Surface Electrical Properties Research Articles

Correlative nanoscopy: A multimodal approach to molecular resolution.

Atomic force microscopy (AFM) is a nano‐mechanical tool uniquely suited for biological studies at the molecular scale. AFM operation is based on mechanical interaction between the tip and the sample, a mechanism of contrast capable of measuring different information, including surface topography, mechanical, and electrical properties. However, the lack of specificity highlights the need to integrate AFM data with other techniques providing compositional hints. In particular, optical microscopes based on fluorescence as a mechanism of contrast can access the local distribution of specific molecular species. The coupling between AFM and super‐resolved fluorescence microscopy solves the resolution mismatch between AFM and conventional fluorescence optical microscopy. Recent advances showed that also the inherently label‐free imaging capabilities of the AFM are fundamental to complement the fluorescence images. In this review, we have presented a brief historical view on correlative microscopy, and, finally, we have summarized the progress of correlative AFM‐super‐resolution microscopy in biological research.

Impact of the meso-PSi substrate on ZnO thin films deposited by spray pyrolysis technique for UV photodetectors

ZnO thin films were successfully deposited via spray pyrolysis technique over various substrates, including glass, silicon, and mesoporous silicon (PSi). The effect of substrate type on the surface morphological, structural, and electrical properties of ZnO thin film was investigated. Scanning Electron Microscopy confirms the morphology of the meso-PSi substrate and displays the morphologies of the deposited ZnO. The (ZnO/PSi) heterojunction shows a porous ZnO layer with a large surface area by comparison to other structures. The patterns of X-ray Diffraction exposed that the deposited ZnO films have a hexagonal wurtzite polycrystalline structure. Ultraviolet (UV) metal-semiconductor-metal photodetectors have been investigated. The fabricated (ZnO/PSi) UV photodetector showed much higher photocurrent than other structures.

Dielectric and surface properties of wood modified with NaCl aqueous solutions and treated with FE-DBD atmospheric plasma

The hygroscopic and electrical properties of the wood surface of Norway spruce (Picea abies (L.) Karst.) and common beech (Fagus sylvatica L.) were altered by the application of differently concentrated NaCl aqueous solutions. The presence of Na+ and Cl– ions increased the equilibrium moisture content in both woods in environments with a relative humidity of 75% to a nearly saturated state. The electrical resistance of the wood decreased, while the electrical capacitance of the wood increased with increasing amounts of NaCl introduced. Inverse trends were observed for both properties in wood modified with the two most concentrated solutions (18 and 36% molality). Microscopic analysis of the outer layers of the wood samples using scanning electron microscopy and energy-dispersive X-ray spectroscopy showed that the amount of NaCl decreased linearly up to about 1 mm from the modified surface. The presence of Na+ and Cl– ions in wood increased the intensity and improved the homogeneity of the plasma discharge generated during treatment of samples in air at atmospheric pressure. Both modification of wood with NaCl and subsequent treatment with plasma increased the surface roughness of the substrates. Finally, it was shown that the wettability of wood with a waterborne coating was improved after plasma treatment, regardless of the presence of NaCl on the surface. These findings have a good potential not only for the study of surface treatment processes of wood with plasma discharges, but also for other technical applications of lignocellulosic materials.

Synthesis and characterization studies of high-density polyethylene -based nanocomposites with enhanced surface energy, tribological, and electrical properties

High-density polyethylene (HDPE) and different weight fractions of multi-wall carbon nanotubes (MWCNTs) in the weight fraction of 1, 2, 3, and 5% were successful fabricated using magnetic stirring-twin screw extrusion and subjected to wear tests at two load variations maintaining a fixed speed. Three wt. % MWCNTs/HDPE nanocomposites exhibited the best tribological performance, so this composition was selected to develop hybrid nanocomposites with the addition of 0.6, 1.2, 1.8, 2.4, and 3 wt % Nano-alumina particles. Three wt. % MWCNTs+1.2 wt % Al2O3/HDPE nanocomposites outperformed other compositions and exhibited leading tribological performance and the lowest friction coefficient attributed to creating stable, coherent, and adherent transfer film. MWCNTs and Al2O3 reinforcement mutated the wettability (from contact angle of ~93° ± 2°–~116.6° ± 3°) and surface energy (from ~25 to ~17.6 mN/m) of nanocomposites compared to pure HDPE. Investigations on electrical properties revealed that the conductivity remained unaffected up to 2 wt % of MWCNTs. Three wt. % MWCNTs/HDPE nanocomposites marked a sharp increase in the conductivity up to a frequency of 4.75 × 106 Hz, after which it decreased and followed the same trend as pure HDPE, and 1, 2 wt % nanocomposites. The permittivity of the nanocomposites increased with the increment in wt. % of MWCNTs at low frequency, and beyond a critical frequency, it became frequency independent. The percolation threshold of MWCNTs/HDPE nanocomposites appeared between 2 and 3 wt %.

Determination of surface morphology and electrical properties of MoO3 layer deposited on GaAs substrate with RF magnetron sputtering

Determination of surface morphology and electrical properties of MoO3 layer deposited on GaAs substrate with RF magnetron sputtering

Surface modification of TiO2 nanoparticles with terephthalic acid in supercritical carbon dioxide

This paper presents a supercritical CO2 strategy for surface modification of TiO2 nanoparticles with carboxylic acids. The reaction between TiO2 nanoparticles and terephthalic acid molecules in sc-CO2 provides carboxylic acid-modified TiO2 nanoparticles with a modification efficiency much higher than the conventional solvent immersion method. From the statistical method of response surface methodology, modifier ratio 4.04 (mol/mol), temperature 401.5 K, and pressure 14.8 MPa resulted in an optimum modification rate of 25.34%. The modified TiO2 was characterized by FTIR, TG-DTA, FE-SEM, TEM-EDS, and zeta potential analysis. The results showed the surface modification of TiO2 in sc-CO2 is made of modifier molecules bonding chemically. Surface modification by terephthalic acid affects the surface electrical property of TiO2 nanoparticles in water, leading to a positive charge surface. Since this method is ecologically and environmentally friendly, it can be applied in precursor composites for the synthesis materials of biomedical application.

Aluminum Doping Contents Dependent Photoluminescence and Resistivity of ZnO Nanofilms

Using sol–gel spin-coating technique Al-doped ZnO nanofilms (AZONFs) were made on Si(100) substrates and characterized. The obtained nanofilms were annealed at 500 °C for 3 h in air. The effects of changing Al doping level (0 to 5 at%) on the structures, morphologies, electrical and photoluminescence characteristics of the nanofilms were evaluated. The XRD patterns of the AZONFs confirmed the formation of wurtzite hexagonal ZnO lattice with preferred growth along (101) lattice plane. In addition, the c-axis orientation of the AZONFs became weaker with the increase in Al doping contents. The surface morphologies, structures, electrical and optical properties of the AZONFs were found to be very sensitive to the Al contents changes. The nanofilm prepared with 1 at% of Al displayed lowest resistivity of 4.238 × 10−3 Ω.cm measured by the four-point probe method. The optical band gap energy (increased from 3.22 to 3.304 eV) and carrier mobility of the AZONFs were improved with the increase in Al contents. The proposed AZONFs may be advantageous for various high performance optoelectronic device applications.

Mixture of Graphene Oxide/Phosphoric Acid/Melamine as Coating for Improved Fire Protective Performance and Enhancement of Surface Electrical Properties on Wood Chipboard.

Looking for multifunctional materials, an assessment of the performances both as fire retardant and generator of electrically conductive surfaces for a three component mixture of graphene oxide, phosphoric acid and melamine applied on wood chipboard was performed. A simple approach was used to investigate the intumescent char formation and quantify the loss mass during vertical burning tests, in which the prepared samples were exposed for a certain time interval to a flame generated by an ethanol lamp in ambient conditions. Moreover, mass loss evolution and structural changes that occur during the burning process were more comprehensive investigated by differential thermal and thermogravimetric (DTA/TGA) techniques. By comparing the performances between the wood chipboard samples without any coverage and those covered with one or multiple component mixture, an increase of protection against the fire action was noticed when the three component mixture was used. Also, an improvement of the electrical properties was observed, after flame exposure of the samples covered with multiple layers (i.e., two and three), when the three component mixture was used. Morphological and structural investigations by microscopy (optical and electronic-SEMEDX), X-ray diffraction (XRD) and spectral (Raman, FTIR) methods are described. An assessment of market potential is also discussed.

Features of field modeling of electromagnetic processes of trolley busbar

Purpose. Research and analysis trolley busbar’s parameters in condition of higher current harmonic actions, with taking into account the structural features of nonlinearity of magnetic and electrical properties of materials, proximity effects, surface and external surface effects.
 Methodology. The researches were carried out using the electromagnetic field theory methods, the electrical circuit theory, mathematical physics, finite elements, interpolation, approximation and regression analysis.
 Findings. The mathematical spatial model of electromagnetic processes in a steel trolley busbar in time statement of a problem of distribution of an electromagnetic field is developed. The dependences of the distribution of equipotential lines of the resulting z-component of the magnetic potential vector along the busbar, as well as the distribution of the resulting normal component of magnetic induction and magnetic field strength in the transverse (XY) cross section at non-sinusoidal current in busbar trolleys is obtained. Along the length of the busbar, in their cross section, the magnetic field tends to a plane-parallel shape it is proved. The error of the modulus of the vector magnetic potential along the length of the busbar does not exceed 0.9-1.2%. To reduce the dimension of the problem, computational resources and calculation time, a two-dimensional plane-parallel mathematical model in the frequency setting of the electromagnetic field distribution is proposed. To take into account the nonlinear magnetic properties of steel trolleys, to determine the effective magnetization curve for the nonlinear two-dimensional problem of the electromagnetic field of the busbar it is proposed. The verification results, according to the calculated voltage drop, confirm the high accuracy of the calculation and the reliability of the obtained results (error does not exceed 1.88% ÷ 2.06%) of the two-dimensional model in the frequency setting relative to the spatial model in the problem of time-dependent electrical -magnetic field is obtained.
 Originality. A mathematical two-dimensional model of electromagnetic processes in the frequency formulation of the problem of electromagnetic field distribution in a trolley busbar is proposed, which takes into account design features, nonlinearity of magnetic and electrophysical properties of materials, proximity effects, surface and external surface effects, influence of harmonic current components power transmission, which allows with high accuracy and efficiency of numerical implementation to determine the parameters of the bus trolls for the corresponding values of the amplitudes and frequencies of the frequencies harmonics of the current.
 Practical value. Verification of the calculated voltage drop confirms the high accuracy of the calculation and the reliability of the results (error does not exceed 1.88% ÷ 2.06%) of the two-dimensional model in the frequency reference relative to the spatial model in the problem of time-dependent electromagnetic field distribution is performed.

Low-Voltage Operating Field-Effect Transistors and Inverters Based on In₂O₃ Nanofiber Networks

Electrospinning one-dimensional (1-D) semiconductor nanofibers have been regarded as one of the most promising building blocks for future nanoelectronics with high performance because they can exhibit a broad range of device functions. However, electronic devices based on electrospinning-driven nanofibers often suffer from poor performance and inferior quality. In current works, continuous and uniform high-quality indium oxide (In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) nanofibers were obtained by electrospinning. The surface morphology, crystallinity, optical, and electrical properties of the In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> nanofibers were investigated by X-ray diffraction, scanning electron microscopy, optical spectroscopy, and electrical measurements. It has been detected that the field-effect transistors (FETs) with optimized electrospinning time of 30 s demonstrated superior electrical performance, including a high field-effect mobility ( μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FE</sub> ) of 9.1 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> · <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> and a large I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> /I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> . The high- k Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> dielectric layer has also been used to greatly reduce the operating voltage (from 30 to 3 V), significantly improve μ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">FE</sub> (to 27.7 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·V <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> · <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> ), and strengthen stability over cycling. To prove the device's potential in more complex logic circuit applications, a resistor-loaded inverter was further integrated, and the maximum voltage gain of 9.8 was demonstrated at an ultralow operating voltage of 3 V. The present findings have demonstrated that electrospinning can potentially be used as a straightforward and cost-effective means for the assembly of 1-D nanostructures for use in next-generation low-power devices.

Improving passivation properties using a nano-crystalline silicon oxide layer for high-efficiency TOPCon cells

High conversion efficiency can achieve by superior surface passivation and material quality. In this study, a novel passivation contact structure based on nanocrystalline silicon oxide (nc-SiOx) films was investigated. Traditionally, poly silicon junctions in tunnel oxide passivated contact (TOPCon) solar cells possess exceptional junction characteristics, but current losses are noted due to their optical absorption if they are applied in solar cell devices. In this study, we replaced the poly-Si layer in TOPCon solar cells with nc-SiOx to enhance transparency. By employing the nc-SiOx layer, effective surface passivation, carrier selectivity, electrical properties and optical transmission can be used to improve, all are vitally important in devise operation. We optimized the deposited nc-SiOx layer on an ultra-thin (~1.5 nm) silicon dioxide (SiO2) tunnel oxide layer to improve recombination current density and carrier lifetime. The passivation characteristics were improved by varying the annealing temperature and thickness of the nc-SiOx layer. The 50 nm thick nc-SiOx layer was capable of yielding a high implied open-circuit voltage (i-Voc) of 739 mV and low contact resistivity (ρ) of 14.2 (mΩ/cm2) in addition to a low depleted recombination current density (Jo) of 1.1 fA/cm2 with a post-deposition annealing temperature up to 950 °C. Improved passivation characteristics are the result of a more prominent annealing temperature. Our proposed technique has immense potential for achieving higher efficiency for fabricating various structures of TOPCon solar cells. As per AFORST Het simulation results by using nc-SiOx for TOPCon structure, we got Voc of 761.5 mV, Jsc of 43.5 mA/cm2, FF of 83%, and η of 27.49%, respectively.

Bio-composites from banana tree fibers ambient with multi-walled carbon nanotubes: manufacturing and properties

A biodegradable composite fibers have been fabricated from easily available banana tree fibers (BTFs) using a simple dip-drying technique, where carbon nanotubes (CNTs) are used as reinforcing agent. A safe radio frequency oxygen plasma processing method is used to functionalize the surface of the CNTs with hydrophilic oxygen-containing group. The fibers are chemically treated with NaOH followed by oxygen plasma treatment to increase the heat conduction between the fibers in thermal contact. The implications of incorporating CNTs in the BTFs are observed by studying the surface morphology, structural, thermal, electrical and mechanical properties. The homogeneous CNT coverage on the BTFs surface is featured by the scanning electron micrographs of the CNT/treated BTF. The crystallinity index is exposed through X-ray diffraction analysis, which indicates the crystalline feature of the nanocomposites. The surface modification by CNT treatment has improved the thermal stability and flame retardancy of BTFs. A gradual decrease of resistivity of these composite fibers is observed from 5.69 to 0.0021 Ω m by increasing the number of dip-drying cycle of BTFs in the CNTs solution. The electrical conductivity of the CNT/treated BTF becomes 163.75 S/m under the applied voltage of 100 V. The developed composite fibers exhibit an increase in the mechanical strength with the CNT coating. Therefore, the developed CNT-reinforced composite fibers affirm its aptitude as reliable reinforcement in electronic devices and as conductive fillers in composites industries.

Bubble‐Induced In Situ Property Modulation of Liquid Metal

AbstractAlterable surface tension and electrical properties of liquid metals are of great significance to their applications in intelligent robots, bionic applications, and electronics. To further understand the interfacial properties of liquid metals, the highly effective and in situ modulation strategy is imperative to be developed. Here, a bubble‐induced in situ modulation strategy to achieve the on‐demand surface tension and electrical properties is initially demonstrated. The size and shape of bubbles are modulated by virtue of thermal effect under the laser irradiation. As a consequence of the regulated location of bubbles, the surface tension and electrical potential are in situ adjusted reversibly and periodically. In situ surface property modulation of liquid metal may provide promising prospects for efficient property tuning strategies and innovative on‐demand applications.

Defects and Surface Electrical Property Transformation Induced by Elemental Interdiffusion at the p-n Heterojunction via High-Temperature Annealing.

Heterojunction annealing is widely used to improve the efficiency of kesterite thin-film solar cells. However, the efficiency will decrease when the annealing temperature is high, and the reason why high-temperature postdeposition annealing results in the deterioration of device performance is not well-studied, which restricts the efficiency promotion of kesterite solar cells. This study investigates the effect of high-temperature postdeposition annealing on the p-n heterojunction and, thus, on the performance of the solar cell. The surface potential of the absorber layer inverts, the number of deep-level defects increases, and the CdS/CZTSe interface barrier height increases after high-temperature postdeposition annealing. A combination of different characterization methods reveals that excessive elemental diffusion at the p-n heterojunction during high-temperature postdeposition annealing is the key reason for deterioration of the performance of CZTSe devices. This study discloses the mechanism for the change in device properties with high-temperature postdeposition annealing and will also be helpful for understanding the mechanism of efficiency change as the solar cell keeps working.

Highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/nylon 6 nanofiber web treated with repetitive coating cycles and dimethyl sulfoxide multi-step treatment for electronic textiles

Highly conductive nylon 6 nanofiber web was fabricated with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and dimethyl sulfoxide (DMSO) for electronic textiles. To improve electrical conductivity, repeated coating with PEDOT:PSS and multi-step treatment of DMSO was performed. The effects of these treatments on electrical conductivity, surface properties, and chemical structures were investigated. For repetitive coating cycles, pristine PEDOT:PSS dispersion was dropped onto a nylon 6 nanofiber web for between one and four times of coating. For DMSO multi-step treatment, in the one-step treatment, the nanofiber web was repeatedly treated using PEDOT:PSS doped with DMSO. In the two-step treatment, the nanofiber web was repeatedly treated with doped PEDOT:PSS at first and, then, it was immersed in a DMSO bath. As a result, the sheet resistance decreased dramatically as the number of coating cycles increased. When the two-step treatment was applied, the sheet resistance was much lower compared to that of the one-step treatment, and thereby sample PD4-D with the lowest resistance showed 6.56 Ω/sq. As a result, the surface of the nanofiber web was covered with more PEDOT:PSS as the coating cycle was repeated. The PEDOT particles became large and long shapes after the two-step treatment of DMSO. This inferred that the contact area among conducting PEDOT particles increased because insulating PSS was removed by DMSO. In addition, the presence of PEDOT:PSS and nylon 6 was confirmed. This study proved that the simultaneous treatments of repeated coating with PEDOT:PSS and multi-step treatment of DMSO can improve electrical conductivity, and it developed the highly conductive PEDOT:PSS/nylon 6 nanofiber web.

Laser Grinding of Single-Crystal Silicon Wafer for Surface Finishing and Electrical Properties.

In this paper, we first report the laser grinding method for a single-crystal silicon wafer machined by diamond sawing. 3D laser scanning confocal microscope (LSCM), X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), laser micro-Raman spectroscopy were utilized to characterize the surface quality of laser-grinded Si. Results show that SiO2 layer derived from mechanical machining process has been efficiently removed after laser grinding. Surface roughness Ra has been reduced from original 400 nm to 75 nm. No obvious damages such as micro-cracks or micro-holes have been observed at the laser-grinded surface. In addition, laser grinding causes little effect on the resistivity of single-crystal silicon wafer. The insights obtained in this study provide a facile method for laser grinding silicon wafer to realize highly efficient grinding on demand.

Pulsed laser modification of layered B-C and mixed BCx films on sapphire substrate

The effect of pulsed laser annealing (PLA, i.e., action of nanosecond laser pulses in air atmosphere) on surface morphology, structure, chemical state, and electrical properties of thin films consisting of boron and carbon atoms was studied. The nanolayered В/С and mixed ВСx~3 thin film precursors (with a thickness ~110–140 nm) were created on sapphire substrates by using the pulsed laser deposition. Scanning electron microscopy and Raman scattering measurements indicate that the process of stratification of the multilayer B/C films dominated during PLA of the films. The outer layers were removed, and closer to the substrate, the B and C layers were preserved, and they were not mixed. For the mixed ВСх films deposited at elevated temperatures, the PLA treatment enhances ordering of initially amorphous film structure. At the stage of melting of these films, oxygen (from surrounded air) penetrated inside the top layer of the film leading to the formation of a multiphase structure from g-BCx and B-doped GO/rGO after solidification. Studies of the chemical state of elements in the irradiated film have shown that О atoms, which penetrated the under-surface layers of the film, facilitated the formation of new chemical bonds in the B–C–O system. The concentration of O atoms in the depth of the film could reach 8%. The preferential oxidation of boron in a homogeneous mixture of B–C–O atoms indicated that intercalation of carbon matrix could be due to the incorporation of not only O atoms, but also B–O molecules. The laser irradiated ВСх films have a relatively low resistivity (~1.6 mΩ·cm) and semi-metallic dependence on temperature in the range 4.2–300 К. The spatial distribution of conductivity zones after PLA has an irregular structure, and its pattern looks like sand dunes, indicating that the PLA treatment leads to mixing zones of high with those of lower conductivity. The contact-tip resistivity inside the areas of high conductivity of the ВСx/Al2O3 samples may be significantly lower than that of pure graphite.

Near-white light-emitting diode from p-CuO/n-GaN heterojunction with an i-CuO electron blocking layer

• Near-white LED based on p-CuO/i-CuO/n-GaN was realized by magnetron sputtering and annealing treatment. • CuO could be used as hole injection layer and electron blocking layer under different annealing condition. • The chromaticity coordinates and related color temperatures of the devices were about (0.2381, 0.2606) and 22,505 K. • The i-CuO layer could improve the stability of electron injection and optimize the structure of diode. White light-emitting diodes (WLEDs) have advantages of high efficiency, energy saving, and long working-life, which are ideal choice for next generation of solid-state light sources. Herein we fabricated the near-white light-emitting diode based on the structure of p-CuO/i-CuO/n-GaN heterojunction by magnetron sputtering and annealing treatment. The surface morphology, crystal quality and electrical properties of the CuO layer were investigated by X-ray diffractometer, field emission-scanning electron microscope and Hall measurement. And the influence of the CuO electron blocking layer (EBL) on the diode characteristics were discussed. The current-voltage (I-V) characteristics of those diodes revealed typical p-n junction. Compared with p-CuO/n-GaN heterjunction diode, the EL spectrum of p-CuO/i-CuO/n-GaN heterjunction diode exhibited blue shift and higher intensity. It was found that the addition of CuO EBL enhanced the stability of the diode through analyzing the I-V and EL properties of the diodes. Moreover, at the injection current of 50 mA, the chromaticity coordinates of p-CuO/n-GaN and p-CuO/i-CuO/n-GaN heterojunction diodes are about (0.2686, 0.3334) and (0.2381, 0.2606), and the color temperature are 9205 K and 22,505 K, respectively. Eventually, the EL working mechanism of the two diodes was analyzed in the aspect of the energy band diagram. This study demonstrates the possibility of p-CuO/n-GaN heterojunction with an i-CuO electron blocking layer and their potentials for applications in WLEDs.

Modulating surface interactions for regenerable separation of oil-in-water emulsions

Developing antifouling coatings is of both fundamental and practical significance, but challenging, for membrane separation of oil-in-water (O/W) emulsions with charged surfactants, which has been conventionally achieved through the short-range hydration interaction from hydrophilic membrane surfaces as a physical barrier. Herein, we report a mussel-inspired antifouling coating formed by carboxyl and quaternary ammonium moieties bearing adjustable surface charge property, employing tunable long-range electrostatic interaction to achieve adaptive antifouling performance in response to the varying electrical characteristic of emulsions. The surface force measurement results showed that modulating the surface electrical properties of the coatings through varying the solution pH could effectively alter their electrostatic interactions with emulsions from attraction to repulsion, in combination with hydrodynamic interactions, to enable emulsion repellence of the coatings. Such functional coatings were further applied on a PVDF membrane with an enhanced water permeability and reusability achieved to separate both the positively and negatively charged emulsions. By properly modulating the membrane surface charge, the modified membrane demonstrated its adaptive antifouling performance for efficient and universal water treatment. This work provides useful insights into the antifouling mechanisms of membranes to O/W emulsions, as well as developing functional materials with tunable surface interactions for various engineering applications.

Characteristics and electrical properties of polyimide films fluorinated for different durations

Surface fluorination of polyimide films was conducted for different durations (30, 60, and 90 min) in a laboratory vessel using an F2/N2 gas mixture containing 12.5 % F2 by volume. The differences in the structural, morphology, wettability, surface free energy, and electrical properties of the fluorinated polyimide films were systematically studied to assess the effects of fluorination and fluorination time, and to investigate the relationship between the surface electrical properties and surface physicochemical properties. The obtained results indicated that fluorination cracked the film surface, with the number of cracks increasing with increasing fluorination time. Fluorination also enhanced the surface wettability and polarity. Surface conductivity and surface potential decay measurements consistently showed that the surface-fluorinated samples had a higher surface conductivity than unfluorinated samples, and that the surface potential rapidly decayed because the surface conductivity increased with enhanced water adsorption on the surface. The increased occurrence of surface cracks, as well as enhanced polarity and surface conductivity of the films, were mainly attributed to the increase in the degree of chain scission that occurred with increasing fluorination time.