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FP6

NANODEV Sintesi della relazione

Project ID: 510103
Finanziato nell'ambito di: FP6-MOBILITY
Paese: Netherlands

Final Activity Report Summary - NANODEV (Medical sensing and nanodevices)

The goal was to gain expertise and to develop new chemometris based spectral analysis detection scheme (multivariate optical element (MOE)) for industrial and consumer implementation in the field of blood analyses, mainly for detection and quantification of malaria pigment crystals in blood, a waste product of the malaria parasite. Raman spectra of malaria pigment were successfully measured in aqueous solutions of high concentration, but a feasibility study revealed that the MOE technology in combination with Raman spectroscopy is not sensitive enough for the detection of malaria pigment in physiological concentrations. As a result the project shifted from technology focus (MOE) to application focus (malaria), exploring other technological options to diagnose malaria.

The most promising one identified was computer-aided, image-based diagnosis of malaria using light microscopy. A study of image contrast mechanisms was undertaken, comparing the suitability for enhancing contrast by use of staining, Ultraviolet (UV) absorption, fluorescence, differential interference contrast, phase contrast and dark field microscopy. It was found that the use of DNA stain delivered the highest diagnostic specificity at the lowest instrument complexity. Philips has pursued research in the field of image-based malaria diagnosis. Currently, this work has gone into its second year with considerable progress and has been broadened beyond technology to also explore social and economic components.

Nanotechnology metal-organic vapour phase epitaxy growth conditions have been optimised to control nanowire structure to a large extend. At lower temperature growth is mainly axial, at increased temperature a film is deposited on the nanowires walls (radial growth). This radial growth mode was used to incorporate impurity dopants in the shell, enabling to quantitatively control dopant levels in nanowires. The Gap-Gaas interface morphology was studied as a function of growth temperature and V/III precursor ratio. Transmission electron microscopy tomography allowed to resolve the three-dimensional morphology and to discriminate between the effect of axial (core) and radial (shell) growth on the morphology.

A temperature and precursor dependent structure diagram for the Gap nanowire core morphology, and the evolution of the different types of side facets during Gaas and Gap shell growth was constituted. Considering the role of the catalytic metal particle in the growth, we discovered a counterintuitive 'synergetic' effect resulting in an increase of the growth rate for decreasing wire-to-wire distance: the growth rate is proportional to the catalyst area fraction. The effect has its origin in the catalytic decomposition of precursors and is applicable to a variety of nanowire materials and growth techniques. The crystal structure of the Inp is affected by impurities or dopants. Importantly, when sufficient Zn is added to the system, the nanowires precipitate in the zinc blende crystal structure. Strikingly, at even higher Zn-precursor pressure the nanowires develop a twinning superlattice as twin planes exhibiting a constant spacing for a given Zn concentration and wire diameter are obtained. The electrical properties of nanowires were studied together with Delft technical university.

Based on this research we are now able to produce and to control n- and p-doped nanowires made out of Inp or Gap by incorporating sulphur or zinc in the nanowire. Also, Inp wires with a p-n junction have been made, which were contacted using e-beam lithography. Electric field microscopy demonstrates that the potential across this device drops at the p-n junction; while in forward bias electroluminescence was observed. Short segments of a ternary material, InAsP, were grown between the n-type and p-type segment to control the emission wavelength.

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