Preparation of oriented cadmium sulfide nanocrystals

Abstract

Cadmium sulfide (CdS) particulate films, composed of highly oriented, rod-like nanocrystals have been generatedin situ by the exposure of stearic acid (SA) Langmuir monolayer-coated aqueous CdCl ₂ solutions to hydrogen sulfide (H ₂ S). The SA-coated CdS particulate films were transferred to a solid substrate and examined by transmission electron microscopy (TEM) and Auger electron energy spectroscopy. It was found for the first time that the electron diffraction pattern was a composite one with six sets of diffraction patterns which were contributed by the different oriented CdS nanocrystals in these particulate films system. The epitaxial growth of rod-like CdS nanocrystals has been rationalized in terms of matching the d ₂₂₀ spacing of the cubic CdS crystals and the d ₁₀₀ spacing of the hexagonal closed-packed SA monolayer. The presence of a negatively charged monolayer at the air/water interface was an essential requirement for the oriented growth of CdS nanocrystals. This leads to a novel means of fabrication of highly oriented semiconductor quantum wires.