A new, simple, and easily reproducible method of preparing single-atom tips by electroplating Pd or Pt on single-crystal W(111) tips followed
by thermal annealing in a vacuum is reported. These tips are both thermally and chemically stable and can also be regenerated when accidentally
damaged. The atomic structures of the tips are identical to those prepared by vacuum evaporation, as observed by field ion microscopy. The
corresponding field emission characteristics are investigated with field emission microscopy.
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 Ne þ 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.
The relation between magnetic properties and microscopic structure for a metal/semiconductor system is described. Cobalt films on a CoSi interface possess an in-plane easy axis of magnetization as the result of magnetocrystalline anisotropy of the Co∕CoSi interface. On a Si(111)-7×7 surface, direct evidence for the formation of CoSi2 compounds at the interface was found by the appearance of doubled spot defects in scanning tunneling microscopic images. The interfacial effects cause the easy axis of magnetization of a Co∕Si interface to be canted out of plane.
We report a reliable method for preparing a pure Ir single-atom tip by thermal treatment in oxygen. The atomic structure of the tip apex and its ion emission characteristics are investigated with field ion microscopy. We have shown that the Ir single-atom tip can be a good field ion emitter, capable of emitting a variety of gas ion beams, such as He+, H2+, N2+, and O2+, with high brightness and stability. In addition, this tip can easily be maintained and regenerated in vacuum, ensuring it has sufficient lifetime for practical applications.
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.
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