Influence of MgO(100) substrate surfaces on epitaxial growth of Ti films

The growth of Ti films prepared on MgO(100) substrates by an electron-beam heating method has been studied using transmission electron microscopy. The 10 nm thick Ti films deposited on as air-cleaved chemically-polished MgO(100) substrates without heat treatment showed fee electron diffraction spots due to TiHx crystallites (x is approximately equal to 1.5) with NaCl structure and TiOy crystallites (y is approximately equal to 1.0) with CaF2 structure, which were formed by compound layer containing H and O atoms, in addition to hcp Ti rings. When a 50 nm thick Ti was deposited at room temperature (RT) on chemically-polished MgO(100) substrates with heat treatment at 900 degrees C for 30 min, hcp Ti crystallites with only (10.1) orientation were formed. The Ti films heat treated at 800 degrees C for 30 min in vacuum after being deposited at RT indicated the existence of discrete and fully oriented hcp Ti crystallites. On the other hand, when a 50 nm thick Ti was deposited at RT on as air-cleaved ones without heat treatment, hcp Ti crystallites with only (00.1) orientation grew on most of the surface. This result shows that the epitaxial growth of Ti film is not necessarily inhibited by the exposure of MgO substrate surface to atmosphere, and that such surface is very effective for the growth of epitaxial films with preferred orientations.