EPM: Engineering Transparent Conducting Superlattices from Liquid Metal Printed 2D Oxides

Dartmouth College, Hanover NH

Investigators

Abstract

Nontechnical Description: Two-dimensional (2D), atomically thin materials have unique optical and electronic properties that could enable emerging technologies, from chemical sensors to low power microelectronics. However, fabricating atomically thin layers at a large-scale while controlling their electrical properties remains challenging. This project seeks to harness a new class of ultrathin oxide layers formed on the surface of the molten metals gallium and indium to efficiently fabricate highly conductive and ultra-transparent nanosheets. The primary goal of this work is to thoroughly understand and precisely control the nanoscale atomic composition, crystallinity, and electron transport properties of these 2D oxide materials by stacking multiple layers and by engineering the oxidation of liquid metal alloys formed from tin, zinc, and gallium. These methods enhance the electron mobility and light transmittance, as well as tuning of the electron concentration in these materials for enabling applications to photodetectors, solar cells, and displays. Integrated with the research efforts, this plan builds on practices that have successfully engaged undergraduate students from underrepresented groups in research to train a diverse and inclusive engineering workforce. The education plan involves development of remote deployable liquid metal science demonstrations for experiential learning by undergraduates and K-12 students. This project also includes efforts to broaden graduate level STEM participation via the principal investigator’s organization and hosting of a panel discussion series in collaboration with diverse engineering student groups. Technical Description: The overarching goal of this project is to develop a new paradigm of ultra-transparent, highly flexible, and optoelectronically tunable 2D metal oxides via superlattice engineering. These high-performance transparent conducting materials leverage a fundamentally new synthetic strategy for printing 2D oxide nanosheets from the solid oxide skin of liquid metals. Initial studies of 2D oxides reveal their unique overlapping grain morphologies, quantum-confined electronic structure, and ultrahigh electron mobility. This work identifies the nanoscale material origins of these exceptional optoelectronic properties and controls the composition, crystallinity, and conductivity of multicomponent 2D oxides by engineering the physics of liquid metal surface oxidation. These studies specifically investigate how metal alloy composition impacts the logarithmic growth kinetics of surface oxidation and then connect this process physics with 2D oxides’ chemical composition through detailed material characterization. These experiments test the hypothesis that surface-driven defect modulation doping from type-II heterojunctions with insulating wide bandgap oxides (e.g. gallium oxide) can directly enhance the conductivity of 2D metal oxides. Extracting the electronic density of states in combination with optical absorption spectroscopy can also quantitatively link alloy composition with the surface oxides’ electronic structure. These studies are of broad significance because this fundamental knowledge unlocks emerging applications in flexible electronic devices including low-power emissive displays, electrochromic smart windows, and high-efficiency solar cells that demand high-performing semiconductors and transparent electrodes with tunable properties. This project is jointly funded by the Electronic and Photonic Materials program and the Established Program to Stimulate Competitive Research (EPSCoR). This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.