Thin Al2O3 Research Articles

Microstructure and properties of Al-coating on AZ31 magnesium alloy prepared by pack-cementation

Al-containing coatings were prepared on AZ31 magnesium alloy by pack-cementation technology. X-ray diffraction (XRD), backscattered electron imaging (BSEI) and energy dispersive spectroscopy (EDS) were jointly employed to characterize the phases, microstructure and composition of the coated samples. The results show that the feedstock composition has a significant impact on the phases, microstructure and thickness of the coatings. For the sample with AlCl3 powder as the activator, the coating is very thick and composed of gradient phases and structures from surface to inside, including small amount of β-Mg2Al3, coarse eutectic-like structure of γ-Mg17Al12 + δ-Mg, and fine γ-Mg17Al12 precipitations. In contrast, for the sample with AlCl3 and pure Al composite powders as the activator, the coating is relatively thin and contains a thin Al2O3 layer and a small amount of fine γ-Mg17Al12 precipitates. For the pack-cementation aluminizing that is not protected by high-vacuum or inert gas, the addition of pure Al powders can easily introduce the Al2O3 layer into the coating to prevent active Al ions further penetrating into the magnesium matrix, resulting in the thin Al-containing coating. The microhardness and corrosion behavior of the two kinds of aluminized coatings were also studied and discussed.

Advances in novel SDC@Al2O3 core−shell electrolyte for low‐temperature solid oxide fuel cell

AbstractThe preparation of electrolyte with excellent ionic conduction is an important development direction in the practical application of solid oxide fuel cell (SOFC). Traditional methods to improve ion conduction was structure doping to develop electrolyte materials. In this work, the ionic conductor Ce0.8Sm0.2O2‐δ (SDC) was modified by insulator Al2O3 to enhance ion conduction and apply as electrolytes for the SOFC. The transmission electron microscopy (TEM) characterization clearly clarified that a thin Al2O3 layer in the amorphous state coated on SDC to form the SDC@Al2O3 core−shell structure. The SDC@Al2O3 electrolyte with the core−shell structure possesses a super ionic conductivity of 0.096 S cm−1 and results in advanced cell performance of 1190 mW cm−2 at 550°C. The X‐ray photoelectron spectroscopy (XPS) analysis revealed that the concentration of oxygen vacancies in the SDC@Al2O3 core–shell structure significantly improved in comparison with pure SDC, the newly produced oxygen vacancies can promote the oxygen ion transport. Moreover, the interface between SDC and Al2O3 provides a fast channel for the proton transport. In addition, the SDC‐based SOFC was usually suffered from the reduction of the SDC electrolyte and the accompanying generated electron conduction should deteriorate the cell performance, this is the main challenge for the SDC electrolyte application. In our case, the Al2O3 shell on the SDC surface not only can avoid the contact between SDC and hydrogen to eliminate the reduction of SDC but also can restrain electron conduction due to the electron insulation characteristic of the Al2O3 shell. This work demonstrates an efficient approach to develop the advanced low‐temperature SOFC technology from material fundamentals.

Thermal cyclic resistance and long term inter-diffusion properties of slurry aluminide coatings modified with Si

High temperature oxidation resistant aluminide coatings fail due to their inability to maintain a protective scale. The corresponding mechanism of protection is based on of forming a thin Al2O3 layer, which depends on the availability of Al at the interface with the intermetallic coating. However, the Al content in the coating’s surface decreases with time at high temperatures due to interdiffusion with the substrate and/or frequent regeneration of the protective Al2O3 scale when it spalls. Si addition is known to enhance the life of Ni aluminide coatings under certain corrosion environments. In an effort to develop a stable, long lasting coating for industrial components exposed to metal dusting, diffusion aluminide coating has been produced by applying Al-Si slurries of various compositions on alloy 601. Aluminide coatings were prepared by applying a water base, Al slurry to which 1, 10 and 20 wt. % of Si were added, followed by a diffusion heat treatment. The microstructures of the coatings were similar, exhibiting an outer layer consisting of an Al-rich β-NiAl matrix, an almost stoichiometric β-NiAl inner layer and an interdiffusion zone between the coating and the alloy. Thermal cyclic tests in air at 1100 °C have demonstrated good adhesion and stability of all coatings. In addition, long term isothermal tests at 850 °C for up to 3 months in air showed high oxidation resistance of the coating but different degree of coating degradation depending on the composition. The coating with the lowest Si addition was the most stable.

Facile Synthesis, Analysis of Physico-Chemical Properties and Tape Casting of Al2O3 Nanoparticles

Alumina (Al2O3) powder was synthesized by simple wet-chemical precipitation method. The phase study was done using XRD confirming the FCC phase. FTIR showed the presence of Al-O vibrations. Particle size analysis (PSA) confirmed the presence of particles in the range of 300 nm. The EDX confirmed the presence of Al and O elements in the samples only and no impurity elements. SEM exhibited the ultrafine nature of the particles. The tape casting of Al2O3 nanoparticles was carried out with suitable organic ingredients. Based on the trials, the best composition for alumina tape casting was optimized. The SEM of green alumina thin sheet resulted in good surface behaviour. Optimized composition may be used for fabricating thin Al2O3 based electrical components for application in electronics industry.

Highly enhanced visible light photodetection properties of a ZnO phototransistor via an additional solution processed thin Al2O3 layer

A visible-light phototransistor have been fabricated by adding a solution-processed thin Al2O3 layer under the ZnO layer to improve the visible-light photodetection.

Enhanced Raman scattering on two-dimensional palladium diselenide.

Two-dimensional (2D) semiconductors with atomic layers, and a flat and active surface provide an attractive platform for the study of surface-enhanced Raman scattering (SERS). Many 2D layered materials, including graphene and transition metal dichalcogenide (TMD), have been exploited as potential Raman enhancers for SERS-based molecule sensing. Herein, atomically-thin palladium diselenide (PdSe2) used as a SERS substrate for molecule detection was systematically studied. Stable Raman enhancement for molecules such as rhodamine 6G (R6G), crystal violet (CV), and rhodamine B (RhB) on few-layer PdSe2 has been verified. A detection limit as low as 10-9 M and an enhancement factor of 105 for the R6G molecule on monolayer PdSe2 are achieved. With the insertion of a thin Al2O3 layer, the Raman spectra confirm the predominant charge transfer mechanism for the large Raman enhancement. Furthermore, the strong thickness-dependent properties, good in-plane anisotropy and excellent air-stability of Raman enhancement are also explored for 2D PdSe2. Our findings provide not only a promising Raman enhancement platform for sensing applications but also new insights into the chemical mechanism (CM) process of SERS.

Enabling water-free PEDOT as hole selective layer in lead-free tin perovskite solar cells.

Metal halide perovskites are set to revolutionise photovoltaic energy harvesting owing to an unmatched combination of high efficiency and low fabrication costs. However, to improve the sustainability of this technology, replacing lead with less toxic tin is highly desired. Tin halide perovskites are approaching 15% in power conversion efficiency (PCE), mainly employing PEDOT:PSS as a hole-selective layer. Unfortunately, PEDOT:PSS is processed from an aqueous solution, which is hardly compatible with the strict anoxic requirements for processing tin halide perovskites due to tin's instability to oxidation. Here, we present a water-free PEDOT formulation for developing tin-based lead-free perovskite solar cells. We show that the main difference between the PCE of devices made from aqueous and water-free PEDOT is due to the marked hydrophobicity of the latter, which complicates the perovskite deposition. By modifying the surface of water-free PEDOT with a thin Al2O3 interlayer, we could achieve good perovskite morphology that enabled perovskite solar cells with a PCE of 7.5%.

CORROSION INHIBITORY EFFECTS OF POTASSIUM DICHROMATE ON ALUMINIUM ALLOY IN CHLORIDE SOLUTION

Aluminium and its alloys have excellent corrosion resistance. When aluminium is exposed to the atmosphere, a thin invisible oxide Al2O3 is formed, protecting the metal from further oxidation. Compared to pure metals, alloys can have higher corrosion resistance depending on the content of certain alloying elements. Various substances such as organic or inorganic inhibitors can affect the corrosion of aluminium alloys and thus slow down the degradation of the material. In this paper, we studied the inhibitory effect of potassium dichromate on the corrosion processes of aluminium alloy. All measurements were performed in 0.5 M sodium chloride solution with the addition of different concentrations of inhibitors. The methods used were potentiodynamic polarization, cyclic voltammetry, and chronoamperometry.

Epitaxial growth by atomic layer deposition and properties of high-k barium strontium titanate on Zintl-templated Ge (001) substrates

This work reports the atomic layer deposition (ALD) and epitaxial growth of 10–12 nm BaxSr1−xTiO3 (x ∼ 0.5) thin films on Zintl-templated Ge (001) substrates, formed with 0.5 monolayers of Ba. The best thin films were grown using two steps. An amorphous 2–3 nm layer was deposited at 225 °C and then was converted to a crystalline film by annealing for 15 min at 650 °C under vacuum to generate the seed layer that had an abrupt interface with the Ge (001) substrate. A 7–10 nm layer was subsequently grown and crystallized at the same conditions as the seed layer. Metal-insulator-semiconductor structures that employed Au electrodes were used to assess leakage currents and dielectric properties. Interfacial effects inherent to the ∼10 nm BaxSr1−xTiO3 films affect the capacitance measurements leading to k of 87 and 140 for 10.9 and 14.6 nm films, respectively. The epitaxial films have high k in the bulk. Using capacitance measurements for BaxSr1-xTiO3 films that are 13–18.4 nm thick, a bulk k of ∼2000 and low interfacial capacitance density (C/A) of ∼100 fF/μm2 were extracted from thickness dependent relationships. The 10 nm films display a high leakage current (∼102 A/cm2 at −1.0 V) that can be reduced (to ∼10−1 A/cm2 at −1.0 V) by capping the film with ∼1 nm Al2O3 using ALD before depositing the Au electrode or by annealing in O2 at 300 °C for 15 min. The thin low-k Al2O3 layer or the GeOx formed during the O2 annealing step, while improving leakage current, introduces a capacitor in series that further reduces the film dielectric constant such that a 9.9 nm Al-capped film and a 9.8 nm O2-annealed film yield dielectric constants of 80 and 41, respectively.

From coating to doping: Effect of post-annealing temperature on the alumina coating of LiNi0.5Mn1.5O4 cathode material

Spinel LiNi0.5Mn1.5O4 is considered as one of the most promising cathode materials due to high working voltage and high energy density. However, the fast capacity degradation, mainly induced by the instability of electrode/electrolyte interface and bulk structure, heavily prevents its commercial application. To alleviate above two issues, LiNi0.5Mn1.5O4 material was first coated with Al(OH)3 via double hydrolysis reactions between NaAlO2 and AlCl3·6H2O, where the corrosion of LiNi0.5Mn1.5O4 material is avoided by controlling the feeding sequence, and the uniform coating of Al(OH)3 on particle surface is achieved by controlling the feeding rate. The Al(OH)3-coated LiNi0.5Mn1.5O4 material was post-annealed at different temperatures, and the effects of different post-annealing temperatures on the structure, morphology and electrochemical performance of LiNi0.5Mn1.5O4 material were systematically investigated. It is found that the LiNi0.5Mn1.5O4 material after post-annealing treatment at 600 ​°C exhibits the optimal rate and cycling performances, which can be mainly attributed to the synergistic effect of Al2O3 surface coating and doping. The uniform and thin Al2O3 coating layer can avoid the direct contact of electrode with electrolyte, capture corrosive HF and increase oxygen vacancy on particle surface, while Al3+ doping can eliminate LixNi1-xO impurity phase, reduce Mn3+ content, strengthen the spinel structure and make Li+ ions diffusion easier, thus leading to the simultaneous improvement of interfacial and structural stability of LiNi0.5Mn1.5O4 material.

Improved hydrothermal durability of Cu-SSZ-13 NH3-SCR catalyst by surface Al modification: Affinity and passivation

To improve the hydrothermal durability of Cu-SSZ-13 selective catalytic reduction (SCR) catalyst, a thin Al2O3 modification layer was coated on the external surface of Cu-SSZ-13 by a chemical liquid deposition (CLD) method. The high-temperature SCR activity of the Al-modified Cu-SSZ-13 can be maintained upon 750–800 °C hydrothermal aging, and over-oxidation of NH3 is largely inhibited. Based on H2-TPR and EPR results, it is revealed that CuAl2O4-like species forms upon Al modification and converts further to CuAlO2-like species during aging, while the accumulation of CuO-like species is inhibited. The high affinity of Al-containing species (i.e., Al2O3 and CuAl2O4-like species) with Cu(OH)2 is suggested by DFT calculations, indicating that Cu(OH)2 detached from ion-exchange sites are captured by Al to form CuAlO2-like species instead of CuO-like species. The passivation of detached Cu species by coated Al leads to somewhat weakened low-temperature SCR activity, but successfully preserves the high-temperature SCR performance upon aging, which can be applied to high-temperature SCR scenarios.

Tribological wear of Fe-Al coatings applied by gas detonation spraying

Comparative tests of gas detonation (GDS) coatings were carried out in order to investigate the influence of spraying parameters on abrasive wear under dry friction conditions. The tests were carried out using the pin-on-disc (PoD) method at room temperature. The microstructure of the coatings was analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM / EDS) methods. The results showed that with specific GDS process parameters, the main phases in both coatings were FeAl and Fe3Al involving thin oxide films Al2O3. The tribological tests proved that the coatings sprayed with the shorter barrel of the GDS gun showed higher wear resistance. The coefficient of friction was slightly lower in the case of coatings sprayed with the longer barrel of the GDS gun. During dry friction, oxide layers form on the surface, which act as a solid lubricant. The load applied to the samples during the tests causes shear stresses, thus increasing the wear of the coatings. During friction, the surface of the coatings is subjected to alternating tensile and compressive stresses, which lead to delamination and is the main wear mechanism of the coatings.

Limitations of Ultrathin Al2O3 Coatings on LNMO Cathodes.

This study demonstrates the application of Al2O3 coatings for the high-voltage cathode material LiNi0.5–xMn1.5+xO4−δ (LNMO) by atomic layer deposition. The ultrathin and uniform coatings (0.6–1.7 nm) were deposited on LNMO particles and characterized by scanning transmission electron microscopy, inductively coupled plasma mass spectrometry, and X-ray photoelectron spectroscopy. Galvanostatic charge discharge cycling in half cells revealed, in contrast to many published studies, that even coatings of a thickness of 1 nm were detrimental to the cycling performance of LNMO. The complete coverage of the LNMO particles by the Al2O3 coating can form a Li-ion diffusion barrier, which leads to high overpotentials and reduced reversible capacity. Several reports on Al2O3-coated LNMO using alternative coating methods, which would lead to a less homogeneous coating, revealed the superior electrochemical properties of the Al2O3-coated LNMO, suggesting that complete coverage of the particles might in fact be a disadvantage. We show that transition metal ion dissolution during prolonged cycling at 50 °C is not hindered by the coating, resulting in Ni and Mn deposits on the Li counter electrode. The Al2O3-coated LNMO particles showed severe signs of pitting dissolution, which may be attributed to HF attack caused by side reactions between the electrolyte and the Al2O3 coating, which can lead to additional HF formation. The pitting dissolution was most severe for the thickest coating (1.7 nm). The uniform coating coverage may lead to non-uniform conduction paths for Li, where the active sites are more susceptible to HF attack. Few benefits of applications of very thin, uniform, and amorphous Al2O3 coatings could thus be verified, and the coating is not offering long-term protection from HF attack.

Thermoluminescence and optically stimulated luminescence response of Al2O3 coatings deposited by mist-chemical vapor deposition

Aluminum oxide (Al2O3) is a widely used ceramic material which can be applied as a protective coating on metallic structures to improve corrosion resistance and mechanical properties. Al2O3 also has great potential as a functional thin film device in optoelectronics. When it is doped with carbon (Al2O3:C), this material system can serve as a reliable radiation dosimeter. The combination of optoelectronic, dosimetric, and protective properties demonstrated by Al2O3 uniquely positions it for dual use applications in nuclear forensics, nonproliferation and safeguards, emergency response, retrospective dosimetry, and nondestructive inspection. In this study, an innovative ultrasonic mist-chemical vapor deposition (Mist-CVD) system was used to deposit thin (nm level) Al2O3 coatings on 304 stainless steel substrates. The single aliquot regeneration (SAR) and additive dose reconstruction techniques were then used to investigate the thermoluminescence (TL) and optically stimulated luminescence (OSL) response of the coated substrates to increasing doses of β irradiation. This study demonstrates that nm-thick Al2O3 coatings hold promise as novel nano-dosimeters which could be leveraged for a series of applications such as nonproliferation and safeguards, retrospective dosimetry, and nondestructive inspection.

Excellent ferroelectric Hf0.5Zr0.5O2 thin films with ultra-thin Al2O3 serving as capping layer

Hf0.5Zr0.5O2 (HZO) has become one of the most popular HfO2 based ferroelectric thin films due to its huge potential to integrate low-cost high-density nonvolatile ferroelectric memory. Most researchers sandwiched the HZO between metals, such as TiN, and then adopted post-deposition high temperature anneal to improve the ferroelectricity and reliability of the film. In this work, the effect of a thin dielectric Al2O3 layer with different thicknesses to replace a metallic capping layer on the ferroelectric properties of a HZO (10 nm) thin film is evaluated, and we also compared the effects of TiN and W bottom electrodes on the properties of a capacitor. The results showed that the TiN/Al2O3 (1 nm)/HZO/W capacitor performed the best with a maximum 2Pr as high as 31.4 μC/cm2 at an electric field of ±3 MV/cm and very low leakage currents. In addition, the fatigue studies demonstrated the capacitor's excellent endurance properties with continuous cycling up to 1010 cycles. The use of an ultra-thin Al2O3 layer with excellent capping effects would significantly simplify the integration process of HfO2-based ferroelectric memory.

Thin Al2O3 Coatings Produced by Electrochemical Method, Subjected to Thermo-Chemical Treatment

The article presents the effect of the anodizing parameters, as well as the thermo-chemical treatment, of Al2O3 layers produced on an aluminum alloy on the characterization of structure, geometrical structure of the surface (SGS), the thickness of the oxide layers, the phase composition, and their microhardness. The oxide layers were produced by the method of direct current anodizing in a three-component electrolyte. Then, thermo-chemical treatment was carried out in distilled water and aqueous solutions of sodium dichromate and sodium sulphate. The anodizing parameters and compounds for the thermo-chemical treatment were selected on the basis of Hartley’s plans. The research showed the effect of anodizing parameters on the thickness of the Al2O3 layers and the increase in the thickness of the layers as a result of the thermo-chemical treatment. The research showed a significant increase in the microhardness of the layers as a result of thermo-chemical treatment and its influence on the phase composition of Al2O3 layers. A significant influence of the thermo-chemical treatment on the geometrical structure of the surface was also found.

High-performance ultrathin Cu(In,Ga)Se2 solar cell optimized by silvaco tools

In this work, we investigated the influence of the cell pitch, opening width, Ga/(In + Ga) ratio, absorber layer thickness, and doping on ultrathin CIGS solar cell performance by using ATLAS tools. First, to validate our investigated solar cell, we discuss and compare our simulation models with fabricated cells with/without rear-passivation Al2O3/Cu(In1−xGax)Se2. We observed significant improvements in cell performance while using a thin film Al2O3 for the rear-passivation with a high density of negative charge, where the rear side contact recombination losses can then be reduced. The simulation results follow the experimental trends, highlighting the beneficial effects of rear-passivation in the ultrathin absorber layer. However, poor passivation was observed when a rear-passivation layer is with a high density of positive charge or in high contact resistance at Ag/CIGS interface. Consequently, the optimum combination led to achieving 14.30% with 1016 cm−3, 2.5 µm, and 250 nm for absorber doping, cell pitch, and cell width, respectively. The obtained results from the simulated cells were compared to the recently published research work.

A Study on Solution-Processed Y2O3 Films Modified by Atomic Layer Deposition Al2O3 as Dielectrics in ZnO Thin Film Transistor

In this work, Y2O3–Al2O3 dielectrics were prepared and used in ZnO thin film transistor as gate insulators. The Y2O3 film prepared by the sol–gel method has many surface defects, resulting in a high density of interface states with the active layer in TFT, which then leads to poor stability of the devices. We modified it by atomic layer deposition (ALD) technology that deposited a thin Al2O3 film on the surface of a Y2O3 dielectric layer, and finally fabricated a TFT device with ZnO as the active layer by ALD. The electrical performance and bias stability of the ZnO TFT with a Y2O3–Al2O3 laminated dielectric layer were greatly improved, the subthreshold swing was reduced from 147 to 88 mV/decade, the on/off-state current ratio was increased from 4.24 × 106 to 4.16 × 108, and the threshold voltage shift was reduced from 1.4 to 0.7 V after a 5-V gate was is applied for 800 s.

Rapid fabrication of extremely thin Nano-Al2O3 transparent ceramic wafers through nonaqueous tape casting

Al2O3 transparent ceramics have important applications in electronics, solid-state lighting, military and 5G industries. At present, thin and large-size Al2O3 ceramics are urgently required by enterprises. Tape casting method has emerged as a powerful tool in producing transparent ceramics, but the preparation of the slurries is generally very time consuming. In this study, a one-step ball milling process was proposed to fabricate Al2O3 transparent ceramics through non-aqueous tape casting, in which green tapes were obtained with uniform texture and no distortion. Thickness of the Al2O3 transparent ceramics approached 0.1 mm. The effects of dry pressing on single and double-layer tapes were also compared. It was found that dry pressing has essentially no effect on monolayer samples, but contributed to improve the densification and promoted grain growth of the bilayer samples. Our results could be used as reference for the preparation of extremely thin Al2O3 transparent ceramic wafers.

Enhanced Battery Cell Lifespan of Lithium Metal Battery Via Using Lithium Metal Alloy Protective Layer Anode and Aluminum Oxide Modified NMC Cathode

Lithium-metal batteries (LMBs) have much attention over the state-of-the-art lithium-ion batteries (LIMs) in term of the energy density. As compared with the conventional graphite anode of LIBs, lithium anode has a high theoretical specific capacity (3860 mA h g-1) and a low electrochemical potential (-3.04 V vs SHE). Nonetheless, no stable solid-electrolyte interphase (SEI) forms on the surface of lithium metal. The continuous electrolyte consumption along with the non-uniform lithium deposition leads to the limited cell lifespan and cell safety concern, both of which impede their LMBs practical applications. To address the problems, herein, we introduce an alloying protective layer on lithium metal anode integrating with thin Al2O3 layer modified on LiNi0 .8Co0 .1Mn0 .1O2 (NMC811) cathode to prolong lifespan of batteries. By using the lithium alloy protective layer, the LMB exhibits good stability performance better than the fresh Li metal approximately 20%. We hope that this perspective together can be a guiding principle for the next-generation practical batteries. Figure 1