Total electron yield measurements of extended x-ray absorption fine structures (EXAFS) of Ni and Fe thin foils, and adsorption of Ni on polycrystalline Fe substrates

X-ray absorption spectra of Fe and Ni K edges have been obtained at room temperature by means of a total electron yield technique for a clean Fe foil on which Ni was subsequently deposited, and a Ni foil. This technique involves the measurement of the specimen current. The total yield is found to be approx.1 x 10-2 electron per photon absorbed at the Fe K edge for a 1/4 mil foil. Dramatic increase in surface sensitivity is gained over transmission EXAFS by using this technique to study Ni overlayers on Fe surface. The EXAFS of the deposited Ni overlayers (several monolayer coverage) are compared with those of the pure elements and of Ni/Fe alloys in the α(bcc) and γ(fcc) phases. The results indicate that the average Ni--Ni bond in the deposited Ni overlayers does not contract relative to that in the bulk in contrast to previously observed contraction of Ni deposition on carbon substrates. The feasibility of this technique and its application are discussed