Abstract
Experimental transmission electron microscopy (TEM) images of dislocations do not always follow the usual extinction rules. Besides, they are sometimes far from agreeing with computed images obtained from the assumption of an elastic field extending in an infinite continuum. However, if use is made of the elastic displacement field of a dislocation piercing the free surface of a semi infinite continuum, the computed images then describe correctly the main contrast features of all the experimental images. Illustrations are given from two-beam TEM observations of dislocations with large Burgers vectors in a thin Al2Cu(theta) single crystal.