Patterns of alternating bright and dim stripes (a few micrometers wide and a few tens of micrometers long), parallel to [110], appeared - alongside cleavage planes - at the surface of (001) epitaxial layers which exhibited atomic ordering between crossed polarizers. It was shown that these patterns were associated with twinned regions of the sample, where each stripe corresponded to a large single-variant domain. The patterns were a consequence of the spontaneous trigonal strains that resulted from atomic ordering. The strains, being oriented differently in the 2 variants of the CuPtB structure, gave rise to 2 index ellipsoids which were distinctly oriented in each variant domain. The boundaries between 2 adjacent variants had to be (1¯10) planes, in order to maintain strain compatibility. In a polarizing microscope, these boundary planes appeared as [110] lines at the sample surface. The same (1¯10) planes clearly separated large adjacent CuPtB domains, starting from substrates that were patterned with [110]-oriented grooves.

J.Sapriel, A.Hassine: Physical Review B, 1997, 56[12], R7112-5