Our work focuses on the growth of complex oxide thin films, mulitlayers, superlattices and nanostructures for electronic and energy applications. These applications include next-generation memory and logic devices, quantum computation, catalysis and photovoltaics. Materials such as SrTiO3 and BaTiO3 have excellent properties for these applications, but have a bandgap that is too large to absorb light in the visible regime. Through a variety of doping techniques and epitaxial growth techniques, we are looking at ways to reduce the bandgap in the materials.
We use molecular beam epitaxy to grow extremely high quality epitaxial films. We employ in situ x-ray photoelectron spectroscopy (XPS) to measure the film stoichiometry to ensure that we are making ideal films. Descriptions of these systems that are currently being designed can be found here. Our XPS capabilities also allow us to measure valence band structure, band alignment across interfaces, built-in electric fields and the oxidation state of the constituent ions in the lattice. This allows us to understand the properties of our materials as they are grown and allows us to quickly generate high impact results.
To further evaluate the properties of these materials, we employ characterization techniques including optical absorption, temperature dependent electronic transport, x-ray diffraction, transmission electron microscopy and spectroscopic ellipsometry. We also collaborate with Lane Martin at UC Berkeley, Jason Baxter at Drexel and Patrick Hopkins at Virginia for a variety of other measurements on our samples. Through collaborations with Steve Heald at the Advanced Photon Source at Argonne National Lab we are able to perform x-ray absorption spectroscopy measurements on our films. We have also developed a collaboration with Chuck Fadley at UC Davis and the Advanced Light Source to perform standing-wave x-ray photoelectron spectroscopy measurements on SrTiO3-LaCrO3 superlattice samples that I have fabricated. Using this approach we have been able to perform separate angle-resolved photoelectron spectroscopy measurements with sensitivity to both the STO and LCO layers of the superlattice.
Prof. Comes graduate research at the University of Virginia focused on the growth of epitaxial nanocomposite films comprised of a spinel oxide pillar embedded in a perovskite oxide matrix. For my thesis work I demonstrated the ability to direct the self-assembly of these materials by controlling the nucleation of the pillars with island templates on the substrate surface. This work will continue at Auburn, as we are also able to grow composite thin films using MBE, opening new opportunities to explore the properties and applications of these materials.