Ultrahigh-pressure (HP) polymorphs such as diamond exhibit unique physical properties. There are many HP polymorphs that can be recovered to the ambient pressure to be utilized in industry. However, some of the HP polymorphs that are thermodynamically stable under HP (> 10 GPa) transforms into amorphous structure or different crystalline phases during decompression. If this back-transformation can be suppressed, we can obtain some useful HP polymorphs to be utilized in future. As a possible solution, we combined the epitaxial thin film growth technique with HP synthesis method using a multi-anvil apparatus.
We first investigated a HP-phase, α-PbO2-type titanium dioxide (α-TiO2, orthorhombic, a = 0.454 nm, b = 0.549 nm, c = 0.491 nm). Unfortunately, most of the reported data was about the product in form of powder, and only a few reports about the fabrication of single crystals are currently available. In particular, single-phase α-TiO2 epitaxial thin films has not been reported. In this study, we report the fabrication of the high-quality single-phase α-TiO2(100) epitaxial thin films.
Thin films of epitaxial rutile TiO2(100) (thickness: ~100 nm) were deposited as precursors on Al2O3(001) (5 mm in diameter and 0.5 mm in height) using pulsed laser deposition. HP treatment for thin films was performed using a Kawai-type multi-anvil high-pressure apparatus. The precursor thin film was heated up to 1000°C under HP of 8 GPa, and then kept for 0.5 h. After the heating step, cooling was started down to room temperature (RT), followed by decompression.
As a result, a successful single-phase α-TiO2(100) epitaxial thin film has been obtained. It should be stressed here that rocking-curve full width at half maximum of the 200 peak showed a quite small value of 0.113°, indicating very high crystallinity. Our present study indicates that HP treatment to thin film samples allows us to fabricate high-quality HP-phase epitaxial thin films.
5:00 PM–7:00 PM Apr 23, 2019 (US - Arizona)
PCC North, 300 Level, Exhibit Hall C-E