ON THE MECHANISM OF CONTRAST CREATION IN DIRECTIONAL AUGER-ELECTRON SPECTROSCOPY (DAES)

In (DAES), maxima in the dependence of the Auger signal from a crystal line sample on the primary electron beam incidence angle are used for determination of a sample crystalline structure. To determine a mechan ism responsible for creation of those maxima, azimuth profiles in the vicinity of the ((1) over bar 1 (1) over bar) plane for the elastic pe ak height, current of backscattered (with different Delta E) electrons , and Auger Cu M2,3VV peak height were measured (using an RFA) at diff erent incidence angles for the Cu(011) face. The highest contrasts of the elastic peak were found for incidence angles corresponding to the [011] and [121] directions. However, about two times smaller contrast was still found for other incidence angles when the primary beam pass only the ((1) over bar 1 (1) over bar) plane, and no close-packed dire ction. This indicates that channeling of primary electrons on close-pa cked planes plays an important role in the creation of the elastic pea k contrast. For backscattered (Delta E > 300 V) electrons and for the Auger peak, the contrast corresponding to the cross of the ((1) over b ar 1 (1) over bar) plane was 2-3 times smaller than that for the elast ic peak. This indicates that the Auger electrons excited by backscatte red electrons are mainly responsible for the contrast of the low-energ y Auger peak. Thus, information on the crystalline structure given by low-energy DAES concerns in an appreciable part the sample layer at th e dept comparable with the extinction distance of primary beam electro ns. It was shown for Ag MNN DAES profiles obtained for silver monolaye r on the Cu(001) face that maxima concerned with the substrate structu re vanished if the primary beam energy is as low as 600 eV. Thus, info rmation given by DAES concerns only the first atomic layers in this ca se.