The Low-Temperature Redox-Assisted Seeded Growth of CdSe Nanocrystals

Date of Completion

January 2011

Keywords

Chemistry, Inorganic|Chemistry, Polymer|Engineering, Materials Science

Degree

Ph.D.

Abstract

Semiconducting CdSe nanocrystals (NCs) are a unique class of materials that exhibit properties that are dependant on their size, morphology and composition. When the radius of a nanocrystal is decreased below its Bohr exciton radius, the nanocrystal exhibits quantum confinement, and the bandgap of the material increases as the radius decreases. When the morphology of a NC is changed from a zero-dimensional quantum dot (QD) to a one-dimensional quantum rod (QR), the material begins to show new properties such as the emission of polarized light and switching behavior in electric fields. Synthesis of QRs is not trivial, however, and to date a number of different approaches have been developed using an initial QD which acts as a seed for further rod growth. One such method of this seeded growth of QRs is the low-temperature redox-assisted growth of NCs in 9:1 3-amino-1-propanol:water mixtures. By tuning the concentration of dissolved O2 in 9:1 3-amino-1-propanol:water, the growth of NCs can be directed along the NCs c-axis at high O2 concentrations, and can proceed in three dimensions when the concentration of O2 is reduced. This occurs because of selective O2 passivation of the nonpolar NC facets while on the polar facets remain relatively unpassivatcd. By adding different precursors to the NC growth solution, the growth can be further tuned to produce high aspect ratio rods or promote large scale three dimensional growth. Low-temperature, redox-assisted growth can also be used to fabricate both one-dimensional rod and three-dimensional core-shell heterostructures. Finally, this growth method can be tuned to fuse NCs in a film that is deposited on a substrate, which has profound implications for devices such as photovoltaics.^ The role of O2 on directing seeded CdSe NC growth, as well as the fabrication of one-dimensional CdSe/CdxHg1−x Se heterostructures, is described in Chapter 2 of this dissertation. The role of the anionic precursor is explored in Chapter 3 of this dissertation, which can lead to the fabrication of a CdSeCdSexTe1−x core-shell heterostructure, which is reported in Chapter 4. Finally, the deposition and growth of CdSe films, including NC fusion is reported in Chapter 5. The use of this technology to fabricate a crude Grätzel-type of photovoltaic is also reported in Chapter 5, highlighting the general applicability of the low-temperature, redox-assisted growth of CdSe NCs.^

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