  The cobalt oxide system LaCoO$_3$ and its Sr-doped child compounds have been
intensively studied for decades due to their intriguing magnetic and electronic
properties. Preparing thin La$_{1-x}$Sr$_x$CoO$_3$ (LSCO) films on different
substrates allows for studies with a new type of perturbation, as the films are
subject to substrate-dependent epitaxial strain. By choosing a proper substrate
for a thin film grow, not only compressing but also tensile strain can be
applied. The consequences for the fundamental physical properties are dramatic:
while compressed films are metallic, as the bulk material, films under tensile
strain become insulating. The goal of this work is to determine the strain
tensor in LSCO films prepared on LaAlO$_3$ and SrTiO$_3$ substrates by pulsed
laser deposition using RBS/channelling methods. Apart from the composition and
defect structure of the samples, the depth dependence of the strain tensor, the
cell parameters, and the volume of the unit cell are also determined.
Asymmetric behaviour of the strained cell parameters is found on both
substrates. This asymmetry is rather weak in the case of LSCO film grown on
LaAlO$_3$, while stronger on SrTiO$_3$ substrate. The strain is more effective
at the interface, some relaxation can be observed near to the surface.
