STRUCTURE OF CDS-CD-ARACHIDATE ARACHIDIC ACID COMPOSITE MULTILAYERS/

A composite multilayer consisting of semiconducting CdS distributed in Cd-arachidate/arachidic acid layers was prepared by exposing the prec ursor Cd-arachidate multilayers to H2S. The structures of the precurso r multilayers and the modified multilayers were studied by grazing inc idence reflection/diffraction using X-rays from a conventional generat or and a synchrotron source. The formation of CdS in arachidic acid/Cd -arachidate composite multilayers resulted in the introduction of a ne w layered structure with a period of 4.37 nm compared to the precursor multilayer period of 5.55 nm. The reduction in the period of the mult ilayers is consistent with the observation of a tilted structure found in alkanethiol and H2S exposed Cd-stearate multilayers. The lateral m orphology of CdS which is replicated between the successive layers in the vertical direction is different when compared to the head group mo rphology in the precursor multilayer. The molecular arrangement in the plane of the Cd-arachidate precursor multilayer is found to be orthor hombic while the CdS molecules in the modified multilayer are arranged in a hexagonal array. The lateral size of the CdS domains/particles i s found to be similar to 13 nm, at least an order of magnitude greater than the layer thickness. This clearly indicates that the CdS particl es are quasi-2D in nature and are disk shaped.