Vertically aligned single wall carbon nanotubes (SWCNTs) with large scale control of diameter, length and alignment have successfully been grown by plasma enhanced chemical vapor deposition (PECVD) system. The nickel (Ni) as catalyst deposited on silicon (Si) substrate was used to grow the SWCNTs. Field emission (FE) characteristics of the as grown SWCNTs were measured using indigenously designed setup in which a diode is configured in such a way that by applying negative voltage on the copper plate (cathode) with respect to stainless steel anode plate, current density can be recorded. To measure the FE characteristics, SWCNTs film pasted on the copper plate with silver epoxy was used as electron emitter source. The effective area of anode was similar to 78.5 mm(2) for field emission measurements. The emission measurements were carried out under high vacuum pressure of the order of 10(-6) Torr to minimize the electron scattering and degradation of the emitters. The distance between anode and cathode was kept 500 mu m (constant) during entire field emission studies. The grown SWCNTs are excellent field emitters, having emission current density higher than 25 mA/cm(2) at turn-on field 1.3 V/mu m. In order to enhance the field emission characteristics, the as grown SWCNTs have been treated under nitrogen (N-2) plasma for 5 min and again field emission characteristics have been measured. The N-2 plasma treated SWCNTs show a good enhancement in the field emission properties with emission current density 81.5 mA/cm(2) at turn on field 1.2 V/mu m. The as-grown and N-2 plasma treated SWCNTs were also characterized by field emission scanning electron microscope (FESEM), high resolution transmission electron microscope ( HRTEM), Raman spectrometer, Fourier transform infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS). (C) 2014 Elsevier B.V. All rights reserved.