Thermally induced atomic and electronic structure evolution in nanostructured carbon film by in situ TEM/EELS analysis

Abstract

The atomic and electronic structures of nanostructured carbon film are of fundamental importance due to their dominant role in carbon films' physical, chemical and mechanical properties. Here, we reported thermally induced atomic and electronic structure evolution of nanostructured carbon film by in-situ transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Two nanostructured carbon films were synthesized by electron cyclotron resonance (ECR) plasma sputtering under ion and electron irradiation, respectively. We observed that even though the two carbon films had similar initial sp2/sp3 hybridization ratio, they exhibited very different performance during the same heating process. The electron irradiated film only had a relative slight clustering of sp2 carbon crystallites and almost maintained its sp2/sp3 ratio till 1000 °C; while the ion irradiated film had a significant sp2 crystallites clustering, started its sp3-to-sp2 conversion from 200 °C and almost completed at 400 °C. Argon signal was only found in the ion irradiated carbon film and its content reduced simultaneously with the sp3-to-sp2 conversion process. We suggest that the heated argon trapped inside the carbon film were responsible for triggering the sp3-to-sp2 conversion. The result will guide the future application of the nanostructured carbon film in the proper operation temperature range and help to choose appropriate irradiation method for thin film surface modification.