Ma. Anderson et al., A HYBRID ELECTROCHEMICAL CHEMICAL SYNTHESIS OF SUPPORTED, LUMINESCENTCADMIUM-SULFIDE NANOCRYSTALS/, JOURNAL OF PHYSICAL CHEMISTRY B, 101(31), 1997, pp. 5895-5899
A hybrid electrochemical/chemical (E/C) method is employed to synthesi
ze epitaxially oriented CdS nanocrystallites - size selectively - on g
raphite surfaces. The E/C synthesis involves three steps: (1) cadmium
metal nanocrystals (NCs) are electrochemically deposited on the graphi
te 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 NC
s of the semiconducting salt, cadmium sulfide. Dispersions of E/C-synt
hesized 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 r
esolved photoluminescence spectroscopy. It is demonstrated that indivi
dual 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 iden
tical azimuthal orientations. Photoluminescence spectra reveal transit
ions that are assigned to band gap and surface trap states.