Preparation of single-atom tips and their field emission behaviors

We have developed a simple and reliable method for preparing single-atom tips. Electrochemical techniques are applied to deposit a noble metal film on the W <111> tip. With the protection of the metal film, the tip can be stored and transferred in the ambient condition. After a gentle annealing of the plated tip in vacuum, a thermally and chemically stable nano-pyramid with single atom sharpness can be generated at the tip apex. The atomic structure of the tip is imaged by a field ion microscope (FIM) layer by layer through field evaporation. The corresponding field emission patterns can also be determined by the field emission microscopy (FEM). Most importantly, the single atom sharpness as well as the pyramidal structure can be regenerated for tens of times in vacuum simply by annealing if the apex is accidentally damaged. Field emission measurements indicate that the single-atom tips can emit stable electron beams of high brightness with a small extension angle. These desirable features make the single-atom tips very promising for future applications.