The faceting structures and related issues on Rh and Ir covered W tips Abstract The faceting structures of Rh and Ir covered W tips are observed by field ion microscope. Two kinds of the single atom pyramidal tips are found for both of the Rh and Ir covered W tips. One we named type I , which the top three layers are constituted with 1, 3, and 10 atoms. The other we named type II , which constituted with 1, 6, and 15 atoms for the top three layers. To get the energy state of two kinds pyramidal tips, the appearance probability distribution are counted by repeated observing and annealing. The difference of activation barriers and binding energy of these two types are determined to be 0.08eV and 0.064eV for Rh covered single atom tip, and 0.05eV and 0.14eV for Ir covered single atom tip. Additionally, we found the double pyramidal structure on Ir covered W tip at 1029K. This new pyramid is sited on W{221} facet. Finally, we conclude the common phenomenon for Pd, Pt, Rh and Ir covered W single atom pyramidal tips and compare their different characters to provide users’ proper choice for different purposes.