The ongoing development of conjugated polymer electronic materials has shown that alterations of ... more The ongoing development of conjugated polymer electronic materials has shown that alterations of the structure of these materials and the means of processing can lead to large variations in the performance observed. Continued growth in this field requires the development of ...
High performance, solution processable semiconductors are critical to the realization of low cost... more High performance, solution processable semiconductors are critical to the realization of low cost, large area electronics. We show that a signature molecular packing motif side-chain interdigitation correlates to high performance for a large and important class of organic semiconductors. ...
The real-time shape evolution of nanoimprinted polymer patterns is measured as a function of anne... more The real-time shape evolution of nanoimprinted polymer patterns is measured as a function of annealing time and temperature using critical dimension small-angle X-ray scattering (CD-SAXS). Periodicity, line width, line height, and sidewall angle are reported with nanometer resolution for parallel line/space patterns in poly(methyl methacrylate) (PMMA) both below and above the bulk glass transition temperature (T(G)). Heating these patterns below T(G) does not produce significant thermal expansion, at least to within the resolution of the measurement. However, above T(G) the fast rate of loss in pattern size at early times transitions to a reduced rate in longer time regimes. The time-dependent rate of polymer flow from the pattern into the underlying layer, termed pattern "melting", is consistent with a model of elastic recovery from stresses induced by the molding process.
Applications employing block copolymers such as templating mesoporous inorganic structures and pa... more Applications employing block copolymers such as templating mesoporous inorganic structures and patterning would benefit from reduction in domain size formed in well-ordered block copolymer templates. The extent to which the domain size can be reduced is limited by the minimum required segregation strength, chiN, where N determines the size of block copolymer chains and the domain size. We have shown
Proceedings of Spie the International Society For Optical Engineering, Mar 1, 2007
Characterizing pattern structures using X-ray reflectivity. [Proceedings of SPIE 6518, 651813 (20... more Characterizing pattern structures using X-ray reflectivity. [Proceedings of SPIE 6518, 651813 (2007)]. Hae-Jeong Lee, Christopher L. Soles, Hyun Wook Ro, Shuhui Kang, Eric K. Lin, Alamgir Karim, Wen-li Wu, DR Hines. Abstract. ...
Proceedings of Spie the International Society For Optical Engineering, Mar 1, 2008
Exploring the limitations of x-ray reflectivity as a critical dimension pattern shape metrology. ... more Exploring the limitations of x-ray reflectivity as a critical dimension pattern shape metrology. [Proceedings of SPIE 6922, 692224 (2008)]. Hae-Jeong Lee, Sangcheol Kim, Christopher L. Soles, Eric K. Lin, Wen-Li Wu. Abstract. Specular ...
ABSTRACTThe basic tetrahedra of silica are readily assembled into eight cornered cages known as c... more ABSTRACTThe basic tetrahedra of silica are readily assembled into eight cornered cages known as cubic silsesquioxanes ([RSiO1.5]8). Silsesquioxane cubes represent one of the smallest possible units of ceramic silica. The corners of these nanometer-sized ceramic cubes are readily functionalized with reactive groups and incorporated into organic polymers. In this work, we characterize the structures that result from varying the length of the flexible organic segments used to connect the cubes in a series of hybrid network materials. For very short organic segments, steric hindrances inhibit high degrees of network conversion and the resulting network is very inhomogeneous. As the length of the flexible organic segment increases, the added degrees of freedom allow a more ‘ordered’ glassy material to evolve. If the length of the organic segment becomes very long in comparison to the size of the cube, a disordered polymer-like network is obtained.
The measurement and optimization of microstructure development in organic semiconductor films is ... more The measurement and optimization of microstructure development in organic semiconductor films is valuable because microstructure in many cases critically impacts electronic performance. We demonstrate a general method to measure microstructure thickness dependence in thin films using surface-sensitive near edge X-ray absorbance fine structure (NEXAFS) spectroscopy. The method is applied to an oligofluorene derivative DDFTTF, which consists of a fluorene-bithiophene-fluorene core that is end-substituted with linear dodecyl groups. The substrate-relative orientations of the aromatic core and the aliphatic end chains are independently determined, and comparing these orientations to terrace heights from atomic force micrographs proves that the end chains are interdigitated or folded. By measuring microstructure development from 6 to 150 nm, we find that DDFTTF exhibits two different preferential microstructures: one with large terraces within which molecules exhibit a strongly vertical orientation, and one with much smaller domains within which molecules exhibit a mildly horizontal orientation. The relative distribution of these two preferential microstructures depends on the distance of the domains from the substrate and the substrate temperature during deposition. The utility of this method is tested using a lamination technique to measure the saturation hole mobility at the top and bottom interface of DDFTTF films. We find that local microstructures with greater pi orbital alignment in the source-drain plane correlate directly to better local saturation hole mobilities.
A molecular mechanism is proposed for the toughness enhancement observed in double-network (DN) h... more A molecular mechanism is proposed for the toughness enhancement observed in double-network (DN) hydrogels prepared from poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) polyelectrolyte network and poly(acrylamide) (PAAm) linear polymer. It is an extension of the phenomenological model set forth recently by Gong et al. ( Macromolecules 2007, 40, 6658- 6664 ). This mechanism rationalizes the changes in molecular structure of the DN gel constituents observed via in situ neutron scattering measurements, the composition dependence of the solution viscosity, and the thermodynamic interaction parameters of PAMPS and PAAm molecules obtained previously from neutron scattering studies. More specifically, this proposed mechanism provides an explanation for the observed periodic compositional fluctuations in the micrometer range induced by large strain deformation.
ABSTRACTNeutron reflectometry is used to measure the rate of interdiffusion between bilayer sampl... more ABSTRACTNeutron reflectometry is used to measure the rate of interdiffusion between bilayer samples of deuterated and hydrogenated poly(methyl methacrylate) (PMMA) films with the polymerpolymer interface near the native oxide surface of a silicon wafer. In this work, the effects of a favorable substrate interaction and the molecular weight of each polymer layer are determined. Both the film thickness and the molecular weight of the lower d-PMMA layer are kept constant with a thickness of approximately one radii of gyration (Rg) of the polymer and the molecular weight of the upper hydrogenated layer is varied. Earlier experiments show that the mobility of the polymer chains within Rg of the substrate is much lower than that of the bulk, suggesting that the mobility of surface-pinned polymers controls the interdiffusion rate. In this study, we find that the rate of interdiffusion is strongly dependent upon the molecular weight of the top layer.
The ongoing development of conjugated polymer electronic materials has shown that alterations of ... more The ongoing development of conjugated polymer electronic materials has shown that alterations of the structure of these materials and the means of processing can lead to large variations in the performance observed. Continued growth in this field requires the development of ...
High performance, solution processable semiconductors are critical to the realization of low cost... more High performance, solution processable semiconductors are critical to the realization of low cost, large area electronics. We show that a signature molecular packing motif side-chain interdigitation correlates to high performance for a large and important class of organic semiconductors. ...
The real-time shape evolution of nanoimprinted polymer patterns is measured as a function of anne... more The real-time shape evolution of nanoimprinted polymer patterns is measured as a function of annealing time and temperature using critical dimension small-angle X-ray scattering (CD-SAXS). Periodicity, line width, line height, and sidewall angle are reported with nanometer resolution for parallel line/space patterns in poly(methyl methacrylate) (PMMA) both below and above the bulk glass transition temperature (T(G)). Heating these patterns below T(G) does not produce significant thermal expansion, at least to within the resolution of the measurement. However, above T(G) the fast rate of loss in pattern size at early times transitions to a reduced rate in longer time regimes. The time-dependent rate of polymer flow from the pattern into the underlying layer, termed pattern "melting", is consistent with a model of elastic recovery from stresses induced by the molding process.
Applications employing block copolymers such as templating mesoporous inorganic structures and pa... more Applications employing block copolymers such as templating mesoporous inorganic structures and patterning would benefit from reduction in domain size formed in well-ordered block copolymer templates. The extent to which the domain size can be reduced is limited by the minimum required segregation strength, chiN, where N determines the size of block copolymer chains and the domain size. We have shown
Proceedings of Spie the International Society For Optical Engineering, Mar 1, 2007
Characterizing pattern structures using X-ray reflectivity. [Proceedings of SPIE 6518, 651813 (20... more Characterizing pattern structures using X-ray reflectivity. [Proceedings of SPIE 6518, 651813 (2007)]. Hae-Jeong Lee, Christopher L. Soles, Hyun Wook Ro, Shuhui Kang, Eric K. Lin, Alamgir Karim, Wen-li Wu, DR Hines. Abstract. ...
Proceedings of Spie the International Society For Optical Engineering, Mar 1, 2008
Exploring the limitations of x-ray reflectivity as a critical dimension pattern shape metrology. ... more Exploring the limitations of x-ray reflectivity as a critical dimension pattern shape metrology. [Proceedings of SPIE 6922, 692224 (2008)]. Hae-Jeong Lee, Sangcheol Kim, Christopher L. Soles, Eric K. Lin, Wen-Li Wu. Abstract. Specular ...
ABSTRACTThe basic tetrahedra of silica are readily assembled into eight cornered cages known as c... more ABSTRACTThe basic tetrahedra of silica are readily assembled into eight cornered cages known as cubic silsesquioxanes ([RSiO1.5]8). Silsesquioxane cubes represent one of the smallest possible units of ceramic silica. The corners of these nanometer-sized ceramic cubes are readily functionalized with reactive groups and incorporated into organic polymers. In this work, we characterize the structures that result from varying the length of the flexible organic segments used to connect the cubes in a series of hybrid network materials. For very short organic segments, steric hindrances inhibit high degrees of network conversion and the resulting network is very inhomogeneous. As the length of the flexible organic segment increases, the added degrees of freedom allow a more ‘ordered’ glassy material to evolve. If the length of the organic segment becomes very long in comparison to the size of the cube, a disordered polymer-like network is obtained.
The measurement and optimization of microstructure development in organic semiconductor films is ... more The measurement and optimization of microstructure development in organic semiconductor films is valuable because microstructure in many cases critically impacts electronic performance. We demonstrate a general method to measure microstructure thickness dependence in thin films using surface-sensitive near edge X-ray absorbance fine structure (NEXAFS) spectroscopy. The method is applied to an oligofluorene derivative DDFTTF, which consists of a fluorene-bithiophene-fluorene core that is end-substituted with linear dodecyl groups. The substrate-relative orientations of the aromatic core and the aliphatic end chains are independently determined, and comparing these orientations to terrace heights from atomic force micrographs proves that the end chains are interdigitated or folded. By measuring microstructure development from 6 to 150 nm, we find that DDFTTF exhibits two different preferential microstructures: one with large terraces within which molecules exhibit a strongly vertical orientation, and one with much smaller domains within which molecules exhibit a mildly horizontal orientation. The relative distribution of these two preferential microstructures depends on the distance of the domains from the substrate and the substrate temperature during deposition. The utility of this method is tested using a lamination technique to measure the saturation hole mobility at the top and bottom interface of DDFTTF films. We find that local microstructures with greater pi orbital alignment in the source-drain plane correlate directly to better local saturation hole mobilities.
A molecular mechanism is proposed for the toughness enhancement observed in double-network (DN) h... more A molecular mechanism is proposed for the toughness enhancement observed in double-network (DN) hydrogels prepared from poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) polyelectrolyte network and poly(acrylamide) (PAAm) linear polymer. It is an extension of the phenomenological model set forth recently by Gong et al. ( Macromolecules 2007, 40, 6658- 6664 ). This mechanism rationalizes the changes in molecular structure of the DN gel constituents observed via in situ neutron scattering measurements, the composition dependence of the solution viscosity, and the thermodynamic interaction parameters of PAMPS and PAAm molecules obtained previously from neutron scattering studies. More specifically, this proposed mechanism provides an explanation for the observed periodic compositional fluctuations in the micrometer range induced by large strain deformation.
ABSTRACTNeutron reflectometry is used to measure the rate of interdiffusion between bilayer sampl... more ABSTRACTNeutron reflectometry is used to measure the rate of interdiffusion between bilayer samples of deuterated and hydrogenated poly(methyl methacrylate) (PMMA) films with the polymerpolymer interface near the native oxide surface of a silicon wafer. In this work, the effects of a favorable substrate interaction and the molecular weight of each polymer layer are determined. Both the film thickness and the molecular weight of the lower d-PMMA layer are kept constant with a thickness of approximately one radii of gyration (Rg) of the polymer and the molecular weight of the upper hydrogenated layer is varied. Earlier experiments show that the mobility of the polymer chains within Rg of the substrate is much lower than that of the bulk, suggesting that the mobility of surface-pinned polymers controls the interdiffusion rate. In this study, we find that the rate of interdiffusion is strongly dependent upon the molecular weight of the top layer.
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