Nanoridge domains in α-phase W films

Two types of nanoridge domains oriented with each other with an angle ranging between 109° and 124° were measured by scanning tunneling microscopy on the α-W film sputter deposited on an oxidized Si surface. Each domain contains nanoridges with a period of 7.5 ± 1.0 nm. No such domains were observed on the β-W film surface. We argued that due to the anisotropy of the W(1 1 0) surface, the impinging W atoms diffuse faster along the 〈111〉 directions on the surface to form the nanoridge structure. There are two equivalent 〈111〉 directions, which give rise to two orientational domains with an angle of ∼110°. An isotropic β-W(1 0 0) phase has no preferred diffusion direction for the impinging W atoms and therefore, no nanoridge domain structure was observed.