Appearance of a knee on the Fowler-Nordheim plot of carbon nanotubes on a substrate

Existing theories for electron-field emission of carbon nanotubes (CNTs) cannot interpret why there appears in certain cases a knee on some Fowler-Nordheim (F-N) plots while not on others. We consider the interaction between substrate and CNTs and introduce a double-barrier model to explain the knee on the F-N plot. The knee on the F-N plot is a consequence of the transition from direct tunneling to F-N tunneling. The absence of the knee for the CNT films on titanium is attributed to the removal of the interface barrier by the formation of a conductive titanium carbide interlayer. The double-barrier model is helpful in understanding the field emission mechanism of CNTs and can explain the experimental results regardless whether or not there is a knee on F-N plot. (c) 2006 Elsevier Ltd. All rights reserved.