Semiconductor nanocrystals covalently bound to metal surfaces with self-assembled monolayers

TLDR: In this paper, a method for attaching semiconductor nanocrystals to metal surfaces using self-assembled difunctional organic monolayers as bridge compounds is described, and three different techniques are presented.

Abstract: A method is described for attaching semiconductor nanocrystals to metal surfaces using self-assembled difunctional organic monolayers as bridge compounds. Three different techniques are presented. Two rely on the formation of self-assembled monolayers on gold and aluminum in which the exposed tail groups are thiols. When exposed to heptane solutions of cadmium-rich nanocrystals, these free thiols bind the cadmium and anchor it to the surface. The third technique attaches nanocrystals already coated with carboxylic acids to freshly cleaned aluminum. The nanocrystals, before deposition on the metals, were characterized by ultraviolet-visible spectroscopy, X-ray powder diffraction, resonance Raman scattering, transmission electron microscopy (TEM), and electron diffraction. Afterward, the nanocrystal films were characterized by resonance Raman scattering, Rutherford back scattering (RBS), contact angle measurements, and TEM. All techniques indicate the presence of quantum confined clusters on the metal surfaces with a coverage of approximately 0.5 monolayers. These samples represent the first step toward synthesis of an organized assembly of clusters as well as allow the first application of electron spectroscopies to be completed on this type of cluster. As an example of this, the first X-ray photoelectron spectra of semiconductor nanocrystals are presented. 51 refs., 17 figs.