Thin (50-80 nm) iron carbide films were grown on carbon-coated copper grids in an r.f. glow discharge using iron pentacarbonyl and hydrogen as starting materials. The substrate temperatures were varied in the range 200-500 degrees C. The microstructure and phases present in these films are compared with the corresponding results previously obtained by X-ray diffraction, atomic force microscopy, scanning electron microscopy and Auger electron spectroscopy for thick (200-1100 nm) films grown on glass substrates. Transmission electron microscopy studies show that the 50-80 nm films contain a mixture of phases at all deposition temperatures. Transmission electron micrographs of annealed films and films deposited at high temperatures show a clear indication of grain growth.