SMARTech Collection: Undergraduate Research Option Theses

Graphene nanoribbon array fabrication by oxygen gas plasma etching through sub-micrometer porous filters

Thu, 06 Aug 2009 22:58:59 GMT

Title: Graphene nanoribbon array fabrication by oxygen gas plasma etching through sub-micrometer porous filters

Authors: Shaw, David

Abstract: We investigate a novel method of fabricating a network of graphene nanoribbon structures. The process is a sharp departure from conventional nanolithographic techniques in both method and amount of time required. Epitaxial graphene prepared on single crystal 4H-SiC was etched with O2 plasma through 0.2 ìm porous filters adhered to the surface of the sample. Thickness measurements using ellipsometry and topological mappings using atomic force microscopy were conducted to ascertain the extent of graphene nanoribbon formation. Sheet resistance of the samples was measured using the four-point van der Pauw method to ensure the existence of electrical conductivity in the etched samples. Furthermore, the etch-rate of multilayer epitaxial graphene was determined.

Investigation of Adjoint Based Shape Optimization Techniques in NASCART-GT using Automatic Reverse Differentiation

Sun, 03 May 2009 22:58:59 GMT

Title: Investigation of Adjoint Based Shape Optimization Techniques in NASCART-GT using Automatic Reverse Differentiation

Authors: Verma, Siddhartha

Abstract: Automated shape optimization involves making suitable modifications to a geometry that can lead to significant improvements in aerodynamic performance. Currently available mid-fdelity Aerodynamic Optimizers cannot be utilized in the late stages of the design process for performing minor, but consequential, tweaks in geometry. Automated shape optimization involves making suitable modifications to a geometry that can lead to significant improvements in aerodynamic performance. Currently available mid-fidelity Aerodynamic Optimizers cannot be utilized in the late stages of the design process for performing minor, but consequential, tweaks in geometry. High-fidelity shape optimization techniques are explored which, even though computationally demanding, are invaluable since they can account for realistic effects like turbulence and viscocity. The high computational costs associated with the optimization have been avoided by using an indirect optimization approach, which was used to dcouple the effect of the flow field variables on the gradients involved. The main challenge while performing the optimization was to maintain low sensitivity to the number of input design variables. This necessitated the use of Reverse Automatic differentiation tools to generate the gradient. All efforts have been made to keep computational costs to a minimum, thereby enabling hi-fidelity optimization to be used even in the initial design stages. A preliminary roadmap has been laid out for an initial implementation of optimization algorithms using the adjoint approach, into the high fidelity CFD code NASCART-GT.High-fidelity shape optimization techniques are explored which, even though computationally demanding, are invaluable since they can account for realistic effects like turbulence and viscocity. The high computational costs associated with the optimization have been avoided by using an indirect optimization approach, which was used to dcouple the effect of the flow field variables on the gradients involved. The main challenge while performing the optimization was to maintain low sensitivity to the number of input design variables. This necessitated the use of Reverse Automatic differentiation tools to generate the gradient. All efforts have been made to keep computational costs to a minimum, thereby enabling hi-fidelity optimization to be used even in the initial design stages. A preliminary roadmap has been laid out for an initial implementation of optimization algorithms using the adjoint approach, into the high fidelity CFD code NASCART-GT.

The Role of Iron Oxides in Marine Phosphorus Cycling

Sun, 03 May 2009 22:58:59 GMT

Title: The Role of Iron Oxides in Marine Phosphorus Cycling

Authors: Snow, Samuel

Abstract: Dissolved and particulate phase iron (Fe) and phosphorus (P) concentrations were characterized in Effingham Inlet, a fjord located on the west coast of Vancouver Island. The effect of redox conditions on Fe and P cycling was investigated through comparison of sediment and water samples taken above and below a water column redox boundary in the fjord. The data show that sharp increases in the concentration of dissolved P across the redox boundary cannot be explained solely by release of absorbed phosphorus associated with dissolution of iron oxide phases. These findings support new theories of P cycling in oceans, which suggest that redox sensitive cycling of polyphosphates by microorganisms may be a significant source of dissolved phosphorus in marine environments.

Detection of Respiratory Syncytial Virus DNA with Gold Nanorod Surface Enhanced Raman Spectroscopy Active Substrates

Sun, 03 May 2009 22:58:59 GMT

Title: Detection of Respiratory Syncytial Virus DNA with Gold Nanorod Surface Enhanced Raman Spectroscopy Active Substrates

Authors: Siemens, Katherine

Abstract: Surface enhanced Raman scattering (SERS) is a powerful spectroscopic tool that can be used to identify and characterize compounds at low concentrations. Recent literature reports suggest that SERS may be applicable for the detection and identification of viruses present in biofluids. In this investigation, gold nanorod arrays were evaluated as SERS substrates with the specific purpose of probing spectral differences between single stranded (ssDNA) and hybridized, or double stranded (dsDNA) DNA. This was deemed as the first step in developing a SERS-based hybridization assay for viral identification. Hybridization was carried out both off and on the substrate surface to determine whether there are observable spectral differences from the two different methods of hybridization. Studies were also carried out to determine if it was possible to detect mismatched DNA pairs after hybridization had been attempted. Gold SERS active substrates were utilized instead of silver giving the advantage that these substrate do not oxidize under ambient conditions. It has also been found that ozone cleaning gold substrates before sample application increases the hydrophilicity of the gold, making the use of smaller sample volumes possible. Ozone cleaning the gold substrate after ample binding time has passed increases the SERS signal as well. It is believed that this cleaning immediately prior to SERS acquisition cleans the gold surface to a point where the plasmon being formed is more likely to move up the sample which increases the intensity of the SERS signal. In addition to examining the possibility of using gold instead of silver for the SERS substrates, a method allowing for 36 separate DNA assays to be run at one time was investigated. This is accomplished by creating wells with polymer. Up to 36 wells fit on one glass microscope slide meaning that anywhere from 1 to 36 DNA probes can be attached within individual wells. This allows for either 36 different biological assays for the same virus or 1 biological sample to be tested for 36 different viruses or virus strains.