Surface Preparation of Silicon for Polymer Adsorption Studies

The silicon surfaces that result from common preparation methods were evaluated on the basis of purity, reproducibility, and stability for use as a substrate in adsorption studies. Comparisons concerned (i) resulting adsorption-desorption kinetics of polystyrene adsorbed from cyclohexane solution near the θ temperature, (ii) the surface interaction parameter (χ₉) inferred from displacement experiments, and (iii) the surface chemistry measured by surface analytical techniques. Subtle differences in surface chemistry induced large undesirable variations in dynamics. These differences showed up in the rates of (i) conformational equilibration and (ii) exchange between the adsorbed state and free solution, but not in the steady-state mass adsorbed onto an intially-bare silicon surface. Freshly etched surfaces were unstable over periods of hours. The most consistent results were obtained by exposing the silicon to oxygen plasma or ultraviolet radiation, such that formation of the homogeneous silicon oxide was favored.