Symposium Organizers
Harry Radousky Lawrence Livermore National Laboratory/
Univ. of California-Davis
Rama Venkatasubramanian RTI International
Hong Liang Texas A&M University
Symposium Support
Lawrence Livermore National Laboratory
National Science Foundation, Thermal Transport Processes Program
E2: Magnetic/Mechanical Harvesting
Session Chairs
Viktoria Greanya
Harry Radousky
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
2:30 PM - **E5.1
Primary Photonic Processes in Energy Harvesting.
David Andrews 1 , Garth Jones 1
1 Chemistry, University of East Anglia, Norwich United Kingdom
Show AbstractIn molecular solar energy harvesting systems, quantum mechanical features may be apparent in the physical processes involved in the acquisition and migration of photon energy. With a sharply declining distance-dependence in transfer efficiency, the excitation energy generally takes a large number of steps en route to the site of its utilization; quantum features are rapidly dissipated in an essentially stochastic process. In the case of engineered dendrimeric polymers, each such step usually takes the form of an inward hop between chromophores in neighboring generation shells. A physically intuitive, structure-determined adjacency matrix formulation of the energy flow was previously developed to model the key harvesting and inward funneling processes. A numerical method based on this analytic approach has now been developed and is able to deliver results on significantly larger dendrimeric polymers, with the help of large multi-processor computers. Central to this study is the interpretation of key features such as the relevance of a spectroscopic gradient and the presence of traps or irregularities due to conformational changes and folding. With the objective of fine-tune the funneling process, this model now allows the incorporation of parameters derived from quantum chemical calculations, affording new insights into the detailed operation of the harvesting process in a variety of dendrimer systems.
E3: Poster Session: Energy Harvesting - All Topics I
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
2:30 PM - **E2.1
Thermal Energy Harvesting with a Hybrid Magnetostructural Materials System.
Laura Lewis 1
1 Chemical Engineering Department, Northeastern University, Boston, Massachusetts, United States
Show AbstractWhile there are many energy harvesting devices on the market today, plenty of room remains for innovation and performance improvement. Multifunctional materials systems offers exciting opportunities for energy harvesting by virtue of their ability to mix the characteristic order parameters of diverse functional materials for benefit in energy harvesting device design. In this presentation, a novel composite of a magnetostructural material combined with an electromagnetically-active polymer is proposed to create a hybrid multiphase thermal energy harvesting system. The materials characteristics of the hybrid system allow it to capture and transform thermal energy via two mechanisms: volume expansion to drive a piezoelectric effect, and abrupt magnetic polarization change to trigger a magnetoelectric response. Both effects are anticipated to simultaneously contribute a large electric potential difference that may be exploited to transform waste ambient thermal energy to electric energy.Magnetostructual materials exhibit simultaneous structural and magnetic phase transitions that may be driven by temperature, strain or magnetic field excursions. These phase transitions are characterized by significant changes in the unit cell volume and/or the crystal structure of the compound. Electroactive polymers (EAPs) are typically employed as components to exhibit a strain response upon exposure to an applied electric field, with applications such as artificial muscles. EAPs can also exhibit the inverse effect and produce an electric field when subjected to strain, such as that delivered by the volume change of a magnetostructural material in conformal contact. Beyond the primary piezoelectric-type response, a secondary magnetoelectric effect may be also be cultivated in this hybrid system through incorporation of magnetoelastic particles distributed throughout the EAP matrix. A suitable model materials system comprised of intermetallic FeRh particles within an EAP matrix is described. The key component in this proposed system is the FeRh compound that exhibits a unique and abrupt antiferromagnetic (AF)-to-ferromagnetic (F) transition at T = 370 K upon heating, accompanied by a large 1% volume change. The ideal incarnation of the proposed hybrid thermal energy harvesting system consists of a quasi-continuous layer of aligned FeRh macroscopic particles coated in a thin electroactive polymer containing a fine dispersion of aligned magnetoelastic particles. Materials and design challenges inherent to each system component and to the system overall are described.Acknowledgements: This work is supported by a linked grant through the materials world network scheme by the National Science Foundation under Grant No. DMR-0908767 and the UK Engineering and Physical Sciences Research Council, Grant No. EP/G065640/1.
E2: Magnetic/Mechanical Harvesting
Session Chairs
Viktoria Greanya
Harry Radousky
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
3:00 PM - **E5.2
Solar Thermoelectric Energy Conversion.
Daniel Kraemer 1 , Bed Poudel 2 , Hsien-Ping Feng 1 , J. Christopher Caylor 2 , Giri Joshi 3 , Bo Yu 3 , Xiao Yan 3 , Yi Ma 3 , Xiaowei Wang 3 , Dezhi Wang 3 , Andrew Muto 1 , Kenneth McEnaney 1 , Matteo Chiesa 4 1 , Zhifeng Ren 3 , Gang Chen 1
1 Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 , GMZ Energy, Waltham, Massachusetts, United States, 3 Physics, Boston College, Chestnut Hill, Massachusetts, United States, 4 Mechanical Engineering, Masdar Institute of Science and Technology, Abu Dhabi United Arab Emirates
Show AbstractThe conversion of sunlight into electricity has been dominated by two approaches: photovoltaic (PV) and solar-thermal power generation. Photovoltaic cells are mostly deployed as flat panels on rooftops or solar farms, while solar-thermal electricity generation technology relying on bulky optical concentrating systems and mechanical heat engines are used in large power plants. We discuss in this paper the potential of solar thermoelectric energy conversion. Theoretical modeling was carried out to predict the efficiencies of different types of solar thermoelectric generators. Prototype solar thermoelectric generators were constructed and achieved an efficiency of 4.6% under AM1.5G conditions and 5.2% at a solar intensity of 1.5 kWm-2.Acknowledgments: This material is partially based upon work supported as part of the “Solid State Solar-Thermal Energy Conversion Center (S3TEC), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number: DE-SC0001299 (G.C. and Z.F.R.), and by MIT-Masdar program (G.C. and M.C.).
E3: Poster Session: Energy Harvesting - All Topics I
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
3:00 PM - **E2.2
Energy Harvesting from Motion: Devices and Applications.
Eric Yeatman 1
1 Electrical Engineering, Imperial College London, London United Kingdom
Show AbstractEnergy harvesting – the collection of otherwise unexploited energy in the local environment – is attracting increasing attention for the powering of electronic devices. The key motivation is to avoid the need for battery replacement or recharging in portable or inaccessible devices. For devices at the cm size scale and smaller, the power levels that can be reached are typically modest, i.e. microwatts to milliwatts. However, this is sufficient for a reasonable number of applications, and as power requirements of electronic circuits fall, this number is increasing. Wireless sensor networks are a particularly important application: the availability of essentially maintenance free sensor nodes, as enabled by energy harvesting, will greatly increase the feasibility of large scale sensor networks, in the paradigm often known as pervasive sensing. Such pervasive sensing networks, used to monitor buildings, structures, outdoor environments or the human body, offer significant potential benefits for large scale energy efficiency, health and safety, and many other areas.Ambient motion is a key source of energy for harvesting, particularly where other sources such as light and thermal gradients are not available. A wide range of motion-powered energy harvesters have been proposed or demonstrated, particularly at the micro-scale. These have used a wide variety of transduction mechanisms and fabrication approaches. Besides power density, frequency of operation and bandwidth are important performance metrics, and the optimal design depends strongly on the intended application.This talk will review the principles and state-of-art in miniature mechanical energy harvesters, including MEMS devices, and discuss trends, suitable applications, and possible future developments.
E2: Magnetic/Mechanical Harvesting
Session Chairs
Viktoria Greanya
Harry Radousky
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
3:30 PM - E5.3
Broadband Antireflecting Conductive Metamaterial Films.
Nafiseh Pishbin 1 , David Crouse 1 2 , Igor Bendoym 1 , Michael Crouse 2
1 Electrical Engineering, City College of New York, New York, New York, United States, 2 , Phoebus Optoelectronics LLC, New York, New York, United States
Show AbstractA polarization-independent, broadband, antireflecting compound aperture array is designed, fabricated and characterized. The structure is composed of an aluminum film with a periodic array of perforations (apertures) configured in a square lattice with a unit cell consisting of two apertures with different diameters, both filled with silicon oxynitride. Light-channeling waveguide cavity modes of different energies are excited within the two different apertures within each unit cell thereby transmitting different parts of the solar spectrum into the substrate. Experimental characterization shows low reflection (<10%) and low diffuse backscatter. Numerous applications of the films include light detecting and emitting structures and devices. The broadband aspect of our device makes it a very good candidate for the use of this film as antireflecting electrodes for solar cells. The perforated films can be easily fabricated using common semiconductor fabrication techniques. They can be manipulated to transmit a wide range of bandwidths of light and can be either broadband or narrowband filters.
E3: Poster Session: Energy Harvesting - All Topics I
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
3:30 PM - E2.3
Effect of Piezoelectric Coupling on Performance in Piezoelectric Vibration Energy Harvesting.
Miso Kim 1 2 , Seungbum Hong 2 , John Dugundji 1 , Brian Wardle 1
1 , Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Materials Science Division, Argonne National Laboratory, Lemont, Illinois, United States
Show AbstractMechanical vibration based piezoelectric energy harvesters (PEHs) have received considerable attention as an enabling technology for self-powered wireless sensor networks. However, the biggest challenge with PEHs has been their insufficient power generation for practical applications, which necessitates creative and disruptive materials and structure design at various scales. To date, research in piezoelectric energy harvesting has focused on the development of more power efficient devices through the system optimization both in design level and fabrication. In this work, special emphasis is placed on the design and selection of optimal piezoelectric materials in terms of more power generation. Using a macroscopically verified analytical electromechanical coupled beam model, sensitivity of device performance to material properties of piezoelectric element such as elastic stiffness, dielectric constants, and piezoelectric coupling coefficients, is thoroughly analyzed both analytically and numerically. Notable in the observation that piezoelectric constant dominantly influences harvested power at off-resonance as widely noted, but that at the resonances an optimal value for a given device exists. This is intriguing because it is in contrast with the widely-held perception that higher piezoelectric coupling yields increased power generation. By showing how this optimization scheme can be applied to the actual piezoelectric harvesting system, materials design and selection for power-optimized piezoelectric energy harvesters is presented along with physical interpretation of optimal piezoelectric coupling as it relates to tunable device parameters such as system impedance.
E2: Magnetic/Mechanical Harvesting
Session Chairs
Viktoria Greanya
Harry Radousky
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
3:45 PM - E5.4
High Capacity Thermal Energy Storage Material for Low Grade Heat.
Joel Schmidt 1 2 , Douglas Dudis 1 , Douglas Miller 1 3
1 , Air Force Research Laboratory, Wpafb, Ohio, United States, 2 Department of Chemical and Materials Engineering, University of Dayton, Dayton, Ohio, United States, 3 Department of Science and Mathematics, Cedarville University , Cedarville, Ohio, United States
Show AbstractPhase change materials (PCMs) often have higher specific energy storage capacities at elevated temperatures. Thermal management systems capable of handling high heat fluxes in the temperature range from 20-50°C are necessary lacking. State of the art PCMs in this temperature range are usually paraffin waxes with energy densities on the order of a few hundred kJ/kg. However, for applications where system weight and size are limited, such as on aircraft, it is necessary to improve this energy density by at least an order of magnitude. The compound ammonium carbamate, NH2COONH4, is a solid formed from the reaction of anhydrous ammonia and carbon dioxide which endothermically decomposes back to CO2 and NH3 in the temperature range 20-50°C with an enthalpy of decomposition of ~1,800 kJ/kg. Various methods to use this material for thermal management of low-grade, high-flux heat have been evaluated including: bare powder, thermally conductive carbon foams, thermally conductive metal foams, hydrocarbon based slurries, and a slurry in ethylene glycol. A slurry in ethylene glycol is a promising system medium for enhancing heat and mass transfer for thermal management. Progress on system property characterization will be presented.
E3: Poster Session: Energy Harvesting - All Topics I
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
3:45 PM - E2.4
Surface and Size Manipulation of the Magnetic Properties of CdSe Quantum Dots.
Tony van Buuren 1 , Jonathan Lee 1 , Scott McCall 1 , Robert Meulenberg 2 , Daniel Haskel 3 , Jonathan Lang 3 , Lou Terminello 4
1 , LLNL, Livermore, California, United States, 2 Dept Phys & Astron, Surface Sci & Technol Lab, Univ Maine, Orono, Maine, United States, 3 , Argonne National Laboratory, Argonne, Illinois, United States, 4 , Pacific Northwest National Laboratory, Richland, Washington, United States
Show AbstractThe appearance of magnetism in otherwise nonmagnetic materials had previously been reported for a number of nanoscale systems and is the subject of substantial and ongoing research efforts. This is because coupling the size-dependent optical and electronic properties of the nanocrystalline materials with magnetic behavior opens the possibility for an extended range of technological applications. Significantly, conflicting origins are proposed in the literature for the magnetic behavior exhibited by a range of nanocrystals, which include the presence of dangling bonds on their surfaces, an intrinsic property only present at the nanoscale and an effect of ligands used to passivate the nanostructured material. We provide conclusive evidence that organic ligands used to coat CdSe nanocrystals have a fundamentally important effect upon their magnetic properties. Using x-ray absorption spectroscopy, magnetometry and x-ray magnetic circular dichroism, the research team demonstrate that the choice of organic ligand can be used to tune the magnetic properties. Moreover, their research indicates that a π-backbonding mechanism between the surface Cd atoms and the organic surfactants is responsible for some of the magnetic behavior of the nanocrystals and that, contrary to previous reports, they are paramagnetic and not ferromagnetic. The potential impact of this research in the field is considerable with the possibility of magneto-optic luminescent nanostructures and potential energy harvesting a point that is emphasized by recognition of the work as a ‘Research Highlight’ in Nature 2009, 459, 302-303
E2: Magnetic/Mechanical Harvesting
Session Chairs
Viktoria Greanya
Harry Radousky
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
4:00 PM - E2: Mag/Mech
BREAK
E3: Poster Session: Energy Harvesting - All Topics I
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
4:00 PM - E3: All I
BREAK
E2: Magnetic/Mechanical Harvesting
Session Chairs
Viktoria Greanya
Harry Radousky
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
4:30 PM - E5.5
Synthesis and Optical Spectroscopy of Highly Luminescent Type-II ZnTe/CdSe Colloidal Heteronanowires.
Esther Groeneveld 1 , Susanne van Berkum 1 , Celso de Mello Donega 1
1 Chemistry, Utrecht University, Utrecht, Utrecht, Netherlands
Show AbstractColloidal semiconductor nanocrystals (NCs) have opened up exciting new possibilities in the field of materials science. Control over the size and shape of the NCs makes it possible to tune the material’s optoelectronic properties without changing its composition. The tunability of the emission color, associated with large absorption cross sections over a wide spectral range, makes semiconductor NCs promising materials for energy harvesting applications. Semiconductor heteroNCs are particularly attractive because in these nanostructures the spatial localization of the photoexcited charge carriers can be tailored by manipulating the energy offsets between the valence and conduction band levels of the materials that are combined at the heterointerface. In type-I heteroNCs both carriers are primarily localized in the same material, whereas in type-II heteroNCs electrons and holes are spatially separated, leading to the formation of an indirect exciton. This offers the possibility of directly controlling the electron-hole overlap, and consequently the material optoelectronic properties (e.g. emission wavelength, exciton radiative lifetimes, etc.), with important consequences for a number of potential applications. ZnTe-CdSe is an attractive semiconductor combination for type-II heteroNCs, since the energy offsets between the bulk valence and conduction bands are large (viz., 0.9 and 1.5 eV, respectively) and the lattice mismatch between the two materials is very small (<1%). In this work we have synthesized highly luminescent ZnTe/CdSe colloidal heteronanowires by using a multistage approach in which ZnTe magic size clusters are used as seeds. The optical and structural properties of the nanowires were investigated by a number of techniques (viz. absorption, emission and excitation spectroscopy, PL quantum yields, exciton lifetimes, transmission electron microscopy, and X-ray diffraction). The ZnTe/CdSe nanowires are very narrow (~2 nm in diameter) and can be up to ~50 nm long. The exciton photoluminescence (PL) ranges from ~600 to 750 nm with high quantum yields (up to 55%). The exciton radiative lifetime is up to ~500 ns and the absorption cross section at emission wavelengths is rather small. These optical properties clearly indicate the formation of an indirect exciton, and make ZnTe/CdSe colloidal heteronanowires attractive materials for solar energy harvesting and conversion. The indirect exciton formation and large surface/volume ratio should facilitate charge carrier separation and extraction and therefore enhancing the efficiency of photovoltaic devices based on the nanowires as active components. Moreover, ZnTe/CdSe nanowires are promising light converters in solar concentrators due to their large absorption cross-sections in the UV-Visible range associated with small emission reabsorption and high PL quantum yields.
E3: Poster Session: Energy Harvesting - All Topics I
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
4:30 PM - **E2.5
Thermomagnetic Energy Harvesting Using Ferromagnetic Materials.
Greg Carman 1 , Chin-Jui "Ray" Hsu 1
1 Mechanical & Aerospace Engineering Department, University of Californa-Los Angeles, Los Angeles, California, United States
Show AbstractPrevious analytical studies on thermomagnetic generation suggest efficiencies on the order of 50% of Carnot, substantially superior to current Seebeck devices (10-20% of Carnot). However, experimental and analytical studies conducted at UCLA indicate that multi-domain ferromagnetic elements efficiencies are on the order of 10%, i.e. similar to current Seebeck devices. The efficiency of thermomagnetic generation is proportional to ΔM/ΔT in a thermomagnetic cycle; and therefore, by increasing the magnetization energy during a given cycle or minimizing the temperature change during a given cycle will increase efficiencies. The work conducted at UCLA to increase the efficiencies of a thermomagnetic system focuses on ferromagnetic thin films and nanoscale single domain structures fabricated using ebeam evaporation, ebeam lithography and lift-off process. The results include fabricating and characterizing the magnetic properties of Gd and Ni thin films (~50nm) and nanoscale structures (~1000x200x50nm3) using XRD, TEM, MFM, and SQUID measurement techniques. Results indicate that the magnetization energy during a thermal cycle can be increased for single domain structures providing an increase in efficiencies.
E2: Magnetic/Mechanical Harvesting
Session Chairs
Viktoria Greanya
Harry Radousky
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
4:45 PM - E5.6
Multifunctional Fiber Solar Cells with Nanocomposite Materials.
Adam Rice 1 , Zuki Tanaka 2 , Bin Chen 3
1 Department of Chemistry, Carnegie Mellon Univ/NASA USRP Fellow, Pittsburg, Pennsylvania, United States, 2 , UCSC, Santa Cruz, California, United States, 3 , NASA/UCSC, Moffett Field, California, United States
Show AbstractFiber solar cells provide an opportunity to surpass both the efficiency and functionality of traditional flat panel solar cells. We report the lab version of the fiber lighting/PV device development with composite materials. This lighting/PV multifunctional device has the advantage of high efficiency light usage due to the following features: 1) different wavelengths of light are absorbed by various wavelength sensitive coating materials at various locations on the surface of the waveguide; and 2) unabsorbed light remains inside the waveguide due to optical confinement (total internal reflection) until exit at the fiber tips for lighting. The waveguide-like fiber device can be optimized to transmit visible light through total internal reflection, and absorb the evanescent light in the solar cells fabricated around optical fibers. These cells can be created without using silicon, resulting in both an efficient and economical solar cell. To maximize efficiency, the absorption layer must strongly absorb in both the visible and infrared (IR) regions of the electromagnetic spectrum. PbS quantum dots (strong IR absorbance) are placed onto TiO2 nanotubes (strong UV absorbance) by chemical deposition to achieve a broad absorption spectrum. The conducting polymer Poly(3-hexylthiophene) (P3HT) is added to improve visible absorption and promote electron injection into the nanotubes. PbS and P3HT were also chosen for their band gap energies that favorably align with the TiO2 nanotubes, increasing the transfer of excited electrons into the nanotubes. These new solar cells based around cylindrical optical fibers, provides two distinct advantages over flat panels that should both lead to increased efficiency. First, internal reflection occurs within the fiber. If light enters the fiber and is not absorbed by the cell, it is reflected further down the length of the cell until it is absorbed, or transmitted and used for lighting. This is in stark contrast to flat panels, where any light not absorbed upon hitting the cell is reflected. The second advantage is that the cylindrical shape provides a greater absorption surface area compared to flat panels. The three-dimensional structure results in the absorption layer having a greater surface area than the traditional two-dimensional absorption layer. Both advantages can then be maximized by extending the length of the fiber, resulting in an increased number of internal reflections and an increased absorption surface area without making the end of the fiber cell any larger.
5:00 PM - E5.7
Prolonging Charge Separation in Highly Enriched Semiconducting SWNT:P3HT Composites.
Josh Holt 1 , Andrew Ferguson 1 , Nikos Kopidakis 1 , Brian Larsen 1 , Justin Bult 1 , Garry Rumbles 1 , Jeffrey Blackburn 1
1 , National Renewable Energy Lab, Golden, Colorado, United States
Show AbstractSeveral unique properties of single-walled carbon nanotubes (SWNTs) have motivated their investigation as potential replacements for fullerene derivatives as the acceptor phase of bulk heterojunction (BHJ) organic photovoltaic (OPV) devices. Although replacement of the ubiquitous fullerene acceptors by SWNTs in OPV devices has shown limited success thus far, the number of fundamental investigations of charge transfer between SWNTs and conjugated polymers is rather low. A consideration of the continuous density of states (lack of a true gap) for m-SWNTs suggests these species should act as recombination centers when interfaced with conducting polymers. We show the first experimental evidence that m-SWNTs indeed limit the generation efficiency and lifetime of the charge-separated state in these composites. We first demonstrate effective re-dispersion of isolated, highly enriched semiconducting and metallic SWNTs into the conjugated polymer P3HT, a critical step for forming a well-dispersed BHJ that optimizes interfacial area for charge transfer. Time-resolved microwave conductivity (TRMC) is utilized to probe the generation efficiency and lifetime of charge separation due to its inherent sensitivity to mobile charge carriers. TRMC results on BHJs containing varying proportions of s- and m-SWNTs demonstrate that the proportion of long-lived carriers produced by charge separation can be at least tripled by eliminating the metallic species. The negative impact of metallic nanotubes, which act as fast charge recombination centers, is discussed and encourages future implementation of SWNTs in photovoltaic active layers based on semiconducting-rich processing. Additionally, since the diameter of incorporated SWNTs affects both nanotube electronic structure and polymer interfacing, we also investigate varying diameters of SWNTs dispersed into conjugated polymer. Using various techniques, we characterize the role of SWNT diameter on charge transfer and discuss its implications on mating polymers to nanotubes for OPV applications.
E3: Poster Session: Energy Harvesting - All Topics I
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
5:00 PM - E2.6
Energy Conversion and Batteryless Nanosensors.
Yinmin (Morris) Wang 1 , Xianying Wang 1 , Donald Sirbuly 2 , Alex Hamza 1
1 Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Department of NanoEngineering, University of California, San Diego, La Jolla, California, United States
Show AbstractEnergy conversion is a fascinating field where multi-disciplinary scientists come together to tackle problems involved in the conversion of different energy sources. While the large-scale energy conversion has focused on solar energy and thermal energy, there are other types of nanoscale energy-conversions that also play significant roles in our daily life, e.g., for applications in powering nanoelectronics and sensors. This type of energy conversion unfortunately requires careful material selection and nanoscale device design such that the architecture can target multiple energy sources. This imposes tremendous challenges in the research. In this talk, we will present a versatile energy nanoconverter based on semiconductor ZnO nanowires that allows us to convert different types of energy sources into electrical power. We will demonstrate our device potentials by directly converting thermal and chemical energy into electricity by using the same platform. The physical principles and potential applications of our devices will be discussed. Finally, we will present a new type of self-powered chemical sensors that evolve from our energy-conversion platform.
E2: Magnetic/Mechanical Harvesting
Session Chairs
Viktoria Greanya
Harry Radousky
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
5:15 PM - E5.8
Improving Short-wavelength Response of HIT PV Solar Cells Using Down-converting Luminescent Nanoparticles.
Davood Shahrjerdi 1 , Bahman Hekmatshoar 1 , Ali Khakifirooz 1 , Arjang Hassibi 1 , Devendra Sadana 1
1 , IBM T J Watson Research Center, Yorktown Heights, New York, United States
Show AbstractSemiconductor luminescent nanoparticles may find application in photovoltaic (PV) solar cell technology by improving the intrinsic spectral response conventional solar cell structures. The photoluminescence characteristics of these nanoparticles can be engineered by the particle size and choice of material to create optical energy down-converters. The idea is to implement specific particles which absorb at short wavelengths (e.g., λ<400nm) where the PV cell exhibits poor spectral response while emit at long wavelengths (e.g., λ>600nm) where the cell has an acceptable spectral response. In this work, we have studied both in theory and practice, the impact of CdSe/ZnS core-shell nanoparticles on the performance of Heterojunction with Intrinsic Thin layer (HIT) solar cells. The HIT solar cell structure is attractive as it offers low-temperature processing (<200C), while producing >20% energy conversion efficiency. We fabricated the HIT solar cells on n-type crystalline silicon substrates, by first growing two stacks of intrinsic/doped a-Si:H (~10nm) on both sides of a silicon wafer. Next, an indium thin oxide anti-reflection coating was sputtered on the front side of the cell, followed by the deposition of the front and the back metal contacts. Due to the strong absorption properties of the solar spectrum in a-Si:H, the HIT cells suffer from poor spectral response in the λ<450nm wavelength range. Additionally, from the solar cell reliability viewpoint, it is favorable to convert the high-energy photons to photons with lower energies. After the cell fabrication, several types of CdSe/ZnS core-shell nanoparticles, dispersed in toluene, were spuncast onto the PV cells surface. The spectral response of the cells was examined through quantum efficiency (QE) measurements with and without nanoparticles. The QE results indicate improvements in UV/blue range up to 100% after the application of ‘proper-sized’ nanoparticles, while the QE of the cells remained unchanged over the visible and infra-red range. Furthermore, the reflectance of the cells remained unchanged upon in the presence of the nanoparticles. From the QE and absorption data, it can be inferred that the improvement of the spectral response of the PV cells at the short wavelengths is attributed to the conversion of short wavelength photons to those with wavelengths in the visible range, i.e., successful optical down-conversion. In addition to the experimental data, we will present analytical formulations which can predict the effectiveness of luminescent nanoparticles in a given PV technology.
E3: Poster Session: Energy Harvesting - All Topics I
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
5:15 PM - E2.7
Hybrid BaTiO3-PVDF Piezoelectric Composites for Vibration Energy Harvesting Applications.
Veronica Corral-Flores 1 , Dario Bueno-Baques 1 , Ronald Ziolo 1
1 Advanced Materials, Research Center for Applied Chemistry, Saltillo, Coahuila, Mexico
Show AbstractHybrid piezoelectric composites were obtained by embedding barium titanate (BTO) nanofibers into a polyvinylidene fluoride (PVDF) matrix. Green BTO fibers were obtained by electrospinning a precursor polymeric solution under an electric field ranging from 1 to 2 kV/cm. A network of non-woven ceramic BTO fibers was obtained after calcination of the green fibers. A PVDF solution was deposited over the ceramic fibers by spin-coating and then subjected to a low temperature heat treatment, to evaporate the solvent and promote the crystallization of the polar beta phase of PVDF.In average, the diameter of the ceramic fibers ranged from 250 to 700 nm, presenting ribbon-like shape in some cases. Crystalline phases of BTO and PVDF were confirmed by X-ray diffraction and infrared spectroscopy, respectively. The piezoelectric composites were subjected to a two-step DC-AC poling protocol to enhance the polarization of both the ceramic and polymer phases. Relaxation fenomena in the hybrid piezoelectric composites were investigated by impedance spectroscopy. Dielectric properties, electromechanical coupling coefficient as well as remanent polarization hysteresis of the poled composites were obtained to infer its suitability as piezoelectric transducer for vibration energy harvesting in applications where weight is a critical factor.
E2: Magnetic/Mechanical Harvesting
Session Chairs
Viktoria Greanya
Harry Radousky
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
5:30 PM - E5.9
Characterization and Performance of a Novel Squaraine Dye Near-infrared Absorbing Layer in a Tandem Bulk Heterojunction Photovoltaic Device.
Susan Spencer 1 , Jason Staub 1 , Amber Monfette 1 , Christopher Collison 1 2
1 NanoPower Research Laboratories, Rochester Institute of Technology, Rochester, New York, United States, 2 Department of Chemistry, Rochester Institute of Technology, Rochester, New York, United States
Show AbstractOrganic solution-processed photovoltaics offer a cost-effective and easily implementable alternative to conventional photovoltaic silicon-based devices. One of the fundamental issues facing the commercialization of these organic solar cells is their comparatively low efficiency. In order to increase the device efficiency both the structure of the device and the materials has been modified extensively. By incorporating a near-infrared absorbing layer into a tandem monolithic stack device a larger portion of the solar spectrum can be harvested increasing the IPCE of the device. We demonstrate comparatively high spectral response and open circuit voltage of the near-infrared absorbing layer based on inclusion of novel synthesized squaraine dyes as the acceptor and PCBM as the donor in a solution-processed spin-cast bulk heterojunction device. The devices demonstrated a range of EQE from 22 to 24 % over the spectral range of 590 to 725 nm. The devices exhibited VOC from 0.42 to 0.52 V. These devices have been measured at a variety of dye:PCBM ratios and with further optimization, efficiencies exceeding 3 % are predicted, which will give the tandem cell a predicted efficiency of greater than 7 %. We believe that through continuing optimization of the donor-acceptor interface morphology through techniques such as steady state and time-correlated spectroscopy, microscopy, and time-correlated single photon counting fluorescence lifetime characterization, a fundamental understanding of the charge carrier generation and diffusion processes will allow for the creation of the tandem device at the predicted efficiency. inclusion of novel synthesized squaraine dyes as the acceptor and PCBM as the donor in a solution-processed spin-cast bulk heterojunction device. The devices demonstrated a range of EQE from 22 to 24 % over the spectral range of 590 to 725 nm. The devices exhibited VOC from 0.42 to 0.52 V. These devices have been measured at a variety of dye:PCBM ratios and with further optimization, efficiencies exceeding 3 % are predicted, which will give the tandem cell a predicted efficiency of greater than 7 %. We believe that through continuing optimization of the donor-acceptor interface morphology through extensive spectral, microscopy, and fluorescence lifetime characterization the blend ratio and spin-coating conditions will allow for the creation of the tandem device at the predicted efficiency.
E3: Poster Session: Energy Harvesting - All Topics I
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Exhibition Hall (Moscone West)
5:30 PM - E2.8
Advances in Vibration Energy Harvesting Using Micromachined Piezoelectric Devices.
Dong-Joo Kim 1 , Jung-Hyun Park 1 , Seon-Bae Kim 1 , Hosang Ahn 1 , Bart Prorok 1 , Seung-Hyun Kim 2
1 Mechanical Engineering, Auburn University, Auburn, Alabama, United States, 2 Engineering, Brown University, Providence, Rhode Island, United States
Show AbstractWith higher integration, smaller size, and automated processes, sensors and wireless devices have seen dramatic enhancements to their quality, robustness, and reliability. Recent efforts have been made toward developing autonomous, self-powered remote sensor systems that can offer enhanced applicability and performance with cost savings. The technological challenge of realizing such a system lies in the construction and fabrication of a miniaturized power generator. This work focuses on the development of microscale piezoelectric energy harvesting devices to achieve maximum efficiency of power conversion. The two main factors in this work are the optimally structured materials and device structure and the highly effective electrical circuits to store and deliver piezoelectrically generated charges. MEMS-scale devices were designed and fabricated based on the modeling of macroscale PZT devices. The current design of MEMS-scale devices comprises a seismic mass made of silicon connected to the substrate by a thin PZT cantilever beam. Factors relating to power improvement and reliability of the device are discussed by addressing the shape of the piezoelectric layer, piezoelectric mode, piezoelectric materials, and environmental temperature. Tapering a beam shape resulted in higher power due to uniform strain along the beam direction compared with a rectangular shape. The generated power from individual electrodes built near the anchor, middle, and mass in a beam has good agreement with the strain distribution analyzed by an FEM simulation. Two modes in piezoelectric coefficients, i.e. d33 and d31, are compared by constructing PZT MEMS devices using interdigitated and planar electrodes. The d33 mode device is expected to present a higher output power, but presumed incomplete poling to the in-plane direction of a film may induce lower values compared with simulation results. The potential use of a relaxor PMN-PT for piezoelectric thin film is pursued for this application. Issues with the fabrication and materials’ constant are discussed. Current progress of MEMS and macroscale piezoelectric vibration harvesters is also summarized.
E1: Thermoelectrics I
Session Chairs
Joe Poon
Rama Venkatasubramanian
Tuesday PM, April 26, 2011
Room 2004 (Moscone West)
6:00 PM - E1: Thermo I
WITHDRAWN 02/23/11 In-situ Study of Morphology and Phase Evolution of Thermoelectric Materials During Heating.
Fei Ren 1 , Larry Walker 1 , Roberta Meisner 1 , Eldon Case 2 , Edgar Lara-Curzio 1 , Jane Howe 1
1 Materials Science and Technology Division, Oak Ridge Natinal Laboratory, Oak Ridge, Tennessee, United States, 2 Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
Show AbstractThe advancement of thermoelectric (TE) power generation technology depends on the development of novel TE materials. For practical applications, TE materials need to be stable over the temperature range for which they are designed. Since most TE materials are complex semiconductors, their thermal stability requires special attention. In addition, powder processing has become more popular for TE materials fabrication. Thus, the stability of TE powders at elevated temperatures also requires more thorough investigation. The current project examines the thermal stability of powders of LAST (Pb-Sb-Ag-Te) TE material. In particular, the morphology and phase evolution of LAST powders between room temperature and 823 K are studied under vacuum via in-situ scanning electron microscopy and X-ray diffraction. Our preliminary results indicate Sb-rich inclusions are less stable than the PbTe matrix while evaporation of Pb from the matrix results in a new phase containing Ag and Te. The new phase is likely Ag2Te.
Symposium Organizers
Harry Radousky Lawrence Livermore National Laboratory/
Univ. of California-Davis
Rama Venkatasubramanian RTI International
Hong Liang Texas A&M University
Symposium Support
Lawrence Livermore National Laboratory
National Science Foundation, Thermal Transport Processes Program
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
9:30 AM - **E7.1
Thermoelectric Properties of Half-Heusler Alloys and Nanocomposites.
Joseph Poon 1 , Di Wu 1 , Wenjie Xie 2 , Terry Tritt 2 , P. Thomas 3 , R. Venkatasubramanian 3
1 Physics, U. Virginia, Charlottesville, Virginia, United States, 2 Department of Physics & Astronomy, Clemson University, Clemson, South Carolina, United States, 3 Center for Solid State Energetics, RTI International, Research Triangle Park, North Carolina, United States
Show AbstractIn recent years, new approaches for controlling electron and phonon transports through nanostructuring have been developed, leading to a significant enhancement in the thermoelectric performance of existing materials. Half-Heusler (HH) alloys are investigated from the aspects of electronic structure and thermal transport for enhancing the dimensionless figure of merit, ZT, in the high temperature region 800-1000 K. Grain refinement and embedment of nanoparticles are employed to produce fine-grained as well as nanostructured bulk materials and nanocomposites. The first part of the talk will review electronic bandstructure of HH alloys in the vicinity of the band gap due to doping and substitutions of the different sublattice sites in light of first-principles electronic structure calculations. Preliminary results on fine-grained and nanocomposite half-Heusler alloys have shown ZT~1. Thermal transport in these materials will be discussed in terms of various phonon relaxation mechanisms, in particular that due to grain structure. Investigation is underway to further enhance ZT in these materials. We will also report on the results with p-n couples in these materials and power generation efficiency over a range of temperatures, with both conventional and nano HH alloys.Acknowledgement: Work supported by Army Research Laboratory through a Honeywell Contract No. 4202361403E at RTI International, UVA and Clemson University.
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
9:30 AM - **JJ1.1
Regulation of Stem Cells by the Mechanics of Cell-material Interactions.
Jianping Fu 1 , Humphrey Wang 1 , Wesley Legant 1 , Christopher Chen 1
1 Bioengineering, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Show AbstractAdhesion of cells to materials, natural or synthetic, appears to be a central regulator of cellular functions, including proliferation, differentiation, migration, and suicide. Adhesion involves not only receptor binding, but also changes in cell shape and the generation of mechanical stresses at these adhesions. Using microengineered materials as substrates for cell adhesion, we explore the relative contributions of these different aspects of adhesion to regulating cell function. In this presentation, we will present our recent progress on using microfabricated arrays of elastomeric posts as substrates for cell adhesion. The geometry of the microposts specify their rigidity, and their deflections report the forces generated by attached cells. Our studies demonstrate that mechanical forces generated either internally by the cytoskeleton or externally regulate cell structure and cell-matrix adhesions, and in so doing, modulate signals that control cell function. We show that these force are central to driving growth, multicellular patterning, and stem cell lineage commitment. We will also show some early studies on the development of a new approach to extend force measurements to the context of cells embedded within a 3D hydrogel. These studies highlight the importance of novel engineering and materials approaches to inform our basic understanding of how cells respond to their environment.
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
10:00 AM - E7.2
Microstructures-lattice Thermal Conductivity Correlation in Bulk Nanostructured Zr0.25Hf0.75NiMxSn (M=Ni, Co) Composites.
Dinesh Misra 1 , Julien P. A. Makongo 1 , Michael R. Shabetai 1 , Pierre F.P. Poudeu 1 2
1 Advance Materials Research Institute, University of New Orleans, New Orleans, Louisiana, United States, 2 Department of Chemistry, University of New Orleans, New Orleans, Louisiana, United States
Show AbstractThe reduction in the thermal conductivity and the understanding of its causes in terms of microstructural feature has become the current interest in maximizing the thermoelectric properties in existing half-Heusler alloys. We report microstructural studies of bulk nanostructured Zr0.25Hf0.75NiMxSn half-Heusler (HH) composites containing metallic full-Heusler (FH) nanoinclusions fabricated via solid state reaction of pre-synthesized bulk Zr0.25Hf0.75NiSn matrix with excess elemental Ni or Co. A drastic reduction (~55%) in the lattice thermal conductivity was observed for the Zr0.25Hf0.75Ni1.6Sn composite containing 60 mole % of the FH phase. The observed large reduction in the lattice thermal conductivity is attributed to the formation of nanometer scale regions of alternated layers of HH and FH phases within the composite with a spatial composition modulation of ~2 nm. The lattice thermal conductivities of the synthesized nanocomposites are correlated to microstructural details such as spinodal decomposition regions, nanometer scale precipitates, defects and interfacial dislocations.*Corresponding author. Tel: +1-504-280-1057; Fax: +1-504-280-3185 E-mail address:
[email protected] (P.F.P. P)
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
10:00 AM - **JJ1.2
The Role of Surfaces in Protein Structure and Function: Amyloid Fibril Formation.
Zoya Leonenko 1 2
1 Physics and Astronomy, University of Waterloo, Waterloo, Ontario, Canada, 2 Biology, University of Waterloo, Waterloo, Ontario, Canada
Show AbstractMany proteins are known to actively interact with biologically relevant as well as inorganic and synthetic surfaces that are widely used in nano- and bio-technology. The surfaces interact strongly with proteins and significantly affect their structure and function. Amyloid fibrils are insoluble protein aggregates in beta-sheet conformation that are implicated in at least 20 diseases for which neither the cure nor the diagnostics are currently available. The role of surfaces in amyloid fibril formation and toxicity is not well understood. Currently, the experimental data available for amyloid fibril formation both on lipid membrane and inorganic surfaces is limited. The goal of our study is to investigate how the physical properties of the surfaces affect binding of amyloid peptides and fibril formation. We use scanning probe microscopy to study amyloid beta (1-42) binding and fibril formation on model surfaces, which are functionalized with thiol monolayers with negatively or positively charged or hydrophobic functional groups. We also study interaction of amyloid peptides with model lipid membranes, which are widely used to mimic cell membrane surfaces. Effect of lipid composition, surface charge, and presence of cholesterol will be discussed. Investigation of interactions of proteins with surfaces and lipid membranes is of significant importance for the development of novel biosensing platforms.
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
10:15 AM - **E7.3
The Evolution of TAGS: Rare Earth Additions for ZT > 1.5.
Bruce Cook 1
1 Ames Laboratory, Iowa State University, Ames, Iowa, United States
Show AbstractThermoelectric materials based on solid solutions of AgSbTe2 in a GeTe matrix have been the subject of numerous research efforts ever since the discovery of an exceptionally low lattice thermal conductivity at the 80 and 85 mole percent GeTe compositions back in 1976. While the dimensionless figure of merit of these alloys is typically reported at slightly greater than unity in the 600 to 750 K temperature range, the inherent complexity of these materials offers pathways for additional improvement. One such approach, the addition of 1 to 2 percent of the rare earth elements Ce, Yb, or Gd, was recently found to yield a substantial increase in ZT. Minor additions of these rare earth elements form a dilute magnetic semiconductor with non-interacting localized moments that obey the Curie law. At 700K the electrical conductivity of the Ce- and Yb-doped compositions is similar to that of neat TAGS-85, while the thermal conductivity and Seebeck coefficient are increased by 6% and 16%, respectively, giving a net increase in ZT of ~ 25%. Mechanisms responsible for the increase in Seebeck coefficient may include i) formation of resonant states near the Fermi level, ii) carrier scattering by lattice distortion and/or by paramagnetic ions, and iii) stabilization of the higher-symmetry cubic polymorph. Prototype power generation devices have been assembled utilizing these materials as p-legs with conventional PbTe as the n-leg, and results of initial power tests are compared with devices based on neat TAGS-85.
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
10:30 AM - JJ1.3
Dynamic Measurement of TAT Membrane Penetration.
Elizabeth Hager-Barnard 1 , Benjamin Almquist 1 , Nicholas Melosh 1
1 Materials Science and Engineering, Stanford University, Stanford, California, United States
Show AbstractWe present a combined experimental and theoretical study of the interactions between cell-penetrating peptides (CPPs) and lipid bilayers using dynamic AFM measurements. Understanding how CPPs can pass through cell membranes is critical for designing drug delivery agents. While CPPs like HIV-TAT have been widely studied, their ability to penetrate membranes directly, without active transport, is still a matter of considerable debate. Here, we directly measure TAT-lipid mechanics during the actual membrane translocation event using TAT-functionalized AFM probes to penetrate through a stack of lipid bilayers. Dynamic force spectroscopy revealed that both the bilayer breakthrough force and bilayer thickness depended on the TAT-bilayer contact time. The results provide a detailed view of how TAT interacts with the bilayer. Upon contact, TAT inserts into the bilayer headgroup to a depth of ~1nm in ~0.5ms. During this same timescale the bilayer thins from 4.2 to 3.2 nm, likely reflecting TAT-driven reorganization. Unexpectedly, the energy barrier for penetration actually increases 52 kT after the bilayer thins, indicating the new conformation has not weakened the bilayer and suggesting TAT cannot penetrate unassisted. Controls with polylysine or mercaptoundecanoic acid do not show this thinning behavior, implying the unique TAT-lipid interactions play a significant role. This approach can be further generalized to the interaction of a variety of peptides or membrane-active molecules with lipid bilayers. Theoretical modeling of dynamic force spectroscopy measurements shows distinct features related to the timescale and disruption of lipid membranes upon contact with a molecular species. By adapting existing AFM protocols to look for these features it will be possible to directly characterize, with microsecond resolution, the dynamics and energetics of the interactions between lipid bilayers and a wide range of peptides and molecular species.
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
10:45 AM - E7.4
PbTe/GeTe Hybrid Nano Structures with 2-di Superlattices and 1-di Nano-rods.
Rama Venkatasubramanian 1 , Phil Barletta 1 , Gary Bulman 1 , Judy Stuart 1 , Thomas Colpitts 1
1 , RTI International, Research Triangle Park, North Carolina, United States
Show AbstractNanoscale materials – superlattices (SL), nano dots, and bulk materials with second phases or nano-inclusions – have become the dominant approach to enhancing the figure of merit (ZT) in thermoelectric materials. The primary mechanism for ZT improvement has been the significant reduction in lattice thermal conductivity through phonon scattering processes in nanoscale materials without affecting the electron/hole transport, by phonon-blocking electron-transmitting structures. We have looked at PbTe/GeTe SL structures as potential mid-temperature (200 to 450 Celsius) thermal-to-electric energy conversion materials. The PbTe and GeTe materials on BaF2 substrates have been characterized by FTIR transmission measurements and they indicate similar bandgaps of about 0.32 eV and 0.31 eV, respectively; thus they should provide an ideal hetero-interface for efficient cross-plane carrier transport to enable useful devices. At the same time, these two materials have significant lattice size differences; hence we expect significant acoustic mismatch resulting in enhanced phonon scattering and/or phonon reflections and/or weak localization of phonons at the SL interfaces, leading to significant lattice thermal conductivity reduction. The transport properties of PbTe/GeTe SL structures were improved dramatically with the use of a Bi2Te3-terminated GaAs substrate. Transmission electron microscopy of the PbTe/GeTe structures shows 2-di SL co-existing with naturally forming 1-di nano-rod structures. The SL periods were optimized for power factor; we have observed 300K power factors in the range of 40 microWatt/cm-K-K. The thermal conductivities of these hybrid nano structured films have been characterized by the 3-omega method and these films show lower lattice thermal conductivities compared to conventional PbTe and GeTe. The temperature dependence of the power factor and thermal conductivities have been characterized and it appears that ZT>1.5 can be achieved for T~500K. Early results on devices with these nanomaterials would be described as well.
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
10:45 AM - JJ1.4
Amine-rich Polyelectrolyte Adhesion Layers as an Alternative to APTES for Surface Immobilization of Biomolecules.
Stefan Stoianov 1 , Jason Ridley 1 , Hans Robinson 1
1 , Virginia Polytechnic Institute and State Univerisity, Blacksburg, Virginia, United States
Show AbstractWe evaluate amine enriched poly (styrene sulfonate)/poly (allylamine hydrochloride (PSS/PAH) self-assembled multilayers for the purpose of fixating freestanding or solution suspended nanostructures and biomolecules onto silicon dioxide surfaces. Unlike common strategies such as silylation of the surface with amine-containing ligands, PSS/PAH multilayers can be fabricated rapidly, without using aggressive chemicals, do not require inert processing conditions to achieve an optimal result, and can be applied to a larger variety of surfaces. PSS/PAH multilayers fabricated at pH above 8.5 are enriched in amines that promote adhesion when exposed on the surface of the film. Exposure is achieved by cycling the film to pH values below 4 and back to neutral, which causes the film to swell substantially as the amine groups are protonated. Conversely, cycling to pH 10 and back causes the amines to pack tightly into hydrophobic regions. This makes it possible to protect the surface from contamination until just before use.In addition, exposed PAH/PSS film can be selectively passivated by acetylation with acetic anhydride. The resulting surface exhibits negligible non-specific binding of negatively charged proteins. Parts of the surface covered with metal or other structures are not affected by this, making patterned adhesion easy to accomplish.We find that PSS/PAH yields at least as good adhesion of nanostructures to the surface as silylsation with 3-aminopropyltriethoxysilane (APTES). These results, along with quantitative results from ongoing investigation of biomolecule adhesion on the films will be presented.
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
11:00 AM - E5:Solar/Thermal
BREAK
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
11:00 AM - E6: All II
BREAK
11:15 AM - **JJ1.5
Biologically Inspired Catechol Based Materials for Medicine.
Phillip Messersmith 1 2 3
1 Biomedical Engineering, Northwestern University, Evanston, Illinois, United States, 2 Chemistry of Life Processes Institute, Northwestern University, Evanston, Illinois, United States, 3 Institute for Bionanotechnology in Medicine, Northwestern University, Chicago, Illinois, United States
Show AbstractCatechols are widely distributed in nature in the form of biopigments, iron sequestering compounds, neurotransmitters and adhesive protein secretions of sessile marine organisms. A plethora of chemical interactions are associated with catechols, including redox reactions, high affinity for metal ions, and strong interfacial activity. This rich landscape of potential chemical interactions confers upon catechol containing natural and synthetic compounds a large variety of potential chemical and biochemical properties. In this talk I will provide several examples of novel biomimetic materials that integrate catechols for specific functional purposes. One example is given by catecholic polymers that mimic marine wet adhesives. Marine and freshwater mussels secrete a family of specialized proteins collectively referred to as mussel adhesive proteins (MAPs). This family of proteins contain 3,4-dihydroxy-L-phenylalanine (DOPA), a catechol containing amino acid found in high concentration in MAPs. DOPA is believed to be essential for the cohesive and adhesive properties of mussel adhesive proteins.Recently we have investigated the use of catechol containing polymers for potential biomedical applications. For example, catechol-derivatized water soluble synthetic polymers have been formulated into rapid-setting liquid adhesives for tissue repair. We have investigated the use of these compounds for sealing of fetal membrane wounds, where they effectively seal fetal membrane puncture wounds and elicit a favourable tissue response in comparison to other candidate sealants. Another arena for biologically inspired catechol based materials is in surface modification, where the strong interactions of catechols towards surfaces can exploited for grafting antifouling polymers onto surfaces for control of biofouling, and for anchoring biomolecules and multifunctional coatings onto surfaces.
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
11:30 AM - **E7.5
Thermoelectric Material Efficiency Improvements by Microstructural Refinement.
Carl Koch 1 , Tsung-ta Chan 1 , Rama Venkatasubramanian 2
1 Materials Science and Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 Center for Solid State Energetics, RTI International, Research Triangle Park, North Carolina, United States
Show AbstractThermoelectric science, technology and applications are in accelerated development because of their current or potential use for direct conversion of heat to electricity as well as for electronic refrigeration. Thermoelectric material efficiency needs to be improved in order for thermoelectric devices to make a major impact on energy harvesting. One approach that has been successful in increasing the efficiency of thermoelectric materials, that is, raising the value of the figure of merit, ZT, is to decrease the external or microstructural dimensionality of the material. The figure of merit, ZT, is expressed as ZT = α2 σT/κ where α,σ,T, and κ are the Seebeck coefficient, electrical conductivity, absolute temperature, and thermal conductivity, respectively. The Seebeck coefficient can potentially be increased by the quantum confinement effect of charge carriers within low-dimensional structures that have dimensions comparable to the electronic wavelength. The lattice thermal conductivity can be significantly reduced since low-dimensional structures can introduce phonon scattering at the boundaries and interfaces. This talk will describe some of the advances in the properties of thermoelectric materials prepared with zero-dimensional, one-dimensional, and two-dimensional refined length scales. In many of these cases, the external dimensions of the material provide the low-dimensionality such as in superlattice thin films and nanowires, For bulk thermoelectric materials, it is the internal structure, e.g. grain boundaries or second phase interfaces, that can provide the low-dimensionality. Recent results on the improvement of ZT in bulk thermoelectric materials due to microstructural refinement will be emphasized. A review of these results from the literature and from the authors’ laboratories will be presented.
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
11:45 AM - JJ1.6
Antioxidant is a Key Factor in Mussel Protein Adhesion.
Jing Yu 1 , Wei Wei 2 , Eric Danner 3 , Jacob Israelachvili 1 , J. Herbert Waite 3
1 Chemical Engineering, University of California, Santa Barbara, Santa Barbara, California, United States, 2 Materials Research Laboratory, University of California, Santa Barbara, Santa Barbara, California, United States, 3 Department of Molecular, Cell & Developmental Biology, University of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractThe underwater adhesion of marine mussels relies on mussel foot proteins (mfps) rich in the catecholic amino acid 3, 4-dihydroxyphenylalanine (dopa). As a side-chain, dopa is capable of strong bidentate interactions with a variety of surfaces, but its susceptibility to oxidation often renders it unreliable for adhesion. Mussels limit dopa oxidation by imposing an acidic, reducing regime in the confined space of mfp deposition. Using the Surface Forces Apparatus (SFA) technique, we demonstrate that the adhesion of mfp-3 to mica is closely coupled with dopa redox and pH. Raising the pH from 3 to 7.5 decreases the adhesion energy of mfp-3 on mica 20-fold and appears to be driven by the pH-dependent oxidation of dopa. Addition of thiol-rich mfp-6 restores mfp-3 adhesion by coupling the oxidation of thiols to the reduction of dopaquinones. How mussels preserve adhesive dopa-containing proteins from oxidation has considerable biological and technological value.
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
12:00 PM - E7.6
Characterization of Bi2Te3 Alloys And Interconnect Interfaces for Power Generation from Low Grade Heat.
Alfredo Morales 1 , Karla Reyes-Gil 1 , Wiley Neel 1 , Peter Sharma 1 , Nancy Yang 1 , Daniel Wesolowski 2 , Christopher Apblett 2
1 , Sandia National Laboratories, Livermore, California, United States, 2 , Sandia National Laboratories, Albuquerque, New Mexico, United States
Show AbstractBi2Te3 alloys are currently the best choice for thermoelectric power generation using low grade heat. It is well known that the materials parameters that determine the thermoelectric figure of merit ZT and the thermal efficiency η depend on physical properties such as transport, scattering mechanisms, band structure, and doping levels. These physical properties are in turn determined by the composition, microstructure, and interfaces in thermoelectric materials. Thermally activated processes like grain coarsening, diffusion, and bulk and interface decomposition will thus change the physical properties in thermoelectric alloys and cause changes in ZT and η. In this talk we will present our recent work measuring ZT from room temperature to 250° C in thermally aged Bi2Te3 alloys with and without metallization. It was found that Bi2Te3 alloys heated at 250° C underwent negligible changes in ZT. Our measurements indicated a decrease in ZT at high temperature probably due to an extrinsic to intrinsic semiconductor transition at about 200° C. Microscopy data documenting changes in the alloy microstructure and interfaces will also be presented.
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
12:00 PM - JJ1.7
S-layer Crystallization on Biomimetic and Inorganic Surfaces: The Importance of Multi-stage Pathways to the Crystalline State Driven by Conformational Changes.
Sungwook Chung 1 2 , Seong-Ho Shin 1 3 4 , Stephen Whitelam 1 3 , Babak Sanii 1 3 , Carolyn Bertozzi 1 3 4 , James De Yoreo 1 3
1 Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 2 Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 3 Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California, United States, 4 Department of Chemsitry, University of California, Berkeley, Berkeley, California, United States
Show AbstractSelf-assembled protein architectures exhibit a wide range of structural motifs with functions that include selective transport, structural scaffolding, mineral templating and propagation of pathogenesis. Although the primary sequences of the individual proteins define their governing interactions, their functions depend on the quaternary architecture that emerges from self-assembly. Surface layer proteins (S-layers), which form the outermost membrane of many bacteria, provide well-studied examples in which proteins assemble into 2D sheets, but the mechanisms and pathways of assembly are poorly understood. Here we report results using in situ AFM to follow 2D crystallization of S-layers on both supported lipid-bilayers (SLBs) and atomically flat mica surface at molecular-scale. In terms of the assembly process on SLBs, We show that the assembly process begins with adsorption of monomers of extended conformation that form a mobile phase on the SLBs. The proteins condense into amorphous clusters, which undergo a phase transition into 2D crystalline clusters of 2 - 15 folded tetramers. Growth of the ordered clusters proceeds by new tetramer formation from monomers on the SLB exclusively at lattice sites along the cluster edges, suggesting tetramer formation is self-catalytic. Analysis of cluster growth dynamics leads to a quantitative model in which the rate limiting parameter is the probability of tetramer creation. The estimated energy barrier of ~51 KJ/mol for this process is much less than expected from scaling laws for folding of isolated proteins, suggesting a kinetic driver for two-stage assembly. In studies of assembly on mica, we observe the emergence of two distinct phases of S-layer organization in 2D. The two phases are both composed of crystalline S-layers having the same P4 unit cell symmetry and ca. 15 nm lateral spacing between tetramers, but the domain heights are different by 2 - 3 nm. Moreover, the relative coverage of the two phases depends on growth time, temperature, and protein concentration during growth. In situ AFM reveals that the phase with the lower domain height spontaneously transforms into the taller phase, a phenomenon that may be due to a conformational change in the proteins. The results both on SLBs and mica show that kinetic constraints imposed by conformational changes lead to complex multistage pathways of protein crystallization in 2D.
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
12:15 PM - E7.7
Investigation of the Thermoelectric Properties of GaSb/InAs Superlattice Structures.
Philip Barletta 1 , Gary Bulman 1 , Geza Dezsi 1 , Bryson Quilliams 1 , Rama Venkatasubramanian 1
1 , RTI International, Research Triangle Park, North Carolina, United States
Show AbstractWe will report on our investigation of GaSb/InAs superlattice structures for mid-temperature (200 to ~500°C) thermoelectric (TE) applications. Several material property trends indicate that III-V materials with high lattice constants are potentially good candidates for TE applications. First, thermal conductivities in III-V materials decrease with increasing lattice constant. Second, for a given pseudo-binary III-V alloy system, electron mobility typically increases with lattice constant. Third, relatively small bandgaps are optimal for TE device operation near 200 to 500°C (Eg should be ~0.41 eV for operation ~500°C, while Eg should be ~0.26 eV for operation at 225°C). Thus, the most promising candidates for III-V TE materials appear to be those from the GaInAsSb material system. These materials are characterized by large lattice constants (a=6.06-6.48Å, the highest among all III-Vs), low bandgaps (0.18-0.7 eV), and the highest electron mobilities among most semiconductors. Our work in this area has focused the GaSb/InAs superlattice system. It is well established that superlattice structures can be designed to reduce thermal conductivity, as has already been demonstrated in Bi2Te3/BixSb2-xTe3 superlattices, where record ZT values have been achieved. MOCVD growth of GaSb/InAs superlattice structures was carried out, and relevant structural, thermal, and electrical characterization has been performed. TEM and XRD results demonstrate a well-ordered superlattice structure. Thermal conductivity measurements (via the 3ω technique) reveal thermal conductivity reduction in the GaSb/InAs superlattice system; the measured thermal conductivity value at 25°C for optimal GaSb/InAs superlattice structures (4.4 W/m-K) is lower than that for either binary GaSb (32 W/m-K) or InAs (27 W/m-K). Additionally, we have worked to optimize the thermoelectric power factor (α2/ρ), studying both Se- and Te-doping of the superlattice structures, in an effort to demonstrate optimal thermoelectric performance over a range of temperatures up to 400°C. Power factor values of 22.0 µW/cm-K2 at 25°C have been demonstrated. Our results suggest considerable promise for the GaSb/InAs SL structures for medium-temperature thermal energy harvesting applications.
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
12:15 PM - JJ1.8
Vesicle Adsorption in Holes of a Contracted Supported Lipid Bilayer.
Kimberly Weirich 1 , Deborah Fygenson 1 2
1 Biomolecular Science & Engineering, University of California, Santa Barbara, California, United States, 2 Physics, University of California, Santa Barbara, California, United States
Show AbstractSupported lipid bilayers (SLB)s are molecularly thin fluids that are adsorbed on a solid surface. They are commonly used as model systems in which to study biological membrane processes. One method of SLB formation involves vesicle adsorption and rupture on silica glasses. Experiments indicate that bilayer edge plays a catalytic role in SLB formation, enhancing vesicle-surface affinity and promoting rupture [K. L. Weirich, J. N. Israelachvili and D. K. Fygenson (2010) Biophys. J. 98(1):85-92]. Here we extend these investigations by controlling the surface to edge ratio. We take advantage of the large mismatch in coefficients of thermal expansion between bilayer and glass to form µm-sized holes in an SLB (regions of bare glass bounded by bilayer edge). Using fluorescence microscopy, we monitor the time-course of lipid surface coverage as vesicles adsorb and rupture within the holes as a function of hole size, lipid chain length and temperature.
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
12:30 PM - E7.8
Thermoelectric Properties of Er-doped InGaN Alloys for High Temperature Applications.
Bed Pantha 1 , Krishna Aryal 1 , I-wen Feng 1 , Jing Li 1 , Jingyu Lin 1 , Hongxing Jiang 1
1 Department of Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas, United States
Show AbstractAlthough III-nitrides possess the outstanding properties such as ability for high power and high temperature operation, high mechanical strength and stability, which are suitable for thermo-power generation at high temperature and in extreme environmental conditions, these are mostly studied for emitters, detectors, and power electronics. Only a few reports concerning the thermal and thermoelectric (TE) properties of III-nitrides have been documented. Recently these materials have attracted a growing interest as potential TE materials for high temperature applications. We have previously demonstrated that InxGa1-xN with high In content (In = 0.36) possesses TE figure of merit (ZT) as good as that of SiGe alloys in measured temperature range (300 to 450 K). However, such a high In content may not be stable for prolonged high temperature operation above 1000 K. Since the decomposition temperature of InGaN alloys increases with decreasing In content, we are therefore interested in investigating TE properties of InGaN in low In content (below In = 0.15) by incorporating Er-atoms to reduce the thermal conductivity. Er-doped InGaN alloys, co-doped with Si, were grown by metal organic chemical vapor deposition. It was found that doping of InGaN alloys with Er atoms of concentration N[Er] larger than 5x1019 cm-3 has substantially reduced the thermal conductivity κ in low In content InGaN alloys. It was observed that κ decreases as N[Er] increases in Si co-doped In0.10Ga0.90N alloys. A room temperature ZT value of ~0.05 was obtained in In0.14Ga0.86N: Er + Si, which is much higher than that obtained in un-doped InGaN with similar In content (In = 0.16). High temperature measurements indicate that In0.10Ga0.90N alloys are quite stable up to 1125K. TE power generators based on (Er+Si)-doped InGaN are fabricated and characterized.
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
12:30 PM - JJ1.9
Hydroxyapaptite Growth on Nano-porous Silicon Substrates in a Hydrogels based Double Diffusion System.
Jason Dorvee 1 , Adele Boskey 1 , Lara Estroff 1
1 Material Science and Engineering, Cornell University, Ithaca, New York, United States
Show AbstractInspired by Nature’s strategy for controlling crystal growth in hydrogel-like environments, we have successfully modified a hydrogel-based double diffusion system to incorporate a functionalizable, bioactive, nano-porous silicon (pSi) substrate. The pSi substrate acts as a nucleating surface, while the hydrogel matrix acts as a crystal growth modifier for hydroxyapatite (HA). The resulting model system provides a platform with which to produce and study bioactive materials in an ECM-like environment.Using oxidized pSi allows the nucleating surface to lie normal to the precipitation front while still allowing ions to diffuse through the substrate. More traditional substrates cannot be used in the doudle-diffusion geometry. For this study, we examined the native silicon oxide as well as two physiosorbed proteins, milk casein and bovine serum albumin (BSA), on the pSi surface. Milk Casein is a known inhibitor of HA when free in a hydrogel, while BSA serves as a control, with no known effect on HA mineralization. Membranes were fabricated from highly doped P++ (100) silicon via anodic etching in 3:1 HF:ethanol solution. These surfaces were then placed in the center of a tube containing 10 w/v % gelatin. Calcium and phosphate ions were diffused into the tubes from either side to create a mineralized band of gelatin. Samples were removed at days 3 and 5, and characterized via x-ray diffraction and electron microscopy to determine the size, shape, and phase of the mineral both in the gel and on the pSi. Results show that by day 5 the mineral formed in both the hydrogel and on the pSi was HA. For all substrates, growth in the hydrogel will be compared to deposition from solution. While in the hydrogel the oxidized pSi acts as a template to adsorb organic material as seen by FE-SEM in images compared before and after placement in the hydrogel matrix, subsequently the adsorbed organic material on the substrate acts as a nucleator for the HA. This model platform, utilizing a porous membrane in a double diffusion system, facilitates the exploration of various surface functionalities and surface coatings for use on various biomedical implants.
E5: Solar/Thermal Energy Harvesting
Session Chairs
Harry Radousky
Choongho Yu
Wednesday PM, April 27, 2011
Room 2004 (Moscone West)
12:45 PM - E7.9
Thermoelectric Power by the Diffusion of Protons in a Nanoporous Structure.
Michael Reznikov 1
1 , Physical Optics Corporation, Torrance, California, United States
Show AbstractSynthetic nano-porous materials are widely used as proton conductive membranes for fuel cells. The protons are thermally transferred between hopping places separated by a few nanometers by the Grotthuss mechanism. These hopping places (local states) are separated by energy barrier and the material behaves similarly to quantum dot superlattice thermoelectric material but for ion charge carriers. Over the gradient of temperature, the probability to hop over the energy barriers against this gradient increases, and consequently the mobile protons are displaced toward the cold side. As a result, the quasi-static equilibrium is established along the material, and the formed gradient of charge density creates the electric voltage (ionic Seebeck voltage), and this changes the electrochemical (RedOx) potential of protons at the electrodes. Because the dissociation of water typically increases with temperature (below 250°C), according to the van't Hoff equation , this also supports the flow of mobile protons against the temperature gradient (ionic Thomson effect). As a result of these combined effects, an electric current is generated in the external circuit that connects the electrodes. The model of this thermionic effect in the ionic conductor is established and compared with experimental data.
E6: Poster Session: Energy Harvesting - All Topics II
Session Chairs
Hong Liang
Harry Radousky
Rama Venkatasubramanian
Thursday AM, April 28, 2011
Salons 7-9 (Marriott)
12:45 PM - JJ1.10
Cell Internalisation Pathway of Multi-walled Carbon Nanotubes into Non-phagocytic Cells .
Hannah Nerl 1 , Alexandra Porter 1 , Khuloud Al-Jamal 2 , Karin Muller 5 , Hanene Ali-Boucetta 2 , Peter Haynes 1 , Maurizio Prato 3 , Alberto Bianco 4 , Kostas Kostarelos 2
1 Materials, Imperial College London, London United Kingdom, 2 Centre for Drug Delivery Research, The School of Pharmacy, University of London, London, WC1N 1AX, United Kingdom, 5 Department of Physiology, University of Cambridge, Cambridge United Kingdom, 3 Department of Pharmaceutical Sciences, University of Trieste, Trieste Italy, 4 CNRS, Institut de Biologie Moléculaire et Cellulaire, Strasbourg France
Show AbstractCarbon nanotubes (CNTs) are being investigated for use as carriers for targeted drug delivery and diagnostic agents. Despite extensive study, little is known about the pathways which by carbon nanotubes enter cells or the intracellular distribution of CNTs after uptake. The “nanoneedle” hypothesis [1], of direct penetration into cells by CNTs, has been a controversial issue and its visualization has been achieved in 2D bright field imaging only [2] [3] which is not sufficient as a technique to visualize the relative position of the plasma membrane with respect to the CNTs. Understanding the exact uptake mechanism is critical as a screening strategy to assess nanoparticulate materials for their suitability as drug-targeting vectors destined for specific intracellular sites. In this work we carried out short (24 h) and long-term exposures (up to 14 days) of lung epithelial cells (A549) and human macrophage cells (HMMs) to NH3+-functionalised multi-walled carbon nanotubes (f-MWNTs) to study the long-term fate of CNTs after uptake. Herein, we report, using a combination of 3-D electron tomography and energy filtered transmission electron microscopy (EFTEM) techniques, that NH3+-functionalised MWNTs (100nm length) (f-MWNTs) enter A549 via two distinct uptake mechanisms. 3-D electron tomography reconstructions confirmed that the NH3+-MWNT inserted directly into the plasma membrane of cells as “nanoneedles” and enter the cell cytoplasm. Individual NH3+-MWNTs were also found engulfed by endocytic pathways via membrane wrapping. We therefore propose a new model for the active uptake mechanism of CNTs by non-phagocytic cells. Wherein CNTs are taken up individually via membrane wrapping and then transported into the cells only to fuse with intracellular vesicles at a later stage forming large clusters of CNTs inside lysosomes.References: [1] C.F. Lopez et al., Proc. Natl. Acad. Sci. U. S. A 101, (2004) 4431-4434.[2] A.E. Porter et al., Nature Nanotech. 2 (2007) 713-717.[3] Q. Mu et al., Nanoletters (2009) Vol.9, No12, 4370-4375.