The idea of doping carbon nanotubes (CNTs) with boron (B) and/or nitrogen (N) looks attractive in view of the changes brought in their electronic structures by the dopants [1-3]. The field electron emission studies of boron (B) and nitrogen (N) doped CNTs grown in situ on pointed tungsten (W) tip and flat silicon (Si) substrate surfaces have been reported in this paper. The CNTs were grown by pyrolysis of ferrocene [4-5] with suitable dopants. The morphology of the B-doped and N-doped CNTs on flat Si substrate was observed under SEM (Fig 1a & b). The B-doped CNTs on flat Si and pointed W tip have rope like structure and are also found to be considerably long (～50 μm). This may be attributed to the dopant atoms of Boron, which act as catalysts for further growth of the CNTs along the tube axis. N-doped CNTs were, however, short (～ 5 μm), uniform and very densely packed. The Fowler-Nordheim (F-N) plots obtained from the I-V curves of doped field emitters show non-linear behavior (Fig 2 a and b). This non-linearity may be attributed to strong field penetration into the emitter apex region resulting into the local large variations of the electric field in the electron tunneling region [6-7]. The local field enhancement factor (β) and the current density (J) have been calculated from the slopes of the F-N plots. Field emission micrographs from the B- and N- doped CNTs on W tips reveal geometrical structures, typical of CNT bundles [5]. The FEM images corresponding to B and N-doped CNTs on flat Si substrates show streaky structures. Typical field emission currents upto 200 μA drawn from both B and N-doped CNTs are remarkably stable over periods greater than 3 hours (Fig 3 a and b). But in case of B-doped CNTs on flat Si, the set current of 400 μA decreases slowly for about an hour and then gets stabilised at 300 μA.
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