alpha-SiC thin layers were successfully grown on silicon (111) by pyrolysis of the organic liquid dip-coating films and polyimide Langmuir-Blodgett (LB) films containing nanometer sized amorphous silicon nitride powders (NASNP) at 900-1000 degrees C in vacuum. The products were characterized by X-ray diffraction (XRD), infrared absorption (IR) and Raman spectra, the results of which strongly support the formation of preferred orientated 4H-SiC in the layers by pyrolysis of LB films containing NASNP. Based on the IR spectra of samples pyrolyzed at different temperatures and the computed values of the Gibbs free energy changes of the reactions, the mechanism of formation of alpha-SiC is discussed.