MSE Colloquium Series
Autumn Quarter 2009
Starting Autumn Quarter 2009 each colloquium consists of two talks: 1 hour invited talk and a 15 minute MSE student/postdoc presentation showcasing research within MSE.
Fridays at 3:15 to 4:45 in McCullough Bldg, Room 115
Date |
Speakers |
|---|---|
Oct. 2 |
Taek-Soo Kim, Ph.D. Candidate Diffusion under Nanoscale Confinement The mobility of organic molecules when confined at nanometer length scales differ greatly from properties in the bulk. We demonstrate the surprising finding that linear alkane molecules exhibit a free volume dependent mobility under nanoconfinement in nanoporous organosilicate films that is exactly opposite to the conventional relationship observed in the bulk. As described by the free volume theory of diffusion, linear alkane molecules typically exhibit a lower free volume and mobility with longer chain lengths. However, under nanoscale confinement the molecular free volume appears to increase and the activation energy decreases with increasing chain length. The effects of molecular polarity and pore diameter on mobility are also considered. We further report on surfactant mobility in the nanoporous films which was found to exhibit signatures of reptation and be sensitive to molecular weight, hydrophilic/hydrophobic chain lengths, and molecular structure of linear and branched surfactants. ************ Shan X. Wang NanoMagnetic Materials and Devices for Biomedical Diagnostics Reproducible and multiplex protein assays are greatly desired by cancer biologists as well as clinical oncologists to rapidly follow numerous proteins in clinical samples. By simply applying patient serum or tissue samples to the magneto-nano sensor chip developed in our group, one can readily and quantitatively ascertain the presence or absence of a large number of tumor markers, such as those involved in HER-kinase axis pathway, in a multiplex format. This will allow physicians to determine the efficacy of relevant chemotherapy in real time. Combined with a different set of tumor markers, the new protein assays will also allow physicians to detect cancer early, e.g, stage 1 ovarian cancer, so that cancer survival rates can be improved greatly with early intervention. Combined with yet another set of protein markers such as CDKN1A and CRP, this new tool will permit the rapid triaging of individuals with <2 Gy or >2 Gy exposure in mass radiation exposure scenarios. We have now successfully applied magneto-nano biochips based on giant magnetoresistance (GMR) spin valve sensor arrays and magnetic nanoparticle labels (nanotags) to the detection of biological events in the form of multiplex protein assays (4- to 64-plex) with great speed (30 min. – 2 hours), sensitivity (1 picogram/milliliter concentration levels), selectivity, and economy [1,2]. Specifically, we have prototyped protein chips with an 8 x 8 array of 64 giant magnetoresistance (GMR) spin valve sensors. Each sensor is about 100 um by 100 um in area and covered with a unique protein feature which can be spotted robotically or mannually. The total area of the chip is about 10 mm by 12 mm, while the active 8 x 8 sensor array occupies an area of only 3 mm x 3 mm. Moreover, the sensors under an ultrathin passivation layer have proven to be chemically stable in aqueous solutions or serum samples. These chips are ideal for measuring multiple protein levels in a volume of only 10-50 uL of serum sample, from a human patient with minimal invasiveness. Our results indicate that magneto-nano protein chips have now become a realistic option for biomedical diagnostics, e.g., for multiplex molecular diagnostics of cancer, viral genotypes, ionizing radiation exposure, cardiovascular diseases, and other complex diseases. This work is supported by US National Cancer Institute, National Science Foundation, and Defense Threat Reduction Agency. References: Wang SX, Li G (2008) Advances in GMR Biosensors with Magnetic Nanoparticle Tags: Review and Outlook (Invited Review for Advances in Magnetics), IEEE Trans. Magn. 44:1687-1702. [2] Osterfeld SJ, Yu H, Gaster RS, Caramuta S, Xu L, Han SJ, Hall DA, Wilson RJ, Sun S, White RL, Davis RW, Pourmand N, Wang SX (2008), PNAS, 105, 20637-20640. |
Oct. 9 |
Sebastian Osterfeld, Ph.D. Candidate Fundamentals of GMB Biosensors To detect a superparamagnetic nanoparticle with a magnetoresistive sensor, how strong should the externally applied magnetic polarizing field be? Too little field, and the particle is not sufficiently magnetized (no signal). Too high a field, and the sensor saturates (no signal). A clear optimum field strength is observable in experiments. A simple analytical math model can be derived from a force balance (x- and y- components), which shows excellent agreement with the experiment. The extended 3-variable math model shows good experimental agreement with transverse field, longitudinal field, and sensor width signal dependence. ************ Matthew Kanan Catalytic Materials for a Fuel-Based Renewable Energy Cycle Storing renewable energy sources as chemical fuels and extracting electricity from these fuels on demand constitutes a renewable energy cycle that has the capacity to replace fossil fuel use. Such a cycle requires efficient electrocatalysts to mediate multi-electron oxidation and reduction reactions. This talk will describe a recently discovered cobalt-phosphate water oxidation catalyst and surface-modified O2 reduction catalysts. The cobalt-phosphate catalyst forms as an amorphous deposit on a variety of metallic and semiconductor substrates upon application of anodic potentials. X-ray absorption spectroscopy under operating conditions and electrochemical kinetic experiments have revealed the local structure in this material and enabled the formulation of a plausible mechanism. The electrodeposition methodology provides exquisite control over catalyst thickness and morphology. Implications of these capabilities for interfacing cobalt-phosphate with photoelectrodes in water-splitting photoelectrochemical cells will be discussed. In addition to the preparation of novel catalytic materials, electrodeposition can be used to modify the surfaces of existing heterogeneous catalysts. Recently, we have used this technique to deposit Lewis acidic layers on O2 electroreduction catalysts. Under suitable conditions in aqueous solutions, these redox-inactive layers enhance the O2 reduction activity of the underlying substrate. Possible origins of this effect will be discussed in the context of developing a general strategy to tailor heterogeneous electroreduction catalysts with surface-deposited functionality. |
Oct. 16 |
Ben Almquist, PhD Candidate Fusion of Biomimetic 'Stealth' Probes into Lipid Bilayer Cores The ability to specifically and non-destructively incorporate inorganic structures into or through biological membranes is essential to realizing full bio-inorganic integration. However, molecular delivery and interfaces to inorganic objects, such as patch-clamp pipettes, generally rely upon destructive membrane holes and serendipitous adhesion, rather than selective penetration and attachment to the bilayer. In fact, materials greater than a few nanometers have not been shown to penetrate lipid bilayers without disrupting the continuity of the membrane. I will discuss the development of nanofabricated probes that spontaneously insert into the hydrophobic membrane core by mimicking the hydrophobic banding of transmembrane proteins, forming a well-defined bio-inorganic lateral junction. These biomimetic 'stealth' probes consist of hydrophilic posts with 2-10 nm hydrophobic bands formed by molecular self-assembly, and are easily fabricated onto a variety of substrates including silicon wafers, nanoparticles, and AFM tips. By fabricating this architecture onto AFM probes, we have directly measured the penetration behavior and adhesion force of different molecular functionalities within the bilayer. Following insertion, stealth probes remain anchored in the center of the bilayer, while purely hydrophilic probes have no preferred location. The strength of the stealth probe adhesion varies greatly between short and long chain alkane functionalizations, indicating that chain mobility, orientation, and hydrophobicity all contribute to stability within the bilayer. In addition, the consequences of geometric factors such as band thickness and the presence of multiple bands on interface stability have been established. By selectively choosing the desired properties of the hydrophobic band, it is possible to tune the failure tension of the interface from values comparable to that of pristine lipid vesicles to only a fraction of the strength. Fan Yang Stem Cell and Biomaterials Engineering for Regenerative Medicine Tissue loss and organ failure is one of the most devastating and costly medical problems in current health care. Regenerative medicine aims to restore lost tissue structure and function via engineering biological tissue equivalents. Stem cells are attractive cell sources for tissue regeneration due to their unique capacity of self-renewal and differentiation into multiple lineages. However, methods must be developed to control stem cell differentiation before they can be used clinically. My research aims to overcome this hurdle by developing biomaterials to: (1) engineer stem cells via intrinsic genetic programming and (2) engineer stem cell microenvironment via extrinsic signaling. It is clear that genetic signals can promote lineage-specific differentiation of stem cells. Current major barrier is the lack of safe and efficient methods to deliver genetic signals into stem cells. Using high-throughput approach, large polymer libraries were synthesized and screened, which led to discovery of materials that can efficiently deliver genetic signals (DNA or siRNA) into stem cells with high efficiency, with minimal toxicity. In comparison to Lipofectamine 2000, one of the best commercially available transfection reagents, our materials showed 5x higher efficiency in DNA delivery to human mesenchymal stem cells, and virus-like efficacy in DNA delivery to human embryonic stem cell-derived cells. These materials were used to direct stem cell differentiation by either “turning on” a target gene, through DNA delivery, or “turning off” a gene via siRNA delivery. The therapeutic potential of such genetically modified stem cells is demonstrated in promoting angiogenesis and treating ischemic diseases. Example of engineering stem cells microenvironment via extrinsic signaling is also shown using functionalized hydrogel or osteoconductive scaffolds, and their potential to treat bony defects was evaluated in a mouse cranial defect model. The technology platforms described here also hold great promise for treating various disorders such as cancer, neurological and cardiovascular diseases. |
Oct. 23 |
Seok-Woo Lee, Ph.D Candidate Uniaxial compression of FCC Au nanopillars on an MgO substrate: the effects of prestraining and annealing The size dependent strength of FCC metals, as revealed by uniaxial compression of nanopillars, suggests that plasticity is dislocation source-controlled, with fewer sources in smaller pillars producing a “smaller is stronger” effect. To further investigate this phenomenon we have studied the effects of prestraining and annealing on the deformation properties of [001] Au nanopillars. By making pillars from an epitaxial film of [001] Au on [001] MgO, using focused ion beam machining, we are able to create both puck-shaped pillars that can be stably prestrained and pillars with a high aspect ratio, which can be tested in uniaxial compression. We find that prestraining dramatically reduces the flow strength of nanopillars while annealing restores the strength to the pristine levels. These are unusual effects are not seen in bulk FCC metals, which behave in an opposite way. We discuss their possible causes in terms of dislocation densities using transmission electron microscopy. ************ Peter Peumans In many solar cells, there exists a trade-off between ensuring complete light absorption across the solar spectrum and efficient charge collection. Complete light absorption requires that thick active layers are used, while charge collection improves for thinner layers. By enhancing the light intensity in the absorber layer, this trade-off can be circumvented resulting in more efficient solar cells. I will review how light trapping is done using ray optics and discuss the limits of this approach. Then, I will show how light trapping can be implemented in thin-film solar cells using photonic crystals and metal nanostructures (plasmonics) and will show that the limit of this approach is identical to that obtained in the ray optics regime. I will also discuss how metal nanostructures can be used as transparent conductors and will compare this approach to the various other approaches to low-cost transparent conductors that have been developed recently including those that use graphene or carbon nanotubes. |
Oct. 30 |
James R (Randy) Groves, PhD. Candidate Biaxial texturing of inorganic photovoltaic thin films using low energy ion beam irradiation during growth Ion beam assisted deposition (IBAD) is a process that can deposit polycrystalline films with defined crystallographic texture. A unique aspect of the IBAD process is its ability to deposit biaxially-aligned polycrystalline thin films on many different types of substrates (glass, plastic, metal tape, etc.) at room temperature. One possible application is the use of an IBAD template film for the heteroepitaxial deposition of inorganic photovoltaic materials such as silicon, germanium or CZTS. I will discuss some recent progress on the use of IBAD template films for the subsequent growth of silicon and germanium and for the direct deposition of textured polycrystalline silicon for solar cells. However, the exact mechanism for texture development of these template layers is not well understood. One well-studied system, magnesium oxide (MgO), has been successfully used as a biaxially textured template film for the heteroepitaxial deposition of high temperature superconductors, tunable microwave materials, and ferroelectrics. Here, I present data on the initial nucleation mechanism of biaxial texture in MgO. Experimental data shows that the initially polycrystalline MgO film textures at a thickness of ~2 nm. Reflected High-Energy Electron Diffraction images show the onset of texture occurs quickly and is somewhat analogous to a solid phase re-crystallization process. Increased understanding of the IBAD process through examination of this model system can be used to select and optimize other materials systems for photovoltaic applications. ************ Nanowires for Catalytic and Microfluidic Applications Nano science offers the promise of producing revolutionary advances in many areas of technology. This presentation will provide two application examples of nanowires (NWs) in the areas of catalytic oxidation of methane and flow velocity measurement respectively. First, catalytic oxidation of methane is critical to the usage of natural gas and emission control from combustion process. Catalysts based on one-dimensional (1D) nanostructures have the potential to predominantly expose a more reactive crystal plane and hence lead to higher catalytic activity per unit surface area. Catalytic transition metal oxides (α-Fe2O3 and CuO) were first synthesized by a simple and yet rapid flame synthesis method by directly oxidizing metals in the post-flame region of a flat flame. Rapid growth rates were observed for both oxides which are attributed to both the presence of H2O vapor and CO2 in the gas phase and a large initial heating rate of the metal substrate in the flame, that together generate thin and porous oxide layers that greatly enhance the diffusion of the deficient metal to the nanostructure growth site, and enable growth at higher temperatures than previously demonstrated. The catalytic properties of CuO NWs were further tested in the oxidation of methane reactions and nearly 40% of CH4 can be converted into CO2 in the presence of CuO NWs. Moreover, the catalytic activity of CuO NWs can be further improved by a brief H2 plasma treatment, indicating Cu(I) species is more reactive than Cu(II) in catalytic reaction. This study shows that transition metal oxides NWs are promising catalysts candidates for oxidation of methane or other hydrocarbons, and have the potential for large scale applications. Second, silicon nanowire (SiNW) configured as field effect transistors (FETs) were demonstrated to be able to measure the flow velocity of electrolytic solutions. The direction of conductance change of SiNWs depends on the doping type of the SiNWs and their location inside the microfluidic channel, and the magnitude of conductance change varies with the ionic strength and compositions of the electrolytic solution. The flow velocity sensing is a consequence of the streaming potential that is generated by the movement of counterions inside the electrical double layer. The streaming potential, which varies with the flow velocity and the ionic properties of the electrolytic solution, acts in the same way as the charged analytes in affecting the conductance of SiNWs by changing the surface potential. This study highlights the importance of considering the ionic transport, which can significantly change the conductance of nanowire FET sensors, in analyzing and optimizing sensing. |
Nov. 6 |
Paul Kempen, PhD Candidate Electron microscopy characterization of surface enhanced Raman spectroscopy (SERS) nanoparticles conjugated to biological materials SERS nanoparticles have a very strong and distinct Raman signal that can be used to track nanoparticles as they interact with biological materials. This makes them ideal candidates for use in cancer detection. We utilize both scanning and transmission electron microscopy (SEM/TEM) to locate and study these nanoparticles on and inside the biological material. Through SEM and TEM analysis we can study any aggregation that may occur as well as the effectiveness of any targeting agents that are used. In this way we can suggest improvements to the surface coatings of these nanoparticles to more successfully target cancer cells. ************ Dr. Dragan P. Uskokovic General Strategies for Multi-scale Designing of Fine Particles at Molecular Level Synthesis of fine particles is the first step to obtaining contemporary materials, whether for the direct application of their powders or for their further processing. Various bottom-up and top-down approaches for the designing of fine particles at molecular level, enabling the preparation of powders and compact materials of highly controlled properties, are the focus of our research programs in the field of advanced materials and nanotechnology. Oxide, non-oxide, metallic, polymer and nanocomposite core-shell particles, with ideal spherical particles with narrow size distribution, can be obtained by synthesis procedures developed in our laboratory. Wide classes of functional materials, including electronic, energy-related, sensor, optical, catalytic and biomedical materials, are the subject of this investigation. The aim of all these activities is to approach the solutions of some of the critical problems of sustained development in the field of energy, health, environment, water and other global challenges dominating our present and near future. |
Nov. 13 |
Jia Zhu, PhD Candidate Nanocone Structure for Advanced Photovoltacis Advanced photon management, involving both absorption enhancement and reflection reduction, is critical to all the photovoltaic devices, since it could improve the efficiency by minimizing optical and electrical losses, and cut cost by reducing material usage, process time and capital investment. Here we demonstrate a novel solar cell structure with an efficient photon management design. The centerpiece of the design is the nanocone structure, which is fabricated by a scalable low temperature process. With this design, devices with very thin active layer can achieve near perfect absorption because of both efficient antireflection and absorption enhancement over a broad band of spectra and a wide range of angles of incidence. The device efficiency of this design is significantly better compared to conventional devices. More excitingly, the design and process is in principle not limited to any specific materials, hence it opens up exciting opportunities for a variety kinds of photovoltaic devices. ************ Dr. Harry A. Atwater Hyper-Light Trapping Solar Cells: Light-Matter Interactions in Wire and Sheet Absorbers for Solar Energy Conversion Photovoltaics is currently transcending its former status as an elegant but expensive boutique energy technology, and is rapidly developing the potential to have a significant impact on global energy supply. Reaching this ultimate goal requires a reduction in the cost per Watt of generated electricity, which motivates effort toward both increased conversion efficiency and reduction in material utilization. Both are facilitated by enhancing the optical absorption in solar cell active layers. I will describe the use of micro- and nano-structures to enhance light absorption and reduce material use in solar cells, including high quantum efficiency wire array solar cells that enhance light absorption and photocarrier collection and plasmonic solar cell designs to enhance light trapping. Focusing on fundamental light-matter interactions we will explore solar cell light absorption relative to 'classical' light trapping limits for planar sheet absorbers. |
Nov. 20 |
Shankar Swaminathan, Ph.D. Candidate Nanoscale ALD interface layers for Germanium MOS devices ************ Kenneth E. Goodson Thermal Phenomena in Nanostructured Materials Novel materials based on nanowires, nanoparticles, and thin-film multilayers are enabling breakthroughs for energy conversion, computation, and data storage. Heat transfer in these materials plays a central role in performance and reliability, and this poses a wealth of fundamental questions: How is heat generated and conducted within nanowire transistors? What is the thermal conductivity of films laden with nanoparticles? Can nanowire films efficiently convert waste heat to electrical power? This seminar summarizes our research on the physics, metrology, and simulation techniques involved with thermal phenomena in nanostructured materials. Focus applications include phase change memory (PCRAM), thermoelectric energy converters, and thermal interface materials for microelectronics. |
Dec. 4 |
No Colloquium |