CuAl single crystals of a low stacking fault energy have been deformed along the
〈111〉 direction in an apparatus which consists of a compression machine
interfaced with an atomic force microscope. The emergence process of dislocations has
been in situ studied during deformation. Plasticity occurs in this material by
propagation of Shockley dislocations which generate two possible kinds of stacking
faults, extrinsic or intrinsic. The fine structure of slip lines has been investigated
by atomic force microscopy. A differentiation between these two possible twin
mechanisms in this alloy is attempted. It is concluded that twinning in this material
can not only be explained by the intrinsic stacking faults and that the contribution
of extrinsic faults has to be considered.