Herstellung und Charakterisierung von Sensormembranen aus Chalkogenidglasschichten für den Einsatz als Schwermetallsensoren in Flüssigkeiten

Abstract Nowadays, the detection and monitoring of environmental parameters such as heavy metals is of increasing significance. One possibility for the measurement of heavy metals in aqueous solution offer ion-selective electrodes based on chalcogenide glass materials. However, the fabrication of this kind of materials is time-consuming and cost-intensive. Furthermore, their miniaturisation in order to fabricate sensor systems for ''on-site''-measurements has not been solved, so far.Therefore, in this work chalcogenide glass-based thin films for the detection of cadmium, lead, copper, thallium and silver in aqueous solution will be prepared by means of the pulsed laser deposition (PLD) process. The thin films are deposited onto silicon substrates. The physical characterisation of the thin films is carried out by means of video-microscopy, Rutherford backscattering spectrometry (RBS) and scanning electron microscopy (SEM). The fabricated thin films are electrochemically characterised by means of ion-selective potentiometry as well as impedance spectroscopy. Furthermore, the investigated thin films have been integrated into a silicon-based sensor array. For extended material characterisation, field-effect-based sensor structures such as the electrolyte/ insulator/ semiconductor (EIS) structure, the light-addressable potentiometric sensor (LAPS) and the ion-selective field-effect transistor (ISFET) have been chosen as different transducer systems. For a better understanding of the potential-generating mechanism at the interface ''solid/ liquid'' of the chalcogenide glass thin film, a cadmium-selective chalcogenide glass material has been additionally characterised by means of impedance spectroscopy. A theoretical model based on an electrical equivalent circuit for the investigated material is presented and compared together with the measured data. The application of the developed sensor system for the analysis of complex liquid mixtures on the basis of an ''electronic tongue''-type device will be discussed.Die Detektion und Überwachung von Umweltparametern wie z.B. Schwermetallen gewinnt in der heutigen Zeit zunehmend an Bedeutung. Eine Möglichkeit zur Messung von Schwermetallen bieten ionenselektive Elektroden auf der Basis von Chalkogenidgläsern. Allerdings ist die Herstellung dieser Materialien zeit- und kostenintensiv. Weiterhin fehlt die Möglichkeit der Miniaturisierung für die Herstellung von Sensorsystemen für ''Vor-Ort''-Messungen. Um dieses Problem zu lösen, werden im Rahmen dieser Arbeit Chalkogenidglasschichten für den Nachweis von Cadmium, Blei, Kupfer, Thallium und Silber in Flüssigkeiten mittels gepulster Laserabscheidung (PLD: Pulsed Laser Deposition) hergestellt und charakterisiert. Die Abscheidung der Schichten erfolgt auf Silizium-Substrate. Die physikalische Charakterisierung der Schichten erfolgt mittels Video-Mikroskopie, Rutherfordrückstreuung (RBS) und Rasterelektronenmikroskopie (REM). Elektrochemisch werden die hergestellten Schichten mittels ionenselektiver Potentiometrie sowie Impedanzspektroskopie untersucht. Weiterhin werden die charakterisierten Schichten in ein siliziumbasiertes Sensorarray integriert und untersucht. Für eine zusätzliche Materialcharakterisierung werden feldeffektbasierte Sensorstrukturen, wie die Elektrolyt/ Isolator/ Halbleiter (EIS)-Struktur, der lichtadressierbare potentiometrische Sensor (LAPS) und der ionenselektive Feldeffekttransistor (ISFET) verwendet. Für ein besseres Verständnis der Vorgänge zum Potentialbildungsmechanismus an der Phasengrenze ''Fest/ Flüssig'' der Chalkogenidglasschichten wird exemplarisch ein Cadmium-selektives Chalkogenidglasmaterial mittels Impedanzspektroskopie charakterisiert. Für das untersuchte System wird ein theoretisches Modell in Form eines elektrischen Ersatzschaltbildes erstellt und mit den gemessenen Daten verglichen. Der Einsatz des entwickelten Sensorsystems für die Untersuchung von komplexen Flüssigkeitsmischungen auf der Basis einer ''elektronischen Zunge'' wird diskutiert

A First Step Towards a Microfabricated Thin-Film Sensor Array on the Basis of Chalcogenide Glass Materials

A first step towards a microfabricated potentiometric thin-film sensor array for the simultaneous detection of Pb2+, Cd2+ and Cu2+ has been realized. The sensitive layers used are on the basis of chalcogenide glass materials. These thin-film chalcogenide glass materials that consist of mixtures of Pb-Ag-As-I-S, Cd-Ag-As-I-S or Cu-Ag-As-Se have been prepared by pulsed laser deposition technique. The developed sensor array has been physically characterized by means of scanning electron microscopy and Rutherford backscattering spectrometry. The electrochemical sensor characterization has been performend by potentiometric measurements

Novel Organic Membrane-based Thin-film Microsensors for the Determination of Heavy Metal Cations

Abstract: A first step towards the fabrication and electrochemical evaluation of thin-film microsensors based on organic PVC membranes for the determination of Hg(II), Cd(II), Pb(II) and Cu(II) ions in solutions has been realised. The membrane-coating mixture used in the preparation of this new type of microsensors is incorporating PVC as supporting matrix, o-nitrophenyloctylether (o-NPOE) as solvent mediator and a recently synthesized Hg[dimethylglyoxime(phene)] 2+ and Bis-(4-hydroxyacetophenone)-ethylenediamine as electroactive materials for Hg(II) and Cd(II), respectively. A set of three commercialised ionophores for Cd(II), Pb(II) and Cu(II) has been also used for comparison. Thin-film microsensors based on these membranes showed a Nernstian response of slope (26-30 mV/dec.) for the respective tested cations. The potentiometric response characteristics (linear range, pH range, detection limit and response time) are comparable with those obtained by conventional membranes as well as coated wire electrodes prepared from the same membrane. The realisation of the new organic membrane-based thin-film microsensors overcomes the problem of an insufficient selectivity of solid-state-based thinfilm sensors