This document summarizes research on the influence of oxygen present during the deposition of a calcium cathode on the performance of polymeric light emitting diodes (pLEDs). The researchers varied the oxygen background pressure during calcium deposition from 10-8 to 10-5 mbar and measured the resulting oxygen concentration profiles and device characteristics. They found that increasing oxygen pressure resulted in decreasing external efficiency and brightness, with the current showing a minimum at intermediate pressures. pLEDs with fully oxidized calcium were non-operational. The best performance was obtained with the lowest possible oxygen concentration during calcium evaporation.
This document describes how synchrotron-based X-ray spectroscopy techniques like XANES and STXM can provide insights into structure-performance relationships in battery materials to enable faster optimization. These techniques allow mapping of local chemistry, bonding structure, and phase distributions. Studies have shown how surface coatings and composite designs can influence properties like conductivity and stability. Chemical mapping of electrodes also revealed non-uniform reactions related to "hot spots" that correlate with performance. Faster screening of materials and correlation of structural properties with electrochemical data could significantly reduce battery development timelines.
Band edge engineering of composite photoanodes for dye sensitized solar cellsvenkatamanthina
This document discusses engineering the band edges of composite photoanodes for dye-sensitized solar cells through doping. Specifically, it doped ZnO nanorods with cobalt to lower its conduction band minimum and doped TiO2 nanoparticles with zirconium to raise its conduction band minimum in order to overcome an energy barrier preventing electron transfer. Characterization with diffuse reflectance spectroscopy and open circuit voltage measurements under illumination confirmed the doping shifted the band edges as intended. However, dye-sensitized solar cells fabricated with the composite nanostructures did not show improved performance. The paper details a methodology for producing and measuring band edge shifts but notes limitations in applying it to improve device operation.
Zr doped TiO2 nanocomposites for dye sensitized solar cellsvenkatamanthina
This document discusses engineering the band edges of a composite photoanode for dye-sensitized solar cells through doping. ZnO nanorods were doped with cobalt to lower their conduction band minimum energy, and TiO2 nanoparticles were doped with zirconium to raise their conduction band minimum energy. This was done to overcome an energy barrier that previously prevented electron transfer from TiO2 to ZnO in the composite. Characterization showed the doping incorporated into the materials as desired without other changes. Open circuit photovoltage measurements indicated the doping shifted the band energies to enable electron transfer, but devices using the materials did not show improved performance. The methodology for producing and measuring band edge shifts through doping is detailed.
Pd-Substituted (La,Sr)CrO3 for Solid Oxide Fuel Cell AnodesEmmaReneeDutton
Presentation of independent honors research thesis (June 2011) for Bachelor of Science in Materials Science & Engineering at Northwestern University.
Solid oxide fuel cells (SOFCs) use solid ceramic electrolytes to transport oxygen ions between the cathode and anode. They can operate on hydrogen or natural gas fuels from 700-1000°C. Perovskite materials are commonly used as electrodes or electrolytes due to their mixed ionic and electronic conductivity. SOFCs offer clean electricity generation but challenges remain in reducing costs and operating temperatures before widespread commercialization. Research is ongoing to develop new materials with improved performance at lower temperatures.
This document describes research on fabricating a novel graphene electrode embedded with zirconium dioxide nanoparticles for electrochemical capacitors. The electrode showed a maximum specific capacitance of 11.84 F g−1. SEM images showed ions redepositing as agglomerates on the electrode surface after one charge/discharge cycle, accompanied by a decrease in surface area. Electrochemical tests confirmed pseudocapacitive behavior and low resistance. The research aims to investigate how electrolyte ion and active material redeposition affects the electrode's charge distribution ability.
The document summarizes a study that characterized the corrosion of a nickel-aluminum (Ni-Al) composite coating compared to a pure nickel coating after 72 hours of immersion in 2M NaCl solution. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques were used, and scanning electron microscopy was used to examine the corrosion product layers. Results showed the Ni-Al composite had a porous, cracked corrosion product layer that decreased corrosion potential and increased corrosion currents compared to the more protective layer formed on pure nickel. Thus, the Ni-Al composite exhibited lower corrosion resistance than pure nickel in the higher chloride concentration solution.
Synthesis and optimisation of ir o2 electrocatalysts by adams fusion method f...materials87
The document describes the synthesis and optimization of iridium dioxide (IrO2) electrocatalysts for oxygen evolution reaction (OER) in solid polymer electrolyte electrolyzers. IrO2 was synthesized using an Adams fusion method by varying synthesis duration (0.5-4 hours) and temperature (250-500°C). Characterization showed that increasing synthesis time and temperature improved crystallinity and increased particle size. Electrochemical testing revealed that IrO2 synthesized for 2 hours at 350°C exhibited the best electrocatalytic activity toward OER compared to a commercial IrO2 catalyst. Higher temperatures and longer times favored larger, more crystalline particles but decreased surface area and activity.
This document describes how synchrotron-based X-ray spectroscopy techniques like XANES and STXM can provide insights into structure-performance relationships in battery materials to enable faster optimization. These techniques allow mapping of local chemistry, bonding structure, and phase distributions. Studies have shown how surface coatings and composite designs can influence properties like conductivity and stability. Chemical mapping of electrodes also revealed non-uniform reactions related to "hot spots" that correlate with performance. Faster screening of materials and correlation of structural properties with electrochemical data could significantly reduce battery development timelines.
Band edge engineering of composite photoanodes for dye sensitized solar cellsvenkatamanthina
This document discusses engineering the band edges of composite photoanodes for dye-sensitized solar cells through doping. Specifically, it doped ZnO nanorods with cobalt to lower its conduction band minimum and doped TiO2 nanoparticles with zirconium to raise its conduction band minimum in order to overcome an energy barrier preventing electron transfer. Characterization with diffuse reflectance spectroscopy and open circuit voltage measurements under illumination confirmed the doping shifted the band edges as intended. However, dye-sensitized solar cells fabricated with the composite nanostructures did not show improved performance. The paper details a methodology for producing and measuring band edge shifts but notes limitations in applying it to improve device operation.
Zr doped TiO2 nanocomposites for dye sensitized solar cellsvenkatamanthina
This document discusses engineering the band edges of a composite photoanode for dye-sensitized solar cells through doping. ZnO nanorods were doped with cobalt to lower their conduction band minimum energy, and TiO2 nanoparticles were doped with zirconium to raise their conduction band minimum energy. This was done to overcome an energy barrier that previously prevented electron transfer from TiO2 to ZnO in the composite. Characterization showed the doping incorporated into the materials as desired without other changes. Open circuit photovoltage measurements indicated the doping shifted the band energies to enable electron transfer, but devices using the materials did not show improved performance. The methodology for producing and measuring band edge shifts through doping is detailed.
Pd-Substituted (La,Sr)CrO3 for Solid Oxide Fuel Cell AnodesEmmaReneeDutton
Presentation of independent honors research thesis (June 2011) for Bachelor of Science in Materials Science & Engineering at Northwestern University.
Solid oxide fuel cells (SOFCs) use solid ceramic electrolytes to transport oxygen ions between the cathode and anode. They can operate on hydrogen or natural gas fuels from 700-1000°C. Perovskite materials are commonly used as electrodes or electrolytes due to their mixed ionic and electronic conductivity. SOFCs offer clean electricity generation but challenges remain in reducing costs and operating temperatures before widespread commercialization. Research is ongoing to develop new materials with improved performance at lower temperatures.
This document describes research on fabricating a novel graphene electrode embedded with zirconium dioxide nanoparticles for electrochemical capacitors. The electrode showed a maximum specific capacitance of 11.84 F g−1. SEM images showed ions redepositing as agglomerates on the electrode surface after one charge/discharge cycle, accompanied by a decrease in surface area. Electrochemical tests confirmed pseudocapacitive behavior and low resistance. The research aims to investigate how electrolyte ion and active material redeposition affects the electrode's charge distribution ability.
The document summarizes a study that characterized the corrosion of a nickel-aluminum (Ni-Al) composite coating compared to a pure nickel coating after 72 hours of immersion in 2M NaCl solution. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques were used, and scanning electron microscopy was used to examine the corrosion product layers. Results showed the Ni-Al composite had a porous, cracked corrosion product layer that decreased corrosion potential and increased corrosion currents compared to the more protective layer formed on pure nickel. Thus, the Ni-Al composite exhibited lower corrosion resistance than pure nickel in the higher chloride concentration solution.
Synthesis and optimisation of ir o2 electrocatalysts by adams fusion method f...materials87
The document describes the synthesis and optimization of iridium dioxide (IrO2) electrocatalysts for oxygen evolution reaction (OER) in solid polymer electrolyte electrolyzers. IrO2 was synthesized using an Adams fusion method by varying synthesis duration (0.5-4 hours) and temperature (250-500°C). Characterization showed that increasing synthesis time and temperature improved crystallinity and increased particle size. Electrochemical testing revealed that IrO2 synthesized for 2 hours at 350°C exhibited the best electrocatalytic activity toward OER compared to a commercial IrO2 catalyst. Higher temperatures and longer times favored larger, more crystalline particles but decreased surface area and activity.
Synthesis and optimisation of ir o2 electrocatalysts by adams fusion method f...sudesh789
This document discusses the synthesis and optimization of iridium dioxide (IrO2) electrocatalysts for use in solid polymer electrolyte electrolyzers through an adaptation of the Adams fusion method. The synthesis duration and temperature were varied to determine their effect on the physical and electrochemical properties of the IrO2 catalysts. X-ray diffraction analysis showed that increasing the synthesis duration and temperature increased the crystallinity and particle size of the IrO2. Chronoamperometry testing revealed that a synthesis of 2 hours at 350°C produced an IrO2 catalyst with better electrocatalytic activity for oxygen evolution than a commercial IrO2 catalyst.
Dye-sensitized solar cells (DSSCs), also known as Gratzel cells, provide a low-cost alternative to conventional solar cells. A DSSC consists of a photo-sensitized anode, a cathode separated by an electrolyte, and a mechanism whereby photons are converted to electrons. When light strikes the photo-sensitized anode, electrons are generated and travel through an external circuit before being regenerated at the cathode. DSSCs have higher efficiency than traditional solar cells, are lightweight and flexible, and can operate in low light conditions. However, their liquid electrolytes limit stability and scalability.
Solid oxide fuel cells (SOFCs) directly convert chemical energy from fuels into electrical energy through electrochemical reactions. SOFCs operate at high temperatures between 600-1800°C using fuels like natural gas, methane or propane. The electrolyte is made of ceramic materials like zirconium and doped perovskite. SOFCs have efficiencies between 45-60% and costs around 2700 INR/KW. They produce clean energy, have modular construction and long lifetimes up to 100,000 hours. Challenges include reducing costs through lower material costs and operating temperatures while increasing power outputs.
IRJET- Design and Fabrication of Air Breathing Solid Oxide Fuel Cell and its ...IRJET Journal
1) Researchers at St. Joseph's Institute of Technology designed and tested an air-breathing solid oxide fuel cell (SOFC) that uses hydrogen gas as fuel.
2) The SOFC was fabricated using nickel oxide and yttria-stabilized zirconia for the anode, yttria-stabilized zirconia for the electrolyte, and lanthanum strontium manganite for the cathode.
3) Testing of the SOFC involved supplying it with hydrogen gas at 800°C and measuring its voltage, current, current density, and power density output under varying loads. The SOFC achieved a maximum current density of 44 mA/cm2 and open circuit
The document summarizes research on modifying the bandgap of n-TiO2 through carbon doping to enable its use in photoelectrochemical water splitting using visible light. Carbon-modified n-TiO2 (CM-n-TiO2) films were synthesized using spray pyrolysis. Increased carbon doping was achieved by calcining in inert atmosphere. CM-n-TiO2 exhibited photoresponse in the visible spectrum due to carbon doping reducing the bandgap and introducing an intragap band. This modified the band structure of n-TiO2 to extend utilization of solar energy into the visible region.
This document summarizes Bing Hsieh's research journey from 1990 to 2014. It covers his work in conducting polymers for OLEDs from 1990-2002, then toner and cartridge recycling from 2003-2007. From 2008-2011 he worked on solid electrolytes and ionic liquids for lithium batteries. From 2011-2014 his focus was on printed organic electronics and graphene supercapacitors. The document provides details on his research into issues with printed transistors, block copolymers as solid electrolytes, dendrite formation in batteries, and preliminary work printing graphene oxide inks for supercapacitors. Diagrams and images supplement the technical descriptions.
The document summarizes research on the electrochemical deposition of lead dioxide nanostructured thin films. Key findings include:
- Lead dioxide nanostructures were successfully deposited on gold-coated substrates by anodic electrochemical deposition using nitric acid and lead chloride as reactants. The morphology was influenced by deposition parameters like potential, temperature, and pH.
- Deposition at higher temperatures (60°C vs room temperature) resulted in faster growth rates and denser nanostructures, as seen by SEM images.
- Both anodic and cathodic deposition were studied. Cathodic deposition allowed formation of different lead oxide phases depending on conditions, while anodic deposition selectively formed PbO2.
- The work provides a
1) Incident light excites dye molecules which transfers electrons to the conduction band of the semiconductor.
2) The electrons flow through an external circuit producing electricity before being collected at the counter electrode.
3) The electrolyte regenerates the dye and redox mediator by accepting the electrons, completing the cycle so that the process can repeat with subsequent light absorption.
The document discusses the state of the art of solid oxide electrolyser stacks (SOEC) for hydrogen production and the RelHy project. It summarizes that current SOEC stacks show good cell performance but poor durability and efficiency at the stack level. The RelHy project aims to [1] achieve high cell performance of ~1 A/cm2 at ≤1.5V and >60% water conversion at 800°C, [2] decrease degradation rates of single repeating units (SRUs) to ~1% per 1000 hours, and [3] integrate optimized materials and design innovations into a 25-cell electrolyzer stack prototype to be tested. The goal is to develop a reliable and efficient SOEC stack by
Nano-materials for Anodes in Lithium ion Battery - An introduction part 1Ahmed Hashem Abdelmohsen
The document discusses approaches to improving lithium ion battery anodes using nanomaterials. It provides a general introduction to lithium batteries and their components. Nanometal oxides like iron oxide nanoparticles coated on carbon aerogel are discussed as an anode material with high capacity and excellent cycleability. Nanostructured silicon anodes are also covered, which can provide high capacity due to silicon's ability to alloy with lithium at room temperature. Finally, graphene-coated pyrogenic carbon is presented as an anode material that provides a reversible high discharge capacity through the unique properties of graphene.
Structural, compositional and electrochemical properties of Aluminium-Silicon...IOSR Journals
This document summarizes the structural, compositional and electrochemical properties of an Aluminium-Silicon-Chromium alloy thin film for use as an anode in lithium thin film batteries. Key points:
1) An Al-Si-Cr alloy thin film was deposited using DC magnetron sputtering. XRD and EDAX analysis confirmed the film had a nanocrystalline structure and composition matching the sputtering target.
2) Electrochemical testing showed lithium could be reversibly inserted into and removed from the Al-Si-Cr film. The film displayed higher initial capacity and better capacity retention over 50 cycles compared to pure silicon film.
3) SEM analysis indicated cycling caused
This document summarizes the synthesis, characterization, and evaluation of various IrO2-based binary metal oxide electrocatalysts for the oxygen evolution reaction. IrO2, IrxRu1-xO2, IrxSnx-1O2 and IrxTax-1O2 (where x is between 1 and 0.7) were synthesized via an adapted Adams fusion method. X-ray diffraction and electron microscopy showed the materials formed nanocrystalline solid solutions. Electrochemical testing found that adding RuO2, SnO2, or Ta2O5 to IrO2 improved its catalytic performance for oxygen evolution. Specifically, Ir0.7Ru0.3O2 exhibited the best
This document summarizes the electrochemical synthesis and corrosion inhibiting properties of a poly N-methyl aniline coating doped with di-N-propyl malonic acid on stainless steel. Cyclic voltammetry was used to polymerize N-methyl aniline in a solution containing di-N-propyl malonic acid on a stainless steel electrode. An adherent red polymer film was obtained. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques showed that this polymer coating provided excellent corrosion protection of stainless steel in 0.5M sulfuric acid solution, with inhibition efficiencies above 99% as indicated by large increases in charge transfer resistance and decreases in corrosion current density compared to uncoated stainless steel.
This document discusses electroluminescence and the polymer polyparaphenylene vinylene (PPV). It explains that PPV is a conducting polymer that emits bright yellow fluorescence, making it suitable for applications in light-emitting diodes and photovoltaic devices. PPV was used in the first polymer light-emitting diode and is still used in organic light-emitting diodes (OLEDs) due to its stability and optical properties. OLEDs use a layer of organic material like PPV between electrodes that emits light when electric current is applied.
This document summarizes research on using electrodeposited manganese dioxide (MnO2) coatings on porous carbon substrates for capacitive deionization (CDI) applications. Two carbon substrates with different surface areas and morphologies were coated with MnO2 using galvanostatic and cyclic voltammetric deposition. Characterization of the coated electrodes found mixed MnO2 phases present. Testing in half-cell configurations showed that maximum ion uptake per mass was not necessarily optimal for practical CDI applications, where performance per electrode area is more important. The results suggest the structure and deposition method can impact how effectively the electrode volume participates in ion removal reactions.
Recent progress in non platinum counter electrode materials for dye sensitize...Science Padayatchi
This document discusses recent progress in developing non-platinum counter electrode materials for dye-sensitized solar cells (DSSCs). It reviews various platinum-free materials that have been studied as alternatives to the traditionally used platinum counter electrodes in DSSCs. These include carbon-based materials like graphene and carbon nanotubes, conducting polymers, metal oxides and sulfides, transition metal nitrides and carbides, and composite materials. The document analyzes the advantages of these materials and their potential to lower the cost of DSSCs while maintaining good performance compared to expensive platinum electrodes.
Edinburgh | May-16 | Future Battery Chemistries – The Rôle of SodiumSmart Villages
This document summarizes sodium-ion battery chemistry and its potential advantages over lithium-ion batteries. Sodium-ion batteries have similar properties to lithium-ion batteries due to the similarities between sodium and lithium. However, sodium-ion batteries also have some unique features such as stronger tendencies for layered electrode structures and access to the Fe3+/Fe4+ redox couple. Sodium-ion batteries could be lower cost than lithium-ion batteries due to sodium's abundance and the lack of need for copper current collectors. Their performance is promising and in some cases rivals that of lithium-ion batteries.
Depositacion electroforetica dentro de campos electricos moduladosMario ML
This document reviews electrophoretic deposition (EPD) under modulated electric fields such as pulsed direct current (PDC) and alternating current (AC). Classical EPD uses continuous direct current which can lead to issues depositing from aqueous suspensions due to water electrolysis. Modulated electric fields can reduce electrolysis and produce more uniform coatings. PDC and AC offer advantages over continuous DC like reducing bubble formation and particle aggregation. While deposition rates may decrease under modulated fields, they allow for depositing biochemical and biological materials in more active states. The document discusses EPD mechanisms and modulated field types, and their applications including in biotechnology.
This document summarizes a study that compared a single chamber microbial fuel cell (SC-MFC) to a double chamber microbial fuel cell (DC-MFC) using different electron acceptors. The SC-MFC used oxygen from the air as the cathode, while the DC-MFC used diluted hydrogen peroxide. Testing found the DC-MFC produced a higher open circuit voltage of 448mV compared to 200mV for the SC-MFC. The DC-MFC also generated more power, with a maximum power of 7.57mW and coulombic efficiency of 9.2%, versus 0.46mW and 1.88% respectively for the SC-MFC. This suggests hydrogen per
This document summarizes the state of knowledge regarding age-related dielectric properties of tissues and their relevance for assessing children's exposure to electromagnetic fields. It outlines that Gabriel et al established the first extensive dielectric database in 1996 through a literature review and experimental measurements spanning 10 Hz to 20 GHz. This database is still widely used but was expanded upon in a recent study that measured dielectric properties in vivo for 58 porcine tissues. Key findings included variability in properties like grey matter and bone with age and differences between in vivo and in vitro measurements.
El documento discute los desafíos que enfrentan los sistemas de salud, incluyendo el envejecimiento de la población, el aumento de costos y la introducción de nuevas tecnologías. También destaca la importancia de basar las decisiones clínicas en evidencia científica para mejorar la calidad y reducir la variabilidad en la atención. Propone el uso de guías de práctica clínica fundamentadas en evidencia para lograr estos objetivos.
Synthesis and optimisation of ir o2 electrocatalysts by adams fusion method f...sudesh789
This document discusses the synthesis and optimization of iridium dioxide (IrO2) electrocatalysts for use in solid polymer electrolyte electrolyzers through an adaptation of the Adams fusion method. The synthesis duration and temperature were varied to determine their effect on the physical and electrochemical properties of the IrO2 catalysts. X-ray diffraction analysis showed that increasing the synthesis duration and temperature increased the crystallinity and particle size of the IrO2. Chronoamperometry testing revealed that a synthesis of 2 hours at 350°C produced an IrO2 catalyst with better electrocatalytic activity for oxygen evolution than a commercial IrO2 catalyst.
Dye-sensitized solar cells (DSSCs), also known as Gratzel cells, provide a low-cost alternative to conventional solar cells. A DSSC consists of a photo-sensitized anode, a cathode separated by an electrolyte, and a mechanism whereby photons are converted to electrons. When light strikes the photo-sensitized anode, electrons are generated and travel through an external circuit before being regenerated at the cathode. DSSCs have higher efficiency than traditional solar cells, are lightweight and flexible, and can operate in low light conditions. However, their liquid electrolytes limit stability and scalability.
Solid oxide fuel cells (SOFCs) directly convert chemical energy from fuels into electrical energy through electrochemical reactions. SOFCs operate at high temperatures between 600-1800°C using fuels like natural gas, methane or propane. The electrolyte is made of ceramic materials like zirconium and doped perovskite. SOFCs have efficiencies between 45-60% and costs around 2700 INR/KW. They produce clean energy, have modular construction and long lifetimes up to 100,000 hours. Challenges include reducing costs through lower material costs and operating temperatures while increasing power outputs.
IRJET- Design and Fabrication of Air Breathing Solid Oxide Fuel Cell and its ...IRJET Journal
1) Researchers at St. Joseph's Institute of Technology designed and tested an air-breathing solid oxide fuel cell (SOFC) that uses hydrogen gas as fuel.
2) The SOFC was fabricated using nickel oxide and yttria-stabilized zirconia for the anode, yttria-stabilized zirconia for the electrolyte, and lanthanum strontium manganite for the cathode.
3) Testing of the SOFC involved supplying it with hydrogen gas at 800°C and measuring its voltage, current, current density, and power density output under varying loads. The SOFC achieved a maximum current density of 44 mA/cm2 and open circuit
The document summarizes research on modifying the bandgap of n-TiO2 through carbon doping to enable its use in photoelectrochemical water splitting using visible light. Carbon-modified n-TiO2 (CM-n-TiO2) films were synthesized using spray pyrolysis. Increased carbon doping was achieved by calcining in inert atmosphere. CM-n-TiO2 exhibited photoresponse in the visible spectrum due to carbon doping reducing the bandgap and introducing an intragap band. This modified the band structure of n-TiO2 to extend utilization of solar energy into the visible region.
This document summarizes Bing Hsieh's research journey from 1990 to 2014. It covers his work in conducting polymers for OLEDs from 1990-2002, then toner and cartridge recycling from 2003-2007. From 2008-2011 he worked on solid electrolytes and ionic liquids for lithium batteries. From 2011-2014 his focus was on printed organic electronics and graphene supercapacitors. The document provides details on his research into issues with printed transistors, block copolymers as solid electrolytes, dendrite formation in batteries, and preliminary work printing graphene oxide inks for supercapacitors. Diagrams and images supplement the technical descriptions.
The document summarizes research on the electrochemical deposition of lead dioxide nanostructured thin films. Key findings include:
- Lead dioxide nanostructures were successfully deposited on gold-coated substrates by anodic electrochemical deposition using nitric acid and lead chloride as reactants. The morphology was influenced by deposition parameters like potential, temperature, and pH.
- Deposition at higher temperatures (60°C vs room temperature) resulted in faster growth rates and denser nanostructures, as seen by SEM images.
- Both anodic and cathodic deposition were studied. Cathodic deposition allowed formation of different lead oxide phases depending on conditions, while anodic deposition selectively formed PbO2.
- The work provides a
1) Incident light excites dye molecules which transfers electrons to the conduction band of the semiconductor.
2) The electrons flow through an external circuit producing electricity before being collected at the counter electrode.
3) The electrolyte regenerates the dye and redox mediator by accepting the electrons, completing the cycle so that the process can repeat with subsequent light absorption.
The document discusses the state of the art of solid oxide electrolyser stacks (SOEC) for hydrogen production and the RelHy project. It summarizes that current SOEC stacks show good cell performance but poor durability and efficiency at the stack level. The RelHy project aims to [1] achieve high cell performance of ~1 A/cm2 at ≤1.5V and >60% water conversion at 800°C, [2] decrease degradation rates of single repeating units (SRUs) to ~1% per 1000 hours, and [3] integrate optimized materials and design innovations into a 25-cell electrolyzer stack prototype to be tested. The goal is to develop a reliable and efficient SOEC stack by
Nano-materials for Anodes in Lithium ion Battery - An introduction part 1Ahmed Hashem Abdelmohsen
The document discusses approaches to improving lithium ion battery anodes using nanomaterials. It provides a general introduction to lithium batteries and their components. Nanometal oxides like iron oxide nanoparticles coated on carbon aerogel are discussed as an anode material with high capacity and excellent cycleability. Nanostructured silicon anodes are also covered, which can provide high capacity due to silicon's ability to alloy with lithium at room temperature. Finally, graphene-coated pyrogenic carbon is presented as an anode material that provides a reversible high discharge capacity through the unique properties of graphene.
Structural, compositional and electrochemical properties of Aluminium-Silicon...IOSR Journals
This document summarizes the structural, compositional and electrochemical properties of an Aluminium-Silicon-Chromium alloy thin film for use as an anode in lithium thin film batteries. Key points:
1) An Al-Si-Cr alloy thin film was deposited using DC magnetron sputtering. XRD and EDAX analysis confirmed the film had a nanocrystalline structure and composition matching the sputtering target.
2) Electrochemical testing showed lithium could be reversibly inserted into and removed from the Al-Si-Cr film. The film displayed higher initial capacity and better capacity retention over 50 cycles compared to pure silicon film.
3) SEM analysis indicated cycling caused
This document summarizes the synthesis, characterization, and evaluation of various IrO2-based binary metal oxide electrocatalysts for the oxygen evolution reaction. IrO2, IrxRu1-xO2, IrxSnx-1O2 and IrxTax-1O2 (where x is between 1 and 0.7) were synthesized via an adapted Adams fusion method. X-ray diffraction and electron microscopy showed the materials formed nanocrystalline solid solutions. Electrochemical testing found that adding RuO2, SnO2, or Ta2O5 to IrO2 improved its catalytic performance for oxygen evolution. Specifically, Ir0.7Ru0.3O2 exhibited the best
This document summarizes the electrochemical synthesis and corrosion inhibiting properties of a poly N-methyl aniline coating doped with di-N-propyl malonic acid on stainless steel. Cyclic voltammetry was used to polymerize N-methyl aniline in a solution containing di-N-propyl malonic acid on a stainless steel electrode. An adherent red polymer film was obtained. Electrochemical impedance spectroscopy and potentiodynamic polarization techniques showed that this polymer coating provided excellent corrosion protection of stainless steel in 0.5M sulfuric acid solution, with inhibition efficiencies above 99% as indicated by large increases in charge transfer resistance and decreases in corrosion current density compared to uncoated stainless steel.
This document discusses electroluminescence and the polymer polyparaphenylene vinylene (PPV). It explains that PPV is a conducting polymer that emits bright yellow fluorescence, making it suitable for applications in light-emitting diodes and photovoltaic devices. PPV was used in the first polymer light-emitting diode and is still used in organic light-emitting diodes (OLEDs) due to its stability and optical properties. OLEDs use a layer of organic material like PPV between electrodes that emits light when electric current is applied.
This document summarizes research on using electrodeposited manganese dioxide (MnO2) coatings on porous carbon substrates for capacitive deionization (CDI) applications. Two carbon substrates with different surface areas and morphologies were coated with MnO2 using galvanostatic and cyclic voltammetric deposition. Characterization of the coated electrodes found mixed MnO2 phases present. Testing in half-cell configurations showed that maximum ion uptake per mass was not necessarily optimal for practical CDI applications, where performance per electrode area is more important. The results suggest the structure and deposition method can impact how effectively the electrode volume participates in ion removal reactions.
Recent progress in non platinum counter electrode materials for dye sensitize...Science Padayatchi
This document discusses recent progress in developing non-platinum counter electrode materials for dye-sensitized solar cells (DSSCs). It reviews various platinum-free materials that have been studied as alternatives to the traditionally used platinum counter electrodes in DSSCs. These include carbon-based materials like graphene and carbon nanotubes, conducting polymers, metal oxides and sulfides, transition metal nitrides and carbides, and composite materials. The document analyzes the advantages of these materials and their potential to lower the cost of DSSCs while maintaining good performance compared to expensive platinum electrodes.
Edinburgh | May-16 | Future Battery Chemistries – The Rôle of SodiumSmart Villages
This document summarizes sodium-ion battery chemistry and its potential advantages over lithium-ion batteries. Sodium-ion batteries have similar properties to lithium-ion batteries due to the similarities between sodium and lithium. However, sodium-ion batteries also have some unique features such as stronger tendencies for layered electrode structures and access to the Fe3+/Fe4+ redox couple. Sodium-ion batteries could be lower cost than lithium-ion batteries due to sodium's abundance and the lack of need for copper current collectors. Their performance is promising and in some cases rivals that of lithium-ion batteries.
Depositacion electroforetica dentro de campos electricos moduladosMario ML
This document reviews electrophoretic deposition (EPD) under modulated electric fields such as pulsed direct current (PDC) and alternating current (AC). Classical EPD uses continuous direct current which can lead to issues depositing from aqueous suspensions due to water electrolysis. Modulated electric fields can reduce electrolysis and produce more uniform coatings. PDC and AC offer advantages over continuous DC like reducing bubble formation and particle aggregation. While deposition rates may decrease under modulated fields, they allow for depositing biochemical and biological materials in more active states. The document discusses EPD mechanisms and modulated field types, and their applications including in biotechnology.
This document summarizes a study that compared a single chamber microbial fuel cell (SC-MFC) to a double chamber microbial fuel cell (DC-MFC) using different electron acceptors. The SC-MFC used oxygen from the air as the cathode, while the DC-MFC used diluted hydrogen peroxide. Testing found the DC-MFC produced a higher open circuit voltage of 448mV compared to 200mV for the SC-MFC. The DC-MFC also generated more power, with a maximum power of 7.57mW and coulombic efficiency of 9.2%, versus 0.46mW and 1.88% respectively for the SC-MFC. This suggests hydrogen per
This document summarizes the state of knowledge regarding age-related dielectric properties of tissues and their relevance for assessing children's exposure to electromagnetic fields. It outlines that Gabriel et al established the first extensive dielectric database in 1996 through a literature review and experimental measurements spanning 10 Hz to 20 GHz. This database is still widely used but was expanded upon in a recent study that measured dielectric properties in vivo for 58 porcine tissues. Key findings included variability in properties like grey matter and bone with age and differences between in vivo and in vitro measurements.
El documento discute los desafíos que enfrentan los sistemas de salud, incluyendo el envejecimiento de la población, el aumento de costos y la introducción de nuevas tecnologías. También destaca la importancia de basar las decisiones clínicas en evidencia científica para mejorar la calidad y reducir la variabilidad en la atención. Propone el uso de guías de práctica clínica fundamentadas en evidencia para lograr estos objetivos.
El documento conmemora el 50 aniversario del IPE y contiene fotos de varios miembros asistiendo al evento, incluyendo a Liliana, Claudio, Silvia, José, Patricia, Silvia Piccirilli, Alberto, Graciela y Mónica, ya sea antes de ir al acto o frente a la iglesia durante el mismo.
El documento presenta una lección sobre embriología para estudiantes. Explica el proceso de fecundación, comenzando con la penetración del espermatozoide a través de la corona radiada y la zona pelúcida del ovocito. Luego describe la fusión de los pronúcleos masculino y femenino, formando el cigoto diploide con 46 cromosomas, y las consecuencias de restablecer el número diploide y la variación genética. Finalmente, indica que la presentación cumple con los objetivos de un curso de extensión sobre embri
El documento resume los procesos de la reproducción humana, incluyendo la fecundación, el desarrollo del embrión, la implantación, el crecimiento del feto y la placenta, y el parto. Durante la fecundación, los espermatozoides se capacitan para penetrar el óvulo, y si uno lo logra, evita la poliespermia. Luego el blastocisto se implanta en el útero, generalmente en la pared posterior. La placenta permite el intercambio de oxígeno, dióxido de carbono y nutrientes
Numerical computation of eigenenergy and transmission coefficient of symmetri...IAEME Publication
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Water-splitting photoelectrodes consisting of heterojunctions of carbon nitri...Pawan Kumar
Quinary and senary non-stoichiometric double perovskites such as Ba2Ca0.66Nb1.34-xFexO6-δ (BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO2 reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba2Ca0.66Nb0.68Fe0.33Co0.33O6-δ (BCNFCo), exhibited an optical absorption edge at ~ 800 nm, p-type conduction and a distinct photoresponse upto 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C3N4 (CN) was prepared via a facile solvent assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C3N4 followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskite and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm-2 for sunlight-driven water-splitting with a Faradaic efficiency as high as ~ 88%.
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White-light emitting diodes (WLEDs) are semiconductor light sources whose construction design is usually made up of a single pumping chip and a single light-conversion film of phosphor compound. The outstanding problem of this traditional setting is the inadequate chroma rendering index (CRI). Introducing a cluster of multiple blue chips with more than one phosphor layer is demonstrated to address that flaw of W-LEDs. This package is called the dual-film remote-phosphor multi-chip WLED. As a consequence, both the light brightness and the CRI are improved. However, for the maximum results, the test on the second layer of phosphor has been performed to continually alter the proportions and densities of phosphor within the silicone. The researchers employed a unique hue design to control the white-light light emitting diode (LED) module. When comparing the actual result to the simulated color coordinates under the hue standard of international commission on illumination (CIE) 1931, the highest difference is found to be around 0.0063 for correlated color temperatures (CCT) of 6600 K and 7700 K. Experiments indicate that the setting of multi-chip and dual-phosphorus is the optimal design for supporting CRI quality and luminous intensity.
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The document summarizes research on aluminum-doped zinc oxide (AZO) films grown by atomic layer deposition for use as transparent electrodes. Key findings:
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International Journal of Engineering Research and DevelopmentIJERD Editor
This document summarizes a study of various physical properties of lithium-borosilicate glass samples. Glass samples were prepared with compositions of 42.5Li2O-(57.5-x)B2O3-xSiO2, where x ranged from 0-57.5 mol%. Density, molar volume, oxygen packing density, ionic concentration, and inter-ionic distance were measured for the samples. The results showed that molar volume, inter-ionic distance, and polaron radius decreased with increasing SiO2 content, indicating a more loosely packed glass structure. Oxygen packing density and ionic concentration also decreased with higher SiO2. The glass transition temperature was found to decrease with increasing
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Influence of a_partially_oxidized_calcium_cathode_on_the_performance_of_polymeric_light_emitting_diodes
1. Influence of a partially oxidized calcium cathode on the performance of
polymeric light emitting diodes
G. G. Andersson, M. P. de Jong, F. J. J. Janssen, J. M. Sturm, L. J. van IJzendoorn et al.
Citation: J. Appl. Phys. 90, 1376 (2001); doi: 10.1063/1.1383577
View online: http://dx.doi.org/10.1063/1.1383577
View Table of Contents: http://jap.aip.org/resource/1/JAPIAU/v90/i3
Published by the American Institute of Physics.
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3. J. Appl. Phys., Vol. 90, No. 3, 1 August 2001 Andersson et al. 1377
FIG. 1. Scheme of the LED production facility.
FIG. 2. Scheme of the investigated structure.
LEDs. Oxygen is expected to have a strong influence on the
performance of LEDs using reactive low work function met-
als such as magnesium and calcium. LEDs is determined with OPT301 photodiodes from Burr
The influence of the presence of oxygen during the Brown which have been calibrated with a luminescence
deposition of the calcium cathode was investigated by meter LS 110 from Minolta. The temperature of the samples
evaporating the calcium in an oxygen atmosphere of during operation can be measured with NTCs and with a
10Ϫ8 – 10Ϫ5 mbar. We determined both the current–voltage LUXTRON Fluoroptic thermometer. The temperature of the
(I – V)-light characteristics and the concentration of oxygen. devices in the glove box is 23Ϯ2 °C.
The concentration depth profiles have been determined with The LEDs or the half fabricates can be transported under
elastic recoil detection analysis ͑ERDA͒. We found a strong dry nitrogen atmosphere to setups where the elemental com-
correlation between the presence of oxygen in the calcium position of the surface and the bulk can be analyzed. For
cathode and the characteristics of the devices. The best LEDs analysis of the surface we apply low energy ion scattering
were obtained with the lowest possible concentration of oxy- and x-ray photoelectron spectroscopy. For analysis of the
gen present during calcium evaporation. bulk RBS, ERDA, and particle induced x-ray emission are
applied.
II. EXPERIMENT We used ITO as the anode, a 130 nm thick layer of the
electroluminescent polymer OC1C10-PPV as the emissive
A. pLED fabrication and IV-light characterization
layer, 80 nm calcium as the cathode, and aluminum as the
The devices are fabricated in a closed setup sketched in protecting layer. The glass/ITO substrates ͑100 nm ITO, 30
Fig. 1. Six devices can be fabricated at the same time under ⍀/ᮀ, Merck͒ were cleaned in ultrapure acetone ͑Uvasol
identical conditions. The setup consists of a glove box with from Merck͒ and 2-propanol ͑Secsolv from Merck͒ each for
less than 1 ppm oxygen and moisture, an UV-ozone pretreat- 10 min in an ultrasonic bath. This wet cleaning step was
ment chamber and an UHV evaporation chamber. The setup followed by an UV-ozone treatment for 20 min. Directly af-
is constructed such that samples may be transferred between ter this treatment, the samples were transferred to the glove
the different chambers without exposure of the samples to box with a dry nitrogen atmosphere without being exposed to
air. The UV-ozone treatment is useful to remove hydrocar- air. The OC1C10-PPV layer was spin coated in the glove box
bons from the surface of ITO substrates.9 The polymer layers from a 0.71 wt % toluene solution. The samples were trans-
are spin coated in the glove box, which is equipped with an ferred into an UHV evaporation chamber without having
activated carbon filter in order to remove the evaporated or- contact to air. The calcium cathode and aluminum protection
ganic solvents. The window of the glove box is covered with layers were evaporated from effusion cells at temperatures of
a foil in order to prevent the polymers from the exposure to 510 and 1150 °C, respectively, the deposition rates at these
light of short wavelengths. The samples are introduced via a temperatures are for calcium 4 Å/s and aluminum 1 Å/s. At a
transfer chamber ͑base pressure of 5ϫ10Ϫ8 mbar͒ into the partial pressure of Ͻ10Ϫ9 mbar oxygen the concentration of
UHV ͑base pressure of 1ϫ10Ϫ9 mbar͒ chamber. The partial oxygen will be less than 0.1 at. % in the calcium layer at this
pressures in the UHV are measured with a residual gas ana- deposition rate. Oxygen can be introduced into the UHV
lyzer Leybold Quadruvac Q 100 with a detection limit of chamber by means of a leakage valve. The pressure during
ϳ10Ϫ9 mbar. The UHV chamber is equipped with an infra- deposition of calcium was varied from less than 10Ϫ9 to
red lamp for soft bake of the organic layers. We can evapo- 10Ϫ5 mbar. The fabrication of the devices was finished by
rate three different metals from commercial Riber ABN 135 evaporation of the aluminum layer. A scheme of the devices
L effusion cells. The layer thicknesses are determined with is shown in Fig. 2. 1 h after finishing the evaporation of the
an Intellemetrics IL 150 quartz crystal monitor, which was aluminum layer the devices have a temperature of 45Ϯ2 °C.
calibrated with Rutherford backscattering spectrometry Within 15 h the equilibrium temperature in the UHV of
͑RBS͒. The temperatures of the samples are measured during about 28Ϯ2 °C is reached.
evaporation with NTC thermistors. IV-light characteristics of From each set of LEDs we investigated oxygen and car-
the LEDs can be measured either directly after fabrication in bon concentration depth profiles with ERDA at cryogenic
the UHV chamber or in the glove box. The brightness of the temperatures.
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4. 1378 J. Appl. Phys., Vol. 90, No. 3, 1 August 2001 Andersson et al.
FIG. 3. I – V-light characteristics of LEDs with deposition of the calcium FIG. 4. Current and brightness for different partial pressures of oxygen at a
cathode in an oxygen pressure of Ͻ10Ϫ9 and 5ϫ10Ϫ7 mbar. The charac- bias of 5 V. 10Ϫ9 mbar means that no oxygen was let into the UHV chamber
teristics are measured in the glove box. during deposition of the calcium, i.e., the oxygen pressure was some orders
of magnitude lower than 10Ϫ9 mbar. At an oxygen pressure around 5
ϫ10Ϫ6 mbar the current and brightness of the devices changes rapidly with
the pressure. Due to their position with respect to the oxygen inlet the
B. Oxygen depth profiling with cryogenic ERDA samples marked with # experienced a somewhat higher oxygen pressure,
and we attribute the difference between the groups thus to the high sensi-
ERDA is a suitable method to determine concentration tivity of the device performance on the oxygen pressure in this range. Dif-
depth profiles of light elements such as carbon and oxygen ferences greater than 15% within one set of devices were observed only in
up to a depth of approximately 1 m. A depth resolution of this case, for all other experiments it was less than that.
10 nm can be achieved. The pLEDs were transferred in dry
nitrogen to our cryogenic RBS/ERDA setup.10 This setup has
been especially developed for RBS/ERDA analysis of or- For devices that are prepared under comparable conditions,
ganic samples, which are in general very sensitive to ion these current and brightness values are reproducible with an
irradiation. Ion irradiation of organic materials leads to the accuracy of 15% at bias voltages у4 V.
formation of small volatile species along the ion track. Cool- The characteristics of devices that were fabricated in an
ing the samples to cryogenic temperatures reduces drastically oxygen pressure у10Ϫ8 mbar show a decrease of the bright-
the mobility of these species. Measuring at room temperature ness with increasing oxygen pressure, but the current is re-
would distort the concentration depth profiles, whereas the duced only in a certain pressure regime. Current and bright-
influence of the ion irradiation at cryogenic temperatures is ness of the devices at a bias of 5 V are plotted in Fig. 4. The
negligible. In our cryogenic setup, the samples are cooled data points plotted at the x value of 10Ϫ9 mbar correspond to
with a Gifford–McMahon cryocooler by APD cryogenics LEDs that were prepared without admitting oxygen to the
Inc, which has a cooling power of 2 W at 10 K. The sample UHV chamber during deposition of the calcium ͑10Ϫ9 mbar
temperature depends critically on the heat load transferred by is the detection limit for oxygen for the residual gas ana-
the ion beam and the thermal contact between the samples lyzer͒. The oxygen pressure in an UHV system with the men-
and the cooler. For the experiments reported in this article tioned base pressure is usually about several orders of mag-
the sample temperature is estimated as less than 30 K. At nitude lower than 10Ϫ9 mbar. Each data point is an average
these conditions, damage suppression has been demonstrated over the six devices fabricated in one set. All error bars refer
successfully in Ref. 10. to the reproducibility of the device fabrication at
The cryogenic ERDA measurements were performed us- Ͻ10Ϫ9 mbar oxygen. The uncertainty within a set is some-
ing a 13.4 MeV Heϩϩ beam produced by our 2–30 MeV what smaller. For an oxygen pressure around 5ϫ10Ϫ6 mbar
AVF cyclotron, taking advantage of a broad resonance in the a larger variance even within a single set of samples was
4
He͑16O,16O͒4He scattering cross section at 13.4 MeV.11 The observed and will be discussed later. The brightness de-
recoil detection angle was set to 30° with respect to the ion creases continuously from an oxygen pressure of
beam; the angle between the sample normal and the ion Ͻ10Ϫ9 mbar to 10Ϫ7 mbar by about a factor of 2.5. It possi-
beam was 70°. To discriminate between scattered He ions bly shows a minimum between 10Ϫ7 and 10Ϫ6 and drops to
and recoiled C and O ions, pulse-shape discrimination12 with zero at a pressure of 1ϫ10Ϫ5 mbar. The current reaches a
low resistively passivated implanted planar silicon minimum between 10Ϫ7 and 10Ϫ6 mbar and drops also to
detectors13 was applied. zero at a pressure of 1ϫ10Ϫ5 mbar. The resulting external
efficiency is plotted in Fig. 5. It decreases continuously from
Ͻ10Ϫ9 to 5ϫ10Ϫ6 mbar, in total by about a factor of 2. At a
III. RESULTS
pressure of 5ϫ10Ϫ6 mbar the current and brightness of the
The characteristic of a device without exposure to oxy- devices changes rapidly with the pressure. This will be dis-
gen during calcium deposition is shown in Fig. 3. At a volt- cussed below. At this pressure we found two different groups
age of 5 V we achieve a current of 22 mA/cm2 and a bright- in the sets of six samples. Within both groups we found
ness of 115 Cd/m2 in the glove box at device temperature of nearly identical results. The samples marked with* have
23°. This corresponds to an external efficiency of 0.53 Cd/A. been placed further from the oxygen inlet than the devices
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5. J. Appl. Phys., Vol. 90, No. 3, 1 August 2001 Andersson et al. 1379
FIG. 5. External efficiency for different oxygen pressures at a bias of 5 V.
For the data points at 10Ϫ9 mbar and the measurements marked with* and #
holds the same as described in the caption of Fig. 4.
FIG. 6. ERDA spectrum ͑black curve͒ of an oxygen-free prepared pLED.
The dotted curve represents the RUMP simulation. The energies of recoiled
carbon ͑7.54 MeV͒ and ͑6.44 MeV͒ oxygen, present at the surface, are
marked with #. The group marked with # had 4 times less marked with arrows. Also indicated are the features of carbon and oxygen in
the OC1C10-PPV film. The aluminum capping is partially oxidized, which
current and 7 times less brightness compared with the other results in the peak at the surface energy of oxygen. The small peak at about
group. Due to their position with respect to the oxygen inlet 6.1 MeV is due to calcium oxide at the interface between calcium and
the samples marked with # experienced a somewhat higher aluminum.
oxygen pressure, and we attribute the difference between the
groups thus to the high sensitivity of the device performance
on the oxygen pressure in this range. Differences greater than
15% within one set of devices were observed only in this
case, for all other experiments it was less than that.
An ERDA measurement of a device with an oxygen
pressure Ͻ10Ϫ9 mbar during calcium deposition is shown in
Fig. 6. The number of the recoiled particles is plotted against
their energy which depends, among others, on the depth in
the target from which they originate. The energy of the re-
coiled particle decreases with increasing mass and increasing
depth.
The energies of recoiled carbon and oxygen, present at
the surface, are marked in the spectrum. The feature between
6.8 and 7.1 MeV is due to carbon from the PPV. The step
below 5.8 MeV results from oxygen in the PVV. The peaks
at 6.44 and 6.1 MeV are thin oxide layers at the surface of
the aluminum and at the interface of calcium and aluminum.
In a large number of experiments slight variations ͑ϳ30%͒ in
the oxygen areal densities corresponding to the aluminum
surface (ϳ9ϫ1015/cm2 ) and calcium/aluminum interface
(ϳ5ϫ1015/cm2 ) have been observed. However, these varia-
tions did not significantly influence the I – V-light character-
istics of the LEDs. Oxygen within the calcium layer causes
signals between 5.8 and 6.1 MeV. The amount of oxygen in
the calcium layer in Fig. 6 is less than 2%, which is the
detection limit in this case. The ERDA spectra for the oxy-
gen pressures of 10Ϫ7 and 5ϫ10Ϫ6 mbar are shown in Fig.
7. We find an increasing amount of oxygen within the CaOx
layer with increasing oxygen pressure. The values of the
amount of oxygen in the CaOx layer determined by simulat- FIG. 7. ERDA spectrum ͑thin black line͒ of a pLED in which the calcium
ing the ERDA spectra with a modified version of the RUMP cathode was deposited in a background pressure of ͑a͒ 10Ϫ7 mbar and ͑b͒
5ϫ10Ϫ6 mbar of oxygen. The thick dotted line represents the RUMP simu-
code are given in Fig. 8. The simulations are plotted in Figs. lation. The arrows indicate the energies of carbon ͑7.54 MeV͒ and oxygen
6 and 7 as dotted lines. The maximum of the oxygen content ͑6.44 MeV͒ present at the surface. Also indicated are the features of carbon
͑41 at. %͒ is almost reached at a pressure of 5ϫ10Ϫ6 mbar, in the OC1C10-PPV film and oxygen in the calcium cathode.
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6. 1380 J. Appl. Phys., Vol. 90, No. 3, 1 August 2001 Andersson et al.
FIG. 10. Current and brightness before and after the first contact with the
glove box atmosphere. For the data points at 10Ϫ9 and 5ϫ10Ϫ6 mbar holds
FIG. 8. Oxygen content in the calcium cathode. The amount of oxygen is the same as described in the caption of Fig. 4.
determined from the simulations of the ERDA measurements.
of 3 and is independent of the oxygen partial pressure during
where the LEDs are still operating. The failure of the devices the calcium deposition. Measurements of current and bright-
at pressures Ͼ5ϫ10Ϫ6 mbar is due to the fully oxidized and ness at a constant voltage during operation of several hours
nonconducting CaOx layer. Complete oxidation of calcium is within UHV and the glove box are shown in Fig. 11. In UHV
reached at a flux ratio onto the surface of oxygen to calcium the LEDs show a gradual decrease in current and brightness
of ϳ3:1, assuming a sticking coefficient of 1 for the calcium in the first 7 h. After that time the performance decreases
in the evaporation process. only slightly within a total operation time up to 60 h. The
The onset voltage of the brightness is shown in Fig. 9. LED in the glove box started at a lower current and bright-
The onset voltage increases with increasing oxygen pressure ness but shows only a slight decrease. The relative differ-
until 5ϫ10Ϫ7 mbar from a value of 2.1–2.3 V, as measured ences in current and brightness between operation in both
for the samples in the glove box. environments remain constant after operation for 7 h at a
All LEDs have been characterized in UHV within 1 h factor of 1.5. Storage of the LEDs in UHV without operation
after their fabrication. The LEDs lose about a factor of 3 in also causes a loss of current and brightness but with a some-
current and brightness, when they are transferred from the what smaller factor than the operated LEDs. From Fig. 9 we
UHV into the glove box. The time necessary for the transport also see that the onset voltage for the brightness is shifted to
is a few minutes. After the first contact with the glove box higher values by about 0.2 V. Further storage of the LEDs in
environment the LEDs keep the same characteristics after the glove box does not change the performance of the LEDs
reintroduction into the UHV chamber as they exhibited in the significantly within 7 days.
glove box. The current and brightness due to the different
environments at a voltage of 5 V are given in Fig. 10. The IV. DISCUSSION
relative loss for both current and brightness is about a factor The current, brightness, and efficiency decrease with in-
creasing oxygen pressure during deposition of the calcium
cathode. We find a minimum in the current, a decrease of the
FIG. 9. Onset voltages of the brightness at different oxygen pressures. For FIG. 11. Degradation of the LEDs during the first hours of operation in the
the data points at 10Ϫ9 mbar and the measurements marked with* and # UHV and in the glove box environment. The devices are both fabricated at
holds the same as described in the caption of Fig. 4. an oxygen pressure Ͻ10Ϫ9 mbar.
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7. J. Appl. Phys., Vol. 90, No. 3, 1 August 2001 Andersson et al. 1381
brightness possibly with a small minimum, a continuous loss that of an unoxidized atom which hinders the diffusion of
of the efficiency, and an increase of the onset voltage of the the, calcium into the PPV. This might lead to a sharpening of
brightness. It can be excluded that an increase of the resis- the CaOx /PPV interface by suppression of the diffusion of
tance of the calcium layer with increasing oxygen content individual calcium atoms or ions into the PPV. As a conse-
causes the changes of the characteristics. It can be shown quence the trap distribution of holes near the interface asso-
that the I – V curves of LEDs with different oxidized calcium ciated with calcium is altered ͑probably lowered͒ which will
cannot be shifted onto each other by correcting the applied increase the hole current.
voltage for an additional resistor in the CaOx layer. Such a The brightness of the devices decreases more strongly
correction involves a voltage drop over the partially oxidized than the current with increasing oxygen pressure, which re-
calcium layer which is proportional to the current, while the sults in a decreasing efficiency. A reason for the decrease of
additional resistance of the CaOx layer is kept constant for a the brightness could be a decrease of the area of the
certain LED. PPV/CaOx interface, from which electrons can be injected. If
Blom and de Jong developed a model for the charge calcium oxide would grow in islands, the interface of the
transport in organic LEDs for the case that the current is not PPV with CaOx would consist of small areas of fully and of
limited by injection barriers between the electrodes and the unoxidized calcium. The fully oxidized islands will be insu-
organic layer.14 They showed that LEDs fabricated with the lating and charges would be injected only from the areas
same materials and the same structure as we used have neg- where the calcium is not oxidized. As a result, the active area
ligible injection barriers of less than 0.2 eV and that the of the LEDs would be reduced. However, since calcium is
current is dominated by hole transport. In their model the very reactive with oxygen, it is very unlikely that the oxygen
current is described as space charge limited with a tempera- atoms will move over the calcium surface in order to form
ture and field dependent mobility and a trap distribution for islands of fully oxidized calcium, instead the oxygen will be
the electrons. The I – V curves are fitted by determining nu- chemisorbed immediately.
merically the field distribution, the charge carrier concentra- The decrease of the brightness can be explained, in our
tion, and the electron–hole recombination rate in the PPV opinion, by assuming that the electron injection from the
layer. The I – V characteristics with the lowest current— cathode is reduced. The reason could be a reduction of the
LEDs fabricated at 5ϫ10Ϫ7 mbar and characterized in the work function of the partially oxidized calcium, which would
glove box—are nearly identical to that published by Blom also explain an increase of the onset voltage of the bright-
and de Jong in Ref. 14, which are space charge limited. All ness. The increase of the work function could be accompa-
other LEDs showed a higher current and even a steeper in- nied by the creation of electron traps at the PPV CaOx inter-
crease of the current at a bias Ͼ3 V. Only for the set marked face caused by the partially oxidized PPV, which decreases
with # in Fig. 4 the current was lower. Thus, all the LEDs the current of electrons into the recombination zone of elec-
fabricated at oxygen pressures less than or approximately 5 trons and holes and thus decreases the brightness.
ϫ10Ϫ6 mbar have a current which is space charge but not The decrease in current and brightness during storage in
injection limited. the UHV and during the transport from the UHV to the glove
It seems plausible to explain the decrease of the current box can be explained very well with the change in the tem-
with a decrease of the injection of electrons because the cath- perature of the devices and thus the change of the mobility of
ode is modified. It can be expected that fewer electrons are the charge carriers using the parameter published by Blom
injected from the oxidized calcium, e.g., due to a change of and de Jong.14
the work function. However, it should be noted that the de-
vices still have I/V curves characteristic for space charge V. CONCLUSIONS
limited charge transport. Since the current shows a pro-
nounced minimum at 5ϫ10Ϫ7 the overall I/V behavior can In our setup we are able to fabricate LEDs with a high
be attributed only partially to a blocking of the electron in- reproducibility. We have correlated the oxygen pressure dur-
jection with increasing oxygen pressure during deposition of ing the deposition of the calcium cathode with the changes in
the calcium. The reduction of the current simply due to the structure of the LEDs and the performance of the devices
blocking would not allow us to restore the current to the by determining oxygen concentration depth profiles with
value of the unmodified cathode when the electron injecting cryogenic ERDA of characterized LEDs. The best LEDs are
electrode is nearly oxidized at 5ϫ10Ϫ6 and must be attrib- obtained at an oxygen pressure Ͻ10Ϫ9 mbar, which is in
uted to other effects. Since the holes are the major charge contradiction to the results from Salaneck and co-workers.7
carriers, a decrease of the current upon oxygen exposure This may be due to different preparation conditions before
must be also due to either a change in the hole mobility or to depositing the calcium electrode, e.g., by spin coating the
a change in the trap distribution of the holes and thus of the PVV in air, which would result in a partially oxidized PPV. It
charge carrier concentration and the field distribution in the could be also due to differences in the chemical structure of
polymer layer. A plausible explanation is that the decrease of the used PPV. Comparing our results with those published by
the current for oxygen pressures Ͻ10Ϫ7 mbar is induced by Blom and de Jong show, that the performance of LEDs is
oxidation of calcium in the CaOx /PPV interface region. For significantly affected by the residual gas present during the
oxygen background pressures near 5ϫ10Ϫ6 mbar the cal- deposition of the calcium electrode in a high vacuum system.
cium is nearly oxidized during the deposition process. The We showed that the presence of oxygen during calcium
mobility of an oxidized calcium atom is probably lower than deposition results in a decrease in brightness and efficiency.
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8. 1382 J. Appl. Phys., Vol. 90, No. 3, 1 August 2001 Andersson et al.
The degradation process is attributed to the blocking of the ACKNOWLEDGMENTS
electron injection and a decrease in hole mobility close to the
PPV/CaOx interface, to an increase in work function of the This work has been sponsored by grants from the Dutch
partially oxidized PPV or the creation of traps. Foundation for Fundamental Research ͑FOM͒ and the Prior-
After correction of the I – V-light behavior of the devices ity Program Materials of the Organization for Scientific Re-
as measured in the UHV chamber for the difference in tem- search ͑PPM-NWO͒.
peratures, we find that device performance after transport
into the glove box is virtually the same as measured in the
1
UHV chamber directly after preparation. This shows that the ¨
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2 ¨
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to 1 ppm. Consequently, in our opinion, the device perfor- 3
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4
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¨
7 ´
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can be incorporated in the devices, e.g., during spin coating R. Salaneck, Adv. Mater. 9, 1027 ͑1997͒.
8 ¨
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10
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13
Canberra Semiconductor N. V. ͑www.canberra.com͒, B-2250 Olen, Bel-
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