  We have studied structural and transport properties of epitaxial NaxCoO2 thin
films on (0001) sapphire substrate prepared by topotaxially converting an
epitaxial Co3O4 film to NaxCoO2 with annealing in Na vapor. The films are c
axis oriented and in-plane aligned with [10 1 0] NaxCoO2 rotated by 30 degrees
from [10 1 0] sapphire. Different Na vapor pressures during the annealing
resulted in films with different Na concentrations, which showed distinct
transport properties.
