Phase pure, epitaxial (101) rutile TiO2 films were grown on (012) sapphire substrates at temperatures between 485 and 725 °C using metal-organic molecular beam epitaxy with titanium tetraisopropoxide as the Ti source. Growth modes and rates were investigated as a function of substrate temperature using reflection high-energy electron diffraction, x-ray reflectivity, atomic force microscopy, and transmission electron microscopy. Growth rates were as high as 125 nm/h. The influence of additional oxygen supplied from a rf plasma source was investigated. Without oxygen plasma, the growth rate exhibited reaction and flux-limited regimes and layer-by-layer growth was observed in the initial stages of film growth. With oxygen plasma the growth rate became independent of temperature; films grew initially in step-flow mode and were insulating. The mechanisms for the different growth modes as a function of film thickness, temperature, and presence of oxygen are discussed.
|Original language||English (US)|
|Number of pages||4|
|Journal||Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films|
|State||Published - 2009|
Bibliographical noteFunding Information:
The authors thank John English and Adam J. Williams for help with the construction of the MBE system and Professor Jim Speck and Professor Chris Palmstrøm for many useful discussions. This research was supported by the National Science Foundation through the UCSB MRL (Award No. DMR 05-20415) and by the ONR (Award No. N00014-08-1-0655). Acquisition of the MBE system was made possible through a NSF MRI grant (No. NSF DMR 0619698). One of the authors (R.E.-H.) thanks the Alexander-von-Humboldt Foundation for support through the Feodor Lynen program.