Skip navigation
SuUB logo
DSpace logo

  • Home
  • Institutions
    • University of Bremen
    • City University of Applied Sciences
    • Bremerhaven University of Applied Sciences
  • Sign on to:
    • My Media
    • Receive email
      updates
    • Edit Account details

Citation link: https://doi.org/10.26092/elib/1128
dissertation_simon_fischer.pdf
OpenAccess
 
by-sa 3.0 de

Strongly strained growth of vanadium dioxide thin films on microscale ruthenium dioxide islands


File Description SizeFormat
dissertation_simon_fischer.pdfPDF-Datei mit Dissertation46.46 MBAdobe PDFView/Open
Authors: Fischer, Simon  
Supervisor: Falta, Jens  
1. Expert: Falta, Jens  
Experts: Eickhoff, Martin 
Abstract: 
Vanadium dioxide exhibits a metal-insulator transition (MIT) which comprises an electronic and a structural component. Accordingly, it is often understood as a cooperative effect of a structure-induced Peierls transition and a electron correlations-induced Mott transition. The structural transition can be exploited by subjecting VO2 thin films to epitaxial stress, which stabilizes either the low temperature insulating or the high temperature metallic phase. Through this strain engineering approach, the transition temperature can be tuned from its bulk value of 68 °C, tailoring the material towards technological applications.

In the present thesis, massively strained thin films of VO2 on micron-sized RuO2 islands are grown and analyzed. This is done, in large parts, in a low energy electron microscope (LEEM) instrument. The instrument allows for following surface processes in situ during oxidation and deposition experiments, giving microscopic and structural information on the material.

First, the RuO2 islands are fabricated by oxidizing a Ru(0001) surface using atomic oxygen from a thermal cracker. The resulting complex island morphology, which encompasses four different phases of RuO2, is studied during and after growth, assessing the kinetic and thermodynamic aspects that lead to their formation. It is found that a microcrystalline oxide phase serves as a nucleation hub for adjacent (110)- and (101)-oriented RuO2 structures, which then outgrow the incubator phase. The structural registry of a separate RuO2(100) phase to the substrate has been resolved and is found to lead to the distinct growth behavior that this phase exhibits compared to the others.

On samples prepared in this way, VO2 was grown, again with the aid of atomic oxygen. This, as confirmed by x-ray absorption spectroscopy (XAS) and x-ray photoelectron spectroscopy (XPS), ensures that the stoichiometry of the films is correct. In situ low energy electron diffraction (LEED) measurements showed that during the growth of VO2 on RuO2(110), the lattice parameters stay constant. This indicates a very high strain near the pseudomorphic case (8.78 %). The VO2(110) surface was also found to exhibit a (2 × 2) reconstruction due to an oxygen-rich surface termination. Conversely, VO2 was found to grow relaxed on the (100)-oriented islands. Its VO2(100) surface is heavily faceted, indicating a high surface energy.

Complementary measurement of the x-ray linear dichroism in these films finds that the VO2(110)/RuO2(110) islands exhibit spectra that are characteristic for the metallic phase. This may indicate that the MIT is suppressed in high-strain conditions. On VO2(100)/RuO2(100) islands, indications of a MIT are found. However, the VO2 films experience reduction due to the synchrotron beam, which can also induce the transition into the metallic state.

Alongside a deeper understanding of Ru oxidation kinetics using atomic oxygen, this work opens up a remarkably high window of accessible strain for VO2 thin film growth and gives important insights into the surface of VO2, which until recently was often neglected.
Keywords: Physics; Low Energy Electron Diffraction; x-ray photoelectron spectroscopy; x-ray absorption spectroscopy; low energy electron microscopy; surface science; vanadium dioxide; vo2; ruthenium dioxide; ruo2; mott insulator; peierls instability; strain; ruthenium; oxidation
Issue Date: 28-Sep-2021
Type: Dissertation
DOI: 10.26092/elib/1128
URN: urn:nbn:de:gbv:46-elib53643
Institution: Universität Bremen 
Faculty: Fachbereich 01: Physik/Elektrotechnik (FB 01) 
Appears in Collections:Dissertationen

  

Page view(s)

112
checked on May 29, 2022

Download(s)

76
checked on May 29, 2022

Google ScholarTM

Check


This item is licensed under a Creative Commons License Creative Commons

Legal notice -Feedback -Data privacy
Media - Extension maintained and optimized by Logo 4SCIENCE