Surface Activity of Highly Hydrophobic Surfactants and Platelike PbSe and CuSe Nanoparticles

Lead selenide (PbSe) and copper selenide (CuSe) nanoparticles were synthesized in aqueous phase at a relatively mild temperature (85 °C) in the presence of various cationic Gemini surfactants (12−2−12, 12−0−12, and 16−2−16) as capping/stabilizing agents. All nanoparticles exhibited clear core−shell (surfactant) morphologies. PbSe reactions produced predominantly platelike cubic morphologies along with long Se nanorods (NRs) as a reaction byproduct. CuSe particles were polyhedral thin plates with perforations. High resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), and X-ray diffraction (XRD) measurements were used to characterize the shape and structure of the particles. HRTEM allowed us to measure the precise thickness of the surfactant shell around each nanocrystal (NC) which was in excellent agreement with the length of the surfactant hydrocarbon tail. Infrared spectroscopic (FT-IR) studies suggested a strong affinity of cationic surfactant for NC surface which was the driving force for the monolayer formation in the form of a shell. Energy dispersive X-ray spectroscopic (EDS) analysis demonstrated that PbSe and CuSe particles were always in 1:1 stoichiometry, and Se NRs were made up of only pure Se and no Pb contents were observed. Stronger interfacial adsorption of a surfactant with greater hydrophobicity controlled the morphology to produce platelike geometries. The size of PbSe and CuSe particles increased while the thickness decreased as the hydrophobicity of the surfactant increased in the order of 12−2−12 < 12−0−12 < 16−2−16.