The role of the oxide/organic and organic/organic interfaces in small-molecule planar-Heterojunction (PHJ) photovoltaics was investigated with three interrelated projects: i) indium-tin oxide (ITO) bottom contact electrodes were modified with gold nanoparticles (Au-NPs) to improve rates of charge-transfer at the donor/oxide interface, ii) donor layers in OPVs were textured to increase charge generation at the organic/organic' interface, and iii) the effect of co-facial overlap on device performance via tuning of the electron acceptor orientation at the organic/organic interface. The modification of ITO with Au-NPs showed increased performance in small-molecule OPVs when compared to non-processed ITO devices due to the interactions between the Au-NPs and the donor material. Textured TiOPc increased overall device performance by a factor of 2X via the increased surface area, near-IR absorption, and increased mobilities. Modified and un-modified PTCDA acceptors showed that co-facial overlap at the organic/organic' interface is a large determinant in device performance, while the performance in small-molecule planar-heterojunction photovoltaics were severely affected by the pre-treatment process, most likely due to the particular interactions between the oxide and the donor material.

To overcome the challenge in radiation therapy of delivering the prescribed dose to cancer cells while sparing normal tissue, preferential introduction of high Z material to tumour cells works as a method of radiation sensitization. Gold nanoparticles (GNPs) are very useful in this respect. It has been shown that the size, shape, and surface properties of GNPs affect their cellular uptake. Manipulation of the cell cycle to arrest cells at different stages offers a unique strategy to study the molecular and structural events as the cell cycle progresses. To optimize delivery of GNPs into tumour cells and enhance the effect of radiosensitization, nanoparticle (NP) uptake in synchronized populations of MDA-MB-231 breast cancer cells was investigated. Populations of MDA-MB-231 cells were first synchronized in S-phase using double-thymidine block, and allowed to progress through cell cycle in synchronization. Synchronized cells were incubated with 5 nm GNPs, 15 nm GNPs, 46 nm GNPs and two formulations of lipid NP encapsulated 5 nm GNPs. Uptake of NPs was visualized using hyperspectral optical imaging and quantified with inductively coupled plasma mass spectrometry (ICP-MS). Following internalization of GNPs, cells were irradiated with 6 MV photon beams from a linear accelerator, and the survival fraction and induced deoxyribonucleic acid (DNA) damage were studied. Cell cycle analysis after a double-thymidine block showed that the cell population was well synchronized. Uptake of NPs was 1.5-2 times higher in synchronized cell population compared to the control where cells were at different stages of the cell cycle. Clonogenic studies were used to evaluate the cell survival following radiation treatment. After a dose of 2 Gy, there was a decrease in cell survival fraction in synchronized cells treated with GNPs prior to radiation treatment compared to unsynchronized cells (control) indicating GNP-mediated dose-enhancement. The protein γ-H2AX, which is recruited to sites of DNA double strand breaks, was fluorescently labeled to evaluate damage due to the radiation treatment. Our results show more DNA double strand breaks in cells treated with GNPs prior to radiation. Interaction of ionization radiation with GNPs inside of cells produce secondary electrons. These secondary electrons can interact with water molecules and produce additional free radicals. These low energy electrons and free radicals interact with important cell structures and could cause cellular damage. Cell cycle synchronization has been shown to enhance GNP/PEG/RGD uptake in MDA-MB-231 cells resulting in greater cell radiosensitization and cellular damage. Cell synchronization is therefore an additional method available that can be employed to improve GNP uptake in cells. / Graduate

Gold (Au) implantation in silicon (Si) has been a topic of great interest from both fundamental and applied perspectives. Ion implantation is a versatile technique due to its ability to form surface-embedded nanoparticles that provide better adhesion. Also, being an integral part of the substrate lattice, the nanoclusters produced by ion implantation are free from impurities and their size distribution can be controlled by carefully optimizing the beam parameters. During our experiments to produce nanoclusters of Au on Si for use as seeds for the growth of nanowires, we stumbled across an unusual pattern formation process under specific conditions. This unique self-assembly process is observed only within a critical threshold implantation fluence and above a threshold annealing temperature. Fabrication of ordered arrays of metal nanoparticles on Si substrates is of significance for both fundamental science associated with low-dimensional physics and technical app lications. The application of functional nanostructures strongly depends on their assembly in ordered one- or two- dimensional arrangements. These arrangements may play an important role in fabricating ordered arrays of semiconductor/oxide nanowires.This thesis discusses a systematic study performed to understand the temperature and time dependent nucleation, growth of Au nanoclusters and evolution of the self-assembled patterns. A growth model is proposed to show the re-crystallization behaviour of Au supersaturated amorphous silicon (a-Si) on Si substrate. The observed self-assembled periodic patterns of Au nanoclusters bear resemblance to the Liesegang ring structures prevalent in some chemical reaction-diffusion systems. Based on this systematic study of the growth and morphology of Au nanoclusters, a tentative growth mechanism has been proposed for the formation mechanism of this unusual self-assembled pattern. The pattern formation of this non-equilibrium process is expected to originate due to instabilities of the three scales of Au nanoclusters at elevated temperatures. The kinetics of pattern formation from a supersaturated solid solution (a-Si/Au alloy) is demonstrated using numerical solutions obtained by a two-dimensional growth model, which takes into account the nucleation, diffusion and the aggregation process. The numerical solution of the diffusion equations appear to be in good agreement with the experimental results.

The binding affinity of single stranded DNA (ssDNA) for gold nanoparticle surface is studied in this work. The data indicate that the strength of interaction between ssDNA and Au particle surface is closely related to the particle size, with smaller particles (5 nm) producing the most pronounced effects. From these experimental findings, a single stranded DNA (ssDNA) based method to assimilate 13 and 5 nm gold nanoparticles was developed, and verified by transmission electron microscopy (TEM). / Singapore-MIT Alliance (SMA)

Molecular dynamic simulation is utilized to investigate the adsorption mechanism of water molecules surrounding Au nanoparticle of different sizes. We selected 13, 55, 147 atoms icosahedral gold nanopartilce in our model and their diameter are 7.92Å, 13.2Å, 18.5Å, respectively. We calculated density profile of water molecules and found that there were two adsorption layers out of the surface of gold nanoparticles. We also calculated average number of hydrogen bonds per water . It is higer in the adsorption layer than in bulk water region and we found that the direction of hydrogen bonds are numerously parallel with gold surface in the adsorption layer. We also claculated orientational order parameter for water molecules and explore the difference of the tetrahedral structure of the water molecules between the adsorption layer and bulk water region. Besides, we compared of cases of different gold sizes.

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