Author : Kathryn Ann Newton
Publisher :
ISBN 13 : 9781392640050
Total Pages : pages
Book Rating : 4.6/5 (4 download)
Book Synopsis Microwave-assisted Synthesis and Ligand Exchange of Germanium and Germanium-tin Alloy Nanoparticles by : Kathryn Ann Newton
Download or read book Microwave-assisted Synthesis and Ligand Exchange of Germanium and Germanium-tin Alloy Nanoparticles written by Kathryn Ann Newton and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Germanium is an indirect band gap semiconductor in Group IV. Ge has a bulk band gap of 0.67 eV and a Bohr radius of 24 nm. Because of its large Bohr radius, Ge nanoparticles (Ge NPs) are quantum confined over a wide size range, and its band gap can be tuned as a function of particle size, composition, or surface passivation. Ge NPs have been achieved by colloidal synthesis routes using convection and microwave-assisted heating methods. The presented work applies microwave-assisted heating to the synthesis and ligand exchange of colloidal Ge NPs and germanium-tin alloy nanoparticles (Ge[subscript 1-x]Sn[subscript x] NPs). Chapter 1 is a brief introduction to Group IV semiconductor nanoparticles. It reviews research in the colloidal synthesis and ligand exchange of Ge and Ge[subscript 1-x]Sn[subscript x] NPs. Chapter 2 demonstrates the synthesis of Ge NPs by the reduction of GeI2 and GeI4 in oleylamine using microwave-assisted heating. The effects of precursor ratio, temperature, and solvent are considered. An optimized ligand exchange procedure, using N2H4 to remove the oleylamine ligand from the surface of Ge NPs, is also presented. In Chapter 3, microwave-assisted methods are applied to the synthesis and ligand exchange of Ge[subscript 1-x]Sn[subscript x] NPs, which are prepared by the reduction of GeI2 and bis[bis(trimethylsilyl)amino]tin(II). It is demonstrated that reaction temperature can be used to control particle size over a narrow Sn composition range. Surface passivation with dodecanethiol is achieved by ligand exchange without loss of Sn composition. Tauc plot analysis of optical absorbance spectra confirm an indirect band gap for Ge[subscript 1-x]Sn[subscript x] NPs. Microwave-assisted heating methods are applied to the reduction of GeI2 in the presence of SiI4 in oleylamine in Chapter 4. The synthesized Ge NPs are observed to increase in size and crystallinity, relative to Ge NPs synthesized without SiI4 in the reaction, as the amount of SiI4 in the reaction is increased. SEM-EDS and STEM-EELS confirm Si is in the nanoparticle ensemble and is localized around the outside of the Ge NPs. Quantum confinement is confirmed by optical spectroscopy, and cyclic voltammetry shows changes in band gap originate from changes in conduction band energy. Additional investigation of the effects of nanoparticle synthesis temperature, solvent, and ligand concentration on ligand exchange are also presented. In Chapter 5, ligand exchange using dioctadecyl disulfide as a ligand precursor is demonstrated in the re-passivation of oleylamine-capped Ge NPs with octadecanethiol. Oleylamine is removed from the surface of Ge NPs by sonication with N2H4. Re-passivation is achieved by stirring solutions of uncapped-Ge NPs, dioctyldecyl disulfide, and diphenylphosphine. Microwave-assisted heating of this solution at 150 °C also achieves re-passivation. Direct ligand exchange methods, in which oleylamine-capped Ge NPs are stirred with dioctadecyl disulfide and diphenylphosphine, are also demonstrated to achieve octadecanethiol passivation. Appendix 1 provides details of additional investigation in the colloidal synthesis of Ge[subscript 1-x]Sn[subscript x] NPs. The reduction of GeI2 and bis[bis(trimethylsilyl)amino]tin(II) in hexadecylamine using microwave-assisted heating is demonstrated to yield alloy NPs with Sn impurities. It is shown that reaction temperature can be used to control Sn composition over a narrow particle size range when GeI2 and bis[bis(trimethylsilyl)amino]tin(II) are reduced in octylamine. The effects of reaction volume were also investigated. The effects of size and morphology of nano tungsten(VI) oxide (WO3) on photocatalytic water oxidation are presented in Appendix 2. Nanodots (32 ± 16 nm), nanoplates (476 ± 98 nm by 58 ± 16 nm), and WO3 microcrystals (~2 [mu]m) were applied as anode materials for the photocatalytic oxidation of water, generating 31.6, 16.5, and 2.9 [mu]mol h-1 O2 (g), respectively. Photoelectrochemistry experiments demonstrate that anodic photocurrent decreases with particle size but little change in photo-onset potential is observed. The one-dimensional continuity model is used to describe trends in photocatalytic activity, which are attributed to minority and majority carrier transport kinetics.