摘要
The apex structure of a scanning tunneling microscope (STM) tip consists of a base with radius of tens of nanometers and protrusion with atomic-scale sharpness. We characterized the tip base radius and sharpness on the basis of field emission resonance (FER) energies. We derived two quantities from the first- through sixth-order FER energies, which were related to tip sharpness and base radius. The base radius can remain unchanged while the sharpness varied, and the tips can have identical sharpness but different base radii. The base radius can significantly affect the peak intensities of FER, which corresponds to the mean lifetime of FER electrons, on a Ag(100) surface but not on those of FER on a Ag(111) surface. This difference results from the surface dipole layer and quantum trapping effect (QTE) on the Ag(100) surface which are greater than those on the Ag(111) surface.