Highly textured fresnoite thin films synthesized in situ by pulsed laser deposition with CO_2 laser direct heating

摘要

Fresnoite Ba_2TiSi_2O_8 (BTS) thin films were grown and crystallized in situ using pulsed laser deposition (PLD) with CO_2 laser direct heating of the a-plane sapphire (1 1 0) substrates up to 1250 ℃. Starting with 775 ℃ growth temperature, (0 0 1)- and (1 1 0)-textured BTS and BaTiO_3 phases, respectively, could be assigned in the films, and the typical fern-like BTS crystallization patterns appear. For higher process temperatures of 1100 to 1250 ℃, atomically smooth, terraced surface of the films was found, accompanied by crystalline high-temperature phases of Ba-Ti-Si oxides. HAADF micrographs taken in both scanning transmission electron microscopy and energy-dispersive x-ray spectrometry mode show details of morphology and elemental distribution inside the films and at the interface. To balance the inherent Si deficiency of the BTS films, growth from glassy BTS × 2 SiO_2 and BTS × 2.5 SiO_2 targets was considered as well. The latter targets are ideal for PLD since the employed glasses possess 100% of the theoretical density and are homogeneous at the atomic scale.