Field Emission Properties Of Multi-walled Carbon Nanotubes Research Articles

Field emission properties of laser ablated multi-walled carbon nanotubes

In the present study, the field emission properties of multi-walled carbon nanotubes (MWCNTs) treated with laser ablation have been investigated. The MWCNTs were synthesized by chemical vapor deposition method. The laser ablation treatment was performed in liquid medium for laser ablation time of 40 min and 60 min. The morphology of MWCNTs films was characterized by using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy. The results exhibit that the field emission properties of MWCNTs are dependent on the laser ablation time. The Raman spectra of laser-ablated MWCNTs clearly showed disorder and increase in graphitic content. The SEM and TEM results clearly revealed the separation of MWCNTs after laser ablation treatment. The field emission characteristics of the MWCNTs showed that the turn-on fields and current density are improved for the nanotubes treated with laser ablation. The enhancement in the field emission characteristics of MWCNTs is attributed to the disorder as well as the increase in the aspect ratio which causes more pathways for electron emission.

Computer simulation of the field emission properties of multiwalled carbon nanotubes for flat panel displays

Multiwalled carbon nanotubes (MWCNTs) have great potential in several applications such as being field emitters for flat panel displays. A particle-in-cell computer simulation code MAGIC was used in this work to investigate the field emission characteristics of both closed-capped and open-ended MWCNTs. The influence of various geometric parameters on the field emission properties of MWCNTs, such as the radius of curvature of the tips for the closed tubes, the edge sharpness, the inner and outer diameters of the open tubes, and the distance between neighboring tubes, are particularly studied. It is found that the circular corner edges of the open-ended MWCNT has to be much sharper than the closed-capped single tip MWCNT in order to achieve a similar magnitude of emission current. The simulation results also indicate that a space charge effect will occur at high emission currents in the order of 0.1 mA at the simulation conditions of this study. It is also found that the height of the MWCNTs can affect the emission current significantly. For open-ended MWCNTs, smaller diameter MWCNTs will have larger emission currents. On the other hand, for closed-capped MWCNTs, the diameter is not an issue as long as the radius of the curvature of the tip is kept unchanged. One important finding is that the number density of MWCNTs on the substrate can affect the emission current greatly due to the screening effect of nearby MWCNTs. For the simulated 100 and 200 nm height MWCNTs, it is found that the spacing between neighboring MWCNTs should be kept at least larger than 200 nm to avoid serious screening effects.