Adsorption of azomethane on Cu(110) and Cu(111) surfaces

The interactions of azomethane on Cu(1 1 0) and Cu(1 1 1) have been investigated with XPS and HREELS under various exposure and surface temperature conditions. It is shown that with substrate at 90 K, the chemisorbed molecule is likely in cis-form on the Cu(1 1 0) surface, but retains the trans-form on Cu(1 1 1). The adsorbed azomethane desorbs molecularly when the Cu(1 1 1) surface is annealed to 190 K. In contrast, the interaction between CH3N2CH3 and Cu(1 1 0) weakens the strength of N=N bond leading to the formation of NCH2 and NCH3 above 190 K. In addition, some adsorbed molecules undergo C-N cleavage accompanied with dehydrogenation reaction to form CH2. Characteristic vibrational frequencies for the observed radicals on Cu(1 1 0) are determined. From ICPS data, the binding energies of C(1s) and N(1s) of azomethane are found to be near 286.3 and 401.4 eV, respectively. These values shift to 285.4 and 400.3 eV when azomethane dissociates to form NCH3 and NCH2. (C) 2001 Elsevier Science B.V. All rights reserved.