Diffusion studies of nickel on the W(121) and the W(111) planes by probe-hole field emission microscopy

In a probe-hole field emission microscopy experiment, doses of nickel have been in situ deposited onto a thermally cleaned tungsten tip held at 300 K in clean ultra high vacuum conditions. The deposited doses of nickel were annealed successively at temperatures ranging from 340 to 2215 K to cause diffusion of the deposited amount on various tip surfaces. The changes in the work function (ΔΦ) and in the pre-exponential function (ln B) have been calculated from ten point Fowler–Nordheim (F-N) plots for the total tip surface, the W(121) and the W(111) surfaces at each successive stage of annealing. These variations are discussed in terms of diffusion of nickel atoms on the tungsten tip surface.