Quantitative analysis of electron field-emission characteristics of individual carbon nanotubes: the importance of the tip structure.

Electron field-emission measurements on individual carbon nanotubes (CNTs) were performed inside the transmission electron microscope (TEM). The field-emission characteristics of CNTs with different tip structures were compared, and their field conversion factor and emission area were studied systematically. It was found that the field-emission characteristics of a CNT depend sensitively on its tip structure, and in particular an opened CNT was shown to be superior to a capped CNT. High-resolution TEM observations revealed that the tip of an opened CNT may, in general, be regarded as being composed of irregular shaped graphitic sheets, and these graphitic sheets have been found to improve dramatically the field-emission characteristics, but the sharp edge may result in larger error in the calculated emission area. The influence of uncertainty in the work function of the CNTs on the field conversion factor and emission area calculation was also investigated.