Inkjet printing of carbon nanotubes for electronic applications
1University of Oulu, Faculty of Technology, Department of Electrical and Information Engineering
2University of Oulu, Faculty of Technology, Microelectronics and Materials Physics Laboratories
3University of Oulu, Infotech Oulu
|Online Access:||PDF Full Text (PDF, 4.5 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:9789514293092
|Publish Date:|| 2009-11-24
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic dissertation to be presented with the assent of the Faculty of Technology of the University of Oulu for public defence in Auditorium TS101, Linnanmaa, on 4 December 2009, at 12 noon
Professor Thomas F. George
Doctor Asta Kärkkäinen
In this thesis, preparation of carbon nanotube (CNT) inks and inkjet printing of aqueous dispersions of CNTs for certain electrical applications are studied. The nanotube inks prepared in this work are based on chemically oxidized CNTs whose polar side groups enable dispersion in polar solvents. Subsequent centrifugation and decanting processes are used to obtain stable dispersions suitable for inkjet printing. The inks are based on either carboxyl functionalized multi-walled carbon nanotubes (MWCNTs), carboxyl functionalized single wall carbon nanotubes (SWCNTs) or SWCNT-polymer composites.
The applicability of MWCNT inks is firstly demonstrated as printed patterns of tangled nanotube networks with print resolution up to ∼260 dpi and surface resistivity of ∼40 kΩ/□. which could be obtained using an ordinary inkjet office printer. In addition, MWCNT inks are found to exhibit spatial ordering in external magnetic fields due to entrapped iron catalyst nanoparticles in the inner-tubular cavity of the nanotubes. Ordering of nanotubes in the inks and in drying droplets placed in relatively weak magnetic fields (B ≤ 1 T) is demonstrated and studied.
The high electrical conductivity and optical transparency properties of SWCNTs are utilized for enhancing the conductivity of transparent poly(3,4-ethylenedioxythiophene):poly(styrenesulphonate) (PEDOT:PSS) films. Polymer-nanotube composite materials are inkjet printed on flexible substrates. It is demonstrated that incorporation of SWCNTs in the thin polymer films significantly increases the electrical conductivity of the film without losing the high transparency (> 90%). The structure of composite films is studied using atomic force microscopy (AFM).
The electronic properties of deposited random SWCNT networks are studied. The amount of deposited SWCNT is controlled by the inkjet printing technique. In dense networks the current-voltage behaviour is linear whereas for sparse films the behaviour is nonlinear. It is shown that the conduction path in dense films is through the metallic nanotubes, but in sparse films the percolation occurs through random networks of metallic and semiconducting SWCNTs having Schottky-type contacts. The existence of Schottky-junctions in the films is demonstrated with field-effect transistors (FET) on Si-chips and on polymer substrates. The latter is demonstrated as fully printed transistors using a single ink as a material source. FETs are further utilized as chemical-FET sensor applications. The performance of resistive CNT sensors and their comparisons with chem-FETs in terms of selectivity are studied for H2S gas.
Acta Universitatis Ouluensis. C, Technica
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