Thermal stability of Al–Mo thin film alloys

Thin Al_xMo_100−x films (40 ≤ x ≤ 90 with x in steps of 5 at % Al) were prepared by magnetron co-deposition onto alumina, glass, and sapphire substrates at room temperature. The film thickness was about 400 nm, and they were amorphous for 45 ≤ x ≤ 85. The films' structural changes upon heating were investigated by measurement of the electrical resistivity variation with temperature, ρ(T), during the isochronal heating. Thus obtained results were complemented, and conclusions confirmed, by GIXRD analysis for selected heating temperatures. The dynamical temperatures of crystallization, T_x, were determined from the sharp increase of the derivative of ρ with respect to temperature. No systematic dependence of T_x on film substrate has been observed. Except for the Al₈₅Mo₁₅ film, the ρ of the amorphous films increase on the crystallization. The temperature of crystallization exhibits maximum around 530 °C for alloy compositions with x = 55 and 60. Electrical resistivity of both amorphous and crystallized films show a strong dependence on alloy composition, with a maximum for Al₇₅Mo₂₅ alloy. The resistivity of Al₇₅Mo₂₅ film is very large and amounts to 1000 μΩ cm and 3000 μΩ cm in amorphous and crystallized film, respectively, with the large negative temperature coefficient of −10 × 10⁻⁴ K⁻¹ and −14 × 10⁻⁴ K⁻¹, respectively. Although the crystallization temperature observed for the examined amorphous Al–Mo alloys is not very high, it might allow to exploit excellent corrosion properties of such films at some elevated temperatures. - Highlights: • Al_xMo_100-x thin films (40 < x < 90) were grown by magnetron co-deposition. • Electrical resistivity was measured during annealing of the films. • Crystallization temperature and room temperature resistivity were determined. • The phase composition was determined with grazing incidence X-ray diffraction