An EXAFS and XRD study of the structure of nanocrystalline Ti-B-N thin films

Abstract

Measurements of extended x-ray absorption fine structure (EXAFS) have been used in conjunction with glancing-angle x-ray diffraction (XRD) to study the structure of sputter-deposited nanocrystalline Ti-B-N thin films of various compositions. The chemical composition of the films was established by x-ray photoelectron spectroscopy and the equilibrium phase composition was calculated from an established phase diagram for the bulk Ti-B-N system. For the Ti-B-N layers low in nitrogen content a nanocrystalline TiB2-type structure in accordance with the predictions of the phase diagram was found. However, for a nitrogen-rich layer with the composition TiB1.7N1.8 the expected Ti-containing phases, principally TiN, did not appear to be well formed. For this layer, the local structure around the central Ti atoms as deduced from EXAFS showed the Ti atoms mainly to be situated in disordered regions, possibly extremely small Ti-B or Ti-N clusters with no long-range crystalline order. The study has illustrated how the EXAFS technique can help one to understand the structure of poorly crystallized materials, especially in situations in which XRD measurements cannot be unambiguously interpreted.