Bonding of nitrogen atoms on Cu(001) surfaces: A cluster approach

A study of the chemisorption of nitrogen atoms on a copper surface has been performed, based on an analysis of the electronic structure of the Cu₅N cluster obtained from self-consistent-field Xα scattered-wave calculations. Our calculations show that the chemisorption of nitrogen on Cu(001) surfaces induces peaks below and above the Cu d-band region in the total density of states curve. The bonding orbitals formed between the N 2p and the Cu valence orbitals are generally found near the bottom of the Cu d-band region, while the antibonding orbitals formed between the N 2p and Cu orbitals are found to lie above the Cu d-band region. These hybridized orbitals involving the N 2p orbital gave a satisfactory interpretation of the adsorbate-induced structure reported in N/Cu(001) ultraviolet photoemission (UPS) studies. In addition, the separate contributions of the N 2p⊥ and 2p∥ states to the total density of states curve of the Cu₅N cluster are given. This information may be useful in interpreting angleresolved UPS data.