Growth of untwinned Bi2Sr2Ca n?1Cu n O2n+4+δ thin films on Nd : YAlO3 substrates

Thin film growth of Bi₂Sr₂Ca _n?1Cu _n O_2n+4+δ by molecular beam epitaxy is performed on Nd : YAlO₃ (001) substrates. It was revealed that the orthorhombicity of the Nd:YAlO₃ substrate is quite effective to the growth of untwinned Bi₂Sr₂Ca _n?1Cu _n O_2n+4+δ thin films. In all phases withn=1～3, the incommensurate structural modulation lies parallel to the Nd : YAlO₃ 100] direction, and this relation holds even in the case of superlattices. The origin of the epitaxial relation is discussed from the viewpoint of the lattice misfit. The orthorhombicity of the substrate competes with the step edges on a vicinally polished substrate for determining the in-plane growth direction. The rotation of the modulation direction was observed when the off angles are varied.