The microstructure of inclusions in nanocrystalline carbon films deposited at low temperature

Abstract

Nanocrystalline growth has been observed in carbon films deposited from a CH 4-Ar r.f. plasma. The films were deposited on Si and glass substrates held at low temperature. X-ray analysis of the films grown on n-type Si (100) indicates the presence of diamond crystals up to 50 nm in diameter, with some evidence for oriented growth in the [111] direction parallel to Si [100]. The X-ray data also indicate the presence of SiC with the diamond. Transmission electron microscopy of the films deposited on glass shows smaller crystals up to 10 nm in diameter which can group themselves into large dendrite-like features. Parallel electron energy loss spectroscopy of these smaller crystals and the surrounding amorphous matrix confirms that the crystals are predominantly carbon. However, the electron diffraction data are not consistent with those expected for diamond or graphite. Instead, the five diffraction rings observed from these crystals can be fitted either to a tetragonal structure with a = 5.00 A ̊ and c = 3.26 A ̊ or to a hexagonal structure with a = 4.46 A ̊ and c = 3.26 A ̊ . Further work is required to be able either to distinguish between these two possibilities or perhaps to explain the ring sequence in terms of a completely different crystal structure.