Crystalline structures of carbon complexes in amorphous carbon films

Amorphous carbon (a-C) films, 20 Mm thick, were deposited by sputtering on (001) Si substrates. A negative bias voltage was applied to the substrate during deposition to induce Ar+ ion bombardment with an energy of similar to 230 eV. The film microstructure was investigated by conventional transmission electron microscopy as well as high-resolution electron microscopy. The films consist of an amorphous carbon matrix and crystallites with a platelet form. The crystallites are energetically metastable and easily degrade under electron beam irradiation. In addition. they are usually oriented along their sixfold or threefold axes, exhibiting lattice parameters larger than those of graphite and diamond. X-ray reflectivity density measurements and high-resolution electron microscopy observations indicate that these crystallites consist of packed complex carbon clusters. X-ray diffraction measurements in rocking curve geometry support the existence of oriented crystallites with interplanar spacings corresponding to those observed by transmission electron microscopy. (C) 2000 Elsevier Science S.A. All rights reserved.