(Received September 1, 2003; revised October 10, 2003; accepted October 27, 2003; published April 9, 2004)
A new dual elementary-steps growth mechanism was observed during our research on the CdHg(SCN)4(H6C2OS)2 (CMTD) crystals. Namely two types of elementary-step sources with different step height can be produced on the same crystal surface during the growth of some crystals. Furthermore the sum of these elementary-step heights is equal to the corresponding interplanar distance dhkl. The heights of these elementary steps were determined by crystal structure as well as growth motif and they have no relation to crystal defects. The elementary steps referred in this paper are completely different to sub-step mentioned by Min in 1988. Only one step height h was included in normal growth rate formulas for the dominant crystal growth theories at present such as BCF spiral growth mechanisms and the classic two-dimensional nuclear growth modes. Without considering the effects of the dual elementary-steps h1 and h2 to the growth procedure, the classic formulas containing the parameter h (step height) should be modified when they are applied to the research on crystals growing with dual elementary-steps growth mechanism.