In all cases XRD patterns reveal the presence of crystalline magnesium silicide for both temperatures, without any MgO traces, regardless of the duration used. The lattice constant gradually varies from 6.345 Å at lower deposition times to 6.350 Å at higher ones, increasing the crystallinity of the grown layers. This is also confirmed by optical measurements; IR reflectivity showed a reflectivity peak at ∼270 cm−1 along with a shoulder at ∼320 cm−1, associated with the phonons on the Mg2Si. Fitting analysis indicated that for both deposition temperatures, the strongest phonon mode is blue shifted increasing deposition times from ∼269 cm−1 reaching the expected value of 272 cm−1 which corresponds to stoichiometric magnesium silicide at 180 min.
Surface roughness is also affected by deposition time. At both deposition temperatures, the surface has elevated roughness with distinguishable low depth craters, at low deposition times, while, layers grown at longer times show absence of craters and surface roughness is found progressively decreasing with deposition time. This is also confirmed by IR reflectivity analysis.
Comparing the layers grown at 500 °C and 650 °C, at high deposition times, EDS scan analysis along a line from the free surface to the substrate shows that the overall Mg (and Si) content in the film is almost constant, resulting on a chemical composition of the silicide Mg:Si = 2:1, with a slight depletion in Mg content for the first 20 μm of the grown layers. This slight depletion is believed to be responsible for the slightly higher free carrier concentration (higher unintentionally doping level) for the layers grown at 500 °C. Electrical conductivity was found to be in very good agreement with the corresponding reported in the literature for undoped Mg2Si.
Grown layers were found stable to oxidation up to 465 °C. The optimum conditions for magnesium silicide coatings included the temperature of 650 °C and the deposition time of 180 min; this selection was supported by the values of Mg-to-Si ratio, the reduced roughness as well as the main phonon mode reaching the expected value of 272 cm−1 for stoichiometric Mg2Si.