Determination of the surface composition of the Cu−Ni alloys for clean and adsorbate−covered surfaces

Abstract

In previous Auger studies of the Cu−Ni alloys, most workers, using Auger transitions at ∠900 eV, have found that the ’’surface composition’’ and bulk composition are the same. We have measured the surface composition of four Cu−Ni alloys using the M1M4,5M4,5 transitions at ∠100 eV. In all samples studied [polycrystalline 10%/90%, (100) 10%/90%, (110) 10%/90%, and (100) 50%/50%, Cu/Ni], the copper concentration in the surface is significantly larger than that in the bulk. The discrepancy between our results and those of the early workers is due to the different escape depth of the emitted electrons as a function of electron energy. We estimate that the 100 eV transitions are sensitive to about one to two layers, whereas the high−energy transitions are sensitive to five to eight layers. The presence of adsorbates can alter the surface composition. This effect will also be discussed.