Tests by TEM contrast simulations of the elastic field of a buried (001) low angle twist boundary in silicon

A buried (001) low angle twist boundary (misorientation angle 0.48°) in silicon is investigated by the technique of two-beam transmission electron microscopy using bright-field images obtained from diffracting vectors g{400}, g{311} and g{220}, and g{nnn} with n = 3 and 4. To analyse its elastic field, the concept of interfacial relaxation centres is assumed, for which the relative displacement field of the two crystals is zero. These centres are located in the middle of each square formed by a dislocation unit cell. This assumption is tested positively for the first time for a double periodic network of screw dislocations. For the image contrast calculations, the elastic field of the network is that of two perpendicular families of screw misfit dislocations in the sense of Bonnet (1981). Since the two-beam bright-field approximation is weak to explain the experimental images taken with g{nnn} and n = 3 and 4, extra N beam image calculations involving N