Nitrogen ion irradiation of Au(110): Photoemission spectroscopy and possible crystal structures of gold nitride

Photoemission spectroscopy demonstrates the formation of a surface gold nitride upon irradiation of a Au(110) surface with 500 eV nitrogen ions at room temperature. After irradiation two N1s peaks are observed at binding energies of 396.7±0.2 eV and 397.7±0.2 eV along with a broadening of the Au4d_5∕2 line. Changes in valence-band spectra are also observed, including an additional density of states at 1.6 eV binding energy and new states at ∼3.1 eV. Annealing experiments indicate that the two N1s lines are associated with nitrogen compounds of differing thermal stability, possibly due to the formation of more than one nitride phase. To further investigate the properties of gold nitride we have undertaken ab initio pseudopotential calculations on the most likely nitride stoichiometry, Au₃N, and identified a novel triclinic crystal structure of a significantly lower energy than the anti-ReO₃ expected from a simple consideration of the periodic table, although the latter structure is also found to be stable. The triclinic structure is determined to be metallic, of importance to possible applications.