On the deposition of Langmuir-Blodgett films of Q-state CdS nanoparticles through electrostatic immobilization at the air-water interface

Abstract

The deposition of ordered multilayer Langmuir-Blodgett films of carboxylic acid derivatized Q-state CdS nanoparticles through electrostatic interaction with octadecyl amine Langmuir monolayers is demonstrated in this communication. The degree of nanoparticle incorporation into the Langmuir monolayer can be controlled by varying the charge on the amine molecules through the colloidal subphase pH. Pressure-area isotherms were used to follow the adsorption of the Q-state colloidal CdS particles at the amine surface while quartz crystal microgravimetry (QCM), optical absorption spectroscopy and ellipsometry were used to characterize the multilayer LB films. The films were found to grow in the classical γ-type mode. Ellipsometry measurements indicated a bilayer thickness of 8.2 nm which yields a cluster size of 3.2 nm, in reasonable agreement with a mean cluster size of ∼3.5 nm determined from the position of the band edge obtained from optical absorption measurements. Incorporation of clusters into inorganic matrices as outlined in the communication shows promise for the growth of superlattice structures, mixed cluster systems, etc., which are not realizable by currently-used experimental methods.