ABSTRACT 12 An appropriate choice of the cathode material and the process of cathode deposition i... more ABSTRACT 12 An appropriate choice of the cathode material and the process of cathode deposition is a key issue in the development of polymer light emitting devices. In this paper, we report on the impact of low work function metals on the luminescence efficiency of thin films of polyfluorene type polymers. Photoluminescence as well as electroluminescence experiments are presented, and in both cases, a strong correlation between the metal layer thickness and the luminescence efficiency is demonstrated. By means of time-of-flight secondary ion mass spectroscopy (TOF-SIMS), the distribution of the metal contamination within the polymer layers is determined. The results strongly suggest that impurity quenching of excitons by metal atoms inside the polymer layer takes place and strongly affects luminescence and device efficiency.
* This document has been approved for public release and sale: its distribution is unlimited S85"... more * This document has been approved for public release and sale: its distribution is unlimited S85" 8 12 099 DoJ 1AM 12 1473 SCCUITN' CLASSIFICATION ZP-NIS X4GrL 'Whomu ^&#a £Aww...e CUO(ZNIC SAMPLE STAGE FOR THE CANECA IMS-3f ION MICROSCOPE
Electron attachment Iineshapes, cross sections and rate constants at ultra-low energies in severa... more Electron attachment Iineshapes, cross sections and rate constants at ultra-low energies in several halomethyl and haloethyl molecules
Two references in our review article were in error; we regret the oversight. The technical points... more Two references in our review article were in error; we regret the oversight. The technical points of disagreement are discussed, and a table comparing the University of Chicago scanning ion microprobe and the Cornell stigmatic ion microscope is provided to clarify one by R. Levi-Setti [Rev. Sci. Instrum. 59, xxx (1988)].
Wherein a fast (50 ns) rise-time high-frequency square-wave generator capable of switching betwee... more Wherein a fast (50 ns) rise-time high-frequency square-wave generator capable of switching between arbitrary voltages of high potential difference (1000 V or more) is described utilizing solid-state circuitry of low power consumption. Power field effect transistors are used as the active switching element, which afford compact size and simplified circuit construction. With the addition of monostable multivibrators, high-voltage square-wave pulse trains of controllable phase are produced. The generator should find application in a wide variety of situations where fast switching between high voltages is required, such as in time-of-flight, coincidence, and beams-modulation experiments.
A new, pulsed, high-current, in-line reversal electron attachment ionizer/detector is described. ... more A new, pulsed, high-current, in-line reversal electron attachment ionizer/detector is described. The ionizer is capable of delivering a beam of electrons into an electrostatic mirror field to form a planar wall of electrons having zero kinetic energy. Electron attachment to a molecular target at the reversal point produces either parent or fragment negative ions through a zero-energy (s-wave) state. The atomic or molecular ion is pulsed out of the attachment region approximately 2 μs after the electrons are pulsed off, and focused onto the entrance plane of a quadrupole mass analyzer. The sensitivity of the apparatus is preliminarily assessed, and its higher-energy behavior with regard to molecular attachment and ionization is described.
This paper reviews and critically assesses progress in the field of surface and near-surface imag... more This paper reviews and critically assesses progress in the field of surface and near-surface imaging microscopies based on secondary ion mass spectrometry. The ion microscope performs a variety of analytical functions, including complete mass spectra and isotope ratios from areas on the submicron scale, and lateral distribution analysis using ion imaging, with high sensitivity for all elements of the periodic table. Recent developments have improved the ion microscope’s ability to image a specimen’s elemental morphology with spatial resolutions below 100 nm. Criteria for the quantitative evaluation of ion images and the instruments that produce them are reviewed within the framework of information-transmission theory. A complete and general description of the physical principles guiding the types of instrumentation available is thus presented, with emphasis on the accuracy and precision of an analytical measurement. Several directions for future developments are proposed.
We describe an improved design and operation of a prototype high-voltage full-floating, high-freq... more We describe an improved design and operation of a prototype high-voltage full-floating, high-frequency square-wave generator over that first described in this journal [Rev. Sci. Instrum. 60, 779 (1989)]. The final design is seen to be more versatile, overcomes possible momentary simultaneous ON states in the totem-pole MOSFET configuration, and is less susceptible to deleterious effects caused by component aging, and replacements with nonidentical parts.
Figure 3. Photoacoustic detection of azulene in supercritical C02. elution of 20-pL injected samp... more Figure 3. Photoacoustic detection of azulene in supercritical C02. elution of 20-pL injected sample of azulene 6.26 X ... York, 1968. Melhulsh, WH NBS Spec. Publ. ( US . ) 1973, No. 378, 137-150. Brannon, JH; Magde, D. J. Phys. Chem. 1078, 82, 705-709. Harrison, D.; ...
Light-emitting polymers have been studied intensively as materials for light-emitting diodes (LED... more Light-emitting polymers have been studied intensively as materials for light-emitting diodes (LEDs). Here research efforts toward developing these materials for commercial applications are reviewed. The Figure shows the preferred two-layer device structure for commercial polymer LEDs as well as polyfluorene, one of the polymers discussed.
Efficient blue electroluminescence, peaked at 436 nm, is demonstrated from polymer light-emitting... more Efficient blue electroluminescence, peaked at 436 nm, is demonstrated from polymer light-emitting diodes operating at high brightness. A dioctyl-substituted polyfluorene was used as the emissive layer in combination with a polymeric triphenyldiamine hole transport layer. The luminance reaches 600 cd/m2 at a current density of 150 mA/cm2 for a bias voltage of 20 V, corresponding to an efficiency of 0.25 cd/A and a luminosity of 0.04 lm/W. These values are optimized at a critical emissive layer thickness.
A combination electrostatic octupole stigmator and cosine deflector has been incorporated into th... more A combination electrostatic octupole stigmator and cosine deflector has been incorporated into the secondary ion-optical lattice of the stigmatic ion microscope. Distortion-free images are obtained with a ∼15% improved image resolution and a ∼10% increased secondary ion signal measured at the detector, the latter improvement being beneficial also for depth-profile (ion microprobe) work. The details outlined in this paper, which are easy to implement, are offered to users of the CAMECA IMS-3f secondary ion mass spectrometer for a significant improvement in its imaging capability.
Inorganic cations (Na+, K+, Ca+ +, etc.) play important roles in cell function, and cultured cell... more Inorganic cations (Na+, K+, Ca+ +, etc.) play important roles in cell function, and cultured cells provide an excellent system to understand the role of ions in the state of health and disease. Ion microscopy, based on secondary ion mass spectrometry (SIMS), provides a powerful technique for such studies (1). The unique ion optics of the instrument are capable of producing visual ion images showing cell morphology with a lateral resolution of ~0.5 µm. However, reliable means of sample preparation and an understanding of SIMS effects is necessary before such studies can be undertaken.
2& SECtiRITY CLASSIMIA ..... v3. rT IC ELECTE h* is dcocunent has been approved for public releas... more 2& SECtiRITY CLASSIMIA ..... v3. rT IC ELECTE h* is dcocunent has been approved for public release and sale: its distribution is unlimited 85 10 8 154A &15
We report our progress in the preparation of a variety of high molecular weight polymers based on... more We report our progress in the preparation of a variety of high molecular weight polymers based on fluorene ring system. A portfolio of fluorene-related homopolymers and copolymers has been developed through Suzuki coupling of 9,9-disubstituted 2,7-bis-1,3,2-di-Ž. oxaborolanyl-fluorene with a variety of aromatic dibromides. In the case of fluorene homopolymers, the polyphenylene PP main chain provides the mechanical, electrical as well as the electronic properties while the presence of carbon-9 forces the phenyl rings to be in plane resulting in improved conjugation. Additionally, carbon-9 provides a site for polymer property modification without altering effective conjugation. In the case of alternating polymers, the optical and electronic properties of the polymers are tailored through selective incorporation of different aromatic units into the system. These polymers are soluble in common organic solvents and are readily Ž. Ž .Ž. processed into thin films of high quality by spin casting. Unlike light emitting diodes LEDs based on poly phenylenevinylene PPV and related materials which have holes as the majority carriers, devices with fluorene polymers appear to have electrons as the majority carrier and their performance is markedly improved when modified with an appropriate polymeric hole transporting layer. Red and green devices have shown lifetimes exceeding 1000 h at a brightness of 150 cdrm 2 with minimal voltage change.
Abstract The lifetime-limiting failure mechanisms of CuInGaSSe (CIGSS) solar devices made by Shel... more Abstract The lifetime-limiting failure mechanisms of CuInGaSSe (CIGSS) solar devices made by Shell Solar Industries (SSI) were investigated. In our study, SSI minimodules were exposed to dry-heat 85Ã ÂC, damp-heat 85Ã ÂC/85% RH and aerobic and anaerobic ...
This paper presents a structure-property model for carbon fiber derived from a polyethylene (PE) ... more This paper presents a structure-property model for carbon fiber derived from a polyethylene (PE) precursor that relates tensile modulus to the elastic properties and angular distribution of constituent graphitic layers, as measured using wide-angle x-ray diffraction of individual carbon fiber filaments. The observed relationship and interpretation of data using a uniform-stress model has revealed fundamental differences in the nature of the microstructure present in carbon fiber produced from polyethylene compared to carbon fiber produced from polyacrylonitrile (PAN) or pitch precursors. Specifically, it was found that the shear modulus, indicative of the shear between adjacent graphitic layers of the carbonized fiber is lower for polyethylene-derived carbon fiber than for PAN-or pitch-derived carbon fiber, suggesting that the covalent CC sp 3 crosslink density connecting adjacent graphitic layers in PE-derived carbon fiber is reduced. This structure that is less crosslinked is anticipated to be easier to orient during carbonization and high-temperature graphitization processes, yielding a highly oriented structure necessary for high tensile modulus.
ABSTRACT 12 An appropriate choice of the cathode material and the process of cathode deposition i... more ABSTRACT 12 An appropriate choice of the cathode material and the process of cathode deposition is a key issue in the development of polymer light emitting devices. In this paper, we report on the impact of low work function metals on the luminescence efficiency of thin films of polyfluorene type polymers. Photoluminescence as well as electroluminescence experiments are presented, and in both cases, a strong correlation between the metal layer thickness and the luminescence efficiency is demonstrated. By means of time-of-flight secondary ion mass spectroscopy (TOF-SIMS), the distribution of the metal contamination within the polymer layers is determined. The results strongly suggest that impurity quenching of excitons by metal atoms inside the polymer layer takes place and strongly affects luminescence and device efficiency.
* This document has been approved for public release and sale: its distribution is unlimited S85"... more * This document has been approved for public release and sale: its distribution is unlimited S85" 8 12 099 DoJ 1AM 12 1473 SCCUITN' CLASSIFICATION ZP-NIS X4GrL 'Whomu ^&#a £Aww...e CUO(ZNIC SAMPLE STAGE FOR THE CANECA IMS-3f ION MICROSCOPE
Electron attachment Iineshapes, cross sections and rate constants at ultra-low energies in severa... more Electron attachment Iineshapes, cross sections and rate constants at ultra-low energies in several halomethyl and haloethyl molecules
Two references in our review article were in error; we regret the oversight. The technical points... more Two references in our review article were in error; we regret the oversight. The technical points of disagreement are discussed, and a table comparing the University of Chicago scanning ion microprobe and the Cornell stigmatic ion microscope is provided to clarify one by R. Levi-Setti [Rev. Sci. Instrum. 59, xxx (1988)].
Wherein a fast (50 ns) rise-time high-frequency square-wave generator capable of switching betwee... more Wherein a fast (50 ns) rise-time high-frequency square-wave generator capable of switching between arbitrary voltages of high potential difference (1000 V or more) is described utilizing solid-state circuitry of low power consumption. Power field effect transistors are used as the active switching element, which afford compact size and simplified circuit construction. With the addition of monostable multivibrators, high-voltage square-wave pulse trains of controllable phase are produced. The generator should find application in a wide variety of situations where fast switching between high voltages is required, such as in time-of-flight, coincidence, and beams-modulation experiments.
A new, pulsed, high-current, in-line reversal electron attachment ionizer/detector is described. ... more A new, pulsed, high-current, in-line reversal electron attachment ionizer/detector is described. The ionizer is capable of delivering a beam of electrons into an electrostatic mirror field to form a planar wall of electrons having zero kinetic energy. Electron attachment to a molecular target at the reversal point produces either parent or fragment negative ions through a zero-energy (s-wave) state. The atomic or molecular ion is pulsed out of the attachment region approximately 2 μs after the electrons are pulsed off, and focused onto the entrance plane of a quadrupole mass analyzer. The sensitivity of the apparatus is preliminarily assessed, and its higher-energy behavior with regard to molecular attachment and ionization is described.
This paper reviews and critically assesses progress in the field of surface and near-surface imag... more This paper reviews and critically assesses progress in the field of surface and near-surface imaging microscopies based on secondary ion mass spectrometry. The ion microscope performs a variety of analytical functions, including complete mass spectra and isotope ratios from areas on the submicron scale, and lateral distribution analysis using ion imaging, with high sensitivity for all elements of the periodic table. Recent developments have improved the ion microscope’s ability to image a specimen’s elemental morphology with spatial resolutions below 100 nm. Criteria for the quantitative evaluation of ion images and the instruments that produce them are reviewed within the framework of information-transmission theory. A complete and general description of the physical principles guiding the types of instrumentation available is thus presented, with emphasis on the accuracy and precision of an analytical measurement. Several directions for future developments are proposed.
We describe an improved design and operation of a prototype high-voltage full-floating, high-freq... more We describe an improved design and operation of a prototype high-voltage full-floating, high-frequency square-wave generator over that first described in this journal [Rev. Sci. Instrum. 60, 779 (1989)]. The final design is seen to be more versatile, overcomes possible momentary simultaneous ON states in the totem-pole MOSFET configuration, and is less susceptible to deleterious effects caused by component aging, and replacements with nonidentical parts.
Figure 3. Photoacoustic detection of azulene in supercritical C02. elution of 20-pL injected samp... more Figure 3. Photoacoustic detection of azulene in supercritical C02. elution of 20-pL injected sample of azulene 6.26 X ... York, 1968. Melhulsh, WH NBS Spec. Publ. ( US . ) 1973, No. 378, 137-150. Brannon, JH; Magde, D. J. Phys. Chem. 1078, 82, 705-709. Harrison, D.; ...
Light-emitting polymers have been studied intensively as materials for light-emitting diodes (LED... more Light-emitting polymers have been studied intensively as materials for light-emitting diodes (LEDs). Here research efforts toward developing these materials for commercial applications are reviewed. The Figure shows the preferred two-layer device structure for commercial polymer LEDs as well as polyfluorene, one of the polymers discussed.
Efficient blue electroluminescence, peaked at 436 nm, is demonstrated from polymer light-emitting... more Efficient blue electroluminescence, peaked at 436 nm, is demonstrated from polymer light-emitting diodes operating at high brightness. A dioctyl-substituted polyfluorene was used as the emissive layer in combination with a polymeric triphenyldiamine hole transport layer. The luminance reaches 600 cd/m2 at a current density of 150 mA/cm2 for a bias voltage of 20 V, corresponding to an efficiency of 0.25 cd/A and a luminosity of 0.04 lm/W. These values are optimized at a critical emissive layer thickness.
A combination electrostatic octupole stigmator and cosine deflector has been incorporated into th... more A combination electrostatic octupole stigmator and cosine deflector has been incorporated into the secondary ion-optical lattice of the stigmatic ion microscope. Distortion-free images are obtained with a ∼15% improved image resolution and a ∼10% increased secondary ion signal measured at the detector, the latter improvement being beneficial also for depth-profile (ion microprobe) work. The details outlined in this paper, which are easy to implement, are offered to users of the CAMECA IMS-3f secondary ion mass spectrometer for a significant improvement in its imaging capability.
Inorganic cations (Na+, K+, Ca+ +, etc.) play important roles in cell function, and cultured cell... more Inorganic cations (Na+, K+, Ca+ +, etc.) play important roles in cell function, and cultured cells provide an excellent system to understand the role of ions in the state of health and disease. Ion microscopy, based on secondary ion mass spectrometry (SIMS), provides a powerful technique for such studies (1). The unique ion optics of the instrument are capable of producing visual ion images showing cell morphology with a lateral resolution of ~0.5 µm. However, reliable means of sample preparation and an understanding of SIMS effects is necessary before such studies can be undertaken.
2& SECtiRITY CLASSIMIA ..... v3. rT IC ELECTE h* is dcocunent has been approved for public releas... more 2& SECtiRITY CLASSIMIA ..... v3. rT IC ELECTE h* is dcocunent has been approved for public release and sale: its distribution is unlimited 85 10 8 154A &15
We report our progress in the preparation of a variety of high molecular weight polymers based on... more We report our progress in the preparation of a variety of high molecular weight polymers based on fluorene ring system. A portfolio of fluorene-related homopolymers and copolymers has been developed through Suzuki coupling of 9,9-disubstituted 2,7-bis-1,3,2-di-Ž. oxaborolanyl-fluorene with a variety of aromatic dibromides. In the case of fluorene homopolymers, the polyphenylene PP main chain provides the mechanical, electrical as well as the electronic properties while the presence of carbon-9 forces the phenyl rings to be in plane resulting in improved conjugation. Additionally, carbon-9 provides a site for polymer property modification without altering effective conjugation. In the case of alternating polymers, the optical and electronic properties of the polymers are tailored through selective incorporation of different aromatic units into the system. These polymers are soluble in common organic solvents and are readily Ž. Ž .Ž. processed into thin films of high quality by spin casting. Unlike light emitting diodes LEDs based on poly phenylenevinylene PPV and related materials which have holes as the majority carriers, devices with fluorene polymers appear to have electrons as the majority carrier and their performance is markedly improved when modified with an appropriate polymeric hole transporting layer. Red and green devices have shown lifetimes exceeding 1000 h at a brightness of 150 cdrm 2 with minimal voltage change.
Abstract The lifetime-limiting failure mechanisms of CuInGaSSe (CIGSS) solar devices made by Shel... more Abstract The lifetime-limiting failure mechanisms of CuInGaSSe (CIGSS) solar devices made by Shell Solar Industries (SSI) were investigated. In our study, SSI minimodules were exposed to dry-heat 85Ã ÂC, damp-heat 85Ã ÂC/85% RH and aerobic and anaerobic ...
This paper presents a structure-property model for carbon fiber derived from a polyethylene (PE) ... more This paper presents a structure-property model for carbon fiber derived from a polyethylene (PE) precursor that relates tensile modulus to the elastic properties and angular distribution of constituent graphitic layers, as measured using wide-angle x-ray diffraction of individual carbon fiber filaments. The observed relationship and interpretation of data using a uniform-stress model has revealed fundamental differences in the nature of the microstructure present in carbon fiber produced from polyethylene compared to carbon fiber produced from polyacrylonitrile (PAN) or pitch precursors. Specifically, it was found that the shear modulus, indicative of the shear between adjacent graphitic layers of the carbonized fiber is lower for polyethylene-derived carbon fiber than for PAN-or pitch-derived carbon fiber, suggesting that the covalent CC sp 3 crosslink density connecting adjacent graphitic layers in PE-derived carbon fiber is reduced. This structure that is less crosslinked is anticipated to be easier to orient during carbonization and high-temperature graphitization processes, yielding a highly oriented structure necessary for high tensile modulus.
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