A HYBRID ELECTROCHEMICAL CHEMICAL SYNTHESIS OF ZINC-OXIDE NANOPARTICLES AND OPTICALLY INTRINSIC THIN-FILMS/

A hybrid electrochemical/chemical (E/C) synthesis of zinc oxide (ZnO) nanoparticles and films is described. The E/C procedure involves two s teps: Zinc metal was first electrochemically deposited at basal-plane oriented graphite electrode surfaces from dilute aqueous solutions; th en this deposit was permitted to spontaneously oxidize and dehydrate a t open circuit in the pH = 1.0 plating solution. Deposition was size-s elective, and wurtzite phase ZnO nanocrystallites having mean diameter s in the range from 15 to 100 Angstrom were obtained using this approa ch. Relative standard deviations of the particle diameter for ZnO part icle dispersions varied from 25 to 50%. Polycrystalline ZnO films of 1 00-400 Angstrom in thickness were also obtained by depositing larger q uantities of zinc metal in the first step of the synthesis. For ZnO pa rticles (dia. < 80 Angstrom), electron diffraction analysis revealed a preferred orientation for ZnO crystallites where the c-axis of the wu rtzite unit cell was oriented perpendicular to the plane of the graphi te surface, but X-ray powder diffraction data indicated that this orie ntational preference was lost when larger quantities of zinc were depo sited and ZnO films were obtained. Luminescence spectra for the ZnO fi lms prepared using this E/C method consisted of a single exciton band near 3.2 eV at room temperature with no deep trap state emission. At l ow temperatures (20 K), this exciton band split into a cleanly resolve d and fully assignable phonon loss progression.