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Nanowires for sensing applications

Aim of this work package is to exploit the complementary competences of the “NANOWIRING” network to devise innovative devices based on ZnO and SiC nanowires. The applications that will be addressed in this WP are the following:

The groups involved in this WP have complementary competences in the growth, structural, optical and electrical characterisation of ZnO nanowires. Moreover CNR-IMEM also has a strong background in the controlled synthesis of SiC needles. The major focus of this WP will be the training of young researches in growing the above-mentioned NWs in a controlled and repeatable way (diameter, aspect ratio, stoichiometry and so on). The team will work toward the realisation of prototype device systems driven by the industrial need proposed by FIAT, but also motivated by the increasing demand of biocompatible, cheap and accurate bio-sensors.

The synergic work conducted by the four groups that grow and/or characterise NWs (see table below) will benefit from their complementary skills and instrumentations. In particular the correlation between the optical/electrical properties and the synthetic methodologies will provide partners with an iterative feedback for the development of growth strategies tailored to selected sensing applications.

Nanowires as gas sensor

Gas sensor prototypes will be realised and tested in an effort to obtain high reproducibility, sensitivity and good stability. One of the applications in which young researchers will be trained consists of the fabrication, characterisation, and property measurements of ZnO nanostructures for transdermal measurement of the alcohol (EtOH) uptake of a car driver: both electrical and luminescence characterisation of EtOH sensing will be exploited to achieve large sensitivity and selectivity. Devices will be realised thanks to the controlled assembling and contacting of single nanowires (dielectrophorese in liquid) developed in the Univ. of Jena.

The main issues that will be addressed during the project development are: (i) control of NW’s stoichiometry (oxygen vacancies), defects and surface termination (ii) improvements of reliability, stability, refreshing after a detection event, and false alarm rate.

Nanowires as piezoelectric sensors

Piezoelectric ZnO and SiC nanowires can be used for pressure sensing and viscosity measurements. The aim of this part of the project is to investigate how the piezoelectric coefficient of NWs depends on the deformation of their structure at the nanoscale and to measure the I-V characteristics as a function of the deformation work on the wire. To this end the tip of an AFM will be used to give the electric continuity to a single nanowire and to allow the I-V characterisation. A key role will be played by an ER who will perform those piezoelectric tests at CNR-IMEM (first studies have already been done on oxides). After a training period to acquire basic understanding, the main goal of this activity will be to fabricate a first working device.

Nanowires as bio-sensors

Silicon Carbide (SiC) has recently been proposed for specific sensor applications due to its biocompatibility at the blood level, and operational stability in harsh environments and at high temperatures. Although SiC wires have already been produced, an optimisation of the growth process to avoid polytypism (responsible for kinks and irregular wire shape) and to control the NWs aspect ratio is urgently required. After completing this optimisation, the group at CNR-IMEM will work in close collaboration with Tyndall on surface reactivity of SiC NWs and to develop protocols for the chemical attachment of molecules carrying NH2, COOH, OH groups. The attachment will be demonstrated by PL measurements (i.e. NW emission modification following molecule binding). Sensing studies will start with the optical detection and characterisation of well known-biotin-streptavidin interaction.

Innovative biosensors will also be realised based on ZnO NWs: Bonding of polar-liquid molecules to oxide nanostructures appears to alter the polarisation-induced positive surface charge, leading to changes in the effective carrier density and hence the drain–source current in biased nanorods. This suggests the possibility of functionalizing the surface for application as biosensors, especially given the excellent biocompatibility of the ZnO surfaces, which should minimise degradation of adsorbed cells.

In this WP theoretical modelling will be conducted by a young researcher at CNR-IMEM to investigate fundamental aspects of the chemo/physical properties of SiC and ZnO nanowires, with particular attention to organic surface modification and piezoelectric properties at the nanoscale.