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炼、纯净和结晶的纳米结构半导体。这将对未来的光电子、能源和传感技术产生巨大影响。密歇根大学的马尔多纳多教授开发了一种无需高温或苛性试剂就能合成晶态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，它通过混合两种通常不同的策略来工作，即电化学和熔体晶体生长。在许多显著特征中，EC-LLS策略可以在室温或接近室温的水和周围大气中执行。这项工作旨在将EC-LLS概念进一步发展为环境友好型和低成本半导体制造的变革性方法。实验旨在确定EC-LLS中决定晶体形状、大小和纯度的控制功能。这里提出的基础科学相应地横跨电化学、材料科学、高级电子显微镜和X射线光谱分析方法，为参与的本科生和研究生提供这些领域的广泛培训。通过这个项目，马尔多纳多教授还将基础化学和电化学教学的教学工具扩展到初级学生。具体地说，电沉积薄膜被介绍为制备太阳能电池的平台，供高中生使用。化学部高分子、超分子和纳米化学计划提供的资金支持是促进对以液态金属为原料的半导体纳米材料的电化学合成的了解和控制。具体地说，电化学液-液-固(EC-LLS)概念用于晶体共价半导体的合成，为在异常有利的反应条件下形成技术相关的半导体纳米材料提供了一种独特的方法。液态金属既是促进多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合成材料的结构、物理化学和电学性质的预测性影响。本文的研究重点是利用两种正交法--原位电子显微镜和原位X射线光谱分析，系统地研究了电致发光晶体生长的操作特性。需要检验的主要假设是：(1)EC-LLS中的过饱和程度，而不是特定的液态金属，最强烈地决定了晶体生长的形式，以及(2)电极/电解液界面上液态金属的结构影响EC-LLS的启动方式。第一个假设是通过使用液舱的原位电子显微镜在各种条件下可视化半导体纳米线的EC-LLS合成来研究的。第二种假设是通过对EC-LLS初期液态金属/液态电解液界面的浅角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，更精细的EC-LLS方法正在被开发出来，以合成更先进的纳米材料。马尔多纳多教授关于钙钛矿型太阳能电池的本科实验室课程正在为高中生调整。其目的是充分简化电沉积平台，以便即使是最开始的学生也可以对关于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NSF的法定使命，并通过使用基金会的智力优势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.