Grafting of high-density poly(ethylene glycol) monolayers on Si(111)

A strategy has been developed for the grafting of poly(ethylene glycol) (PEG) monolayers onto the atomically flat Si(111) surface. This process involves the direct interaction of the HO-functional group on PEG with a chlorine-terminated silicon surface. The resulting monolayers show exceptional flatness, with mean roughness on the angstrom scale. Film thickness is determined by ellipsometry, X-ray photoelectron spectroscopy, and atomic force microscopy. Results for different molecular weights reveal that the grafted PEG molecules are in a brushlike configuration at low molecular weight (MW = 200, 300) and a more coil-like configuration at higher molecular weight (MW = 1000, 2000). The surface density of grafted PEG molecules is significantly higher than those reported in the literature and decreases with increasing molecular weight, from 92% at MW = 300 to 35% at MW = 2000. Both the brushlike and the coil-like configurations show excellent properties of protein resistance.