Noble Metal/W(111) Single-Atom Tips and Their Field Electron and Ion Emission Characteristics

We have developed a simple, reliable and reproducible method for preparing single-atom tips. With electrochemical techniques, a very small amount of a noble metal is plated on the surface of a clean Wh111i tip. Upon annealing the tip at an appropriate temperature in vacuum, a three-sided {211} pyramid with a single-atom sharpness is formed spontaneously at the tip apex by adsorbate-induced faceting. This tip is both thermally and chemically stable, and can be regenerated several ten times when accidentally damaged. We use a field ion microscope to examine the atomic structure of the tip apex layer by layer and characterize the corresponding electron emission in the field emission mode. Some properties of Neþ ions emitted from a single-atom tip are also measured, indicating a high brightness and a small extension angle. Many desirable features make the single-atom tips very promising for future particle beam applications in nanoscience and nanotechnology. [DOI: 10.1143/JJAP.45.8972]