The objectives of this thesis were to optimize the synthesis and surface coating of metallic and semiconductor nanoparticles, to understand how these materials interact with cells and physiological systems and to investigate how they can be used to deliver thermal therapy for medical applications. Reproducible high-yield synthesis of gold nanorods and surface coating with a variety of polymers and silica was optimized. Using gold nanorods as a model system, the relationship between particle surface chemistry, surface charge and cellular uptake was studied, as well as the toxicity of nanoparticles of different surface chemistry. Low toxicity in vitro was encouraging and was confirmed in vivo by intravenously injecting Sprague-Dawley rats with semiconductor quantum dots of various surface coatings. Low toxicity was found during biochemical, haematological and pathological assessment, and these results indicate that applications of nanoparticles should be further investigated. One such application is the use of near infrared absorbing gold nanorods in remotely activated hyperthermia. It was shown that gold nanorods act synergistically with the chemotherapeutic cisplatin to improve cytotoxicity, and reduce the required cytotoxic drug dose to 33% of the unheated amount. Due to the success of hyperthermia treatment in vitro, continuing and future work involves the use of gold nanorods ex vivo on excised human corneas in a novel application to weld corneal tissue for improved wound closure following cataract surgery.

Ruthenium oxide (RuO2) nanorods are an emergent technology in nanostructure devices. As the physical size of electronics approaches a critical lower limit, alternative solutions to further device miniaturization are currently under investigation. Thin-film nanorod growth is an interesting technology, being investigated for use in wireless communications, sensor systems, and alternative energy applications. In this investigation, self-assembled RuO2 nanorods are grown on a variety of substrates via a high density plasma, reactive sputtering process. Nanorods have been found to grow on substrates that form native oxide layers when exposed to air, namely silicon, aluminum, and titanium. Samples were analyzed with Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) techniques. Conductive Atomic Force Microscopy (C-AFM) measurements were performed on single nanorods to characterize structure and electrical conductivity. The C-AFM probe tip is placed on a single nanorod and I-V characteristics are measured, potentially exhibiting rectifying capabilities. An analysis of these results using fundamental semiconductor physics principles is presented. Experimental data for silicon substrates was most closely approximated by the Simmons model for direct electron tunneling, whereas that of aluminum substrates was well approximated by Fowler-Nordheim tunneling. The native oxide of titanium is regarded as a semiconductor rather than an insulator and its ability to function as a rectifier is not strong. An electronic model for these nanorods is described herein.

In this study, samples of nanoscale structures of nickel (Ni) nanorods were prepared using the glancing angle deposition (GLAD) technique. Annealing was done using a split- top tube furnace at high vacuum chamber pressure. The pre-melting of the nanorods was maintained at 500 °C for 30 minutes in all the samples. Using the samples with 90 minutes of GLAD time, the annealing behavior of the nanorods was studied at 300 °C, 400 °C, 500 °C and 600 °C. The nanorods were then imaged using scanning electron microscopy. Using X-ray diffraction, the crystalline microstructures of the nanorods were studied. It was found that with increasing annealing temperatures, the intensity of peaks for both Ni (111) and Ni (200) increased, which indicates that better crystals were formed. The results indicate that re-crystallization occurs after annealing, leading to the formation of larger grain sizes compared to as-deposited grain sizes. Annealing substantially changed the structure of the nanorods, leading to different smoother, more connected crystal structures for the annealed nanorods compared to as-deposited ones.

Uniformly distributed ZnO nanorods with diameter 70-100 nm and 1-2μm long have been successfully grown at low temperatures on GaN by using the inexpensive aqueous solution method. The formation of the ZnO nanorods and the growth parameters are controlled by reactant concentration, temperature and pH. No catalyst is required. The XRD studies show that the ZnO nanorods are single crystals and that they grow along the c axis of the crystal plane. The room temperature photoluminescence measurements have shown ultraviolet peaks at 388nm with high intensity, which are comparable to those found in high quality ZnO films. The mechanism of the nanorod growth in the aqueous solution is proposed. The dependence of the ZnO nanorods on the growth parameters was also investigated. While changing the growth temperature from 60°C to 150°C, the morphology of the ZnO nanorods changed from sharp tip (needle shape) to flat tip (rod shape). These kinds of structure are useful in laser and field emission application. / Singapore-MIT Alliance (SMA)

The aim of this thesis work was to fabricate a hybrid LED using organic-inorganic ZnO materials. The goal of the project was to get an efficient white light emission from zinc oxide (ZnO) nanorods active layer. Since most of the organic materials are good for hole mobility and most of the inorganic materials are good for electron mobility, it is possible to fabricate a high performance heterostructure electroluminescence device from organic-inorganic materials. This thesis work was an attempt towards fabricating such a high electroluminescence LED from hybrid materials in which polymer acts as a p-type material and ZnO acts as a n-type material. The growth mechanism of ZnO nanorods using low-temperature aqueous solution method has been studied and nanorods (NRs) growth was examined with scanning electron microscope (SEM). Optimum hole injection polymers have been studied. Finally, the fabricated device was characterized using parameter analyzer. The fabricated device worked as a diode i.e. it rectified current as expected and the desirable light emission has almost been achieved.

This thesis describes the synthesis and assembly of metal and semiconductor nanoparticles (NPs). The two research topics include i) hetero-assembly of metal and semiconductor NPs, ii) effect of ionic strength on homo-assembly of gold nanorods (GNRs). First, we present hetero-assembly of GNRs and semiconductor quantum dots (QDs) in a chain using biotin-streptavidin interaction. We synthesized alloyed CdTeSe QDs and modified them with mercaptoundecanoic acid to render them water-soluble and to attach streptavidin. We synthesized GNRs by a seed-mediated method and selectively modified the ends with biotin. Hetero-assembly of QDs and GNRs depended on the size, ligands, and ratio of QDs and GNRs. Second, we controlled the rate of homo-assembly of GNRs by varying the ionic strength of the DMF/water solution. The solubility of polystyrene on the ends of GNRs depended on the ionic strength of the solution, which correlated with the rate of assembly of GNRs into chains.

This thesis describes the synthesis and assembly of metal and semiconductor nanoparticles (NPs). The two research topics include i) hetero-assembly of metal and semiconductor NPs, ii) effect of ionic strength on homo-assembly of gold nanorods (GNRs). First, we present hetero-assembly of GNRs and semiconductor quantum dots (QDs) in a chain using biotin-streptavidin interaction. We synthesized alloyed CdTeSe QDs and modified them with mercaptoundecanoic acid to render them water-soluble and to attach streptavidin. We synthesized GNRs by a seed-mediated method and selectively modified the ends with biotin. Hetero-assembly of QDs and GNRs depended on the size, ligands, and ratio of QDs and GNRs. Second, we controlled the rate of homo-assembly of GNRs by varying the ionic strength of the DMF/water solution. The solubility of polystyrene on the ends of GNRs depended on the ionic strength of the solution, which correlated with the rate of assembly of GNRs into chains.

In this thesis, two series of self-assembled GaN and AlxGa1-xN nanorods are grown by plasma-assisted molecular beam epitaxy (PAMBE) on Si(111) wafer. The Al contents in AlxGa1-xN nanorods is varied from 6% to 75% by changing the Al cell beam flux (BFM). Second, the GaN/AlGaN multiple quantum wells (MQWs) with variation thickness are grown on the GaN nanorods with a p-GaN layer on the top. Al concentration is determined by electron probe x-ray micro-analysis (EPMA) and x-ray diffraction (XRD). The reflection high-energy electron diffraction (RHEED) and scanning electron microscopy (SEM) images show that the height, density and morphology of nanorods depend on the Al content. The (micro-)PL, CL and Raman spectra also show the variation of the characterization from those of GaN to AlN. The transmission electron microscopy (TEM) images show that the GaN/AlGaN MQWs structures with well widths of 1, 2, 3, 4, 6, 8 and 16 c-LC (Lattice constant on c-direction) were successful grown on the nanorods. The (micro-)PL and CL spectra show red-shift of the peak position with the decrease of Mg-doped concentration. When the well thickness is less then 4 c-LC, the CL spectra show blue-shift of the peak position with the decrease of the well thickness due to the Quantum-confined effect and the polarization effect in MQWS.

After hydrolyzing zinc acetate in methanol solution, spherical ZnO nanoparticles in the size range from about 2.5 to 5 nm were synthesized by maintaining a ZnO concentration of 0.02M. Compared to ZnO nanoparticles prepared via other methods, the particles prepared using our novel colloidal chemistry exhibit narrow size distribution and a high sensitivity to the surrounding environment. The structure and composition of the white powders precipitated from the colloidal solution can vary, depending on how the powder samples are prepared. Factors such as desorption and adsorption of methanol, binding of water and exposure to humid air have been studied to correlate to the structure and composition observed from the precipitated powder. Methanol desorption rate and excess KOH on the particle surface have played an important role in the structural changes. Furthermore, upon annealing, the white precipitate is recovered to wurtize ZnO. XRD and TEM are used to study the structural transformation of ZnO nanoparticles.

<p>The aim of this thesis work was to fabricate a hybrid LED using organic-inorganic ZnO materials. The goal of the project was to get an efficient white light emission from zinc oxide (ZnO) nanorods active layer. Since most of the organic materials are good for hole mobility and most of the inorganic materials are good for electron mobility, it is possible to fabricate a high performance heterostructure electroluminescence device from organic-inorganic materials. This thesis work was an attempt towards fabricating such a high electroluminescence LED from hybrid materials in which polymer acts as a p-type material and ZnO acts as a n-type material. The growth mechanism of ZnO nanorods using low-temperature aqueous solution method has been studied and nanorods (NRs) growth was examined with scanning electron microscope (SEM). Optimum hole injection polymers have been studied. Finally, the fabricated device was characterized using parameter analyzer. The fabricated device worked as a diode i.e. it rectified current as expected and the desirable light emission has almost been achieved.</p>