Example Summer 2008 REU Projects.
More projects will be available.
Deformation in multilayers and metal-polymer film systems (Advisor: D.F. Bahr)
Many of the emerging microelectromechanical systems (MEMS) and flexible electronics applications require the use of hard coatings (nickel or tungsten) on polymeric films or substrates, or even metals that are nominally ductile on more compliant substrates (gold on Kapton). Other mechanical systems have utilized combinations of hard and soft metallic multilayers to demonstrate significant strength improvements. Previous work with REU students (Kim Weaver) has documented these failures in hard – soft metallic systems (tungsten on aluminum), but extending this to larger mis-matched properties requires probing metal – polymer systems. The REU student will work with the faculty and senior graduate students to compare the strength of 6 layer Pt/Mo films (a system tested by a previous REU student, Stephanie Candelaria) measured via nanoindentation and bulge testing. The student will learn basic clean room techniques (spin coating and sputtering) for sample fabrication, and then measure the individual film properties using nanoindentation. After nanoindentation, the yield strength will be measured using a pressurized bulge testing system. The effects of multilayer thicknesses and periodicity will be used as the structural variation, and then compare the differences between a localized test (nanoindentation) versus a more macroscopic assessment of deformation. The area around the indentation test will be characterized using atomic force micrsocopy to identify if local microstructure (grain size) is impacting the hardness of the films.
CNF-reinforced nanocomposites (Advisor, W.H. “Katie” Zhong)
Carbon nanofibers (CNFs) are a type of low cost nanoscale reinforcement agent for polymers. However, uniform dispersion of CNFs into polymer materials is still problematic due to their high aspect ratio, and presently the overall performances of the nanocomposites have not reached their expected potential, which is most likely due to the dispersion problem. In our lab, we have been investigating the dispersion of CNFs in various polymers such as epoxy, PE and PP. In order to improve the uniformity of the dispersion of CNFs into polymers, we applied various kinds of approaches including twin-screw extrusion and sonication for making nanocomposites with enhanced mechanical properties. The REU student researcher will be involved in doing the research on characterization of electrical and thermal conductivities as well as dielectric properties of the CNF nanocomposites using the equipment in Dr. Zhong’s lab. To verify the dispersion improvements, the researchers will use scanning electron microscopy (SEM) and/or transmission electron microscopy (TEM) imaging techniques to observe and assess the dispersion of the CNFs in the polymers, and correlate these structures to the resulting properties. The results generated from this project will be very significant for understanding of the property enhancement through addition of nano-additives into polymers.
Processing and characterization of nanosprayed organic films (Advisor: K.W. Hipps)
Recent reports in the literature suggest a new method of depositing molecules on surfaces that may be particularly appropriate to the organometallic monolayers that we and others have worked on for several years. Previous REU students have demonstrated this research topic, within the larger on campus organic thin films group, is amenable to publication . This new technique uses a commercial pulse injector (similar to those used in modern engines) to pulse a tiny amount of solution into a vacuum chamber just above a surface. Because there is no heating or exposure to air required, almost any material can be deposited by this method. Whether it is an ordered surface that results depends on the particular molecule/solvent combination. This project is designed to recruit an engineering student to work in a group in chemistry (as done in previous REU projects with this group). The student will collect and review the appropriate literature, and design an adapter flange to allow this new technique to be performed in an existing vacuum chamber coupled with a scanning probe system. After device fabrication, the student will collaborate with a faculty to create surfaces modified by electroactive materials, and characterize these surfaces by Scanning Tunneling Microscopy.
Attachment of CNTs to substrates for biological fuel cells (Advisor S. Ha)
The objective of the proposed work is to improve the performance of enzymatic biofuel cells by investigating the use of various nanomaterials (Single Walled Carbon Nanotubes (SWCNT), Mesoporous Carbon (MC), etc.) as novel supports for electrically connecting the active site of glucose oxidase (GOx) directly onto an electrode. In existing enzymatic biofuel cells, either diffusional mediators or hydrogels are used to establish this electrical communication. However, these methods have been identified as the step that limits cell power density. Additionally, the half life of GOx within these systems is insufficiently short to allow for commercial application. In this proposal, the direct attachment of GOx onto various nanomaterials will be investigated as a possible solution to these technological barriers. SWCNT and MC have a right dimension to make a close contact with the active site of GOx, whereby electrons can be directly transferred, eliminating the requirement of electron transport mediators or hydrogels. Furthermore, the immobilization of enzymes on SWCNT and MC may aid in increasing their half life by preventing a change of their 3-D structures. For each enzyme-immobilized nanomaterial sample, its morphology will be characterized using SEM or TEM, and correlated to its catalytic activity and stability.
Characterization of Carbon Nanotube Turf Structures (Advisor D.P. Field)
Recent developments in nanostructures have brought to light exceptional electromagnetic, thermal and optical properties of a class of foam-like nanostructures formed of disordered intertwined structural units (nanowires, nanobelts, nanotubes). Such disordered assemblies are named turfs. Applications include thermal switches, flat panel displays, hard discs drives, and, chemical and biological sensors. Quantitative characterization of complex structures is possible using 2D planar or projected images, or, 3D imaging techniques that use stereo images to retrieve the 3D structure. In this effort, the student will develop a procedure to obtain optimal images from the FESEM for stereo image reconstruction to obtain 3D images. In addition, stereological techniques will be used to obtain similar information from the projected sections. These will be compared with one another by using measures of turf density, average tortuosity (by way of mean curvature or inflection count metrics), and connectivity of the structures. It is anticipated that the result of the proposed work will be a description of the nano-topology of structures processed by various procedures. Measurement of the topological character of these structures is important in itself, but will also eventually be used in models of mechanical behavior for such materials.
Ammonia effects on the performance of catalysts for low-temperature reactions (Advisor: J. Ahn)
It was shown that Pt catalyst reduction using ammonia during the combustion of hydrocarbons significantly improves the catalyst performance, but only for low flow rates, corresponding to conditions with low maximum temperatures. With Pt catalysts, a self-sustained reaction at Re ~ 1 can be obtained. Under these conditions, self-sustaining chemical reaction of hydrocarbons (e.g. propane) can be maintained at maximum temperatures below 55 ?C with ignition temperatures below 90 ?C. However, no similar such low-temperatures were found if the Pt were not subjected to exposure to ammonia prior to combustion. Even for catalytic reactions, the minimum self-sustaining chemical reaction temperature went up to over 125 ?C without this pre-treatment. To examine difference of Pt catalyst surfaces with NH3 treatment, initial SEM images were taken. After NH3 pre-treatment, SEM images reveal varied surface structures that appear to be linked to crystallographic features. This change in structure with NH3 treatment is noteworthy in that it increases the performance of the catalyst, but only for low-temperature reactions. The SEM images show what look like grain boundaries separating different topographies of the Pt surface. For 2008 the REU student will carry out Electron Backscatter Diffraction (EBSD) on polished Pt foils prior to exposure to NH3 in relationship to small fiduciary marks, and then the same grains will be mapped for topographic changes to determine the preferred texture to generate these 100 nm scale topography that appears to be responsible for the enhanced low temperature catalytic response.