We present the results of an in situ atomic force microscopy investigation of the growth mechanisms of CdHg(SCN)(4)(H6C2OS)(2)CMTD crystals. The results show that spiral growth at screw dislocations dominates at a supersaturation sigma = similar to0.1%. On the (001) surface, alternate CMTD layers are related through a 2(1) screw axis and the development of a spiral protuberance was observed with alternate growth modes having two different characteristic layers. The growth of the first CMTD layer continued for 16 min before the next layer began to grow on top of it. However, it took only 2 min for the next layer to continue its growth. We felicitously refer to them as ACTIVE layers and LAZY layers in this paper. The LAZY layers separated into two different types of elementary-steps with step height h(1) = 0.69 nm and h(2) = 0.72 nm on top of the spiral protuberance on the {0 0 1} face of the CMTD crystals. Two different types of straight edge always in the same direction were periodically observed when the screw protuberance grows. (C) 2003 Elsevier B.V. All rights reserved.