Estimation on Surface Atomic Layer Spacing of Nickel and Iron Single Crystals

The distance between the atomic planes close to the surface of Ni(f.c.c.) and Fe(b.c.c.) single crystals was estimated using a method based on a pairwise force model as represented by the Morse potential function. The interaction energy of surface atoms is lowered when the surface atomic layers have spacings wider than those in the interior of the crystals. The interaction energy of surface atoms is rather higher when all the surface interplaner spacing is constant throughout the crystal. The excess spacings between the first and second atomic layers of Ni and Fe crystal surfaces are found to be Ni(110)–1.57, Ni(100)–0.99, Ni(111)–0.26, Fe(111)–11.57, Fe(100)–3.68 and Fe(110)–0.20; where the excess to normal spacing ratios are given in percent. These values are compared with the results from LEED analysis. Even though fairly good agreements are obtained for Ni surfaces, no satisfactory agreement is obtained for Fe(111) and Fe(100) surfaces.