David C. Martin, Ph.D. - US grants

They propose a scheme to construct and characterize the structure and properties of polymer grain boundaries in a controlled manner. The essential idea is to carefully and systematically establish the influence of well-defined, specific grain boundary defects on the physical properties of polymers. Conventionally processed crystalline polymers have small crystallites (10-20 nm), which implies a large defect density in the solid state. Although this means that structural defects play an important or even dominant role in polymer systems, it also makes it difficult to isolate the effect of a particular devect on a macroscopically observed property. However, the development of solid-state and thin-film polymerization mechanisms have facilitated the synthesis of highly organized and ordered polymers. These systems provide a unique opportunity to isolate and investigate in detail the structure of covalently bonded solids near defects and the effect of these defects on the properties of the material. They will examine structure-property relationships in poly(diacetylene) thin films and crystals. They describe procedures for growing crystals of diacetylene monomers, joining these together to make a grain boundary, and then polymerizing through the grain boundary by exposure to Co60 radiation. With this approach it will be possible to prepare "polymer bicrystals". A simple scheme for measuring the photoconductive response of these bicrystals will be used, a transport property which should depend on the structure of the boundary. Structural characterization involving X-ray scattering and Transmission Electron Microscopy (TEM) will be also carried out.

The research to be undertaken includes: ultrastructural studies of solid polymers and polymer composites including dislocations, disclinations, and grain boundaries; thermodynamics and kinetics of phase transitions; the organization of macromolecules near surfaces and interfaces; molecular mechanisms of plastic deformation; and morphology of synthetic poly(peptides).

9412254 This award will permit the principal investigator to acquire modern x-ray equipment that will be used for the study of polymer crystals. The University of Michigan is sharing the cost of this acquisition. %%% ***

This ultra-low load indentation instrument will provide excellent capability for highly spatially resolved, ultralow load indentation on a wide variety of materials, and will enable a significant enhancement and extension of existing NSF-sponsored research aimed at understanding and improving the mechanical and physical properties of advanced materials and materials systems. There is immediate need for this capability in a large number of university research activities that span a wide spectrum of materials that are synthesized by a variety of advanced techniques. The commonality of these activities, with respect to the proposed instrumentation acquisition, is that the materials under study either involve extremely small microstructural scale or are synthesized in small quantities or with small bulk dimensions (e.g. thin films, microlaminates and coatings) that severely limit the use of conventional experimental methods for the study of synthesis/structure/property relationships. Examples include, ductile phase toughening in metal/oxide microlaminates produced by ion beam deposition, film softening effects in intermetallics and refractory metals and the role of low energy ion beam assisted deposition on the synthesis and properties of carbon nitride. Other studies involve examination of the relationships between mechanical behavior and cooperative molecular relaxations in polymers to fundamental studies of mechanical properties and microstructure in ordered polymers and an investigation of the influence of damage accumulation processes during fatigue of ceramic matrix composites.

9707975 Martin This research project will investigate the microstructure and macroscopic properties of specific grain boundary defects in crystalline, semiconducting polymer materials. The long-term goal of this work is to isolate individual grain boundaries so that their microstructure and influence on macroscopic properties can be determined unambiguously. "Polymer bicrystals" make it possible to examine the mechanical and electrical properties of these materials as a function of defect geometry. Measurements of the mechanical strength and photocurrent transport both decrease with increasing misorientation between component grains. These properties measurements are corroborated by structural investigations using opticalmicroscopy, scanning electron microscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and white-beam synchrotron X-ray topography (WBSXT). The current research project will involve (1) investigations of new materials of current interest for device applications, (2) processing schemes for introducing defects into crystalline organic semiconductors in a controlled manner, (3) structural characterization by transmission electron microscopy, electron diffraction, and WBSXT, and (4) measurements of macroscopic properties by mechanical and electrical testing. Of particular scientific and technological interest is the manner in which carrier transport and mechanical deformation is accommodated across individual grain boundaries. The manner in which slip deformation is accommodated across the engineered grain boundary interfaces as a function of tilt and twist misorientation angle will be investigated. From these results we will learn about the manner in which planes of oriented polymer molecules laterally translate by what are expected to be dislocatio n-mediated mechanisms of slip. %%% This research should provide an insight into the defect- limited behavior of ordered polymer and organic solids. These efforts will provide fundamental information about the relationship between microstructure and macroscopic properties of these materials in the solid-state. Optoelectrically active polymers are of considerable interest for devices such as thin film transistors, flat panel displays, chemical sensors, and injection lasers. Recent publications have identified the critical role of grain boundary defects in limiting the performance of these flexible, organic-based electronic devices for low cost, large scale applications. ***

9704175 Martin This award provides support for the acquisition of a Gatan Imaging Filter (GIF) accessory for the JEOL 4000 EX High Resolution Transmission Electron Microscope (HREM) located in the University of Michigan Electron Microbeam Analysis Laboratory (EMAL). The GIF consists of a curved magnetic sector lens that acts as a prism to disperse the transmitted electron beam as a function of energy. The dispersed beam can then be filtered to create images or diffraction patterns from selected portions of the electron energy loss spectra. This instrument would significantly enhance the microanalytical capabilities of the electron optics instrumentation at EMAL. Additional functionality provided by the GIF which is not presently available includes: (1) high resolution elemental and electronic state mapping of low atomic number elements, (2) improved contrast of polymer and organic thin films on substrates, (3) improved electron diffraction analysis by removal of inelastically scattered radiation, and (4) improved contrast in convergent beam electron diffraction patterns. Research underway in our laboratory which wi11 directly benefit from this acquisition includes the construction and characterization of grain boundary defects in optoelectronically active ordered polymers; the synthesis, and processing and characterization of thermally reactive benzocyclobutene functionalized polymers; the processing and microstructure of genetically engineered polypeptides for biocompatibility of micromachined silicon sensors for neural prosthetics, and the microstructure of polymers and polymer composites near surfaces. The instrument will also provide useful capabilities for other research projects in Materials Science and Engineering, Chemical Engineering, and Nuclear Engineering and Radiological Sciences departments, as detailed in the text of the proposal. %%% The GIF will provide an enhancement of the electron optics facility at EMAL, directly influencing the re search opportunities available for students, staff, and faculty who use these instruments. It will also be used in the curriculum as part of the laboratory sessions for graduate and undergraduate courses in Microstructure of Materials (MSE 460, MSE 560, and MSE 662). The GIF will also be used in summer short courses on Polymer Microscopy offered through the University of Michigan Continuing Engineering Education program. ***

Curvature deformations have been previously observed in thin films of optoelectronically active polymers and in single crystals showing uniform twist. However, the detailed manner in which three-dimensionally ordered polymer and molecular crystals are distorted by curvature remains to be clearly established. Direct imaging of the mechanisms of curvature will obtained using low dose high-resolution electron microscopy (HREM). Samples of organic molecular and polymer crystals with a variety of degrees of curvature will be prepared by depositing droplets onto solid surfaces, evaporating droplets in a column, electrospinning samples into nanometer diameters with oscillations in diameter, and by electric-field alignment of thin silicon nitride membranes. HREM images of the lattice spacings both parallel and perpendicular to the direction of curvature will be obtained and examined in detail. Theoretical considerations show that by examining the distance between partial dislocations that mediate curvature, and by measuring the characteristic distance between stacking faults, it is possible obtain estimates of the stacking fault energy on various crystallographic planes. These result will be compared with the predicted geometric distortions in the vicinity of the dislocation core as obtained by molecular modeling.
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The results of this work will be useful in the design, synthesis, and processing of new organic materials with precisely controlled nanostructures. This research will facilitate the ongoing development of inexpensive, soft electronic devices. By elucidating the detailed means by lattice curvature is accommodated in synthetic molecular crystals, it should also be possible to learn how natural biological systems develop useful structures with similar symmetries.

OIA-0116331
PI: Solomon
Abstract

The PI and six colleagues in the Departments of Chemical engineering, Materials Science and Engineering, Biomedical Engineering, and Electrical and Computer Engineering at the University of Michigan are requesting funds to purchase a confocal laser scanning microscope. This will enhance their research and research training in nanoscale engineering of complex fluids and biomaterials. Specifics proposed applications of the instrument are: to quantify defect dynamics during annealing of colloidal crystals, to detect self-assembled proteins, to observe microfluidic flows on cellular development, and to facilitate the efficient design of microfabricated devices.

This grant provides support for the acquisition of a high resolution Transmission Electron Microscope (HRTEM) for the University of Michigan Electron Microbeam Analysis Laboratory (EMAL). High-resolution electron microscopy (HREM) has become a critical technique in the characterization of nanostructured materials at the University of Michigan (U of M). EMAL equipment is available to all research groups on campus, outside university researchers and to industry. This instrument will become the primary HREM for materials research in EMAL. In the past 15 years, over 50 research groups, from within the U of M, other universities and industry, have used the existing, outdated electron microscope. Through this usage, their research has resulted in more than 1150 publications at the U of M, and more than 350 graduate students at the U of M have used the old equipment for a major portion of their thesis research. The new instrument will provide essential capabilities to the University's research programs, attract new research programs, and allow more advanced training of graduate students in HREM. The new HREM will be an essential part of numerous materials research programs across campus, involving 14 faculty from several departments including Materials Science and Engineering, Nuclear Engineering and Radiological Sciences, Chemical Engineering, Physics and Geological Sciences.

This new high resolution electron microscope (HREM) will allow the research community to more effectively pursue their studies of materials at the nanoscale, while also promoting the teaching, training and learning of the graduate and undergraduate students. About 40 students and post-docs actively use HREM in their research. Most faculty, who use the HREM have undergraduate students in their research groups actively working on characterization of materials. Summer high school interns are also able to participate in research and laboratory management. The new instrument will be used in summer research projects for minority high school students and young women. The new instrument will be available to any researcher on campus who needs these new capabilities.

The project will lead to the acquisition of a X-ray photoelectron spectroscopy (XPS) instrument, which represents a major advance in commercially available instrumentation. XPS has become a critical technique in the characterization of the chemical composition, oxidation and bonding states in various materials, including polymers, catalysts, metals, and semiconductors. The XPS instrument will provide real time chemical state and elemental imaging capabilities using the full range of pass energies and multi-point analysis from either real time or scanned images without the need for sample translation. The instrumentation further comes with the ability to obtain data over a large field of view, while maintaining photoelectron and Auger peak positions. The initial research foci of the instrument will include fundamental studies of: designer surfaces for biomedical applications; advanced micro-probes for neural prostheses; chemo-mechanical nanopatterning of polymer substrates for cell culture; surface-modified nano-fibrous scaffolds for tissue engineering applications; surface-modified microfabricated chemical analysis devices; controlled anchoring of DNA molecules at chemically tailored surfaces; coaxial semiconductor nanowires; smart surfaces assembled from molecular switches; directed self assembly of nanostructures by focused ion beam patterning; fuel processors for PEM fuel cells; lean NOx traps for automotive emission control; semiconductor alloy surfaces; surfaces and interfaces for electronic devices; and GaInNAs for high efficiency solar cells. The instrument will also have broad impact upon the research and educational infrastructure at U of M. Most faculty involved in the project have Undergraduate Research Opportunities Program (UROP) and Research Experience for Undergraduates (REU) students in their research groups actively working on characterization of materials. The instrument will be used in summer research projects for minority high school students and young women. For example, a number of students from under-represented groups participating in the NASA Summer High School Apprenticeship Program (SHARP) have worked on projects with instruments at the University of Michigan's Electron Microbeam Analysis Laboratory (EMAL), which will be the home of the new XPS instrument. As soon as the proposed instrument is installed, it will be included in this program.

The project will lead to the acquisition of a X-ray photoelectron spectroscopy (XPS) instrument with advanced capabilities. XPS has become a critical technique in the surface characterization of various materials, including polymers, catalysts, metals, and semiconductors. The XPS instrument will enable the real time chemical state and elemental imaging of surfaces. In essence, it will allow us to determine and image the chemical composition of the outermost layers of a material. Initially, the instrumentation will support research in the areas of biomaterials, surface science, nanoscience, catalysis, and fuel cells. The instrument will also have broad impact upon the research and educational infrastructure at U of M. The new XPS instrument will be used in the undergraduate and graduate curriculum, as well as in summer research projects for minority high school students and young women.

TECHNICAL SUMMARY:

There is intense continuing interest in the use of polymer and organic molecular materials for the construction of a variety of optoelectronically-active devices. Despite the importance of these materials, the relationship between the morphology of the organic molecular film and its macroscopic properties remains incompletely understood. The nature of the structural defects in organic molecular crystals and their influence on macroscopic properties still needs to be determined in detail. Because of the extended molecular connectivity of these solids, the energetics, structure, and mobility of the grain boundary (2-D), dislocation (1-D), and vacancy (0-D) defects can be quite different than those seen in inorganic crystals. We have been focusing on fundamental studies of specific defect structures and properties in organic molecular and polymer materials that are optoelectronically active. Most recently, we have investigated the processing and structure of TIPS-pentacene, a soluble variant that packs with the acene rings face-to-face. We have developed Low Dose High Resolution Electron Microscopy (HREM) imaging techniques for the direct observation of defect microstructures in crystalline and liquid crystalline polymers and organic molecular films. We now propose additional studies on the structure and properties of pentacene variants with functionalities designed to better control their solid-state packing and macroscopic properties. We will concentrate our efforts on a series of pentacene derivatives designed to enhance solubility in organic solvents, stabilize the formation of liquid crystalline mesophases, and promote face-to-face packing between the acene rings in the solid-state. The structural characterization of these new materials will take advantage of a variety of instrumentation available at the University of Michigan including Optical Microscopy, Wide and Small Angle X-ray Scattering, Scanning Electron Microscopy, Scanned Probe Microscopy, and Transmission Electron Microscopy. The intellectual merit of this proposal is its focus on the characteristic morphologies and defect structures of a new series of highly crystalline, functionalized pentacene derivatives of interest for organic electronic devices. We will determine relationships between the microstructure and the macroscopic properties of these new materials. We expect that our results will continue to be useful for optimizing processing conditions of existing materials and for motivating future molecular designs.

NON-TECHNICAL SUMMARY:

There is considerable interest in the development of organic molecular and polymer materials for "plastic electronic" applications such as radio-frequency identification tags, flexible displays, and biosensors. This project will investigate the detailed microstructure of these materials using advanced microscopic techniques available at the University of Michigan. The information obtained will make it possible to design new materials with enhanced performance. The project will involve full-time support for a graduate student in Materials Science and Engineering, and will also provide research experience for undergraduates through the University Research Opportunity Program (UROP), the Marian Sarah Parker program for female engineering students, the Minority Engineering Program Office (MEPO), the NASA/Sharp summer program for high school students, and an outreach summer research program with Greenhills High School in Ann Arbor.

ABSTRACT: Defect Structures and Properties of Liquid Crystalline Polymer Semiconductors, DMR-0802655, Prof. David C. Martin, The University of Michigan, Department of Materials Science and Engineering.

TECHNICAL SUMMARY

Polymer and organic molecular semiconductors are of considerable interest for creating inexpensive electronic devices. Previous studies of polycrystalline organic molecular films have shown evidence that grain boundary defects play an important role in limiting the performance of these materials. However the detailed relationship between the microstructure and macroscopic properties of these materials remains obscure and controversial. Liquid crystalline polymer and organic molecular semiconductors are of particular current interest, because it is expected that the more modest distortions near grain boundaries and other defects in the solid-state may not lead to the large reductions in properties seen in polycrystalline films. The microstructure of liquid crystalline polymer and organic molecular semiconductors will be investigated using an array of instruments and techniques including optical microscopy, wide angle X-ray diffraction, small angle X-ray diffraction, scanned probe microscopy, scanning electron microscopy, transmission electron microscopy, low voltage electron microscopy, and high resolution electron microscopy. These microstructural details will be correlated with information about sample performance on thin-film transistor devices, and with impedance spectroscopy of the carrier transport. The fundamental scientific challenge is to determine if and how the increased order provided by liquid crystalline order makes it possible to create films that have better performance than either the amorphous or polycrystalline structures seen in other organic molecular solids.


NON-TECHNICAL SUMMARY

There is considerable interest and future potential in developing new materials for all-organic "plastic" electronics. Examples of such devices include soft, flexible computers and displays printed on flexible substrates, and biomedical components that can be directly implanted into the body. However there are many important questions about these materials that are not yet known, such as the detailed relationship between their local structure and the properties that they exhibit when used in devices. This research project will make it possible to develop improved materials that can be easily and inexpensively processed and manufactured into components. This project will provide for financial support for graduate students from Materials Science, Macromolecular Science, and Biomedical Engineering. Research opportunities for undergraduate students will be provided through the University Research Opportunity Program, the Sarah Marian Parker Women in Engineering and the Minority Engineering Programs. We also have summer students from high schools in the Ann Arbor area. Established collaborations and interactions will be continued with colleagues at the University of Michigan, the University of Kentucky, Georgia Tech, the Fraunhofer Institute in Bremen, Germany, the National Institute of Science and Technology, Chulalongkorn University in Bangkok, Thailand, the University of Wollongong, Australia, and Suwan University in Seoul, South Korea. Industrial interactions will be extended with companies including Ford Motor Company (Dearborn, MI), Cochlear (Australia), BioControl (Israel), Plexon (Dallas, TX), Biotectix (Quincy, MA) and NeuroNexus (Ann Arbor, MI).

DESCRIPTION (provided by applicant): Project Summary / Abstract - Perhaps the most important problem limiting the performance and utility of electronic biomedical devices that are implanted in tissue is the reactive response near the electrode that limits performance over extended periods of time. In the cortex, this is known to involve the activation of microglia and astrocytes, and the associated die-off of target cells (neurons) in a region of ~100 microns proximal to the probe surface. Strategies to overcome this problem have included the use of anti-inflammatory agents and neurotrophic factors. However, it is not clear that inflammatory agents will work over the long term. Attracting the neurons to the electrode is also a strategy that may not work well, since the inorganic electrode surface represents an interface between the hard metallic or semiconducting engineered device and the much softer organic tissue, and is thus inevitably a mechanically unstable environment that is dangerous for cell viability. It would therefore be useful if there were some alternative means to create nanoscale, electronically active filaments that were an extension of the metal electrodes, providing an efficient means of communication across the reactive scar and out into the surrounding tissue. Here we propose a method that may accomplish this by the direct, in- vivo polymerization of conducting polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT). PEDOT is a conjugated polymer that is effective at facilitating charge transport between metallic electrodes and ionically conductive tissue. In previous work in our laboratory, we have shown that PEDOT coatings can help to improve the performance of biomedical devices such as microfabricated cortical probes in vivo. We have also demonstrated that PEDOT can be electrochemically polymerized around living cells both in-vitro and in-vivo. In slice cultures, we have shown that PEDOT can be grown out and into cortical tissue for 1000 microns or more, much larger than the ~100 micron size typical of the reactive cell layer. However many questions remain about the detailed methods of polymerization, including monomer delivery rates, influence of healing, and the viability and remodeling of cells in the polymerization zone. In this project we will investigate the in-vivo polymerization of PEDOT into living tissue, and will evaluate its impact on the performance of the biomedical devices of interest. We will investigate the role of wound healing around the probe on the subsequent polymerization and associated cell physiology in the reactive zone by waiting for different periods of time before initiating the reaction. We will focus our attention on microfabricated cortical electrodes of interest to the Center for Neural Communications Technology at the University of Michigan, directed by Daryl Kipke. This method has the potential to revolutionize the performance of a wide variety of implantable electronic biomedical devices including cortical probes, retinal implants, deep brain stimulators, and cardiac pacemakers. If this novel research eventually proves to be successful, there is considerable potential to move these methods from the laboratory to further development. Certain aspects of this work are related to inventions disclosed to the University of Michigan Technology Transfer Office, and under commercial development by Biotectix LLC, a spin-off company. Prof. Martin is a Co- Founder and Chief Scientific Officer for Biotectix LLC (www.biotectix.com).

TECHNICAL SUMMARY

This project will investigate in detail the relationship between the chemistry, solid-state microstructure, and macroscopic charge transport properties of solution-processable conjugated polymers. Aligned assemblies of conjugated nanofibers will be created and their performance measured both parallel and perpendicular to the direction of the molecular backbone. The microstructure will be examined in using optical and electron microscopy, with a particular focus on defect structures observed by low dose electron diffraction and high resolution electron microscopy. Electrical properties will be measured over a range of frequencies using impedance spectroscopy. The primary materials of interest will be functionalized poly(propylene dioxythiophenes) (Poly(ProDOT+)) using monomers designed and synthesized in the PI's laboratory.


NON-TECHNICAL SUMMARY

This research project will provide fundamental information about the structure and properties of conjugated polymers; plastics that can conduct electricity. These materials are of interest for a variety of devices including biomedical electrodes, chemical sensors, transistors, light-emitting diodes, and photovoltaics. These devices are providing improvements in health care, national security, and reducing our energy requirements. The project will provide direct support for graduate students in science and engineering, and will make it possible to continue current outreach activities with undergraduate students. The PI's research group will also continue established interactions with industrial and international collaborators.

PART 1: NON-TECHNICAL SUMMARY

This project will directly monitor the formation of solid electrically conducted polymers (also known as "synthetic metals") from liquid solutions using a special high-resolution electron microscope which allows direct observation of the cyrstallization process as it takes place. These organic materials are used in many advanced applications including flexible batteries, solar cells, and biomedical devices. However, the way their complicated structures actually form at the molecular level is not well understood scientifically. The project will examine the formation and growth of these complex materials during an electrochemical reaction. The experiments will use a special sample stage that will make it possible to watch and monitor within the electron microscope what happens as the materials change from liquid to solid. The research project will teach students in materials science and engineering how to establish a detailed understanding about the relationship between microstructure and properties of electrically active polymers, as well as contribute to their broader interdisciplinary education.


PART 2: TECHNICAL SUMMARY

This research project will investigate the electrochemical deposition of functionalized poly(thiophenes) using in-situ transmission electron microscopy (TEM). Conjugated poly(thiophenes), including poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(3,4-propylenedioxythiophene) (PProDOT), are of considerable scientific and commercial interest, but the detailed mechanisms of electrochemical deposition are not yet known. An in-situ sample holder will be used to examine the deposition from liquid monomer solution to solid polymer directly in a TEM. These experiments will make it possible to monitor the oxidative polymerization of thiophene monomers in the region of the electrode-electrolyte interface, providing detailed information about the structural evolution of the resulting polymer films as a function of total charge delivered to the electrode. The results will be correlated with measurements of charge transport properties using impedance spectroscopy and cyclic voltammetry. Correlations will also be made with images obtained by complementary imaging techniques including optical and scanning electron microscopy.