Ga Oxide Research Articles

Liquid Metal Electrocatalyst with Ultralow Pt Loading for Ethanol Oxidation

Developing efficient and durable electrocatalysts for ethanol electro‐oxidation is crucial for enabling the application of direct ethanol fuel cell technology. Herein, it is demonstrated that Pt–Ga liquid metal‐based nanodroplets can serve as an efficient electrocatalyst to drive ethanol oxidation. The mass activity of Pt is significantly improved by alloying with liquid gallium. Guided by machine learning neural networks, a low‐concentration alkaline electrolyte is specifically formulated to allow electrodes with ultralow Pt loading to demonstrate remarkable activity toward ethanol oxidation with a mass activity as high as 13.47 A mg−1Pt, which is more than 14 times higher than that of commercial Pt/C electrocatalysts (i.e., 0.76 A mg−1Pt). Computational studies reveal that the superior activity is associated with the presence of Ga oxides adjacent to Pt on the catalyst surface which leads to energetically favorable pathways for the oxidation process. The findings reveal untapped opportunities in the realm of liquid metal catalysis and hold great promise for the future development of high‐performance alcohol fuel cells.

Structure, Raman spectroscopy, and magnetic properties of new Al, Ga, and Mn-based high entropy oxides

Recent advancements in high entropy oxides (HEOs) have sparked significant interest as a promising frontier in materials research, revolutionizing the landscape of material design and properties. They exhibit outstanding stability, intriguing functional properties, and unparalleled design flexibility enabled by the inclusion of multiple cations in these materials. In this study, we successfully stabilized several new high entropy spinel oxides with compositions (Ni0.2(Mg/Mn)0.2Co0.2Cu0.2Zn0.2)B2O4 (B = Al, Ga, Mn). The room temperature X-ray diffraction (RT-XRD), field emission scanning electron microscopy (FE-SEM), and energy dispersive spectroscopy (EDS) measurements highlight the crystal structure of the materials with excellent chemical homogeneity at the micro-scale. RT-XRD and Raman spectroscopy confirmed the formation of single-phase cubic spinel structures. However, the Mn-based sample exhibited tetragonal distortion. Magnetic measurements show remarkable variation in the magnetic properties: (Ni0.2Mg0.2Co0.2Cu0.2Zn0.2)Mn2O4 shows complex ferrimagnetic behavior, Al and Ga based diamond lattice (Ni0.2Mg0.2Co0.2Cu0.2Zn0.2)B2O4 (B = Al and Ga) materials revealed extremely high magnetic frustration and absence of magnetic ordering down to 1.8 K, indicative of exotic frustrated state. Magnetic transitions (spin-glass like) are observed in (Ni0.2Mn0.2Co0.2Cu0.2Zn0.2)B2O4 (B = Al and Ga) materials. Our study highlights the potential to finely tune the magnetic responses through compositional engineering, thus paving the way for the development of tailored magnetic materials for various applications.

Plasmonic Al, Ga and in-doped zinc oxide nanoparticles as key components for the design of electrophoretic inks with MWIR and LWIR absorbance properties

Doped zinc oxide nanocrystals (NCs) are halfway through semiconductors and metals. They exhibit unique optoelectronic properties from a high surface density of free-charge-carriers, which are responsible for localized surface plasmon resonance (LSPR). Here, a one-pot approach is presented to synthesize doped aluminum, gallium or indium zinc oxide NCs, making them all stable in non-polar media. The effect of doping on the growth mechanisms and the final crystalline structure were studied as a function of the aliovalent doping atom used. Doping atoms were integrated by substitution of Zn atom into the crystalline mesh of ZnO with a wurtzite phase identified as the primary crystalline phase for all samples by X-ray Diffraction (XRD). Typical aluminiun doped ZnO NCs (AZO) or Gallium doped NCs (GZO) nanoflowers were identified as a single crystalline structure by High-Resolution-Transmission Electron Microscopy (HR-TEM). Indium doped ZnO NCs (IZO) and pristine ZnO appeared significantly different with spherical and heart-like shapes, respectively. The doping level tendency was identified through Energy Dispersive X-ray (EDX) and increased form Al to Ga and In doping atoms. All plasmonic doped NCs have broadband infrared absorption in the Middle-wave (MWIR) and Long-wave infrared (LWIR) wavelengths, making them interesting for thermal regulation or thermal camouflage. As part of the latter application, dispersions of doped ZnO NCs were formulated as electrophoretic inks and their IR-absorbing performances determined by using a homemade setup including an infrared camera. AZO, GZO, and IZO NCs based inks achieved temperature contrasts of 15 °C and 6 °C in the MWIR and LWIR wavelengths.

Sustainable sonoprocess for synthesizing γ-Ga2O3/In3Sn core–shell submicron particles via acoustic emulsification and oxidation of molten EGaInSn at room temperature

This study investigated the sustainable room-temperature synthesis of In3Sn/γ-Ga2O3 core–shell particles via an acoustic route using molten eutectic Ga–In–Sn alloy (EGaInSn). Sonication was used for the emulsification and oxidation steps. During the emulsification step, the sonication of molten EGaInSn in ethanol (EtOH) at 45 kHz facilitated the formation of the smallest EGaInSn particles (average diameter, Dav = 782 nm). In terms of EGaInSn particle size, 45 kHz sonication was suitable for emulsification of molten EGaInSn and ethanol system than 24 kHz sonication.During the oxidation step, the preferential oxidation of Ga in the EGaInSn particles occurred via sonication in a solution of EtOH and hydrazine monohydrate (N2H4·H2O). This selective oxidation of Ga on the surface of the EGaInSn particles resulted in the formation of In3Sn/γ-Ga2O3 core–shell particles via sonication at 45 kHz and room temperature.The entire process eliminated the need for dispersants and high-temperature treatments. Additionally, the process did not generate waste fluid containing counter anions, such as chloride anions. This sustainable sonochemical method offers a carbon–neutral approach for synthesizing functional nanocomposites with improved safety, simplicity, and energy efficiency.

Surface Oxidation of GaN(0001) Simulated by Charge‐Transfer‐Type Molecular Dynamics

In this study, the oxidation of Ga–polar GaN(0001) surface simulated by using originally developed charge‐transfer‐type interatomic potential is reported on. The adjusted potential parameters reproduce the cohesive energies in the range of 0.3 eV atom−1 and atomic forces with correlation coefficient as high as 0.9, compared to the results of first‐principles calculations for more than 9000 structures associated with oxidation of GaN. The oxidation simulations reveal the formation of a periodic gallium oxide (GaOx) layer grown on GaN(0001) with O atoms replacing N atoms. The atomic distance between Ga–Ga in the GaOx layer along GaN[0001] direction is 3.05 Å, which is longer than wurtzite GaN (2.63 Å) and is quantitatively in agreement with the recent photoelectron holography measurement. The distances of the Ga atoms projected onto the GaN(11–20) plane are determined to be 3.19 Å for the GaOx layer and 2.79 Å for the interfacial GaN. These distances also align quantitatively with the scanning transmission electron microscopy imaging of the native oxide on GaN(0001). Further oxidation simulation in a larger model of 2304 atoms suggests the formation of the layered structure even in the subsequent layers away from the interface of GaN and gallium oxide.

Active metal-free CaO-based dual-function materials for integrated CO2 capture and reverse water–gas shift

Integrated CO2 capture and conversion into CO via the reverse water–gas shift reaction (ICCC-RWGS) using CaO-based dual-function materials (DFMs) offers an attractive avenue for mitigating anthropogenic CO2 emissions. Active metal-free CaO-based DFMs have advantages such as no CO formation at the CO2 capture stage and high CO selectivity across a broad temperature range at the CO2 conversion stage, yet they face challenges with low CO yield. Herein, we report the enhanced performance of CaO-based DFMs co-doped with gallium (Ga) and zirconium (Zr) oxides in the ICCC-RWGS process. This improvement can be attributed to the synergistic interaction among Ca, Ga and Zr oxides, resulting in reduced CaO crystallites, enhanced surface basicity, and increased concentration of oxygen vacancies. The most promising DFM consists of 90 wt% CaO, 4.5 wt% Ca3Ga4O9 and 5.5 wt% CaZrO3 (with a Ga/Zr molar ratio of 1). When exposed to a simulated flue gas (5 % O2, 10 % H2O, 15 % CO2, and 70 % N2), this DFM exhibits a stable CO2 capture capacity of 11.90 mmol/gDFM over 20 consecutive isothermal ICCC-RWGS cycles at 650 °C. Meanwhile, its CO2 conversion and CO yield are maintained at 83.4 % and 10.26 mmol/gDFM, respectively. This study highlights the significance of a multi-metal oxide synergistic strategy in CaO-based DFMs to achieve superior performance in the ICCC-RWGS process.

Electronic perturbation-promoted interfacial pathway for facile C–H dissociation

Interface has often played significant role in the behavior of metal-based catalysts during various heterogeneous reactions. Herein, we reported a novel interfacial pathway for propane dehydrogenation on Pt-GaOx dual sites. The active ensemble, composing Pt particles and Ga2O3 clusters, facilitates the facile dissociation of C–H bonds (energy barrier < 0.30 eV) through H-abstraction by O sites, coupled with alkyl stabilization on the Pt surface. Notably, the electronic perturbation of the Pt slab induces higher-lying O 2p states at the interface, accompanied by a substantial density of states around fermi level. This is in stark contrast to the O species present in Ga2O3 crystals or clusters alone, leading to an exceptionally strong affinity for H and a robust ability for C–H scission. The Pt/Ga-Al2O3 catalysts prepared with Pt nanoparticles decorated by Ga oxide exhibit superior performance compared to Pt/Al2O3 and PtSn/Al2O3 catalysts. This insight into interfacial catalysis contributes to a broader understanding of the origin of the high catalytic efficiency observed in metal-based catalysts.

Self-healing transparent ionogel polymerized by liquid metal for strain sensor

Flexible electronic devices, sensing human movement and monitoring physiological signals, might be useful for performing research in the area of intelligent detection. Gallium (Ga), a liquid metal (LM), is often used as a soft conductive material in the form of droplets because of its unique properties. Herein, a liquid metal-induced ionogel is synthesized by polymerizing acrylic acid (AA) with the existence of poly(diallyldimethylammonium chloride) (PDDA) and Ga droplets. In the system, the free radical formed from Ga oxidation process initiates the polymerization of AA. Meanwhile, the Ga3+ produced by Ga oxidation forms a coordination with the –COO− on PAA chains. The coordination crosslinking sites create slip when the gel is exposed to external force, increasing the stretchability (5000 %) of the ionogel. When the Ga droplets are completely oxidized to Ga3+, the gel changes from silvery gray to transparent (80 %). In addition, the ionic liquids and the electrostatic interactions within the network enable the resultant ionogel anti-dehydration (98 %) and self-healing performances in a wide temperature range (-20 ∼ 20 °C). The liquid metal-induced ionogel can be assembled into a flexible sensor with adequate sensitivity, rapid response time (240 ms), and cyclic stability, demonstrating human movement patterns with accuracy to keep track of physiological signs.

Nanoengineering Liquid Metal Core–Shell Nanostructures

AbstractNanoengineering the composition and morphology of functional nanoparticles endows them to perform multiple tasks and functions. An intriguing strategy for creating multifunctional nanomaterials involves the construction of core–shell nanostructures, which have enabled promising applications in biomedicine, energy, sensing, and catalysis. Here, a straightforward nanoengineering approach is presented utilizing liquid metal nanoparticles and galvanic replacement to create diverse core–shell nanostructures. Controlled nanostructures including liquid metal core‐gold nanoparticle shell (LM@Au), gold nanoparticle core‐gallium oxide shell (Au@Ga oxide), and hollow Ga oxide nanoparticles are successfully fabricated. Remarkably, these investigations reveal that LM@Au exhibits exceptional photothermal performance, achieving an impressive conversion efficiency of 65.9%, which is five times that of gold nanoparticles. By leveraging the high photothermal conversion efficiency and excellent biocompatibility of LM@Au, its promising application in hyperthermia cancer therapy is demonstrated. This simple yet powerful nanoengineering strategy opens new avenues for the controlled synthesis of complex core–shell nanostructures, advancing various fields beyond biomedicine.

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.

Unravelling the Surface Oxidation-Induced Evolution of the Electronic Structure of Gallium.

Gallium is widely used in liquid metal catalyst fabrication, and its oxidized species is a well-known dielectric material. In the past decades, these two species have been well studied separately. However, the surface oxide layer-induced impact on the chemical and electronic structure of (liquid) gallium is still mostly unclear because of the extreme fast formation of thermodynamically stable surface Ga2O3. In this study, we used a combination of direct and inverse photoemission complemented by scanning electron microscopy to examine the surface properties of Ga and Ga oxide (on a SiOx/Si support) and the evolution of the surface structure upon stepwise oxidation and subsequent reduction at an elevated temperature. We find oxidation time-dependent self-limited formation of a substoichiometric Ga2O3-δ surface layer on the Ga nanoparticles. The valence band maximum (conduction band minimum) for this Ga2O3-δ is located at -3.8 (±0.1) eV [1.4 (±0.2) eV] with respect to the Fermi level, resulting in an electronic surface band gap of 5.2 (±0.2) eV. Upon annealing in ultrahigh vacuum conditions, the Ga2O3-δ surface layer can efficiently be removed when using temperatures of 600 °C and higher. This study reveals how the surface properties of Ga nanoparticles are influenced by stepwise oxidation-reduction, providing detailed insights that will benefit the optimization of this material class for different applications.

Mechanistic Insights into Myofibrillar Protein Oxidation by Fenton Chemistry Regulated by Gallic Acid.

Gallic acid (GA, 3,4,5-trihydroxybenzoic acid) is a widely used natural food additive of interest to food chemistry researchers, especially regarding its effects on myofibrillar protein (MP) oxidation. However, existing studies regarding MP oxidation by GA-combined with Fenton reagents are inconsistent, and the detailed mechanisms have not been fully elucidated. This work validated hydroxyl radical (HO·) as the primary oxidant for MP carbonylation; in addition, it revealed three functions of GA in the Fenton oxidation of MP. By coordination with Fe(III), GA reduces Fe(III) to generate Fe(II), which is the critical reagent for HO· generation; meanwhile, the coordination improves the availability and reactivity of Fe(III) under weakly acidic and near-neutral pH, i.e., pH 4-6. Second, the intermediates formed during GA oxidation, including semiquinone and quinone, promoted Fenton reactivity by accelerating Fe catalytic cycling. Finally, GA can scavenge HO· radicals, thus exhibiting a certain degree of antioxidant property. All three functions contribute to MP oxidation as observed in GA-containing meat.

Unraveling surface structures of gallium promoted transition metal catalysts in CO2 hydrogenation

Gallium-containing alloys have recently been reported to hydrogenate CO2 to methanol at ambient pressures. However, a full understanding of the Ga-promoted catalysts is still missing due to the lack of information about the surface structures formed under reaction conditions. Here, we employed near ambient pressure scanning tunneling microscopy and x-ray photoelectron spectroscopy to monitor the evolution of well-defined Cu-Ga surfaces during CO2 hydrogenation. We show the formation of two-dimensional Ga(III) oxide islands embedded into the Cu surface in the reaction atmosphere. The islands are a few atomic layers in thickness and considerably differ from bulk Ga2O3 polymorphs. Such a complex structure, which could not be determined with conventional characterization methods on powder catalysts, should be used for elucidating the reaction mechanism on the Ga-promoted metal catalysts.

Element Distribution in Porous Ga Oxide Obtained by Anodizing Ga in Phosphoric Acid

A STEM/EDS study of a porous Ga oxide film formed by an anodization process was conducted in this study to examine the crystalline structure of the film and the elemental distribution in the oxide film before and after heat treatment. The as-formed anodic film with a morphology resembling the well-known porous anodic Al oxide film was amorphous, crystallizing after heat treatment at 600 °C without changing the morphology and elemental distribution. The EDS elemental maps disclosed the duplex nature of the pore wall oxide; the phosphate anion was contaminated in the outer oxide layer next to the pores, and the inner layer consisted of relatively pure Ga oxide, practically free from phosphate. The similarity of morphology and elemental distributions between the porous anodic Al and Ga oxides suggests that the growth of both anodic oxide films proceeds under the same mechanism. In addition, crystallized porous Ga oxides are expected to be applied to fabricate various functional devices requiring geometrically controlled semiconductor nanohole arrays, such as devices for hydrogen formation.

Formation of porous Ga oxide with high-aspect-ratio nanoholes by anodizing single Ga crystal

I developed a simple crystal growth process to obtain a single Ga crystal. The crystal orientation of a Ga plate could be controlled by a crystal growth process using a seed Ga crystal. By anodizing a [100]-direction highly oriented Ga plate, I realized the formation of a highly ordered array of high-aspect-ratio straight nanoholes. It was observed that the nanohole growth direction depends on the crystal orientation of a Ga plate. To date, this dependence has yet to be observed in materials other than porous Ga oxide obtained by an anodization process. The present fabrication process is expected to be applied to the fabrication of various functional devices requiring a porous Ga oxide with high-aspect-ratio straight nanoholes, such as hydrogen formation devices and functional filters.

Ultrafast RTA induced the structural properties of the deficient oxygen β-Ga2O3 film

The RF-sputtered β-Ga2O3 films prepared on sapphire substrates were treated by rapid thermal annealing (RTA) with an ultrafast processing time of 30 s. The effects of RTA at different process temperatures from 600 to 800 °C on the β-Ga2O3 films were researched. Meanwhile, the schematic diagram for the RTA-induced lattice expansion of films was proposed. The experimental results showed that the variation of Ga oxidation states and lattice oxygen was demonstrated, revealing a greater value of lattice oxygen at 700 °C. The (-201) orientation of Ga2O3 films is observed at 700 °C and 800 °C, where the (111) orientation additionally appeared at 800 °C. The larger grain size and interplanar distance of 4.71 Å for the (−201) orientation were also obtained at 700 °C, accounting for the high-quality β-Ga2O3 films and their lattice expansion. As a result, this RF-sputtered β-Ga2O3 films via the RTA process not only provide a new reference condition but also suitable for optoelectronic devices requiring control of crystallizing temperature and lattice variation.

Oxidation of Pu alloys stabilized in δ–phase: Study of Ga alloying element behavior by using EXAFS analysis and Reverse Monte Carlo simulation

Studies were performed to improve the knowledge about Ga behavior during oxidation of Pu alloys stabilized in δ–phase. The coupling of EXAFS experiments with Reverse Monte Carlo (RMC) simulation of 3D material structure has achieved the characterization of the atomic local environment around Pu and Ga atoms in the outer PuO2 layer formed on a δ−PuGa 1 at% alloy. No formation of Ga aggregates or Ga oxides was detected. The RMC analysis of experimental data has revealed the presence of Ga atoms within the lattice of the oxide scale in Pu substitutional sites or octahedral sites. Nevertheless, this incorporation leads to a large local disorder with a displacement of Ga atoms from their initial high symmetry crystallographic site. Finally, the results obtained bring new insights explaining the destabilization of the δ−phase by the diffusion of Ga atoms likely into Pu vacancies in PuO2 lattice during oxidation.

XPu(CO)n (X = B, Al, Ga; n = 2 to 4): π Back-Bonding in Heterodinuclear Plutonium Boron Group Compounds with an End-On Carbonyl Ligand.

The bonding situation and the oxidation state of plutonium in heterodinuclear plutonium boron group carbonyl compounds XPu(CO)n (X = B, Al, Ga; n = 2 to 4) were investigated by systematically searching their ground-state geometrical structures and by analyzing their electronic structures. We found that the series of XPu(CO)n compounds show various interesting structures with an increment in n as well as a changeover from X = B to Ga. The first ethylene dione (OCCO) compounds of plutonium are found in AlPu(CO)n (n = 2, 3). A direct Ga-Pu single bond is first predicted in the series of GaPu(CO)n, where the bonding pattern represents a class of the Pu → CO π back-bonding system. There is a trend where the Pu-Ga bonding decreases and the Pu-C(O) covalency increases as the Ga oxidation state increases from Ga(0) to Ga(I). Our finding extends the metal → CO covalence back-bonding concept to plutonium systems and also enriches plutonium-containing bonding chemistry.

Atomic structures and electronic properties of molecular oxygen adsorption on In0.19Ga0.81As(100) surface: Ab-initio study combined with XPS/UPS analysis

Due to the surface oxidation issues, the performances of InGaAs photocathodes are hindered in practical applications, so it is necessary to carry out the corresponding research from theory to experiment. Through ab-initio study based on density functional theory, molecular oxygen adsorption at different sites on the nonpolar In0.19Ga0.81As(100) β2(2 × 4) surface is investigated from the perspectives of atomic and electronic properties. By chemical absorption, molecular oxygen easily dissociates into atomic oxygen when combining with two surface atoms of the same type. The calculation results show that As oxides have the largest destructive effect, followed by Ga oxides, while the In oxides are the least destructive. In addition, the most stable adsorption is the bonding of O atom with Ga atoms, while the bonding of O atom with As atoms is relatively unstable. Combined with the surface analysis method of photoelectron spectroscopy, it is found that the unstable As oxides are the easiest to remove, followed by the In oxides, while the Ga oxides are the most difficult to remove. It is concluded that the work function of the InGaAs surface decreases with the reduction of these oxides, which is conducive to the subsequent preparation of negative-electron-affinity InGaAs photocathodes.

Sonochemical synthesis of supersaturated Ga–Al liquid-alloy fine particles and Al3+-doped γ-Ga2O3 nanoparticles by direct oxidation at near room temperature

In this study, we investigated the fabrication of supersaturated gallium (Ga)–aluminum (Al) liquid alloy and Al3+-doped γ-Ga2O3 nanoparticles (NPs) at near room temperature (60 °C) using sonochemical and sonophysical effects. Supersaturated Ga–Al liquid alloy microparticles (Dav = 1.72 µm) were formed and stabilized at 60 °C by the thermal nonequilibrium field provided by sonochemical hot spots. Compared with liquid Ga, supersaturated Ga–Al liquid alloy was rapidly oxidized to a uniform oxide without Al2O3 or Al deposition. Thus, ultrafine Al3+-doped γ-Ga2O3 NPs were obtained after only 1 h of ultrasonic irradiation at 60 °C. The oxidation of liquid Ga was remarkably accelerated by alloying with metallic Al and ultrasonic irradiation, and the time was shortened. The average diameter and surface area of the γ-Ga2O3-based NPs were 59 nm and 181 m2/g, respectively. Compared with γ-Ga2O3, the optical bandgap of the Al3+-doped γ-Ga2O3 NPs was broadened, and the thermal stability improved, indicating Al3+-doping into the γ-Ga2O3 lattice. However, the lattice constant of γ-Ga2O3 was almost unchanged with or without Al3+-doping. Al3+ was introduced into the defect sites of Ga3+, which were massively induced in the defective spinel structure during ultrasonic processing. Therefore, sonochemical processing, which provides nonequilibrium reaction fields, is suitable for the synthesis of supersaturated and metastable materials in metals and ceramics fields.