Coverage-Dependent N₂ Adsorption and Its Modification of Iron Surfaces Structures

Spin-polarized density functional theory calculations were performed to investigate N 2 dissociative adsorption on iron (100), (110), (111), (210), (211), (310), and (321) surfaces. An ordered c (2 × 2) structure was found on Fe(100) at 0.5 monolayer coverage, which is in excellent agreement with the experiment; and a c (4 × 2) ordered structure is also found at 0.75 monolayer saturation coverage. Strong surface reconstruction is found on Fe(110) upon nitrogen adsorption, where the densely packed (110) is reconstructed into (100)-alike. Under the consideration of temperature and N 2 partial pressure, the estimated N 2 desorption temperature on Fe(100) at 925 K agrees with the experimentally detected 920–950 K. In addition, N 2 pretreatment results in Fe(100) to be mostly exposed, while that of H 2 pretreatment favors Fe(110). Further direct comparison of N 2 and H 2 adsorptions has been made to show their differences and similarities.