Functionalized CNT as ultrahigh resolution local probes
The small diameter and very high aspect ratio of CNT, combined with their chemical stability, structural robustness, and electrical conductivity, makes them extremely attractive as nanoscale probes of physical and biological samples. Particularly promising is the attachment to or growth of CNT on standard atomic force microscopy tips. Such CNT-functionalized probes have previously been used for topographical imaging, and, when functionalized with a ferromagnetic coating, for magnetic force imaging. Optimizing molecular beam epitaxy cobalt deposition on single walled carbon nanotubes, we have demonstrated sub-10 nm resolution and non-perturbative imaging of domains and spin nanostructures in hard and soft magnetic materials, all at ambient conditions with no special vacuum, temperature or humidity controls.
We have also shown that biased CNT-based probes can also be used to switch the ferroelectric polarization in epitaxial thin films. A recently developed rigidification process with a SiO2 coating by Intel allows buckling of the CNT to be avoided during this process, giving full control over sub 5 nm domains. In such rigidified tips, we have demonstrated enhanced carrying current capacity, with the dielectric coating acting as both a sink for Joule heating, and a protective barrier against oxidation. In contact with gold surfaces, these probes can carry currents of 0.12 mA at a power of 1.5 mW, and show no measurable change in resistance at current densities of 10 12 A/m2 over a time scale of 1000 s.