Surface Diffusion of Adatom on Tungsten Material Evaluated by Density Functional Theory Calculation*

We are interested in tungsten nano structure (fuzz), which is formed due to helium irradiation with relatively low incident energy (less than about 100 eV), and have studied by use of numerical simulations. Its formation mechanism is not clear and is believed that multiple processes are involved. Motion of adatom which is trapped on a surface is regarded as one of these elementary processes.

In the present work, migration energy of adatom on tungsten surface, which is related to surface diffusion process, is evaluated by ab initio calculation based on density functional theory (DFT). For a case of tungsten adatom, the evaluated migration energy is 1.96 eV and corresponding moving path is that an adatom moves onto the lattice point on the surface and the surface atom pops out on the surface.

Other cases where adatom is other than tungsten will be reported in the presentation.