Two kinds of cadmium sulfide (CdS) particulate films have been generated in situ by exposing stearic acid (SA) Langmuir monolayer at the air−aqueous CdCl2 interface to hydrogen sulfide (H2S) gas:  particulate films composed of oriented rodlike nanocrystals (A-type particulate films), and those of dotlike nanocrystals which formed a stripelike domain with straight edges aligned with 6-fold symmetry (B-type particulate films). The SA- coated CdS particulate films were transferred to a solid substrate and examined by transmission electron microscopy (TEM) and photoacoustic spectroscopy (PAS). The dark field image and the transmission electron diffraction of the TEM were used to study the morphology and growth mechanisms of the CdS particulate films in detail. The PAS of the CdS particulate films composed of the oriented rodlike nanocrystals shows a new peak at 417.5 nm. This peak implies some new physical phenomena corresponding to the ordered alignment of the semiconductor nanocrystals, which exists in the ordered nanosystems. The novel synthesis method described here leads to the fabrication of the highly oriented semiconductor quantum wires and provides a new method to investigate the structure of the Langmuir monolayer at the air−water interface.

Cadmium sulfide (CdS) particulate films, composed of highly oriented, rod-like nanocrystals have been generated in 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 101´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 of CdS nanocrystals. This leads to a novel means of fabrication of highly oriented semiconductor quantum wires.