Solid-solution of Cd(formula)Zn(formula)S nanocrystals in the channels of mesostructured silica films

Abstract

Mesostructured silica can be used as a reaction medium to produce solidsolution of Cd1-xZnxS nanocrystals as thin films. These films were synthesized from oligo(ethylene oxide) non-ionic surfactant (CH3(CH2)11(OCH2CH2)10OH, (C12EO10)), cadmium and zinc nitrate salts ([Cd(H2O)4](NO3)2 and [Zn(H2O)6](NO3)2), water, and tetramethylorthosilicate (TMOS, as silica source) mixtures using a liquid crystalline templating (LCT) approach and metal containing liquid crystalline (MLC) mesophase. Metal ion to surfactant mole ratio was 1.0 which determines the stability and structure of the mesostructured silica. The mesostructured silica film has a 3D hexagonal structure with oriented channels. The silica pore size can be controlled by controlling ageing temperature and time. The pore diameter of the silica channels that aged at room temperature (RT) for two days is 4.7 nm and the one aged at 2500 C for 30 minutes is 3.3 nm. Cd(II) and Zn(II) incorporated film samples can be reacted at RT under H2S atmosphere to produce zinc blend, Cd1-xZnxS nanocrystals (nano-Cd1-xZnxS-meso-SiO2) in the channels of the mesostructured silica. The band gaps of the nano-Cd1- xZnxS-meso-SiO2 vary between 2.6 eV for CdS and 4.1 eV for ZnS. The Cd (II) rich nanoparticles are larger (4.4 nm) than Zn (II) rich nanoparticles (3.1 nm). The silica wall thickness that can be controlled by ageing at different temperatures confines the growth of the Cd1-xZnxS nanocrystals in the pores. By controlling the size of the silica channel between 4.7 and 3.3 nm, one can control the band-gap of the CdS nanocrystals between 2.6 and 2.8 eV.