DYNAMICAL CALCULATIONS FOR RHEED FROM A PARTIALLY-ORDERED CU3AU(111) SURFACE

A multislice formalism of Cowley and Moodie [Acta Cryst. 10 (1957) 609 ] with a recently developed edge patching method has been applied to t he RHEED analyses on the order-disorder transition of the Cu3Au(111) s urfaces. The results give the R(I)-S relation as R(I) = 0.4S(2.224) (R (I)- ratio of reflection intensities, S - long-range order parameter). By combining the R(I)-T relation experimentally observable by RHEED w ith the simulated R(I)-S relation, the needed S-T relation for the tra nsition can be resolved in a straightforward way. The results confirm what was suggested by the experiments [Mater. Res. Sec. Symp. Proc. 23 7 (1993) 517]: the intensities of the RHEED superstructure reflections from ordering of the Cu and Au is more than 90% sensitive to the oute r monolayer alone, thus making RHEED valuable for studies of surface o rder. The results of the analyses on the attenuation of elastically sc attered electrons inside crystal in RHEED are useful to RHEED-related surface analytical techniques: AES, REEL, EDS and RHEED-TRAXS. The inv estigation on the errors resulting from potential sampling has shown t hat choosing proper sampling rates in all three dimensions is importan t to the multislice simulation of RHEED.