A Method for Precise Measurement of Dispersion Energy at Distances Below 50 nm

Measurement of Casimir–Lifshitz forces with high enough precision at separations below 50 nm is problematic due to the snap-in instability. The method of the adhered cantilever is not influenced by this problem. This method has demonstrated a relative precision of 10%, mostly because of systematic errors related to inhomogeneous thickness and the twisting of the cantilever. In this paper, we measure the thickness along the length of the cantilever and reduce the effect of twisting by modifying the measuring chip. It is demonstrated that the adhesion energy between Si and Ru can be measured with a precision of about 1%, which is comparable to the best experiments at distances of 100–200 nm. Only dispersion and, to a lesser degree, electrostatic forces contribute to the adhesion energy. A standard way to discriminate between these forces is the application of a compensating electric potential; however, for the present setup, this is not possible. To separate the forces, a method based on elastoplastic mechanics is proposed. In spite of its lower precision, it gives quite a strong restriction on the electrostatic interaction. The average distance between contacting surfaces is not measured directly but predicted using the distance dependence for electrostatic and Casimir–Lifshitz forces. The combination of the two measurements allows for quite a narrow range of parameters in the distance-potential plane. At a fixed potential, an unprecedented precision for Casimir-type experiments of −0.15 nm in the determination of the average separation distance can be reached.