Field emission from dense, sparse, and patterned arrays of carbon nanofibers

We compare the field emission characteristics of dense ${\text{(10}}^9\hspace{0.17em}{\mathrm{nanofibers/cm}}^2\mathrm{),}$ sparse ${\text{(10}}^7\hspace{0.17em}{\mathrm{nanofibers/cm}}^2\mathrm{),}$ and patterned arrays ${\text{(10}}^6\hspace{0.17em}{\mathrm{nanofibers/cm}}^2)$ of vertically aligned carbon nanofibers on silicon substrates. The carbon nanofibers were prepared using plasma-enhanced chemical vapor deposition of acetylene and ammonia gases in the presence of a nickel catalyst. We demonstrate how the density of carbon nanofibers can be varied by reducing the deposition yield through nickel interaction with a diffusion layer or by direct lithographic patterning of the nickel catalyst to precisely position each nanofiber. The patterned array of individual vertically aligned nanofibers had the most desirable field emission characteristics, highest apparent field enhancement factor, and emission site density.