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Crystalline Nanoporous Frameworks: a Nanolaboratory for Probing Excitonic Device Concepts

Allendorf, Mark; Azoulay, Jason; Ford, Alexandra C.; Foster, Michael E.; El Gabaly, Farid; Leonard, Francois; Leong-Hau, Kirsty; Stavila, Vitalie; Talin, Albert A.; Wong, Brian M.; Brumbach, Michael T.; Van Gough, D.; Lambert, Timothy N.; Rodriguez, Mark A.; Spoerke, Erik D.; Wheeler, David R.; Deaton, Joseph C.; Centrone, Andrea; Haney, Paul; Kinney, R.; Szalai, Veronika; Yoon, Heayoung P.

Electro-optical organic materials hold great promise for the development of high-efficiency devices based on exciton formation and dissociation, such as organic photovoltaics (OPV) and organic light-emitting devices (OLEDs). However, the external quantum efficiency (EQE) of both OPV and OLEDs must be improved to make these technologies economical. Efficiency rolloff in OLEDs and inability to control morphology at key OPV interfaces both reduce EQE. Only by creating materials that allow manipulation and control of the intimate assembly and communication between various nanoscale excitonic components can we hope to first understand and then engineer the system to allow these materials to reach their potential. The aims of this proposal are to: 1) develop a paradigm-changing platform for probing excitonic processes composed of Crystalline Nanoporous Frameworks (CNFs) infiltrated with secondary materials (such as a complimentary semiconductor); 2) use them to probe fundamental aspects of excitonic processes; and 3) create prototype OPVs and OLEDs using infiltrated CNF as active device components. These functional platforms will allow detailed control of key interactions at the nanoscale, overcoming the disorder and limited synthetic control inherent in conventional organic materials. CNFs are revolutionary inorganic-organic hybrid materials boasting unmatched synthetic flexibility that allow tuning of chemical, geometric, electrical, and light absorption/generation properties. For example, bandgap engineering is feasible and polyaromatic linkers provide tunable photon antennae; rigid 1-5 nm pores provide an oriented, intimate host for triplet emitters (to improve light emission in OLEDs) or secondary semiconducting polymers (creating a charge-separation interface in OPV). These atomically engineered, ordered structures will enable critical fundamental questions to be answered concerning charge transport, nanoscale interfaces, and exciton behavior that are inaccessible in disordered systems. Implementing this concept also creates entirely new dimensions for device fabrication that could both improve performance, increase durability, and reduce costs with unprecedented control of over properties. This report summarizes the key results of this project and is divided into sections based on publications that resulted from the work. We begin in Section 2 with an investigation of light harvesting and energy transfer in a MOF infiltrated with donor and acceptor molecules of the type typically used in OPV devices (thiophenes and fullerenes, respectively). The results show that MOFs can provide multiple functions: as a light harvester, as a stabilizer and organizer or the infiltrated molecules, and as a facilitator of energy transfer. Section 3 describes computational design of MOF linker groups to accomplish light harvesting in the visible and facilitate charge separation and transport. The predictions were validated by UV-visible absorption spectroscopy, demonstrating that rational design of MOFs for light-harvesting purposes is feasible. Section 4 extends the infiltration concept discussed in Section to, which we now designate as "Molecule@MOF" to create an electrically conducting framework. The tailorability and high conductivity of this material are unprecedented, meriting publication in the journal Science and spawning several Technical Advances. Section 5 discusses processes we developed for depositing MOFs as thin films on substrates, a critical enabling technology for fabricating MOF-based electronic devices. Finally, in Section 6 we summarize results showing that a MOF thin film can be used as a sensitizer in a DSSC, demonstrating that MOFs can serve as active layers in excitonic devices. Overall, this project provides several crucial proofs-of- concept that the potential of MOFs for use in optoelectronic devices that we predicted several years ago [ 3 ] can be realized in practice.

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TYPE SAND Report YEAR 2014
DOIOSTI

Electrostatically tuned self-assembly of branched amphiphilic peptides

Journal of Physical Chemistry B

Frischknecht, Amalie L.; Stevens, Mark J.; Spoerke, Erik D.

Electrostatics plays an important role in the self-assembly of amphiphilic peptides. To develop a molecular understanding of the role of the electrostatic interactions, we develop a coarse-grained model peptide and apply self-consistent field theory to investigate the peptide assembly into a variety of aggregate nanostructures. We find that the presence and distribution of charged groups on the hydrophilic branches of the peptide can modify the molecular configuration from extended to collapsed. This change in molecular configuration influences the packing into spherical micelles, cylindrical micelles (nanofibers), or planar bilayers. The effects of charge distribution therefore have important implications for the design and utility of functional materials based on peptides. © 2014 American Chemical Society.

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TYPE Journal Article YEAR 2014
DOIOSTIScopus

Electrostatically tuned self-assembly of branched amphiphilic peptides

Journal of Physical Chemistry B

Ting, Christina L.; Frischknecht, Amalie L.; Stevens, Mark J.; Spoerke, Erik D.

Electrostatics plays an important role in the self-assembly of amphiphilic peptides. To develop a molecular understanding of the role of the electrostatic interactions, we develop a coarse-grained model peptide and apply self-consistent field theory to investigate the peptide assembly into a variety of aggregate nanostructures. We find that the presence and distribution of charged groups on the hydrophilic branches of the peptide can modify the molecular configuration from extended to collapsed. This change in molecular configuration influences the packing into spherical micelles, cylindrical micelles (nanofibers), or planar bilayers. The effects of charge distribution therefore have important implications for the design and utility of functional materials based on peptides. © 2014 American Chemical Society.

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TYPE Journal Article YEAR 2014
ScopusOSTIDOI

Conical nanopores fabricated via a pressure-biased chemical etch

RSC Advances

Small, Leo J.; Wheeler, David R.; Spoerke, Erik D.

Controlling the size and shape of nanopores in polymer membranes can significantly impact transport of molecular or ionic species through these membranes. Here we describe a facile method to controllably form conical nanopores in ion-tracked polycarbonate membranes. Commercial polycarbonate ion-tracked membranes were placed between a concentrated alkaline solution and an acidic solution. By varying the height of the acidic solution, the hydrostatic pressure was controlled, regulating the acid flux through the nanopores. The resulting asymmetric etching of the membrane produced conical pores with controllable aspect ratios. Scanning electron microscopy of both the pores and nickel nanostructures electrolessly templated in the pores confirms their conical shape. This safe, straightforward approach obviates the need to use large voltages, currents, and/or plasma etching equipment traditionally employed to create conical nanopores. © 2014 The Royal Society of Chemistry.

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TYPE Journal Article YEAR 2014
OSTIScopus

The influences of excess sodium on low-temperature NaSICON synthesis

Journal of the American Ceramic Society

Bell, Nelson S.; Edney, Cynthia; Ingersoll, David; Spoerke, Erik D.

Controlling the materials chemistry of the solid-state ion conductor NaSICON is key to realizing its potential utility in emerging sodium-based battery technologies. We describe here the influence of excess sodium on phase evolution of sol-gel synthesized NaSICON. Alkoxide-based sol-gel processing was used to produce powders of Na3Zr2PSi2O12 NaSICON with 0-2 atomic % excess sodium. Phase formation and component volatility were studied as a function of temperature. NaSICON synthesis at temperatures between 900-1100C with up to 2% excess sodium significantly reduced the presence of zirconia, sodium phosphate, and sodium silicate secondary phases in fired NaSICON powders. Insights into the role of sodium on the phase chemistry of sol-gel processed NaSICON may inform key improvements in NaSICON development.

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TYPE Journal Article YEAR 2014
OSTIScopus

Nano-ordering of donor-acceptor interactions using Metal-Organic Frameworks as scaffolds

ECS Transactions

Leong, Kirsty; Foster, Michael E.; Wong, Bryan M.; Spoerke, Erik D.; Gough, Dara; Deaton, Joseph C.; Allendorf, Mark

Metal-Organic Frameworks (MOFs) are nanoporous materials with tunable pore sizes that can accommodate and stabilize small molecules. Because of their long-range order and wellunderstood pore environment, the nano-confinement of donoracceptor materials within MOFs offers a new methodology for creating uniform phase-segregated donor-acceptor interfaces. Phase segregation and the photo-physical effects of confining α,ω-Dihexylsexithiophene (DH-6T) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) in several MOFs and the potential role of the MOF in creating a nano-heterojunction for organic photovoltaics are discussed. We demonstrate infiltration of both molecules into MOF pores and use luminescence and absorption spectroscopies to characterize the MOF-guest energy transfer processes. Comparison with density functional theory allows us to determine the energetics and band alignment within the MOF. The results demonstrate the utility of MOFs as scaffolds for sub-nanoscale ordering of donor and acceptor species within a highly uniform environment, allowing both the interaction and separation distance to be much more controlled than in the classical bulk heterojunction. © The Electrochemical Society.

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TYPE Conference YEAR 2013
ScopusOSTIDOI

Rapid thermal pyrolysis of interferometrically patterned resist

Carbon

Spoerke, Erik D.; Polsky, Ronen; Burckel, David B.; Bunker, B.C.

In recent years pyrolysis of interferometrically-patterned photoresists has produced three-dimensionally nanopatterned, electrically conductive carbon films with applications from energy storage to biological sensing. We investigate here conditions for rapid thermal pyrolysis that drastically reduce film processing time (from hours to minutes) while preserving the films' unique nanoscale morphology, film adhesion, and electrochemical properties. We specifically show that heating rate dramatically affects nanoscale morphology, while reducing atmosphere composition, dwell time, and dwell temperature impact the electrochemical performance of these rapidly pyrolyzed nanostructures. Accelerated processing with rapid thermal pyrolysis may facilitate the expanded applicability and rapid fabrication of these promising nanostructured materials. © 2012 Elsevier Ltd. All rights reserved.

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TYPE Journal Article YEAR 2012
OSTIScopus

Tunable arrays of ZnO nanorods and nanoneedles via seed layer and solution chemistry

Crystal Growth and Design

Lee, Yun J.; Sounart, Thomas L.; Liu, Jun; Spoerke, Erik D.; Mckenzie, Bonnie; Hsu, Julia W.; Voigt, James A.

We have systematically studied the effect of pH and 1,3-diaminopropane additive concentration on the morphology of ZnO nanorod and nanoneedle arrays grown in aqueous solution using a variety of seed layers. Increase in the growth solution pH from 6.8 to 13.2 resulted in a near doubling of the growth rate in the [0001] direction possibly due to attractive interaction between the zinc species and the growth surface at high pH, leading to nanorod arrays with reduced faceting and higher aspect ratios. Increases in 1,3-diaminopropane concentration initially enhanced and subsequently inhibited growth of tapered ZnO nanoneedles on seed layers consisting of ZnO nanoparticles, oriented ZnO films, or columnar facets of ZnO microrods. The final nanoneedle dimensions, packing density, and alignment were strongly affected by 1,3-diaminopropane concentration and seed layer type, which can be explained in terms of the relative strength of zinc chelation by 1,3-diaminopropane, the areal density of seeds, and other factors. The precise tuning of ZnO crystalline morphology via the control of seeding and growth conditions may be beneficial to many potential applications that require these aligned crystalline nanostructures. © 2008 American Chemical Society.

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TYPE Journal Article YEAR 2008
ScopusOSTIDOI

Active assembly for large-scale manufacturing of integrated nanostructures

Bachand, George D.; Orendorff, Christopher; Mckenzie, Bonnie; Bunker, B.C.; Spoerke, Erik D.

Microtubules and motor proteins are protein-based biological agents that work cooperatively to facilitate the organization and transport of nanomaterials within living organisms. This report describes the application of these biological agents as tools in a novel, interdisciplinary scheme for assembling integrated nanostructures. Specifically, selective chemistries were used to direct the favorable adsorption of active motor proteins onto lithographically-defined gold electrodes. Taking advantage of the specific affinity these motor proteins have for microtubules, the motor proteins were used to capture polymerized microtubules out of suspension to form dense patterns of microtubules and microtubule bridges between gold electrodes. These microtubules were then used as biofunctionalized templates to direct the organization of functionalized nanocargo including single-walled carbon nanotubes and gold nanoparticles. This biologically-mediated scheme for nanomaterials assembly has shown excellent promise as a foundation for developing new biohybrid approaches to nanoscale manufacturing.

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TYPE SAND Report YEAR 2006
DOIOSTI

Assembly and actuation of nanomaterials using active biomolecules

Sasaki, Darryl Y.; Koch, Steven J.; Thayer, Gayle E.; Corwin, Alex D.; De Boer, Maarten P.; Bunker, B.C.; Bachand, George D.; Rivera, Susan B.; Gaudioso, Jennifer M.; Trent, Amanda M.; Spoerke, Erik D.

The formation and functions of living materials and organisms are fundamentally different from those of synthetic materials and devices. Synthetic materials tend to have static structures, and are not capable of adapting to the functional needs of changing environments. In contrast, living systems utilize energy to create, heal, reconfigure, and dismantle materials in a dynamic, non-equilibrium fashion. The overall goal of the project was to organize and reconfigure functional assemblies of nanoparticles using strategies that mimic those found in living systems. Active assembly of nanostructures was studied using active biomolecules to drive the organization and assembly of nanocomposite materials. In this system, kinesin motor proteins and microtubules were used to direct the transport and interactions of nanoparticles at synthetic interfaces. In addition, the kinesin/microtubule transport system was used to actively assemble nanocomposite materials capable of storing significant elastic energy. Novel biophysical measurement tools were also developed for measuring the collective force generated by kinesin motor proteins, which will provide insight on the mechanical constraints of active assembly processes. Responsive reconfiguration of nanostructures was studied in terms of using active biomolecules to mediate the optical properties of quantum dot (QD) arrays through modulation of inter-particle spacing and associated energy transfer interaction. Design rules for kinesin-based transport of a wide range of nanoscale cargo (e.g., nanocrystal quantum dots, micron-sized polymer spheres) were developed. Three-dimensional microtubule organizing centers were assembled in which the polar orientation of the microtubules was controlled by a multi-staged assembly process. Overall, a number of enabling technologies were developed over the course of this project, and will drive the exploitation of energy-driven processes to regulate the assembly, disassembly, and dynamic reorganization of nanomaterials.

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TYPE SAND Report YEAR 2005
DOIOSTI
Results 201–300 of 302
Results 201–300 of 302