Structural and thermodynamic aspects of the evolution of supersmooth surface of oxide crystals

• Published in: Applied surface science 2021-07, Vol.553, p.149541, Article 149541
• Main Authors: Butashin, Andrei V., Chernyshev, Alfred P., Muslimov, Arsen E., Asvarov, Abil Sh, Kanevsky, Vladimir M.
• Format: Article
• Language: English
• Subjects: Annealing; Crystal; Diffusion; Oxide; Sapphire; Steps; Supersmooth surface
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2021.149541

[Display omitted] •Concepts for evolution the morphology of supersmooth surfaces of oxide single crystals.•Transformation of a supersmooth crystal surface begins at the Tamman temperature.•The step height on vicinal (0001) faces is either equal to c/6 or multiple of this value.•Annealing of a (0001) cleavage face of LaMgAl11O19 leads to the formation of prisms. Evolution of the α-Al2O3, La3Ga5SiO14, and LaMgAl11O19 single crystals supersmooth surfaces at annealing in air was investigated using thermodynamic calculations. In particular the characteristic temperatures and annealing ranges were calculated when the surface melting phenomena took place or atomically smooth steps were formed and moved due to the surface diffusion processes. Later conclusion was confirmed in the surface probe microscopy experiments with regard to the crystal structure data of α-Al2O3, La3Ga5SiO14, and LaMgAl11O19, specifically the surface diffusion processes dominated at comparably low annealing temperatures (less than surface melting temperature Tsm). In this temperature range the crystal structure near the surface was rather stable, that is why one could assume the electrically neutral clusters of Al2O3, LaMgAl11O19 и La3Ga5SiO14 involved in the surface diffusion processes instead of single atoms. A further increase in annealing temperature to Tsm resulted in the La3Ga5SiO14 crystal surface thermodestruction due to probably incongruent melting of La3Ga5SiO14 compound and related friability of its structure if to compare it with Al2O3 and LaMgAl11O19 structures with the layers of close-packed oxygen atoms.