Continuous phase evolution of iron nitride epitaxial films based on structural commonality

Iron nitrides have a wide spectrum of applications in wear resistance coatings, catalysis, biomedical fields and spintronics due to their diverse phase structures. Thus it is important to fundamentally understand and precisely control the phase structures of iron nitrides. However, there is no work showing structural relationships among the phases. Here a structural commonality of iron nitride is proposed. All iron nitrides are alternately composed of close packed Fe atomic layers and interstitial N atomic layers, where the Fe layers have ideal or quasi two dimensional hexagonal configurations. Based on this commonality, successive phase evolution of iron nitride epitaxial films on MgO(111) substrate was realized. And a nitrogen flow rate-substrate temperature phase diagram was constructed. Moreover, the structural commonality is also found in other transition metal nitrides. Therefore, these results not only offer new insights into the phase evolution of iron nitrides but also provide a good choice for the fabrication of the heterostructures of transition metal nitrides with different crystal structures.