Evidence of weak antilocalization in epitaxial TiN thin films

Defect engineering provides a tremendous opportunity to impart novel functionalities to nanomaterials. This report is focused on TiN metallic system, where the unpaired spin structure and electron-transport are controlled by injecting nitrogen vacancies (V-N). The TiN films are epitaxial, with the TiN/Al2O3 epitaxial relationship given by: (1 1 1) TiN//(0 0 0 1) Al2O3 as out-of-plane, and <1<(1)over bar>0> TiN//<1 0 <(1)over bar> 0> Al2O3 and <1 1 <(2)over bar> > TiN//<1 1 <(2)over bar>0> Al2O3 as in-plane, after 30 degrees rotation. Epitaxy in such a large misfit system (similar to 9.24%) is rationalized to arise via domain matching epitaxy (DME) paradigm. Following the report of room-temperature ferromagnetism [1] in TiN1-x films formed by injecting nitrogen vacancies, we provide direct experimental evidence of weak antilocalization (WAL) effects by plugging V-N using nitrogen annealing of TiN films. This evidence with simultaneous loss of magnetization in nitrogen annealed TiN films is the tell-tale sign of V-N acting as magnetically active defects in TiN, as their removal facilitates Berry's phase formation and generation of time-reversal symmetry. Through detailed EELS and Raman analysis, we have explicitly shown the absence of Ti+2 polarons in TiN films on N-2 annealing. The resistivity minima in TiN films are attributed to the WAL effect with persistent log T behavior under 0-7 Tesla magnetic fields. The temperature-dependent coherence length analysis also highlights the emergence of WAL under the two-dimensional localization theory. The WAL effect in TiN is similar to topological insulators, quenching on the introduction of magnetically active defects, while stable against nonmagnetic defects. Our findings demonstrate the prime importance of nitrogen vacancies in tuning the magentotransport characteristics in epitaxial nitride films for optoelectronic device applications.