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

Abstract

Spin-polarized density functional theory calculations were performed to investigate N2 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 N2 partial pressure, the estimated N2 desorption temperature on Fe(100) at 925 K agrees with the experimentally detected 920–950 K. In addition, N2 pretreatment results in Fe(100) to be mostly exposed, while that of H2 pretreatment favors Fe(110). Further direct comparison of N2 and H2 adsorptions has been made to show their differences and similarities.