Ultrathin Layer Research Articles

Air Corrosion of Layered Cathode Materials for Sodium-Ion Batteries: Cation Mixing and a Practical Suppression Strategy

Air Corrosion of Layered Cathode Materials for Sodium-Ion Batteries: Cation Mixing and a Practical Suppression Strategy

MXene/COFs membrane with sandwich structure for rapid salt/dye separation by layer-by-layer electrophoretic deposition

Covalent organic frameworks (COFs) have evolved into a transformative category of nanofiltration materials due to their intrinsic pore channels and high porosity, sparking a burgeoning interest in fully harnessing the potential of COFs for applications in nanofiltration. Herein, a sandwich structured MXene/COFs membrane was fabricated by the technique of layer-by-layer electrophoretic deposition (LBL EPD), with COFs nanospheres (COFs NPs) serving as the intermediate layer. During the EPD process, controlling the deposition time allows for convenient regulation of each layer's thickness, enabling rapid production of defect-free MXene/COFs membranes. The ultra-thin MXene layer offers excellent film-forming properties for COFs NPs, whereas the intermediate layer of COFs NPs plays a primary sieving function. Moreover, the pore-rich COFs NPs, the ultra-thin MXene layer, and the COFs NPs layer with abundant slits guarantee short and successive mass transport pathways. Under optimal conditions, the MXene/COFs membrane provided a permeance as high as 200.2 L‧m−2‧h−1‧bar−1 and a rejection rate of Congo red (CR) as high as 98.9 %. This exceptional performance holds steadfast even within pH ranges of 7–11 and during long-term operation. Meanwhile, MXene/COFs membranes exhibit commendable salt/dye separation performance, achieving an excellent separation factor of 121.1 for NaCl/CR. Moreover, the membrane's exceptional robustness and mechanical strength further facilitate its stable utilization under high transmembrane pressure (1–5 bar). To summarize, MXene/COFs membranes, characterized by their excellent nanofiltration and salt/dye separation performance, highlight the advantages of COFs within the nanofiltration field. This study introduces an innovative alternative approach to designing COFs membranes for highly efficient and high-precision molecular separations.

Sensitivity of a Process for Heating Thin Metal Film Described by the Dual-Phase Lag Equation with Temperature-Dependent Thermophysical Parameters to Perturbations of Lag Times

In the paper, an equation with two delay times (dual-phase lag Equation (DPLE)) in a version that takes into account the dependence of thermophysical parameters (volumetric specific heat and thermal conductivity) on temperature is considered. In particular, an analysis of the sensitivity of transient temperature field in relation to disturbances in delay times (the relaxation and thermalization times) is performed. The sensitivity model concerns the process of heating an ultrathin metal layer with a laser beam. First, the equation with two delay times in the case of temperature-dependent thermophysical parameters is presented. Next, the sensitivity equations with respect to delay times are derived using the direct method. The algorithms for solving the basic and sensitivity tasks are also briefly presented. At the stage of computations, an authorial program based on the implicit scheme of a finite-difference method is developed. In the final part of the paper, examples of numerical solutions (for layers made from gold and nickel) are presented. The research conducted here shows that disturbances in the temperature field are clearly visible and depend, on the one hand, on the thermophysical parameters of the material, and on the other hand, on the intensity of heating with an external heat source.

Progress in Research on White Organic Light-Emitting Diodes Based on Ultrathin Emitting Layers

White organic light-emitting diodes (WOLEDs) hold vast prospects in the fields of next-generation displays and solid-state lighting. Ultrathin emitting layers (UEMLs) have become a research hotspot because of their unique advantage. On the basis of simplifying the device structure and preparation process, they can achieve electroluminescent performance comparable to that of doped devices. In this review, we first discuss the working principles and advantages of WOLEDs based on UEML architecture, which can achieve low cost and more flexibility by simplifying the device structure and preparation process. Subsequently, the successful applications of doping and non-doping technologies in fluorescent, phosphorescent, and hybrid WOLEDs combined with UEMLs are discussed, and the operation mechanisms of these WOLEDs are emphasized briefly. We firmly believe that this article will bring new hope for the development of UEML-based WOLEDs in the future.

An MgO passivation layer and hydrotalcite derived spinel Co2AlO4 synergically promote photoelectrochemical water oxidation conducted using BiVO4-based photoanodes.

MxCo3-xO4 co-catalysed photoanodes with high potential for improvement in PEC water-oxidizing properties are reported. However, it is difficult to control the recombination of photogenerated carriers at the interface between the catalyst and cocatalyst. Here, an ultra-thin MgO passivation layer was introduced into the MxCo3-xO4/BiVO4 coupling system to construct a ternary composite photoanode Co2AlO4/MgO/BiVO4. The photocurrent density of the electrode is 3.52 mA cm-2, which is 3.2 times that of BiVO4 (at 1.23 V vs. RHE). The photocurrent is practically increased by 0.86 mA cm-2 and 1.56 mA cm-2 in comparison with that of Co2AlO4/BiVO4 and MgO/BiVO4 electrodes, respectively. Meanwhile, the Co2AlO4/MgO/BiVO4 electrode has the highest charge separation efficiency, the lowest charge transfer resistance (Rct) and best stability. The excellent PEC performance could be attributed to the inhibitive effect provided by the MgO passivation layer that efficaciously suppresses the electron-hole recombination at the interface and drives the hole transfer outward, which is induced by Co2AlO4 to capture the electrode/electrolyte interface for efficient water oxidation reaction. In order to understand the origin of this improvement, first-principles calculations with density functional theory (DFT) were performed. The theoretical investigation converges to our experimental results. This work proposes a novel idea for restraining the recombination of photogenerated carriers between interfaces and the rational design of efficient photoanodes.

Influence of Silsesquioxane-Containing Ultra-Thin Polymer Films on Metal Oxide Gas Sensor Performance for the Tunable Detection of Biomarkers

Influence of Silsesquioxane-Containing Ultra-Thin Polymer Films on Metal Oxide Gas Sensor Performance for the Tunable Detection of Biomarkers

Numerical simulation of a highly efficient perovskite solar cell based on FeSi2 photoactive layer

AbstractThe primary aim of this work is to investigate the use iron di‐silicide (FeSi2) as a photoactive layer in order to achieve superior performance in the solar cell architecture—ITO/TiO2/FeSi2/CuSCN/Ni. The optimum thickness of the absorber layer was found to be 1000 nm, which gave optimal properties of the proposed cell—a short‐circuit current density (Jsc) of 51.41 mAm−2, an open‐circuit voltage (Voc) of 0.93 V, a fill factor (FF) of 77.99%, and power conversion efficiency (PCE) of 37.17%. The introduction of an ultrathin interfacial layer between the electron transport layer (ETL), the perovskite interface, and the hole transport layer (HTL) enhanced the electrical output of the proposed solar cell. The Jsc increased to 51.86 mAcm−2, Voc rose to 0.97 V, while FF and PCE increased to 82.86% and 41.84%, respectively. Accordingly, the proposed cell architecture is promising and can be introduced into the manufacturing workflow for commercial applications. Moreover, because of its exceptional photon absorption capabilities, FeSi2 is a potentially excellent photoactive material for solar cell fabrication. The detailed findings of this study have therefore indicated that high‐performance FeSi2‐based solar can be achieved in future.

One-step preparation of large-size 1.5-μm-thick robust YSZ electrolyte for high CH4 conversion SOFCs at 600 °C

Ultrathin electrolytes can lower the operating temperature of yttria-stabilized zirconia (YSZ)-based solid oxide fuel cells (SOFCs) to below 600 °C, accelerating their commercialization. However, current technologies for fabricating robust electrolytes with large areas and a thickness of a few microns for SOFCs suffer from substantial practical limitations, including high manufacturing costs, intricate technical demands, and multistep fabrication processes. This study introduces a low-cost, high-yield, and facile one-step phase inversion technology to fabricate large-area and shape-variable ultrathin YSZ electrolyte-based SOFCs (disc diameter >12 cm and area of 10 cm × 10 cm). An integrated form of SOFCs with dendritic YSZ microchannels supporting a 1.5-μm-thick dense YSZ thin film was fabricated. The ultrathin electrolyte layer lowered ohmic and polarization losses, enhancing SOFC electrochemical performance. The integrated anode/electrolyte structure overcame the interfacial thermal mismatch, resulting in more than 210 h of long-term stability even with cells operating in rapidly changing environments. The single cell also exhibited a high CH4 conversion efficiency (55%), which was attributed to the fast gas diffusion and excellent catalytic activity within the integrated anode. In addition, our 4 cm × 4 cm flat SOFCs exhibited a high power output (5.1 W) at 600 °C, paving the way for the mass production of ultrathin and robust YSZ electrolytes.

Short-Wave Infrared Colloidal QD Photodetector with Nanosecond Response Times Enabled by Ultrathin Absorber Layers.

Ultrafast short-wavelength infrared (SWIR) photodetection is of great interest for emerging automated vision and spatial mapping technologies. Colloidal quantum dots (QDs) stand out for SWIR photodetection compared to epitaxial (In,Ga)As or (Hg,Cd)Te semiconductors by their combining a size-tunable bandgap and a suitability for cost-effective, solution-based processing. However, achieving ultrafast, nanosecond-level response time has remained an outstanding challenge for QD-based SWIR photodiodes (QDPDs). Here, record 4ns response time in PbS-based QDPDs that operate at SWIR wavelengths is reported, a result reaching the requirement of SWIR light detection and ranging based on colloidal QDs. These ultrafast QDPDs combine a thin active layer to reduce the carrier transport time and a small area to inhibit slow capacitive discharging. By implementing a concentration gradient ligand exchange method, high-quality p-n junctions are fabricated in these ultrathin QDPDs. Moreover, these ultrathin QDPDs attain an external quantum efficiency of 42% at 1330nm, due to a 2.5-fold enhanced light absorption through the formation of a Fabry-Perot cavity within the QDPD and the highly efficient extraction (98%) of photogenerated charge carriers. Based on these results, it is estimated that a further increase of the charge-carrier mobility can lead to PbS QDPDs with sub-nanosecond response time.

Assessing the effects and impacts of the CdSTe interlayer in the performance of the CdTe-CdS thin film solar cells through simulations

CdTe based solar cells have proved to be the most successful thin film PV solar cells with their full industrial production. However, the needed improvement in output efficiency of these cells is constrained by major issues such the poor understanding of the ternary CdSxTe1-x interlayer, formed at the CdS-CdTe interface. While it is believed to have both beneficial and negative effects on the cell performance, its exact mechanism and extent are not fully explored. In this work, the AMPS-1D software was used to model this interlayer, using several of its variables such as thickness, bandgap as well as the thickness of the bounding CdS layer. Results show that the interlayer thickness reduces cell performance, through Jsc, Voc, FF and J-V curves, with best efficiencies of 17.892% (Jsc=27.043mA/cm3, Voc=0.871V, FF=0.8) obtained at zero thickness, falling down by nearly 20% at CdSxT1-x thickness of 100nm. As the bandgap is varied, maximum cell performance of 17.85% (Jsc=27.76, Voc=0.91V and FF=0.81) was found at 1.7eV. Similarly, increasing CdS thickness also reduced cell performance, by reducing the quantum efficiency. The results indicate that if the CdSxTe1-x layer has a thickness of up to 100nm, and a bandgap of around 1.7eV, then cell efficiencies of around 18% were feasible even for ultra-thin CdTe layers of 1μm.

Ultra-thin wideband frequency tunable metamaterial absorber and its application for antenna radar cross section reduction

Abstract A metamaterial absorber (MMA) with broadband and efficient absorption performance based on ultra-thin dielectric layer is proposed. In this unique configuration, the absorption frequency of the MMA can be continuously and dynamically tuned across a wide frequency range by manipulating the reverse voltage of the central varactor diode. From both the equivalent circuit and field distribution perspectives, we analyze the mechanisms behind broadband tuning and superior absorption. Simulation and experimental results demonstrate that the absorption peak of MMA can be continuously tuned over a range of 5.16-8.16 GHz, with the absorption rate consistently exceeding 90%, and the thickness is only 0.5 mm. Integrating MMA array with a microstrip patch antenna in a suitable manner can dynamically mitigates the radar cross section (RCS) within the associated frequency range, with virtually negligible impact on the antenna's radiation performance.

Enhanced electrocatalytic CO2 reduction through constructing chemically homogeneous interfaces via ultrathin carbon encapsulated tin oxide

Electrocatalytic CO2 reduction to high-value chemicals has significant potential to combat environmental and energy crises. The strength and mode of adsorption of reaction species play a crucial role in determining the CO2 reduction products. Therefore, it is vital to construct catalytic interfaces with high catalytic activity, selectivity and chemically homogeneous for efficient CO2 reduction. Herein, ultra-thin carbon layer encapsulated sub-5 nm SnO2 quantum dots (SnO2@u-C) has been prepared by Sn-MOFs derivation for efficient electrocatalytic CO2 reduction. Specifically, the Faradaic efficiency of formate (FEformate) and energy efficiency of formate production (EEformate) exceed 80% and 50% respectively, over a wide potential range, with the highest value reaching 95.7% for FEformate and 58.2% for EEformate. Moreover, SnO2@u-C electrode shows excellent stability over 10h with FEformate about 89% at −1.17V versus reversible hydrogen electrode. DFT calculations and experimental characterization reveal that the ultrathin carbon layer coating on the surface of SnO2 forms a chemically homogeneous catalytic interface, facilitating the adsorption and conversion of reaction species to achieve exceptional formate selectivity. Moreover, the carbon layer builds a three-dimensional rapid electron conduction network that supports electron transfer to CO2 molecules and suppressing SnO2 reduction.

Enhancing ferroelectricity in HfAlOx-based ferroelectric tunnel junctions: A comparative study of MFS and MFIS structures with ultrathin interfacial layers

This study explores the potential advantages of metal–ferroelectric–insulator–semiconductor (MFIS) structures compared with established metal–ferroelectric–semiconductor (MFS) and metal–ferroelectric–metal structures in the context of nonvolatile memory devices. Despite the superior performance of MFS structures in terms of electric field maintenance, switching speed, and power consumption, the presence of interface-related issues between the ferroelectric material and the semiconductor may degrade device performance. We propose an MFIS structure incorporating ultrathin interfacial layers (ILs) of SiO2, HfO2, and ZrO2 to address these issues. These insulator layers enhance device endurance by reducing physical stress and trap density at the interface, thereby improving electrical performance and long-term stability. Moreover, the presence of an IL reduces charge leakage between the ferroelectric layer and semiconductor, contributing to the resolution of the sneak path current problem. An additional feature of MFIS devices is their self-rectifying behavior, simplifying circuit design and manufacturing processes by eliminating the need for an external rectification circuit, consequently reducing costs. Through a series of experiments, this study evaluates the performance of the MFIS structure, investigates the ferroelectric properties of HfAlOx-based FTJs, and examines the conduction mechanism of the MFIS structure. By comparing the o-phase of MFS, SiO2, HfO2, and ZrO2 devices via grazing incidence X-ray diffraction (GIXRD) and using the positive-up-negative-down method to extract polarization and coercive voltage, we provide a comprehensive investigation of the impact of ultrathin ILs on ferroelectric properties. This research aims to offer valuable insights into the advancement of memory device technologies, presenting the MFIS structure as a promising platform for next-generation memory technologies. Further sections will elaborate on the experimental setup, methodology, and detailed study findings.

Ultra-thin layer HTaMoO6 catalyst for the upgrading of carbohydrates into 5-hydroxymethylfurfural

The conversion of carbohydrates into 5-hydroxymethylfurfural (HMF), a vital and valuable platform chemical, is sought after in industrial applications but poses significant challenges. In this research, we engineered an ultra-thin layer HTaMoO6 catalyst using ball-milling/liquid-exfoliation technique, demonstrating its efficiency in catalyzing the transformation of carbohydrates to HMF. In contrast to the conventional method utilizing tetra(n-butylammonium) hydroxide as the intercalation agent, the ball-milling/liquid-exfoliation technique not only reduces catalyst preparation time (within 12 h) but also enhances the efficient intercalation, leading to the formation of an ultra-thin layer structure. The resulting catalyst exhibits high total acidity, a favorable Brønsted/Lewis acid ratio, and improved accessibility of active sites due to the thin layer structure post-exfoliation. Compared with bulk LiTaMoO6, the ultrathin layer HTaMoO6 catalyst enables complete fructose dehydration with an HMF yield reaching 89.1 % under moderate reaction conditions (120 °C, 1 h) and 47.2 % yield of HMF is obtained from sucrose at 130 °C. This work provides a new method to fabricate the solid acid for the transformation of carbohydrates.

Enhancement in electrical properties of dual-active-layer amorphous SiZnSnO/SiInZnO thin film transistors

Bi-layer thin film transistors (TFTs) have been fabricated with a channel structure comprising a dielectric layer, a semiconducting amorphous-Si-In-Zn-O (a-SIZO) layer, and a semiconducting amorphous-Si-Zn-Sn-O (a-SZTO) layer, aiming to improve field effect mobility and stability. These films were deposited using RF sputtering at room temperature. The TFTs with a bottom gate top contact, processed at 500 °C, exhibited high mobilities (>32 cm2V−1s−1) along with a current on/off ratio of approximately 108 and a subthreshold swing (SS) value below 0.5 V decade−1 primarily because of reduced trap density and presence of highly conducting ultrathin a-SIZO layer. Furthermore, the bi-layer TFTs demonstrated notable stability under negative and positive bias temperature stress conditions.

Construction of PDMS@ZIF-8 composite membrane on PVDF hollow fiber inner surface for ultrafast ethanol/water separation

Construction of ultra-thin and defect-free separation membrane on inner surface of hollow fiber supports is significant but challenging for molecular separation. In this study, the highly permeable PDMS@ZIF-8/PVDF composite membranes were successfully fabricated upon the inner-surface of polyvinylidene fluoride (PVDF) hollow fiber membrane for pervaporation (PV) ethanol/water separation. The efficient preparation of hierarchical PDMS@ZIF-8/PVDF composite membranes benefited from the precise regulation of ZIF-8 layer through interfacial synthesis and sequential coating of PDMS matrix. The thickness of the PDMS layer was only 16±2 nm, which admirably eliminated the non-selective defects in ZIF-8 layer. Owning to the optimal combination of MOF layer and ultra-thin polymer layer, the as-prepared membrane exhibited the excellent ethanol flux of 1.34 kg m-2 h-1 with an ethanol concentration in permeate of 31.3 wt.% for separating 5 wt.% ethanol aqueous solution at 40°C. The separation performance of the resultant membrane was superior to that of the other ethanol selective PV membranes. These findings herein provided a new way for preparing high-performance hollow fiber composite membranes for PV separation.

Unveiling Enhanced PEC Water Oxidation: Morphology Tuning and Interfacial Phase Change in α-Fe2O3@K-OMS-2 Branched Core-Shell Nanoarrays.

A simple fabrication method that involves two steps of hydrothermal reaction has been demonstrated for the growth of α-Fe2O3@K-OMS-2 branched core-shell nanoarrays. Different reactant concentrations in the shell-forming step led to different morphologies in the resultant composites, denoted as 0.25 OC, 0.5 OC, and 1.0 OC. Both 0.25 OC and 0.5 OC formed perfect branched core-shell structures, with 0.5 OC possessing longer branches, which were observed by SEM and TEM. The core K-OMS-2 and shell α-Fe2O3 were confirmed by grazing incidence X-ray diffraction (GIXRD), EDS mapping, and atomic alignment from high-resolution STEM images. Further investigation with high-resolution HAADF-STEM, EELS, and XPS indicated the existence of an ultrathin layer of Mn3O4 sandwiched at the interface. All composite materials offered greatly enhanced photocurrent density at 1.23 VRHE, compared to the pristine Fe2O3 photoanode (0.33 mA/cm2), and sample 0.5 OC showed the highest photocurrent density of 2.81 mA/cm2. Photoelectrochemical (PEC) performance was evaluated for the samples by conducting linear sweep voltammetry (LSV), applied bias photo-to-current efficiency (ABPE), electrochemical impedance spectroscopy (EIS), incident-photo-to-current efficiency (IPCE), transient photocurrent responses, and stability tests. The charge separation and transfer efficiencies, together with the electrochemically active surface area, were also investigated. The significant enhancement in sample 0.5 OC is ascribed to the synergetic effect brought by the longer branches in the core-shell structure, the conductive K-OMS-2 core, and the formation of the Mn3O4 thin layer formed between the core and shell.

Ultrathin layer TAFC on BiVO4 with ligand-to-metal charge transfer enhances built-in electric field for boosting photoelectrochemical water oxidation

To reveal the mechanism of charge transfer between interfaces of BiVO4-based heterogeneous materials in photoelectrochemical water splitting system, the cocatalyst was grown in situ using tannic acid (TA) as a ligand and Fe and Co ions as metal centers (TAFC), and then uniformly and ultra-thinly coated on BiVO4 to form photoanodes. The results show that the BiVO4/TAFC achieves a superior photocurrent density (4.97 mA cm−2 at 1.23 VRHE). The charge separation and charge injection efficiencies were also significantly higher, 82.0 % and 78.9 %, respectively. From XPS, UPS, KPFM, and density functional theory calculations, Ligand-to-metal charge transfer (LMCT) acts as an electron transport highway in TAFC ultrathin layer to promote the concentration of electrons towards metal center, leading to an increase in the work function, which enhances the built-in electric field and further improves the charge transport. This study demonstrated that the LMCT pathway on TA-metal complexes enhances the built-in electric field in BiVO4/TAFC to promote charge transport and thus enhance water oxidation, providing a new understanding of the performance improvement mechanism for the surface-modified composite photoanodes.

Enhanced stability in InSnO transistors via ultrathin in-situ AlOx passivation

In this study, we present the impact of an ultrathin in-situ AlOx passivation layer on the electrical performance and stability of InSnO (ITO) transistors. Devices incorporating an ultrathin (∼2 nm) AlOx passivation layer demonstrate satisfactory electrical performance and stability, characterized by a decent field-effect mobility, enhancement mode operation, notably reduced subthreshold swing, negligible hysteresis, and, notably, a significantly reduced threshold voltage shift under negative bias stress (NBS) and positive bias stress (PBS), respectively. The total trap density (Ntot), extracted through the sub-threshold slope, and the trap density (Nt), measured using low-frequency noise (LFN) for the AlOx-passivated ITO transistors, are significantly decreased. Those improvements can be attributed to the suppression of oxygen vacancy formation during the reactively-sputtered AlOx and subsequent annealing processes, as demonstrated by comparing the in-depth X-ray photoelectron spectroscopy (XPS) results of the AlOx-passivated and un-passivated ITO films. These results underscore the potential of in-situ reactively-sputtered ultrathin AlOx passivation layers to enhance the stability of thin-film transistors with In-rich channels.

Sub-5 nm ultrathin IGO film transistor printed by micro-doped InGa liquid alloy

In this study, we introduce a novel perspective that the formation of the atomically ultrathin oxide layer on the surface of liquid alloys is primarily governed by thermodynamic laws and is additionally influenced by the surface tension of the liquid alloys. In this case, we control the competition of Gibbs free energy and surface tension to effectively address the severe segregation problem of Ga2O3 and realize the precise doping of Ga2O3 in the preparation process of two dimensional IGO film through the liquid InGa alloy printing approach. Importantly, the Ga2O3 content in the IGO films can be tailored in the full range and a sub-5 nm ultrathin IGO film transistor is innovatively fabricated. The oxidation law, band gap, Fermi level, field-effect mobility, subthreshold swing, and other properties of IGO films in sub-5 nm scale are systemically investigated in detail. It has been demonstrated that the incorporation of Ga2O3 in the doping process dramatically reduced the device's turn-off current and enhanced its ability to resist ultraviolet interference. This novel doping process opens up a significant opportunity for future developments of atomically ultrathin transparent conducting film.