The lab got good news on a new research project, as Dr. Comes was awarded an NSF CAREER award from the Division of Materials Research. The 5 year grant provides $650k in research funding to pursue studies of oxide interfaces and superlattices in 4d and 5d systems grown by hybrid molecular beam epitaxy. You can read about the award here and see the NSF abstract here.
Our new Rigaku SmartLab XRD supported by an NSF Major Research Instrumentation grant was delivered in January and installed in the Chemistry building over the past two weeks. The FINO Lab and our collaborators in the Farnum group have each collected data on the system and now will be going through remote applications training on the system over the coming weeks. More good news for materials research infrastructure here at Auburn!
Miles’ paper on the electronic and structural properties of epitaxial Co1+xMn2-xO4 spinel thin films is now out in the Journal of Physics: Condensed Matter. In this paper we examine the role of the Jahn-Teller distortion in stabilizing the electronic structure of the material as well as Co and Mn ionic coordination and valence. We show the polarization-dependent X-ray absorption studies of these materials and observe a strong polarization dependence in the Mn K edge data due to the Jahn-Teller distortion that has not previously been observed in spinels. Through density functional theory modeling performed by Jonathan Heath and Prof. Marcelo Kuroda at Auburn, Rutherford back scattering performed by Tami Isaacs-Smith, X-ray absorption spectroscopy performed by Dr. Steve Heald at the Advanced Photon Source, along with spectroscopic ellipsometry performed by by Dr. Tiffany Kaspar, X-ray diffraction performed by Dr. Mark Bowden, and scanning transmission electron microscopy performed by Drs. Bethany Matthews and Steven Spurgeon (all at Pacific Northwest National Lab), this was truly a team effort! The paper will be appearing in the 2020 JPCM Emerging Leaders special issue.
Our summer group writing project reviewing the integration of X-ray photoelectron spectroscopy (XPS) with oxide thin film synthesis is out in the Journal of Materials Research! This invited review for the Early Career Scholars issue focuses on ways to improve film growth using XPS, accurately interpret XPS data, and design experiments to probe charge transfer and band alignment at interfaces. We use this framework to review many of the current research areas focusing on interfaces in complex oxide heterostructures. One of the recurring themes is the importance of in situ studies to decouple the effects of interfacial phenomena from the effects of atmospheric exposure. We hope that an audience of film growers and spectroscopists will appreciate our perspective!
Our group will soon have access to a state-of-the-art Rigaku SmartLab X-ray Diffractometer thanks to a new National Science Foundation grant through the Major Research Instrumentation program. Dr. Comes, Prof. Byron Farnum in Chemistry (a FINO Lab collaborator on our NSF project), and Profs. Majid Beidaghi, Peng Li, Tae-Sik Oh, and Masoud Mahjouri-Samani in the College of Engineering collaborated on the proposal. Each group will benefit from access to the system for X-ray reflectometry, reciprocal space maps, and high-resolution X-ray diffraction (XRD) of thin film materials. It will be the only high-resolution XRD in a university in the state of Alabama with an area detector for rapid data acquisition. The system will be installed during February and March and will be open to users from around the region as well as undergraduate students participating in the Auburn Collaborative Approaches Among Scientist and Engineers REU program. If outside users are interested in performing experiments, please contact Dr. Comes by email.
Our first lead author paper has been published in Physical Review Materials! Dr. Sydney Provence led this work on k-means clustering and principal component analysis (PCA) of films grown in our lab and in Prof. Bharat Jalan’s lab at the University of Minnesota. Using these big-data analysis approaches, we examined how the film surface evolves during the early stages of growth. We showed that k-means clustering can accurately determine when strain relaxation occurs in BaSnO3 and shuttering-steps in MBE growth of LaNiO3. PCA and k-means also can be used to infer order/disorder transitions in the growth process of SrTiO3 and determine whether a homoepitaxial film is stoichiometric. With the clustering we are able to determine what features in the RHEED pattern are changing the most during layer-by-layer growth of SrTiO3 on TbScO3. The key takeaway is that there is a great deal more information that can be gleaned from RHEED than simply monitoring oscillations of the specular peak.
Sydney has shared the code through her GitHub account. We encourage other groups to record videos of all their growths and use the code for further analysis of their data. There is a rich playground to extract information from RHEED during growth and we are only beginning to scratch the surface. If you’re interested in learning more, please contact Sydney or Ryan for more information. This work was supported in part by our NSF project, DMR-1809847.
The FINO Lab had a busy and fun trip to Orlando in January, with students Miles Blanchet, Suresh Thapa, and Rajendra Paudel presenting along with postdoc Sydney Provence, and Dr. Comes presenting an invited talk. All of their work is headed towards journal submission, so look for it soon!
Dr. Comes’ proposal entitled Metastable Oxides for High-Mobility and Spin-Orbit 2D Electronics has been chosen as one of 40 projects to be funded through the 2020 Air Force Young Investigator Program! This grant for $450,000 will begin in 2020 and support the group’s research in the use of hybrid molecular beam epitaxy to stabilize oxides that act as strong donors across interfaces and exhibit high spin-orbit coupling. Graduate student Suresh Thapa has already been hard at work developing these capabilities and now the group will be able to dive into the project. To learn more about the project, take a look at the Auburn news release.
Dr. Comes spent three great days in Lisbon, Portugal at the Fusion Oxide Thin Films Conference where he presented an invited talk on our group’s work studying the surfaces of SrTiO3 films by hybrid MBE using our in vacuo XPS. Ph.D. student Suresh Thapa is leading the work, along with contributions from Rajendra Paudel and Sydney Provence. In addition to some great talks and discussions, he was awarded the Emerging Young Investigator Award from the conference organizers. It was a nice honor to recognize the new research directions we’re able to pursue in FINO Lab at Auburn with our unique hybrid MBE+XPS capabilities.
Dr. Comes’ collaborative paper with Stony Brook University and the University of Virginia focusing on V1-xNbxO2 thin films has been published in Physical Review B. In this paper we look at the effect of alloy composition in these materials and show that niobium ions donate an electron to vanadium, reducing conductivity in films near x = 0.5. Using ultrafast THz spectroscopy and temperature-dependent transport we confirm this for thin films. At Auburn, we used our ion accelerator to perform Rutherford back scattering measurements that confirm the composition of these materials. Thanks to Tami Isaacs-Smith for performing the RBS measurements!