Anisotropy of growth hillocks on KDP crystal (101) faces observed by in situ interferometry

A platform for the Michelson interference experiment was built to observe in situ growth of KDP crystal (101) faces in aqueous solution. The pattern of interference fringes changed with the growth of the KDP cone-head seed crystal. The surface morphology of the KDP crystal and growth rate of steps was studied. The normal growth rates and tangential velocity of hillocks increased gradually with a rise of supersaturation and temperature. Slopes increased with increasing supersaturation but had little relationship with temperature. Based on the relationship between slopes and supersaturation, the surface free energy was calculated. The surface free energy of three adjacent planes was anisotropic, (i.e., alpha(I), alpha(II) > alpha(III)) and decreased with increasing temperature. The anisotropy of growth hillocks on (101) faces was also connected to the steps forming adjacent planes in different directions. The activation energy of three vicinal planes was calculated to be E-I = 55.7 kJ mol(-1), E-II = 79.4 kJ mol(-1), and E-III = 50.5 kJ mol(-1), respectively.