The Preparation Of Ordered Iron Nitride Epitaxial Films And Their Magnetic And Transport Properties

Iron nitride is a typical transition metal nitride,and the N atoms introduce chemical stresses in the crystal lattice by occupying interstitial sites of Fe atoms in an orderly manner.With the difference of nitrogen content,the iron nitride exhibits a rich phase structure,including tetragonal ?"-Fe16N2,cubic ?'-Fe4N,hexagonal ?-Fe3-xN(0?x<1),Orthoxy-Fe2N,cubic-structured ?"-and ?"'-FeN orthorhombic structures.The rich phase structure makes the iron nitride has good oxidation resistance,corrosion resistance,wear resistance and excellent ferromagnetism,so the iron nitride is in the field of material surface modification,catalysis,biomedical and spintronic,etc.There is a wide range of applications.The physical properties and applications of materials depend largely on their structure and morphology.Therefore,it is an important research topic to deeply understand the structural characteristics of iron nitride and precisely control the structure of the iron nitride.However,the existing research work lacks deep thinking on the commonness of the iron nitride structure and faces many challenges in the preparation of the iron nitride epitaxial film,which greatly limits the application of the iron nitride.To address these two issues,we have conducted the following research work.1)Commonness of iron nitride structure and experimental verification.It was found that the iron nitrides of different phases all have a structure in which Fe and N atomic layers are alternately arranged,and the Fe atomic layer is a close-packed crystal plane of Fe sub-lattice,having a two-dimensional hexagonal or quasi-hexagonal structure.This structural commonality greatly eliminates the large differences in the crystal structure of the iron nitride,and provides the possibility to experimentally continuously control the phase structure of the epitaxial film of the iron nitride.Based on the structural features of the close-packed surface of Fe atoms,a MgO(111)single crystal substrate was selected as the substrate,and a series of iron nitride films were prepared by magnetron sputtering by changing the partial pressure of nitrogen.The results of X-ray diffraction show that highly oriented ?-Fe(110),?'-Fe4N(111),?-Fe3-xN(001)(0?x?1),?'appear in order as nitrogen flow increases.The ?"-FeN(111),?"'-FeN(111)films were further measured by cross-sectional transmission electron microscopy to confirm that the films were epitaxially grown.Based on this,the phase diagram of substrate temperature-nitrogen partial pressure for preparing the epitaxial film of iron nitride is given.The research work not only verifies the correctness of the commonness of the iron nitride structure,but also provides an effective means for precisely controlling the phase structure of the iron nitride epitaxial film.2)Extension of the commonness of the iron nitride structure and preparation of heterostructures.The phase structure of iron nitride is the most complex among the 3d transition metal nitrides,and its crystal structure basically covers the crystal structure of other 3d transition metal nitrides.This objective fact raises us the following question:To what extent is the structural commonality of iron nitride applicable to other transition metal nitrides.For this purpose,we analyzed the crystal structures of the 3d transition metal nitride and the third main group nitride one by one,and found that the involved metal nitrides almost all have the structural commonality of iron nitride.This shows that the use of transition metal close-packed surfaces enables heteroepitaxy of transition metal nitrides with different crystal structures,which greatly facilitates and extends the preparation of transition metal nitride heterostructures.To verify this point of view,we subsequently successfully fabricated a cubic ?'-Fe4N(111)/hexagonal ?-Fe3-xN(001)bilayer film.Given the diverse crystal structure and rich physical properties of transition metal nitrides,heterostructures will greatly promote the use of transition metal nitrides in electronic devices.In conclusion,the structural commonality of iron nitride and the continuous control of the phase structure of the iron nitride epitaxial film have verified the correctness of the commonness of the iron nitride structure.The commonality of this structure is further extended to the entire transition metal nitride,which provides a good choice for the preparation of transition metal nitride heterostructures.Therefore,this work not only deepens the understanding of the structures of iron nitrides and even transition metal nitrides,but also has important significance for the application of transition metal nitride heterostructures in electronic devices.