Synthesis, Surface Functionalization and Application of Group 14 Nanomaterials

• Author / Creator

  JavadiCharani, Morteza

• The elements of Group 14 show an extensive range of chemical behaviors. Lying at the boundary between metals and non-metals, some members of Group 14, namely silicon and germanium, are intermediate in their properties. These semiconductors are extremely important in science and technology. Si, Ge, SixGe1-x, and corresponding compounds (e.g., oxides and carbides) hold potential for far-reaching modern impacts and numerous optoelectronic applications. The discovery of size-dependent optical responses from nanostructures of these semiconductors has opened new avenues for further studies and enhanced their potential for various uses. Although Si-based nanostructures (e.g., Si nanocrystals and porous-Si) have been widely studied, Ge-based nanostructures have received significantly less attention, presumably because of their complex chemistry and the lack of convenient/predictable methods for their preparation. In this context, germanium dioxide nanoparticles (GeO2 NPs) of varied sizes and morphologies were prepared via facile sol-gel synthesis without the addition of surfactant (Chapter two). Morphology control was readily achieved by tailoring the water/ethanol ratio in the reaction mixture. Through judicious tailoring of reaction parameters, surfactant-free crystalline GeO2 nano-cubes and nano-eggs exhibiting currently unparalleled narrow size distributions were obtained. After that, tetraethoxysilane (TEOS) based sol-gel reactions were used to form a robust shell of Stöber SiO2 around previously prepared GeO2 NPs and form GeO2@SiO2 core-shell nano-cubes or nano-eggs (Chapter three). Subsequently, the core and the shell of these NPs were selectively reduced by 5% H2/95% Ar and elemental magnesium to yield Ge@SiO2 and Ge@Si core-shell NPs, respectively. In the fourth and fifth chapters, we turned our attention to the synthesis of germanium nanocrystals (GeNCs) with well-defined surface chemistry. This research area is of considerable interest because of the attractive optoelectronic properties of GeNCs with sizes smaller than the germanium Bohr-exciton radius (i.e., <24 nm). In the Chapter four, we reported a straight-forward route for synthesizing GeNCs in high-yield and also clarified some chemistry regarding the Ge (II) precursor. Both the precursor and procedure were modified to yield GeNCs of various morphologies. Modifying and tailoring GeNC surface chemistry was the subject of the fifth Chapter, due to the important role of surface functionalization in solubility and stability of GeNCs. In this context, hydride-terminated GeNCs (H-GeNCs) were freed from their germania matrices by chemical etching of the GeNC/GeO2 composite and were then derivatized using a series of hydrogermylation approaches (i.e., thermally-activated, radical-initiated, and borane-catalyzed). We found that surface functionalization occurred under all conditions investigated; however, the nature of the surface species (i.e., monolayers vs. multilayers) and surface coverage varied depending on the conditions employed. Application of functionalized NCs is the subject of sixth Chapter. The nanostructures of Group 14 semiconductors are well suited for use in biological systems due to their biocompatibility and fairly low toxicity compared to typical quantum dots such as CdSe. The size/surface dependent optical response of Si nanocrystals (SiNCs) is well-known and more developed than GeNCs. Therefore, we chose acid-functionalized SiNCs as the pioneer for making nano-hybrids with Fe3O4 NPs. We demonstrated proof-of-concept confocal cell imaging using these magnetic nano-hybrids. Finally, Chapter seven summarises what has been achieved for each Chapter of current Thesis. The aim of this Chapter is to provide a summary for synthesize and surface functionalization of Group 14 semiconductors nanomaterials and outline some possible future direction for continuing this Thesis.

• Subjects / Keywords

  • Germanium
  • Group 14 Semiconductors
  • Nanoparticles
  • Silicon

• Graduation date

  Fall 2017

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3S46HP0T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.