Crack Healing Between Rough Polycrystalline Silicon Hydrophilic Surfaces in n-Pentanol and Water Vapors

The crack healing rates of polycrystalline silicon microcantilevers in contact with a substrate are measured in n-pentanol vapor at different partial pressures, p/p _s. The absolute value of the slope of the logarithmic average crack healing velocity \(\bar{v}\) versus the energy release rate G, \(|d[\log (\bar{v})]/dG|\), is constant and decreases with increasing p/p _s. The slope dependence on p/p _s is equivalent to that in a water vapor environment. This slope is independent of p/p _s in glass stress corrosion cracking experiments due to chemical kinetics, while the present experiments reflect a capillary bridge nucleation mechanism across nanometer-scale gaps created by surface roughness. Equilibrium measurements of adhesion versus p/p _s are also compared for n-pentanol and water vapor. For p/p _s ≤ 0.5, adhesion is comparable for the two vapors, while for p/p _s > 0.5, adhesion in water vapor is approximately twice that in n-pentanol vapor. At lower p/p _s, this is explained by the larger Kelvin radius and the larger adsorbed layer thickness of n-pentanol. This combination enables larger asperity gaps to be bridged by capillary liquids. At higher p/p _s, adhesion in water vapor is larger because the work of adhesion of capillary bridges becomes twice that of n-pentanol.