SYNTHESIS OF SIZE-CONFINED METAL SULFIDES IN LANGMUIR-BLODGETT-FILMS

Size-confined sulfides of lead, zinc and copper as well as a mixture of cadmium and lead sulfides have been synthesized in Langmuir-Blodgett (LB) matrices by the repeated processes of sulfidation, by exposing the metal ion-binding LB films to a flow of H2S gas, and intercalation, by immersing the metal sulfide-bearing LB films into an aqueous solution of the corresponding metal ion. Quantum state PbS and ZnS were formed and grown stepwise in the stearate LB films. The interconversion of carboxylate groups between ionic and acidic forms played a key role in the stepwise growth of the metal sulfides. For the synthesis of copper sulfide, however, the stearate LB matrix was unavailable owing to the instability of a copper stearate LB film, but copper sulfide, possibly Cu2S, was successfully synthesized in an n-octadecylacetoacetate LB film in which the interconversion between the beta-ketonic and enolic forms was responsible for the binding and release of CU2+ ions. When the CdS-bearing stearate LB film was subjected alternately to intercalation of Pb2+ and sulfidation, it was suggested that PbS was formed and grown on the surface of the preformed CdS.