Our work 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.

1. Suresh Thapa, Sydney R. Provence, Devin Jessup, Jason Lapano, Matthew Brahlek, Jerzy T. Sadowski, Petra Reinke, Wencan Jin, and Ryan B. Comes. “Correlating surface stoichiometry and termination in SrTiO₃ films grown by hybrid molecular beam epitaxy,” Journal of Vacuum Science and Technology A, 39, 053203, Sep 2021. DOI: 10.1116/6.0001159
2. Suresh Thapa+, Rajendra Paudel+, Miles Blanchet+, Patrick Gemperline+ and Ryan B. Comes. “Probing surfaces and interfaces in complex oxide films via in situ X-ray photoelectron spectroscopy,” Journal of Materials Research, 36, 26-51, Jan 2021. DOI: 10.1557/s43578-020-00070-9 
3. Miles D. Blanchet, Jonathan J. Heath, Tiffany C. Kaspar, Bethany E. Matthews, Steven R. Spurgeon, Mark E. Bowden, Steve M. Heald, Tamara Issacs-Smith, Marcelo A. Kuroda, and Ryan B. Comes. “Electronic and Structural Properties of Single-crystal Jahn-Teller Active Co_1+xMn_2-xO₄ Thin Films,” Journal of Physics: Condensed Matter, 33, 124002, Jan 2021. DOI: 10.1088/1361-648X/abd573
4. Sydney R. Provence, Suresh Thapa, Rajendra Paudel, Tristan Truttmann, Abhinav Prakash, Bharat Jalan, and Ryan B. Comes. “Machine Learning Analysis of Perovskite Oxides Grown by Molecular Beam Epitaxy,” Physical Review Materials, 4, 083807, Aug 2020. DOI: 10.1103/PhysRevMaterials.4.083807. 
5. Ryan B. Comes, Steven R. Spurgeon, Mark H. Engelhard, Despoina M. Kepaptsoglou, Tiffany C. Kaspar, Quentin M. Ramasse, Peter V. Sushko, and Scott A. Chambers. “Probing the Origin of Interfacial Carriers in SrTiO3-LaCrO3Superlattices,” Chemistry of Materials, 29, 1147–1155, Feb 2017. DOI: 10.1021/acs.chemmater.6b04329
6. Ryan B. Comes and Scott A. Chambers. “Interface structure, band alignment and built-in potentials at LaFeO₃/n-SrTiO₃ heterojunctions,” Physical Review Letters, 117, 226802, Nov 2016. DOI: 10.1103/PhysRevLett.117.226802
7. Peng Xu, Yilikal Ayino, Christopher Cheng, Vlad Pribiag, Ryan B. Comes, Peter V. Sushko, Scott A. Chambers and Bharat Jalan. “Understanding and controlling charge density in the two-dimensional electron gas at a polar/non-polar oxide interface,” Physical Review Letters, 117, 106803, Sep 2016. DOI: 10.1103/PhysRevLett.117.106803
8. Ryan B. Comes, Steven R. Spurgeon, Steve M. Heald, Despoina M. Kepaptsoglou, Lewys Jones, Phuong Vu Ong, Mark E. Bowden, Quentin M. Ramasse, Peter V. Sushko, and Scott A. Chambers. “Interface-induced Polarization in SrTiO₃-LaCrO₃ Superlattices,” Advanced Materials Interfaces, 3(10), 1500779, May 2016. DOI: 10.1002/admi.201500779
9. Ryan B. Comes, Peter V. Sushko, Steve M. Heald, Robert J. Colby, Mark E. Bowden, and Scott A. Chambers. "Band-Gap Reduction and Dopant Behavior in La, Cr Co-doped SrTiO₃ Thin Films," Chemistry of Materials, 26, 7073-7082, Dec 2014. DOI: 10.1021/cm503541u
10. Ryan Comes, Hongxue Liu, Mikhail Khokhlov, Richard Kasica, Jiwei Lu and Stuart A. Wolf. "Directed Self-Assembly of Epitaxial CoFe₂O₄-BiFeO₃ Nanocomposites," Nano Letters, 12 (5), 2367-2373, May 2012. DOI: 10.1021/nl3003396