Hot Solution Research Articles

Effectively using heat to thermally enhance pressure retarded osmosis

Thermal energy from solar radiation and industrial waste heat is abundant and can be used to improve the performance of membrane processes for water treatment and power generation. In this study, we investigate the concept of using heat to thermally enhance pressure retarded osmosis for improved energy recovery from salt gradients. A laboratory apparatus is used to demonstrate performance at temperatures between 20 and 50 °C, and improvements in water flux and power density of up to 110 % are observed. Temperature of the feed solution is found to be more important than draw temperature. A finite element model is experimentally validated and used to identify what transport dynamics are responsible for the priority to heat feed. It is found that a hot feed solution produces a warmer membrane (thereby encouraging higher permeability and mitigated polarization), and this principally because the feed boundary offers little thermal resistance as it is typically well-mixed during pressure retarded osmosis. Finally, a new metric of effectiveness is introduced to evaluate power increases relative to the change in temperature. It is found that although operation at higher temperatures may yield higher power, operation at low temperatures of ~30 °C may represent a more effective use of thermal energy.

Novel Synthesis of 3D Mesoporous FePO4 from Electroflocculation of Iron Filings as a Precursor of High-Performance LiFePO4/C Cathode for Lithium-Ion Batteries.

This study presents an economic and environmentally friendly method for the synthesis of microspherical FePO4·2H2O precursors with secondary nanostructures by the electroflocculation of low-cost iron fillers in a hot solution. The morphology and crystalline shape of the precursors were adjusted by gradient co-precipitation of pH conditions. The effect of precursor structure and morphology on the electrochemical performance of the synthesized LiFePO4/C was investigated. Electrochemical analysis showed that the assembly of FePO4·2H2O submicron spherical particles from primary nanoparticles and nanorods resulted in LiFePO4/C exhibiting excellent multiplicity and cycling performance with first discharge capacities at 0.2C, 1C, 5C, and 10C of 162.8, 134.7, 85.5, and 47.7 mAh·g-1, respectively, and the capacity of LiFePO4/C was maintained at 85.5% after 300 cycles at 1C. The significant improvement in the electrochemical performance of LiFePO4/C was attributed to the enhanced Li+ diffusion rate and the crystallinity of LiFePO4/C. Thus, this work shows a new three-dimensional mesoporous FePO4 synthesized from the iron flake electroflocculation as a precursor for high-performance LiFePO4/C cathodes for lithium-ion batteries.

Buckwheat waste depolymerization using a subcritical ethanol solution for extraction of bioactive components: from the laboratory to pilot scale

Buckwheat waste (BW) is rich in bioactive components such as antioxidants and saccharides. To effectively extract these compounds, subcritical ethanol solution treatment (SEST) was conducted from laboratory to pilot scale. Extraction at 80 °C with hot water and ethanol solutions, and at 120 °C with subcritical water and subcritical ethanol solutions were evaluated in laboratory scale. Then, the SEST was scaled up to the pilot level using a batch reactor with a volume scale factor of 1000. Degradation of lignin and dissolution of extractives increased the total phenolics yield. The increase in the temperature led to the degradation of some flavonoid components. Reducing sugars were mainly present as polysaccharides because of the low extraction temperature. Water and ethanol exhibited synergistic effects under subcritical conditions, which resulted in degradation of more lignin and extraction of more bioactive components than hydrothermal extraction, while retaining cellulose and hemicellulose. In the pilot-scale experiment, the total yields of phenolics, flavonoids, and reducing sugars were 29.8 ± 0.1, 13.9 ± 0.5, and 33.9 ± 0.5 g/kg, respectively. The turbidity and Brix values of the liquid samples obtained by SEST were high because of breakdown of the structure of the BW and the dissolution of the bioactive components. Additionally, compared with the laboratory scale, better results were obtained on the pilot scale because of greater feedstock homogeneity and equipment parameters. SEST is a promising approach that could be used on the pilot scale to depolymerize BW and extract bioactive components.

A Novel Hydro-Thermal Synthesis of Nano-Structured Molybdenum-Iron Intermetallic Alloys at Relatively Low Temperatures

Nano-structured Mo/Fe intermetallics were synthesized from precursors that contained 72/28% and 30/70% molar ratios of Mo/Fe, which were given as precursors A and B, respectively. These precursors were prepared from the co-precipitation of aqueous hot solutions of ammonium heptamolybdate tetrahydrate (AHM) and ferrous oxalate. The dry precipitates were thermally treated using TG-DSC to follow up their behavior during roasting, in an Ar atmosphere of up to 700 °C (10° K/min). The TG profile showed that 32.5% and 55.5% weight losses were measured from the thermal treatment of precursors A and B, respectively. The DSC heat flow profile showed the presence of endothermic peaks at 196.9 and 392.5-400 °C during the thermal decomposition of the AHM and ferrous oxalate, respectively. The exothermic peak that was detected at 427.5 °C was due to the production of nano-sized iron molybdate [Fe2(MoO4)3]. An XRD phase analysis indicated that iron molybdate was the only phase that was identified in precursor A, while iron molybdate and Fe2O3 were produced in precursor B. Compacts were made from the pressing of the nano-sized precursors, which were roasted at 500 °C for 3 h. The roasted compacts were isothermally reduced in H2 at 600-850 °C using microbalance, and the O2 weight loss that resulted from the reduction reactions was continuously recorded as a function of time. The influence of the reduction temperature and precursor composition on the reduction behavior of the precursors was studied and discussed. The partially and completely reduced compacts were examined with X-ray powder diffraction (XRD), a reflected light microscope (RLM), and a scanning electron microscope (SEM-EDS). Depending on the precursor composition, the reduction reactions of the [Fe2(MoO4)3] and Fe2O3 proceeded through the formation of intermediate lower oxides, prior to the production of the MO/Fe intermetallic alloys. Based on the intermediate phases that were identified and characterized at the early, intermediate, and final reduction degrees, chemical reaction equations were given to follow up the formation of the MoFe and MoFe3 intermetallic alloys. The mechanism of the reduction reactions was predicted from the apparent activation energy values (Ea) that were computed at the different reduction degrees. Moreover, mathematical formulations that were derived from the gas-solid reaction model were applied to confirm the reduction mechanisms, which were greatly dependent on the precursor composition and reduction temperature. However, it can be reported that nano-structured MoFe and MoFe3 intermetallic alloys can be successfully fabricated via a gas-solid reaction technique at lower temperatures.

Comparative study between Kashkaval from raw milk and chilled curd

The influence of chilled curd on Kashkaval cheese microbiological, functional, textural and sensorial characteristics was studied. It was found that salting the curd in a hot solution influenced to a greater degree the microflora reduction from the starter culture in Kashkaval cheese obtained from fresh curd. In terms of species composition, Streptococcus ssp. had a higher survival rate compared to Lactobacillus ssp. During maturation, this trend changed and the number of Lactobacillus ssp. increased, while that of Streptococcus ssp. remained constant and even slightly decreased in both studied samples. Melting and textural characteristics of the two studied cheese samples did not differ significantly at the end of the maturation process. The overall scores of the sensory profile were higher in the cheese obtained from fresh curd but no statistical differences (p>0.05) between separate sensory indices were established. The obtained results indicated that “Cagliata” can be successfully used as an alternative raw material for fresh curd in the production of Kashkaval cheese.

First Report of <i>Aphanurus stossichii</i> (Digenea: Hemiuridae) from <i>Engraulis encrasicolus</i> on the Turkish Coast of the Black Sea, with Light and Scanning Electron Microscopic Observations

The aim of this study is to investigate in detail the morphological features of the digenean parasite Aphanurus stossichii isolated from the European anchovy Engraulis encrasicolus using light and scanning electron microscopy (SEM). The specimens of A. stossichii were obtained from the pharynx and stomach of the European E. encrasicolus caught by commercial fishing vessels in the Black Sea. Parasites were killed in a hot normal saline solution, preserved in to 70% ethanol for light microscopic (LM) studies, and in 2.5% glutaraldehyde for SEM. The morphological diagnostic features of A. stossichii were studied in detail under both LM and SEM. The morphological characteristics of the examined adult A. stossichii specimens were found to be similar to the original descriptions describing the basic characteristics of forebody and hindbody shape, the position and shape of the vitellarium, ovary, and and testes, and the shapes of oral and ventral sucker. The measurement data for all morphological diagnostics were provided; photomicrographs of each part of the parasite were presented. Infection prevalence, mean intensity and mean abundance values were 8.89%, 4.5 and 0.4, respectively. All available records of A. stossichii morphology are based on light microscope, this is the first study to identification the morphological features of the parasite with SEM. This research is the first on A. stossichii presence in E. encrasicolus on the Turkish Black Sea coast.

Electrochemical response of MgO/Co3O4 oxide layers produced by plasma electrolytic oxidation and post treatment using cobalt nitrate

This work looked into the influence of the sealing treatment on the structural feature and electrochemical response of AZ31 Mg alloy coated via plasma electrolytic oxidation (PEO). Here, the inorganic layers produced by PEO in an alkaline-phosphate electrolyte were subsequently immersed for different periods in cold (60 °C) and hot (100 °C) aqueous solutions containing either 1 or 3 gr of cobalt nitrate hexahydrate in the presence of hydrogen peroxide as an initiator. The results showed that the sealing treatments in the hot solutions could trigger the hydration reactions of PEO coating which would largely assist the surface incorporation of Co 3 O 4 into the coating. In contrast, the sealing in cold solutions led to less compact coatings, which was attributed to the fact the hydration reactions would be restricted at 60 °C. A nearly fully sealed coating with a porosity of ∼ 0.5 % was successfully formed on the sample immersed in the hot solution containing 1 gr of cobalt nitrate hexahydrate. Thus, the electrochemical stability of this fully sealed coating was superior to the other samples as it had the lowest corrosion current density (4.71 × 10 −10 A.cm −2 ) and the highest outer layer resistance (3.81 × 10 7 Ω.cm 2 ). The composite coatings developed in this study are ideal for applications requiring high electrochemical stability.

Degradation behavior of multilayer packaging films in the presence of a highly acidic sauce

Highly acidic condiments such as hot sauce can deteriorate multilayer packaging films. To date, only a multilayer polymeric film (polyethylene terephthalate/ink/polyethylene/foil/polyethylene/SiO x coated polyethylene terephthalate/adhesives/Barex®) utilizing a proprietary resin, Barex® as one of its polymeric layers can preserve hot sauce for military rations. However, the production of Barex® stopped in 2016. To identify substitutes for Barex®, an immersion study of films in hot sauce was conducted with several commercially available multilayer films (Polyethylene terephthalate/ink/adhesive/polyamide/adhesive/polypropylene and polyethylene terephthalate/waste low-density polyethylene/aluminum foil/adhesive/polyester/low-density polyethylene) and a monolayer Barex® (acrylonitrile methyl acrylate copolymer) film. All films were immersed in hot sauce, acetic acid, and sodium chloride solutions at 50 °C for 12 weeks. The mass, thickness, morphology, and chemical compositions of each film were analyzed every three weeks. Hot sauce and acetic acid solution similarly deteriorated multilayer films, causing delamination and oxidative degradation, but not sodium chloride solutions. This indicates that the failure of the multilayer packaging of hot sauce was likely caused by the low pH environment, not heat or salt ions. The two primary innovations in this study are: 1) the finding that acidic components in hot sauce deteriorate multilayer packaging by transforming aluminum foil into a soluble salt and by oxidizing polyethylene, and 2) surface erosion plays a significant role in inducing polyethylene oxidation. This is the first study to describe how a highly acidic food deteriorates multilayer packaging used for military rations. Possible deterioration mechanism of the multilayered structure (Film 2) in presence of a highly acidic hot sauce. • Acetic acid in hot sauce reacts with aluminum foil used in multilayer films. • Acids in hot sauce oxidatively degrade polyethylene (PE) layers in multilayer films. • PE in multilayer films oxidizes more in hot sauce than in acetic acid solutions. • PE in multilayer films surface erodes when immersed in hot sauce and acetic acid. • Potential multilayer film is identified for replacing Barex® for military rations.

Evaluation of hot water and GRAS salt solutions for the control of postharvest gray and green molds of pomegranate fruit

Evaluation of hot water and GRAS salt solutions for the control of postharvest gray and green molds of pomegranate fruit

Soil Carbon and Nitrogen Forms and Their Relationship with Nitrogen Availability Affected by Cover Crop Species and Nitrogen Fertilizer Doses

Cover crops and N fertilization strongly impact the forms of soil organic C and N and their availability, which change the responses of plants to N fertilization and soil organic C accumulation. Our study objectives were to evaluate the effects of cover crops and N doses on soil total and soluble C and N contents, N fractions, and potentially available N in a long-term no-till experiment. The experiment was conducted in a randomized block design with split plots and four replicates. The main treatments were cover crops species, jack bean, lablab bean, millet, velvet bean, and fallow cultivated prior to maize. Secondary treatments included two doses of mineral N (0 and 120 kg ha−1). Soil samples were collected at depths of 0–5, 5–10, 10–20, and 20–40 cm, which were analyzed for total and water-soluble C and N contents, N fractions (acid hydrolysis method), and potentially available N (hot KCl solution and direct steam distillation methods). Cover crop velvet bean resulted in the highest soil organic carbon levels, and cover crop millet plus fertilization resulted in the highest levels of soil total N. The amino sugar was the largest N fraction, which decreased by 8% with N fertilization. The soluble C and N content strongly correlated with total and available N content. The changes in soil N were influenced by cover crop species and fertilization and the interactions of both, so the combination of fertilization regime and cover crops must be chosen with care. Additionally, legumes are a good source of plant and soil N in systems with low input of N via fertilizer; however, the combination of N fertilizer with legumes can reduce soil N reserves, leading to its long-term depletion.

Metallogels from Silver Nanoparticles and Peptide Nanofibers as Antimicrobial Surfaces

Peptide amphiphiles (PAs) are elusive candidates to construct soft materials possessing various functionalities, including potent antimicrobial activity. It is imperative to look for a broad-spectrum antibiotic against which the genesis of drug resistance is difficult. Herein, a histidine-based PA is found to form a transparent metallohydrogel when AgNO3 is added to a hot solution of the PA in 2:1 (PA/AgNO3) molar ratio. Exposure to 365 nm UV lamp results in blue light-emitting silver nanocluster (NC) formation inside the hydrogel matrix. Interestingly, when the metallohydrogel is turned in solution through sheer thinning and rested for 12–14 h in ambient light, the gel reforms along with the formation of non-fluorescent silver nanoparticles (NPs). Thus, two different nanomaterials can be synthesized separately inside the gel matrix with modulation of the conditions. As the NC and NP formation takes place, ordered growth of these nanomaterials can be observed along the nanofibrous hydrogel network. Rheological measurements show enhancement of storage modulus in NC- and NP-containing hybrid hydrogels. This new nanohybrid system comprising peptide gel-based nanofibers and silver NC/NPs has potential applications against Gram-positive and Gram-negative bacteria. Furthermore, the plausible mechanism of the antimicrobial effects has been thoroughly investigated. The elevated levels of reactive oxygen species (ROS) found in the bacteria in the presence of the hybrid hydrogels establish that intra-cellular ROS generated in the cytosol of the bacteria is responsible for the death of bacteria. The current work indicates the hybrid hydrogel’s utility as a potent antimicrobial agent.

A Study of the Mechanisms and Characteristics of Fluorescence Enhancement for the Detection of Formononetin and Ononin.

In this work, the origins for the spectral difference between two isoflavones, formononetin (F) and ononin (FG), are revealed via a comparison study of the fluorescence molecular structure. The fluorescence enhancement of FG in hot alkaline conditions is reported for the first time. For F, there is almost no fluorescence under acidic conditions, but when the pH is >4.8, its fluorescence begins to increase due to the deprotonation of 7-OH. Under a pH between 9.3 and 12.0, the anionic form of F produces a strong and stable fluorescence. The fluorescence quantum yield (Yf) of F is measured to be 0.042. FG shows only weak fluorescence in aqueous solutions under a wide range of pH until it is placed in hot alkaline solutions, which is attributed to the cleavage reaction of the γ-pyrone ring in FG. The Yf of FG is determined to be 0.020. Based on the fluorescence sensitization methods of F and FG, the quantitative analysis and detection of two substances can be realized. The limit of the detections for F and FG are 2.60 ng·mL-1 and 9.30 ng·mL-1, respectively. The linear detection ranges of F and FG are 11.7~1860 ng·mL-1 and 14.6~2920 ng·mL-1, respectively. Although the structural relationship between F and FG is glycoside and aglycone, under hot alkaline conditions, the final products after the cleavage and hydrolysis reactions are essentially different. The different fluorescence characteristics between F and FG pave a way for further identification and a quantitative analysis of the corresponding components in Chinese herbal medicine.

Effects of crystal rotation on the carbon transport in the top-seeded solution growth of SiC single crystal

To achieve a high and uniform growth rate for the solution growth of silicon carbide (SiC), the fluid flow and carbon transport in the solution should be well estimated and controlled. The application of crystal rotation is effective in controlling the flow pattern and carbon transport in the SiC growth system. In this paper, the effects of crystal rotation on the solution flow, carbon concentration and growth rate for growing SiC crystals were numerically investigated by using a global heat and mass transfer model. The results indicated that crystal rotation strongly enhances the convection in the solution and makes the upward flow proceed deeper, resulting in the distribution of radial temperature along the growth interface turning from convex to concave towards the solution with the increase in the crystal rotation rate. Consequently, the carbon transport in the solution is strengthened, leading to an increase in the maximum value of the growth rate with a higher crystal rotation rate. However, the radial uniformity of the crystal growth rate along the growth interface becomes poor due to the hot solution moving upward to the center of the seed crystal with the increase in the crystal rotation rate. In the present study, it is found that the intensity of the forced convection vortex generated by an intermediate crystal rotation rate is beneficial to obtain a uniform distribution of growth rate and a relatively high growth rate.

Ultraviolet photodetector based on RbCu2I3 microwire

Copper-based halide perovskites have shown great potential in lighting and photodetection due to their excellent photoelectric properties, good stability and lead-free nature. However, as an important piece of copper-based perovskites, the synthesis and application of RbCu2I3 have never been reported. Here, we demonstrate the synthesis of high-quality RbCu2I3 microwires (MWs) by a fast-cooling hot saturated solution method. The prepared MWs exhibit an orthorhombic structure with a smooth surface. Optical measurements show the RbCu2I3 MWs have a sharp ultraviolet absorption edge with 3.63 eV optical band gap and ultra-large stokes shift (300 nm) in photoluminescence. The subsequent photodetector based on a single RbCu2I3 MW shows excellent ultraviolet detection performance. Under the 340 nm illumination, the device shows a specific detectivity of 5.0 × 109 Jones and a responsivity of 380 mA·W−1. The synthesis method and physical properties of RbCu2I3 could be a guide to the future optoelectronic application of the new material.

Effect of oxidizing ions on the corrosion behavior of SiN stainless steel in high-temperature nitric acid solution

The oxidizing ions, abundantly existing in spent fuel reprocessing process, play a vital role in the corrosion behavior of stainless steels due to the inherently high electrode potential. However, the systematic research on the effect of these ions on the corrosion mechanism of stainless steels in high-temperature nitric acid media is rarely reported. Herein, the electrochemical behavior and the passive film characteristics of SiN stainless steel in hot nitric acid solution containing different ions with various concentrations were investigated. The oxidizing Cr6+, V5+ and Ce4+ affected both the anodic and the cathodic reactions, while the non-oxidizing Fe3+ only changed the cathodic reactions. Meanwhile, the passive film characteristics of SiN stainless steel are partly altered with the change in ion concentration, and the passive film primarily consisted of Fe2O3, Cr2O3, Cr(OH)3 and silicate. The existence of silicate with high chemical stability improved the protection of passive film, displaying a high resistance to intergranular corrosion in the transpassive domain. In addition, a critical concentration phenomenon was observed in nitric acid with oxidizing ions, and the deposition theory was proposed to reveal the mechanism of critical concentration phenomenon.

Anodic Etching of Amorphous Ni81P19 Alloy in Hot Concentrated Chloride Solution for Enhanced Hydrogen Evolution in Alkaline Water Electrolysis

AbstractHighly active and easily available electrocatalysts are of great importance for a wider use of water electrolysis for hydrogen production. Herein, electroactivity toward hydrogen evolution reaction was examined in 1.0 M KOH on commercial Ni81P19 (MBF‐60) and Ni70Cr6Fe2B14Si8 (MBF‐20A) amorphous alloys and for comparison on Ni, untreated and modified by anodic etching in hot concentrated NaCl solutions. This treatment increased the electroactivity of all the materials, but especially of Ni81P19 and particularly of matte side of its ribbons, decreasing overpotential at −10 mA cm−2 to −0.14 V. XRD, SEM/EDS and XPS studies were carried out. EIS measurements indicated that the rise of hydrogen evolution after etching was related mainly to the increase of surface area, and only slightly to the rise of intrinsic electroactivity, probably being due to the formation of NiO. It is proposed that etched Ni81P19 might be an efficient cathode for hydrogen production by water electrolysis.

Fast-response photothermal bilayer actuator based on poly(N-isopropylacrylamide)-graphene oxide-hydroxyethyl methacrylate/polydimethylsiloxane.

Demands for highly deformable and responsive intelligent actuators are increasing rapidly. Herein, a photothermal bilayer actuator consisting of a photothermal-responsive composite hydrogel layer and a polydimethylsiloxane (PDMS) layer is presented. The photothermal-responsive composite hydrogel is prepared by compositing hydroxyethyl methacrylate (HEMA) and the photothermal material graphene oxide (GO) with the thermal-responsive hydrogel poly(N-isopropylacrylamide) (PNIPAM). The HEMA improves the transport efficiency of water molecules inside the hydrogel network, eliciting a fast response and large deformation, facilitating greater bending behavior of the bilayer actuator, and improving the mechanical and tensile properties of the hydrogel. Moreover, GO enhances the mechanical properties and the photothermal conversion efficiency of the hydrogel in the thermal environment. This photothermal bilayer actuator can be driven under various conditions, such as hot solution, simulated sunlight, and laser, and can achieve large bending deformation with desirable tensile properties, broadening the application conditions for bilayer actuators, such as artificial muscles, bionic actuators, and soft robotics.

Processing of natural lignocellulosic coir fibres for enhanced flame retardancy using aluminium trihydrate

The high lignin cellulose ratio in coir fibres makes it more susceptible to fire, whereby coir and its allied products are pushed back away from fire retardant applications. These fibres are subjected to treatments by soaking in hot dilute solution of aluminium trihydrate for enhanced fire retardancy. The treated fibres exhibited improved flame retardant properties with reduced water absorption and showed no remarkable change on the physical and mechanical characteristics. The time of burning was significantly reduced from 182 to 65 seconds and the treated fibres did not produce smoke when burnt. The flame propagation rate was reduced by 2.5 times and limiting oxygen index elevated by 1.2 times compared to the raw fibre. As a low toxic, sparingly soluble substance, aluminium trihydrate is a better halogen-free fire retardant addition for coir fibres in product manufacturing in the coir sector.

Физико-химические характеристики нанокомпозитов Fe3O4/TiO2 и Fe3O4/SiO2/TiO2, синтезированных гид-ротермальным пероксидным методом

In the present paper the composite materials based on Fe3O4/TiO2 and Fe3O4/SiO2/TiO2 ox-ides, synthesized by the hydrothermal peroxide method, were studied. At the first stage, magnet-ite nanoparticles were precipitated by ammonium hydroxide from a mixture of aqueous solutions of iron(II) sulfate and iron(III) chloride under continuous exposure to ultrasound, after which they were washed with distilled water. At the second stage, the resulting hydrated magnetite particles were stabilized with polyvinyl alcohol (PVA) by dispersing them under the action of ultrasound in a hot saturated aqueous PVA solution. At the third stage, the photocatalytically active particles based on titanium oxide were introduced into the composite by mixing the stabilized magnetite suspension with an aqueous solution of peroxotitanic acid (optionally introducing a sol of silicic acid), followed by hydrothermal treatment of the mixture at 180°C for 24 hours, washing, and drying under vacuum followed by calcination in a muffle furnace. The effect of the molar content of iron and titanium on the properties of the samples, the introduction of silicon dioxide into them, as well as various calcination temperatures, were studied. The photocatalytic properties of the synthesized samples during photodegradation of methyl orange and methylene blue, as well as their magnetic recovery from suspension, were studied. The physicochemical characterization of the samples was performed using high-resolution scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, powder X-ray diffraction, low-temperature nitrogen sorption porosimetry, inductively coupled plasma mass spectrometry, thermal analysis (TG–DSC), combined with mass spectrometry of gaseous thermolysis products. The optimal conditions for the synthesis of composites exhibiting the best combination of photocatalytic and magnetic properties were determined. The resulting photocatalysts can be used to purify water from dyes, followed by extraction using a magnet

Low leakage current and high breakdown voltage of AlGaN/GaN Schottky barrier diodes with wet-etching groove anode

AlGaN/GaN heterojunction epitaxies with wide bandgap, high critical electric field as well as high density and high mobility two-dimensional electron gas have shown great potential applications in the next-generation high-power and high-frequency devices. Especially, with the development of Si-based GaN epitaxial technique with big size, GaN devices with low cost also show great advantage in consumer electronics. In order to improve the rectification efficiency of AlGaN/GaN Schottky barrier diode (SBD), low leakage current and low turn-on voltage are important. The GaN Schottky barrier diode with low work-function metal as anode is found to be very effective to reduce turn-on voltage. However, the low Schottky barrier height makes the Schottky interface sensitive to damage to groove surface, which leads to a high leakage current. In this work, a novel wet-etching technique with thermal oxygen oxidation and KOH corrosion is used to prepare the anode groove, and the surface roughness of groove decreases from 0.57 to 0.23 nm, compared with that of the dry-etching surface of groove. Meanwhile, the leakage current is suppressed from 1.5 × 10<sup>–6</sup> to 2.6 × 10<sup>–7</sup> A/mm. Benefiting from the great corrosion selectively of hot KOH solution to AlGaN barrier layer and GaN channel layer after thermal oxygen oxidation, the spikes of the edge of groove region caused by the nonuniform distribution of plasma in the cavity is improved, and the breakdown voltage of the fabricated AlGaN/GaN SBDs is raised from –1.28 to –1.73 kV.