Growth-twins in CrN/AlN multilayers induced by hetero-phase interfaces

Abstract

We carry out a detailed transmission electron microscopy study of growth-twins in a high stacking-fault energy transition-metal nitride (TMN) multilayer comprising of 4.2 nm-thin CrN and 1 to ~8 nm-thin AlN layers. A high density of rock-salt TMN twins with Σ3{112} incoherent twin boundaries (ITB) were found in the {111}||{0002} textured film area near the substrate. The extensive high-resolution transmission electron microscopy (HRTEM) observations reveal that rock-salt TMN twins with ITBs are frequently formed in wurtzite {0002} interface with a single-atomic-layer terrace (1 × d{0002}w-AlN). However, twins with ITBs were hardly observed in the wurtzite {0002} interface with a double atomic-layer terrace (2 × d{0002}w-AlN). The formation of twins with ITBs can be interpreted by the rs-CrN/w-AlN interface structure (with a mirror-symmetry)-induced energetically stable nucleation. Furthermore, we see that the growth-twins with Σ3 {111} coherent twin boundaries (CTB) appear in the non-textured film area further away from the substrate. Based on the HRTEM observations and atomic model analyses, supplemented with theoretical calculations, several nucleation modes of twins with Σ3 {112} ITB and Σ3 {111} CTB are proposed. These findings offer a new perspective on the formation mechanism of growth-twins in transition-metal nitride materials.