A hybrid electrochemical/chemical synthesis of supported, luminescent cadmium sulfide nanocrystals

A hybrid electrochemical/chemical (E/C) method is employed to synthesize epitaxially oriented CdS nanocrystallites - size selectively - on graphite surfaces. The E/C synthesis involves three steps: (1) cadmium metal nanocrystals (NCs) are electrochemically deposited on the graphite basal plane surface; (2) cadmium NCs are oxidized at high pH to Cd(OH)(2); (3) upon immersion of the Cd(OH)(2) NCs in an aqueous sulfide solution, displacement of OH- by S2- occurs yielding wurtzite phase NCs of the semiconducting salt, cadmium sulfide. Dispersions of E/C-synthesized CdS nanocrystallites having mean diameters ranging from 20 to 80 Angstrom were prepared and characterized using noncontact scanning force microscopy, transmission and high-resolution electron microscopy, selected area electron diffraction, and micrometer-scale spatially resolved photoluminescence spectroscopy. It is demonstrated that individual CdS nanocrystals ate oriented with the c-axis of the crystallite perpendicular to basal plane (i.e. (0001)), and NCs located within the boundaries of a single grain on the graphite basal plane possess identical azimuthal orientations. Photoluminescence spectra reveal transitions that are assigned to band gap and surface trap states.