Home Institution: Mount Holyoke College
Major/Minor: Chemistry
MRSEC Mentor: Frank Bates
Amphiphilic Block Copolymer Interactions with Biological Model Membranes
Cell membrane lipid layers, comprised of lipids, proteins, and cholesterol, are susceptible to the formation of stabilized pores, which compromise membrane integrity. This work focuses on the use of commercially available, amphiphilic block copolymers, specifically Pluronic F68, consisting of poly(ethylene oxide) and poly(propylene oxide) blocks, to seal permeablized cell membranes. The underlying physical mechanism of membrane sealing is not yet understood, though it is known that block copolymer molecular weight and chemical composition are critical to polymer integration into the amphiphilic lipid bilayer. By using model cell membranes derived from rabbit skeletal muscle tissue, we hope to gain a physiologically relevant understanding of the interaction between the model membrane and Pluronic F68. We will use a Langmuir trough to investigate polymer interactions with lipid monolayers and to verify polymer insertion and persistence in the monolayered membrane model. We will simultaneously visualize the resultant membrane morphologies using fluorescence microscopy. Finally, we will determine the impact of subphase composition on the behavior of monolayered membrane models by investigating several subphase formulations.
Home Institution: Angelo State University
Major/Minor: Physics
MRSEC Mentor: JianPing Wang
Development of Magnetic Tunnel Junction Based and All Spin Magnetic Logic Devices
As current complementary metal oxide semiconductor technologies are scaled, they are reaching limitations which have been increasing the demand for alternative forms of technology. One possible technology is magnetic based logic. As part of the summer MRSEC Research Experience for Undergraduate students, I will be working on fabrication and developing magnetic tunnel junction based and all spin magnetic logic devices. A top down process will be used in the NFC using tools such as e- beam lithography, photolithography, milling, reactive ion etching, and PECVD. Spin transfer torque and magneto resistive measurements will be used to test the operation of these devices. I will also be creating computer programs to assist in the testing and analysis of data taken from the completed samples.
Home Institution: Minnesota State University, Mankato
Major/Minor: Chemistry/Mathematics
MRSEC Mentor: Dan Frisbie
Structure-Property Relationships of Statistical Copolymers for Photovoltaic Applications
Polymer solar cells, based on solution- processable conjugated polymers, are among the most promising candidates for easily fabricated, low-cost devices. An important advantage of conjugated polymers is their compatibility with flexible substrates so that thin, lightweight devices can be constructed in a roll to roll manner. To obtain maximum efficiency it is critical to optimize the physical and optoelectronic properties of the active layer material (e.g. solubility, band gap, HOMO/LUMO, carrier mobility, absorption strength, stability). Advantageously, for conjugated polymeric materials these properties are synthetically tunable. For this investigation the synthetic route used for property tuning was statistical (random) copolymerization of structurally and electronically distinct monomers. By systematically controlling the fraction of monomer constituents in the polymer chain the optoelectronic properties of the resulting material were tuned. To investigate the structure-property relationships of these conjugated copolymers and their subsequent effect on device performance, three key optoelectronic properties were studied: the energy levels (HOMO and LUMO), the absorbance characteristics, and the charge transport properties. The study utilized cyclic voltammetry, UV-Vis absorbance spectroscopy, and thin film transistor methods respectively. Tuning various properties of conjugated materials through statistical copolymerization is an attractive route toward the development of higher performance polymer solar cells, and potentially an inexpensive, clean source of renewable energy.
Home Institution: Iowa State University
Major/Minor: Chemical Engineering/Mathematics
MRSEC Mentor: Efie Kokkoli
Synthesis and Characterization of PMDO
Targeted drug delivery has been explored as a viable option to better control treatments for diseases, such as cancer, by targeting specific characteristics that are enhanced in diseased cells. Promising drug delivery vessels, polymer vesicles, are made of amphiphilic diblock polymers that self-assemble in water. The zinc-catalyzed polymerization of 2-methyl-1,3-dioxan-4-one (MDO) will be studied and optimized for use in such an amphiphilic diblock polymer. The resulting polymer’s self-assembly properties in aqueous solutions, as well as its degradation properties, will also be studied. Additionally, these properties of PMDO will be compared to properties of a previously studied polymer, poly(γ-methyl-ε-caprolactone).
Home Institution: University of Pennsylvania
Major/Minor: Chemical & Biomolecular Engineering/ Energy & Sustainability, Chemistry
MRSEC Mentor: Tim Lodge
Efficient Formation of Multicomponent Ion Gels by Stepwise Self-Assembly of Thermoresponsive ABC Triblock Terpolymers
The gelation behavior of a poly(ethylene-alt-propylene)-b-poly(ethylene oxide)-b-poly(N- isopropyl acrylamide) (PON) triblock terpolymer in a room-temperature ionic liquid, 1-ethyl- 3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM] [TFSI]), will be studied by rheology over the concentration range 1-5 wt%. We expect to see gelation of the PON terpolymer at a much lower concentration and with a sharper sol-gel transition than comparable ABA triblock copolymers. We believe this is due to a stepwise gelation of PON terpolymers involving micellization at elevated temperatures and gelation at lower temperatures, which results in a two- compartment network that we hope to observe.
Home Institution: University of Pennsylvania
Major/Minor: Chemical and Biomolecular Engineering
MRSEC Mentor: Eray Aydil
Characterization of Cu2ZnSnS4 (CZTS) Thin Films for Photovoltaic Devices
Thin film photovoltaic devices are attractive because they possess both direct bandgaps and high absorption coefficients. This results in the need for much less material compared to silicon based cells. Currently however, most thin film devices contain relatively rare and expensive materials that could be a barrier to large scale commercial deployment. An appealing alternative is Cu2ZnSnS4 (CZTS) based solar cells, which utilize both non-toxic and more abundant elements. In this project, precursor Cu- Zn-Sn films will be deposited via co-sputtering. The films will then be sealed in an evacuated quartz ampoule and sulfidized at elevated temperatures (500°C - 600°C). By changing the ratios of Cu, Zn and Sn in the precursor films and studying the resulting morphologies, better control and understanding of the process can be obtained. X-ray diffraction and Raman spectroscopy will be used to identify CZTS and other secondary phases and will be supplemented with scanning electron microscopy. Ultimately, we hope this will bring us closer to developing impurity free, stoichiometric and phase controlled CZTS devices.
Home Institution: Rochester Community College / University of Minnesota
Major/Minor: Chemical Engineering and Earth Sciences
MRSEC Mentor: Michael Tsapatsis
Synthesis of 5-hydromethyfurfural (HMF) following the isomerization of fructose from glucose through the use of Zeolite
With carbohydrates accounting for close to 75% of the annual renewable biomass, fructose presents itself as a highly viable source for the synthesis of 5-hydroxymethylfurfural (HMF) which is considered a key intermediate chemical in the production of various valuable chemicals. Industrial isomerization of fructose from glucose is perceived as the critical step for the total effective production of HMF. However, current industrial processes are relative expensive due to the need for multiple reactors, various purification processes, the use of enzymes, and environmentally unfriendly catalysts and solvents. Furthermore, apart from the relatively high cost, the current preferred industry practice for the isomerization of fructose sees only a lowly 42% yield and this would propagate to a lower resultant yield of HMF. Numerous strategies are currently under development and amongst these strategies include the use of zeolites which exists in over a hundred different framework types. By the use of zeolites for the isomerization of glucose to fructose, and the further dehydration of fructose in dimethyl sulfoxide (DMSO), extraordinarily high selectivity of HMF of up to 92% has been reported. Through the adoption of specialized analytical techniques and equipment such as the High Performance Liquid Chromatography (HPLC) used to study the retention time of fructose, insight that will contribute toward the development of a more efficient overall conversion of glucose to HMF by the application of a highly selective catalyst can be established.
Home Institution: Louisiana State University
Major/Minor: Physics
MRSEC Mentor: Chris Leighton
Spin transport characterization of NiCu non-local spin valves at the Curie temperature transition
Investigation into the interaction of spin currents in magnetic devices is important to developing new spin-based electronics. The use of a pure spin current as opposed to a spin-polarized charge current can effectively circumvent unwanted phenomena caused by charge currents, such as the Anomalous Hall effect. One method for creating a spin current utilizes a non-local spin valve. The spin-dependent properties of this approach have not yet been characterized at the Curie temperature transition. NiCu non-local spin-valves are to be synthesized in a four terminal geometry using electron beam lithography and the spin transport properties will be characterized at the Curie temperature transition.
Home Institution: University of Texas-Pan American
Major/Minor: Chemistry/Communication
MRSEC Mentor: Chris Douglas
Investigative study: A closer look at the interaction of donor and acceptor molecules in diarylindenotetracene/C60 organic photovoltaic cells.
With a new diarylindenotetracene donor material for organic photovoltaic cells synthesized, questions about the interaction of the donor and acceptor layers at the interface level begin to arise. Does the donor layer react with the acceptor layer, and if so, what does this mean for the functionality of the solar cell? Are new compounds formed at the interface? If so, what are the structures? How can we detect it in the solar cell device? If formed at the interface in solar devices, what’s its role in the device, if anything? Does this give us a handle on optimizing the interface of the two layers? Direct and indirect approaches will be examined to characterize and understand the role of any new molecule that may form during device fabrication; as well as to understand the impact they may have on functionality of organic photovoltaic cells fabricated from these promising new materials.
Home Institution: University of Texas-Pan American
Major/Minor: Chemistry/Physics
MRSEC Mentor: Dan Frisbie
Organic Thin film Transistors (OTFTs) are emerging as a viable option for creating new and improved electrical products. Organic semiconductors offer low cost and easily processable flexible electronics. The accumulation layer, first few monolayers on top of the gate dielectric, is critical for transistor performance due to the current modulation within these layers. Two n-channel organic semiconductors, PTCDI-C8 and DNTT, will be fabricated onto silicon dioxide (SiO2), using thermal evaporation with varying deposition rates and substrate temperatures. Specific microstructure-property relationships in polycrystalline organic semiconductor films of N-channel PTCDI-C8 and DNTT will be examined using different variants of Atomic Force Microscopy (AFM) including Lateral Force Microscopy (LFM) and Kelvin Probe Force Microscopy (KFM). These scanning probe techniques will help elucidate the structure and electrical transport behavior in organic semiconductors such as electron and hole mobility on molecular structure, crystal packing, intermolecular bonding, and defects in organic crystals and films. Furthermore, research on n-channel organic semiconductors offers the potential of ambipolar OFET that increase the spectrum of available energy potential of transistors applicable in electronics of the future.
Home Institution: Bucknell University
Major/Minor: Chemical Engineering/Mathematics
MRSEC Mentor: Chris Macosko
Rheological Behavior of Branched Poly (lactic acid)
Poly (lactic acid) (PLA) is polymerized from corn products and is one of the first commercially produced biodegradable polymers. Recently PLA has begun to replace some traditional petroleum based products in applications such as food packaging. Until recently PLA could not be used in foaming processes due to its low extensional viscosity. The formation of foams requires good cell nucleation and cell growth, while preventing cell coalescence and cell collapse. Higher extensional viscosities make the cells stronger thereby reducing cell coalescence and collapse, however, if the extensional viscosity is too high processing becomes difficult. Branched and chain extended PLA has been produced in an attempt to improve the rheological properties of the material. Branched polypropylene exhibits an increased extensional viscosity compared to its linear form and the same trend is expected for branched PLA. The focus of this project is characterizing the rheology of the branched and chain extended structures to determine their viscoelastic properties and suitability for foaming processes. The characterization of these properties will be carried out using shear and capillary rheometry. A secondary focus is to further investigate the PLA structure through determination of glass transition temperatures and stereoisomerism using methods such as dynamic scanning calorimetry and nuclear magnetic resonance imaging.
Home Institution: University of Texas-Pan American
Major/Minor: Mechanical Engineering
MRSEC Mentor: Uwe Kortshagen
UV-Stable Silicon Nanocrystals to Enhance Solar Cell Efficiencies
Silicon nanocrystals possess an indirect band gap that has the potential to enhance photovoltaic (PV) efficiencies through luminescent downshifting. The nanocrystals absorb high-energy photons that are ineffectively utilized by the solar cells and downshifts them into low energy photons, which can then be efficiently converted into charge carriers by the cell. Nanocrystals with high conversion efficiencies, or photoluminescent quantum yields, are produced in a non- thermal plasma. Through a post-synthesis thermal hydrosilylation process, alkenes are attached onto the nanocrystals’ surface, which decreases surface defects and allows effective electron- hole recombination. Quantum yields of over 60% have been achieved; however, the conversion efficiencies of these nanocrystals degrade with exposure to UV light. To overcome this effect, a photochemical hydrosilylation process is proposed in lieu of the thermal hydrosilylation process.
Home Institution: University of Puerto Rico at Humacao
Major/Minor: Industrial Chemistry
MRSEC Mentor: R. Lee Penn
Hydrophilic Stability and Dispersion from Ligand Exchange
The conversion of hydrophobic nanoparticles into a water dispersible state is of great importance and generates active interest of researchers throughout the world. Ligand exchange to convert nanoparticles from hydrophobic to hydrophilic improves stability and dispersibility in water. Exchanging a BULKY ligand with a smaller one helps to decrease the separation distance between particles and, thus, increase the interparticle conductivity. Methods like X- ray diffraction (XRD), dynamic light scattering (DLS), and Ultra-violet Visible light (UV-Vis) spectroscopy will be employed to characterize ligand-exchanged nanoparticles. In particular, the band gap, the dispersion state, the average size of aggregates and primary nanoparticles will be quantified. Finally, RAMAN Spectroscopy will be used to determine the solid-state composition, and Attenuated Total Reflectance- Fourier Transform Infrared Spectroscopy (ATR- FTIR) analysis will be used to detect the surface-bound ligands before and after ligand-exchange, respectively.
Home Institution: University of Texas Pan-American
Major/Minor: Manufacturing Engineering
MRSEC Mentor: Andre Mkhoyan
Computer Simulated BF-CTEM and ADF-STEM of Modifed (MWW & MFI) Zeolites
I am studying zeolite structures modified to incorporate substitute atoms for novel catalytic applications. The modified zeolite structures will perform a particular task when encountered by a molecule diffusing through a substitute-functionalized pore, such as breaking down the molecule that has come into contact with the substitute atom (Ti or Sn). My specific job during this study is running computer simulations of bright-field conventional transmission electron microscopy (BF-CTEM) and annular-dark-field scanning transmission electron microscopy (ADF-STEM) to make sure that we can identify and locate catalytically active substitute atoms within the zeolite structure. Although experimental efforts to produce Sn and Ti substitutions in zeolite nanosheets are still in progress, and the imaging simulations I use do not include the effects of electron-beam-induced damage to the zeolites, these simulation results will determine the conditions in which BF-CTEM and ADF-STEM may be used to detect prospective substitute atoms in zeolites.
Home Institution: University of Texas Pan-American
Major/Minor: Chemistry/Biology
MRSEC Mentor: Ronald Siegel
Living Polymerization and Characterization of AB and ABC Block Polymers
Block polymers exist in different morphologies depending on both the number and composition of the blocks. Block polymers self assemble into structures that may change in response to environmental stimuli. For example, AB diblock and ABC triblock polymers can form micelles or hydrogels, respectively when placed in proper solution environments. Hydrogels and micelles formed from N- isopropylacrylamide (NIPAm: A block), acrylic acid (AA: B block) and N,N-diethylacrylamide (C block) exhibit temperature- and pH-sensitive behaviors, which may have applications in biomaterials and drug delivery. In this project, I will build up these AB and ABC block polymers using living reversible addition fragmentation (RAFT) polymerization. At each step, polymers will be characterized using matrix- assisted laser desorption ionization mass spectrometry (MALDI), ¹H -NMR, potentiometric titration, UV- spectrophotometry, and dynamic light scattering in order to determine block polymer molecular weight, composition and structure. Phase behaviors, including micellization and gelation, will be characterized as a function of pH and temperature.
Home Institution: University of Florida
Major/Minor: Materials Science and Engineering
MRSEC Mentor: Paul Crowell
Low-temperature annealing of non-ferromagnetic contacts to n-type GaAs
The measurement of spin transport in semiconducting materials depends on a heavily doped Schottky barrier contact. To reduce noise when taking measurements, there is a need for both ferromagnetic and nonferromagnetic contacts on the same device. The goal is to create such a device using low temperature annealing methods, and determining which annealing method results in the least noise when the contact is used as a voltage probe. Layers of PdGeAu and NiGeAu is deposited on to a GaAs/FeAlAu wafer and etched away to create contacts. Then, they will be annealed by one of the following proposed methods: laser annealing, local application of a high current, and low temperature furnace. Measurements of these contacts will be taken to determine method results in the best properties.
Home Institution: Florida A&M University
Major/Minor: Chemistry
MRSEC Mentor: Russ Holmes
Investigating a relationship between exciton decay rates of rubrene and tetra-para- CH3 rubrene and their molecular behavior
When an electron is excited from its ground state of energy, it jumps to a higher energy level. As this electron returns to a lower energy level; it could undergo two pathways: spontaneous and stimulated emission. We will focus on spontaneous emission which involves non-radiative and radiative exciton decay. Non-radiative decay produces phonons, or heat; whereas radiative decay ejects a photon. Both of these decay mechanisms are analyzed by testing various diluted solutions of rubrene and tetra-para-CH3 rubrene using a fluorimeter and photon counter. How these molecules interact with each other and alone are the main points of our research. Could exciton decay rates employ insight on the molecular behavior of rubrene and tetra-para-CH3 rubrene?
Home Institution: Carleton College
Major/Minor: Chemistry, Spanish
MRSEC Mentor: Phil Buhlmann
Integration of monolayer-protected Au cluster and tetrakis(4-chlorophenyl)borate anion doped nanocluster films in three-dimensionally oriented macroporous carbon contacts in solid contact ion-selective electrodes
The cost-effective fabrication, durability, maintenance-free operation, and high analytical performance of solid contact ion-selective electrodes (SC-ISEs) make them the most promising generation of potentiometric ion sensors to date. Tetrakis(4-chlorophenyl)borate (TB-) anion doped nanocluster films as solid contacts (SCs) have been shown to perform well when faced with most of the signal stability problems of ion-selective electrodes. Furthermore, monolayer-protected Au cluster (MPC) films have proven to be particularly capable SC transducers- yielding low potential drift and stable and reproducible linear range, sensitivity, and standard potential. We plan to synthesize MPC and TB- films and integrate them with three-dimensionally ordered macroporous (3DOM) carbon contacts, which have been shown to exhibit excellent long-term stabilities and good resistance to interferences from oxygen and light, in our SC-ISEs.
Home Institution: Xavier University of Louisiana
Major/Minor: Chemistry ACS/Mathematics
MRSEC Mentor: Aaron Massari
Interfacial Spectroscopy of Organic Electronics
Poly(3-hexylthiophene), P3HT, has long been studied within the realms of both chemistry and engineering because of its ability to efficiently conduct electricity with a primary focus on applications in organic electronics and solar energy. Though years of research has provided a sound foundation of knowledge on the system, many unknowns regarding stability and characterization of the materials remain. In particular, little is understood about what occurs electronically at the boundary the polymer would share with other organic substances, metals, or insulators. In this project, P3HT will be prepared as uniform thin films on appropriate substrates via a spin-coating process, and the characteristics of the interfaces will be measured through spectroscopy. In a first approach, films of varying thicknesses will be characterized by ellipsometry and UV-visible spectroscopy to extrapolate to the electronic absorption spectrum of the interfacial regions. A more sophisticated spectroscopic technique, second harmonic generation, will then be used to directly measure the electronic spectrum of the interfacial P3HT molecules. In this manner, we aim to divulge more about the electronic structure and properties of this interesting system and how the interface influences them.
Home Institution: Xavier University of Louisiana
Major/Minor: Chemistry ACS, Mathematics
MRSEC Mentor: Valerie Pierre
MRI is an in vitro imaging method; other imaging methods can’t do in vitro studies because skin absorbs light. MRI needs a contrast agent because it lacks spatial resolution. Magnetite nanoparticles have been under study due to their magnetic characteristics and role in biomedical devices such as magnetic resonance imaging. This study will investigate the induced aggregation of magnetite via Cu(I). The ligands, Dop-PEG-N3 and Dop-PEG-C≡CH, will be synthesized from using commercially bought NHS-PEG-Boc. Once these ligands are synthesized, Fe3O4 will be attached to each ligand. Then Fe3O4@Dop-PEG-N3 and Fe3O4@Dop- PEG-C≡CH will be “clicked” together using Cu(I)-catalyzed Huisgen cycloadditions. These particles will be characterized using TEM which will measure the size of the nanoparticles, relaxivity which shows how well the particles respond to magnetism, and XRD which shows the chemical composition of the nanoparticles synthesized.
Home Institution: Minneapolis Edison
MRSEC Mentor: Kevin Dorfman
Simple and Robust Engineering Projects for High School
This continued effort to provide low cost, but robust, engineering activities for high schools focuses on a stirred tank. Using modified building toys, students can design different impeller systems and compare their designs with others through dimensionless numbers such as the Reynold's and Power Numbers. This project allows students to investigate how material properties affect engineering design, and is simple way for teachers to implement the new Minnesota engineering standards into their lessons.
Home Institution: KMS High School
MRSEC Mentor: Bharat Jalan
Molecular Beam Epitaxy
Molecular beam epitaxy (MBE) is a method of depositing single crystals. MBE is widely used in the manufacture of semiconductor devices, including transistors for cellular phones and WiFi. Recently, the world's most efficient solar cells have been demonstrated with MBE and are being commercialized.
Home Institution: Aurora Charter School
MRSEC Mentor: Uwe Kortshagen
Bringing Materials Science Research into the Middle School Classroom
Semiconductor nanocrystals have attracted considerable interest for a wide range of applications including light-emitting devices and displays, photovoltaic cells, nanoelectronic circuit elements, thermoelectric energy generation and luminescent markers in biomedicine. Nanostructured materials research will contribute significantly to potential advances in next generation photovoltaics through development of new architecture for the design of highly efficient solar cells. In recent years, silicon nanocrystals (SiNCs) have become an attractive material for opto-electronic devices due to their unique properties which set them apart from their bulk material counterpart. This is my first summer working with materials science research. As a middle school teacher, I am interested in the development of analogies that challenge my students with some of the same issues that materials scientists do, while still working at an appropriate developmental level. One way to do that is using the Parallel Task approach. In this research experience I've been studying that gas-phase impaction of plasma-synthesized doped SiNCs has potential as an efficient method for depositing the n-type emitter layer for np junction solar cells.
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
P: 612-626-0713 | F: 612-626-7805