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NANOCHEMSENS Informe resumido

Project ID: 505895
Financiado con arreglo a: FP6-NMP
País: Germany

Final Report Summary - NANOCHEMSENS (Nanostructures for Chemical Sensors)

The NANOCHEMSENS project has identified and advanced appropriate surface science tools and nanotechnology for the development of chemical sensing nanodevices. It was the intention of the project to understand the nanoscale phenomena that control sensor nanostructures and functionalised surfaces.

The first objective of the project was the development of suitable techniques for atomically controlled fabrication of nanostructured sensors. The second objective was to extend our understanding of length scales, the degree of complexity associated with nanostructure behaviour, processes of relevance for chemical sensors and sensor / molecule interactions on functionalised surfaces having sensitive structures of nanosize dimension. The third objective was to test the sensor performance of model nanostructures and to develop potential routes from fundamental studies to sensor development for nanostructured sensors.

Conventional electronic conductance sensors with semiconducting metal oxides rely on materials and structures of high complexity of the sensing layer with respect to bulk, surfaces, grain boundaries, and interfaces with the contacts and the substrate. Because of the strong influence of the morphology of the sensing layer, a distinction is commonly made between compact layers, for which the interaction with gases takes place only at the geometric surface, and porous layers. In the context of the NANOCHEMSENS project, it seems more suitable to distinguish between the following basic types of sensors:
- heterojunctions;
- metal-oxide-metal tunnel junctions;
- pn junctions;
- epitaxial and thin layers;
- nanorod assemblies; and
- functional organic molecules and ionophores for mass-sensitive devices
and to use model systems for experimental studies towards the above-mentioned objectives of the project.

Apart one independent non-profit institution (FORCE Technology), four SMEs belong to the consortium of the NANOCHEMSENS project. PBI-Dansensor A/S is a worldwide supplier of high quality gas instrumentation equipment for on-line and off-line process control and laboratories.

The company develops, manufactures and markets gas analysers, gas mixers, automated gas purging systems, leak detectors and permeability testers. The portfolio of Vegatec includes, among various micro- and nanotechnological technologies, gas panel and gas handling instrumentation. Bernt Messtechnik is a developer of complete metrological equipments and installations, mainly for gas analysis. Danish Micro Engineering A/S, being one of the oldest manufacturers of AFM, STM, and SNOM equipment on the market, provides software, microelectronics, and SPM microscopes. In conclusion, the industrial partners have minor to a medium-level research capacities in the nanotechnological area.

The industrial partners have been fully involved at all management activities of project, in many work packages, including the last project year which was supervised by PBI. Specifically, active cooperations between the research teams of the universities and the industrial partners started during the second year. This concerns the use of functional organic molecules, deposited over quartz microbalance sensors, which are studied in a cooperative effort. The main focus was the possible use of arrays of QMB sensors for odour recognition in animal farms. The deposition of WO3 nanorods over SiO2/Si and a possibly improved or controlled growth by ion implantation techniques is a subject of interest for VEG, besides the test of such structures. A closer cooperation has been achieved between Udesam and VEG on WO3-based film and nanorod structures. Specifically, experiments have been performed to grow WO3 nanorods on oxidised silica wafer and study the role of potassium promotors. BER has provided know-how to UDUS in the context of the development of eight sensor electronics in the last project year. PBI is a partner with a variety of sensor test facilities, providing also interfaces / electronics parts, as well as information about the needs of end users. The applicability of atomic force microscopy and scanning tunnelling microscopy to study sensor surfaces has been studied by DME in cooperation with UDUS and other partners.

The major achievements for the different model systems are:
- For Pt/TiO2 heterojunctions, the research team succeeded to determine the current-voltage curves of a single Pt particle with a diameter of 8 nm, deposited on a clean titanium oxide surface; the shape of nonlinear I-V-curve depends on the oxygen partial pressure.
- For clean TiO2 surfaces a number of surface reactions, relevant in the context of cross-sensitivity of oxide sensors towards humidity, could be identified by scanning tunnelling microscopy. Concerning the doping of clean surfaces, the main reactions of molybdenium surface additives have been investigated.
- The structural characterisation of ultrathin TiOx films on single crystal platinum surfaces has been completed; doping experiments with nanosized Au clusters were performed that indicates a route towards narrow size distributions of such additives.
- Prototypes of WO3 thin film sensors have been developed and tested; a multisensory electronics was constructed for this sensor device. Assemblies of WO3 nanorods were prepared and their sensing properties were determined. Based on these studies, well-defined percolation-type sensors seem to be accessible.
- A heterojunction based on zinc oxide and copper oxide have been synthesised in ultrahigh-vacuum; first electrical measurements were performed.
- Metal oxide / organic film blends have been explored for their use as sensing layers for detection of volatile organic compounds. TiO2 surfaces have been modified with phendione; this compound may provide sensitivity towards ethylene via a guest-host interaction.

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