Designing Defect Structure and Interfacial Strain in an Epitaxial VN Bilayer Film by Tailoring N Concentration

ABSTRACT A bilayer of V _0.49 N _0.51 /V _0.56 N _0.44 has been grown epitaxially on MgO(001) by reactive high‐power pulsed magnetron sputtering in an industrial‐scale deposition system at a temperature of 400°C, and it is demonstrated that the defect structure and interfacial strain are governed by the N concentration. Based on the lattice mismatch between MgO and V _0.49 N _0.51 with V vacancies, an interfacial strain of −2.3(1)% is expected. From ab initio calculations, X‐ray diffraction, and transmission electron microscopy data, it is inferred that the V _0.49 N _0.51 layer exhibits V vacancies, N Frenkel pairs, and a high dislocation density of ≈0.20 nm ⁻² , causing an interfacial strain of −1.4(5)% at the MgO/V _0.49 N _0.51 interface. The phase formation of understoichiometric V _0.56 N _0.44 is governed by N vacancy formation, while the dislocation density is reduced to ≈0.04 nm ⁻² at the V _0.49 N _0.51 /V _0.56 N _0.44 interface and to < 0.01 nm ⁻² within V _0.56 N _0.44 at a distance of ≈35 nm from the interface. Based on ab initio calculations, a strain of −1.7(6)% is predicted at the V _0.49 N _0.51 /V _0.56 N _0.44 interface in very good agreement with the experimentally obtained value of −1.6(8)%. It is evident that control of the N concentration allows for the design of layered architectures with well‐defined strained interfaces and tailored defect structures.