Necessary Conditions for Two-Lobe Patterns in Field Emission Microscopy

Abstract

We investigate the mechanism by which small organic molecules adsorbed on a field emission tip form cloverleaf patterns. This phenomenon was discovered by Müller in 1950. Many theories have been subsequently proposed for the formation of these patterns. However, their formation mechanism is not well understood. In a previous study, we obtained images of emission sites by field ion microscopy that contained the same shapes as cloverleaf patterns. In the present study, we experimentally determine the necessary conditions for obtaining cloverleaf patterns. Experiments using simple gas and liquid molecules with σ- or π-bonds clearly revealed that there are two main conditions for obtaining cloverleaf patterns: molecules must contain π-bonds and their adsorption state must be modulated by the electron current.

Subnanometeric optical modulation of a single-molecule electron source

“…These peculiar patterns and their variations were rst observed around 70 years ago [25] . However, no satisfactory theoretical model has yet been developed to explain the formation mechanism of the patterns [21,[24][25][26][27][28][29] .…”

“…standing up to lying down [23,[25][26][27][28] . However, none of these ideas has provided a consistent explanation [29,34] . In contrast, our simulation model consistently reproduced those emission patterns, as shown in the lower panels of Figures 2(a)-2(d).…”

Field emission microscope for a single fullerene molecule

“…1(b). These peculiar patterns were already observed seventy years ago, but their interpretation was not clari ed [7][8][9][10][11][12][13]. Because of this shortcoming, there are relatively few numbers of studies on molecules using FEM compared to STM.…”

“…Around the protrusion, electric elds are further enhanced, and an electron emission is driven from the molecules at the top of the protrusions. However, it was not clear whether the molecules at the top are single or clustered [7][8][9][10][11][12][13], unless one could undertake an exceptional study with an ultra-sharp tip [14] or a single molecule emitter [15]. For instance, the authors in reference [10] consider the protrusions to consist of a cluster of oxygen atoms, and each spot in the emission patterns representing a single atom.…”