Browsing by Subject "Surface"

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Comparison and Methods For Estimating Soil Surface Area
    (2016-01-14) Chi, Brian
    Soil Surface Area is important when analyzing land management and agriculture practices. Indirect methods of measuring Soil Surface Area are usually done through clay content. For this research I have compared both the Hydrometer method and Laser Particle Size Analyzer (LPSA) method as a means of analyzing soil texture. I then compared the Clay Content given from the Hydrometer and compared it to the Soil Surface Area data from the Brunauer–Emmett–Teller (BET) method. I found out that the LPSA didn't correlate to the Hydrometer method when analyzing soil texture. This means we can't use it as a reliable means of soil texture analysis. There needs to be further research on this subject before proving of it. The clay content given from the Hydrometer soil texture data correlated well with the BET SSA data. This means that the clay content does correspond to the soil surface area, this means that it can be used as a cheaper method to predict soil surface area. This discovery will be useful for future research within the soil science field.
  • Thumbnail Image
    Item
    Computational and experimental studies of dye sensitized solar cells
    (2013-09) Vatassery, Rajan Nayar
    The dye-sensitized solar cell (DSSC) has been studied by observing charge transfer from an organic terthiophene dye into a CdS nanoparticle. Using NMR and UV-Vis, we find characteristics of dye aggregation and a concomitant reduction in the electron transfer efficiency as measured by ultrafast transient absorption (TA) spectroscopy. Specifically, the NMR and UV-Vis spectra of the dye molecules indicate aggregates are readily formed at high surface loading, or roughly a 20:1 dye:nanoparticle ratio. Upon analysis by TA spectroscopy the same samples show a dominant S1 state quenching process separate from the expected intersystem crossing and electron transfer (ET) S1 quenching pathways. We propose that the dominant process is concentration-quenching because it only appears at high surface coverage where aggregates are detected spectroscopically; at lower surface coverage (ratios of dye:nanoparticle of roughly 1:1) the ET mechanism is the dominant pathway for S1 reduction and the parasitic concentration-quenching pathway is not observed. We therefore suggest that planar oligothiophene dyes should be modified to frustrate packing on the surface in an effort to avoid concentration quenching losses, or that dye loading be considered when creating a DSSC from planar dye molecules. Classical molecular dynamics (MD) simulations are also presented to corroborate the experimental picture described above. These simulations show that dyes aggregate in a variety of orientations, and that dye molecules are stabilized by these aggregation events even in the presence of explicit solvent. The ability of the dye molecules to pack more densely than is found experimentally shows that the surface of the CdS nanoparticle is likely undersaturated. In this situation, dye molecules can be either uniformly distributed around the surface of the nanoparticle, or they can be concentrated in islands on certain crystallographic faces, leaving other faces unoccupied. The experimental signs of aggregation support the latter.
  • Thumbnail Image
    Item
    Structural and surface correlations to the optical properties of nonthermal plasma-produced silicon nanoparticles
    (2011-06) Anthony, Rebecca Joy
    Nanomaterials have diverse capabilities to enable new technology and to deepen our understanding of our world, providing exciting prospects for scientists and the public alike in a vast span of uses. In the past decade, however, the potential held by nanotechnology has been reframed in the context of helping to slow global climate change and to alter the ways in which we use our energy to reflect more efficient technology and renewable energy sources. Silicon is a standout material in this new framework: as a nanomaterial, silicon can emit light when exposed to an applied voltage or ultraviolet optical excitation source. Silicon nanocrystals also exhibit size-dependent light emission, due to quantum confinement. This thesis is an exploration of the synthesis and processing parameters that affect the optical performance of silicon nanocrystals produced in a nonthermal plasma reactor. The efficiency of this light emission is sensitive to both synthesis environment and post-synthesis treatment. The work presented here is an attempt to deepen our understanding of the effects of different reactor and treatment parameters on the light emission efficiency from silicon nanoparticles, such that the luminescence behavior of the nanoparticles can be specifically engineered. Being able to fine-tune the structure, surface, and optical characteristics of the silicon nanocrystals is key in maximizing their use in luminescence applications. For all of the experiments described here, a nonthermal plasma flow-through reactor has been used to create the silicon nanoparticles. Silane gas is dissociated in the plasma and fragments come together to form silicon clusters, then grow to create nanoparticles. The nanoparticles were collected from the reactor for further processing, characterization, and experiments. The first discovery in this project was that by adjusting the power to the plasma reactor, the crystallinity of the silicon particles can be tuned: low power results in amorphous silicon nanoparticles, and high power yields crystalline nanoparticles. Even more important, the crystallinity of a nanoparticle ensemble relates directly to the photoluminescence (PL) efficiency, or quantum yield, from the ensemble: crystalline silicon nanoparticle samples, after alkyl functionalization, exhibit PL efficiencies of 40% or greater, while amorphous samples emit light with very poor efficiency (<2%). Additional studies of the plasma reactor revealed the importance of injecting a flow of hydrogen gas into the afterglow of the plasma, which turns out to have dramatic implications for the ultimate PL quantum yields of the nanocrystals. This injection scheme was systematically studied by varying the injected gas and its position. Hydrogen injected directly into the plasma afterglow was found to be vital for achieving high quantum-yield silicon nanocrystals, likely due to a reduction in surface trap states due to additional hydrogen passivation at the nanocrystal surface.Further investigations into the nanocrystal surface and how it relates to PL quantum yield showed that the photoluminescence from silicon nanocrystals is not only dependent on synthesis parameters, but also on processing temperatures and procedures following synthesis. While the highest PL efficiencies are found for silicon nanocrystals capped with alkyl chains, the PL efficiency of a nanocrystal ensemble can also be improved simply by heating the sample to temperatures between 150-200° C. This heating step also leads to a change in the hydride structure at the nanocrystal surface, which appears to be brought about by the effusion of silyl (or disilane) groups. Finally, details of the construction of a silicon-nanocrystal-based LED will be discussed. The LED project is part of a collaboration, and while the majority of device-specific aspects of the project were carried out in the lab of Professor R. Holmes by his Ph.D. student Kai-Yuan Cheng, the processing and alterations made to the nanocrystals used in the LED were all the responsibility of the author. The details of the project and a summary of the results bear discussion here in this thesis, as well as outlining of a novel scheme for deposition of SiNCs for device construction.
  • Thumbnail Image
    Item
    Surface Treatment to Promote Endothelialization, UROP Summer 2022
    (2022-10) Hruby, Lukas
    This project analyzed the use of new surface coatings on tissue culture plastic to determine whether the proposed coating material would act as an effective alternative to endothelialization on TCP. The main method involved seeding cells onto 18 total TCP well plates, all with varying concentrations. Nine of the plates had fibronectin applied first, followed by the application of Poly-L-Lysine, with the other nine reversing the order. Based on the results, the plates that had Poly-L-lysine applied first had better overall cell count, and subsequently adhesion, than the plates with fibronectin first. Further experimentation must be done to determine whether the combination of substrates is overall more effective than solely using one substrate to complete endothelialization. This project outlines the importance of forming a monolayer of endothelial cells and is the first step to eventually synthesizing a completely biological transplant organ.