Multiwalled carbon nanotubes (MWCNTs) are leading-field electron emitters (FEE) for cold cathode applications. This is due to their unique properties such as a high aspect ratio and low turn-on field. Cold cathodes are in demand for highly brilliant electron sources in high-resolution electron microscopes, portable X-ray imaging systems and in plasma displays. Therefore, developing new nanostructuring strategies to enhance the emission properties of MWCNTs is of interest. Reporting in Nanotechnology, researchers develop original hierarchical MWCNT nanostructures using two-step processing.

Graphenated multiwalled carbon nanotubes

The Canadian researchers are based at the Energy, Materials and Telecommunications Center of The Institut National de la Recherche Scientifique (INRS), located in Varennes (QC, Canada). In the first step, they identify the plasma-enhanced chemical vapour deposition (PECVD) growth conditions that lead to the formation of graphenated-MWCNTs (g-MWCNTs). This is where the tips of the MWCNTs are made of deployed graphene sheets.

Graphene "canopy"

Such a graphene “canopy” on the top of the forest-like MWCNTs’ film provides a much higher density of electron-emitting sites under an applied electrical field. Taking advantage of the unique geometry of such a “graphene canopy”, they capitalize on their long expertise in pulsed laser deposition (PLD) of nanomaterials. They decorate these g-MWCNTs, in a second processing step, with gold nanoparticles (of 2–3 nm in diameter).

Low work function

These novel nanohybrid (NH) emitters are found to exhibit not only a lower work function but also a much higher field enhancement factor than the pristine MWCNTs. The turn-on electrical field of these NHs (to extract a current density of 0.1 µA/cm²) was less than 1 V/µm. These hierarchically designed nanohybrid emitters open up new research and development opportunities in the FEE field. This is also true for associated applications through the prospect of tailoring the nano-characteristics of the NH components.