January 20, 2006

Molecular electronics- carbon nanotubes linked by organic molecules in an electronic switch

In the Jan. 20, 2006, issue of Science, Columbia scientists explain how they have developed a unique way to connect the ends of carbon nanotubes by forming robust molecular bridges between them. The Columbia team was able to combine the best qualities of carbon nanotubes and organic molecules in a single electronic switch, the journal reported. Attaching molecular wires to single-walled nanotubes involves cutting a tube using nanolithography combined with a localized oxidation process that leaves a nanotube with two ends that are capped with carbon-based acid groups and separated by a molecule-sized gap. In that tiny space, a molecule can be chemically joined with each end to form a robust nanotube/molecule complex, which operates as a nanoscale transistor.

January 19, 2006

Deterministic chaos found and analyzed in atomic force microscope

Chaotic oscillations of microcantilever tips in dynamic Atomic Force Microscopy (AFM) are reported and characterized. Systematic experiments performed using a variety of microcantilevers under a wide range of operating conditions indicate that softer AFM microcantilevers bifurcate from periodic to chaotic oscillations near the transition from the non-contact to the tapping regimes. Careful Lyapunov exponent and noise titration calculations of the tip oscillation data confirm their chaotic nature. AFM images taken by scanning the chaotically oscillating tips over the sample show small, but significant metrology errors at the nanoscale due to this "deterministic" uncertainty.