Dual ion beam deposition and characterization of TiOx thin films

Ion assisted deposition techniques of titania films allow the control of optical, mechanical and chemical properties without heating the substrate. In the present work a set of TiOX samples have been grown by dual ion beam deposition, using a 1.5 keV Ar ion beam impinging on a titanium target and a 300 eV argon-oxygen mixed ion beam directed onto the growing film, to assist the deposition. Taking care to mantain a constant total flux of the assistance beam (4 seem), the gas fluxes ratio, O-2/Ar, was varied in the range 0.1-0.9. The films have been characterized by X-ray Photoelectron Spectroscopy and Optical Spectroscopy, in order to correlate the composition and the refractive index to the deposition parameters. Both analyses showed the presence of two regions in the films: an internal one, characterized by uniform composition and constant optical parameters, and a surface region with a lower refractive index and a higher oxygen content. The best result obtained, in term of high thermal stability, high refractive index and low absorption, was found for a O-2/Ar flux ratio of 0.8-0.9. In correspondence with this ratio, the compositional analysis indicated a film with a stoichiometric formula near to TiO2 The optical analyses pointed out an extinction coefficient near to 10(-4) and an average refractive index of 2.4. These are suitable values for the preparation of high refractive index thin films in a multilayer.