Very regular single-helix carbon microcoils of outer coil diameter 1 - 3 mum, inner coil diameter 0.5 - 2 mum, and coil pitch 1 - 2 mum were prepared by the WS2-catalyzed pyrolysis of acetylene in the presence of thiophene impurity. The effects of reaction temperature and thiophene gas flow rate on the growth of single-helix carbon microcoils and the morphology were examined in detail. The optimum reaction temperature was 780degreesC, and optimum gas flow rate of thiophene, acetylene, hydrogen and argon for obtaining regular single-helix carbon coils with a constant coil diameter were 0.2, 40, 90, and 30 sccm, respectively. The formation mechanism of the single-helix carbon microcoils is discussed. (C) 2004 Kluwer Academic Publishers.