Co-reporter:John B. Cook, Hyung-Seok Kim, Terri C. Lin, Shauna Robbennolt, Eric Detsi, Bruce S. Dunn, and Sarah H. Tolbert
ACS Applied Materials & Interfaces June 7, 2017 Volume 9(Issue 22) pp:19063-19063
Publication Date(Web):May 9, 2017
DOI:10.1021/acsami.6b16447
This work aims to improve the poor cycle lifetime of silicon-based anodes for Li-ion batteries by tuning microstructural parameters such as pore size, pore volume, and specific surface area in chemically synthesized mesoporous silicon. Here we have specifically produced two different mesoporous silicon samples from the magnesiothermic reduction of ordered mesoporous silica in either argon or forming gas. In situ X-ray diffraction studies indicate that samples made in Ar proceed through a Mg2Si intermediate, and this results in samples with larger pores (diameter ≈ 90 nm), modest total porosity (34%), and modest specific surface area (50 m2 g–1). Reduction in forming gas, by contrast, results in direct conversion of silica to silicon, and this produces samples with smaller pores (diameter ≈ 40 nm), higher porosity (41%), and a larger specific surface area (70 m2 g–1). The material with smaller pores outperforms the one with larger pores, delivering a capacity of 1121 mAh g–1 at 10 A g–1 and retains 1292 mAh g–1 at 5 A g–1 after 500 cycles. For comparison, the sample with larger pores delivers a capacity of 731 mAh g–1 at 10 A g–1 and retains 845 mAh g–1 at 5 A g–1 after 500 cycles. The dependence of capacity retention and charge storage kinetics on the nanoscale architecture clearly suggests that these microstructural parameters significantly impact the performance of mesoporous alloy type anodes. Our work is therefore expected to contribute to the design and synthesis of optimal mesoporous architectures for advanced Li-ion battery anodes.Keywords: anode; high energy density; high power density; Li ion battery; magnesiothermic reduction; mesoporous; silicon;
Co-reporter:Thomas Coquil;Torsten Brezesinski;Christian Reitz;E. Joseph Nemanick;Laurent Pilon
The Journal of Physical Chemistry C July 29, 2010 Volume 114(Issue 29) pp:12451-12458
Publication Date(Web):2017-2-22
DOI:10.1021/jp103251t
This paper reports the cross-plane thermal conductivity of amorphous and crystalline mesoporous titania thin films synthesized by evaporation-induced self-assembly. Both sol−gel and nanocrystal-based mesoporous films were investigated, with average porosities of 30% and 35%, respectively. The pore diameter ranged from 7 to 30 nm and film thickness from 60 to 370 nm, while the average wall thickness varied from 3 to 50 nm. The crystalline domain sizes in sol−gel films varied from 12 to 13 nm, while the nanocrystal-based films consisted of monodisperse nanocrystals 9 nm in diameter. The cross-plane thermal conductivity was measured at room temperature using the 3ω method. The average thermal conductivity of the amorphous sol−gel mesoporous titania films was 0.37 ± 0.05 W/m·K. It did not show strong dependence on pore diameter, wall thickness, and film thickness for sol−gel amorphous mesoporous titania thin films. This result can be attributed to the fact that heat is carried, in the amorphous matrix, by localized nonpropagating vibrational modes. The thermal conductivity of crystalline sol−gel mesoporous titania thin films was significantly larger at 1.06 ± 0.04 W/m·K and depended on the organic template used to make the films. The thermal conductivity of nanocrystal-based thin films was 0.48 ± 0.05 W/m·K and significantly lower than that of the crystalline sol−gel mesoporous thin films. This was due to the fact that the nanocrystals were not as well interconnected as the crystalline domains in the crystalline sol−gel films. These results suggest that both connectivity and size of the nanocrystals or the crystalline domains can provide control over thermal conductivity in addition to porosity.
Co-reporter:John B. Cook;Terri C. Lin;Johanna Nelson Weker;Eric Detsi
Nano Letters February 8, 2017 Volume 17(Issue 2) pp:870-877
Publication Date(Web):January 5, 2017
DOI:10.1021/acs.nanolett.6b04181
Tin metal is an attractive negative electrode material to replace graphite in Li-ion batteries due to its high energy density. However, tin undergoes a large volume change upon alloying with Li, which pulverizes the particles, and ultimately leads to short cycling lifetimes. Nevertheless, nanoporous materials have been shown to extend battery life well past what is observed in nonporous material. Despite the exciting potential of porous alloying anodes to significantly increase the energy density in Li-ion batteries, the fundamental physics of how nanoscale architectures accommodate the electrochemically induced volume changes are poorly understood. Here, operando transmission X-ray microscopy has been used to develop an understanding of the mechanisms that govern the enhanced cycling stability in nanoporous tin. We found that in comparison to dense tin, nanoporous tin undergoes a 6-fold smaller areal expansion after lithiation, as a result of the internal porosity and unique nanoscale architecture. The expansion is also more gradual in nanoporous tin compared to the dense material. The nanoscale resolution of the microscope used in this study is ∼30 nm, which allowed us to directly observe the pore structure during lithiation and delithiation. We found that nanoporous tin remains porous during the first insertion and desinsertion cycle. This observation is key, as fully closed pores could lead to mechanical instability, electrolyte inaccessibility, and short lifetimes. While tin was chosen for this study because of its high X-ray contrast, the results of this work should be general to other alloy-type systems, such as Si, that also suffer from volume change based cycling degradation.Keywords: alloy anodes; in situ; Li-ion battery; operando; porous silicon; porous tin; tin; transmission X-ray microscope;
Co-reporter:John B. Cook, Eric Detsi, Yijin Liu, Yu-Lun Liang, Hyung-Seok Kim, Xavier Petrissans, Bruce Dunn, and Sarah H. Tolbert
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 1) pp:
Publication Date(Web):December 7, 2016
DOI:10.1021/acsami.6b09014
Next generation Li-ion batteries will require negative electrode materials with energy densities many-fold higher than that found in the graphitic carbon currently used in commercial Li-ion batteries. While various nanostructured alloying-type anode materials may satisfy that requirement, such materials do not always exhibit long cycle lifetimes and/or their processing routes are not always suitable for large-scale synthesis. Here, we report on a high-performance anode material for next generation Li-ion batteries made of nanoporous Sn powders with hierarchical ligament morphology. This material system combines both long cycle lifetimes (more than 72% capacity retention after 350 cycles), high capacity (693 mAh/g, nearly twice that of commercial graphitic carbon), good charging/discharging capabilities (545 mAh/g at 1 A/g, 1.5C), and a scalable processing route that involves selective alloy corrosion. The good cycling performance of this system is attributed to its nanoporous architecture and its unique hierarchical ligament morphology, which accommodates the large volume changes taking place during lithiation, as confirmed by synchrotron-based ex-situ X-ray 3D tomography analysis. Our findings are an important step for the development of high-performance Li-ion batteries.Keywords: alloy anode; high capacity anode; nanoporous metal; porous materials; tin; transmission X-ray microscopy; TXM;
Co-reporter:Eric Detsi, John B. Cook, Benjamin K. Lesel, Christopher L. Turner, Yu-Lun Liang, Shauna Robbennolt and Sarah H. Tolbert
Energy & Environmental Science 2016 vol. 9(Issue 2) pp:540-549
Publication Date(Web):09 Dec 2015
DOI:10.1039/C5EE02509E
A major challenge in the field of water electrolysis is the scarcity of oxygen-evolving catalysts that are inexpensive, highly corrosion-resistant, suitable for large-scale applications and able to oxidize water at high current densities and low overpotentials. Most unsupported, non-precious metals oxygen-evolution catalysts require at least ∼350 mV overpotential to oxidize water with a current density of 10 mA cm−2 in 1 M alkaline solution. Here we report on a robust nanostructured porous NiFe-based oxygen evolution catalyst made by selective alloy corrosion. In 1 M KOH, our material exhibits a catalytic activity towards water oxidation of 500 mA cm−2 at 360 mV overpotential and is stable for over eleven days. This exceptional performance is attributed to three factors. First, the small size of the ligaments and pores in our mesoporous catalyst (∼10 nm) results in a high BET surface area (43 m2 g−1) and therefore a high density of oxygen-evolution catalytic sites per unit mass. Second, the open porosity facilitates effective mass transfer at the catalyst/electrolyte interface. Third and finally, the high bulk electrical conductivity of the mesoporous catalyst allows for effective current flow through the electrocatalyst, making it possible to use thick films with a high density of active sites and ∼3 × 104 cm2 of catalytic area per cm2 of electrode area. Our mesoporous catalyst is thus attractive for alkaline electrolyzers where water-based solutions are decomposed into hydrogen and oxygen as the only products, driven either conventionally or by photovoltaics.
Co-reporter:Michael T. Yeung;Jialin Lei;Reza Mohammadi;Christopher L. Turner;Yue Wang;Richard B. Kaner
Advanced Materials 2016 Volume 28( Issue 32) pp:6993-6998
Publication Date(Web):
DOI:10.1002/adma.201601187
Co-reporter:John B. Cook;Hyung-Seok Kim;Yan Yan;Jesse S. Ko;Shauna Robbennolt;Bruce Dunn
Advanced Energy Materials 2016 Volume 6( Issue 9) pp:
Publication Date(Web):
DOI:10.1002/aenm.201501937
The ion insertion properties of MoS2 continue to be of widespread interest for energy storage. While much of the current work on MoS2 has been focused on the high capacity four-electron reduction reaction, this process is prone to poor reversibility. Traditional ion intercalation reactions are highlighted and it is demonstrated that ordered mesoporous thin films of MoS2 can be utilized as a pseudocapacitive energy storage material with a specific capacity of 173 mAh g−1 for Li-ions and 118 mAh g−1 for Na-ions at 1 mV s−1. Utilizing synchrotron grazing incidence X-ray diffraction techniques, fast electrochemical kinetics are correlated with the ordered porous structure and with an iso-oriented crystal structure. When Li-ions are utilized, the material can be charged and discharged in 20 seconds while still achieving a specific capacity of 140 mAh g−1. Moreover, the nanoscale architecture of mesoporous MoS2 retains this level of lithium capacity for 10 000 cycles. A detailed electrochemical kinetic analysis indicates that energy storage for both ions in MoS2 is due to a pseudocapacitive mechanism.
Co-reporter:Justin C. Ondry, Shauna Robbennolt, Hyeyeon Kang, Yan Yan, and Sarah H. Tolbert
Chemistry of Materials 2016 Volume 28(Issue 17) pp:6105
Publication Date(Web):July 27, 2016
DOI:10.1021/acs.chemmater.6b01681
Block copolymer templating of ligand-stripped nanocrystals followed by thermal degradation of the polymer template is a robust method that has been applied in making a variety of mesoporous nanocrystal-based films. However, the use of thermal processing to remove the polymer template can have detrimental effects on other material properties such as grain size and crystal structure that affect size-dependent properties such as the band gap. Here we present a new method for forming mesoporous films of cadmium and lead chalcogenide nanocrystals that avoids thermal processing. In our method, nanocrystals are first assembled with a diblock copolymer template. The resulting films are then soaked in a solution of a small molecule cross-linking agent to lock the nanocrystals into the structure. Finally, the polymer template is gently dissolved out of the film, leaving behind a porous film of nanocrystals. These films show disordered but homogeneous porosity, quantified by electron microscopy and ellipsometric porosimetry. Importantly, both X-ray diffraction and optical absorption spectroscopy indicate that the initial nanocrystal size is fully preserved in the final porous structure. This new synthetic method has exciting potential as a building block for composite structures where precise control of quantum confinement effects is needed.
Co-reporter:Benjamin K. Lesel, Jesse S. Ko, Bruce Dunn, and Sarah H. Tolbert
ACS Nano 2016 Volume 10(Issue 8) pp:7572
Publication Date(Web):July 29, 2016
DOI:10.1021/acsnano.6b02608
Charge storage devices with high energy density and enhanced rate capabilities are highly sought after in today’s mobile world. Although several high-rate pseudocapacitive anode materials have been reported, cathode materials operating in a high potential range versus lithium metal are much less common. Here, we present a nanostructured version of the well-known cathode material, LiMn2O4. The reduction in lithium-ion diffusion lengths and improvement in rate capabilities is realized through a combination of nanocrystallinity and the formation of a 3-D porous framework. Materials were fabricated from nanoporous Mn3O4 films made by block copolymer templating of preformed nanocrystals. The nanoporous Mn3O4 was then converted via solid-state reaction with LiOH to nanoporous LixMn2O4 (1 < x < 2). The resulting films had a wall thickness of ∼15 nm, which is small enough to be impacted by inactive surface sites. As a consequence, capacity was reduced by about half compared to bulk LiMn2O4, but both charge and discharge kinetics as well as cycling stability were improved significantly. Kinetic analysis of the redox reactions was used to verify the pseudocapacitive mechanisms of charge storage and establish the feasibility of using nanoporous LixMn2O4 as a cathode in lithium-ion devices based on pseudocapacitive charge storage.Keywords: cathode; high rate; LiMn2O4; lithium-ion battery; mesoporous; nanocrystal templated; pseudocapacitor
Co-reporter:Rachel C. Huber, Amy S. Ferreira, Jordan C. Aguirre, Daniel Kilbride, Daniel B. Toso, Kenny Mayoral, Z. Hong Zhou, Nikos Kopidakis, Yves Rubin, Benjamin J. Schwartz, Thomas G. Mason, and Sarah H. Tolbert
The Journal of Physical Chemistry B 2016 Volume 120(Issue 26) pp:6215-6224
Publication Date(Web):April 14, 2016
DOI:10.1021/acs.jpcb.6b02202
Poly(fluorene-alt-thiophene) (PFT) is a conjugated polyelectrolyte that self-assembles into rod-like micelles in water, with the conjugated polymer backbone running along the length of the micelle. At modest concentrations (∼10 mg/mL in aqueous solutions), PFT forms hydrogels, and this work focuses on understanding the structure and intermolecular interactions in those gel networks. The network structure can be directly visualized using cryo electron microscopy. Oscillatory rheology studies further tell us about connectivity within the gel network, and the data are consistent with a picture where polymer chains bridge between micelles to hold the network together. Addition of tetrahydrofuran (THF) to the gels breaks those connections, but once the THF is removed, the gel becomes stronger than it was before, presumably due to the creation of a more interconnected nanoscale architecture. Small polymer oligomers can also passivate the bridging polymer chains, breaking connections between micelles and dramatically weakening the hydrogel network. Fits to solution-phase small-angle X-ray scattering data using a Dammin bead model support the hypothesis of a bridging connection between PFT micelles, even in dilute aqueous solutions. Finally, time-resolved microwave conductivity measurements on dried samples show an increase in carrier mobility after THF annealing of the PFT gel, likely due to increased connectivity within the polymer network.
Co-reporter:Amy S. Ferreira, Jordan C. Aguirre, Selvam Subramaniyan, Samson A. Jenekhe, Sarah H. Tolbert, and Benjamin J. Schwartz
The Journal of Physical Chemistry C 2016 Volume 120(Issue 39) pp:22115-22125
Publication Date(Web):August 29, 2016
DOI:10.1021/acs.jpcc.6b03300
The performance of polymer:fullerene bulk heterojunction (BHJ) photovoltaics is highly sensitive to the morphology of the polymer within the active layer. To tune this morphology, we constructed both blend-cast and sequentially processed BHJ devices from the fullerene derivative [6,6]-phenyl-C60-butyric acid methyl ester (PCBM), in combination with a series of random poly(3-butylthiophene-co-3-octylthiophene)s with different fractions of each monomer, with the goal of controllably varying the average polymer side-chain length. What we found, however, was that the most important parameter for predicting device performance across this series of polymers was the regioregularity of the particular synthetic batch of polymer used, not the average side-chain length. Moreover, we found that regioregularity affected device performance in different ways depending on the processing route: lower regioregularity led to improved performance for sequentially processed devices, but was detrimental to the performance of blend-cast devices. We argue that the reason for this anticorrelation is that regioregularity is the single most important determinant of the relative crystalline of the polymer. The relative crystalline fraction, in turn, determines the ability of the polymer to swell in the presence of solvents. Polymer swelling is key to BHJ formation via sequential processing, but can lead to overly mixed systems using traditional blend-casting methods. As a result, we find that the best performing polymer for sequentially processed devices is the worst performer for blend-cast devices and vice versa, highlighting the importance of using both processing methods when exploring new materials for use in BHJ photovoltaics.
Co-reporter:Rachel C. Huber;Daniel Kilbride;Nicholas S. Knutson;J. Reddy Challa;Amy S. Ferreira;Daniel B. Toso;Robert Thompson;Benjamin J. Schwartz;Lekshmi Sudha Devi;Yves Rubin;Z. Hong Zhou
Science 2015 Volume 348(Issue 6241) pp:
Publication Date(Web):
DOI:10.1126/science.aaa6850
Photoinduction of long-lived polarons
Photosynthetic complexes and organic photovoltaics can rapidly create separated charges upon photoexcitation. However, unproductive charge recombination often occurs in the human-made system. This is in part because the charge acceptor and donor structures are much larger. Huber et al. created aqueous micelles that pair conjugated polyelectrolyte charge donors with fullerene acceptors at a much smaller interface. They observed the photoinduced formation of polarons—stable pairs of separated charges—with lifetimes of several days.
Science, this issue p. 1340
Co-reporter:D. Tyler Scholes; Steven A. Hawks; Patrick Y. Yee; Hao Wu; Jeffrey R. Lindemuth; Sarah H. Tolbert;Benjamin J. Schwartz
The Journal of Physical Chemistry Letters 2015 Volume 6(Issue 23) pp:4786-4793
Publication Date(Web):November 10, 2015
DOI:10.1021/acs.jpclett.5b02332
We demonstrate that solution-sequential processing (SqP) can yield heavily doped pristine-quality films when used to infiltrate the molecular dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) into pure poly(3-hexylthiophene) (P3HT) polymer layers. Profilometry measurements show that the SqP method produces doped films with essentially the same surface roughness as pristine films, and 2-D grazing-incidence wide-angle X-ray scattering (GIWAXS) confirms that SqP preserves both the size and orientation of the pristine polymer’s crystallites. Unlike traditional blend-cast F4TCNQ/P3HT doped films, our sequentially processed layers have tunable and reproducible conductivities reaching as high as 5.5 S/cm even when measured over macroscopic (>1 cm) distances. The high conductivity and superb film quality allow for meaningful Hall effect measurements, which reveal p-type conduction and carrier concentrations tunable from 1016 to 1020 cm–3 and hole mobilities ranging from ∼0.003 to 0.02 cm2 V–1 s–1 at room temperature over the doping levels examined.
Co-reporter:Laura T. Schelhas;Richard A. Farrell;Udayabagya Halim
Advanced Functional Materials 2014 Volume 24( Issue 44) pp:6956-6962
Publication Date(Web):
DOI:10.1002/adfm.201401921
Block co-polymer patterns are attractive candidates for nanoparticle assemblies. Directed self-assembly of block co-polymers in particular allows for long range ordering of the patterns, making them interesting scaffolds for the organization of magnetic particles. Here, a method to tune the channel width of polymer-derived trenches via atomic layer deposition (ALD) of alumina is reported. The alumnia coating provides a much more thermally robust pattern that is stable up to 250 °C. Using these patterns, magnetic coupling in both ferromagnetic and superparamagnetic nanocrystal chains is achieved.
Co-reporter:Iris E. Rauda;Veronica Augustyn;Laura C. Saldarriaga-Lopez;Xinyi Chen;Laura T. Schelhas;Gary W. Rubloff;Bruce Dunn
Advanced Functional Materials 2014 Volume 24( Issue 42) pp:6717-6728
Publication Date(Web):
DOI:10.1002/adfm.201401284
Solution processing of colloidal nanocrystals into porous architectures using block co-polymer templating offers a simple yet robust route to construct materials with open porosity and high surface area. These features, when realized in materials that show efficient redox activity and good conductivity, should be ideal for electrochemical energy storage because they allow for efficient electrolyte diffusion and ample surface and near-surface redox reactions. Here, a route to synthesize nanoporous pseudocapacitors is presented using preformed ITO nanocrystals to make a conductive scaffold, coated with a conformal layer of vanadia deposited using atomic layer deposition (ALD). Two vanadia thicknesses are deposited, 2 and 7 nm, to examine the kinetics of Li+ diffusion into vanadia in a system where all other chemical and structural parameters are fixed. Porosity measurements show that the internal surface area of 2 nm vanadia samples is fully accessible; whereas for the 7 nm vanadia, there is some pore blockage that limits electrolyte diffusion. Despite this fact, composites with both thick and thin vanadia layers show high levels of pseudocapacitance, indicating fast diffusion of Li+ through even the 7 nm thick vanadia. This work thus sets a minimum accessible length-scale of 7 nm for intercalation pseudocapacitance in orthorhombic V2O5.
Co-reporter:Guangye Zhang ; Rachel C. Huber ; Amy S. Ferreira ; Shane D. Boyd ; Christine K. Luscombe ; Sarah H. Tolbert ;Benjamin J. Schwartz
The Journal of Physical Chemistry C 2014 Volume 118(Issue 32) pp:18424-18435
Publication Date(Web):July 18, 2014
DOI:10.1021/jp5054315
Although most polymer/fullerene-based solar cells are cast from a blend of the components in solution, it is also possible to sequentially process the polymer and fullerene layers from quasi-orthogonal solvents. Sequential processing (SqP) not only produces photovoltaic devices with efficiencies comparable to the more traditional bulk heterojunction (BHJ) solar cells produced by blend casting (BC) but also offers the advantage that the polymer and fullerene layers can be optimized separately. In this paper, we explore the morphology produced when sequentially processing polymer/fullerene solar cells and compare it to the BC morphology. We find that increasing polymer regioregularity leads to the opposite effect in SqP and BC BHJ solar cells. We start by constructing a series of SqP and BC solar cells using different types of poly(3-hexylthiophene) (P3HT) that vary in regioregulary and polydispersity combined with [6,6]-phenyl-C61-butyric-acid-methyl-ester (PCBM). We use grazing incidence wide-angle X-ray scattering to demonstrate how strongly changes in the P3HT and PCBM crystallinity upon thermal annealing of SqP and BC BHJ films depend on polymer regioregularity. For SqP devices, low regioregularity P3HT films that possess more amorphous regions allow for more PCBM crystallite growth and thus show better photovoltaic device efficiency. On the other hand, highly regioregular P3HT leads to a more favorable morphology and better device efficiency for BC BHJ films. Comparing the photovoltaic performance and structural characterization indicates that the mechanisms controlling morphology in the active layers are fundamentally different for BHJs formed via SqP and BC. Most importantly, we find that nanoscale morphology in both SqP and BC BHJs can be systematically controlled by tuning the amorphous fraction of polymer in the active layer.
Co-reporter:Steven A. Hawks ; Jordan C. Aguirre ; Laura T. Schelhas ; Robert J. Thompson ; Rachel C. Huber ; Amy S. Ferreira ; Guangye Zhang ; Andrew A. Herzing ; Sarah H. Tolbert ;Benjamin J. Schwartz
The Journal of Physical Chemistry C 2014 Volume 118(Issue 31) pp:17413-17425
Publication Date(Web):July 8, 2014
DOI:10.1021/jp504560r
Polymer:fullerene bulk heterojunction (BHJ) solar cell active layers can be created by traditional blend casting (BC), where the components are mixed together in solution before deposition, or by sequential processing (SqP), where the pure polymer and fullerene materials are cast sequentially from different solutions. Presently, however, the relative merits of SqP as compared to BC are not fully understood because there has yet to be an equivalent (composition- and thickness-matched layer) comparison between the two processing techniques. The main reason why matched SqP and BC devices have not been compared is because the composition of SqP active layers has not been accurately known. In this paper, we present a novel technique for accurately measuring the polymer:fullerene film composition in SqP active layers, which allows us to make the first comparisons between rigorously composition- and thickness-matched BHJ organic solar cells made by SqP and traditional BC. We discover that, in optimal photovoltaic devices, SqP active layers have a very similar composition as their optimized BC counterparts (≈44–50 mass % PCBM). We then present a thorough investigation of the morphological and device properties of thickness- and composition-matched P3HT:PCBM SqP and BC active layers in order to better understand the advantages and drawbacks of both processing approaches. For our matched devices, we find that small-area SqP cells perform better than BC cells due to both superior film quality and enhanced optical absorption from more crystalline P3HT. The enhanced film quality of SqP active layers also results in higher performance and significantly better reproducibility in larger-area devices, indicating that SqP is more amenable to scaling than the traditional BC approach. X-ray diffraction, UV–vis absorption, and energy-filtered transmission electron tomography collectively show that annealed SqP active layers have a finer-scale blend morphology and more crystalline polymer and fullerene domains when compared to equivalently processed BC active layers. Charge extraction by linearly increasing voltage (CELIV) measurements, combined with X-ray photoelectron spectroscopy, also show that the top (nonsubstrate) interface for SqP films is slightly richer in PCBM compared to matched BC active layers. Despite these clear differences in bulk and vertical morphology, transient photovoltage, transient photocurrent, and subgap external quantum efficiency measurements all indicate that the interfacial electronic processes occurring at P3HT:PCBM heterojunctions are essentially identical in matched-annealed SqP and BC active layers, suggesting that device physics are surprisingly robust with respect to the details of the BHJ morphology.
Co-reporter:Iris E. Rauda, Veronica Augustyn, Bruce Dunn, and Sarah H. Tolbert
Accounts of Chemical Research 2013 Volume 46(Issue 5) pp:1113
Publication Date(Web):March 13, 2013
DOI:10.1021/ar300167h
Growing global energy demands coupled with environmental concerns have increased the need for renewable energy sources. For intermittent renewable sources like solar and wind to become available on demand will require the use of energy storage devices. Batteries and supercapacitors, also known as electrochemical capacitors (ECs), represent the most widely used energy storage devices. Supercapacitors are frequently overlooked as an energy storage technology, however, despite the fact that these devices provide greater power, much faster response times, and longer cycle life than batteries. Their limitation is that the energy density of ECs is significantly lower than that of batteries, and this has limited their potential applications.This Account reviews our recent work on improving pseudocapacitive energy storage performance by tailoring the electrode architecture. We report our studies of mesoporous transition metal oxide architectures that store charge through surface or near-surface redox reactions, a phenomenon termed pseudocapacitance. The faradaic nature of pseudocapacitance leads to significant increases in energy density and thus represents an exciting future direction for ECs. We show that both the choice of material and electrode architecture is important for producing the ideal pseudocapacitor device.Here we first briefly review the current state of electrode architectures for pseudocapacitors, from slurry electrodes to carbon/metal oxide composites. We then describe the synthesis of mesoporous films made with amphiphilic diblock copolymer templating agents, specifically those optimized for pseudocapacitive charge storage. These include films synthesized from nanoparticle building blocks and films made from traditional battery materials. In the case of more traditional battery materials, we focus on using flexible architectures to minimize the strain associated with lithium intercalation, that is, the accumulation of lithium ions or atoms between the layers of cathode or anode materials that occurs as batteries charge and discharge. Electrochemical analysis of these mesoporous films allows for a detailed understanding of the origin of charge storage by separating capacitive contributions from traditional diffusion-controlled intercalation processes. We also discuss methods to separate the two contributions to capacitance: double-layer capacitance and pseudocapacitance. Understanding these contributions should allow the selection of materials with an optimized architecture that maximize the contribution from pseudocapacitance.From our studies, we show that nanocrystal-based nanoporous materials offer an architecture optimized for high levels of redox or surface pseudocapacitance. Interestingly, in some cases, materials engineered to minimize the strain associated with lithium insertion can also show intercalation pseudocapacitance, which is a process where insertion processes become so kinetically facile that they appear capacitive.Finally, we conclude with a summary of simple design rules that should result in high-power, high-energy-density electrode architectures. These design rules include assembling small, nanosized building blocks to maximize electrode surface area; maintaining an interconnected, open mesoporosity to facilitate solvent diffusion; seeking flexibility in electrode structure to facilitate volume expansion during lithium insertion; optimizing crystalline domain size and orientation; and creating effective electron transport pathways.
Co-reporter:Iris E. Rauda;Laura C. Saldarriaga-Lopez;Brett A. Helms;Laura T. Schelhas;Daniel Membreno;Delia J. Milliron
Advanced Materials 2013 Volume 25( Issue 9) pp:1315-1322
Publication Date(Web):
DOI:10.1002/adma.201203309
Co-reporter:Iris E. Rauda, Robert Senter and Sarah H. Tolbert
Journal of Materials Chemistry A 2013 vol. 1(Issue 7) pp:1423-1427
Publication Date(Web):17 Dec 2012
DOI:10.1039/C2TC00239F
Templating provides a powerful tool to control both shape and orientation in anisotopric nanomaterials. Here we utilize confinement of a (C6H5C2H4NH3)2SnI4 perovskite semiconductor within anodic-alumina nanochannels to convert this layered material into wire arrays composed of concentric multilayers. The semiconducting arrays exhibit reasonable charge-transport normal to the substrate, showing that space confinement can be used to both restructure and reorient nanophase materials.
Co-reporter:Andrew P.-Z. Clark, Chenjun Shi, Benny C. Ng, James N. Wilking, Alexander L. Ayzner, Adam Z. Stieg, Benjamin J. Schwartz, Thomas G. Mason, Yves Rubin, and Sarah H. Tolbert
ACS Nano 2013 Volume 7(Issue 2) pp:962
Publication Date(Web):January 24, 2013
DOI:10.1021/nn304437k
In an effort to favor the formation of straight polymer chains without crystalline grain boundaries, we have synthesized an amphiphilic conjugated polyelectrolyte, poly(fluorene-alt-thiophene) (PFT), which self-assembles in aqueous solutions to form cylindrical micelles. In contrast to many diblock copolymer assemblies, the semiconducting backbone runs parallel, not perpendicular, to the long axis of the cylindrical micelle. Solution-phase micelle formation is observed by X-ray and visible light scattering. The micelles can be cast as thin films, and the cylindrical morphology is preserved in the solid state. The effects of self-assembly are also observed through spectral shifts in optical absorption and photoluminescence. Solutions of higher-molecular-weight PFT micelles form gel networks at sufficiently high aqueous concentrations. Rheological characterization of the PFT gels reveals solid-like behavior and strain hardening below the yield point, properties similar to those found in entangled gels formed from surfactant-based micelles. Finally, electrical measurements on diode test structures indicate that, despite a complete lack of crystallinity in these self-assembled polymers, they effectively conduct electricity.Keywords: amphiphilic assembly; hydrogel; polymer micelle; self-assembly; semiconducting polymer; water-soluble conjugated polymer
Co-reporter:Reza Mohammadi ; Miao Xie ; Andrew T. Lech ; Christopher L. Turner ; Abby Kavner ; Sarah H. Tolbert ;Richard B. Kaner
Journal of the American Chemical Society 2012 Volume 134(Issue 51) pp:20660-20668
Publication Date(Web):November 21, 2012
DOI:10.1021/ja308219r
To enhance the hardness of tungsten tetraboride (WB4), a notable lower cost member of the late transition-metal borides, we have synthesized and characterized solid solutions of this material with tantalum (Ta), manganese (Mn), and chromium (Cr). Various concentrations of these transition-metal elements, ranging from 0.0 to 50.0 at. %, on a metals basis, were made. Arc melting was used to synthesize these refractory compounds from the pure elements. Elemental and phase purity of the samples were examined using energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), and microindentation was utilized to measure the Vickers hardness under applied loads of 0.49–4.9 N. XRD results indicate that the solubility limit is below 10 at. % for Cr and below 20 at. % for Mn, while Ta is soluble in WB4 above 20 at. %. Optimized Vickers hardness values of 52.8 ± 2.2, 53.7 ± 1.8, and 53.5 ± 1.9 GPa were achieved, under an applied load of 0.49 N, when ∼2.0, 4.0, and 10.0 at. % Ta, Mn, and Cr were added to WB4 on a metals basis, respectively. Motivated by these results, ternary solid solutions of WB4 were produced, keeping the concentration of Ta in WB4 fixed at 2.0 at. % and varying the concentration of Mn or Cr. This led to hardness values of 55.8 ± 2.3 and 57.3 ± 1.9 GPa (under a load of 0.49 N) for the combinations W0.94Ta0.02Mn0.04B4 and W0.93Ta0.02Cr0.05B4, respectively. In situ high-pressure XRD measurements collected up to ∼65 GPa generated a bulk modulus of 335 ± 3 GPa for the hardest WB4 solid solution, W0.93Ta0.02Cr0.05B4, and showed suppression of a pressure-induced phase transition previously observed in pure WB4.
Co-reporter:Iris E. Rauda, Raffaella Buonsanti, Laura C. Saldarriaga-Lopez, Kanokraj Benjauthrit, Laura T. Schelhas, Morgan Stefik, Veronica Augustyn, Jesse Ko, Bruce Dunn, Ulrich Wiesner, Delia J. Milliron, and Sarah H. Tolbert
ACS Nano 2012 Volume 6(Issue 7) pp:6386
Publication Date(Web):June 25, 2012
DOI:10.1021/nn302789r
Block copolymer templating of inorganic materials is a robust method for the production of nanoporous materials. The method is limited, however, by the fact that the molecular inorganic precursors commonly used generally form amorphous porous materials that often cannot be crystallized with retention of porosity. To overcome this issue, here we present a general method for the production of templated mesoporous materials from preformed nanocrystal building blocks. The work takes advantage of recent synthetic advances that allow organic ligands to be stripped off of the surface of nanocrystals to produce soluble, charge-stabilized colloids. Nanocrystals then undergo evaporation-induced co-assembly with amphiphilic diblock copolymers to form a nanostructured inorganic/organic composite. Thermal degradation of the polymer template results in nanocrystal-based mesoporous materials. Here, we show that this method can be applied to nanocrystals with a broad range of compositions and sizes, and that assembly of nanocrystals can be carried out using a broad family of polymer templates. The resultant materials show disordered but homogeneous mesoporosity that can be tuned through the choice of template. The materials also show significant microporosity, formed by the agglomerated nanocrystals, and this porosity can be tuned by the nanocrystal size. We demonstrate through careful selection of the synthetic components that specifically designed nanostructured materials can be constructed. Because of the combination of open and interconnected porosity, high surface area, and compositional tunability, these materials are likely to find uses in a broad range of applications. For example, enhanced charge storage kinetics in nanoporous Mn3O4 is demonstrated here.Keywords: block copolymer; evaporation-induced self-assembly; ligand exchange; mesoporous; microporous; nanocrystals; templated
Co-reporter:Jin Fang ; Chris B. Kang ; Yi Huang ; Sarah H. Tolbert ;Laurent Pilon
The Journal of Physical Chemistry C 2012 Volume 116(Issue 23) pp:12926-12933
Publication Date(Web):May 16, 2012
DOI:10.1021/jp302531d
This paper reports the cross-plane thermal conductivity of ordered mesoporous nanocrystalline silicon thin films between 25 and 315 K. The films were produced by evaporation-induced self-assembly of mesoporous silica followed by magnesium reduction. The periodic ordering of pores in mesoporous silicon was characterized by X-ray diffraction and direct SEM imaging. The average crystallite size, porosity, and film thickness were about 13 nm, 25–35%, and 140–340 nm, respectively. The pores were arranged in a face-centered cubic lattice. The cross-plane thermal conductivity of the mesoporous silicon thin films was measured using the 3ω method. It was between 3 and 5 orders of magnitude smaller than that of bulk single crystal silicon in the temperature range considered. The effects of temperature, film thickness, and copolymer template on the thermal conductivity were investigated. A model based on kinetic theory was used to accurately predict the measured thermal conductivity for all temperatures. On one hand, both the measured thermal conductivity and the model predictions showed a temperature dependence of k ∝ T2 at low temperatures, typical of amorphous and strongly disordered materials. On the other hand, at high temperatures the thermal conductivity of mesoporous silicon films reached a maximum, indicating a crystalline-like behavior. These results will be useful in designing mesoporous silicon with desired thermal conductivity by tuning its morphology for various applications.
Co-reporter:Benny C. Ng, Stephanie T. Chan, Jason Lin, and Sarah H. Tolbert
ACS Nano 2011 Volume 5(Issue 10) pp:7730
Publication Date(Web):September 25, 2011
DOI:10.1021/nn202493w
Cowpea chlorotic mottle virus is a single-stranded RNA plant virus with a diameter of 28 nm. The proteins comprising the capsid of this virus can be purified and reassembled either by themselves to form hollow structures or with polyanions such as double-stranded DNA or single-stranded RNA. Depending on pH and ionic strength, a diverse range of structures and shapes can form. The work presented here focuses on using these proteins to encapsulate a fluorescent polyanionic semiconducting polymer, MPS-PPV (poly-2-methoxy-5-propyloxy sulfonate phenylene vinlyene), in order to obtain optically active virus-like particles. After encapsulation, fluorescence from MPS-PPV shows two distinct peaks, which suggests the polymer may be in two conformations. A combination of TEM, fluorescence anisotropy, and sucrose gradient separation indicate that the blue peak arises from polymer encapsulated into spherical particles, while the redder peak corresponds to polymers contained in rod-like cages. Ionic strength during assembly can be used to tune the propensity to form rods or spheres. The results illustrate the synergy of hybrid synthetic/biological systems: polymer conformation drives the structure of this composite material, which in turn modifies the polymer optical properties. This synergy could be useful for the future development of synthetic/biological hybrid materials with designated functionality.Keywords: CCMV; cowpea chlorotic mottle virus; fluorescence anisotropy; MPS-PPV; poly(2-methoxy-5-propyloxy sulfonate phenylene vinylene); self-assembly; virus-like particles
Co-reporter:Thomas E. Quickel, Van H. Le, Torsten Brezesinski and Sarah H. Tolbert
Nano Letters 2010 Volume 10(Issue 8) pp:2982-2988
Publication Date(Web):July 27, 2010
DOI:10.1021/nl1014266
In this work, we report the synthesis of periodic nanoporous cobalt ferrite (CFO) that exhibits tunable room temperature ferrimagnetism. The porous cubic CFO frameworks are fabricated by coassembly of inorganic precursors with a large amphiphilic diblock copolymer, referred to as KLE. The inverse spinel framework boasts an ordered open network of pores averaging 14 nm in diameter. The domain sizes of the crystallites are tunable from 6 to 15 nm, a control which comes at little cost to the ordering of the mesostructure. Increases in crystalline domain size directly correlate with increases in room temperature coercivity. In addition, these materials show a strong preference for out-of-plane oriented magnetization, which is unique in a thin film system. The preference is explained by in-plane tensile strain, combined with relaxation of the out-of-plane strain through flexing of the mesopores. It is envisioned that the pores of this ferrimagnet could facilitate the formation of a diverse range of exchange coupled composite materials.
Co-reporter:Torsten Brezesinski, John Wang, Robert Senter, Kirstin Brezesinski, Bruce Dunn and Sarah H. Tolbert
ACS Nano 2010 Volume 4(Issue 2) pp:967
Publication Date(Web):January 26, 2010
DOI:10.1021/nn9007324
In this work, we report the synthesis and characterization of highly ordered mesoporous CeO2 thin films with crystalline walls. While this article focuses on electrochemical studies of CeO2 with periodic nanoscale porosity, we also examine the mechanical properties of these films and show how pore flexing can be used to facilitate intercalation of lithium ions. Mesoporous samples were prepared by dip-coating using the large diblock copolymer KLE as the organic template. We establish that the films have a mesoporous network with a biaxially distorted cubic pore structure and are highly crystalline at the atomic scale when heated to temperatures above 500 °C. Following a previously reported approach, we were able to use the voltammetric sweep rate dependence to determine quantitatively the capacitive contribution to electrochemical charge storage. The net result is that mesoporous CeO2 films exhibit reasonable levels of pseudocapacitive charge storage and much higher capacities than samples prepared without any polymer template. Part of this increased capacity stems from the fact that these films are able to expand normal to the substrate upon intercalation of lithium ions by flexing of the nanoscale pores. This flexing relieves stress from volume expansion that normally inhibits charge storage. Overall, the results described in this work provide fundamental insight into how nanoscale structure and mechanical flexibility can be used to increase charge storage capacity in metal oxides.Keywords: block copolymer templating; CeO2; ceria; electrochemical charge storage; mesoporous materials; nanostructured materials; pore flexibility; supercapacitors
Co-reporter:Neal J. Hutchinson, Thomas Coquil, Erik K. Richman, Sarah H. Tolbert, Laurent Pilon
Thin Solid Films 2010 Volume 518(Issue 8) pp:2134-2140
Publication Date(Web):1 February 2010
DOI:10.1016/j.tsf.2009.08.006
In this study, cubic and hexagonal mesoporous amorphous silica thin films were synthesized using evaporation-induced self-assembly process followed by calcination leaving highly ordered spherical or cylindrical pores in a silica matrix. The films featured pores with diameter between 4 and 11 nm, lattice parameter from 7.8 to 24 nm, and porosity between 22% and 45%. All films were dehydrated prior to reflectance measurements except for one film which was fully hydrated. The present study compares the spectral reflectance measured experimentally between 400 and 900 nm with that computed numerically by solving three-dimensional Maxwell's equations in mesoporous silica thin films with the same morphology as those synthesized. The matrix was assumed to have the same optical properties as bulk fused silica. The pore optical properties were either those of air or liquid water whether the film was dehydrated or hydrated, respectively. Excellent agreement was found between experimental and numerical reflectance for both cubic and hexagonal mesoporous silica films. This study experimentally validates our simulation tool and offers the prospect of ab-initio design of nanocomposite materials with arbitrary optical properties without using effective medium approximation or mixing rules.
Co-reporter:Jonathan B. Levine;Richard B. Kaner
Advanced Functional Materials 2009 Volume 19( Issue 22) pp:3519-3533
Publication Date(Web):
DOI:10.1002/adfm.200901257
Abstract
Dense transition metal borides have recently been identified as superhard materials that offer the possibility of ambient pressure synthesis compared to the conventional high pressure, high temperature approach. This feature article begins with a discussion of the relevant physical properties for this class of compounds, followed by a summary of the synthesis and properties of several transition metal borides. A strong emphasis is placed on correlating mechanical properties with electronic and atomic structure of these materials in an effort to better predict new superhard compounds. It concludes with a perspective of future research directions, highlighting some recent results and presenting several new ideas that remain to be tested.
Co-reporter:Michelle B. Weinberger, Jonathan B. Levine, Hsiu-Ying Chung, Robert W. Cumberland, Haider I. Rasool, Jenn-Ming Yang, Richard B. Kaner and Sarah H. Tolbert
Chemistry of Materials 2009 Volume 21(Issue 9) pp:1915
Publication Date(Web):April 14, 2009
DOI:10.1021/cm900211v
Interest in new ultraincompressible hard materials has prompted studies of transition metal diboride solid solutions. We have synthesized pure RuB2 and solid solutions of Os1−xRuxB2. The mechanical properties of these materials are investigated using in situ high-pressure X-ray diffraction and Vickers hardness testing techniques. Both bulk moduli and hardness vary linearly with composition in accordance with Vegard’s law, whereas the differing behavior among end-members can be explained by relativistic effects, core electron density, and differences in the cohesive energy of the parent metals. The results provide a refinement of the rules previously reported for the design of new superhard materials.
Co-reporter:Scott D. Korlann, Andrew E. Riley, Bongjin Simon Mun and Sarah H. Tolbert
The Journal of Physical Chemistry C 2009 Volume 113(Issue 18) pp:7697-7705
Publication Date(Web):April 9, 2009
DOI:10.1021/jp806857v
Inorganic/organic coassembly provides a powerful route to the formation of periodic, nanostructured materials. In this work, the surfactant cetyltriethylammonium bromide is used as an organic structure directing agent, and the inorganic phase is formed from the condensation of metal cations with reduced main group clusters know as Zintl clusters. These anionic clusters are formed by alloying alkali metals with various main group elements. The chalcogenide-based Zintl clusters used here have an affinity for gold and other transition metals and will thus nucleate the formation of films on metal surfaces. Interface nucleated inorganic/organic co-organization results in thin films with the periodicity of a liquid crystal phase, but with a cross-linking inorganic network surrounding the surfactant domains. In this work, we investigate the extent to which the band structure of these films can be tuned by altering the elemental composition of the inorganic framework of these periodic nanocomposites. For the semiconducting films investigated here, the band gap and valence and conduction band energies of the inorganic network can be independently tuned by 1−2 eV by varying different elemental components. All trends in the data can be qualitatively understood by considering the orbital contribution to the band structure, in analogy to chalcogenide glass semiconductors. A variety of applications are anticipated for nanostructured semiconducting films for which band properties can be independently tuned across a broad range and films can be synthesized using low cost solution phase methods.
Co-reporter:Alexander L. Ayzner, Christopher J. Tassone, Sarah H. Tolbert and Benjamin J. Schwartz
The Journal of Physical Chemistry C 2009 Volume 113(Issue 46) pp:20050-20060
Publication Date(Web):October 27, 2009
DOI:10.1021/jp9050897
The most efficient organic solar cells produced to date are bulk heterojunction (BHJ) photovoltaic devices based on blends of semiconducting polymers such as poly(3-hexylthiophene-2,5-diyl) (P3HT) with fullerene derivatives such as [6,6]-penyl-C61-butyric-acid-methyl-ester (PCBM). The need for blending the two components is based on the idea that the exciton diffusion length in polymers like P3HT is only ∼10 nm, so that the polymer and fullerene components must be mixed on this length scale to efficiently split the excitons into charge carriers. In this paper, we show that the BHJ geometry is not necessary for high efficiency, and that all-solution-processed P3HT/PCBM bilayer solar cells can be nearly as efficient as BHJ solar cells fabricated from the same materials. We demonstrate that o-dichlorobenzene (ODCB) and dichloromethane serve nicely as a pair of orthogonal solvents from which sequential layers of P3HT and PCBM, respectively, can be spin-cast. Atomic force microscopy, various optical spectroscopies, and electron microscopy all demonstrate that the act of spin-coating the PCBM overlayer does not affect the morphology of the P3HT underlayer, so that our spin-cast P3HT/PCBM bilayers have a well-defined planar interface. Our fluorescence quenching experiments find that there is still significant exciton splitting in P3HT/PCBM bilayers even when the P3HT layer is quite thick. When we fabricated photovoltaic devices from these bilayers, we obtained photovoltaic power conversion efficiencies in excess of 3.5%. Part of the reason for this high efficiency is that we were able to separately optimize the roles of each component of the bilayer; for example, we found that thermal annealing has relatively little effect on the nature of P3HT layers spin-cast from ODCB, but that it significantly increases the crystallinity and thus the mobility of electrons through PCBM. Because the carriers in bilayer devices are generated at the planar P3HT/PCBM interface, we also were able to systematically vary the distance the carriers have to travel to be extracted at the electrodes by changing the layer thicknesses without altering the bulk mobility of either component or the nature of the interfaces. We found that devices have the best fill-factors when the transit times of electrons and holes through the two layers are roughly balanced. In particular, we found that the most efficient devices are made with P3HT layers that are about four times thicker than the PCBM layers, demonstrating that it is the conduction and the extraction of electrons through the fullerene that ultimately limit the performance of both bilayer and BHJ devices based on the P3HT/PCBM material combination. Overall, we believe that polymer-fullerene bilayers provide several advantages over BHJ devices, including reduced carrier recombination and a much better degree of control over the properties of the individual components and interfaces during device fabrication.
Co-reporter:Bertrand Tremolet de Villers, Christopher J. Tassone, Sarah H. Tolbert and Benjamin J. Schwartz
The Journal of Physical Chemistry C 2009 Volume 113(Issue 44) pp:18978-18982
Publication Date(Web):October 13, 2009
DOI:10.1021/jp9082163
Plastic photovoltaic devices offer a real potential for making solar energy economically viable. Unfortunately, bulk heterojunction (BHJ) solar cells fabricated from blends of the commonly used materials poly(3-hexylthiophene), P3HT, and phenyl-C61-butyric acid methyl ester, PCBM, sometimes exhibit low efficiencies even when the procedures followed often produce solar cells with efficiencies exceeding 5%. In this Letter, we show that this irreproducibility is caused by subtleties in the film processing conditions that ultimately lead to poor electron extraction from the devices. For low-performing devices, photogeneration and charge extraction with a linearly increasing voltage ramp (photo−CELIV) measurements show an order-of-magnitude difference in the effective mobilities of the electrons and holes. Atomic force microscopy (AFM) experiments reveal that the top surface of these low-performing devices is nearly pure P3HT. We argue that small variations in the solvent evaporation kinetics during spin-coating of the BHJ active layer, which are difficult to control, cause PCBM to segregate toward the bottom of the P3HT film to different extents, explaining why electron extraction from the PCBM component of the BHJ is so difficult in poorly performing devices. Finally, we show that electron extraction can be greatly improved by spin-coating a thin PCBM layer on top of the BHJ before deposition of the cathode, allowing the reproducible fabrication of high-efficiency polymer solar cells.
Co-reporter:Benny C. Ng, Marcella Yu, Ajaykumar Gopal, Leonard H. Rome, Harold G. Monbouquette and Sarah H. Tolbert
Nano Letters 2008 Volume 8(Issue 10) pp:3503-3509
Publication Date(Web):September 20, 2008
DOI:10.1021/nl080537r
We demonstrate that a semiconducting polymer [poly(2-methoxy-5-propyloxy sulfonate phenylene vinylene), MPS-PPV] can be encapsulated inside recombinant, self-assembling protein nanocapsules called “vaults”. Polymer incorporation into these nanosized protein cages, found naturally at ∼10,000 copies per human cell, was confirmed by fluorescence spectroscopy and small-angle X-ray scattering. Although vault cellular functions and gating mechanisms remain unknown, their large internal volume and natural prevalence within the human body suggests they could be used as carriers for therapeutics and medical imaging reagents. This study provides the groundwork for the use of vaults in encapsulation and delivery applications.
Co-reporter:Marcella Yu, Benny C. Ng, Leonard H. Rome, Sarah H. Tolbert and Harold G. Monbouquette
Nano Letters 2008 Volume 8(Issue 10) pp:3510-3515
Publication Date(Web):September 20, 2008
DOI:10.1021/nl080536z
Vaults are ubiquitous, self-assembled protein nanocapsules with dimension in the sub-100 nm range that are conserved across diverse phyla from worms to humans. Their normal presence in humans at a copy number of over 10 000/cell makes them attractive as potential drug delivery vehicles. Toward this goal, bifunctional amine-reactive reagents are shown to be useful for the reversible cross-linking of recombinant vaults such that they may be closed and opened in a controllable manner.
Co-reporter:Erik K. Richman, Chris B. Kang, Torsten Brezesinski and Sarah H. Tolbert
Nano Letters 2008 Volume 8(Issue 9) pp:3075-3079
Publication Date(Web):August 15, 2008
DOI:10.1021/nl801759x
This paper describes the process of making ordered mesoporous silicon (Si) thin films. The process begins with mesoporous silica (SiO2) thin films that are produced via evaporation induced self-assembly (EISA) using sol−gel silica precursors with a diblock copolymer template. This results in a film with a cubic lattice of 15 nm diameter pores and 10 nm thick walls. The silicon is produced through reduction of the silica thin films in a magnesium (Mg) vapor at 675 °C. Magnesium reduction preserves the ordered pore−solid architecture but replaces the dense silica walls with 10−17 nm silicon crystallites. The resulting porous silicon films are characterized by a combination of low and high angle X-ray diffraction, combined with direct SEM imaging. The result is a straightforward route to the production of ordered nanoporous silicon.
Co-reporter:Abby Kavner;Hsiu-Ying Chung;Robert W. Cumberland;Jonathan B. Levine;Jenn-Ming Yang;Michelle B. Weinberger;Richard B. Kaner
Science 2007 Volume 318(Issue 5856) pp:1550
Publication Date(Web):07 Dec 2007
DOI:10.1126/science.1147704
Abstract
Dubrovinskaia et al. question our demonstration that rhenium diboride (ReB2) is hard enough to scratch diamond. Here, we provide conclusive evidence of a scratch through atomic force microscopy depth profiling and elemental mapping. With high hardness, high-bulk modulus, and the ability to withstand extreme differential stress, ReB2 and related materials should be investigated regardless of their cost, which is not prohibitive.
Co-reporter:Hsiu-Ying Chung;Michelle B. Weinberger;Abby Kavner;Jonathan B. Levine;Jenn-Ming Yang;Richard B. Kaner
Science 2007 Volume 316(Issue 5823) pp:436-439
Publication Date(Web):20 Apr 2007
DOI:10.1126/science.1139322
Abstract
The quest to create superhard materials rarely strays from the use of high-pressure synthetic methods, which typically require gigapascals of applied pressure. We report that rhenium diboride (ReB2), synthesized in bulk quantities via arc-melting under ambient pressure, rivals materials produced with high-pressure methods. Microindentation measurements on ReB2 indicated an average hardness of 48 gigapascals under an applied load of 0.49 newton, and scratch marks left on a diamond surface confirmed its superhard nature. Its incompressibility along the c axis was equal in magnitude to the linear incompressibility of diamond. In situ high-pressure x-ray diffraction measurements yielded a bulk modulus of 360 gigapascals, and radial diffraction indicated that ReB2 is able to support a remarkably high differential stress. This combination of properties suggests that this material may find applications in cutting when the formation of carbides prevents the use of traditional materials such as diamond.
Co-reporter:Andrew E. Riley
Research on Chemical Intermediates 2007 Volume 33( Issue 1-2) pp:111-124
Publication Date(Web):2007 January
DOI:10.1163/156856707779160816
In this work, we demonstrate the synthesis of semiconducting tin telluride inorganic/organic composite materials with nanoscale periodicity prepared using solution phase self-assembly. Oligomerization of anionic SnTe44− clusters by halogen-mediated tellurium elimination in the presence of surfactant leads to the formation of a meosotructured composite. The composites initially forms as a mixture of mesophases, usually some combination of a layered phase and a phase based on cylindrical building blocks. Post synthetic treatment leads to a solid-state structural change which converts the composites to a single mesophase architecture with a hexagonal honeycomb (p6mm) morphology on the nanometer length scale. A by product of this reaction, however, is bulk tellurium. Changes in the electronic structure of the materials during synthesis and solid-state restructuring are probed using electron spin resonance (ESR) spectroscopy.
Co-reporter:Andrew E. Riley Dr.;Scott D. Korlann;Erik K. Richman
Angewandte Chemie 2006 Volume 118(Issue 2) pp:
Publication Date(Web):28 NOV 2005
DOI:10.1002/ange.200501361
Anorganische Cluster-Anionen (Zintl-Ionen) wurden durch Übergangsmetalle in Gegenwart von Alkylammonium-Tensiden und Gold-Substraten zu nanostrukturierten dünnen Filmen vernetzt (siehe Bild), die hexagonale, kubische, lamellare und wurmförmige Phasen bilden. Die Filme sind laut optischer Messungen halbleitend, und die I-V-Kennlinien zeigen ein Gleichrichterverhalten an.
Co-reporter:Dong Sun, Andrew E. Riley, Ashley J. Cadby, Erik K. Richman, Scott D. Korlann
and Sarah H. Tolbert
Nature 2006 441(7097) pp:1126
Publication Date(Web):
DOI:10.1038/nature04891
Co-reporter:Andrew E. Riley, Scott D. Korlann, Erik K. Richman,Sarah H. Tolbert
Angewandte Chemie International Edition 2006 45(2) pp:235-241
Publication Date(Web):
DOI:10.1002/anie.200501361
Co-reporter:B. L. Kirsch;X. Chen;E. K. Richman;V. Gupta;S. H. Tolbert
Advanced Functional Materials 2005 Volume 15(Issue 8) pp:
Publication Date(Web):25 JUL 2005
DOI:10.1002/adfm.200400454
We examine the effects of controlling nanoscale architecture on the tensile properties of honeycomb-structured silica/polymer composite films. The hexagonal films are produced using evaporation-induced self-assembly and uniaxially strained using a home-built tensile testing apparatus. Significant differences in the yield strain, failure strain, and tensile moduli between the axes parallel and perpendicular to the film-deposition direction are observed for the thinnest films examined and are attributed to anisotropy in the film nanostructure that is further characterized with transmission electron microscopy and atomic force microscopy. For properly oriented composites, these films have tensile moduli comparable to the Young's modulus of bulk silica but exhibit failure strains that are about an order of magnitude larger than those seen in typical bulk-silica systems. The yielding and failure processes are explored using X-ray diffraction and optical microscopy and are characterized by irreversible changes in the nanoscale architecture. We show that tuning the nanoscale architecture can provide control over the tensile properties of composites, allowing for materials with combinations of stiffness and elasticity unachievable in the analogous bulk systems.
Co-reporter:D. Sun;C. W. Kwon;G. Baure;E. Richman;J. MacLean;B. Dunn;S. H. Tolbert
Advanced Functional Materials 2004 Volume 14(Issue 12) pp:
Publication Date(Web):9 DEC 2004
DOI:10.1002/adfm.200400056
In this paper, we explore the relationship between the nanoscale structure and electrochemical performance of nanoscale scrolls of vanadium oxides (vanadium oxide nanorolls). The vanadium oxide nanorolls, which are synthesized through a ligand-assisted templating method, exhibit different morphologies and properties depending upon the synthetic conditions. Under highly reducing conditions, nearly perfect scrolls can be produced which have essentially no cracks in the walls (well-ordered nanorolls). If the materials are produced under less reducing conditions, nanorolls with many cracks in the oxide walls can be generated (defect-rich nanorolls). Both types of samples were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoemission spectroscopy (XPS) to characterize their local structure, local redox state, and nanoscale structure. After ion-exchange to replace the templating ammonium ions with Na+, the ability of these materials to electrochemically intercalate lithium reversibly was investigated. In sweep voltammetry experiments, the well-ordered nanorolls showed responses similar to those seen in crystalline orthorhombic V2O5. In contrast, the defect-rich vanadium oxide nanorolls behaved electrochemically more like sol–gel-prepared vanadium oxide materials. Moreover, the specific capacity of the well-ordered nanorolls was about 240 mA h g–1 while that of the defect rich nanorolls was found to be as much as 340 mA h g–1 under these same conditions. Disorders on both the atomic and nanometer length scales are believed to contribute to this difference.
Co-reporter:B.L. Kirsch;S.H. Tolbert
Advanced Functional Materials 2003 Volume 13(Issue 4) pp:
Publication Date(Web):11 APR 2003
DOI:10.1002/adfm.200304267
In this work, we explore the high-temperature phase stability of isolated, alumina-coated zirconia nanocrystals with a goal of understanding how interfacial energy affects phase stability. Isolated tetragonal and hydrous amorphous zirconia colloids were synthesized and coated with alumina through the hydrolysis of aluminum isopropoxide. Alumina-coated samples exhibited phase behavior that was markedly different from that of the uncoated analogs. Uncoated tetragonal particles transformed to the monoclinic phase at 1100 °C while alumina-coated tetragonal particles did not transform until 1400 °C. Uncoated hydrous amorphous particles crystallized to the tetragonal phase after heating at 600 °C and transformed to the monoclinic phase after heating at 800 °C. Alumina-coated hydrous amorphous particles crystallized only after heating at 1050 °C, and transformed to the monoclinic phase after heating at 1400 °C. Differences in phase behavior are postulated to depend on the zirconia–alumina interface, which must be disrupted before zirconia particles can fuse and facilitate the tetragonal-to-monoclinic phase transition. By coating the nanocrystals with a thin alumina shell and studying the resultant phase stability, we explore the effect of reproducibly modified interfacial chemistry on phase behavior in nanoscale ceramic composites.
Co-reporter:A.E. Riley;G.W. Mitchell;P.A. Koutentis;M. Bendikov;P. Kaszynki;F. Wudl;S.H. Tolbert
Advanced Functional Materials 2003 Volume 13(Issue 7) pp:
Publication Date(Web):1 JUL 2003
DOI:10.1002/adfm.200304223
A 5,7-dioctadecylquinoxalinophenazine zwitterion 1 has been investigated to determine its thermal phase behavior. A combination of differential scanning calorimetry (DSC), variable temperature low- and high-angle X-ray diffraction (XRD), and deuterium solid-state NMR spectroscopy were used to characterize the different phases of the tetraazapentacene 1. This molecule is found to exist in a variety of crystalline solid phases between room temperature and 167 °C, with different room-temperature phases resulting from crystallization from solution compared with cooling from the melt. Interestingly, the molecule exhibits liquid-crystalline behavior at high temperatures, between 167 °C and 186 °C, above which it becomes an isotropic fluid. The presence of liquid-crystalline behavior in a zwitterionic system opens up the potential for the use of these or related molecules in optoelectronic switching.
Co-reporter:T.-Q. Nguyen;J. Wu;S. H. Tolbert;B. J. Schwartz
Advanced Materials 2001 Volume 13(Issue 8) pp:
Publication Date(Web):18 APR 2001
DOI:10.1002/1521-4095(200104)13:8<609::AID-ADMA609>3.0.CO;2-#
How fast does energy transfer along a conjugated polymer chain, and how fast between chains? A semiconducting polymer/mesoporous silica composite, which provides just enough space for one polymer chain per pore (see Figure), provides the answer through investigations of the polymer's luminescence anisotropy, with remarkable results.
Co-reporter:Hyungsuk K. D. Kim ; Laura T. Schelhas ; Scott Keller ; Joshua L. Hockel ; Sarah H. Tolbert ;Gregory P. Carman
Nano Letter () pp:
Publication Date(Web):February 11, 2013
DOI:10.1021/nl3034637
Here we demonstrate electric-field induced magnetic anisotropy in a multiferroic composite containing nickel nanocrystals strain coupled to a piezoelectric substrate. This system can be switched between a superparamagnetic state and a single-domain ferromagnetic state at room temperature. The nanocrystals show a shift in the blocking temperature of 40 K upon electric poling. We believe this is the first example of a system where an electric field can be used to switch on and off a permanent magnetic moment.
Co-reporter:Iris E. Rauda, Robert Senter and Sarah H. Tolbert
Journal of Materials Chemistry A 2013 - vol. 1(Issue 7) pp:NaN1427-1427
Publication Date(Web):2012/12/17
DOI:10.1039/C2TC00239F
Templating provides a powerful tool to control both shape and orientation in anisotopric nanomaterials. Here we utilize confinement of a (C6H5C2H4NH3)2SnI4 perovskite semiconductor within anodic-alumina nanochannels to convert this layered material into wire arrays composed of concentric multilayers. The semiconducting arrays exhibit reasonable charge-transport normal to the substrate, showing that space confinement can be used to both restructure and reorient nanophase materials.
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