Sublayer Structure Research Articles

Nanoscale Graded Nitrogen-Doping of TiO2 via Pulsed Laser Deposition for Enhancing Charge Transfer in Perovskite Solar Cells.

An electron transport layer (ETL) for highly efficient perovskite solar cells (PSCs) should exhibit superior electrical transport properties and have its band levels aligned with interfacing layers to ensure efficient extraction of photo-generated carriers. Nitrogen-doped TiO2 (TiO2:N) is considered a promising ETL because it offers higher electrical conductivity compared to conventional ETLs made from spray-pyrolyzed TiO2. However, the application of highly doped TiO2:N in PSCs is often limited by the misalignment of energy band levels with adjacent layers and reduced optical transparency. In this study, a novel approach is introduced to enhance the charge transport characteristics and accurately align the electronic band alignment of TiO2:N layer through nanoscale doping level grading, achieved through the pulsed laser deposition (PLD) technique. The TiO2:N ETL with a graded doping profile can combine characteristics of both highly doped and lightly doped phases on each side. Furthermore, a nanoscale doping gradation, employing an ultrathin sub-layer structure with graded doping levels, creates a smoothly cascading band-level alignment that bridges the adjacent layers, enhancing the transport of photo-generated carriers. Consequently, this method leads to a substantial increase in the power conversion efficiency (PCE), exceeding 22%, which represents a relative improvement of 11% compared to traditional spray-pyrolyzed TiO2-based PSCs.

Feasibility evaluation of near dissolved organic matter microfiltration (NDOM MF) for the efficient removal of microplastics in the water treatment process

Microfiltration (MF) using membranes with a mean pore size smaller than 0.45 μm has generally been used for particle removal from water, given that materials larger and smaller than 0.45 μm are regarded as particulates and dissolved organic matter (DOM), respectively. It is also the case for removing small-size microplastics (MPs). However, given their sizes (ca. 1 μm), there is room for further improvement of the productivity (i.e., water flux) in the pore size range of 0.45–1 μm on the condition that the removal rate is maintained. With this in mind, MF's water flux and removal rate were tested using seven different MF membranes, and the right pore, with the size of 0.8 μm, was found for MP removal, which is called near DOM (NDOM) MF. In the filtration test using polystyrene surrogate beads with an average particle diameter of 1.20 μm, NDOM MF exhibited a 1.7 to 13 times higher permeate flux than the conventional MF using 0.1, 0.2, and 0.45 μm membranes while maintaining a higher removal rate than 2 log. The excellent removal rate of the NDOM MF was attributable to the following three factors: (1) smaller mean pore size than the average particle diameter, (2) particle screening effect enhanced by the secondary layer formed by surface deposition, and (3) 3D mesh sublayer structure favorable for capturing penetrated particles. Furthermore, the outstanding filtration performance also appeared in a low-temperature (< 10°C) process, demonstrating that NDOM MF is feasible independently of temperature. Additionally, in constant flux filtration, NDOM MF demonstrated the long-term feasibility by lowering the transmembrane pressure and specific filtration energy by more than 2 times.

Surface modification of polysulfone reverse osmosis membrane with chitosan-modified zinc oxide for water desalination

ABSTRACT Decreasing groundwater levels, increasing world population, and pollution of water resources by industries lead to the use of new technologies for augmenting the fresh water supply such as its desalination. Chitosan-modified zinc oxide (C-ZnO) nanoparticles were synthesized and used for surface modification of polysulfone (PSf) in water desalination. PSf /C-ZnO membrane was fabricated through the phase inversion method and characterized by Fourier transfer infrared (FTIR), X-Ray diffraction (XRD), field emission scanning electron microscope (FESEM), atomic force microscope (AFM), energy dispersive X-ray (EDX), Braunauer-Emmett-Teller (BET), and contact angle. The nanoparticle effect on the membrane properties was investigated by measuring the pure water flux and solute rejection under two constant pressures, at 6 and 10 bar, and the salts concentration of MgSO4, MgCl2, NaCl, and CaCl2 at 1 gL−1. The results showed that nanoparticles increased the hydrophilicity of the pristine PSf membrane while slightly decreasing the water permeability. Moreover, the salt rejection increased with the nanoparticle addition up to 0.2 wt.% while it decreased with 0.5 wt.% nanoparticle due to changing the membrane finger-like pores sublayer structure.

Underwater superoleophobic membrane with hydrophobic bump and hydrophilic sublayer structure for effective oil-in-water emulsions separation

Underwater superoleophobic membranes are competitive strategy for accomplishing efficient oil-in-water emulsions separation. However, permeating flux of water probably may be dropped with the reduction of pore size. Moreover, the plenty of oil phase may block pore canal resulting the decrease of separation performance. Herein, an underwater superoleophobic membrane with hydrophobic bump and hydrophilic sublayer structure was fabricated through spinning hexadecyltrimethoxysilane (HDTMS) modified SiO2 (H-SiO2) micro-particles on polydopamine (PDA) hydrophilized polyvinylidene fluoride (PVDF, PDP) membrane. Therefore, the sieving of hydrophilic PDP membrane sublayer and oil absorption-flotation of hydrophobic H-SiO2 bump are ongoing simultaneously in separation processes, thus effective decreasing oil fouling to break the trade-off effect between separation efficiency and permeation flux. Interestingly, the PDPS membrane not only could efficiently separate diverse emulsions involving low and high-viscosity oil/water emulsions, but also possessed excellent mechanical (200 times of bending test) and chemical (separation of oil-in-corrosive waster emulsions) stabilities. More importantly, the separation performance of PDP-H-SiO2 (PDPS) membrane with bump-sublayer structure is obviously superior to the single PDP membrane. The idea of rationally combing opposite wetting and bump-sublayer structures has certain significance towards the fabrication and development about oil/water separation materials.

Meta-Learning the Difference: Preparing Large Language Models for Efficient Adaptation

Abstract Large pretrained language models (PLMs) are often domain- or task-adapted via finetuning or prompting. Finetuning requires modifying all of the parameters and having enough data to avoid overfitting while prompting requires no training and few examples but limits performance. Instead, we prepare PLMs for data- and parameter-efficient adaptation by learning to learn the difference between general and adapted PLMs. This difference is expressed in terms of model weights and sublayer structure through our proposed dynamic low-rank reparameterization and learned architecture controller. Experiments on few-shot dialogue completion, low-resource abstractive summarization, and multi-domain language modeling show improvements in adaptation time and performance over direct finetuning or preparation via domain-adaptive pretraining. Ablations show our task-adaptive reparameterization (TARP) and model search (TAMS) components individually improve on other parameter-efficient transfer like adapters and structure-learning methods like learned sparsification.

Evidence that uniform momentum zones originate from roughness sublayer structure interactions in fully rough channel turbulence

Fully rough wall-sheared turbulence is composed of an inner and outer layer, the former occupied by sinuous structures sustained by the well-known autonomous inner cycle, the latter occupied by inclined parcels of momentum deviations relative to the average. The outer-layer structures are also known as uniform momentum zones (UMZs), where the presence of successive UMZs manifests instantaneously with a distinct ‘staircase’ pattern in streamwise velocity. Direct numerical simulation (DNS) of fully rough channel turbulence was recently used to interpret UMZs as wakes originating from antecedent bluff-body-like interactions within the inner layer (Anderson &amp; Salesky, J. Fluid Mech., vol. 906, 2020, A8). Wake-scaling arguments agreed precisely with instantaneous results from DNS. Foremost among these results was evidence that the instantaneous wall-normal gradient of streamwise velocity exhibited scaling of ${\sim }x_3^{-1/2}$ , where $x_3$ is wall-normal location; this is in contrast to logarithmic scaling, which requires the wall-normal gradient of streamwise velocity to scale as ${\sim }x_3^{-1}$ . Herein, wake-scaling arguments have been advanced and compared against results from wall-modelled large-eddy simulation (LES). New results from the ‘bottom up’ wake-scaling arguments agree with LES results, such that the shear associated with the instantaneous staircase-like streamwise velocity follows a clear trend. We have leveraged conditional sampling during LES – predicated upon instantaneous low-frequency, high-magnitude surface stress values known to correspond to large-scale inertial-layer coherence – to further assess the predictive value of the wake-scaling arguments. Model results compare favourably.

Facile fabrication of PVDF-CTFE microporous membranes with optimized surface and sublayer structure via non-solvent induced phase separation

Poly (vinylidene fluoride) (PVDF) has been widely implemented in fabricating membranes, but pure PVDF membrane need to be modified by blending or copolymerization to cope with its weak alkali resistance. In this work, the function of chlorotrifluoroethylene (CTFE) chain segment was studied, PVDF/ECTFE blending membranes and poly (vinylidene difluoride-co-chlorotrifluoroethylene) (PVDF-CTFE) membranes were prepared via non-solvent induced phase separation (NIPS) method. The effect of modification methods and solvents on the membrane morphology, micropore and physicochemical structure, permeability, ultrafiltration performance, anti-fouling property and alkali resistance were investigated systematically. More than that, the surface charge and roughness of membrane prepared by different solvents were determined in the varying environment to better understand the anti-fouling property. The result presented that the comprehensive properties of PVDF-CTFE copolymerization membrane were better than that of PVDF/ECTFE blending membrane. The microporous structure of PVDF-CTFE membrane surface and sublayer was optimized by adjusting the solvent. The effect of solvent on the rate of L-L de-mixing during phase inversion was investigated from thermodynamic and kinetic factors. The prepared PVDF-CTFE membrane using N-methylpyrrolidone (NMP) as solvent broke the trade-off between the permeability and selectivity, so it was simultaneously possessed superior pure water flux (306.5 L·m−2·h−1) and higher BSA rejection rate (98.4%). The combination of NMP and PVP significantly decreased the rate of phase inversion without changing the polymer content, and provided a simple and feasible improvement idea for non-solvent-induced phase separation. In addition, the PVDF-CTFE membranes possessed better alkali resistance compared to PVDF membranes, demonstrating its promising potential in harsh environment.

Enhancing oxygen transport in the ionomer film on platinum catalyst using ionic liquid additives

The O2 permeation barrier across the nanoscale ionomer films on electrocatalysts contributes to a major performance loss of proton exchange membrane (PEM) fuel cells under low Pt loading. Enhancing O2 transport through the ionomer films is essential for developing low Pt loading catalyst materials in high-performance PEM fuel cells. This study found that adding an ionic liquid (IL) can effectively mitigate the dense ionomer ultrathin sublayer formed on the Pt surface, which severely hinders O2 transport to the catalyst sites. The molecular dynamics simulation results show that adding the IL significantly alters the ionomer ultrathin sublayer structure by inhibiting its tight arrangement of perfluorosulfonic acid chains but scarcely impacts the ultrathin sublayer thickness. Additionally, the IL addition provides a larger free space for O2 dissolution in the ultrathin sublayer. Consequently, due to IL molecules’ presence, the O2 density in the ultrathin sublayer on the Pt surface is improved by an order of magnitude, which will benefit the catalytic efficiency, and the O2 permeation flux across the ionomer film is increased by up to 8 times, which will reduce the O2 transport loss of the catalyst layer.

Effect of polymer molecular weight on structure and performance of PVDF hollow fiber membranes prepared via TIPS process with co-extrusion of solvent using triple orifice spinneret

The co-extrusion of solvent at the outer layer of a dope solution in a thermally induced phase separation (TIPS) process has led to significant improvements in membrane characteristics, especially pure water permeability stability. This work investigates the effects of the poly (vinylidene fluoride) (PVDF) molecular weight and concentration on the characteristics of hollow fiber membranes prepared using this method. The PVDF molecular weight had little effect on the phase diagram of the PVDF/diphenyl carbonate (DPC) system, and effectively controlled the penetration depth and quantity of the extruded solvent (propylene carbonate (PC)) inside the polymer dope solution as well as the overall performance of the hollow fiber membranes. When the PVDF concentration was low, the PVDF molecular weight was crucial in controlling the penetration of the extruded solvent. For a PVDF/DPC system that led to the mainly bicontinuous structure which resulted from L-L phase separation, the penetration of the PC inside the membrane considerably changed the surface and sublayer structure from a bicontinuous structure with spherulite to a composite spherulite embedded in the bicontinuous structure and isolated spherulite structure. To obtain an appropriate membrane with considerable water permeability stability, it is necessary to choose an appropriate polymer molecular weight and concentration.

The effect of different solvents on the morphology and performance of the ZIF-8 modified PVDF ultrafiltration membranes

In this research, the PVDF-based nanocomposite membranes modified with ZIF-8 nanocrystals were prepared with various casting solvents containing, DMSO, NMP, DMF and DMAc. The SEM, EDX and AFM analyses were applied to study morphology, distribution of the ZIF-8 in the matrix of the polymer, and surface roughness characteristic of the mixed matrix membranes, respectively. The impact of the solvent type on the structure and filtration efficiency of the resulting membranes was studied by considering the thermodynamic and kinetic factors of the membrane formation. A significant correlation was found between the diffusion rates of the solvent/non-solvent and the sub-layer structure of the membranes. Membranes cast with DMAc and DMF solvents (with relatively high diffusion rates) presented a bigger number of the finger-like cavities with a smaller size compared with membranes prepared by DMSO and NMP with lower diffusion rates. Blending of the ZIF-8 nanoparticles within the membrane matrix with a proper concentration (up to 0.2 wt%) resulted in an increase in the size of the finger-like cavities, lead to increase in the permeability of the resulting membranes. With increasing the ZIF-8 content to 0.5 and 1 wt%, the finger-like pores turned to sponge-like pores. The pure water permeation of the unmodified membranes cast with DMSO, NMP, DMAc and DMF was 258.64, 179.52 156.65 and 10.52 L/m2h, respectively, which was in good agreement with the observed trend for porosity and surface hydrophilicity of the membranes.

Interfacial structure and formation mechanism of tungsten/steel HIP diffusion bonding joints using Ni interlayer

Tungsten and steel were successfully bonded using hot isostatic pressing (HIP) diffusion bonding with Ni interlayer. The influences of surface roughness, post-weld heat treatment (PWHT) and interlayer thickness on the properties of W/steel joint were researched, and the interfacial structure as well as the formation mechanism was investigated systematically. The results indicated that, the interfacial structure of the joint is steel/diffusion layer/reaction layer/W. The number of voids at the interface will be decreased greatly by reducing the roughness of the surfaces to be joined, which leads to the compactness of joints improving obviously. For the joints with thin (5-20μm) interlayers, after PWHT, the brittle reaction layer will further grow into W substrate and reduce the joint strength. While for those joints with thick (30-80μm) interlayers, PWHT is beneficial to increase the thickness of the helpful diffusion layer which shows the positive effect on the joint strength. A surprising result in this work is that, due to the different element concentration gradients, the structure of reaction layers is various with different interlayer thickness. With the very thin (≤20μm) interlayer, the reaction layer is a double-layer structure including W2Ni(Fe) layer and sublayer. When the thickness of the interlayer is 30μm, it is a W2Ni(Fe) single-layer structure. As the interlayer thickness increases to 50μm, the reaction layer shows a WNi and W2Ni double-layer structure. While when the interlayer thickness further increases to and above 80μm, it is a W2Ni and sublayer structure. Among the layers mentioned above, the sublayer close to W substrate is the decisive area to influence joint strength.

Effect of mixed diluents during thermally induced phase separation process on structures and performances of hollow fiber membranes prepared using triple-orifice spinneret

In this study, polyvinylidene fluoride hollow fiber membranes were prepared using a triple-orifice spinneret in thermally induced phase separation. A solvent, propylene carbonate (PC), was extruded through the outermost layer of the spinneret. Through the use of this method, all the membranes were developed an entirely porous surface with similar pore size and porosity. Using mixed diluents with different concentrations of diphenyl carbonate and PC, the membrane bulk structures were controlled from an entirely bicontinuous network, a combination of bicontinuous and spherulitic structures, to an entirely spherulitic structure. The tailored bulk structures showed significant effects on the permeability, rejection, and mechanical strength of the membrane. Furthermore, the membrane sub-layer structure was modified to form different types from the composite-like structure of the combination of the spherulites and bicontinuous network to entirely spherulites, which controlled the membrane permeation stability within an extensive range of 6% to nearly 100%. A change in the polymeric dope solution phase diagram, as well as the interfacial behaviors of the polymeric dope solution and extruded PC, played important roles in appropriately tailoring membrane structures and performances. These novel and solid findings regarding the connections between structures and performances provide an advisable venue for the design of hollow fiber membranes with satisfactory performances.

Advanced porous polyphenylsulfone membrane with ultrahigh chemical stability and selectivity for vanadium flow batteries

ABSTRACTPorous polyphenylsulfone (PPSU) membranes are facilely prepared via the nonsolvent‐induced phase separation method. The typical asymmetric structure of such prepared porous membranes can be controlled by optimizing the sulfonation degree of the sulfonated poly(ether ether ketone) to 84.7% in the casting solution. Scanning electron microscopy images show that the porous membrane comprises a thin dense top skin layer, a sublayer structure with distinct long finger‐like pores and the large pores in the substructure. The porous PPSU membrane was then used in vanadium flow battery (VFB). The optimized porous membrane yields an admirable performance, including excellent selectivity, chemical stability, and high columbic efficiency. Furthermore, the low cost of porous PPSU membranes indicates the promise of this technology for use in VFB applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47752.

A Comparative Study on the Application of Porous PES and PEI Hollow Fiber Membranes in Gas Humidifcation Process

Humidification process is one of the applications of membrane contactor in which partial pressure of a vapor in the gas stream increases. In this study, two different polyethersulfone and polyetherimide hollow fiber membranes were fabricated and characterized by various test methods and their performance in humidification process under different operating conditions was investigated. The PES membrane has more porous skin layer which its mean pore size and gas permeance are 191% and 566% more than PEI membrane, respectively but its porosity is lower that can be related to its more spongelike structure and higher concentration of the polymer at the cloud point. On the other hand, the water vapor flux of PEI membrane is higher than PES membrane that can be related to the difference in the sublayer structure of the membranes which causes water vapor to condense along the pores of the membrane. Furthermore, the difference in water vapor fluxes between PEI and PES membrane increases as the operating pressure/liquid temperature increases that may be related to the intensification of pore condensation phenomenon. The results of this research show that the structure of membrane sublayer has critical effect on the vapor flux in the humidification process.

Impact of Cross-Linked Chitosan Sublayer Structure on the Performance of TFC FO PAN Nanofiber Membranes.

Polyacrylonitrile (PAN) is a popular material in membrane field because of its excellent mechanical property, thermal stability, and chemical resistance. Unfortunately, PAN nanofibers produced by electrospinning are not suitable for interfacial polymerization process directly due to its hydrophobicity and large average pore size. In this work, the cross-linked chitosan (CS) solution was coated on the nanofiber surface to fabricate a sublayer, based on which thin-film composite (TFC) membranes were prepared using m-phenylenediamine and 1,3,5-trimesoyl chloride as the monomers. The impact of the different sublayers on the performances of TFC PAN nanofiber membranes for forward osmosis (FO) was studied by varying cross-linked CS concentrations. The results indicated that the increased CS concentration not only led to the relatively denser polyamide layer, but also changed its morphology. In the reverse osmosis process, NaCl rejection increased from 46.5 to 83.5%. Salt flux from feed solution to draw solution decreased from 25.8 to 8.9 g·m–2·h–1 (0.1 M NaCl solution as feed, 2 M glucose solution as draw solution, FO mode). This study found that the sublayer had noteworthy impact on the separation layer and helped us to pave the way to design high-performance FO membranes.

Metal-Based Graphical SiO₂/Ag/ZnS/Ag Hetero-Structure for Visible-Infrared Compatible Camouflage.

A brand-new approach to realizing visible-infrared compatible camouflage is proposed based on a metal-based graphical hetero-structure (MGHS) SiO2/Ag/ZnS/Ag. For different thicknesses (20, 40, and 60 nm) of color-controlling sub-layer, high-contract and large-span structure colors (yellow, navy, and cyan) were observed due to reintroducing constructive interference with a matching intensity of reflected waves. Ultra-low infrared emissivity values of 0.04, 0.05, and 0.04 (with high average reflectance values of 95.46%, 95.31%, and 95.09%) were obtained at 3–14 μm. In addition, the well-performing trisecting-circle structure further indicates that it is feasible to design on-demand compatible camouflage patterns using the easily-prepared MGHS.

INFLUENCE OF COPPER SUBLAYER ON NUCLEATION OF DIAMOND CRYSTALS ON SURFACE OF TUNGSTEN CARBIDE

The buffer copper sublayer on the surface of tungsten carbide was obtained with the chemical deposition from aqeous solutions. With the using the methods of SEM, AFM, XRF it was established that at temperature of 23 °C the layer structure is porous that do not observed at negative temperatures. The sublayer structure influences the character of nucleation of diamond crystals and their form. The phase composition was determined with Raman spectroscopy. The spectrum shows the lines of diamond (1334 cm-1), sp2 of carbon and trans-polyacetylene (1170 сm-1).

Self‐Consistent Modeling of Electron Precipitation and Responses in the Ionosphere: Application to Low‐Altitude Energization During Substorms

AbstractWe report a new modeling capability that self‐consistently couples physics‐based magnetospheric electron precipitation with its impact on the ionosphere. Specifically, the ring current model RAM‐SCBE is two‐way coupled to an ionospheric electron transport model GLOW (GLobal airglOW), representing a significant improvement over previous models, in which the ionosphere is either treated as a 2‐D spherical boundary of the magnetosphere or is driven by empirical precipitation models that are incapable of capturing small‐scale, transient variations. The new model enables us to study the impact of substorm‐associated, spectrum‐resolved electron precipitation on the 3‐D ionosphere. We found that after each substorm injection, a high‐energy tail of precipitation is produced in the dawn sector outside the plasmapause, by energetic electrons (10 &lt; E &lt; 100 keV) scattered by whistler‐mode chorus waves. Consequently, an ionospheric sublayer characterized by enhanced Pedersen conductivity arises at unusually low altitude (∼85 km), with its latitudinal width of ∼5–10° in the auroral zone. The sublayer structure appears intermittently, in correlation with recurrent substorm injections. It propagates eastward from the nightside to the dayside in the same drift direction of source electrons injected from the plasma sheet, resulting in global impact within the ionosphere. This study demonstrates the model's capability of revealing complex cross‐scale interactions in the geospace environment.

Stability of the platinum electrode during high temperature annealing

The modifications of the structure, electrical resistivity and surface morphology of platinum thin films on Pt/Ti/Si and Pt/TiO2/boron-phosphor-silicate glass/Si structures resulted from high-temperature annealing in the presence of oxygen were studied. It was established that regardless of the sublayers used while annealing caused platinum to recrystallize and texturize in the direction [111], and the texture is suppressed in the directions [200] and [220]. The annealing caused the drop of the volume resistivity of thin films from 0.2 to ca. 0.15 μOhm×m, and practically shown no dependence on the film thickness in case it exceeded 200 nm.As a result of recrystallization Pt films became unsmooth at low annealing temperatures and as the temperature increased hillocks were formed on the film surface. Relaxation of the compressive stress in the Pt film, facilitating the reduction of its free energy and modification of the lattice parameter towards the equilibrium value, is known to be the major hillock formation mechanism. The level of intrinsic stress in the film and the annealing temperature both determine the initial hillock formation. The final hillock height, density, and size are related to the Pt layer thickness, sublayer structure, and to the annealing time and temperature. Optimization of the sublayer structure and annealing modes makes it possible to increase the annealing temperature to ca. 780°С without causing any substantial damages to Pt microrelief. That enables us to use these structures as the bottom electrode in ferroelectric memory cells.

High-performance reverse osmosis membranes fabricated on highly porous microstructured supports

Increasing the surface porosity of a support membrane has been proposed as an effective way to improve the water permeability of thin-film composite (TFC) reverse osmosis (RO) membranes by reducing the diffusion pathway in the active layer. In this work, we prepared a highly porous microstructured (HPμS) support membrane with a suitable mechanical strength to enhance the water permeability of an RO membrane. The HPμS support membrane was prepared by increasing the thermodynamic instability of a 10 wt% polymer solution and thereby facilitating rapid desolvation. The rapid desolvation formed the narrow and regularly arranged pore structure in the sublayer, and we proposed the mechanism for the sublayer structure formation based on analyses of the thermodynamic properties of such a binary system. Owing to the narrow and regular structure, the HPμS support membranes showed the exceptional mechanical strength, which was comparable to the strength of support membranes used for conventional RO membranes. Also, the HPμS support membranes successfully endowed an in-house RO membrane with the performance (water permeability of 4.68 L m−2 h−1 bar−1 and NaCl rejection of 98.3%) surpassing commercial RO membranes and thin-film nanocomposite membranes recently reported in the literature.