Adhesion of gold particles to silicon and gold substrates in ultrahigh vacuum

By use of an ultracentrifuge, the force of adhesion between small gold spheres (2–8 μ in diameter) and the following types of substrates has been measured: (111) cleavage planes of silicon single crystals with or without a chemisorbed oxygen monolayer and, alternatively, cleavage planes covered with oxide layers 40 and 130 A thick. Further, instead of the silicon, gold substrates prepared in three different ways were used. The experiments were carried out at room temperature under ultrahigh vacuum (uhv) conditions. The experimentally determined forces are compared with the results of the theory of van der Waals interaction between extended solid bodies.