Characterization of mechanical properties of VO2 thin films on sapphire and silicon by ultra-microindentation

Mechanical properties of very thin (100 nm) VO2 films of the epitaxial (on sapphire) and the polycrystalline (on Si) type were investigated with ultra -microindentation using a spherical diamond indenter of 200 nm in radius wi th a maximum force of 0.5 or 1.0 mN. The epitaxial films on sapphire exhibi ted a Meyer's hardness (HM) of 13 GPa and a composite modulus (E*) of 240-2 60 GPa, with little change for films formed at different substrate temperat ures. The polycrystalline films on Si showed a HM of 7-9 GPa and an E* of 1 40-170 GPa, i.e. with a HM slightly lower than and an E* being almost compa rable to that of Si. The values of HM and E* for films on Si reasonably rep resent the intrinsic mechanical properties of a polycrystalline VO2, while the higher values for epitaxial films on sapphire are presumably due to the compressive stress from a lattice mismatch. (C) 1999 Elsevier Science S.A. All rights reserved.