Controllable growth, structure, and low field emission of well-aligned CNx nanotubes

A large area and controllable synthesis of well-aligned CKx nanotubes with a high content of nitrogen (x less than or equal to 9%) was carried out by pyrolyzing metal phthalocyanine on an n-type Si(100) substrate. The diameters of the CNx nanotubes range widely from 20 to 200 nm, and the lengths range from 1 to 100 mum. The impressive bamboo-like CNx nanotubes consist of a few uniform, small, and well-ordered compartments. Investigation on morphology and elemental composition of the CNx 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 CNx 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 CNx nanotubes began to emit electrons at an electric field of 1.5 V/mum, and current densities of 80,muA/cm(2) have been realized at an applied field as low as 2.6 V/mum. 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 pi system of the hexagonal framework. The controllable synthesis of well-aligned CNx nanotubes with high N ratio may open a route to improve the field emission properties of nanotubes.