Herman Schoo | TNO Holst Centre (original) (raw)
Papers by Herman Schoo
Organic Photovoltaics Iv, 2004
Polymer bulk hetero junction solar cells were made from poly(2-methoxy-5-(3,7-dimethyloctyloxy)-1... more Polymer bulk hetero junction solar cells were made from poly(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) as donor and poly(cyanoetherphenylenevinylene) (PCNEPV) derivatives as acceptor material. In this paper we start out with discussing the synthesis of the materials. Subsequently, the main issues concerning the devices are treated. Annealing the devices yielded devices with encouraging efficiencies of 0.5% (1 sun, 100mW/cm 2 ), as calculated from the maximum power points (MPP). AFM studies revealed that this anneal step improves especially the interface of the active layer with the under laying PEDOT:PSS, although mobility and morphology changes can not be ruled out. Lowering the molecular weight (Mw) of the MDMO-PPV gave a slight improvement of the device performance. Decreasing the Mw of the acceptor material, MDMO-PCNEPV (PCNEPV derivative with the same side chains as MDMO-PPV) and optimizing the layer thickness led to a device with an efficiency of 0.65%. Finally we looked into the influence of the nature of the side chains on the acceptor polymer. The results suggest that the closer the resemblance between donor and acceptor is the better the device performance.
The operation characteristics of polymer light-emitting diodes (PLEDs) are strongly dependent on ... more The operation characteristics of polymer light-emitting diodes (PLEDs) are strongly dependent on materials, processing and the structure of the device. The device structure developed at Philips Research is presented together with some typical results for brightness, ef®ciency, response times and stability. The PLEDs typically operate at a voltage of 3±4 V for a brightness of 100 cd m À 2 and have an ef®ciency ranging from 2 cd A À 1 for orange emitting polymers (610 nm) up to 16 cd A À 1 for green emitting polymers (550 nm). The response time under conditions for display operation is determined by the charge carrier transport properties and amounts to 43 ns. Lifetimes of several thousand hours have been obtained for large orange emitting devices of 8 cm 2 for daylight visibility at room temperature.
Organic Light-Emitting Materials and Devices, 1997
ABSTRACT In this paper on polymer LEDs we discuss the formation of black spots, surface treatment... more ABSTRACT In this paper on polymer LEDs we discuss the formation of black spots, surface treatments of the anode, and photochemical degradation of the emissive polymer. We find that small pinholes in the cathode layer are the origin of the black spots. The black spots form when H2O or O2 diffuse through the pinholes and react with the cathode at the polymer-cathode interface.A model is presented that describes the growth of the spots. We find that for both indium-tin-oxide (ITO) and Au anodes, an UV/O3 or an O2 plasma cleaning treatment increases the work function by 0.8-0.9 eV. A higher work function may lead to a better hole injection and a reduction in the operating voltage. We present a method to measure the quantum yield for bleaching, (gamma) equals 1.6$MN4 and (gamma) equals 1.7 10-7 for bleaching of dialkoxy-PPV in air and vacuum, respectively, indicating that the polymer is 1000 times more stable in vacuum than in air.
Organic Field-Effect Transistors VII and Organic Semiconductors in Sensors and Bioelectronics, 2008
Sensors based on organic electronic devices are emerging in a wide range of application areas. He... more Sensors based on organic electronic devices are emerging in a wide range of application areas. Here we present a sensor platform using organic light emitting diodes (OLED) and organic photodiodes (OPD) as active components. By means of lamination and interconnection technology the functional foils with OLED and OPD arrays form an in-plane optical sensor platform (IPOS). This platform can be extended with a wireless data and signal processing unit yielding a sensor node. The focus of our research is to engage the node in a healthcare application, in which a bandage is able to monitor the vital signs of a person, a so-called Smart Bandage. One of the principles that is described here is based on measuring the absorption modulation of blood volume induced by the pulse (photoplethysmography). The information from such a bandage could be used to monitor wound healing by measuring the perfusion in the skin. The OLED and OPD devices are manufactured on separate foils and glass substrates by means of printing and coating technologies. Furthermore, the modular approach allows for the application of the optical sensing unit in a variety of other fields including chemical sensing. This, ultimately enables the measurement of a large variety of physiological parameters using the same bandage and the same basic sensor architecture. Here we discuss the build-up of our device in general terms. Specific characteristics of the used OLEDs and OPDs are shown and finally we demonstrate the functionality by simultaneously recorded photoplethysmograms of our device and a clinical pulseoximeter.
Electro-Optical Remote Sensing, Detection, and Photonic Technologies and Their Applications, 2007
Monitoring of personal wellbeing and optimizing human performance are areas where sensors have on... more Monitoring of personal wellbeing and optimizing human performance are areas where sensors have only begun to be used. One of the reasons for this is the specific demands that these application areas put on the underlying technology and system properties. In many cases these sensors will be integrated in clothing, be worn on the skin, or may even be placed
Physical Review B, 2000
The dc mobility of holes in four poly(p-phenylene vinylene) (PPV) derivatives (three fully conjug... more The dc mobility of holes in four poly(p-phenylene vinylene) (PPV) derivatives (three fully conjugated polymers with different side chains and one partially conjugated PPV) is examined as a function of temperature T and applied electrical field E. In all cases the mobility μ follows the ...
physica status solidi (b), 2000
The influence of side chains on hole transport in poly(p-phenylene vinylene) is examined as a fun... more The influence of side chains on hole transport in poly(p-phenylene vinylene) is examined as a function of temperature T and electrical field E by means of current±voltage experiments, and impedance spectroscopy which probes the transit time of injected carriers. The data are analyzed using a model for hopping in a Gaussian site-energy distribution. Energetic disorder predominantly governs the conductive properties of the PPV derivatives.
Optical Materials, 1998
Polymer LEDs have a number of attractive properties that make them suitable for many applications... more Polymer LEDs have a number of attractive properties that make them suitable for many applications. Operating at low voltage, bright large-area devices can be made by simple technology. One of the limitations that prohibited industrialization of polymer LEDs was ...
Optical Materials, 1999
In order to exploit the extensive potential of polymer light-emitting diodes in commercial applic... more In order to exploit the extensive potential of polymer light-emitting diodes in commercial applications a number of lifetime specifications have to be met. In this paper we report on the performance and stability of polymer light-emitting diodes based on fully conjugated PPV. Lifetime measurements have been performed on small (5 mm2) and large (8 cm2) area devices under different conditions,
Macromolecules, 1996
ABSTRACT The relaxation behavior of substituted bisphenol-A polycarbonates is investigated in the... more ABSTRACT The relaxation behavior of substituted bisphenol-A polycarbonates is investigated in the glassy state by mechanical spectroscopy. Conventional bisphenol-A polycarbonate (BA-PC) is compared with polycarbonates based on 1,1‘-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (TMC-PC) and 1,1‘-spiro[bis(3,3-dimethyl-6-hydroxyindane)] (SBI-PC) and random copolymers of the latter with bisphenol-A. In SBI-PC the phenyl flip is not just hindered but completely locked due to the chemical bridge via the spiro linkage. Despite the impossibility of phenyl motion, the γ-relaxation is observed for SBI-PC at roughly the same temperature as for the other two polycarbonates. This is real proof that the phenyl motion is not required for the typical γ-relaxation of polycarbonate at low temperature. Consequently, the polymer chain can get its mobility only from the flexibility of the carbonate linkage. It was also found that the width of the γ-relaxation peak in the SBI copolycarbonates decreases systematically with increasing spiro content. This means that in the rather broad peak in BA-PC there is a contribution of a second damping mechanism at the higher temperature side which is affected by the spiro linkage. That damping contribution is therefore ascribed to the phenyl motion. This also explains why the γ-relaxation of polycarbonates with ortho-substituted phenyls occurs at much higher temperatures. There the carbonate motion couples to the phenyl motion due to sterical hindrance, which is not the case in SBI-PC.
Macromolecules, 2005
The morphology of spin-cast films of poly(p-phenylenevinylene) (PPV) derivatives is studied as a ... more The morphology of spin-cast films of poly(p-phenylenevinylene) (PPV) derivatives is studied as a function of the substitution pattern of the conjugated backbone. Moreover, the influence of concentration in the casting solution, annealing, the choice of solvent, and the role of defects are addressed. By using a recently developed scanning-probe technique, we are able to visualize individual polymer chains and aggregates on the surface of spin-cast films. We find that a symmetric substitution pattern strongly promotes interchain aggregation in the surface layer, whereas an unsymmetric pattern in some cases leads to intrachain or self-aggregation. The nature of these intrachain aggregates is further investigated using molecular dynamics simulations. The observed molecular morphologies can in most cases be qualitatively related to macroscopic electrooptical properties. Therefore, our results strongly suggest that the surface morphology may be regarded as indicative of the morphology of the entire film.
Macromolecules, 1996
ABSTRACT Physical properties relating to chain stiffness are determined for a series of copolycar... more ABSTRACT Physical properties relating to chain stiffness are determined for a series of copolycarbonates of Bisphenol A and 1,1‘-spiro[bis(3,3‘-dimethyl-6-hydroxyindan)] (SBI) of varying composition. The entanglement molecular weight, Me, is derived from the rubbery plateau modulus. The recoverable compliance, is determined from the dynamic moduli as well as from steady shear creep and recovery experiments. It is found that all properties change in a nonlinear fashion with SBI content. For small SBI content the entanglement density is hardly affected, whereas Tg and increase strongly. With further increase in SBI content the effect on Tg is less pronounced. Me, however, starts increasing progressively to about 10 times that of pure Bisphenol A polycarbonate. The functional dependence of Me on composition is not predicted correctly from group contributions.
Langmuir, 2009
Miniaturization of biosensors is envisaged by the development of biochips consisting of parallel ... more Miniaturization of biosensors is envisaged by the development of biochips consisting of parallel microarray patterns of binding sites on rigid substrates, such as glass or silicon. Thin plastic substrates are promising flexible alternatives because of the possibility for large-area roll-to-roll manufacturing of disposable chips at lower costs. Mature optical lithography technology faces many challenges when used to pattern flexible foils as a result of the substrate instabilities, especially at higher temperatures. In this work, flexible biochips with gold electrode patterns were fabricated on thin polyethylene naphthalate (PEN) foils using photolithography. The gold electrode structures of the chips were manufactured by direct metal patterning and by lift-off processing. Both methodologies resulted in well-defined electrode patterns as concluded from optical microscopy and scanning electron microscopy (SEM) characterization and resistance measurements. The biochips were successfully employed for the electrical and optical detection of DNA molecules. The DNA detection was based on the immobilization of capture DNA between electrode gaps, hybridization with biotin-labeled target DNA, and enzymatic silver enhancement.
Journal of the American Chemical Society, 1997
For the construction of a CPEL-LED the use of a PPV derivative is preferred because of the favora... more For the construction of a CPEL-LED the use of a PPV derivative is preferred because of the favorable luminescence efficiency that can be attained in solid films of these polymers. First, enantiomerically pure poly{[2,5-bis[(S)-2-methylbutoxy]phenylene]vinylene} (BMB-PPV) has been ...
Journal of the American Chemical Society, 2006
Butyl, hexyl, and decyl derivatives of the liquid-crystalline organic semiconductor 5,5′′-bis(5al... more Butyl, hexyl, and decyl derivatives of the liquid-crystalline organic semiconductor 5,5′′-bis(5alkyl-2-thienylethynyl)-2,2′:5′,2′′-terthiophene were synthesized and studied with respect to their structural, optical, and electrical properties. By means of an optimized thermal annealing scheme the hexyl and decyl compounds could be processed into self-assembled monodomain films of up to 150 mm in diameter. These were investigated with X-ray diffractometry, which revealed a clearly single-crystalline monoclinic morphology with lamellae parallel to the substrate. Within the lamellae the molecules were found to arrange with a tilt of about 50°with the rubbing direction of the polyimide alignment layer. The resulting, close side-to-side packing was confirmed by measurements of the UV/vis absorption, which showed a dichroic ratio of 19 and indicated H-aggregation. AFM analyses revealed self-affinity in the surface roughness of the monodomain. The compounds showed bipolar charge transport in TOF measurements, with hole mobilities reaching up to 0.02 cm 2 /Vs and maximum electron mobilities around 0.002 cm 2 /Vs. The hexyl derivative was processed into large-area monodomain top-gate field-effect transistors, which were stable for months and showed anisotropic hole mobilities of up to 0.02 cm 2 /Vs. Compared to multidomain bottom-gate transistors the monodomain formation allowed for a mobility increase by 1 order of magnitude.
Journal of Applied Polymer Science, 2005
ABSTRACT Poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) blended with p... more ABSTRACT Poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) blended with poly[oxa-1,4-phenylene-1,2-(1-cyanovinylene)-2-methoxy,5-(3,7-dimethyloctyloxy)-1,4-phenylene-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV) has been used as the active layer for an all-polymer photovoltaic cell. The photovoltaic performance of devices is improved by a thermal treatment, which alters the morphology of the active layer. The morphology of the MDMO-PPV/PCNEPV blend has been studied with conventional transmission electron microscopy and energy-filtered transmission electron microscopy based on electron energy loss spectroscopy. The nitrogen of the cyano group within the PCNEPV has been be detected, and two-dimensional nitrogen distribution maps have been acquired. Nitrogen-rich domains have a size of approximately 20–50 nm and are homogeneously distributed over the entire film. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1001–1007, 2005
Chemistry of Materials, 2004
Photovoltaic properties of solution-processed semiconducting polymer blends have been studied. It... more Photovoltaic properties of solution-processed semiconducting polymer blends have been studied. It is demonstrated that photoinduced charge transfer occurs in binary mixtures of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and poly-[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV). Further, it is shown that the photovoltaic performance is improved by a thermal treatment which alters the morphology of the photoactive layer. The temperature necessary to achieve the enhanced performance is related to transition temperatures of the pure polymers. Device optimization yields solar cells with a power conversion efficiency of 0.75% under standard test conditions (AM 1.5, 1000 W/m 2 ).
… , 2008. SAS 2008. …, 2008
Advanced Materials, 2005
... [16] LE Euliss, SG Grancharov, S. O' Brien, TJ Deming, GD Stucky, CB Murray, GA Held... more ... [16] LE Euliss, SG Grancharov, S. O' Brien, TJ Deming, GD Stucky, CB Murray, GA Held, Nano Lett. 2003, 3,1489. ... By Paulette Prins, Luis P. Candeias, Albert JJM van Breemen, Jörgen Sweelssen, Peter T. Herwig, Herman FM Schoo, and Laurens DA Siebbeles* ...
Advanced Functional Materials, 2005
The influence of the substitution pattern (unsymmetrical or symmetrical), the nature of the side ... more The influence of the substitution pattern (unsymmetrical or symmetrical), the nature of the side chain (linear or branched), and the processing of several solution processable alkoxy-substituted poly(p-phenylene vinylene)s (PPVs) on the charge-carrier mobility in organic field-effect transistors (OFETs) is investigated. We have found the highest mobilities in a class of symmetrically substituted PPVs with linear alkyl chains (e.g., R 1 , R 2 = n-C 11 H 23 , R 3 = n-C 18 H 37 ). We have shown that the mobility of these PPVs can be improved significantly up to values of 10 ±2 cm 2 V ±1 s ±1 by annealing at 110 C. In addition, these devices display an excellent stability in air and dark conditions. No change in the electrical performance is observed, even after storage for thirty days in humid air.
Organic Photovoltaics Iv, 2004
Polymer bulk hetero junction solar cells were made from poly(2-methoxy-5-(3,7-dimethyloctyloxy)-1... more Polymer bulk hetero junction solar cells were made from poly(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene) (MDMO-PPV) as donor and poly(cyanoetherphenylenevinylene) (PCNEPV) derivatives as acceptor material. In this paper we start out with discussing the synthesis of the materials. Subsequently, the main issues concerning the devices are treated. Annealing the devices yielded devices with encouraging efficiencies of 0.5% (1 sun, 100mW/cm 2 ), as calculated from the maximum power points (MPP). AFM studies revealed that this anneal step improves especially the interface of the active layer with the under laying PEDOT:PSS, although mobility and morphology changes can not be ruled out. Lowering the molecular weight (Mw) of the MDMO-PPV gave a slight improvement of the device performance. Decreasing the Mw of the acceptor material, MDMO-PCNEPV (PCNEPV derivative with the same side chains as MDMO-PPV) and optimizing the layer thickness led to a device with an efficiency of 0.65%. Finally we looked into the influence of the nature of the side chains on the acceptor polymer. The results suggest that the closer the resemblance between donor and acceptor is the better the device performance.
The operation characteristics of polymer light-emitting diodes (PLEDs) are strongly dependent on ... more The operation characteristics of polymer light-emitting diodes (PLEDs) are strongly dependent on materials, processing and the structure of the device. The device structure developed at Philips Research is presented together with some typical results for brightness, ef®ciency, response times and stability. The PLEDs typically operate at a voltage of 3±4 V for a brightness of 100 cd m À 2 and have an ef®ciency ranging from 2 cd A À 1 for orange emitting polymers (610 nm) up to 16 cd A À 1 for green emitting polymers (550 nm). The response time under conditions for display operation is determined by the charge carrier transport properties and amounts to 43 ns. Lifetimes of several thousand hours have been obtained for large orange emitting devices of 8 cm 2 for daylight visibility at room temperature.
Organic Light-Emitting Materials and Devices, 1997
ABSTRACT In this paper on polymer LEDs we discuss the formation of black spots, surface treatment... more ABSTRACT In this paper on polymer LEDs we discuss the formation of black spots, surface treatments of the anode, and photochemical degradation of the emissive polymer. We find that small pinholes in the cathode layer are the origin of the black spots. The black spots form when H2O or O2 diffuse through the pinholes and react with the cathode at the polymer-cathode interface.A model is presented that describes the growth of the spots. We find that for both indium-tin-oxide (ITO) and Au anodes, an UV/O3 or an O2 plasma cleaning treatment increases the work function by 0.8-0.9 eV. A higher work function may lead to a better hole injection and a reduction in the operating voltage. We present a method to measure the quantum yield for bleaching, (gamma) equals 1.6$MN4 and (gamma) equals 1.7 10-7 for bleaching of dialkoxy-PPV in air and vacuum, respectively, indicating that the polymer is 1000 times more stable in vacuum than in air.
Organic Field-Effect Transistors VII and Organic Semiconductors in Sensors and Bioelectronics, 2008
Sensors based on organic electronic devices are emerging in a wide range of application areas. He... more Sensors based on organic electronic devices are emerging in a wide range of application areas. Here we present a sensor platform using organic light emitting diodes (OLED) and organic photodiodes (OPD) as active components. By means of lamination and interconnection technology the functional foils with OLED and OPD arrays form an in-plane optical sensor platform (IPOS). This platform can be extended with a wireless data and signal processing unit yielding a sensor node. The focus of our research is to engage the node in a healthcare application, in which a bandage is able to monitor the vital signs of a person, a so-called Smart Bandage. One of the principles that is described here is based on measuring the absorption modulation of blood volume induced by the pulse (photoplethysmography). The information from such a bandage could be used to monitor wound healing by measuring the perfusion in the skin. The OLED and OPD devices are manufactured on separate foils and glass substrates by means of printing and coating technologies. Furthermore, the modular approach allows for the application of the optical sensing unit in a variety of other fields including chemical sensing. This, ultimately enables the measurement of a large variety of physiological parameters using the same bandage and the same basic sensor architecture. Here we discuss the build-up of our device in general terms. Specific characteristics of the used OLEDs and OPDs are shown and finally we demonstrate the functionality by simultaneously recorded photoplethysmograms of our device and a clinical pulseoximeter.
Electro-Optical Remote Sensing, Detection, and Photonic Technologies and Their Applications, 2007
Monitoring of personal wellbeing and optimizing human performance are areas where sensors have on... more Monitoring of personal wellbeing and optimizing human performance are areas where sensors have only begun to be used. One of the reasons for this is the specific demands that these application areas put on the underlying technology and system properties. In many cases these sensors will be integrated in clothing, be worn on the skin, or may even be placed
Physical Review B, 2000
The dc mobility of holes in four poly(p-phenylene vinylene) (PPV) derivatives (three fully conjug... more The dc mobility of holes in four poly(p-phenylene vinylene) (PPV) derivatives (three fully conjugated polymers with different side chains and one partially conjugated PPV) is examined as a function of temperature T and applied electrical field E. In all cases the mobility μ follows the ...
physica status solidi (b), 2000
The influence of side chains on hole transport in poly(p-phenylene vinylene) is examined as a fun... more The influence of side chains on hole transport in poly(p-phenylene vinylene) is examined as a function of temperature T and electrical field E by means of current±voltage experiments, and impedance spectroscopy which probes the transit time of injected carriers. The data are analyzed using a model for hopping in a Gaussian site-energy distribution. Energetic disorder predominantly governs the conductive properties of the PPV derivatives.
Optical Materials, 1998
Polymer LEDs have a number of attractive properties that make them suitable for many applications... more Polymer LEDs have a number of attractive properties that make them suitable for many applications. Operating at low voltage, bright large-area devices can be made by simple technology. One of the limitations that prohibited industrialization of polymer LEDs was ...
Optical Materials, 1999
In order to exploit the extensive potential of polymer light-emitting diodes in commercial applic... more In order to exploit the extensive potential of polymer light-emitting diodes in commercial applications a number of lifetime specifications have to be met. In this paper we report on the performance and stability of polymer light-emitting diodes based on fully conjugated PPV. Lifetime measurements have been performed on small (5 mm2) and large (8 cm2) area devices under different conditions,
Macromolecules, 1996
ABSTRACT The relaxation behavior of substituted bisphenol-A polycarbonates is investigated in the... more ABSTRACT The relaxation behavior of substituted bisphenol-A polycarbonates is investigated in the glassy state by mechanical spectroscopy. Conventional bisphenol-A polycarbonate (BA-PC) is compared with polycarbonates based on 1,1‘-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane (TMC-PC) and 1,1‘-spiro[bis(3,3-dimethyl-6-hydroxyindane)] (SBI-PC) and random copolymers of the latter with bisphenol-A. In SBI-PC the phenyl flip is not just hindered but completely locked due to the chemical bridge via the spiro linkage. Despite the impossibility of phenyl motion, the γ-relaxation is observed for SBI-PC at roughly the same temperature as for the other two polycarbonates. This is real proof that the phenyl motion is not required for the typical γ-relaxation of polycarbonate at low temperature. Consequently, the polymer chain can get its mobility only from the flexibility of the carbonate linkage. It was also found that the width of the γ-relaxation peak in the SBI copolycarbonates decreases systematically with increasing spiro content. This means that in the rather broad peak in BA-PC there is a contribution of a second damping mechanism at the higher temperature side which is affected by the spiro linkage. That damping contribution is therefore ascribed to the phenyl motion. This also explains why the γ-relaxation of polycarbonates with ortho-substituted phenyls occurs at much higher temperatures. There the carbonate motion couples to the phenyl motion due to sterical hindrance, which is not the case in SBI-PC.
Macromolecules, 2005
The morphology of spin-cast films of poly(p-phenylenevinylene) (PPV) derivatives is studied as a ... more The morphology of spin-cast films of poly(p-phenylenevinylene) (PPV) derivatives is studied as a function of the substitution pattern of the conjugated backbone. Moreover, the influence of concentration in the casting solution, annealing, the choice of solvent, and the role of defects are addressed. By using a recently developed scanning-probe technique, we are able to visualize individual polymer chains and aggregates on the surface of spin-cast films. We find that a symmetric substitution pattern strongly promotes interchain aggregation in the surface layer, whereas an unsymmetric pattern in some cases leads to intrachain or self-aggregation. The nature of these intrachain aggregates is further investigated using molecular dynamics simulations. The observed molecular morphologies can in most cases be qualitatively related to macroscopic electrooptical properties. Therefore, our results strongly suggest that the surface morphology may be regarded as indicative of the morphology of the entire film.
Macromolecules, 1996
ABSTRACT Physical properties relating to chain stiffness are determined for a series of copolycar... more ABSTRACT Physical properties relating to chain stiffness are determined for a series of copolycarbonates of Bisphenol A and 1,1‘-spiro[bis(3,3‘-dimethyl-6-hydroxyindan)] (SBI) of varying composition. The entanglement molecular weight, Me, is derived from the rubbery plateau modulus. The recoverable compliance, is determined from the dynamic moduli as well as from steady shear creep and recovery experiments. It is found that all properties change in a nonlinear fashion with SBI content. For small SBI content the entanglement density is hardly affected, whereas Tg and increase strongly. With further increase in SBI content the effect on Tg is less pronounced. Me, however, starts increasing progressively to about 10 times that of pure Bisphenol A polycarbonate. The functional dependence of Me on composition is not predicted correctly from group contributions.
Langmuir, 2009
Miniaturization of biosensors is envisaged by the development of biochips consisting of parallel ... more Miniaturization of biosensors is envisaged by the development of biochips consisting of parallel microarray patterns of binding sites on rigid substrates, such as glass or silicon. Thin plastic substrates are promising flexible alternatives because of the possibility for large-area roll-to-roll manufacturing of disposable chips at lower costs. Mature optical lithography technology faces many challenges when used to pattern flexible foils as a result of the substrate instabilities, especially at higher temperatures. In this work, flexible biochips with gold electrode patterns were fabricated on thin polyethylene naphthalate (PEN) foils using photolithography. The gold electrode structures of the chips were manufactured by direct metal patterning and by lift-off processing. Both methodologies resulted in well-defined electrode patterns as concluded from optical microscopy and scanning electron microscopy (SEM) characterization and resistance measurements. The biochips were successfully employed for the electrical and optical detection of DNA molecules. The DNA detection was based on the immobilization of capture DNA between electrode gaps, hybridization with biotin-labeled target DNA, and enzymatic silver enhancement.
Journal of the American Chemical Society, 1997
For the construction of a CPEL-LED the use of a PPV derivative is preferred because of the favora... more For the construction of a CPEL-LED the use of a PPV derivative is preferred because of the favorable luminescence efficiency that can be attained in solid films of these polymers. First, enantiomerically pure poly{[2,5-bis[(S)-2-methylbutoxy]phenylene]vinylene} (BMB-PPV) has been ...
Journal of the American Chemical Society, 2006
Butyl, hexyl, and decyl derivatives of the liquid-crystalline organic semiconductor 5,5′′-bis(5al... more Butyl, hexyl, and decyl derivatives of the liquid-crystalline organic semiconductor 5,5′′-bis(5alkyl-2-thienylethynyl)-2,2′:5′,2′′-terthiophene were synthesized and studied with respect to their structural, optical, and electrical properties. By means of an optimized thermal annealing scheme the hexyl and decyl compounds could be processed into self-assembled monodomain films of up to 150 mm in diameter. These were investigated with X-ray diffractometry, which revealed a clearly single-crystalline monoclinic morphology with lamellae parallel to the substrate. Within the lamellae the molecules were found to arrange with a tilt of about 50°with the rubbing direction of the polyimide alignment layer. The resulting, close side-to-side packing was confirmed by measurements of the UV/vis absorption, which showed a dichroic ratio of 19 and indicated H-aggregation. AFM analyses revealed self-affinity in the surface roughness of the monodomain. The compounds showed bipolar charge transport in TOF measurements, with hole mobilities reaching up to 0.02 cm 2 /Vs and maximum electron mobilities around 0.002 cm 2 /Vs. The hexyl derivative was processed into large-area monodomain top-gate field-effect transistors, which were stable for months and showed anisotropic hole mobilities of up to 0.02 cm 2 /Vs. Compared to multidomain bottom-gate transistors the monodomain formation allowed for a mobility increase by 1 order of magnitude.
Journal of Applied Polymer Science, 2005
ABSTRACT Poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) blended with p... more ABSTRACT Poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) blended with poly[oxa-1,4-phenylene-1,2-(1-cyanovinylene)-2-methoxy,5-(3,7-dimethyloctyloxy)-1,4-phenylene-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV) has been used as the active layer for an all-polymer photovoltaic cell. The photovoltaic performance of devices is improved by a thermal treatment, which alters the morphology of the active layer. The morphology of the MDMO-PPV/PCNEPV blend has been studied with conventional transmission electron microscopy and energy-filtered transmission electron microscopy based on electron energy loss spectroscopy. The nitrogen of the cyano group within the PCNEPV has been be detected, and two-dimensional nitrogen distribution maps have been acquired. Nitrogen-rich domains have a size of approximately 20–50 nm and are homogeneously distributed over the entire film. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1001–1007, 2005
Chemistry of Materials, 2004
Photovoltaic properties of solution-processed semiconducting polymer blends have been studied. It... more Photovoltaic properties of solution-processed semiconducting polymer blends have been studied. It is demonstrated that photoinduced charge transfer occurs in binary mixtures of poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) and poly-[oxa-1,4-phenylene-(1-cyano-1,2-vinylene)-(2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene)-1,2-(2-cyanovinylene)-1,4-phenylene] (PCNEPV). Further, it is shown that the photovoltaic performance is improved by a thermal treatment which alters the morphology of the photoactive layer. The temperature necessary to achieve the enhanced performance is related to transition temperatures of the pure polymers. Device optimization yields solar cells with a power conversion efficiency of 0.75% under standard test conditions (AM 1.5, 1000 W/m 2 ).
… , 2008. SAS 2008. …, 2008
Advanced Materials, 2005
... [16] LE Euliss, SG Grancharov, S. O' Brien, TJ Deming, GD Stucky, CB Murray, GA Held... more ... [16] LE Euliss, SG Grancharov, S. O' Brien, TJ Deming, GD Stucky, CB Murray, GA Held, Nano Lett. 2003, 3,1489. ... By Paulette Prins, Luis P. Candeias, Albert JJM van Breemen, Jörgen Sweelssen, Peter T. Herwig, Herman FM Schoo, and Laurens DA Siebbeles* ...
Advanced Functional Materials, 2005
The influence of the substitution pattern (unsymmetrical or symmetrical), the nature of the side ... more The influence of the substitution pattern (unsymmetrical or symmetrical), the nature of the side chain (linear or branched), and the processing of several solution processable alkoxy-substituted poly(p-phenylene vinylene)s (PPVs) on the charge-carrier mobility in organic field-effect transistors (OFETs) is investigated. We have found the highest mobilities in a class of symmetrically substituted PPVs with linear alkyl chains (e.g., R 1 , R 2 = n-C 11 H 23 , R 3 = n-C 18 H 37 ). We have shown that the mobility of these PPVs can be improved significantly up to values of 10 ±2 cm 2 V ±1 s ±1 by annealing at 110 C. In addition, these devices display an excellent stability in air and dark conditions. No change in the electrical performance is observed, even after storage for thirty days in humid air.