Abstract
A ternary Cr2AlB2 phase was deposited as a film using magnetron sputtering. Its anisotropic structure displays both structural and chemical similarities with the nanolaminated MAX phases (Mn+1AXn (n = 1–3) where M usually is an early transition metal, A is typically an element in group 13–14 and X is C or N), and can be described as CrB slabs separated by layers of Al. Combinatorial sputtering was used to optimise the sputtering process parameters for films with the Cr2AlB2 composition. The influences of substrate, temperature and composition were studied using X-ray diffraction, X-ray photoelectron spectroscopy and electron microscopy. Films deposited at room temperature were X-ray amorphous but crystalline films could be deposited on MgO substrates at 680 °C using a composite Al-B, Cr and Al targets. X-ray diffraction analyses showed that the phase composition and texture of the films was strongly dependent on the chemical composition. Films with several phases or with a single Cr2AlB2 phase could be deposited, but an additional Al target was required to compensate for a loss of Al at the high deposition temperatures used in this study. The microstructure evolution during film growth was strongly dependent on composition, with a change in texture in Al-rich films from a preferred [010] orientation to a [100]/[001] orientation. A model based on Al desorption from the surface of the growing grains is proposed to explain the texture variations.
Highlights
Compounds with a nanolaminated crystal structure may exhibit unique chemical and physical properties
Films of Cr2 AlB2 have been deposited for the first time using a combinatorial sputtering approach
The results in this study show that it is difficult to deposit single-phase Cr2 AlB2 films with a dense microstructure
Summary
Compounds with a nanolaminated crystal structure may exhibit unique chemical and physical properties. One example is the so-called MAX phases with the chemical composition Mn+1 AXn (n = 1–3) where M usually is an early transition metal, A is typically an element in group 13–14 and X is C or N. From a structural point of view, the MAX phases can be described as MX slabs separated by a layer of A atoms. The M-A bonds are weaker than the M-X bonds leading to a nanolaminated structure with unique mechanical properties [1]. By removing the A atoms using chemical etching with e.g., HF, it is possible to produce 2D materials called MXenes with potential applications in e.g., batteries [2]. The MAX phases are deposited as thin films with magnetron sputtering but as a general rule a fairly high deposition temperature is required to obtain high quality films [3]
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