Growth of Transition Metal Oxides and Sulfides on Liquid Metal Core-Shell Particles for Optically Responsive Soft Electronics

Ga-based liquid metals (LM) are gaining significant noteriety as functional soft materials utilized as stretchable conductors, catalytic substrates, and a platform for materials development. Rapid formation of a surface oxide enables core-shell micro or nanoscale particle structures for LMs, further increasing their functional capabilities. However, the utility of these particles are often governed by the properties of the native gallium oxide shell which hinders their potential application space. In particular, the optical properties of eutectic Ga-In alloys (eGaIn) is limited to the UV absorption spectrum¹ compared to other noble metal nanoparticles which absorb light in the IR-Vis range. Transition metal oxides or sulfides are commonly employed as optically responsive materials for flexible electronics and sensing devices^2-4, with absorption frequencies that extend into IR-Vis. Recent research investigated the synthesis of such materials on a LM substrate due to its electron-rich surface⁵, opening new opportunities for materials development. Having a synergistic combination of optically responsive coatings, with a soft conductive core can potentially lead to new hybrid materials for the next generation of optically tunable, stretchable electronics and sensors. In this work, we investigate a solution-based method to directly synthesize tungsten oxide/sulfide coatings on eGaIn surface during particle processing. The reactive surface of eGaIn drives the reduction and deposition of these materials from a single precursor, which can be tuned by multiple processing parameters. Specifically, we elucidate factors such as precursor concentration, reactive ion species, and solvent selection that can influence the favorability of tungsten sulfide or oxide growth on eGaIn particles. Additionally, we characterize the compositional and optical properties of these core-shell structures to gain better insight into their structure-property relationships. This method yields a simple and generalizable pathway for producing functional LM particles with tunable optical behavior that show potential usage in soft optoelectronic applications.<br/><br/>[1] Reineck, Philipp, et al. UV plasmonic properties of colloidal liquid metal eutectic gallium indium alloy nanoparticles. <i>Scientific reports</i> 9.1 (2019): 1-7.<br/>[2] Chi, Yuan, et al. Insights into the Interfacial Contact and Charge Transport of Gas Sensing Liquid Metal Marbles. <i>ACS Applied Materials & Interfaces</i> 14.26 (2022): 30112-30123.<br/>[3] Ren, Long, et al. General Programmable Growth of Hybrid Core Shell Nanostructures with Liquid Metal Nanodroplets. <i>Advanced Materials</i> 33.11 (2021): 2008024.<br/>[4] Alsaif, Manal MYA, et al. 3D Visible Light Driven Plasmonic Oxide Frameworks Deviated from Liquid Metal Nanodroplets. <i>Advanced Functional Materials</i> 31.52 (2021): 2106397.<br/>[5] Wang, Yifang, et al. Self Deposition of 2D Molybdenum Sulfides on Liquid Metals. <i>Advanced Functional Materials</i> 31.3 (2021): 2005866.