A Microstructural Study of Iron Carbides Formed by Plasma-Enhanced Chemical Vapor Deposition (50–800 nm Thick)

Thin Mirror-like iron carbide films were prepared by introducing iron pentacarbonyl [Fe(CO)5] and hydrogen [H2] into a glow discharge. The deposition temperatures were varied from 200–500°C. The iron to carbon ratios of the resulting films were controlled by adjusting the gas flow ratios. The Microstructure and phase transformations occurring in these films were studied before and after annealing at 400°C for four hrs. Characterization techniques used included x-ray diffraction, electron diffraction, Auger spectroscopy and atomic force Microscopy.X-ray diffraction data of plasma-deposited films on glass substrates maintained at 400°C showed the presence of only Fe3C. However, the x-ray diffraction data of films on carbon coated glass, and transmission electron microscopy selected area diffraction patterns of films on carbon coated copper grids indicated the presence of a second phase, the closely related Metastable Fe7C3, as well as small amounts of Fe3O4. Atomic force microscopy of crystallites on the surface of films deposited at 400°C and annealed at 400°C for four hours revealed a periodic structure of oblate spheroids. The Measured spacings and angle, when compared to projected models of high reticular density planes, suggested the surface to have a structure corresponding to that of bulk FesC or Fe3C or Fe7C3. However the data were not of sufficient quality to unambiguously determine such.