Investigation of the effects of GaAs substrate orientations on the electrical properties of sulfonated polyaniline based heterostructures

In this work we present a detailed study of the influence of the GaAs substrate orientation on the electrical properties of heterojunctions based on GaAs and sulfonated polyaniline (SPAN) using Current-Voltage (I-V), Capacitance-Voltage (C-V), Deep-Level Transient Spectroscopy (DLTS) and Laplace DLTS techniques. Three different GaAs substrate orientations have been investigated, namely (1 0 0), (3 1 1)A and (3 1 1)B. The I-V results revealed that the turn-on voltage (Von) of SPAN/(3 1 1)B GaAs heterojunction is higher than that for SPAN/(1 0 0) GaAs and SPAN/(3 1 1)A GaAs heterojunctions. The DLTS results showed that the number of electrically active defects present in devices based on the lower index (1 0 0) plane of GaAs substrate is higher than those of higher index (3 1 1)A and (3 1 1)B GaAs substrates, corroborating with I-V results. In order to investigate the role of interface states, capacitance-frequency measurements were performed in forward bias on all three devices

A comprehensive study on the effects of gamma radiation on the physical properties of a two-dimensional WS2 monolayer semiconductor

© 2020 The Royal Society of Chemistry. This article reports the effects of gamma radiation on the structural, optical and magnetic properties of monolayer tungsten disulfide (WS2) grown by a scalable van der Waals epitaxial (VdWE) process on a SiO2 coated Si substrate. We found that ionizing radiation (gamma ray) interacts strongly with two-dimensional WS2, which induces effective p-doping in the samples. As the radiation dose increases, the p-doping concentration increases substantially. In addition, in the small radiation dose regime, the WS2 monolayers exhibit usual diamagnetic behavior. However, a remarkable ferromagnetic hysteresis emerges when the WS2 monolayer is irradiated with 400 Gys. This is attributed to the presence of irradiation-induced complex vacancies composed of one tungsten and a pair of its nearby sulfurs. Moreover, these results have shown that the detector based on the large scale monolayer VdWE-grown two-dimensional WS2 is an appealing candidate for sensing high-energy photons at small radiation doses

Simple and lowecost transition metal-free borophosphate glass catalyst for aromatic alcohol oxidation by sodium hypochlorite

The oxidation of primary and secondary alcohols to their respective aldehydes/ketones is one of the most important reactions in fine chemistry due to the industrial application of these products. Based on this, a large number of new catalysts and oxidants have been tested using this reaction as a catalytic model, mainly looking for a process that ensures high aldehyde selectivity. In this paper, we have used moisture stable borophosphate glass doped with 10 mol% Al2O3 as a heterogeneous catalyst in the oxidation of sodium hypochlorite, an effective, greener, and low-cost oxidant, using acetonitrile as solvent under mild conditions. The glass catalyst mass and the particle size were evaluated, as were the reaction temperature and oxidant amount, to determine the ideal reaction conditions where the conversions achieved 87.0 mol% for 1-phenylethanol to acetophenone and 79.4 mol% for benzyl alcohol to benzaldehyde, with benzaldehyde selectivity above 95%. Although sodium hypochlorite is a strong oxidant, benzaldehyde was the main product of the oxidation of benzyl alcohol due to the formation of a biphasic organic-aqueous system that protects the aldehyde from oxidation and allows the reaction to occur without the use of a phase transfer catalyst (PTC). HPLC analysis of both phases showed that alcohols, aldehyde, and ketone were mostly present in the organic phase (concentrations above 98.7%). During the reaction, a small amount of alcohol is transferred to the aqueous phase, where the oxidation took place. Once formed, the products are transferred back to the organic phase. ICP-OES analysis indicates that borophosphate glass acts in the reaction by partially releasing phosphate-based groups, reducing the pH of hypochlorite to 9. In this sense, borophosphate glasses prove to be a simple and inexpensive alternative for the development of new catalysts

Dynamic of the structural alteration of biochar in ancient Anthrosol over a long timescale by Raman spectroscopy

The presence of biochar with high carbon accumulation capacity and nutrient adsorption is causally associated with archeological soils. Although this type of soil organic matter has been known for a long time, the knowledge of its structure and environmental behavior is still limited. This work used Raman spectroscopy to obtain structural information and identify alterations in biochar particles. To this end, we studied biochar particles found in an archaeological site with a temporal window lasting 12451 to 11080 yr cal BP. The molecular, structural and sp2/sp3 characteristics of the charcoal particles were determined at the time of burning and associated with the temperature, time and characteristics of the burnt material. We propose that the process of oxidation of the biochar occurs during the first 2000 years after its genesis. The oxidation process is a reflection of decreases in the number of defects related to sp2 bonds on amorphous carbons and increases in the number of defects associated with ionic impurities, which clearly indicate the interaction between biochar particles and the soil matrix. The data confirm the hypothesis that the persistence of biochar in the environment is due to its graphite structure and suggest that over a 12000 year timeframe, biochar particles undergo several changes that occur in the disordered phase and are rapidly oxidized

Effect of erbium-doping concentration on the electrical, structural and morphological properties of heterostructures based on TiO2 thin films

Effect of erbium (Er) doping on the electrical, structural and morphological properties of TiO2 thin films deposited by the combination of a simple sol–gel process and spin-coating technique on p-type silicon substrates, has been investigated. A systematic study of the effect of concentration of Er on the properties of heterostructures was carried out. Raman spectroscopy and atomic force microscopy have been used to study the structural and morphology properties of devices based on Er-doped TiO2/Si heterostructures. Deep level transient spectroscopy (DLTS) has been also employed to study the electrically active defects within the band gap of Er-doped TiO2 thin films. DLTS that has proved to be a powerful tool in analysing traps in semiconductors devices showed that undoped TiO2-based devices exhibit five defects. However, three defects have been detected in the low erbium-doped TiO2 devices and only one defect was observed in the higher erbium-doped devices. These results provide strong evidence that Er doping annihilates oxygen-related defects and demonstrate the effective proof of doping process in TiO2 thin film. This finding contributes to the improved activities (e.g., photocatalytic) of TiO2 since the increase in charge traps can reduce bulk recombination and consequently, separates photogenerated electrons and holes more efficiently. Furthermore, it is found that the overall electrical properties of the devices are improved by increasing Er doping concentration. This study provides an important understanding of the deep and shallow level defects in Er-doped TiO2 thin films, which is essential for the manufacturing of future devices including UV detectors

Effect of growth techniques on the structural, optical and electrical properties of indium doped TiO2thin films

We have investigated the effect of the growth techniques on the structural, the electrically and optically active defects in Indium doped TiO2 thin films grown by pulsed laser deposition (PLD) and sputtering techniques. X-ray diffraction (XRD) and Raman spectroscopy patterns revealed both rutile and anatase phases for the sputtering samples. On the other hand, only the anatase phase was observed for the PLD samples. The photoluminescence (PL) spectra have unveiled several peaks which were explained by defect related optical transitions. Particularly, the PL bands are fully consistent with anatase/rutile TiO2 phases and the formation of In2O3 during the preparation of our samples. It was also observed that at −4 V reverse bias, the PLD samples have lower leakage currents (∼1.4 × 10−7 A) as compared to the sputtering samples (∼5.9 × 10−7 A). In addition, the PLD samples exhibited lower ideality factors and higher barrier heights as compared to those grown by sputtering. Finally, the Deep Level Transient Spectroscopy (DLTS) measurements have shown only one defect in the PLD samples whereas five defects have been detected in the sputtering samples. Therefore, our results provide strong evidence that the PLD technique is better suited for the growth of In-doped TiO2 thin films

The feasibility of recycled micro polyethylene terephthalate (PET) replacing natural sand in hot-mix asphalt

Microplastic pollution is contaminating the human food chain worldwide. At the same time, construction excessively exploits natural sand, requiring the incorporation of alternative materials to achieve sustainable development. From this scenario, the study evaluates the potential of recycled micro-PET replacing natural sand on hot-mix asphalt (HMA) mechanical behavior by weight and volume. The materials’ characterization occurred via XDR, XRF, TGA/DTG, FTIR, SEM, and AFM tests. The Superpave mix design, X-ray micro-tomography (μ-CT), indirect tensile strength (ITS), resilient modulus (RM), and moisture damage tests were performed in conventional and PET-incorporated mixtures, considering 2% (in wt.), 4% (in wt.), and 8% (in wt. and vol.) substitutions. The 8% PET replacing sand by volume showed no significant change in the mixture’s optimum asphalt content (OAC) due to the binder absorption equivalence between the materials’ surfaces. For the same binder content, the increase in PET content in weight decreased the binder film thickness and increased the volume of voids, visualized as non-permeable micropores in μ-CT. Although adding and incrementing PET reduced the mixtures’ ITS and RM values, its most significant contribution was enhancing the resistance to moisture damage, especially for regions where the pavement deterioration process is associated with an intensive rainfall regime, thus demonstrating this application’s practical feasibility in concrete asphalt paving

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