[[alternative]]The growth of pyramidal structure on Pd covered W tip and research on relative atomic processes

[[abstract]]The growth of a single-atom sharp pyramidal structure on the Pd covered W tip was observed in this study. Its pro-perties such as thermal stability and repeated regeneration processes are found. Using Field Ion Microscopy, we also investigated such atomic processes in relation to the pyramidal facet growth, including terrace diffusion and descending diffusion of Pd adatoms on W(112), (110), and (111) surfaces, ascending diffusion of Pd adatoms onto W(111) surface, detachment of Pd adatoms from the kink sites of W(111) boundary and the free energy anisotropy of W(111) surfaces. The activation barriers for the terrace diffusion of Pd adatoms on W(112), (110) and (111) surfaces are determined to be 0.32±0.02, 0.51±0.03, 1.02±0.06eV, respectively. And the extra reflective barriers for the descending diffusion are determined to be 0.29±0.03, 0.27±0.02, 0.61±0.01eV, respectively. The mechanism of des-cending diffusion for Pd adatoms on W surfaces should be hopping. The activation energy for the ascending diffusion for Pd adatoms at W(111) steps is derived to be Ea＝1.84±0.07eV and for the detachment from the kink sites is derived to be Edet＝1.72±0.07eV. The free energy anisot-ropy near the W(111) surface is also derived to be 0.013eV/4.47Å. The investigation of the mechanism and energetics of the atomic processes gives us more information for the growth of pyramidal structure. We also try to use such a W tip with single-atom sharp apex as the scanning probe of Scanning Tunneling Microscopy. The work is currently in progress.