Field Emission from Carbon Films with No Protrusions with High Aspect Ratios

Field emission features from Si and W tips are drastically improved upon coating even with simple carbon ˆlms. In this paper, in order to obtain clues to clarify the mechanism, we examine atomistic STM observations including local barrier height (LBH) and ˆeld emission imagings of the carbon ˆlms. And we also examine the ˆeld emission features from the shape-controlled W tips before and after the carbon coatings, enabling us to estimate the local electric ˆeld at the tip apex. From the STM observations, we ˆnd that the carbon ˆlm 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 eŠective 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 ˆlms thinner than 1 nm. On the basis of the observed results, we discuss the mechanism of low macroscopic ˆeld emission from carbon ˆlms.