Field emission features from Si and W tips are drastically improved upon coating even with simple carbon films. In this paper, in order to obtain clues to clarify the mechanism, we examine atomistic STM observations including local barrier height (LBH) and field emission imagings of the carbon films. And we also examine the field emission features from the shape-controlled W tips before and after the carbon coatings, enabling us to estimate the local electric field at the tip apex. From the STM observations, we find that the carbon film consists of nm-scale grains with various electronic properties and that the FE current varies grain by grain and is higher near the edge of each grain. The effective work functions evaluated from the slopes of the Fowler-Nordheim (FN) plot are constant regardless of the thickness of the carbon coating, although they are largely scattered for the films thinner than 1 nm. On the basis of the observed results, we discuss the mechanism of low macroscopic field emission from carbon films.
