Aluminum Vacancies Research Articles

High-pressure supercritical CO2-assisted fabrication of two-dimensional LaAlO3 and its room temperature ferromagnetism

Abstract Spintronics applications in two-dimensional (2D) magnetic materials can significantly contribute to the miniaturization and energy efficiency of semiconductor devices. However, current 2D ferromagnetic materials face challenges such as ferromagnetic instability and low Curie temperature (Tc), which limit their broader application. In this study, 2D room-temperature ferromagnetic LaAlO3 was successfully prepared with supercritical carbon dioxide (SC CO2). With the enhanced stress effect of CO2 molecules, the contents of oxygen vacancies OV, aluminium vacancies AlV, and AlO4 in the 2D structure are elevated, and then the ferromagnetic properties of LaAlO3 appeared to be significantly enhanced due to defects and spatial symmetry breaking of the octahedron. Notably, the 2D intrinsic ferromagnetic LaAlO3 exhibited a Tc above 350 K. Therefore, this work supplies a new means for SC CO2 to modulate the microstructure and ferromagnetic properties of 2D LaAlO3, which is conducive to expanding the applications of LaAlO3.

Atomic defects (vacancy, substitutional, and Stone-Wales) in monolayer aluminum nitride: a density-functional-theory simulation

Abstract Aluminum nitride (AlN) is a mechanically strong material with a high melting point and excellent thermal conductivity. In this study, the AlN is modeled with defects in vacancies, substitutions, and Stone-Wales using a density functional theory (DFT). We model six configurations, two configurations of monovacancies: aluminum vacancy (VAl) and vacancy nitrogen (VN), two configurations of substitutions: aluminum substitution (SN→Al) and nitrogen substitution (SAl→N), the interchange (IAl↔N), and Stone-Wales (S–W). We find structural changes in each defect with outward relaxation and VN with inward relaxation. the band structure calculations show that the geometric structure introduces new states near the Fermi level except for the VAl system.

Hydrogen interactions with intrinsic point defects and hydrogen diffusion in tungsten doped Al2O3

In light of the extensive use of tungsten (W) in fusion experimental devices and the importance of hydrogen isotopes permeation, based on the first principle approaches we study the effects of W doping on the formation energies of intrinsic point defects, hydrogen interactions with such defects, and hydrogen diffusion in bulk of α-Al2O3. Our investigation demonstrated that W doping enhances the formation of oxygen and aluminum vacancies (Vo and VAl) in α-Al2O3. In W doping α-Al2O3, hydrogen primarily exists in the form of Ho− (hydrogenation of the bulk VO3−) and Hi− (H interstitial) defects, while it hardly occupies VAl. Hydrogen is firmly trapped by Vo with a formation energy −3.35eV, and Hi− diffusion become extremely challenging because W doping significantly raises the Hi− diffusion barrier to 4.44 eV. Our findings indicate that W doping is beneficial for hydrogen permeation resistance in α-Al2O3.

Computer simulations on the microscopic mechanisms for the nucleation of hydrogen bubbles in aluminum

Trapping of multiple hydrogen (H) atoms inside vacancies in aluminum (Al) is related to the formation of H bubbles, which ultimately results in embrittlement of the material. However, the formation mechanisms of H bubbles are still not well known. In this work, we perform systematical ab initio simulations to study the trapping of H atoms inside vacancies, and its influence on the growth of vacancies. It is found that monovacancy can trap as many as 8 H atoms, forming Vac1H8. H atoms prefer the off-center positions close to tetrahedral sites in vacancy. The shortest H–H bond length in vacancy is 2.10 Å among H atoms, which suggests that it is impossible to form H2 molecule in monovacancy. The accumulation of H atoms reduces the vacancy formation energy closest to Vac1Hm, promoting the formation of new vacancy. The newly produced vacancy can bind tightly with Vac1Hm and form Vac2Hm. With the similar way, the continuous formation of new vacancies and aggregation of H atoms may ultimately result in growth of VacnHm and formation of superabundant vacancies and H bubbles in Al.

Aluminum vacancy‐rich MOF‐derived carbon nanosheets for high‐capacity and long‐life aqueous aluminum‐ion battery

AbstractEco‐friendly and safe aqueous aluminum‐ion batteries as energy storage devices with low economic burden, high stability and fast ion transport have been lucubrated deeply in response to the call for sustainable development. However, the poor cycle performance caused by difficult (de‐)intercalation hinders the development prospect. In this work, the aluminum vacancy‐rich MOF‐derived carbon is constructed to achieve reversible aluminum storage during the charge‐discharge cycles. The MOF‐derived carbon with anti‐stacking waxberry‐like structure exhibits high capacity (282.1 mAh g−1 at 50 mA g−1) and long cycle performance (84.4% capacity retention rate at 1 A g−1 after 5000 cycles). Further investigations demonstrate that (de‐)intercalation occurs among the vacancies of carbon nanosheets in the form of hydrated aluminum ions. Meanwhile, the introduced nitrogen as energy storage sites contributes part of the capacity. The proposed aluminum vacancy engineering improves the current situation of the capacitive energy storage mode for 2D carbon materials, which may exploit an advanced theoretical model for the design of aqueous batteries.

Design of gelatin-based bionic device for neural computing applications

This study introduces an approach to the development of resistive random-access memory (RRAM) devices by utilizing gelatin-based materials and incorporating an ultrathin Al2O3 interface layer fabricated using atomic layer deposition (ALD). The integration of the ALD technology for Al2O3 deposition ensures precise control over the layer thickness and quality, contributing to enhanced device uniformity and stability. The AGAI device can withstand more than 200 switching cycles while maintaining a high ON/OFF ratio exceeding 103, and it also successfully emulates synaptic plasticity characteristics, including long-term synaptic plasticity and short-term synaptic plasticity, as demonstrated by their responses to paired-pulse facilitation and paired-pulse depression, respectively, thereby validating their potential for neural computing applications. Additionally, the hybrid conduction mechanism in the AGAI device, involving aluminum and oxygen vacancy filaments, provides remarkable control over the switching process, leading to repeatability in synaptic characteristics and resistance states. These capabilities introduce new possibilities for the development of neuromorphic computing systems, which aim to mimic the functionality of the human brain in processing and storing information.

Characterizations of two-photon absorption process induced by defects in aluminum nitride using Z-scan method

In this work, we reported two-photon absorption (TPA) measurements for aluminum vacancies in Aluminum nitride single crystals. We measured the linear transmission and identified the defect levels. Using the Z-scan method, we measured the TPA coefficients of the transitions between defect levels from 380 nm to 735 nm. The transition occurs between the aluminum vacancies defect levels. Furthermore, the power dependence shows good linear fitting, confirming the TPA mechanism. These results will be helpful for the design and fabrication of ultra-low loss waveguides and integrated photonics in the ultraviolet spectral range.

Effects of firings in hydrogen on the insulation performances of a 95 wt% alumina ceramic

To investigate the effects of point defects on the insulation performances of alumina ceramics, we fire a 95 wt% alumina ceramic in wet hydrogen, dry hydrogen, and supplementary air, to change the concentrations of aluminum vacancy (VAl‴) and oxygen vacancy (VO••). The dielectric breakdown strength (DBS) and flashover voltage (FV) are tested, and the point defects are characterized by XPS and optical reflectance. Firing in wet hydrogen decreases the concentration of VO••, improving DBS but deteriorating FV. Nevertheless, firing in dry hydrogen increases the concentration of VAl‴, improving FV but deteriorating DBS. Supplementary firing in air weakens the effects of firing in dry hydrogen on the point defects and insulation performances. The effects of firings on insulation performances are attributed to the concentrations of electrical carriers that are determined by the point defects, and this is confirmed by the results of electrical resistivity.

The isomorphous substitution of Si(4Al) with P in FAU zeolite and its stabilization effect

It's a dream to make zeolites more stable so as to keep the activity and stability of the catalyst. Phosphorus modification is an effective method, however, the known post-modification predominantly presents as non-framework P, and the P-loss is a big trouble in application. We have discovered that in the reaction of PCl3 or SiCl4 + PCl3 with NaY zeolite, a portion of P enters the framework of the zeolite, forming a PO4-AlO4 structure. Further investigations revealed that P cannot be incorporated into the framework through P for Al isomorphous substitution, but rather through isomorphous substitution with Si(4Al). PCl3 exhibits two effects in reaction: at lower quantities, it mainly undergoes isomorphous substitution with Si(4Al); at higher quantities, it leads to zeolite dealumination generating aluminum vacancies, which disrupt the zeolite framework or promotes Si for Al isomorphous substitution. After hydrothermal aging at 800 °C for 4 h, the stable presence of framework PO4-AlO4 implies that the weakest site Si(4Al) becomes the more stable site P(4Al) in the Y zeolite framework. Compared with the JPY (prepared by impregnating (NH4)2HPO4 solution to high silica Y zeolite) sample, after 10 cycles of hydrothermal and water washing treatment, the P2O5 loss rate of DPY (prepared by SiCl4 + PCl3 with NaY) zeolite ranged from 0.4 % to 3.5 %, significantly lower compared to the range of 18.7 % to 25.9 % observed in the JPY sample. This indicates that in DPY zeolite, the interaction between P and the zeolite is stronger and less prone to loss. Moreover, P is more uniformly distributed on the surface and bulk phase of DPY than JPY sample.

A Comprehensive Study of Al2O3 Mechanical Behavior Using Density Functional Theory and Molecular Dynamics.

This study comprehensively investigates Al2O3's mechanical properties, focusing on fracture toughness, surface energy, Young's modulus, and crack propagation. The density functional theory (DFT) is employed to model the vacancies in Al2O3, providing essential insights into this material's structural stability and defect formation. The DFT simulations reveal a deep understanding of vacancy-related properties and their impact on mechanical behavior. In conjunction with molecular dynamics (MD) simulations, the fracture toughness and crack propagation in Al2O3 are explored, offering valuable information on material strength and durability. The surface energy of Al2O3 is also assessed using DFT, shedding light on its interactions with the surrounding environment. The results of this investigation highlight the significant impact of oxygen vacancies on mechanical characteristics such as ultimate strength and fracture toughness, drawing comparisons with the effects observed in the presence of aluminum vacancies. Additionally, the research underscores the validation of fracture toughness outcomes derived from both DFT and MD simulations, which align well with findings from established experimental studies. Additionally, the research underscores the validation of fracture toughness outcomes derived from DFT and MD simulations, aligning well with findings from established experimental studies. The combination of DFT and MD simulations provides a robust framework for a comprehensive understanding of Al2O3's mechanical properties, with implications for material science and engineering applications.

Synthesis of Platinum–Rare-earth Sub-Nanoclusters via an aluminum vacancy trapping strategy

Synthesizing homogeneous supported bimetallic sub-nanoclusters (with a diameter below 1 nm) that exhibit excellent stability and resistance to sintering at elevated temperatures remains a significant challenge. Herein we report on the synthesis of 14 combinations of platinum with rare earth metal (PtxLn/Al2O3) via an innovative aluminum (Al) vacancy trapping route, resulting in a particle size of approximately 0.4 nm. The salts containing Pt and Ln (Ln denotes rare earth metals) were selected to adsorb on the Al vacancies. When tested in propane dehydrogenation at 580 °C, the supported bimetallic sub-nanoclusters (PtxLn/Al2O3) demonstrated a significant improvement in catalytic performance, with an increase of 2∼7 times compared to Pt-rare earth metal nanoparticle catalysts of similar nature. These sub-nanoclusters exhibited exceptional stability and resistance to carbon deposition.

High-Transconductance and Low-Leakage Current Single Aluminum Nitride Nanowire Field Effect Transistor

This study presents electrical transport properties of a catalyst-free grown single aluminum nitride nanowire field effect transistor (AlNNW-FET) exhibiting a very high transconductance of 26.9 pS, high on/off current ratio of 795.9, high conductivity of 9.8 x 10-4 Ω-1.cm-1, and a very low leakage current of 10 pA. The conductivity of AlN nanowire is two orders of magnitude higher than the reported studies. The AlNNW-FET reveals a dominant p-type conductivity. The p-type conductivity can be attributed to aluminum vacancies and complexes composed of Al vacancies and oxygen impurities. In consequence, the fabricated AlNNW-FET with high-performance, cost-effectiveness, and high-power efficiency is very well suited for use in low power and high temperature nanoelectronic and piezoelectric sensor applications, as well as integrated electro-optical devices including optomechanical devices and pyroelectric photodetectors.

Ab initio study on electronic structure and magnetism of AlN and InSe monolayer

Based on the first-principle calculations, the magnetism and electronic structures of AlN and InSe monolayers have been investigated. Calculation results show that the system exhibits spin-polarization when the AlN monolayer contains aluminum vacancy (VAl) or nitrogen vacancy (VN), generating magnetic moments of 3.0 μВ and 1.0 μВ, respectively. The formation energy study indicates that VN defects are more likely to be formed than VAl defects. Besides, the 3d transition metal atoms Cr, Mn, Fe, Co, and Ni doped the AlN monolayer, which generated magnetic moments in the order of the atoms 3.0 μВ, 4.0 μВ, 5.0 μВ, 4.0 μВ, and 3.0 μВ, respectively. Mn–Mn is dominated by ferromagnetic coupling at distant distances. Research results express that the InSe film produced a magnetic moment of 1 μВ when the material contained In vacancies (VIn). The magnetism of the film does not change by applying strain.

Influence of vacancies on the stability and mechanical properties of V2AlC: Guidelines for etching MAX phases via ab initio calculations

This study focuses on the ideal etching of defective MAX phases in a mechanical exfoliation process to produce vanadium-based MXenes. Two-dimensional MXenes exhibit high structural stability and excellent electrical conductivity, and can be applied as electrode materials. Mechanical exfoliation can be facilitated by modifying the vacancy in the V2AlC MAX phase, which makes etching challenging. We report the effects of M (vanadium), A (aluminum), and X (carbon) vacancies on the mechanical behavior of V2AlC via ab initio calculations. To this end, the anisotropic mechanical properties and strain–stress curves were calculated for MAX phases with different vacancies (x = 0.08, which corresponds to 8.33 at.%). The presence of vanadium vacancies significantly deteriorated the structural and mechanical properties compared to those of aluminum and carbon vacancies. Thus, it was confirmed that vanadium vacancies had a significant effect on the mechanical exfoliation of the MAX phases. These findings provide further insights into the design of MXenes.

Understanding the Intrinsic Rectification Properties of Nanoporous Anodic Alumina by Selective Chemical Etching.

The distribution of oxygen and aluminum vacancies across the hemispherical barrier oxide layer (BOL) of nanoporous anodic alumina (NAA) relies intrinsically on the electric field-driven flow of electrolytic species and the incorporation of electrolyte impurities during the growth of anodic oxide through anodization. This phenomenon provides new opportunities to engineer BOL's inherited ionic current rectification (ICR) fingerprints. NAA's characteristic ICR signals are associated with the space charge density gradient across BOL and electric field-induced ion migration through hopping from vacancy to vacancy. In this study, we engineer the intrinsic space charge density gradient of the BOL of NAA under a range of anodizing potentials in hard and mild anodization regimes. Real-time characterization of the ICR fingerprints of NAA during selective etching of the BOL makes it possible to unravel the distribution pattern of vacancies through rectification signals as a function of etching direction and time. Our analysis demonstrates that the space charge density gradient varies across the BOL of NAA, where the magnitude and distribution of the space charge density gradient are revealed to be critically determined by anodizing the electrolyte, regime, and potential. This study provides a comprehensive understanding of the engineering of ion transport behavior across blind-hole NAA membranes by tuning the distribution of defects across BOL through anodization conditions. This method has the potential to be harnessed for developing nanofluidic devices with tailored ionic rectification properties for energy generation and storage and sensing applications.

Purification mechanism of microbial metabolism in kitchen-oil wastewater enhanced by cationic vacancies on γ-Al2O3

The use of catalyst materials to mediate the enhancement of microbial degradation in wastewater is a new economic and energy saving breakthrough in water treatment technology. In this study, γ-Al2O3, which is commonly used as catalyst/carrier, is used as biological filler to treat kitchen-oil wastewater with low biodegradability, and the COD removal rate is about 50 %. It is found that the complexation of cationic vacancies on Al2O3 surface with extracellular polymeric substance (EPS) secreted by microorganisms in wastewater lead to the polarization of electron distribution on biofilm. The efficient degrading bacteria are enriched on reaction interface and obtain electrons to maintain electron dynamic balance by enhancing the transmembrane metabolism of pollutants. The aluminum vacancies on Al2O3 surface accelerate the microbial degradation of pollutants. The cationic vacancies in the structure of catalyst accelerate the acquisition of exogenous electrons by microorganisms without the addition of external energy, which provides a new idea for catalytic fillers to enhance wastewater degradation.

The crystallographic orientation dependent anisotropic corrosion behavior of aluminum in 3.5 wt% NaCl solution

In this paper, a quantitative method to evaluate the degree of differences in corrosive behavior of different crystallographic-oriented planes of Al and Al alloys in 3.5 wt% NaCl solution is provided. The corrosion potential Ucorr, corrosion current density Icorr and electrochemical corrosion rate of (100), (110) and (111) ideal surfaces and corresponding surfaces with vacancy and chloride ion adsorption considerations in single-crystal aluminum were derived by first principles calculation. The results show that the corrosion potential and corrosive current density increases in the order of U(110)corr<U(100)corr<U(111)corr and I(111)corr<I(100)corr<I(110)corr, respectively, and the electrochemical corrosion rate of (111) surface is 0.01×10-3 mm/a, showing the superior corrosion resistance. Moreover, the effect of the addition of alloying elements on the corrosion behavior of M−alloying Al alloy matrix in comparison with pure Al was further investigated by first principles calculation, and elements of Li, Mg, Zn, Ag and Cd are selected to improve the corrosion resistance of Al alloy.

Densification process of a 95% alumina ceramic during the intermediate stage of sintering in air, and O2

Sintering in pure O2 can enhance the densification of oxide ceramics during the final stage of sintering, but little attention has been paid on its effect on the densification process during the intermediate stage of sintering. This paper measures the shrinkage processes of a 95% alumina ceramic during the intermediate stage of sintering in air and O2 at different heating rates, and analyzes them by the master sintering curve (MSC) theory. It is found that the densification of the alumina ceramic sintered in air is obviously rapider than that in O2 at the heating rate of 15 K/min, while it is slower than that in O2 at the heating rate of 2.5 K/min. MSC analysis reveals that the apparent activation energy of sintering in O2 is lower than that in air, and this might be attributed to it that O2 restrains the diffusion of aluminum vacancies together with oxygen vacancies stoichiometrically, but favors the diffusion of aluminum vacancies and the transformation between O2 and aluminum vacancies on the surface.

Interaction of hydrogen with aluminum vacancies in the Y$$_3$$Al$$_5$$O$$_{12}$$ garnet and effects on positron trapping

Interaction of hydrogen with aluminum vacancies in the Y$$_3$$Al$$_5$$O$$_{12}$$ garnet and effects on positron trapping

Evaluation of argon ion impact parameters in aluminium oxide by means of SRIM program and investigation of the effect of argon ion implantation on the thermoluminescence properties aluminium oxide

The thermoluminescence properties of aluminium oxide (alumina) implanted with 80 keV argon ions at fluences in the range of were investigated. The unimplanted and implanted samples were irradiated at a dose of 40 Gy and heated at a rate of 1°C/s. The glow curve of unimplanted and implanted samples shows 5 distinct peaks; the main dosimetric peak and four other peaks of lower intensity. In this study, our analysis has focussed on the main dosimetric peak located at 180°C, 191°C, 177°C, 208°C, 219°C and 207°C for the unimplanted sample and implanted samples respectively. It was observed that the TL intensity decreases with fluence of implantation. This suggests that ion implantation decreases the concentration of electron traps responsible for thermoluminescence. It can also be suggested that competition effects involving radiative pathways and non-radiative competitor traps may lead to a low thermoluminescence signal in the implanted samples in comparison to the unimplanted thermoluminescence signal. These competitive processes will tend to favour first-order kinetics, and consequently lead to a strong stability of the glow curve shapes. The creation of defect clusters as well as extended defects could also be responsible for the reduction in TL signal. The stopping and range of atoms in matter (SRIM) was used to evaluate the ion impact parameters including ion range, vacancy distribution and energy loss in Al2O3. Subsequent to ion implantation, it was found that the number of oxygen vacancies which are related to electron traps are higher than the number of aluminium vacancies. Kinetic analysis was carried out by means of the initial rise, Chen’s peak shape, various heating rate, the whole glow curve, glow curve fitting and isothermal decay methods. The activation energy was found to be around and the frequency factor to be of the order regardless of the implantation fluence. The dosimetric features of samples were also investigated at doses in the range of 40–200 Gy. Samples generally showed a superlinear response at doses less than 140 Gy and sublinear response at doses higher than 160 Gy.