Indium Alloy Research Articles

Band Offsets at κ-([Al,In]xGa1-x)2O3/MgO Interfaces.

Conduction and valence band offsets are among the most crucial material parameters for semiconductor heterostructure device design, such as for high-electron mobility transistors or quantum well infrared photodetectors (QWIP). Because of its expected high spontaneous electrical polarization and the possibility of polarization doping at heterointerfaces similar to the AlGaN/InGaN/GaN system, the metastable orthorhombic κ-phase of Ga2O3 and its indium and aluminum alloy systems are a promising alternative for such device applications. However, respective band offsets to any dielectric are unknown, as well as the evolution of the bands within the alloy systems. We report on the valence and conduction band offsets of orthorhombic κ-(AlxGa1-x)2O3 and κ-(InxGa1-x)2O3 thin films to MgO as reference dielectric by X-ray photoelectron spectroscopy. The thin films with compositions xIn ≤ 0.27 and xAl ≤ 0.55 were grown by pulsed laser deposition utilizing tin-doped and radially segmented targets. The determined band alignments reveal the formation of a type I heterojunction to MgO for all compositions with conduction band offsets of at least 1.4 eV, providing excellent electron confinement. Only low valence band offsets with a maximum of ∼300 meV were observed. Nevertheless, this renders MgO as a promising gate dielectric for metal-oxide-semiconductor transistors in the orthorhombic modification. We further found that the conduction band offsets in the alloy systems are mainly determined by the evolution of the band gaps, which can be tuned by the composition in a wide range between 4.1 and 6.2 eV, because the energy position of the valence band maximum remains almost constant over the complete composition range investigated. Therefore, tunable conduction band offsets of up to 1.1 eV within the alloy systems allow for subniveau transition energies in (AlxGa1-x)2O3/(InxGa1-x)2O3/(AlxGa1-x)2O3 quantum wells from the infrared to the visible regime, which are promising for application in QWIPs.

Size of liquid metal particles influences actuation properties of a liquid crystal elastomer composite.

Composites of liquid crystal elastomer (LCE) that are electrically conductive have the potential to function as soft "artificial muscle" actuators that can be reversibly stimulated with electrical Joule-heating. Conductivity can be achieved by embedding the LCE with droplets of an alloy of gallium and indium that is liquid at room temperature. These soft artificial muscles are capable of >50% reversible actuation with an applied load. The key to actuation at high loadings of liquid metal (LM) is that the droplets deform with the surrounding matrix. By controlling the size of LM droplets through simple processing techniques, we show that the actuator properties of the LM-LCE muscle can be tuned. For example, composites with smaller liquid metal particles (ca. 10 μm or less) are stiffer than those with larger liquid metal particles (ca. >100 μm) and are capable of greater force output. However, smaller particles reduce actuation strain and composites with large particles exhibit significantly greater stroke length. Such tunability in actuation properties permits the fabrication of specialized soft artificial muscles, where processing of the composite controls actuation strain and actuation force.

High-Resolution Rapid Prototyping of Liquid Metal Electronics by Direct Writing on Highly Prestretched Substrates.

A rapid and inexpensive method to produce high-resolution liquid metal patterns and electronics on stretchable substrates was introduced. Two liquid-phase gallium–indium (GaIn) alloy patterns, conductive lines, and interdigitated electrodes, were directly written or shadow mask-printed on a prestretched elastomeric substrate surface. Then, the prestretched substrate was released to recover its original length, and thus, electronic patterns simultaneously shrank on it. After these patterns were transferred to another prestretched substrate by the stamp printing method, the patterning resolution was demonstrated to increase by totally 50 times for the two successive stretch–release–shrink operations. Additionally, the resistance of the handwritten liquid metal conductive line traces remained nearly unchanged during the stretching process, which is believed to be feasible for electrical connections in stretchable electronics. The rapid prototyping of a serpentine strain sensor was successfully demonstrated to be highly sensitive and repeatable with a stretching ratio ranging from 0 to 200%. The proposed method paves a new way to fabricate stretchable electronic devices with high patterning resolution.

Electrodeposition of Sn–In Alloys Involving Deep Eutectic Solvents

Tin–indium alloys represent attractive lead-free solder candidates. They show lower values of melting point than pure indium, so that they are investigated as materials with significant applications potential in the electronic industry. Electrodeposition is a very convenient route to prepare Sn–In alloys. The paper presents several experimental results regarding the electrodeposition of Sn–In alloy coatings involving deep eutectic solvents (DESs), namely using choline chloride-ethylene glycol eutectic mixtures. The influence of the main operating parameters on the Sn–In alloy composition and characteristics are presented. Adherent and uniform Sn–In alloy deposits containing 10–65 wt % In have been obtained on Cu substrates. The In content was found to increase as both the In:Sn molar concentration ratio of ionic species in the electrolyte and the applied temperature increased. The use of pulsed current allowed the use of higher current densities leading to slightly higher values of In content in the alloy deposit. X-ray diffraction (XRD) analysis revealed the presence of InSn4 and In3Sn phases in agreement with the phase diagram. According to thermogravimetric analysis (TGA) measurements, values of melting points in the range of 118.6 and 127.5 °C were obtained depending on the alloy composition. The solder joints’ behavior and alloy coatings corrosion performance were also discussed.

Catalytic Metal Foam by Chemical Melting and Sintering of Liquid Metal Nanoparticles

AbstractMetal foams are highly sought‐after porous structures for heterogeneous catalysis, which are fabricated by templating, injecting gas, or admixing blowing agents into a metallic melt at high temperatures. They also require additional catalytic material coating. Here, a low‐melting‐point liquid metal is devised for the single‐step formation of catalytic foams in mild aqueous environments. A hybrid catalytic foam fabrication process is presented via simultaneous chemical foaming, melting, and sintering reaction of liquid metal nanoparticles. As a model, nanoparticles of tertiary low‐melting‐point eutectic alloy of indium, bismuth, and tin (Field's metal) are processed with sodium hydrogen carbonate, an environmentally benign blowing agent. The competing endothermic foaming and exothermic sintering reactions are triggered by an aqueous acidic bath. The overall foaming process occurs at a localized temperature above 200 °C, producing submicron‐ to micron‐sized open‐cell pore foams with conductive cores and semiconducting surface decorations. The catalytic properties of the metal foams are explored for a range of applications including photo‐electrocatalysis, bacteria electrofiltration, and CO2 electroconversion. In particular, the Field's metal‐based foams show exceptional CO2 electrochemical conversion performance at low applied voltages. The facile process presented here can be extended to other low‐temperature post transition and transition metal alloys.

Electrochemical behavior of Mg-Al-Zn-Ga-In alloy as the anode for seawater-activated battery

The effect of indium alloying on the corrosion and discharge behaviors of Mg-Al-Zn-Ga alloys is investigated via materials characterization, immersion test and electrochemical methods. The results indicate that indium alloying can effectively modify the distribution of intermetallic phases in Mg matrix via promoting the segregation of Al in the form of Mg17Al12 in matrix. The addition of indium can effectively activate Mg-Al-Zn-Ga alloy evidenced by increased hydrogen evolution volume and weight loss, negative shift of corrosion and discharge potentials, increase of corrosion current density, decrease of polarization resistance and promoted Faradic efficiency. Nonetheless, excessive indium alloying (2.0 wt.%) would strikingly deteriorate the electrochemical performance of Mg-Al-Zn-Ga anode due to the exorbitant active effect. The Mg-6 wt.%Al-3 wt.%Zn-1 wt.%Ga-1 wt.%In in as-cast state with acceptable corrosion rate and desirable discharge performance is a low cost, non-toxic and well-performance magnesium alloy, which is a promising anode materials for seawater-activated batteries.

Effective Delivery of Anti-Cancer Drug Molecules with Shape Transforming Liquid Metal Particles.

Liquid metals are being studied intensively because of their potential as a drug delivery system. Eutectic gallium–indium (EGaIn) alloy liquid metals have a low melting point, low toxicity, and excellent tissue permeability. These properties may enable them to be vascular embolic agents that can be deformed by light or heat. In this study, we developed EGaIn particles that can deliver anticancer drugs to tumor cells in vitro and change their shapes in response to external stimuli. These particles were prepared by sonicating a solution containing EGaIn and amphiphilic lipids. The liquid metal (LM)/amphiphilic lipid (DSPC, 1,2-distearoyl-sn-glycero-3-phosphocholin) particles formed a vehicle for doxorubicin, an anticancer drug, which was released (up to 50%) when the shape of the particles was deformed by light or heat treatment. LM/DSPC particles are non-toxic and LM/DSPC/doxorubicin particles have anticancer effects (resulting in a cell viability of less than 50%). LM/DSPC/doxorubicin particles were also able to mimic blood vessel embolisms by modifying their shape using precisely controlled light and heat in engineered microchannels. The purpose of this study was to examine the potential of EGaIn materials to treat tumor tissues that cannot be removed by surgery.

Solidification and melting phase change behavior of eutectic gallium-indium-tin

The room-temperature liquid metal alloy of gallium, indium, and tin (galinstan) has been studied as a deformable conductive element for stretchable electronics and soft robotics. While these applications are predicated on the soft and conformable behavior of galinstan, little work has been done to understand the solidification of the liquid metal in order to fully identify its operational range and that of devices using it. In this paper, the solidification and melting of galinstan is studied in bulk through rheology, x-ray scattering, and differential scanning calorimetry. It is determined that there is a gap of 20 degrees between solidification of galinstan at around -10°C and melting at 10°C. Crystallinity is observed below -10°C, suggesting ordering of the gallium, indium, and tin phases which is unstable through repeated solidify-melt cycles and possibly rearranges in structure below -30°C. Dispersions of galinstan in PDMS remain soft below -20°C while galinstan channels in PDMS appeared to solidify at length scales down to 500µm. Overall, galinstan can offer “liquid-like” performance down to -10°C however, at lower temperatures, solidification can occur at temperature and time that is dependent on the dispersion/ confinement state. If solidification occurs, galinstan must be heated substantially to regain its “liquid-like” performance.

Self‐Limiting Galvanic Growth of MnO2 Monolayers on a Liquid Metal—Applied to Photocatalysis

AbstractLiquid metals offer unprecedented chemistry. Here it is shown that they can facilitate self‐limiting oxidation processes on their surfaces, which enables the growth of metal oxides that are atomically thin. This claim is exemplified by creating atomically thin hydrated MnO2 using a Galvanic replacement reaction between permanganate ions and a liquid gallium–indium alloy (EGaIn). The “liquid solution”–“liquid metal” process leads to the reduction of the permanganate ions, resulting in the formation of the oxide monolayer at the interface. It is presented that under mechanical agitation liquid metal droplets are established, and simultaneously, hydrated gallium oxides and manganese oxide sheets delaminate themselves from the interfacial boundaries. The produced nanosheets encapsulate a metallic core, which is found to consist of solid indium only, with the full migration of gallium out of the droplets. This process produces core/shell structures, where the shells are made of stacked atomically thin nanosheets. The obtained core/shell structures are found to be an efficient photocatalyst for the degradation of an organic dye under simulated solar irradiation. This study presents a new research direction toward the modification and functionalization of liquid metals through spontaneous interfacial redox reactions, which has implications for many applications beyond photocatalysis.

Wetting behavior and interfacial characteristic of eutectic In-Ag solders on Au thin films

Soldering electrical contacts to gold thin films is a matter of consideration due to high soldering temperature, restricted wetting, excessive scavenging and low strength offered by most of the common soldering alloys. Indium alloys offer certain benefits for gold soldering justifying their increased cost. In the present study, hypo-, hyper- and eutectic In-Ag solder were prepared and investigated for compositional and structural homogeneity, soldering temperature, contact angle, spreading factor, scavenging zone and scavenging phase (i.e. AuIn2). It was found that addition of silver (~3.5%) ameliorated the above mentioned characteristics for better control of soldering practice with gold thin films besides lowering the soldering temperature.

Electrically induced spreading of EGaIn on Cu substrate in an alkali solution under wetting and non-wetting conditions

Electrically actuated movement of liquid metals is quite promising in mechanical engineering and applied physics. However, little work has so far been performed on the effect of current polarity on the actuation of the eutectic gallium–indium (EGaIn) alloy moving on metal substrates. In this work, the spreading of EGaIn on copper (Cu) substrate under different direct-current (DC) polarities in the 0.5 mol/L NaOH solution was investigated, and the underlying mechanisms were addressed. When the Cu substrate was connected to cathode, the wetting was essentially attributed to the reduction in the oxidized surface of the Cu substrate; whereas, under the opposite polarity, the spreading was related to the tension gradient along the EGaIn–solution interface, which induced Marangoni flow, despite the fact that the EGaIn–Cu system was non-wetting in this case.

Influence of Indium on Microstructure and Properties of Sn-Pb Binary Alloy Applied in Photovoltaic Ribbon

In this work, the conductivity, melting point, microstructure, spreading behavior, and mechanical properties of three types of Sn-Pb-In(indium) alloys are investigated along with Sn60Pb40 alloy as a reference. The results show that the In element improves the comprehensive properties of the Sn-Pb alloys. The maximum conductivity of the Sn-Pb-In alloys is 7.08 MS/m when the content of the In element is 3 wt.%. With an increasing content of the In element, the melting points of the Sn-Pb-In alloys gradually decrease from 183 to 166 °C. The microstructures of the alloys are refined with the addition of In. The intermetallic compound (IMC) InSn4 is only found in Sn60Pb34In6, except for the α-Pb and β-Sn phases. A spread test shows that only IMC Cu6Sn5 is present at the Cu/solder interface of the solder joints. The Sn60Pb34In3 solder joint shows the highest ultimate tensile strength of 54 MPa. The microhardness of the alloys slightly increases from 12.76 HV0.05 to 13.56 HV0.05 with the In content increasing from 0 to 3 wt.%, while a sharp increase to 15.53 HV0.05 is observed when the amount of In exceeds 3 wt.%.

Improvement of Vacuum Free Hybrid Photovoltaic Performance Based on a Well-Aligned ZnO Nanorod and WO3 as a Carrier Transport Layer.

Well-aligned zinc oxide nanorods (WA-ZnO Nrods) with different lengths were synthesized and the effects of the growth times on the optical, morphological, and electrical properties of the WA-ZnO Nrods were examined. We also investigated the application of WA-ZnO Nrods as an electron transport layer (ETL) and tungsten trioxide (WO3) as a hole transport layer (HTL) to vacuum free hybrid photovoltaic (HPV) performance. The eutectic gallium–indium (EGaIn) alloy was used as a top electrode coated using a brush-painting method. A device with the structure of indium tin oxide (ITO)/WA-ZnO Nrods/(P3HT:PCBM)/WO3/EGaIn was optimized and fabricated. The maximum power conversion efficiency (PCE) was ~4.5%. Improvement of the device performance indicates that the well-aligned ZnO Nrods and WO3 can effectively be applied as charge carrier transport layer for vacuum free hybrid (HPV).

The Concept of a Hybrid Pulsed Plasma Thruster for Small-Size Space Satellites

A concept of a hybrid plasma source to be used as a micro satellite thruster is proposed, where the propellant is a liquid gallium–indium alloy. The plasma source operates in two modes: 1) generation of laser ablation plasma and 2) generation of plasma in a laser-triggered, low-voltage vacuum-arc discharge. The cathode in the discharge cell of the source represents a stainless-steel capillary filled with the working liquid. The laser beam target is the working liquid meniscus. Without any voltage in the discharge gap, only laser-ablated plasma is generated. Upon application of even a relatively low voltage (<1 kV), the ablation initiates a high-current vacuum-arc discharge. In the experiments, the discharge current and voltage waveforms were recorded and so were the images of plasma glow obtained with a HSFC-Pro 4-channel high-speed camera. Regularities of current flow in the high-current vacuum-arc discharge, initiated by the cathode laser ablation, are investigated.

Liquid metal antenna-based pressure sensor

In this paper, a centre-fed, finite-length, infinitesimally thin dipole antenna is presented as a pressure sensor to monitor pressure changes in geotechnical engineering. The antenna consists of a liquid metal (eutectic gallium–indium alloy) injected in microfluidic channels, which are enclosed in the elastic material polydimethylsiloxane (PDMS); therefore, the liquid antenna is stretchable and frequency reconfigurable and can thus be used as a pressure sensor when the length of the elastic material PDMS is changed under pressure. The effects of the geometrical parameters of the dipole antenna on its resonant frequency are investigated using the finite-element software HFSS. Based on the numerical results, the liquid-metal antenna is designed, fabricated and measured, and its resonant frequencies are recorded under different pressures. According to the experimental results, the relation between the resonant frequency of the liquid antenna and the applied pressure is defined, and it is consistent with the numerical and theoretical results. Moreover, the experimental results show that the relation between the displacement and the resonant frequency is in good agreement with the numerical and theoretical results. Thus, there is a linear relation between the resonant frequency of the antenna and the applied pressure as well as between the resonant frequency and the displacement. Therefore, this frequency-reconfigurable liquid-metal dipole antenna is suitable for use as a pressure sensor.

Removal and Recovery of Indium from ITO Coated Glass and Scraps Using Molten Salt Electrolysis

Indium is an important strategic resource due to the scarcity for the metal. In the present study, molten salt electrolysis is used to reduce indium from ITO coated glass and scraps in order to seek a new way to recycle the value resource. The electrochemical behavior of indium and tin oxides was studied by cyclic voltammetry at 450°C in molten LiCl-KCl. The reduction peaks were observed in the cathodic scan for In2O3 and SnO2. Constant voltage electrolysis was performed at 1.7 V and 450°C for ITO. The deposits between ITO layer and the cathode were collected and analyzed by XRD. The reduction reaction occurred at the interface of the oxide pellets and the cathode. Metallic indium and Sn-In alloys were detected after electrolysis. The ITO covered glass was reduced by electrochemical method in molten LiCl-KCl at 450°C under argon with Mo wire contacting electrode. The findings, together with SEM and EDX analyses, confirmed ITO layer was removed from the glass surface.

Formation of particle of bismuth–indium alloys and particle diameter by ultrasonic cavitation

The miniaturization of electronic equipment requires fine bonding. Therefore, it is necessary to miniaturize the solder particles used for bonding different materials. Ultrasonic cavitation is a technique that uses ultrasonic irradiation to synthesize such microparticles. In this study, we investigated the effects of ultrasonic irradiation conditions on synthetic microparticles produced by this technique. Spherical particles were obtained by irradiating Bi-45 wt% In melted in a solvent with ultrasonic waves for 15 s, and the resultant metal composition was found to be equivalent to the raw material composition. We found a clear correlation between the ultrasonic irradiation time and particle size. When irradiated for 60 min, the average particle diameter was 3.3 μm. In addition, the particle division rate decreased as the irradiation time increased, which is probably due to attenuation of the vibration wave as the boundary surface increased with the refinement of the particle.

Critical Factors in the Growth of Hyperdoped Germanium Microwires by Electrochemical Liquid–Liquid–Solid Method

Factors that affect crystalline growth of germanium (Ge) micro- and nanowires by the electrochemical liquid–liquid solid (ec-LLS) method in water have been identified. Alloys of gallium and indium (Ga1–xInx) were used as liquid metal microdroplet electrodes in ec-LLS to determine whether the resultant conductivity of as-grown Ge could be strongly modulated by adjusting the fraction of Ga. Current–potential measurements on individual microwires were performed as a function of alloy composition. All alloys of Ga and In yielded Ge microwires with low resistivity and showed evidence of metal incorporation beyond the solubility limit (i.e., hyperdoping). The observed Ge crystal growth rates were insensitive to the alloy composition. In contrast, lowering the concentration of GeO2 dissolved in solution and/or increasing the density of droplets noticeably slowed down the microwire growth rate. Cumulatively, these data help define what parameters should be useful in refining the ec-LLS method to produce materials...

Elucidating the Role of Molecule-Electrode Interfacial Defects in Charge Tunneling Characteristics of Large-Area Junctions.

Interfacial chemistry at organic-inorganic contact critically determines the function of a wide range of molecular and organic electronic devices and other systems. The chemistry is, however, difficult to understand due to the lack of easily accessible in-operando spectroscopic techniques that permit access to interfacial structure on a molecular scale. Herein, we compare two analogous junctions formed with identical organic thin film and different liquid top-contacts (water droplet vs eutectic gallium indium alloy) and elucidate the puzzling interfacial characteristics. Specifically, we fine-tune the surface topography of the organic surface using mixed self-assembled monolayers (SAMs): single component SAM composed of rectifier (2,2'-bipyridyl-terminated n-undecanethiolate; denoted as SC11BIPY) is systematically diluted with nonrectifying n-alkanethiolates of different lengths (denoted as SC n where n = 8, 10, 12, 14, 16, 18). Characterization of the resulting mixed SAMs in wettability and tunneling currents with the two separate liquid top-contacts allows us to investigate the role of phase segregation and gauche defect in the SAM//liquid interfaces. The results reported here show the difference in length between SC11BIPY and SC n is translated into nanoscopic pits and gauche-conformer defects on the surface, and the difference in contact force-hydrostatic vs user pressures-and hence conformity of contact account for the difference in wettability and rectification behaviors. Our work provides an insight into the role of molecule-electrode interfacial defects in performance of molecular-scale electronic devices.

Liquid Metal Corrosion Effects on Conventional Metallic Alloys Exposed to Eutectic Gallium–Indium Alloy Under Various Temperature States

The effects of liquid metal corrosion on the thermophysical properties of three conventional metallic alloys, including T2 copper, 304 stainless steel and anodized 6061 aluminum alloy, in the range of 100–400 °C were comprehensively clarified in this paper. It was experimentally found that the corrosion products on the copper surface existed as the intermetallic compound of CuGa2, and that FeGa3 and Cr3Ga4 were formed on the surface of stainless steel. The heat conductivity of copper plate decreased with the increasing corrosion temperature. The heat conductivity of the corroded copper sample sharply decreased at the beginning stage. When the copper plate was exposed in liquid eutectic gallium–indium over 12 h, the trend of the tested heat conductivity changing curve showed a smooth tendency and reached a steady state finally. The heat conductivity of the corroded copper plate was decided by the corrosion speed with an exponential function of $$ v = a^{t} (0.4 < a < 0.6) $$ . Corrosion phenomena were not found on the surface of the anodized 6061 aluminum alloy according to the experimental results from ambient temperature to 400 °C, which disclosed their suitability as the structural material. The present findings would serve as an important reference for the use of liquid metal cooling in high-power electronic devices and high-temperature systems.