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

In a probe-hole held emission microscopy experiment, doses of nickel have b een in situ deposited onto a thermally cleaned tungsten tip held at 300 K i n clean ultra high vacuum conditions. The deposited doses of nickel were an nealed successively at temperatures ranging from 340 to 2215 K to cause dif fusion of the deposited amount on various tip surfaces. The changes in the work function (Delta Phi) and in the pre-exponential function (In B) have b een 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 an nealing. These Variations are discussed in terms of diffusion of nickel ato ms on the tungsten tip surface. (C) 1999 Elsevier Science S.A. All rights r eserved.