MORPHOLOGY AND GROWTH MECHANISM OF THE$\{11\bar{2}0\}$FACE OFYb:YAl3(BO3)4CRYSTAL

Yb:YAl3(BO3)4(YbYAB) is a self-doubling frequency laser crystal. Based on atomic force microscopy (AFM) observations, a series of growth morphologies formed after different growing times on the smooth$\{11\bar{2}0\}$face are reported in this paper. No two-dimensional nuclei or growth steps have been found on this face after growth of several seconds, or even several minutes. This reflects the fact that at the beginning stage, the growth rate of the$\{11\bar{2}0\}$face is much slower than that of the{$\{10\bar{1}1\}$cleavage face of YbYAB crystal (reported in our previous work). The reason is the different properties of nonsaturated bonds on the surfaces between a cleavage face and a natural face. After growth of 50 min, checklike morphologies of a special kind develop on the face. These morphologies result from twin structure. The growth steps with small heights (~ 0.6nm) cannot cross the two twinned crystal regions, but those with large heights (6–8 nm) can cross by changing the directions at the twin boundaries. We have also observed the rough morphology of the$\{11\bar{2}0\}$face obtained by spontaneous nucleation growth at a high rate. The rough morphology is composed of many small$\{11\bar{2}0\}$faces with the same orientation but very different heights. This reflects the fact that the rough face does not grow by accumulating the growth units irregularly.