Structural evolution of polycrystalline tungsten tips with palladium oxide reservoirs

We present herein a method to prepare thermodynamically stable tungsten (W) nanopyramids. First, the sides of a W needle are coated with a collodion containing powdered palladium oxide. The W needle is subsequently annealed under ultrahigh vacuum to adsorb palladium (Pd) atoms onto the apex of the W needle via surface diffusion and thereby produce a W nanotip coated with a monolayer Pd film. Field ion microscopy reveals that {111} planes of the W nanotip are contracted by faceting the {211} planes surrounding the {111} plane. This structural change is analogous to the formation of three-sided W nanopyramids. The W nanopyramids appear generally the same as the existing nanopyramids. However, as opposed to the existing nanopyramids, the tip of the proposed nanopyramids does not comprise a single atom.