Correlation between deposition parameters of periodic titanium metal/oxide nanometric multilayers and their chemical and structural properties investigated by STEM-EELS

We analyze structure and composition of titanium-based metal/oxide periodic multilayers prepared by reactive sputtering. The reactive gas pulsing process is involved to periodically inject the oxygen gas during the multilayers deposition. This approach allows the growth of regular and tunable nanometric TiO2/Ti periods with thicknesses ranging from 14 to 50 nm. The interfacial layer between oxide and metallic layers is mainly the fcc-TiO phase as clearly pointed out by transmission electron microscopy and associated electron spectroscopies. In addition, sharp transitions are produced at Ti/TiO2 interfaces (with a high density of defects) whereas the smoothest ones are obtained at TiO2/Ti interfaces. Similarly, the real-time measurements of the target voltage vs. time correlate with periodic alternations formed by a mixture of amorphous + rutile TiO2 compound, the fcc-TiO phase and the hcp metallic Ti phase through the films thickness. An abrupt transition from metallic to oxidized sputtering mode takes place when oxygen is injected and correlates with the sharp Ti/TiO2 interface. On the other hand, when oxygen is stopped, the restoration to the metallic sputtering mode is longer and corresponds to the occurrence of the fcc-TiO phase at the smooth TiO2/Ti interfaces.