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Effect of substrate orientation on the crystal quality and surface roughness of Nb-doped TiO2 epitaxial films on TiO2

Published online by Cambridge University Press:  31 January 2011

Y. Gao  and
S. A. Chambers
Y. Gao
Affiliation:
Environmental Molecular Sciences Laboratory, Pacific Northwest Laboratory, P.O. Box 999, MS K2–12, Richland, Washington 99352
S. A. Chambers
Affiliation:
Environmental Molecular Sciences Laboratory, Pacific Northwest Laboratory, P.O. Box 999, MS K2–12, Richland, Washington 99352
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Abstract

We have grown Nb-doped TiO2 epitaxial films on (100) and (110)-oriented TiO2 rutile substrates by molecular beam epitaxy. Nb substitutionally incorporates at cation sites in the rutile lattice, forming NbxTi1−xO2 solid solutions. However, the crystal quality and surface roughness of the films depend strongly on the substrate orientation. Surface roughening and defect formation occur at lower values of x on (100) than on (110). This result is due to anisotropic changes in the metal-oxygen bond lengths within the rutile structure in going from TiO2 to NbO2; there are 1% and 12% changes in the metal atom to octahedron-base oxygen and metal atom to octahedron-vertex oxygen bond lengths, respectively. Every metal atom in the (100) growth surface has in-plane components of the 12% mismatch. However, only half of the metal atoms in the (110) growth plane have such components. Thus, there is substantially larger in-plane lattice mismatch when the growth surface is (100) compared to (110), resulting in surface roughening and formation of defects at a lower doping level for (100)-oriented NbxTi1−xO2 epitaxial films.

Type
Articles
Information
Journal of Materials Research , Volume 11 , Issue 4 , April 1996 , pp. 1025 - 1029
Copyright
Copyright © Materials Research Society 1996

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