Date of Award

Winter 12-15-2014

Author's School

Graduate School of Arts and Sciences

Author's Department

Chemistry

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

The main objective of this project is to prepare and isolate the smallest, discrete, magic-size nanoclusters of cadmium selenide (CdSe) and to grow crystalline, wurtzite CdSe quantum platelets (QPs) at room temperature. The achievement of these goals enables us to provide a general synthesis of II-VI semiconductor magic-size nanoclusters and low-temperature routes to well-passivated nanocrystals having a range of compositions and morphologies.

The magic-size nanocluster (CdSe)13 is grown in a lamellar-bilayer soft template at room temperature. The results described in this thesis strongly suggest that [(CdSe)13(n-octylamine)13] is the most thermodynamically stable nanocluster and serves as a key intermediate in the formation of CdSe quantum belts. Upon ligand exchange, sheet-like structures of [(CdSe)13(n-octylamine)x(oleylamine)13-x] and free clusters of [(CdSe)13(oleylamine)13] are released from the template. The kinetically stabilized magic-size nanolcusters prefer to grow to larger sizes once the steric protection of the primary-amine ligation is compromised by small-ligand substitution.

Several discrete [(CdSe)13(RNH2)13] derivatives (R = n-propyl, n-pentyl, n-octyl, and oleyl) are prepared in the corresponding primary amine solvent. For the first time, the soft-template method has been employed on the gram scale to prepare pure (CdSe)13 as a solid, isolable derivative. This achievement enables us to study the intrinsic physical properties of (CdSe)13, like size and melting points. The access to preparative quantities of (CdSe)13 will promote further experimental studies of its structure, reactivity, and use as a nanocrystal precursor.

A novel method is introduced to synthesize crystalline wurtzite, two-dimensional CdSe quantum platelets (QPs) by employing primary amine and secondary amine cosolvent mixtures. This is the first preparation of thickness-controlled CdSe nanocrystals under mild conditions. The thickness of the QPs is dependent on temperature, and the length is affected by the nature of secondary amine. Reaction monitoring establishes that the magic-size nanocluster (CdSe)34 is a key intermediate in the formation of the QPs. [(CdSe)34(n-octylamine)16(di-n-pentylamine)2] is isolated, which functions as critical size crystal nuclei that may be stored in a bottle.

Language

English (en)

Chair and Committee

William E. Buhro

Committee Members

Richard A. Loomis, Liviu Mirica, Bryce Sadtler, Li Yang

Comments

Permanent URL: https://doi.org/10.7936/K78P5XN6

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