Surface Science of Magnetite

Magnetite (Fe 3 O4 ) is a naturally abundant half-metallic ferrimagnet with wide-ranging applications in current and emerging technologies. While much research effort has focused on understanding its intriguing bulk properties, Fe3 O4 surfaces often limit its performance in applications. The emergence of a valid surface model coupled to reproducible preparation makes Fe3 O4 (001) a prime candidate for investigations of Fe3 O4 surface properties and a model system to study metal-oxide surface chemistry. Recent STM studies by our group have found that an unusual surface reconstruction dominates adsorption processes at the Fe3 O4 (001) surface. Many adsorbates preferentially bind at one location within a distorted surface layer, producing a nanotemplating effect that DFT calculations link to charge ordering in the subsurface layers. Several unusual effects result including room temperature water splitting, surface Fe dimers, and the stability of isolated Au adatoms up to 400 C. In this project we use our knowledge of the Fe3 O4 (001) surface as a basis to jump to the next level of complexity and study its surface chemistry, aiming to link macroscopic reactivity to fundamental processes occurring at the atomic scale. This task requires the combined application of atomically resolved STM, state of the art DFT calculations, and the full array of spectroscopic techniques available on a newly constructed oxide surface chemistry system, designed and built by the applicant. The work plan is based on the application of a common methodology to study three distinct but related model systems. First, we aim to discover how the templated adsorption observed in atomic scale studies of Fe3 O4 (001) translates into macroscopic reactivity. Then, using our ability to tailor the surface termination, we will investigate how undercoordinated surface cations modify the surface and with it, adsorption processes and reactivity. Finally, we will use the templating effect to study the reactivity of Fe3 O4 supported isolated gold adatoms and clusters, a controversial topic in catalysis. The direct comparison of data in each phase of the work will allow the role of the nano Au to be unambiguously determined. We request funds to employ a graduate student and two masters students to work alongside Dr. Parkinson, a junior faculty starting his independent research program. Funding this project will establish a network between junior faculty both inside and outside the TU, firmly establish Dr. Parkinson as a scientist in the field of surface science, and represent a challenging and exciting opportunity for a student to work at the forefront of fundamental research with impact in technologies.

Magnetite (Fe3O4) is a common mineral in the environment, and has many applications in fields as diverse as medicine, electronics, and catalysis. Processes occurring at the surface turn out to be crucial in almost all cases (e.g. chemical reactions occur at the surface of a catalyst, charge must be transferred across an interface in an electronic device), and this project sought to better understand how the atomic-scale structure at the surface affects the material properties. We started out by determining how the atoms are arranged in the outermost layers of a common surface of magnetite; the (100) surface. This was not an easy task because magnetite is a complex material, but through a combination of different experimental and theoretical methods we were able to show that the accepted model for the surface structure was incorrect, and propose a new structure that is consistent with all existing experimental results. Our paper Subsurface Cation Vacancy Stabilization of the Magnetite (001) Surface was published in the prestigious journal Science.With the structure understood, we began to study how the surface interacts with molecules and metals. The most important discovery was that this surface reconstruction prevents the agglomeration of metal atoms into large clusters. This unique property allows us to study how the atoms move around, interact with each other and the environment, and then how nanoparticles are formed. The surface is highly promising to study if (and then how) single atoms can catalyse chemical reactions in so-called single-atom catalysis. Ultimately, this concept laid the foundation for my successful application for the 2015 FWF START prize, and this exciting work will be further developed over the next 6 years.Our studies of molecular adsorption focussed on organic molecules, in order to better understand the use of magnetite as a catalyst. We began simple representative molecules for the classes of acids and alcohols; methanol and formic acid. Whereas formic acid binds all over the surface, methanol binds only at specific defects in the structure. This aspect is also an important prelude to study how drugs are attached to magnetite nanoparticles via oleic acid.