Due to the malleable quality of liquid metals and the existence of surface oxide film, exploration of contact performance and interface charge transfer has proved difficult for liquid metal-based systems. .
Study: knowledge on the interfacial contact and the transport of load of liquid metallic marbles with gas detection. Image credit: HaHanna / Shutterstock.com
In research published in the journal ACS Applied Materials & Interfaces, eutectic indium gallium nano / micro size droplets with tungsten trioxide nanoparticles were included to generate a liquid metal marble matrix where charge transport was governed by contact. of the inherently semiconductor tungsten interface. trioxide.
What are liquid metals?
Alloys and metals with low melting points, commonly called liquid metals, include gallium (Ga) and its alloys. They are a developing class of multifunctional materials used in sensors, catalytic processes, flexible electronics and several different fields. Sonication, for example, can easily decompose a significant volume of liquid metals into nano / microdroplets.
Interface engineering has been used to generate ideal surface morphologies and structures for a variety of these nano- / microdroplets based on liquid metals, either by adjusting the component elements or by subsequent alterations to the surface. The reason for the active surfaces of liquid metals is that they are essentially metals or metal alloys.
Interface complexities of liquid metals
Most liquid metals develop a self-restricting surface oxide film in ambient air and a surface hydroxide film in many solvents, culminating in interface passivation. Given the complexity of liquid metal interfaces, a thorough knowledge of their surface composition and behaviors in various environmental circumstances is crucial for designing and processing materials.
This is especially relevant for liquid metal marbles formed by the functionalization of liquid metal droplets with surface micro / nanoparticle coatings. Filling liquid metal droplets with selected particles is a potential method for producing microscale / nanoscale materials with improved capabilities, scalability, and adaptability.
Determining the nature of the contact between the micro / nanoparticles they cover and the liquid metal droplets, as well as their interactions, is critical. Furthermore, when referring to the development of the surface oxide film, it is not certain whether the direct interaction between the surface particles and the liquid metal is conceivable or whether the surface oxide film can also play a role. .
Why was WO3 / EGa the focus of this study?
In this study, the team examined tungsten trioxide (WO3) nanoparticles (NP) as an encapsulation material for eutectic gallium and indium gallium (EGaIn) liquid metal alloy droplets. The liquid phase of EGAIn was selected at near room temperature.
It shows excellent heat and electricity conduction while being non-toxic. Due to its high elasticity and fluidity, EGaIn can be sonicated and micronized at low energies to produce liquid metal nano / microdroplets.
In addition, tungsten trioxide nanoparticles allow a homogeneous distribution on the EGaIn surface without the need for surfactants, which allows an excellent exchange of free charge carriers between the two elements.
Qualities of tungsten trioxide
Tungsten trioxide is a natural n-type semiconductor with an empty band range of 2.6-3.2 eV. Although reasonably robust at room temperature, tungsten trioxide shows a commitment to various gases at higher temperatures by various methods.
Whenever subjected to reducing gases that supply unattached electrons to the surface, the resistance of tungsten trioxide decreases, while it increases when introduced to oxidizing gas species that create an exhausted zone of electrons by extracting electrons from atoms. of tungsten surface.
Tungsten trioxide is understood to generate substoichiometric forms (WO3-x) by a number of simple mechanisms, leading to an increase in electrical conductance due to an oxygen deficit.
Important results of the study
IV profiles generated from the WO3 / EGaIn liquid metal marble frame and a macroscopic interface configuration suggested that the WO3 / EGaIn interface had almost ohmic electricity conduction characteristics.
Simulations of the system’s functional density theory (DFT) revealed affinities between the gallium and indium atoms of EGAIn and the oxygen atoms of tungsten trioxide, providing an atomic understanding of nature. of interaction. Therefore, the inherent position of the Fermi level of tungsten trioxide shifted above the tungsten trioxide conduction band, resulting in the formation of an almost ohmic interface contact.
Contact of the WO3 / EGaIn interface with good charge transfer efficiency was shown to improve gas detection capabilities (for oxygen and water molecules).
This research sheds light on the nature of the interface contacts formed between liquid metals and semiconductor substances, as well as the charge transfer properties of these surfaces. The results of the study extend beyond liquid metal marble networks to composites and various other liquid metal-based systems.
Reference
Chi, Y., Han, J. et al. (2022). Information on the interfacial contact and the transport of load of liquid metallic marbles with gas detection. Materials and interfaces applied ACS. Available at: https://doi.org/10.1021/acsami.2c06908
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