Desorption of Al and Phase Transformation of Ti2AlN MAX Thin Film upon Annealing in Ultra-High-Vacuum

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• 作者：Zheng Zhang ; Hongmei Jin ; Jianwei Chai ; Lu Shen ; Hwee Leng Seng ; Jisheng Pan ; Lai Mun Wong ; Michael B. Sullivan ; Shi Jie Wang
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：September 11, 2014
• 年：2014
• 卷：118
• 期：36
• 页码：20927-20939
• 全文大小：1879K
• ISSN：1932-7455

文摘

Phase stability of single-crystalline Ti₂AlN thin film in ultra-high vacuum has been studied in situ by X-ray photoelectron spectroscopy as a function of annealing temperature and ex situ by atomic force microscopy, secondary ion mass spectroscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, and nanoindentation. Ti₂AlN is stable up to 600 掳C. At 700 掳C, Al is preferentially desorbed from the surface and becomes nearly undetected at 900 掳C by XPS, where single-crystalline Ti₂AlN with terrace morphology transforms into polycrystalline 未-TiN_1鈥?i>x and 尉-TiN_0.75鈥?i>y phases with voids on the surface and reduced film thickness. Mechanical properties including hardness and Young鈥檚 modulus are also observed to have deteriorated. Density functional theory calculation shows that Al atoms prefer to diffuse out from the Ti₂AlN horizontally along the Al basal planes. The subsequent desorption of Al from surface due to its high vapor pressure results in the decreased Al composition, the void formation on the surface, and the decomposition of Ti₂AlN. A kinetic model involving diffusion and desorption processes is proposed to describe the Al behavior and voids formation above 700 掳C.