Electrodeposition of nanostructures by electrochemical atomic layer epitaxy (EC-ALE)
Mathe, Mahlanyane Kenneth
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An automated flow deposition system was used in the electrodeposition of II-VI and IV-VI thin films and nanostructures by electrochemical atomic layer epitaxy (EC-ALE). The II-VI compounds studied were CdSe, HgSe, CdSe/HgSe and HgTe. PbSe thin films and PbTe/PbSe nanostructures were the IV-VI compounds studied. Cyclic voltammograms were used to establish a range of underpotential (upd) deposition potentials for all the systems presented here in these studies. EC-ALE exploits the use of surface limited reactions, underpotential deposition (upd) to deposit thin films one layer at a time on Au substrates. Upd is a well-documented phenomenon in which one element deposits onto another element at a potential prior to (under) that necessary to deposit the element onto itself. The resulting deposit is limited to an atomic layer. CdSe thin films were studied to optimize the deposition program and simplify the precursor solutions. 200 cycle deposits were formed with reproducibility and were characterized by: X-ray diffraction (XRD) for the crystal structure and Atomic Force Microscopy (AFM) for the morphology. Electron Probe Microanalysis (EPMA) was used to determine the stoichiometry, with deposit thicknesses measured by Ellipsometry. The bandgap were determined by ultraviolet spectroscopy (UV-VIS), photoconductivity, or absorption (FTIR) measurements. Other compounds formed were also characterized, FT-IR only, plus EPMA, XRD and AFM. PbSe thin films were modeled for quantum confinement using effective mass approximations for the hyperbolic and parabolic band models. The dependence of the bandgap on the thickness of the films was described as well.