Muruganathan Ramanathan - Academia.edu (original) (raw)

Papers by Muruganathan Ramanathan

(~175 words) The development of wrinkled polymer thin film structures is viewed optimistically fo... more (~175 words) The development of wrinkled polymer thin film structures is viewed optimistically for the potential development of next generation high-tech devices such as stretchable electronics, microlens arrays, and smart surfaces. Here for the first time, we report a fast, facile method of developing wrinkled patterns where the wrinkles are formed spontaneously, in one step, simply upon solvent casting an azlactone-based polymer onto a substrate, without the need to apply any external stress to the system. The directionality of these wrinkles can be easily tailored by changing the mode of deposition of the polymer films onto the substrates. This methodology is not only simple, but also versatile and robust and could easily be adapted for 3D surfaces and other nonplanar, complex geometries. The persistence of these wrinkles over large distances is apparent, as we have noticed a uniform, sinusoidal wrinkling pattern across the full length of a 12 ” wafer. We expect that this simple, straightforward strategy of wrinkle formation in thin films comprised of a reactive polymer offers myriad possibilities for creating spatially and chemically tailored interfaces for modern

Langmuir, 2004

Foam films stabilized by a sugar-based nonionic surfactant,-dodecyl maltoside, are investigated. ... more Foam films stabilized by a sugar-based nonionic surfactant,-dodecyl maltoside, are investigated. The film thickness and the film contact angle (which is formed at the transition between the film and the bulk solution) are measured as a function of NaCl concentration, surfactant concentration, and temperature. The film thickness measurements provide information about the balance of the surface forces in the film whereas the contact angle measurements provide information about the specific film interaction free energy. The use of the glass ring cell and the thin film pressure balance methods enables studies under a large variety of conditions. Thick foam films are formed at low electrolyte concentration. The film thickness decreases (respectively the absolute value of the interaction film free energy increases) with the increase of the electrolyte concentration according to the classical DLVO theory. This indicates the existence of a repulsive double layer electrostatic component of the disjoining pressure. An electrostatic double layer potential of 16 mV was calculated from the data. A decrease of the film thickness on increase of the surfactant concentration in the solution is observed. The results are interpreted on the basis of the assumption that the surface double layer potential originates in the adsorption of hydroxyl ions at the film surfaces. These ions are expelled from the surface at higher surfactant concentration.

Colloids and Surfaces a Physicochemical and Engineering Aspects, Feb 1, 2010

ABSTRACT The paper summarizes the results of a study on the basic properties (film thickness, con... more ABSTRACT The paper summarizes the results of a study on the basic properties (film thickness, contact angle film/meniscus and gas permeability) of foam films stabilized with the anionic perfluoro octane sulfonate (PFOS) surfactant. The surfactant was used as a tetraethyl ammonium salt. The dependencies on the electrolyte (NH4Cl) and surfactant concentration were studied. Strong dependence of the film thickness and the contact angle on the concentration of NH4Cl and PFOS was observed. Well pronounced transition in the film thickness from common black (electrostatically stabilized) films to Newton black (sterically stabilized) films was registered. The critical salt concentration necessary for the formation of NBF was defined to be 0.1M NH4Cl. The contact angles between the films and the meniscus were collected.The gas permeability coefficient (K, cm/s) was measured at various conditions. The permeability coefficient of NBF decreases with increasing surfactant concentration below the cmc and remains constant above it. The gas permeability of the films depends on the salt concentration, respectively the film thickness in a complicated manner which cannot be explained by simple application of the Fick's law of diffusion.

Characterization of Polymer Blends, 2014

Journal of Materials Chemistry C, 2013

We report a simple, one step process for developing wrinkling patterns in azlactone-based polymer... more We report a simple, one step process for developing wrinkling patterns in azlactone-based polymer thin films and brushes on 2D and 3D surfaces. The polymer used in this work wrinkles spontaneously upon deposition and solidification on a substrate without applying any external strain to the substrate, with the mode of deposition defining the direction of the wrinkles. Wrinkle formation is shown to occur on a variety of substrates over large areas. We also find that a very thin brush-like layer of an azlactone-containing block copolymer also exhibits wrinkled topology. Given the spontaneity and versatility of wrinkle formation, we further demonstrate two proofs-of-concept, (i) that these periodic wrinkled structures are not limited to planar surfaces, but are also developed in complex geometries including tubes, cones and other 3D structures; and (ii) that this one step wrinkling process can be used to guide the deposition of metal nanoparticles and quantum dots, creating a periodic, nanopatterned film.

Journal of Materials Chemistry C, 2013

ABSTRACT Block copolymers with metals confined in one or more blocks are emerging as candidate ma... more ABSTRACT Block copolymers with metals confined in one or more blocks are emerging as candidate materials for nanomanufacturing applications due to their unprecedented nanoscale pattern transfer capabilities. In this article we highlight recent developments in metal-containing block copolymers in terms of their novel synthetic methodologies with particular emphasis on sequential infiltration synthesis, their hierarchical self-assembly from nano, meso, and submicron scales, and their applications as an etch mask for high-throughput, high-aspect-ratio nano and meso scale patterning.

MRS Proceedings, 2009

Block copolymers (BCPs) consist of two or more chemically distinct and incompatible polymer chain... more Block copolymers (BCPs) consist of two or more chemically distinct and incompatible polymer chains (or blocks) covalently bonded. Due to the incompatibility and connectivity constraints between the two blocks, diblock copolymers spontaneously self-assemble into microphase-separated nanoscale domains that exhibit ordered 0, 1, 2 or 3 dimensional morphologies at equilibrium. Commonly observed microdomain morphologies in bulk samples are periodic arrangements of lamellae, cylinders, or spheres. Block copolymer lithography refers to the use of these ordered structures in the form of thin films as templates for patterning through selective etching or deposition. The self-assembly and domain orientation of block copolymers on a given substrate is critical to realize block copolymer lithography as a tool for large throughput nanolithography applications. In this work, we survey the morphology of cylinder-forming block copolymers by atomic force microscopy (AFM). Three kind of block copolym...

Langmuir, 2008

A series of tree-shaped, amphiphilic dendrimers was synthesized. The products belong to the famil... more A series of tree-shaped, amphiphilic dendrimers was synthesized. The products belong to the family of one-directional arborols of the form ([9]-n), where the notation signifies that each molecule has nine hydroxyl groups ([9]-) as the hydrophilic head and an alkyl chain as the hydrophobic moiety (n = 6, 8, or 10 carbon atoms). The surfactant character changes dramatically as the number of methylene groups increases. The critical micelle concentration of [9]-6 was determined, and pressure-area isotherms of the less soluble [9]-8 and [9]-10 were obtained. Large structures existed atop the spread layers. Large structures were also found in solutions of [9]-6.

Journal of Materials Chemistry B, 2013

ABSTRACT Charge-regulated synthesis of triangular prisms in aqueous solution using self-assembled... more ABSTRACT Charge-regulated synthesis of triangular prisms in aqueous solution using self-assembled polyelectrolyte micelles as templates is described in detail. Micelles formed from amphiphilic polystyrene-block-sulfonated poly(1,3-cyclohexadiene) (PS-b-sPCHD) serve as templates to direct the formation of novel triangular prisms of CuCl2 single crystals. We demonstrate that the edge lengths of these triangular prisms can be easily tailored at room temperature from the nanoscale to the mesoscale by simply adjusting the ratio of charged micelles to protons in the solution. This approach can be extended to the preparation of different ordered crystal structures with a precision hard to achieve via other approaches.

Progress in Polymer Science, 2011

In the midst of an exciting era of polymer nanoscience, where the development of materials and un... more In the midst of an exciting era of polymer nanoscience, where the development of materials and understanding of properties at the nanoscale remain a major R&D endeavor, there are several exciting phenomena that have been reported at the mesoscale (approximately an order of magnitude larger than the nanoscale). In this review article, we focus on mesoscale morphologies in polymer thin films from the viewpoint of origination of structure formation, structure development and the interaction forces that govern these morphologies. Mesoscale morphologies, including dendrites, holes, spherulites, fractals and honeycomb structures have been observed in thin films of homopolymer, copolymer, blends and composites. Following a largely phenomenological level of description, we review the kinetic and thermodynamic aspects of mesostructure formation outlining some of the key mechanisms at play. We also discuss various strategies to direct, limit, or inhibit the appearance of mesostructures in polymer thin films as well as an outlook toward potential areas of growth in this field of research.

Polymer International, 2013

ABSTRACT Synthetic polymers containing metals and metal centers have experienced rapid growth in ... more ABSTRACT Synthetic polymers containing metals and metal centers have experienced rapid growth in the last two decades. Metal-containing polymers have an unprecedented role to play in modern high-tech applications including nanomanufacturing, sensing, separation and catalysis. Advancement in synthetic strategies for macromolecules has enabled the synthesis of novel, exotic and use-inspired metallopolymers. Using state-of-the-art design strategies, it is now possible to perform targeted synthesis of macromolecules with varied complexity that contain a range of metal centers either in the backbone or in the side chains of the organic moiety. The presence of an inorganic element (metals and metal centers) in organic moieties has led to a number of new physicochemical properties while implementing novel functionality to the polymer matrix. This review covers nanotechnology influenced by distinctive features of metal-containing macromolecular systems, particularly in developing flexible, functional materials. © 2013 Society of Chemical Industry

Physical Chemistry Chemical Physics, 2013

This perspective article summarizes research on the self-assembly of amphiphilic molecules such a... more This perspective article summarizes research on the self-assembly of amphiphilic molecules such as lipids, surfactants or block copolymers that are a focus of interest for many colloid, polymer, and materials scientists and which have become increasingly important in emerging nanotechnology and practical applications. Solution systems are introduced before progression to interfacial systems, which are roughly categorized as (i) basic properties of amphiphiles, (ii) self-assembly of amphiphiles in bulk phases, (iii) assembly on static surfaces, (iv) assembly at dynamic interfaces, and (v) advanced topics from simulation to application.

Nanotechnology, 2010

Palladium has been extensively studied as a material for hydrogen sensors because of the simplici... more Palladium has been extensively studied as a material for hydrogen sensors because of the simplicity of its reversible resistance change when exposed to hydrogen gas. Various palladium films and nanostructures have been used, and different responses have been observed with these diverse morphologies. In some cases, such as with nanowires, the resistance will decrease, whereas in others, such as with thick films, the resistance will increase. Each of these mechanisms has been explored for several palladium structures, but the crossover between them has not been systematically investigated. Here we report on a study aimed at deciphering the nanostructure-property relationships of ultrathin palladium films used as hydrogen gas sensors. The crossover in these films is observed at a thickness of approximately 5 nm. Ramifications for future sensor developments are discussed.

Nanoscale, 2013

Buffer layers that control electrochemical reactions and physical interactions at electrode/film ... more Buffer layers that control electrochemical reactions and physical interactions at electrode/film interfaces are key components of an organic photovoltaic cell. Here the structure and properties of layers of semirigid poly(3-hexylthiophene) (P3HT) chains tethered at a surface are investigated, and these functional systems are applied in an organic photovoltaic device. Areal density of P3HT chains is readily tuned through the choice of polymer molecular weight and annealing conditions, and insights from optical absorption spectroscopy and semiempirical quantum calculation methods suggest that tethering causes intrachain defects that affect co-facial p-stacking of brush chains. Because of their ability to modify oxide surfaces, P3HT brushes are utilized as an anode buffer layer in a P3HT-PCBM (phenyl-C 61-butyric acid methyl ester) bulk heterojunction device. Current-voltage characterization shows a significant enhancement in short circuit current, suggesting the potential of these novel nanostructured buffer layers to replace the PEDOT:PSS buffer layer typically applied in traditional P3HT-PCBM solar cells.

Journal of the American Chemical Society, 2006

Supporting information S1. Experimental S1.1) Setup: Our setup consists of a homebuilt Langmuir t... more Supporting information S1. Experimental S1.1) Setup: Our setup consists of a homebuilt Langmuir trough with a fluorescence microscope that works with a 100x water immersion objective, numerical aperture 1.0, built into the bottom of the temperature controlled film balance. The same objective is used to focus an

Journal of Physics: Conference Series, 2013

High-heat-load studies on Si double crystal monochromator that is internally cooled with liquid n... more High-heat-load studies on Si double crystal monochromator that is internally cooled with liquid nitrogen flow were performed as APS-Upgrade planned to increase ring current to 150 mA. The monochromator consists of two separated Si crystals with diffraction surfaces oriented along (111), diffracting vertically to produce a fixed 35 mm beam offset. Rocking curves were measured for the beam footprint on the first crystal lying both above and away from cooling channels. The beam was produced by two collinear APS undulators type A, each 2.4 m long with 3.3 cm period. Most of the data were obtained for a monochromator set to Bragg diffract at 8 keV for the Si (111) reflection. Through the use of aluminium filters between two sequential ion chambers, we also measured the Si (333) reflection diffracting at 24 keV. We measured the FWHM of rocking curves with either one or both undulators tuned so that the energy of the 1 st harmonic matched the Si (111) Bragg energy. Our results show sensitivity to the distance between the beam footprint above and away from cooling channels under high power conditions.

Journal of Nanoscience and Nanotechnology, 2014

Poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS) is a metal-containing block copolymer tha... more Poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS) is a metal-containing block copolymer that exhibits certain advantages as a scaffold for nanoporous membranes and as a mask for lithographic applications. These advantages include compatibility with a wide range of substrates, ease of control over domain morphologies and remarkable stability, which aid in the development of robust nanoporous networks or high-aspect-ratio patterns. An asymmetric cylinder-forming PS-b-PFS copolymer is subjected to different processing to manipulate the morphology of the phase-separated domains. Control of film structure and domain morphology is achieved by adjusting the film thickness, mode of annealing, and/or annealing time. Changing the process from thermal or solvent annealing to hybrid annealing (thermal and then solvent annealing in sequence) leads to the formation of mesoscale spherulitic and dendritic morphologies. In this communication, we show that reversing the order of the hybrid annealing (solvent annealing first and then thermal annealing) of relatively thick films (> 100 nm) on homogeneously thick substrates develops a discontinuous lamellar structure. Furthermore, the same processing applied on a substrate with a thin, mechanically flexible window in the center leads to the formation of sub-micron scale concentric ring patterns. Enhanced material mobility in the thick film during hybrid annealing along with dynamic rippling effects that may arise from the vibration of the thin window during spin casting are likely causes for these morphologies.

(~175 words) The development of wrinkled polymer thin film structures is viewed optimistically fo... more (~175 words) The development of wrinkled polymer thin film structures is viewed optimistically for the potential development of next generation high-tech devices such as stretchable electronics, microlens arrays, and smart surfaces. Here for the first time, we report a fast, facile method of developing wrinkled patterns where the wrinkles are formed spontaneously, in one step, simply upon solvent casting an azlactone-based polymer onto a substrate, without the need to apply any external stress to the system. The directionality of these wrinkles can be easily tailored by changing the mode of deposition of the polymer films onto the substrates. This methodology is not only simple, but also versatile and robust and could easily be adapted for 3D surfaces and other nonplanar, complex geometries. The persistence of these wrinkles over large distances is apparent, as we have noticed a uniform, sinusoidal wrinkling pattern across the full length of a 12 ” wafer. We expect that this simple, straightforward strategy of wrinkle formation in thin films comprised of a reactive polymer offers myriad possibilities for creating spatially and chemically tailored interfaces for modern

Langmuir, 2004

Foam films stabilized by a sugar-based nonionic surfactant,-dodecyl maltoside, are investigated. ... more Foam films stabilized by a sugar-based nonionic surfactant,-dodecyl maltoside, are investigated. The film thickness and the film contact angle (which is formed at the transition between the film and the bulk solution) are measured as a function of NaCl concentration, surfactant concentration, and temperature. The film thickness measurements provide information about the balance of the surface forces in the film whereas the contact angle measurements provide information about the specific film interaction free energy. The use of the glass ring cell and the thin film pressure balance methods enables studies under a large variety of conditions. Thick foam films are formed at low electrolyte concentration. The film thickness decreases (respectively the absolute value of the interaction film free energy increases) with the increase of the electrolyte concentration according to the classical DLVO theory. This indicates the existence of a repulsive double layer electrostatic component of the disjoining pressure. An electrostatic double layer potential of 16 mV was calculated from the data. A decrease of the film thickness on increase of the surfactant concentration in the solution is observed. The results are interpreted on the basis of the assumption that the surface double layer potential originates in the adsorption of hydroxyl ions at the film surfaces. These ions are expelled from the surface at higher surfactant concentration.

Colloids and Surfaces a Physicochemical and Engineering Aspects, Feb 1, 2010

ABSTRACT The paper summarizes the results of a study on the basic properties (film thickness, con... more ABSTRACT The paper summarizes the results of a study on the basic properties (film thickness, contact angle film/meniscus and gas permeability) of foam films stabilized with the anionic perfluoro octane sulfonate (PFOS) surfactant. The surfactant was used as a tetraethyl ammonium salt. The dependencies on the electrolyte (NH4Cl) and surfactant concentration were studied. Strong dependence of the film thickness and the contact angle on the concentration of NH4Cl and PFOS was observed. Well pronounced transition in the film thickness from common black (electrostatically stabilized) films to Newton black (sterically stabilized) films was registered. The critical salt concentration necessary for the formation of NBF was defined to be 0.1M NH4Cl. The contact angles between the films and the meniscus were collected.The gas permeability coefficient (K, cm/s) was measured at various conditions. The permeability coefficient of NBF decreases with increasing surfactant concentration below the cmc and remains constant above it. The gas permeability of the films depends on the salt concentration, respectively the film thickness in a complicated manner which cannot be explained by simple application of the Fick's law of diffusion.

Characterization of Polymer Blends, 2014

Journal of Materials Chemistry C, 2013

We report a simple, one step process for developing wrinkling patterns in azlactone-based polymer... more We report a simple, one step process for developing wrinkling patterns in azlactone-based polymer thin films and brushes on 2D and 3D surfaces. The polymer used in this work wrinkles spontaneously upon deposition and solidification on a substrate without applying any external strain to the substrate, with the mode of deposition defining the direction of the wrinkles. Wrinkle formation is shown to occur on a variety of substrates over large areas. We also find that a very thin brush-like layer of an azlactone-containing block copolymer also exhibits wrinkled topology. Given the spontaneity and versatility of wrinkle formation, we further demonstrate two proofs-of-concept, (i) that these periodic wrinkled structures are not limited to planar surfaces, but are also developed in complex geometries including tubes, cones and other 3D structures; and (ii) that this one step wrinkling process can be used to guide the deposition of metal nanoparticles and quantum dots, creating a periodic, nanopatterned film.

Journal of Materials Chemistry C, 2013

ABSTRACT Block copolymers with metals confined in one or more blocks are emerging as candidate ma... more ABSTRACT Block copolymers with metals confined in one or more blocks are emerging as candidate materials for nanomanufacturing applications due to their unprecedented nanoscale pattern transfer capabilities. In this article we highlight recent developments in metal-containing block copolymers in terms of their novel synthetic methodologies with particular emphasis on sequential infiltration synthesis, their hierarchical self-assembly from nano, meso, and submicron scales, and their applications as an etch mask for high-throughput, high-aspect-ratio nano and meso scale patterning.

MRS Proceedings, 2009

Block copolymers (BCPs) consist of two or more chemically distinct and incompatible polymer chain... more Block copolymers (BCPs) consist of two or more chemically distinct and incompatible polymer chains (or blocks) covalently bonded. Due to the incompatibility and connectivity constraints between the two blocks, diblock copolymers spontaneously self-assemble into microphase-separated nanoscale domains that exhibit ordered 0, 1, 2 or 3 dimensional morphologies at equilibrium. Commonly observed microdomain morphologies in bulk samples are periodic arrangements of lamellae, cylinders, or spheres. Block copolymer lithography refers to the use of these ordered structures in the form of thin films as templates for patterning through selective etching or deposition. The self-assembly and domain orientation of block copolymers on a given substrate is critical to realize block copolymer lithography as a tool for large throughput nanolithography applications. In this work, we survey the morphology of cylinder-forming block copolymers by atomic force microscopy (AFM). Three kind of block copolym...

Langmuir, 2008

A series of tree-shaped, amphiphilic dendrimers was synthesized. The products belong to the famil... more A series of tree-shaped, amphiphilic dendrimers was synthesized. The products belong to the family of one-directional arborols of the form ([9]-n), where the notation signifies that each molecule has nine hydroxyl groups ([9]-) as the hydrophilic head and an alkyl chain as the hydrophobic moiety (n = 6, 8, or 10 carbon atoms). The surfactant character changes dramatically as the number of methylene groups increases. The critical micelle concentration of [9]-6 was determined, and pressure-area isotherms of the less soluble [9]-8 and [9]-10 were obtained. Large structures existed atop the spread layers. Large structures were also found in solutions of [9]-6.

Journal of Materials Chemistry B, 2013

ABSTRACT Charge-regulated synthesis of triangular prisms in aqueous solution using self-assembled... more ABSTRACT Charge-regulated synthesis of triangular prisms in aqueous solution using self-assembled polyelectrolyte micelles as templates is described in detail. Micelles formed from amphiphilic polystyrene-block-sulfonated poly(1,3-cyclohexadiene) (PS-b-sPCHD) serve as templates to direct the formation of novel triangular prisms of CuCl2 single crystals. We demonstrate that the edge lengths of these triangular prisms can be easily tailored at room temperature from the nanoscale to the mesoscale by simply adjusting the ratio of charged micelles to protons in the solution. This approach can be extended to the preparation of different ordered crystal structures with a precision hard to achieve via other approaches.

Progress in Polymer Science, 2011

In the midst of an exciting era of polymer nanoscience, where the development of materials and un... more In the midst of an exciting era of polymer nanoscience, where the development of materials and understanding of properties at the nanoscale remain a major R&D endeavor, there are several exciting phenomena that have been reported at the mesoscale (approximately an order of magnitude larger than the nanoscale). In this review article, we focus on mesoscale morphologies in polymer thin films from the viewpoint of origination of structure formation, structure development and the interaction forces that govern these morphologies. Mesoscale morphologies, including dendrites, holes, spherulites, fractals and honeycomb structures have been observed in thin films of homopolymer, copolymer, blends and composites. Following a largely phenomenological level of description, we review the kinetic and thermodynamic aspects of mesostructure formation outlining some of the key mechanisms at play. We also discuss various strategies to direct, limit, or inhibit the appearance of mesostructures in polymer thin films as well as an outlook toward potential areas of growth in this field of research.

Polymer International, 2013

ABSTRACT Synthetic polymers containing metals and metal centers have experienced rapid growth in ... more ABSTRACT Synthetic polymers containing metals and metal centers have experienced rapid growth in the last two decades. Metal-containing polymers have an unprecedented role to play in modern high-tech applications including nanomanufacturing, sensing, separation and catalysis. Advancement in synthetic strategies for macromolecules has enabled the synthesis of novel, exotic and use-inspired metallopolymers. Using state-of-the-art design strategies, it is now possible to perform targeted synthesis of macromolecules with varied complexity that contain a range of metal centers either in the backbone or in the side chains of the organic moiety. The presence of an inorganic element (metals and metal centers) in organic moieties has led to a number of new physicochemical properties while implementing novel functionality to the polymer matrix. This review covers nanotechnology influenced by distinctive features of metal-containing macromolecular systems, particularly in developing flexible, functional materials. © 2013 Society of Chemical Industry

Physical Chemistry Chemical Physics, 2013

This perspective article summarizes research on the self-assembly of amphiphilic molecules such a... more This perspective article summarizes research on the self-assembly of amphiphilic molecules such as lipids, surfactants or block copolymers that are a focus of interest for many colloid, polymer, and materials scientists and which have become increasingly important in emerging nanotechnology and practical applications. Solution systems are introduced before progression to interfacial systems, which are roughly categorized as (i) basic properties of amphiphiles, (ii) self-assembly of amphiphiles in bulk phases, (iii) assembly on static surfaces, (iv) assembly at dynamic interfaces, and (v) advanced topics from simulation to application.

Nanotechnology, 2010

Palladium has been extensively studied as a material for hydrogen sensors because of the simplici... more Palladium has been extensively studied as a material for hydrogen sensors because of the simplicity of its reversible resistance change when exposed to hydrogen gas. Various palladium films and nanostructures have been used, and different responses have been observed with these diverse morphologies. In some cases, such as with nanowires, the resistance will decrease, whereas in others, such as with thick films, the resistance will increase. Each of these mechanisms has been explored for several palladium structures, but the crossover between them has not been systematically investigated. Here we report on a study aimed at deciphering the nanostructure-property relationships of ultrathin palladium films used as hydrogen gas sensors. The crossover in these films is observed at a thickness of approximately 5 nm. Ramifications for future sensor developments are discussed.

Nanoscale, 2013

Buffer layers that control electrochemical reactions and physical interactions at electrode/film ... more Buffer layers that control electrochemical reactions and physical interactions at electrode/film interfaces are key components of an organic photovoltaic cell. Here the structure and properties of layers of semirigid poly(3-hexylthiophene) (P3HT) chains tethered at a surface are investigated, and these functional systems are applied in an organic photovoltaic device. Areal density of P3HT chains is readily tuned through the choice of polymer molecular weight and annealing conditions, and insights from optical absorption spectroscopy and semiempirical quantum calculation methods suggest that tethering causes intrachain defects that affect co-facial p-stacking of brush chains. Because of their ability to modify oxide surfaces, P3HT brushes are utilized as an anode buffer layer in a P3HT-PCBM (phenyl-C 61-butyric acid methyl ester) bulk heterojunction device. Current-voltage characterization shows a significant enhancement in short circuit current, suggesting the potential of these novel nanostructured buffer layers to replace the PEDOT:PSS buffer layer typically applied in traditional P3HT-PCBM solar cells.

Journal of the American Chemical Society, 2006

Supporting information S1. Experimental S1.1) Setup: Our setup consists of a homebuilt Langmuir t... more Supporting information S1. Experimental S1.1) Setup: Our setup consists of a homebuilt Langmuir trough with a fluorescence microscope that works with a 100x water immersion objective, numerical aperture 1.0, built into the bottom of the temperature controlled film balance. The same objective is used to focus an

Journal of Physics: Conference Series, 2013

High-heat-load studies on Si double crystal monochromator that is internally cooled with liquid n... more High-heat-load studies on Si double crystal monochromator that is internally cooled with liquid nitrogen flow were performed as APS-Upgrade planned to increase ring current to 150 mA. The monochromator consists of two separated Si crystals with diffraction surfaces oriented along (111), diffracting vertically to produce a fixed 35 mm beam offset. Rocking curves were measured for the beam footprint on the first crystal lying both above and away from cooling channels. The beam was produced by two collinear APS undulators type A, each 2.4 m long with 3.3 cm period. Most of the data were obtained for a monochromator set to Bragg diffract at 8 keV for the Si (111) reflection. Through the use of aluminium filters between two sequential ion chambers, we also measured the Si (333) reflection diffracting at 24 keV. We measured the FWHM of rocking curves with either one or both undulators tuned so that the energy of the 1 st harmonic matched the Si (111) Bragg energy. Our results show sensitivity to the distance between the beam footprint above and away from cooling channels under high power conditions.

Journal of Nanoscience and Nanotechnology, 2014

Poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS) is a metal-containing block copolymer tha... more Poly(styrene-block-ferrocenyldimethylsilane) (PS-b-PFS) is a metal-containing block copolymer that exhibits certain advantages as a scaffold for nanoporous membranes and as a mask for lithographic applications. These advantages include compatibility with a wide range of substrates, ease of control over domain morphologies and remarkable stability, which aid in the development of robust nanoporous networks or high-aspect-ratio patterns. An asymmetric cylinder-forming PS-b-PFS copolymer is subjected to different processing to manipulate the morphology of the phase-separated domains. Control of film structure and domain morphology is achieved by adjusting the film thickness, mode of annealing, and/or annealing time. Changing the process from thermal or solvent annealing to hybrid annealing (thermal and then solvent annealing in sequence) leads to the formation of mesoscale spherulitic and dendritic morphologies. In this communication, we show that reversing the order of the hybrid annealing (solvent annealing first and then thermal annealing) of relatively thick films (> 100 nm) on homogeneously thick substrates develops a discontinuous lamellar structure. Furthermore, the same processing applied on a substrate with a thin, mechanically flexible window in the center leads to the formation of sub-micron scale concentric ring patterns. Enhanced material mobility in the thick film during hybrid annealing along with dynamic rippling effects that may arise from the vibration of the thin window during spin casting are likely causes for these morphologies.