Wetting of Silicon Wafers by n-Alkanes

We examine the wetting behavior of various n -alkanes on both oxide-coated and silane-coated Si wafers. n -Hexane and n -heptane completely wet a silane-coated Si wafer while n -octane exhibits a wetting transition at T w ≃ 60 °C. In the complete wetting region, the wetting layer thicknesses as a function of temperature and height are markedly thinner than that which would be predicted by a long-ranged nonretarded dispersion interaction in competition with a gravitationally determined chemical potential. By contrast, the isothermal pressure measurements of Beaglehole and Christenson ( J. Phys. Chem. 1992, 96, 3395) for n -pentane on an oxide-coated Si wafer display a much thicker wetting film than would be predicted when the dispersion and pressure-induced chemical potential are taken into account. We resolve these disparate experimental results as a function of temperature, height, and pressure by considering the influence of a number of medium-ranged interactions.