Fabrication of a single-atom electron source by noble-metal surface diffusion

For application as single-atom emitters, the authors have developed a new method for preparing atomic-scale pyramids with three amids). In the new method, palladium covers the backward area of the tungsten tip, approximately 1 mm from the sharpened end, rather than the end itself. The palladium was deposited via surface diffusion promoted by elevating the temperature. Field ion microscopy exhibited typical signs indicating that, with the added annealing, identical nanopyramids grew spontaneously. The field emission characteristics of these nanopyramids were investigated and compared with those produced by the two established preparation methods. The authors found that field emission patterns for single-atom tips were narrow circles at low extractor voltages and three-pronged stars, indicating the presence of three ridges of the nanopyramid, at high voltages. The patterns are the same for tips prepared by whichever method. As for field emission stability, clear differences were also not seen across the preparation methods, except for a minute difference in fluctuation ratios obtained from time-dependent current data.