Nanotubes for Flat Ligth Sources
Nitrogen Doped Carbon Nanotube Cathodes for Flat Panel Displays and Flat Lamps
Tech Area / Field
- MAT-SYN/Materials Synthesis and Processing/Materials
8 Project completed
Senior Project Manager
Mitina L M
Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, Russia, Novosibirsk reg., Novosibirsk
- Korea Advanced Institute of Science and Technology, Korea, Taejon
Project summaryOne of the unique properties of carbon nanotubes (CNTs) is electron emission at low voltage of the applied electric field. At the present time CNTs are already utilized for elaboration of displays and flat vacuum lamps. The field emission (FE) characteristics of cathodes are dependent on the morphology of cathode surface and physical and chemical properties of CNTs. The structure and composition of CNTs define electron work function, tube conductivity and field-enhancement factor. Chemical vapour deposition (CVD) process is ideally suited to preparing CNTs cathodes because it allows controlling the tube geometry (diameter and length) and growing the aligned CNTs on planar substrates such as silicon or glass. Moreover, the CVD is low-cost method for large-scale production of CNTs that is very important for commercialization of emitters.
The filed emission (FE) characteristics of cathodes can be improved in the result of chemical modification of CNTs. For example, embedding of nitrogen atoms into CNT walls will cause redistribution of electronic density and decrease of electron work function. Nitrogen-doped CNTs can be produced using nitrogen-containing hydrocarbons (amines, pyridine, acetonitrile, etc.) as precursors. Our investigations have revealed the catalyst composition has significant impact on the concentration of the embedded nitrogen. During the project realization the CVD parameters (kind of catalyst, temperature, sources of carbon and nitrogen atoms) will be optimized to provide high yield of CNTs with the greatest nitrogen content. The arrays of aligned CNx nanotubes will be grown on various supports; the silicon supports will be chemically pretreated to enhance adhesion of carbon film. The film texture will be controlled by regimes of gas flow, time of synthesis, and procedure of catalytic particles formation.
The main FE characteristics of CNx nanotubes will be determined. To understand the electron emission process in detail the quantum-chemical calculations on nitrogen-doped carbon nanotubes will be carried out. The program utilized the Green functions approach will be developed for computation of current-voltage dependencies for finite size carbon nanotubes incorporating nitrogen. The computed dependencies will be compared with the experimental ones. The research results will be used in technology for production of cathodes for flat panel displays and flat lamps.
The goal of the present project is development of CVD technology for production of aligned CNTs films with improved field electron emission characteristics (threshold voltage, current density, long-term stability, emission site density) for using in flat panel displays and flat lamps. Three strategies will be used for improvement of FE behaviour of cathodes: (1) increase of current density and decrease of threshold voltage due to modification of the electronic properties of CNTs by incorporation of nitrogen atoms into the carbon network, (2) gain in field emission stability with enhancement of CNT adhesion to silicon support, and (3) better uniformity of phosphor screen glow in the result of growing of films being uniform in thickness. Nitrogen, being an electron donor, should reduce the ionization potential for CNTs and thus intensifying the field emission. The high alignment, equal length and inter-tube distances within the CNTs film will provide uniformity of emission site density.
The research work includes two stages covering 1-12 months (period I) and 13-24 months (period II).
During the period I, the catalysts and starting compounds for synthesis of aligned CNTs films, differed in thickness, tube diameter, and nitrogen content, will be adjusted. The film texture will be determined and its impact on the FE characteristics of cold cathode will be studied.
During the period II the influence of chemical treatment of support surface on the adhesion and alignment of CNTs will be investigated. The CVD conditions will be optimized to produce films having even surface. The role of substrate on the FE characteristics of cathode will be examined, as well as prototypes of flat panel device will be elaborated.
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