Thin Active Layer Research Articles

Unlocking large compressive strains in thin active elastocaloric layers

• • Durable composites enabling compression of elastocaloric layers are demonstrated. • • Elastocaloric materials can be in any thin-layer geometry, e.g., strip, plate, foil. • • Composites achieve 8.1 K temperature change at 2.5% strain. • • Mechanical and thermal properties are stable after 104 loading cycles at 2% strain. Elastocaloric cooling attracts broad interest and rapidly growing attention due to its potential for high efficiency and low environmental impact. While it is common knowledge that triggering reversible entropy and temperature changes with stress applied in compression prevents rapid failures of materials, realizing this regime in elastocaloric systems is highly challenging because nearly all geometries suited for efficient heat transfer are prone to buckling even under modest loads. This work describes a concept of a novel composite, where an active NiTi layer is embedded into a polymer support structure such that the elastocaloric material is entirely in compression when the assembly is subjected to bending. The active layer achieves 8.1 K temperature change at 2.5% compressive strain without buckling. After 10,000 cycles at 2% compressive strain, the composite maintains mechanical integrity without degradation of the elastocaloric effect. The results show that NiTi and, potentially, other elastocalorically active materials in geometries previously thought impossible can be successfully implemented in regenerative cooling systems operating in compression.

Enhanced Charge Extraction in Metal–Perovskite–Metal Back-Contact Solar Cell Structure Through Electrostatic Doping: A Numerical Study

In conventional perovskite solar cells (PSCs), a thin active layer of perovskite is sandwiched between two charge transport layers (CTLs)-electron transport layer (ETL) and hole transport layer (HTL). CTLs help in extracting and navigating the photogenerated electron-hole (e-h) pairs to the respective electrodes. Although this phenomenon gives high-energy conversion efficiencies but leads to quite a few performances as well as fabrication challenges. The ways to partially overcome these challenges are to have a device without the need of having CTLs altogether and opting for the back-contact (BC) design for PSCs. Dipole fields (DFs) present at the metal perovskite interface may be thought for their possible utilization to have CTL-free BC PSC. However, the performance of such devices is limited by the difference between the metal work functions across the perovskite layer. In this article, we report the results for our studies to establish that an electrostatically doped DF-assisted metal perovskite metal back-contact (ED-DF-MPM) PSC structure has the ability to overcome the limitations of DF-assisted metal perovskite metal back-contact (DF-MPM) PSCs. As a part of the work carried out here, ED p-n-junction and corresponding built-in potential have been combined for DF-assisted extraction of generated carriers within the perovskite layer so as to enhance the collection probability and open-circuit voltage. Quantitively, 32.7%, 10.6%, and 8.6% improvement in short-circuit current density (J <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SC</sub> ), open-circuit voltage (V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> ), and fill factor (FF) are obtained, respectively, which resulted in an observation of 59.4% improvement in power conversion efficiency (PCE) for ED-DF-MPM PSC compared to DF-MPM PSC. Besides that, the reported ED-DF-MPM PSC structure delivers the photovoltage and photocurrent of 659 mV and 14.19 mA ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> , respectively. The work reported in this article may pave the way for the development of “transport layer-free” ED scalable and low-cost PSCs in future.

Fabrication, optimization, and performance of a novel double-skinned Al2O3.TiO2 ceramic nanocomposite membrane for forward osmosis application

Abstract In this study, a thin film nanocomposite ceramic membrane with an Al2O3 substrate and TiO2 as the thin film active layer was fabricated via dip coating technique and optimized for application in FO purification of groundwater. The effect of parameters including sol aging, calcination temperature, and dip time was investigated. Based on the results, the least water flux was obtained during 6 h after sol preparation. Furthermore, boosting the synthesis temperature and dip time led to flux reduction. According to the optimization results, 6.75 h sol aging, 17.00 s dip time and a 319 °C calcination temperature, led to the maximal water flux of 168 L/m2 h bar and 48% salt rejection. In addition, by covering the substrate with 10 layers of TiO2, water flux was reduced to 10.82 L/m2 h bar. FO process using MgCl2 solution (2 M) as draw and DI water as feed solutions, resulted in an initial water flux of 17.04 L.m−2 h−1 (LMH). Replacing DI water with a 0.01 M NaCl solution as feed, the initial water flux was decreased to 15.5 LMH. Also, using groundwater as the feed solution with an EC of 1407, 14.1 LMH initial water flux was obtained.

Modelling and Calculation of Characteristic Parameters of the Active and Buffer Layers in Organic Solar Cell

Background: The active layer not only must have a strong light absorption in the visible spectrum but must also be sufficient for charge carrier transport to the electrodes. Electrons in conducting polymer transport by hopping between different energy levels resulted in much lower charge mobility. Therefore, the thickness of the active layer must be limited, so the separated charge can reach the corresponding electrodes without recombination. However, a thin active layer has weaker light absorption, resulting in the low photogenerated current in organic solar cell devices. Furthermore, buffer layers usually have high charge mobility, which in turn would enhance the transportation of charge from the active layer to electrodes. Metal oxides have been studied to be used as a cathode buffer layer, such as titanium dioxide (TiO2), zinc oxide (ZnO), etc. Objective: In this work, behaviors of the photon-electrical characteristics with variation in thickness of the active (poly(3-hexylthiophene-2,5-diyl) and phenyl-C61 butyric acid methyl ester blend) and buffer (zinc oxide) layers were investigated. Methods: The influences of the thickness of the active and buffer layers on characteristic parameters of organic solar cells were investigated by solving the drift and diffusion equation with the photogenerated current given by the Hetch equation. Results: The optimum thickness was obtained around 100 nm and below 10 nm for the active and the ZnO buffer layers, respectively. Conclusion: Thinner active layer resulted in lower photocurrent due to poor light absorption while at 150 nm thick and above, PCE of the device reduced rapidly because of the high recombination rate of photogenerated electron-hole pairs. ZnO buffer layer was used as an electron transport layer and a hole blocking layer in order to improve the cell’s performance. The addition of ZnO enhanced the PCE up to 2.48 times higher than the conventional device.

Elucidating the Full Potential of OPV Materials Utilizing a High-Throughput Robot-Based Platform and Machine Learning

•Automated robot-based organic solar cell fabrication and characterization •A high-quality dataset enables machine-learning-based predictions •Reliable screening of more than 100 processing variations within 70 h •A platform and methodology for broader research areas in solution-processed devices Evaluating the potential of organic photovoltaic (OPV) materials and devices for industrial production is a multidimensional optimization process with an incredibly large parameter space. Here, we demonstrate automated OPV material and device characterization in terms of efficiency and photostability. Gaussian process regression (GPR) prediction based on optical absorption features guided the optimization process with promising prediction accuracy for PV parameters and burn-in losses. With ∼100 process conditions, screening for efficiency and photostability can be finished within 70 h. The highest power conversion efficiency (PCE) of 14% was achieved by fully automated device fabrication in air with a model material system PM6:Y6. Improving molecular ordering has been identified as the most promising motif for further efficiency optimization. Thin active layers combined with medium thermal annealing temperature are favorable to simultaneously improve efficiency and suppress burn-in losses. The platform and protocol may be expanded to any solution-processed organic semiconductor and interface materials. Evaluating the potential of organic photovoltaic (OPV) materials and devices for industrial production is a multidimensional optimization process with an incredibly large parameter space. Here, we demonstrate automated OPV material and device characterization in terms of efficiency and photostability. Gaussian process regression (GPR) prediction based on optical absorption features guided the optimization process with promising prediction accuracy for PV parameters and burn-in losses. With ∼100 process conditions, screening for efficiency and photostability can be finished within 70 h. The highest power conversion efficiency (PCE) of 14% was achieved by fully automated device fabrication in air with a model material system PM6:Y6. Improving molecular ordering has been identified as the most promising motif for further efficiency optimization. Thin active layers combined with medium thermal annealing temperature are favorable to simultaneously improve efficiency and suppress burn-in losses. The platform and protocol may be expanded to any solution-processed organic semiconductor and interface materials.

Low-cost, universal light-harvesting coating layer for thin film solar cells by employing micro-prism films

Reduction of optical loss in thin-film solar cells, such as polymer solar cells and perovskite solar cells, is a key issue to promote device performance. A number of optical strategies have been investigated to enhance absorption. Among them, the light management layer provides an effective approach. This work designed and fabricated a micro-prism film with a simple technology. It significantly improved the light absorption of the solar cells after coating on the device incident windows. A specific optical model was built by combining ray optics and wave optics to explore the light trapping properties of the micro-prism films. Theoretically, the micro-prism film presented great anti-reflection ability. Its light trapping efficiency depended on the thickness periodically. However, within a wide thickness range in each period, the absorption enhancement remained at the maximum, which lowered the difficulties of thickness control in fabrication. Experimentally, coated with a micro-prism film, the JSC value of the polymer solar cells increases by 13.8%, leading to the power conversion efficiency (PCE) enhancing by 12.1%. On the other hand, perovskite solar cells with a thin active layer were prepared. JSC increased by 10.1% and PCE was enhanced by 6.0%, which were close to those of the device with a typical thick active layer. This also provided a physical way to reduce the heavy metal lead and lower environment pollution risk.

Origin of performance improvement in solution-processed indium–gallium–zinc-oxide thin-film transistors having thin active layer and asymmetric dual gate structure

In this paper, we report the electrical characteristics of thin active layer indium–gallium–zinc-oxide thin-film transistors (IGZO TFTs) having an asymmetric dual gate structure. It was observed that the performance of IGZO TFTs significantly improved when the TFT is operated in the dual gate mode though the performance of the top gate mode shows very poor performance of low field-effect mobility and large subthreshold slope. We found that the channel electrons are coupled in the bulk region when the active layer is very thin, and top gate biasing provides additional electrons to the coupled channel region, which improves the electrical performance of dual gate mode IGZO TFTs. Bias stress instability measurements also indicate that dual gate mode IGZO TFTs show better stability compared to the other mode because coupled electrons are mainly formed in the bulk region, which reduce the effect of interfacial defect density of states. Therefore, the improvements of performance of dual gate electrode IGZO TFTs can be realized regardless of the relatively poor performance of the top gate mode.

Permafrost warming near the northern limit of permafrost on the Qinghai–Tibetan Plateau during the period from 2005 to 2017: A case study in the Xidatan area

AbstractPermafrost that exists near the boundary of the permafrost zone is generally more sensitive to climate change. By analyzing ground temperatures observed from two 30‐m‐deep boreholes, a case study was conducted to present some characteristics of recent permafrost warming in the Xidatan area, near the northern limit of the permafrost zone on the Qinghai–Tibetan Plateau. The rate of permafrost degradation from top to bottom in the area was far less than that from bottom to top. Local conditions produced spatial differences in permafrost characteristics, and thus the site covered by alpine meadow had a thinner active layer and lower rate of change than the site with desert steppe. With permafrost warming, the depths of zero annual amplitude at the two sites showed significant decreasing trends, suggesting that the warming could change the proportion of unfrozen water and ice in permafrost, and then lead to a decrease in the mean thermal diffusivity of formation. Mean annual permafrost temperatures at depth of zero annual amplitude of the two boreholes were respectively −0.4°C and −0.7°C, indicating that high‐temperature permafrost is widely distributed in the study area. The lower temperature permafrost had a higher warming rate and a higher upward shift rate of the permafrost base. The pattern of permafrost degradation near the limit of permafrost was characterized by nonuniform speed and staged development.

Minimizing Residual Images of Amorphous Indium Gallium Zinc Oxide Thin-Film Transistor-Based Flexible Organic Light-Emitting Diode Displays by Controlling Oxygen Partial Pressure.

Plastic organic light emitting diode displays suffer from residual image, which is closely connected with the hysteresis of the driving thin-film transistor in the pixels. Therefore, in researching paper, we manufactured an OLED display comprise a polyimide substrate and an amorphous indium gallium zinc oxide thin film transistor active layer. Paper proposed a solution for reducing hysteresis through oxygen partial pressure control and evaluated it using hysteresis analysis. The results showed that hysteresis is strongly dependent on the threshold voltage is settled by the oxygen partial pressure while active layer deposition of the TFT. Moreover, hysteresis decreases with increasing temperature.

Constructing Positively Charged Thin-Film Nanocomposite Nanofiltration Membranes with Enhanced Performance.

Using polyethylenimine (PEI) as the aqueous reactive monomers, a positively charged thin-film nanocomposite (TFN) nanofiltration (NF) membrane with enhanced performance was developed by successfully incorporating graphene oxide (GO) into the active layer. The effects of GO concentrations on the surface roughness, water contact angle, water flux, salt rejection, heavy metal removals, antifouling property, and chlorine resistance of the TFN membranes were evaluated in depth. The addition of 20 ppm GO facilitated the formation of thin, smooth, and hydrophilic nanocomposite active layers. Thus, the TFN-PEI-GO-20 membrane showed the optimal water flux of 70.3 L·m−2·h−1 without a loss of salt rejection, which was 36.8% higher than the thin-film composite (TFC) blank membrane. More importantly, owing to the positively charged surfaces, both the TFC-PEI-blank and TFN-PEI-GO membranes exhibited excellent rejections toward various heavy metal ions including Zn2+, Cd2+, Cu2+, Ni2+, and Pb2+. Additionally, compared with the negatively charged polypiperazine amide NF membrane, both the TFC-PEI-blank and TFN-PEI-GO-20 membranes demonstrated superior antifouling performance toward the cationic surfactants and basic protein due to their hydrophilic, smooth, and positively charged surface. Moreover, the TFN-PEI-GO membranes presented the improved chlorine resistances with the increasing GO concentration.

III-Nitrides Resonant Cavity Photodetector Devices.

III-nitride resonant cavity-enhanced Schottky barrier photodetectors were fabricated on 2 µm thick GaN templates by radio frequency plasma-assisted molecular beam epitaxy. The optical cavity was formed by a bottom distributed Bragg reflector based on 10 periods of Al0.3Ga0.7N/GaN, an Au-based Schottky contact as top mirror, and an active zone of 40 nm-thick GaN layer. The devices were fabricated with planar geometry. To evaluate the main benefits allowed by the optical cavity, conventional Schottky photodetectors were also processed. The results revealed a planar spectral response for the conventional photodetector, unlike the resonant devices that showed two raised peaks at 330 and 358 nm with responsivities of 0.34 and 0.39 mA/W, respectively. Both values were 80 times higher than the planar response of the conventional device. These results demonstrate the strong effect of the optical cavity to achieve the desired wavelength selectivity and to enhance the optical field thanks to the light resonance into the optical cavity. The research of such a combination of nitride-based Bragg mirror and thin active layer is the kernel of the present paper.

Electrospun hierarchical fibrous composite membrane for pomegranate juice concentration using osmotic membrane distillation

A dual-layered hierarchical fibrous composite (HFC) membrane with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as a thin active layer and poly(ethylene terephthalate) (PET) as a thick support layer was fabricated through electrospinning process. The membrane was tested for the concentration of clarified pomegranate juice through the osmotic membrane distillation (OMD) process. Experimental data showed that the transmembrane water flux until 8.621 ± 0.235 kg.m−2. h−1 was achieved at 25 ± 1 °C, which is about 4-fold higher than most of the reported work. The juice was successfully concentrated to 51.3 ± 0.052°Bx in a total time of 25.5 h. Membrane hydrophobicity analysis showed that the contact angle of the membrane dropped from 143.7°±3° to 120.1°±3°, while the liquid entry pressure decreased from 28.0 ± 1.8–25.0 ± 1.7 kPa, after the completion of the OMD process. Detailed morphology analysis depicted that pore blockage occurred due to the gel layer formation when the juice viscosity increased exponentially during the final stages of OMD process. Gel layer formation along with random fouling spots were found to be the main cause of drop in water vapor flux. However, simple washing of the membrane with deionized water effectively cleaned the fouling areas and removed the gel layer from the pores of the membrane. The first-ever application of dual-layered electrospun HFC membrane in the OMD concentration of pomegranate juice thus displayed a satisfactory performance, benefiting from the unique structures of the HFC membrane having the minimized mass transfer resistance and durable antifouling performance.

Facile fabrication of COF-LZU1/PES composite membrane via interfacial polymerization on microfiltration substrate for dye/salt separation

Covalent organic frameworks (COFs) have attracted great interest as advanced membrane materials due to their uniform channel structure and high porosity. In this work, COF-LZU1/PES composite membranes were prepared via interfacial polymerization (IP) process, and the thin and defectless COFs active layers were successfully grown on poly (ether sulfone) (PES) microfiltration substrates with 1,3,5-triformylbenzene (TFB) and p-phenylenediamine (PDA) as precursors. The prepared COF-LZU1/PES composite membranes exhibit a high rejection rate (>99.0%) for the dyes with molecular size above 1.5 nm and nonselective permeation for inorganic salts (<12.0%). At the same time, a water permeance above 80.0 L m-2 h-1·bar-1 is achieved, which is much higher than many other membranes with similar rejections. Long-term filtration demonstrates that COF-LZU1/PES membranes have good water stability. The excellent water permeance, high dyes separation performance and great stability endow COF-LZU1/PES membranes the performance of removing dyes from saline wastewater.

Self-powered broadband photo-detection and persistent energy generation with junction-free strained Bi2Te3 thin films.

We experimentally demonstrate efficient broadband self-powered photo-detection and power generation in thin films of polycrystalline bismuth telluride (Bi2Te3) semiconductors under inhomogeneous strain. The developed simple, junction-free, lightweight, and flexible photo-detectors are composed of a thin active layer and Ohmic contacts on a flexible plastic substrate, and can operate at room temperature and without application of an external bias voltage. We attribute the observed phenomena to the generation of an electric field due to a spontaneous polarization produced by strain gradient, which can separate both photo-generated and thermally-generated charge carriers in bulk of the semiconductor material, without a semiconductor junction. We show that the developed photo-detectors can generate electric power during both the daytime and the nighttime, by either harnessing solar and thermal radiation or by emitting thermal radiation into the cold sky. To the best of our knowledge, this is the first demonstration of the power generation in a simple junction-free device under negative illumination, which exhibits higher voltage than the previously used expensive commercial HgCdTe photo-diode. Significant improvements in the photo-detector performance are expected if the low-charge-mobility polycrystalline active layer is replaced with high-quality single-crystal material. The technology is not limited to Bi2Te3 as the active material, and offers many potential applications in night vision, wearable sensors, long-range LIDAR, and daytime/nighttime energy generation technologies.

Understanding of multiple resistance states by current sweeping in MoS2-based non-volatile memory devices

Recently, various two-dimensional materials have been reported to exhibit non-volatile resistance switching phenomenon. The atomristors, featuring memristor effect in atomically thin nanomaterials such as monolayer transition metal dichalcogenides and hexagonal boron nitride, have drawn much attention due to the extremely thin active layer thickness with the advantages of forming-free characteristic, large on/off resistance ratio and fast switching speed. To investigate the switching mechanisms in the 2D monolayers, we introduced an electrical characterization method by current sweeping to illustrate the detailed information hidden in the commonly used voltage-sweep curves. Multiple transition steps have been observed in the SET process of MoS2-based resistance switching devices. The different behaviors of transition steps were attributed to the number of defects or vacancies associated with the switching phenomenon, which is consistent with the previously reported conductive-bridge-like model for 2D atomristors. This work provides an approach using current sweeping to precisely characterize the resistance switching effect and inspires further research to optimize the defect distribution in 2D materials for the applications in multi-bit non-volatile memory and neuromorphic computing.

High-performance semitransparent polymer solar cells floating on water: Rational analysis of power generation, water evaporation and algal growth

Abstract Compared to conventional ground-mounted photovoltaic (PV) cells, floating photovoltaic (FPV) cells open new opportunities for scaling-up solar power generation, especially in highly populated countries that may have competing uses for the available land. Large-scale FPV projects normally deploy old-fashioned crystalline silicon panels that are brittle and difficult to integrate. Polymer solar cells (PSCs) are regarded as a newer and more versatile concept that make quite a splash today. High absorption coefficients, thin active layers and tunable absorption spectra through a synergy of molecular and device engineering promote extensive research on the integration of semitransparent polymer solar cells (ST-PSCs) with smart architecture to deliver both practical and aesthetic benefits. In this work, we propose a new concept of extending ST-PSCs to the field of FPV cells and explore the potential of regulating aquatic environments and organisms. Three groups of high-performance ST-PSCs are fabricated. Maximum efficiency of 13% and average visible transmittance over 20% deliver an optimum trade-off between power generation and transparency among the best-performing ST-PSCs. We develop new experimental approaches and propose a feasibility study on the water evaporation and algal growth by placing the large-area ST-PSCs on bodies of water. To the best of our knowledge, we demonstrate for the first time that the specific transmittance windows with controlled light intensities generated by the ST-PSCs are capable of regulating water evaporation and algal growth, which provides insight into responsible scale-up of FPVs instead of simply blocking the sunlight. The new functions of ST-PSCs pave an intriguing prospect of developing ST-PSCs for practical FPV applications in the near future.

Highly efficient, green-solvent processable, and stable non-fullerene polymer solar cells enabled by a random polymer donor

Abstract Rapid development of non-fullerene polymer solar cells (NF–PSCs) with high efficiency have gained wide research attention recently, however, high-performance large-area NF–PSCs are still lacking since most developed NF–PSCs use a thin active layer around 100 nm, which is not compatible with the fabrication of large-area devices. Herein, we fabricate high-performance and green-solvent processed NF–PSCs with thick active layer using a random copolymer (2TRA) and non-fullerene acceptors. Compared to its highly-crystallized analogue (2TRR), 2TRA with rearranged backbone enables better blend morphology, higher exciton generation rate, more efficient excitons dissociation, and less recombination in NF–PSCs. With O-IDTBR and IEICO-4F as non-fullerene electron acceptors, highly-efficient photovoltaic devices with PCE of 10.08% and 12.06% are achieved. Moreover, 2TRA-based NF–PSCs show good compatibility with multiple processing solvents, low sensitivity to the active layer thickness (up to 300 nm), and excellent photostability. The combined advantages of 2TRA-based solar cell devices indicate that 2TRA is a promising polymer donor for the application in large-area PSC modules through roll-to-roll technology, and the rearrangement design on polymer donors could be useful to design high-performance polymers for practical application.

Sacrificial graphene oxide interlayer for highly permeable ceramic thin film composite membranes

In this study, we report a facile and straightforward graphene oxide pre-coating method to prepare defect-free, ultrathin film composite ceramic hollow fiber membranes. By coating a graphene oxide (GO) interlayer, the defect-free thin alumina active layer with sub-micrometer thicknesses was successfully coated on highly porous substrates without thick interlayers. The GO interlayer not only prevents the pore-clogging of the substrate by boehmite nanoparticles but also helps the thin and uniform formation of active layers. Since the ultrathin GO interlayer was naturally removed during the calcination process of the active layer over 400 °C, the ceramic thin-film composite (TFC) membranes with controllable active layer thickness and pore size were obtained. Prepared ceramic TFC membranes showed outstanding separation performance, which was 2–8 times higher water flux at the same MWCO, compared to commercial multilayered ceramic ultrafiltration membranes. The results demonstrate the superior separation properties of ceramic TFC membranes, and the potential of cost-effective GO interlayer pre-coating methods for fabricating inorganic based membranes for various molecular separation applications.

Hydrothermal processes of near-surface warm permafrost in response to strong precipitation events in the Headwater Area of the Yellow River, Tibetan Plateau

Permafrost is mostly warm and thermally unstable on the Tibetan Plateau (TP), particularly in some marginal areas, thereby being susceptible to degrade or even disappear under climate warming. The degradation of permafrost consequently leads to changes in hydrological cycles associated with seasonal freeze-thaw processes. In this study, we investigated seasonal hydrothermal processes of near-surface permafrost layers and their responses to rain events at two warm permafrost sites in the Headwater Area of the Yellow River, northeastern TP. Results demonstrated that water content in shallow active layers changed with infiltration of rainwater, whereas kept stable in the perennially frozen layer, which serves as an aquitard due to low hydraulic conductivity or even imperviousness. Accordingly, the supra-permafrost water acts as a seasonal aquifer in the thawing period and as a seasonal aquitard in the freezing period. Seasonal freeze-thaw processes in association with rain events correlate well with the recharge and discharge of the supra-permafrost water. Super-heavy precipitation (44 mm occurred on 2 July 2015) caused a sharp increase in soil water content and dramatic rises in soil temperatures by 0.3–0.5 °C at shallow depths and advancement thawing of the active layer by half a month. However, more summer precipitation amount tends to reduce the seasonal amplitude of soil temperatures, decrease mean annual soil temperatures and thawing indices and thin active layers. High salinity results in the long remaining of a large amount of unfrozen water around the bottom of the active layer. We conclude that extremely warm permafrost with TZAA (the temperature at the depth of zero annual amplitude) >−0.5 °C is likely percolated under heavy and super-heavy precipitation events, while hydrothermal processes around the permafrost table likely present three stages concerning TZAA of <−0.5 °C, −0.5–0 °C, and >0 °C.

High-performance polyamide nanofiltration membrane with arch-bridge structure on a highly hydrated cellulose nanofiber support

Nanofiltration (NF) membranes with outstanding performance are highly demanded for more efficient desalination and wastewater treatment. However, improving water permeance while maintaining high solute rejection by using the current membrane fabrication techniques remains a challenge. Herein, polyamide (PA) NF membrane with arch-bridge structure is successfully prepared via interfacial polymerization (IP) on a composite support membrane of salt-reinforced hydrophilic bacterial cellulose nanofibers (BCNs) nanofilm/polytetrafluoroethylene (BCNs/PTFE). The strong hydration of BCNs promotes Marangoni convection along water/organic solvent interface during the IP process, which creates extra area for interfacial reaction and produces a thin PA active layer with arch-bridge structures. These arch-bridge structures endow the resulting PA active layer with substantial larger active area for water permeation. Consequently, the PA NF membrane exhibits exceptional desalination performance with a permeance up to 42.5 L m−2 h−1 bar−1 and a rejection of Na2SO4 as high as 99.1%, yielding an overall desalination performance better than almost all of the state-of-the-art NF membranes reported so far in terms of perm-selectivity.