Nitrogen atoms and molecules landing, reacting, and rebounding at metal surfaces

Trabajo presentado a la 14th edition of Trends in Nanotechnology International Conference, celebrada en Sevilla (España) del 9 al 13 de Septiembre de 2013.Advances in gas-surface dynamics are largely triggered by the quest for systems and conditions under which reactivity can be controled, enhanced or inhibited. Nitrogen on metal surfaces is a common subject of studies in this field. The closed shell nature of molecular N2, as well as its high binding energy, makes the molecule quite inert. In contrast, atomic N is generally reactive, recombines easily with other atoms, and strongly adsorbs at surfaces. This dichotomy turns the Nitrogen dynamics at surfaces into a rich and intriguing problem. Here we review recent theoretical work on elementary reactive processes taking place when Nitrogen atoms and molecules interact with clean and decorated metal surfaces. The theoretical framework relies on ab-initio built potential energy surfaces and full-dimensional classical dynamics. Energy exchange with the surface is included through the excitation of electron-hole pairs and phonons. We actually evaluate the role of these two energy dissipation channels in the scattering and adsorption of N2 on W(110) and N on Ag(111). We show that, in atomic N adsorption, phonons are responsible for determining the adsorption probability but electronic excitations are relevant at a later stage to fix the atoms to the adsorption positions. In the case of N atoms incident on N-covered Ag(111), we show that the Eley-Rideal recombination process between gas-phase N atoms and N adsorbates is a highly efficient mechanism for N2 formation. Finally, we show that strain can be a useful tool to promote reactivity: N2 molecules adsorb and dissociate with higher rates at the strained Fe/W(110) surface than at the Fe(110) surface. We conclude that relatively small variations in interaction energies can lead to drastic changes in the dynamics and thus to modifications in the final output of the scattering process.Peer Reviewe