Solid Ga Research Articles

4d Metal-doped liquid Ga for efficient ammonia electrosynthesis at wide N2 concentrations

Electrocatalytic nitrogen reduction reaction under ambient conditions is a promising pathway for ammonia synthesis. Currently nitrogen reduction reactions are carried out in N2-saturated environments and use high-purity nitrogen as feedstock, which is costly. Here, we prepared carbon-coated ultra-low 4d metal Ru-doped liquid metal Ga (Ru0.06/LM@C) for NRR over a wide range of N2 concentrations. Comprehensive analyses show that the introduction of the ultra-low 4d element Ru can effectively adjust the electronic structure through orbital interactions, thus enhancing the adsorption of nitrogen-containing intermediates. The liquid catalyst utilized its mobility to provide a higher density of active sites. In addition, the material Ru0.06/Ga@C itself has the ability to promote product desorption. The three act synergistically to optimize the N2 mass transfer path, thereby increasing the *NNH coverage and further improving the ammonia yield over a wide range of N2 concentrations. The maximum NH3 yield of the catalyst can reach 126.0 μg h−1 mgcat−1 (at –0.3 V vs. RHE) with high purity N2 as feed gas, and the Faraday efficiency is 60.4% at –0.1 V vs. RHE. Over a wide range of N2 concentrations, the NH3 yield of the catalyst was greater than 100 μg h−1 mgcat−1 with a Faraday efficiency higher than 47%. The catalytic performance is much higher than that of solid Ga@C and reported p-block metal-based catalysts.

Observation of the liquid metal phase transition in optofluidic microcavities

Gallium (Ga) exhibits remarkable potential in flexible electronics, chemistry, and biomedicine due to its exceptional physical properties. The phase transition and supercooling characteristics of Ga have led to the emergence of numerous valuable applications. In this paper, we capitalize on this foundation by utilizing optofluidic microcavities supporting both high quality factor optical and optomechanical modes to investigate the phase transformation process and supercooling properties of Ga. Our study provides comprehensive insights into the dynamic behavior of Ga during the complete phase transition, such as measuring a hysteresis loop between the solid-to-liquid and liquid-to-solid transitions, revealing nonreciprocal resonance wavelength shift, and identifying a unique metastability state of Ga during melting. The linear thermal expansion coefficients of Ga were precisely measured to be 0.41 × 10−5 K−1 and −0.75 × 10−5 K−1 for solid and liquid Ga, respectively. Our research provides a comprehensive and versatile monitoring platform for newly fabricated liquid metal alloys, offering multidimensional insights into their phase transition behavior.

Local surface plasmon contrast between liquid and solid Ga nanostructure：strong shape dependence and small size effect

Gallium (Ga) is highly valuable as an “active" plasmon in nanooptics due to its low melting point. We numerically investigate the surface plasmon difference between liquid and solid states for spherical and cylindrical Ga nanostructures. In the deep UV–visible region, it is found that the liquid Ga nanostructures can exhibit more pronounced plasmon than the solid, and very high liquid-solid optical contrast is achieved in cylindrical Ga nanostructures. However, for spherical Ga particles in vacuum, the liquid-solid optical contrast is very low, and only extremely small Ga spheres have high liquid-solid optical contrast. In order to achieve high liquid-solid optical contrast, an appropriately large aspect ratio or small size of Ga nanostructures is required.The research will promote the fundamental understanding of the surface plasmon of liquid and solid Ga, and be important for optical sensing, phase-change optical storage and high-contrast optical switches.

Predicting the Density of Solid and Liquid Near-Eutectic Ga–In–Sn Alloy

Predicting the Density of Solid and Liquid Near-Eutectic Ga–In–Sn Alloy

High growth rate magnetron sputter epitaxy of GaN using a solid Ga target

Magnetron sputter epitaxy (MSE) is a promising processing route for group-III nitride semiconductors, with the potential to enable high-quality and low cost GaN growth for widespread use. However, fundamental technological hurdles must be overcome to enable the adoption of MSE in industrial production. Here, we present a new UHV-compatible magnetron design with high-performance cooling, enabling high GaN growth rates at high growth temperatures using a solid Ga target. The magnetron is tested with a wide range of process parameters and a stable process is feasible while maintaining the solid state of the Ga target. High GaN growth rates of up to 5 μm/h are achieved at room temperature and a growth rate of 4 μm/h at high temperature, which is one order of magnitude higher compared to MSE with a liquid target. We grow GaN on c-plane sapphire substrates and show the impact of partial pressure ratio and target-to-substrate distance (TSD) on growth rate, film morphology and crystal quality of GaN films with scanning electron microscopy and X-ray diffraction. While the growth rate and film morphology are strongly impacted by the process parameter variation, the crystal quality is further impacted by the overall film thickness. For a 2 μm thick GaN film a full width at half maximum of X-ray rocking curve (ω-FWHM) of GaN 10 1‾ 1 reflection of 0.32° is achieved. We demonstrate a process window for growth of dense and smooth GaN films with high crystal quality using low N2 flow rates and high TSD. By introducing a 20 nm AlN nucleation layer prior to the growth of 390 nm GaN, the ω-FWHM of GaN 0002 reflection of 0.19° is achieved. The epitaxially grown crystalline structure is precisely examined by transmission electron microscopy.

Chemical vapor deposition growth of [formula omitted] on Si- and C- face off-axis 4H–SiC at high temperature

Realization of β‐Ga2O3 on a high-thermal-conductivity substrate is crucial to overcome the poor thermal conductivity of β‐Ga2O3 which is one of the major roadblocks against its era in power electronics. We investigated low-pressure chemical vapor deposition (LPCVD) growth on both Si and C- face (0001) 4H–SiC at a high growth temperature of 925 °C using Ga metal and O2 gas source. Growths on C-face 4H–SiC resulted polycrystalline β‐Ga2O3 for the entire O2-flow range, whereas under optimized O2-flow conditions, step flow growth of (−201) β‐Ga2O3 was achieved on Si-face 4H–SiC with 3.7 nm rms surface roughness and rocking curve FWHM of 0.54° at a growth rate reaching 2.48 μm/h 4° off-axis nature of the substrate promoted the growth of some of the in-plane rotational domains while suppressing others. Raman measurements further verified the pure β‐Ga2O3 nature of the grown films. Using a customized LPCVD with solid source Ga, a cost-effective, safe and industrially scalable method was shown to pave the way to enable β‐Ga2O3 heteroepitaxy on 4H–SiC for high-power electronics.

Fundamental study on optical performance of low-melting-point metal mirrors for space telescopes

The installation of telescopes with larger primary mirrors in outer space is required for the study of the early universe. However, the shipping, assembling and maintenance of the primary mirror are technical challenges. The primary mirror made of low-melting-point metal (LMPM) enables to simplify these procedures. The rotating liquid metal surface is shaped into a parabola and solidified on the site. The technological feasibility depends on the dynamic transformation of the parabolic LMPM mirror and its optical reflectance. The dynamic transformation of LMPM mirror was clarified by means of experiments with liquid gallium (Ga) which has a melting point of 302.91 K. The parabolic shape of solid Ga mirror was produced by the axial rotation and the solidification. The parabolic shape agreed with the theoretical curve obtained by a physical model. The reflectance spectra on the surface of various LMPMs solidified (i.e., Ga, lead (Pb), tin (Sn), bismuth (Bi), lead-bismuth eutectic (Pb-Bi) and Wood’s metal (Bi-Pb-Sn-Cd)) were measured. The reflectance of Ga solidified was approximately 70 % and was not degraded in the near-infrared wavelength due to the favorable optical characteristics. The reflectance both for p-polarized and s-polarized light of Ga solidified was measured by the spectrophotometer with the polarizer at the angle of incidence of 30°, 45°, 60° and 75°. The trend of measured reflectance agreed with theoretical prediction.

Smart Adhesive Patches of Antibacterial Performance Based on Polydopamine-Modified Ga Liquid Metal Nanodroplets

Patches have been widely used in medical and healthcare, motion detection, and other fields. Patches are required to possess strong adhesive forces to keep them effectively adhered to the skin during use and to be removed from the skin with relative ease after usage. Moreover, a large number of bacteria will proliferate at the interface between the patch and the skin, when the patch is used for lengthy durations, which is harmful to human health. Hence, there is an increasing demand for patches with combined switchable adhesions and excellent antibacterial performances. Inspired by the natural adhesive performance of snail slime in wet (liquid) and dry (solid) states, smart Ga liquid metal nanodroplet-based polymer patch (GxPP, x = 10, 30, 50) with switchable adhesion properties were prepared by incorporating polydimethylsiloxane (PDMS) into polydopamine (PDA)-modified Ga nanodroplets (PDA-Ga). Since the melting point of Ga is 29.8 °C, solid Ga melts to the liquid state at temperatures above 29.8 °C, and this significantly decreases the modulus of GxPP, resulting in significantly decreased adhesive strength of GxPP. The adhesion of G30PP decreased from 40.4 to 22.1 kPa. In addition to this obvious change in the adhesion properties of GxPP, the unique antibacterial performances of Ga imparted GxPP with excellent antibacterial effects. Compared with the PDMS, the antibacterial rates of G30PP against Escherichia coli and Staphylococcus aureus were 98 and 99%, respectively. The excellent antibacterial performance and smart switchable adhesion properties of GxPP revealed its high application prospects in the field of wearable flexible skin electronics.

Fast Solidification of Pure Gallium at Room Temperature and its Micromechanical Properties

AbstractWith excellent electrical conductivity, fluidity, rheological property, and biocompatibility, gallium has been intensively studied in the fields of flexible electronics and devices, thermal management, and soft robotics. However, the large degree of supercooling of gallium presents a large limitation for phase transition‐related applications such as the very low temperature required for solidification, the impurities, and side effects brought in by nucleating agents. In this study, solidification process of liquid gallium by using solid gallium as a nucleating agent is discovered to be fast and facile at room temperature compared with other agent materials including copper, iron, and nickel. Quantificationally, solidified gallium as a nucleating agent, can effectively reduce the supercooling degree from about 66.3 to 14.8 °C. The freezing velocity can reach to 200 mm3 min−1. The possible mechanism is reducing the energy barrier via adding nucleation site, allowing rapid solidification at room temperature accompanying heat dissipation. Moreover, micromechanical properties are compared between raw solid Ga and the solidified Ga induced by Ga agent, which suggests a slight decrease in mechanical strength at room temperature with the nucleating agent. It will be beneficial to understand the phase change and also provide guidance for the application of gallium regarding its mechanical properties.

Structural and ultraviolet photo-detection properties of laser molecular beam epitaxy grown GaN layers using solid GaN and liquid Ga targets

GaN epitaxial layers have been grown on sapphire (0001) substrate by laser molecular beam epitaxy technique using laser ablation of polycrystalline GaN solid and liquid Ga metal targets in the ambient of nitrogen plasma. In-situ reflection high energy electron diffraction and exsitu atomic force microscopy observations revealed that GaN growth using solid target yields rough surface under three-dimensional growth mode while a flat surface GaN is obtained using liquid Ga target. From X-ray rocking curve measurement, it is also observed that the GaN layer grown using solid GaN target has a relatively better structural quality. X-ray photoelectron spectroscopy confirmed Ga–N bond formation and near-stoichiometric composition of the GaN epilayers. The influence of threading dislocation density on the ultraviolet (UV) photoresponse properties of GaN layers have been studied using metal-semiconductor-metal (MSM) based device structure. It is found that the GaN MSM structure obtained using solid GaN target with lesser screw and dislocation densities exhibits a higher responsivity with fast response and recovery time.

Vibration-enhanced direct contact heat exchange using gallium as a solid phase change material

This study experimentally addresses cooling hot liquid in a heat sink under mechanical vibrational excitations. We investigated vibration-enhanced direct contact heat exchange between hot water and a heat sink composed of a phase change material, solid gallium (Ga). The whole sink assembly was vibrated with a sinusoidal wave in the vertical direction. Latent heat and low melting temperature of Ga restricted the maximum temperature rise and the superheating of molten Ga between the water and the solid Ga body. The total amount of Ga melted during the heat exchange with water was measured, providing the share of latent and, in turn, sensible heat absorbed by Ga during the process. Vibration drastically enhanced the cooling rates of hot water under the tested frequencies (20 and 50 Hz) and amplitudes (0.3, 0.5 and 0.7 mm). The enhancement in water cooling was better pronounced for amplitudes higher than 0.3 mm. Under 50 Hz frequency and 0.7 mm amplitude, 99% of heat lost by water was dumped into the gallium sink and 1% was dissipated into the surrounding environment. Under static non-vibrating conditions the heat sink could only capture about 60% of the heat lost by the water. The rest was dissipated into the environment.

Electrochemical Behavior of Dysprosium in Fused LiCl–KCl Eutectic at Solid Inert Mo and Liquid Active Ga Electrodes

Cathodic reduction of Dy3+ ions on inert Mo and active Ga electrodes in fused 3LiCl–2KCl eutectic was studied at 723–843 K in inert atmosphere by transient electrochemical techniques. It was established that the cathodic reaction on solid Mo electrode is irreversible, proceeds in one stage, and controlled by the charge transfer rate. The dependence of the apparent standard potential of Dy3+/Dy couple vs temperature was determined. The apparent standard Gibbs energy change, enthalpy, and entropy of dysprosium trichloride formation from the elements in fused 3LiCl–2KCl eutectic were calculated. The electrode reactions of the LiCl–KCl–DyCl3 solution at liquid Ga electrode were investigated by open-circuit potentiometry. The red-ox potential of the Dy3+/Dy couple on Ga electrode was observed at more positive potential values than at the inert electrode. This potential shift was thermodynamically analyzed by lowering of activity of Dy in the metal phase due to the formation of intermetallic compounds. The apparent standard potentials of Dy–Ga alloys, and the activity coefficients of dysprosium in liquid Ga based alloys between 723 and 843 K were determined. The principle thermodynamic properties of the alloys were calculated.

Axial GaAs/Ga(As, Bi) nanowire heterostructures

Bi-containing III-V semiconductors constitute an exciting class of metastable compounds with wide-ranging potential optoelectronic and electronic applications. However, the growth of III-V-Bi alloys requires group-III-rich growth conditions, which pose severe challenges for planar growth. In this work, we exploit the naturally-Ga-rich environment present inside the metallic droplet of a self-catalyzed GaAs nanowire (NW) to synthesize metastable GaAs/GaAs1−xBix axial NW heterostructures with high Bi contents. The axial GaAs1−xBix segments are realized with molecular beam epitaxy by first enriching only the vapor–liquid–solid (VLS) Ga droplets with Bi, followed by exposing the resulting Ga-Bi droplets to As2 at temperatures ranging from 270 °C to 380 °C to precipitate GaAs1−xBix only under the NW droplets. Microstructural and elemental characterization reveals the presence of single crystal zincblende GaAs1−xBix axial NW segments with Bi contents up to (10 ± 2)%. This work illustrates how the unique local growth environment present during the VLS NW growth can be exploited to synthesize heterostructures with metastable compounds.

Phase Separation in Liquid Metal Nanoparticles

Nanoparticles produced from gallium-based liquid metal alloys have been explored for developing applications in the fields of electronics, catalysis, and biomedicine. Nonetheless, physical properties, such as phase behavior at micro-/nanosize scale, are still significantly underexplored for such nanoparticles. Here, we conduct an in situ investigation of phase behavior for gallium-based liquid metal nanoparticles and discover the unprecedented coexistence of solid particles in spherical liquid metal shells without the support of a crystalline substrate. The particles can also transform into solid Janus nanoparticles after temperature cycling. In addition, we investigate the optical properties of the nanoparticles before and after phase separation using in situ electron energy-loss spectroscopy. Most importantly, we discover that increasing the content of indium within the nanoparticle can stabilize the solid-core/liquid-shell structure at room temperature. This study provides a foundation to engineer liquid metal nanoparticles for developing new applications in nanoscale optical platforms and shape-configurable transformers.Although various electronic, chemical, and biomedical applications have been demonstrated for nanoparticles made from gallium-based liquid metal alloys, fundamental physical properties such as phase behavior of such nanoparticles are still significantly underexplored. Here, Tang and coworkers present the in situ investigation of phase separation in binary and ternary spherical liquid metal nanoparticles upon cooling, and demonstrate the coexistence of solid core/liquid shell without the support of a crystalline substrate. This study provides insight into engineering such nanoparticles for the development of new applications.Despite gallium-based liquid metal alloys attracting extensive attention for various applications, their phase behavior at the nanoscale is still underexplored. Understanding the impact of phase separation in nanoparticles can be extremely useful for developing new structures and exploring suitable applications. Here, we report on the investigation of phase behavior for spherical nanoparticles made from gallium-based liquid metal alloys upon cooling. We discover the thermally stable coexistence of solid cores in spherical liquid metal shells without the support of a crystalline substrate at room temperature. Given the unique properties of liquid metal, together with the facile process for producing core-shell and Janus nanoparticles, this work will encourage further investigation of the properties of such nanoparticles for developing applications in the fields of electronics, catalysis, nanomedicine, and beyond.

Interfacial phenomena associated with Li electrodeposition on liquid Ga substrates in propylene carbonate

Li electrodeposition on liquid Ga substrates was carried out in PC-LiClO4 at 40 °C. It was found that interfacial flow phenomena were induced by differences in interfacial tension between the liquid Ga and the liquid Ga-Li alloy formed on the substrate under potentiostatic electrolysis at −1.0 V (vs. Li+/Li), which caused the interfacial shape change of the liquid Ga electrode. We carried out in-situ observations in order to understand why such interfacial phenomena occur between the liquid electrolyte and the liquid metal cathode. Moreover, a significant difference in electrochemical response between liquid and solid Ga substrates was also noticed employing the current-time transient technique. These experimental results suggest that the process of liquid Ga-Li phase formation by the dissolution of electrodeposited Li atoms into the liquid Ga substrate dominated during the initial stage of Li electrodeposition. In contrast, the typical peaks induced by growth of solid Ga-Li alloy phase and Li metal phase were observed on solid Ga substrates. These results provide new insight into the design of electrochemical processing involving liquid electrolyte/liquid metal interface.

Low-pressure CVD-grown β-Ga2O3 bevel-field-plated Schottky barrier diodes

We report (010)-oriented β-Ga2O3 bevel-field-plated mesa Schottky barrier diodes grown by low-pressure chemical vapor deposition (LPCVD) using a solid Ga precursor and O2 and SiCl4 sources. Schottky diodes with good ideality and low reverse leakage were realized on the epitaxial material. Edge termination using beveled field plates yielded a breakdown voltage of −190 V, and maximum vertical electric fields of 4.2 MV/cm in the center and 5.9 MV/cm at the edge were estimated, with extrinsic RON of 3.9 mΩ·cm2 and extracted intrinsic RON of 0.023 mΩ·cm2. The reported results demonstrate the high quality of homoepitaxial LPCVD-grown β-Ga2O3 thin films for vertical power electronics applications, and show that this growth method is promising for future β-Ga2O3 technology.

Vapor–Solid growth of InP and Ga2O3 based composite nanowires

InP/Ga 2 O 3 core-shell nanowires were grown on Si substrate at 400 oC in the hydrazine (N 2 H 4 ) vapor diluted with 3 mol. % H 2 O. The crystalline InP and solid Ga served as source materials for the growth of nanowires. According to TEM and EDX data the nanowires consisted of wurtzite InP core with an amorphous Ga 2 O 3 shell. The minimum diameter of NWs was 14 nm, while the maximum lengths reached several micrometers. The twinned planes appeared in WZ InP core at increased nanowire diameters. Based on the obtained results and possible chemical reactions, the following mechanism was proposed for the growth of core-shell nanowires: pyrolytic decomposition of hydrazine caused the appearance of intermediate NH 2 , NH and H species in the vapor. At elevated temperatures the crystalline InP source was also dissociated to In droplets and phosphorus precursors. At source temperatures close to 600 oC, due to the interaction of In and Ga sources with water molecules and hydrazine decomposition products the volatile Ga 2 O and In 2 O were formed. These molecules reached the Si substrate which was heated to 400oC. The final chemical reaction involved Ga 2 O 3 , I 2 O 3 and phosphorus precursors. As a result of a spontaneous reaction the Ga 2 O 3 and InP phases were produced and segregated. The InP crystallized as a core while Ga 2 O 3 created the amorphous shell, because the growth temperature was insufficient for its crystallization.

Localization of electromagnetic field on the “Brouwer-island” and liquid metal embrittlement

Liquid metal embrittlement (LME) manifests itself as a sudden destruction of a metal sample if it is covered by a thin liquid film of eutectic mixture of specially selected metals. The proposed theoretical model of this phenomenon is based on an assumption related to the possibility of electromagnetic field localization in folds of interface between the phases or components of eutectic mixture filling cracks in solid metal surface (the typical example is In–Ga eutectic on Al-surface). Based on simultaneous presence of three different components in each space point of eutectic mixture (homogeneous In + Ga melt, solid In, and solid Ga), the system of interface folds could be simulated by the Brouwer surface – well known in topology. This surface separates three different components presented at each of its point. Such fractal surfaces posses by a finite volume. The volume occupied by the surface is defined as a difference between the eutectic mixture volume and the sum of volumes of its components. We investigate localization of external electromagnetic radiation in this system of folds. Due to very large magnitude of effective dielectric permeability of the considered system, at relative small volume change and fractal dimension of interface close to the value 3, the wave length of incident radiation inside the system is considerably decreased and multiscale folds are filled with localized photons. A probability of this process and the life time of the localized photons are calculated. The localized photons play crucial role in destruction of primary cracks in the metal surface. They are capable “to switch of” the Coulomb attraction of charge fluctuations on opposite “banks” of the crack filled with the eutectic. As a result, the crack could break down.

Flotation separation of gallium from aqueous solution – Effects of chemical speciation and solubility

This work aimed to investigate dispersed gas flotation for Ga(III) removal as influenced by the speciation and solubility of Ga(III). Theoretical Ga(III) solubility was the lowest (0.615*10−4mM) in pH range of 4.9–5.8, and experimental solubility of Ga(III) generally showed a good agreement with theoretical predictions. In flotation separation, removal efficiency of Ga(III) dramatically increased from 43.0% to 87.3% as pH increased from 2.5 to 6.0. In contrast, the efficiency sharply declined to 41.4% once pH further increased to 10.3. At pH 2.5, Ga(III) removal efficiency substantially increased with increasing SDS concentration; however, the removal efficiency slightly rose with SDS concentration at pH 6.0 and remained unchanged at pH 10.3. The clear correlation between SDS dose and Ga(III) separation efficiency showed that the electrostatic interactions resulted in flotation separation of cationic species of soluble Ga(III). In addition, anionic SDS became adsorbed on the positively charged surface of colloidal solid Ga(III) via electrostatic force facilitated attachment of nitrogen gas and Ga(III) separation by foam. Nitrogen flow rate accelerated reaction rate of flotation process, while ionic strength slightly hindered removal efficiency of Ga(III).

Selective Growth of GaN Rods on the Apex of GaN Pyramids by Metal Organic Vapor Phase Epitaxy

We report on the growth and characterization of GaN rods selectively grown on the apex of hexagonal GaN pyramids. SiO2 near the apex of the hexagonal GaN pyramids was removed by an optimized photolithography process and subsequently subjected to Au deposition and selective growth of GaN rods by metal organic vapor phase epitaxy (MOVPE). It was observed that there were preferred GaN rods orientations toward <1100> directions. The GaN rods had triangular cross section enclosed with (1122), (1122), and (0001) side facets. A particular feature was that each rod has sharp edge at its very end. We found that the GaN rods could be formed not by vapor–liquid–solid (VLS) process but Ga–Au intermediate state. This work opens up new growth methods for position and density controlled III–nitride nano- and micro-structures which have potential use in high functional devices, such as field emitters and gas sensors.