CORDIS - EU research results

Conductive nanowires for applications in microwave, magnetic and chemical sensing devices based on polymer track etched templates (NANOPTT)


This project aims to develop new generations of templates for preparation of magnetic and conductive polymer nanowires. Patterning of track etched membranes, high electrical conductivy of polymer nanotubules, current control of magnetism and large saturation magnetization and permeability of metallic nanowires will be studied and optimized in order to design microwave filters, non volatile memories and chemical sensors. The templates preparation will start with track etched membranes and will finish with ultra small holes (<10nm) in thin supported patterned films. These templates will have ideal hole size and shape for nanowires production (metals , conductive polymers) and for their fundamental properties study. More complex templates will also be prepared in order to allow the devices design. The economical outputs of the project are mobile phone , data storage, chemical detectors, lab on a chip.
UCL-POLY has prepared and supplied the partners with substantial quantities (>500) of thick (10-20 µm) polycarbonate (PC) templates; the pore size ranging between 10 and 150 nm and the pore density between 106 and 1010 cm-2. A significant result has been achieved with the preparation of high temperature resistant templates (polyimide - PI, polyvinylidene fluoride - PVDF, polyetherether ketone - PEEK). The track etching process has been optimised for PI with homogeneous pore size and pore shape control (PATENT) and a lab-scale production of PI templates has been realised. The feasibility of the track etching substrate supported spin coated layers has been demonstrated with PC and PI. A major process enhancement was the improvement of the polymer - support adhesion. Current lab-scale production was optimised and structured nanotemplates including microelectrode circuitry have been prepared. A patterning process where pores are confined in restricted areas has been optimised; the resolution of this process is 1 µm2 for PC and 10 µm2 for PI IPFD has been involved in the characterisation of self-supported and supported templates (PC and PI): pore size homogeneity, pore shape and pore alignment in these templates have been determined. Some X-ray scattering experiments have been also carried out on heavy ion irradiated PI film but no contrast has been observed between tracks and virgin PI. Finally, templates filled with metals and conductive polymers have been also characterised.

UCL-PCPM has developed a strong expertise in electrochemical and chemical methods for filling the pores of nanoporous templates with metallic and polymer materials. The development of both single bath and multi-bath techniques has allowed to prepare a variety of nanowire arrays including single metal, magnetic alloys of controlled composition, multilayers formed by the stacking of ultra-thin layers of non magnetic, magnetic or oxide materials as well as hydrides organic/inorganic nanocomposites. This template method has a number of interesting and useful features: first, it is very general, as it can be used to prepare arrays of well-aligned nanowires, tubules or dots. Furthermore, cylindrical nanostructures with monodisperse and ultra-small diameters, down to 10nm, can be prepared - something that would be difficult to achieve using lithographic methods. Arrays of nanoparticles prepared by template methods might be interesting systems for a wide range of applications including microwave devices, recording media, magnetic or chemical sensor, nanobiotechnology, field or light emission, tips for atomic or magnetic force microscopy.

A potentiostatic electropolymerisation method has been developed at UCL-POLY for filling the nanopores of the different track-etched templates with different conducting polymers. Several electrolytic baths have been developed in order to synthesise polyaniline (PANi) and polypyrrole (PPy) nanotubes (? diameters) with various doping agents [PSS, ClO4-, DS, p-TS, BF4-,PF6-] selected for their potential application in gas sensors. Optimisation of the electrosynthesis conditions has been performed in order to get high filling ratio (> 80%). A large number of arrays (> 60) of different conductive polymer nano-structures have been prepared at the lab-scale and most of these samples have been used for gas sensing measurements. The major results of this study are that PPy nanotubes are sensitive to ozone (O3), even to very low concentration (down to 25 ppb) and to reducing gases such as ammonia (NH3). The sensitivity to these gases depends on the nature of the doping anion but also on the outer diameter of the nanotubes - smaller tubes being more sensitive. It has also been demonstrated that this behaviour is linked to the electrical conductivity behaviour of the PPy nanotubes - smaller tubes being more conductive. It has thus been demonstrated that PPy nanotubes are potentially interesting materials to be used as gas sensing layers (alone or in combination with other materials used as gas sensing devices) for environmental applications.

Collaboration between UCL, ULP - Spintec and UMP-CNRS has permitted to understand and control the reversal magnetisation of single ferromagnetic nanowires. Different methods and characterisation techniques have been developed to manipulate nanowires including the probing of a single nanowire. The principle result is a better comprehension of the mechanism of the reversal magnetisation induced by a spin-polarised current that could have a revolutionary impact in all the devices where you need to pilot a magnetisation.

A strong collaboration has been established between UCL and Thales concerning the development of microwave devices. Basic research concerning the high frequency properties of various types of nanowires has been carried out, whereas the identification, modelling and experimental development of an innovative non reciprocal device for radar systems has been developed. One of the main outputs of this project is thus the identification and protection a new and highly innovative concept of non-reciprocal system to be inserted in a radar system.

Integration within microchemical and biological devices of nanoporous templates that include electrodes for electrochemical measurement has been researched. Information concerning the fabrication of these devices and electrochemical measurements characterising the benefits of different electrode geometries including nanowires has been obtained. Microchemists and biologists use two main system formats, microfluidic channels with pump and valve flow control and automated micropipetting systems using arrays of containment wells or microtitre plate formats; nanoporous and metal nanowire containing templates have been integrated in devices for both these formats. One of the main outputs of this project is the identification of some of the benefits of nanoporous templates in devices for the miniaturisation of chemical and biological processes in application areas including biological research tools, healthcare diagnostics and fine chemical synthesis.

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2,Place Sainte Barbe 2

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