Structure of Ti films deposited on MgO(001) substrates

The growth and structure of Ti thin films deposited by electron beam evaporation at 273 K in a vacuum of about 10−7 Pa on MgO(001) have been studied by means of transmission electron microscopy. It is found that a thin layer, whose thickness is up to about 4 nm, is fcc (or tetragonal) structure. When the thickness increases to more than about 6 nm, the structure gradually changes to an hcp structure with two different orientations: one is (00.1)hcpTi//(001)fccTi//(001)MgO, and the other is (03.5)hcpTi//(001)fccTi. The electron diffraction patterns from 60 nm thick Ti film also show reflection spots at {110} points on fcc Ti reciprocal plane, which show metastable γ-hydride precipitation takes place in the layer. The orientation relationships and growth mechanism of the epitaxial Ti films on MgO(001) are discussed using molecular dynamics simulations performed by Hara et al. for MBE growth of a Lennard-Jones system.