REU - RESEARCH EXPERIENCES for UNDERGRADUATES ! |
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NCMN - Nebraska Center for Materials and Nanoscience Funded by National Science Foundation
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NANOMATERIALS and NANOSCIENCE
Catalysis is the key to developing new technologies for converting alternative feedstocks, such as biomass into value-added products and environmental remediation of toxic chemicals. Nanostructured materials often exhibit unusual chemical reactivities than those of their bulk forms. Particularly, gold clusters dispersed on suitable oxide support can exhibit distinctive catalytic activity for carbon monoxide (CO) oxidation at low temperature. This suggests that nanogold catalysts can be potentially exploited for CO combustion in fuel cell or automobile emission control. This unusually high oxidation activity is often attributed to the strong metal-support interaction which depends critically on the sizes of the metal clusters on the metal oxide support. Reducible metallic oxide semiconducting nanotubes are potentially ideal supports for these nanogold catalysts because they have large surface area for the loading of the precious metal particles. The goal of this project is to explore a new class of nanostructured catalysts composed of gold clusters on reducible nanotube oxide support such as titania and ceria oxide nanotubes for the oxidation of carbon monoxide. The project will capitalize on the expertise of rare-earth refractory nanomaterials synthesis in Cheung's group.
Undergraduates who join this project are expected to carry out and learn (a) the synthesis of ceria and titania nanotubes with different rare earth metal dopants and decorated with gold clusters of different sizes by the hydrothermal method, (b) the characterization of the nanomaterials by scanning electron microscopy (SEM) and x-ray diffractometry, and (c) measurement of the catalytic activities of these nanotubes catalysts for the oxidation of CO to CO2. The students will evaluate the reaction conditions and the efficiency of oxidation reactions with respect to the nanotube structures and compositions. They will also correlate the dopant concentration in the catalyst to their oxidation reactivities. Each student will be mentored daily by a graduate student. The students will learn chemical synthetic skills and vacuum techniques. They will be trained to use the SEM and x-ray diffractometery for sample characterization. They will be required to present the research results in a group meeting. Cheung will hold weekly meetings with the students and his daily mentor to discuss project progress.
The discovery of the growth and characterization of chiral nanostructures established a new field in solid state materials research. The ability to control the shape and scale of the nanoobjects allows tailoring of the basic functionality of chiral media, providing promise for applications in a wide variety of technologies, including magnetic storage media, optical filters, tunable electromagnetic resonator structures in the Terahertz region or nano-electromechanical precision actuators. Chiral nanostructures can be fabricated by glancing angle deposition using an extremely oblique angle of incidence for the particle flux and a synchronized substrate motion, for condition that support the growth of helices, posts, chevrons or screws.
Undergraduate students will utilize glancing angle deposition via electron beam evaporation to grow chiral nanostructures from metals (cobalt, aluminum). The growth will be optimized regarding shape, size and crystallinity by a variation of the particle flux angle of incidence, substrate rotation speed and substrate temperature. They will determine the structural characteristics by examining the structures with scanning electron microscopy and x-ray diffraction.
Undergraduate students will use several magneto-optical systems to study a variety of magnetic nanostructures, with the goal of understanding both their static and dynamic magnetic properties. Investigations will include the use of a femtosecond pulse laser to study the precession of magnetic moments with picosecond time resolution. Students will also benefit from learning about other characterization tools, including x-ray diffraction and alternating gradient force magnetometry.
Human mucin MUC1 is a well-characterized biomarker for the diagnosis of various ductal adenocarcinomas such as pancreatic cancer. While various biosensing platforms have been developed for the detection of MUC1, a simple colorimetric biosensor has yet to be realized. Our proposed sensing mechanism is based on gold nanoparticles (GNP) aggregation, which causes color changes that are due to both electronic dipole-dipole coupling between neighboring particles and scattering. Dispersed GNPs having interparticle distances substantially greater than their average particle diameter appear red, whereas the color of the aggregates changes to purple as the interparticle distance drops below the average particle diameter. To date, GNP aggregation-based sensors have been demonstrated for the detection of DNA, proteins and ions. However, studies focused on the detection of MUC1 mucin have not been reported. Thus motivated, this project aims at detecting MUC1 mucin, utilizing an aptamer that specifically targets the underglycosylated variable tandem repeat (VTR) that is commonly present in cancer cells. Of note, each MUC1 mucin has 18 to over 100 VTRs, this unique property allows GNPs to aggregate extensively even at extremely low protein concentrations. Initial studies will utilize synthetic peptide targets with 3-5 repeats of the VTR, successful results from this study will be the first step towards the detection of MUC1 mucin in pancreatic cancer cell lysates.
Undergraduates on this project will (a) learn to synthesize aptamer-modified gold nanoparticles (week 1-3), (b) study the effect of target concentration on sensor behavior (week 4-6), and (c) investigate the effects of ionic strength and sample matrix on sensor performance (week 7-10). Through these studies, the student will receive training and exposure to basic optical techniques and knowledge in nanoparticles and biosensor design. The undergraduates will work closely with a graduate student or postdoctoral researcher in the Lai group. The student must keep and maintain a laboratory notebook, which will be examined regularly by the supervising graduate student or postdoctoral researcher. The student will also be required to participate in the weekly group meeting and submit a written report on their work at the end of the program.
NANOSTRUCTURED MATERIALS
Magnetic interactions in nanoscale structures result in permanent magnet materials with significantly enhanced magnetic properties. The development of novel nanostructures via eutectic and other phase transformations during rapid solidification offers the potential to significantly improve permanent magnet performance, leading to higher energy products. The objective of this project is to develop new materials and processing routes for high-energy permanent magnets. Rapid solidification processing effectively refines the scale of the phases to the nanoscale level necessary for effective exchange interactions between grains and phases.
Undergraduate student projects will include determining the solidification microstructure in arc-melted ternary (and higher) alloys using optical and scanning electron microscopy, and phase analysis by x-ray diffractometry and use this information to construct microstructural selection maps for various alloys. Selected compositions will then be rapidly solidified by melt spinning. The resulting ribbons will be characterized using x-ray diffractometry and magnetometry, while the microstructures will be investigated by transmission electron microscopy. Students will conduct all of the analysis except TEM.
This project encompasses the processes of growth, characterization, development and control of a new class of semiconductors based on icosahedral building blocks and epitomized by the semiconductor boron carbide. The University of Nebraska-Lincoln's process of plasma-enhanced chemical vapor deposition has successfully produced a semiconducting form of boron carbide. The object here is a detailed understanding of how growth parameters, structure and electronic properties are intertwined, a necessary objective in order to make use of this rather unique semiconductor. Advanced characterization tools and continual feedback will provide the rapid advances necessary to make headway in this intricate materials problem. From a technological standpoint, understanding and materials development will lead to a wide range of devices enabled by the unique properties of this semiconductor. Two of these, an all solid-state neutron detector and magnetic tunnel junctions using boron carbide as the barrier layer will be developed and tested in depth.
Nebraska boasts a strong program on heterostructures with unique magnetic and magnetotransport properties. The functionality of these nanometric spintronics devices is based on the electric control of the interface magnetization in exchange bias heterosystems using molecular beam epitaxy (MBE) growth of magnetoelectric/ferromagnetic exchange coupled thin films. A major goal is the realization of a spintronics prototype device. This challenging task must be broken down into several steps. An important step on the way toward a working spintronic multilayer device is the growth of pinhole free and epitaxial (111) oriented Cr2O3 thin films of a few nanometer thickness. Recently, our group succeeded in growing these films on an Al2O3 surface by evaporation of metallic Cr and simultaneous O2 inlet into the UHV chamber. In addition to the optimization of the magnetoelectric susceptibility and the antiferromagnetic ordering temperature of Cr2O3 thin films, it is paramount to improve the dielectric properties of the films for spintronic applications. The dielectric characterization can be done by four-point resistance measurements at temperatures between 20 and 470 K.
Undergraduate participants involved in this area will be introduced to the four-point measurement technique and determine the temperature-dependent resistance of the films. In addition, characterization of the magnetic properties of all Cr2O3 films grown by MBE is routinely done by, for example, atomic force microscopy. With the resulting data, the quality of the films from a magnetic and dielectric point of view can be determined. This characterization of each individual Cr2O3 film is an important step for further processing of the films. Additionally, participants will be able to study the impact of magnetoelectric annealing on the antiferromagnetic domain structure of the Cr2O3 films. Recently we evidenced the theoretical prediction of an unperturbed surface magnetic moment when the films are in a single domain state. Magnetoelectric annealing allows the single domain state to be approached, and, hence, provides a mechanism to tune the surface moment of the film. Magnetoelectric annealing requires the simultaneous presence of electric and magnetic fields when cooling below the Néel temperature. Applying a magnetic field is easily achieved with our new magnet, which is designed to be compatible with the new cryostat. Applying electric fields requires an electrical contact on the films with the help of optically transparent electrodes. Making such contacts and performing magnetic and dielectric characterization after magnetoelectric annealing are well-defined but challenging tasks for an undergraduate student.
NANOSCALE RESPONSE of MATERIAL
Residual stresses are of practical importance in bulk materials and coatings, which critically affects their mechanical integrity and reliability. In the recent years the method of nanoindentation has been effectively used to investigate the local stresses in metallic components of MEMS. With the increasing application of polymers in micro- and nano-mechanical systems it is expected that the unavoidable residual stresses have an enormous effect on their mechanical performance as well. However, unlike metals and alloys the mechanical performance of polymers is strongly affected by their viscoelastic properties. Therefore the present models and methods have to be adapted to the specifics of polymers.
The first task of the undergraduate student will be a construction of a 4-point bending-beam sample holder to be used in an existing high precision nano-mechanical scanning probe along the lines of the assemblies used for metals. With this apparatus the polymer blocks will be held under various defined stresses during the nano-indentation experiments. Afterwards, with the help of the mentor, the student will develop a testing routine of quasi-static as well as dynamic indentation experiments to investigate the time-dependent surface and subsurface responses of the polymers. With this project we expect at least one publication of high interest for nano-mechanical systems manufacturer.
Undergraduate students on this project will learn the fundamentals of scanning probe microscopes (SPM) including atomic force microscopes (AFM) and depth sensing indentation (DSI) instruments for nanoindentation. These techniques are essential tools used today for determining mechanical properties (storage modulus, loss modulus, hardness, etc.) of nanoscale materials. Quantitative measurements and imaging techniques will be emphasized. The students will work with a graduate student mentor on the equipment to perform training of each measurement mode until they are at a level sufficient to use the instrument alone. Then the student will be assigned a material system (e.g,. polymer composite, biomaterial, biological sample, etc.) that they will use as their sample for a small term project. The students will also learn about relevant contact mechanics associated with these probes so that they are aware of assumptions used in the instrumentation for extraction of mechanical properties.
Career Information and Job Opportunities for Undergraduate and Graduate Students:
American Institute of Physics Career Web Site
