Oxidation of Single Crystalline Ti2AlN Thin Films between 300 and 900 °C: A Perspective from Surface Analysis

Abstract

High temperature oxidation of 300 nm single crystalline Ti2AlN MAX phase thin film deposited on MgO(111) substrate between 300 and 900 °C has been investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), and mass spectrometry. As shown by XRD, Ti2AlN remained structurally stable up to 700 °C, before it began to react with MgO substrate and ambient O2 to form MgTi2O5 and MgAl2O4 at 900 °C. However, as revealed by XPS, oxidation of Ti2AlN occurred at room temperature from its surface by forming TiO2, TiNxOy and Al2O3 with surface enrichment of Al. This initial oxidation continued up to 300 °C, until Ti and Al in the surface layer (∼7.1 nm thick) have been completely oxidized into TiO2 and Al2O3 at 500 °C, where Al in the subsurface preferentially diffused to the edges of the terraces and agglomerated into Al2O3 islands. At 700 °C and above, surface of Ti2AlN lost its characteristic hexagonal terrace morphology by transforming into round islands as a res...