CAREER: Linking the Forward and Reverse Vapor-Liquid-Solid Mechanisms to Synthesize Ordered Integrated Metal Oxide Nanostructures

我们生活在一个依赖材料的社会，特别是那些能够产生或储存能源的材料，其所需的效率正在不断提高。这种材料的功能越来越依赖于创造高效和紧密间隔的晶体界面，包括例如用于太阳能设备的大面积p-n结阵列。这一理解和开发固-液-气机理的项目将为设计具有高效单晶成分的纳米结构复合材料提供一种新的途径，从而对金属氧化物材料的定向设计和依赖它们的社会产生重大的积极影响。基于这项研究和为支持这项研究而开发的基础设施，是一系列的教育和推广活动，旨在增加肯塔基大学本科生的研究经验。技术说明尽管气-液-固(VLS)机制在金属催化的纳米线生长中的作用已经被广泛研究，但这个过程的相反--固-液-蒸汽(SLV)机制--还没有被很好地理解，但它可以很好地为理解和利用VLS生长的线提供关键。因此，迫切需要确定控制SLV机制的关键因素及其与VLS增长的基本关系。本项目的目标是确定控制金属氧化物中SLV机制的关键参数，以及将SLV与VLS机制联系起来的关系。中心假设是，如果单个金属纳米液滴可以用于纳米线的VLS生长，它也将催化同一材料的SLV溶解，其结晶学特性与原始生长相当。其基本原理是，更好地了解SLV及其与VLS的关系可以提供一条通往高度特定的多孔材料的途径，以及一种通过“自下而上”方法合成的高质量纳米线的精确放置方法。这些研究的成功完成有望对功能性金属氧化物材料的定向设计产生重大的积极影响，因为它将能够生产高度可控和复杂的结构、组成和界面布置。这项研究意义重大，因为将SLV与VLS相结合将首次实现对纳米线-模板界面的控制，本质上是“合成”具有特定化学、结晶学和间距的界面。

Non-technical Description.We live in a society with reliance on materials, in particular those that enable the generation or storage of energy, for which the efficiencies that are required are ever growing. The function of such materials increasingly relies on creating highly-efficient and closely-spaced crystal interfaces including, for example, large area p-n junction arrays for solar devices. This project to understand and exploit the solid-iquid-vapor mechanism should provide a new approach to engineer nanostructured composite materials with highly efficient single-crystalline components, thus having a significant positive impact on the directed design of metal oxide materials, and on the society that relies on them. Based on this research and the infrastructure developed to support it, are a series of educational and outreach activities, designed to increase participation in research experiences by University of Kentucky undergraduates.Technical Description.Though the vapor-liquid-solid (VLS) mechanism has been extensively studied in its role in metal-catalyzed nanowire growth, the reverse of this process - the solid-liquid-vapor (SLV) mechanism - is not well understood, yet it could well provide the key to understanding and utilizing VLS-grown wires. Thus, there is a critical need to determine the key factors governing the SLV mechanism and its fundamental relationship to VLS growth. The objective in this project is to determine the key parameters that govern the SLV mechanism in metal oxides, and the relationship linking SLV to the VLS mechanism. The central hypothesis is that if a single metal nanodroplet can be used in the VLS growth of a nanowire, it will also catalyze the SLV dissolution of the same material, with crystallographic specificity equivalent to that of the original growth. The rationale is that a greater understanding of SLV and its relation to VLS could provide a route to highly-specified porous materials, as well as a method of precise placement for high-quality nanowires synthesized with a "bottom-up" approach. The successful completion of these studies is expected to have a significant positive impact on the directed design of functional metal oxide materials since it will enable the production of structures, compositions, and arrangements of interfaces with a high degree of control and complexity. This research is significant because combining SLV with VLS will for the first time enable control of the nanowire-template interface, essentially "synthesizing" interfaces with specific chemistry, crystallography, and spacing.