Binding of glycine and L-cysteine on Si(111)-7×7

Abstract

The adsorption of glycine and L-cysteine on Si(111)-7×7 was investigated using high-resolution electron energy loss spectroscopy (HREELS) and X-ray photoelectron spectroscopy (XPS). The observation of the characteristic vibrational modes and electronic structures of NH 3 + and COO- groups for physisorbed glycine (L-cysteine) demonstrates the formation of zwitterionic species in multilayers. For chemisorbed molecules, the appearance of v(Si-H), v(Si-O), and v(C=O) and the absence of v(O-H) clearly indicate that glycine and L-cysteine dissociate to produce monodentate carboxylate adducts on Si(111)-7×7. XPS results further verified the coexistence of two chemisorption states for each amino acid, corresponding to a Si-NH-CH2-COO-Si [Si-NHCH(CH 2SH)COO-Si] species with new σ-linkages of Si-N and Si-O, and a NH2-CH2-COO-Si [NH2CH(CH2SH)COO-Si] product through the cleavage of the O-H bond, respectively. Glycine/Si(111)-7×7 and L-cysteine/Si(111)-7×7 can be viewed as model systems for further modification of Si surfaces with biological molecules. © 2007 American Chemical Society.