The effect of nanoparticles on rough surface adhesion

Particulates can strongly influence interfacial adhesion between rough surfaces by changing their average separation. In a cantilever beam adhesion test structure, a compressive zone exists just beyond the crack tip, which may act to deform such particles. To explore this phenomenon quantitatively, we compared finite element method calculations of the interface to load-displacement experiments of individual particles. Below a certain threshold density, we show that the stress distribution at the interface is sufficient to deform individual particles. In this regime, the adhesion is controlled by the intrinsic surface roughness and under dry conditions is mainly due to van der Waals forces across extensive noncontacting areas. Above this threshold density, however, the particles introduce a topography that is more significant than the intrinsic surface roughness. As a result, the interfacial separation is governed by the particle size and the adhesion is lower but stochastic in nature. We demonstrate that the particles on the micromachined surfaces are silicon carbide (SiC). The cantilever test structures were fabricated using standard surface micromachining techniques, which consisted of depositing, patterning, and etching two polycrystalline silicon (polysilicon) layers separated by a tetraethylorthosilicate (TEOS) sacrificial oxide layer. High temperature annealing in the fabrication process allows residual carbon in the TEOS sacrificial oxide layer to migrate to the polysilicon surface and form the SiC particles. (c) 2006 American Institute of Physics.