Hong Shi Kuo

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 W 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 Ne+ 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.

Gas field ion source from an Ir∕W⟨111⟩ single-atom tip

We show that a thermally stable Ir∕W⟨111⟩ single-atom tip is a very good point ion source for rare gases (He, Ar) and reactive gases (H2, O2). The ion beams are emitted from the topmost atom with a very small opening angle (<1°) and, most importantly, they exhibit high brightness. In addition, the ion currents are very stable. These good properties together with the long lifetime of the tip and the reliable tip preparation method make this tip especially suitable for applications in gas field ion source focused ion beam systems.

Fabrication of ultra-sharp single atom tips

Ultra high vacuum - field ion microscopy (UHV-FIM) with atomic resolution was used to study the methods of preparing ultra-sharp single atom tips. Several treatments including annealing, depositing, exposing to special gas, keep in a given atmosphere, and so on were the possible tactics to sharpen the tips. The sharpen results of various treatments were observed by field ion microscope. Two kinds of magnetic nano tips were formed. One is a PtCo pyramidal tip formed by surface faceting, the other is a Pt based Co tip formed by the SK mode epitaxy.