Effect of nitrogen vacancies on the growth, dislocation structure, and decomposition of single crystal epitaxial (Ti1-xAlx)Ny thin films

K.M Calamba,J Salamania,M.P Johansson Jõesaar,L.J.S Johnson,R Boyd,J.F Pierson,M.A Sortica,D Primetzhofer,M Odén

doi:10.1016/j.actamat.2020.116509

Abstract

The effect of varying nitrogen vacancies on the growth, microstructure, spinodal decomposition and hardness values of predominantly single crystal cubic phase c-(Ti1-xAlx)Ny films was investigated. Epitaxial c-(Ti1−xAlx)Ny films with y = 0.67, 0.79, and 0.92 were grown on MgO(001) and MgO(111) substrates by magnetron sputter deposition. High N vacancy c-(Ti1−xAlx)N0.67 films deposited on MgO(111) contained coherently oriented w-(0001) structures while segregated conical structures were observed on the films grown on MgO(001). High resolution STEM images revealed that the N-deficient growth conditions induced segregation with small compositional fluctuations that increase with the number of N vacancies. Similarly, strain map analysis of the epitaxial c-(Ti1−xAlx)Ny (001) and (111) films show fluctuations in strain concentration that scales with the number of N vacancies and increases during annealing. The spinodal decomposition coarsening rate of the epitaxial c-(Ti1−xAlx)Ny films was observed to increase with decreasing N vacancies. Nanoindentation showed decreasing trends in hardness of the as-deposited films as the N vacancies increase. Isothermal post-anneal at 1100 °C in vacuum for 120 min revealed a continuation in the increase in hardness for the film with the largest number of N vacancies (y = 0.67) while the hardness decreased for the films with y = 0.79 and 0.92. These results suggest that nitrogen-deficient depositions of c-(Ti1-xAlx)Ny films help to promote a self-organized phase segregation, while higher N vacancies generally increase the coherency strain which delays the coarsening process and can influence the hardness at high temperatures.

Highlights

Defect engineering of transition metal nitrides has attracted special attention due to the capability to tune their electronic and thermodynamic properties [1]
Nitrogen vacancy concentration was shown to have a significant effect on the growth, nanostructure and microstrain evolution during spinodal decomposition as well as mechanical properties in (Ti1−xAlx)Ny (y
Epitaxial c-(Ti1−xAlx)Ny thin films with the most vacancies (y = 0.67) grown on MgO(001) contained conical features with segregated domains while those grown on MgO(111) substrates contained coherently oriented and conical shaped w-(0001) structures as the film grew thicker

Summary

Introduction

Defect engineering of transition metal nitrides has attracted special attention due to the capability to tune their electronic and thermodynamic properties [1]. A recent study shows that depending on the Al content, one can tune these coatings to have high tensile strength or high toughness which proves valuable for a variety of coating applications [5]. Another impact on cubic to wurtzite transition [15]. Coatings grown by cathodic arc deposition contain varying density of macroparticles [22] and grain boundaries [23] that influence their functional properties [24] Synthesis of single crystal materials with tunable defect concentrations may provide fundamental and detailed information of the effect of nitrogen vacancies on the properties of (Ti1-xAlx)Ny films, including microstrain evolution and thermal stability

Results

Discussion

Conclusion