Atomic-scale structure of η-phase Mn3N2(0 1 0) studied by scanning tunneling microscopy and first-principles theory

The (0 1 0) surface of η-phase Mn3N2 grown on MgO(0 0 1) by molecular beam epitaxy is studied using scanning tunneling microscopy. The images show that the surface is composed of rows with spacing of 6.07 Å. Two types of domains with their c-planes perpendicular are observed in which the domain boundary is oriented at ∼45° to the c-planes. In other cases, the angle between the c-planes of the two domains is closer to 87°, consistent with a twin model in which the two domains meet along a (1 0 1) plane. Atomic resolution images vary with the sample bias. At lower sample bias, primarily Mn1 atoms are observed. At higher sample bias, both Mn1 and Mn2 atoms can be resolved. The dependence of the atomic resolution image on sample bias is explained by the ratio of the integrated local density of states of Mn1 to that of Mn2, which are based on first-principles theory. Simulations of the STM atomic-scale height profiles using the integrated local densities of states vs. sample bias voltage are in excellent agreement with the experimental line profiles.