Probing CdS Nanocrystal Surfaces with Laser-Polarized Xenon

Abstract

This paper describes the application of optically pumped xenon NMR to probe the surface of semiconductor nanocrystals by physisorption at 123 K. These experiments were made possible by using highly spin ordered [sup 129]Xe, prepared by optical pumping and spin exchange of a rubidium xenon gas mixture, to increase the NMR signal strength. CdS nanocrystals were prepared by regulated growth in inverse micelles and precipitated by surface derivatization with thiophenol. Nanocrystals of 11.8, 12.8, and [angstrom] radii with 26%, 63%, and 57% thiophenol surface coverage, respectively, were characterized. Within this sample parameter space, the [sup 129]Xe spectra, recorded at varying xenon coverages, depended strongly on thiophenol surface coverage but were not sensitive to the crystallite size. In addition, the nanocrystals with low thiophenol coverage yielded a xenon line shape consisting of two components, interpreted as xenon signals arising from district surface domains. 23 refs., 4 figs., 1 tab.