Bulk material of VO2 shows a metal-insulator transition at 68°C which is characterized by an extreme change in its electrical resistivity and optical properties in the near infrared spectral region. In this work nanocrystalline precipitates of vanadium dioxide (VO2) embedded in fused silica have been selectively synthesized by sequential ion implantation of the elements V and O followed by a rapid thermal annealing step. The atomic structure and metal-insulator phase transition have been investigated as a function of temperature by µ-Raman spectroscopy and spectral ellipsometry. It will be shown that vanadium oxide chemical phase selection can be achieved by adjusting the implanted V to O fluence ratio to the desired stoichiometry under otherwise identical synthesis conditions. In this way layer of nanocrystalline VO2 ensembles with sub-100nm diameters have been produced. This layer of isolated but densely packed VO2 nanocrystallites show a wide temperature hysteresis extending the metal-insulator bistability down to room temperature and above that of bulk material. We were able to tailor the hysteresis by generation of reversible point defects by He irradiation avoiding at the same time electronic doping. It was found that the thermal hysteresis of the metal-insulator transition successively closes with increasing He ion fluences. The generated point defects determine strongly the thermodynamic domain stability in these nanomaterials. These findings allow engineering these effects in VO2 nanocomposite planar optical waveguide and grid structures by ion beams for application in optical memory and switching devices.

Helmut Karl*, University Augsburg, Germany
Jing Peng, University Augsburg, Germany
Anne-Kathrin Jambreck, University of Augsburg, Germany
Bernd Stritzker, University Augsburg, Germany

*presenting author