Surface Modification of II-VI Semiconducting Nanocrystals

This dissertation presents the compositional analysis of semiconductor materials by inductively coupled plasma optical emission spectroscopy (ICP-OES), a novel low-temperature shell growth precursor and installation pathway, and L-type for Z-type ligand exchange experiments conducted with four metal dithiocarbamate ligands. The techniques employed in the compositional analysis of semiconductor materials by inductively coupled plasma optical emission spectroscopy (ICP-OES) have a profound influence on the accuracy and reproducibility of the results. In Chapter 3, we describe methods for sample preparation, calibration, standard selection, and data collection. Specific protocols are suggested for the analysis of II-VI compounds and nanocrystals containing the elements Zn, Cd, S, Se, and Te. In Chapter 4, cadmium bis(phenyldithiocarbamate) [Cd(PTC)2] is prepared and structurally characterized. The compound crystallizes in the monoclinic space group P21/n. A one-dimensional polymeric structure is adopted in the solid state, having bridging PTC ligands and 6-coordinate pseudo-octahedral Cd atoms. The compound is soluble in DMSO, THF, DMF, and insoluble in EtOH, MeOH, CHCl3, CH2Cl2, and toluene. {CdSe[n-octylamine]0.53} quantum belts and Cd(PTC)2 react to deposit epitaxial CdS shells on the nanocrystals. With an excess of Cd(PTC)2, the resulting thick shells contain spiny CdS nodules grown in the Stranski-Krastanov mode. Stoichiometric control affords smooth, monolayer CdS shells. A base-catalyzed reaction pathway is elucidated for the conversion of Cd(PTC)2 to CdS, which includes phenylisothiocyanate and aniline as intermediates, and 1,3-diphenylthiourea as a final product. Chapter 5 investigates the exchange of n-alkylamine ligands on the surface of {CdSe[n-octylamine]0.53} quantum belts with four metal dithiocarbamate compounds: zinc n,n-diethyldithiocarbamate (Zn(Et2DTC)2), zinc n-methyl-n-phenyldithiocarbamate (Zn(MePhDTC)2), cadmium n,n-diethyldithiocarbamate (Cd(Et2DTC)2, and cadmium n-methyl-n-phenyldithiocarbamate (Cd(MePhDTC)2). Direct exchange of L-type n-alkylamine for M(DTC)2 failed to follow trends established in other L-type for Z-type ligand exchange experiments. Experiments to test the exchange of n-alkylamine for Z-type Cd(oleate)2 for Z-type M(DTC)2 followed. The reasons for differences in ligand exchange experiments conducted with M(DTC)2s and other Z-type ligands are discussed in detail