Thermal stability of Nb thin films on sapphire
- Institut fuer Werkstoffwissenschaft, Max-Planck-Institut fuer Metallforschung, 70174 Stuttgart (Germany)
The Nb/{alpha}{endash}Al{sub 2}O{sub 3} system has been used as a model study for investigating the stability of different MBE grown epitaxial Nb films on {alpha}{endash}Al{sub 2}O{sub 3} substrates. The films were grown at 800{degree}C in ultrahigh vacuum. The growth process was monitored {ital in} {ital situ} by reflection high energy electron diffraction (RHEED). After deposition the structure of the film was investigated by x-ray diffraction (XRD) and conventional transmission electron microscopy (CTEM) which emcompasses also selected area diffraction (SAD). Both techniques revealed the following orientation relationship between the Nb film and the {alpha}{endash}Al{sub 2}O{sub 3} substrate: (0001){alpha}{endash}Al{sub 2}O{sub 3}{parallel} (111)Nb; [2{bar 1}{bar 1}0]{alpha}{endash}Al{sub 2}O{sub 3}{parallel}[1{bar 1}0]Nb. The stability of the niobium films was investigated by annealing the Nb-film/{alpha}{endash}Al{sub 2}O{sub 3} system to temperatures up to 1500{degree}C for different periods of time. Surprisingly, the orientation relationship between the Nb film and the substrate changed to (0001){alpha}{endash}Al{sub 2}O{sub 3}{parallel} (110)Nb;[01{bar 1}0]{alpha}{endash}Al{sub 2}O{sub 3}{parallel} [001]Nb. A model will be developed which shows that above a critical film thickness the growth orientation is metastable with respect to its crystallographic orientation. Furthermore, high resolution transmission electron microscopy (HREM) was performed to investigate the defect structure of the annealed Nb/{alpha}{endash}Al{sub 2}O{sub 3} interface. {copyright} {ital 1996 Materials Research Society.}
- OSTI ID:
- 284277
- Journal Information:
- Journal of Materials Research, Vol. 11, Issue 5; Other Information: PBD: May 1996
- Country of Publication:
- United States
- Language:
- English
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