Measurement Of Casimir Force In The Nanometer Range

In 1948, H. B. G. Casimir predicted the existence of attractive force between two neutral ideal metallic plates in vacuum, which was later named after him. This effect is a macroscopic quantum effect and plays a signi?cant role in quantum field theory, gravitation and cosmology, atomic and molecular physics, condensed matter physics and nano/nicro-electromechanical system.Since the milestone experiment by Lamoreaux's group which demonstrated the existence of the force unambiguously, scientists have performed a series of experiments with different materials, diverse geometric shapes and various temperatures. They have achieved a number of successful measurements and considerable knowledge of Casimir effect. With the size of the mechanical-devices and the separation between different mechanical elements being reduced to nanometer, the Casimir attraction may highly in?uence the behavior of these structures. Thereby it is necessary to investigate Casimir force in the nanometer range. The precision measurement of the Casimir force can also be used to set a constraint on non-Newtonian force in the nanometer range.Using Frequency Modulation Atomic Force Microscope(FM-AFM), we measure the gradient of the Casimir force between a gold sphere and a gold coated silicon plate at liquid nitrogen temperature. In order to perform the measurement at a separation less than 100 nm, we adopt a qPlus probe as the force sensor as its spring constant is stiff enough to avoid jump-to-contact. A precise measurement of Casimir force requires high qualities of the two interacting surfaces regarding of the smoothness and cleanliness. We prepared one surface by thermal evaporation of gold film on a silicon wafer in the ultrahigh vacuum preparation(PREP) chamber. The wafer was then transferred from the PREP chamber to the SPM chamber to avoid surface contamination by keeping it in the vacuum. At the closest separation(20nm), we achieved a relative precision of 4.5%. Our best results indicate that the deviation between the experimental data and the theoretical calculation with Drude model is less than 10% in 25 nm~64 nm, while the differences with Plasma is from 8.6% to 61.2%. The deviation might due to the unknown uncertainties that are not considered yet. The observation of this work provides useful information for the design of next high precision Casimir experiment.