Synthesis of cadmium sulphide in pure and mixed Langmuir-Blodgett films ofn-octadecylsuccinic acid

Cadmium sulphide (CdS) nanoparticles were grown by the reaction of sodium s ulphide (Na2S) with Langmuir-Blodgett (LB) films of cadmium salts of n-octa decylsuccinic acid (ODSU) and with LB films of ODSU in mixtures of octadecy lamine and octadecyl alcohol. The results indicate that heterogeneous nucle ation and aggregation in the pure ODSU LB films due to processes like Ostwa ld ripening are destabilized by the presence of the long-chain amine and al cohol in mixed systems. CdS nanoparticles in the LB films were monitored by UV-visible absorption spectra, which allow an estimation of the size of th e particles. The morphology, size and nature of the nanocrystallites formed depend on whether the sulphidation was done on the pure film or in the mix ed films. It is seen that particles of size around 1.6 nm were formed in OD SU/octadecylalcohol and ODSU/octadecylamine mixed LB films while in pure OD SU films the size was about 2.7 nm. These films showed typical needle-shape d structures, as observed by the optical microscopic technique. Mean size a nd morphology were confirmed by transmission and scanning electron microsco py, while selective area electron diffraction patterns showed six-fold symm etry and indicated that the CdS crystals grow epitaxially with respect to t he monolayer. Further, the crystallisation enhanced in the mixed LB films s howed a characteristic zinc oxide (Wurtzite) structure compared with the pu re ODSU matrix.