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Physical foundations of directional auger electron spectroscopy (DAES) and calculation of DAES profiles in single scattering cluster approach are presented. Limitations of this method (application only to investigation of the crystalline structure of homogeneous samples) is shown and explained as the result of participation of inelastically scattered electrons in the Auger signal generation. To extend the DAES application for the interface structure, the use of as low as possible energy of primary electrons is proposed because in such a case the participation of inelastically scattered electrons becomes negligible and single scattering cluster calculation should describe correctly the DAES profiles for interfaces. Besides, the extension of single scattering cluster calculations to the second elastic scattering is recommended. To check the technical possibility of DAES use in the proposed version, the Auger spectrum of Cu LM M peaks was recorded for a Cu 3 Au(001) sample with the use of a retarding field analyzer with the primary beam energy 1200 eV. Quality of this spectrum seems to be good enough for using in DAES.PACS numbers: 61.05.J-, 68.35.Rh Description of DAES method and SSC approximationThe influence of the primary electron beam direction on the Auger signals measured for crystalline samples is well recognized for many years (see, for example, reviews [1, 2] and references therein). Namely, distinct maxima of the measured Auger signal appear when the primary electron beam is parallel to the direction of some set of close packed rows of atoms in the crystal investigated. This opportunity was seen as the difficulty in a quantitative Auger analysis. On the other hand, it was used as a base of the method giving information about the crystalline structure of ultrathin layers and about the epitaxial relation between the deposited layer and its substrate (directional Auger electron spectroscopy -DAES in [3] and primary-beam diffraction-modulated electron emission -PDMEE in (S-93)

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The composition of the first atomic layer of Cu3Au (001) crystal (about half-and-half copper and gold atoms) changes only slowly even at temperatures much higher than that of the order-disorder transition (TC = 663 K). Theoretical and experimental works show a general trend of these changes but they differ in quantitative findings. In the present work we used directional elastic peak electron spectroscopy and directional Auger electron spectroscopy to investigate changes of atomic order and composition in the first atomic layers of the Cu 3 Au(001) crystal during the sample temperature increase. The height of central maximum in DEPES polar profile of the sample investigated was measured as a function of sample temperature. It was found that the measured dependence is linear, but the slope of this dependence changes abruptly around TC. This change seems to be connected with disappearance of the atomic order in the first and second atomic layers. In DAES the height of the Auger peaks for copper and gold low energy transitions (M V V and N V V , respectively) were measured in the dN (E)/dE mode as a function of the primary electron beam incidence angle. The composition of the first, second, and third atomic layers was determined by fitting the ratio of calculated DAES polar profiles for copper and gold to such a ratio for the measured profiles.PACS numbers: 61.05.J-, 68.35.Rh