This project has made the bridge between three very different areas of science: the track etching of polymer membranes, electro-deposition chemistry and the physics of GMR.
A) To build on the patented PTM technology of the University of Louvain-La-Neuve, Belgium to develop the basic science and control over process parameters to be able to produce nPTMs of well controlled pore size and to explore markets for these materials.
B) To fill the nano-pores of these membranes with multi-layers of different metals by electro-deposition such multi-layers exhibiting low and high field GMR effects.
C) To measure the GMR properties of these nano-wires, to develop the theory of perpendicular transport and relate this to the experimental results and to assess the potential application of these materials as active substrates for sensors and data storage.
During this Brite EuRam Programme, methods have been developed for achieving control over pore size and shape in nPTMs made of polycarbonate. This means that actually, the technology consisting of:
i) a bombardment of a polycarbonate film with energetic heavy ions accelerated by a Cyclotron,
ii) pre-treatment and chemical etching which allows the preparation of membranes with nanopores in the range 10 - 100nm with controlled shape and pore density.
This technology is subject of a patent application. Also in polycarbonate, and additional to the original goals of the project, the feasibility of patterning the membrane has been demonstrated. This new method, which is also the subject of a patent application, will be further developed within the scope of a new project funded under the Growth Programme of Framework V programme and starting on February 1st, 2000.
The translation of these developments to other polymers such as polyethylene terephthalate, polyimide and polyvinylidene flouride was less successful and more work is still required in these areas.
The method for making nanoporous poly-carbonate membranes was scaled up and substantial quantities of material has been produced for use in further R & D work and for market application. Some problems are still arising which concern the pore shape and the scaling-up method must be improved in the future. Concerning other polymers, the scaling up has not been envisaged due to the problems encountered during the lab-scale studies.
Concerning the second goal, electro-deposition methods were successfully developed for filling the nano pores with different metals by electro-deposition from appropriate solutions. Single metals such as Au, Ag, Ni, Cu, Co and the alloy NiFe were successfully deposited. Multilayer structures of alternating metals and/or alloys of layers typically 1 - 2nm thick were also successfully produced for high field systems such as Co/Cu, Fe/Cu, Co/Au and Co/Ag and for low field system such as Cu/NiFe.
Early experiments on the possibility of developing a multi-bath technique for certain metallic systems which do not lend themselves for deposition from a solution containing both ions identified numerous technical hurdles and this feasibility task was dropped at the Mid Term Review.
Controlled deposition and lithographic techniques were successfully developed for contacting single nanowires in order to make transport measurements on them to aid the fundamental theoretical work. Excellent agreement was demonstrated between the theoretical models and experimental data. This is now the subject of several publications in leading journals.
The third goal was devoted to GMR applications. GMR measurements and characterisation of a wide variety of systems such as Co/Cu, NiFe/Cu and Fe/Cu has generated a wealth of data and insight whilst the measurement of magnetic properties of single metal nanowires has revealed a reorientation of the magneto-crystalline anisotropy as a function of diameter. This effect is only apparent in nanowires of less than 50nm diameter and is not yet completely understood and will be the subject of further research under a recently funded programme within Framework V.
The prospects for using these systems (i.e. multilayered stacks in nanoporous membranes) in sensors and data storage applications have been assessed.
The demand from industry for ultrapure separations is pushing the technological limits of membrane manufacture. Whilst microporous particle track etched membranes (PTM), with pore sizes in the range 0.1 m (100 nm) to 12 m, are regularly manufactured by Whatman, Europe's only local supplier; existing technology does not permit the controlled manufacture of nanoporous membranes with pore sizes in the range 5-10 nm
The first goal of this project is to build on the patented PTM technology of the University of Louvain-la-Neuve, Belgium to develop the basic science and processes for the efficient production of nanoporous PTMs. Although the initial work will be carried out on polycarbonate membranes, the project will also develop know-how for manufacture of nanoporous PTMs in other polymers which will extend their application range. These materials will be sampled to potential customers in the second part of this project.
Giant magnetoresistance (GMR) is a remarkable property of certain metallic multilayers which are able to detect tiny magnetic fields. GMR has application in magnetic data storage technology and in magnetic sensors and Thomson, France (partner) is a leading company in this field.
Recent work by three of the project partners has shown that multilayered nanowires, produced in nanoporous PTMs, also exhibit perpendicular GMR effects. The combination of nano-geometry and GMR effect has significance for the development of very high density magnetic storage systems. The multilayered nanowires are deposited using electrodeposition technology, this is a low cost, ambient temperature method which will produce robust materials enabling the GMR effect to be exploited in a large range of magnetic sensors and other applications.
The GMR part of this project will develop the basic science and theoretical understanding of these new GMR nanowires, develop processes for the controlled deposition of both 'hard' and 'soft' multilayers and explore the potential for single metal nanowires in magnetic recording.
The consortium comprises a membrane manufacturer (Whatman), a manufacturer of electronic systems and components (Thomson), the Polymer and Solid State Physics departments of the University of Louvain-la-Neuve, Belgium (UCL), the magnetic phenomena laboratories of the Universities of Paris Sud and Strasbourg (U. Paris Sud + U. Louis Pasteur) plus the Industry Microelectronics Center, Sweden (IMC) who brings considerable experience of electrodeposition of metallic multilayers.
The Brite/Euram III Areas covered by the proposal are 2.1.3L, 2.1.4M and 2.1.6M
Funding SchemeCSC - Cost-sharing contracts