Investigation of the Nucleation and Growth of Colloidal Indium Phosphide: from Molecular Precursors to Semiconductor Nanocrystals through In37P20(O2CR)51 as a Magic-Size Intermediate

Thesis (Ph.D.)--University of Washington, 2016-06

Semiconductor nanocrystals have drawn a considerable amount of interest in recent decades from both academia and industry. These crystallites possess a unique property in which the energy of electromagnetic radiation absorbed and/or emitted by the crystallites is inversely correlated with the particle’s size. This phenomenon (dubbed the quantum confinement effect) is immediately integrable with current downconversion technology employed in LCD displays. Substitution of the traditional yttrium aluminum garnet (YAG) phosphors, employed in such displays, with red and green emitting nanocrystals offers superior energy efficiency and a wider color palette. In order to attain such enhancements, the nanocrystals employed require minimal size disparity. Cadmium selenide (CdSe) nanocrystals are the preferred choice for such displays as their syntheses have matured to afford nearly monodisperse samples across a wide range of sizes. The toxicity of cadmium, however, poses a serious health and environmental risk as well as a barrier to further commercialization. Indium phosphide (InP) stands as the ideal candidate to replace current cadmium based nanocrystals since indium is relatively benign and InP possesses a bulk bandgap that would enable tuning across a wide region of the electromagnetic spectrum through the quantum confinement effect. Attempts to adapt the synthetic techniques which have been proven successful for cadmium based nanocrystal have failed to produce an InP sample with size distributions narrow enough to be competitive. This thesis discusses insights into the nucleation and growth of InP nanocrystals which should prove a valuable resource in rationally designing syntheses of InP with more narrow size distributions. After a brief introduction on the topic, chapter 2 discusses the protonolysis of the P3– precursor, P(Si(CH3)3)3, along with the impact this reaction has on the nucleation and growth of InP. Chapter 3 investigates the effect of precursor conversion kinetics on the final particle size and size distribution. In chapter 4, a magic-size cluster is implicated in the inherent difficulty of temporally separating nucleation and growth. The physical structure and electronic properties of the cluster identified in chapter 4 are discussed in chapter 5 as determined by X-ray crystallography and DFT calculations. Finally, chapter 6 investigates the role of primary amines on surface chemistry and thermal stability of magic-size clusters in an attempt to consolidate conflicting literature reports on the effect of primary amines on precursor conversion kinetics.