest electron–hole separation efficiency. However, 15% (m–m) Y–Mo had the least charge separation due to the formation of recombination centres at high degrees of metal doping. The multiphased systems also showed a red shift in the UV–Vis absorption spectrum. The Mott–Schottky plot obtained from electroimpedance spectroscopy confirmed the formation of a phase junction in the multiphased systems which resulted in an improvement of the photocurrent to twice that of the intrinsic BiVO4 NPs for the 10% Y–Mo BiVO4 NPs. The photocurrent for 10% Y–Mo was 0.025 A cm−2, while that of the intrinsic BiVO4 NPs was about 0.014 A cm−2. This increase in photocurrent proves the improvement of charge separation. BET results showed that surface area increased with an increase in the degree of doping and that the 10% Y–Mo dual-doped BiVO4 nanomaterials had a surface area of 9.009 m2/g. The 10% Y–Mo dual-doped BiVO4 reached 99.1% Cr6+ removal in 60 min.

One-step introduction of metallic Bi and non-metallic C in Bi2WO6 with enhanced photocatalytic activity

One-step introduction of metallic Bi, non-metallic C into Bi2WO6 was successfully prepared via a facile hydrothermal synthetic route. The obtained materials were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy (XPS), nitrogen absorption–desorption isotherms, photoluminescence spectroscopy, photocurrent responses, electrochemical impedance spectroscopy (EIS), electron paramagnetic resonance (EPR), UV–vis diffuse reflectance spectra (DRS). As a result, C/Bi codecorated Bi2WO6 shows profoundly photocatalytic activity in comparison with undoped Bi2WO6 for decomposition of various industrial pollutants, including phenol, ciprofloxacin, bisphenol A, rhodamine B, and methyl orange under visible light (λ ≥ 420 nm). The enhanced photocatalytic properties may be ascribed to the fact that the synergistic effects of the SPR effect of Bi metal and the hybrid orbital constructed by C doping not only enhance the absorption of visible light but also accelerate the separation and migration of photo-generated carriers. Moreover, on the basis of the radical species trapping experiments, EPR analyses, DRS technique and Mott–Schottky plots, we proposed a simple photocatalytic mechanism.