Modelling and experimental study of nanoscratching process on PMMA thin-film using AFM tip-based nanomachining approach

This paper proposes a nanogroove machined depth prediction model for the atomic force microscopy (AFM) tip-based scratching method on the polymer thin-film. This model is used to predict the normal load required to just cut through the polymer thin-film without contacting the silicon substrate excessively to reduce the tip wear. In this proposed theoretical model, the AFM tip is assumed as a rectangular pyramid with a spherical apex. The elastic recovery, material pile-up, adhesive friction coefficient and mounted angle of the tip on the AFM head are considered in the developed model. Nanogrooves are scratched on a poly(methyl methacrylate) (PMMA) thin film by a silicon AFM tip. Results show that the bulk volume of the material pile-up can be enlarged after scratching with a relatively sharp tip. The equivalent height value of the material pile-up is thus introduced into the theoretical model, and the relationship between the equivalent height values of the material pile-up and the radius of the tip is analyzed in detail. Based on the proposed model and the experimental results, the effect of the radius of the AFM tip on the flow stress and adhesive friction coefficient is studied. Finally, several nanogrooves when the tip just cutting through the polymer thin-film are achieved on the polymer thin-films with different thicknesses using the tips with various radii.