Effects of Surface and Chemical Composition on the Charge Carriers of Alloyed Quantum Dots
Keene, Joseph Daniel
The surface chemistry of nanocrystals of different semiconductor materials is characterized by nuclear magnetic resonance spectroscopy and the charge carrier dynamics of graded alloy quantum dots are investigated. The native oleic acid ligands of CdSe nanocrystals are modified via a two-step, post-synthetic procedure and replaced with pyridine-functionalized semiconductor polymer poly(3-hexylthiophene). The ligation of the polymer is characterized via 1H nuclear magnetic resonance spectroscopy. The ligands bound to CuxInyS2 nanocrystals are investigated with 1H, 31P, and 14N nuclear magnetic resonance spectroscopy and enables determination of the cause of the plasmonic modes of these nanocrystals. Both plasmonic and non-plasmonic CuxInyS2 nanocrystals possess the same surface chemistry, which implicates the differing cation stoichiometry between the nanocrystals as the cause of the plasmonic modes. The structural characterization, femtosecond fluorescence upconversion spectroscopy, and analysis of the ultrafast carrier dynamics of graded alloy CdSxSe1-x nanocrystals are presented. The heterogeneous chemical composition alters the band structure within the nanocrystals to prevent excited charge carrier (hole) overlap with the surface of the nanocrystals. This elimination of the excited hole-surface overlap inhibits hole trapping at the nanocrystal surface and results in enhanced optical properties of the quantum dots.