Home Institution: College of Menominee Nation
Major/Minor: Physics
MRSEC Mentor: Jim Kakalios
Optical Absorption of Mixed-Phase Thin Film Semiconductors
My summer research has been on the optical absorption of mixed-phase thin film semiconductors. For this work our lab fabricated many films of amorphous silicon with nanoparticle inclusion. The level of nanocrystals was varied each time and optical absorption tests were ran to characterize the samples. The test ran was the constant photocurrent method (CPM). CPM is a process to determine the optical absorption coefficient of samples. The optical absorption coefficient is then used to find out about the film's density of states, the Tauc or Optical Gap (minimum energy to make a band to band transition), and the Urbach Slope (measure of disorder in the sample). I compared the optical characteristics against the percent of nanocrystallites included in the sample to find trends. The main comparisons against nanoparticle concentration were absorption in low photon energies, change in the Urbach Slope, and change in the Tauc Gap.
Home Institution: Saint Mary's University of Minnesota
Major/Minor: Biochemistry
MRSEC Mentor: Uwe Kortshagen
Functionalization of Silicon Nanoparticles for Purposes of Bio-Imaging
One of the most exciting characteristics of silicon nanoparticles is their size-dependent ability to fluoresce at different wavelengths. This quality, combined with silicon's biocompatible nature, makes silicon nanoparticles an attractive option for bio-imaging applications. The goal of this project is to explore the potential of silicon nanoparticles for purposes of bio-imaging. The first step will be to functionalize said nanoparticles in order to readily disperse them in aqueous solutions. There are two methods of achieving this hydrophilicity. The first method involves the modification of silica (Si2) nanoparticles with amine and methyl phosphonate functional groups via the organosilane compounds 3-(Aminopropyl)triethoxysilane (APTS) and 3-(trihydroxysilyl)propylmethylphosphonate (THPMP). Another possible method involves encapsulating silicon nanoparticles inside a reverse micelle composed of a methoxy (polyethylene glycol) (mPEG) polymer. The second step of the project will be to maximize the functionalized particles' quantum yield, which is a measure of the particles' ability to fluoresce. In addition, the stability of the functionalized particles in water over extended periods of time will be improved.
Home Institution: University of California Berkeley
Major/Minor: Physics
MRSEC Mentor: Dan Dahlberg
Magnetic Response vs. Lift Height of Thin Ferromagnetic Films
When a magnetic force microscope scans a thin ferromagnetic film, theory predicts that the magnetic interaction between the microscope's magnetized tip and the sample's magnetic moments is a simple energy exchange that results in the same interaction energy, and therefore the same magnetic image, for all types of ferromagnetic materials. When comparing the magnetic interaction responses of different ferromagnets as a function of the scanning lift height, however, past experimental results showed response curves that did not align. The current research tests the validity of these results by running a more controlled version of the past experiment.
Home Institution: University of Puerto Rico at Mayaguez
Major/Minor: Chemical Engineering
MRSEC Mentor: Michael Tsapatsis
Synthesis and Characterization of C-Oriented MFI Membranes
MFI membranes have been widely investigated because of their potential applications for energy efficient separation processes. Interest in such materials rests in their ability to discriminate molecules based on size and shape as well as their high thermal and chemical stability. MFI membranes are synthesized under hydrothermal conditions in order to form a continuous zeolite layer on the substrate surface and following the deposition of 100 nanometers of zeolite particles. Zeolites particle morphology and concentration can affect the zeolite crystal orientation in the layer. C-oriented MFI membranes are interested because of their pore orientation, which is perpendicular to the support. A rapid calcination technique may be used to remove organic molecules occluded in the MFI pore structure, as well as limit debilitating crack formation, resulting in a higher quality membrane for separations applications.
Home Institution: University of Wisconsin Eau Claire
Major/Minor: Physics/Math
MRSEC Mentor: Steve Campbell
Atomic Layer Deposition of Titanium Oxide for use in Semiconducting Devices
Electro-optical devices such as LED's that incorporate nanoparticles as luminescent elements require several layers to function appropriately. Depending on the design, this may include electrodes, electron transport layers, hole transport layers, windows, and other blocking layers. Each component, if present, must be chosen with the appropriate energy levels and transport properties, so that the layers can work together to form a well-functioning device, where current flows uniformly through the device while efficiently generating light. Even when chosen appropriately, however, there can still be problems with the layers, which can cause them to short, burn out, or redirect current in an undesirable way. This project focuses on the refinement of two device layers planned for use in silicon quantum dot light emitting diodes: Titanium Oxide (TiO2), and nanoparticle doped Silicon Dioxide. Developments in Atomic Layer Deposition allow transition metal oxides such as Titanium Oxide to be deposited with excellent thickness control, high conformity, and low surface roughness, particularly compared to other deposition methods. Low surface roughness promotes a more uniform current distribution, which improves control of current flow. For this reason, the deposition of Titanium Oxide through the use of Atomic Layer Deposition is investigated, as an alternative electron transport layer. Nanoparticle layers themselves can be difficult to use, as current can flow along the edges of the particles without electron-hole pairs recombining within them. To create a more effective layer, the nanoparticles can be encapsulated in a much higher bandgap material, such as Silicon Dioxide. If the particles are packed densely enough, carriers will percolate through the nanoparticles by tunneling, without entering the conduction or valence bands of the oxide coating. However, the surface of the layer following encapsulation can be very uneven due to the nanoparticle morphology, so this project also investigates Silicon Dioxide with high concentrations of silicon nanoparticles, to refine the layer properties to a useable configuration.
Home Institution: Harvey Mudd College
Major/Minor: Physics
MRSEC Mentor: Dan Dahlberg
Magnetic Domain Wall Resistance in Permalloy Films
The behavior of magnetic domain walls in permalloy films will be explored using magnetic force microscopy (MFM) and vibrating sample magnetometry (VSM). NdFeB permanent magnets will be used magnetize permalloy films in opposite directions, creating a domain wall across the sample. In an effort to observe how NdFeB placement can “compress” the domain walls, MFM techniques will be used to observe the thickness of these walls as the magnets are moved closer together. Four-probe measurements across the sample will indicate how resistance is affected by the change in the size of magnetic domain walls.
Home Institution: Winona State University
Major/Minor: Chemistry/Math
MRSEC Mentor: Chris Douglas
Iridium complexes as organic semiconductors, synthesis and characterization
Solar energy is an important resource for the world as traditional energy supplies dwindle. One prospect for the future of solar energy is organic photovoltaic cells. They can be printed on large-area, flexible substrates, and seem to be much more cost-effective than traditional silicon solar cells. Although the best organic solar cells currently are around 5-6% efficient, recent advances show promise for the future. In this research, an iridium complex with a benzoquinoxaline ligand was synthesized and employed as a phosphorescent sensitizer in the donor layer of a bi-layer organic photovoltaic device. It has been shown that a guest phosphorescent sensitizer can allow for a long-lived triplet state in the host compound. This will enhance the exciton diffusion length as well as the overall efficiency.
Home Institution: Harvey Mudd College
Major/Minor: Physics
MRSEC Mentor: Chris Leighton
Iridium complexes as organic semiconductors, synthesis and characterization
Doped perovskites cobaltites are of considerable current interest as they display magnetic phase separation, and are suspected to have high magnetocrystalline anisotropy. We performed torque magnetometry on La0.70Sr0.30CoO3 (LSCO) crystals in order to directly determine the magnetocrystalline anisotropy constants. Standard practice in such measurements is to acquire torque magnetometry curves in magnetic fields large enough to completely saturate the torque. Surprisingly, we observed clear non-saturation in the torque vs. field curves of LSCO, preventing simple analysis. In order to explain this anomalous behavior we hypothesize that small non-ferromagnetic (non-FM) regions (arising due to magnetic phase separation) contribute significantly to the torque, but little to the magnetization. We discuss a fitting method designed to separate FM and non-FM components, enabling determination of the intrinsic FM anisotropy.
Home Institution: University of Pittsburgh
Major/Minor: Chemical Engineering
MRSEC Mentor: Lorraine Francis
Polymer Based Silica Coatings Research
Coatings are usually made of a solution, water in most cases, and particles such as silica. When this coating dries and solution leaves, the particles left behind are caught on the surface of the substrate with binder. Properties of the coating are thus directly related to how the particles are positioned and how they got there. The main regions or pathways that they take are evaporation, sedimentation, and diffusion. In this project, a new experiment is done where the coating is made of mostly a polyvinyl alcohol and water solution rather than pure water. The polymer chains complicate the process because they do not evaporate like water does when the coating dries but rather are entangled with the particles in the dry coating. The project looks at how the polymer behaves in the above three pathways, how the particles interact with it, and the properties of this new polymer based coating. To begin, the polymer solution is made and its viscosity is measured for various polymer concentrations. This is used to find important relationships like the Peclet and Sedimentation numbers. Through previous work, a drying map has been developed that predicts the drying behavior of a monodispersed particulate system containing no soluble polymer based on these Peclet and sedimentation numbers. The regions in which the particles could lay on the drying map are evaporation, sedimentation, and diffusion. Experiments are run to see this in actuality at different regions of drying in the coating through different pathways and conditions. To image this, the sample can be frozen in liquid nitrogen and broken to be analyzed microscopically at the cross section with a Scanning Electron Microscope (SEM). The silica made was around 200 nm, 500 nm, and 1 um in diameter and the polymer will have a certain viscosity based on the concentration of the coating. Standards such as these are needed in order to have only the desired effect changing so that an accurate analysis can be made and the behavior predicted. Also with these standards it will be possible to see when samples move between the regions or pathways such as from evaporation to diffusion.
Home Institution: University of Minnesota Morris
Major/Minor: Chemistry
MRSEC Mentor: Efie Kokkoli
The Study of the Degradation of pH-sensitive Biodegradable Polymersomes for Cancer Targeting
Fighting cancer has continued to be a fundamental issue in the scientific community. Methods like conventional chemotherapy are being used, but they can have detrimental side effects to the patient. Self-assembled, nanoscale polymeric vesicles, also known as polymersomes, are drug delivery vehicles that can accumulate in tumors and release drugs in order to combat cancer cells. By modifying the surface of the particle with active moieties, specific cancer cells can be targeted with biodegradable polymers that are pH-sensitive. The goal of this research is to study the degradation of the diblock copolymers PMCL-b-PEO and (PMCL-co-PLA)-b-PEO. This will be done by tracking the release of fluorescent dye and the degradation of the polymers by chromatography at multiple values of pH. These two methods will provide data in order to determine at what pH each of the polymers will degrade as well as how long it will take for each to degrade. By knowing this, the polymers can be altered in order to find the optimal level of degradation which will reduce serious side effects through intracellular release and safe clearance from the body.
Home Institution: Case Western Reserve University
Major/Minor: Chemical Engineering
MRSEC Mentor: Eray Aydil/David Norris
Environmentally benign sulfide nanoparticles for solar cells
Excitonic solar cells made from nanocrystal quantum dots are being explored as an alternative to the currently used bulk or thin film solar cells due to a potential for increasing efficiency and lowering cost. However, most nanocrystal solar cells explored to date have been fabricated from materials containing lead or cadmium which being harmful to the environment limits the possibility of their commercial use. Cu2ZnSnS4 (CZTS) is being researched as an alternate to these materials. CZTS contains copper, zinc, tin and sulfur which are environmentally friendly, low-cost and abundant elements. Nanocrystal-based electronic devices require monodisperse nanocrystals for efficient operation. In order to synthesize size-selected, monodisperse single phase CZTS nanocrystals, complexes of copper, zinc and tin were used as precursors in an air-free synthesis.
Home Institution: Alabama
Major/Minor: Chemical and Biological Engineering
MRSEC Mentor: John Bischoff
Thermochemical Ablation Potential of H2SO4 and H3PO4, Polyprotic Mineral Acids
Thermochemical ablation is the use of reaction energy from the mixing of two reagents to generate enough heat to destroy cells. This practice is being tested to create a means of destroying tumor cells that are currently inoperable due to surgical limitations. The purpose of this experiment is to determine the amount of heat that can be generated by strong polyprotic acids, such as H2SO4 or H3PO4, when mixed with a strong base, such as NaOH or NH4OH. By sequentially injecting first acid and then base into an in vitro gel phantom and measuring the temperature profile inside the reaction bubble over a time interval, the amount of heat the reaction is generating can be determined and utilized for the most efficient ablation of harmful tumor cells. After running experiments testing the energy created by the removal of each proton in various molar concentration of each acid and base, it can be seen that H2SO4 and H3PO4both show great potential for thermochemical ablation. Other than the potentially harmful salt build up in the H3PO4 - NaOH reaction and the loss of heat in the 3rd equivalent of the H3PO4 - NH4OH reaction, due to the unstable salt (NH4)3OH endothermically reverting back to its dibasic form, all experiments generated heat as hypothesized and show that polyprotic acids are a great next step in thermochemical ablation.
Home Institution: Macalester
Major/Minor: Chemistry
MRSEC Mentor: Ron Siegel
Analysis of Glucose Mediated Crosslinking Mechanism in A MPBA-co-AAm Hydrogel
Hydrogels are crosslinked polymer networks that are used in biomedical applications. Of specific interest are glucose-sensitive hydrogels based on poly(3-methacrylamideophenylboronic acid-co-acrylamide) (MPBA-co-AAm), which may be useful in glucose-sensing applications for treating diabetes mellitus. These hydrogels are prepared by redox copolymerization with different amounts of MPBA, and AAm, plus a crosslinker, methylenebisacrylamide (Bis). MPBA-co-AAm hydrogels undergo shrinking/swelling as a function of glucose concentration, due to the reversible formation/disruption of glucose mediated crosslinks between polymer chains, which coexist with the permanent crosslinks due to Bis. Thorough characterization of equilibria and dynamics of the glucose-mediated crosslinks will be needed in order to fully exploit the hydrogels for their intended purposes. Our experiment will consist of the following components: (1) Synthesis of MPBA from AAm and phenyboronic acid, by established procedures (2) Synthesis of MPBA-co-AAm copolymer hydrogels containing 10 and 20 mol% MPBA (3) Hydrogel Swelling: Cylindrical hydrogen will be immersed in PH 10 buffer containing various glucose and fructose concentrations. Control samples will be placed in sugar-free buffer solutions. When hydrogels have reached swelling equilibrium, their swelling degree will be assessed. (4) Compression test: Swollen cylindrical hydrogels will be placed between two parallel plates of a rheometer and hydrogels will be uniaxially compressed to 95% of their original thickness, and then hold at that thickness for several minutes. The force exerted by the hydrogel on the upper plate will be continuously recorded during the relaxation. We expect the force-time curve will reach a peak in the very beginning and decay as time goes by till it stays constant. The compression test will be used to mathematically formulate the relationship between the glucose concentration and the density of glucose croslinks in the hydrogels.
Home Institution: Iowa State University
Major/Minor: Chemical Engineering
MRSEC Mentor: Ed Cussler
Characterization of Gas Separation Polymer Membranes
This work focuses on membranes used for natural gas purification. Raw natural gas must be processed to remove excess carbon dioxide before it is sold. This has proved problematic in the past, because carbon dioxide plasticizes membranes reducing their selectivity. A new membrane was created by cross-linking poly(norbornenylethylstyrene)-b-poly(N,N-dimethylaminoethyl methacrylate) (PNS-b-PDMAEMA) with cyclooctene (COE). The resulting membrane has a carbon dioxide permeable phase, the PDMAEMA block, while the rest of the membrane is essentially gas impermeable. The cross-linking provides a structure for the permeable phase. This reduces the plasticizing effect. At this point, research is focused on measuring the permeability and selectivity properties of the membrane.
Home Institution: Augsburg
MRSEC Mentor: Lee Penn
Synthesis and Characterization of Dendrimer Encapsulated Iron Nanoparticles (Fe-DEN)
Dendrimers are three-dimensional polymers that can be used as nano-reactors to aid the synthesis of monodispersive metal nanoparticles. Our goal is to synthesize and characterize zero-valence monometallic Fe, and bimetallic FeAu core-shell nanoparticles using the dendrimer encapsulation method. The size distribution, chemical composition, and the oxidation behaviors of these monometallic and bimetallic particles are evaluated. Fe- and FeAu-DENs could have potential applications in biomedical application due to their abundant functional groups on the dendrimer surfaces and the magnetic cores. These particles could also be of interest in the applications of environmental remediation.
Home Institution: Winston Salem University
MRSEC Mentor: Tim Lodge
Analyzing Block Copolymers in the Formation of Micelles
Block Copolymers are defined as a polymer composed of molecules in which two or more polymeric segments of different chemical compositions are attached end-to-end. Block copolymers are used for drug delivery and commercial applications. Two types of block copolymers used in this experiment are poly-butadiene and poly-ethylene-oxide. Both of these block copolymers are observed and analyzed based on their behavior and interaction when mixed with ionic liquid and/or the cosolvent, dichloromethane. This process is also being analyzed in the formation of micelles. Micelles are described as an aggregate of surfactant molecules dispersed in a liquid colloid. Micelles are used in industry for detergency and solubilizing agents. A technique used to analyze this procedure is called dynamic light scattering. Dynamic light scattering is used to measure hydrodynamic radius of micelles as a cosolvent concentration to identify the formation of micelles. Through an interpretation of graph it is determined if micelles are formed and the size of the micelle using different cosolvent concentrations. This project will help in understanding the mechanism of formation of micelles.
Home Institution: Penn State, Hazelton
MRSEC Mentor: Dan Frisbie
Terminally Functionalized Oligothiophenes for Molecular Wires
Organic molecular wires consist of long conjugated capable of charge transport. We propose to prepare new thiophene- based molecular wires. Our strategy will have the following components: (1) Preparation of the thioaldehyde for anchoring onto a gold surface (self-assembled monolayer); HS-T-CHO, (2) Preparation of thiophene dialdehydes and acetonitriles for the step-wise synthesis of molecular wires by means of Knovenagle reaction. (3) A similar strategy will be used for building molecular wires utilizing Schiff base (imine) chemistry for which we will prepare the diaminothiophenes. Advantages of the Knovenagle approach include the lowering of the LUMO levels due to the strong election accepting nature of the cyano group, and the planar structures anticipated due to the CN…S interactions we observed in our lab working with the TCE and DCV chemistry. Synthesis of the dialdehydes is to be achieved following literature procedures, while that of the diaminothiophenes is less well-known as these molecules are unstable. We will attempt alternate routes such as the addition of electron withdrawing groups and phenyl spacers. Basic synthetic methodology employs bromination, Suzuki coupling, Stille Coupling, and Knovenagle reactions. Analysis of Polymers will include, NMR, X-ray crystallography, IR, thermal analysis and Mass spectroscopy data.
Home Institution: Florida A&M University
MRSEC Mentor: Ron Siegel
Effects of Polymer and Crosslinker Concentration on Porosity of Polyethylene Glycol and Gelatin, Crosslinked by Genipin or D,L-Glyceraldehyde
Polymer matrix systems have received increasing attention for the past few decades in many areas such as absorption, separation, and catalysis. Others uses have been in the areas of drug delivery, bone tissue engineering and biosensing. Our long term goal is to develop porous crosslinked polymeric networks to be used as supports or eluting systems for drugs, biomolecules, and cells. It has been shown that the polymer and crosslinker composition can influence the pore size of a matrix, and we wish to investigate these phenomena in a pair of biopolymers namely polyethylene glycol (PEG) crosslinked with genipin, and gelatin crosslinked with genipin or D,L -glyceraldehyde. We will also examine microwave processing to physically crosslink gelatin. We will characterize the tensile strength of our products by mechanical testing, and determine pore size distributions by mercury invasion, surface to volume ratios by B.E.T., and we will use scanning electron microscopy (SEM) to extract more detailed morphological information. Using factorial design approaches we hope to be able to identity the optimal concentrations of polymer and crosslinker leading to desired pore sizes in the biomaterials that we are studying.
Home Institution: Edina High School
MRSEC Mentor: Sang-Hyun Oh
Home Institution: Champlin Park High School
MRSEC Mentor: Frank Bates/Marc Hillymer
Toughening Epoxies
Varied weight percentages of block copolymer (poly(ethylene-alt-propylene) and poly(ethylene oxide)) modified epoxies were cured and tested. Controllable epoxy thermosets were used to create average molecular weights of 600, 2900, and 3700 g/mol between crosslinks. The study utilized a high molecular weight and low molecular block copolymer. The samples were tested to determine which formulation created the toughest epoxy. High school students will test different epoxies to determine which epoxy is the toughest. Students will use epoxy to fuse together a wood rod. Students will crack the epoxy using a razor blade and add weights to the horizontally positioned rod until the epoxy breaks. Students will calculate the force needed to break each epoxy.
Home Institution: Chicago Hope Academy
MRSEC Mentor: Chun Wang
Adapting Biomedical Engineering for the High School Classroom
In current research at the University, DNA plasmids are delivered to mammalian cells using a polymer for efficient uptake for development of DNA vaccines. Transfection is observed using a GFP (Green Fluorescent Protein) on the plasmid or a Fluorochrome die. In the Biology classroom, this basic process will be utilized to connect high school students to the modern uses of this biological engineering.
Home Institution: Minneapolis Edison
MRSEC Mentor: Kevin Dorfman
Shrinky Dink Microfluidics In the High School Classroom
Bringing microfluidics to the high school classroom has been helped by research showing that the children's toy, Shrinky Dinks, can be used to create inexpensive molds. This research uses the printed Shrinky Dink (SD) itself as the microfluidic device. Patterns of channels are created on the SD plastic using a laser printer. The channels are printed on the SD such that the ink forms the channel boundary. When heated, the plastic and the ink patterns shrink to about one-third their original length and width, while becoming up to nine times thicker. Printed and unprinted SD are shrunk together, sandwiching the ink between them, which channels forming in the un-inked areas. Fluid can then flow through the channels via capillary action.
Home Institution: Anoka Hennepin ISD 11
MRSEC Mentor: Eray Aydil
Inquiry Using Dye Sensitized Solar Cells
The curriculum for using Dye Sensitized Solar Cells (DSSC's) in a high school science classroom will cover the following National Science Standards: Inquiry, Motions and forces, Interactions of energy and matter, Earth and space energy in the earth system and Science and technology. This curriculum is intended for use in a Physical Science, Earth Science, or Environmental Science classroom. The curriculum could be adapted for a Physics or Chemistry course. The students will be constructing a DSSC and applying inquiry based activities to learn more about this type of solar cell.
Funded by the National Science Foundation through the University of Minnesota MRSEC under Award Number DMR-1420013
UMN MRSEC
435 Amundson Hall, 421 Washington Ave. SE, Minneapolis, MN, 55455
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