Controllable Growth, Structure, and Low Field Emission of Well-Aligned CNx Nanotubes

Abstract

A large area and controllable synthesis of well-aligned CN x nanotubes with a high content of nitrogen (x⩽9%) was carried out by pyrolyzing metal phthalocyanine on an n-type Si(100) substrate. The diameters of the CN x nanotubes range widely from 20 to 200 nm, and the lengths range from 1 to 100 μm. The impressive bamboo-like CN x nanotubes consist of a few uniform, small, and well-ordered compartments. Investigation on morphology and elemental composition of the CN x nanotubes suggests that the overall tube morphology depends strongly on the nitrogen concentration. The higher the N content, the more compartmentalized of nanotubes become, which results in the formation of more curved CN x nanotubes. Our studies show that three different types of N atoms can be present in these materials. These are “pyridinic”, “pyrrolic”, and “graphitic” nitrogen with binding energies of 398.1, 401.0, and 405.1 eV, respectively. Field emission measurements suggest that the CN x nanotubes began to emit electrons at an electric field of 1.5 V/μm, and current densities of 80 μA/cm 2 have been realized at an applied field as low as 2.6 V/μm. Doping carbon nanotubes with N enhances their electron-conducting properties because of the presence of additional lone pairs of electrons that act as donors with respect to the delocalized π system of the hexagonal framework. The controllable synthesis of well-aligned CN x nanotubes with high N ratio may open a route to improve the field emission properties of nanotubes.