Glycine adsorption and photo-reaction over ZnO(000ī) single crystal

• Published in: Surface science 2014-06, Vol.624, p.112-117
• Main Authors: Gao, Y.K., Traeger, F., Wöll, C., Idriss, H.
• Format: Article
• Language: English
• Subjects: Adsorption; Amino acids; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Cross sections; Cross-disciplinary physics: materials science; rheology; Deposition; Exact sciences and technology; Glycine; Glycine adsorption; Glycine–zwitterion; photoreaction cross section; Physics; Single crystals; Surface chemistry; X-ray photoelectron spectroscopy; ZnOE(000ī) single crystal
• ISSN: 0039-6028; 1879-2758
• DOI: 10.1016/j.susc.2014.02.002

The adsorption and reaction of the amino acid glycine (NH2CH2COOH) are studied experimentally on the polar single crystal surface of zinc oxide, ZnO(000ī), by X-ray photoelectron spectroscopy (XPS) under UV light in presence and absence of molecular O2. Deposition at 350K mainly resulted in a largely deprotonated monolayer (NH2CH2COO−(a)+OH(s); where O is surface oxygen, (a) is for adsorbed and (s) is for surface species) identified by its XPS C1s binding energy at 289.3eV (COO), 286.7eV (CH2) and XPS O1s at 531.8eV (COO). A decrease in the signals of all functional groups of the adsorbed glycine (monitored by their C1s, O1s, and N1s lines) is seen upon UV excitation in the absence and presence of O2 pressures up to 5×10−6mbar. The photoreaction cross sections extracted from the decrease in the C1s peaks were found to be =2.6×10−18 (COO(a)) and 1.4×10−18(CH2) cm2. The photoactivity of the ZnO(000ī) surface under UHV-conditions is found to be comparable to that seen in direct photolysis of amino acids in solution. A plot of ln (C/Co) as a function to time for the COO and -CH2- groups of adsorbed glycine under UV excitation in presence of 5×10−6Torr of O2. [Display omitted] •The adsorption and reaction of glycine is studied experimentally on ZnO(000ī)•Deposition at 350K mainly resulted in a deprotonated monolayer (NH2-CH2-COO−(a)+OH(s)•UV-excited surfaces indicated a decrease in the N1s, C1s and O1s signals•Photoreaction cross sections were=2.6x10-18 (COO(a)) and 1.4x10-18 (-CH2-) cm2