Controlling thin film structure for the dewetting of catalyst nanoparticle arrays forsubsequent carbon nanofiber growth

Abstract

Vertically aligned carbon nanofiber (CNF) growth is a catalytic chemical vapordeposition process in which structure and functionality is controlled by the plasmaconditions and the properties of the catalyst nanoparticles that template thefiber growth. We have found that the resultant catalyst nanoparticle networkthat forms by the dewetting of a continuous catalyst thin film is dependent onthe initial properties of the thin film. Here we report the ability to tailor thecrystallographic texture and composition of the nickel catalyst film and subsequently thenanoparticle template by varying the rf magnetron sputter deposition conditions.After sputtering the Ni catalyst thin films, the films are heated and exposedto an ammonia dc plasma, to chemically reduce the native oxide on the filmsand induce dewetting of the film to form nanoparticles. Subsequent nanoparticletreatment in an acetylene plasma at high substrate temperature results in CNFgrowth. Evidence is presented that the texture and composition of the nickel thinfilm has a significant impact on the structure and composition of the formednanoparticle, as well as the resultant CNF morphology. Nickel films with a preferred(111) or(100) texture were produced and conditions favoring interfacial silicidation reactions wereidentified and investigated. Both compositional and structural analysis of the films andnanoparticles indicate that the properties of the as-deposited Ni catalyst film influences thesubsequent nanoparticle formation and ultimately the catalytic growth of the carbonnanofibers.