Side-face structure and growth mechanism of tabular silver bromide crystals

Recently, it has become possible to grow large tabular silver bromide crystals from organic solvents, which makes direct observation of the side faces possible. Solving the side-face structure is a key to understanding the (lateral) growth mechanism of tabular silver bromide crystals. The side-face structure of 42 tabular crystals was determined in detail. The side-face structure of the tabular crystals is built up by flat {111} and {100} cubo-octahedral faces and there are three different kinds of tabular morphology. In all observations, ridge structures were found showing no acute lips. From these determinations, the number of parallel twin planes of the tabular crystals was directly reduced from the side-face structure. The lateral growth of the tabular crystals is described by a substep mechanism. This mechanism explains the increase of growth rate of a {111} side face that is linked with a twin plane to a {100} side face. The proposed substep mechanism is based on a theory of Ming, which is universal and not only valid for the case of silver bromide. The interpretation assumes the presence of only cube-octahedral faces and the absence of acute lips as observed.