Non-topographic current contrast in scanning field emission microscopy

Abstract

In scanning field emission microscopy (SFEM), a tip (the source) is approached to few (or a few tens of) nanometres distance from a surface (the collector) and biased to field-emit electrons. In a previous study (Zanin et al. 2016 Proc. R. Soc. A 472 , 20160475. ( doi:10.1098/rspa.2016.0475 )), the field-emitted current was found to change by approximately 1% at a monatomic surface step (approx. 200 pm thick). Here we prepare surface domains of adjacent different materials that, in some instances, have a topographic contrast smaller than 15 pm. Nevertheless, we observe a contrast in the field-emitted current as high as 10%. This non-topographic collector material dependence is a yet unexplored degree of freedom calling for a new understanding of the quantum mechanical tunnelling barrier at the source site that takes into account the properties of the material at the collector site.

Electronic Processes at the Carbon-Covered (100) Collector Tungsten Surface

“…The above process could be expected to hold for all carbon-covered tungsten surfaces since they are the result of purely coulombic interactions. We tentatively argue that they may also be responsible for the observed decrease in the workfunction of the carboncovered tungsten collector (110) surface in [1].…”

“…Several experiments at ETH [1] under the title Scanning Field Emission Microscopy have demonstrated that tungsten (110) surfaces covered by monolayers of several adatoms in various complicated structures (such as 12 × 15) acting as collectors under an external electric field show increased received current compared to the pure metallic tungsten substrate. The experiments referred to field emission in a nanometric tunnel diode operating in a point facing plane configuration in which the current was shown to increase by an epitaxial carbon or other adatom cover of the tungsten collector.…”