INVESTIGATION OF ULTRA-THIN CA CD-ARACHIDATE FILMS BY GRAZING-INCIDENCE DIFFRACTION (GID) WITH A CONVENTIONAL X-RAY TUBE AND A SYNCHROTRON-RADIATION SOURCE/

We examined the lateral atomic order and the correlation length of cry stalline domains in ultra thin Ca/Cd-arachidate Langmuir Blodgett (LB) films by means of a surface sensitive Grazing Incidence Diffraction ( GID) technique with a conventional Cu X-ray tube (E(tube) = 8.05 keV), as well as a synchrotron radiation source (E(syn) = 9.1 keV). The con ventional X-ray tube GID and the synchrotron radiation GLD yield compa rable results for the lateral lattice parameter. We determined a cente red rectangular lattice for 25 layers of Ca-arachidate and for 9 layer s of Cd-arachidate. The crystalline lattice parameters for 9 layers of Cd-arachidate amount to a = 0.478 nm/b = 0.733 nm (synchrotron radiat ion GID) and a = 0.486 nm/b = 0.729 nm (X-ray tube GLD). For the later al lattice constants of 25 layers of Ca-arachidate, the values a = 0.4 93 nm/b = 0.727 nm (synchrotron radiation GID) and a = 0.489 nm/b = 0. 721 nm (X-ray tube GID) were determined. All length scale parameters w ere calculated with an accuracy of 2.5 percent. For 9 layers of Cd-ara chidate, the correlation length of crystalline domains is greater than that of 25 layers of Ca-arachidate. Furthermore, we introduced a deco nvolution procedure for the correction of the experimental collimation error for this GID set-up. This correction influences mainly the resu lts for the correlation length.