Tremendous excitement has recently been generated by experimental breakthroughs that have led to realistic possibilities of using carbon nanotubes in (1) field-emission-based flat panel displays; and (2) electromechanical sensors. We have used First-Principles Density Functional Theory to address important questions in both application areas.
For the first application, we have investigated the effect of adsorbates at the nanotube tip on field emission current. In particular, we show that polar adsorbates like water are attracted to the tube tip under emission conditions, and make the HOMO unstable, thereby reducing the work function . The nanotube-water interaction as well as the instability of the HOMO become more pronounced with increase in the number of adsorbed water molecules on the nanotube tip. Non-polar molecules, e.g., H2, do not have a significant interaction with the tube tip, and therefore do not affect field emission current.
For the second application, we have investigated differences in the deformation of a nanotube under two types of mechanical forces: (a) bending, and (b) pushing with an AFM tip. We show that bent tubes maintain an all-hexagonal network up to large bending angles . In contrast, AFM-probed tubes can display a range of behavior depending upon how the AFM-tip is represented. This can range from sp3 coordination for some atoms close to the tip , to a non-uniform stretching of the tube that can lead to opening of band-gaps and substantial decrease in electrical conductivity [3, 4].
A. Maiti, J. Andzelm, N. Tanpipat, P. von Allmen, Phys. Rev. Lett., submitted.
A. Maiti, Chem. Phys. Lett. 331, 21 (2000).
A. Maiti, Phys. Stat. Sol., July (2001), in press.
A. Maiti, A. Svizhenko, and M. P. Anantram, in preparation.