Measurement of the adhesion energy between Si and Au caused by dispersion forces

The forces induced by electromagnetic field fluctuations have been thoroughly studied at distances around 100 nm. However, only a few measurements have been conducted at distances below 50 nm. Meanwhile, the distance range below 50 nm has practical significance for microelectromechanical systems (MEMS), as in this range, soft elements of MEMS are susceptible to spontaneous stiction. We use the method of adhered cantilever, which maintains stability at small distances, to measure the adhesion energy due to dispersion forces. Silicon minicantilevers with a length of 12 mm, width of $200\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$, and thickness of $10\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$ were microfabricated. One end of the cantilever is firmly fixed at a height of about $5\phantom{\rule{0.28em}{0ex}}\ensuremath{\mu}\mathrm{m}$, while the other end adheres to a gold-coated substrate. The shape of the cantilever is measured using an interferometric technique with a precision of 2 nm over the entire length. The adhesion energy is determined using parameters extracted from the shape measurements. A careful analysis of the surface roughness shows that the effects of short-range forces and capillary bridges can be neglected, while the main contribution to the adhesion energy comes from dispersion forces with a smaller part from electrostatic interaction. Using the Lifshitz theory, we determined from the adhesion energy the distance on contact with a precision of 1--2 nm. These distances, different for each cantilever, are varied in a range of 30--41 nm due to different realization of the roughness. The results of this study not only provide a better understanding of dispersion forces but also have practical implications for MEMS applications. Ways to significantly improve measurement precision are discussed.