Preparation and Characterization of Quantum-Sized PbS Grown in Amphiphilic Oligomer Langmuir−Blodgett Monolayers

Abstract

Three kinds of amphiphilic oligomers, poly(maleic acid) with octadecanol ester (PMAO) with 2.0:1, 3.7:1, and 6.0:1 between the carboxylic groups and the hydrocarbon chains, were synthesized and have been used as a matrix to form and grown the quantum-sized PbS. Pure Y-type PbPMAO Langmuir−Blodgett (LB) films were prepared at a dipping speed of 4.0 cm/min and surface pressure of 18 mN/m. The results from Fourier tranform IR spectroscopy and X-ray diffraction measurements showed that an ordered structure was obtained from the PbPMAO LB films. The quantum-sized PbS particles were prepared by exposure of PbPMAO LB films to H2S and nanoparticulate PbS monolayers were formed without destroying the layered structure. The result from structured UV−vis absorption spectra shows that the PbS particles within the LB matrix are relatively monodispersed. It was found that the PbS within PMAO LB films indicated a larger blue shift of the optical absorption edge with the decrease of the ratio between the carboxylic groups and the hydrocarbon chains. Meanwhile, it can be deduced that the size of the aggregate of the sulfides within PMAO LB films is smaller than that formed in stearic acid LB films. The observed absorption peaks showed similarity with the monomolecular PbS.