Friction force of smooth surfaces of SiO2-SiO2 as a function of residual pressure

Experiments were carried out to study aspects of the dry friction of 'smoot h' surfaces of silicon monocrystal wafers covered with SiO2 over a wide ran ge of residual pressure from 10(5) to 10(-8) Pa. The experiments show that a plot of the dynamic friction coefficient, f(d), versus residual pressure, P, for smooth surfaces is mole complex than the same for 'traditional' sur faces and confirm the existence of four ranges of pressure with different b ehavior of f(d) in each: (1) surface tension, (2) quasi-viscous, (3) adhesi ve and (4) cohesive friction. The behavior of f(d) in the pressure range P= 10(-2)-10(-9) Pa ensures the basis of the criterion of the extremely high v acuum (EHV) formulation. The friction coefficient f(d) decreases with press ure in the ultrahigh vacuum (UHV) range P=18(-2)-10(-7) Pa and increases in the pressure range P<10(-7) Pa (UHV). (C) 1999 Elsevier Science B.V. All r ights reserved.