ELECTRON-MICROSCOPIC INVESTIGATION OF AGBR NEEDLE CRYSTALS

Needle shaped AgBr crystals are investigated using electron diffractio n and conventional transmission electron microscopy. It will be shown that the particular morphology and growth of the needles result from t he defect structure of the crystals, which consists of three non-paral lel twin planes, i.e. two (111) type and one (221) type twin planes. U nilateral growth is shown to occur in a [110] type direction, being th e intersection of the two non-parallel (111) twin planes. On both ends of the needle, three self-perpetuating reentrant grooves are present, responsible for the rapid growth of the needle.