Characterization of ultrathin poly(ethylene glycol) monolayers on silicon substrates

Low molecular weight poly(ethylene glycol) silanes (PEG silanes) have been grafted onto the surface of silicon wafers in a one-step procedure yielding ultrathin and stable PEG monolayers. Structural investigation by means of X-ray reflectivity provided data on the thickness of the PEG monolayers. Th e layer thickness varied between 10 and 17 A depending on the PEG silane co ncentration applied. These results have been confirmed by X-ray photoelectr on spectroscopy measurements Atomic force microscopy data indicate very smo oth and homogeneous coverages with roughnesses of less than 3 Angstrom . Th e PEG layers are hydrophilic as determined with advancing water contact ang les between 36 and 39 degrees.