The results of molecular dynamics (MD) simulations of nanoindentation and nanoscratching of titanium dioxide lattices are presented. The TiO2 surfaces investigated are the (001) and {110} rutile surfaces and the anatase {100} and (001) surfaces. A spring model consisting of a cube cornered indenter connected to supports, via a set of springs, was used to model the cantilever in an atomic force microscope. Indentations were conducted to depths of 12 and 18 Å on each surface and scratching simulations were conducted for a length of 80 Å and at a depth of 6 Å. Pile-up patterns were found to be dependent on the crystal surface orientation. No evidence of the activation of slip systems was discovered. The relative values of the contact pressure and Young’s modulus were in reasonable agreement with experiment and the coefficient of friction was found to be independent of the TiO2 polymorph.

Simulations of nanoindentation into a typical optical coatings stack employed in energy efficient glazing have been performed using classical molecular dynamics (MD) and a coupled finite element/MD methodology. The coatings stack consists of a low emissivity material, Ag, sandwiched between two layers of a transparent conducting oxide (TCO), ZnO. Simulations into both the ZnO and the coatings stack show a strong interaction between the tip symmetry and crystal symmetry in the observed displacement field. A large amount of elastic recovery is observed for both the ZnO system and the coatings stack, but with an impression left on the surface that looks like a crack but extends no further than the tip imprint at maximum depth. The full stack is observed to have a lower hardness once there is a significant penetration of the displacement field into the Ag, when compared to the pure ZnO system. A comparison between the coupled finite element/MD methodology and the fixed boundary MD only model shows that the boundary conditions have little influence on the calculated results.

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