PREPARATION OF ORIENTED CADMIUM-SULFIDE NANOCRYSTALS

Cadmium sulfide (CdS) particulate films, composed of highly oriented, rod-like nanocrystals have been generated in situ by the exposure of s tearic acid (SA) Langmuir monolayer-coaled aqueous CdCl2 solutions to hydrogen sulfide (H2S). The SA-coated CdS particulate films were trans ferred to a solid substrate and examined by transmission electron micr oscopy (TEM) and Auger electron energy spectroscopy. It was found for the first time that the electron diffraction pattern was a composite o ne 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 rationali zed in terms of matching the d(220) spacing of the cubic CdS crystals and the d(<10(1)over bar 0>) 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 o f CdS nanocrystals. This leads to a novel means of fabrication of high ly oriented semiconductor quantum wires.