SCANNING-TUNNELING-MICROSCOPY, TUNNELING SPECTROSCOPY, AND PHOTOELECTROCHEMISTRY OF A FILM OF Q-CDS PARTICLES INCORPORATED IN A SELF-ASSEMBLED MONOLAYER ON A GOLD SURFACE

Films of AOT-capped (AOT = dioctyl sulfosuccinate) cadmium sulfide nan oparticles (Q-CdS) prepared by incorporation into a self-assembled mon olayer (SAM) of hexanethiol on Au were prepared. These were imaged at negative substrate bias in air by scanning tunneling microscopy, and Q -CdS particles were shown to cover most of the area on the SAM. Contin uous scanning of the tip over the substrate removed Q-CdS particles to the outside of the scanning area because of tip-substrate interaction s. Scanning tunneling spectroscopy was carried out in air with the tip held over the thin CdS film (100 nm) and over individual Q-CdS partic les in the layer. The i vs V and di/dV vs V curves indicated that the energy band gap of the Q-CdS particles is wider than that of the thin CdS films. The results of photoelectrochemistry also indicated that th e onset photopotential is more negative for smaller Q-CdS particles an d is related to the level of conduction band.