We produced atomic pyramids with three 211 facets at the apex of a blunt W <111 > tip. The blunt W tip was preliminarily subjected to a remolding treatment to sharpen its end, which was aimed at reducing the burden of atom transport necessary for the growth of the pyramids, i.e., 211 faceting around the (111) plane. The effects of the remolding treatment were investigated in detail by field emission microscopy (FEM). From the results of a systematic experiment, a phase diagram of the tip-end structures was successfully represented as a function of remolding temperature and voltage. Consequently, remolding treatment at 2100 K was found to induce 211 faceting most significantly under all the conditions examined. Additional processes of Au deposition and postdeposition annealing were found to yield unique FEM patterns including typical signs of nanopyramid growth. The emission current stability exhibited by the resultant tip indicated that the source areas were comparable to the atomic dimensions.

Articles you may be interested inElectron wave interference induced by electrons emitted from Pt field emitter fabricated by focused-ion-beaminduced deposition J. Vac. Sci. Technol. B 28, C2A9 (2010); 10.1116/1.3333440 Determination of atomic potential energy for Pd adatom diffusion across W (111) islands and surfaces J. Vac. Sci. Technol. A 20, 897 (2002); 10.1116/1.1472429 Crossover among structural motifs in transition and noble-metal clustersFor application as single-atom emitters, the authors have developed a new method for preparing atomic-scale pyramids with three {211}-facet sides (nanopyramids). 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.

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We fabricated nanometer-size pyramids with three {211} -facet sides (nanopyramids) on blunt W tip and observed their atomic structures by field ion microscopy (FIM). The blunt W tip was preliminary subjected to remolding treatment in order to sharpen its end. Owing to the atomic resolution of FIM, we found that the {211} and {110} planes faceted markedly as a result of the remolding treatment and clearly detected the neighboring {211} and {110} planes were separated by a monoatomic chain along the ⟨111⟩ direction. In addition, the (111) plane was raised and narrowed owing to the faceting of the three surrounding {211} planes. Dimension of the narrowed (111) plane was about 3 nm. By using the surface of the remolded-tip end as a substrate, we grew the nanopyramid by depositing Pd atoms and elevating the sample temperature to 1000 K. The FIM observation indicated typical signs for the nanopyramid growth such as markedly-faceted {211} planes, monoatomic linear chains for the pyramid ridge, and extremely narrow top of the pyramid. In this study, the top was the third layer of the ideal nanopyramid counting from the top. Along with previous field emission data [E. Rokuta, T. Nakagawa, H. Murata, S. Fujita, H. Shimoyama, and C. Oshima, Jpn. J. Appl. Phys. 50, 115001 (2011).], the remolding treatment was proven to be useful for the nanopyramid growth on the blunt end of the W tip.

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