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

建议编号：CBET：0729924首席研究员：杰弗里·J·德比大学/机构：明尼苏达大学双子城分校标题：从溶液中生长结晶氧化锌纳米线：从理论到应用将进行多尺度建模和实验相结合的计划，以了解纳米线形式的结晶氧化锌生长的最重要方面。这些结构的阵列是从过饱和的液体中生长出来的，对于制造基于纳米线的、染料敏化的太阳能电池特别感兴趣。这些低成本的光伏设备特别有吸引力，因为它们具有非常低的成本和良好的效率。氧化锌纳米线阵列的质量、微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。改进这些器件的关键是更基本地了解晶体纳米线从液体溶液中生长的机理。拟议工作的总体目标是开发和验证描述晶体从液体中生长的基本机制模型，并应用这些模型来更好地理解氧化锌纳米线晶体的生长。需要这样的知识来将生长条件与影响纳米线阵列密度的晶体结构完整性和成分的微观属性以及晶体形状的特征，即生长习惯和大小联系起来。基于相场方法的多尺度理论模型将被用来模拟过饱和液体中晶体表面的纳米级螺旋生长。我们将对溶液生长氧化锌进行实验，利用新颖的纳米压痕技术通过种子纳米晶体阵列选择性地放置位错。纳米线的生长动力学将在没有和有从这些位错演变而来的生长螺旋的情况下进行测量。理论和实验将被用来检验这一假设，即该系统中的长宽比纳米线主要是由与单面生长螺旋相关的动力学因素引起的。模型和实验之间的协同作用将使仅靠理论或实验不可能取得的进展成为可能。学术价值：这项工作解决了晶体生长的基本科学问题，并有一个明确的目标，以改进实际应用。通过相场方法，整体输运和阶跃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谨性和关联性。这样的模型将使我们能够从根本上探索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。这项工作的一个具体成果将是更好地理解晶体锌纳米线的液相生长。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，特别是促进基于纳米线的、染料敏化的太阳能电池。其他涉及溶液晶体生长的应用也可能受到本研究提供的理解的影响。例如，溶液结晶是化工和制药行业中最常用的单元操作，用于在室温和压力下提纯和分离作为固体的化学产品。溶液生长也被应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方面的教育，以及明尼苏达州科学博物馆参与的面向普通公众的外联计划。

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.