In-Situ Studies of the Growth of Nanostructured Covalent Semiconductors by Electrochemical Liquid-Liquid-Solid Processes

该项目寻求一种简单、绿色的方法来制备完全精制、纯净和结晶的纳米结构半导体。这将对未来的光电、能源和传感技术产生巨大影响。密歇根大学的Maldonado教授开发了一种无需高温或苛性碱试剂合成晶体半导体纳米材料的方法。这种独特的方法被称为电化学液-液-固（ec-LLS）策略，它通过混合电化学和熔体晶体生长两种通常不同的策略来工作。在许多显著特征中，ec-LLS策略可以在水和环境大气中在室温或接近室温下执行。这项工作旨在进一步发展ec-LLS概念，使其成为环保和低成本半导体制造的变革性方法。实验旨在确定ec-LLS的控制特征，这些特征决定了晶体的形状、大小和纯度。因此，这里提出的基础科学涵盖电化学，材料科学，高级电子显微镜和x射线光谱方法，为参与这些领域的本科生和研究生提供广泛的培训。通过这个项目，Maldonado教授也将基础化学和电化学的教学工具扩展到初级学生。具体来说，介绍了电沉积薄膜作为高中生教育太阳能电池的制备平台。由化学部的大分子、超分子和纳米化学项目提供的资金支持，正在推进用液态金属电化学合成半导体纳米材料的知识和控制。具体来说，用于合成晶体共价半导体的电化学液-液-固（ec-LLS）概念为在异常良性的反应条件下形成技术上相关的半导体纳米材料提供了一种独特的方法。液态金属既是促进非均相还原反应的工作电极，又是指导半导体晶体生长的溶剂。该项目的目的是获得对所得材料的结构、物理化学和电学性质的预测影响。本研究主要采用原位透射电子显微镜（TEM）和原位x射线光谱学两种正交方法，系统地研究了ec-LLS晶体生长的操作特征。要测试的主要假设是：(1)ec-LLS中过饱和的程度，而不是特定的液态金属，最强烈地决定了晶体生长的形式；(2)电极/电解质界面处液态金属的结构影响ec-LLS的启动方式。第一个假设是通过在不同条件下用原位透射电镜观察半导体纳米线的ec-LLS合成来研究的。第二种假设是通过在ec-LLS初始阶段对液态金属/液态电解质界面的浅角度x射线反射和衍射研究来探索的。通过这些不同方法的结合，人们正在开发更精细的ec-LLS方法来合成更先进的纳米材料。Maldonado教授关于钙钛矿太阳能电池的本科实验课程正在针对高中生进行调整。目的是充分简化电沉积平台，以便即使是非常初级的学生也可以为光伏的原始材料化学研究做出有意义的贡献。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。

This project seeks a simple, green method for preparing fully refined, pure, and crystalline nanostructured semiconductors. This would have tremendous impact on future optoelectronic, energy, and sensing technologies. Prof. Maldonado of the University of Michigan has developed a method to synthesize crystalline semiconductor nanomaterials without high temperatures or caustic reagents. This singular approach is called the electrochemical liquid-liquid-solid (ec-LLS) strategy and it works by blending two normally distinct strategies, electrochemistry and melt crystal growth. Among many salient features, the ec-LLS strategy can be performed at or near room temperature in water and the ambient atmosphere. This work aims to further develop the ec-LLS concept into a transformative methodology for environmentally-friendly and low cost semiconductor manufacture. Experiments are designed to identify the controlling features in ec-LLS that dictate crystal shape, size, and purity. The basic science proposed here accordingly spans electrochemistry, materials science, advanced electron microscopy, and X-ray spectroscopic methods, offering extensive training in these areas for participating undergraduate and graduate students. Through this project, Prof. Maldonado also expands pedagogical tools for teaching basic chemistry and electrochemistry to beginning students. Specifically, electrodeposited thin films are introduced as platforms for preparing solar cells for the education of high school students.The funding support provided by the Macromolecular, Supramolecular & Nanochemistry Program of the Chemistry Division is advancing knowledge and control over the electrochemical synthesis of semiconductor nanomaterials with liquid metals. Specifically, the electrochemical liquid-liquid-solid (ec-LLS) concept for the syntheses of crystalline covalent semiconductors offers a unique way to form technologically relevant semiconductor nanomaterials under unusually benign reaction conditions. A liquid metal is both a working electrode that facilitates heterogeneous reduction reactions and a solvent that directs semiconductor crystal growth. The purpose of this project is to gain predictive influence over the structure, physicochemical, and electrical properties of the resultant materials. The underlying research focus uses two orthogonal methods, in-situ transmission electron microscopy (TEM) and in-situ X-ray spectroscopy, to study systematically the operational features of crystal growth in ec-LLS. The chief overarching hypotheses to be tested are: (1) the extent of supersaturation in ec-LLS, rather than the specific liquid metal, most strongly dictates the form of the crystal growth and (2) the structure of the liquid metal at the electrode/electrolyte interface impacts how ec-LLS initiates. The first hypothesis is being investigated by visualizing ec-LLS syntheses of semiconductor nanowires under a variety of conditions by in-situ TEM with a liquid holder. The second hypothesis is being explored through shallow angle X-ray reflection and diffraction studies of liquid metal/liquid electrolyte interfaces during the initial stages of ec-LLS. Through the combination of these different methods, more refined ec-LLS methods are being developed to synthesize more advanced nanomaterials. Prof. Maldonado's undergraduate laboratory curriculum on perovskite solar cells is being adapted for high school students. The intent is to simplify electrodeposition platforms sufficiently so that even very beginning students can contribute meaningfully to original materials chemistry research on photovoltaics.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.