Example Summer 2012 REU Projects.
More projects may be available.
Characterizing "3D-printed" gypsum-based cryogenic composite structures (Advisor: Jacob Leachman)
This project will characterize gypsum-based composite structures generated via rapid-prototyping as structural components for cryogenic liquid hydrogen fuel tanks. Liquid hydrogen is a promising fuel for Unmanned Aerial Vehicles (UAV) having 2.8 times more energy per mass than conventional jet fuels. However the extremely low temperatures (21 K, -421.8°F) required to store liquid hydrogen require complex storage tanks. The storage tanks must be robust to large temperature changes, low weight, highly insulating, and structural members of the UAV airframe. A new Zcorp ZPrinter 350 will be used to generate gypsum composite test coupons to be used as structural supports in cryogenic systems. Vacuum bagging will impregnate the coupons with leading cryogenic epoxy binders. The samples will be load tested for Mode I and Mode II loadings. Cryogenic cycling will be conducted through immersion in liquid nitrogen. Cryogenic thermal conductivity and optical microscopy tests will also be conducted.
Molecular modeling of the photoactive layer of organic photovoltaic solar cells (Advisor: Soumik Banerjee)
Organic photovoltaic (OPV) solar cells, which comprise photoactive layers with organic nanoparticle acceptors dispersed in conjugated polymers, have generated great scientific interest. The ease of manufacturing, relative low costs, light weight, flexibility and low operating temperature of OPVs also make them attractive candidates for commercial use. The power conversion efficiency (PCE) is still limited to less than 8-9% in OPVs due, in part, to the recombination losses of excitons. Such losses can be diminished by maximizing the contact surface area between the electron donor and acceptor materials in the photoactive layer. The photoactive layer is most often synthesized through spin coating of a solvent containing nanoparticles dispersed in a polymer. The molecular interactions between the solvent, nanoparticles and polymers during the spin coating process influence the morphology of the photoactive layer and hence determine the PCE. Prediction of optimal synthesis parameters, such as choice of solvent, processing temperature, and concentration of nanoparticles and polymers, requires fundamental understanding of the mechanisms that govern the agglomeration of nanoparticles and polymers in solvents. As part of the summer project, the student will acquire experience in atomistic simulations of systems relevant to OPVs. Analysis of the results from the numerical simulations will aid the selection of novel polymers and nanoparticles for OPVs.
Graphene as an electrical contact of "zero" height(Advisor: K W Hipps)
Graphene is an exciting material that is essentially a single sheet of the Graphite "chicken wire" structure. It has excellent electrical conductivity and can be doped to become semiconducting. Single layers are only a few tenths of nm high and have high visible light transparency. The project this summer will involve the making of gaphene by chemical vapor deposition methods and then transferring the graphene to insulating substrates for use as electrical contacts.
CNF-reinforced nanocomposites (Advisor, W.H. “Katie” Zhong)
How to correlate structures and properties for a nanocomposite has been critical for the quality control of the nanocomposite. An important factor for the nanocomposite structure is the dispersion of the nanoparticles in the polymers. Based on our exploratory work revealing AC/DC conductivity difference variation dependence on size of carbon nanofiber (CNF) agglomerates, we will characterize the agglomerate levels of CNFs in polymers using SEM, TEM and optical microscopy for the nanocomposite samples prepared through appropriate processing procedures, and then measure the AC and DC conductivities. According to the ratio of the AC/DC conductivities, the dispersion situations will be evaluated quantitatively.
Analyze twin boundaries and other defects in deformed metals(Advisor D.P. Field)
Electron channeling contrast imaging (ECCI) has been used to analyze structural defects in many types of materials. The topic to be researched in the summer of 2012 involves using ECCI as well as electron backscatter diffraction (EBSD) on a field emission scanning electron microcsope to analyze twin boundaries and other defects in deformed metals. Twinning induced plasticity steels will be analyzed to measure twin boundary content as well as dislocation structure evolution. The student will get experience in both deforming steel specimens as well as performing the imaging techniques discussed above. Appropriate data analysis and interpretation will result in material that is suitable for publication -- an expected outcome of the project.
Microstructure development in low melting liquid phase sintered metals (Advisor I.Dutta)
A range of low melting metals based on Sn, In and Bi have recently gained prominence for a wide range of potential applications in the electronics and energy sectors as next generation interconnect, thermal management and energy storage materials. These materials, which are processed by liquid phase sintering (LPS), have a composite microstructure comprising one high-melting, high-conductivity majority phase and a low-melting minority phase. The high-melting phase dominates the electrical and thermal properties of the composite, whereas the low-melting phase provides either mechanical compliance or phase-change capabilities (for electronic and energy storage applications, respectively). The principal challenges include optimizing the LPS process-window to minimize interfacial solution / reaction, composition and microstructure control (volume fraction, particle size/shape, etc.) to optimize properties, and microstructural stability during long term service. Addressing these challenges requires a range of experimental approaches well suited to summer REU students, wherein they can obtain experience in powder processing and sintering, optical and scanning electron microscopy, measurement of mechanical, electrical and thermal properties, as well as statistical analysis. During the summers of 2009 and 2010, two REU students (Paul Rottman and Stephen Merkley) worked on these materials in the Multi-Physics Effects in Materials Laboratory at WSU as part of a team, and one publication involving Mr. Rottman has already resulted . During 2011 we expect to involve students in an array of structure-property-processing correlation in LPS materials.
Microstructure of Sn Whisker Materials (Advisors U. Sahaym and M.G. Norton)
For over 50 years it has been known that pure Sn films deposited on Cu and Cu alloys are prone to spontaneous whisker formation. Tin whiskers are single-crystal filaments that grow on platings causing short circuit failure in electronic components. One way of preventing whisker formation is to alloy Pb into the Sn coatings. However, the restriction on the use of Pb demands the development of alternative methods for preventing whisker growth. Controlling electroplating variables such as plating time, temperature and current density, electrolyte composition, and the composition and nature of the substrate can prevent/enhance whisker formation. In summer 2009, the effect of electroplating bath temperature on the surface brightness/reflectivity and the evolution of surface morphology of electrodeposited pure Sn films, and its subsequent effect on whisker formation was investigated. The REU student was responsible for electroplating and subsequent characterization using scanning electron microscopy. In summer 2010, the effect of electrolyte pH on whisker growth was investigated. We will continue to investigate the effects of various other plating variables with an ultimate goal of developing a strategy of mitigating Sn whisker formation. This work will mainly involve characterization of electroplated Sn films using electron microscopy. This will be helpful in understanding the mechanism of Sn film deposition under various plating conditions as well as the mechanism of Sn whisker growth.
Organic Nanostructures: Preparation and Characterization (Advisors: K.W. Hipps and U. Mazur)
Two students on a joint project, one focused on fabrication, one on characterization. In this project organic nanostructures formed by ionic association from electroactive and photoactive materials will be made and studied to determine their detailed structure, electrical conductivity, and photoconductivity. Preparation involves simple solution chemical reactions. Structural characterization will utilize scanning probe microscopy, scanning electron microscopy, and transmission electron microscopy. Electronic properties will be evaluated using STM, scanning conductance microscopy, and interdigitated electrode experiments. Optical properties will be measured using UV-Visible techniques, and photoconductivity will be assessed with illuminated samples on interdigitated electrodes.
Characterization of bio-inspired functionally graded TiN coatings (Advisor Amy P. C. Wo)
Naturally occurring high toughness and deformation resistant materials often exhibit multilayered, functionally graded hierarchical structures. The functionally graded structure is found to be effective in promoting load transfer, redistributing stress and improving adhesion between dissimilar layering materials, which prevents delamination. In this project, the REU student will evaluate the mechanical behavior and adhesion of titanium nitride thin films that exhibit different designs of bio-inspired functionally graded structures as candidates for protective coatings. The mechanical properties and adhesion strength of these thin films will be studied by nanoindentation and nano-scratch testing. Subsequently, SEM and TEM will be used to study the deformation structure, which will be helpful in understanding the interrelationship between microstructure and mechanical properties of the thin films. Key features in the functionally graded structure will be identified by comparing performance of model thin films of different structural designs. This would guide the synthesis of bio-inspired thin films with exceptional strength, toughness and adhesion to the substrate.
Uncertainties on the calculation of the dislocation mobility (Advisors: H. Zbib and I. Mastorakos)
The evaluation of dislocation mobility using Molecular Dynamics is usually achieved by fitting the velocity – stress curves. However, this velocity is the result of an averaging of the dislocation core displacement vs. time plot. The dislocation core is identified using the central symmetry parameter and keeping the atoms that have a value within a certain range. Furthermore, as the temperature increases, the dislocation is vibrating while moving due to the increased thermal vibrations of the lattice that also affects the velocity measurements. All the above factors introduce uncertainties to the measurement of the dislocation mobility that are independent on the material considered or the lattice type. However, for the development of an inclusive theory that will describe the mobility of the dislocations these issues must be resolved, especially since there are no other reliable computational techniques to study this property. For this purpose we will perform molecular dynamics simulations on edge dislocations in FCC systems that were chosen because the extended dislocation core spreading exhibits more extended uncertainties. During the simulations the central symmetry parameter range and the temperature will vary to allow the evaluation of dislocation mobility as a function of the range and various core positions between the minimum and maximum location due to the thermal fluctuations. The results will allow us to study the uncertainties introduced during the simulation by the parameters described above and will lead to a better understanding of the evolution of the dislocation structures identified during material characterization.
Polymeric and Composite materials for photovoltaic devices (Advisor L. Scudiero)
The nanoengineering of hybrid polymer-metal,i-iii -metal oxide,iv -semiconductors,v, vi , -polymers,vii, viii and –fullerenesix thin films is a fast developing field of nanotechnology. These new composite materials show promise for a variety of applications in novel organic optoelectronics such as solid state electronics,x, xi electroluminescent devices and photovoltaicsxii-xiv - and photodetectors.xv
In this study we propose to investigate the morphology/microstructure of nanocomposite materials by atomic force microscopy (AFM) and the absorption spectrum by UV-Vis spectroscopy. The polymer of interest is a newly synthesized oligomerxvi (tertmethoxy di-triphenylamine di-thiophene-benzothiadiazole; DTBT-DTPA-TMeO; D-A-D) owing to its high charge mobilityXvii that will be co-deposited with metallic nanoparticles such as copper or gold. This nanocomposite material will be spin coated on a transparent conducting substrate (ITO) for future photoelectron spectroscopy (XPS and UPS) measurements. It has been shown that the morphology and the microstructure of deposited films play an important role in the performance and efficiency of photovoltaic devices.xviii, xix The selected solvent and the quality of the deposited film (free of pinholes, kinks) and roughness are parameters affecting not only the absorption spectrumxx but also the efficiency of the photoinduced charge transport of the devicexix.
Geometrical and spectroscopic information collected by AFM, UV-Vis, and XPS/UPS will play a crucial role in the design of photovoltaic devices. Furthermore, by changing the volume ratio polymer/metal in these nanocomposites, it is possible to control and tailor the desired charge injection barrier heightxxi, a very important parameter in the design of solar cells.
Finally, the nanocomposite material showing the best quality film, the rougher surface (AFM) and the optimal absorption spectrum (UV-Vis) will be used to a heterogeneous bulk device by adding a top electrode. The addition of the top Al electrode will allow for I-V measurements in the dark and under 100mW/cm2 to obtain open circuit voltage (Voc), short circuit current density (Jsc) and power conversion efficiency (h= JscVocFF/Po) values.____________________________
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