Studies of threading dislocations in Nb(011) films

We obtain strain contrast in low-energy electron microscopy, by dark-field imaging of the strain-sensitive variants of a surface reconstruction. This is employed to make visible the strain fields of dislocations in Nb(011) thin single-crystal films. The strain field symmetries reveal the dislocation Burgers vectors and identify the existence of [111]a/2 and [100]a Burgers vectors for threading dislocations in these epitaxial materials. The contrast also allows interfacial and screw dislocations to be imaged.