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

Regents Of The University Of Michigan - Ann Arbor, Ann Arbor MI

Investigators

Abstract

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.