NSF Award
2327667
Non-technical summary: <br/><br/>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. <br/><br/>Technical summary: <br/><br/>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.<br/><br/>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.
