Testing the Performance of Field Emission Data-Analysis Plots: Comprehensive Comparison

Abstract

In field electron emission studies, interpretation of measured current-voltage characteristics and extraction of emitter characterization parameters are usually carried out using three graphical plots: Millikan-Lauritsen plots, Fowler-Nordheim plots, and Murphy-Good plots. Millikan-Lauritsen plots were commonly used in the early days of field emission analysis, but most modern analysis uses Fowler-Nordheim plots.   Theoretically, it is now known that Millikan-Lauritsen and Fowler-Nordheim plots are predicted to be slightly curved, but a Murphy-Good plot will be "very nearly straight". Hence (because Murphy-Good theory is "better physics" than 1928 Fowler-Nordheim theory) expectation is that parameter extraction using a Murphy-Good plot will be more accurate than extraction using either Millikan-Lauritsen or Fowler-Nordheim plots.   In field electron emission literature, current-voltage characteristics are often converted into other forms. Thus, measured voltage may be converted to (apparent) macroscopic field, and/or current values may be converted to macroscopic current densities. Thus, four data-input forms can be found in the context of analysing field electron emission results.   To assist with field electron emission current-voltage data interpretation, a simple user-friendly webtool has been designed to apply the so-called orthodoxy test, using any of the recognized plot types and any of the common data-input forms, and then (where appropriate) extract characterization parameters. This study demonstrates the webtool’s flexibility and usefulness.   The present study reports the following: (1) systematic tests of the webtool, using simulated input data prepared using Extended Murphy-Good field electron emission theory; (2) systematic comparisons of the three different data-plot types, again using simulated data, in respect of the accuracy with which extracted characterization parameter values match the simulation input values; (3) an analysis of experimental current-voltage characteristics taken (in a field electron microscope) from two single-tip molybdenum emitters, both exhibiting ideal behavior at low measured voltages but non-ideal behavior at higher voltages. It is suggested that simulating the ideal system behavior over the whole voltage range, using characterization parameters extracted from low-voltage behavior, could be a useful technique for investigating the non-ideal high-voltage behavior.   An important result is to confirm that, particularly in respect of the extraction of formal emission areas, the Murphy-Good plot has noticeably better performance when compared to that of Fowler-Nordheim and Millikan-Lauritsen plots. This result is important for field electron emission science because it is now known that differences as between different theories of field electron emission often affect the formal emission area.

Keywords: Murphy-Good plots, Fowler-Nordheim plots, Millikan-Lauritsen plots, Field emission orthodoxy test, Field emission data analysis