GPa, a Poisson ratio of 0.29 for iron [40], 130 GPa

With the Young's modulus of 205 GPa, a Poisson ratio of 0.29 for iron [40], 130 GPa and 0.279 for a silicon <100> surface [41], an effective modulus of E* = 87 GPa is calculated. For values of R = 1 pirn and F L = 50 /xN, this results in a contact radius of a = 76 nm and an average contact pressure of Pavg = 2.8 GPa. Since the yield stress of iron is below 350 MPa [40], plastic deformation will readily occur under these conditions. Since the yield stress of silicon is > 1 GPa [42], the particles are mainly expected to deform. This is strongly supported by the fact that after the particle adhesion has increased due to high load, adhesion force measurements at a different location on the wafer with low loads result in the same magnitude of the adhesion force. An analogous calculation can be done for the contact between two CIP powder particles. If we assume that the contact between the particles occurs at single asperities with a reduced radius of R = 10 nm and an adhesion force of Fadh = 10 nN, we obtain a contact radius of a = 0.9 nm and a mean contact pressure of P = 4.2 GPa, which is much higher than the yield stress. Therefore, one expects the effective contact areas to be substantially larger due to plastic deformation.