Epitaxial Growth of Single-Phase Magnesium Dihydride Thin Films

We describe the epitaxial growth process of single-phase magnesium dihydride (MgH2) thin films on MgO(100) substrates, achieved by reactive magnetron sputtering. We find that direct growth at substrate temperatures higher than 100 °C leads to partial MgH2 decomposition to Mg, hindering single-phase epitaxy of MgH2. To improve the crystallinity and suppress the decomposition of Mg, we optimize MgH2 growth using a two-step process, consisting of (1) precursor growth at room temperature and (2) postdeposition annealing at 380 °C, under a pressure of 1.0 × 105 Pa with H2 (4%)/Ar (96%) premixed gases. Using this two-step process, we obtain single-phase MgH2 epitaxial films with high crystallinity, transparency, and resistivity. Further, the application of this method to grow MgH2 thin films on different MgF2 and Al2O3 substrates enables us to use the epitaxial effects to control the growth orientation of MgH2 thin films; we show that MgH2(100) and MgH2(001) epitaxial thin films can be grown on Al2O3(001) and MgF2(001) substrates, respectively.