  Field angle dependent critical current, magneto-optical microscopy, and high
resolution electron microscopy studies have been performed on YBa2Cu3O7-d thin
films grown on mis-cut substrates. High resolution electron microscopy images
show that the films studied exhibited clean epitaxial growth with a low density
of anti-phase boundaries and stacking faults. Any anti-phase boundaries (APBs)
formed near the film substrate interface rapidly healed rather than extending
through the thickness of the film. Unlike vicinal films grown on annealed
substrates, which contain a high density of anti-phase boundaries, magneto
optical imaging showed no filamentary flux penetration in the films studied.
The flux penetration is, however, asymmetric. This is associated with intrinsic
pinning of flux strings by the tilted a-b planes and the dependence of the
pinning force on the angle between the local field and the a-b planes. Field
angle dependent critical current measurements exhibited the striking vortex
channelling effect previously reported in vicinal films. By combining the
results of three complementary characterisation techniques it is shown that
extended APB free films exhibit markedly different critical current behaviour
as compared to APB rich films. This is attributed to the role of APB sites as
strong pinning centres for Josephson string vortices between the a-b planes.
