Richard G. Forbes

A recent paper in Physica Scripta discusses the influence of temperature on field-assisted electron emission from accelerator surfaces, concluding that the emission comes from the surface of a dielectric microparticle rather than from a metallic protrusion. This conclusion has not been validly reached, because the theory used contains many known errors. This Comment re-states standard theory for electron emission effects influenced by both temperature and electrostatic fields and re-examines the reported experimental results. It is concluded that the reported experimental temperature effects are not compatible with Murphy-Good field-electron emission theory (which is a useful and significant result), but that further research is needed before any firm conclusion can be reached about the actual mechanism of emission.

Field electron emission (FE) sources are made close to atomic-scale to reach the highest spatial resolution and stable emission for electron microscopy, electron beam inspection, and lithography. At present, no single agreed method exists for 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 analyze experimental data. The present paper reports an experimental method of finding the apparent emission area, based on using field ion and field electron microscopes (FIM+FEM). The emission area discrepancy between the FIM+FEM method and MG-based analysis is a factor of 8.2, but the discrepancy with simplified FN-based analysis is about 28, confirming that MG theory is better for FE data analysis. The result allows the deduction of key indicators, including source energy spread, reduced brightness, and emission efficiency. A downloadable program is made available to help with data analysis. Our work provides a new experimental method of characterizing FE sources, especially atomic-scale cold cathodes, for which existing plot-based data-analysis methods are not suitable.

Atom probe tomography (APT) fills a crucial need in the characterization workflow of materials by its ability to inform the three-dimensional local composition at the nanoscale. As with any characterization technique, APT has strengths and limitations that inform the interpretation of the data. Therefore, a challenge for the materials characterization community, and the APT community in particular, is the need to establish repeatable and reproducible workflows around the APT data acquisition, reconstruction, analysis, and sharing, in order to inform interpretation. Data interpretation also requires the continued development of our understanding of the physical processes responsible for field evaporation. We review recent developments in the experimental analysis of field evaporation and in the modeling of field evaporation, leading to a new understanding of common artifacts observed in reconstructed data. We then discuss current challenges with data analysis, translation of results, and data interpretation in the absence of community-agreed standards, and therefore, the crucial need for standardization at every stage of APT research, from data collection all the way to data reporting. This perspective is a summary of the invited presentations and discussions that took place during a workshop (August 4–5, 2024, Alexandria, Virginia).

This tutorial/technical note provides a high-level overview of the current state of basic field electron emission (FE) theory, as suitable for use in the context of technological applications of the FE theory. At present, there is significant theoretical confusion in the technological FE literature. Even in sensitive technological contexts, many papers have stated or used out-of-date theory that makes current-density predictions that are several hundred times less than those of the modern FE theory. A primary aim of this note is to help modernize the theory used in the future published FE literature, where needed. It is not intended as a detailed review of the FE theory.