Growth of crystalline ZnO nanowires from solution: From theory to application

项目编号：CBET: 0729924首席研究员：Jeffrey J. DerbyUniversity/Institution: University of Minnesota Twin cititle：晶体氧化锌纳米线的生长：从理论到应用将进行多尺度建模和实验相结合的计划，以了解以纳米线形式生长的晶体氧化锌（ZnO）的最重要方面。这些结构的阵列是从过饱和液相中生长出来的，对于制造基于纳米线的染料敏化太阳能电池特别感兴趣。这些低成本的光电设备因其极低的成本和良好的效率而特别具有吸引力。ZnO纳米线阵列的质量、微观结构和尺寸决定了太阳能电池的性能，但缺乏工艺水平变量对这些结构制造的影响的定量知识。改进这些装置的关键是对晶体纳米线从液体溶液中生长的机制有更基本的了解。该工作的总体目标是开发和验证描述晶体从液相生长的基本机制模型，并应用这些模型来更好地理解ZnO纳米线晶体的生长。这些知识需要将生长条件与晶体结构完善和组成的微观特性以及晶体形状特征（即生长习惯和尺寸）联系起来，这些特征会影响纳米线阵列的密度。基于相场方法的多尺度理论模型将用于模拟过饱和液体中晶体表面的纳米级生长螺旋。实验将利用新型纳米压痕技术通过一系列种子纳米晶体选择性地放置位错，从而实现ZnO的溶液生长。生长动力学将测量纳米线的生长动力学，包括没有和有从这些位错演变而来的生长螺旋的纳米线。理论和实验将用于验证该系统中的长纵横比纳米线主要由与单面生长螺旋相关的动力学因素产生的假设。模型和实验之间的协同作用将使理论或实验无法单独实现的进步成为可能。知识价值：这项工作解决了晶体生长的基本科学问题，并为改进实际应用提出了明确的目标。通过相场方法，块状输运与阶梯生长动力学的耦合将导致溶液晶体生长的多尺度模型具有新的严严性和相关性。这些模型将对溶液晶体生长过程中流体流动、传质和界面动力学的耦合因素进行基础性的探索。这项工作的一个具体成果将是对晶体锌纳米线的液相生长有更深入的了解。更广泛的影响：这项工作获得的结果将增加对晶体如何从液体溶液中生长的基本理解，特别是推进基于纳米线的染料敏化太阳能电池。涉及溶液晶体生长的其他应用也可能受到本研究提供的理解的影响。例如，溶液结晶是化学和制药工业中最常用的单元操作，用于在室温和常压下纯化和分离固体化学产品。溶液生长也适用于许多无机晶体的生产，从大规模光学材料的生长到外延层的生长。更广泛的活动包括对研究生进行多尺度建模和纳米技术的教育，以及涉及明尼苏达科学博物馆的面向公众的推广计划。

Proposal Number: CBET: 0729924 Principal Investigator: Jeffrey J. DerbyUniversity/Institution: University of Minnesota Twin CitiesTitle: Growth of Crystalline ZnO Nanowires from Solution: From Theory to Application A combined program of multi-scale modeling and experiments will be conducted to understand the most significant aspects of the growth of crystalline zinc oxide (ZnO) in the form of nanowires. Arrays of these structures are grown from supersaturated liquid phases and are of particular interest for the fabrication of nanowire-based, dye-sensitized solar cells. These low-cost, photovoltaic devices are especially attractive due to their potential for very low cost and good efficiency. The quality, microstructure, and dimensions of the ZnO nanowire array determine the solar cell's performance, yet quantitative knowledge of the effects of process-level variables on the fabrication of these structures is lacking. Key to improving these devices is a more fundamental understanding of the mechanisms by which the crystalline nanowires grow from liquid solution.The overall objectives of the proposed work are the development and validation of fundamental, mechanistic models describing the growth of crystals from the liquid phase and the application of these models to better understand the growth of ZnO nanowire crystals. Such knowledge is needed to link growth conditions to microscopic properties of crystalline structural perfection and composition, as well as characteristics of crystal shape, i.e., growth habit and size, that affect the density of the nanowire arrays. Multi-scale, theoretical models, based on the phase-field approach, will be developed to simulate nano-scale growth spirals on crystal surfaces in a supersaturated liquid.Experiments will be conducted on the solution growth of ZnO that utilize novel nano-indentation techniques to selectively place dislocations through an array of seed nanocrystals. Growth kinetics will be measured for nanowires both without and with growth spirals that have evolved from those dislocations. Theory and experiment will be applied to test the hypothesis that long-aspect-ratio nanowires in this system arise primarily from kinetic factors associated with a growth spiral on one face. The synergy between model and experiment will enable advances not possible by theory orexperimentation alone. Intellectual merit: The work addresses fundamental scientific issues of crystal growth together with a clear goal toward improving a practical application. The coupling of bulk transport with step growth kinetics, via the phase-field approach, will result in multi-scale models for solution crystal growth of new rigor and relevance. Such models will enable a fundamental exploration of the coupled factors of fluid flow, mass transfer, and interfacial kinetics in solution crystal growth processes. A specific outcome of this work will be a greater understanding of the liquid-phase growth of crystalline, ZnOnanowires. Broader impacts: Results obtained by this work will increase the fundamental understanding of how crystals grow from liquid solutions and specifically advance nanowire-based, dye sensitized solar cells. Other applications involving solution crystal growth are also likely to be affected by the understanding provided by this research. For example, solution crystallization is the most commonly used unit operation in the chemical and pharmaceutical industries for the purification and separation of chemical products that are solids at room temperature and pressure. Solution growth is also applied for the production of many inorganic crystals, ranging from the growth of large-scale optical materials to the growth of epitaxial layers. Broader activities include the education of graduate students in multi-scale modeling and nanotechnology, as well as an outreach program for the general public involving the Science Museum of Minnesota.