Uniform Al2O3 Research Articles

Effect of Al2O3 Passivation on Structured Si/PEDOT:PSS Hybrid Solar Cell

Recently, silicon/organic heterojunction solar cells (HSCs) attain great attention because of its attractive characteristics such as rationally high efficiency, low cost, and simple device fabrication technique. However, inferior junction conformity between structured Si and PEDOT: PSS still remains a great challenge. Here, a superior, conformal, and uniform Al2O3 thin layer is deposited on structured pyramid n-Si wafer to enhance the front junction conformity using atomic layer deposition (ALD) technique. The deposited Al2O3 thin layer provides better wettability of PEDOT:PSS compared to native oxide, which minimizes pores, and pin-hole density usually occurs in spin-coating process. Additionally, Al2O3 thin layer acts as an electron-blocking and hole-transporting layer, resulting in an effective charge separation as well as transport, which boosts the power conversion efficiency. The interface-modified device demonstrates a high open-circuit voltage of 0.612 V as well as a fill factor of 70.7%, leading to a stable efficiency of 14.3% for structural n-Si/PEDOT: PSS HSCs.

Al₂O₃‐Functionalized Carbon Nanomembranes with Enhanced Water Permeance and Selectivity for Efficient Air Dehumidification

AbstractPrecise control of pore size and surface properties is crucial for effective and efficient membrane separation, yet it remains challenging with conventional polymer‐based membranes. In this study, this gap is addressed by integrating atomic layer deposition (ALD) of Al2O3 with nanometer‐thin carbon nanomembranes (CNMs) to achieve ultra‐selective separation properties. Structural characterizations confirm uniform Al2O3 deposition and the preservation of the CNM structure. The ALD process allows for precise modulation of the nanopore structure. Despite the pore shrinkage upon ALD, the increased hydrophilicity offered by Al2O3 enhances water permeance, achieving an exceptionally high water vapor permeation rate of 1.9 × 10−5 mol · s−1 · m−2 · Pa−1 and a water vapor/nitrogen selectivity higher than 1 × 104, surpassing that of conventional polymer and graphene oxide‐based membranes. These results demonstrate the potential of Al2O3‐functionalized CNMs for advanced applications in gas separation and air dehumidification.

Low-loss and low-temperature Al2O3 thin films for integrated photonics and optical coatings

Amorphous aluminum oxide (Al2O3) is a key material in optical coatings due to its notable properties, including a broad transparency window (ultraviolet to mid-infrared) and excellent durability. Moreover, its higher refractive index contrast relative to silica cladding layers and high solubility of rare-earth ions make it well suited for optical waveguides and the development of various functionalities in integrated photonics. In many coatings and integrated photonics applications, the substrates are temperature and stress sensitive, while relatively thick (∼1 μm) alumina layers are required; thus, it is crucial to fabricate low optical loss alumina thin films at low deposition temperatures, while maintaining high deposition rates. In this study, plasma-assisted reactive magnetron sputtering, operated in an alternating current mode, is investigated as a reliable, straightforward, and wafer-scale compatible technique for the deposition of high optical quality and uniform Al2O3 thin films at low temperature. One-micrometer-thick amorphous Al2O3 planar waveguides, deposited at 150 °C and a rate of 23.3 nm/min, exhibit optical losses below 1 dB/cm at 638 nm and as low as 0.1 dB/cm in the conventional optical communication band.

Bilateral Production Shield Enabling Highly Efficient Perovskite Photovoltaics.

Enhancing the intrinsic stability of perovskite and through encapsulation to isolate water, oxygen, and UV-induced decomposition are currently common and most effective strategies in perovskite solar cells. Here, the atomic layer deposition process is employed to deposit a nanoscale (≈100nm), uniform, and dense Al2O3 film on the front side of perovskite devices, effectively isolating them from the erosion caused by water and oxygen in the humid air. Simultaneously, nanoscale (≈100nm) TiO2 films are also deposited on the glass surface to efficiently filter out the ultraviolet (UV) light in the light source, which induces degradation in perovskite. Ultimately, throughthe collaborative effects of both aspects, the stability of the devices is significantly improved under conditions of humid air and illumination. As a result, after storing the devices in ambient air for 1000h, the efficiency only declines to 95%, and even after 662h of UV exposure, the efficiency remains at 88%, far surpassing the performance of comparison devices. These results strongly indicate that the adopted Al2O3 and TiO2 thin films play a significant role in enhancing the stability of perovskite solar cells, demonstrating substantial potential for widespread industrial applications.

Characterization of Al2O3 coating of Nb fiber-reinforced TiAl composite

The Al2O3 coating was synthesized on surface of the Nb fiber via cathodic plasma electrolytic deposition (CPED) method. The microstructure and composition of the coating were elaborately analyzed. The results revealed that compact and uniform Al2O3 is fully contact with TiAl matrix and Nb fiber, which was composed of κ-Al2O3 and α-Al2O3 and successfully hold back the oxidation reactions at the juncture and refrain from formation of detrimental phases. Especially, three-dimensional characterization information can be obtained from two-dimensional converging beam electron diffraction (CBED) pattern, from which the crystal constants of Al2O3 can be obtained directly under only one applicable zone axis.

An innovative strategy towards highly efficient flame-retardant silk

As a luxurious textile raw material, silk fiber (SF) and its products are widely favored by consumers because of their elegant appearance and excellent comfort. However, their flammability causes potential fire risks and hazards in daily fires and has gained significant attention in recent years. In this work, an ultrathin and uniform TiO2, Al2O3, and ZnO nanofilms with thicknesses of 1 ∼ 200 nm (less than one in a hundred of SF diameter) were deposited on the surface of a silk fabric (SFR) by atomic layer deposition (ALD). By tuning the types of metal oxides and nanofilm thickness, the modified SFR quickly self-extinguished, and its pristine weave was completely preserved after exposure to a flame in a torch burn test, representing superior performance compared to numerous conventional coating technologies reported with higher loadings. An expanded charcoal residue formed on the surface of the modified SFR, acting as a physical barrier that enhanced flame retardancy. Furthermore, the modified SFR showed excellent laundering durability, which helps improve the service life of the fabric. Most importantly, the nanofilms had a negligible impact on the intrinsic comfort and other comprehensive properties of the silk.

Improved Performance of High‐Entropy Disordered Rocksalt Oxyfluoride Cathode by Atomic Layer Deposition Coating for Li‐Ion Batteries

Lithium‐excess cation‐disordered rocksalt materials are a promising class of transition metal‐based cathodes that exhibit high specific capacity and energy density. The exceptional performance is achieved through participation of anionic redox in addition to cationic redox reactions in the electrochemistry. However, anionic redox reactions accompanied by oxygen evolution, accelerated electrolyte breakdown, and structural evolution lead to voltage hysteresis and low initial Coulombic efficiency. Herein, an Al2O3 layer with varying thickness has been coated onto a high‐entropy disordered rocksalt oxyfluoride cathode through atomic layer deposition to enhance battery performance. The results indicate that the utilization of a uniform Al2O3 coating improves the capacity retention and rate capability of the cathode, with the performance being strongly dependent on the layer thickness. Further investigation into cathode–electrolyte interfacial reactions reveals that the thin protecting Al2O3 coating can reduce the decomposition of electrolyte on the cathode surface but cannot prevent bulk phase degradation during prolonged cycling. These findings highlight the need for optimized coating design on the disordered rocksalt cathode to improve battery performance.

Prolonging the Cycle Stability of Anion Redox P3-Type Na0.6Li0.2Mn0.8O2 through Al2O3 Atomic Layer Deposition Surface Modification.

Sodium-ion batteries (SIBs) are becoming an alternative option for large-scale energy storage systems owing to their low cost and abundance. The lattice oxygen redox (LOR), which has the potential to increase the reversible capacity of materials, has promoted the development of high-energy cathode materials in SIBs. However, the utilization of oxygen anion redox reactions usually results in harmful lattice oxygen release, which hastens structural deformation and declines electrochemical performance, severely hindering their practical application. Herein, a ribbon-ordered superstructured P3-type Na0.6Li0.2Mn0.8O2 (NLMO) cathode with a uniform Al2O3 coating through atomic layer deposition (ALD) was synthesized. The cycling stability and rate capability of the materials were improved by a proper thickness of the Al2O3 layer. Differential electrochemical mass spectrometry (DEMS) results clearly suggest that the Al2O3 coating can inhibit the CO2 release caused by the highly active surface of the NLMO material. Moreover, the results of transmission electron microscopy (TEM) and etching X-ray photoelectron spectroscopy (XPS) show that the Al2O3 coating can effectively prevent electrolyte and electrode side reactions and the dissolution of Mn. This surface engineering strategy sheds light on the way to prolong the cycling stability of anionic redox cathode materials.

Effect of Ge Contents on Oxidation Resistance of Ni‐15Cr‐5Al Alloy at 1000°C

A Ni‐15Cr‐5Al‐6Ge alloy was prepared using powder metallurgy technology. The effect of Ge on the oxidation resistance of Ni‐Cr‐Al alloy at 1000°C was investigated. The results indicate that the addition of Ge reduces the oxidation rate of the alloy interface in the range of 0 to 6 wt.% Ge. When the Ge content reaches 6 wt.%, a continuous and dense oxide film forms on the surface of the matrix, imparting the alloy with the best oxidation resistance. The addition of Ge improves the selective oxidation of Al and inhibits the diffusion rate of Ni and Cr elements to the alloy surface, resulting in the formation of a single, uniform Al2O3 oxide film on the alloy surface with a thickness of approximately 1.45 micrometers. An appropriate amount of Ge (6 wt.%) reduces surface defects, while an excessive amount of Ge (8 wt.%) increases surface defects, thereby adversely affecting the oxidation resistance of the alloy.

Al2O3 atomic layer deposition on a porous matrix of carbon fibers (FiberForm) for oxidation resistance

Atomic layer deposition (ALD) was used to coat a porous matrix of carbon fibers known as FiberForm with Al2O3 to improve oxidation resistance. Static trimethylaluminum (TMA) and H2O exposures for Al2O3 ALD were used to obtain the uniform coating of this high porosity material. The carbon surfaces were initially functionalized for Al2O3 ALD by exposure to sequential exposures of nitrogen dioxide and TMA. A gravimetric model was developed to predict the mass gain per cycle under conditions when the ALD reactions reached saturation during each reactant exposure. The uniformity of the Al2O3 ALD coating on FiberForm was confirmed by scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) analysis. The SEM, EDS, and gravimetric models were all consistent with a uniform Al2O3 ALD coating on the porous carbon fiber network when the ALD reactions reached saturation on the entire surface area. In contrast, the profile of the Al2O3 ALD coating on the FiberForm was also characterized using undersaturation conditions when the ALD reactions did not reach saturation throughout the FiberForm sample. Based on comparisons with results from models for ALD in porous substrates, these Al2O3 coverage profiles were consistent with diffusion-limited Al2O3 ALD. Oxidation of the FiberForm and the Al2O3 ALD-coated FiberForm was also investigated by thermogravimetric analysis (TGA). TGA revealed that a 50 nm thick Al2O3 coating deposited using 400 Al2O3 ALD cycles enhanced the oxidation resistance. The Al2O3 ALD coating increased the oxidation onset temperature by ∼200 °C from 500 to 700 °C. The oxidation of the FiberForm removed carbon and left the Al2O3 ALD coating behind as a white “skeleton” that preserved the shape of the original FiberForm sample. The Al2O3 ALD coating also decreased the oxidation rate of the FiberForm by ∼30%. The oxidation rate of the Al2O3 ALD-coated FiberForm samples was constant and independent of the thickness of the Al2O3 ALD coating. This behavior suggested that the oxidation is dependent on the competing O2 diffusion into the FiberForm and CO2 diffusion out of the FiberForm.

Stable and efficient As2O3 removal from simulated flue gas using Al2O3/CaSiO3 prepared by anhydrous grinding and calcination method

CaSiO3 exhibits good arsenic capture performance, but it falls short of meeting the actual needs of power plants due to its susceptibility to acidic gases that inhibit its arsenic capture ability. In this study, an Al2O3/CaSiO3 adsorbent was prepared by combining the anhydrous grinding and calcining methods. Arsenic vapor capture was conducted in flue gas containing or free of SO2 and HCl within the temperature range of 800–1000 ℃. The research indicated that the preparation method used in this study resulted in uniform Al2O3 doping that was less prone to agglomeration, thereby creating a good pore structure. The Al2O3/CaSiO3 adsorbent exhibited the strongest arsenic capture capacity when the atomic molar ratio of Al/Si was 1:5, with an arsenic capture amount of 871.2 mg/kg, which was significantly higher than the capture capacity of the control group calcium silicate. The doping of Al atoms altered the structure and charge distribution of CaSiO3 silica-oxygen chains, resulting in the formation of Al active sites with higher adsorption energy, which is more favorable for the adsorption of arsenic. Although the Al2O3/CaSiO3 adsorbent reacts with acidic gases to form CaSO4 and CaCl2, which can inhibit arsenic capture, it still maintains a high arsenic capture rate. Al2O3/CaSiO3 has excellent arsenic removal, sintering resistance, and acid resistance, making it a promising composite adsorption material for arsenic removal.

Hydrogen absorption and embrittlement of Zn-Al coated medium-Mn steel

In this study, we investigated the influence of the austenitizing condition on H absorption and hydrogen embrittlement (HE) in a Zn-Al coated medium-Mn steel. The specimen, which underwent austenitization at 750 °C for 5 min, demonstrated high resistance to HE due to its low diffusible H content. The presence of a uniform Al2O3 oxide layer and a low H diffusion rate contributed to this low H content. However, an increase in austenitizing temperature accelerated H absorption due to the enhanced diffusion rate of H atoms, resulting in decreased resistance to HE.

Production of Al2O3-SiC composites from micrometer α-Al2O3 powder obtained via sol-gel

Alumina (Al2O3) is an advanced ceramic material developed for different applications as refractories, precision tools, pacemaker, etc. Solid state sintering of alumina or matrix ceramic composites (CMCs) compacts starts from powders. Once method to produce high quality aluminum oxide powders is the sol-gel technique. Alumina begins as pseudo-crystallized aluminum hydroxide gel which is produced under moderate reaction conditions trough a colloidal suspension. In this work, Al2O3 powder was produced by precipitation of pseudoboehmite (PB) through sol-gel process. Subsequently, a mixture of Al2O3/SiC powders with 5 wt.% of SiC as reinforcement was produced. This mixture was used to manufacture green compacts by uniaxial pressing at 440 MPa. Afterward, some samples were applied a heat treatment (pre-sintered) at 1200°C for 6 h in air. Sintering was carried out in a vertical dilatometer Linseis L75 V up to 1500°C for 2h under argon atmosphere. Pseudobohemite, alumina powders and Al2O3/SiC composites were characterized through X-ray diffraction technique and Scanning Electron Microscopy (SEM). Dilatometric shrinkage data into densification curves obtained were analyzed. Images obtained with SEM showed a uniform Al2O3 powder morphology of submicron size, otherwise Al2O3/SiC composite images showed the interaction of the reinforcement particles on the ceramic matrix. Experimental results demonstrated the pre-sintering reduce the decomposition of SiC particles on the compact surface. This behavior was attributed to formation of SiO2 around the reinforcement particle due it act as protective barrier.

Systematic microstructure modification effect on nanomechanical, tribology, corrosion, and biomineralization behavior by optimized anodic alumina nanotubes coated Ti–6Al–4V alloy

Electrochemical anodization is a cost-effective surface modification method that has been used in recent years not only for creating protective layers but also for the fabrication of porosity in biomedical applications. This method allows for the optimized fabrication of self-ordered nanotubular or nanoporous oxide structures. In this study, the structural characteristics, mechanism, adhesion, scratch hardness, wettability, nanoindentation, wear resistance, corrosion behavior, and in-vitro bioactivity of aluminum/alumina (Al/Al2O3) nanotube coating on Ti–6Al–4V (Ti64) were systematically studied. As the primary layer, a thin layer of pure Al was sputtered onto a Ti64 substrate via physical vapor deposition. Consequently, a dense and uniform Al2O3 nanotubes layer was fabricated as the second layer by anodization in a 0.35 wt% NH4F electrolyte solution (90 ethylene glycol:10 water) at 60 V (constant potential) for various durations, followed by optimization of the sealing to remove the oxide layer and transform the nanoporous into nanotubes. Optimized anodizing, sealing, and annealing resulted in a homogeneous nanotube structure with a mean diameter of 85 nm and a length of 1.58 μm. Systematic improvements in the adhesion, scratch hardness, nanoindentation, and wettability were achieved in each modification process. The corrosion rate and the coefficient of friction also reached 0.7297 × 10−1 (mm year−1) and 0.208 (load of 10 N) after 1 h of anodization and 30 min sealing followed by annealing at 450 °C, respectively. When a thick apatite layer with the desired Ca/P ratio was created on the annealed Al2O3 nanotube structure, an excellent improvement in surface bioactivity was demonstrated.

Enhanced Magnetic Properties and Thermal Conductivity of FeSiCr Soft Magnetic Composite with Al2O3 Insulation Layer Prepared by Sol-Gel Process

FeSiCr soft magnetic composites (SMCs) were fabricated by the sol-gel method, and an Al2O3/resin composite layer was employed as the insulation coating. By the decomposition of boehmite (AlOOH) gel into Al2O3 in the temperature range of 606–707 °C, a uniform Al2O3 layer could be formed on the FeSiCr powder surface. The Al2O3 insulation coating not only effectively reduced the core loss, increased the resistivity, and improved the quality factor, but it also increased the thermal conductivity of SMCs. The best overall properties with saturation magnetization Ms = 188 emu/g, effective permeability μe = 39, resistivity ρ = 8.28 × 105 Ω·cm, quality factor Q = 94 at 1 MHz, and core loss = 1173 mW/cm3 at 200 kHz and 50 mT were obtained when the SMC was prepared with powders coated by 0.5 wt.% Al2O3 and resin. The optimized SMC exhibited the lowest core loss with 27% reduction compared to the resin only-insulated sample and 71% reduction compared to the sample without insulation treatment. Importantly, the thermal conductivity of the SMCs is 5.3 W/m·K at room temperature, which is higher than that of the samples prepared by phosphating and SiO2 coating owing to the presence of a high thermal conductive Al2O3 layer. The high thermal conductivity is beneficial to enhancing the high temperature performance, lifetime, and reliability of SMCs. This work is expected to be a valuable reference for the design and fabrication of SMCs to be applied in high-temperature and high-frequency environments.

The surface Al2O3 coating and bulk Zr doping drastically improve the voltage fade and cycling stability of Li(Ni0.8Mn0.1Co0.1)O2 cathode materials

One of the major hurdles of the high Ni content layered oxides (NLOs) in making lithium-ion batteries is their low cycling stability, especially for the NLOs with Ni content ≥ 60%; such NLOs have clear drawbacks including severely fading capacities and impedance increase during cycling. Two promising surface and bulk modifications of such NLOs to alleviate the drawbacks are: (1) the surface coatings by electrochemically inert inorganic compounds and/or (2) the lattice doping by cations. In this work, isopropanol alcoholysis has been used to achieve uniform surface Al2O3 coating on one of NLOs: LiNi0.8Co0.1Mn0.1O2 (NCM811). The bulk Zr4+ doping and surface Al2O3 coating have been realized after annealing at ≥ 800 °C, which enhance the specific capacity of discharge and cycling life of the NCM@Al2O3 +Zr active material, and effectively suppress the voltage attenuation during cycling process. The main finding of this work is the enhanced cycling stability and the diminished impedance of the coated/doped NCM811, being provided by a synergetic effect of the Al2O3 coating and the Zr4+ doping.

Tailoring the performance of the LiNi0.8Mn0.1Co0.1O2 cathode using Al2O3 and MoO3 artificial cathode electrolyte interphase (CEI) layers through plasma-enhanced atomic layer deposition (PEALD) coating.

The Ni-rich layered oxide cathode has shown high energy density, proper rate capability, and longevity of the rechargeable battery, while poor stability and capacity fading are assumed to be its common cons. To address this obstacle, prospective cathode materials are synthesized by integrating the lithium transition metal oxides with an artificial cathode electrolyte interphase (CEI) layer. Herein, plasma-enhanced atomic layer deposition (PEALD) is employed to coat the LiNi0.8Mn0.1Co0.1O2 (NMC811) electrode with Al2O3 and MoO3. The combined results from morphological examinations revealed the formation of uniform Al2O3 and MoO3 sheets after 200 cycles of PEALD coating. Consistent results from the XRD analysis demonstrate that Al2O3 and MoO3 artificial CEIs can reduce Li-Ni mixing. The cyclic voltammetry tests show the oxidation-reduction kinetic. The modified NMC811 structures with Al2O3 and MoO3 represent a remarkable improvement in terms of capacity retention. The coated cathode with Al2O3 clearly outperforms the modified configuration with MoO3 concerning ionic conductivity, charge/discharge reversibility, and capacity retention. The promising results obtained in this study open the possibility of synthesizing Ni-rich cathodes with enhanced electrochemical performance.

Evolution of coating layers during high-temperature annealing and their effects on magnetic behavior of Fe(Si) soft magnetic composites

Low-loss Fe(Si) soft magnetic composites (SMCs) with atomic-layer-deposition coated layer were successfully prepared in this work. The continuous, compact and uniform Al2O3 layer is found to form tight bonding with the powder base. Evolution of the coating layers has been investigated under different annealing temperatures and closely linked to the magnetic performance of the composites. Results indicate that 1100 °C was the optimal annealing temperature, at which the Fe(Si) SMCs showed lowest core loss of 1237 mW/cm3 and the highest permeability of 99.7 simultaneously (100 mT/100 kHz). Integrity of the coating layer ensures the maximum grain growth and stress removal of powder particles at the highest possible temperature, so as to reduce the hysteresis loss. Formation of high resistivity oxides and silicates (Al2O3, Fe2SiO4 and 3Al2O3·SiO2) after annealing result in a low inter-particle eddy current loss. Besides, high temperature vacuum annealing is helpful to eliminate impurity atoms and decrease the anomalous eddy current loss. The improvement in effective permeability caused by high-temperature annealing is mainly attributed to the relaxation of residual stresses and the reduction of defects. While excessive temperature leads to the decomposition and destruction of the insulation layer, resulting in a significant increase in hysteresis loss, inter-particle and anomalous eddy current loss.

High temperature oxidation enhanced by laser remelted of CoCrFeNiAlx (x = 0.1, 0.5 and 1) high-entropy alloys

In order to further improve the oxidation resistance of CoCrFeNiAlx (x = 0.1, 0.5, and 1) high entropy alloys (HEAs), the surface of CoCrFeNiAlx prepared by vacuum arc melting is controlled by laser surface remelting (LSM) and the high-temperature oxidation properties of CoCrFeNiAlx before and after LSM is systematically studied. The results revealed that, with the increase of Al content, the parabolic velocity constant kp value gradually decreased after LSM treatment. Moreover, CoCrFeNiAl0.1 formed a continuous Cr2O3 oxide layer, CoCrFeNiAl0.5 formed an outer layer of Cr2O3 oxide film and an inner layer of Al2O3 precipitation, and CoCrFeNiAl1 formed a uniform and dense Al2O3 oxide layer on the entire area. After 100 h of oxidation, the oxide film thickness of three alloys is around 5 µm, 4 µm, and 3 µm, respectively. The improvement in oxidation resistance after LSM can be ascribed to the formation of a dense re-melted layer, uniform distribution of the elements, refinement of the re-melted layer.

High temperature oxidation resistance of arc ion plating NiCoCrAlY coating modified via laser shock peening

In this study, laser shock peening (LSP) was used to treat NiCoCrAlY coating prepared via arc ion plating (AIP), which is to improve the high temperature oxidation resistance of NiCoCrAlY coating. The oxidation condition is continuous oxidation at 1100 ℃. The results showed that after 150 h oxidation, the samples without LSP treatment had oxide film damage and large-area internal oxidation, and the coating nearly failed. The samples treated by LSP had intact oxide film and strong antioxidant properties. This is attributed to the fact that LSP helps to eliminate large particle clusters on the sample surface, which provides a prerequisite for the uniform growth of thermally grown oxide (TGO). Furthermore, LSP introduces high density dislocations, high density stacking faults and twins, which refines the grains of the coating and provides more diffusion channels for the selective oxidation of Al elements. Due to above reasons, LSP treated sample can form a continuous and uniform Al2O3 oxide scale faster at the initial stage of oxidation, which hinders the diffusion reaction of other elements and keeps TGO in a stable growth stage for a long time. It is proved that LSP is a potential technology for improving the oxidation resistance of NiCoCrAlY coating.