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Published online by Cambridge University Press: 25 February 2011
Nb/MgO/Nb/Al2O3 multilayer stacks were prepared by MBE growth of Nb and MgO films on a (0112)A1203 sapphire substrate. Sequential deposition of Nb followed by MgO on the sapphire substrate resulted in three different interfaces: one between Nb deposited on sapphire as the substrate (the Nb1/Al2O3 interface), one between MgO deposited on Nb as the substrate (the MgO/Nb1 interface), and finally one between Nb deposited on MgO as the substrate (the Nb2/MgO interface). Cross-sectional TEM specimens from the multilayer were prepared and the various interfaces were investigated by high resolution electron microscopy (HREM). Orientation relationships between Nb1 and Al2O3 and also between MgO and Nb1 were determined and misfit dislocations, steps and facets at the Nb1/Al2O3 and MgO/Nb1 interfaces were analyzed. The HREM observations showed that an intterfacial phase forms at the Nb1/Al2O3 interface by a solid state reaction under electron beam irradiation.