Interface study of metal nitride films on MgO and Al2O3 substrate using CS ‐corrected TEM

Abstract

Transition metal nitrides have found wide‐spread applications in the cutting‐ and machining‐tool industry due to their extreme hardness, thermal stability and resistance to corrosion. The increasing demand of these nitrides requires an in‐depth understanding of their structures at the atomic level. This has led to some experimental and theoretical researches [1‐6]. In this paper, we will present our recent results on the atomic and electronic structures of the interface between various metal nitride thin films (CrN, VN and TiN) on MgO and Al 2 O 3 substrate using C S ‐corrected HRTEM and STEM, EELS/EDXS, quantitative atomic measurement and diffraction analysis as well as theoretical calculations. Interfacial detailed atomic and electronic structures are revealed and compared. Interface induced phenomena between nitride films and substrates are unveiled [1‐4]. Figure 1 shows two typical interfacial atomic structures, frequently accompanied by interface atom reconstruction and interface dislocations to accommodate the misfit strains between two lattices. Particular studies on the effects of N defects in the metal nitride (CrN) film have been carried out. Combining the image analysis and spectrum analysis, some generalized conclusions are derived. (i) a relationship between the lattice constant and N vacancy concentration in CrN is established [5], (ii) the ionicity of CrN crystal is correlated with the N vacancy concentration; (iii) especially, a direct relationship between electronic structure change (L 3 /L 2 ratio) and elastic deformation (lattice constants) in CrN films has been experimentally deduced, indicating that the elastic deformation may trigger a noticeable change in the fine structure of Cr‐L 2,3 edge ( Figure2 ). The experiment demonstrates an indirect approach to acquire electronic structure changes during the elastic deformation. The effect of randomly distributed defects in the films has been explored in a quantitative way using electron diffraction, complemented with HRTEM and EELS analysis. Some quantitative relations are also established [5].