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Research Projects
The group's current efforts involve two primary thrusts with a common thread of using polymers
as a versatile platform to develop new materials for existing and emerging technologies. First,
polymers are being examined as sacrificial templates to make nanostructured inorganic films. Both
top-down (photolithography and other patterning techniques) and bottom-up (self-assembly) processing
are utilized. These processes used in tandem create unique hierarchical materials for diverse applications.
Second, conjugated polymers are utilized as active layers in electronic devices. The property-structure-
processing relationships are elucidated through fundamental measurements of the thin film morphology and careful
analysis of the electrical properties. Additionally, techniques are being developed to control the interfacial
structure of these materials to improve device performance.
Templated inorganic films- B.D. Vogt, H.-J. Lee, W.-l. Wu, Y. Liu. “Specular x-ray reflectivity and small angle neutron scattering for structure determination of ordered mesoporous films.” Journal of Physical Chemistry B 2005 109(39) 18445-18450.
- B.D. Vogt, R.A. Pai, H.-J. Lee, R.C. Hedden, C.L. Soles, W.-l. Wu, E.K. Lin, B.J. Bauer, J.J. Watkins. “Characterization of mesoporous silica films prepared using supercritical carbon dioxide with small angle neutron scattering and x–ray porosimetry.” Chemistry of Materials 2005 17(6) 1398-1408.
- M.L. Chabinyc, F. Endicott, B.D. Vogt, D.M. DeLongchamp, E.K. Lin, Y. Wu, P. Liu, B.S. Ong. “Effects of humidity on unencapsulated poly(thiophene) thin film transistors.” Applied Physics Letters 2006 88(11) 113514.
- D.M. DeLongchamp, B.D. Vogt, C.M. Brooks, K. Kano, J. Obrzut, C. Richter, O. Kirrilov, E.K. Lin. “The influence of a water rinse on the structure and properties of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) films.” Langmuir 2005 21(24) 11480-11483.
- C.M. Stafford, B.D. Vogt, C. Harrison, D. Julthongpiput, R. Huang. “Elastic moduli of ultrathin amorphous glassy polymer films.” Macromolecules 2006 39(15) 5095-5099.
- R. Huang, C.M. Stafford, B.D. Vogt. “Effect of surface properties on wrinkling of ultrathin films.” Journal of Aerospace Engineering 2007 20(1) 38-44.
Nanostructured inorganic films have the potential to be ubiquitous materials. Potential applications include
dielectric layers in microelectronics, catalysts, membranes for separations, sensors, and photonic crystals.
Materials of different characteristics are required depending upon the applications. Our work focuses on development
of improved materials and methods for characterizing the nanostructured films. Control of the structure from the
atomic scale to the macroscopic scale is ultimately necessary. A methodology utilizing preformed polymer templates
and supercritical carbon dioxide as the reaction medium separates the template formation and reaction allowing for
improved control of the final film morphology in comparison to the solution based processes that require simultaneous
self-assembly of the template and reaction. We are currently examining this supercritical fluid synthesis route
fundamentally using in-situ characterization techniques.
Representative publicationsAdvances in polymer synthesis techniques have enabled new conjugated polymers with improved properties for both
conducting and semiconducting materials. These developments have invigorated efforts towards creating manufacturable low
cost, large area electronic devices on flexible substrates using conjugated polymers as the active materials. Our group
focuses on elucidating the influence of the polymer structure in the thin film on the electrical properties and the ultimate
device performance. X-ray and neutron scattering techniques are used to determine the morphology of these materials on a
molecular level. External fields are used to control the orientation and morphology of the conjugated polymers during film
formation to improve the performance of devices using these films. Through understanding property-structure-processing
relationships for conjugated polymers, we suspect that the properties of existing materials can be improved such that they
are commercially viable.
Mechanics of nanoscale and nanostructured materials
One of the major remaining fundamental problems in condensed matter physics is an understanding of
glass formation and glassy behavior. The properties of glassy materials have been extensively investigated on the nanometer
length scale in attempts to understand the origins of glassy behavior. Thin films of polymers have been used as model systems
extensively due to their ability to form stabile ultrathin films that maintain their integrity. These measurements have
demonstrated deviations from bulk behavior when probing their thermal properties. However, the impact of these deviations
on the mechanical properties is less clear. An improved understanding of the thermoelastic properties of these ultrathin polymer
glasses could result in tremendous advances in addressing fundamentals of glass formation and glassy behavior.
In addition to this strong fundamental drive, there are many application-based instances that demand an understanding of the mechanical properties of polymers on the nanometer size scale. The microelectronics industry has been a key driver in the U.S. economy over the past several decades.5 The growth of the microelectronics industry is underscored by Moore’s Law, an observation made by Gordon Moore, founder of Intel, who states that the number of transistors on a chip doubles approximately every two years. This doubling has continued into the present enabled by the ever-decreasing lithographically printed feature sizes. Intel recently announced plans for a new chipset for the end of this year containing 65 nm gate lengths. While it is well understood that the constant decrease in feature size cannot continue indefinitely due to atomic limitations, it is unclear as to the point at which size limitations will occur – with electronic properties at the nanoscale, with the inability to efficiently print lithographically, or with materials failure. The latter predicament has been seriously investigated indirectly using polymeric-based photoresists that enable the printing of sub-100 nm features by monitoring the properties of ultrathin film photoresists.
We utilize a novel approach to probing the mechanical properties of ultrathin (<100 nm) polymer films exploiting the wrinkling instability resulting from the difference in modulus between a soft substrate (PDMS) and a glassy thin polymer film. Results from this methodology will lead to an improved understanding of the properties of confined polymer systems and will be important for microelectronics where the stability of polymer nanostructures is crucial for device manufacturing.
Representative publicationsIn addition to this strong fundamental drive, there are many application-based instances that demand an understanding of the mechanical properties of polymers on the nanometer size scale. The microelectronics industry has been a key driver in the U.S. economy over the past several decades.5 The growth of the microelectronics industry is underscored by Moore’s Law, an observation made by Gordon Moore, founder of Intel, who states that the number of transistors on a chip doubles approximately every two years. This doubling has continued into the present enabled by the ever-decreasing lithographically printed feature sizes. Intel recently announced plans for a new chipset for the end of this year containing 65 nm gate lengths. While it is well understood that the constant decrease in feature size cannot continue indefinitely due to atomic limitations, it is unclear as to the point at which size limitations will occur – with electronic properties at the nanoscale, with the inability to efficiently print lithographically, or with materials failure. The latter predicament has been seriously investigated indirectly using polymeric-based photoresists that enable the printing of sub-100 nm features by monitoring the properties of ultrathin film photoresists.
We utilize a novel approach to probing the mechanical properties of ultrathin (<100 nm) polymer films exploiting the wrinkling instability resulting from the difference in modulus between a soft substrate (PDMS) and a glassy thin polymer film. Results from this methodology will lead to an improved understanding of the properties of confined polymer systems and will be important for microelectronics where the stability of polymer nanostructures is crucial for device manufacturing.
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