ABSTRACT
EFTEM image resolution and contrast were explored systematically by varying the size of the objective aperture and both the position and the width of the energy windows. The locations of the selected 20eV wide windows are shown in Fig. la. Although a theoretical optimum objective aperture semi-angle of 4.1 mrad was derived using the method of Krivanek et al. (1995) (Fig. lb), the predicted resolution was considered to be pessimistic and the intensity of the signal was low. A 12.2 mrad aperture was found to provide adequate resolution with acceptable intensity for image acquisition times of between 20 and 40 s.
