Adsorption of hydrazine on the perfect and defective copper (111) surface: A dispersion-corrected DFT study

We have investigated the adsorption of hydrazine (N₂H ₄) on perfect and defect-containing copper (111) surfaces by first-principles calculations. The long-range interactions are included in the geometry optimization through the application of the generalised gradient approximation with dispersion correction, DFT-D2 in the method of Grimme. We have studied three types of defects at the surfaces: monoatomic steps, Cu-adatoms and vacancies, where our calculations show that the adsorption energy increases as the coordination of the adsorption sites decreases. The ideal (111) is the most stable surface with the weakest adsorption of hydrazine, whilst the stepped (111) surface is the least stable and hence more reactive surface with the highest adsorption energy, where the hydrazine bridges across the step edge. We found that inclusion of the dispersion correction results in significant enhancement of molecule-substrate binding, thereby increasing the adsorption energy. This strong adsorption results in a bridging adsorption geometry for hydrazine, with a rotation around the NN bond where the torsional angle changes from a gauche towards an eclipsed conformer to help the molecule to bridge through both nitrogen atoms, in agreement with experimental evidence. The core-level binding shifts for the N(1 s) states upon N₂H ₄ adsorption have been calculated at DFT level to provide further insight into the N₂H₄ adsorption process on the copper surfaces.