Abstract
Ti/Al2O3 bilayer stacks are used as model systems to
investigate the role of atomic layer deposition (ALD) and
chemical vapor deposition (CVD) to prepare 30–180 nm thick
amorphous alumina films as protective barriers for the medium
temperature oxidation (500–600 8C) of titanium, which is
employed in aeronautic applications. X-ray diffraction (XRD),
transmission electron microscopy (TEM) with selected area
electron diffraction (SAED), and X-ray photoelectron spectroscopy
(XPS) results show that the films produced from the
direct liquid injection (DLI) CVD of aluminum tri-isopropoxide
(ATI) are poor oxygen barriers. The films processed
using the ALD of trimethylaluminum (TMA) show good
barrier properties but an extensive intermixing with Ti which
subsequently oxidizes. In contrast, the films prepared from
dimethyl aluminum isopropoxide (DMAI) by CVD are
excellent oxygen barriers and show little intermixing with
Ti. Overall, these measurements correlate the effect of the
alumina coating thickness, morphology, and stoichiometry
resulting from the preparation method to the oxidation barrier
properties, and show that compact and stoichiometric
amorphous alumina films offer superior barrier properties.
