Conformal graphene coating on high-aspect ratio Si nanorod arrays by a vapor assisted method for field emitter

Abstract

Carbon materials like nanotubes and graphene have been previously used for field emission application due to their high emission currents and low turn-on voltages. However, in most cases, these devices show low reliability and poor endurance after a few hours of testing. The poor performance is usually attributed to lack of alignment, poor structure quality, and/or non-conformal coating. In this paper, a hybrid structure of graphene–silicon nanorod arrays (NRAs) was demonstrated by direct growth of self-crystallized graphene with Ni vapor-assisted growth via a conventional chemical vapor deposition (CVD) system. By carefully adjusting parameters and reducing the deposition rate, thicknesses of graphene layers can be systematically coated in a controllable manner, even on high aspect ratio surfaces such as aligned silicon NRAs. Detailed surface morphologies and microstructures of the graphene–NRAs core–shell hybrid structures were investigated. Findings in field emission measurements indicate that the graphene coating exhibits a remarkable enhancement by lowering the turn-on field, increasing the current density over 4 orders of magnitude, and greatly improving the endurance. The endurance test shows a stable current density of 1000 μA cm−2 after more than 15 hours of operation under a constant applied high bias stress.