Amorphous Oxide Layer Research Articles

Hierarchical design of self-standing FeNi-based metallic glass by in-situ surface amorphous oxide construction for durable and efficient oxygen evolution

As the driving force to accelerate water electrolysis in commercialization, electrocatalysts concurrently satisfying electrocatalytic activity, mechanical flexibility and low cost are essential in the design to lower the kinetic barriers of oxygen evolution reaction (OER). Herein, we present a strategy to in situ construct amorphous metal oxide nanolayers on different compositions of self-standing non-precious FexNiyP20 (at.%) metallic glasses (AMO-MG). With the mechanical flexibility, the processed FexNiyP20 MGs, particularly at Fe30Ni50P20, reaches low OER overpotentials of 238 at a current density of 10 mA cm−2 and a Tafel slope of 33 mV dec−1 in 1.0 M KOH solution while preserving a long-term durability exceeding 60 h. Further studies indicate these robust OER activities appear to be directly linked with the unique surface patterns of the in situ formed AMO nanolayer providing abundant active sites, low charge transfer resistance and superior structural-integration. Modelling analysis further shows that both Fe and Ni sites in the AMO nanolayer act as active sites leading to a strong charge transfer for effective H2O adsorption and an optimization of rate-determining step of OER process. Such in situ AMO-MG hierarchical structure therefore provides a novel structure-integration strategy and win–win situation to design and commercialize high-performance alloy catalysts for OER.

Unraveling the Role and Impact of Alumina on the Nucleation and Reversibility of β‐LiAl in Aluminum Anode Based Lithium‐Ion Batteries

AbstractAluminum, due to its high abundance, very attractive theoretical capacity, low cost, low (de−) lithiation potential, light weight, and effective suppression of dendrite growth, is considered as a promising anode candidate for lithium‐ion batteries (LIBs). However, its practical application is hindered due to multiple detrimental challenges, including the formation of an amorphous surface oxide layer, pulverization, and insufficient lithium diffusion kinetics in the α‐phase. These outstanding intrinsic challenges need to be addressed to facilitate the commercial production of Al‐based batteries. The native passivation layer, Al2O3, plays a critical role in the nucleation and reversibility of lithiating aluminum and is thoroughly investigated in this study using high precision electrochemical micro calorimetry. The enthalpy of crystallization of β‐LiAl is found to be 40.5 kJ mol−1, which is in a strong agreement with the value obtained by calculation using Nernst equation (40.04 kJ mol−1). Surface treatment of the active material by the addition of 25 nm of alumina increases the nucleation energy barrier by 83 % over the native oxide layer. After the initial nucleation, the added alumina does not negatively impact the reversibility at 0.1 C rate, suggesting the removal of alumina is not necessary for improving the cyclability of aluminum anode based lithium‐ion batteries. Moreover, the coulombic efficiencies are also found to be slightly higher in the alumina treated samples compared to the untreated ones.

Selective double-layer on black Ni-P enhances solar absorption and reduces corrosion

This work investigates a double-layer configuration for the black Ni-P layers used in solar adsorption technology, aiming to increase the absorption of a broader range of solar wavelengths. This multilayer configuration has a surface with increased roughness and absorption area. The valleys were porous materials, which were connected to an underlying metallic sub-layer that is susceptible to corrosion. In turn, this corrosion induced changes to the top layer. The Ni-P layer was deposited by the electroless technique using an acid nickel sulfate bath as a source of metal ions and a reducing agent of sodium hypophosphite. Etching initiated an oxidation process on the surface, forming a layer of amorphous black nickel oxide for absorption. The surface features of the black Ni-P double layer consist of an uneven surface that aids sunlight adsorption. Carbon steel (AISI 1018) with different surface finishes was used for depositing Ni-P and black Ni-P, aiming to establish correlations with solar adsorption. The sample with an increased surface roughness obtained a higher absorption percentage than a single layer. The corrosion rate was calculated as 7 mmpy for the black Ni-P layer by applying polarization curves. A 6 µm-thick Ni-P double layer was obtained, achieving 96% absorption within the 300–2,000 nm range.

Polishing performance and material removal mechanism in the solid-phase Fenton reaction based polishing process of SiC wafer using diamond gel disc

The use of SiC wafer is widespread in many fields, especially in aerospace, energy, 5 G communications, and microelectronics. Chemical-mechanical polishing (CMP) is the primary method used for achieving an ultra-smooth surface on SiC wafers. However, CMP suffers from low efficiency, leading to increased processing time and costs. To address this issue, we developed a novel diamond gel polishing disc that incorporates SiO2/Fe3O4 (S/F) powder. The disc enhances polishing efficiency through a solid-phase Fenton reaction between the disc and SiC. The research investigates the reaction mechanism and the material removal model of the polishing process using SEM, TEM, and XPS analysis. Experimental studies are conducted to assess the polishing performance and validate the effectiveness of the theoretical model. The findings indicate that SiC undergo a solid-phase Fenton reaction with polishing disc mixed S/F powder (SG-S/F disc) during polishing. The Fenton reaction generates hydroxyl radicals (·OH), which break the Si-C and Si-Si bonds in the crystal structure, leading to the formation of a softer nanoscale amorphous oxide layer on the SiC surface. The cyclic generation and removal of this oxide layer enable highly efficient polishing of SiC wafers. Compared to a gel disc without S/F (SG disc), SiC polished with the SG-S/F disc exhibits superior surface quality. Additionally, the material removal rate (MRR) of the SG-S/F disc reaches 1.42 μm/h, representing a 51.1 % improvement over that of the SG disc. These results clearly demonstrate that the solid-phase Fenton reaction significantly enhances the polishing performance of the gel polishing disc.

Photoelectrocatalytic Water Splitting by Conformal Copper‐Oxide on Hematite Nanostructures: Dependence on Surface‐States

AbstractUnderstanding the pivotal role of surface co‐catalysts is paramount in the strategic design of forthcoming photoelectrodes. However, the nuanced impacts of co‐catalysts remain elusive, particularly in promoting the water oxidation reaction on hematite, especially in connection to surface states denoted as S1 (higher energy) and S2 (lower energy). For this purpose, we tailored two isomorphous hematite nanoarrays with a thin layer of amorphous copper oxide (CuOx), composed of a blend of Cu(I) and Cu(II) species, via a soft electrodeposition technique. Remarkably, we discovered that in pristine hematite (α‐Fe2O3), the S2 state played a pivotal role in activating the CuOx ad‐layer for water oxidation. At lower external biases (approximately 0.9–1.1 VRHE), CuOx served as charge reservoir in equilibrium with the S2 state. Notably, beyond 1.1 VRHE, where the high‐energy holes of the S1 state became available, CuOx was activated indirectly through the equilibrium with the S2 state, and a pronounced enhancement in photocurrent was observed. Conversely, in the case of Ti‐doped hematite (Ti : α‐Fe2O3) devoid of the S2 state, the presence of CuOx resulted in a decline in charge transfer efficiency. Instead of facilitating water oxidation, CuOx adversely affected the S1 surface sites and reduced the charge carrier density in Ti : α‐Fe2O3.

High Capacitance Porous Ruthenium Nitride Films with High Rate Capability for Micro-Supercapacitors.

The demand for high-performance energy storage devices to power Internet of Things applications has driven intensive research on micro-supercapacitors (MSCs). In this study, RuN films made by magnetron sputtering as an efficient electrode material for MSCs are investigated. The sputtering parameters are carefully studied in order to maximize film porosity while maintaining high electrical conductivity, enabling a fast charging process. Using a combination of advanced techniques, the relationships among the morphology, structure, and electrochemical properties of the RuN films are investigated. The films are shown to have a complex structure containing a mixture of crystallized Ru and RuN phases with an amorphous oxide layer. The combination of high electrical conductivity and pseudocapacitive charge storage properties enabled a 16µm-thick RuN film to achieve a capacitance value of 0.8Fcm-2 in 1m KOH with ultra-high rate capability.

Research on bubble-free Si/SiC hydrophilic bonding approach for high-quality Si-on-SiC fabrication

The electrical device fabricated by the Si-on-SiC substrate exhibits superior heat dissipation and minimal RF loss. However, a common challenge in hydrophilic direct bonding is the inevitable formation of bubbles at the Si/SiC interface, which compromises material utilization efficiency. To address this issue, a multi-bonding process was introduced in this research. Experimental findings revealed that this method effectively mitigated interfacial bubble formation, especially when incorporating a multi-step annealing–separating–bonding approach, yielding even more promising results. Ultimately, a bubble-free 3 × 3 cm2 Si-on-SiC substrate was fabricated. Material characterization techniques confirmed the high crystal quality and minimal surface roughness for the Si functional layer. Transmission electron microscopy further revealed the presence of an amorphous oxide layer (∼3.5 nm) at the interface, devoid of any defects or nanovoids. It is believed that with its excellent physical properties, Si-on-SiC will have a broader application prospect in extreme environments.

Synergetic Catalytic Effect between Ni and Co in Bimetallic Phosphide Boosting Hydrogen Evolution Reaction.

The application of electrochemical hydrogen evolution reaction (HER) for renewable energy conversion contributes to the ultimate goal of a zero-carbon emission society. Metal phosphides have been considered as promising HER catalysts in the alkaline environment, which, unfortunately, is still limited owing to the weak adsorption of H* and easy dissolution during operation. Herein, a bimetallic NiCoP-2/NF phosphide is constructed on nickel foam (NF), requiring rather low overpotentials of 150 mV and 169 mV to meet the current densities of 500 and 1000 mA cm-2, respectively, and able to operate stably for 100 h without detectable activity decay. The excellent HER performance is obtained thanks to the synergetic catalytic effect between Ni and Co, among which Ni is introduced to enhance the intrinsic activity and Co increases the electrochemically active area. Meanwhile, the protection of the externally generated amorphous phosphorus oxide layer improves the stability of NiCoP/NF. An electrolyser using NiCoP-2/NF as both cathode and anode catalysts in an alkaline solution can produce hydrogen with low electric consumption (overpotential of 270 mV at 500 mA cm-2).

Oxidation and mechanical properties of SiC fibers after high temperature exposure in air and steam

SiC fibers are widely used in composites exposed to high temperature oxidizing environments. The present study compares the oxidation behavior of SiC fibers and the associated changes in tensile strength upon their exposure to dry air and steam for up to 50 hours at temperatures from 950°C to 1350°C. In both cases, the scale thickness and oxide microstructure were analyzed by scanning electron microscopy. When the SiC fibers were oxidized in air, a crack-free amorphous oxide layer formed at temperatures up to 1200°C, whereas a cracked, crystallized oxide layer was found at 1350°C. By contrast under steam environment, a crystalline oxide forms at 950°C for oxidation times longer than 30 h. In both environments, the fiber strength decreased with increasing exposure time and temperature, the degradation being faster after oxidation in steam compared to dry air. This appears to relate to residual stress in the oxide scale and a reduction in the cross section of the load-bearing unoxidized SiC. An increase in defect size may also contribute to the loss of strength. The oxide scale follows parabolic growth kinetics in both dry air and in steam from 950°C to 1350°C, except at 1350°C for over 30 hours. The oxidation rate in steam is faster than that in dry air, with activation energies of 79.8±1.4 kJ/mol in steam and 153.6±3.4 kJ/mol in dry air, respectively. This work is relevant to the application of SiC fibers and SiC fiber reinforced composites in air and steam environments at high temperature.

A restricted dynamic surface self-reconstruction toward high-performance of direct seawater oxidation

The development of highly efficient electrocatalysts for direct seawater splitting with bifunctionality for inhibiting anodic oxidation reconstruction and selective oxygen evolution reactions is a major challenge. Herein, we report a direct seawater oxidation electrocatalyst that achieves long-term stability for more than 1000 h at 600 mA/cm2@η600 and high selectivity (Faraday efficiency of 100%). This catalyst revolves an amorphous molybdenum oxide layer constructed on the beaded-like cobalt oxide interface by atomic layer deposition technology. As demonstrated, a new restricted dynamic surface self-reconstruction mechanism is induced by the formation a stable reconstructed Co-Mo double hydroxide phase interface layer. The device assembled into a two-electrode flow cell for direct overall seawater electrolysis maintained at 1 A/cm2@1.93 V for 500 h with Faraday efficiency higher than 95%. Hydrogen generation rate reaches 419.4 mL/cm2/h, and the power consumption (4.62 KWh/m3 H2) is lower than that of pure water (5.0 KWh/m3 H2) at industrial current density.

Stable and low loss oxide layer on α-Ta (110) film for superconducting qubits

The presence of amorphous oxide layers can significantly affect the coherent time of superconducting qubits due to their high dielectric loss. Typically, the surface oxides of superconductor films exhibit lossy and unstable behavior when exposed to air. To increase the coherence time, it is essential for qubits to have stable and low dielectric loss oxides, either as barrier or passivation layers. In this study, we highlight the robust and stable nature of an amorphous tantalum oxide layer formed on α-Ta (110) film by employing chemical and structural analyses. Such kind of oxide layer forms in a self-limiting process on the surface of α-Ta (110) film in piranha solution, yielding stable thickness and steady chemical composition. Quarter-wavelength coplanar waveguide resonators are made to study the loss of this oxide. One resonator has a Qi of 3.0 × 106 in the single photon region. The Qi of most devices are higher than 2.0 × 106. Moreover, most of them are still over 1 × 106 even after exposed to air for months. Based on these findings, we propose an all-tantalum superconducting qubit utilizing such oxide as passivation layers, which possess low dielectric loss and improved stability.

Impact of Gas Pressure on the Adhesion Process of Cold-sprayed Titanium Dioxide layers on Unalloyed Metals

Applying ceramic materials like TiO2 through cold spraying is acknowledged as a complex procedure. The intricacy stems from the need for feedstock particles to undergo plastic deformation to bond with the substrate during cold spraying. However, inducing such deformation in ceramics, known for their hardness and brittleness, is not straightforward. Additionally, the underlying bonding mechanism is not fully clear. This study sought to understand the effects of different substrates and gas pressures on the TiO2 application method. We experimented with TiO2 particles and metals such as copper and aluminum, exposing them to varied gas pressures to delve deeper into the dynamics of cold spraying ceramics onto metallic surfaces. We utilized sophisticated instruments like the focused ion beam and the transmission electron microscope to scrutinize the interfacial structures of TiO2 particles with pure copper (C1020) as well as pure aluminum (AA1050). The data revealed that as we adjusted the gas pressure from 0.7 to 3.0 MPa, there was a corresponding increase in the coating\'s bond strength, registering between 1.52 to 3.46 MPa for C1020 and 0.45 to 4.15 MPa for AA1050. An ultra-thin amorphous oxide layer, under 5 nm in thickness, was detected at the juncture of TiO2 with both metals. The shift in process gas pressure emerged as a pivotal element affecting the bond strength of the TiO2 layer.

Controllable growth of (Hf, Zr)B2 solid solution coating via CVD for ultra-high temperature ablation of C/C composites

In this paper, we have successfully addressed the challenges of cracking and spalling in HfB2 coatings during ablation through the novel synthesis of (Hf, Zr)B2 solid solution coatings using the chemical vapor deposition (CVD) method. The ablation resistance of the coating exhibited an initially improving trend followed by a subsequently deterioration as the Zr content increased. When the Hf/Zr molar ratio in the (Hf, Zr)B2 solid solution coating was 1:1, a thicker Hf-Zr-O amorphous oxide layer was formed during ablation, which acted as a barrier, preventing the inward diffusion of oxygen. As a result, the (Hf0.5Zr0.5)B2 solid solution coating exhibited superior ablation resistance with a mass ablation rate of only −0.216 mg/s and a linear rate of −0.089 µm/s. These findings underscore the enormous potential of boride solid solution UHTC as exceptional candidates for ultra-high temperature ablation resistant applications.

A new perspective about the surface structure of FGH96 superalloys powders

Understanding of the surface structure of FGH96 alloy powders has implications for the subsequent evolution in sintering. The results from this work indicate that the oxide film of powder surface was composed of TiO2 particles and homogeneous oxide layer. Two types of carbides with size of about 30–50 nm and 250 nm are founded, which can further lead to the differences in low-temperature oxidation during the atomization process, resulting in the presence of amorphous TiO2 particles of similar size to the precipitates above them. The oxidation of the γ leads to a uniform amorphous oxide layer with a thickness of approximately 14 nm above the powder matrix.

Dual‐Mode Operation of Epitaxial Hf0.5Zr0.5O2: Ferroelectric and Filamentary‐Type Resistive Switching

Since the discovery of its ferroelectricity, hafnium oxide is widely used for applications in ferroelectric field‐effect transistors and ferroelectric tunnel junctions. is especially favored for its robust ferroelectricity and high remanent polarization at low thicknesses. In addition, is well established as amorphous or crystalline oxide layer in resistive switching devices. Herein, ferroelectric switching is found coexisting with high on/off ratio resistive switching in sub‐10 nm epitaxial . The resistive switching shows typical characteristics of a filamentary‐type valence change memory (VCM), clearly contradicting the polarization charges as the origin of different resistance states. In contrast to previous observations, no electroforming step is required to initiate VCM switching. The bottom electrode enables a RESET to the virgin state, allowing subsequent ferroelectric hysteresis measurements. It is possible to change between both switching schemes repeatedly without impacting the ferroelectric performance. This indicates that ferroelectric switching and oxygen vacancy movement do not interfere with each other, and both switching phenomena can exist independently. This finding opens up ways to unite the different strengths of both switching mechanisms in the same stack. It becomes possible to assign the two operating principles to artificial neural network training and inference according to their respective advantages.

Improved photoelectrochemical water splitting performance of Sn-doped hematite photoanode with an amorphous cobalt oxide layer

Hematite with a suitable band gap is a promising candidate as the photoanode for photoelectrochemical water splitting, but it suffers from low catalytic activity and severe electron-hole recombination. Herein, a novel two-step solvothermal synthetic strategy is developed to fabricate a uniform CoOx amorphous layer with a thickness of 5 nm on Sn-doped Fe2O3 nanowire photoanode. The CoOx surface layer increases the roughness of the photoanode significantly, and thus enlarges the electrochemical active area. Furthermore, the CoOx layer brings Co2+/Co3+ redox couples, enhances the concentration of oxygen vacancies and increases the charge carrier density. The bulk and surface charge separation efficiencies are both improved. The surface charge transfer process and the oxygen evolution reaction are accelerated. The photocurrent density of the Sn–Fe2O3 photoanode at 1.23 V (vs. reversible hydrogen electrode) is improved from 0.83 to 1.40 mA cm−2 after the deposition of the CoOx surface layer.

Chitosan-photocatalyst nanocomposite on polyethylene films as antimicrobial coating for food packaging

Chitosan (CS), an edible and non-toxic natural biopolymer, has been widely used in food preservation attributed to its intrinsic antimicrobial, biodegradable, and excellent film-forming properties. In this work, we report photocatalyst-loaded chitosan coating on commercial polyethylene (PE) film with enhanced antimicrobial properties for food packaging application. To improve the chemical stability of zinc oxide (ZnO) photocatalyst in acidic chitosan matrix, a thin layer (1–5 nm) of amorphous tin oxide (SnOx) was coated on ZnO nanoparticles. Consequently, the charge transfer efficiency of ZnO is improved and most of the surface defects are retained according to the studies of UV–Vis and fluorescence spectroscopy. The thin SnOx coating on ZnO was observed by high-resolution transmission electron microscopy (HRTEM) and its effects on crystallinity and particle size of ZnO were examined using X-ray diffraction (XRD) and particle sizer, respectively. The addition of ZnO@SnOx particles in chitosan coating increases water contact angle (WCA) and enhances thermal stability of chitosan coating. The antimicrobial activity of chitosan, ZnO-SnOx nanoparticles, and CS-ZnO@SnOx coated PE films were examined against both Gram-negative (E. coli, A. faecalis) and Gram-positive (S. aureus, B. subtilis) bacteria. Compared to the limited antimicrobial effects of chitosan, ZnO-SnOx demonstrates an improved inhibition effect on bacterial growth over 48 h period under light. For the CS-ZnO@SnOx nanocomposite coated PE films, no inhibition zone was observed due to the limitation of disc diffusion method. Meanwhile, there were no bacterial colonies found to develop on the film, rendering this CS nanocomposite coating a good candidate for food packaging applications.

Iron-doped cobalt nitride as an efficient electrocatalyst towards energy saving hydrazine assisted seawater splitting in near neutral to highly alkaline pH achieving industry level current density

Replacing sluggish anodic oxygen evolution reaction by hydrazine oxidation reaction in seawater electrolysis is one of the smartest ways of getting multiple benefits as it offers an energy saving route for hydrogen production keeping the cell voltage way smaller than responsible voltage for corrosive chloride oxidation. Here, we report iron-doped Co3N as highly active electrocatalyst towards hydrazine oxidation reaction and hydrogen evolution reaction in wide pH range of 7–14. The two-electrode electrolyser system reached industry scale current density of 1000 mA cm−2 at ultralow cell voltage of 0.65 V, and found sustainable at 500 mA cm−2 over 95 h in hydrazine assisted alkaline seawater splitting. The electrolyser system also achieved 200 mA cm−2 current density at 0.75 V in hydrazine assisted neutral seawater medium. Interestingly, a thin amorphous iron oxide layer formed in Fe-doped Co3N provided much needed protection during electrocatalysis offering long term stability at industry level current density.

Investigation of the role of pre-existing oxide in the initial degradation mechanism in AlGaN/GaN HEMTs under ON-state stress

The role of pre-existing oxide in the initial degradation mechanism of AlGaN/GaN high electron mobility transistors during ON-state stressing was systematically studied. The pre-existing oxide was revealed to exist as an amorphous oxide layer consisting primarily of Ni and Ga oxides with a small amount of Al oxide at the GaN-cap/Ni-gate interface. Through an ON-state stressing experiment carried out in vacuum that excluded the influence of atmospheric oxygen, we discovered that the pre-existing interfacial oxide participated in an electrochemical reaction, accounting for the initial degradation in AlGaN/GaN HEMTs. The thickening of the oxide layer at the gate edge reduces the effective gate length of the device, thereby causing a decrease in the drain saturation current.

In situ formed nickel tungsten oxide amorphous layer on metal–organic framework derived ZnxNi1−xWO4 surface by self-reconstruction for acid hydrogen evolution reaction

Noble metal free electrocatalysts for hydrogen evolution reaction (HER) in acid play an important role in proton exchange membrane-based electrolysis. Here, we develop an in situ surface self-reconstruction strategy to construct excellent acidic HER catalysts. Firstly, free-standing zinc nickel tungstate nanosheets inlaid with nickel tungsten alloy nanoparticles were synthesized on carbon cloth as pre-catalyst via metal–organic framework derived method. Amorphous nickel tungsten oxide (Ni-W-O) layer is in situ formed on surface of nanosheet as actual HER active site with the dissolution of NiW alloy nanoparticles and the leaching of cations. While the morphology of the free-standing structure remains the same, keeping the maximized exposure of active sites and serving as the electron transportation framework. As a result, benefiting from disordered arrangement of atoms and the synergistic effect between Ni and W atoms, the amorphous Ni-W-O layer exhibits an excellent acidic HER activity with only an overpotential of 46 mV to drive a current density of 10 mA cm−2 and a quite good Tafel slope of 36.4 mV dec−1 as well as an excellent durability. This work enlightens the exploration of surface evolution of catalysts during HER in acidic solution and employs it as a strategy for designing acidic HER catalysts.