Field emission from multiwall carbon nanotubes in controlled ambient gases, H2, CO, N2 and O2.

Adsorption and desorption on clean pentagons at a tip of multiwall carbon nanotube (MWNT) have been investigated by field emission microscopy (FEM) in an atmosphere of various gases, i.e., hydrogen, carbon monoxide, nitrogen and oxygen. A MWNT with clean surface which is obtained by heat treatment gives FEM patterns consisting of six bright pentagonal rings. Adsorbates are recognized as bright spots in the FEM pattern. They reside preferentially on the pentagonal sites where the strong electric field is concentrated, and bring about stepwise increase in the emission current. Heat treatment of the MWNT emitter at about 1300K allows adsorbates to desorb. After the desorption of hydrogen and nitrogen, the original clean surface with pentagons is recovered, while the tip structure is destroyed after the desorption of oxygen.

Energy distributions of field emitted electrons from a multi-wall carbon nanotube.

Field emission energy distributions of electrons from one of the six pentagons located at the end of a multi-wall carbon nanotube have been measured by means of a high-resolution cylindrical energy analyzer. In a clean pentagon, the sub-peak was obtained at about 500 meV below the main peak, exhibiting a shift with increasing applied voltage. For electrons emitted from an adsorbate onto the pentagon, no fine structure was observed in the spectra. The broadening of the leading edge was also observed for both clean and adsorbed pentagon, indicating the field penetration into the nanotube due to its semimetallic nature. The full-width at half-maximum was 280 meV at the applied voltage of 660 V and increased linearly with applied voltage.