Dislocations in charge-ordered Pr0.5Ca0.5MnO3 epitaxial thin films prepared by a two-step growth technique

Charge-ordered Pr0.5Ca0.5MnO3 (PCMO) thin films epitaxially grown on SrTiO3 (100) substrates were prepared by a two-step growth technique which resulted in a 10 nm thick first layer and a 70 nm thick main layer. The dislocations in the as-received films were investigated using conventional and high-resolution transmission electron microscopy. Pure-edge misfit dislocations with Burgers vectors a < 011 > and line directions < 100 > were found to be the major interfacial defects responsible for the full misfit relief in the PCMO films. These dislocations constitute a square grid of dislocation lines parallel to the PCMO/SrTiO3 interface. In contrast, two types of dislocations were identified within the first layer. One is of edge type with Burgers vectors a < 110 > and line directions < 001 >; the other, of screw type with Burgers vectors a < 110 > and line directions < 110 >. Cross-slip of the latter may contribute to the multiplication of misfit dislocations necessary for a total misfit relaxation. Few threading dislocations were observed in the main layer. The dislocation configurations in the films are discussed in detail.