Techn. University, Diss., 2003--Berlin.

Der seit vielen Jahren etablierte Summenparameter DOC (dissolved organic carbon - gelöster organischer Kohlenstoff) wird u. a. standardmäßig für die Überwachung der Wasserqualität und zur Bewertung der Effizienz von Verfahren der Wasserbehandlung eingesetzt. Für eine möglichst kurze Reaktionszeit, z. B. im Fall von Havarien oder anderen Ereignissen, sind zeitlich hoch aufgelöste und verlässliche DOC-Daten von großer Bedeutung. Die konventionellen DOC-Bestimmungsmethoden basieren in der Regel nach einer Probenahme auf Konservierung, Transport und anschließender Analyse der Probe in einem stationären Labor. Bei einer schlechten Laborinfrastruktur birgt dieser Ansatz das Risiko, durch längere Lagerung bzw. Transport der Proben falsche und verspätete Ergebnisse zu liefern. Das Ziel der vorliegenden Arbeit be-stand darin, einen tragbaren und dennoch zuverlässigen Analysator für die DOC-Analyse vor Ort zu entwickeln. Basis dieses Messgerätes bildet eine ungeteilte, gal-vanostatisch betriebene Elektrolysezelle mit bordotierter Diamantelektrode. Die anodische Generierung von •OH- und SO4•--Radikalen als Oxidationsmittel, die In- situ-Bildung des Trägergases und die Kinetik des DOC-Abbaus wurden systematisch untersucht. Zudem wurde der Einfluss wichtiger verfahrenstechnischer und hydro-chemischer Parameter betrachtet und für eine Anwendung in der Umweltanalytik optimiert. Abgeschlossen wurde die Entwicklung mit der technischen Optimierung eines tragbaren Prototyps. Dieser wurde validiert und mit etablierten Verfahren ver-glichen sowie erfolgreich im Rahmen eines aktuellen Monitoringprogramms in Nordindien eingesetzt. Die wichtigsten Merkmale des tragbaren DOC-Analysators sind die kompakte Bauweise sowie der Verzicht auf hochreine Gase, Katalysatoren oder eine Verbrennungstechnologie. Zudem weist die Bestimmungsmethode eine hohe Robustheit in Bezug auf Art und Konzentration der Analyten sowie der Matrix auf und ermöglicht eine kurze Analysezeit sowie eine zuverlässige Bestimmung des DOC vor Ort. / Dissolved organic carbon (DOC) is an indispensable analytical parameter for water quality control. This applies to both monitoring of aquatic ecosystems and evaluation of the efficiency of drinking and waste water treatment processes. The conventional DOC determination methods consist of on-site sampling and subsequent analysis in a stationary laboratory. Storage and transport of samples may lead to significant un-certainties in measurement results and delayed findings. For this reason, the availability of suitable on-site analysis techniques is particularly important in coun-tries with an insufficient laboratory infrastructure. Therefore, the objective of the present study was to develop a portable and reliable analyzer for on-site DOC analy-sis. The core element of this analyzer is an undivided electrolysis cell equipped with a boron doped diamond electrode for an in-situ generation of •OH and SO4•- radicals as oxidizing agents. The influence of process and hydrochemical parameters on the generation of in-situ oxidizing agents, in-situ carrier gas and the DOC decomposition kinetic were systematically investigated and optimized for environmental analyses. Finally, a technical optimization of the portable prototype was conducted. The result-ing prototype was validated and successfully compared with established methods. Subsequently, the developed prototype was used in an ongoing monitoring program in northern India. The key features of the portable DOC analyzer are the independ-ence from high-purity gases, catalysts or combustion technology. In addition, this determination method shows a high robustness in terms of type and concentration of analytes and matrices. The short analysis time as well as a reliable determination of the DOC on site prove the practicality of the new technical approach.

In this work, well-defined and stable thin films based on polythiophene and its derivative, are employed as the hole-injection contact of organic light-emitting diodes (OLED). The polymer films are obtained by the electropolymerization or the electrochemical doping/dedoping of a spin-coated layer. Their electrical properties and energetics are tailored by electrochemical adjustment of their doping levels in order to improve the hole-injection from the anode as well as the performance of small molecular OLEDs. By using dimeric thiophene and optimizing the electrodeposition parameters, a thin polybithiophene (PbT) layer is fabricated with well-defined morphology and a high degree of smoothness by electro-polymerization. The introduction of the semiconducting PbT contact layer improves remarkably the hole injection between ITO anode and the hole- transport layer (NPB) due to its favourable energetic feature (HOMO level of 5.1 eV). The vapor-deposited NPB/Alq3 bilayer OLEDs with a thin PbT interlayer, show a remarkable reduction of the operating voltage as well as enhanced luminous efficiency compared to the devices without PbT. Investigations have also been made on the influence of PbT thickness on the efficiency and I-V feature as well as device stability of the OLED. It is demonstrated that the use of an electropolymerization step into the production of vapor deposited molecular OLED is a viable approach to obtain high performance OLEDs. The study on the PbT has been extended to poly(3,4-ethylenedioxythiophene) (PEDT) and the highly homogenous poly(styrenesulfonate) (PSS) doped PEDT layer from a spin-coating process has been applied. The doping level of PEDT:PSS was adjusted quantitatively by an electrochemical doping/dedoping process using a p-tuoluenesulfonic acid containing solution, and the redox mechanism was elucidated. The higher oxidation state can remain stable in the dry state. The work function of PEDT:PSS increases with the doping level after adjusting at an electrode potential higher than the value of the electrochemical equilibrium potential (Eeq) of an untreated film. This leads to a further reduction of the hole-injection barrier at the contact of the polymeric anode/hole transport layer and an ideal ohmic behavoir is almost achieved at the anode/NPB interface for a PEDT:PSS anode with very high doping level. Molecular Alq3-based OLEDs were fabricated using the electrochemically treated PEDT:PSS/ITO anode, and the device performance is shown to depend on the doping level of polymeric anode. The devices on the polymer anode with a higher Eeq than that for the unmodified anode, show a reduction of operating voltage as well as a remarkable enhancement of the luminance. Furthermore, it is found that the operating stability of such devices is also improved remarkably. This originates from the removal of mobile ions such as sodium ions inside the PEDT:PSS by electrochemical treatment as well as the planarization of the ITO surface by the polymer film. By utilizing an Al/LiF cathode with an enhanced electron injection and together with a high Eeq- anode, a balanced injection and recombination of hole and electron is achieved. It leads to a further reduction of the operating voltage and to a drastic improvement of EL efficiency of the device as high as 5.0 cd/A. The results demonstrate unambiguously that the electrochemical treatment of a cast polymer anode is an effective method to improve and optimize the performance of OLEDs. The method can be extended to other polythiophene systems and other conjugated polymers in the fabrication of the OLEDs as well as organic transistors and solar cells.

In dieser Arbeit werden kalt-abgeschiedene Mehrkomponentenschichtelektroden hin-sichtlich ihrer elektrokatalytischen Eigenschaften untersucht. Die Mehrkomponenten-schichten aus Gold, Nickel und ggf. Antimon werden auf einem Kohlenstoffträgermaterial abgeschieden. Dabei handelt es sich um Metallkomponenten, die sich unter ther-modynamischen Bedingungen nicht mischen. Unter UHV-Bedingungen wird ein hochdispergierter bzw. amorpher Zustand erzwungen. Die frisch hergestellte Mehrkomponentenschicht ist elektrochemisch inert. Zyklovoltammetrische Untersuchungen führen zu dem Schluß, daß sich die Oberflächenschicht im elektrochemischen Experiment verändert. Die Elektrooxidation der Alkohole Methanol, Ethanol und Ethylenglykol in KOH-Lösung tritt erst nach einer Aktivierungsphase auf. Die elektrokatalytischen Eigenschaften der reinen Metalle treten zutage. Mittels der in situ Infrarotspektroskopie werden Formiat, Acetat und Glykolat als Oxidationsprodukte der obengenannten Alkohole identifiziert. Oberflächen-Ramanmessungen werden unter der Fragestellung durchgeführt, ob die kalt-abgeschiedenen Schichten einen Oberflächenverstärkungseffekt (SERS-Effekt) zeigen: Es werden Ramanmessungen von Pyridin als Sondenmolekül in KOH-Lösung an Mehrkomponentenschichtelektroden und an massiven Mehrkomponentenelektroden durchgeführt. / The electrooxidation of methanol, ethanol and ethylene glycol at cold deposited trimetallic thin layers of gold, nickel and antimony on glassy carbon in contact with an alkaline electrolyte solution was studied with cyclic voltammetry and in situ infrared reflection absorption spectroscopy. A new procedure of spectra acquisition resulting in an improved suppression of spurious bands caused by volatile components in the sample chamber of the infrared spectrometer was employed. Formate, acetate and glycolate are detected as oxidation products. The thin layer electrodes are also investigated with Raman spectroscopy (surface enhanced Raman spectroscopy), whereby pyridine is used as probe molecule.

In dieser Arbeit werden kalt-abgeschiedene Mehrkomponentenschichtelektroden hin-sichtlich ihrer elektrokatalytischen Eigenschaften untersucht. Die Mehrkomponenten-schichten aus Gold, Nickel und ggf. Antimon werden auf einem Kohlenstoffträgermaterial abgeschieden. Dabei handelt es sich um Metallkomponenten, die sich unter ther-modynamischen Bedingungen nicht mischen. Unter UHV-Bedingungen wird ein hochdispergierter bzw. amorpher Zustand erzwungen. Die frisch hergestellte Mehrkomponentenschicht ist elektrochemisch inert. Zyklovoltammetrische Untersuchungen führen zu dem Schluß, daß sich die Oberflächenschicht im elektrochemischen Experiment verändert. Die Elektrooxidation der Alkohole Methanol, Ethanol und Ethylenglykol in KOH-Lösung tritt erst nach einer Aktivierungsphase auf. Die elektrokatalytischen Eigenschaften der reinen Metalle treten zutage. Mittels der in situ Infrarotspektroskopie werden Formiat, Acetat und Glykolat als Oxidationsprodukte der obengenannten Alkohole identifiziert. Oberflächen-Ramanmessungen werden unter der Fragestellung durchgeführt, ob die kalt-abgeschiedenen Schichten einen Oberflächenverstärkungseffekt (SERS-Effekt) zeigen: Es werden Ramanmessungen von Pyridin als Sondenmolekül in KOH-Lösung an Mehrkomponentenschichtelektroden und an massiven Mehrkomponentenelektroden durchgeführt. / The electrooxidation of methanol, ethanol and ethylene glycol at cold deposited trimetallic thin layers of gold, nickel and antimony on glassy carbon in contact with an alkaline electrolyte solution was studied with cyclic voltammetry and in situ infrared reflection absorption spectroscopy. A new procedure of spectra acquisition resulting in an improved suppression of spurious bands caused by volatile components in the sample chamber of the infrared spectrometer was employed. Formate, acetate and glycolate are detected as oxidation products. The thin layer electrodes are also investigated with Raman spectroscopy (surface enhanced Raman spectroscopy), whereby pyridine is used as probe molecule.

In this work, well-defined and stable thin films based on polythiophene and its derivative, are employed as the hole-injection contact of organic light-emitting diodes (OLED). The polymer films are obtained by the electropolymerization or the electrochemical doping/dedoping of a spin-coated layer. Their electrical properties and energetics are tailored by electrochemical adjustment of their doping levels in order to improve the hole-injection from the anode as well as the performance of small molecular OLEDs. By using dimeric thiophene and optimizing the electrodeposition parameters, a thin polybithiophene (PbT) layer is fabricated with well-defined morphology and a high degree of smoothness by electro-polymerization. The introduction of the semiconducting PbT contact layer improves remarkably the hole injection between ITO anode and the hole- transport layer (NPB) due to its favourable energetic feature (HOMO level of 5.1 eV). The vapor-deposited NPB/Alq3 bilayer OLEDs with a thin PbT interlayer, show a remarkable reduction of the operating voltage as well as enhanced luminous efficiency compared to the devices without PbT. Investigations have also been made on the influence of PbT thickness on the efficiency and I-V feature as well as device stability of the OLED. It is demonstrated that the use of an electropolymerization step into the production of vapor deposited molecular OLED is a viable approach to obtain high performance OLEDs. The study on the PbT has been extended to poly(3,4-ethylenedioxythiophene) (PEDT) and the highly homogenous poly(styrenesulfonate) (PSS) doped PEDT layer from a spin-coating process has been applied. The doping level of PEDT:PSS was adjusted quantitatively by an electrochemical doping/dedoping process using a p-tuoluenesulfonic acid containing solution, and the redox mechanism was elucidated. The higher oxidation state can remain stable in the dry state. The work function of PEDT:PSS increases with the doping level after adjusting at an electrode potential higher than the value of the electrochemical equilibrium potential (Eeq) of an untreated film. This leads to a further reduction of the hole-injection barrier at the contact of the polymeric anode/hole transport layer and an ideal ohmic behavoir is almost achieved at the anode/NPB interface for a PEDT:PSS anode with very high doping level. Molecular Alq3-based OLEDs were fabricated using the electrochemically treated PEDT:PSS/ITO anode, and the device performance is shown to depend on the doping level of polymeric anode. The devices on the polymer anode with a higher Eeq than that for the unmodified anode, show a reduction of operating voltage as well as a remarkable enhancement of the luminance. Furthermore, it is found that the operating stability of such devices is also improved remarkably. This originates from the removal of mobile ions such as sodium ions inside the PEDT:PSS by electrochemical treatment as well as the planarization of the ITO surface by the polymer film. By utilizing an Al/LiF cathode with an enhanced electron injection and together with a high Eeq- anode, a balanced injection and recombination of hole and electron is achieved. It leads to a further reduction of the operating voltage and to a drastic improvement of EL efficiency of the device as high as 5.0 cd/A. The results demonstrate unambiguously that the electrochemical treatment of a cast polymer anode is an effective method to improve and optimize the performance of OLEDs. The method can be extended to other polythiophene systems and other conjugated polymers in the fabrication of the OLEDs as well as organic transistors and solar cells.