Abstract Submitted to the    NANOTUBE'06 Conference:

Nanotube Peapods: A New Class of Carbon Nanotube Hybrids

Hisanori Shinohara

Department of Chemistry & Institute for Advanced Research, Nagoya University

noris@cc.nagoya-u.ac.jp

III. Formation and Characterization of Unusual Nanostructures

During the past decade, carbon nanotubes encapsulating fullerenes, metallofullerenes (the so-called ‘peapods’) and other functional molecules have been synthesized and characterized by HRTEM, STM/STS, Raman, X-ray, FET and other measurements. In many cases, these nano-peapods have found to exhibit structural and electronic properties which are not normally observed in conventional carbon nanotubes. The novelty in electronic structure for the peapods comes mainly from hole or electron doping to the nanotubes from the encaged molecules. Here, we will report synthesis, structures and electronic properties of nano-peapods encaging a series of metallofullerenes and other functionalized molecules.
One of the fascinating features of metallofullerene-peapods such as Gd@C82, Ce@C82 and Ti@C82 peapods is that one can perform a ‘local band gap engineering’ at the site where metallofullerenes are endothermally inserted. TEM and STM images together with electron energy loss spectra have suggested that the metallofullerenes can be spaced regularly as close as 1.1 nm in a high-density ‘peapod’ structure, while 1.1 - 3 nm spacing has often been observed in a low-density peapod. About 10% of over 200 SWNT images showed locally modified semiconducting band gaps. We found that the synthetic yield of metallofullerene peapods varies considerably from one fullerene to another.
Furthermore, metallofullerene-peapods have exhibited ambipolar FET behavior with both n- and p-channels easily accessible by simple electrostatic gates. Similar results were obtained from more than 10 independent devices composed of a small bundle of metallofullerene peapods. Because the encaged metallofullerenes provide 2-6 electrons to the carbon nanotubes (electron-doping), the electronic transport properties of these peapods can drastically be altered with respect to the intact nanotubes.

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