Seminar ÚFKL: Vlastimil Křápek

  • 1 November 2023
    11:00 AM
  • Seminars take place in the lecture room F1 (building 6, Kotlářská 2).

Department of Condensed Matter Physics (ÚFKL) invites you to lecture

Vlastimil Křápek (CEITEC, Vysoké učení technické v Brně): Metal-insulator transition in vanadium dioxide inspected by analytical electron microscopy

Vanadium dioxide (VO2) stands out among materials exhibiting metal-insulator phase transition (MIT) due to the proximity of its transition temperature to the room temperature, which makes it a promising candidate for applications in photonics including fast optical switching or tunable optical metasurfaces [1]. The nature of the MIT in VO2 is not yet fully understood, with the Mott transition and Peierls transition being the most considered scenarios. Here we probed the MIT in a scanning transmission electron microscope (STEM) with in-situ heating. A combination of imaging, diffraction, and spectroscopy with nanometer spatial resolution allowed us to locally correlate the optical properties of VO2 with applied temperature and local variations in stoichiometry.

We fabricated a thin layer of VO2 by evaporation and verified the presence of MIT by ellipsometric characterization of the refractive index. Next, we fabricated lamellas for STEM by focused ion beam milling. Energydispersive X-ray spectroscopy revealed a rather homogeneous composition with only discernible contamination by Ga ions implanted during the milling. High-resolution and annular dark field STEM imaging revealed pronounced structural inhomogeneity – a porous and polycrystalline character of the examined lamella. A thinned part of the lamella has been examined by core-loss and low-loss electron energy loss spectroscopy at temperatures well below and above the MIT, and the experimental loss spectra were interpreted by ab-initio simulations and by comparison with recent literature [2,3]. We observed that the thin part of the lamella is dominated by reduced vanadium oxides (VO, V2O3) and exhibit no switching. This fact presents an important limit for the fabrication of VO2 nanostructures. The thicker parts of the lamella are dominated by VO2 and exhibit signatures of thermal-induced switching.

References
[1] Tripathi, A. et al. 2021. ACS Photonics, 8, 1206–1213. https://pubs.acs.org/doi/10.1021/acsphotonics.1c00124
[2] Gloter, A. et al. 2001. Eur. Phys. J. B, 22, 179–186. https://doi.org/10.1007/PL00011142
[3] Hébert, C. et al. 2002. Eur. Phys. J. B, 28, 407–414. https://doi.org/10.1140/epjb/e2002-00244-4

Loading map…

Share event

You are running an old browser version. We recommend updating your browser to its latest version.

More info