Structural modification and enhanced electron emission from multiwalled carbon nanotubes grown on Ag/Fe catalysts coated Si-substrates

Multiwalled carbon nanotubes and carbon nano-filaments were grown using Fe as the main catalyst and Ag as a co-catalyst by microwave plasma enhanced chemical vapour deposition. In this work we demonstrate the growth behaviour of carbon nanotubes (CNTs) grown on pure Fe-film and Ag–Fe films. We find that using Ag film beneath Fe film significantly abate the catalyst–substrate interactions by acting as a barrier layer as well as enhances the nucleation sites for the growth of CNTs due to the limited solubility with Fe and silicon. Scanning electron microscopy and transmission electron microscopy studies were carried out to image the microstructures of the samples. It was observed that the length of Fe catalyzed CNTs was ∼500 nm and Ag–Fe catalyzed CNTs varied from ∼600 nm to 1.7 μm. Micro Raman spectroscopy confirmed the improved crystalline nature of Ag–Fe CNTs. It was found that I_D/I_G ratio for Fe catalyzed CNTs was ∼1.08 and for Ag–Fe catalyzed CNTs was ∼0.7. The Ag–Fe catalyzed CNTs were found to be less defective as compared to Fe catalyzed CNTs. Field emission measurements using diode configuration, showed that electron emission from Ag–Fe catalyzed CNTs was much stronger as compared to Fe catalyzed CNTs. The threshold field for Ag–Fe catalyzed CNTs was (2.6 V μm⁻¹) smaller as compared to Fe catalyzed CNTs (3.8 V μm⁻¹) and thus shows better emission properties. This enhancement in electron emission mechanism as a result of introduction of Ag underlayer is attributed to the increased emitter sites and improved crystallinity.