Evaluation of a CeB6 Virtual Source Electron Gun Using a Custom-Made SEM to Enhance the Brightness and Resolution in Electron Microscopy.

The electron source is a critical component determining electron microscope performance. Commercial electron microscopes typically employ Schottky emitters or cold field emitters that provide high brightness but require ultra-high vacuum operation. In contrast, the conventional crossover mode cerium hexaboride (CeB6) gun operates under a high vacuum, offering advantages in terms of vacuum requirements and cost. This study developed a virtual source mode CeB6 electron gun to enhance brightness and integrated it into a custom-made scanning electron microscope (SEM) with a single objective lens. Because the electron optical parameters of the SEM column were well defined, the two operating modes were analyzed by correlating simulation results with experimental measurements. The virtual source mode gun was measured a probe diameter of 23 nm (FW50) and reduced brightness of 1.2 × 105 A/m2 sr V, approaching the Langmuir limit, at an accelerating voltage of 2 kV. Compared to crossover mode operation in the fixed-magnification column, it produced a smaller probe diameter by more than 50 times and a higher brightness by more than tenfold. These results demonstrate that virtual source mode CeB6 operation offers high vacuum compatibility, superior brightness, and minimal probe size, with significant potential for advanced applications including bioimaging, semiconductor defect inspection, and next-generation electron beam systems.