Paper on SrNbO3 Film Synthesis Published in APL Materials

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  • Publication date September 23, 2022
  • Categories: Papers
Nb 3d core level and valence band XPS for SrNbO3 thin films capped with and without SrHfO3 capping layers. (a) uncapped, (b) thin (0.8 nm) capped, (c) medium (1.2 nm) capped, and (d) thick (1.6 nm) capping of SHO. Fits to the data show spin–orbit split peaks of Nb4+ (low binding energy) and Nb5+ (high binding energy) features. (e) Valence band data showing density of states near the Fermi level for all four samples with DFT model.

Our paper on the growth of SrNbO3 by hybrid molecular beam epitaxy is out in APL Materials today. This work was led by former student Suresh Thapa as part of his Ph.D. and is the first demonstration of SrNbO3 by MBE. Suresh used a new kind of metal-organic precursor to grow these materials, which are very promising as interfacial donors. He did a great job with this challenging project and even built a DFT model in collaboration with Dr. Marcelo Kuroda to compare our experimental results with theoretical expectations!

One of the biggest challenges with d1 transition metal oxides is preserving a stable surface that doesn’t over-oxidize. To do that, we also developed a growth recipe for SrHfO3 that is critical if the samples are going to be accurately characterized. Our former postdoc Sydney Provence and current Ph.D. student Patrick Gemperline made big contributions to that part of the project. Our in situ XPS measurements from the figure above show that the capping layer preserves free electrons at the Fermi level, which is critical for use in interfacial heterostructures. Steven Spurgeon and Bethany Matthews from PNNL did a great job with STEM to show that we can preserve crystalline SrNbO3 down to 2 unit cells with a cap after atmospheric exposure. Steve Heald from the Advanced Photon Source conducted X-ray absorption spectroscopy on the capped samples to measure the valence after atmospheric exposure, which showed that the cap preserves the Nb4+ charge state.

Thanks to Air Force Office of Scientific Research (AFOSR) for funding support on the project through the Young Investigator Program as well as the Alabama EPSCOR Graduate Research Scholars Program for supporting Suresh’s studies in his last year.