Dependence of Curvature Radii of the Apexes of W Tips on Growth of Au- and Pd-Coated Nanopyramid

Atomic scale tungsten (W) pyramids coated with monolayer films of noble metals can be produced on the apex of a W tip sharpened by means of chemical etching. In this work, we produced Pd- and Au-coated nanopyramids using W tips with different apex curvature radii as a substrate and examined the yield ratios of the nanopyramid formation. When the curvature radius is larger than 15 nm, both Pd- and Au-coated W nanopyramids grow. However, when the radius is less than 15 nm, only Au-coated nanopyramids grow. We propose that the preferential growth for the Au case is associated with previous calculation results demonstrating that the difference in the anisotropy of the surface energy between the Au/W(111) and Au/W(211) systems is substantial [S. P. Chen, Surf. Sci. 274, L619 (1992)].