Synthesis of and New Functionality in Heteroepitaxial Gallate / Ferrite Core@Shell Nanoparticles

非技术摘要：晶体材料中的外延是一种材料在另一种材料上的规则生长，就像在几层红砖上生长一层黄色的乐高积木一样。当两块砖的长度略有不同时，就会产生应变，因此黄色层以略大的间距(拉伸应变)或略小的间距(压缩)生长。在二维薄膜中，外延应变可以引起物理性质的巨大变化，但这种类型的外延应变在球形纳米颗粒和其他纳米结构中一直没有得到充分的利用。在核/壳结构中生长纳米颗粒导致不同物理特性的组合，类似于由覆盖着巧克力和硬糖壳的花生组成的糖果与覆盖着糖壳的固体巧克力的糖果具有不同的味道(物理特性)。在材料研究部固态和材料化学项目的支持下，南佛罗里达大学的达里奥·阿雷纳教授和他的团队将探索具有相同类型的晶格结构但物理性质截然不同的核和壳材料。核心将是一种氧化物(没食子酸锌)，它具有对生物医学成像有用的光学性质。外壳将是一种名为磁铁矿的氧化铁，这种材料的某些磁性特征可以用来确认磁铁矿在没食子酸锌核心上的外延生长。实现这种外延光学活性核心和磁敏壳的组合，为高频电子、气体传感、环境修复和生物医学应用开辟了新的可能性，这些应用将诊断+治疗功能结合到单个纳米颗粒中。技术概述：许多矿物和其他化合物在其原子晶格中采用尖晶石结构。在该项目中，在美国国家科学基金会材料研究部固态和材料化学计划的支持下，将通过化学方法合成结合两种不同类型氧化物尖晶石的核/壳纳米颗粒。没食子酸锌(ZnGa2O4)将形成核心，磁铁矿(Fe3O4)将成为外壳材料。没食子酸锌和磁铁矿具有相同的尖晶石晶体结构，这将使磁铁矿外壳在没食子酸锌核心上外延生长。没食子酸锌将使磁铁矿外壳产生0.7%的压缩应变，而磁铁矿外壳仍然相对薄弱。磁铁矿壳层的高度外延将通过在~105K下的Verwey转变(样品磁矩的突然下降)来验证，只有具有良好结晶度和合适的铁氧比的样品才会出现Verwey转变，而磁测量为筛选有前景的合成策略提供了一种有效的方法。在表现出尖锐的Verwey转变的样品中，外延将通过先进的电子显微镜、x射线光谱和散射以及中子散射技术来验证。这些尖晶石铁氧体和没食子酸盐的组合以前从未生长过，这种组合为高频电子、气体传感、环境修复和生物医学/治疗(诊断+治疗)应用开辟了新的可能性。该项目还将支持两名研究生的博士学习，并将帮助促进与一个或多个少数民族服务学院的研究生项目的合作。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。

Non-technical summary: Epitaxy in crystalline materials is the regular growth of one material on top of another, like the growth of a layer of yellow Lego bricks on top of several layers of red bricks. Strain occurs when the length of the two bricks is slightly different, so that the yellow layer grows with a slightly larger spacing (tensile strain) or slightly smaller (compressive). In two-dimensional thin films, epitaxial strain can produce dramatic variations in physical properties, but this type of epitaxial strain has been under-exploited in spherical nanoparticles and other nanostructures. Growing nanoparticles in a core / shell structure results in the combination of different physical properties, similar to how a candy comprised of a peanut covered with chocolate and hard sugar shell has a different flavor (a physical property) than a candy that is a solid piece of chocolate covered with the sugar shell. With support from the Solid State and Materials Chemistry program in the Division of Materials Research, Prof. Dario Arena and his team at the University of South Florida will explore core and shell materials with the same type of lattice structure, but very different physical properties. The core will be a type of oxide (zinc gallate) that has optical properties which are useful for biomedical imaging. The shell will be an iron oxide called magnetite and certain magnetic signatures of this material can be used to confirm epitaxial growth of the magnetite on the zinc gallate core. Realizing this combination of epitaxial optically-active cores and magnetically-sensitive shells opens up new possibilities for high-frequency electronics, gas sensing, environmental remediation, and biomedical applications that combine diagnostic + therapeutic capabilities in a single nanoparticle. Technical summary: Many minerals and other chemical compounds adopt the spinel structure in their atomic lattice. In this project, supported by the Solid State and Materials Chemistry program in the NSF’s Division of Materials Research, core / shell nanoparticles that combine two different types of oxide spinels will be chemically synthesized. Zinc gallate (ZnGa2O4) will form the core and magnetite (Fe3O4) will be the shell material. Zinc gallate and magnetite share the same spinel crystal structure which will enable the epitaxial growth of magnetite shell on the zinc gallate core. The zinc gallate will impart a compressive strain of 0.7% on the magnetite shell, which is still relatively weak. A high degree of epitaxy in the magnetite shell will be verified with temperature dependent magnetometry by identifying the Verwey transition (an abrupt drop in the sample magnetic moment) at ~105 K. Only samples with excellent crystallinity and which have the proper iron to oxygen ratio will exhibit the Verwey transition, and the magnetometry provides an efficient method of screening promising synthesis strategies. In samples that exhibit a sharp Verwey transition, the epitaxy will be verified with advanced electron microscopy, x-ray spectroscopy and scattering, and neutron scattering techniques. These combinations of spinel ferrites and gallates have not been grown before and the combination opens up new possibilities for high-frequency electronics, gas sensing, environmental remediation, and biomedical / theranostic (diagnostic + therapeutic) applications. The project will also support the PhD study of two graduate students and will help foster collaboration with the graduate program of a one or more Minority Serving Institutions.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.