Extraction of scattered low-energy electrons in field emission conditions

Recently we demonstrated a prototype instrument that employs a new technique for determining surface structures. The instrument consists of a scanning tunneling microscope tip as a field emission gun and a detector for projecting electron scattering patterns. Previous results showed a low efficiency in detecting scattered electrons, because the potential between the tip and the sample drew the electrons back toward the sample. To improve the efficiency, we attempted detection using a tip-shield that can extract the scattered electrons toward a vacuum region effectively. Our results confirmed that the tip-shield improves detection efficiency. Consequently, we observed an extra beam that might be scattered toward the surface-parallel direction. The results of our electron trajectory calculations agreed qualitatively with the experimental data. We have tentatively designated the two spots we obtained as (0 0) and (1 0) diffraction beams of the graphite surface.