Atomic structure of carbon clusters laser-produced diamond-like carbon films

Abstract

Structural state of thin diamond-like carbon films has been studied by high-resolution transmission microscopy. Diamond-like carbon films have been obtained by vapor-gas phase carbon concentration on glass substrates, using defocused NTS 300 laser beam for graphite targets evaporation in vacuum. Defocused laser beam provided an area of 3 mm in diameter on the target for carbon direct evaporation. It has been established that diffraction of electrons identifies diamond reflections (111) and (220), and this corresponds to interplane spacing d111 = 0.207 nm, d220 = 0.119 nm of the diamond lattice. The obtained values of interplanar distances are close to the values of interplanar distances of carbon macroscopic crystals with d111 = 0.205 nm and d220 = 0.125 nm. The research of the film atomic structure shows that sp3-bonding generally participate in assembling carbon atoms into diamond clusters having the size less than 1 nm. The ratio of graphite clusters formed by sp2-bonds within the structure of diamond-like carbon films is negligible. In spite of the pronounced cluster pattern of the structure, the film is not an analogue of the polycrystalline one with graded junction from one crystalline domain to another observed. As distinguished from polycrystals, there is no structure stepwise changing on the mating clusters boundaries. It is shown that clusters are linked with each other into homogeneous cluster structure by sp3- and sp2-bonds. These bonds are well-identified in the diamond-like carbon film structure, as the length of sp2-bonds exceeds considerably the length of sp3- bonds. Carbon film properties are determined by diamond clusters due to domination of clusters with tetragonal diamond lattice, for instance, the film is a good dielectric.