Michael F. Toney

University of California, Berkeley, Berkeley, California, United States

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Publications (430)2558.8 Total impact

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    ABSTRACT: Conjugated polymers are widely used materials in organic photovoltaic devices. Owing to their extended electronic wave functions, they often form semicrystalline thin films. In this work, we aim to understand whether distribution of crystallographic orientations affects exciton diffusion using a low-band-gap polymer backbone motif that is representative of the donor/acceptor copolymer class. Using the fact that the polymer side chain can tune the dominant crystallographic orientation in the thin film, we have measured the quenching of polymer photoluminescence, and thus the extent of exciton dissociation, as a function of crystal orientation with respect to a quenching substrate. We find that the crystallite orientation distribution has little effect on the average exciton diffusion length. We suggest several possibilities for the lack of correlation between crystallographic texture and exciton transport in semicrystalline conjugated polymer films.
    ACS Applied Materials & Interfaces 08/2015; DOI:10.1021/acsami.5b02968 · 6.72 Impact Factor
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    ABSTRACT: Morphology control of solution coated solar cell materials presents a key challenge limiting their device performance and commercial viability. Here we present a new concept for controlling phase separation during solution printing using an all-polymer bulk heterojunction solar cell as a model system. The key aspect of our method lies in the design of fluid flow using a microstructured printing blade, on the basis of the hypothesis of flow-induced polymer crystallization. Our flow design resulted in a ∼90% increase in the donor thin film crystallinity and reduced microphase separated donor and acceptor domain sizes. The improved morphology enhanced all metrics of solar cell device performance across various printing conditions, specifically leading to higher short-circuit current, fill factor, open circuit voltage and significantly reduced device-to-device variation. We expect our design concept to have broad applications beyond all-polymer solar cells because of its simplicity and versatility.
    Nature Communications 08/2015; 6:7955. DOI:10.1038/ncomms8955 · 11.47 Impact Factor
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    ABSTRACT: The conclusions reached by a diverse group of scientists who attended an intense 2-day workshop on hybrid organic-inorganic perovskites are presented, including their thoughts on the most burning fundamental and practical questions regarding this unique class of materials, and their suggestions on various approaches to resolve these issues. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Advanced Materials 07/2015; 27(35). DOI:10.1002/adma.201502294 · 17.49 Impact Factor
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    ABSTRACT: The elevated level of atmospheric carbon dioxide (CO2) has caused serious concern of the progression of global warming. Geological sequestration is considered as one of the most promising techniques for mitigating the damaging effect of global climate change. Investigations over wide range of length-scales are important for systematic evaluation of the underground formations from prospective CO2 reservoir. Understanding the relationship between the micro morphology and the observed macro phenomena is even more crucial. Here we show Synchrotron based X-ray micro tomographic study of the morphological buildup of Sandstones. We present a numerical method to extract the pore sizes distribution of the porous structure directly, without approximation or complex calculation. We have also demonstrated its capability in predicting the capillary pressure curve in a mercury intrusion porosimetry (MIP) measurement. The method presented in this work can be directly applied to the morphological studies of heterogeneous systems in various research fields, ranging from Carbon Capture and Storage, and Enhanced Oil Recovery to environmental remediation in the vadose zone.
    Scientific Reports 06/2015; 5:10635. DOI:10.1038/srep10635 · 5.58 Impact Factor
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    Linda Y Lim · Shufen Fan · Huey Hoon Hng · Michael F Toney
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    ABSTRACT: Operando X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS) studies of Ge anodes are carried out to understand the effect of cycling rate on Ge phase transformation during charge/discharge process and to relate that effect to capacity. It is discovered that the formation of crystalline Li15Ge4 (c-Li15Ge4) during lithiation is suppressed beyond a certain cycling rate. A very stable and reversible high capacity of ≈1800 mAh g−1 can be attained up to 100 cycles at a slow C-rate of C/21 when there is complete conversion of Ge anode into c-Li15Ge4. When the C-rate is increased to ≈C/10, the lithiation reaction is more heterogeneous and a relatively high capacity of ≈1000 mAh g−1 is achieved with poorer electrochemical reversibility. An increase in C-rate to C/5 and higher reduces the capacity (≈500 mAh g−1) due to an impeded transformation from amorphous LixGe to c-Li15Ge4, and yet improves the electrochemical reversibility. A proposed mechanism is presented to explain the C-rate dependent phase transformations and the relationship of these to capacity fading. The operando XRD and XAS results provide new insights into the relationship between structural changes in Ge and battery capacity, which are important for guiding better design of high-capacity anodes.
    Advanced Energy Materials 06/2015; 5(15). DOI:10.1002/aenm.201500599 · 16.15 Impact Factor
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    ABSTRACT: A class of tunable, mesostructured self-assembled hydrogels has been developed based on a library of π–π stacking ABA-type telechelic triblock copolymers prepared by organocatalytic ring-opening polymerization (ROP). Poly(ethylene glycol) (PEG) served as a macroinitiator for ROP of methylene tricarbonate-benzyl ester (MTC-OBn), a benzyl-ester functionalized cyclic carbonate monomer, resulting in polymers with well-defined length and narrow polydispersity. Self-assembled hydrogels were formed by dissolving poly(MTC-OBn)-b-PEG-b-poly(MTC-OBn) copolymers in water. Physical cross-links in the hydrogels formed through hydrophobic and π–π stacking intermolecular interactions between poly(MTC-OBn) segments. The mesoscale material properties were probed using small angle X-ray scattering (SAXS) and dynamic mechanical measurements. SAXS spectra show a scattering peak, corresponding to a molecular domain spacing of 20–25 nm, which we attribute to the formation of electron-dense poly(MTC-OBn) assemblies. Results from oscillatory shear experiments were analyzed in conjunction with SAXS data in order to develop an understanding of the influence that nanoscale structure has on the mechanical properties of self-assembled gels. Modeling of scattering peaks using the Bragg spacing model demonstrated that the hydrophilic PEG network chains connecting the scattering moieties behaved as a two-dimensional self-avoiding walk. We compared the observed microstructural features with the mechanical properties of self-assembled gels and determined that the molecular weight of the polycarbonate and PEG segments controls the gel structure on both the mesoscale and macroscale. A central contribution of this work is a synthetic strategy that utilizes ROP to control polymer structure, which in turn controls both the structure and mechanical properties of these biodegradable self-assembled hydrogels.
    Polymer 05/2015; 65. DOI:10.1016/j.polymer.2015.03.029 · 3.56 Impact Factor
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    ABSTRACT: The solution shearing method has previously been used to tune the molecular packing and crystal thin film morphology of small molecular organic semiconductors (OSCs). Here, we study how the solution shearing method impacts the thin film morphology and causes structural rearrangements of two polymeric OSCs with interdigitated sidechain packing, namely P2TDC17FT4 and PBTTT-C16. The conjugated backbone tilt angle and the thin film morphology of the P2TDC17FT4 polymer were changed by the solution shearing conditions, and an accompanying change in the charge carrier mobility was observed. For PBTTT-C16, the out-of-plane lamellar spacing was increased by solution shearing, due to increased disorder of side chains. The ability to induce structural rearrangement of polymers through solution shearing allows for an easy and alternative method to modify OSC charge transport properties.
    Chemistry of Materials 04/2015; 27(7):2350-2359. DOI:10.1021/cm503780u · 8.35 Impact Factor
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    ABSTRACT: Vapor-deposited organic glasses can be produced with enhanced thermal stability and tunable molecular orientation by controlling the substrate temperature during deposition. Recent work has also shown improved charge carrier mobility associated with anisotropic molecular packing in organic electronics. Here grazing-incidence wide angle x-ray scattering (GIWAXS) is used to characterize the structural anisotropy in glasses of a hole transport material, N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine, commonly referred to as TPD. The TPD glasses were prepared by physical vapor deposition at substrate temperatures between 0.79 Tg and 0.98 Tg, where Tg is the glass transition temperature. A GIWAXS-derived orientation order parameter is used to quantify the anisotropy observed in the scattering patterns of the glasses. The GIWAXS-order parameter exhibits both positive and negative values as a function of substrate temperature, indicating either face-on or edge-on packing, and correlates well with a spectroscopic ellipsometry-derived order parameter that is sensitive to molecular orientation. We propose molecular packing arrangements based on the combination of the two order parameters and explore the relationship between kinetic stability and glass structure.
    Chemistry of Materials 04/2015; 27(9):150413092114002. DOI:10.1021/acs.chemmater.5b00583 · 8.35 Impact Factor
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    ABSTRACT: The reversible electrochemical insertion of multivalent ions into materials has promising applications in many fields, including batteries, seawater desalination, element purification, and wastewater treatment. However, finding materials that allow for the insertion of multivalent ions with fast kinetics and stable cycling has proven difficult because of strong electrostatic interactions between the highly charged insertion ions and atoms in the host framework. Here, an open framework nanomaterial, copper hexacyanoferrate, in the Prussian Blue family is presented that allows for the reversible insertion of a wide variety of monovalent, divalent, and trivalent ions (such as Rb+, Pb2+, Al3+, and Y3+) in aqueous solution beyond that achieved in previous studies. Electrochemical measurements demonstrate the unprecedented kinetics of multivalent ion insertion associated with this material. Synchrotron X-ray diffraction experiments point toward a novel vacancy-mediated ion insertion mechanism that reduces electrostatic repulsion and helps to facilitate the observed rapid ion insertion. The results suggest a new approach to multi­valent ion insertion that may help to advance the understanding of this complex phenomenon.
    Advanced Energy Materials 04/2015; 5(12). DOI:10.1002/aenm.201401869 · 16.15 Impact Factor
  • Elyse Coletta · Michael F. Toney · Curtis W. Frank
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    ABSTRACT: An understanding of the structure and properties of polymer electrolyte systems can be crucial to a variety of different applications. The current work performs a study of the composition, structure and properties of poly(ethylene glycol) (PEG)-aromatic polyimide systems incorporating ionic liquids that are relevant to several applications especially fuel cell membranes. Composition was varied through using different aromatic dianhydrides, aromatic diamines and in some cases synthesis solvent. Properties were characterized using Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, small-angle x-ray scattering, electrochemical impedance spectroscopy and cyclic voltammetry. By varying solvent, aromatic regularity and expected rigidity can be tuned, impacting average conductivity by 30%. Varying the aromatic diamine can influence the length scale and amount of aromatic regularity, which can ultimately affect the conductivity by a factor of four. The maximum conductivity reached was 83 mS/cm at 80 °C and 70 %RH. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015
    Journal of Polymer Science Part B Polymer Physics 04/2015; 53(7). DOI:10.1002/polb.23664 · 3.83 Impact Factor
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    ABSTRACT: There is high demand for efficient, robust and automated routines for tomographic data reduction, particularly for synchrotron data. Registration of the rotation axis in data processing is a critical step affecting the quality of the reconstruction and is not easily implemented with automation. Existing methods for calculating the center of rotation have been reviewed and an improved algorithm to register the rotation axis in tomographic data is presented. The performance of the proposed method is evaluated using synchrotron-based microtomography data on geological samples with and without artificial reduction of the signal-to-noise ratio. The proposed method improves the reconstruction quality by correcting both the tilting error and the translational offset of the rotation axis. The limitation of this promising method is also discussed.
    Journal of Synchrotron Radiation 03/2015; 22(2). DOI:10.1107/S160057751402726X · 2.74 Impact Factor
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    ABSTRACT: Rapid thermal processing (RTP) is widely used for processing a variety of materials, including electronics and photovoltaics. Presently, optimization of RTP is done primarily based on ex-situ studies. As a consequence, the precise reaction pathways and phase progression during the RTP remain unclear. More awareness of the reaction pathways would better enable process optimization and foster increased adoption of RTP, which offers numerous advantages for synthesis of a broad range of materials systems. To achieve this, we have designed and developed a RTP instrument that enables real-time collection of X-ray diffraction data with intervals as short as 100 ms, while heating with ramp rates up to 100 °Cs−1, and with a maximum operating temperature of 1200 °C. The system is portable and can be installed on a synchrotron beamline. The unique capabilities of this instrument are demonstrated with in-situ characterization of a Bi2O3-SiO2 glass frit obtained during heating with ramp rates 5 °C s−1 and 100 °C s−1, revealing numerous phase changes.
    Review of Scientific Instruments 02/2015; 86(1):013902. DOI:10.1063/1.4904848 · 1.61 Impact Factor
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    ABSTRACT: We observed a thermotropic phase transition in poly[3,4-dihexyl thiophene-2,2':5,6'-benzo[1,2-b:4,5-b']dithiophene] (PDHBDT) thin films accompanied by a transition from a random orientation to an ordered lamellar phase via a nearly-hexagonal lattice upon annealing. We demonstrate the effect of temperature-dependent molecular packing on charge carrier mobility (µ) in organic field-effect transistors (OFETs) and photovoltaic characteristics, such as exciton diffusion length (L<sub>) and power conversion efficiency (PCE), in organic solar cells (OSCs) using PDHBDT. The µ was continuously improved with increasing annealing temperature and PDHBDT films annealed at 270 oC resulted in a maximum µ up to 0.46 cm2/V∙s (µavg = 0.22 cm2/V∙s), which is attributed to the well-ordered lamellar structure with close a π-π stacking distance of 3.5 Å as shown by grazing incidence-angle X-ray diffraction (GIXD). On the other hand, PDHBDT films with a randomly orientated molecular orientation are more effective in photovoltaic devices than films with an ordered hexagonal or lamellar phase based on current-voltage characteristics of PDHBDT/C60 bilayer solar cells. This observation corresponds to an enhanced dark current density (JD) and a decreased LD upon annealing. This study provides insight into the dependence of charge transport and photovoltaic characteristics on molecular packing in polymer semiconductors, which is crucial for the management of charge and energy transport in a range of organic optoelectronic devices.
    Chemistry of Materials 02/2015; 27(4):150201103427005. DOI:10.1021/cm503773j · 8.35 Impact Factor
  • Johanna Nelson Weker · Michael F. Toney
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    ABSTRACT: Electrical vehicles (EVs) are an attractive option for moving towards a CO2 neutral transportation sector, but in order for widespread commercial use of EVs, the cost of electrical energy storage (i.e., batteries) must be reduced and the energy storage capacity must be increased. New, higher performing but Earth abundant electrodes are needed to accomplish this goal. To aid the development of these materials, in situ characterization to understand battery operation and failure is essential. Since electrodes are inherently heterogeneous, with a range of relevant length scales, imaging is a necessary component of the suite of characterization methods. In this Feature Article, the rapidly growing and developing field of X-ray based microscopy (XM) techniques is described and reviewed focusing on in situ and operando adaptations. Further, in situ transmission electron microscopy (TEM) is briefly discussed in this context and its complement to XM is emphasized. Finally, a perspective is given on some emerging X-ray based imaging approaches for energy storage materials.
    Advanced Functional Materials 02/2015; 25(11):n/a-n/a. DOI:10.1002/adfm.201403409 · 11.81 Impact Factor
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    ABSTRACT: Much is known about the rate of photoexcited charge generation in at organic donor/acceptor (D/A) heterojunctions overaged over all relative arrangements. However, there has been very little experimental work investigating how the photoexcited electron transfer (ET) rate depends on the precise relative molecular orientation between D and A in thin solid films. This is the question that we address in this work. We find that the ET rate depends strongly on the relative molecular arrangement: The interface where the model donor compound copper phthalocyanine is oriented face-on with respect to the fullerene C60 acceptor yields a rate that is approximately 4 times faster than that of the edge-on oriented interface. Our results suggest that the D/A electronic coupling is significantly enhanced in the face-on case, which agrees well with theoretical predictions, underscoring the importance of controlling the relative interfacial molecular orientation.Keywords: organic photovoltaic; core-hole clock; resonant photoemission; charge-transfer state; electron dynamics; resonant Auger
    Journal of Physical Chemistry Letters 01/2015; 6(1):6-12. DOI:10.1021/jz502253r · 7.46 Impact Factor
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    ABSTRACT: Secondary phase segregation is hypothesized to have detrimental impacts on Cu2ZnSnS4 (CZTS) thin-film solar cells. In this study, we demonstrate the potential of using kinetic stabilization to inhibit phase decomposition in CZTS. By growing CZTS films at low temperature, we achieve a kinetically stabilized alloy with an expanded solid solution window in the pseudoternary CuS-ZnS-SnS phase diagram. Using X-ray absorption spectroscopy, we study the structural evolution and stability of this metastable alloy upon annealing. For near-stoichiometric samples, we observe a continuous emergence of short-range order toward crystalline CZTS that is nearly complete after a 1-min anneal at 450 °C. For Zn-rich samples, we detect precipitation of ZnS upon annealing, which suggests that the excess Zn exists as cation antisite defects in metastable CZTS.
    IEEE Journal of Photovoltaics 01/2015; 5(1):372-377. DOI:10.1109/JPHOTOV.2014.2360334 · 3.17 Impact Factor
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    ABSTRACT: Organo-metal halide perovskites are an intriguing class of materials that have recently been explored for their potential in solar energy conversion. Within a very short period of intensive research, highly efficient solar cell devices have been demonstrated. One of the heavily debated questions in this new field of research concerns the role of chlorine in solution-processed samples utilizing lead chloride and 3 equiv of methylammonium iodide to prepare the perovskite samples. We utilized a combination of X-ray photoelectron spectroscopy, X-ray fluorescence, and X-ray diffraction to probe the amount of chlorine in samples before and during annealing. As-deposited samples, before annealing, consist of a crystalline precursor phase containing excess methylammonium and halide. We used in situ techniques to study the crystallization of MAPbI3 from this crystalline precursor phase. Excess methylammonium and chloride evaporate during annealing, forming highly crystalline MAPbI3. However, even after prolonged annealing times, chlorine can be detected in the films in X-ray fluorescence measurements.
    Chemistry of Materials 12/2014; 26(24). DOI:10.1021/cm503828b · 8.35 Impact Factor
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    ABSTRACT: The use of small volumes of a high boiling point liquid as a “solvent additive” is a deposition processing method that has been implemented in most high/record performing polymer:fullerene-based bulk heterojunction (BHJ) solar cell devices. Recently, solvent additive processing has been employed in a solution processable small molecule (SPSM) BHJ system, viz., 5,5′-bis{(4-(7-hexylthiophen-2-yl)thiophen-2-yl)-[1,2,5]thiadiazolo[3,4-c]pyridine}3,3′-di-2-ethylhexylsilylene-2,2′-bithiophene:[6,6]-phenyl C71 butyric acid methyl ester (p-DTS(PTTh2)2:PC71BM), when a small amount, 0.25 v/v %, diiodooctane (DIO) was added to the casting solution, several key device metrics increased, leading to a high power conversion efficiency (PCE) of 6.7%. X-ray diffraction experiments show that the amount of additive added to the casting solution to make p-DTS(PTTh2)2:PC71BM thin films has several effects on the structure at multiple length scales: for example, the number and orientation of p-DTS(PTTh2)2 crystallites, different π–π stacking distances, and the nanoscale domain size. Additionally, we utilize energy filtered transmission electron microscopy (EFTEM), a technique that significantly enhances the contrast between p-DTS(PTTh2)2 and PC71BM in real space, to further verify the effect of increasing domain size as the additive concentration is increased. Tomographic reconstruction of the TEM micrographs provides a 3D representation of the BHJ structure. These studies show how domain size and tortuosity in all dimensions change due to solvent additive processing, and the overall finding is that the nanostructures of p-DTS(PTTh2)2 have enhanced connectivity when 0.25 v/v % DIO was used. Finally, we show evidence of solvent additive retention in p-DTS(PTTh2)2:PC71BM films when 1 v/v % DIO is used (but absent for 0.25%). This finding, in conjunction with the appearance of two populations of π–π stacking distances when 1 v/v % DIO is used, leads to the identification of one of the specific points of interaction between DIO and p-DTS(PTTh2)2.
    Chemistry of Materials 11/2014; 26(22-22):6531-6541. DOI:10.1021/cm5031987 · 8.35 Impact Factor
  • E. Coletta · M.F. Toney · C. W. Frank
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    ABSTRACT: Polymer electrolyte membrane (PEM) fuel cells can provide alternatively sourced energy, but current PEMs lose performance under certain conditions. The current work examines composition, structure and properties of poly (ethylene glycol)-aromatic polyimide-ionic liquid systems for PEM applications, as poly (ethylene glycol) (PEG) is an ion conductor and polyimides are stable. To evaluate polymer interactions, different PEG concentrations (0-50% by weight) and different PEG molecular weights (990-6000 g/mole) were examined. Characterization techniques included Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, small-angle x-ray scattering, electrochemical impedance spectroscopy and cyclic voltammetry. By increasing the PEG amount, PEG domains and polymer flexibility are increased, which increases conductivity by two to three orders of magnitude. By increasing PEG molecular weight, PEG segmental motion and PEG-polyimide interface quality are decreased, which decreases conductivity by a factor of two. The maximum conductivity was 64 mS/cm at 80 degrees C and 70 %RH.
    Polymer 11/2014; 55(26). DOI:10.1016/j.polymer.2014.10.075 · 3.56 Impact Factor
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    ABSTRACT: The crystallization and electrical characterization of the semiconducting polymer poly(3-hexylthiophene) (P3HT) on a single layer graphene sheet is reported. Grazing incidence X-ray diffraction revealed that P3HT crystallizes with a mixture of face-on and edge-on lamellar orientations on graphene compared to mainly edge-on on a silicon substrate. Moreover, whereas ultrathin (10 nm) P3HT films form well oriented face-on and edge-on lamellae, thicker (50 nm) films form a mosaic of lamellae oriented at different angles from the graphene substrate. This mosaic of crystallites with π–π stacking oriented homogeneously at various angles inside the film favors the creation of a continuous pathway of interconnected crystallites, and results in a strong enhancement in vertical charge transport and charge carrier mobility in the thicker P3HT film. These results provide a better understanding of polythiophene crystallization on graphene, and should help the design of more efficient graphene based organic devices by control of the crystallinity of the semiconducting film.
    Advanced Functional Materials 11/2014; 25(5). DOI:10.1002/adfm.201403418 · 11.81 Impact Factor

Publication Stats

16k Citations
2,558.80 Total Impact Points


  • 2013
    • University of California, Berkeley
      Berkeley, California, United States
    • Diamond Light Source
      XPW, England, United Kingdom
    • Harvard University
      • Department of Chemistry and Chemical Biology
      Cambridge, Massachusetts, United States
  • 2012
    • King Abdullah University of Science and Technology
      Djidda, Makkah, Saudi Arabia
  • 2009–2012
    • National Institute of Standards and Technology
      • Polymers Division
      Maryland, United States
  • 1993–2012
    • Stanford University
      • • Department of Chemical Engineering
      • • Department of Materials Science and Engineering
      Palo Alto, California, United States
  • 2011
    • Carnegie Mellon University
      • Department of Materials Science and Engineering
      Pittsburgh, Pennsylvania, United States
  • 2007
    • Palo Alto Research Center
      Palo Alto, California, United States
    • University of Houston
      • Department of Chemical & Biomolecular Engineering
      Houston, Texas, United States
  • 2006
    • Pacific Northwest National Laboratory
      Ричленд, Washington, United States
  • 2005
    • New Jersey Institute of Technology
      • Department of Physics
      Newark, New Jersey, United States
  • 2004
    • University of Minnesota Duluth
      • Department of Chemistry and Biochemistry
      Duluth, Minnesota, United States
  • 1999
    • Sogang University
      Sŏul, Seoul, South Korea
  • 1998
    • University of Wales
      Cardiff, Wales, United Kingdom
  • 1995
    • William Penn University
      Worcester, Massachusetts, United States
  • 1991–1994
    • University of Washington Seattle
      • Department of Physics
      Seattle, Washington, United States