2, United States Air Force Nuclear Weapons Center, Kirtland Air Force Base,, New Mexico, United States
Titanium dioxide (hereafter, titania or TiO2) is a well-studied material, but despite of its 100 year history we still don't know everything about this material. It used to be thought that only one of the tetragonal phases of titania - rutile - can be grown on sapphire substrates. That is the reason why a comprehensive study of annealing effects on both phases of titania on c-cut sapphire doesn't exist. In previous works, we developed two pulsed-laser deposition protocols to grow both pure rutile and pure anatase films on this substrate, these protocols are used as the basis of this study.
Titania has a number of properties that make it useful for a wide variety of applications; these include using titania as the basis for energy efficient solar cells, as photocatalytic materials to clean air and water, for self-cleaning coatings, as components of various sensor devices, and as a gate dielectric in MOSFET technologies. Further, because it is a wide bandgap semiconductor, titanium dioxide is becoming increasingly important for many next-generation modern optical and electronics applications, such as transparent electronics systems, transparent thin-film transistors, and see-through active matrix displays. The success of each of these applications depends critically upon the particular crystallographic state (anatase, rutile, or brookite) of the titania being utilized. This is why the annealing effects on the resulting phase of this material can be very important.
Titania thin films were grown via pulsed-laser deposition technique on c-cut sapphire substrates using two pre-determined recipes: one leading to creating pure rutile, and one creating pure anatase films.
Each of the resulting films was post-annealed in a vacuum furnace at different temperatures in 200 to 900 °C in 100 degree increments and at different oxigen pressures (5, 35 and 50 mTorr). The phase of the resulting films was later determined using x-ray diffractometry. Phase content of the films was later analyzed based on the fraction of each phase in overall peak intensity. The quality of each film was was studied using atomic force microscopy.