The adsorption of glycine and l-cysteine on Si(111)-7 x 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 NH3+ and COO- groups for physisorbed glycine (l-cysteine) demonstrates the formation of zwitterionic species in multilayers. For chemisorbed molecules, the appearance of nu(Si-H), nu(Si-O), and nu(C=Omicron) and the absence of nu(O-H) clearly indicate that glycine and l-cysteine dissociate to produce monodentate carboxylate adducts on Si(111)-7 x 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(CH2SH)COO-Si] species with new sigma-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 x 7 and l-cysteine/Si(111)-7 x 7 can be viewed as model systems for further modification of Si surfaces with biological molecules.
3-Chloro-1-propanol (HO−CH2−CH2−CH2−Cl) covalently binds onto Si(100)-2×1 through the thermal dissociation of the OH group to form Si−O−CH2−CH2−CH2−Cl surface intermediates, evidenced by the appearance of the Si−H stretching mode (2110 cm−1) and the retention of C−Cl stretching mode (654 cm−1) in the high-resolution electron energy loss spectroscopy (HREELS) spectrum of chemisorbed 3-chloro-1-propanol molecules and the chemical downshift of O1s binding energy (BE) in the X-ray photoelectron spectroscopy (XPS) study. The C−Cl bonds in the chemisorbed 3-chloro-1-propanol can be cleaved upon 193 nm irradiation, resulting in Si−O−CH2CH2CH2−CH2CH2CH2−O−Si through lateral diradical coupling. Upon covering the chemisorbed 3-chloro-1-propanol with physisorbed molecules, photoinduced diradical coupling between physisorbed and chemisorbed molecules was also evidenced, achieving the secondary attachment of 3-chloro-1-propanol on the Si surface and forming Si−O−CH2CH2CH2−CH2CH2CH2−OH.
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