Symmetry driven control of optical properties in WO3 films

• Published in: APL materials Vol. 5; no. 6; pp. 066106 - 066106-7
• Main Authors: Herklotz, A., Rus, S. F., KC, S., Cooper, V. R., Huon, A., Guo, E.-J., Ward, T. Z.
• Format: Journal Article
• Language: English
• Published: United States American Institute of Physics (AIP) 01.06.2017; AIP Publishing LLC
• Subjects: CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
• ISSN: 2166-532X; 2166-532X
• DOI: 10.1063/1.4989395

In this work, we demonstrate that the optical bandgap of WO3 films can be continuously controlled through uniaxial strain induced by low-energy helium implantation. The insertion of He into epitaxially grown and coherently strained WO3 films can be used to induce single axis out-of-plane lattice expansion of up to 2%. Ellipsometric spectroscopy reveals that the optical bandgap is reduced by about 0.18 eV per percent expansion of the out-of-plane unit cell length. Density functional theory calculations show that this response is a direct result of changes in orbital degeneracy driven by changes in the octahedral rotations and tilts.