Influence of thin film nickel pretreatment on catalytic thermal chemical vapor deposition of carbon nanofibers

• On the formation of nanoparticles required for carbon nanofiber (CNF) synthesis
• Various evaporated thin films on oxidized silicon and fused silica: Ni and Ni/Ta
• Pretreatment of nickel-based thin films in vacuum, nitrogen, air and hydrogen
• Only on reduced Ni/Ta fast – within 3 min – initiation of CNF nucleation and growth

Nickel and other metal nanoparticles are known to be active as catalysts in the synthesis of carbon nanofibers. In this paper we investigate how dewetting and break-up of nickel thin films depends on film thickness, film–substrate interaction and pretreatment conditions. This is evaluated for films evaporated on oxidized silicon and fused silica substrates with or without tantalum coating, which were subsequently exposed to different pretreatment atmospheres (vacuum, nitrogen, air and hydrogen; 1 h, 650 °C). Atomic force microscopy, scanning electron microscopy and energy dispersive X-ray analysis were used to characterize the films. Pretreated Ni films were subjected to a thermal catalytic chemical vapor deposition procedure with brief ethylene exposures (0.5–3 min, 635 °C). It was found that only on the spherical nanoparticles originating from a hydrogen pretreatment of a Ni film with Ta adhesion layer, homogeneously distributed, randomly-oriented, well-attached, and semi-crystalline carbon nanofibers be synthesized.