Formation of CdS and HgS nanoparticles in LB films

Langmuir-Blodgett (LB) films were constructed on hydrophobic quartz substra tes from monolayers of behenic acid on subphases containing only Cd2+ or Hg 2+ and containing a mixture of Cd2+ and Hg2+ ions. The reaction of these fi lms with H2S to form metal sulphide particles was investigated using UV/vis ible spectroscopy and X-ray photoelectron spectroscopy (XPS). For the mixed metal ion system it was concluded that reaction with H2S results in indivi dual CdS and HgS particles forming rather than a mixed cadmium mercury sulp hide. In order to investigate the kinetics of the H2S reaction, the frequen cies of MBe (M = Cd or Hg) coated quartz crystal microbalances were followe d as a function of H2S exposure time. Immersion of CdS particles into a Hg2 + solution resulted in a change in the UV-visible absorbance spectrum attri buted to the exchange of Cd2+ ions in the particles for Hg2+ ions most like ly resulting in a HgS layer around the CdS core. (C) 1999 Elsevier Science B.V. All rights reserved.