A Well Defined Electron Beam Source Produced by the Controlled Field Assisted Etchingof Metal Tips to < 1 nm Radius

Well defined and ultra-sharp tips are highly demanded in scanning probe microscopy for acquiring atomic resolution as well as for the manipulation and characterization of molecules and nano-structures. There is also an increasing interest in developing electron beam sources with a high brightness and coherency as these factors have a direct impact on the resolution of electron microscopes, particularly the Transmission Electron Microscope (TEM). In this case the optimum resolution requires nano-size electron sources. Moreover, nano-tips with a single atom apex may enable high resolution in-line holography. Recently we have developed a new technique for fabricating atomically scale tips based on a spatially controlled reaction with field assisted reactive gases. In this work we show that the field emission investigations of single atom tips produced by the same technique always exhibit an ideal field emission pattern, which is confined to a single circular spot of a very small area. The progression of the field emission pattern from a regular (most likely rough) tip, then atomically clean and finally single atom tips is presented along with the corresponding atomic resolution Field Ion Microscope (FIM) images. We also demonstrate that similar features can be produced repeatedly regardless the original tip shape or crystal orientation.