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Development of a new machinery for nanotubes mass production based on the channel spark ablation technique (NANOSPARK)

Final Report Summary - NANOSPARK (Development of a new machinery for nanotubes mass production based on the channel spark ablation technique)

The aim of the NANOSPARK project was to develop a new machinery based on a cheap technological procedure, the channel spark ablation (CSA), to produce high quality single-walled carbon nanotubes (SWCNTs) which should yield the same quality as laser ablation but at much lower costs.

CSA is a technique based on the pulsed electron-beam generation from the glow-discharge plasma environment. It is able to deposit conducting and non-conducting materials with deposition rates ranging from 0.01 Angstrom/pulse up to about 100 Angstrom/pulse. This feature makes CSA a versatile technique able to be switched between epitaxial layers and thin coatings.

The carbon nanotubes (CNTs) produced by this machinery is then used for different applications and in particular as passive electronic elements into innovative solar cells and dye sensitised solar cells exploiting the outstanding properties of conductivity and chemical stability.

During the execution of the project the following activities have been carried out:

1. Design and development of a CSA based machinery for SWCNTs production
Many scientific and technological aspects of the CSA have been deeply investigated in order to make it exploitable for carbon nanotubes production:
a) Design of an electron-beam generator and the plasma environment characterisation
The CSA is an ablation process based on the pulsed electron-beam generation from the glow-discharge plasma environment. The glow-discharge plasma produced depends on the characteristics of the cathode-anode system therefore a characterisation of this component is indispensable to gather cathode information of plasma generation within the reaction chamber.
b) Reaction chamber design
the reaction chamber configuration. The configuration of the chamber consisting of the beam generation chamber and the target ablation chamber with the following CNTs formation were studied and designed according to the peculiar operating conditions necessary for plasma formation.
c) Reduction of the energy consumption
The energy consumption for CSA system is much lower than laser ablation (about two orders of magnitude) and its abatement strongly affects the final products price. Reduction in energy consumption was one of the most important aspects for future exploitation of the NANOSPARK machinery.
d) Differential vacuum system
Pressure conditions within the machinery represented one of the major issues. Differential pressure systems have been developed in order to create the proper operating conditions. A plasma window has been designed and implemented on the system together with a vacuum system.
e) Installation cost
Installation cost for CSA equipment can be 5 times cheaper than commercial pulsed laser deposition set-ups. Conversely to UV-lasers the main advantages of CSA systems are simplicity and high efficiency in converting electric energy in beam energy. Conversion rate is 50 %-70 %. The possibility to easily scale up the process using more guns limits cost increase, whereas laser ablation which is practically unscalable.

2. Methodology for carbon nanotubes preparation: purification and preparation in different media CNTs are unique material which can be extremely complicated to be used in industrial applications.
Nanotubes cannot be used as they are but required of several purification treatments after production. Even the dispersion of the nanostructured material into different media required a deep theoretical and experimental study on the basis of the industrial application desired. CNTs were produced and dispersed in different media according to their final application.

3. Development of new solar systems
Concerning the applications of CNTs the project aimed at designing and developing new solar energy systems with low manufacturing costs, up to 50 % lower than traditional crystalline cell modules. The research included the study of the complete process for the deposition of nanotubes and realisation of devices so as the implementation of new deposition processes of SWCNTs suspensions upon substrates to be used to fabricate solar cells.
Two different systems were investigated:
1) dye sensitised solar cells (Graetzel-like cells);
2) organic solar cells with bulk hetero-junctions.

The work performed was carried out in the following work packages (WPs):
1) WP1: Preliminary technical study
2); WP2: Development of the CSA for SWCNT production;
3) WP3: Mechanical design and prototyping;
4) WP4: Tests and refining of the NANOSPARK equipment;
5) WP5: Field testing on solar energy systems;
6) WP6: Dissemination and exploitation.

The main deliverable results of the project were:
- development of the CSA technique for CNTs production
- NANOSPARK system for CNTs production
- characterisation and purification of CNTs
- solar energy systems

The NANOSPARK project has demonstrated that the channel spark ablation is capable of producing carbon nanotubes from graphite with a lower energy consumption and high quality of the final product. Nanotubes produced can be commercialised at a lower cost as different products: nanotubes powder, suspensions or dispersed in polymeric thins film, etc. Development and characterisation of the channel spark ablation have been carried out focusing on:
- definition and optimisation of the plasma conditions generated during target ablation within the reaction chamber;
- design and development of the reaction chamber as core of the NANOSPARK system;
- design and development of mechanical components, electronics and control system.

The result consists in the characterisation of the channel spark ablation for carbon nanotubes production. Experimental results and theoretical explanation of plasma deposition phenomena have been published in two papers in Journal of Applied Physics:
- characterisation of a channel spark discharge and generated electron beam;
- pressure and electron energy measurements in a channel spark discharge