Pencil lead tips: A field ion and field electron emission microscopic study

Abstract

Pencil lead tips composed of graphite flakes were subjected to field ion and field emission microscopic investigations. The ion micrographs showed elongated images of ledge atoms of the graphite flakes due to uneven magnification over the layers of the flake. The gross features of the field evaporated tip surface were observed by scanning electron microscopy. The field emission pattern showed emitting lobes which displayed intensity fluctuations consisting of a combination of emission spots turning on and off randomly and a localized flicker of individual spots. These effects gave rise to noise in the emission current involving isolated spikes of rapid rise time and trains of digital pulses of constant height. The variation of noise with residual gas pressure, emission current, and temperature has also been investigated. The results are discussed in view of the microtopography of the pencil lead tips and the nature of the emitting sites on the surface.