Epitaxial growth of single-crystalline Al(2)O(3) films on Cr(2)O(3)(0001)

Thin, crystallographically oriented single-crystalline Al2O3 films can be grown epitaxially on Cr2O3(0001) by codeposition of Al vapor and O2 at a substrate temperature of 825 K. The properties and growth of these films were monitored by Auger electron spectroscopy (AES), low-energy electron diffraction (LEED), low-energy ion scattering (LEIS), and X-ray photoelectron spectroscopy (XPS). Two routes of preparation were investigated: (i) stepwise growth by alternating deposition of Al at room temperature and subsequent exposure to O2 at elevated temperatures; (ii) codeposition of Al and O2 at T > 800 K. The first route was consistently found to result in the growth of a complex interfacial oxide followed by the growth of polycrystalline Al2O3. The second mode of preparation provided homogeneous and ordered, probably (0001)-oriented, films of Al2O3 that maintained a LEED pattern up to a thickness around 10 A. The surface sensitive Cr MVV Auger transition at 34 eV was completely attenuated once the Al2O3 layer had reached a thickness of 6 A, pointing to film homogeneity at an early stage. This was confirmed by the absence of a significant Cr signal in LEIS spectra.