HREM studies typically examine only one projection of a structure and information in the electron beam direction is lost. In most cases, the structure in this direction is uniform and already known, but in others a second projection needs to be observed. This could involve preparing a second specimen sectioned at right angles to the first, or as described here, tilting a specimen through /plus minus/45/degree/ and observing the same volume in orthogonal projections. The specimen used here was of GaAs islands on silicon, examined in the Atomic Resolution Microscope at LBL. 5 refs., 2 figs
