Mechanisms for carbon nanotube growth on oxidized 316L stainless steel substrates

Abstract

We investigated the growth of carbon nanotubes (CNTs) directly on stainless steel substrates. The CNTs were grown using a two-step process: oxidation of the stainless steel surface and CNT growth. The samples were oxidized in an 800 °C furnace fed with a flow of air for 4 min. CNTs were grown by switching the flow to ethylene, which both reduces the oxide and initializes CNT growth. The time of CNT growth was varied to understand how the samples evolved over time. To better understand the growth mechanisms, we isolated cross-sections of the CNT-substrate interface using a focused ion beam. These cross-sections were investigated with transmission electron microscopy and energy dispersive X-ray spectroscopy. CNTs were seen to grow from iron-rich nanoparticles embedded in the oxide layer. The oxide layer was also seen to lose iron over time, suggesting that these iron nanoparticles were reduced out of the oxide. The base particles were embedded in the oxide layer, leaving cavities when the CNTs were removed. The diameters of the nanotubes were also seen to grow over time as a result of carbon infiltration. The effects of the embedded particle and infiltration quickly isolate the catalyst, leading to short CNTs (1–10 µm).