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

非技术描述：二维（2D）原子薄材料具有独特的光学和电子特性，可以实现从化学传感器到低功耗微电子等新兴技术。然而，在控制其电性能的同时大规模制造原子薄层仍然具有挑战性。该项目旨在利用在熔融金属镓和铟表面形成的一种新型超薄氧化层来有效地制造高导电性和超透明的纳米片。这项工作的主要目标是通过多层堆叠和工程氧化锡，锌和镓形成的液态金属合金，彻底了解和精确控制这些二维氧化物材料的纳米级原子组成，结晶度和电子传输特性。这些方法提高了电子的迁移率和透光率，以及调整这些材料中的电子浓度，使其能够应用于光探测器、太阳能电池和显示器。与研究工作相结合，该计划建立在成功吸引来自代表性不足群体的本科生参与研究的实践基础上，培养了一支多元化和包容性的工程人才队伍。教育计划包括开发远程可部署的液态金属科学演示，供本科生和K-12学生体验式学习。该项目还包括通过与不同的工程学生团体合作，通过首席研究员组织和主持小组讨论系列，努力扩大研究生水平的STEM参与。技术描述：该项目的总体目标是通过超晶格工程开发一种超透明、高度柔性和光电可调的2D金属氧化物的新范例。这些高性能透明导电材料利用一种全新的合成策略，从液态金属的固体氧化物表面打印2D氧化物纳米片。二维氧化物的初步研究揭示了其独特的重叠晶粒形态、量子限制电子结构和超高电子迁移率。这项工作确定了这些特殊光电特性的纳米级材料来源，并通过设计液态金属表面氧化的物理特性来控制多组分2D氧化物的组成、结晶度和电导率。这些研究专门研究了金属合金成分如何影响表面氧化的对数生长动力学，然后通过详细的材料表征将这一过程物理与二维氧化物的化学成分联系起来。这些实验验证了ii型异质结与绝缘宽禁带氧化物（如氧化镓）的表面驱动缺陷调制掺杂可以直接增强二维金属氧化物的导电性的假设。结合光学吸收光谱提取状态的电子密度也可以定量地将合金成分与表面氧化物的电子结构联系起来。这些研究具有广泛的意义，因为这一基础知识解锁了柔性电子设备的新兴应用，包括低功率发射显示器，电致变色智能窗口，以及需要高性能半导体和具有可调谐特性的透明电极的高效太阳能电池。该项目由电子和光子材料计划和促进竞争研究的既定计划（EPSCoR）共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

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 whilecontrolling 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.