Researchers at Motorola have used Accelrys' DMol3 to investigate the interaction of water with a nanotube tip. Such an understanding is critical in designing commercial quality flat panel displays based on carbon nanotubes.
Figure 1. H-Bonded water cluster on a close-capped (5, 5) nanotube stabilized under field emission conditions. The cluster is found to lower the Ionization Potential of the tube by almost 0.5 eV.
Carbon Nanotubes in Flat Panel Displays
Of the various potential application areas of carbon nanotubes, Field-Emission-based Flat Panel display is the closest to realizing the first commercial application. A practical challenge to make an efficient display is to reduce the operating voltage. One way to achieve this is to introduce adsorbates that might effectively lower the Ionization Potential (IP) and facilitate the extraction of electrons from the tube tip. Important experiments in this context were recently performed at Motorola, showing that the presence of water significantly enhances the field emission current from carbon nanotubes.
Investigating The Interaction between Water and The Nanotube Tip
In order to gain an atomistic understanding, scientists at Accelrys and Motorola have investigated the interaction of water with the nanotube tip using Accelrys' DFT code DMol3. It was found that the interaction is weak in the absence of any voltage.
The Interaction between Water and The Nanotube Tip under Field Emission Conditions
However, under field emission conditions, large electric fields present at the tube tip are found to: (1) increase the binding energy significantly, thereby stabilizing the adsorbate; and (2) lower the IP, thereby making it easier to extract electrons. Net binding and IP lowering are both enhanced by an increase in the number of water molecules adsorbed on the tip. In contrast, molecules with small or zero dipole moments are found to interact weakly with tube-tip even in large electric fields, and should not affect the field emission behavior, as is observed experimentally.
Conformation of Concept Using Computer Modelling
The above idea of IP reduction in carbon nanotubes was re-confirmed by DMol3 calculations from the group of M. Grujicic (Clemson University) who also investigated additional polar molecules like HCl, HCN, and LiH.