Phase separation in carbon-nickel films during hyperthermal ion deposition

Abstract

Microstructure evolution as a function of the substrate temperature and metal content of C:Ni nanocomposite films grown by hyperthermal ion deposition is investigated. The films were grown by pulsed filtered cathodic vacuum arc on thermally oxidized Si substrates held at temperatures in the range from room temperature (RT) to 500 °C and with the metal content ranging from 7 to 40 at. %. The elemental depth profiles and composition were determined by elastic recoil detection analysis. The film morphology and phase structure were studied by means of cross-sectional transmission electron microscopy and selected area electron diffraction. For RT deposition a transition from repeated nucleation dominated toward self-organized growth of alternating carbon and crystalline nickel carbide layers is observed at a Ni threshold content of ∼40 at. %. The surface diffusion increases concomitantly with the growth temperature resulting in the formation of elongated/columnar structures and a complete separation of the film constituents into the coexisting carbon and fcc Ni phases. At the highest growth temperature (500 °C) Ni shows a tendency to segregate at the surface of the growing film and to form a continuous layer for integrated Ni contents of ≥30 at. %. A corresponding structure zone model diagram is presented, and the results are discussed on the basis of the ion induced atomic displacement, temperature activated adatom diffusion, and the metallic island coalescence processes whose complex interplay results in the observed variety of the microstructures.