G1: 3D Fabrication Methods: Top-Down Approaches
Tuesday PM, November 29, 2011
Back Bay D (Sheraton)
9:30 AM - **G1.1
Microscale Patterning of Hierarchical Oxide, Metallic, and Polymeric Architectures.
Jennifer Lewis 1 Show Abstract
1 Materials Research Laboratory, University of Illinois, Urbana, Illinois, United States
The ability to pattern functional materials in planar and three-dimensional forms is of critical importance for several emerging applications, including energy harvesting and storage, microvascular self-healing materials, and tissue engineering scaffolds. Direct-write assembly enables one to rapidly design and fabricate materials in arbitrary shapes without the need for expensive tooling, dies, or lithographic masks. Recent advances in the development of concentrated inks composed of inorganic and organic building blocks with tailored rheological properties will be highlighted with an emphasis on omnidirectional printing of oxide and metallic electrodes for energy harvesting and storage devices as well as self-healing polymer structures with embedded microvascular pathways. Ongoing efforts to scale up our filamentary printing approach to enable manufacturing of large 3D structures will also be highlighted.
10:00 AM - **G1.2
Laser Mediated Biomimetic Nanofabrication.
Hong-Bo Sun 1 Show Abstract
1 , Jilin University, Changchun, Jilin, China
Many biosurfaces consist of hiarchical structures. A important mission of biomimetics is mimicking the surface structures and functions of biospecies. This is a challenging task since none of the currently available nanofabrication technologies is ideal, which should have (a)sufficiently high spatial resolution to depict the details of biosurfaces till nanometric precision; (b)the capability of complex shape prototying including three-dimensional (3D) structures, and (c)the potential to use as more as possible types of functional materials. Laser nanofabrication can satisfy the above strict requirments to a large degree. By modifing local material properties with a force comparable with covalent bond strength, arising from the focused light electric field, various surfaces and even 3D micronanostructures may be readily created. In this talk, we will introduce our recent research on laser biomimetic fabrication, for example, relization of compound eyes with a view angle larger than 90 degrees, finding of the origination of directional sliding angle of a rice leaf, direct interference laser ablation production of moth structures, and so forth. The technologies are basically summarized as femtosecond laser direct writing or multiple laser beam interference. Both have the capability to create hiarchical surface structures, sometimes need aid of other postprocessing technlogies. The laser approach may find great usage on fabrication of biomimetic structures.
10:30 AM - G1.3
Rapid Hierarchical Patterning of Photoactivated Chemically Amplified Resists by Focused Laser Spike (FLaSk) Annealing.
Jonathan Singer 1 2 , Lin Jia 1 2 , Juan Ybarra 1 2 , Tyler Hamer 2 , Steven Kooi 2 , Edwin Thomas 1 2 Show Abstract
1 Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States, 2 Institute for Soldier Nanotechnologies, Massachusetts Institute of Technology, Cambridge, Massachusetts, United States
Lithographic alternatives to conventional layer-by-layer processes for the design of 3D structures such as photonic or phononic devices usually present a dichotomy: patterning control versus patterning area. We demonstrate a combined technique of large area interference lithography (IL) and local area direct write focused laser spike (FLaSk) annealing that can enable the microscale patterning of hierarchical structures defined in their nanoscale morphology by the IL and defined in placement and shape by the direct write. This is accomplished by doping chemically amplified photoresists with an absorbing dopant to provide thermal activation at a wavelength disparate from that causing UV crosslinking. In this way, the necessary post-exposure bake to complete the crosslinking of the resist is performed locally by the FLaSk laser, rather than globally on a hotplate. Both the presence and also (by varying dose parameters) the relative fill fraction of the structures defined by the IL may be controlled within the same larger structure with either discrete or continuous variation. The ability to controllably place and tune IL defined substructure opens up a wide range of pattern symmetries (both periodic and quasiperiodic) and length scales. Further, by utilizing the same experimental setup as used by a 3D direct write (3DDW) system, it is possible to integrate another level of patterning by enabling fully dense, arbitrarily written features on multiple length scales. Via this method and guided by finite element simulations, we have successfully fabricated locally defined 3D periodic structures containing 3DDW supports and designer defects with patterning speeds 1-3 orders of magnitude faster than possible by conventional 3DDW. In addition to optimization of this novel process, we have investigated the potential of this technique for the fabrication of photonic and phononic devices with multiple IL alignments and motifs.
10:45 AM - G1.4
3D Laser Writing of Silver Nanostructures for Photonic Applications.
Kevin Vora 1 , SeungYeon Kang 1 , Shobha Shukla 1 , Eric Mazur 1 Show Abstract
1 SEAS, Harvard University, Cambridge, Massachusetts, United States
Metal fabrication techniques have become increasingly important for photonic applications with rapid developments in the fields of plasmonics, nanophotonics and metamaterials. While two-dimensional (2D) techniques to create high resolution metal patterns are readily available, it is more difficult to fabricate 3D metal structures that are required for new applications in these fields. Multiphoton absorption lithography has been actively researched over the past fifteen years as it enables true 3D fabrication at the micro- and nano-scales through nonlinear light-matter interactions. The technique requires a relatively straightforward experimental setup to achieve resolutions smaller than the diffraction limit of the excitation laser source. The bulk of the research in multiphoton absorption lithography has focused on patterning dielectrics such as glasses and polymers. However, it is also possible to create metal structures using this technique. A promising method to fabricate metal structures in 3D is to induce the photoreduction of metal ions through non-linear absorption in a solution doped with metal salts and other precursors. The photoreduction processes lead to metal nanoparticle nucleation and growth in the focal volume. High intensity femtosecond laser pulses are used to induce the chemical reactions. Silver is commonly used in direct metal writing experiments because of its high reduction potential as well as its material properties that make it useful for electronic and photonic applications. Recent developments have increased the resolution of 3D femtosecond laser direct writing of silver to below 300 nm by optimizing the chemical composition of the irradiated medium and using slow processing speeds. However, no technique allows for patterning disconnected silver nanostructures in 3D; heretofore, 3D demonstrations of multiphoton direct writing of silver been limited to self-supporting structures. We present an ultrafast laser growth technique for direct writing arbitrary dielectric-supported silver nanostructures in 3D, combining top-down patterning and bottom-up growth. We use femtosecond laser pulses to create silver nanostructures inside a focal volume fixed in a polymer that acts as a support matrix. We show the first demonstration of high resolution 3D disconnected silver nanostructure patterning, enabling structures such as 3D arrays of metal dots. The focal volume is scanned rapidly by means of a computer-controlled translation stage to produce arbitrary patterns. Additionally, our technique is over an order of magnitude times faster than previous demonstrations of high resolution 3D direct writing of silver, making it feasible to fabricate devices for photonic applications.
11:30 AM - **G1.5
Towards Smaller Feature Sizes in Direct Laser Writing.
Georg von Freymann 1 2 3 Show Abstract
1 Physics and Research Center OPTIMAS, University of Kaiserslautern, Kaiserslautern Germany, 2 Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe Germany, 3 Institute of Applied Physics and DFG-CFN, Karlsruhe Institute of Technology, Karlsruhe Germany
Direct Laser Writing (DLW) is an established and commercially available technique for rapid prototyping of three-dimensional nano- and micro-architectures. A variety of different photoresist materials can directly be structured based on two-photon polymerization. Common direct laser writing systems are based on ultrafast lasers operating at near-infrared wavelengths. 100 nm lateral feature sizes are routinely achieved using lasers with 780 nm emission wavelength. However, conversion into high-index-of-refraction materials, e.g., silicon [1,2] is needed to reach index-of-refraction contrasts to open complete photonic bandgaps. The resulting high effective refractive index demands a further reduction in feature size. Here, we report on recent progress on the fabrication of photonic crystals with a complete bandgap containing functional defects . The challenge is further reducing the feature sizes to comfortably reach telecommunication wavelengths or wavelengths even below. Three approaches will be presented: (i) A continuous-wave laser operating in the green (532 nm) , (ii) sDLW (Stimulated-emission depletion inspired DLW), and (iii) improved photoresists. While (i) increases the robustness of the system and decreases the lateral feature size due to the reduced diffraction limit, (ii) might completely overcome the diffraction limit and allow for smaller feature sizes in the lateral and possibly also the axial directions . (iii) Improved photoresists, providing higher stability for smaller feature sizes, might combine positive aspects of the other two approaches.
 N. Tetréault et al., Adv. Mater. 18, 457 (2006)
 I. Staude et al., Opt. Lett. 35, 1094 (2010)
 I. Staude et al., Opt. Lett. 36, 67 (2011)
 M. Thiel et al., Appl. Phys. Lett. 97, 221102 (2010)
 J. Fischer et al., Adv. Mater. 22, 3578 (2010)
12:00 PM - G1.6
Net-Shaped 3D Porous Elastomers Formed by Proximity-Field Nanopatterning for Enhancing the Stretching Limit.
Junyong Park 1 , Ming Li 2 , Shuodao Wang 2 , Yonggang Huang 2 , John Rogers 3 , Seokwoo Jeon 1 Show Abstract
1 Materials Science and Engineering, KAIST, Daejeon Korea (the Republic of), 2 Mechanical Engineering, Northwestern University, Evanston, Illinois, United States, 3 Materials Science and Engineering, University of Illinois, Urbana, Illinois, United States
A key technical issue in flexible electronics is the realization of materials that endure large, repeating deformations (i.e., stretches, bends, and twists) without any degradation of material properties. Recently, several groups reported simple methods to improve the stretching limit of elastomer films more than its intrinsic stretchability by mechanically perforating with net-shaped structures. The periodic in-plane holes can effectively deconcentrate tensile strains during deformation. Huge potential remains for enhancing stretchability by using deconcentration mechanism of three-dimensionally (3D) perforated elastomers. After patterning 3D nanostructures as a template, infiltration of elastomers into the template embodies net-shaped 3D porous elastomers. Still, the removal of the template is not an easy task because soft materials cannot endure harsh etching conditions (i.e., strong acids, plasma, high temperature). In this work, we fabricate thin poly(dimethylsiloxane) (PDMS) membranes with 3D porous nanostructures, without much difficulty in removing the template, by using easily removable positive-tone resist as a template material. The 3D templates are formed by optical 3D patterning method known as Proximity-field nanoPattening (PnP). Following steps including the infiltration of PDMS and the removal of the positive-tone template by organic solution yield the 3D nanostructured PDMS film. The resulting net-shaped 3D porous PDMS shows extremely higher stretchability than solid PDMS due to the effective deconcentration of tensile strains during elongation. For better understanding of this mechanism, the von Mises stresses of 3D porous structures are carefully estimated by 3D finite element analysis (FEA), and those computational work are compared with experimental results. Also, highly stretchable, conductive elastomers which are fabricated by infiltrating the mixture of conductive fillers (i.e., carbon nanotubes, silver nanoparticles) and PDMS into 3D templates will be introduced.
12:15 PM - G1.7
Nanoscale Origami for 3D Optics.
Jeong-Hyun Cho 1 , Michael Keung 1 , Niels Verellen 2 3 , Liesbet Lagae 2 3 , Victor Moshchalkov 3 , Pol Van Dorpe 2 , David Gracias 1 Show Abstract
1 Chemical and Biomolecular Engineering, Johns Hopkins University, Baltimore, Maryland, United States, 2 , imec, Leuven Belgium, 3 Department of Physics and Astronomy, INPAC-Institute for Nanoscale Physics and Chemistry, Leuven Belgium
We describe nanoscale self-folding of electron-beam lithography patterned samples using extrinsic stresses towards the creation of three dimensional nanostructured devices for optics and biosensing. Specifically cubic nanostructures with split ring resonators (SRRs) were patterned on all faces to create a 3D optically active nanostructure. We describe the use of self-folding methods to create 3D patterned optical metamaterials as well as their optical characteristics. As compared to planar or stacked devices, these structures feature optical elements in all three dimensions and the assembly process is highly parallel with a pattern resolution of 15 nm in 3D.
12:30 PM - G1.8
3-D Chiral Photonic Crystals Replicated from Butterfly Wing Scales.
Christian Mille 1 , Eric Tyrode 2 , Robert Corkery 1 Show Abstract
1 , YKI, Institute for Surface Chemistry, Stockholm Sweden, 2 KTH, Royal Institute of Technology, Division of Surface and Corrosion Science, Stockholm Sweden
Photonic crystals are ordered materials used to manipulate light by preventing the propagation of certain wavelengths. Calculations have shown that triply-periodic minimal surfaces, like the cubic gyroid, are good candidates for photonic crystals with full band gaps. Given the difficulties in manufacturing 3-D photonic crystals, templating the biopolymeric structures behind the striking colours displayed by many animals offers a suitable alternative. Among these are the wing scales of Callophrys rubi. They consist of cubic bicontinuous polycrystalline domains of mutually interpenetrating networks of chitin and air, with the chiral space-group symmetry I4132. This space group contains two chiral structures along the 100 and 111 crystallographic directions respectively, each with opposite chirality.Here we use the structures of the wing scale of C. rubi as template to produce chiral silica replicas with the gyroid structure using a sol-gel infiltration method. By using FESEM in combination with cross section polishing the nano-scale structure was characterized and by measuring reflectance of a silica wing scale the long range order was confirmed. The photonic response is very similar to the butterfly with a blue-shift in reflectance maxima, which can be seen in optical micrographs, showing blue silica structures. In addition the replicated wing scales show optical activity and circular dichroism, as confirmed by imaging the sample under cross polarized light and by observing differences in the handedness of the reflected light. The chirality implies the usefulness of the material as a metamaterial with a number of extraordinary effects predicted, such as negative refractive index. Also, by using other materials as templates the photonic response could be tuned through for example magneto-optic effects.
G2: 3D Fabrication Methods: Self-Assembly
Tuesday PM, November 29, 2011
Back Bay D (Sheraton)
2:30 PM - **G2.1
Inverse Opal Scaffolds and Their Biomedical Applications.
Younan Xia 1 Show Abstract
1 Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, United States
We have demonstrated the fabrication of novel inverse opal scaffolds with uniform, well-controlled pore sizes and interconnected pore structures by templating against cubic-close packed lattices of polymer microspheres. We further explored these scaffolds in biomedical applications, including tissue engineering (e.g., cell culture, vascularization, and differentiation of stem cells) and tumor model development (e.g., formation of cell bodies). Most recently, we also extended their use to the formation of embryoid bodies (EBs), which can serve as a good model system to investigate molecular and cellular interactions in the earliest stages of embryo development. In this talk, I will cover recent advances in both fabrication and biomedical applications.
3:00 PM - G2.2
Novel Porous Ceramic Materials via Magnetically Driven Self-Assembly of Non-Magnetic Nanoparticles.
Marco Furlan 1 , Marco Lattuada 1 Show Abstract
1 DCHAB, ETH Zurich, Zurich Switzerland
The preparation of porous materials via self-assembly of nano- and microparticles is a topic of great scientific and technological relevance. Applications for such materials can be found in many areas, such as chromatography, membrane production, catalyst supports, bio-inspired materials, and scaffolds for tissue engineering.Conventional materials, which can be prepared from colloidal suspension of polymers or ceramics, have usually a random porous structure. The preparation of these materials with better organized pores is of paramount interest for many applications.In this work we introduce a new technique for the preparation of porous materials with anisotropic structure. This new method takes advantage of the alignment in the presence of a magnetic field of non-magnetic colloidal nanoparticles, either polymeric or ceramic (e.g. silica, alumina), dispersed in an aqueous highly stable ferrofluid. Once the magnetic field is applied, the non-magnetic nanoparticles act as magnetic holes, i.e., they acquire a magnetic moment in the opposite direction to that of the external field. These moments generate dipolar interactions capable of aligning non-magnetic particles in the direction of the applied field.The obtained structures can be frozen by adding a water-soluble monomer, a crosslinker and an initiator to the aqueous solution, so that once the structure is formed a free radical polymerization process can be utilized to produces a hydrogel that locks it. Once the obtained anisotropic structure is blocked inside the hydrogel, the ferrofluid can be removed by immersing the hydrogel in a concentrated hydrochloric acid solution. The anisotropic structure can then be hardened by depositing via a sol gel process either the same material of the nanoparticles or a different one, by simply immersing the monolith in a solution of the sol-gel precursor. After removing of the hydrogel by thermal treatment a hard porous monolith can be obtained. The resulting materials have a complex and organized structure, which was studied and characterized using SEM microscopy and mercury porosimetry. A. T. Skjeltorp, Phys. Rev. Lett. 1983, 51, 2306.
3:15 PM - G2.3
Directed Assembly of Block Copolymer Templates for the Fabrication of Mesoporous Silicate Films with Controlled Architectures via 3-D Replication in Supercritical Fluids.
Li Yao 1 , John Ell 1 , James Watkins 1 Show Abstract
1 Polymer Science and Engineering, University of Massachusetts Amherst, Amherst, Massachusetts, United States
Mesoporous silica films with controlled architectures are of interest for many applications including microfluidics, microelectronics, sensors, catalysis and energy conversion. We previously reported an efficient pathway to well-ordered, robust mesoporous films with tailored morphologies through the infusion and selective condensation of silica and organosilicate precursors within one phase domain of a pre-formed block copolymer template dilated with supercritical carbon dioxide. The template is subsequently removed to produce the mesoporous oxide films. This strategy has been applied to the synthesis of films with spherical pores for use as ultra-low dielectric constant materials, to the fabrication of films with vertically and horizontally oriented cylindrical nanochannels of prescribe diameter, and most recently to the direct patterning of mesoporous films without the need for etching.Here we turn our attention to the preparation of mesoporous films containing well aligned nanochannels of prescribed diameter and the preparation of mesoporous films with bicontinuous morphologies. Long-range alignment of cylindrical pores enables the fabrication of massively parallel pore arrays that can be incorporated into device architectures for separations and sensing. The fabrication of films with bicontinuous morphologies has long been sought for membrane-based separations. The architecture of the silica films is controlled by the microphase separated morphology of the block copolymer used as their template. In this work we use polystyrene-b-poly(tert-butyl acrylate) (PS-b-PtBA) block copolymers as templates. Replication of the templates in CO2 yields mesoporous silica films containing cylindrical channels and bicontinuous channels with periods between 20-80 nm.One advantage of the 3-D replication approach is that virtually all the structural details imparted to the solid template film can be conveyed to the silica film. Here we employed self-assembly of the block copolymer on topographically patterned substrates fabricated by top-down method to direct the orientation and long range order in templates containing cylindrical morphologies prior to infusion. The block copolymer films were cast on etched silicon substrates containing trench structures between 25 nm to 90 nm deep with trench and mesa widths between 200 nm and 1 micron. Atomic Force Microscopy (AFM) and Grazing-Incidence Small-Angle X-ray Scattering (GISXAS) were used to characterize the alignment and orientation of the block copolymer domains and the corresponding mesoporous silica films prepared using the aligned templates. These measurements confirmed high fidelity replication of the block copolymer morphology and fabrication of the well aligned nanochannel arrays.  R. A. Pai, J. J. Watkins, Science 2004, 303, 507. Nagarajan, S.; Russell, T.P.; Watkins, J.J. Adv. Funct. Mater. 2009, 19, 2728. H.-C. Kim, S.-M. Park, W. D. Hinsberg, Chemical Reviews 2009, 110, 146.
3:30 PM - G2.4
Vectorial-Orientation of Ion-Channel Membrane Proteins on Inorganic Substrates by Directed-Assembly and Self-Assembly at Liquid/Water and Solid/Liquid Interfaces.
Sanju Gupta 1 , J. Liu 1 , J. Blasie 1 Show Abstract
1 Chemistry & Biophysics, University of Pennsylvania, Philadelphia, Pennsylvania, United States
One subunit of the prokaryotic voltage-gated potassium ion channel from Aeropyrum pernix (KvAP) is comprised of six transmembrane α-helices, of which S1-S4 form the voltage-sensor domain (VSD) and S5-S6 contribute to the pore domain (PD) of the functional homo-tetramer. However, the mechanism of electromechanical coupling interconverting the closed-to-open (i.e. non-conducting to K+ conducting) states remains undetermined. A fuller understanding of these ubiquitous proteins, essential for organisms across the animal kingdom, will have tremendous impact for structural biology and mankind. Here, we have successfully developed a surface conjugation protocol and vectorially-oriented the detergent (OG)-solubilized VSD in single monolayers by two independent approaches, namely “directed-assembly” and “self-assembly” to achieve a high in-plane density. Both utilize Ni coordination chemistry to tether the protein to an alkylated inorganic surface via its C-terminal His6-tag. Subsequently, the detergent is replaced by phospholipid (POPC) via exchange, intended to reconstitute a phospholipid bilayer environment for the protein. X-ray interferometry, in which interference with a multilayer reference structure is used to both enhance and phase the specular X-ray reflectivity from the tethered single membrane, was used to determine directly the electron density profile structures of the VSD protein solvated by detergent versus phospholipid, and with either a moist He (moderate hydration) or bulk aqueous buffer (high hydration) environment to preserve a native structure conformation. Difference electron density profiles, with respect to the multilayer substrate itself, for the VSD:OG monolayer and VSD:POPC membranes at both the solid-vapor and solid-liquid interfaces, reveal the profile structures of the VSD protein dominating these profiles and further indicate a successful reconstitution of a lipid bilayer environment. The self-assembly approach was similarly extended to the intact full-length KvAP channel for comparison. The spatial extent and asymmetry in the profile structures of both proteins confirm their uni-directional vectorial orientation within the reconstituted membrane and indicate retention of the protein’s folded 3-D tertiary structure upon completion of membrane bilayer reconstitution. Moreover, the resulting high in-plane density of vectorially-oriented protein within a fully-hydrated single phospholipid bilayer membrane at the solid-liquid interface will enable investigation of their conformational states as a function of the transmembrane electric potential .  Gupta et al. PRE (2011).This work is financially supported by NIH Program Project.
3:45 PM - G2.5
3D Optical Metamaterial Made by Chiral Self-Assembly.
Pedro Cunha 1 , Silvia Vignolini 1 , Nataliya Yufa 1 , Stefan Guldin 1 , Ilia Rushkin 2 , Morgan Stefik 3 , Kahyun Hur 3 , Ulrich Wiesner 3 , Jeremy Baumberg 1 , UIlrich Steiner 1 Show Abstract
1 Cavendish Laboratory, University of Cambridge, Cambridge United Kingdom, 2 Department of Mathematics, University of Nottingham, Nottingham United Kingdom, 3 Department of Materials Science and Engineering, Cornell University, Ithaca, New York, United States
Block copolymer self-assembly provides an excellent path to ordered nanostructured materials for applications as varied as microfluidics, photovoltaics, fuel cells and photonics. In combination with this self-assembly, top-down techniques, such as optical or electron-beam lithography can result in perfectly ordered, macroscopic domains which have features on the scale of 10 nm. Since polymers are often limited in their range of optical properties, we have constructed a metallic structure by using a block copolymer as a scaffold. We start with a triblock copolymer in the alternating gyroid phase and etch away one of the two gyroid networks. We then backfill the resulting pores with metal using electrodeposition. The remaining polymers are then removed, resulting in a free standing metal gyroid structure with 10-nm feature size, 50-nm unit cell and ~10-micron crystalline domains. This new material is physically chiral and exhibits interesting new optical properties .Optical characterization reveals a large and spectrally-dispersive linear and circular dichroism, seen via a color change as a function of the angle between incident polarization and domain orientation. Both reflection and transmission shows strong plasmonic resonances dependent on relative orientation of the domain and the optical field. The expected difference in transmission is seen for left- and right-handed polarizations as the sample is rotated in and out of the chiral direction. S. Vignolini et al., submitted (2011)
4:30 PM - **G2.6
Biological Units for Hierarchical Assembly Strategies.
Rajesh Naik 1 Show Abstract
1 Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB, Dayton, Ohio, United States
Functional biological units such as peptides and proteins are used in the assembly of hierarchical structures in biological systems. By combining interactions such as hydrogen bonding and electrostatic interactions, structures created across multiple length scales can be created. One of the exciting aspects of biological systems involves emergent properties that arise by combining various facets of biological processes using hierarchical assemblies and complexation with inorganic materials. The knowledge gained from studying biological systems can provide a means to develop strategies for the construction of hierarchical assemblies for a desired application. Achieving such a goal would provide a fundamentally new way of creating materials and technologies for use in energy harvesting, energy storage and conversion, electronic circuitry components, structural applications and sensing technologies, along with a host of other potential uses. In my talk, I will cover our work in creating functional biological units that are used in hierarchical assemblies and determining the rules that govern these interactions.
5:00 PM - G2.7
Ordered Nanoholes in Silicon Substrates Obtained by Self-Assembling of Diblock Copolymers.
Cristina Garozzo 1 , Antonino La Magna 1 , Vittorio Privitera 1 , Silvia Scalese 1 , Rosaria Puglisi 1 Show Abstract
1 Istituto per la Microelettronica e Microsistemi, Consiglio Nazionale delle Ricerche, Catania Italy
Silicon radial junctions formed in three-dimensional structures provide a potential solution to increase the efficiency of Si based solar cells, because their innovative architecture allows to optimize independently the photons absorption path and the carriers collection path. Radial junctions are usually fabricated in 3D structures such as wires or rods where the two electrical contacts are realized in the shell and in the core of the structure respectively. An alternative possibility to form radial junctions is represented by the opposite geometry, i.e. vertical holes in a Si substrate. In this case the junction is realised in the walls of the hole and the carriers channel is in between the holes. This approach is less popular, but it provides a larger robustness to mechanical stress with respect to the wires, while maintaining the advantages of the radial junction. For this approach it is very important to control the characteristic size of the holes, such as their diameter and relative distance, in order to properly couple the structure to the visible wavelength while maintaining proper diffusive lengths. We propose the formation of vertical nanoholes controlled in size and position by using an innovative bottom-up Lithography based on block CoPolymers self-assembling (LCP). This lithography is low cost, VLSI compatible and allows the formation of controlled and highly dense nanofeatures on wafer scale. The formation of nanoholes is obtained through LCP and successive plasma etch. The latter is a critical step due to the very small size and chemical instability of the copolymer which acts as the resist. The crucial parameters such as plasma power and gas chemistry to increase the holes depth will be discussed and it will be shown that the etch rate is limited by the intrinsic surface reaction rate, and not by the supply of active species.
5:15 PM - G2.8
High, Anisotropic Proton Conductivity in Organic Molecular Porous Materials.
Minyoung Yoon 1 2 , Kyungwon Suh 1 , Hyunuk Kim 1 , Yonghwi Kim 1 , Narayanan Selvapalam 1 2 , Kimoon Kim 1 2 Show Abstract
1 Center for Smart Supramolecules, and Department Chemistry, Pohang University of Science and Technology, Pohang, Kyungbook, Korea (the Republic of), 2 Division of Advanced Materials and Science (WCU Project), Pohang University of Science and Technology, Pohang, Kyungbook, Korea (the Republic of)
The search for new high proton conducting materials has been a subject of intense research because of their potential applications in fuel cell, sensor and other areas. In recent years, metal-organic frameworks (MOFs) with well-defined pores have been investigated for this purpose because guest molecules such as water and imidazole in the channels, and/or functional groups lining the channels can provide proton conduction pathways. Similar to MOFs, in principle, organic molecular porous materials may serve as good proton conductors, but their proton conduction behavior has never been investigated. Here we present the high, anisotropic proton conductivity of cucurbituril-based organic molecular porous materials. The isostructural organic porous materials showed different proton conductivity depending on the nature and amount of acid molecules present in the 1D channels. The porous cucurbituril containing sulfuric acid in the channels showed the highest conductivity and the lowest activation energy among the series, which are comparable to the highest values of MOFs or organic proton conducting materials. In addition, the highly anisotropic conduction behavior through the 1D channels of the porous CB was studied by single crystal conductivity measurements. Much higher conductivity along the channel direction than that perpendicular to the channel direction was observed. To the best of our knowledge, the porous CB showed the highest anisotropic proton conductivity (σ∥/σ⊥ = 8600) among the known proton conducting materials so far. The highly anisotropic proton conductivity compared to that of polymeric materials suggests their potential utility in device applications in which highly directional proton conduction is desired.
5:30 PM - G2.9
Self-Assembly of Nanorods onto Patterned Surfaces: A Computer Simulation Study.
Folusho Oyerokun 1 , Dhriti Nepal 1 , Kyoungweon Park 1 , Richard Vaia 1 Show Abstract
1 Nanostructured and biological materials branch, AFRL, Wright-Patterson AFB, Ohio, United States
The uniform arrangement of nanoparticles beyond random ordering and across multiple length scales represents one of the most challenging obstacles to wide-spread utilization of bottom-up approaches as means of creating three dimensional (3D) hierarchical structures suitable for applications in several functional devices. For example in the design of plasmonics based materials, it is often necessary to arrange the constituent nanometer-size particles of predetermined shape in a well-defined three dimensional array in order to achieve the desired electromagnetic response. The current state-of-the-art techniques for fabricating these materials rely on a top down approach, such as electron beam lithography. Despite their initial promise, lithography based methods are hampered by a host of issues ranging from poor control over interparticle spacing and surface roughness, and the inability to fabricate nanostructures in the desired sub-wavelength scale. One proposed strategy for overcoming these limitations synergistically combines self-assembly ideas with lithographic techniques to create low cost and high yield fabrication routes for these nanostructures. Within this framework, the spatial organization of the nanosized constituents is first fabricated in two dimensions via directed assembly of surface functionalized nanoparticles onto a patterned surface. The desired 3D structure is then realized via layer-by-layer assembly. For proof of concept, we consider the adsorption of monodisperse nanorods from a dilute solution onto a patterned 2D flat surface consisting of alternating hydrophobic and hydrophilic striped layers. The preferential adsorption of the nanorods onto specific regions within the patterned surface is accomplished via their surface functionalization with appropriate (charged or neutral) alkyl or polymeric ligands. The strength of the repulsive rod-rod interactions can then be tuned by varying the nature and size of the linker molecules and the ionic strength of the solution. Our computational study explores the fundamental aspects of the self-assembly process, namely how the resulting surface composition and the 2D structure on the adsorbed layer depends on properties of the nanorods (its aspect ratio, solution concentration), strength and nature of the rod-rod and rod-wall interactions. We also investigate how the ordering of the nanorods depends on the thickness and pitch of the surface patterns. The result of our computer simulation will be compared with recent experiments on sub-100nm patterning of gold nanorods on PS/P2VP patterned surfaces.
G3: Poster Session
Wednesday AM, November 30, 2011
Exhibition Hall C (Hynes)
9:00 PM - G3.10
Effect of Nano-Filler Geometry on Coating Performance.
Marielle Wouters 1 , Pascal Buskens 1 , Corné Rentrop 1 Show Abstract
1 Innovative Materials, TNO, Eindhoven Netherlands
State of the art coatings consist of all kinds of ingredients amongst which (inorganic) filler particles are important compounds. Dispersion of these particles is of utmost importance in the performance (the looks and functionality) of the final product and its application. Inorganic nanoparticles can be dispersed in coatings and polymers by modification of their surfaces. This surface modification allows the nanoparticles to fully disperse or segregate in the coating systems thus altering the properties of the coating in the bulk and at the surface. Knowledge of particle modification and chemistry of the coating formulation allows us to tailor the properties of the coatings and thus its performance and-or applicability.Our expertise has shown that we are able to adjust the barrier properties of layers, as well as wettability and optical performance of the coatings. Recently nanocomposite coating systems are produced by multiple modification of anisotropic nanoparticles. These nanoparticles are functionalised with two or more different organic groups on the surface and the edges of the nanoparticles thus giving the nanoparticle more than one function. The introduction of a coating compatible component and a coating incompatible component on one single nanoparticle can amongst others result in the creation of a coating with a nanostructured surface. By the use of this ‘multiple functionality’ structuring can result in hydrophilic-hydrophobic structured surfaces as well as anti-fouling surfaces.In this paper the modification of different particles will be presented as well as the effect of the particle modification on coating performance for different applications.
9:00 PM - G3.11
Optimization of 3D ZnO/Si Branched Nanowire Heterostructures for Efficient Photoelectrochemical Solar Water Splitting.
Alireza Kargar 1 , Ke Sun 1 , Yi Jing 1 , Chulmin Choi 2 , Heesoo Jung 3 , Gun Young Jung 3 , Sungho Jin 2 , Deli Wang 1 2 4 Show Abstract
1 Electrical and Computer Engineering, UC San Diego, La Jolla, California, United States, 2 Materials Science and Engineering Program, UC San Diego, La Jolla, California, United States, 3 School of Materials Science and Engineering, Gwangju Institute of Science and Technology , Gwangju Korea (the Republic of), 4 California Institute of Telecommunication and Information Technology, UC San Diego, La Jolla, California, United States
Direct solar water splitting to produce hydrogen using photoelectrochemical (PEC) cells has attracted considerable attention due to the potentials in cost-effectiveness and the nature of carbon emission free. Semiconductor nanowire (NW) and heterostructure based photoelectrodes offer superior PEC performance because they provide improved light absorption, reduced recombination of photogenerated carriers and enhanced charge separation, enhanced carrier transportation and collection, and thus overall higher efficiency. Branched NW heterostructures have recently shown promising performances for optoelectronic applications and as well as revealed the enhanced photocathodic behaviors for efficient PEC solar water splitting and hydrogen production due to increased surface area for surface redox reaction and enhanced gas evolution due to large curvature of NWs, compared to bare Si NW arrays or core/shell NW heterostructures. Herein, we report the fabrication of highly ordered three-dimensional (3D) branched NW heterostructures, consisting of vertical Si NW cores and uniform ZnO NW branches and their application as PEC photoelectrodes. We demonstrate that by tuning the doping in the p-type Si NW core, selective photoelectrochemical generation of H2 or O2 can be accomplished. The photocurrents of these unique 3D Si/ZnO branched NW heterostructures are orders of magnitudes higher than that of the bare Si NW photoelectrodes. The PEC performances, including photocurrent, photoresponse, and PEC hydrogen generation efficiency, and relationship to the different sizes of Si and ZnO NWs are studied. Specifically, p-Si/n-ZnO branched NW arrays show broadband absorption from UV to near IR region and photocathodic generation of H2, while p+-Si/n-ZnO branched NW array electrodes show photoanodic O2 generation with photoresponse only to UV light. We also note that in both cases the photocurrents are orders of magnitudes higher than that of the bare Si NW photoelectrodes. This study reveals the promise of using the unique 3D branched NW heterostructures to implement design for high efficient photoelectrochemical generation of H2. Moreover, these 3D nanowire photoelectrodes can be fabricated using simple and cost-effective solution methods and can be easily scaled up.
9:00 PM - G3.12
Hierarchical Structures for Surface-Enhanced Raman Spectroscopy of Nanoparticles
Limei Chen 1 , Kathrin Kroth 1 , Sabrina Darmawi 1 , Torsten Henning 1 , Peter Klar 1 Show Abstract
1 , I. Physical Institute, Justus-Liebig University of Giessen, Giessen Germany
Nanoparticles are intensively used for special tasks and are employed in a wide range of products including mass product such as additives for engine oils, varnish, cosmetics, drugs etc. The potential hazards caused by nanoparticles on health and on the environment are hardly examined in detail. It is necessary to have fast, quantitative methods for analysing the chemical identity of single nanoparticles with dimensions below 300 nm. We are developing a method to analyse aqueous suspensions of nanoparticles on the basis of surface-enhanced Raman spectroscopy. Sensor substrates consisting of regular arrangements of sub 100 nm gold tips made by optical lithography or Au nanoparticles in sub-micrometer of openings in hydrophilic films are produced. With the help of the meniscus force deposition method, the nanoparticles from the suspension drop into openings of comparable sizes next to the gold structures by self-organization. By means of surface-enhanced Raman spectroscopy we are able to analyse directly individual particles with help of the antenna effects from the gold structures.
9:00 PM - G3.14
Structural Transformation by Electrodeposition on Patterned Substrates (STEPS) – A New Versatile Nanofabrication Method.
Philseok Kim 1 2 , Alexander Epstein 2 , Mughees Khan 1 , Lauren Zarzar 3 , Darren Lipomi 3 , George Whitesides 3 1 , Joanna Aizenberg 1 2 3 Show Abstract
1 Wyss Institute for Biologically Inspired Engineering, Harvard University, Cambridge, Massachusetts, United States, 2 School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts, United States, 3 Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts, United States
Sophisticated 3D structures such as arrays of high-aspect-ratio (HAR) nano- and microstructures are of great interest for designing surfaces for applications in energy harvesting and storage, optics, and bio-nano interfaces. However, the difficulty of systematically and conveniently tuning the geometries of these structures significantly limits their design and optimization for specific applications. We have developed a low cost, high-throughput benchtop method that enables a HAR array to be reshaped with nanoscale precision by electrodeposition of conductive polymers. The method—named STEPS (structural transformation by electrodeposition on patterned substrates)—makes it possible to create patterns with proportionally increasing size of original features, to convert isolated HAR features into a closed-cell substrate with a continuous HAR wall, and to transform a simple parent two dimensional HAR array into new three-dimensional patterned structures with tapered, tilted, anisotropic, or overhanging geometries by controlling the deposition conditions. STEPS allowed for the fabrication of substrates with continuous or discrete gradients of nanostructure features, as well as libraries of various patterns, starting from a single master structure. By providing exemplary applications in plasmonics, bacterial patterning, and formation of mechanically reinforced structures, we show that STEPS enables a wide range of studies of the effect of substrate topography on surface properties leading to optimization of the structures for a specific application. Our work identifies solution-based deposition of conductive polymers as a new tool in nanofabrication and allows access to 3D architectures that were previously difficult to fabricate.
9:00 PM - G3.15
Formation of Hierarchically Porous Metals and Metal Oxides by Nitrate Infiltration of Mesoporous Silica Monoliths.
Franchessa Sayler 1 , Amy Grano 1 , Jan-Henrik Smatt 2 , Martin Bakker 1 Show Abstract
1 Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 2 Physical Chemistry, Abo Akademi University, Turku Finland
Hierarchically porous materials are of interest in a wide range of applications. If the materials are electronic or ionic conductors such materials are of interest as electrodes for use in fuel cells, flow batteries and pseudo/supercapacitors. Using sol-gel synthesis, hierarchically porous silica templates with porosity on three difference length scales are readily formed. By infiltration of metal nitrate solutions followed by decomposition under controlled atmospheres the silica structure can be replicated. Removal of the silica template leaves a hierarchically porous monolith of the desired metal or metal oxide. We will present results on the synthesis and characterization of hierarchically porous monoliths of copper, silver, cobalt, nickel, silver alloy and cobalt, nickel and zinc oxides.
9:00 PM - G3.16
Application of 3-D Hierarchically Porous Silver, Cobalt Oxide and Zinc Oxide Monoliths to Chromatographic Separations.
Franchessa Sayler 1 , Amy Grano 1 , Susanne Wiedmer 3 , Jan-Henrik Smatt 2 , Martin Bakker 1 Show Abstract
1 Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 3 Analytical Chemistry, The University of Helsinki, Helsinki Finland, 2 Physical Chemistry, Abo Akademi University, Turku Finland
Hierarchically porous silica monoliths were introduced into liquid phase chromatography at the beginning of the last decade. The high surface area, high void volume and bicontinuous nature of the porosity of the materials are significant advantages over existing chromatographic supports and have resulted in rapid acceptance of these materials into the chromatography market.We report here on the synthesis of 3-D porous silver, cobalt oxide and zinc oxide monoliths, their materials characterization, fabrication as liquid chromatographic columns and initial chromatographic characterization. The, as prepared, columns gave very low back pressure, consistent with the bicontinuous nature of the columns. Cobalt oxide and zinc oxide both demonstrated retention of a number of nitrogen heterocycles, providing the basis for molecular separation.We report also on on-going efforts to develop more complicated column structures, particularly tubular designs, and how short comings in the mechanical properties of the silica template and resulting metal and metal oxides monoliths are being addressed.
9:00 PM - G3.17
Direct-Write Assembly of Three-Dimensional Li-Ion Microbatteries.
Ke Sun 1 , Bok Yeop Ahn 1 , Teng-Sing Wei 1 , Shen Dillon 1 , Jennifer Lewis 1 2 Show Abstract
1 Materials Science and Engineering, UIUC, Urbana, Illinois, United States, 2 Chemical & Biomolecular Engineering, UIUC, Urbana, Illinois, United States
Developing energy storage devices in three-dimensions that enable autonomous micro/nano devices are of importance for the next generation electronics. Emerging applications require highly integrated patterning approaches for defining the spatial location and composition of metal oxide and carbon-based electrodes as well as polymer separators. Many patterning techniques require complex lithography or etching processes, which are either costly or difficult to scale in the third dimension. In this presentation, we describe recent efforts to create concentrated nanoparticle inks composed of LiMn2O4, Li4Ti5O12, LiFePO4 and graphite powders. By tailoring the ink composition and rheological behavior, we have demonstrated 3D Li-ion microbattery designs with interpenetrating high-aspect ratio or 3D woodpile structures via layer-by-layer printing. Ink formulation, printing, electrical characterization, and packaging strategies for these Li-ion microbatteries will be discussed.
9:00 PM - G3.18
Self-Organized Nanostructure Formation for Anti-Reflection Glass Surfaces.
Joern Achtelik 1 , Ricarda Kemper 1 , Werner Sievers 1 , Joerg Lindner 1 Show Abstract
1 Dept. of Physics, University of Paderborn, Paderborn Germany
Photovoltaic cells need to be protected with glass covers which allow for a high transmission of light in the visible and UV range onto the active semiconductor device underneath in order to minimize reflective losses and to maximize the energy harvesting process. The evolution of insects has demonstrated how reflective losses at a surface can be reduced, i.e. by the formation of well-known moth-eye structures on the eyes of many nocturnal species. Such structures typically have dimensions much smaller than the wavelength of light. The question arises if these nanostructures are yet optimized and if they can be technically replicated by affordable technologies on large area surfaces. To this end, two approaches to create periodically ordered and irregularly nanostructured glass surfaces, respectively, are studied and compared in the present paper. Nanostructures are formed either by nanosphere lithography (NSL) combined with physical vapour deposition of nickel and reactive ion etching (RIE), or by a plasma treatment of nickel thin films on glass and RIE. In the latter case, plasma induced dewetting of the Ni thin film is meant to lead to a characteristic irregular surface pattern. Thus, both techniques use self-organization effects and are therefore particularly affordable pattern formation processes as required for energy materials. Different RIE processes are used to transfer the surface pattern into the substrate. The resulting surfaces are inspected by scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical reflectometry in the 400 – 700 nm region. It is shown that the reflectivity can be reduced most effectively by more than two thirds using a simple plasma process, resulting in a irregular surface structure. From AFM data of the topography an optical model is derived on the basis of effective medium theory and transfer matrix method which describes satisfactorily the measured spectral dependence of reflectivity.
9:00 PM - G3.19
Hydrophobicity of Teflon Coated Well-Ordered Silver Nanorod Arays.
Arif Alagoz 1 , Wisam Khudhayer 1 , Tansel Karabacak 1 Show Abstract
1 Applied Science, University of Arkansas at Little Rock, Little Rock, Arkansas, United States
From wings of flies to plant leafs hydrophobic surfaces are well-common in nature. Many of these surfaces have micro and nano hierarchical structure coated with low surface energy layer. In this work, we mimicked similar hierarchical structure by fabricating Teflon coated well-ordered silver nanorod arrays and investigated effect nanorod separation on water contact angle. Silver nanorod arrays were prepared by using glancing angle deposition on patterned silicon substrates and coated with thin film Teflon by oblique angle deposition technique. A systematic increase in water contact angle is observed with increasing nanorod separation which is attributed to decrease in solid liquid interface.
9:00 PM - G3.2
Artificial Photosynthesis on a Chip: Microfluidic Cofactor Regeneration and Photoenzymatic Synthesis under Visible Light.
Joon Seok Lee 1 , Sahng Ha Lee 1 , Jae Hong Kim 1 , Chan Beum Park 1 Show Abstract
1 Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon Korea (the Republic of)
Mimicking natural photosynthesis is an attractive route to developing sustainable systems for the conversion of solar energy into renewable resources. During the photosynthesis in green plants, both light-dependent and independent reactions take place simultaneously in the organelle of micron-sized chloroplasts that contain light-harvesting thylakoid membranes. In the light-dependent reaction, photo-induced electrons regenerate a reducing power in the form of nicotinamide cofactors, NAD(P)H, which is then consumed by redox enzymatic synthesis of organic compounds during light-independent reactions (i.e., Calvin cycle). The natural photosynthesis occurs in highly sophisticated, spatially arranged micro/nano-structures that provide mechanical support to the leaf and enable efficient transport of water, minerals, and photosynthates through microtube networks such as phloem and xylem in the plant. Many efforts have been made thus far to unveil the mechanism of photosynthesis and to further mimic natural photosynthesis; however, an integrated platform that enables the immobilization of light-harvesting components and the microfluidic transport of key chemicals for light-dependent/independent reactions is not well-developed. Herein, we report on the development of a microfluidic artificial photosynthetic system for in situ regeneration of reducing power (i.e., NADH cofactor) and redox enzymatic synthesis of fine chemicals under visible light. The microfluidic artificial photosynthetic platform incorporates Quantum dots (QDs) and L-glutamate dehydrogenase (GDH) for light-induced NADH regeneration and photoenzymatic synthesis. Similar to natural photosynthesis, photochemical regeneration of the NADH cofactor takes place in the light-dependent reaction zone, which is then coupled with the light-independent, enzymatic synthesis in the downstream of the microchannel. Both yields of NADH regeneration and L-glutamate synthesis were significantly affected by the retention time and light availability. High stability of immobilized CdSe QDs and GDH within the separate microchannel zones allowed repeated photosynthesis. Our findings provide a new strategy for developing a sustainable, integrated light-harvesting system that mimics the natural photosynthetic process.Our Recent Publications Related to This Presentation:1. J. S. Lee, S. H. Lee, J. H. Kim, and C. B. Park. Lab on a Chip (2011), DOI: 10.1039/c1lc20303g. 2. S. H. Lee, J. Ryu, D. H. Nam, and C. B. Park. Chemical Communications 47: 4643-4645 (2011)
9:00 PM - G3.21
Surface-Enhanced Raman Scattering on Multilayered Nanodot Prepared by Using Anodic Porous Alumina Membrane.
Toshiaki Kondo 2 , Kazuyuki Nishio 1 2 , Hideki Masuda 1 2 Show Abstract
2 , Kanagawa Academy of Science and Technology, Sagamihara Japan, 1 , Tokyo Metropolitan University, Hachioji Japan
The fabrication of three-dimensional (3D) ordered arrays of metal nanostructures has attracted increasing attention owing to their capability to enhance the electric field of incident light based on localized surface plasmon resonance (LSPR).1,2 A multilayered structure composed of metal and dielectric materials has been proposed as a candidate for the structures, which can produce the accumulated nanogaps with controlled sizes. The small gaps formed in the multilayer of metal and dielectric material are effective for the enhancement of the electric field of incident light.3 In this presentation, we describe the fabrication of a multilayered nanodot array, which produces accumulated nanogaps between metal and dielectric materials, using an anodic porous alumina as the evaporation mask, and its application to the substrate for surface-enhanced Raman scattering (SERS) measurements. Metal (Au) and dielectric (Al2O3) were deposited alternately onto the substrate through the nanoholes of the alumina mask using an electron-beam sputtering apparatus. The thicknesses of the Au and Al2O3 layers were controlled using a film thickness monitor. After the deposition, the multilayered nanodot array on the substrate was obtained by removing the alumina mask. Raman scattering spectra of pyridine were measured using a Raman scattering spectrometer equipped with a He-Ne laser (633 nm) as a light source. The obtained structure was dipped in a pyridine solution and dried in air before the measurement. The Raman peaks from the adsorbed pyridine molecules were observed at 1014 cm-1 and 1040 cm-1. Larger SERS signals were obtained at larger numbers of multilayers and smaller gap seizes, corresponding to the effective enhancement of the electric field of incident light. In addition to this, the effect of making air nanogaps between Au layers on the SERS intensity was studied. Air nanogaps were formed by etching Al2O3 layer. Large SERS signals were obtained at air nanogaps. The obtained multilayered structures will be used for the SERS substrate with high sensitivity.  T. Kondo, K. Nishio, H. Masuda, Appl Phys. Express, 2, 032001 (2009). T. Kondo, T. Fukushima, K. Nishio, H. Masuda, Appl. Phys. Express, 2, 125001 (2009). T. Kondo, H. Miyazaki, K. Nishio, H. Masuda, J. Photochem. Photobiol. A, in press.
9:00 PM - G3.22
Assembly and Characterization of Organic-Inorganic Hybrid Photoswitchable Plasmonic Nanoparticle Clusters.
Yunqi Yan 1 , Jennifer Chen 1 , David Ginger 1 Show Abstract
1 Chemistry, University of Washington, Seattle, Washington, United States
We assemble and characterize photoswitchable metal nanoparticle aggregates by incorporating biomolecules as linkers which respond to optical stimuli. We show that the interparticle coupling and the resulting optical properties of these nanophotonic clusters are tunable upon exposure to light and are fully reversible. We investigate the thermodynamics and kinetics of the hierarchical assembly process and determine the quantum efficiency of photoswitching in different configurations. By optimizing experimental conditions, we demonstrate photoswitching the nanoparticle clusters for many cycles with little attenuation in signal and a clearly distinguishable color change due to shifts in plasmonic coupling between the metal particles. We also describe efforts to incorporate these materials into photoswitchable and phototriggered plasmonic biosensors.
9:00 PM - G3.24
Surface Morphology of Electron Beam Treated Natural Fibers by Atomic Force Microscopy.
I. Na Sim 1 , Seong Ok Han 1 Show Abstract
1 , Energy Materials Research Center, Korea Institute of Energy Research, Yuseong-gu, Daejeon Korea (the Republic of)
Natural fiber is most abundant polymer in nature. The utilization of natural fiber is getting dramatically increased nowadays such as reinforcement of biocomposite, absorbent, functional fiber, etc. The natural fiber needs to be treated properly for the good performance of the final products. For example, the natural fiber should be treated with electron beam, chemicals in order to remove the impurities and impart functionalities on the surface. This surface treatment imparts the good mechanical performance of biocomposites resulting from the improved interfacial adhesion between natural fiber and polymer matrix. This Electron beam is very effective for surface treatment of the natural fiber in terms of clean, dry, and energy efficient process. The low dosage of 10 kGy is enough to remove the impurities from the surface of the natural fiber and maintain the mechanical strength of the cellulose. It means that irradiation with 10kGy electron beam can remove the pectin, waxy and P layer thereby expose the S layer for the cellulose. Also, the electron beam can be effective to expose the nano pores and nano layers on the surface of the S layer of cellulose, so the large surface area of S layer can provide many interlocking areas between natural fiber and polymer matrix. We investigated the surface morphologies of electron beam and thermal treated natural fiber on a nanometer scale by atomic force microscopy. The natural fibers were immobilized on stubs with adhesive tabs for imaging using the AFM. All images were obtained using the true non contact mode with silicon cantilever under atmospheric conditions. Root mean square roughness data were obtained by analyzing topography images. The electron beam effect on the interfacial performance between natural fiber and polymer matrix is proved from the interlaminar shear strength of biocomposite.
9:00 PM - G3.3
Templateless and Surfactantless Coating of Hierarchical Nanoporous Platinum on Rigid and Flexible Substrates with Good Adhesion and Its Application in Dye-Sensitized Solar Cells.
Jianyong Ouyang 1 , Swee Jen Cho 1 Show Abstract
1 Department of Materials Science & Engineering, National University of Singapore, Singapore Singapore
Porous materials have important application in many areas, such as catalysis and biosensors. Bicontinuous porous platinum has gained particular attention for its catalysis in electrochemical energy systems, such as fuel cells and dye-sensitized solar cells. The existing methods of fabricating bicontinuous porous platinum, such as template deposition, nanoparticle sintering and dealloying, are complicate and not cost effective. This paper reports facile and scalable methods to coat hierarchical nanoporous platinum by chemical reducation of a platinum precursor at relative low temperature. Nontoxic chemicals are used, and the process can be completed in a few minutes. Thus, they are green methods. Hierarchical nanoporous platinum can be coated on both rigid and flexible substrates like polymer with good adhesion. It has excellent catalysis, and its application as the counter electrode of dye-sensitized solar cells will be presented as well.
9:00 PM - G3.4
Direct-Write Assembly of 3D Functional Materials.
Cheng Zhu 1 , Douglass Tanaka 2 , David Kolesky 2 , Kyle Sullivan 1 , Alex Gash 1 , Andrew Pascall 1 , Joshua Kuntz 1 , Christopher Spadaccini 1 , Jennifer Lewis 2 , Eric Duoss 1 Show Abstract
1 , Lawrence Livermore National Lab, Livermore, California, United States, 2 , university of illinois at Urbana-Champaign, Urbana-Champaign, Illinois, United States
The ability to pattern functional inks with high-speed and low-cost printing techniques is required for many emerging applications including sensors, displays, solar cells, and antennas. Direct-write assembly is a low-cost, mask-less printing route that enables rapid design and patterning of planar and three-dimensional (3D) structures. In this filamentary printing approach, a concentrated ink with tailored rheological properties is extruded through a micronozzle(s) that is translated using a three-axis positioning stage. The ink rapidly solidifies to maintain its shape so that spanning or free-standing structures can be deposited both in- and out-of-plane. With this approach, we aim to demonstrate multi-scale (e.g., from the nano- to macro- length scales) assembly of arbitrarily complex, hierarchical 3D structures composed of multiple materials (e.g., polymers, metals, and ceramics). Here, we present our recent work on developing functional inks for printing 3D microstructures with designs that have been optimized for structural, thermal, and/or functional properties.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
9:00 PM - G3.5
ZnO Nanowire Array Growth on Three-Dimensional (3D) Spherical Substrate: Facile Synthesis of Multi-Component Koosh Ball Structures.
Zheng Ren 1 2 , Yanbing Guo 1 2 , Gregory Wrobel 1 2 , Pu-Xian Gao 1 2 Show Abstract
1 Materials Science and Engineering, University of Connecticut, Storrs, Connecticut, United States, 2 Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Unique koosh ball structure composed of multiple components(Iron oxide, SiO2 and ZnO) was obtained by a facile wet chemistry synthesis. It is the first time that ZnO nanowires have been conformally grown onto the 3D spherical substrate. The as-prepared koosh ball nanostructure was characterized by electron microscopy and X-ray diffraction. The interesting hierarchical koosh ball structure was well characterized by dark-field transmission electron microscopy (TEM) imaging and scanning transmission electron microscopy (STEM) elemental mapping. A possible growth mechanism was proposed and various experimental parameters were adjusted to achieve rationally controlled morphology. It was found that the concentrations of precursors played a key role in determining the dimentionality and dispersion of ZnO nanowires. In addition, the optical property of this multi-component structure was investigated. We believe our koosh ball structure material system will serve as a versatile candidate in environment and energy applications as well as biomedical technology due to the enabling combination of desired functional nanostructures.
9:00 PM - G3.6
Hierarchical 3D Graphene-Based Structures for Energy Storage.
Marcus Worsley 1 , Matthew Suss 1 3 , Michael Stadermann 1 , Monika Biener 1 , Tammy Olson 1 , Peter Pauzauskie 2 , Juergen Biener 1 , Joe Satcher 1 , Theodore Baumann 1 Show Abstract
1 , Lawrence Livermore Nat'l Lab, Livermore, California, United States, 3 , Stanford University, Palo Alto, California, United States, 2 , University of Washington, Seattle, Washington, United States
Graphene has shown the potential to significantly impact a number of different technologies, including energy storage. Properties such as high surface areas and electrical conductivity make it a promising material for hydrogen storage, battery, and ultra capacitor applications. One route to realizing the full potential of graphene in energy storage applications is the assembly of three-dimensional macroscopic graphene networks that retain the properties of individual graphene sheets. Herein we present a class of porous materials consisting of a 3D graphene-based network that represents a significant step toward realizing the properties of individual graphene sheets in a macroscopic monolith. These 3D graphene structures possess high electrical conductivities, and surface areas that approach the theoretical value expected for a single graphene sheet. In addition, they possess hierarchical structure (macro-, meso-, and microscale), including mesopore volumes among the highest reported to date. The impact of these hierarchical 3D graphene-based structures on energy storage applications (e.g. electrical, hydrogen) will be presented. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the DOE Office of Energy Efficiency and Renewable Energy.
9:00 PM - G3.7
In situ Detection and Removal of Metal Ion by Porous Gold Electrode.
Younghun Kim 1 , Cheon Seok Oh 1 Show Abstract
1 Chemical Engineering, Kwangwoon University, Seoul Korea (the Republic of)
A sensing electrode for the detection of heavy metal ions in aqueous solution selectively measured the concentrations of target materials on its functionalized surface, which has affinity to target metal ions. Target ions were adsorbed simultaneously on the functionalized electrode during the sensing process. Therefore, to understand this, experiments on the amperometric response and isotherms with an initial concentration of Hg2+ were tested. Herein, a porous gold electrode was fabricated on ITO and functionalized with thiol groups for binding mercury ion. HDT/PAu/ITO substrate acted as both a sensor and adsorbent for mercury ion. To determine the adsorption capacity of Hg2+ on the electrode, an isotherm test was carried out at different initial concentrations (Co). During the sensing step for metal ion, Hg2+ was adsorbed on the electrode, and thus the equilibrium concentration adsorbed on the electrode was correlated with Co. Correlation of the detection current versus removal capacity showed that it is possible to estimate the adsorbed concentration on the electrode during the sensing step. For practical application, porous gold electrode with a regular nanopore structure and large surface area similar to mesoporous silica should be developed to simultaneously detect and remove target metal ions from aqueous solution. Therefore, we found that HDT/PAu/ITO electrode has potential in dual applications as both a sensing electrode and adsorbent for the removal of heavy metal ions.
9:00 PM - G3.8
SERS Efficiency of Silver-Decorated Cylindrical Pores: Simulation of Electromagnetic Field and Chemical Enhancement.
Rajesh Kodiyath 1 , Jian Wang 3 , Zachary Combs 1 , Theodoros Papadopoulos 2 , Hong Li 2 , Jean-Luc Bredas 2 , Richard J Brown 3 , Vladimir Tsukruk 1 Show Abstract
1 School of materials science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 3 Analytical Science Division, National Physical Laboratory, Teddington, Middlesex, United Kingdom, 2 School of Chemistry and Biochemistry, Georgia Institute of Technology, Atlanta, Georgia, United States
We employed both electromagnetic and density functional simulation studies to get insight into the SERS phenomenon that occurs in 3D PAM-based substrates. Electromagnetic simulation of silver nanoparticle dimer clusters placed at different positions and pore depths within alumina membranes of various pore diameters suggest that membranes with pore diameters of around 400 nm and the incorporation of nanoparticles within the first 10 µm beneath the surface are critical for the optimization of SERS substrates showing high enhancement factors for common Raman markers and nonresonant molecules like perchloric acid. We also employed density functional theory calculations to investigate the SERS of perchloric acid on silver clusters of different sizes and crystallinity. The size of the clusters and orientation of the molecule are found to have significant effect on the SERS behavior. Finally, we investigated contribution of chemical enhancement toward SERS of nonresonant molecule and compare the simulated results with experimental SERS of perchloric acid. Overall, the current study provides an example of a comprehensive approach that considers the transmission of light confined in cylindrical pores toward designing highly optimized 3D SERS substrates with record enhancement factors.
9:00 PM - G3.9
Hierarchically Porous TiO2 Electrodes for Dye-Sensitized Solar Cells.
Chang-Yeol Cho 1 , Jun Hyuk Moon 1 Show Abstract
1 Chemical and Biomolecular Engineering, Sogang Univerisity, Seoul Korea (the Republic of)
Dye-sensitized solar cells (DSSCs) are of great interest due to their projected cost-effectiveness, their relatively high photo-electric conversion efficiency, and the unique advantages of transparent cells over conventional silicon photovoltaics. Hierarchical porous structures have attracted attention recently due to the synergistic advantages of mesoporous and macroscale morphologies. For example, assemblies of both mesoporous TiO2 particles (with diameters of several hundred nanometers) and nanostructured TiO2 fibers have been applied in this regard. Here we introduce a method to generate hierarchical electrodes consisting of meso- and macroscale pores by a dual templating method. Mesoscale colloidal particles and lithographically patterned macropores were used as the dual templates, with the colloidal particles assembled within the macropores. Our hierarchical TiO2 electrodes showed a maximum efficiency of 5% with 50 nm pores and a 6 μm thickness. This was comparable to the efficiency of conventional TiO2 electrodes with the same thickness, and was attributed to the strong scattering and suppression of charge recombination in hierarchical TiO2 electrodes.
G4: Hierarchical Materials I
Wednesday AM, November 30, 2011
Back Bay D (Sheraton)
9:30 AM - **G4.1
Directional Physical Properties of Hierarchical Asymmetric Structures.
Hyunsik Yoon 1 , Kahp Y. Suh 2 , Kookheon Char 1 Show Abstract
1 School of Chemical and Biological Engineering, Seoul National University, Seoul Korea (the Republic of), 2 School of Mechanical Engineering, Seoul National University, Seoul Korea (the Republic of)
Directional physical properties are attractive for various applications such as artificial adhesives, microfluidics, and optical devices because of their adhesion hysteresis, directional liquid flow without driving force and selective transmission for desired viewing angles. In order to realize the asymmetry in various types of structures, we utilized a concept of hybridization of polymeric structures with metal films. We have designed the Janus nanopillars bent by the difference in thermal expansion coefficients between the two components of hybrids showing the adhesion hysteresis (i.e., the shear adhesion force in the pulling direction is stronger than that in the opposite direction). With asymmetric pillar structures, we could also demonstrate the directional liquid spreading toward the bending direction. Furthermore, with relevant modifications in the design of hybrid structures, we could demonstrate reinforced nanopillars preventing the capillary force driven clustering of nanopillars in water or humid conditions as well as optical films only visible in desired positions, which are essential for applications such as privacy filters and three-dimensional displays without wearing special glasses.
10:00 AM - **G4.2
Bioinspired Reversible Adhesives.
Aranzazu del Campo 1 Show Abstract
1 , MAx-Planck-Institut für Polymerforschung, MAinz Germany
10:30 AM - G4.3
Superhydrophobic Nanoflake Surfaces Induced by Hierarchical Wrinkling of Polyelectrolytes/Metal Hybridized Films.
Young Hun Kim 1 , Yong Man Lee 2 , Pil J. Yoo 1 2 Show Abstract
1 School of Chemical Engineering, Sungkyunkwan University, Suwon Korea (the Republic of), 2 SKKU Advanced Institute of Nanotechnology, Sungkyunkwan University, Suwon Korea (the Republic of)
Inspired by intriguing behaviors observed in plant or animal surfaces in nature, artificial nanostructures have drawn much attention to fabricate superhydrophobic surfaces due to its strong potential for vast applications, such as self-cleaning or anti-sticking surfaces. Especially, superhydrophobic surfaces fabricated by the integration of one-dimensional (1D) nanomaterials have utilized the advantages of the controlled packing density, uniformity and directional alignment of nanostructures. However, for an industrial application, it is essentially needed to acquire the mechanical stability as well as the capability for a large area demonstration. In this presentation, we demonstrate a novel method to fabricate the superhydrophobic surface via controlled surface wrinkling through the incorporation of Ag nanoparticles into the surface-deposited polyelectrolyte multilayers (PEMs) and the subsequent selective dry-etching of the residual surface polymeric layer, resulting in a highly rough and hierarchically structured Ag nano-flakes surface. After the preparation of PEM films formed by the alternate depositions of polycation (linear polyethylenimine) and polyanion (poly(acrylic acid)), the Ag nanoparticles can be readily synthesized within the PEM thin films through cationic exchange reaction. During this incorporation step, an excessive amount of Ag nanoparticles is formed on the surface layer, thus, brings about a substantial accumulation of the compressive stress. As a result of exceeding the critical wrinkling stress between upper hybridized metal/polymer layer and underlying polymeric layer, hierarchically wrinkled surfaces are spontaneously formed. Structural characteristics of the wrinkled-surface such as wavelength, amplitude or topological hierarchy, can be sophisticatedly manipulated by the thickness ratio of the underlying PEMs to the capping Ag layers or the amount of incorporated Ag nanoparticles. Since plasma ashing process only removes the polymeric species in Ag/polymer hybrid layer, the exposed metallic nanostructures can be stably remained on the surface. Interestingly, the shape characteristic of Ag nanostructures shows vertically-stood and hierarchically structured nano-flakes, which show a notable mechanical stability upon repeated exposures to the external stimuli. After being chemically modified with fluorinated self-assembled monolayers, the nano-flakes surface completely exhibits the superhydrophobic characteristic, where the water contact angle increases up to 170 degrees. More importantly, as compared to conventional approaches employing vertically aligned 1D nanomaterials, the surfaces with vertically stood Ag nano-flakes can provide the additional advantages in the mechanical stability and durability. Therefore, presented means in this study can allow for a facile and robust fabrication of large-scale superhydrophobic surfaces.
10:45 AM - G4.4
Imaging and Nonimaging Transfer-Printed Gradient Index Optical Devices.
Joseph Geddes 1 2 , Seok Kim 1 2 , Paul Braun 1 2 , John Rogers 1 2 Show Abstract
1 Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
We show how thin scales or plates of nanostructured porous material can be stacked to create gradient index optical elements and devices. The pore structuring can be created in the scales, for example, by electrochemical etching of aluminum to nanoporous alumina, whereby engineering of changing current density across the parent material creates gradients in pore sizes and hence effective refractive index. Scales with radial gradients of effective refractive index can be used as lenses, while those with linear gradients of refractive index can be used as prisms. We report designs showing how scales possessing refractive index gradients can be stacked via transfer printing to make a simple flat microscope and spectrum splitter.
11:30 AM - G4.5
Fabrication of Stiff Neuromast-like Nanostructures.
Hyunsik Yoon 1 , Kahp Y. Suh 1 , Kookheon Char 1 Show Abstract
1 , Seoul National University, Seoul Korea (the Republic of)
Bio-inspired polymeric high aspect-ratio (AR) nanostructures have recently received much attention in many research areas due to their unique mechanical, optical, and surface properties. One potential limitation for the widespread use in such applications is that soft high AR structures are susceptible to mechanical instabilities such as delamination, clumping, and clustering between neighboring features when they are used in the arrayed format. Among these, the capillary force driven clustering of nanopillars is the major hurdle to overcome in many practical applications because many assembled bio-related devices or systems are typically operated in water or humid environment. In order to improve the mechanical properties of polymeric pillars or line arrays, we developed a simple, yet robust method for enhancing the mechanical properties of high-density nanopillar arrays by the replica molding after the oblique metal deposition on a master. The structure we present here is fairly similar to that of superficial neuromasts found in the sensing system of fishes. The structure is essentially the assembly of nanopillars, the stem region of which is coated with metal layers and thus strengthened, with the top part of the pillars intact and soft, thus the name “stiff neuromast-like” structure. This stiff neuromast-like structure of reinforced polymer nanopillars finds unique applications. For example, these pillars could be used as functional units for biosensors after the integration with functional nanoparticles or lipid layers at the top of the polymer surface. They are also useful for studying the directed cell migration on the surfaces of different rigidity with the same chemical composition. As will be demonstrated, the reinforced nanostructures show remarkable stability against the structural collapse due to capillary force driven clustering.
11:45 AM - G4.6
Bio-Enabled Synthesis of High-Aspect-Ratio, Porous-Wall, Aligned Titania Nanotube Arrays.
John Berrigan 1 , Tae-Sik Kang 2 , Ye Cai 1 , James Deneault 2 , Taylor McLachlan 1 , Richard Vaia 2 , Michael Durstock 2 , Kenneth Sandhage 1 Show Abstract
1 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials and Manufacturing Directorate, United States Air Force Research Laboratory, Wright-Patterson Air Force Base, Ohio, United States
Aligned, high-aspect-ratio, transition metal oxide nanotube arrays with high surface areas can be attractive structures for use in a number of (bio)chemical, electrical, and optical applications (e.g., high throughput (photo)catalysis, selective (bio)molecular separators, sensitive and rapid gas sensors, efficient electrodes for solar cells or batteries). One general strategy for fabricating such aligned oxide nanotube arrays is to apply a conformal oxide coating to a template possessing well-aligned vertical channels (e.g., a porous anodic alumina membrane or a track-etch polymer membrane), followed by selective removal of the underlying template. In this presentation, a protein-enabled method to convert oriented-nanochannel templates into high-aspect-ratio, aligned nanotube arrays with thin walls (34 nm) composed of co-continuous networks of pores and titania nanocrystals (15 nm ave. size) is discussed. Prior work with bacteriophage display biopanning has indicated that polycationic peptides are capable of inducing the precipitation of high yields of titania from a water soluble precursor (Ti(IV) bisammonium-lactato-dihydroxide, TiBALDH). Protamine, a relatively inexpensive and readily-available arginine-rich protein harvested from a variety of fish (e.g., salmon, herring, trout, tuna), has also been found to be capable of binding to silica and titania, and of inducing the formation of conformal Ti-O-bearing coatings from a TiBALDH-bearing solution. In this presentation, a protamine-enabled coating process, consisting of alternating exposure of porous anodic alumina membranes to aqueous protamine-bearing and titania precursor (TiBALDH) solutions, is discussed. The ability of protamine to bind to alumina and titania, and to induce the formation of a Ti–O-bearing coating upon exposure to the TiBALDH precursor, enabled the layer-by-layer deposition of conformal protamine/Ti–O-bearing coatings within the nanochanneled alumina template. Subsequent protamine pyrolysis yielded highly porous coatings composed of interconnected titania nanoparticles. Selective dissolution of the underlying alumina template through the pores in the coating then yielded freestanding, aligned, porous-wall titania nanotube arrays. The pores within the nanotube walls allowed for enhanced loading of functional molecules (such as Ru-based N719 dye), whereas the interconnected titania nanoparticles enable the high-aspect-ratio, aligned nanotube arrays to be used as electrodes (e.g., dye-sensitized solar cells).
T-.S. Kang, et al., Nano Lett., 9  601 (2009).
M. B. Dickerson, et al., Chem. Mater., 20, 1578 (2008).
Y. Fang, et al., Chem. Mater., 21, 5704 (2009).
12:00 PM - G4.7
Flexible Nanomembranes for Potential THz Radiation Applications.
Richard Rojas Delgado 1 , Francesca Cavallo 1 , Roberto Paiella 2 , Max Lagally 1 Show Abstract
1 Materials Science Program, University of Wisconsin Madison, Madison, Wisconsin, United States, 2 , Boston University, Boston, Massachusetts, United States
We fabricate periodically wrinkled (“corrugated”) group IV nanostructures by laying semiconductor nanomembranes on pre-patterned surfaces, including arrays of ridges or posts with a carefully selected periodicity. Fabrication of corrugated nanostructures with a wide range of periodicities is enabled by the exceptional compliance of nanomembranes. We show that single-crystal Si nanomembranes conform to the pre-patterned surface at a scale, so far, of periodicities of a few micrometers and amplitudes of ~ 200 nm. We fabricate device structures integrating single-crystal Si and Si/SiGe based corrugated nanomembranes and present initial electrical-characterization measurements. We discuss the concept of radiation from carriers accelerating/decelerating when traveling along a sinusoidal trajectory through a corrugated nanostructure1 in the context of our nanostructures, including potential application of the corrugated structures as radiative elements in the terahertz (THz) range. Despite the potential of THz radiation in large variety of applications (e.g., biology and medical diagnostics, homeland security, food quality control, astrophysics, and ultra-fast spectroscopy), to date the only compact and continuous-wave THz sources are III-V based quantum cascade lasers operating at low temperature. In contrast our approach may allow fabrication of a group IV based THz source potentially operating at room temperature, even though current dimensions and mean free paths are not sufficient to achieve that goal. Our fabrication approach is general and can be applied to a large variety of nanomembranes and pre-patterned substrates, both rigid and flexible.1A. I. Fedorchenko, H. H. Cheng, G. Sun, and R. A. Soref, Appl. Phys. Lett. 96, 113104 (2010)Supported by AFSOR and DOE.
G5: Hierarchical Materials II
Wednesday PM, November 30, 2011
Back Bay D (Sheraton)
2:30 PM - **G5.1
Hierarchical Materials for Advanced Aerospace Structural Applications.
Brian Wardle 1 Show Abstract
1 Aero/Astro, MIT, Cambridge, Massachusetts, United States
Bulk nanostructured materials offer tremendous opportunity for re-inventing materials, but also pose many challenges both in terms of characterization, design, processing, and scaling. This presentation will focus on recent work developing hieararchical nano-engineered advanced composites for aerospace applications. Such hybrid multi-scale engineered materials employ aligned carbon nanotubes (CNTs) to enhance laminate-level multifunctional properties of existing aerospace-grade advanced composites. Intrinsic and scale-dependent characteristics of the CNTs are used to engineer laminate-level property improvements: interlaminar shear strength, interlaminar toughness, tension-bearing strength, therma and electrical conductivity results will be discussed and the underlying mechanisms elucidated. Fundamental studies on polymer-CNT interactions led to the development of a combined top-down and bottom-up fabrication methodology that addresses several of the key issues (agglomeration, viscosity, CNT wetting, scale, alignment) that have frustrated the use of CNTs in nanocomposites and nano-engineered composites. Current research to answer key outstanding “questions of the day” related to CNT contributions to bulk composite properties will be overviewed, including a novel experimental platform to investigate nanoscale interactions in a well-controlled manner. New research results and directions stemming from ongoing work, particularly new applications in related disciplines, will be discussed.
3:00 PM - G5.2
Highly Sensitive and Selective Gas Sensors Based on ZnO Nanowire Arrays with Different Metal Oxides Modification.
Haiqiao Su 1 , Weilie Zhou 1 , Jiajun Chen 1 , Kai Wang 1 , Kun Yao 1 Show Abstract
1 AMRI/Chemistry, Advanced Materials Research Institute/UNO, New Orleans, Louisiana, United States
Three dimensional (3D) nanoarchitectures are attracting more attention recently for device and sensor fabrication because of their unique structures. For highly selective gas detection, fabrication of different materials nanowire arrays is essential. In this presentation, we mimicked the biological olfactory receptor array and present our recent research on exploring different metal oxides modified ZnO nanowire arrays for selective detection. In this experiment, In2O3, SnO2, and WO3 were sputtered on ZnO nanowire array surface as active materials, targeting at selective detection of H2S, NO2, CO, NH3, and H2. The gas sensors showed high sensitivity to H2S and NO2 down to part per billion (ppb) levels at room temperature, attributed to the large surface area of 3D structure. With principal component analysis (PCA) combined with the response speeds, different gases could be discriminated by this set of the nanowire arrays, which provides a potential method to prepare 3D highly sensitive and selective gas sensors using materials which are hardly grown as nanowire arrays.
3:15 PM - G5.3
CeO2 Nanowire Arrays on 2D and 3D Substrates for Automobile Emission Control.
Zhonghua Zhang 1 , Nathan Freedman 1 , Yanbing Guo 1 , Pu-Xian Gao 1 Show Abstract
1 Department of Chemical, Materials and Biomolecular Engineering, Institute of Materials Science, University of Connecticut, Storrs, Connecticut, United States
Ceria-based materials have been attractive due to their widespread applications in catalysis, fuel cells, optical films, polishing materials, gas sensors, and other fields. Particularly these materials are used as oxygen storage promoters in the three way catalysts (TWCs). Herein, we present a template- and surfactant-free electrochemical method for the fabrication of CeO2 nanowire array on 2D and 3D substrates. They have much higher surface area than the nanoparticles and exhibit excellent catalytic activity for CO and NO oxidation. They have also been demonstrated to have a good mechanical, thermal and chemical stability in both oxidative and reductive environments. A possible mechanism for the formation of CeO2 nanowire arrays in the electrodeposition has also been explored.
3:30 PM - G5.4
Electrospray Ionization as a Method for Hierarchical Deposition of PTFE.
Marriner Merrill 1 , Gabriel Mendez Velez 2 Show Abstract
1 Multifunctional Materials, Naval Research Laboratory, Washington, District of Columbia, United States, 2 , University of Puerto Rico at Arecibo, Arecibo, Puerto Rico, United States
Electrospray ionization (ESI) is proposed as a potential 1-step method for developing controlled hierarchical structures. ESI has long been a standard method for translating polymers, nanoparticles, proteins, and other materials from a liquid solution to a gas-phase for analysis in mass spectrometers. More recently, work examining ESI as a deposition method has also been performed. As a result, ESI is known to work with materials ranging in size from angstroms to hundreds of nanometers, to create electrostatically charged species which can be guided with electrical fields, and to be potentially scalable. In addition, current models of the ESI process predict that the asymmetry of the coloumb fission process intrinsic to ESI results in a stair-step size distribution of produced particles. In other words, a single solution can produce discrete particles with a series of narrow size distributions. Since both the charge on particles and the size distribution can be controlled, ESI offers an intriguing new range of potential hierarchical films and coatings. This report presents experimental work examining the validity of that hypothesis for the case of PTFE, a material with broad applicability. First, a commercially available PTFE solution is modified to be electrosprayed. Second, flow rate and driving voltage are varied and several films are created. Finally, these films are compared with the same solution deposited via spin-coating. From this, conclusions regarding both general ESI deposition and specific PTFE film creation will be discussed.
3:45 PM - G5.5
Formation and Applications of Hierarchically Porous Carbon, Metals and Metal Oxides Formed by Nanocasting.
Martin Bakker 1 , Franchessa Sayler 1 , Amy Grano 1 , Jan-Henrik Smatt 2 Show Abstract
1 Department of Chemistry, The University of Alabama, Tuscaloosa, Alabama, United States, 2 Physical Chemistry, Abo Akademi University, Turku Finland
Hierarchically porous materials are of interest in a wide range of applications. If the materials are electronic or ionic conductors such materials are of interest as electrodes for use in fuel cells, flow batteries, electrocatalysis, and pseudo/supercapacitors. We have demonstrated the synthesis of hierarchically porous carbon, metal and metal oxide monoliths. Hierarchically porous silica with porosity at three length scales: 0.5-30 micrometer, 200-500 nm, and 3-8 nm, is used as a template to form these materials. The porosity of the silica template is produced by spinodal decomposition (0.5-30 micrometer), particle nucleation (200-500 nm) and addition of surfactant or block copolymer (3-8 nm). Nanocasting: replication of all or part of the structure via one of a number of chemical replication techniques has been used to produce the carbon, metal oxide and metal replicas. The final surface areas of the materials can be as high as 1200 m2/g for carbon replicas, and >300 m2/g for metals and metal oxides. The use of the nanocasting technique allows for formation of materials that are compositionally or spatially heterogeneous, e.g. this can be used to produce materials consisting of two macroporous bicontinuous networks separated by a nanoporous membrane, nanostructured metal oxide composites and nanostructured alloys. The approach is relatively scalable, with silica templates as large as 1 inch diameter x 5 inches in length being readily attainable. However, nanocasting into such large pieces presents challenges, where trade-offs must be made between the mechanical stability of the replica and the fidelity of the replication process. More complicated shapes, e.g. tubes, are still more challenging, although even such shapes can be obtainable by alternate pathways.We will present results on the synthesis and characterization of hierarchically porous monoliths of carbon, copper, silver, cobalt, nickel, silver alloy and cobalt, nickel and zinc oxides, the use of some of these monoliths in chemical separations including chromatography, and address the interplay between the template and the chemical processing and how this can be used to produce new micro and nanostructures.
4:30 PM - G5.6
Shear-Resistant Ultra-Low-Density Polymer Aerogel Films with Hierarchical Morphologies.
Christoph Dawedeit 1 , Sung Ho Kim 1 , Juergen Biener 1 , Marcus A. Worsley 1 , Kuang Jen Wu 1 , Steve A. Letts 1 , Tony Van Buuren 1 , Tom Braun 1 , Sergei O. Kucheyev 1 , Yinmin Morris Wang 1 , Joe H. Satcher 1 , Alexander A. Chernov 1 , Trevor M. Willey 1 , Christopher C. Walton 1 , Alex V. Hamza 1 Show Abstract
1 , Lawrence Livermore Nat. Lab, Livermore, California, United States
The fabrication of thin aerogel films with hierarchical morphologies has large potential for many energy and catalysis related applications. The formation of such films often involves the application of shear, and the challenge to develop a shear-resistant aerogel chemistry. Here we report on the development of shear-resistant low-density polymer aerogels by tuning their rheological properties. Specifically, we will discuss the development of Dicyclopentadiene (DCPD)-based aerogels that have potential use in future inertial confinement fusion targets where the aerogel could be used to define the shape of Deuterium/Tritium-fuel. Thin DCPD aerogel films were prepared on the inner surfaces of spherical 2mm-diameter capsules and glass cylinders. Properties that were adjusted include pore size, layer thickness (15μm-200μm) and density (20-100mg/cc). This work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
4:45 PM - G5.7
Hollow-Tube Micro-Lattices: Achieving Ultra-Low Density and Functional Ductility by Designing Cellular Architecture at Three Levels of Hierarchy.
Tobias Schaedler 1 , Alan Jacobsen 1 , Anna Torrents 2 , Jie Lian 4 , Julia Greer 4 , Lorenzo Valdevit 2 3 , William Carter 1 Show Abstract
1 Bio- and Nanomaterials Technologies, HRL laboratories, Malibu, California, United States, 2 Mechanical and Aerospace Engineering, University of California, Irvine, Irvine, California, United States, 4 Materials Science, Caltech, Pasadena, California, United States, 3 Chemical Engineering and Materials Science, University of California, Irvine, Irvine, California, United States
Micro-lattice materials with periodic cellular architecture were fabricated using a new process that enables precise control over architecture at three levels of hierarchy at three distinct length scales. Lattice unit cell (~mm-cm), hollow tube lattice member (~µm – mm) and hollow tube wall thickness (~nm - µm) can be controlled independently, enabling the design of micro-lattice materials with unprecedented properties. We achieve hollow tube wall thicknesses <200 nm, resulting in metallic micro-lattices with densities as low as 2 mg/cc, lower than any other metallic material ever reported. This unique hierarchical architecture also results in unprecedented mechanical behavior: complete recovery from compressive strains exceeding 50%, demonstrating the ability of micro-lattice architectures to transform brittle properties of the constituent material into “macroscopically ductile” bulk properties. This “functional ductility” is of interest to energy storage applications where significant volume expansion after intercalation or adsorption is common. Such hollow tube lattice architectures can also reduce charge carrier transport lengths for 3D battery current collectors.© Copyright 2011 HRL Laboratories, LLC
G6: Lithium-Ion Batteries
Jun Hyuk Moon
Thursday AM, December 01, 2011
Back Bay D (Sheraton)
9:00 AM - **G6.1
Three-Dimensional Bicontinuous Ultra-High-Power Bulk Battery Electrodes.
Paul Braun 1 Show Abstract
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Rapid charge and discharge is an increasingly sought-out feature of electrical energy storage devices, but causes dramatic capacity reductions in most rechargeable batteries. Supercapacitors do not suffer from this problem, but have much lower energy densities than batteries. A storage technology that combines the rate performance of supercapacitors with the energy density of batteries would revolutionize portable and distributed power. Here we demonstrate charge and discharge rates of up to 400C and 1,000C for lithium-ion and nickel-metal hydride chemistries, respectively, with minimal capacity loss (400C is a 9 second charge or discharge and 1,000C is a 3.6 second charge or discharge). The final structure also has energy densities comparable to current commercial systems. This is achieved using a self-assembled colloidal crystal templated three dimensional (3D) bicontinuous nanoarchitecture consisting of an electrolytically active material sandwiched between rapid ion and electron transport pathways. Finally, a full-cell lithium-ion battery constructed from a bicontinuous lithiated MnO2 cathode and a conventional graphite anode was charged to 90% capacity in 2 minutes. The 3D bicontinuous electrode approach presented here is quite general, and is applicable to many battery chemistries.
9:30 AM - **G6.2
Electrochemical Characteristics of Polymerized C60 Film as Artificial Solid-Electrolyte Interface on the Surface of Electrode for Lithium Ion Batteries.
Joong-Kee Lee 1 , Arenst Arie 2 , Jung Sub Kim 1 Show Abstract
1 Energy Storage Research Center, Korea Institute of Science and Technology, Seoul Korea (the Republic of), 2 Department of Chemical Engineering, Parahyangan Catholic University , Bandung Indonesia
Batteries are energy storage devices that convert chemical energy in a fixed volume to direct-current electrical energy. The anode and cathode materials of lithium ion secondary batteries serve as hosts for lithium and the lithium intercalation sites in the anode and cathode have different chemical potentials. Basically, the discharge reactions of lithium batteries involve the generation of lithium ions and their migration across the electrolyte and insertion into the crystal lattice of the host electrode materials. In the case of a charge reaction, the ions move in the opposite direction to that of the discharge reaction. Therefore, in order to optimize the design of the electrode materials in the battery system, we should consider the electrode materials from the point of view of the circulation of the ions. This transport process is a key factor in the operation of non aqueous batteries.Hence, the importance of the Solid-Electrolyte Interface (SEI) is well recognized because the migration of ions through the interface is the rate determining step. The solvated lithium ions in the electrolyte lose their salvation shell while penetrating the SEI and are incorporated into the host structure in a solvent free form. Such reactions are desirable, but in some cases lithium intercalates together with the solvated shell, causing the exfoliation of the electrode. This phenomenon leads to the mechanical breakdown of the electrode due to the stress in the SEI caused by the local preferential dissolution of the electrode material. The SEI determines the safety, power capability, morphology of lithium deposits, shelf life and cycle life of the battery. The formation of the SEI involves diverse routes such as the precipitation of insoluble Li2Co3, salt ions and polymerized solvent. Therefore, the chemical composition and structure of the SEI are too complex to control and, hence, the formation of an artificial SEI film at the interface of the solid-electrolyte of lithium ion batteries is one of the alternative ways to improve their electrochemical performance. The purpose of this study is to investigate the effect of depositing such a surface coating using C60 film on the electrochemical performance of a Li ion cell. Through this work, we expect the electrochemical performance of the electrode material to be enhanced, due to the role of the C60 thin film as an artificial passivation layer at the electrode/electrolyte interface. AcknowledgementThis work was supported by the National Research Foundation of Korea Grant funded by the Korean Government(MEST)(NRF-2010-C1AAA001-2010-0028958)
10:00 AM - G6.3
Hybrid Carbon/Titanium Dioxide Aerogels as Active Materials for Lithium Ion Batteries.
Sungwoo Yang 1 , Yue Cai 1 , Yingwen Cheng 1 , Jie Liu 1 Show Abstract
1 Chemistry, Duke University, Durham, North Carolina, United States
Mesoporous titanium dioxide (TiO2) has been widely studied in lithium ion batteries (LIBs) and photocatalysts because the mesopores enable fast diffusion of ions and molecules within the bulk materials, resulting in improved kinetics of electrochemical and photocatalytic reactions. Although TiO2 shows great potential as an anode electrode due to fast Li+ insertion/desertion, its capacity has been limited by slow electron transport compared to that of commercialized carbon electrodes. In this project, we successfully developed a convenient method to synthesize hybrid carbon/TiO2 aerogel materials to improve its electrochemical capacity in LIBs. The Brunauer–Emett–Teller (BET) surface area of hybrid aerogels was between 200 m2 g-1 and 800 m2 g-1. The reversible discharge capacity was 415 mA h g-1 at 100 mA g-1 scan rate and operating voltage between 0.05 and 3.00 V with excellent cyclic capacity retention (> 99%). This reversible capacity is well above current results in LIBs based on carbon/titanium oxide as an alternative anode electrode. In addition, the loading density of the active monolithic material was 50 mg cm-2 which is much higher than the typical loading density of active materials in recent literature. Moreover, a high capacity of 1933 mA h g-1 was obtained in the first discharge with a corresponding charge capacity of 508 mA h g-1. Our hybrid aerogel could serve as an ideal material for solid state LIBs. We believe that the present approach also provides a promising method for the fabrication of other capacitive materials
10:15 AM - G6.4
Three-Dimensional TiO2 Nanoelectrodes for Li-Ion Microbatteries.
Gyanaranjan Pattanaik 1 , Jacob Haag 1 2 , James Deneault 1 2 , Barney Taylor 1 2 , Michael Durstock 1 Show Abstract
1 AFRL/RXBN, US Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States, 2 , Universal Technology Corporation, Dayton, Ohio, United States
Titanium oxide based materials, including both Li-titanates and various TiO2 polymorphs are promising alternatives to carbonaceous anode materials for Li-ion rechargeable batteries because of their higher voltage operation (enhanced safety) and biocompatible non-toxic nature. Nanoscale three-dimensional (3D) architectures of current collectors for microbatteries would significantly increase the areal capacity over their planar counterparts, if the active Li-insertion electrode material could be coated conformally. The nanoscale thickness of the active electrode layer in combination with an electronically conducting 3D nanoarchitecture of the current collector should enable high areal capacity and fast charge-discharge rates. We have used atomic layer deposition (ALD) to grow conformal layers of TiO2 films on high aspect ratio nanoporous Al2O3 templates, template-electrodeposited 3D metal nanowire arrays and vertically aligned carbon nanotube carpets. We have been able to grow conformal layers with controllable thickness and nanometer scale uniformly coated around the high aspect ratio features. A significant increase in areal capacity (up to two orders of magnitude) was obtained in 3D TiO2 nanotube electrode arrays over 2D thin film electrodes of a similar footprint. This presentation will discuss a systematic study of the ALD grown 3D TiO2 nanotube electrodes as Li-ion microbattery anodes.
10:30 AM - G6.5
Fabrication and Characterization of Nanostructured 3-D Anodes for Li-Ion Batteries.
Jacob Haag 1 , Gyanaranjan Pattanaik 1 , Barney Taylor 1 , Michael Durstock 1 Show Abstract
1 , Air Force Research Laboratory, Wright-Patterson AFB, Ohio, United States
Current commercial Li-ion batteries contain carbon based anodes that are limited by their theoretical maximum capacity (372 mAh/g) as well as Li insertion rate which correspondingly limits battery energy and power densities. Therefore, in order to increase energy and power densities, the development of new anodes is required. Metal oxides such as SnO2 have an increased capacity (782 mAh/g) compared to carbon; however, they have been limited by their large expansion and contraction during Li alloying that leads to pulverization. By decreasing the particle size and nanostructuring the electrodes, the volumetric stresses can be minimized for improved cycling and stability. In this talk, we will present new hierarchically designed 3-D battery anode heterostructures consisting of multiwalled carbon nanotubes (MW-CNT) and SnOx. Different carbon nanotube architectural designs have been explored and will be discussed including vertically aligned MW-CNTs and MW-CNT buckypaper. In order to coat these complex carbon structures with SnOx, atomic layer deposition was utilized and will be shown to be an effective method for coating 3-D structures for battery applications. The SnOx / MW-CNT heterostructures were also electrochemically tested as anodes in battery half cells and will be shown to have significantly higher capacities compared to graphite as well as relatively stable cycling performance.
10:45 AM - G6.6
Three-Dimensional Nitrogen-Doped Activated Graphite Felt as Improved Electrode for Redox Flow Battery.
Cristina Flox 1 , Javier Rubio-Garcia 1 , Marcel Skoumal 1 , Teresa Andreu 1 , Juan Ramón Morante 1 Show Abstract
1 Advanced Materials for Energy, IREC, Catalonia Institute for Energy Research, San Adrià del Besós, Barcelona, Spain
Safe, low-cost, high-energy-density and long-lasting rechargeable batteries are highly demanded to address pressing environmental needs for energy storage systems that can be coupled to renewable sources. Liquid electrolyte based redox flow batteries are very promising and they are believed to be a key energy storage technology. The aim of this work is addressed to improve the actual performance increasing the density of active sites in the 3D graphite electrodes. So different treatments are proposed and assessed to improve the incorporation of nitrogen as activation sites of the used graphite felt electrodes based on polyacrylonitrile (PAN). Different conventional activation and functionalization treatments have been applied to the electrodes, e.g., electrochemical and thermal treatments followed by various amoxidation treatments to functionalize the activated electrodes. The structural and morphological characterization of the treated PAN-based graphite felt was carried out by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Moreover, a prototype composed of graphite-felt electrodes has been built and tested using Vanadium as redox couple. The cyclic voltammograms allow us to confirm the effect related to the introduction of nitrogen atoms substituting carbon atoms in the graphite matrix. It leads to the greater enhancement of electroactivity, showing the higher reversibility and current collection. In addition, several experiments were carried out to measure the double-layer capacitance, in order to estimate the effective electroactive area and the percentage of active sites. Electrochemical impedance spectroscopy (EIS) was also used to analyze the electroactivity of all the electrodes. These results reveal that the amoxidation treatment gives the better activation of the PAN electrodes and allows the increase of the number of functional groups on the surface of the felt, resulting in a higher surface area.
11:30 AM - **G6.7
Design and Fabrication of 3D Electrodes and Battery Architectures.
Nicolas Cirigliano 1 , Emilie Perre 1 , Bruce Dunn 1 Show Abstract
1 Materials Science and Engineering, UCLA, Los Angeles, California, United States
Three-dimensional battery architectures have emerged as a new direction for miniaturized power sources. The defining characteristic of 3-D battery designs is that transport between electrodes remains one-dimensional (or nearly so) at the microscopic level, while the electrodes are configured in non-planar geometries. The design rules developed for 3-D battery architectures indicate that it is possible to achieve both high energy density and high power density within a small footprint area. These properties are particularly important for integrated microsystems where the available area for the power source is limited to millimeter dimensions.The present paper reviews recent advances in the development of 3-D microbatteries which incorporate periodic electrode arrays. Calculations for lithium-ion battery systems indicate that high aspect ratio arrays with a small pitch between rods are required in order to achieve areal energy densities in the range of 5 to 10 mAh/cm2. Methods for fabricating the positive and negative electrodes have been demonstrated and tested in half-cell experiments. 3-D carbon arrays are fabricated by combining silicon micromachining with colloidal processing while LiCoO2 electrodes are prepared through sedimentation of a colloidal solution between the rods of the array. Areal energy densities in the range of 5 mAh/cm2 at rates of C/5 or higher are commonly achieved. The 3-D microbatteries and electrode configurations presented here illustrate both the advantages offered by 3-D architectures as well as the challenges facing this technology.
12:00 PM - G6.8
Mass Transport through Porous Battery Electrodes.
Matthew Merrill 1 , Marcus Worsley 1 , Todd Weisgraber 1 , Ted Baumann 1 , Michael Stadermann 1 Show Abstract
1 , Lawrence Livermore National Lab, Livermore, California, United States
The optimal design of a porous battery electrode’s structure substantially increases power density through enhanced mass transport without sacrificing energy density. The pore size distribution and shape of electrode’s structure govern the performance by limiting ionic mass transport of ions and by causing concentration and potential gradients. The complexity and irregularity of conventional porous electrodes prohibit the experimental validation of optimal porous structures designed a priori. Only the evaluation of mass transport and kinetic limitations revealed though accurate modeling methods with minimal approximations and simplifications can facilitate the development of quantitative design rules for porous electrodes. Hexagonally close-packed polymer beads were used for creating templates for carbon electrodes with the well-defined and well-controlled pore structures necessary for accurate modeling. The carbon electrodes were then coated with a thin film nickel oxy-hydroxide active material. The nickel oxy-hydroxide charging and discharging mechanisms were characterized and incorporated into the modeling methods. The performance evaluation of the nickel electrodes of various pore structures has been used to corroborate and refine the modeling methods. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344
12:15 PM - G6.9
Modelling and Characterization of 3D Battery Electrode Arrays.
Nicolas Cirigliano 1 , Peter Malati 1 , Emilie Perre 1 , Jonathan Fang 1 , Guangyi Sun 2 , C. Kim 2 , Bruce Dunn 1 Show Abstract
1 Department of Materials Science and Engineering, University of California, Los Angeles, Los Angeles, California, United States, 2 Mechanical and Aerospace Engineering, University of California, Los Angeles, Los Angeles, California, United States
3D batteries offer original solutions to powering integrated microsystems and other microscale devices with small footprint areas. To a large extent, electrode designs become the defining feature of 3D batteries. Many different architectures exist, ranging from arrays of rods or plates to aperiodic sponge-like foams to inverse opal frameworks. Each design has the fundamental quality of being non-planar. By stacking material vertically, energy density can be maximized while simultaneously minimizing diffusion distancesOur research has emphasized the rod array design due to its dimensional versatility and ability to be incorporated into multiple battery designs, such as concentric tubes and interdigitated rods. Another advantage of the rod array design is the ability to predict the available energy density of the electrode based on modeling of the geometrical constraints. For instance, an electrode with rods 92 μm in diameter, 500 μm in height and a pitch of 170 μm is expected to give us greater than 8 mAh/cm2. By varying electrode features such as rod height, diameter and pitch, we can design electrodes capable of reaching energy densities in the range of 5.0 to 10 mAh/cm2. The electrode array features can be controlled precisely by means of well established silicon micromachining techniques. Using commercially available materials, we have successfully created 3D carbon post arrays of various aspect ratios. In half-cell experiments, we have achieved energy densities up to 6.0 mAh/cm2 at a current densities > 0.5 mA/cm2. Integration of the cathode material can be performed by sedimentation of a colloidal solution between the rods of the array. Experiments with LiCoO2 electrodes show that areal energy densities of 4 to 5 mAh/cm2 can be achieved at rates of C/5.
12:30 PM - G6.10
Engineering Nanoscale Silicon-CNT Heterostructures – Novel Li-Ion Anodes.
Rigved Epur 1 , Moni Datta 2 , Prashant Kumta 1 2 3 Show Abstract
1 MEMS, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 2 Department of Bioengineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States, 3 Department of Chemical Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
Lithium ion batteries have become the preferred workhorse energy storage systems for portable consumer electronic devices such as laptops, video cameras, and mobile phones. Commercial Li-ion systems at present employ graphite as the anode with a theoretical capacity of 372mAh/g. However for hybrid electric vehicles and electrical grid energy storage, batteries with much higher capacity and cycle life are sorely needed. Silicon with a theoretical capacity of 4200mAh/g is widely investigated as a promising alternative candidate anode to graphite for use in next generation lithium ion batteries.Silicon however undergoes colossal volume expansion (>300%) during lithium alloying and de-alloying. This leads to pulverization of the active material resulting in loss of electrical contact with the current collector causing rapid decrease in capacity and consequent failure of the battery. We have developed three dimensional (3-D) hetero-structures of multi-walled carbon nanotubes (MWNTs) and nano-crystalline silicon (nc-Si) employing a simple 2-step liquid injection chemical vapor deposition approach (CVD). The Si-CNT hetero-structures have been vertically grown on quartz and Inconel 600 alloy yielding capacities in excess of 2500 mAh/g capacity with an irreversible loss of less than 15%. The effect of morphology of silicon deposited on CNTs on the resultant electrochemical capacity and cyclability have also been investigated. In addition, the effects of different electronically conducting interface layers on the cyclability of these hetero-structures have been studied. Results of these studies will be presented and discussed.
12:45 PM - G6.11
Highly Ordered Hierarchical Electrodes: Facilitating Charge Transport with Controlled Interconnected Porosity across Multiple Length Scales.
Ryan Maloney 1 , Ezhiylmurugan Rangasamy 1 , Apoorv Shaligram 1 , Isabel David 1 , Jeffrey Sakamoto 1 Show Abstract
1 Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan, United States
Lithium ion and lithium air electrodes may appear two dimensional on a macro scale, but the active material nanoparticles behave as a three-dimensional system. In this work, we present advanced three-dimensional electrode designs to facilitate both charge transport in lithium ion batteries and the formation and dissolution of lithium products in lithium-air semi fuel cells. Through a combination of templating and ablative techniques, meso- and macro-scale porosity can be engineered for either liquid- or solid-electrolyte battery systems. Specifically, ionic transport within the electrode can be optimized by engineering relatively large through-plane channels that connect to smaller pathways in-plane, which then feed into the nanometer-scale porosity inherent in the electrode material. This design emulates that of a human lung, with lithium ions taking the place of oxygen. The effect of this engineered porosity on the electrochemical performance of the electrode is characterized, with special attention given to the rate capability of the material at higher electrode loadings. Finally, we explore the suitability and efficacy of highly ordered hierarchical battery designs for prototypical lithium-ion, solid-state and lithium-air systems. The overarching goal of this work is to decouple energy and power density by improving through-plane charge transport in advanced electrochemical energy storage technology.
G7: Applications: Solar Cells
Thursday PM, December 01, 2011
Back Bay D (Sheraton)
2:30 PM - **G7.1
Shape-Controlled Synthesis of Nanostructural Materials and Their Application in Energy Conversion Devices.
Jong Hyeok Park 1 Show Abstract
1 Chemical Engineering, Sungkyunkwan University, Suwon Korea (the Republic of)
This presentation introduces several controlled nanostructures for the applications to several energy generation devices, such as organic solar cells, dye-sensitized solar cells and solar water splitting systems. The first part of the presentation focuses on positive effects of shape controlled Au and Ag nanoparticles in organic P3HT/PC70BM, PCDTBT/PC70BM, Si-PCPDTBT/PC70BM bulk hetero junction–based photovoltaic devices. The use of an optimized shapes and concentration of Au and Ag nanomaterials in the bulk-hetero junction film increases Jsc, FF, and the IPCE. In the second part of the presentation, I will present several nanostructured interlayers that are located between an electrode and a photoactive layer to efficiently extract charge carriers from the active layer. The third part of my presentation focuses on several unique methods to increase light harvesting efficiency to generate electricity and hydrogen from dye-sensitized solar cells and solar water splitting system by applying nano-concepts to materials and/or devices.
3:00 PM - G7.2
Highly Interconnected Porous Electrodes for Dye-Sensitized Solar Cells Using Viruses as Sacrificial or Synthesizing Templates.
Yong Man Lee 1 , Young Hun Kim 2 , Pil J. Yoo 1 2 Show Abstract
1 SKKU Advanced Institute of Nanotechnology (SAINT), Sungkyunkwan University, Suwon Korea (the Republic of), 2 School of Chemical Engineering , Sungkyunkwan University, Suwon Korea (the Republic of)
With the growing interest in renewable energy sources, dye sensitized solar cells (DSSCs) have received considerable attention due to their advantages in high energy conversion efficiency and inexpensive production cost. Currently, intensive researches on DSSCs have been mainly focused on achieving higher efficiency and better performance. Among various approaches, a specific means to employ a structural design for the photoelectrode material, which generally consists of a semiconductor oxide typically made of TiO2 nanoparticles coated with a monolayer of sensitizer, has been extensively investigated. Since TiO2 nanoparticles provide a medium for electron transport as well as a stabilized interface for dye-sensitizers, the ability to control the structural characteristics for TiO2 photoelectrodes is crucial for obtaining enhanced cell efficiency. However, conventional TiO2 photoelectrodes made of randomly networked nanoparticles have limitation for achieving higher efficiency due to disordered paths of electron and electrolyte. In this presentation, we suggest two approaches to create the optimized interfaces between electrolyte and TiO2 nanoparticles through the incorporation of a viral template; One approach is a uniform complexation between oppositely charged TiO2 nanoparticles and M13 viruses through the electrostatic binding interactions, in which the virus is utilized as a sacrificial template. The other approach is a virus-templated synthesis of TiO2 nanowire through biomineralization of TiO2 nanoparticles along surface proteins of the M13 virus. As a templating biomaterial, a one-dimensionally-shaped M13 virus is adopted due to its structural homogeneity and ease of manipulation. The complexed viruses are thermally decomposed during the sintering process, leaving behind an interconnected structure of hollow channels inside the TiO2 photoelectrode. These hollow channels are used as pathways for electrolyte penetration, such that a stabilized contact between electrolyte and TiO2 nanoparticles can be uniformly extended to the very inner regions of the photoelectrode, much like at the outermost surface. Moreover, the inclusion of one-dimensional viruses enhances the ordered interconnection between TiO2 nanoparticles and reduces a likelihood of generating isolated pores inside the TiO2 photoelectrode. Therefore, it is possible to minimize a concern of nanoparticle aggregation and expect enhanced DSSC performance. These approaches can generate highly porous and three-dimensionally interconnected nanostructures of virus/TiO2 nanocomposites for high surface area and enhanced electron transport capability. Furthermore, the resulting TiO2/virus nanocomosites can be extended to other electrode materials for various types of energy devices.
3:15 PM - G7.3
Vertically Aligned Metal Oxide Structures as Photoanodes for Dye Sensitized Solar Cells.
Rudresh Ghosh 1 , Matthew Brennaman 2 , Thomas Meyer 2 , Rene Lopez 1 Show Abstract
1 Physics, University of North carolina at Chapel Hill, Chapel Hill, North Carolina, United States, 2 Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina, United States
Vertically-aligned bundles of Nb2O5 nanocrystals were fabricated by pulsed laser deposition (PLD) and tested as a photoanode material in dye-sensitized solar cells (DSSC). They were characterized using scanning electron microscopy (SEM), optical absorption spectroscopy (UV-Vis), and incident-photon-to-current efficiency (IPCE) experiments. An optimal background pressure of oxygen during deposition was discovered to produce a photoanode structure that both achieves high surface area and could possibly improve charge transport compared to conventional nanoparticle architecture for enhanced photo-electrochemical performance. The background gas composition and the thickness of the films were also varied. For optimal structures IPCE values up to 40% and APCE values around 90% were obtained with the N3 dye and I3-/I- couple in acetonitrile with open circuit voltage of 0.71V and 2.41 % power conversion efficiency.Current work involves using other metal oxides as photoanodes for dye sensitized solar cells and understanding charge transfer processes in hierarchial semiconductor structures.
3:30 PM - G7.4
ZnO Hierarchical Spheres with Excellent Optical and Electrical Performances towards Highly Efficient Quasi-Solid Dye-Sensitized Solar Cells.
Yantao Shi 1 , Chao Zhu 1 , Lin Wang 1 , Wei Li 1 , Chun Cheng 1 , Ning Wang 1 Show Abstract
1 , Hong Kong University of Science and Technology, HongKong China
Hierarchically structured ZnO photoanodes have been proved to be very effective for dye-sensitized ZnO solar cells (ZnO-based DSCs). Through optimizing dye-loading and light-scattering, a typical high efficent ZnO-based DSC that was prepared by Cao et. al. in 2008 obtained a conversion efficiency of 5.4%. Since then, although many ZnO hierarchical structures were developed, so far, no further promotions in photovoltaic performances has been reported. Most of the newly reported work on ZnO hierarchical structures concentrated on how to improve light-harvesting related optical performance, such as dye-loading and light-scattering. For the photoanodes in DSCs, both optical and electrical (electron transport and carrier recombination, etc.) properties need to be optimized in order to realize further increase in their photovoltaic performance. Through a novel method of facile ultrasonic-assisted precipitation in aqueous solution, we fabricated ZnO hierarchical spheres as the photoanode material for DSCs that were constructed with ultrathin, porous and interlaced monocrystalline nanosheets. Systematic investigations revealed that the photoanodes composed of these ZnO hierarchical spheres possessed excellent optical and electrical properties. This nano-structured materail not only performed well in dye-loading and light-scattering, but also offered fast channels for electron transport. Under AM 1.5, 1 sun illumination, a photoanode (35.6μm thick) generated a conversion efficiency of 6.19% for quasi-solid DSCs, the second highest record so far reported (the highest record of 6.58% was reported by Fujihara et. al. using liquid electrolyte ). Up to now, this is the highest efficiency for the quasi-solid (using PEO gel electrolyte) ZnO-based DSCs and the performance is much better than those of all previously reported ZnO hierarchical structures. The hierarchical ZnO nanostructure consisting of interlaced single crystal nanosheets offers great potential for the development of high-efficiency quasi-solid DSCs in mass production. We believe that the excellent energy harvesting performance of this ZnO photoananode material is due to the unique hierarchical structure that can not only possess advantages of light scattering as well as dye-loading, but also offer excellent electron transport pathway in which the electron diffusion coefficient is greatly enhanced. References: Q. F. Zhang, T. P. Chou, B. Russo, S. A. Jenekhe, G. Z. Cao, Angew. Chem. Int. Ed. 2008, 47, 2402. M. Saito, S. Fujihara, Energy Environ. Sci. 2008, 1, 280.
3:45 PM - G7.5
Study on 3-D Network Formation of Nanoclays in Quasi-Solid State Electrolyte and Its Effects on the Stability of Dye-Sensitized Solar Cells.
Youngsoo Jung 1 , Bo Ding 1 , Jung-Kun Lee 1 Show Abstract
1 Mechanical Engineering & Materials Science, University of Pittsburgh, Pittsburgh, Pennsylvania, United States
The assembly of dye-sensitized solar cells (DSSCs)containing liquid electrolyte requires critical sealing techniques to prevent the leakage and vaporization of liquid component. If the solar cell is not tightly sealed, the unstable liquid electrolyte leads the low durability of DSSCs. In order to improve the stability of DSSCs, different types of electrolytes such as gel-type and solid-state electrolytes, have received a considerable amount of interests to supersede the liquid-type electrolyte. One of the questions accompanying the quasi-solid state electrolyte is how to fill the pores inside the mesoporous photoanode. If a part of the photoanode leaves empty, the empty part becomes the source for the electron-hole recombination and the parasitic current. An effective method to circumvent the problem of partial filling is to employ in-situ gelation of clay based fluids. Clays such as smectite and kaolinite provide excellent thixotropic properties to the fluid, since plate-like clay particles are connected each other in the fluid through surface charge only in a static condition. In this work, synthetic smectite nanoclay was utilized as electrolyte gelator to synthesize clay-based quasi-solid state electrolyte. Then, we systematically investigated the gelation behavior of the quasi-solid state electrolyte and its effect on the performance of DSSCs with an emphasis on the temperature stability of DSSCs. The efficiency of DSSCs was greatly influenced by nanoclay amount and iodine concentration in the solid-state electrolyte. When the ratio of iodine/clay in the quasi-solid state electrolyte was lower than a critical value, the energy conversion efficiency of DSSCs dramatically decreased due to the adsorption of iodine onto the surface of the nanoclay. The addition of the nanoclays into the electrolyte had a positive impact on the temperature stability of DSSCs. The effect of the clay content on the stability of DSSCs is explained from the viewpoint of the gelation which was characterized by measuring the strain-stress relation of the fluid. The change in the viscoelastic behavior of the electrolyte indicates that the addition of 5 wt% clay into the liquid electrolyte causes the strong gelation due to the 3-D network formation in the liquid, which, in turn, improves the reliability of DSSCs.
G8: Applications: Energy Storage Devices
Thursday PM, December 01, 2011
Back Bay D (Sheraton)
4:00 PM - **G8.1
Materials with Hierarchical Porosity for Electrical Energy Storage.
Andreas Stein 1 , Anh Vu 1 , Yuqiang Qian 1 Show Abstract
1 Department of Chemistry, University of Minnesota, Minneapolis, Minnesota, United States
Porous materials with hierarchical porosity and controlled architecture can provide distinct advantages for energy storage applications. They permit transport of matter or charge along specific pathways, providing some control over transport properties that depend on pore architecture and available pore sizes. Furthermore, they may provide stabilization of reactive phases in composite structures with hierarchical porosity. In such composites it is also possible to introduce multiple functionality into a material, such as high storage capacity in one phase and improved conductivity through another phase. Finally, such structures provide a way to achieve easy-to-handle bulk materials with the advantages of nanometer-sized features, but without the potential hazards associated discrete nanoparticles. In this presentation, I will review the state of the art in applications for electrode materials with hierarchical pore structure and then focus on recent advances in our laboratory related to such electrodes for secondary lithium ion batteries, in which templated porous materials provide a platform for efficient electrical energy storage. The role of pore architecture in carbon-based electrodes with hierarchical pore structure will be discussed. Improved rate capabilities for lithiation/delithiation are observed for hierarchically porous carbon electrodes. In composites with tin or tin oxide for anodes, these structures maintain electrical contact between tin-based particles, even when those particles undergo significant volume changes during cycling, and hence the composite anode maintains good capacities over multiple cycles. Composites of hierarchically structured carbon with poorly conducting but otherwise desirable electrode materials (like sulfur or lithium iron phosphate) can be used to overcome limitations in electrical conductivity of those materials, increasing the choice of useful electrode materials.
4:30 PM - **G8.2
Creating Next-Generation Electrochemical Power Sources via Architectural Design in 3D and on the Nanoscale.
Debra Rolison 1 , Jeffrey Long 1 , Christopher Chervin 1 , Megan Sassin 1 , Jean Marie Wallace 1 , Joseph Parker 1 , Joseph Parker 1 , Natalie Brandell 1 , Bradley Willis 1 Show Abstract
1 Surface Chemistry, Naval Research Laboratory, Washington, District of Columbia, United States
Efficient storage of energy is a critical component in developing a sustainable energy portfolio for the planet , including electrochemical energy-storage devices such as batteries and electrochemical capacitors (ECs). Yet electrochemical energy storage has always disregarded Moore’s Law . Improved performance requires redesigning the reaction interphases within which occur the fundamental processes that store energy in batteries and ECs. Energy researchers are now rethinking the requisite multifunction—mass and charge transport, electronic and ionic conductivity, and electron-transfer kinetics—in light of nanoscience and architectural design in three dimensions [3–5]. The design and fabrication of three-dimensional multifunctional architectures from the appropriate nanoscale building blocks for chemical, physical, and physicochemical charge storage will be highlighted, including the use of “nothing” (void space) and deliberate disorder as design components  as well as the importance of reexamining in a nanoscopic form those materials that yielded poor energy-storage performance when used in a macroscopic form.  D.R. Rolison, L.F. Nazar, MRS Bull. 2011, 36(7) in the press. A.G. Fedorov, J. Baxter, Z.-X. Bian, G. Chen, D. Danielson, M. Dresselhaus, T.S. Fisher, C. Jones, U. Kortshagen, E. Maginn, N. Manjooran, A. Manthiram, A. Nozik, L. Pilon, D.R. Rolison, T. Sands, L. Shi, D. Sholl, Y.-Y. Wu, Energy Environ. Sci. 2009, 2, 559–588. J.W. Long, B. Dunn, D.R. Rolison, H.S. White, Chem. Rev. 104 (2004) 4463. D.R. Rolison, J.W. Long, Acc. Chem. Res. 40 (2007) 854. D.R. Rolison, J.W. Long, J.C. Lytle, A.E. Fischer, C.P. Rhodes, T.M. McEvoy, M.E. Bourg, A.M. Lubers, Chem. Soc. Rev. 2009, 38, 226. D.R. Rolison, Science 2003, 299, 1698.
5:00 PM - G8.3
Hierarchical Composite Materials for Structural Energy Storage Devices.
Milo Shaffer 1 , Hui Qian 1 , Matthieu Houlle 2 , Julien Amadou 2 , Alexander Bismarck 3 , Emile Greenhalgh 3 Show Abstract
1 Department of Chemistry, Imperial College London, London United Kingdom, 2 , Nanocyl, Sambreville Belgium, 3 , Imperial College, London United Kingdom
Weight and volume are often at a premium in engineering; any material that does not contribute to the load-carrying capacity is structurally parasitic. Current engineering design pursues optimisation of the individual components by utilising materials with improved specific properties. The alternative is to formulate multifunctional materials which can perform two or more functions simultaneously. This paper introduces a new multifunctional composite material that can simultaneously carry mechanical loads whilst storing (and delivering) electrical energy. The current embodiment is an electrochemical double layer capacitor, based on a multifunctional polymer resin reinforced by carbon and glass fibres. In order to simultaneously maximise the mechanical and electrical performance, the reinforcing fibres have been have been modified to increase electrochemical surface area whilst maintaining their intrinsic performance. Rather than using conventional activated carbon fibres, structural carbon fibres were treated to produce mechanically robust, high surface area material, using a variety of methods. One of the most promising approaches is to combine carbon nanotubes within the carbon fibre layer either by direct growth, or post-growth sizing or coating, to create a hierarchical composite. The nanotubes provide a dramatic increase in active surface area, and have the potential to address mechanical issues associated with matrix-dominated failures.Working structural supercapacitor composite prototypes have been produced and characterised electrochemically using impedance spectroscopy, cyclic voltammetry and charge-discharge measurements. The effect of introducing the necessary multifunctional resin on mechanical properties has also been assessed.
5:15 PM - G8.4
3D Constitutive Relation for an Aligned Carbon Nanotube Polymer Nanocomposite as a Function of Morphology.
Kosuke Takahashi 1 , Roberto Guzman de Villoria 1 , Silvia Chan 1 , J. Marcel Williams 1 , Hulya Cebeci 1 , Ethan Parsons 2 , Simona Socrate 2 , Brian Wardle 1 Show Abstract
1 Aero/Astro, MIT, Cambridge, Massachusetts, United States, 2 Mechanical Engineering, MIT, Cambridge, Massachusetts, United States
Nanostructured polymeric materials are of significant interest for their novel mechanical and transport (electrical, thermal, ionic, etc.) properties. As previously demonstrated in our group, by controlling the composite’s morphology its properties can be tailored to exhibit significant differences along different material axes (e.g., thermal and electrical transport along conductive CNT axes vs. transverse to them). The system studied here comprises an aligned carbon nanotube (A-CNT) forest embedded in an aerospace-grade unmodified thermoset epoxy resin, forming an aligned-fiber polymer nanocomposite, an A-CNT PNC. Importantly, the CNTs are continuous across the samples with continuous-fiber reinforcement of known and quantified morphology. The A-CNT polymer nanocomposite is of interest both to study structure-property relations, but also an element in nano-engineered hierarchical materials comprised of aligned-CNTs in polymer matrices acting in concert with micron-dia. advanced fibers (such as carbon fibers, in a “nanostitch” architecture). A novel mechanical densification process allows volume fraction to be varied between 1 and 20+%. Previous work has studied non-isotropic electrical and thermal conductivities of this system as a function of volume fraction. The current work is the first to provide measurements of the linear elasticity tensor for this class of materials, providing a basis for further constitutive model development. Based on the material microstructure, transversely isotropic symmetry is inferred for the A-CNT PNCs small-strain elastic response. The stiffness relation for the A-CNT PNCs as a function of CNT volume fraction is assessed using standard configurations and optical strain mapping. Significant stiffness biases are noted along the different material directions associated with the CNTs, with relative stiffness increases exceeding 100%. Furthermore, strain ranges of linearity are identified and different behaviors are noted in compression vs. tension. Prior work in this epoxy system has shown no discernible effects of the CNTs in the cross-link density or other characteristics (Tg etc.) of the polymer matrix. These findings allow interpretation of the measured response of the A-CNT PNCs via computational microstructural investigation of structure-property relations focusing on the morphology of the fiber reinforcements (the CNTs). A finite element model (FEM) is implemented that captures the effect of CNT ‘waviness’ (non-collimation) on the resulting homogenized composite properties, and allows us to establish structure-property relations focusing on known features of the CNT reinforcement. Future work will include expanding this testing technique to explore visco-elasticity effects and large-strain behavior. Future modeling work will also focus on CNT-CNT interactions.
5:30 PM - G8.5
Impacts of Different Length Scales on the Electrochemical Capacitance of a 3D Hierarchical Porous Carbon Structure.
Kwong-Yu Chan 1 , Fujun Li 1 Show Abstract
1 Chemistry, University of Hong Kong, Hong Kong Hong Kong
The transport coupled electrochemical processes were investigated with a 3D hierarchical porous carbon structure prepared with possible variations of porositity at three length scales. The carbon structure was template-synthesized from a core-shell silica sphere assembly. The as-synthesized carbon featured an semi-ordered porous structure with hollow macro-cores a few hundred nanometers diameter surrounded by a mesoporous shell containing uniform pores of 3.9 nm. The spherical core-shell domains were assembled with distinct interstitial space between them. In one set of experiments, the mesoporous shell thickness was stepwise increased from 0, 25, 50 to 100 nm while keeping an identical core size of 330 nm to create a family of hierarcical porous structures for a systematic investigation of electrochemical capacitance and ionic transport. A thicker mesoporous shell possessed a higher surface area leading to a proportional increase in electrochemical capacitance which can be fully realised only at low scan rates. For the carbon structure with a shell thickness of 100 nm, electrochemical capacitance per unit area and power density declined at high scan rates and high currents when ionic transport through long mesopores became limiting. The power density of one as-synthesized porous carbon was as high as 11.7 kW/kg with a corersponding energy density of 5.9 Wh/kg. In another set of investigations, structures with the same overall particle size but varying core diameter and shell thickenss were synthesized and tested . Reference: F. Li, M. Morris, K.Y. Chan, "Electrochemical capacitance and ionic transport in the mesoporous shell of a hierarchical porous core–shell carbon structure", J. Mater. Chem. (2011) DOI: 10.1039/c1jm10854a.
5:45 PM - G8.6
Hierarchical Graphene/MnO2-Nanostructured Textiles for Large-Scale, High-Performance Supercapacitors.
Guihua Yu 1 , Liangbing Hu 2 , Yi Cui 2 , Zhenan Bao 1 Show Abstract
1 Chemical Engineering, Stanford University, Stanford, California, United States, 2 Materials Science and Engineering, Stanford University, Stanford, California, United States
Large scale energy storage system with low cost, high energy and power density, and long cycle life is crucial for addressing the current energy problem when connected with renewable energy production from solar and wind. To realize large-scale applications of the energy storage devices, there remain several key challenges including the development of low-cost, high-performance materials that are environmentally friendly and compatible with low-temperature and large-scale processing. In this talk, we will present solution-exfoliated graphene-textile as a conductive platform for rational design of hierarchical nanostructures based on inexpensive yet high-performance capacitive materials for large-scale, high-performance electrochemical supercapacitors. The first example is hybrid graphene/MnO2-based energy textile that shows promising electrochemical characteristics with high capacitance of ~315 F/g, power density of ~110 kW/kg, and exceptional cycling stability of >95% capacitance retention over 5000 cycles. More excitingly, much enhanced supercapacitor performance of graphene/MnO2 nanostructured-textiles can be achieved through three-dimensional (3D) conductive wrapping, with specific capacitance improvement by at least 40%. Such low-cost, high-performance energy textiles based on all-solution-processed hybrid nanostructures offer great promise in grid-scale energy storage device applications.