Contrast and resolution of small dislocation loops in high‐voltage electron microscopy

A study has been made of contrast from small loops in ion implanted silicon using high‐voltage electron microscopy. Theoretical calculations have been carried out to determine the optimum imaging conditions using many‐beam dynamical theory for systematic orientations. It is found that the best imaging conditions are obtained when the crystal is set for excitation near the third order reflection ( ng = 〈111〉) and second order reflection ( ng = 〈220〉) conditions, respectively. It is also shown that for small loops or dipoles, defect visibility in bright and dark field as well as in the weak‐beam condition is very sensitive to small changes in the deviation parameter and effective foil thickness.