Christina Engler conducted research on growing epitaxial cobalt oxide thin films via magnetron sputtering to study how crystal facets influence catalytic activity for CO2 hydrogenation. Several cobalt oxide films with varying crystal structures were deposited using different sputtering parameters. Characterization with XRD and Raman spectroscopy showed spinel structured films, mixed spinel and cubic polycrystalline films, and purely cubic films were produced. Future work will confirm epitaxial growth using WAXS and LEED, and test the films' catalytic activity for CO2 hydrogenation using PM-IRAS to detect adsorbed surface species.

1. Christina Engler
Advisors: Jonathan Kenneth Bunn, Cun Wen, Jason Hattrick-Simpers, Jochen Lauterbach
“Epitaxial Cobalt Oxide Thin Film Synthesis via Magnetron Sputtering”
CO2 is abundant as ever in the atmosphere, and controlling emissions has never been such
an important issue to address in today’s society. CO2 catalytic hydrogenation is one of the most
promising techniques for CO2 mitigation, and our recent results indicate that Cobalt Oxide (Co3O4)
nanorods with (110) facets are significantly more effective for this process. However, it is not clear
how the crystal facets functionalize and influence the catalytic activity and selectivity.
By growing epitaxial Co3O4 thin films, one could do spectroscopic and kinetic studies on
the surface of the single crystal and study how the faceting of the film plays a role in the CO2
hydrogenation reaction mechanism. Growing the epitaxial films has proved challenging due to
the constraints of reactive sputtering, but several films made from varying power and oxygen
partial pressure parameters have been tested and characterized in hopes of growing the single
crystal thin film in one, ordered crystal plane. Based on the nature of this phase investigation,
characterization methods such X-Ray Diffraction (XRD) and Raman spectroscopy were used to
give insight to crystal structure and oxide growth of the deposited films. Spinel structured films,
mixed spinel and cubic polycrystalline films, and purely cubic films were found to be deposited
at different power and oxygen flow parameters. A phase diagram was generated to give insight to
the general trend of samples over the reactive sputtering parameters.
Interestingly, it was found that several reaction parameters provide distinct peak
selectivity, which can hopefully lead to epitaxial growth in the future work. The epitaxial growth
of Co3O4 thin films will be later confirmed through characterization by Wide-Angle X-Ray
Scattering (WAXS) and Low-Energy Electron Diffraction (LEED). The next step will be to test
these epitaxial films in the Polarization-Modulation Infrared Reflection-Adsorption Spectroscopy
(PM-IRAS), where species adsorbed to the catalyst surface can be detected during CO2
hydrogenation for future surface science studies.