Composition of the first two atomic layers in Au0.2Cu0.8 and Au0.8Cu0.2 alloys

Ratios of the M-2,M-3 VV Auger signal of copper for the alloy Au0.2Cu0.8 to that for Cu standard (h(Cua)/h(Cus)) and such a signal of gold for the all oy Au0.8Cu0.2 to that for Au standard (h(Aua)/h(Aus)), expected for particu lar compositions of the first and second atomic layers of alloys mentioned above and for two incidence angles (0 and 60 degrees) of the primary electr on beam in an RFA spectrometer, were calculated with the use of Monte-Carlo computer simulation of the transport of Auger electrons to the sample surf ace, including elastic and inelastic scattering of those electrons. These r atios were fitted to the corresponding ratios obtained from measurements, w hich gave the composition of the first and second atomic layers in both all oys. For the Au0.2Cu0.8 alloy, the relative atomic concentrations of copper atoms in the first and second atomic layer X-Cu1 = 0.77 +/- 0.1 and X-Cu2 = 0.93 +/- 0.5, respectively, were found while for the Au0.8Cu0.2 alloy X-A u1 = 0.81 +/- 0.1 and X-Au2 = 0.44 +/- 0.5 were obtained. These results wer e found to be almost unchanged when the inelastic mean free path of Auger e lectrons is varied from 0.3 to 0.5 nm and the acceptance angle of the RFA a nalyzer is varied from 25 to 35 degrees in calculations mentioned above. On the other hand, the change of the measured ratios h(Aua)/h(Aus) or h(Cua)/ h(Cus) by 3% changes the X-Au1 or X-Cu1, respectively, by about 0.1. The re sults obtained are compared with experimental and theoretical results (conc erning the AuxCu1-x polycrystalline and crystalline samples) known from the literature. A good qualitative agreement is found. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.