Growth behavior and microstructure of arc ion plated titanium dioxide

Titanium dioxide (TiO2) films have been prepared using physical vapor deposition (PVD) processes for several decades. It is often considered as a material for applications such as photocatalysis, self-cleaning and antimicrobial purposes. However, numerous questions regarding the growth behavior and microstructure remain unanswered. This study aims to clarify, using microstructural characterization techniques and optical emission spectroscopy (OES), the conditions under which rutile or anatase phase constituents appear in films deposited by PVD arc ion plating (AIP), to give a better understanding of TiO2 films deposited using different deposition processes. The experimental results show that the calculated free energy for rutile phase growth is lower than for anatase, and that the rutile phase grows preferentially if thermodynamically satisfactory oxygen supply (in terms of oxygen partial pressure) is present, although less activation energy is required for anatase growth. However, OES studies reveal that, with further increased oxygen partial pressure and extended deposition time, oxidation occurring at the cathode surface generates a higher amount of neutral titanium atoms and, consequently, the metastable anatase phase grows. Detailed TEM microstructural characterization of the deposited TiO2 films in this study also explicitly shows that films identified as XRD amorphous actually contain very fine rutile nanocrystallites within the amorphous structure, whereas films revealed by XRD as composed predominantly of the anatase phase are actually as a consequence of later growth, preceded by rutile growth in the initial stage. (C) 2009 Elsevier B.V. All rights reserved.