Methods for characterization of atomic-scale field emission point-electron-source

Field emission (FE) electron sources are made close to atomic-scale to reach the highest spatial resolution as well as stable emission for electron microscopy, electron beam inspection and lithography. At present, no single agreed method exists of using FE current-voltage data to extract the apparent emission area, which is needed for predicting some beam properties. The 1956 theory of Murphy and Good (MG) is better physics than the 1920s theory of Fowler and Nordheim (FN) and colleagues, but many researchers use simplified FN theory to analyse experimental data. The present paper reports an experimental method of finding apparent emission area, based on using field ion and field electron microscopes (FIM-FEM). The discrepancy of emission area between the FIM-FEM method and MG-based analysis is a factor of 7.4, while that with simplified FN-based analysis is about 25, confirming MG theory is better for FE data analysis. The result allows deduction of key indicators, including source energy spread, reduced brightness and emission efficiency. A downloadable program is made available to help analysis. Our work provides a new experimental method of characterizing FE electron sources, especially the atomic-scale cold cathode, for which existing plot-based data-analysis methods are not suitable.

💡 Research Summary

The paper introduces a novel experimental methodology for directly determining the apparent emission area of atomic‑scale field‑emission (FE) electron sources, a parameter that is critical for predicting source brightness, energy spread, and overall performance in electron microscopy, beam inspection, and lithography. Traditional analysis of FE current‑voltage (I‑V) data relies on Fowler‑Nordheim (FN) theory, which assumes a simple triangular tunnelling barrier and often leads to severe under‑estimation of the emission area. In contrast, the Murphy‑Good (MG) theory incorporates the more realistic Schottky‑Nordheim barrier, but experimental validation of its superiority has been lacking.

To address this, the authors combine field‑ion microscopy (FIM) and field‑electron microscopy (FEM) in a single apparatus. They first verify by finite‑element simulations (CST Studio Suite) that electrons and H₂⁺ ions emitted from the same point on a tip with zero initial kinetic energy follow identical trajectories, implying that the linear and area magnifications are the same for both techniques.

Experimentally, a