Synthesis and properties of SiN_x coatings as stable fluorescent markers on vertically aligned carbon nanofibers

The growth of vertically aligned carbon nanofibers (VACNFs) in a catalytic dc ammonia/acetylene plasma process on silicon substrates is often accompanied by sidewall deposition of material that contains predominantly Si and N. In fluorescent microscopy experiments, whereby VACNFs are interfaced to cell and tissue cultures for a variety of applications, it was observed that this material is broadly fluorescent. In this paper, we provide insight into nature of these silicon/nitrogen in-situ coatings. We propose a potential mechanism for deposition of SiN_x coating on the sidewalls of VACNFs during PECVD synthesis and explore the origin of the coating's fluorescence. It is most likely that the substrate reacts with process gases similar to reactive sputtering and chemical vapor deposition (CVD), forming silane and other silicon bearing compounds prior to isotropic deposition as a SiN_x coating onto the VACNFs. The formation of Sinanoclusters (NCs) is also implicated due to a combination of strong fluorescence and elemental analysis of the samples. These broadly luminescent fibers can prove useful as registry markers in fluorescent cellular studies and for tagging and tracing applications.